Water-based organic zinc-rich paint with excellent hydrogen gas generation suppression properties

Description

[Technical Field]

[0001] The present invention relates to an aqueous organic zinc-rich paint with excellent hydrogen gas generation suppression properties. In particular, the present invention relates to an aqueous paint that is applied to steel surfaces to exhibit corrosion protection (especially heavy corrosion protection), and that contains zinc powder and a binder resin. More specifically, the present invention relates to an aqueous zinc-rich paint that can achieve hydrogen gas generation suppression properties. [Background technology]

[0002] Zinc-rich paints are used as heavy-duty corrosion-protective paints for repairing and restoring corrosion-protective coatings on steel products, particularly after the installation of structural materials exposed outdoors (Non-Patent Document 1). The following is written at the beginning of the main text (excluding the abstract) of Non-Patent Document 1 regarding zinc-rich paints:

[0003] Zinc-rich paint is a primer paint that contains a large amount of zinc powder (70-90 wt% in the paint film). Zinc-rich paint is used as a shop primer for steel materials for ships and bridges, and as an anti-corrosion primer paint to protect large steel structures such as bridges and plants from corrosion.

[0004] Zinc-rich paints contain zinc powder and a binder, and may contain additives as needed. In particular, in recent years, water-based zinc-rich paints that have a low VOC (volatile organic compounds) content and can be dried and cured at room temperature have been popular (Patent Documents 1 to 4). Patent Document 1 exemplifies a paint that uses a water-based urethane resin as the binder, and a small amount of finely powdered silica and a small amount of a thickener (such as "polyether polyol and nonionic surfactant") as additives.

[0005] On the other hand, after the formulation of an aqueous zinc-rich paint, hydrogen gas can be generated by the reaction between water and zinc dust. For this reason, under painting conditions such as high humidity, where the paint film takes a long time to dry, and where the paint film is thick at joints or steps in steel materials, if hydrogen gas is generated in the paint film after the surface has dried, this could cause paint film defects (Patent Document 2). Therefore, the examples in Patent Document 2 below disclose the use of "free acids of alkyl phosphate ester compounds," "free acids of alkyl / aryl phosphate ester compounds," "alkylol ammonium salts of copolymers containing phosphate ester groups," and "sulfonic acid ester compounds" as "adhesion promoters."

[0006] The technology using the "adhesion promoter" in Patent Document 2 does not have sufficient hydrogen gas generation suppression capabilities, and there are concerns that hydrogen gas generation may cause coating defects and abnormal appearance when the coating is left in a high humidity environment of nearly 100% for a long period of time. Furthermore, it seems impossible to ensure a pot life of about one week.

[0007] On the other hand, Patent Document 3 exemplifies a technique of blending phosphate or tripolyphosphate to suppress hydrogen gas generation, but even in this case, the ability to suppress hydrogen gas generation is insufficient, and hydrogen gas is generated within a pot life of, for example, about one week, resulting in a problem of reduced quality.

[0008] On the other hand, while chromate-based compounds have been used in anticorrosion paints for zinc-plated steel sheets that do not use zinc-rich paints, research is being conducted to replace them with non-chromium-based compounds (Non-Patent Documents 2 and 3). Table 2-1 in Non-Patent Document 2 shows that hexavalent chromate-based compounds are significantly superior in corrosion prevention performance compared to vanadium phosphate and molybdate phosphate. Non-Patent Document 2 also states that good performance was obtained by using vanadium pentoxide and calcium phosphate and / or calcium silicate as anticorrosion pigments. Furthermore, Non-Patent Document 3 states that corrosion resistance was confirmed in vanadium-based coatings.

[0009] However, the underlying structures of water-based zinc-rich paints and non-water-based, non-zinc-rich paints are fundamentally different, and it is difficult to simply apply the anti-rust pigment to water-based zinc-rich paints.

