A modified layered nanoclay sheet / polyurethane composite coating and a method for preparing the same

Abstract

The application discloses a modified layered nanoclay sheet / polyurethane composite coating and a preparation method thereof, and belongs to the technical field of coatings; namely, the modified layered nanoclay sheet and polyurethane are used to prepare the modified layered nanoclay sheet / polyurethane composite coating by adopting a physical crosslinking method; wherein the modified layered nanoclay sheet is prepared by sequentially performing acid activation and surface modification treatment on nanoclay. The application solves the problems of insufficient weather resistance and adhesion and poor storage stability of the existing polyurethane coating, and also reduces the cost. In addition, the modified layered nanoclay sheet / polyurethane composite coating prepared by the application has excellent corrosion resistance and mechanical properties.

Description

A modified layered nano-clay sheet / polyurethane composite coating and its preparation method Technical Field

[0001] This invention belongs to the field of coating technology, and particularly relates to a modified layered nano-clay sheet / polyurethane composite coating and its preparation method. Background Technology

[0002] Polyurethane coatings are among the fastest-growing and most popular anti-corrosion coatings, meeting the needs of today's end users in terms of safety, application, performance, and cost. However, polyurethane coatings are still relatively expensive, their weather resistance needs improvement, and prolonged exposure to sunlight may lead to coating aging and fading. Furthermore, polyurethane is not completely impermeable to corrosive ions; its permeability can be altered by changing the content of diisocyanates and polyols or by dispersing inorganic or organic fillers in the polyurethane matrix. To reduce costs and strengthen the polyurethane matrix, fillers are typically added to the polyurethane formulation to improve the coating's weather resistance and impermeability while simultaneously lowering costs.

[0003] The dispersion of nanoscale fillers in a polyurethane matrix reduces its permeability to corrosive ions, and the impermeability of nanomaterials creates a tortuous pathway for permanent lateral nanocomposites. Incorporating nanoscale fillers into the polymer matrix can also produce nanocomposites with better weather resistance and adhesion strength. However, the degree of filler dispersion is crucial to coating performance. Currently, fillers for polyurethane are mostly graphene, carbon nanotubes, boron nitride, and metal oxides. However, on the one hand, the preparation processes of fillers such as graphene, carbon nanotubes, and boron nitride are relatively complex and costly; on the other hand, although metal oxides are cheaper than two-dimensional materials, their effect on improving the weather resistance and impermeability of polyurethane coatings is still not ideal, limiting the development of polyurethane in the field of anti-corrosion coatings. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention utilizes lower-cost layered clay materials as fillers in polyurethane coatings, providing a modified layered nano-clay sheet / polyurethane composite coating and its preparation method. First, the nano-clay material is sequentially acid-activated and surface-modified to obtain modified layered nano-clay sheets. These sheets are then added to isocyanate monomers, followed by the addition of a catalyst and thorough dispersion to obtain a nano-clay / isocyanate monomer dispersion. A polyol is then added, followed by a prepolymerization reaction. A chain extender is then added, and after a chain extension reaction, the modified layered nano-clay sheet / polyurethane composite coating is finally obtained.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions:

[0007] A method for preparing a modified layered nano-clay sheet / polyurethane composite coating includes the following steps:

[0008] Modified layered nanoclay sheets and polyurethane were cross-linked using a physical cross-linking method to prepare a modified layered nanoclay sheet / polyurethane composite coating.

[0009] The modified layered nanoclay sheet is prepared by sequentially acid-activating and surface-modifying nanoclay.

[0010] Preferably, the nano-clay includes one or more of vermiculite, montmorillonite, lithium saponite, or diatomite.

[0011] Furthermore, the nano-clay has a multi-level open-pore structure, containing macropores, micropores and mesopores, with a particle size of no more than 200 mesh.

[0012] Preferably, the acidic solution used in the acid activation is sulfuric acid or hydrochloric acid; wherein the concentration of the acidic solution is 1 mol to 6 mol / L, and the acid activation time is 1 to 6 h.

[0013] Beneficial Effects: During acid activation, excessively high acid concentrations or prolonged treatment times can damage the crystal structure of layered nanoclay, altering its physical and chemical properties and reducing its stability. Excessive acid treatment can also dissolve the layered structure on the surface of the nanoclay, reducing its specific surface area, hindering bonding with the coating, and ultimately affecting the coating's mechanical strength and weather resistance. Conversely, insufficient acid concentrations prevent the complete removal of oxides from the layered nanoclay, hindering effective pore clearing and specific surface area increase, and preventing complete exposure of active sites, also hindering bonding with the coating and ultimately affecting its overall performance. Therefore, acid activation within the acid concentration range defined in this invention can increase the specific surface area and pore volume of the nanoclay, further enhancing the ion permeation path after composite with polyurethane resin.

