CN104877107A - Aqueous dual-component polyurethane paint system - Google Patents

Abstract

The invention relates to a polyurethane-based waterborne two-component coating system and its application. It is characterized in that the composition simultaneously includes an aqueous dispersion containing one or more compounds containing OH functional groups; and one or more hydrophobic or hydrophilic modified polyisocyanates; wherein, the composition contains one or more Aqueous dispersions of various OH-functional compounds have glass transition temperatures above 20°C. Compared with the prior art, the water-based two-component coating system of the present invention has both excellent chemical resistance and faster drying speed.

Description

Waterborne two-component polyurethane coating system

technical field

The invention relates to the preparation and application of a water-based quick-drying two-component polyurethane coating composition with good chemical resistance.

Background technique

In the use of paint, the use of water as a solvent has increased significantly in recent years. A decisive factor in the development of this technology was environmental considerations. For example, using water as a solvent when applying paint to substrates can reduce the use of organic solvents, and can also greatly reduce the release of volatile organic compounds that can damage the ozone layer, improving the working conditions of users and reducing disposal. The cost of organic waste gas.

Aqueous two-component polyurethane coating systems are disclosed in many cases in the prior art. However, their properties, such as chemical resistance, curing speed, hardness, etc., are generally inferior to those of solvent-based polyurethane coating systems. Therefore, according to different applications and requirements for coating properties, it is necessary to develop different water-based formulations, which contain polyisocyanate curing agents and water-based resins with specific chemical structures, suitable additives and/or catalysts, etc.

US2011/0251332 discloses a waterborne two-component polyurethane coating system, which contains polyethyleneimine to increase the curing speed. But it does not mention the performance of the coating in terms of chemical resistance and its specific application.

US2010/0233431 discloses a cleanable waterborne two-component polyurethane coating system with high surface energy and low roughness, but does not disclose properties and specific applications regarding cure speed.

In many applications of two-component waterborne polyurethane coating systems, such as roll-to-roll printing or coating, it is usually required that the coating system has good chemical resistance and fast physical drying and/or chemical curing speed. However, coating systems suitable for this application have not been disclosed in the prior art.

Summary of the invention

There is a need in the market for a coating that can be applied to a variety of substrates that facilitate roll-to-roll production processes, including wood, leather, metal, plastic, film and paper. The coating should suitably have good chemical resistance and fast physical drying and/or chemical curing.

The object of the present invention is to provide a polyurethane-based waterborne two-component paint system, which has good corrosion resistance and/or pollution resistance to various organic solvents, acids and bases, paraffin, grease and the like. And under different application conditions, especially in roll-to-roll printing or coating, it can have faster physical drying and/or chemical curing speed, and can be applied to plastic film coating, textile coating and paper coating, etc. At the same time, the formed coating surface has suitable gloss and hardness.

In one aspect, the present invention discloses a polyurethane-based aqueous two-component coating system comprising a) an aqueous dispersion of one or more compounds containing OH functional groups; and b) one or more hydrophobic or Hydrophilic modified polyisocyanate; wherein the glass transition temperature of the aqueous dispersion containing one or more compounds containing OH functional groups is higher than 20°C.

Among them, the aqueous dispersion containing OH functional groups can include acrylic dispersions, and the polyisocyanate can be obtained by using carbonate, sulfonic acid, sulfonate, and/or polyethylene oxide groups and/or polyethylene oxide/ obtained by modifying polypropylene oxide groups.

In another aspect, the present invention also discloses a preparation method of the above-mentioned waterborne two-component coating system and its application in roll-to-roll coating.

Detailed ways

Within the scope of the present invention, "two-component" means at least two components capable of forming a coating system which must be stored separately before use due to mutual reactions.

"Dispersion" means a composition comprising one continuous phase completely dispersed in another discontinuous phase. For example, "aqueous dispersion" refers to a composition comprising particles or solutes dispersed completely in water. One or more co-solvents may also be included in the aqueous dispersion.

Aqueous dispersions containing compounds containing one or more OH-functional groups comprise in principle all compounds which are soluble or dispersible in water and which contain OH-functional groups which are reactive with isocyanates. Although there is no particular limitation on the glass transition temperature of each OH functional group-containing compound contained in the aqueous dispersion alone, the glass transition temperature of the aqueous dispersion containing all OH functional group-containing compounds is suitably higher than 20°C.