[0010] For example, when strontium chromate is applied to a water-based zinc-rich paint, hydrogen gas generation can be suppressed, but the essential sacrificial corrosion protection effect is inhibited, resulting in a significant decrease in corrosion resistance. In short, it is generally difficult to achieve both zinc rust prevention and hydrogen gas generation suppression at the same time. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 5750318 [Patent Document 2] Patent Publication No. 2020-026457 [Patent Document 3] Patent Publication No. 2021-134228 [Patent Document 4] Patent Publication No. 2013-221081 [Non-patent literature]

[0012] [Non-Patent Document 1] "Lecture on Durability and Corrosion Prevention (Lecture 5): Fundamentals and Recent Topics of Zinc-Rich Paints," J. Jpn. Soc. Colour Mater., 88(2)(2015)(https: / / www.jstage.jst.go.jp / article / shikizai / 88 / 2 / 88_51 / _pdf) [Non-patent document 2] "Development of new anti-corrosion pigments for painted steel sheets and elucidation of the corrosion prevention mechanism of sacrificial anti-corrosion coating systems," Hideki Matsuda, Doctoral dissertation, Hiroshima University (https: / / ir.lib.hiroshima-u.ac.jp / 00044628) [Non-patent document 3] "Study on Chemical Conversion Coatings on Zinc Plating Using Chromium Substitute Metals," Tetsuto Kajiyama, Tokyo Metropolitan Industrial Technology Research Center Research Report, No. 4, 2009, pp. 72-73 (https: / / www.iri-tokyo.jp / uploaded / attachment / 836.pdf) [Non-patent document 4] "Roval Water-Based | Roval Corporation" (https: / / www.roval.co.jp / products / aqua / howto.html) Summary of the Invention [Problem to be solved by the invention]

[0013] There is a demand for a water-based zinc-rich paint that can suppress hydrogen gas generation while achieving low toxicity and high corrosion resistance. In particular, there is a demand for such a paint that can be produced at low cost and is easy to handle.

[0014] On the other hand, as described in Non-Patent Document 4, for example, water-based zinc-rich paint is applied after mixing and stirring "zinc powder" and "paint liquid." From an operational standpoint, a longer usable time (pot life) after mixing and stirring is preferable. Pot life decreases with the generation of hydrogen gas due to the reaction between water and zinc, but customers desire a pot life of about one week.

[0015] As a result of extensive research into the potential of zinc-rich paint containing zinc powder, which is our company's specialty, we have discovered that by adding specific inorganic additives to water-based zinc-rich paint, it is possible to sufficiently suppress the generation of hydrogen gas while maintaining high corrosion resistance. [Means for solving the problem]

[0016] In a preferred embodiment, the aqueous zinc-rich paint contains zinc powder in an amount of at least 70% by weight, preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 93% by weight or more, even more preferably 94% by weight or more, and even more preferably 95% by weight or more, based on the dried paint film (solid content of the paint), and may contain 98% by weight or less or 97% by weight or less, for example 80 to 98% by weight or 90 to 97% by weight.

[0017] Furthermore, the vanadium compound should be at least 0.02% by weight or more, preferably 0.05% by weight or more, more preferably 0.1% by weight or more, and even more preferably 0.2% by weight or more, based on the dried coating film (solid content of the paint). There is no particular upper limit, but from the viewpoint of cost, it is preferably 5% by weight or less.

[0018] Furthermore, the binder resin is contained in the coating film (solid content of the paint) after drying in an amount of at least 20% by weight, preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 50% by weight or more, even more preferably 60% by weight or more, and even more preferably 70% by weight or more or 80% by weight or more, based on the weight of the zinc powder and vanadium compound, for example, 70 to 99% by weight or 70 to 100% by weight. Note that the binder resin content is the content of the resin polymer itself.

[0019] The vanadium compound is at least one of vanadic acid or vanadate. Although there are many types of vanadium compounds, few are known to have an effective hydrogen gas generation suppression effect, and many are known to have adverse effects such as reducing the activity of zinc or reducing the storage stability of paint. Preferred examples include strontium vanadate as the vanadate and vanadium pentoxide as the vanadate. However, since vanadium pentoxide is subject to many legal restrictions and is difficult to handle, strontium vanadate is more preferred.

[0020] The vanadium compound has an average primary particle size (D 50) may be preferably 1 to 20 μm or 1 to 10 μm, particularly 2 to 8 μm.

[0021] When the vanadium compound is strontium vanadate, the content of strontium vanadate in the dried coating film (solid content of the paint) is at least 0.05% by weight, more preferably 0.1% by weight or more, and particularly 0.2% by weight or more. There is no particular upper limit, but from the viewpoint of cost, it is preferably 5% by weight or less.

