Amine-free water-based coating composition for protecting back side of glass mirror surface and preparation method of amine-free water-based coating composition

Abstract

The invention relates to the technical field of water-based coatings, in particular to an amine-free water-based coating composition for protecting the back side of a glass mirror surface and a preparation method of the amine-free water-based coating composition. The water-based paint provided by the invention is prepared from the following components in parts by mass: 25.0 to 40.0 parts of amine-free water-based resin, 5.0 to 10.0 parts of titanium dioxide, 25.0 to 60.0 parts of precipitated barium sulfate, 0.1 to 1.0 part of tinting pigment, 1.5 to 3.0 parts of amino crosslinking agent, 3.5 to 7.0 parts of functional additive, 8.0 to 15.0 parts of water and 0.0 to 5.0 parts of blocked isocyanate crosslinking agent. The water-based paint is amine-free, can form a coating with high adhesive force, high hardness, excellent corrosion resistance (acid and alkali resistance and salt fog resistance), yellowing resistance and environmental friendliness, and is suitable for protection of back sides of aluminum mirrors, copper-free silver mirrors and copper-plated silver mirror surfaces.

Description

Technical Field

[0001] The present invention relates to the technical field of water-based coatings, and in particular to an amine-free water-based coating composition for protecting the back side of a glass mirror and a preparation method thereof. Background Art

[0002] The backside of glass mirrors requires a protective coating to prevent the metal layer (such as silver, copper, or aluminum) from being damaged by oxidation, corrosion, or mechanical damage. Traditional mirror backside coatings are mostly solvent-based and contain high levels of volatile organic compounds and heavy metals (such as lead and chromium), posing a threat to the environment and human health.

[0003] In response to environmental regulations, some companies have developed amine-neutralized waterborne mirror back coatings as an alternative. However, these coatings rely on amine neutralizers (such as triethylamine, ammonia, dimethylethanolamine, and 2-amino-2-methyl-1-propanol, commonly known as AMP-95) to adjust the pH value of the resin system, leading to the following problems:

[0004] 1. Amine volatilization: During high-temperature baking, amine volatilization produces a pungent odor, corrodes the drying equipment, and causes ammonia nitrogen pollution and nitrogen oxide emissions.

[0005] 2. Performance defects: The coating softens, resulting in unstable or lost adhesion, the coating is prone to yellowing, and the acid, alkali and salt spray resistance are insufficient.

[0006] 3. Application limitations: The protective effect on alkali-sensitive metal layers such as aluminum mirrors and silver mirrors is limited, and the metal layer is prone to oxidation and blackening after long-term use.

[0007] Existing technical documents (such as CN114591665A) disclose a low-VOC emulsion-type water-based aluminum mirror back coating, but it still requires an amine neutralizer and the VOC content is still relatively high, which makes it difficult to meet the environmental protection requirements of high-end mirror protection.

[0008] Therefore, there is an urgent need to develop a water-based coating composition that does not contain amine neutralizers, has low VOC, and has excellent performance, overcomes the environmental and performance defects of the existing technology, and meets the high standard requirements for back protection of aluminum mirrors, copper-free silver mirrors, and copper-plated silver mirrors. Summary of the Invention

[0009] The purpose of the present invention is to provide a water-based coating for protecting the back side of glass mirrors without the need for amine neutralization and a preparation method thereof, so as to solve the problems of high VOC emissions of existing solvent-based coatings, volatilization of amine substances in amine-neutralized coatings and insufficient performance.

[0010] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0011] The invention provides an amine-free water-based coating composition for protecting the back side of a glass mirror. The composition comprises the following components in parts by mass: 25.0 to 40.0 parts of an amine-free water-based resin, 5.0 to 10.0 parts of titanium dioxide, 25.0 to 60.0 parts of precipitated barium sulfate, 0.1 to 1.0 part of a coloring pigment, 1.5 to 3.0 parts of an amino cross-linking agent, 3.5 to 7.0 parts of a functional additive, 8.0 to 15.0 parts of water, and 0.0 to 5.0 parts of a blocked isocyanate cross-linking agent.

[0012] Optionally, the solid content of the amine-free water-based resin is 35.0-45.0%.

[0013] Optionally, the particle size of the precipitated barium sulfate is 1250-8000 mesh.

[0014] Optionally, the coloring pigment comprises low-color carbon black powder.

[0015] Optionally, the functional additives include a wetting agent, a dispersant, a thickener, polyethylene wax, polyamide wax, benzotriazole and a catalyst.

