Two-component aqueous coating composition for wood substrates and articles made therefrom

Abstract

The invention relates to a two-component water-based coating composition for a wood substrate and an article made of the two-component water-based coating composition. The aqueous coating composition comprises: i) a main agent comprising a) an aqueous polyurethane dispersion (PUD), b) an aqueous acrylic modified polyurethane (PUA), c) an aqueous liquid vehicle, and d) an additional additive; ii) a curing agent composition, wherein the curing agent composition comprises a hydrophilic modified aliphatic polyisocyanate; wherein the mass ratio of the main agent to the curing agent composition is in the range of 100: 5 to 100: 20. The two-component water-based paint composition is longer in activation period and better in construction performance, and a coating formed by the two-component water-based paint composition is particularly excellent in gloss stability.

Description

Technical Field

[0001] The present invention relates to a water-based coating composition for a wood substrate, and more specifically, to a high-performance two-component water-based coating composition for a wood substrate, which is suitable for use as a sealing primer, a transparent or colored primer, a topcoat, a solid color paint, etc., and is particularly suitable for coating on the surface of a wood substrate. Background Art

[0002] At present, the environment and energy are two major challenges facing people. In order to meet this challenge, the coatings industry is gradually turning from traditional products that are highly polluting, energy-intensive, and extremely dependent on petroleum industry products to environmentally friendly and resource-saving products such as water-based coatings, radiation-cured coatings, powder coatings, and high-solid coatings. With the introduction of China's chemical industry standard "Indoor Water-Based Wood Coatings", water-based wood coatings have developed rapidly. At present, the investment in the research and development of water-based wood coatings is increasing significantly, and people's requirements for water-based wood coatings are also increasing.

[0003] The existing water-based coating compositions on the market mainly include a single-component water-based coating composition formed by a self-crosslinkable polyurethane dispersion as a main film-forming resin system and a two-component polyurethane water-based coating composition composed of a hydroxyl functional resin and a polyisocyanate. However, the above two water-based coating compositions have their own defects. For example, the single-component water-based coating composition cannot meet people's growing requirements for paint film performance, and the construction performance of the two-component polyurethane water-based coating composition is limited, and it cannot be widely promoted in practical applications.

[0004]

[0006] Therefore, there remains a continuing need in the coatings industry for improved waterborne coating compositions suitable for use on wood substrates. Summary of the invention

[0005] On the one hand, the present invention provides a water-based coating composition for a wood substrate, comprising: i) a main agent, wherein the main agent comprises a) an aqueous polyurethane dispersion (PUD), b) an aqueous acrylic modified polyurethane (PUA), c) an aqueous liquid carrier, and d) additional additives; and ii) a curing agent composition, wherein the curing agent composition comprises a hydrophilically modified aliphatic polyisocyanate; wherein the mass ratio of the main agent to the curing agent composition is in the range of 100:5 to 100:20.

[0006] In some embodiments of the present invention, the curing agent composition further comprises a hydrophilic modified alicyclic polyisocyanate and an oily aliphatic polyisocyanate in addition to the hydrophilic modified aliphatic polyisocyanate. Preferably, the curing agent composition comprises, relative to the total weight of the curing agent composition, 15-25 wt % of the hydrophilic modified aliphatic polyisocyanate; 25-35 wt % of the oily aliphatic polyisocyanate; and 45-55 wt % of the hydrophilic modified alicyclic polyisocyanate.

[0007] In some embodiments of the present invention, in the main agent, the organic solvent is present in an amount not exceeding 5 wt % relative to the total weight of the main agent.

[0008] In one embodiment of the present invention, the aqueous coating composition has an improvement in workability of about 5% compared to a control coating composition formed by using a hydroxyl-functional acrylate resin and the same curing agent composition, and the workability is measured by construction under different temperature and humidity environments, especially under difficult construction conditions of high temperature (temperature above 35°C) and low humidity (humidity below 40%) and when spraying oversized workpieces.

[0009] In a preferred embodiment of the present invention, the aqueous coating composition prepared by the curing agent composition consisting of hydrophilically modified aliphatic polyisocyanate, oily aliphatic polyisocyanate and hydrophilically modified alicyclic polyisocyanate has at least one of the following properties compared to the aqueous coating composition prepared by the curing agent composition consisting only of hydrophilically modified aliphatic polyisocyanate:

[0010] 25% or less 2-hour viscosity rise;

[0011] The pot life at 35°C is extended by 30% or more; and

[0012] With the same or similar surface drying time, the through drying time is shortened by 15% or more.

[0013] Another aspect of the present invention relates to a wood product, comprising a wood substrate having at least one main surface; and at least one paint film, the paint film being formed by the above-mentioned two-component waterborne coating composition directly or indirectly coated on the main surface. Preferably, the two-component waterborne coating composition according to the present invention can be used as one or all of a sealing primer, a second primer, and a third primer on a wood substrate, preferably as all.

[0014] The inventors of the present invention surprisingly found that when formulating a two-component water-based coating composition, a combination of a water-based polyurethane dispersion (PUD) and a water-based acrylic modified polyurethane (PUA) is compounded with a curing agent composition comprising a hydrophilically modified aliphatic polyisocyanate. The resulting two-component coating composition can produce a paint film with better resistance than a traditional self-cross-linking PUA coating composition. Similarly, compared with a two-component polyurethane (2K PU) system, it has better construction tolerance.

