Protective film for improving surface function of glass fiber reinforced polypropylene base material as well as preparation method and application of protective film

Abstract

The invention discloses a protective film for improving the surface function of a glass fiber reinforced polypropylene base material as well as a preparation method and application of the protective film. The protective film comprises the following raw materials: matrix resin; the reinforcing filler comprises wollastonite and boron nitride, and based on the mass of the matrix resin, the reinforcing filler accounts for 5-20 wt% of the mass of the matrix resin; the functional material comprises an organic silicon modified polyurethane elastomer and erucyl amide, and based on the mass of the matrix resin, the mass of the functional material accounts for 3-16 wt% of the mass of the matrix resin; and the assistant accounts for 0.1-5wt% of the mass of the matrix resin on the basis of the mass of the matrix resin. And the protection film and the bottom protection plate are combined through integrated hot press molding. According to the invention, the protection performance comparable to that of metal and function extension beyond that of a traditional composite material are realized on the glass fiber reinforced polypropylene base material, and popularization and application of the glass fiber reinforced polypropylene base material in the field of bottom guard plates are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and particularly relates to a protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, a preparation method thereof, and an application thereof. Background Art

[0002] The battery pack of a new energy electric vehicle is generally laid flat under the chassis, which can reduce the vehicle's center of gravity, improve the stability of vehicle handling, and reduce the occurrence of rollover. However, the distance between the battery pack and the ground is relatively close, and the bottom of the battery pack needs to be protected. The battery bottom guard is a protective device installed at the bottom of the battery pack (especially the electric vehicle battery), mainly used to prevent physical damage and improve safety.

[0003] The materials of the bottom guard are diverse. For example, the bottom guard can be made of aluminum alloy material, which is the current mainstream lightweight option. The density of the aluminum alloy bottom guard is about 2.7 g / cm 3 , its hardness is only HV80 - 100, the impact load ≤ 8 N (scratches are easily generated under the standard of GMW 14688), and the anti-puncture ability is also significantly insufficient. It can be seen that although the aluminum alloy bottom guard can meet the lightweight requirements, its important protection performance is lacking. The bottom guard can also be made of traditional steel plate materials, such as HC340 / 590DP steel, with a thickness of 1 - 1.5 mm. The surface of the steel plate bottom guard needs a coating to meet the anti-corrosion requirements. The steel plate forms a coating by electrophoresis or coats a PVC coating. However, the scratch resistance of the coating is poor, only reaching 10 N load, and the corrosion rate will increase significantly after the coating is damaged, reaching 0.1 mm / year, resulting in high maintenance costs. In addition, in order to improve the surface performance of the metal bottom guard, anti-corrosion treatment is also carried out on the metal bottom guard. This treatment is directly related to the anti-scratch treatment. However, when the anti-corrosion coating is scratched and the bottom guard surface is exposed, the bottom guard will still be corroded.

[0004] Currently, there is also a new type of bottom guard made of glass fiber reinforced composite material on the existing market. It uses polypropylene (PP) as the matrix and generally has a thickness of 2 - 3 mm. It is a lightweight material that can meet the basic protection requirements and has a low risk of being corroded. However, the scratch resistance of the material surface only reaches 10 N load, and it lacks hydrophobic and self-cleaning capabilities, which is not conducive to the popularization and application of this new material. Based on the existing glass fiber reinforced composite material, the present invention proposes a new type of protective film to improve its surface function. Summary of the Invention

[0005] To solve the above technical problems, the object of the present invention is to provide a protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, and its preparation method and application. The protective film achieves protective performance comparable to that of metals and functional expansion beyond traditional composite materials on the glass fiber reinforced polypropylene substrate, which is beneficial to the popularization and application of the glass fiber reinforced polypropylene substrate in the field of bottom guard plates.

[0006] To achieve the above object of the invention, the technical solutions adopted by the present invention are as follows:

[0007] In the first aspect of the present invention, the present invention provides a protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, and the raw materials include:

[0008] Matrix resin;

[0009] Reinforcing fillers, including wollastonite and boron nitride. Based on the mass of the matrix resin, the reinforcing fillers account for 5-20 wt% of the mass of the matrix resin;

[0010] Functional materials, including organosilicon modified polyurethane elastomer and erucamide. Based on the mass of the matrix resin, the functional materials account for 3-16 wt% of the mass of the matrix resin;

[0011] Auxiliaries. Based on the mass of the matrix resin, the auxiliaries account for 0.1-5 wt% of the mass of the matrix resin.

