Normal-temperature curing type polyphosphazene-based heat-proof coating and preparation method thereof

Abstract

The invention provides a normal-temperature curing type polyphosphazene-based heat-proof coating and a preparation method thereof. The preparation method comprises the following steps: preparation of polyphosphazene resin, preparation of a polyphosphazene-based heat-proof coating, large-thickness coating of the polyphosphazene-based heat-proof coating and curing. Active groups such as amino and hydroxyl are introduced into a polyphosphazene side group, the normal-temperature curing capacity is enhanced, and groups with higher steric hindrance or higher polarity are introduced into the curing agent; a normal-temperature curing process is used; the heatproof coating can be applied to a large thickness of more than 10 mm.

Description

Technical Field

[0001] The invention belongs to the technical field of surface engineering, and in particular relates to a room-temperature curing polyphosphazene-based heat-resistant coating and a preparation method thereof. Background Art

[0002] With the advancement of aerospace technology, the thermal environment in which spacecraft operate has become increasingly demanding. Their heating time and total heating have significantly increased, with maximum surface temperatures now exceeding 1,000 degrees Celsius. The total heating time has also leapt significantly, and the total heating has increased significantly. Thermal protection in a coupled environment with long flight times, high total heating, and high surface temperatures has become a common challenge in the aerospace industry.

[0003] Thermal barrier coatings offer high thermal protection efficiency, excellent toughness, simple construction, and low cost. They are particularly suitable for complex aerodynamic structures and those subject to significant expansion and deformation during operation, and are widely used in the aerospace field. Due to the influence of heating time and total heat output, the design thickness of thermal barrier coating materials has increased significantly, with the maximum thickness reaching decimeters.

[0004] Due to its excellent temperature resistance and outstanding toughness, silicone rubber is currently one of the primary resin matrices used in thermal barrier coatings. Due to the α-helical structure of silicone rubber molecules, the surface of the molecules is coated with a layer of hydrophobic alkyl groups, resulting in a low surface energy. When the coating thickness is too thick, debonding issues easily occur at the interface, resulting in relatively low reliability. Therefore, it is necessary to develop new thermal barrier coatings suitable for long-term, high total heating, and high surface temperature coupled thermal environments. This will improve the reliability of thick thermal barrier coatings and support the development of the next generation of aerospace equipment. Summary of the Invention

[0005] The present invention aims to overcome the above-mentioned deficiencies of the prior art and to provide a room-temperature curable polyphosphazene-based heat-resistant coating and a preparation method thereof. The coating can be cured at room temperature, has good adhesive properties, and can be applied in large thicknesses.

[0006] The present invention provides a method for preparing a room-temperature curing polyphosphazene-based heat-resistant coating, comprising four parts: preparation of a polyphosphazene resin, preparation of a polyphosphazene-based heat-resistant coating, coating of a polyphosphazene-based heat-resistant coating with a large thickness, and a curing process. Polyphosphazene is selected as the main chain of the polymer, and atoms with relatively strong polarity are introduced to improve the polarity and conformation of the main chain and enhance the surface binding force; functional groups with relatively strong activity, such as hydroxyl, amino, and halogen atoms, are introduced into the side chains to further enhance the binding force and improve the room-temperature curing performance. At the same time, non-polar nucleophilic reagents with large steric hindrance, such as long fatty chains or cyclic structures, can be added to the side groups to appropriately reduce the regularity and crystallinity of the polymer, increase the toughness of the polymer, and achieve large-thickness coating. This method meets the urgent needs of a new generation of heat-resistant coatings and lays the foundation for future practical applications.

[0007] The preparation method mainly includes four parts: preparation of polyphosphazene resin, preparation of polyphosphazene-based heat-resistant coating, thick coating of polyphosphazene-based heat-resistant coating and curing process.

[0008] The preparation of the polyphosphazene resin includes main chain preparation and side group structure design and preparation.

[0009] The main chain uses polyphosphazene resin, and the main chain of the polyphosphazene resin is prepared using hexachlorocyclotriphosphazene as raw material, using in-situ thermal ring-opening polymerization or solution thermal ring-opening polymerization; or using phosphorus pentachloride as raw material, using a one-step method or living cationic polymerization method.

