Two-component polyurethane topcoat

Abstract

The present invention relates to a two-component polyurethane topcoat, comprising: a) a film-forming resin composition, the film-forming resin composition comprising i) a polyester resin having a solid content of 65% or more; and ii) a hydroxyl-functionalized acrylic resin; and b) a curing agent component comprising a polyisocyanate, wherein the hydroxyl-functionalized acrylic resin has a viscosity of 62 Pa·s or more at 25° C. and a hydroxyl value of 90 mg KOH / g resin or less, and wherein a weight ratio of the component a) film-forming resin composition to the curing agent component is in the range of 100:40 to 100:60.

Description

Technical Field

[0001] The invention relates to a two-component polyurethane topcoat, and more particularly to a two-component polyurethane topcoat with excellent scratch resistance and low-temperature curing performance. Background Art

[0002] Polyurethane topcoats are widely used in the coatings industry. It is known that after curing, polyurethane paint can obtain a coating with good adhesion to primers (such as epoxy primers) and good weather resistance, corrosion resistance and gloss. Therefore, polyurethane topcoats basically cover all application fields of industrial paints, and the annual demand is even as high as 1 million tons.

[0003] From the perspective of practical application, the surface hardness of polyurethane topcoat (especially its scratch resistance) is one of the factors that determine its application range. However, most polyurethane topcoats currently on the market cannot meet customers' growing requirements for scratch resistance of the paint film surface. Therefore, the coatings industry needs further improved two-component polyurethane topcoats. Summary of the invention

[0004] The present invention provides a two-component polyurethane topcoat, comprising: a) a film-forming resin composition, the film-forming resin composition comprising i) a polyester resin having a solid content of 65% or more; ii) a hydroxyl-functionalized acrylic resin; and b) a curing agent component comprising a polyisocyanate, wherein the hydroxyl-functionalized acrylic resin has a viscosity of 62 Pa·s or more at 25° C. and a hydroxyl value of 90 mg KOH / g resin or less, and wherein a weight ratio of the component a) film-forming resin composition to the curing agent component is in the range of 100:40 to 100:60.

[0005] In another aspect, the present invention relates to a paint film formed by the two-component polyurethane topcoat according to the present invention. Preferably, the paint film has a scratch resistance of at least 5×10 3 The average critical load of 100 g is measured according to GBT 9279.2-2015 (ISO1518-2:2011). In one embodiment of the present invention, the paint film may be a matte paint film.

[0006] As is known to all, most of the polyurethane topcoats currently available in the market cannot meet the increasing customer requirements for the scratch resistance of the paint film surface. Known two-component polyurethane topcoats with the desired scratch resistance are not satisfactory in other aspects. For example, the two-component polyurethane topcoat with the trade name OPX300 purchased from ICA, Italy, usually requires long-term baking at high temperature to form a film, which inevitably affects the wide application of the polyurethane topcoat on heat-sensitive substrates, especially wooden substrate surfaces.

[0007] The inventors of the present invention surprisingly found that in the preparation of a two-component polyurethane topcoat, by introducing a composite resin system comprising a polyester resin with a solid content of 65% or more and a hydroxyl-functionalized acrylic resin with a viscosity of 62 Pa.s or more and a hydroxyl value of 90 mgKOH / g resin or less into a film-forming resin composition, not only can a polyurethane topcoat capable of forming a paint film with excellent scratch resistance be obtained, but the two-component polyurethane topcoat prepared thereby also has excellent low-temperature curing properties and can be cured at a temperature of 25°C or lower, and can even be cured at a temperature of 10°C or lower, which was difficult to foresee before the present application.

[0008] The inventors of the present invention also surprisingly found that in the preparation of the two-component polyurethane topcoat, by introducing a certain amount of silica matting powder into the film-forming resin composition composed of the above-mentioned composite resin system, the components cooperate with each other functionally, so that the two-component polyurethane topcoat formed by the preparation thereof can not only obtain a matte effect, but also the paint film formed by this polyurethane topcoat has a stable gloss and is not easily brightened under pressure.

[0009] 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.

[0010] definition

[0011] As used herein, "a", "an", "the", "at least one" and "one or more" are used interchangeably. Thus, for example, a component containing "an" additive can be interpreted to mean that the component contains "one or more" additives.

[0012] 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.

[0013] 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.

[0014] In this article, "coating" and "paint film" have the same meaning, both of which are formed by applying and curing a two-component polyurethane topcoat.

[0015] In the context of this application, the term "two-component polyurethane topcoat" refers to a paint consisting of two or more separately stored components, the components of which are mixed together when used and can be dried and cured within an acceptable period of time to form a coating or paint film with desired mechanical properties (such as hardness).

[0016] In the context of "two-component polyurethane topcoat", the term "achieves early drying" means that the two-component polyurethane topcoat can achieve drying within a period of less than 24 hours at a specific temperature, so that the articles coated with the topcoat can be packaged, lightly touched, etc. without causing substantial damage to the paint film, such as stains, breakage, etc.