[0012] Preferably, the reinforcing fillers account for 8-20 wt% of the mass of the matrix resin. More preferably, the reinforcing fillers account for 10-18 wt% of the mass of the matrix resin.

[0013] Preferably, the functional materials account for 4-15 wt% of the mass of the matrix resin. More preferably, the functional materials account for 5-12 wt% of the mass of the matrix resin.

[0014] Preferably, the matrix resin includes polypropylene and / or modified polypropylene, and the weight average molecular weight of the matrix resin is 30,000-40,000.

[0015] More preferably, the matrix resin includes maleic anhydride grafted modified polypropylene, and the grafting rate of maleic anhydride is 0.5-1.2 wt%.

[0016] Preferably, based on the mass of the matrix resin, wollastonite accounts for 4-15 wt% of the mass of the matrix resin, and boron nitride accounts for 1-5 wt% of the mass of the matrix resin;

[0017] More preferably, wollastonite accounts for 6-12 wt% of the mass of the matrix resin, and boron nitride accounts for 2-5 wt% of the mass of the matrix resin;

[0018] More preferably, wollastonite accounts for 8-12 wt% of the mass of the matrix resin, and boron nitride accounts for 3-5 wt% of the mass of the matrix resin.

[0019] More preferably, the mass ratio of wollastonite to boron nitride is (1.6 - 4):1, and more preferably, the mass ratio of wollastonite to boron nitride is (2 - 3):1.

[0020] Preferably, based on the mass of the matrix resin, the organosilicon-modified polyurethane elastomer accounts for 2 - 12 wt% of the mass of the matrix resin, and erucamide accounts for 1 - 4 wt% of the mass of the matrix resin;

[0021] More preferably, the organosilicon-modified polyurethane elastomer accounts for 2 - 10 wt% of the mass of the matrix resin, and erucamide accounts for 2 - 3 wt% of the mass of the matrix resin;

[0022] More preferably, the organosilicon-modified polyurethane elastomer accounts for 3 - 8 wt% of the mass of the matrix resin, and erucamide accounts for 2 - 3 wt% of the mass of the matrix resin.

[0023] More preferably, the mass ratio of the organosilicon-modified polyurethane elastomer to wollastonite is (0.25 - 1):1, and more preferably, the mass ratio of the organosilicon-modified polyurethane elastomer to wollastonite is (0.5 - 1):1.

[0024] More preferably, the mass ratio of boron nitride to erucamide is (1 - 2.5):1, and more preferably, the mass ratio of boron nitride to erucamide is (1.5 - 2.5):1.

[0025] In the second aspect of the present invention, the present invention provides a method for preparing a protective film for improving the surface function of a glass fiber-reinforced polypropylene substrate, as follows:

[0026] Mix the matrix resin, reinforcing filler, functional material, and additive evenly and melt and stir, and obtain the protective film after molding.

[0027] In the third aspect of the present invention, the present invention provides an application of a protective film for improving the surface function of a glass fiber-reinforced polypropylene substrate, and the application is that the functional film is used to protect the glass fiber-reinforced polypropylene substrate.

[0028] Existing new energy electric vehicles are constantly demanding lightweight design to reduce the overall weight of new energy vehicles, thereby improving their power performance and reducing energy consumption. As one of the key components of new energy vehicles, the weight of the battery part has a non-negligible impact on the overall weight of the electric vehicle. Technicians in this field are gradually using glass fiber reinforced composite materials as the battery bottom guard plate to replace traditional metal plates to reduce the weight of the battery part. Among them, the glass fiber reinforced composite plate with polypropylene (PP) as the matrix material is a lightweight material that can meet the basic protection requirements of the battery part. However, the scratch resistance of the surface of this material only reaches a load of 10 N, and it lacks the ability of hydrophobicity and self-cleaning, which is not conducive to the large-scale application of this new material. In this case, after the protective film of the present invention is combined with the glass fiber reinforced polypropylene plate by hot pressing, the surface function of the plate is greatly improved, not only improving its scratch resistance, but also significantly improving the cleanliness and reparability of the plate surface. For example, when the bottom guard plate of the battery pack of a new energy electric vehicle is slightly scratched due to external force, the functional film of the present invention can be attached by hot pressing or other means to improve the appearance of the bottom guard plate and at the same time avoid the aggravation of the damage.