[0010] The groups on the side groups include halogen atoms (0-50%), hydroxyl groups (0-30%), amino groups (0-30%), benzene rings (0-30%), phenol groups (0-30%), and the remainder (methyl, ethyl, and hydrogen atoms). The side group structure includes a side group substitution reactant selected from the group consisting of benzene, phenol, ethanol, ethylene glycol, propylene glycol, aminoethanol, p-aminophenol, hydroquinone, and aminoepoxy. Side group substitution can be achieved by polymerization followed by substitution or substitution followed by polymerization.

[0011] The curing agent is selected from one or more of bisphenol A epoxy resin, bisphenol B epoxy resin, bisphenol D epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, isocyanate, and organic peroxide.

[0012] The high-thickness coating technology is characterized in that the coating viscosity is 15-25s, the delivery pressure is 0.02MPa-0.3MPa, the nozzle aperture is 0.5mm-4mm, the atomization pressure is 2.0MPa-3.0MPa, and the coating viscosity (diluent dosage) and delivery pressure are adjusted to achieve high-thickness coating of the heat-resistant coating.

[0013] The curing process is characterized in that the resin matrix can be placed in a pressure environment of 0.01-3 atmospheres by vacuuming or pressurizing, and the ambient humidity is adjusted to be controlled within the range of 5%-70%, and the room temperature curing is completed by placing it at room temperature for 10 minutes to 120 hours.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. The present invention is applicable to a variety of substrates. The present invention introduces a variety of highly polar atoms into the polymer backbone, and the side groups contain polar functional groups such as hydroxyl and amino groups, which enhances the adhesion between the heat-resistant coating and the substrate and can be used on a variety of different types of substrate surfaces;

[0016] 2. Strong bonding between the resin matrix. This invention introduces rigid structures such as double bonds in the main chain, breaking the α-helical configuration of silicone rubber and exposing atoms with strong polarity on the molecular surface, effectively improving the bonding between the resin matrix and enabling large-thickness molding.

[0017] 3. Excellent room-temperature curing performance. The present invention achieves room-temperature curing of the heat-resistant coating by designing the type and ratio of the side groups and adjusting the corresponding type and ratio of the curing agent. By changing other conditions such as pressure, humidity, and curing time at room temperature, the coating can be cured at room temperature. DETAILED DESCRIPTION

[0018] In order to help those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0019] Example 1

[0020] The present invention provides a room-temperature curable polyphosphazene-based heat-resistant coating and its preparation method. The coating's backbone is made of phosphorus pentachloride and ammonium chloride, using cationic polymerization. The side groups comprise the following components: 15% benzene, 15% phenoxy, 60% ethyl, and 10% methyl. The heat-resistant coating formulation is as follows: 100 parts polyphosphazene resin matrix, 10 parts white carbon black, 50 parts aramid fiber, 10 parts carbon fiber, 10 parts zinc borate, 10 parts zirconium oxide, and 2 parts barium sulfate-resistant. An organic peroxide is used as the curing agent.

[0021] After preparing the heat-resistant coating with the aforementioned ratio, the coating and curing agent are thoroughly mixed in a 10:1 ratio. The mixed coating is then placed in a pressure environment of 0.01 atmospheres and a humidity controlled at 50% for 120 hours to complete room-temperature curing. The heat-resistant coating can be up to 10mm thick, with a tensile strength of 1.5MPa and an elongation at break exceeding 100%.

[0022] Example 2

[0023] The present invention provides a room-temperature curable polyphosphazene-based heat-resistant coating and its preparation method. The coating's backbone is made of hexachlorocyclotriphosphazene, polymerized via solution thermal ring-opening polymerization. The side groups comprise the following components: 5% benzene, 10% phenolic groups, 25% hydroxyl groups, and 60% ethyl groups. The heat-resistant coating formulation is as follows: 100 parts polyphosphazene resin matrix, 15 parts zinc oxide, 70 parts boron oxide, 15 parts bismaleimide resin, 15 parts magnesium hydroxide and aluminum hydroxide combined, 15 parts heat-resistant filler silica gel powder, and 5 parts weather-resistant filler polyethylene powder. Isocyanate is used as the curing agent.

[0024] After preparing the heat-resistant coating with the aforementioned ratio, the coating and curing agent are thoroughly mixed in a ratio of 8:1. The mixed coating is placed in an environment with a pressure of 1 atmosphere and a humidity of 70% and allowed to cure at room temperature for 72 hours. The heat-resistant coating can be up to 8mm thick, with a tensile strength of 1.0 MPa and an elongation at break exceeding 80%.

