Performance Analysis and Typical Application of Polypropylene Materials for Vehicles
Plastic is one of the non-metallic materials commonly used in passenger cars. In medium class cars, the amount of plastic has accounted for 12% to 15% of the vehicle mass. Among the automotive plastics, polypropylene is one of the plastics with the fastest development, the highest application proportion and the most frequent use. Taking the disassembly manual data of a mainstream mid class car as an example, polypropylene materials account for about 29% of the vehicle plastic selection frequency, and polypropylene materials account for about 48% of the vehicle plastic consumption.
Therefore, the performance analysis and typical application case study of polypropylene materials have practical significance for the development of raw materials for automobile parts.
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Polypropylene (PP) resin is a nonpolar crystalline plastic polymerized from propylene monomer. PP has the advantages of low price, low density, easy processing and reuse; However, PP has the disadvantages of large molding shrinkage, low temperature brittleness and easy aging. Therefore, physical or chemical modification technology is usually used to improve the comprehensive performance of polypropylene materials by adding talc filler, glass fiber and other reinforcement materials, anti light/thermal oxygen aging agent and other additives to meet the performance requirements of automobile parts.
Types, characteristics and typical components of polypropylene materials for automobiles
In addition to a few parts of the automobile are processed with pure PP resin, most parts are processed with modified PP material. The recommended parts for the selection of Foton models are shown in Table 1 (next page).
The traditional modified polypropylene is mainly used for the bumper, instrument panel guard, door panel, column and other parts of large automobile parts, while the long glass fiber polypropylene is mainly used for the front-end module and instrument panel framework of large automobile parts. The amount of PP used in these large parts accounts for about half of the amount of PP used in the whole vehicle, so the material performance requirements are representative.
The application status and development trend of modified polypropylene materials in related parts are described
(1) Application analysis of PP EPDM-TD materials in bumper exterior trim
The industry has conducted a lot of research on the modified polypropylene material of the front and rear bumper body. The modified PP bumper has the advantages of low cost, light weight, easy painting, recyclability, etc. At present, BAIC Foton passenger car bumper body is mainly made of PP EPDM-TD10 or PP EPDMTD20 modified polypropylene materials. By adding 10-20 phr talcum powder, the shrinkage of materials and the stability of component dimensions can be ensured; Toughened by EPDM or POE elastomer, good low-temperature impact property of components can be ensured.
With the increasing concern of automobile lightweight, lightweight design has put forward a lot of new requirements for the application of plastic materials. The bumper can reduce the weight by reducing the design wall thickness, so the requirements on the melt index and material strength are higher and higher; With the increasing pressure of cost reduction and environmental requirements, spray free bumpers came into being, which put forward higher requirements for the surface quality of modified polypropylene materials, such as scratch resistance.
The large parts of automobile interior parts made of modified PP materials include instrument panel, door panel, pillar trim panel, etc. The industry has carried out a lot of research on modified polypropylene materials for instrument panel body, lower guard board, door panel body, column trim panel and other components. In the development of new models, the selection of components is determined by more comprehensive factors such as model positioning, cost, regulations and performance. For example, due to the cost pressure and lightweight requirements of the target customers and the whole vehicle, there are certain differences in the selection of materials for spare parts for Class A vehicles (entry-level passenger vehicles) and Class B vehicles (intermediate passenger vehicles). Class A passenger cars pay attention to the economy of interior trim, for example, hard instrument panels, hard door panels, and hard columns are generally used, and their surfaces are generally not or rarely decorated with fabrics or leather.
Therefore, the heat and oxygen aging, light aging, scratch resistance, white mark resistance, tackiness resistance and other properties of plastic parts are basically determined by the relevant properties of modified PP plastic particles. Taking the selection of hard dashboard as an example, PP EPDM-TD20 is the main material; In terms of mechanical properties, attention is paid to high modulus, high rigidity and high impact resistance; Key mechanical indexes: tensile strength ≥ 20MPa, modulus ≥ 1800MPa, notch impact ≥ 20kJ/m2. Take the material selection of door panel body and column trim panel as an example, the material is generally PP EPDM-TD20; High rigidity, medium modulus, medium impact performance, key mechanical indicators: tensile strength ≥ 20MPa, modulus ≥ 1400MPa, notch impact ≥ 10kJ/m2. Class B passenger cars pay attention to the decoration of the interior trim, so more fabric or leather trim pieces are added to the surface of the instrument panel frame, door panel and pillar trim panel.
