HC Plastics News: Plastic is one of the commonly used non-metallic materials for passenger cars. In mid-size cars, the amount of plastics has accounted for 12% to 15% of the total vehicle quality. Among automotive plastics, polypropylene is one of the fastest growing plastics with the highest application rate and the highest frequency of use. Taking the data of a mainstream intermediate car dismantling manual as an example, polypropylene materials account for about 29% of the frequency of plastics used in the whole vehicle, and polypropylene materials account for about 48% of the plastics consumption of the whole vehicle.
Therefore, the performance analysis of polypropylene materials and typical application case studies have practical significance for the development of raw materials for automotive parts.
Performance Analysis and Typical Application of Polypropylene Materials
Polypropylene (PP) resin is a non-polar crystalline plastic obtained by polymerizing propylene monomer. PP has the advantages of low price, low density, easy processing and recycling; but PP has the disadvantages of large molding shrinkage, high temperature brittleness and easy aging. Therefore, physical or chemical modification technology is usually used, adding talc filler, glass fiber and other reinforcing materials, anti-light/thermal oxygen aging agent and other additives to improve the comprehensive performance of polypropylene materials to meet the performance requirements of automotive parts.
Types, characteristics and typical components of automotive polypropylene materials
Except for a small number of parts in the car, which are processed with pure PP resin, most of the parts are processed with modified PP material. The recommended parts for Beiqi Foton model selection are shown in Table 1 (next page).
The traditional modified polypropylene is mainly used for large parts of automobiles, such as bumpers, instrument panel guards, door panels, columns, etc. Long glass fiber polypropylene is mainly used in the front part module and instrument panel skeleton of large parts. The PP content of these large parts accounts for about half of the total PP consumption of the whole vehicle, so the material performance requirements are representative.
Explain from the application status and development trend of modified polypropylene materials in related components
(1) Application analysis of PPE PDM-TD materials in bumper exterior parts
A lot of research has been carried out on the modified polypropylene material of the front and rear bumper bodies. The modified PP bumper has the advantages of low cost, light weight, easy coating and recyclability. At present, the selection of Beiqi Futian passenger car bumper body mainly uses PPEPDM-TD10 or PPEPDMTD20 modified polypropylene materials. By adding 10-20 parts of talc powder, the material shrinkage rate and component size can be ensured; the EPDM or POE elastomer is toughened, and the component has good low temperature impact resistance.
As the focus of lightweight vehicles has increased, lightweight design has placed a number of new demands on the application of plastic materials. The bumper can be reduced in weight by designing the thickness of the wall, so that the requirements for the melt index are getting higher and higher, and the requirements for material strength are also improved. With the reduction of cost pressure and increasingly strict environmental protection requirements, the spray-free bumper comes into being. Higher requirements are placed on the surface quality of modified polypropylene materials, such as scratch resistance.
Table 1 Polypropylene materials for passenger cars and typical application parts
(2) Analysis of the application of modified PP on interior parts
The large parts made of modified PP materials for automotive interior parts include instrument panels, door panels, pillar trims and other components. A large amount of research has been conducted in the industry for modified polypropylene materials for components such as instrument panel bodies and lower guard plates, door panel bodies, and pillar trim panels. In the development of new models, the selection of components is more in line with the comprehensive factors such as vehicle positioning, cost, regulations and performance. For example, A-class vehicles (entry-level passenger vehicles) and B-class vehicles (intermediate passenger vehicles) have certain differences in the selection of parts and materials due to target customers and vehicle cost pressures and light weight requirements. Class A passenger cars pay attention to the economics of interior parts. For example, hard instrument panels, hard door panels, and hard pillars are generally used, and the surface is generally not covered with fabric or leather.
Therefore, the properties of the plastic parts such as heat-resistant oxygen aging, light aging resistance, scratch resistance, white mark resistance, and anti-stickiness are basically determined by the properties of the modified PP plastic particles. Taking hard instrument panel material as an example, the material is mainly PPEPDM-TD20; 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, notched impact ≧ 20kJ/m2. Taking the selection of the door body and the pillar trim as an example, the material is generally PPEPDM-TD20; the medium stiffness of the high rigidity medium modulus, the key mechanical indexes: tensile strength ≧20MPa, modulus ≧1400MPa, notched impact ≧10kJ/m2. Class B passenger cars pay attention to the decoration of interior parts, so fabrics or leather trims are added to the surface of the instrument panel skeleton, door panel and pillar trim.