Examples of suitable OH-functional compounds are polymers of ethylenically unsaturated monomers (so-called polyol polyacrylates), polymers of combinations of diols and dicarboxylic acids (so-called polyol polyesters). ), polymers composed of diols, dicarboxylic acids and diisocyanates (so-called polyol polyurethanes) and/or hybrid systems prepared from said polyols, such as polyol polyacrylate-polyester, polyol Polymers of alcohol polyacrylate-polyurethane or polyol polyester-polyurethane. It may contain carboxylic acid, carboxylate group, sulfonate group and/or carboxyl-free (meth)acrylate structural unit with cycloaliphatic structure and any combination thereof. When the aqueous dispersion includes sulfonate groups, the amount of sulfonate groups and carboxylic acid and/or carboxylate groups is 0-4.5 milliequivalents/100g solid resin; when there is no carboxyl group ( In the case of meth)acrylate structural units, at least 25 mol % of the carboxylic acid groups of the dispersion containing OH functionality are present in ethanolamine-neutralized form, preferably at least 40 mol % of the carboxylic acid groups of the dispersion containing OH functionality It exists in the neutralized form of triethanolamine.

The aqueous dispersion is preferably but not limited to acrylic secondary dispersion, acrylic primary dispersion (also known as emulsion), styrene-acrylic emulsion, polyester modified acrylic dispersion, polyurethane dispersion, polyurethane modified acrylic dispersion, Polyester dispersions, particularly acrylic secondary dispersions and acrylic primary dispersions are used in combination.

Suitable aqueous dispersions containing OH functional groups comprise isocyanate-reactive compounds/polymers disclosed in the following patents: -2025690, EP-0537568, EP-0543228, EP-0758007, EP-0841352, EP-1141065, EP-1024184, DE-4439669. Particularly suitable are the acrylic acid primary and secondary dispersions and reaction systems disclosed in the following patents: EP-0557844, EP-0358979, EP-1391469 and EP-1599525. All of the above patent publications are incorporated herein by reference.

The OH content of the acrylic acid primary dispersion is 0-9% by weight, based on the weight of the aqueous hydroxyl compound as 100wt.%, the acid value is 0-150mg KOH/g, and the glass transition temperature is 20-100°C (according to differential scanning calorimetry); the number average molecular weight of the primary dispersion of acrylic acid (determined by gel permeation chromatography) is 500-1,000,000. The preferred OH (hydroxyl) content of the acrylic acid primary dispersion is 1.5%-2.5% by weight, the acid value is 0-7mg KOH/g, and the glass transition temperature is 60-90°C.

The OH content of the acrylic acid secondary dispersion is 1.0-9.0% by weight, the acid value is 0-200mg KOH/g, and the glass transition temperature is 20-70°C; the acrylic acid di The number average molecular weight of the grade dispersion is 500-100,000. The preferred OH (hydroxyl) content of the secondary acrylic acid dispersion is 3.5-4.5% by weight, the acid value is 5-100mg KOH/g, and the glass transition temperature is 40-60°C.

Polyisocyanate component b) consists of any organic polyisocyanate containing free isocyanate groups bonded to aliphatic, cycloaliphatic, arylaliphatic and/or aryl groups, liquid at room temperature, or diluted with a solvent , so that it is liquid at room temperature. The polyisocyanate component b) has a viscosity at 23°C of 10-15000 mPa·s, preferably 50-10000 mPa·s, more preferably 500-6000 mPa·s. The polyisocyanate component b) particularly preferably consists of a polyisocyanate or polyisocyanate mixture containing isocyanate groups bonded exclusively aliphatically and/or cycloaliphatically, with an (average) NCO functionality between 1.8 and 4.2, 23 The viscosity at ℃ is 500-6000mPa·s.

Suitable polyisocyanates include, but are not limited to, isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 1,4-diisocyanatocyclohexane, bis(4-isocyanato Cyclohexyl)methane ( W, Bayer AG, Leverkusen), 1,3-diisocyanatobenzene, 2,4- and/or 2,6-toluene diisocyanate (TDI), diisocyanatodiphenylmethane (MDI), Polyisocyanates of m-xylylene diisocyanate (XDI) and ω,ω′-diisocyanato-1,3-methylcyclohexane (H ₆ XDI).