[0017] In the context of "two-component polyurethane topcoat", the term "scratch resistance" refers to the ability of a paint film formed by the two-component polyurethane topcoat to withstand cuts or scratches that penetrate the coating surface formed by contact with a sharp object, which is measured by GBT 9279.2-2015 (ISO1518-2: 2011) and the results are expressed in terms of an average critical load Fc (in grams), which is calculated using the following formula:

[0018]

[0019] Where d is the distance between the final load point and the point where the scratch just appeared, expressed in millimeters (mm);

[0020] F f represents the final load of the selected stylus load range, expressed in grams (g);

[0021] F j Indicates the initial load for the selected stylus load range, expressed in grams (g).

[0022] In the context of a two-component polyurethane topcoat, the term "pressed gloss" is a parameter used to measure the gloss consistency of a paint film formed from the two-component polyurethane topcoat. It is preferred that the gloss of the paint film does not change substantially when a certain amount of pressure load is applied to the paint film.

[0023] In the context of each component and a mixture of components in this article, the term "solid content" is also referred to as mass solid content, which refers to the mass percentage determined as follows: after the component or mixture to be tested is baked at 110°C for 1 hour under normal pressure conditions, the ratio of the mass of the residue remaining after baking to the original mass of the component or mixture to be tested is calculated, thereby obtaining the mass solid content of the component or mixture to be tested.

[0024] Herein, the term "hydroxyl value" refers to the number of milligrams of potassium hydroxide equivalent to the hydroxyl content in each gram of sample. In an embodiment of the present invention, the hydroxyl value of the resin is determined by titration according to GB12009.3-2009.

[0025] In the context of describing that a component does not contain a certain ingredient, the term "does not contain" means that the component does not contain the intentionally added ingredient. Taking into account the complexity of the actual preparation process, the phrase "a component does not contain a certain ingredient" can be understood as a component containing less than 1% by weight of the ingredient based on the total weight of the component, more preferably less than 0.5% by weight, still more preferably less than 0.3% by weight, even more preferably less than 0.2% by weight, and most preferably less than 0.1% by weight of the ingredient.

[0026] As used herein, the term "topcoat" refers to a coating composition that can be applied over a basecoat or color correction layer and dried, crosslinked or otherwise hardened to form a decorative or protective outermost finish layer. Further, such topcoats are capable of withstanding long-term outdoor exposure without showing visible unsatisfactory degradation, such as fingernail scratches, etc.

[0027] When appearing in this description and claims, the terms "comprises" and "includes" and variations thereof do not have a limiting meaning.

[0028] In the present invention, the numerical range defined by the endpoint includes all the values ​​within the range, for example, the range of 1 to 5 includes the values ​​1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. Moreover, the disclosed numerical range includes all the subset ranges within the broader range, for example, the range of 1 to 5 includes the sub-ranges 1 to 4, 1.5 to 4.5, 1 to 2, etc.

[0029] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1These are pictures of nail scratches on a cured coating formed by a two-component polyurethane topcoat prepared according to Example 1 of the present invention and a cured coating formed by a control two-component polyurethane topcoat A with a brand number of P39005, wherein the left picture is the two-component polyurethane topcoat prepared according to Example 1 of the present invention, and the right picture is the control two-component polyurethane topcoat. DETAILED DESCRIPTION

[0031] The present invention provides a two-component polyamide topcoat, comprising: a) a film-forming resin composition, the film-forming resin composition comprising i) a polyester resin having a solid content of 65% or more; ii) a hydroxyl-functionalized acrylic resin; and b) a curing agent component comprising a polyisocyanate, wherein the hydroxyl-functionalized acrylic resin has a viscosity of 62 Pa·s or more at 25° C. and a hydroxyl value of 90 mg KOH / g resin or less, and wherein a weight ratio of the component a) film-forming resin composition to the curing agent component is in the range of 100:40 to 100:60.

[0032] Film-forming resin composition

[0033] The term "film-forming resin composition" herein refers to the resin composition constituting the main body of the coating formed by the two-component polyurethane topcoat of the present invention, which may include a hydroxyl-functional acrylic resin and a polyester resin having a solid content of 65% and above.

[0034] According to the present invention, "hydroxyl-functionalized acrylic resin" refers to an acrylic resin containing a hydroxyl functional group. According to the present invention, the hydroxyl-functionalized acrylic resin is used to provide a resin component for a film-forming resin composition and a two-component polyurethane topcoat. On the one hand, this resin component acts as a binder to provide adhesion between the coating and the substrate or the bottom layer, and to keep the components (such as pigments) in the film-forming resin composition together and give the coating a certain cohesive strength. On the other hand, this hydroxyl-functionalized resin component has good reactivity with a polyisocyanate curing agent, thereby achieving crosslinking of the polymer chain, thereby forming a coating with suitable mechanical strength.