[0014] Preferably, the surface modification treatment is as follows: ammonia water is added to the acid-activated nano-clay, and the mixture is stirred and ultrasonically dispersed (ultrasonic frequency is 120KHz) for 2-6 hours, and the suspension is reacted in a reactor at 60-80℃ for 4-6 hours.

[0015] Furthermore, the mass-to-volume ratio of the nano-clay, acidic solution, and ammonia is 1g:(15-50)mL:(5-20)mL.

[0016] Furthermore, the mass concentration of the ammonia water is 25% to 28%.

[0017] Beneficial effects: Ammonia water can be used to modify the surface of acid-activated nano-clay. However, if too much ammonia water is used, the cost will be high; if too little ammonia water is used, the purpose of surface ammonia modification cannot be achieved.

[0018] Furthermore, before the surface modification treatment, the acid-activated nanolayered clay needs to be washed with water until the pH is neutral.

[0019] Furthermore, the surface modification treatment also includes: after the reaction is complete, continuously centrifuging and washing until neutral, and freeze-drying to constant weight (the freeze-drying temperature is -50℃ to -40℃) to obtain modified layered clay sheets.

[0020] Preferably, the specific steps of the physical cross-linking method are as follows:

[0021] The modified layered nanoclay sheets and catalyst were added to the isocyanate monomer and dispersed thoroughly to obtain a dispersion.

[0022] A polyol is added to the dispersion to carry out a prepolymerization reaction, resulting in a mixture;

[0023] A chain extender was added to the mixture to carry out a chain extension reaction, and finally a modified layered nano-clay sheet / polyurethane composite coating was obtained.

[0024] Furthermore, the mass ratio of the modified layered nanoclay sheets, catalyst, chain extender, and isocyanate monomer is (0.10~0.45)∶(0.002~0.004)∶(0.003~0.01)∶1;

[0025] The molar ratio of the hydroxyl group in the polyol to the -NCO in the isocyanate monomer is (0.3-0.5):1.

[0026] Beneficial effects: Too much modified layered nanoclay flakes and too little polyurethane not only fail to utilize the modified layered nanoclay flakes effectively but also negatively impact the properties of the polyurethane itself. Conversely, too little modified layered nanoclay flakes prevents them from achieving their optimal effect. Furthermore, improper ratios of polyols, isocyanates, and chain extenders can cause the polymer chains' flexibility, hardness, elasticity, and durability to deviate from design requirements. An excessively high proportion of hard segments makes the material brittle, while an excessive proportion of soft segments makes it soft. Therefore, within the raw material ratio range defined in this invention, the interactions between the raw materials can be better utilized to prepare composite coatings with good weather resistance and impermeability.

[0027] Furthermore, the isocyanate monomer is an aliphatic isocyanate, including one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate.

[0028] Furthermore, the catalyst is an organometallic compound, including one or more of dibutyltin dilaurate, calcium octanoate, cobalt naphthenate, or zinc naphthenate.

[0029] Furthermore, the diol includes one or more of polytetrahydrofuran ether diol, polypropylene oxide diol, or polycaprolactone diol.

[0030] Furthermore, the chain extender is an aromatic diamine chain extender, including 3,3'-dichloro-4,4'-diphenylmethane diamine, 1,3-propanediol bis(4-aminobenzoate), 4,4'-methylene-bis(3-chloro-2,6-diethylaniline), polytetramethylene ether diol bis(p-aminobenzoate), 3,5-diethyltoluene diamine, or 3,5-dimethylthiotoluene diamine.

[0031] Furthermore, the prepolymerization reaction is carried out at a temperature of 70–90°C for 1–3 hours.

[0032] Furthermore, the chain extension reaction temperature is 60–90°C, and the time is 1–4 hours.

[0033] Technical Solution Two:

[0034] The modified layered nano-clay sheet / polyurethane composite coating was prepared by the above preparation method.