[0016] Optionally, the amino cross-linking agent includes fully methylated amino resin; and the blocked isocyanate cross-linking agent includes hexamethylene diisocyanate oligomer.

[0017] Optionally, the water-based paint further comprises 0.0 to 15.0 parts of talc powder and 0.0 to 4.2 parts of neutral silica sol; the particle size of the talc powder is greater than or equal to 3000 mesh.

[0018] The present invention also provides a method for preparing the above-mentioned water-based coating, comprising the following steps:

[0019] 1) mixing titanium dioxide, precipitated barium sulfate, coloring pigment, amino crosslinking agent, functional additive, water and blocked isocyanate crosslinking agent to obtain a premix;

[0020] 2) Grinding the premix, adding an amine-free water-based resin after grinding, adjusting the viscosity, and filtering to obtain a water-based coating.

[0021] Optionally, the mixing speed is 500-800 rpm, and the mixing time is 10-15 minutes.

[0022] Optionally, the grinding is performed until the fineness of the premix is ​​≤20 μm; the stirring is performed after adding the amine-free water-based resin; the stirring speed is 600-800 rpm and the time is 15-20 minutes; the viscosity is adjusted to 3000-4000 cps; and the filtering is performed using a 200-mesh filter.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides an amine-free water-based coating composition for protecting the back side of a glass mirror. The composition is based on an amine-free water-based resin system and is combined with functional pigments and fillers, additives, and a cross-linking agent. By optimizing the formulation and preparation process, the composition achieves stable dispersion and excellent film-forming properties under amine-free conditions, thereby forming a coating with high adhesion, high hardness, excellent corrosion resistance (acid and alkali resistance, salt spray resistance), yellowing resistance, and environmental friendliness. The coating is suitable for protecting the back sides of aluminum mirrors, copper-free silver mirrors, and copper-plated silver mirrors.

[0025] The coating formula provided by the present invention is simple and flexible, green and environmentally friendly, low in VOC, free of heavy metals, supports multiple functional components, and is an amine-free system, eliminating the pollution of ammonia nitrogen and nitrogen oxides to the environment. It is suitable for the anti-corrosion, anti-oxidation and mechanical protection of the back side of glass mirrors, meeting the needs of green manufacturing and high-end mirror protection. In addition, the preparation method is simple, does not require special equipment, and can be seamlessly connected and used with existing oil-based production equipment without modification, which is conducive to rapid switching of the original production line. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The raw materials used in the present invention can be obtained commercially or prepared using existing technologies.

[0032] The invention provides an amine-free water-based coating composition for protecting the back side of a glass mirror. The composition comprises the following components in parts by mass: 25.0 to 40.0 parts of an amine-free water-based resin, 5.0 to 10.0 parts of titanium dioxide, 25.0 to 60.0 parts of precipitated barium sulfate, 0.1 to 1.0 part of a coloring pigment, 1.5 to 3.0 parts of an amino cross-linking agent, 3.5 to 7.0 parts of a functional additive, 8.0 to 15.0 parts of water, and 0.0 to 5.0 parts of a blocked isocyanate cross-linking agent.

[0033] In the present invention, the amine-free waterborne resin is the main film-forming substance of the coating, providing excellent adhesion and other properties, and the molecular structure design ensures stable dispersion under amine-free conditions.

[0034] In the present invention, the water-based paint includes 25.0 to 40.0 parts of amine-free water-based resin, preferably 26.0 to 38.0 parts, more preferably 28.0 to 35.0 parts, and even more preferably 30.0 to 32.0 parts; the solid content of the amine-free water-based resin is 35.0 to 45.0%, preferably 38.0 to 42.0%, and even more preferably 40.0%.

[0035] In the present invention, the amine-free water-based resin is a product developed by the applicant Jiangsu Sanrong Polymer Co., Ltd., with a brand name of 1036. This product is a neutral, amine-free water-based resin emulsion, the main body of which includes a polymer resin with functional groups such as carboxyl and hydroxyl groups, and is pH neutralized by molecular design. It does not contain neutralizing amines (such as dimethylethanolamine, AMP-95, triethanolamine, triethylamine, ammonia and other amine substances), does not contain organic tin catalysts, and does not require acid-base neutralization to form a stable dispersed state. The resin emulsion optionally contains epoxy functional groups, which are derived from epoxy monomers or epoxy prepolymers with a certain molecular weight, and can react with cross-linking agents such as amino groups or isocyanates to form a cross-linked dense coating structure, thereby further improving the adhesion, salt spray resistance, and cross-linking strength of the coating.