[0035] The inventors of the present invention surprisingly found that the introduction of a hydroxyl-functional acrylic resin having a low hydroxyl value and a high viscosity into a film-forming resin composition can significantly improve the curing properties of the topcoat, and the two-component polyurethane topcoat thus formed can achieve early drying at low temperatures, such as at a temperature of 25° C. or lower, or even at a temperature of 10° C. or lower, without the need for baking and drying, which was difficult to foresee before the present application. Therefore, in an embodiment according to the present invention, the hydroxyl-functional acrylic resin has a viscosity of 62 Pa.s or higher at 25° C. and a hydroxyl value of 90 mg KOH / g resin or lower.

[0036] In some preferred embodiments according to the present invention, the hydroxyl-functionalized acrylic resin has a hydroxyl value of 80 mgKOH / g resin or less, preferably 70 mgKOH / g resin or less, more preferably 40 mgKOH / g resin to 70 mgKOH / g resin. The hydroxyl value is determined by titration according to GB12009.3-2009.

[0037] In some preferred embodiments according to the present invention, the hydroxyl-functional acrylic resin has a viscosity of 62 Pa·s to 90 Pa·s at 25° C., preferably 65 Pa·s to 90 Pa·s at 25° C., and more preferably 70 Pa·s to 90 Pa·s at 25° C. The viscosity is measured using a Brookfield viscometer, using a No. 3 spindle and a rotation speed of 10 rpm.

[0038] Preferably, the hydroxyl-functionalized acrylic resin has a weight average molecular weight of 15,000 g / mol or more, a weight average molecular weight of 20,000 g / mol or more, a weight average molecular weight of 30,000 g / mol or more, preferably a weight average molecular weight of 35,000 g / mol or more, more preferably a weight average molecular weight of 40,000 g / mol or more, and even more preferably a weight average molecular weight of 50,000 g / mol or more. There is no upper limit on the weight average molecular weight of the hydroxyl-functionalized acrylic resin. However, from the perspective of practical application, the weight average molecular weight of the hydroxyl-functionalized acrylic resin is preferably not more than 100,000 g / mol. The weight average molecular weight can be determined using GPC. It has been observed that the use of hydroxyl-functionalized acrylic resins with higher weight average molecular weights results in two-component polyurethane topcoats having higher mechanical strength.

[0039] Preferably, the solids content of the hydroxyl-functional acrylic resin is in the range of about 48% to about 58%, preferably in the range of about 48% to about 52%, wherein solids content is understood as the weight percentage of non-volatiles in the hydroxyl-functional acrylic resin.

[0040] The hydroxyl-functionalized acrylic resin disclosed above can be prepared by a suitable polymerization method known to those skilled in the art, such as solution polymerization. Alternatively, as an example of a hydroxyl-functionalized acrylic resin, any suitable commercially available product can be used, such as the acrylic resin SQ1993B of Sherwin-Williams.

[0041] In some embodiments according to the present invention, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, about 10% to about 30% by weight, preferably about 10% to about 20% by weight of a hydroxyl-functionalized acrylic resin. Specifically, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, at least 12%, at least 14%, at least 15%, at least 16%, at least 17%, at least 18%, and at most 28%, at most 26%, at most 25%, at most 24%, at most 23%, at most 22%, at most 21%, at most 19% by weight of a hydroxyl-functionalized acrylic resin.

[0042] In an embodiment according to the present invention, in a film-forming resin composition, a polyester resin is introduced and used in conjunction with the above-mentioned hydroxyl-functionalized acrylic resin to form a composite resin component. In this article, "polyester resin" is understood to be an oligomer or polymer containing at least one -C(O)O-ester group in the molecular chain skeleton. Similarly, according to the present invention, polyester resin is used to provide a resin component for a film-forming resin composition and a two-component polyurethane topcoat. On the one hand, this polyester resin component is used as a binder to provide adhesion between the coating and the substrate or the bottom layer, and to keep the components (such as pigments) in the film-forming resin composition together and give the coating a certain cohesive strength.

[0043] The inventors of the present invention surprisingly found that the introduction of a polyester resin having a high solid content into the film-forming resin composition can significantly improve the surface properties of the topcoat, and the paint film formed by the two-component polyurethane topcoat thus formed has particularly excellent scratch resistance, for example, when subjected to a scratch resistance test, it has a scratch resistance of at least 5×10 3 The average critical load of grams is measured according to GBT 9279.2-2015 (ISO1518-2: 2011). Therefore, in an embodiment according to the present invention, the polyester resin has a solid content of 65% or more. In some preferred embodiments according to the present invention, the polyester resin has a solid content of 70% or more, preferably 80% or more.