[0015] The inventors of the present invention were even more surprised to find that when preparing a two-component water-based coating composition, a combination of an aqueous polyurethane dispersion (PUD) and an aqueous acrylic modified polyurethane (PUA) is compounded with a curing agent composition composed of a hydrophilic modified aliphatic polyisocyanate, an oily aliphatic polyisocyanate and a hydrophilic modified alicyclic polyisocyanate. The resulting two-component coating composition not only has a long activation period, but also has stable gloss under different drying conditions; in addition, when preparing a two-component water-based coating composition, controlling the amount of organic solvent contained in the main agent within a certain range can also significantly improve the gloss stability of the paint film, which was difficult to foresee before the present application.

[0016] The details of one or more embodiments of the invention are set forth in the description which follows. Other features, objects, and advantages of the invention will become apparent from the description and claims.

[0017] definition

[0018] As used herein, without quantifiers, "at least one" and "one or more" are used interchangeably. Thus, for example, a coating composition comprising an additive can be interpreted to mean that the coating composition comprises "one or more" additives.

[0019] Where a composition is described as comprising or including specific components, it is contemplated that optional components not contemplated by the present invention are not excluded from the composition, and that the composition may consist of or be composed of the contemplated components; or where a method is described as comprising or including specific process steps, it is contemplated that optional process steps not contemplated by the present invention are not excluded from the method, and that the method may consist of or be composed of the contemplated process steps.

[0020] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0021] As used herein, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B", which may also be abbreviated as "A and / or B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist). In contrast, the exclusive "or (or)" is represented herein, for example, by terms such as "either A or B" and "one of A or B".

[0022] In the context of the present application, the term "two-component aqueous coating composition" refers to a coating composition generally consisting of two components, which are packaged separately from each other. Before use, the two components are mixed according to a desired ratio and diluted and applied as needed to form a coating.

[0023] In the context of describing that a composition does not contain a certain ingredient, the term "does not contain" means that the composition does not contain the intentionally added ingredient. Considering the complexity of the specific composition of each component in the actual formulation process, the phrase "does not contain a certain ingredient" can be understood as the composition containing less than 1% by weight of the ingredient based on the total weight of the composition, more preferably less than 0.5% by weight, even more preferably less than 0.2% by weight, and most preferably less than 0.1% by weight.

[0024] As used herein, the term "dispersion" conforms to the definition in the IUPAC Compendium of Chemical Terminology (2007), which defines a dispersion as a material comprising more than one phase, wherein at least one phase consists of finely divided phase domains, typically in the colloidal size range, distributed throughout a continuous phase domain.

[0025] As used herein, the term "aqueous dispersion" means that the dispersion medium (solvent or carrier fluid) in the dispersion mainly or primarily comprises water. For example, in some embodiments, the dispersion medium comprises at least about 50 wt %, preferably at least about 60 wt %, more preferably at least 70 wt % and up to about 99 wt %, up to about 100 wt % water based on the total weight of the dispersion medium. For example, the dispersion medium comprises about 80 wt %, about 85 wt %, or about 95 wt % water based on the total weight of the dispersion medium.

[0026] As used herein, the term "aqueous dispersion of a resin" refers to a stable dispersion of a resin (i.e., a polymer) in particulate form in an aqueous liquid medium, optionally with the aid of a suitable dispersing aid such as a surfactant, a cosolvent. Therefore, in this application, when used with respect to a polymer, the terms "aqueous latex" and "aqueous dispersion" may be used interchangeably unless otherwise stated. Methods for preparing aqueous latexes are known in the art, for example, they may be prepared using emulsion polymerization techniques known to those skilled in the art. Aqueous dispersions may also be commercially available.

[0027] As used herein, the term "hydroxy functional" means containing at least one unreacted hydroxy functional group.

[0028] As used herein, the term "hydrophilic curing agent" has a meaning known in the art. Typically, a hydrophilic curing agent is typically obtained by hydrophilically modifying a curing agent. As an exemplary illustration, a hydrophilic curing agent may be, for example, nonionic hydrophilic modified (e.g., Bayhydur 3100 from Covestro), ionic modified, or a combination of nonionic and ionic modified.

[0029] The workable time or pot life or pot life is the time during which, once the mutually reactive components of the coating composition are mixed, the coating composition can still be properly handled or applied and a coating of uncompromised quality can be obtained. In the handling of two-component coating compositions, it is usually necessary to mix the reactive components together shortly before application to avoid premature reaction of the reactive components. The term "shortly before application" is well known to those skilled in the art who work with two-component coating compositions. The period of time during which the ready-to-use coating composition can be prepared before actual use or application depends, for example, on the pot life of the coating composition. Therefore, in order to have a sufficient time window for preparing, mixing and applying the two-component coating composition, a sufficiently long pot life is required. Therefore, the workable time can also be defined as the time during which the paint film formed by brushing has satisfactory properties. In general, at the end of the workable time, the viscosity of the coating doubles. In addition, since water-based resins are different from oil-based resins, a single viscosity cannot be used as a criterion for judging the workable time. For water-based dispersions, at the end of the construction time, the transparency, fullness, gloss and hardness of the paint film after film formation should not show a significant decrease.

[0030] As used herein, the term "cured" means that the applied film of the composition is cured at least to the touch (set-to-touch) as defined in ASTM D5895-Standard Test Methods for Evaluating Drying or Curing During Film Formation of Organic Coatings Using Mechanical Recorder (Standard Test Method for Evaluating Drying or Curing During Film Formation of Organic Coatings Using Mechanical Recorder), which document is also incorporated into this specification by reference. As used herein, the terms "cure" and "curing" mean the process of converting an applied liquid composition from a liquid state to a cured state. The terms "cured", "cure" and "curing" cover the drying process of the composition through solvent volatilization and chemical cross-linking of the components in the composition.