The diisocyanates may optionally be used as such, but derivatives of diisocyanates are generally used. Suitable derivatives include biurets, isocyanurates, uretdiones, carbamates, iminooxadiazine diones (oxadiazine diones), oxadiazinetriones, carbodiimides, acylureas and polyisocyanates with allophanate groups.

Triisocyanates such as TIN (triisocyanatononane) are also suitable.

Hydrophobic polyisocyanates can be used when the aqueous dispersion containing OH functionality is sufficiently hydrophilic, but their viscosity is generally lower.

The polyisocyanate component b) can be hydrophilically modified. For example, water-soluble or water-dispersible polyisocyanates can be obtained by modification with carboxyl, sulfo and/or polyethylene oxide groups and/or polyethylene oxide/polypropylene oxide groups.

For example, polyisocyanates can be hydrophilized by reacting with insufficient amounts of monohydroxy hydrophilic polyether alcohols. The preparation of such hydrophilized polyisocyanates is described, for example, in EP-A 0540985 p.3 line 55 - p.4 line 5. Polyisocyanates containing allophanate groups are also extremely suitable, as described in EP-A-0959087p.3, lines 39-51, which can be obtained by using low-monomer polyisocyanates with polyethylene oxide polyether alcohols in urea Prepared under formic esterification conditions. The water-dispersible polyisocyanate mixtures based on triisocyanatononane described in DE-A10007821p.2, line 66-p.3, line 5 are also suitable, as well as DE10024624p.3, lines 13-33 or WO01/88006 etc. Polyisocyanates hydrophilized with ionic groups (sulfo, phosphino) are described. It is likewise possible to add emulsifiers for external hydrophilization.

The isocyanate component used may also be partially blocked with components reactive with isocyanates, for example up to 1/3 of the isosinase present. In this case, the blocked isocyanate component can be reacted in a later step with further addition of polyol for further crosslinking. Applicable blocking agents are: monohydric alcohols, lactams, phenols, amines, dimethyl maleate, diethyl maleate or dibutyl maleate, etc.

Hydrophilic modified polyisocyanate is preferably but not limited to polyether modified hexamethylene diisocyanate polymer (HDI), polyether modified isophorone diisocyanate polymer (IPDI), ammonium sulfonate modified permanent hexamethylene diisocyanate multimer and ammonium sulfonate modified isophorone diisocyanate multimer, particularly preferably ammonium sulfonate modified hexamethylene diisocyanate multimer. The isocyanate content of the hexamethylene diisocyanate polymer (HDI polymer) modified by the sulfonate ammonium salt is preferably but not limited to 10-25wt.%, particularly preferably 15-24wt.%. The weight of HDI multimer is based on 100wt.%.

In principle, it is of course also possible to use mixtures of different polyisocyanates.

In the waterborne two-component coating system, the ratio of NCO (isocyanate) functionality to OH functionality is 0.5:1-5:1.

In the water-based two-component coating system, the aqueous dispersion a) containing OH functional groups is 80 parts by weight, and the polyisocyanate b) is 20 parts by weight.

The water-based two-component coating system provided by the present invention may further include solvents, additives, additives, waxes and/or silicone resins.

The solvent is preferably but not limited to propylene glycol methyl ether acetate, propylene glycol butyl ether acetate, propylene glycol diacetate, polycarbonate, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, Dipropylene glycol butyl ether, lauryl alcohol ester (texanol). Particular preference is given to propylene glycol methyl ether acetate, ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol butyl ether acetate.

The solvent is used in an amount of 0-15 parts by weight, preferably 3-8 parts by weight.

The auxiliary agent and/or additive can be selected from one or more of the following: wetting and leveling agent, defoamer, thickener, pigment, dispersion aid, catalyst, anti-skinning agent, anti-settling agent , coupling agents, amino resins and/or emulsifiers. The wetting and leveling agent is preferably but not limited to polyether-modified polydimethylsiloxane. The defoamer is preferably but not limited to hydrophobic silicon dioxide modified mineral oil, organosiloxane solution. The auxiliary agent and/or additive is used in an amount of 1-15 parts by weight, preferably 5-15 parts by weight.

The wax is preferably but not limited to polyethylene wax, polypropylene wax, polytetrafluoroethylene wax, carnauba wax, amide wax, organic polymer. Especially preferred are polyethylene wax emulsions and polypropylene wax emulsions. The amount of wax used is 0-15 parts by weight, preferably 4-8 parts by weight.