[0044] In some embodiments according to the present invention, the polyester resin is hydroxyl-functionalized, and thus can be used as a resin component reactive with a polyisocyanate curing agent to achieve crosslinking of polymer chains, thereby forming a coating with suitable mechanical strength. Preferably, the polyester resin has a hydroxyl value of 70 mg KOH / g resin or higher, more preferably a hydroxyl value in the range of 70 to 100 mg KOH / g resin, even more preferably a hydroxyl value in the range of 70 to 90 mg KOH / g resin, and most preferably a hydroxyl value of 80 mg KOH / g resin. The hydroxyl value is determined by titration according to GB12009.3-2009.

[0045] As is well known, polyester resins can generally be prepared by condensing a polyacid or anhydride with a polyol or bisphenol under appropriate esterification conditions. In a specific embodiment of the present invention, the polyester resin contained in the film-forming resin composition is a saturated polyester resin prepared by condensing a carboxylic acid component and an alcohol component under the action of a catalyst and extracting and purifying, wherein the carboxylic acid component contains at least one polyacid having two or more carboxyl functional groups, and wherein the alcohol component contains at least one polyol having two or more hydroxyl functional groups. As described above, in the preparation process of the above polyester resin, an additional purification process is used, so that the polyester resin prepared therefrom is substantially oil-free. In this article, the term "oil" is any small molecule organic compound used in the preparation process of the polyester resin, including but not limited to carboxylic acid components, alcohol components, solvents or other small molecule organic compounds. In other words, in the above embodiment, the content of small molecule organic compounds in the polyester resin is very low, for example, the polyester resin contains small molecule organic compounds of less than 0.5% by weight, less than 0.3% by weight, less than 0.2% by weight, or even less than 0.1% by weight relative to the total weight of the polyester resin. The inventors of the present application surprisingly found that when the oil-free polyester resin with a high solid content formed by the above method is used as a resin component to formulate a two-component polyurethane topcoat, the surface properties of the paint film formed therefrom, such as scratch resistance, can be significantly improved, and there is no need to bake and dry the film, which was difficult to foresee before the present application.

[0046] In one embodiment of the present invention, the polyester resin contained in the film-forming resin composition has an appropriate glass transition temperature, for example, a glass transition temperature of -10°C to 10°C, and the two-component polyurethane topcoat formed therefrom has significantly lower gloss, and can even reach a matte level.

[0047] In one embodiment of the present invention, the polyester resin contained in the film-forming resin composition has a relatively high molecular weight, for example, a weight average molecular weight in the range of 5000 to 15000, and the scratch resistance of the two-component polyurethane topcoat formed therefrom is further improved, and can even have an average critical load of up to 6,000 g. The weight average molecular weight can be measured using GPC.

[0048] The polyester resin disclosed above can be prepared by a suitable polymerization method known to those skilled in the art. Alternatively, as an example of the above polyester resin, any suitable commercially available product can be used, such as the polyester resin AK1278B of Jiangmen Paint Co., Ltd.

[0049] Preferably, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, about 25 wt % to about 50 wt %, preferably about 30 wt % to about 45 wt % of polyester resin. Specifically, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, at least 32 wt %, at least 34 wt %, at least 35 wt %, at least 36 wt %, at least 37 wt %, at least 38 wt %, and at most 45 wt %, at most 44 wt %, at most 43 wt %, at most 42 wt %, at most 41 wt %, at most 40 wt %, at most 39 wt % of polyester resin.

[0050] The inventors of the present invention surprisingly found that the above-mentioned composite resin system cooperates with each other in function, not only can a polyurethane topcoat capable of forming a paint film with excellent scratch resistance be obtained, but also the two-component polyurethane topcoat prepared therefrom also has excellent low-temperature curing performance.

[0051] In some embodiments according to the present invention, the film-forming resin composition may further include a silica matting agent. As is well known, in the coating industry, a matting agent is a reagent that is usually added to a coating composition. After the coating composition formed in this way forms a film, the matting agent particles distributed in the paint film make the surface uneven, increase the scattering of light and reduce reflection, thereby producing a low-gloss matte effect. However, due to the limitations of the properties of the matting agent material itself, common matting agents such as micron-sized silicon dioxide are unevenly dispersed in the polymer emulsion, and the paint film formed by the coating composition prepared therefrom is prone to brightening under pressure. The inventors of the present application were surprised to find that in the preparation of a two-component polyurethane topcoat, by introducing a certain amount of silica matting powder into the film-forming resin composition composed of the above-mentioned composite resin system, the components cooperate with each other in function, so that the two-component polyurethane topcoat formed by the preparation thereof can not only obtain a matte effect, but also the paint film formed by this polyurethane topcoat has a stable glossiness and is not easy to brighten under pressure. The silica matting agent can be any silica matting agent known to those skilled in the art that is suitable for formulating coatings or paints.