[0029] In addition, the functional film of the present invention is not only used for the protection of the bottom guard plate of the battery pack of new energy electric vehicles, but also can be used for the protection of the surfaces of other composite materials, such as automotive interiors, car seats, electronic devices, car surfaces, and so on.

[0030] During the application process of the functional film of the present invention, it can be integrally formed with the glass fiber reinforced composite material, especially the glass fiber reinforced polypropylene substrate, by hot pressing, or the combination of the two can be achieved by other means.

[0031] Beneficial effects:

[0032] The protective film of the present invention has high impact resistance and scratch resistance. When the protective film is impacted or scratched, the wollastonite skeleton in the protective film bears the load first, boron nitride disperses the stress through lamellar slip, and the organosilicon modified polyurethane elastomer absorbs the residual energy to prevent the microcracks from growing continuously, achieving the effect of no damage under a load of 15 N. At the same time, the local temperature rise caused by scratching makes erucamide undergo a phase change flow to fill the microcracks, making the protective film have a certain self-repair function.

[0033] The protective film of the present invention maintains lightweight (density ≤ 1.4 g / cm 3) At the same time, the scratch-resistant load is increased to 15 N (GMW 14688 standard), and no post-treatment coating is required, breaking through the problems of the corrosion sensitivity of metal materials and the brittleness of the surface of composite materials. The present invention effectively solves the industry dilemma of "lightweight and vulnerable, weak surface of composite materials, and bulky metal materials" of the bottom guard plate of new energy battery packs, realizes the protective performance comparable to that of metals and the function expansion beyond traditional composite materials on the glass fiber-reinforced polypropylene substrate, and is conducive to the popularization and application of the glass fiber-reinforced polypropylene substrate in the field of bottom guard plates. Detailed implementation manners

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will describe the specific implementation manners of the present invention. Obviously, for those of ordinary skill in the art, without creative efforts, other implementation manners can also be obtained according to these embodiments.

[0035] The present invention provides a protective film for improving the surface function of a glass fiber-reinforced polypropylene substrate, which combines with a sheet glass fiber-reinforced composite material (hereinafter referred to as a composite material), especially a glass fiber-reinforced polypropylene substrate, to improve the scratch resistance of the composite material.

[0036] The raw materials for preparing the protective film of the present invention include: (1) a matrix resin; (2) a reinforcing filler; (3) a functional material; and (4) an auxiliary agent. The preparation method is: mixing the matrix resin, the reinforcing filler, the functional material and the auxiliary agent evenly and melting and stirring, and obtaining the protective film after molding. For example, the protective film can be prepared by extrusion: after mixing the matrix resin, the reinforcing filler, the functional material and the auxiliary agent evenly, extruding at an extrusion temperature of 200-250 °C on a twin-screw extruder to form the protective film. Except for the above-mentioned preparation methods, the other methods that can fully mix the raw materials belong to the preparation methods of the present invention.

[0037] The thickness of the protective film of the present invention is determined according to actual production requirements. For example, the thickness of the protective film is 0.1-2 mm. Preferably, the thickness of the protective film of the present invention is 0.1-1 mm, and excellent scratch resistance can still be achieved in the case of a relatively thin film.

[0038] The following specifically introduces the protective film of the present invention:

[0039] (1) Matrix resin, which contains the same or similar resin components as the main material of the composite material. For example, when the composite material is a glass fiber-reinforced polypropylene substrate, the matrix resin is a resin containing polypropylene. The similar components of the matrix resin and the composite material are beneficial to improving the bonding force between the protective film and the composite material.

[0040] Preferably, the weight-average molecular weight of the matrix resin is 30000-40000.

[0041] Taking the composite material with a glass fiber-reinforced polypropylene substrate as an example, the matrix resin includes polypropylene and / or modified polypropylene. Polypropylene includes homopolypropylene and / or copolymerized polypropylene.