[0025] Example 3

[0026] The present invention provides a room-temperature curable polyphosphazene-based heat-resistant coating and a preparation method thereof. The coating's backbone is made of hexachlorocyclotriphosphazene, polymerized via solution thermal ring-opening polymerization. The side groups comprise the following components: 5% benzene, 5% phenoxy, 60% ethyl, and 30% amino. The heat-resistant coating formulation is as follows: 100 parts polyphosphazene resin matrix, 5 parts glass fiber, 30 parts phenolic resin, 5 parts low-density polyethylene, 15 parts phenylated polyphosphazene, 5 parts heat-resistant filler zirconium oxide, and 2 parts dicumyl peroxide. The curing agent is bisphenol S epoxy resin.

[0027] After preparing the heat-resistant coating with the aforementioned ratio, the coating and curing agent are thoroughly mixed in a ratio of 0.16:1. The mixed coating is then placed in a pressure environment of 0.01 atmospheres and a humidity level of 5% for 2 hours to cure at room temperature. The heat-resistant coating can reach a thickness of up to 12mm, a tensile strength of 1.5MPa, and an elongation at break exceeding 100%.

[0028] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a room temperature curing polyphosphazene-based heat-resistant coating, comprising the following steps: Preparation of polyphosphazene resin, preparation of polyphosphazene-based heat-resistant coating, coating of polyphosphazene-based heat-resistant coating with large thickness and curing; The preparation of the polyphosphazene resin includes the preparation of a molecular main chain structure and a molecular side group structure.

2. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The molecular main chain structure is prepared by using cyclotriphosphazene as a raw material and adopting an in-situ thermal ring-opening polymerization method or a solution thermal ring-opening polymerization method; or by using phosphorus pentachloride as a raw material and adopting a one-step method or a living cationic polymerization method.

3. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The groups on the side groups include one or more of amino, nitro, hydroxyl, phenolic, halogen atoms, benzene series, methyl, ethyl, and hydrogen atoms; the side group substitution is achieved by polymerization first followed by substitution or substitution first followed by polymerization.

4. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The polyphosphazene-based heat-resistant coating is prepared by comprising 100 parts of a polyphosphazene resin matrix, 5 to 15 parts of a reinforcing filler, 30 to 70 parts of an anti-ablation filler, 5 to 15 parts of a carbon-forming filler, 5 to 15 parts of a flame-retardant filler, 5 to 15 parts of a heat-resistant filler, and 2 to 5 parts of a weather-resistant filler.

5. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 4, characterized in that: The polyphosphazene resin matrix is ​​a hydroxyl or amino polyphosphazene resin that can be cured at room temperature; the reinforcing filler includes one or more of white carbon black, oxide, and glass fiber; the anti-ablation filler is one or more of aramid fiber, phenolic resin, boron oxide, and quartz sand; the carbon-forming filler includes one or more of carbon fiber, bismaleimide resin, and low-density polyethylene; the flame retardant filler includes one or more of zinc borate, phenylated polyphosphazene, magnesium hydroxide, and aluminum hydroxide; the heat-resistant filler is one or more of zirconium oxide, titanium dioxide, silica gel powder, and kaolin; and the weather-resistant filler is one or more of barium sulfate, talc, diisopropylbenzene peroxide, and polyethylene powder.

6. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The polyphosphazene-based heat-resistant coating is applied with a large thickness, specifically with a coating viscosity of 15-25s, a delivery pressure of 0.02MPa-0.3MPa, a nozzle aperture of 0.5mm-4mm, and an atomization pressure of 2.0MPa-3.0MPa.

7. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The curing agent can be selected from one or more of bisphenol A epoxy resin, bisphenol B epoxy resin, bisphenol D epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, isocyanate, organic peroxide and modified products thereof.

8. The method for preparing a room temperature curing polyphosphazene-based heat-resistant coating according to claim 1, characterized in that: The curing step is specifically to evacuate or pressurize the resin matrix so that the resin matrix is ​​placed in a pressure environment of 0.01-3 atmospheres, the humidity is controlled within the range of 5%-70%, and the resin matrix is ​​placed at room temperature for 10 minutes to 120 hours to complete room temperature curing.

9. A room temperature curable polyphosphazene-based heat-resistant coating, prepared using the preparation method according to any one of claims 1 to 8.

10. The room temperature curable polyphosphazene-based heat-resistant coating according to claim 9, characterized in that: Large thickness coating exceeding 10mm can be performed.