[0052] Preferably, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, about 1 wt % to about 10 wt %, preferably 1 wt % to 5 wt %, more preferably about 1 wt % to about 3 wt % of a silica matting agent. Specifically, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, about 2 wt %, about 2.5 wt %, about 3 wt % of a silica matting agent.

[0053] In some embodiments according to the present invention, in order to adjust the viscosity of the two-component polyurethane topcoat, so as to obtain a coating composition suitable for coating, the film-forming resin composition may further include an organic solvent. The solvent used herein is any solvent known in the art that is suitable for coating compositions, including but not limited to aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, terpene solvents, alcohol solvents, ketone solvents, ester solvents, alcohol ethers and ester ether solvents, substituted hydrocarbon solvents or any combination thereof. Preferably, the solvent includes an ester solvent, an aromatic hydrocarbon solvent, an ester ether solvent, a substituted hydrocarbon solvent or any combination thereof.

[0054] Preferably, the film-forming resin composition comprises, relative to the total weight of the film-forming resin composition, about 10 wt % to about 30 wt %, preferably about 20 wt % to about 30 wt % of an organic solvent.

[0055] In the present invention, the film-forming resin composition may further include additional additives commonly used in polyurethane topcoats, which do not adversely affect the coating composition or the cured coating obtained therefrom. Suitable additives include, for example, those reagents that improve the processing properties or manufacturing properties of the composition, enhance the aesthetics of the composition, or improve the specific functional properties or characteristics (such as adhesion to substrate) of the coating composition or the cured composition obtained therefrom. The additives that may be included are, for example, pigments, anti-migration aids, antibacterial agents, chain extenders, lubricants, biocides, plasticizers, defoamers, color extenders, waxes, antioxidants, adhesion promoters, UV stabilizers, or combinations thereof. The content of each optional component is sufficient to achieve its intended purpose, but preferably, such content does not adversely affect the coating composition or the cured coating obtained therefrom. In a preferred embodiment of the present invention, suitable additional additives include pigments, defoamers, bactericides, mildewicides, or any combination thereof. According to the present invention, the total amount of additional additives is in the range of about 0.1% by weight to about 10% by weight relative to the gross weight of the film-forming resin composition.

[0056] In a preferred embodiment of the present invention, the film-forming resin composition comprises, based on the total weight of the film-forming resin composition,

[0057] 10-30 wt %, preferably 10-20 wt % of a hydroxyl-functional acrylic resin;

[0058] 25-50 wt%, preferably 30-45 wt% of polyester resin;

[0059] 1-10 wt %, preferably 1-5 wt % of a silica matting agent;

[0060] 10-30 wt % of an organic solvent; and

[0061] 0.1-10 wt% of additional additives.

[0062] The preparation of the film-forming resin composition of the present invention can be achieved by any suitable mixing method known to those skilled in the art. For example, the film-forming resin composition can be prepared by adding a hydroxyl-functional acrylic resin, a polyester resin, a silica matting agent, an organic solvent and additional additives (if any) into a container, and then stirring the resulting mixture to uniformity.

[0063] Curing agent component

[0064] In the two-component polyurethane topcoat according to the present invention, polyisocyanate is used as the reactive component of the curing agent component. The term "polyisocyanate" used herein refers to a polyisocyanate compound, an isocyanate oligomer or a combination thereof. The polyisocyanate curing agent contains two or more isocyanate functional groups, which can undergo chain extension and crosslinking reactions with active hydrogen polymers, thereby forming a three-dimensional network structure in the coating.

[0065] Suitable polyisocyanate curing agents include aliphatic polyisocyanates, aromatic polyisocyanates or any combination thereof. The term "aliphatic polyisocyanate" as used herein refers to a polyisocyanate compound in which an isocyanate group is directly connected to an aliphatic chain or ring. The term "aromatic polyisocyanate" as used herein refers to a polyisocyanate compound in which an isocyanate group is directly connected to an aromatic ring.

[0066] As an example of a suitable polyisocyanate compound, hexamethylene diisocyanate, dodecamethylene diisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, cyclopentane-1,3-diisocyanate, p-phenylene diisocyanate, toluene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, biphenyl-4,4'-diisocyanate, benzene-1,2,4-triisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, diphenylmethane diisocyanate, butane-1,2,3-triisocyanate or polymethylene polyphenyl polyisocyanate can be used. As an example of a suitable isocyanate compound, N-3390 commercially available from BAYER, Germany can be used.

[0067] As an example of a suitable isocyanate oligomer, a polyurethane prepolymer of any polyisocyanate compound listed above, a polyester prepolymer of any polyisocyanate compound listed above, or a polyether prepolymer of any polyisocyanate compound listed above, and any combination thereof, can be used. Polyurethane prepolymers, polyester prepolymers, or polyether prepolymers can be made by any suitable method known to those of ordinary skill in the art. For example, a polyurethane prepolymer can be made by reacting a polyol monomer with one or more of the polyisocyanate compounds under suitable conditions; a polyester prepolymer or a polyether prepolymer can be made by reacting a polyester polyol or a polyether polyol with one or more of the polyisocyanate compounds under suitable conditions. Alternatively, any suitable commercial product can be used as a polyurethane prepolymer, a polyester prepolymer, or a polyether prepolymer, such as N-75 purchased from BASF in Germany, or TPA-90 purchased from ASAHIKASEI in Japan.