[0031] In the context of this application, "applicability" is a parameter used to measure the ease of application of a coating composition, measured under different temperature and humidity conditions, especially water-based paints under high temperature (temperature above 35°C) and low humidity (humidity below 40%) difficult application conditions and spraying of oversized workpieces. Usually, applicability is rated by applicators, generally divided into 1-5 levels, the higher the level, the better the applicability, where 1 represents the worst applicability; 5 represents the best applicability; 3 represents a very poor applicability state, which is basically not available on the market, and a 5% drop in the rating score is already very obvious to the naked eye.

[0032] In the context of the present application, "gloss stability" is a parameter used to measure the application performance of a coating composition, and is measured by the difference in gloss of a coating formed by a coating composition applied at room temperature and a coating formed by a coating composition applied at 50° C. The greater the difference in gloss, the worse the gloss stability of the coating, and the smaller the difference in gloss, the more excellent the gloss stability of the coating.

[0033] As used herein, the term "primer" refers to a coating composition that can be applied to a substrate and dried, crosslinked or otherwise hardened to form a non-tacky continuous film having sufficient adhesion to the substrate surface, and the continuous film thus formed can have a certain protective effect on the substrate surface.

[0034] As used herein, the term "topcoat" refers to a coating composition that can be applied to a substrate or a primer and dried, cross-linked or otherwise hardened to form a non-tacky continuous film having sufficient adhesion to the substrate or primer surface, and the continuous film thus formed can not only have a certain protective effect on the substrate or primer surface, but also have a decorative effect.

[0035] The terms "preferred" and "preferably" refer to embodiments of the present invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. In addition, the recitation of one or more preferred embodiments does not mean that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present invention. DETAILED DESCRIPTION

[0036] According to a first aspect of the present invention, there is provided a water-based coating composition for a wood substrate, comprising: i) a main agent, the main agent comprising a) an aqueous polyurethane dispersion (PUD), b) an aqueous acrylic modified polyurethane (PUA), c) an aqueous liquid carrier, and d) additional additives; and ii) a curing agent composition, the curing agent composition comprising a hydrophilically modified aliphatic polyisocyanate; wherein the mass ratio of the main agent to the curing agent composition is in the range of 100:5 to 100:20.

[0037] Main agent

[0038] In an embodiment according to the present invention, the main agent comprises an aqueous polyurethane dispersion (PUD) and an aqueous acrylic modified polyurethane (PUA), that is, an aqueous dispersion formed by polyurethane polymer particles or an aqueous dispersion formed by acrylic modified polyurethane polymer particles. As described in the definition section, the aqueous dispersion can be prepared by emulsion polymerization, and can therefore also be referred to as "aqueous latex". In the present invention, the polymer particles can be modified by, for example, modification of organic functional groups (including, but not limited to, carboxyl, hydroxyl, amino, sulfonic acid, etc.) to obtain an aqueous latex with desired properties. Therefore, in the present invention, an aqueous polyurethane dispersion (PUD) refers to a dispersion of unmodified polyurethane polymer particles in an aqueous medium, and an aqueous acrylic modified polyurethane (PUA) refers to a dispersion of polyurethane polymer particles modified by acrylic acid (ester) organic functional groups in an aqueous medium.

[0039] In some embodiments according to the present invention, the aqueous polyurethane dispersion (PUD) contains carboxyl functional groups, preferably having an acid value of 5 to 20 mg KOH / g; and / or, the aqueous polyurethane dispersion (PUD) has a hydroxyl value of 0 to 45 mg KOH / g, which is significantly lower than the common hydroxyl-functionalized polymer film-forming resins on the market.

[0040] In some embodiments according to the present invention, the waterborne acrylic modified polyurethane (PUA) contains a carboxyl functional group, preferably having an acid value of 5 to 20 mg KOH / g; and / or, the waterborne acrylic modified polyurethane (PUA) has a hydroxyl value of 0 to 50 mg KOH / g, which is significantly lower than the common hydroxyl-functionalized polymer film-forming resins on the market.

[0041] As is known to all, the main agent composed of an aqueous polyurethane dispersion (PUD) and / or an aqueous acrylic modified polyurethane (PUA) system is a one-component system that can form a film without adding a curing agent. Compared with a two-component system containing a hydroxyl functionalized resin that requires a curing agent to form a good film, the main agent of this one-component system is more conducive to the fusion and cross-linking of resin particles during film formation. The inventors of the present invention surprisingly found that compared with a two-component coating composition containing a hydroxyl acrylic dispersion, a two-component water-based coating composition according to the present invention, which is formed by using an aqueous polyurethane dispersion (PUD) and / or an aqueous acrylic modified polyurethane (PUA) system as a main agent and a curing agent, has significantly better construction performance.

[0042] Without being bound by any theory, the inventors speculate that after the hydroxyl-functionalized resin is mixed with the polyisocyanate curing agent, the NCO in the curing agent basically reacts with the more active hydroxyl group, and the reaction rate is very fast; in contrast, in the waterborne coating composition according to the present invention, the waterborne polyurethane dispersion (PUD) and / or waterborne acrylic modified polyurethane (PUA) as the main agent has a low hydroxyl value and a certain acid value, so after mixing with the polyisocyanate curing agent, the NCO in the curing agent reacts not only with the hydroxyl group, but also with the carboxyl group in the resin, and the reaction rate is appropriately adjusted, so that the construction performance of the waterborne coating composition thus formulated is more excellent.

[0043] Preferably, in the two-component coating composition according to the present invention, the amount of the aqueous polyurethane dispersion (PUD) can be adjusted as needed, for example, in the range of 15 to 65 wt %, preferably in the range of 20 to 55 wt %.