[0036] In the present invention, the titanium dioxide is used to enhance the hiding power, mechanical strength and wear resistance of the coating.

[0037] In the present invention, the water-based paint includes 5.0 to 10.0 parts of titanium dioxide, preferably 6.0 to 9.0 parts, and more preferably 7.0 to 8.0 parts. In an embodiment of the present invention, the titanium dioxide is preferably rutile titanium dioxide.

[0038] In the present invention, the role of the precipitated barium sulfate is to optimize the coating flatness.

[0039] In the present invention, the water-based paint includes 25.0 to 60.0 parts of precipitated barium sulfate, preferably 30.0 to 55.0 parts, more preferably 35.0 to 50.0 parts, and even more preferably 40.0 to 45.0 parts; the particle size of the precipitated barium sulfate is 1250 to 8000 mesh, preferably 1500 to 7500 mesh, more preferably 2000 to 6000 mesh, and even more preferably 4000 to 5000 mesh.

[0040] In the present invention, the coloring pigments function to provide different color options.

[0041] In the present invention, the water-based paint includes 0.1 to 1.0 parts of coloring pigment, preferably 0.2 to 0.8 parts, and more preferably 0.5 to 0.6 parts; the coloring pigment includes low-pigment carbon black powder.

[0042] In the present invention, the role of the amino crosslinking agent is to provide crosslinking with the resin, thereby improving hardness and chemical resistance.

[0043] In the present invention, the water-based coating comprises 1.5 to 3.0 parts of an amino cross-linking agent, preferably 1.8 to 2.8 parts, and more preferably 2.0 to 2.5 parts; the amino cross-linking agent comprises a fully methylated amino resin.

[0044] In the present invention, the water-based coating comprises 3.5 to 7.0 parts of the functional additive, preferably 4.0 to 6.5 parts, more preferably 4.5 to 6.0 parts, and even more preferably 5.0 to 5.5 parts.

[0045] In the present invention, the functional additives include a wetting agent, a dispersant, a thickener, polyethylene wax, polyamide wax, benzotriazole and a catalyst;

[0046] The function of the wetting agent and dispersant is to improve the dispersibility of pigments and fillers;

[0047] The thickener is used to adjust the viscosity;

[0048] The function of the polyethylene wax is to improve the scratch resistance and slipperiness of the coating;

[0049] The function of the polyamide wax is to prevent the coating from settling;

[0050] The function of the benzotriazole is to enhance the corrosion resistance of the metal layer;

[0051] The role of the catalyst is to promote cross-linking.

[0052] In the present invention, the water-based coating comprises 0.5 to 1.5 parts of a wetting agent, preferably 0.6 to 1.2 parts, more preferably 0.8 to 1 part;

[0053] The water-based paint includes 0.8 to 1.5 parts of a dispersant, preferably 1.0 to 1.3 parts, more preferably 1.1 to 1.2 parts;

[0054] The water-based paint includes 0.5 to 2.0 parts of a thickener, preferably 0.8 to 1.8 parts, more preferably 1.0 to 1.5 parts, and even more preferably 1.2 to 1.4 parts;

[0055] The water-based coating comprises 0.5 to 4.0 parts of polyethylene wax, preferably 1.0 to 3.5 parts, more preferably 1.5 to 3.0 parts, and even more preferably 2.0 to 2.5 parts;

[0056] The water-based coating comprises 0.5 to 1.0 parts of polyamide wax, preferably 0.6 to 0.9 parts, and more preferably 0.7 to 0.8 parts;

[0057] The water-based coating comprises 1.5 to 3.0 parts of benzotriazole, preferably 1.8 to 2.8 parts, more preferably 2.0 to 2.5 parts, and even more preferably 2.2 to 2.4 parts;

[0058] The water-based paint includes 0.2 to 0.5 parts of catalyst, preferably 0.3 to 0.4 parts.

[0059] In an embodiment of the present invention, the wetting agent is preferably an acetylene glycol wetting agent; the dispersant is preferably a polymer dispersant; and the thickener is preferably an associative thickener.

[0060] In the present invention, the catalyst includes a blocked dinonylnaphthalene disulfonic acid catalyst, a dinonylnaphthalene monosulfonic acid catalyst or dodecylbenzenesulfonic acid. In the embodiment of the present invention, the blocked dinonylnaphthalene disulfonic acid catalyst is preferred.