The silicone resin is preferably, but not limited to, silicone polyacrylate with or without hydroxyl groups, and polydimethylsiloxane with or without hydroxyl groups. Especially preferred are hydroxyl-modified polydimethylsiloxane emulsions. The amount of the silicone resin is 0-10 parts by weight, preferably 2-5 parts by weight.

The coupling agent, preferably but not limited to organosiloxane coupling agent, titanate coupling agent, aluminate coupling agent, bimetallic coupling agent, phosphate ester coupling agent, borate ester coupling agent , chromium complexes and other higher fatty acids, alcohols, ester coupling agents, etc., particularly preferably organosiloxane coupling agents, titanate coupling agents. The coupling agent is used in an amount of 0.01-5.0 parts by weight, preferably 0.1-2.0 parts by weight.

The amino resin is preferably but not limited to urea-formaldehyde resin, melamine-formaldehyde resin and polyamide polyamine epichlorohydrin resin, particularly preferably melamine-formaldehyde resin such as methyl etherified melamine formaldehyde resin, butylated melamine formaldehyde resin . The amino resin is used in an amount of 1.0-40.0 parts by weight, preferably 2.0-25.0 parts by weight.

The waterborne two-component coating system of the present invention may also include a catalyst. Catalysts known in the art can selectively and rapidly react isocyanates with alcohols or polyols rather than water. Preferred catalysts include dibutyltin dilaurate (DBTL), zirconium carboxylate, zirconium(IV) acetylacetonate, and compounds of elements from subgroups 5 and 6 of the periodic table, each of which has an oxidation state of at least + 4. Preferred but not limited to acids and acid salts of the above compounds, including organic and/or inorganic salts. For the type, selection and use of catalysts, refer to Journal of Coatings Technology, 2002, 74 (930), 31-36; Paint and Coatings Industry, 2002, 16, 80; WO00/47642 and WO98/41322, etc. The catalyst is used in an amount of 0.0001-5.0 parts by weight, preferably 0.001-2.0 parts by weight.

The water-based two-component coating system of the present invention may also contain reactive diluents, such as hydroxyl-functional polycarbonate polyols disclosed by CN1837251B or compounds containing lactone groups disclosed by CN1781960A. The active diluent is used in an amount of 1-10 parts by weight, preferably 2-5 parts by weight.

The above parts by weight are based on the total weight of the water-based two-component coating system being 100 parts by weight.

When the water-based two-component paint system provided by the present invention is in use, component a), that is, the aqueous dispersion containing OH functional groups can usually be used as a part of the sealed storage of the paint material; component b), that is, polyisocyanate as a curing agent part, sealed and stored for later use; before coating, the curing agent part and the paint part are mixed to obtain a water-based two-component coating system.

Solvents, additives, additives, waxes, silicone resins, catalysts, coupling agents, amino resins, reactive diluents, etc. can be mixed with component a), that is, the aqueous dispersion containing OH functional groups, as part of the paint sealant Store for future use; use component b), namely polyisocyanate, as the curing agent part, seal and store for future use; before coating, mix the curing agent part and the paint part to obtain a water-based two-component coating system.

Parts of solvents, auxiliaries, additives, waxes, silicone resins, catalysts, coupling agents, reactive diluents etc. may optionally also be mixed alone or with component b), ie polyisocyanate.

Coating can be done by a wide variety of spray processes such as compressed air, HVLP, airless, mixed air or electrostatic spray processes. It can also be applied by other methods such as brushing, roller coating or knife coating.

Roll-to-roll coating is preferably but not limited to screen, letterpress, gravure, lithography, screen, inkjet and flexo printing, etc., can be carried out by "roll-to-roll" processing mode, especially gravure and screen coating. The water-based two-component coating system provided by the invention is coated on the surface of the substrate to obtain a polyurethane coating attached to the substrate. The substrate can be carried out in a high-temperature drying tunnel to accelerate drying and improve printing efficiency. After the cloth is put into the curing room, it is matured for 1 to 5 days.

The invention is illustrated by the following examples, which should not be considered limiting. Unless otherwise stated, parts by weight herein are based on 100 parts by weight based on the total weight of the aqueous two-component coating system.