At the same time, the performance of the assembly is improved, and materials with better performance (mechanics, etc.) are required; with the light weight requirement, the lightweight design of the components requires a lighter material. For example: soft instrument panel skeleton material, material is mainly PP-LGF20; main mechanical properties highlight high modulus and high rigidity, key mechanical indicators: tensile strength ≧40MPa, modulus ≧4000MPa, notch impact ≧10kJ/m2. The main material is PP/PE-TD16, or PP/PE alloy (5-8 parts of talc can be added as needed to adjust the shrinkage of the material).
With the improvement of the air quality requirements in the car, the emission characteristics of the plastic parts in the car are becoming more and more strict. The emission characteristics of the interior parts include odor, formaldehyde content, condensed components, and total carbon content. At present, the automobile factory controls the modified particles mainly by the German VDA standard: for example, odor ≦ grade 3, formaldehyde oxime 10g/kg, condensed component ≦ 2mg, total carbon content ≦50μgC/g. In the project, we have encountered cases in which the odor of the modified PP particles is qualified, but the odor of the plastic parts is excessive. After tracking and analysis in the industry chain, it was found that during injection molding, on the one hand, excessive release agent was sprayed to introduce odor, and on the other hand, the injection temperature was too high, which caused partial decomposition of the material to produce odor; finally, the modified PP particles were qualified, but The final plastic parts smell unqualified.
Therefore, in order to completely solve the odor of plastic parts, it is often necessary for the automobile factory, parts and components enterprises, and raw material suppliers to work together. In addition to the emission characteristics, the heat-resistant oxygen aging, photo-oxidative aging, scratch resistance, white-trace resistance, and anti-stickiness of plastic parts are all important items for material approval. For example, in the automotive plant material experiment, the 150 °C heat-resistant oxygen aging test for PP is more to evaluate the reliability of the material itself under long-term use conditions. This requires full consideration of the final product performance requirements prior to the formulation and processing of the modified polypropylene material.
(3) Application analysis of PP-LGF on the front-end module
The research and application of PP-LGF (long glass fiber reinforced polypropylene) material is one of the hotspots in recent years. In PP-LGF materials, glass fibers generally have a length of 15 mm to 30 mm, forming a three-dimensional cross structure. The structure determines the performance, so PP-LGF has higher strength, rigidity and toughness than ordinary 4-7mm short glass fiber materials. For the front end module of the car, the PP-LGF30 material can be used to combine the front end parts of the radiator, the horn, the condenser, the bracket and the like into a whole; compared with the metal parts, the corrosion resistance, the density is small, the weight is light, and the weight loss is about 30%; Compared to fiberglass nylon, there is a clear cost advantage.
With the research and application of automobile lightweighting, "to replace steel with plastic" and "to light weight" have provided a broad space for development of PP-LGF materials. For example, Li Jinghua et al. studied the feasibility of PP-LGF replacing metal to make pedals; Yang Yuwei studied the feasibility of PP-LGF replacing PA66-GF30 to manufacture door handle base, and replacing PBT-GF30 to manufacture fog lamp housing. Feasibility; Li Zhihu et al. studied the application of PP-LGF instead of PA-GF in shifting mechanism. Other automotive components, such as door panel integrated modules, roof window frames / beading, bumpers, car luggage racks, car battery housing / bracket, car seat frame, gear box housing, car exterior mirror frame, car wiper bracket Etc., PP-LGF materials can be used instead of metal and nylon materials.
in conclusion
Modified polypropylene can be divided into toughening type, mineral filling type, glass fiber reinforced type, polypropylene/polyethylene alloy, etc. according to the performance requirements of automobile parts;
The focus of automotive plastic parts can be transformed into the characteristics of modified polypropylene materials. It is necessary to combine the formulation design, processing technology and post-treatment technology to meet the performance requirements of automotive plastic parts;
With the improvement of air quality requirements for passenger cars, the development and application of low-odor polypropylene interior materials is one of the key development directions in the future;
With the lightweight of automobiles, the modified polypropylene materials will be further expanded. The long glass fiber reinforced polypropylene replaces the metal and glass fiber nylon materials with obvious advantages of weight reduction and cost reduction.
Editor in charge: Wang Ning 12
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