[0022] On the other hand, when the vanadium compound is vanadium pentoxide, the vanadium pentoxide content in the dried coating film (solid content of the paint) is at least 0.02 wt % or more, preferably 0.05 wt % or more, more preferably 0.1 wt % or more, and even more preferably 0.2 wt % or more, and is desirably, for example, 0.5 wt % or less.

[0023] In one embodiment, the binder resin may be contained in the paint together with zinc powder or the like in the form of a resin liquid dispersed or dissolved in water or a solvent containing a portion of an organic solvent. Examples of preferred binder resins include, without particular limitation, organic or inorganic resins, and may be any of general film-forming resins selected from acrylic resins, epoxy resins, urethane resins, epoxy ester resins, and the like, or a combination of two or more thereof. The binder resin may be cured in either a one-component or two-component manner, but a one-component type is preferred from the viewpoint of ease of application.

[0024] In some cases, the water-based zinc-rich paint may be inorganic or an organic-inorganic composite containing alkyl silicate, alkali silicate, or the like as a binder.

[0025] The zinc powder has an average primary particle size (D 50 ) is preferably 1 to 20 μm, more preferably 1 to 10 μm, and particularly preferably 2 to 8 μm. The content of metallic zinc in the zinc powder is at least 90% by weight or more, for example, 94% by weight or more, or 95% by weight or more.

[0026] In a preferred embodiment, the aqueous zinc-rich paint may contain an additive for improving corrosion resistance in the dried coating film (solid content of the paint) as needed. The additive for improving corrosion resistance may be selected from, for example, molybdates, tungstates, nitrites, phosphates (phosphoric acid, calcium phosphate, magnesium phosphate, condensed phosphates), tannic acid, thiourea, benzotriazole, and the like. [Effects of the Invention]

[0027] This not only provides corrosion protection but also inhibits hydrogen gas generation in the paint solution and in the undried coating film after application, which opens up the possibility of a one-component water-based zinc-rich paint. DETAILED DESCRIPTION OF THE INVENTION

[0028] In one embodiment, the water-based zinc-rich paint can be easily applied to metal surfaces, wall surfaces, etc. using a conventional paint roller or brush, and can be dried completely within, for example, about 30 minutes or less or 1 hour or less by simply leaving it to stand (standing) at room temperature (typically 15 to 25°C, e.g., 23°C).

[0029] This type of water-based zinc-rich paint can be easily applied to indoor or outdoor steel frames, steel plates, steel pillars, handrails, doorknobs, door handles, etc., and can also be applied to walls, fences, pillars, shelves, storage cases, etc. It is preferable to use it on steel objects because it provides anticorrosion effects, but it can also be used on other metal materials such as aluminum, and on non-metallic objects. [Example]

[0030] The hydrogen gas generation suppression ability and rust prevention properties were confirmed for the examples and comparative examples of the present application.

[0031] The paints used to confirm the hydrogen gas generation suppression ability and rust prevention property are the following (1) to (3).

[0032] (1) Examples and Comparative Examples 1 to 7 Binder resin: One-component water-based urethane resin (Superflex 150, polyurethane water dispersion manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) · Hydrogen gas suppression additive: strontium vanadate or vanadium pentoxide. -The content (by weight) of hydrogen gas suppression additive (vanadium compound) in the coating film (solid content of the paint) after drying: 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, or 5. Zinc content in the dried coating (solid content of the paint): Add zinc powder to make it 93% by weight. (The remaining solid content of the zinc powder and hydrogen gas suppression additive is 7% by weight.) After drying, the binder resin is added to the coating (solid content of the paint) so that it accounts for 95% by weight of the part excluding the zinc powder and vanadium compound. Water was added to the above solids to make a weight ratio of 85:15 to make a paint.

[0033] (2) Comparative Examples 8 to 13 The composition was the same as in Examples and Comparative Examples 1 to 7, except that the hydrogen gas suppression additive was changed as follows. Comparative Example 8: No additives. Comparative Examples 9 and 10: Strontium chromate was added so that the content in the coating film (solid content of the paint) after drying was 0.1% by weight and 0.2% by weight, respectively. Comparative Examples 11 and 12: Magnesium vanadate was added so that the content in the coating film (solid content of the paint) after drying was 0.1% by weight and 0.2% by weight, respectively. Comparative Examples 13 and 14: Calcium vanadate was added so that the content in the coating film (solid content of the paint) after drying was 0.1% by weight and 0.2% by weight, respectively. Comparative Examples 15 and 16: Aluminum vanadate was added so that the content in the coating film (solid content of the paint) after drying was 0.1% by weight and 0.2% by weight, respectively.