[0044] Preferably, in the two-component coating composition according to the present invention, the amount of the waterborne acrylic modified polyurethane (PUA) can be adjusted as needed, for example, in the range of 5 to 60 wt %, preferably in the range of 15 to 55 wt %.

[0045] In some embodiments according to the present invention, the main agent in the two-component coating composition according to the present invention does not contain an aqueous dispersion of a hydroxyl-functional acrylic polymer, and preferably does not contain any other hydroxyl-functional resin. As described above, the phrase "the main agent does not contain an aqueous dispersion of a hydroxyl-functional acrylic polymer" means that the main agent does not contain an aqueous dispersion of an intentionally added hydroxyl-functional acrylic polymer. However, considering the complexity of the specific composition of each component in the actual formulation process, the phrase "the main agent is substantially free of an aqueous dispersion of a hydroxyl-functional acrylic polymer" can be understood as the main agent containing an aqueous dispersion of a hydroxyl-functional acrylic polymer of less than 1% by weight based on the total weight of the main agent, more preferably less than 0.5% by weight, even more preferably less than 0.2% by weight, and most preferably less than 0.1% by weight.

[0046] In the context according to the present invention, hydroxy-functional acrylic polymers have the meaning known in the art. In one embodiment of the present invention, the hydroxy-functional acrylic polymer can be an emulsion-polymerized latex polymer, and its aqueous dispersion is prepared by emulsion polymerization, and thus it can also be referred to as "aqueous latex". Methods for preparing aqueous latexes are known in the art, for example, they can be prepared using emulsion polymerization processes known to those skilled in the art. In another embodiment of the present invention, the hydroxy-functional acrylic polymer can be an organic solution-polymerized acrylic polymer, and its aqueous dispersion is obtained by redispersing the polymer so prepared in water. Methods for preparing acrylic acid polymers using organic solution polymerization are known in the art, for example, they can be prepared using solution polymerization processes known to those skilled in the art.

[0047] Hydroxyl-functional acrylic polymers generally have a relatively high hydroxyl number. The hydroxyl number is generally expressed as the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content in 1 gram of hydroxyl-containing material. According to the present invention, the hydroxyl-functional acrylic polymer has a hydroxyl number of at least 60 mg KOH / g polymer, more preferably at least 70 mg KOH / g polymer, and even more preferably at least 80 mg KOH / g polymer, but preferably does not exceed 200 mg KOH / g polymer.

[0048] According to the present invention, the hydroxyl-containing acrylic polymer in the aqueous dispersion may be any type of acrylic polymer, including pure acrylate polymer, styrene-acrylate polymer, silicone-modified acrylate polymer, polyurethane-modified acrylate polymer or a combination thereof.

[0049] In some embodiments according to the present invention, the main agent in the two-component coating composition according to the present invention comprises a certain amount of aqueous liquid carrier. Suitable aqueous liquid carriers include organic solvents, water and mixtures thereof. The aqueous liquid carrier is selected to adjust the viscosity of the main agent for further preparation.

[0050] Suitable organic solvents include alcohols (e.g., ethanol, n-propanol, isopropanol, n-butanol, isobutanol, etc.); ketones (e.g., acetone, 2-butanone, cyclohexanone, methyl aryl ketone, ethyl aryl ketone, methyl isoamyl ketone, etc.); glycols (e.g., butyl glycol); glycol ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, methoxypropanol, dipropylene glycol methyl ether, etc.), glycol esters (e.g., butyl glycol acetate, methoxypropyl acetate, etc.); and mixtures thereof.

[0051] The amount of aqueous liquid vehicle included in the main agent may vary, for example, depending on the coating method and the desired viscosity. Preferred embodiments of the main agent contain 5-20 wt % aqueous liquid vehicle, more preferably 8-15 wt % liquid vehicle.

[0052] The inventors of the present invention surprisingly found that when preparing a two-component waterborne coating composition, controlling the amount of the organic solvent contained in the main agent within a certain range can also significantly improve the gloss stability of the paint film. Therefore, in a preferred embodiment of the present invention, in the main agent, the organic solvent is present in an amount not exceeding 5% by weight, preferably not exceeding 3.5% by weight, and more preferably not exceeding 2.5% by weight relative to the total weight of the main agent.

[0053] If desired, in coating composition according to the present invention, other additives may be optionally included in the host, and these additives may not adversely affect coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those reagents that can improve the processing properties or manufacturing performance of composition, enhance the aesthetic feeling of composition or improve coating composition or the specific functional properties or characteristics (such as adhesion to substrate) of the cured coating obtained therefrom. The additive that may be included is additional polymer, emulsifier, pigment, metal powder or paste, filler (such as titanium dioxide), anti-migration aid, antibacterial agent, extender, lubricant, coagulant, wetting agent, biocide, plasticizer, defoamer, colorant, wax, antioxidant, corrosion inhibitor, flow control agent, thixotropic agent, dispersant, UV stabilizer, scavenger or its combination. The content of each optional component is enough to play the purpose it is intended to achieve, but preferably, such content may not adversely affect coating composition or the cured coating obtained therefrom.

[0054] In one embodiment of the present invention, the main agent comprises, relative to the total weight of the main agent, 0 to 35 wt % of additional additives, preferably 3 to 30 wt % of additional additives. Preferably, the additional additives include dispersants, titanium dioxide, and one or more of the above-mentioned other additional additives.