[0035] Compared with the prior art, the present invention has the following advantages and technical effects:

[0036] This invention discloses a modified layered nano-clay sheet / polyurethane composite coating and its preparation method. The clay sheets can form physical cross-linking points within the polyurethane matrix, enhancing the overall rigidity and toughness of the material. The layered structure of the clay sheets forms a barrier within the polyurethane, significantly extending the pathway and reducing the permeability of gases (such as oxygen and water vapor) and ions, thereby improving the barrier properties of the polyurethane. Furthermore, the nano-layered clay sheets, as inorganic materials, can significantly improve the chemical resistance and weather resistance of the polyurethane composite coating.

[0037] Before surface modification, this invention further modifies the layered clay by acid treatment, thereby increasing its specific surface area (e.g., the diatomaceous earth used in Example 1 increased from 2.72 cm²). 2 / g increased to 49.17cm 2 The specific surface area increases the pore volume, thus further increasing the ion permeation path of the coating when combined with polyurethane resin. As the specific surface area increases, the number of active sites increases, resulting in more uniform dispersion in the resin. In addition, the layered clay used in this invention is cheaper, reducing the overall cost of polyurethane composite materials. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 shows the SEM morphology of the diatomite used in Example 1;

[0040] Figure 2 shows the pore size distribution of diatomaceous earth in Example 1 before and after acid treatment;

[0041] (a) represents samples that have not undergone acid treatment; (b) represents samples that have undergone acid treatment.

[0042] Figure 3 shows the surface morphology and elemental distribution of the polyurethane / diatomite composite coating prepared in Example 1;

[0043] (a) is a surface morphology diagram; (b) is an elemental distribution diagram. Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] This invention provides a modified layered nanoclay / polyurethane composite coating and its preparation method. First, the nanoclay material undergoes acid activation for structural modification. After washing and drying, the dried nanoclay powder is surface-modified with ammonia. Then, the surface-modified nanoclay sheets are added to an isocyanate monomer, a catalyst is added, and the mixture is fully dispersed. A polyol is added to the modified layered nanoclay / isocyanate monomer dispersion, and after a prepolymerization reaction, a chain extender is added. Following a chain extension reaction, the nanoclay / polyurethane composite material is obtained.

[0050] In some preferred embodiments, the layered nanoclay material includes vermiculite, montmorillonite, lithium saponite, or diatomaceous earth.

[0051] In some preferred embodiments, the structural modification method of layered nanoclay is acid activation, in which an acidic solution is used, including sulfuric acid or hydrochloric acid, the concentration of the acidic solution is 1 mol to 6 mol / L, and the treatment time is 1 to 6 h.

[0052] In some preferred embodiments, the surface modification method involves adding ammonia to acid-activated nanoclay, stirring and ultrasonically dispersing for 2–6 hours, reacting the suspension in a reactor at 60–80°C for 4–6 hours, continuously centrifuging and washing until neutral, and freeze-drying to obtain modified layered clay sheets.

[0053] In some preferred embodiments, the isocyanate monomer is an aliphatic isocyanate, including hexamethylene diisocyanate (HDI), isophorone diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate.

[0054] In some preferred embodiments, the catalyst is an organometallic compound, including dibutyltin dilaurate, calcium octanoate, cobalt naphthenate, or zinc naphthenate.

[0055] In some preferred embodiments, the diol is polytetrahydrofuran ether diol and polypropylene oxide diol or polycaprolactone diol.

[0056] In some preferred embodiments, the chain extender is an aromatic diamine chain extender, including 3,3'-dichloro-4,4'-diphenylmethane diamine, 1,3-propanediol bis(4-aminobenzoate), 4,4'-methylene-bis(3-chloro-2,6-diethylaniline), polytetramethylene ether diol bis(p-aminobenzoate), 3,5-diethyltoluene diamine, or 3,5-dimethylthiotoluene diamine.

[0057] In some preferred embodiments, the mass ratio of modified layered nanoclay sheets to isocyanate monomers is 0.10–0.45:1, the molar ratio of hydroxyl groups in the polyol to ester groups in the isocyanate is 0.3–0.5:1, the mass ratio of catalyst to isocyanate is 0.002–0.004:1, and the mass ratio of chain extender to isocyanate is 0.003–0.01:1.

[0058] In some preferred embodiments, the prepolymerization reaction temperature is 70–90°C and the time is 1–3 h, and the chain extension reaction temperature is 60–90°C and the time is 1–4 h.