[0061] In the present invention, the water-based paint further comprises 0.0 to 15.0 parts of talc powder, preferably 5.0 to 14.0 parts, and more preferably 10.0 to 13.0 parts; the particle size of the talc powder is greater than or equal to 3000 mesh.

[0062] In the present invention, the talc powder is used to reduce the gloss, thereby meeting the customer's requirements for gloss and further reducing costs.

[0063] In the present invention, the water-based coating further comprises 0.0 to 4.2 parts of neutral silica sol, preferably 2.0 to 4.1 parts, and more preferably 3.0 to 4.06 parts.

[0064] In the present invention, the role of the neutral silica sol is to improve the hardness, water resistance and wear resistance of the coating after forming the coating.

[0065] In the present invention, the blocked isocyanate crosslinking agent includes hexamethylene diisocyanate oligomer; the function of the blocked isocyanate crosslinking agent is to release active groups at high temperature and enhance the crosslinking density.

[0066] In the present invention, the water-based coating further comprises 0.0 to 5.0 parts of a blocked isocyanate cross-linking agent, preferably 3.0 to 5.0 parts, and more preferably 4 to 5.0 parts.

[0067] In the present invention, the water acts as an environmentally friendly dispersion medium to ensure low VOC emissions.

[0068] In the present invention, the water-based paint further comprises 8.0 to 15.0 parts of water, preferably 9.0 to 14.0 parts, and more preferably 11.0 to 13.0 parts.

[0069] The present invention also provides a method for preparing the above-mentioned water-based coating, comprising the following steps:

[0070] 1) mixing titanium dioxide, precipitated barium sulfate, coloring pigment, amino crosslinking agent, functional additive, water and blocked isocyanate crosslinking agent to obtain a premix;

[0071] 2) Grind the premix, and strictly control the temperature not to exceed 45°C to avoid irreversible negative effects of overheating of the premix; after grinding, add amine-free water-based resin and continue stirring, then adjust the viscosity with water, and filter to obtain the finished water-based paint.

[0072] In the present invention, the mixing is performed using a stainless steel stirring kettle; and the grinding equipment is a horizontal sand mill.

[0073] In the present invention, the mixing speed is 500-800 rpm, preferably 600-700 rpm, and the mixing time is 10-15 min, preferably 11-14 min, and more preferably 12-13 min.

[0074] In the present invention, the grinding is performed until the fineness of the premix is ​​≤20 μm;

[0075] After adding the amine-free water-based resin, stirring is performed; the stirring speed is 600-800 rpm, preferably 650-750 rpm, and the time is 15-20 min, preferably 16-19 min, and more preferably 17-18 min;

[0076] The viscosity is adjusted by using water to adjust the viscosity to 3000-4000 cps, preferably 3200-3800 cps, and more preferably 3500-3600 cps; and the filtration is performed by using a 200-mesh filter.

[0077] In the present invention, grinding the premix to a fineness of 20 μm or less can ensure a smooth coating.

[0078] In the present invention, the water-based coating can be applied to the back side of the glass mirror by single-pass coating or double-pass coating;

[0079] The single-pass coating is to apply the coating and then bake it at 180°C for 10 minutes, and the dry film thickness formed is 40μm; the double-pass coating is to apply the coating in two passes, the first pass is baked at 180°C for 5 minutes, and the second pass is baked at 180°C for 10 minutes, and the thickness of each pass is 20μm.

[0080] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0081] Example 1

[0082] The components of amine-free water-based coatings are shown in Table 1.

[0083] The preparation method of amine-free water-based coating is as follows:

[0084] 1) Premixing: Mix water, titanium dioxide, precipitated barium sulfate, amino crosslinking agent, and functional additives, and stir at 800 rpm for 20 minutes;

[0085] 2) Grinding: Grinding the premix using a horizontal sand mill to a fineness of ≤20 μm to obtain a slurry;

[0086] 3) Preparation: Add amine-free water-based resin to the ground slurry and stir at 800 rpm for 20 minutes. After stirring, adjust the slurry viscosity to 3000 cps with water and filter through a 200-mesh filter to obtain an amine-free water-based coating.

[0087] Example 2

[0088] Talc was used to partially replace the precipitated barium sulfate. The specific composition is shown in Table 1.

[0089] The preparation method of the amine-free water-based coating is the same as that in Example 1.

[0090] Example 3

[0091] The composition of amine-free water-based coating with low-pigment carbon black powder is shown in Table 1.

[0092] The preparation method of amine-free water-based coating is as follows:

[0093] The preparation method of the amine-free water-based coating is the same as that in Example 1.