[0034] (3) Comparative Examples 17 and 18 A paint was prepared by referring to examples in prior art documents. Comparative Example 17: A paint was prepared with reference to Example 13 of Patent Document 2. Comparative Example 18: A paint was prepared with reference to Example 7 of Patent Document 3.

[0035] <Procedure for checking hydrogen gas generation suppression ability> The hydrogen gas generation suppression ability was confirmed by the following procedure. 1. The paint was added to an aluminum pouch that can seal hydrogen gas, and the aluminum pouch was sealed using a heat seal.The volume of the aluminum pouch (volume before the test) was then measured using the Archimedes method. 2. After leaving the aluminum pouch at 45°C for 7 days (Table 1) or 3 months (Table 2), the volume of the aluminum pouch (volume after test) was measured using the Archimedes method. 3. The volume expansion rate was calculated using the following formula: Volume expansion rate = (volume after test / volume before test - 1) x 100%

[0036] <Confirmation results of hydrogen gas generation suppression ability> The results of confirming the ability to suppress hydrogen gas generation are shown in Tables 1 and 2 below.

[0037] Here, a volume expansion rate of less than 100% was rated "Good", and a volume expansion rate of 100% or more was rated "Poor". The test was conducted with n = 2 samples, and the results were rated as "Good" if they were "Good, Bad", "Good, Good" if they were "Good", and "Good".

[0038] <Procedure for checking rust prevention> The rust prevention properties were confirmed by the following procedure. 1. The prepared paint was stored in a thermostatic chamber set at 45°C for 7 days (Table 1) or 3 months (Table 2), then stirred and applied to a steel plate to a dry film thickness of 80 μm, and then dried at room temperature for 1 week. 2. Salt spray test (hereinafter referred to as SST) for 480 hours (Table 1; test on painted steel plate made with paint after storage at 45°C for 7 days) or 800 hours (Table 2; test on painted steel plate made with paint after storage at 45°C for 3 months).

[0039] <Evaluation criteria for rust prevention> The results of rust prevention are shown in Table 1 below.

[0040] Here, samples in which red rust was not observed from the cut area were rated "Good", and samples in which red rust was observed from the cut area were rated "Poor". The test was conducted with n = 2 samples, and the results were rated as "Good" if they were "Good, Bad", "Good, Good" if they were "Good", and "Good".

[0041] TIFF0007810482000001.tif226170

[0042] As shown in Table 1, in Examples 1 to 7, in which strontium vanadate was added in the range of 0.05 to 5 wt %, excellent results were obtained in both hydrogen gas generation suppression ability and rust prevention. On the other hand, in Comparative Examples 1 and 2, in which the amount of strontium vanadate added was less than in Example 1, the hydrogen gas generation suppression ability was not necessarily sufficient.

[0043] As shown in Table 1, excellent results were obtained in both the hydrogen gas generation suppression ability and rust prevention properties in Examples 3 and 8 to 11, in which 0.2 wt % strontium vanadate was added. On the other hand, in Comparative Example 3, in which the total of the zinc content and the vanadium compound concentration was lower than in Example 11, the rust prevention properties were not necessarily sufficient.

[0044] Furthermore, as shown in Table 1, in Examples 12 to 16, in which vanadium pentoxide was added in the range of 0.02 to 0.5 wt %, excellent results were obtained in both the hydrogen gas generation suppression ability and the rust prevention ability. On the other hand, in Comparative Example 4, in which the amount of vanadium pentoxide added was less than that of Example 12, the hydrogen gas generation suppression ability was insufficient. Furthermore, in Comparative Examples 5 to 7, in which the amount of vanadium pentoxide added was greater than that of Example 16, the rust prevention ability was not necessarily sufficient.

[0045] As further shown in Table 1, Comparative Example 8, in which no vanadium compound or other additives were added, was excellent in rust prevention, but naturally did not exhibit the ability to inhibit hydrogen gas generation.

[0046] On the other hand, in Comparative Examples 9 to 10, in which strontium chromate, which was thought to be an additive with excellent rust-preventing properties, was added instead of the vanadium compound, the ability to suppress hydrogen gas generation was sufficient, but the rust-preventing properties were insufficient.

