High-adhesion graphite synergistic flame-retardant PVC stone chip resistant coating and preparation method thereof

Abstract

The invention discloses a high-adhesion graphite synergistic flame-retardant PVC stone chip resistant coating and a preparation method thereof, and belongs to the technical field of special functional coatings. The coating is composed of PVC resin, a plasticizer, a moisture absorption agent, a composite flame retardant, expanded graphite, nano calcium, a stone impact resistant functional filler, a heat stabilizer, a modified adhesion promoter, a pigment and a solvent. According to the invention, through the specific modified adhesion promoter, the problem that the adhesion of the coating is reduced due to the addition of expanded graphite is effectively solved, and the 0-level adhesion of the GB / T 9286-2021 standard is realized while the UL94 V-0-level flame retardant property and the excellent stone impact resistance are ensured. The high-adhesion graphite synergistic flame-retardant PVC stone-impact-resistant coating is particularly suitable for a protective coating of a bottom protective plate of a power battery pack of a new energy automobile, and has the advantages of high adhesion, good flame retardance, excellent stone-impact resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of special functional coatings technology, specifically relating to a high-adhesion graphite-synergistic flame-retardant PVC anti-stone-impact coating and its preparation method. This coating is applied to the polyvinyl chloride (PVC)-based composite protective coating for the bottom guard plate of a power battery pack in new energy vehicles. This invention aims to solve the technical problem of decreased adhesion of such coatings after the introduction of functional fillers (such as expanded graphite), providing a coating solution that ensures excellent flame retardant and anti-stone-impact properties while possessing extremely strong substrate adhesion. Background Technology

[0002] The coating on the bottom protection plate of new energy vehicle battery packs needs to possess multiple properties, including flame retardancy, stone chip resistance, and lightweighting. Polyvinyl chloride (PVC) coatings are widely used due to their excellent comprehensive performance. To improve flame retardancy, the industry typically adopts a technical route that adds antimony trioxide-based composite flame retardants and combines them with expanded graphite. This combination has been proven to effectively construct a synergistic "gas-solid" flame retardant barrier, meeting high flame retardant standards such as UL94 V-0.

[0003] However, introducing expanded graphite into PVC stone impact resistant coatings has a significant side effect: a sharp decrease in adhesion between the coating and the metal substrate (such as aluminum alloys or steel underbody plates). The lamellar structure, surface inertness, and volume change tendency of expanded graphite during heating or curing disrupt the stress balance within the coating and form a weak interface layer at the coating-substrate interface, making the coating prone to peeling, blistering, or detachment from the substrate. This is a fatal flaw in battery pack underbody plate applications that need to withstand severe road stone impacts, vibrations, and thermal shocks.

[0004] In existing technologies, general-purpose adhesion promoters (such as common polyamides) are typically added to improve the adhesion of PVC coatings. However, these conventional promoters have limited effectiveness in addressing the adhesion degradation problem exacerbated by the addition of expanded graphite. They cannot restore or improve the adhesion to the extremely high level required for the application (such as grade 0 adhesion) while ensuring sufficient expanded graphite is added to maintain a high flame retardant rating. Therefore, how to achieve and maintain excellent coating adhesion in PVC flame-retardant coating systems containing a high proportion of expanded graphite has become a key technical bottleneck restricting the practical application and reliability of such high-performance coatings.

[0005] Existing technology CN112662093A discloses a material for the casing of new energy vehicle batteries and its preparation method, whose raw materials include PVC, antimony trioxide flame retardant, and expanded graphite. However, this scheme discloses an extrusion molding process, with a high proportion of PVC (100 parts) in the raw materials and a relatively small proportion of other components. Furthermore, it does not provide a solution to the problem of decreased adhesion in the coating system due to the addition of expanded graphite. In PVC-based composite protective coatings, the proportion of PVC is very small, and meeting the adhesion requirements is fundamental for the coating's usability. Therefore, the above technology cannot be directly used in PVC-based composite protective coatings. Therefore, research is being conducted on a technical route that adds antimony trioxide-based composite flame retardant and compounded with expanded graphite, and its application in coatings has significant market value. Summary of the Invention

[0006] This invention aims to solve the core problem of insufficient coating adhesion in existing PVC-based battery pack protective coatings containing expanded graphite. Specifically, it addresses the weakening of the interfacial bond between the coating and the metal substrate due to the addition of expanded graphite, making it prone to peeling off from the interface, and the difficulty in achieving and maintaining the 0-level adhesion under the GB / T 9286-2021 standard while meeting high flame retardant standards such as UL94 V-0 (which relies on sufficient expanded graphite).