[0068] In a preferred embodiment of the present invention, the polyisocyanate curing agent can be diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, polyester prepolymer of diphenylmethane diisocyanate, polyether prepolymer of diphenylmethane diisocyanate or any combination thereof. In a further preferred embodiment of the present invention, polymethylene polyphenyl polyisocyanate, polyester prepolymer of diphenylmethane diisocyanate or polyether prepolymer of diphenylmethane diisocyanate is used. In the most preferred embodiment of the present invention, HDI trimer is used.

[0069] Preferably, the curing agent component comprises, relative to the total weight of the curing agent component, from about 30 wt % to about 60 wt %, preferably from about 40 wt % to about 50 wt % of the polyisocyanate.

[0070] According to actual needs, in order to adjust the viscosity of the two-component polyurethane topcoat, an appropriate amount of an inert diluent that does not affect the reactivity of the above film-forming resin composition and the polyisocyanate curing agent can be added. The type of the inert diluent can be the same as the type of the organic solvent in the film-forming resin composition. As an exemplary illustration, the inert diluent includes but is not limited to aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, terpene solvents, alcohol solvents, ketone solvents, ester solvents, alcohol ethers and ester ether solvents, substituted hydrocarbon solvents or any combination thereof.

[0071] Preferably, the curing agent component comprises, relative to the total weight of the curing agent component, about 30 wt % to about 60 wt %, preferably about 40 wt % to about 60 wt % of an organic solvent.

[0072] According to the present invention, the weight ratio of the curing agent component to the film-forming resin composition can vary in the range of 40: 100 to 60: 100. Generally speaking, when the weight ratio of the curing agent component to the film-forming resin composition is less than 40: 100, the curing performance of the resulting coating is poor; when the weight ratio of the curing agent component to the film-forming resin composition is greater than 60: 100, the operating performance of the resulting two-component polyurethane topcoat and / or the mechanical properties of the resulting coating may decrease.

[0073] According to the present invention, the two-component polyurethane topcoat can be prepared as follows: before application, the film-forming resin composition and the polyisocyanate curing agent are simply mixed in a mixing device at a predetermined weight ratio. The two-component polyurethane topcoat thus formulated meets the requirements for the limit of harmful substances of polyurethane topcoats with a glossiness of less than 80 at 60°. Therefore, in one embodiment according to the present invention, the two-component polyurethane topcoat has a volatile organic compound (VOC) content of 650 g / L or less, measured according to GB 18581-2020.

[0074] The two-component polyurethane topcoat according to the present invention can be applied using various methods familiar to those skilled in the art after mixing, including spraying (e.g., air-assisted, airless or electrostatic spraying), brushing, roller coating, overflow coating and dipping. In one embodiment of the present invention, the mixed polyurethane topcoat is applied by spraying. The polyurethane topcoat can be applied to 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). The paint film of the polyurethane topcoat so formed can achieve early curing at a temperature of 25° C. or lower, preferably at a temperature of 10° C. or lower.

[0075] Therefore, another aspect of the present invention relates to a paint film, which is formed by the two-component polyurethane topcoat according to the present invention. Preferably, the paint film can withstand a nail scratch test, which is measured according to GBT 9279.2-2015 (ISO1518-2: 2011). For example, the paint film can have an average critical load of up to 5000g or more. In one embodiment of the present invention, the paint film can be a matte paint film.

[0076] 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 disclosure of the present invention 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 treatment.

[0077] Example

[0078] Test Section

[0079] VOC Content It is measured according to GB 18581-2020.

[0080] Early drying It is a parameter used to measure the early curing performance of two-component polyurethane topcoat. The two-component polyurethane topcoat to be tested is coated on a substrate with a wet film thickness of, for example, 120 microns, and the coated substrate is placed at a specific temperature to dry for 24 hours. If the paint film does not suffer substantial damage, such as staining or breakage, after packaging or gently touching the product coated with the topcoat, the two-component polyurethane topcoat is judged to have passed, otherwise it is judged to have failed.

[0081] Scratch resistance It is measured according to the provisions of the national standard GBT 9279.2-2015 (ISO1518-2:2011).

[0082] Glossiness It is measured according to the provisions of the national standard GB / T 1743-1989.

[0083] Brightens under pressure It is a parameter used to measure the gloss change, which is measured according to the provisions of the national standard GB / T 1743-1989. In an embodiment according to the present invention, a 60° gloss change of more than 5% is considered unqualified, a 60° gloss change of less than 5% is considered qualified, and a 60° gloss change of less than 3% is considered excellent.