[0047] Furthermore, in Comparative Examples 11 to 16 in which other vanadates (magnesium vanadate, calcium vanadate, aluminum vanadate) were added instead of the vanadium compound, neither the hydrogen gas generation suppression ability nor the rust prevention properties were sufficient.

[0048] Considering the results of Comparative Examples 9 to 16, excellent results were obtained only when a specific vanadium compound was used among additives that were considered to be general rust-preventive additives.

[0049] The difference between specific vanadium compounds (i.e., strontium vanadate and vanadium pentoxide) and other vanadates is believed to be due to differences in their solubility in water and the oxidizing power of the dissolved components.

[0050] TIFF0007810482000002.tif152170

[0051] Table 2 summarizes the test results for the hydrogen gas generation suppression ability of paints stored at 45°C for three months, as well as the results of an additional experiment in which coated steel plates prepared using paints stored at 45°C for the same three months were subjected to an 800-hour salt spray test. As shown in Table 2, the paint compositions of Examples 17 to 22 are the same as those of Examples 10, 9, and 1 to 4, respectively. Furthermore, the concentrations of strontium vanadate in the solid content of the paints of Examples 23 to 30 are the same as those of Examples 19 to 22 (same compositions as Examples 1 to 4, respectively). However, the zinc content in the solid content of the paints of Examples 23 to 26 is 94 wt % and that of Examples 27 to 30 is 95 wt %.

[0052] As shown in Table 2, even after storage at 45°C for 3 months, Examples 18, 20 to 22, 24 to 26, and 29 to 30, in which the zinc content in the solid content of the paint was 90% by weight or more and the concentration of strontium vanadate in the solid content of the paint was 0.1% by weight or more, showed good results in terms of hydrogen gas generation inhibition ability and corrosion prevention.

[0053] In contrast, in Example 17 (same composition as Example 10), in which the zinc content in the solid content of the paint was 80% by weight, the concentration of strontium vanadate was 0.2% by weight, so the hydrogen gas generation inhibitory ability was good, but the rust-preventive performance was insufficient. Also, in Examples 19, 23, and 27, in which the concentration of strontium vanadate in the solid content of the paint was 0.05% by weight, the hydrogen gas generation inhibitory ability was insufficient, and therefore the rust-preventive performance was also insufficient.

[0054] As further shown in Table 2, in Comparative Example 19 (same composition as Comparative Example 8) in which no strontium vanadate was added, the hydrogen gas generation suppression ability was insufficient and the rust prevention performance was also insufficient.

[0055] A comparison of the results in Table 1 and Table 2 reveals that the required concentrations of zinc powder and strontium vanadate in the paint solids can vary depending on the storage period and conditions of the paint and the required rust-preventing performance. That is, it was found that the required minimum concentration of zinc powder can vary within the range of 70 to 90% by weight, and the required minimum concentration of strontium vanadate can vary within the range of 0.05 to 0.2% by weight.

Claims

1. A one-component water-based zinc-rich paint containing 80% by weight or more of zinc powder and 0.02% by weight or more of strontium vanadate in the solid content, and containing a binder resin that accounts for 20% by weight or more of the portion other than the zinc powder and strontium vanadate in the solid content.

2. 2. The one-component water-based zinc-rich paint according to claim 1, which contains 90% by weight or more of zinc powder and 0.1% by weight or more of strontium vanadate in the solid content.

3. A coated product coated with the one-component water-based zinc-rich paint according to claim 1 or 2.

4. A one-component water-based zinc-rich paint as described in claim 1, containing 0.05% by weight or more of strontium vanadate.

5. A one-component water-based zinc-rich paint as described in claim 4, which has a volume expansion rate of less than 100% when stored in an aluminum pouch at 45°C for 7 days.

6. A one-component water-based zinc-rich paint as described in claim 4 or 5, containing 90% or more by weight of zinc powder in the solid content.

7. A one-component water-based zinc-rich paint as described in claim 1, containing 0.1% by weight or more of strontium vanadate.

8. A one-component water-based zinc-rich paint as described in claim 6, which has a volume expansion rate of less than 100% when stored in an aluminum pouch at 45°C for three months.

9. A one-component water-based zinc-rich paint as described in claim 7, containing 90% or more by weight of zinc powder in the solid content.

10. A one-component water-based zinc-rich paint as described in claim 8, containing 90% by weight or more of zinc powder in the solid content.