[0007] To solve the above-mentioned technical problems, firstly, the present invention provides a high-adhesion graphite synergistic flame-retardant PVC anti-stone chip coating. While adopting a highly efficient synergistic flame-retardant system containing antimony trioxide, zinc / aluminum / magnesium synergists and expanded graphite, it innovatively introduces a specific modified adhesion promoter system, which can effectively overcome the negative impact of expanded graphite on interfacial adhesion.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating and its preparation method, comprising the following components by weight percentage:

[0010] PVC resin: 15%~30%;

[0011] Plasticizer: 10%~20%;

[0012] Desiccant: 1%~3%;

[0013] Composite flame retardant: 2%~9%;

[0014] Expanded graphite: 5%~20%;

[0015] Nano-calcium: 10%~20%;

[0016] Stone chip resistance filler: 2%~12%;

[0017] Heat stabilizer: 0.2%~1%;

[0018] Modified adhesion promoter: 1%~3%;

[0019] Pigment: 0.2%~1%;

[0020] Solvent: 3%~10%.

[0021] The PVC resin has excellent mechanical properties, chemical resistance, and electrical insulation, which can give the coating good basic properties.

[0022] The plasticizer is a compound of one or more of DOP, DOTP, and DINP with one or more of RDP, BDP, and TCPP in a mass ratio of 7:3. RDP is resorcinol-bis(diphenyl phosphate), BDP is bisphenol A-bis(diphenyl phosphate), TCPP is trichloropropyl phosphate, DOP is dioctyl phthalate, DOTP is dioctyl terephthalate, and DINP is diisononyl phthalate. By scientifically proportioning these plasticizers, this coating can not only effectively regulate the flexibility and processing performance of PVC resin, but also improve the coating's stone chip resistance and flame retardant effect to a certain extent.

[0023] The desiccant is any one or more of calcium oxide, 5A molecular sieve activated powder, and alumina micro powder. These desiccant have good moisture absorption properties, effectively absorbing moisture from the environment and preventing the coating from becoming damp and clumping during storage and use, thus ensuring that the coating always maintains stable quality and good application results.

[0024] The composite flame retardant is a complex containing antimony trioxide and a synergist containing zinc, aluminum, and magnesium elements, with a mass ratio of antimony trioxide to the synergist containing zinc, aluminum, and magnesium elements of 10:0.5~3. The synergist containing zinc, aluminum, and magnesium elements is zinc-aluminum-magnesium hydrotalcite, or a mixture composed of magnesium hydroxide, aluminum hydroxide, and zinc borate. The synergist can cover a wider temperature range, synergistically exerting its heat-absorbing and combustible gas-diluting effects, and can also promote charring on the combustion surface, forming a robust and heat-insulating protective layer, thus enhancing flame retardant and smoke-suppressing effects.

[0025] In some embodiments, in the synergist composed of magnesium hydroxide, aluminum hydroxide, and zinc borate, the mass ratio of magnesium hydroxide, aluminum hydroxide, and zinc borate is 1~5:1~5:1~10.

[0026] The expanded graphite used is expandable graphite with an initial expansion temperature of 180~250℃ and a particle size distribution of 50~300 mesh.

[0027] The nano-calcium has a particle size of 60-90 nm and an oil absorption value of 28-45 g / 100 g. Nano-calcium effectively improves the hardness and abrasion resistance of coatings, while its smaller particle size and suitable oil absorption value help improve the dispersibility and stability of the coating, making it easier to apply during construction and resulting in a smoother, more even film surface.