At the same time, the improvement of assembly performance requires materials with superior (mechanical, etc.) performance; With the requirement of lightweight, lighter materials are needed for lightweight design of components. For example, PP-LGF20 is the main material for soft dashboard framework; The main mechanical properties highlight high modulus and high rigidity. The key mechanical indicators are: tensile strength ≥ 40MPa, modulus ≥ 4000MPa, notch impact ≥ 10kJ/m2. Select materials from the door panel body or column trim panel, and the main material is PP/PE-TD16 or PP/PE alloy (5-8 parts of talcum powder can be added as required to adjust the material shrinkage).
With the improvement of the requirements for the air quality in the vehicle, the emission characteristics of the plastic trim in the vehicle are becoming more and more strict. The emission characteristics of interior trim include odor, formaldehyde content, condensation component and total carbon content. At present, the automobile factory mainly refers to the German VDA standard for the control of modified particles: for example, odor ≤ 3, formaldehyde ≤ 10g/kg, condensate ≤ 2mg, and total carbon content ≤ 50 μ gC/g。 In the project, we have encountered cases where the odor detection of modified PP particles was qualified, but the odor of plastic parts exceeded the standard. Through tracking analysis of the industry chain, it is found that during injection molding, on the one hand, excessive release agent is sprayed to introduce odor, and on the other hand, the injection molding temperature is too high, resulting in partial decomposition of materials and odor; Finally, the smell of modified PP particles was qualified, but the final smell of plastic parts was unqualified.
Therefore, to thoroughly solve the odor of plastic parts, it often requires the joint efforts of automobile manufacturers, parts enterprises and raw material suppliers. In addition to the emission characteristics, the heat and oxygen aging, light and oxygen aging, scratch resistance, white mark resistance, and tackiness resistance of plastic parts are the key items for material approval. For example, the 150 ℃ heat and oxygen aging test for PP in the material test of the automobile factory is more to evaluate the reliability of the material itself under long-term use conditions. This requires that the performance requirements of the final product should be fully considered before the formulation design and processing of the modified polypropylene material.
(3) Application Analysis of PP-LGF in Front End Module and Other Components
The research and application of PP-LGF (long glass fiber reinforced polypropylene) is one of the hot spots in recent years. In PP-LGF materials, the length of glass fiber can generally reach 15mm to 30mm, forming a three-dimensional cross structure. The structure determines the performance, so PP-LGF has higher strength, rigidity, toughness and other advantages than ordinary 4-7mm short glass fiber materials. For the automobile front-end module, PP-LGF30 material is used to combine the radiator, horn, condenser, bracket and other front-end components into a whole; Compared with metal parts, it is corrosion resistant, small in density and light in weight, with a weight reduction of about 30%; Compared with glass fiber nylon, it has obvious cost advantages.
With the research and application of automobile lightweight, "replacing steel with plastic" and "replacing heavy with light" provide a broad development space for PP-LGF materials. For example, Li Jinghua and others studied the feasibility of using PP-LGF to replace metal to make foot pedals; Yang Yuwei studied the feasibility of PP-LGF replacing PA66-GF30 to manufacture the door handle base, and the feasibility of replacing PBT-GF30 to manufacture the fog lamp housing; Li Zhihu et al. studied the application of PP-LGF instead of PA-GF in gear shifting mechanism. Other auto parts, such as door panel integration module, roof window frame/strip, bumper, car luggage rack, car battery shell/bracket, car seat frame, gear box shell, car exterior mirror frame, car wiper bracket, etc., can use PP-LGF material instead of metal and nylon material.
conclusion
According to the performance requirements of automobile parts, modified polypropylene can be divided into toughening, mineral filling, glass fiber reinforcement, polypropylene/polyethylene alloy, etc;
The focus of automotive plastic parts can be transformed into the characteristics of modified polypropylene materials. The formula design, processing technology, post-treatment process and other comprehensive considerations should be combined to meet the performance requirements of automotive plastic parts;
With the improvement of air quality requirements for passenger vehicles, the development and application of low odor polypropylene interior materials is one of the key development directions in the future;
With the lightening of automobiles, modified polypropylene materials will be further expanded and applied. Long glass fiber reinforced polypropylene has obvious advantages in weight reduction and cost reduction instead of metal and glass fiber nylon materials