Example

Raw Materials and Reagents

The coating test items involved in the present invention include anti-liquid paraffin items and drying performance test items. The substrates, pretreatments, and detection and sample preparation methods used are listed in Table 1.

Table 1 Selection and pretreatment of substrates

Coating test samples are prepared, preferably but not limited to, by wire bar coating, and cured in an oven at 60°C for 24 hours. According to actual needs, the wet film thickness is set at 6-120 μm.

Comparative example 1

Preparation of Component A

Put 83.33g in the blender container A XP2588, under medium and low speed (about 1000-1200rpm) stirring, slowly add 16.67g BA in turn, after stirring evenly, use a 400-mesh filter to filter the above finished products, and the obtained finished products should be properly stored in airtight containers. Wait at least 24 hours before use.

Preparation of Component B

L75 with N3390BA is mixed in 3:2 (weight ratio).

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 120.00/25.00, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed and even, ready to use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Example 1

Preparation of Component A

Put 47.00g in the blender container A2601, under medium-low speed (about 1000-1200rpm) stirring, slowly add 11.00g deionized water, 42.00g After A2546, increase the stirring speed to 2500rpm, and keep the stirring speed for 20 minutes to complete the preparation of component A.

Use a 400-mesh filter to filter the above finished products. The finished products should be properly stored in airtight containers and stored for at least 24 hours before use.

Preparation of Component B

Component B is 2487/1, use MPA to dilute with curing agent/MPA=3/1.

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 100.00/25.00, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed and even, ready to use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Example 2

Preparation of Component A

Put 42.00g in the blender container A2601, under medium-low speed (about 1000-1200rpm) stirring, slowly add 11.00g deionized water, 47.00g A2542 then increase the stirring speed to 2500rpm, and keep the stirring speed for 20 minutes to complete the preparation of component A.

Use a 400-mesh filter to filter the above finished products. The finished products should be properly stored in airtight containers and stored for at least 24 hours before use.

Preparation of Component B

Component B is 2487/1, use MPA to dilute with curing agent/MPA=3/1.

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 100.00/28.00, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed evenly before use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Example 3

Preparation of Component A

Put 42.00g in the blender container A2601, under medium-low speed (about 1000-1200rpm) stirring, slowly add 11.00g deionized water, 47.00g A2427 then increased the stirring speed to 2500rpm, and kept the stirring speed for 20 minutes to complete the preparation of component A.

Use a 400-mesh filter to filter the above finished products. The finished products should be properly stored in airtight containers and stored for at least 24 hours before use.

Preparation of Component B

Component B is 304, use MPA to dilute with curing agent/MPA=3/1.

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 100.00/28.50, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed and even, ready to use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Example 4

Preparation of Component A

Put 89.00g in the blender container A2601, under medium-low speed (about 1000-1200rpm) stirring, slowly add 0.40g BYK024, 0.20g BYK348, 0.80g 104BC, 1.80g BG, 0.60g DPnB, 2.20g deionized water, 5.00g Emulsion39235 Then increase the stirring speed to 2500rpm, and maintain this speed for 20 minutes to complete the preparation of component A.

Use a 400-mesh filter to filter the above finished products. The finished products should be properly stored in airtight containers and stored for at least 24 hours before use.

Preparation of Component B

Component B is XP2487/1, 401-70, solvent MPA mixed in ratio of 16.8/8.0/4.2.

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 100.00/29.00, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed and even, ready to use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Example 5

Preparation of Component A

Put 89.00g in the blender container A2601, under medium-low speed (about 1000-1200rpm) stirring, slowly add 0.40g BYK024, 0.20g BYK348, 0.80g Surfynol104BC, 1.80g BG, 0.60g DPnB, 2.20g deionized water, 5.00gEmulsion39235 and then increase the stirring speed to 2500rpm , and maintain this rotation speed to disperse for 20 minutes, that is, the preparation of component A is completed.

Use a 400-mesh filter to filter the above finished products. The finished products should be properly stored in airtight containers and stored for at least 24 hours before use.

Preparation of Component B

Component B is 2487/1, use MPA to dilute with curing agent/MPA=3/1.

Use and sample preparation

Accurately weigh component A and component B according to the mass ratio of 100.00/25.00, mix by hand stirring, and stir for 5 minutes to ensure that component A and component B are fully mixed and even, ready to use.