[0055] Curing agent composition

[0056] According to the present invention, the aqueous coating composition comprises a curing agent composition to improve the performance of a paint film with PUD and / or PUA as a film-forming resin, wherein the curing agent composition comprises a hydrophilically modified aliphatic polyisocyanate. As described above, a hydrophilic curing agent is generally obtained by hydrophilically modifying a curing agent. In an embodiment of the present invention, the curing agent composition comprises a hydrophilically modified aliphatic polyisocyanate. As an exemplary illustration, the hydrophilically modified aliphatic polyisocyanate is selected from hydrophilically modified hexamethylene diisocyanate, hydrophilically modified trimethyl hexamethylene diisocyanate and a combination thereof, preferably selected from hydrophilically modified hexamethylene diisocyanate.

[0057] In the present invention, the hydrophilic modified aliphatic polyisocyanate can be prepared by an appropriate method known to those skilled in the art, or any appropriate commercially available product can be used as an example, such as Wanhua 268, Huaguoshan HOUXIAN 200L, Guanzhi OS-9012, Covestro bayhydur 305, BURNOCK DNW-5500 or a combination thereof.

[0058] In addition to the above hydrophilically modified aliphatic polyisocyanate, the curing agent composition may further include a hydrophilically modified alicyclic polyisocyanate and an oily aliphatic polyisocyanate.

[0059] The inventor of the present invention has found that when preparing a two-component water-based coating composition, a curing agent composition consisting of a hydrophilic modified aliphatic polyisocyanate, an oily aliphatic polyisocyanate and a hydrophilic modified alicyclic polyisocyanate can significantly improve the curing performance of the water-based coating composition compared to a curing agent composition consisting only of a hydrophilic modified aliphatic polyisocyanate. Compared with using a single hydrophilic modified aliphatic polyisocyanate (such as HDI) as a curing agent, a mixed curing agent has the following advantages: due to the rigid structure of the alicyclic polyisocyanate (such as IPDI), the collision probability of the two components of the main agent and the curing agent after mixing is reduced, thereby helping to improve the activation period of the system; at the same time, due to its structural characteristics, although the mixed curing agent introduces more solvents, IPDI is beneficial for the initial hardness establishment, so it does not affect its surface drying time. The addition of an oily curing agent helps to improve the crosslinking density during film formation, thereby helping to improve the actual drying time of film formation and the crosslinking density after film formation. At the same time, the mixed curing agent retains a portion of the hydrophilic modified aliphatic polyisocyanate to ensure the dispersibility of the curing agent in the main agent, without affecting the construction of the mixed system. Therefore, in the preparation of the water-based coating composition according to the present invention, the combination of the hydrophilic modified aliphatic polyisocyanate, the oily aliphatic polyisocyanate and the hydrophilic modified alicyclic polyisocyanate is used as the curing agent composition, which is particularly excellent for improving the curing performance of the coating.

[0060] In addition, the inventors of the present application also discovered that in a system with PUA and / or PUD as the main agent, using a combination of hydrophilically modified aliphatic polyisocyanate, oily aliphatic polyisocyanate and hydrophilically modified alicyclic polyisocyanate as a curing agent composition can further improve the gloss stability of the coating compared to using a single hydrophilically modified aliphatic polyisocyanate as a curing agent composition, which was difficult to predict before the present application.

[0061] In some embodiments according to the present invention, the oily aliphatic polyisocyanate includes oily hexamethylene diisocyanate, oily trimethyl hexamethylene diisocyanate and combinations thereof, preferably selected from oily hexamethylene diisocyanate. In the present invention, the oily aliphatic polyisocyanate can be prepared by an appropriate method known to those of ordinary skill in the art, or any suitable commercially available product can be used as an example, such as DESMODUR N 3600 from Covestro, DESMODURN 3300 from Covestro, DESMODUR N 3900 from Covestro or a combination thereof.

[0062] In some embodiments according to the present invention, the hydrophilic modified alicyclic polyisocyanate is selected from hydrophilic modified isophorone diisocyanate, hydrophilic modified dicyclohexylmethane diisocyanate, hydrophilic modified cyclohexane dimethyl diisocyanate and combinations thereof, preferably selected from hydrophilic modified isophorone diisocyanate. In the present invention, the hydrophilic modified alicyclic polyisocyanate can be prepared by an appropriate method known to those of ordinary skill in the art, or any suitable commercially available product can be used as an example, such as Covestro BAYHYDUR 401-70, Covestro BAYHYDUR 401-60 or a combination thereof.

[0063] In a preferred embodiment according to the present invention, the curing agent composition comprises, relative to the total weight of the curing agent composition,

[0064] 15-25 wt% of a hydrophilically modified aliphatic polyisocyanate;

[0065] 25-35 wt% of an oily aliphatic polyisocyanate; and

[0066] 45-55% by weight of a hydrophilically modified alicyclic polyisocyanate.

[0067] According to the present invention, the two-component waterborne coating composition can be prepared as follows: before application, the main agent and the curing agent composition are simply mixed in a mixing device at a predetermined weight ratio, preferably in the range of 100:5 to 100:20. During the construction process, the obtained mixture is mixed with a certain amount of inert diluent as needed to obtain a coating composition that meets the construction requirements.

[0068] The coating composition according to the present invention can be applied using various methods familiar to those skilled in the art, including spraying (e.g., air-assisted, airless or electrostatic spraying), brushing, roller coating, overflow coating and dipping. In one embodiment of the invention, the mixed coating composition is applied by spraying. The coating composition can be coated into various wet film thicknesses. In an embodiment of the present invention, the wet film thickness preferably provides a dry film thickness of about 13 to about 260 μm (about 0.5 to about 10 mils), and more preferably about 25 to about 75 μm (about 1 to about 3 mils). Can be cured by air-drying the applied coating or by accelerating curing using various drying devices familiar to those skilled in the art (e.g., baking oven).