[0042] Modified polypropylene refers to the modification of polypropylene to improve its properties. For example, modified polypropylene can be polypropylene grafted with polar monomers, such as maleic anhydride and acrylic acid, to improve the compatibility between the matrix resin and reinforcing fillers, functional materials, and additives. For example, modified polypropylene is a block copolymer formed by copolymerizing propylene and ethylene (such as PP-B or PP-R), which can improve the impact resistance and low-temperature resistance of the matrix resin. For example, modified polypropylene is formed by blending polypropylene with elastomers, and the elastomers include ethylene-propylene-diene rubber (EPDM), polyolefin elastomer (POE), styrenic elastomer (SBS / SEBS), etc., to improve the impact resistance, toughness, rigidity, and other properties of the matrix resin. For example, modified polypropylene is formed by blending polypropylene with engineering plastics, and the engineering plastics include nylon (PA) and ABS, etc.

[0043] Preferably, the matrix resin uses polypropylene grafted with maleic anhydride, and the grafting rate of maleic anhydride is 0.5-1.2 wt%. After polypropylene is grafted and modified with maleic anhydride (MAH), polar groups will be introduced into the molecular chain, thus significantly improving its original non-polar characteristics, which is beneficial to improving the bonding strength between the protective film and the polypropylene composite material. In addition, the modified matrix resin is more uniformly mixed with other raw materials.

[0044] (2) Based on the mass of the matrix resin, the reinforcing filler accounts for 5-20 wt% of the mass of the matrix resin. Preferably, the reinforcing filler accounts for 8-20 wt% of the mass of the matrix resin. More preferably, the reinforcing filler accounts for 10-18 wt% of the mass of the matrix resin.

[0045] The reinforcing filler includes wollastonite and boron nitride. Based on the mass of the matrix resin, wollastonite accounts for 4-15 wt% of the mass of the matrix resin, and boron nitride accounts for 1-5 wt% of the mass of the matrix resin.

[0046] Preferably, wollastonite accounts for 6-12 wt% of the mass of the matrix resin, and boron nitride accounts for 2-5 wt% of the mass of the matrix resin.

[0047] More preferably, wollastonite accounts for 8-12 wt% of the mass of the matrix resin, and boron nitride accounts for 3-5 wt% of the mass of the matrix resin.

[0048] The wollastonite and boron nitride are compounded to form a "hard load-bearing - soft dissipation" gradient structure, which can fully absorb and convert the scratching energy. Wollastonite is easy to form a network reinforcement system in the system, playing a role similar to that of glass fiber, and improving the mechanical strength and impact resistance of the protective film. Preferably, acicular wollastonite is selected. Boron nitride is incorporated into the matrix resin, which has lubricating and wear-resistant properties. Flaky boron nitride is preferably used. More preferably, the diameter-thickness ratio of the flaky boron nitride is ≥50:1.

[0049] The protective film is on the surface of the bottom guard plate. The scratch resistance of the protective film is preferably considered, that is, when the protective film is scratched, the scratches should be reduced as much as possible, and when the protective film is damaged, the degree of damage should be reduced as much as possible so as not to expose the bottom guard plate. The network reinforcement system formed by wollastonite in the protective film improves the impact strength of the protective film. The interlayer force of boron nitride is weak, effectively reducing the surface friction of the protective film, and the impacted position is not easily damaged, so as to achieve the effect of multi-scale stress dispersion.

[0050] Wollastonite and boron nitride are better dispersed in maleic anhydride-grafted polypropylene, avoiding agglomeration.

[0051] The present invention preferably uses wollastonite with a smaller particle size, for example, the particle size of wollastonite ≤5 μm.

[0052] In addition, boron nitride also has a good heat conduction effect in the matrix resin, which has a synergistic effect with the functional material.

[0053] In the present invention, the appropriate dosage ratio of wollastonite and boron nitride can better improve the functions of the two in the protective film. Preferably, the mass ratio of wollastonite to boron nitride is (1.6 - 4):1. More preferably, the mass ratio of wollastonite to boron nitride is (2 - 3):1. It is easy to understand that the mass ratio of wollastonite to boron nitride mentioned here refers to the ratio of the more preferred scheme.