[0028] The anti-stone-impact filler is selected from one or more of hollow glass microspheres, double-flying powder, and mica. This filler selection not only effectively adjusts the density and leveling properties of the coating but also enhances its anti-stone-impact performance to a certain extent.

[0029] The heat stabilizer is a calcium-zinc composite stabilizer or an antioxidant, and the antioxidant is any one or a combination of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0030] The modified adhesion promoter is made of modified polyurethane combined with low molecular weight polyamide in a mass ratio of 2.5 to 5:10. Based on the adhesion provided by low molecular weight polyamide, it can further enhance the adhesion. It is suitable for PVC quick-dissolving adhesive, enhances the crosslinking density of polyamide resin, improves the adhesion of PVC coating on substrates such as epoxy electrophoresis plates, steel plates and aluminum plates, and enhances the adhesion.

[0031] The modified polyurethane used has an unblocked NCO% value of 5~7.5% and a viscosity of 40±20 Pa.S, which can effectively improve the adhesion, strength and stone chip resistance of the coating.

[0032] Specifically, the modified polyurethane is a 7-series modified polyurethane produced by Wuxi Shengyi Synthetic Materials Co., Ltd., and exemplary product models and corresponding parameters are as follows:

[0033] Product Model: SY-Z700, Unsealed NCO%: 6.1~7.2%, Viscosity (25℃): 45±15 Pa.S.

[0034] Product Model: SY-Z710, Unsealed NCO%: 5.5~6.7%, Viscosity (25℃): 35±15 Pa.S.

[0035] Low molecular weight polyamides mainly include dimer acid type low molecular weight polyamides with amine values ​​in the range of 200~400 mgKOH / g, with specific models mainly being the 650, 651, 300# (or 3051), 140#, etc. These products typically have molecular weights between 800 and 1500, exhibit good synergistic reactivity with polyurethane systems, and can effectively participate in cross-linking reactions to enhance the cross-linking density and adhesion of PVC plastisol.

[0036] The NCO groups of modified polyurethane react with low-molecular-weight polyamide to form a strong urea bond network, which then forms chemical bonds with active groups (-OH, -NH2, etc.) on the substrate surface. This creates a chemically anchored, densely cross-linked reinforcing layer at the interface, improving the adhesion of PVC coatings to various substrates. The mechanism of action of the modified adhesion promoter can be summarized as a three-in-one approach of "surface activation, interface enhancement, and three-dimensional anchoring." Surface transformation utilizes low-molecular-weight polyamide to transform the inert electrophoretic paint surface into an "active surface" rich in polar groups and easily bonded. Interface enhancement is achieved through the reaction of modified polyurethane and polyamide to construct a hybrid polymer network layer with high cohesive strength and toughness. Three-dimensional anchoring occurs during the curing process, where the hybrid polymer network layer undergoes deep segment interpenetration and possible chemical bonding with the PVC / graphite coating upwards, and strongly anchors downwards to the substrate. Like a three-dimensional fishing net or root system, it not only firmly adheres to the substrate but also firmly holds and entangles the PVC coating body containing a large number of lubricating graphite particles. Ultimately, the lubricity and weak interface problems caused by graphite were overcome. By constructing a reinforcing skeleton that spans the coating thickness direction and has progressively increasing strength, the PVC / graphite coating is locked onto the substrate, thereby achieving a significant improvement in adhesion under extremely difficult conditions.

[0037] In addition, the polyamide segments possess good flexibility and compatibility, acting as a bridge and stress buffer layer between PVC resin and expanded graphite filler, alleviating internal stress caused by the difference in thermal expansion coefficients between expanded graphite and the PVC matrix, as well as the layered structure. The polar functional groups of the modified polyurethane can also interact with the inorganic components in the flame retardant system, reducing interfacial defects.

[0038] The pigments used are inorganic pigments, such as carbon black, iron black, titanium dioxide, iron oxide red, and iron oxide yellow.

[0039] The solvent used is a viscosity reducer, such as D40, D60, D100, or D110 solvent oil. The solvent oil has good solubility and volatility, which can effectively dissolve the components during the coating preparation process and evaporate quickly after the coating is applied and baked, without affecting the final performance of the coating.