[0069] In one embodiment of the present invention, the water-based coating composition has an improvement in workability by about 5% compared to a control coating composition formed by using a hydroxyl-functionalized acrylate resin and the same curing agent composition. The workability is measured under different temperature and humidity conditions, especially under difficult construction conditions of water-based paint at high temperature (temperature above 35°C) and low humidity (humidity below 40%) and spraying of oversized workpieces.

[0070] In one embodiment of the present invention, the aqueous coating composition prepared by the curing agent composition consisting of the hydrophilic modified aliphatic polyisocyanate, the oily aliphatic polyisocyanate and the hydrophilic modified alicyclic polyisocyanate has at least one of the following properties compared to the aqueous coating composition prepared by the curing agent composition consisting only of the hydrophilic modified aliphatic polyisocyanate:

[0071] 25% or less 2-hour viscosity rise;

[0072] The pot life at 35°C is extended by 30% or more; and

[0073] With the same or similar surface drying time, the through drying time is shortened by 15% or more.

[0074] Therefore, the two-component coating composition according to the present invention has a wide range of applications and can be used as a closed primer, a clear primer, a topcoat, a solid color paint, etc. Therefore, the present invention also relates to a wooden product, which includes a wooden substrate having at least one main surface; and one or more layers of paint film, the paint film being formed by the two-component waterborne coating composition of the present invention directly or indirectly coated on the main surface. In some embodiments, the two-component waterborne coating composition of the present invention can be coated on a wooden substrate as one or more of a primer and a topcoat, preferably all.

[0075] As the wooden substrate for making wooden products of the present invention, any suitable wooden substrate known in the art can be used. In the present application, term "wooden substrate" refers to any cellulose / lignin material derived from the hard, fibrous structural organization in the stem and root of trees or other woody plants. Timber includes, for example, hardwood and softwood timber directly cut from trees, and engineered wood composites made of wood strips, wood chips, wood fibers or wood veneers. The example of wood composites includes but is not limited to plywood, oriented strand board (OSB), medium density fiberboard (MDF), particle board etc.

[0076] As exemplary wood substrates, one or more of quercetin, chestnut, oak, red chestnut, tea, eucalyptus, Douglas fir, Japanese cedar, American cypress, Japanese red pine, Japanese cypress, water walnut, black walnut, maple, Japanese beech, Japanese paulownia, birch, sal, magnolia, ash, teak, oak, catalpa, camphor, fir, oak, and rubber wood can be used.

[0077] According to the present invention, the wood products thus obtained can be used in the following applications, including, but not limited to: household furniture, such as tables, chairs, cabinets, etc.; bedroom and bathroom furniture; office furniture; custom furniture, such as school and children's furniture, hospital furniture, restaurant and hotel furniture, kitchen cabinets and furniture; panels for interior design; indoor and outdoor windows and doors; indoor and outdoor window frames and door frames; outdoor and indoor wainscoting and wood flooring.

[0078] Example

[0079] The following examples more specifically describe the disclosure of the present invention, which are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available and can be used directly without further processing.

[0080] Test Method

[0081] Unless otherwise stated, the following test methods were used in the examples.

[0082] Construction performance: A parameter used to measure the ease of construction of a coating composition. It is rated by construction personnel in the coating field under different temperature and humidity conditions, especially under high temperature (temperature above 35°C) and low humidity (humidity below 40%) conditions where water-based paint is difficult to construct and when spraying oversized workpieces. It is generally divided into 1-5 levels. The higher the level, the better the construction performance. Level 1 indicates the worst construction performance; Level 5 indicates the best construction performance; Level 3 indicates a very poor construction state, which basically cannot be circulated on the market. A 5% drop in the rating score is already very obvious to the naked eye.

[0083] Active period: It refers to the time taken for the viscosity of the mixture obtained by mixing the main agent and the curing agent composition to increase to twice its initial viscosity at 35°C, and the viscosity refers to the viscosity of the 4-cup test.

[0084] Surface drying time and actual drying time: It is measured according to GB / T 1728-1989.

[0085] Glossiness:It is measured according to GB 1743-1979 (1989).

[0086] Material

[0087] The raw materials used in each example are as follows:

[0088] Aqueous polyurethane dispersion (PUD): NeoRez R-2180 commercially available from DSM, with an acid value of 5 to 20 mg KOH / g and a hydroxyl value of 0 to 45 mg KOH / g;

[0089] Waterborne acrylic modified polyurethane (PUA): Neopac E-129 commercially available from DSM, with an acid value of 5 to 20 mg KOH / g and a hydroxyl value of 0 to 50 mg KOH / g;

[0090] Hydrophilic modified HDI: Bayhydur XP2655 commercially available from Covestro;

[0091] Oily HDI: DESMODUR N 3600 commercially available from Covestro;

[0092] Hydrophilic modified IPDI: BAYHYDUR 401-60 purchased from Covestro;

[0093] Organic solvents: alcohols, general industrial products

[0094] Dispersant: General industrial product

[0095] Titanium dioxide: general industrial product

[0096] Other additives: general industrial products

[0097] Hydroxyl functional acrylic resin: Houxian 2006 purchased from Houxian, hydroxyl value 120 mgKOH / g

[0098] Coating composition

[0099] Aqueous polyurethane dispersion (PUD), aqueous acrylic modified polyurethane (PUA), alcohols, water, dispersant, titanium dioxide and other additives in the amounts shown in Table 1 below were added to a mixing container and mixed, and then stirred at 800-1000 rpm until uniform, thereby obtaining a main agent. The main agent thus prepared was mixed with a curing agent composition at a weight ratio of 100:10, and a coating composition was determined.