[0084] Raw materials:

[0085] Hydroxyl functionalized acrylic resin: commercially available acrylic resin SQ1993B from Sherwin-Williams, with a hydroxyl value of 70 mg KOH / g resin and a viscosity of 62-90 Pa.s@25°C;

[0086] Comparative hydroxyl-functionalized acrylic resin 1: commercially available acrylic resin SQ0805B from Changxing, hydroxyl value of 60 mg KOH / g resin; viscosity of 3-10 Pa.s@25°C

[0087] Comparative hydroxyl-functionalized acrylic resin 2: Sherwin-Williams acrylic resin SQ1980P, hydroxyl value 80 mgKOH / g resin; viscosity 4-10 Pa.s@25°C

[0088] Comparative hydroxyl-functionalized acrylic resin 3: commercially available acrylic resin SQ0403B from Tongde, with a hydroxyl value of 130 mg KOH / g resin; viscosity of 50-80 Pa.s@25°C

[0089] Polyester resin: polyester resin purchased from Jiangmen Paint Co., Ltd., with a solid content of 80%;

[0090] Control polyester resin: Uralac 3735X60, a polyester resin commercially available from Covestro, with a solid content of 60%;

[0091] Matting agent: micron-sized silica, a general industrial product;

[0092] Dispersant: general industrial product;

[0093] Control polyurethane topcoat A: a two-component polyurethane topcoat with the brand number P39005; and

[0094] Control polyurethane topcoat B: two-component polyurethane topcoat OPX300 purchased from ICA, Italy.

[0095] Two-component polyurethane topcoat

[0096] As shown in Table 1 below, a hydroxyl-functionalized acrylic resin, a polyester resin, a silica matting agent, a dispersant and a solvent are mixed to obtain a film-forming resin composition as component A. Then, a curing agent is mixed with a corresponding solvent to obtain a water-based curing system as component B. Then, the obtained component A is mixed with component B to form two-component polyurethane topcoats of Examples 1-4 and Comparative Examples 1-4 and Reference Example A, wherein Example 1 does not contain a silica matting agent, Examples 2-4 respectively contain different amounts of polyester resin and / or hydroxyl-functionalized acrylic resin; Comparative Examples 1-3 respectively contain control hydroxyl-functionalized acrylic resins 1-3; Comparative Example 4 contains a control polyester resin; Control Example A uses a control two-component polyurethane topcoat A; and Control Example B uses a control two-component polyurethane topcoat B.

[0097] Then, the curing properties of the two-component polyurethane topcoat obtained by the above embodiment and the comparative example at different temperatures, and the VOC content were tested respectively. In addition, according to the above test section, the glossiness, scratch resistance and pressure-brightening results of the paint film formed by the two-component polyurethane topcoat obtained by the above embodiment and the comparative example were measured. The results are summarized in Table 1.

[0098]

[0099] It can be seen from the results of the above Examples 1-4 that in the preparation of a two-component polyurethane topcoat, by introducing a composite resin system comprising a polyester resin with a high solid content and a hydroxyl-functionalized acrylic resin with a high viscosity and a low hydroxyl value into a film-forming resin composition, not only can a polyurethane topcoat capable of forming a paint film with excellent scratch resistance be obtained, but the two-component polyurethane topcoat prepared thereby also has excellent low-temperature curing performance; and the introduction of a certain amount of silica matting powder not only provides a matte effect for the two-component polyurethane topcoat, but also the paint film formed by such a polyurethane topcoat has a stable gloss and is not easily brightened under pressure.

[0100] Compared with Examples 2-4 and Comparative Examples 1-3, the introduction of a hydroxyl-functionalized acrylic resin with high viscosity and low hydroxyl value into the film-forming resin composition is necessary to achieve low temperature curing performance, especially curing at 25° C. or lower. Moreover, compared with Examples 2-4 and Comparative Example 4, the two-component polyurethane topcoat formed by the polyester resin having a high solid content can form a paint film with excellent scratch resistance.

[0101] Moreover, it can be seen from the comparison results of the above Examples 1-4 and Comparative Example A that, compared with the two-component polyurethane matte topcoat currently on the market, the two-component polyurethane topcoat according to the present invention can be matte and has excellent low temperature curing performance and scratch resistance. In comparison, the scratch resistance of the two-component polyurethane matte topcoat currently on the market is far from ideal, with obvious nail scratches, such as Figure 1 shown.

[0102] In addition, it can be seen from the comparison results of the above Examples 1-4 and Comparative Example B that the two-component polyurethane matte topcoat B needs to be baked at high temperature for a long time to form a film, which inevitably affects the wide application of the polyurethane topcoat on heat-sensitive substrates, especially wooden substrate surfaces. In comparison, the two-component polyurethane topcoat according to the present invention can achieve early curing at a lower temperature, has a wider range of applications, and is worthy of vigorous promotion.