[0040] Secondly, this invention also proposes a method for preparing a high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating, comprising the following steps:

[0041] Step 1, Preparation of color paste: Mix the pigment with the plasticizer from the first part, disperse and grind until the fineness is ≤50μm to obtain the color paste;

[0042] Step 2, prepare the main mixture: mix PVC resin, nano calcium, the remaining plasticizer and the color paste obtained in step 1, add moisture absorber, composite flame retardant, anti-stone chip functional filler, heat stabilizer and modified adhesion promoter in sequence while stirring, then add solvent to adjust viscosity and disperse at high speed until a uniform mixture with a fineness ≤100 μm is formed.

[0043] Step 3, Add expanded graphite: Add expanded graphite to the homogeneous mixture and keep stirring to ensure it is mixed evenly;

[0044] Step 4, Degassing and Storage: The mixture obtained in Step 3 is subjected to vacuum degassing to obtain the high-adhesion graphite synergistic flame-retardant PVC anti-stone chip coating.

[0045] As a preferred embodiment of the present invention, in the preparation method, the viscosity of the homogeneous mixture obtained in step two is 50,000~100,000 cps. In step four, the vacuum degree of the vacuum degassing treatment is -0.095 MPa, and the treatment time is 30 min.

[0046] This invention builds upon a mature and efficient flame-retardant system composed of antimony trioxide-based composite flame retardants and specific expanded graphite. Addressing the specific technical obstacle of severely reduced coating adhesion caused by the introduction of expanded graphite, it creatively employs a modified polyurethane combined with a low-molecular-weight polyamide adhesion promoter. This modified promoter, through its unique chemical structure, strongly promotes the interfacial bonding between the coating and the metal substrate, effectively buffering internal stress. Thus, while ensuring no loss of flame-retardant performance, it achieves a qualitative leap in coating adhesion, solving a key bottleneck in the practical application of this system.

[0047] The core design concept of this invention lies in the precise proportioning and compounding of carefully selected composite flame retardants (providing a highly efficient, multi-mechanism flame-retardant base) and expanded graphite with specific parameters (providing the ability to form a barrier through thermal physical expansion), resulting in a multi-stage synergistic flame-retardant effect of "catalysis-char formation-expansion" within the PVC matrix. Simultaneously, anti-stone-impact fillers are introduced to enhance the coating's resistance to stone impact. This ternary system design aims to achieve complementary functions and multiplied performance among the components.

[0048] Compared with the prior art, the present invention has the following significant advantages:

[0049] 1. Completely solves the adhesion problem caused by graphite: By using the modified adhesion promoter specific to this invention, the problem of decreased adhesion caused by the addition of expanded graphite can be completely overcome. The prepared coating can achieve Grade 0 adhesion (completely smooth cut edges, no peeling) according to GB / T 9286-2021 standard on substrates such as aluminum alloys and steel plates.

[0050] 2. Excellent overall performance balance: While achieving a breakthrough improvement in adhesion, it fully maintains the excellent performance of the highly efficient synergistic flame retardant system composed of "composite flame retardant + expanded graphite", and the flame retardant rating can still stably reach UL94 V-0 level. The coating's key mechanical properties such as stone chip resistance (SAE J400), tensile strength, and flexibility are also simultaneously guaranteed and even optimized.

[0051] 3. Improved long-term coating reliability: Strong adhesion means that the coating has better durability in harsh environments such as humid heat cycling, thermal shock, and vibration, and is less likely to fail from the substrate, thus providing more durable and reliable protection for the battery pack.

[0052] 4. Simple preparation process and easy to promote: The overall preparation process of the coating is similar to that of traditional PVC coatings, requiring no complex equipment and facilitating industrial production. Attached Figure Description

[0053] Figure 1 The flowchart illustrates the preparation of a high-adhesion graphite-synergistic flame-retardant PVC anti-stone-impact coating according to the present invention.

[0054] Figure 2 This is a schematic diagram showing the adhesion test results of a sample using a common adhesion promoter.