[0054] (3) Based on the mass of the matrix resin, the functional material accounts for 3 - 16 wt% of the mass of the matrix resin. Preferably, the functional material accounts for 4 - 15 wt% of the mass of the matrix resin. More preferably, the functional material accounts for 5 - 12 wt% of the mass of the matrix resin.

[0055] The functional material includes organosilicon-modified polyurethane elastomer and erucamide. Based on the mass of the matrix resin, the organosilicon-modified polyurethane elastomer accounts for 2 - 12 wt% of the mass of the matrix resin, and erucamide accounts for 1 - 4 wt% of the mass of the matrix resin.

[0056] Preferably, the organosilicon-modified polyurethane elastomer accounts for 2 - 10 wt% of the mass of the matrix resin, and erucamide accounts for 2 - 3 wt% of the mass of the matrix resin.

[0057] More preferably, the silicone-modified polyurethane elastomer accounts for 3-8 wt% of the matrix resin, and erucamide accounts for 2-3 wt% of the matrix resin.

[0058] The silicone-modified polyurethane elastomer is a material formed by combining silicone (polysiloxane) with polyurethane (PU). Elastic microdomains with a size of 0.5-2 μm are formed in the protective film, and the impact energy is absorbed through viscoelastic hysteresis (loss factor tanδ > 0.3). A stress buffer zone is formed at the interface between the silicone-modified polyurethane elastomer and wollastonite to prevent crack propagation across phases, so as to achieve soft-hard gradient energy dissipation.

[0059] Preferably, the Shore A hardness of the silicone-modified polyurethane elastomer is 50-60.

[0060] Preferably, the mass ratio of the silicone-modified polyurethane elastomer to wollastonite is (0.25-1):1. More preferably, the mass ratio of the silicone-modified polyurethane elastomer to wollastonite is (0.5-1):1.

[0061] Erucamide has a lubricating effect. The long carbon chain of erucamide can form a molecular-level lubricating film on the surface of the protective film, improving the scratch resistance of the protective film. Further, erucamide and boron nitride have a synergistic effect. When the protective film is impacted or scratched, the temperature will rise at the stressed area. The thermal conductivity of boron nitride causes the temperature of the area near the stressed point to rise. In this area, erucamide undergoes phase change flow and in-situ repairs the microcracks generated at the stressed area under the lubricating action of boron nitride. The synergistic effect of erucamide and boron nitride forms a dynamic self-repair network in the protective film, improving the scratch resistance of the protective film.

[0062] Preferably, the mass ratio of boron nitride to erucamide is (1-2.5):1. More preferably, the mass ratio of boron nitride to erucamide is (1.5-2.5):1.

[0063] When the matrix resin is maleic anhydride-grafted polypropylene, the silicone-modified polyurethane elastomer and erucamide are better dispersed in the system.

[0064] (4) Based on the mass of the matrix resin, the additives account for 0.1-5 wt% of the matrix resin. In the present invention, the additives are conventional existing additives, such as additives used in coatings or film layers. Specifically, the additives include antistatic agents, slip agents, plasticizers, antioxidants, antistatic agents, light stabilizers, ultraviolet absorbers, adhesives, crosslinking agents, fillers, antibacterial agents, matting agents, colorants, flame retardants, etc. The present invention does not limit the types of additives.

[0065] Preferably, the additives include colorants and antioxidants. The dosage of the additives can be determined according to actual needs. For example, the colorant accounts for 0.1-2 wt% of the matrix resin, and the antioxidant accounts for 0.1-1 wt% of the matrix resin. For example, the colorant can be a black masterbatch (a material composed of carbon black, carbon black carrier, and carbon black wetting agent). The antioxidant is compounded with erucamide, and the antioxidant can be evenly dispersed in the system. For example, the antioxidant includes one or more of hindered phenol antioxidants, phosphite antioxidants, and thioester antioxidants. For example, antioxidant BHT (2,6-di-tert-butyl-4-methylphenol), antioxidant 1010 (pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), antioxidant 1076 (octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), antioxidant 168 (tris(2,4-di-tert-butylphenyl)phosphite), antioxidant 626 (bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite), antioxidant DLTDP (dilauryl thiodipropionate), and antioxidant DSTDP (distearyl thiodipropionate).