[0103] 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 polyurethane topcoat comprising: a) a film-forming resin composition, the film-forming resin composition comprising: i) a polyester resin having a solid content of 65% or more, wherein the polyester resin is hydroxyl functionalized; ii) a hydroxyl-functional acrylic resin; and b) a curing agent component comprising a polyisocyanate, in, The hydroxyl-functional acrylic resin has a viscosity of 62 Pa·s or more at 25° C. and a hydroxyl value of 90 mg KOH / g or less, and wherein the weight ratio of the component a) film-forming resin composition to the curing agent component is in the range of 100:40 to 100:60, and wherein the hydroxyl-functional acrylic resin is present in an amount of 10 wt % to 30 wt % relative to the total weight of the film-forming resin composition, and Wherein, the polyester resin is present in an amount of 25 wt % to 50 wt % relative to the total weight of the film-forming resin composition.

2. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a viscosity of 62 to 90 Pa·s at 25°C.

3. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a viscosity of 65 to 90 Pa·s at 25°C.

4. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a viscosity of 70 to 90 Pa·s at 25°C.

5. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a hydroxyl value of 80 mg KOH / g or less.

6. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a hydroxyl value of 70 mg KOH / g or less.

7. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin has a hydroxyl value in a range of 40 mg KOH / g to 70 mg KOH / g.

8. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl functional acrylic resin has a solid content of 48-58%.

9. The two-component polyurethane topcoat as claimed in claim 1, wherein: The hydroxyl-functional acrylic resin is present in an amount of 10 wt % to 20 wt % relative to the total weight of the film-forming resin composition.

10. A two-component polyurethane topcoat according to any one of claims 1 to 9, wherein The polyester resin has a solid content of 70% or more.

11. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin has a solid content of 80% or more.

12. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin has a hydroxyl value of 70 mg KOH / g or more.

13. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin has a hydroxyl value in the range of 70 to 100 mg KOH / g.

14. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin has a hydroxyl value in the range of 70 to 90 mg KOH / g.

15. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin had a hydroxyl value of 80 mg KOH / g.

16. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin has a weight average molecular weight ranging from 5000 g / mol to 15000 g / mol.

17. A two-component polyurethane topcoat according to any one of claims 1 to 9, wherein The polyester resin has a glass transition temperature in the range of -10°C to 10°C.

18. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin is a saturated polyester resin prepared by a condensation polymerization reaction of a carboxylic acid component and an alcohol component under the action of a catalyst and then purified by extraction, wherein the carboxylic acid component contains at least one polyacid having two or more carboxyl functional groups, and wherein the alcohol component contains at least one polyol having two or more hydroxyl functional groups.

19. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyester resin is present in an amount of 30 wt % to 45 wt % relative to the total weight of the film-forming resin composition.

20. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The film-forming resin composition further includes a silica matting powder, which is present in an amount of 1 wt % to 5 wt % relative to the total weight of the film-forming resin composition.

21. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The film-forming resin composition further includes an organic solvent, which is present in an amount of 10 wt % to 30 wt % relative to the total weight of the film-forming resin composition.

22. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The polyisocyanate is selected from aliphatic polyisocyanates, aromatic polyisocyanates and combinations thereof.

23. A two-component polyurethane topcoat as claimed in claim 22, wherein: The polyisocyanate includes hexamethylene diisocyanate, dodecamethylene diisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, cyclopentane-1,3-diisocyanate, p-phenylene diisocyanate, toluene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, biphenyl-4,4'-diisocyanate, benzene-1,2,4-triisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, diphenylmethane diisocyanate, butane-1,2,3-triisocyanate, polymethylene polyphenyl polyisocyanate, its polyurethane prepolymer, its polyester prepolymer or its polyether prepolymer, or one or more thereof, or any combination thereof.

24. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The curing agent component further comprises an organic solvent, which is present in an amount of 30 wt % to 70 wt % relative to the total weight of the curing agent component.

25. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: The two-component polyurethane topcoat has a volatile organic compound (VOC) content of 650 g / L or less, measured according to GB 18581-2020.

26. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: After the film-forming resin composition is mixed with the curing component, the resulting mixture achieves early drying at a temperature of 25° C. or less.

27. A two-component polyurethane topcoat as claimed in any one of claims 1 to 9, wherein: When the film-forming resin composition is mixed with the curing component, the resulting mixture achieves early drying at a temperature of 10° C. or less.

28. A paint film formed from the two-component polyurethane topcoat according to any one of claims 1 to 27.

29. A paint film as claimed in claim 28, wherein, The paint film has an average critical load of at least 5,000 grams when subjected to a scratch resistance test, the test being determined in accordance with GBT 9279.2-2015 (ISO 1518-2: 2011).

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