[0055] Figure 3 These are schematic photographs of the samples prepared for adhesion testing in Examples 1-3 of this invention.

[0056] Figure 4 These are schematic photographs of the adhesion tests conducted after sample preparation in Examples 1-3 of this invention. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0058] Example 1

[0059] Coating composition (by weight percentage):

[0060] PVC resin: 24%;

[0061] Plasticizer: 18%;

[0062] Nano-calcium: 19%;

[0063] Desiccant: 2%;

[0064] Composite flame retardant: 3%;

[0065] Stone-impact resistant filler: 3%;

[0066] Heat stabilizer: 0.5%;

[0067] Modified adhesion promoter: 1.5%;

[0068] Pigment: 1%;

[0069] Expanded graphite: 20%;

[0070] Solvent: 8%.

[0071] Preparation method:

[0072] Step 1: Add 0.1 kg of pigment (medium-pigment carbon black) to 0.9 kg of plasticizer (DOTP:TCPP weight ratio 7:3), and disperse it in a basket mill until the fineness is ≤50 μm to obtain a mixture (pigment paste).

[0073] Step 2: Weigh the remaining 0.9 kg of plasticizer (DOTP:TCPP weight ratio 7:3), add 2.4 kg of PVC resin and 1.9 kg of nano-calcium, add the mixture dispersed in Step 1, stir at 500 r / min for 3 min, then add 0.2 kg of 5A molecular sieve activation powder, 0.3 kg of composite flame retardant (antimony trioxide to hydrotalcite mass ratio 10:1), 0.3 kg of anti-stone chipping functional filler (double-flying powder), 0.05 kg of heat stabilizer (antioxidant 168), and 0.15 kg of modified adhesion promoter (modified polyurethane: 650 low molecular weight polyamide = 3:10). Add 0.8 kg of solvent (D60) to adjust the viscosity to 50,000~100,000 cps (25℃), and disperse at high speed until a uniform mixture is formed (fineness ≤100 μm required).

[0074] Step 3: Add 2 kg of 300 mesh expanded graphite and stir at 500 r / min for 10 min until well mixed.

[0075] Step 4: Degas the finished product under a vacuum of -0.095 MPa (gauge pressure under standard atmospheric pressure) for 30 min to obtain the coating; put it into a sealed container and store it in a cool and dry place (temperature 15~35℃, relative humidity ≤60%).

[0076] How to use

[0077] The application process uses high-pressure airless spraying equipment, and the specific steps are as follows:

[0078] Operating environment and spraying equipment: Ambient temperature 20~35℃, relative humidity ≤80%; use pneumatic high-pressure airless spray pump with a pump pressure ratio of not less than 55:1; spraying pressure 15~45 MPa; use elliptical fan-shaped spray gun with nozzle orifice diameter of 0.40~0.55mm.

[0079] Substrate pretreatment: Cleaning, degreasing, and drying are performed on the surface of the battery pack bottom cover plate (aluminum alloy or steel) to be sprayed.

[0080] Spraying operation: The spray gun should be 50 cm away from the workpiece surface. The spray gun should move at a uniform speed and overlap the fan-shaped areas by 1 / 3 to 1 / 2. Spray 2 to 8 coats continuously in a wet-on-wet manner until the target wet film thickness is achieved (e.g., when the dry film thickness is 500 μm, the wet film thickness should be 600 to 800 μm).

[0081] Curing and molding: Temperature 140~160℃, time 20~40 min.

[0082] Example 2

[0083] Coating composition (by weight percentage):

[0084] PVC resin: 27%;

[0085] Plasticizer: 20%;

[0086] Nano-calcium: 17%;

[0087] Desiccant: 1%;

[0088] Composite flame retardant: 4%;

[0089] Stone-impact resistant filler: 8%;

[0090] Heat stabilizer: 0.3%;

[0091] Modified adhesion promoter: 2%;

[0092] Pigment: 0.7%;

[0093] Expanded graphite: 15%;

[0094] Solvent: 5%.

[0095] Preparation method:

[0096] Step 1: Add 0.07 kg of pigment (medium pigment carbon black) to 1 kg of plasticizer (DOP:BDP weight ratio 7:3) and disperse it in a basket mill to a fineness of ≤50 μm.