On the substrate, the composition is coated with a wire bar and cured in an oven at 60°C for 24 hours to form a dry film with a thickness of 8-10 microns.

The liquid paraffin resistance of the coating film was tested, and the obtained results are listed in Table 2.

On the substrate, the composition was coated with a wire bar, and dried in an oven at 60°C for 20 seconds to test the drying degree of the coating film. The results are listed in Table 3.

Test Results

Resistance to liquid paraffin is one of the important indicators for judging the quality of polyurethane-based waterborne two-component coating systems, especially when used as printing varnish, and it is also a technical indicator that is difficult to achieve.

Reference standard EN12720 Evaluation method of furniture surface resistance to liquid chemical substances, the detection time is 24 hours

Level 5: best, no change before and after the test;

Level 4: Very slight changes in gloss and color before and after the test, which can only be found when facing the light source;

Level 3: There are slight imprints in the test area, and these imprints can be found from multiple angles;

Grade 2: There are obvious imprints in the test area, but the surface structure is not damaged;

Level 1: Worst, there are obvious imprints in the test area, but the surface structure has been destroyed, or the filter paper is stuck to the surface of the tested object;

It can be seen from Table 2 that the water-based two-component coating system of the present invention has significantly better anti-liquid paraffin performance than commercial solvent-based two-component polyurethane printing varnishes when used as printing varnishes.

Table 2. Comparison of anti-liquid paraffin properties of coating films

The speed at which a coating dries after application is also an important indicator of the performance of a coating system. Fast drying and good drying can make work more efficient.

The present invention is evaluated with the following standard with reference to GB/T1728-1979 paint film hard drying test method:

Level 5: best, the appearance of the coating film does not change, the filter paper can be separated naturally, and the surface of the coating film is not sticky;

Grade 4: <10% of the surface of the coating film is destroyed, the filter paper can be separated naturally, and the surface of the coating film is slightly sticky;

Grade 3: 10% to 50% of the surface of the coating film is damaged, requiring external force to separate the filter paper, and the surface of the coating film is obviously sticky;

Level 2: 50% to 90% of the surface of the coating film is damaged, requiring external force to separate the filter paper, and the surface of the coating film is obviously sticky;

Level 1: Worst, >90% of the surface of the coating film is destroyed, a large external force is required to separate the filter paper, and the surface of the coating film is obviously sticky;

It can be seen from Table 3 that although it is water-based, the coating system of the present invention has a drying performance not inferior to that of a commercial solvent-based two-component coating system.

Table 3. Comparison of drying properties of coating films

Those skilled in the art will readily appreciate that the present invention is not limited to the foregoing specific details, and that the present invention may be implemented in other specific forms without departing from the spirit or main characteristics of the present invention. The described embodiments are therefore to be regarded in all respects as illustrative rather than restrictive, the scope of the invention being indicated by the claims rather than the foregoing description; Within the meaning and scope of the effects, they should be regarded as belonging to the present invention.

Claims (8)

1. Waterborne two-component coating system based on polyurethane, comprising a) an aqueous dispersion containing one or more compounds containing OH functional groups; and b) one or more hydrophobically or hydrophilically modified polyisocyanates; Wherein, the glass transition temperature of the aqueous dispersion containing one or more compounds containing OH functional groups is higher than 20°C. 2. The coating system of claim 1, wherein the aqueous dispersion comprising one or more OH functional group-containing compounds comprises an acrylic dispersion. 3. The coating system of claim 2, wherein the acrylic dispersion comprises a secondary polymer dispersion. 4. The coating system of claim 1, wherein the polyisocyanate is hydrophilically modified. 5. The coating system according to claim 4, wherein the hydrophilic modification of the polyisocyanate can be achieved by using carbonate, sulfonic acid, sulfonate, and/or polyethylene oxide groups and/or poly It is obtained by modifying ethylene oxide/polypropylene oxide groups. 6. The coating system according to claim 1, further comprising auxiliaries and/or additives. 7. The coating system according to claim 6, wherein the auxiliary agent and/or additive comprises defoamer, thickener, pigment, dispersion aid, catalyst, anti-skinning agent, anti-settling agent, coupling agents, amino resins or emulsifiers. 8. Use of the coating system according to claim 1 in roll-to-roll coating.