[0066] In the present invention, the protective film is applied to the bottom guard plate made of glass fiber reinforced polypropylene substrate. Specifically, after the protective film is formed, the protective film covers the surface of the bottom guard plate, and the protective film and the bottom guard plate are integrally formed by hot pressing. Compared with the multi-process flow of stamping, electrophoresis, spraying, etc. of the conventional alloy bottom guard plate, the production cost of the present invention is reduced, and the effect of reducing the production cost by 30% can be achieved. Since the matrix resin of the protective film is similar to or even the same as the main material of the bottom guard plate, the protective film and the bottom guard plate can be tightly combined under the condition of hot pressing treatment.

[0067] Based on the characteristics of the protective film, when the protective film is locally damaged, it can also be repaired by hot pressing, and its maintenance cost can be reduced by 80% compared with the need for overall replacement of the alloy bottom guard plate.

[0068] The technical solution of the present invention will be introduced in detail below with specific embodiments.

[0069] In the following examples and comparative examples:

[0070] The matrix resin is maleic anhydride grafted polypropylene, and the grafting rate of maleic anhydride is 0.5-0.7 wt%, such as PC-3, melt index (10-20), Foshan Nanhai Baichen New Polymer Materials Co., Ltd.;

[0071] The wollastonite is acicular wollastonite, such as HQ-1250, D50 (4-9 μm), Dalian Global Minerals Co., Ltd.;

[0072] The boron nitride is flaky boron nitride, such as PN02, D50 (2.82 μm), Zibo Jingyi Ceramic Technology Co., Ltd.;

[0073] Silicone-modified polyurethane elastomer, such as PU-3109, Sansheng Trading Co., Ltd.;

[0074] Erucamide, such as Lubricant - Erucamide, Croda Sipo Chemical Co., Ltd.;

[0075] The colorant is black, such as PE2718, Cabot Corporation;

[0076] Antioxidant, such as SONOX 1010, Shandong Linyi Sanfeng Chemical Co., Ltd.

[0077] Example 1

[0078] Calculated by mass parts, the raw materials for preparing the protective film include the following composition: 100 parts of matrix resin, 10 parts of wollastonite, 5 parts of boron nitride, 6 parts of silicone-modified polyurethane elastomer, 2 parts of erucamide, 1 part of black pigment, and 1 part of antioxidant.

[0079] The matrix resin, reinforcing filler, functional material, and additives are mixed evenly and then extruded on a twin-screw extruder at an extrusion temperature of 240 °C to form a protective film; subsequently, the protective film and the bottom guard plate made of glass fiber-reinforced polypropylene substrate are integrally hot-pressed to obtain the bottom guard plate product.

[0080] Example 2

[0081] Compared with Example 1, the difference in this example is that the composition of the raw materials is: 100 parts of matrix resin, 12 parts of wollastonite, 5 parts of boron nitride, 8 parts of silicone-modified polyurethane elastomer, 3 parts of erucamide, 1 part of black pigment, and 1 part of antioxidant.

[0082] The preparation steps are the same as those in Example 1.

[0083] Example 3

[0084] Compared with Example 1, the difference in this example is that the composition of the raw materials is: 100 parts of matrix resin, 15 parts of wollastonite, 5 parts of boron nitride, 10 parts of silicone-modified polyurethane elastomer, 4 parts of erucamide, 1 part of black pigment, and 1 part of antioxidant.

[0085] The preparation steps are the same as those in Example 1.

[0086] Example 4

[0087] Compared with Example 1, the difference in this example is that the composition of the raw materials is: 100 parts of matrix resin, 4 parts of wollastonite, 1 part of boron nitride, 4 parts of silicone-modified polyurethane elastomer, 2 parts of erucamide, 1 part of black pigment, and 1 part of antioxidant.

[0088] The preparation steps are the same as those in Example 1.

[0089] Example 5

[0090] Compared with Example 1, the difference in this example lies in that the raw material composition is: 100 parts of matrix resin, 6 parts of wollastonite, 2 parts of boron nitride, 2 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucamide, 1 part of carbon black, and 1 part of antioxidant.

[0091] The preparation steps are the same as those in Example 1.