[0097] Step 2: Weigh the remaining 1 kg of plasticizer (DOP:BDP weight ratio 7:3), add 2.7 kg of PVC resin and 1.7 kg of nano-calcium, add the mixture dispersed in Step 1, stir at 500 r / min for 3 min, then add 0.1 kg of desiccant (calcium oxide), 0.4 kg of composite flame retardant (antimony trioxide to hydrotalcite mass ratio 10:1.3), 0.8 kg of double-flying powder, 0.03 kg of heat stabilizer (antioxidant 1010), 0.2 kg of adhesion promoter (modified polyurethane: 650 low molecular weight polyamide = 3:10), add 0.5 kg of solvent (D60) to adjust the viscosity to 50,000~100,000 cps (25℃), and disperse at high speed until a uniform mixture is formed (fineness ≤100 μm required).

[0098] Step 3: Add 1.5 kg of 200 mesh expanded graphite and stir at 500 r / min for 3 min until well mixed.

[0099] Step 4: Degas the finished product under a vacuum of -0.095 MPa for 30 min to obtain the coating; pack it into a sealed container and store it in a cool, dry place (temperature 15~35℃, relative humidity ≤60%).

[0100] Usage method: Same as Example 1.

[0101] Example 3

[0102] Coating composition (by weight percentage):

[0103] PVC resin: 24%;

[0104] Plasticizer: 18%;

[0105] Nano-calcium: 19%;

[0106] Desiccant: 2%;

[0107] Composite flame retardant: 8%;

[0108] Stone-impact resistant filler: 8%;

[0109] Heat stabilizer: 0.5%;

[0110] Modified adhesion promoter: 1.5%;

[0111] Pigment: 1%;

[0112] Expanded graphite: 10%;

[0113] Solvent: 8%.

[0114] Preparation method:

[0115] Step 1: Add 0.1 kg of pigment (medium pigment carbon black) to 0.9 kg of plasticizer (DOTP:TCPP weight ratio 7:3) and disperse with a basket mill to a fineness ≤50 μm.

[0116] Step 2: Weigh the remaining 0.9 kg of plasticizer (DOTP:TCPP weight ratio 7:3), add 2.4 kg of PVC resin and 1.9 kg of nano-calcium, add the mixture dispersed in Step 1, stir at 500 r / min for 3 min, then add 0.2 kg of desiccant (5A molecular sieve activated powder), 0.8 kg of composite flame retardant (antimony trioxide to hydrotalcite mass ratio 10:1.3), 0.8 kg of anti-stone chipping functional filler (double-flying powder), 0.05 kg of heat stabilizer (antioxidant 168), and 0.15 kg of modified adhesion promoter (modified polyurethane: 650 low molecular weight polyamide = 3:10), add 0.8 kg of solvent (D40) to adjust the viscosity to 50,000~100,000 cps (25℃), and disperse at high speed until a uniform mixture is formed (fineness ≤100 μm required).

[0117] Step 3: Add 1 kg of 300 mesh expanded graphite and stir at 500 r / min for 10 min until well mixed.

[0118] Step 4: Degas the finished product under a vacuum of -0.095 MPa for 30 min to obtain the coating; pack it into a sealed container and store it in a cool, dry place (temperature 15~35℃, relative humidity ≤60%).

[0119] Usage method: Same as Example 1.

[0120] Performance test comparison:

[0121] 1. The same formulation as in Example 1 was used, but a common polyamide (650 low molecular weight polyamide) adhesion promoter was used instead of the modified adhesion promoter in Example 1. Figure 2 As shown, after preparing the coating sample in the comparative proportion on an aluminum plate, an adhesion test was conducted according to the GB / T 9286-2021 standard. The adhesion test results were poor, failing to reach the 0-level standard, with the coating peeling off in one strip, indicating almost no adhesion. In addition, its flame retardant properties and stone chip resistance were also reduced.