[0100]

[0101] Note: Comparative Example 1 above is a two-component coating composition consisting of hydroxy acrylate + curing agent; the control example is a one-component coating composition without a curing agent; Examples 1, 2 and 3 respectively contain PUD, PUA and a combination of the two; the difference between Examples 3 and 4 is a single curing agent or a mixed curing agent; Examples 4-6 are examples with different organic solvent contents. 51. Comparison of the combination of curing agent and different main agents:

[0102] Compare the systems with different main agents and curing agents. The standard sample is the combination of PUA / PUD main agent and mixed curing agent, and the comparison sample is the combination of hydroxyl acrylic acid dispersion emulsion as the main agent and the same curing agent. The spray plate is tested under the same conditions. The results are as follows:

[0103] Table 2

[0104]

[0105] Judging from the test results, the one-component system with PUA / PUD as the main agent has better construction performance than the system with hydroxyl acrylic dispersion. Theoretically, since the main agent of the PUA / PUD system is a one-component system, the system can form a film without adding a curing agent. Compared with the two-component system that requires a curing agent to form a good film, the main agent of this one-component system will be more conducive to the fusion and cross-linking of resin particles during film formation. After the curing agent is added, since the reaction rate of NCO and carboxyl groups will be lower than the reaction rate with hydroxyl groups, the construction performance after mixing will be significantly improved. Moreover, the presence of a relatively small molecule curing agent will help the one-component system to have a better effect after film formation, which is beneficial to the improvement of properties such as scratch resistance and abrasion resistance. Therefore, whether it is a comparison of construction performance or performance after film formation, the combination of this one-component system and a curing agent will be better.

[0106] 2. Comparison of single-component and two-component systems

[0107] The system resistance of the 1K coating composition (PUA / PUD only as the main agent of the resin) (control example) and the 2K coating composition (PUA / PUD as the main agent of the resin with a hydrophilic modified HDI curing agent) (Examples 1 and 2) is compared according to the test standard of GB / T23999-2009. The results are summarized in Table 3 below:

[0108] Table 3:

[0109]

[0110] The 2K system uses hydrophilic modified HDI as a curing agent, and the ratio of the main agent to the curing agent is 100:10. The results show that for a one-component system, the addition of a curing agent can significantly improve the chemical resistance of the paint film. Theoretically, the addition of a curing agent significantly increases the crosslinking density. NCO not only reacts with the residual hydroxyl groups in the system, but also reacts with the carboxyl groups, thereby contributing to the construction of a three-dimensional network of the crosslinking system and improving the crosslinking density of the system.

[0111] 3. Matching of main agent and different curing agents

[0112] The single curing agent and the mixed curing agent were respectively matched with the main agent, and the properties of the coating composition and the obtained coating were tested respectively. The test results are summarized in the following Table 4.

[0113] Table 4

[0114]

[0115] Among them, Example 3 is a PUA / PUD resin system main agent used in combination with a single curing agent of hydrophilic modified HDI, and Example 4 is the same resin system mixed with three different types of curing agents, the three curing agents are hydrophilic modified HDI, oily HDI, and hydrophilic modified IPDI, the ratio is 2:3:5, the total amount of curing agent is 10 parts, the ratio of the main agent to the curing agent is 100:10, and the curing agent is diluted with water in a 1:1 ratio before use.

[0116] The results show that the system with three types of mixed curing agents has the following characteristics compared with the system with only a single-component curing agent:

[0117] a) Extend the potency period of the two-component system: When the initial viscosity is adjusted to 65s, the potency period tested at 35°C is extended from 3h to 4h;

[0118] b) Slow down the rate of viscosity increase: the percentage of viscosity increase within 2 hours decreased from 32.86% to 14.79%;

[0119] c) Speed ​​up the actual drying time while keeping the surface drying time the same;

[0120] Theoretically, compared with using a single hydrophilic modified HDI as a curing agent, a mixed curing agent has the following advantages:

[0121] Due to the rigid structure of IPDI, the collision probability of the two components of the main agent and the curing agent after mixing is reduced, which helps to improve the activation period of the system; at the same time, due to its structural characteristics, although the mixed curing agent introduces more solvents, IPDI is beneficial to the initial hardness establishment, so it does not affect its surface drying time. The addition of oily curing agent helps to increase the cross-linking density during film formation, thereby helping to increase the actual drying time of film formation and the cross-linking density after film formation. At the same time, the mixed curing agent retains a part of the hydrophilic modified HDI to ensure the dispersion performance of the curing agent in the main agent and does not affect the construction of the mixed system. In addition, compared with the combination of mixed curing agent and hydroxyl-containing main agent in other patents, this combination of mixed curing agent and single-component main agent does not need to consider the specific ratio of NCO to hydroxyl. The ratio of 100:10:10 (main agent: curing agent: water) commonly used in water-based two-component PU system can achieve better results than single component. Therefore, the combination of mixed curing agent and main agent of single-component PUA / PUD resin system can achieve the best performance and price.

[0122] 4. Effect of solvent concentration on the matching of main agent and different curing agents

[0123] The samples of Examples 3-6 were coated by spraying, with a coating amount of 100 g / m 2 All samples dried at room temperature were placed in an environment with a relative humidity of 80% and a temperature of 25°C to dry overnight, and all samples dried at 50°C were placed in an oven at 50°C to dry overnight. Then, the glossiness of each sample was measured, and the results are summarized in Table 5 below.