[0092] Example 6

[0093] Compared with Example 1, the difference in this example lies in that the raw material composition is: 100 parts of matrix resin, 8 parts of wollastonite, 4 parts of boron nitride, 2 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucamide, 1 part of carbon black, and 1 part of antioxidant.

[0094] The preparation steps are the same as those in Example 1.

[0095] Example 7

[0096] Compared with Example 1, the difference in this example lies in that the raw material composition is: 100 parts of matrix resin, 15 parts of wollastonite, 2 parts of boron nitride, 10 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucamide, 1 part of carbon black, and 1 part of antioxidant.

[0097] The preparation steps are the same as those in Example 1.

[0098] Comparative Example 1

[0099] This comparative example is a conventional steel alloy bottom guard plate, and a coating is formed on the surface of the bottom guard plate by electrophoresis.

[0100] The data of the scratch resistance test and the scratch test of this comparative example are shown in Table 1.

[0101] Comparative Example 2

[0102] This comparative example is a conventional aluminum alloy bottom guard plate.

[0103] The data of the scratch resistance test and the scratch test of this comparative example are shown in Table 1.

[0104] Comparative Example 3

[0105] Compared with Example 1, the surface of the bottom guard plate in this comparative example is not hot-pressed with a protective film.

[0106] The data of the scratch resistance test and the scratch test of this comparative example are shown in Table 1.

[0107] Comparative Example 4

[0108] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 20 parts of wollastonite, 4 parts of boron nitride, 6 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0109] The preparation steps are the same as those in Example 1.

[0110] Comparative Example 5

[0111] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 10 parts of wollastonite, 8 parts of boron nitride, 6 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0112] The preparation steps are the same as those in Example 1.

[0113] Comparative Example 6

[0114] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 10 parts of wollastonite, 5 parts of boron nitride, 15 parts of organosilicon-modified polyurethane elastomer, 2 parts of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0115] The preparation steps are the same as those in Example 1.

[0116] Comparative Example 7

[0117] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 10 parts of wollastonite, 5 parts of boron nitride, 6 parts of organosilicon-modified polyurethane elastomer, 6 parts of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0118] The preparation steps are the same as those in Example 1.

[0119] Comparative Example 8

[0120] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 20 parts of wollastonite, 8 parts of boron nitride, 12 parts of organosilicon-modified polyurethane elastomer, 6 parts of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0121] The preparation steps are the same as those in Example 1.

[0122] Comparative Example 9

[0123] Compared with Example 1, the difference in this comparative example lies in that the raw material composition is: 100 parts of matrix resin, 2 parts of wollastonite, 1 part of boron nitride, 1 part of organosilicon-modified polyurethane elastomer, 1 part of erucic acid amide, 1 part of black pigment, and 1 part of antioxidant.

[0124] The preparation steps are the same as those in Example 1.

[0125] The raw material dosages of Examples 1-7 and Comparative Examples 4-9 are shown in Table 1.

[0126] The bottom guard plate products of Examples 1-7 and Comparative Examples 1-9 were subjected to scratch resistance tests and scratch tests, and the test results are shown in Table 2.

[0127] The standard for the scratch resistance test is General GMW 14688. The specific steps are as follows: Apply a specified load on the surface of the bottom guard plate using a standard scratch tool (such as the diamond tip of a hardness tester). When a scratch first appears, this load is the scratch resistance load, and the load increment is increased in levels of every 5 N.

[0128] The standard for the scratch test is General GMW 14688. The specific steps are as follows: Generate a scratch on the surface of the bottom guard plate by applying a specified load using a standard scratch tool (such as the diamond tip of a hardness tester). Measure at least 3 points along the length of the scratch and take the maximum value or the average value.

[0129] Table 1 Raw material dosages of Examples 1-7 and Comparative Examples 4-9

[0130]

[0131]

[0132] Table 2 Test data of scratch resistance tests and scratch tests

[0133]

[0134] According to the data in Tables 1 and 2, it can be seen that the protective film of the present invention has excellent protective effects on the bottom guard plate made of composite materials. Compared with Comparative Examples 1-3, the scratch resistance load of the protective film of the present invention is increased to 15 N, and there is no need to coat or treat the coating subsequently, solving the industry problem of relatively large brittleness on the surface of composite materials. Under the condition of a specified load of 15 N, the optimal scratch depth of the protective film of the present invention can reach 5 μm, and the present invention has more advantages compared with Comparative Examples 1-3.