[0094] Example 4

[0095] The composition of amine-free water-based coating with the addition of neutral silica sol is shown in Table 1.

[0096] The preparation method of the amine-free water-based coating is the same as that in Example 1.

[0097] Example 5

[0098] The composition of the amine-free waterborne coating with the addition of a blocked isocyanate crosslinker is shown in Table 1.

[0099] The preparation method of the amine-free water-based coating is the same as that in Example 1.

[0100] Table 1 Components of the amine-free water-based coatings of Examples 1-5

[0101]

[0102] Comparative Example 1

[0103] Amine-neutralized water-based mirror backside coating: prepared according to Example 1 of patent publication CN114591665A.

[0104] Comparative Example 2

[0105] Commercially available solvent-based mirror back coating: the formula consists of modified drying alkyd resin, cross-linking resin, coloring pigment, extender pigment, anti-rust pigment, additives, and solvent.

[0106] Test example

[0107] The amine-free water-based coatings prepared in Examples 1-5 and the mirror back coatings of Comparative Examples 1-2 were flow-coated onto 5 mm thick aluminum mirrors to a dry film thickness of 40 ± 5 μm and then baked at 180°C for 10 minutes. The coating properties were tested using the HG / T5179-2017 Chemical Industry Standard of the People's Republic of China, "Coatings for Aluminum Mirror Backs." The test results are shown in Table 2.

[0108] Table 2 Performance test results of Examples 1-5 and Comparative Examples 1-2

[0109]

[0110]

[0111] As can be seen from Table 2, the amine-free water-based coatings prepared in Examples 1-5 of the present invention have a hardness of 5H to 6H after being applied to the back side of the aluminum mirror; adhesion: peeling value ≤0.20; solvent wiping resistance: no damage after >100 times; acid and alkali resistance: no change in 1 hour; neutral salt spray resistance: no abnormality after 480 hours; environmental protection: no amine, no heavy metals, low VOC, and compliant with RoHS and REACH standards. It can be seen that the water-based coating provided in this embodiment is an amine-free system, which eliminates the pollution of ammonia nitrogen and nitrogen oxides, and has high performance, adhesion and durability better than Comparative Example 1 and Comparative Example 2.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An amine-free water-based coating composition for protecting the back side of a glass mirror, characterized in that: The invention comprises the following components in parts by mass: 25.0-40.0 parts of amine-free water-based resin, 5.0-10.0 parts of titanium dioxide, 25.0-60.0 parts of precipitated barium sulfate, 0.1-1.0 parts of coloring pigment, 1.5-3.0 parts of amino crosslinking agent, 3.5-7.0 parts of functional additive, 8.0-15.0 parts of water, and 0.0-5.0 parts of blocked isocyanate crosslinking agent.

2. The water-based paint according to claim 1, characterized in that The solid content of the amine-free water-based resin is 35.0-45.0%.

3. The water-based paint according to claim 1, characterized in that The particle size of the precipitated barium sulfate is 1250-8000 meshes.

4. The water-based paint according to claim 1, characterized in that The coloring pigment includes low-color carbon black powder.

5. The water-based paint according to claim 1, characterized in that The functional auxiliary agents include wetting agents, dispersants, thickeners, polyethylene wax, polyamide wax, benzotriazole and catalysts.

6. The water-based paint according to claim 1, characterized in that The amino cross-linking agent includes fully methylated amino resin; the blocked isocyanate cross-linking agent includes hexamethylene diisocyanate oligomer.

7. The water-based paint according to claim 1, characterized in that The water-based paint further comprises 0.0 to 15.0 parts of talc powder and 0.0 to 4.2 parts of neutral silica sol; the particle size of the talc powder is greater than or equal to 3000 meshes.

8. A method for preparing a water-based coating according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) mixing titanium dioxide, precipitated barium sulfate, coloring pigment, amino crosslinking agent, functional additive, water and blocked isocyanate crosslinking agent to obtain a premix; 2) Grinding the premix, adding an amine-free water-based resin after grinding, adjusting the viscosity, and filtering to obtain a water-based coating.

9. The preparation method according to claim 8, characterized in that The mixing speed is 500-800 rpm, and the mixing time is 10-15 minutes.

10. The preparation method according to claim 9, characterized in that The grinding is performed until the fineness of the premix is ​​≤20 μm; the amine-free water-based resin is added and then stirred; the stirring speed is 600-800 rpm and the time is 15-20 minutes; the viscosity is adjusted to 3000-4000 cps; and the filtering is performed using a 200-mesh filter.

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