[0059] All raw materials used in the embodiments of this invention were purchased commercially. Specifically, the polycaprolactone diol (2000), 4,4'-dicyclohexylmethane diisocyanate (262.35), nano-clay, such as vermiculite, diatomaceous earth (average particle size 19 μm), catalyst, chain extender and ammonia used in the embodiments of this invention were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Furthermore, the modified layered nano-clay sheet / polyurethane composite coatings prepared in the following examples meet the following national standards in various performance tests: GB / T 1771-2007 Determination of resistance to neutral salt spray of paints and varnishes; GB / T 14522 Artificial weathering test method for plastics, coatings and rubber materials for mechanical industry products using fluorescent ultraviolet lamps; GB / T 9754-2007 Measurement of gloss of coatings and varnishes at 20 degrees, 60 degrees and 85 degrees; GB / T 9754-2007 Determination of hardness of coatings (pencil method); water resistance and salt water resistance are determined according to GB / T1733-1993.

[0060] The technical solution of the present invention will be further illustrated by the following embodiments.

[0061] Example 1

[0062] (1) 15g of nano-diatomaceous earth (nano-clay) was acid-activated with 300mL of 2mol / L hydrochloric acid for 3h. Then, 100mL of ammonia water was added to the acid-activated nano-diatomaceous earth and the mixture was stirred and ultrasonically dispersed (120KHz) for 2h. The suspension was then reacted in a reactor at 80℃ for 6h. After the reaction was completed, the mixture was continuously centrifuged and washed until neutral. The mixture was then freeze-dried to obtain modified layered nano-clay sheets.

[0063] (2) Take 3g of the above modified layered diatomaceous earth sheets and add them to 20g of 4,4'-dicyclohexylmethane diisocyanate. Add 0.06g of catalyst dibutyltin dilaurate and disperse thoroughly to obtain a nano-clay / isocyanate monomer dispersion. Then add 60.99g of polycaprolactone diol to it. The prepolymerization reaction temperature is 85℃ and the stirring time is 3h. Add 0.2g of chain extender 3,3'-dichloro-4,4'-diphenylmethane diamine. The chain extension reaction temperature is 70℃ and the reaction time is 3h to obtain the modified layered nano-clay sheet / polyurethane composite coating.

[0064] After testing, the polyurethane coating prepared in this embodiment can withstand neutral salt spray for up to 69 days; after 500 hours of UV aging, the gloss decreases by 10.8% and the hardness is 3H; the salt water resistance time is 35 days.

[0065] Example 2

[0066] The difference from Example 1 is that the mass ratio of modified layered clay sheets to 4,4'-dicyclohexylmethane diisocyanate is 0.4:1, that is:

[0067] (2) Take 8g of the above modified layered clay sheet and add it to 20g of 4,4'-dicyclohexylmethane diisocyanate. The other conditions are the same as in Example 1.

[0068] After testing, the polyurethane coating prepared in this embodiment can withstand neutral salt spray for up to 71 days; after 500 hours of UV aging, the gloss decreases by 8.2%, the hardness is 3H, and the salt water resistance time is 35 days.

[0069] Example 3

[0070] The difference from Example 1 is that the nano-clay used is vermiculite, while the other conditions are the same as in Example 1.

[0071] After testing, the polyurethane coating prepared in this embodiment can withstand neutral salt spray for up to 70 days; after 500 hours of UV aging, the gloss decreases by 9.2%, the hardness is 3H, and the salt water resistance time is 35 days.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that the mass ratio of modified layered clay sheets to 4,4'-dicyclohexylmethane diisocyanate is 0.5:1, that is:

[0074] (2) Take 10g of the above modified layered clay sheet and add it to 20g of 4,4'-dicyclohexylmethane diisocyanate. The other conditions are the same as in Example 1.

[0075] After testing, the polyurethane coating showed a salt spray resistance time of 62 days; after 500 hours of UV aging, the gloss decreased by 13.4%, the hardness was 3H, and the salt water resistance time was 30 days.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that diatomaceous earth is not added (i.e., step (1) is omitted), and other conditions are the same as in Example 1.

[0078] After testing, the polyurethane coating prepared in this comparative example has a salt spray resistance time of up to 58 days; after 500 hours of UV aging, the gloss decreases by 19.4%, the hardness is 2H, and the salt water resistance time is 30 days.

[0079] Comparative Example 3

[0080] The difference from Example 2 is that 8g of diatomaceous earth that has not undergone acid activation treatment is added (i.e., the acid treatment process in step (1) is not performed), and other conditions are the same as in Example 2.