[0124] Table 5

[0125] Example 3 Example 4 Example 5 Example 6 Gloss @ Room Temperature 38.2 40.4 35.5 36.3 Gloss @50℃ 27.2 30.8 29.3 30.6 Glossiness changes 11 9.6 6.2 5.7 Gloss Change % 28.80％ 23.76％ 17.46％ 15.70％

[0126] Comparing Example 3 with Example 4, the percentage of gloss difference is reduced by about 5%, indicating that the use of a mixed curing agent can stabilize the gloss more than the use of a pure water-based HDI curing agent. Comparing the three sets of data of Examples 4-6, it can be shown that when a mixed curing agent is added, reducing the content of the solvent in the main agent is still helpful to stabilize the gloss.

[0127] Although the invention has been described with reference to a number of embodiments and examples, a person skilled in the art, based on the present disclosure, will recognize that other embodiments can be designed without departing from the scope and spirit of the invention.

Claims

1. A two-component water-based coating composition for a wood substrate, comprising: i) a main agent, the main agent comprising a) waterborne polyurethane dispersion (PUD), b) Waterborne acrylic modified polyurethane (PUA), c) an aqueous liquid carrier, and d) additional additives; ii) a curing agent composition comprising a hydrophilically modified aliphatic polyisocyanate; in, The mass ratio of the main agent to the curing agent composition is in the range of 100:5 to 100:

20.

2. The aqueous coating composition according to claim 1, wherein The curing agent composition further comprises a hydrophilically modified alicyclic polyisocyanate and an oily aliphatic polyisocyanate.

3. The aqueous coating composition according to claim 2, wherein: The curing agent composition comprises, relative to the total weight of the curing agent composition, 15-25 wt% of a hydrophilically modified aliphatic polyisocyanate; 25-35 wt% of an oily aliphatic polyisocyanate; and 45-55% by weight of a hydrophilically modified alicyclic polyisocyanate.

4. The aqueous coating composition according to any one of claims 1 to 3, wherein The hydrophilically modified aliphatic polyisocyanate is selected from hydrophilically modified hexamethylene diisocyanate, hydrophilically modified trimethyl hexamethylene diisocyanate and a combination thereof, preferably selected from hydrophilically modified hexamethylene diisocyanate.

5. The aqueous coating composition according to any one of claims 2 to 3, wherein The oily aliphatic polyisocyanate includes oily hexamethylene diisocyanate, oily trimethyl hexamethylene diisocyanate and a combination thereof, and is preferably selected from oily hexamethylene diisocyanate.

6. The aqueous coating composition according to any one of claims 2 to 3, wherein: The hydrophilically modified alicyclic polyisocyanate is selected from hydrophilically modified isophorone diisocyanate, hydrophilically modified dicyclohexylmethane diisocyanate, hydrophilically modified cyclohexane dimethyl diisocyanate and combinations thereof, preferably selected from hydrophilically modified isophorone diisocyanate.

7. The aqueous coating composition according to claim 1, wherein The aqueous polyurethane dispersion (PUD) comprises carboxyl functional groups, preferably having an acid value of 5 to 20 mg KOH / g; and / or, the aqueous polyurethane dispersion (PUD) has a hydroxyl value of 0 to 45 mg KOH / g.

8. The aqueous coating composition according to claim 1, wherein The waterborne acrylic modified polyurethane (PUA) comprises a carboxyl functional group, preferably having an acid value of 5 to 20 mg KOH / g; and / or, the waterborne acrylic modified polyurethane (PUA) has a hydroxyl value of 0 to 50 mg KOH / g.

9. The aqueous coating composition according to any one of claims 1 to 8, wherein The waterborne coating composition does not contain other hydroxyl-functional resins.

10. The aqueous coating composition according to any one of claims 1 to 8, wherein The main agent comprises, relative to the total weight of the main agent 15 to 65 wt. % aqueous polyurethane dispersion (PUD), preferably 20 to 55 wt. % aqueous polyurethane dispersion (PUD); 5 to 60 wt % of waterborne acrylic modified polyurethane (PUA), preferably 15 to 55 wt % of waterborne acrylic modified polyurethane (PUA); 5 to 20 wt % aqueous liquid carrier, preferably 8 to 15 wt % aqueous liquid carrier; and 0 to 35 wt % of additional additives, preferably 0.5 to 30 wt % of additional additives.

11. The aqueous coating composition according to any one of claims 1 to 8, wherein The aqueous liquid carrier comprises water, an organic solvent or a combination thereof.

12. The aqueous coating composition according to any one of claims 1 to 8, wherein In the main agent, the organic solvent is present in an amount of no more than 5 wt %, preferably no more than 3.5 wt %, and more preferably no more than 2.5 wt %, relative to the total weight of the main agent.

13. The aqueous coating composition according to any one of claims 1 to 12, wherein: The waterborne coating composition has an approximately 5% improvement in workability compared to a control coating composition formed using a hydroxyl-functionalized acrylate resin and the same curing agent composition, wherein the workability is measured under different temperature and humidity conditions, particularly under difficult-to-work conditions of high temperature (temperature above 35°C) and low humidity (humidity below 40%) for waterborne paints and for spraying oversized workpieces.

14. The aqueous coating composition according to any one of claims 12, wherein The aqueous coating composition prepared by the curing agent composition consisting of the hydrophilic modified aliphatic polyisocyanate, the oily aliphatic polyisocyanate and the hydrophilic modified alicyclic polyisocyanate has at least one of the following properties compared to the aqueous coating composition prepared by the curing agent composition consisting only of the hydrophilic modified aliphatic polyisocyanate: 25% or less 2-hour viscosity rise; The pot life at 35°C is extended by 30% or more; and With the same or similar surface drying time, the through drying time is shortened by 15% or more.

15. A product comprising a wood substrate having at least one major surface; and At least one paint film, the paint film being formed by directly or indirectly coating the main surface with the two-component coating composition according to any one of claims 1 to 14.

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