[0122] 2. After preparing the coatings in Examples 1-3 on an electrophoresis plate or aluminum plate, adhesion tests were conducted according to GB / T 9286-2021 standard. All samples met the GB / T 9286-2021 standard level 0. The flame retardancy test reached UL94 V0 level. The stone impact resistance test (M6 nut) was greater than 30 kg. Figure 3These are photos taken after sample preparation and before adhesion testing for Examples 1, 2, and 3. Numbered 1, 2, and 3 correspond to Examples 1, 2, and 3, respectively. Figure 3 The image in the middle left shows the coating applied to an electrophoresis plate. Figure 3 The image on the right shows the coating applied to an aluminum plate. Figure 4 The photos show the adhesion after the test. It can be seen that the adhesion of Examples 1, 2, and 3 all meet the Grade 0 standard of GB / T 9286-2021.

Claims

1. A high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating, characterized in that, It consists of the following components by weight percentage: PVC resin: 15%~30%; Plasticizer: 10%~20%; Desiccant: 1%~3%; Composite flame retardant: 2%~9%; Expanded graphite: 5%~20%; Nano-calcium: 10%~20%; Stone chip resistance filler: 2%~12%; Heat stabilizer: 0.2%~1%; Modified adhesion promoter: 1%~3%; Pigment: 0.2%~1%; Solvent: 3%~10%.

2. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The plasticizer is formulated as a first part by any one or more of dioctyl phthalate, dioctyl terephthalate, and diisononyl phthalate, and as a second part by any one or more of resorcinol-bis(diphenyl phosphate), bisphenol A-bis(diphenyl phosphate), and tri(chloropropyl) phosphate, with the mass ratio of the first part to the second part being 7:

3.

3. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The composite flame retardant is a complex containing antimony trioxide and synergists containing zinc, aluminum, and magnesium elements, with the mass ratio of antimony trioxide to the synergists containing zinc, aluminum, and magnesium elements being 10:0.5~3.

4. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 3, characterized in that, The synergist containing zinc, aluminum, and magnesium is zinc-aluminum-magnesium hydrotalcite, or a mixture of magnesium hydroxide, aluminum hydroxide, and zinc borate, wherein the mass ratio of magnesium hydroxide, aluminum hydroxide, and zinc borate is 1~5:1~5:1~10.

5. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The modified adhesion promoter is made of modified polyurethane combined with low molecular weight polyamide, with a mass ratio of 2.5 to 5:

10. The modified polyurethane has an unblocking NCO% value of 5 to 7.5% and a viscosity of 40 ± 20 Pa·s. The low molecular weight polyamide includes dimer acid type low molecular weight polyamide with an amine value in the range of 200 to 400 mgKOH / g.

6. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The expanded graphite used is expandable graphite with an initial expansion temperature of 180~250℃ and a particle size distribution of 50~300 mesh.

7. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The nano-calcium has a particle size of 60-90 nm and an oil absorption value of 28-45 g / 100 g.

8. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The anti-stone impact filler is any one or more of hollow glass microspheres, double-flying powder, and mica.

9. The high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, The desiccant is any one or more of calcium oxide, 5A molecular sieve activated powder, and alumina micro powder.

10. A method for preparing a high-adhesion graphite-synergistic flame-retardant PVC anti-stone chip coating as described in claim 1, characterized in that, Includes the following steps: Step 1, Preparation of color paste: Mix the pigment with the plasticizer from the first part, disperse and grind until the fineness is ≤50μm to obtain the color paste; Step 2, prepare the main mixture: mix PVC resin, nano calcium, the remaining plasticizer and the color paste obtained in step 1, add moisture absorber, composite flame retardant, anti-stone chip functional filler, heat stabilizer and modified adhesion promoter in sequence while stirring, then add solvent to adjust the viscosity and disperse at high speed until a uniform mixture with a fineness ≤100 μm is formed. Step 3, Add expanded graphite: Add expanded graphite to the homogeneous mixture and keep stirring to ensure it is mixed evenly; Step 4, Degassing and Storage: The mixture obtained in Step 3 is subjected to vacuum degassing to obtain the high-adhesion graphite synergistic flame-retardant PVC anti-stone chip coating.

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