[0081] After testing, the polyurethane coating prepared in this comparative example showed a salt spray resistance time of 64 days. After 500 hours of UV aging, the gloss decreased by 14.3%, the hardness was 3H, and the salt water resistance time was 33 days.

[0082] Comparative Example 4

[0083] The difference from Example 2 is that 8g of diatomaceous earth without ammonia surface modification treatment is added (i.e., the surface activation treatment process in step (1) is not performed), and other conditions are the same as in Example 2.

[0084] After testing, the polyurethane coating prepared in this comparative example showed a salt spray resistance time of 62 days. After 500 hours of UV aging, the gloss decreased by 14.8%, the hardness was 3H, and the salt water resistance time was 30 days.

[0085] Figure 1 shows the SEM morphology of the diatomite used in Example 1. As can be seen from the figure, the diatomite is in the shape of a circular sheet with a hollow cell wall structure and a large number of micropores and channels.

[0086] Figure 2 shows the pore size distribution of diatomaceous earth in Example 1 before and after acid treatment;

[0087] (a) shows the result without acid treatment; (b) shows the result after acid treatment. By comparing the two figures, it can be seen that after acid treatment, the number of pores with a diameter of less than 40 nm in diatomaceous earth increases significantly.

[0088] Figure 3 shows the surface morphology and elemental distribution of the polyurethane / diatomite composite coating prepared in Example 1;

[0089] Among them, (a) is a surface morphology diagram; (b) is an elemental distribution diagram. As can be seen from Figure 3(a), diatomite is uniformly dispersed in the polyurethane matrix. As can be seen from Figure 3(b), the polyurethane / diatomite composite coating contains elements such as C, N, O, and Si, including the C, N, and O elements of polyurethane and the Si and O elements of diatomite, and the distribution is uniform, further proving that diatomite and polyurethane are effectively composited.

[0090] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a modified layered nano-clay sheet / polyurethane composite coating, characterized in that, Includes the following steps: Modified layered nanoclay sheets and polyurethane were used to prepare a modified layered nanoclay sheet / polyurethane composite coating by physical crosslinking. The specific steps of the physical crosslinking method are as follows: the modified layered nanoclay sheets and a catalyst were added to the isocyanate monomer and fully dispersed to obtain a dispersion; a polyol was added to the dispersion to carry out a prepolymerization reaction to obtain a mixture; a chain extender was added to the mixture to carry out a chain extension reaction, and finally the modified layered nanoclay sheet / polyurethane composite coating was obtained. The mass ratio of the modified layered nanoclay sheets, catalyst, chain extender and isocyanate monomer is (0.10~0.10). 45)∶(0.002~0.004)∶(0.003~0.01)∶1; the molar ratio of the hydroxyl group in the polyol to the isocyanate in the isocyanate monomer is (0.3~0.5)∶1; wherein, the modified layered nanoclay sheet is prepared by sequentially acid-activating and surface-modifying the nanoclay; the acidic solution used in the acid activation is sulfuric acid or hydrochloric acid; wherein, the concentration of the acidic solution is 1mol~6mol / L, and the acid activation time is 1~6h; the surface modification treatment is as follows: ammonia water is added to the acid-activated nanoclay, ultrasonically dispersed for 2~6h, and the suspension is reacted in a reaction vessel at 60~80℃ for 4~6h.

2. The method for preparing a modified layered nano-clay sheet / polyurethane composite coating according to claim 1, characterized in that, The nano-clay includes one or more of vermiculite, montmorillonite, lithium saponite, or diatomite.

3. The method for preparing a modified layered nano-clay sheet / polyurethane composite coating according to claim 1, characterized in that, The mass-to-volume ratio of the nano-clay, acidic solution, and ammonia is 1 g : (15~50) mL : (5~20) mL.

4. The method for preparing a modified layered nano-clay sheet / polyurethane composite coating according to claim 1, characterized in that, The catalyst includes one or more of dibutyltin dilaurate, calcium octanoate, cobalt naphthenate, or zinc naphthenate.

5. The method for preparing a modified layered nano-clay sheet / polyurethane composite coating according to claim 1, characterized in that, The prepolymerization reaction is carried out at a temperature of 70-90°C for 1-3 hours; the chain extension reaction is carried out at a temperature of 60-90°C for 1-4 hours.

6. A modified layered nano-clay sheet / polyurethane composite coating, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

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