[0135] According to the test results of Examples 1-7 and Comparative Examples 4-9, although the protective film prepared by adding the materials related to the present invention can reach the conventional scratch resistance load, the results of the protective film in Comparative Examples 4-9 in the scratch depth test are obviously inferior to those of the Examples. Comparing Examples 1-7 with Comparative Examples 4-9, the excellent performance of the protective film of the present invention is achieved based on the synergistic effect of each raw material component. When some of the raw materials are in excess or insufficient amounts, the performance of the protective film will be damaged.

[0136] The above has elaborated in detail on the embodiments provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, characterized in that: Ingredients include: Base resin; Reinforcing fillers include wollastonite and boron nitride. Based on the mass of the matrix resin, the reinforcing fillers account for 5 to 20 wt % of the mass of the matrix resin. Preferably, the reinforcing fillers account for 8 to 20 wt % of the mass of the matrix resin. More preferably, the reinforcing fillers account for 10 to 18 wt % of the mass of the matrix resin. The functional material comprises an organosilicon-modified polyurethane elastomer and erucic acid amide, wherein the functional material accounts for 3 to 16 wt % of the mass of the matrix resin, preferably, the functional material accounts for 4 to 15 wt % of the mass of the matrix resin, and more preferably, the functional material accounts for 5 to 12 wt % of the mass of the matrix resin; The additive accounts for 0.1 to 5 wt% of the mass of the base resin, based on the mass of the base resin.

2. The protective film according to claim 1, characterized in that: Based on the mass of the matrix resin, wollastonite accounts for 4-15wt% of the mass of the matrix resin, and boron nitride accounts for 1-5wt% of the mass of the matrix resin; Preferably, wollastonite accounts for 6-12wt% of the mass of the matrix resin, and boron nitride accounts for 2-5wt% of the mass of the matrix resin; More preferably, wollastonite accounts for 8-12 wt % of the mass of the matrix resin, and boron nitride accounts for 3-5 wt % of the mass of the matrix resin.

3. The protective film according to claim 2, characterized in that: The mass ratio of wollastonite to boron nitride is (1.6-4):1, and more preferably, the mass ratio of wollastonite to boron nitride is (2-3):

1.

4. The protective film according to claim 1, characterized in that: Based on the mass of the base resin, the organosilicon-modified polyurethane elastomer accounts for 2-12wt% of the base resin, and the erucic acid amide accounts for 1-4wt% of the base resin; Preferably, the organosilicon-modified polyurethane elastomer accounts for 2-10 wt% of the mass of the matrix resin, and the erucic acid amide accounts for 2-3 wt% of the mass of the matrix resin; More preferably, the organosilicon-modified polyurethane elastomer accounts for 3-8 wt % of the mass of the matrix resin, and the erucic acid amide accounts for 2-3 wt % of the mass of the matrix resin.

5. The protective film according to claim 4, characterized in that: The mass ratio of the silicone-modified polyurethane elastomer to wollastonite is (0.25-1):1; Preferably, the mass ratio of the organosilicon-modified polyurethane elastomer to wollastonite is (0.5-1):

1.

6. The protective film according to claim 4, characterized in that: The mass ratio of boron nitride to erucamide is (1-2.5):1; Preferably, the mass ratio of boron nitride to erucamide is (1.5-2.5):

1.

7. The protective film according to any one of claims 1 to 6, characterized in that: The base resin includes polypropylene and / or modified polypropylene, and the weight average molecular weight of the base resin is 30,000-40,000.

8. The protective film according to claim 7, characterized in that: The base resin includes polypropylene modified by grafting of maleic anhydride, and the grafting rate of maleic anhydride is 0.5-1.2wt%.

9. A method for preparing a protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, characterized in that: The protective film according to any one of claims 1 to 8 is prepared as follows: The base resin, reinforcing filler, functional material and additives are mixed evenly, melted and stirred, and then formed to obtain a protective film.

10. An application of a protective film for improving the surface function of a glass fiber reinforced polypropylene substrate, characterized in that: The protective film as described in any one of claims 1 to 8 is combined with the bottom guard plate through integrated hot pressing molding.

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