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          New Technology of Polyurethane Foaming Material Applied in Automobile

          Times: 2020-07-22 | Hit:476

          1 Overview of the application of polyurethane materials

              

          Polyurethane materials are more and more widely used in the automotive industry, and they have become one of the most used plastics in automobiles. The annual use of polyurethane in the global automotive manufacturing industry exceeds 10 million tons. In 2006, the annual output of my country's automobile industry exceeded 7.2 million vehicles, and the total consumption of polyurethane will reach more than 100,000 tons. Polyurethane generally accounts for 15% of automotive plastics. The average usage per car is 15 kg, and most of them use MDI series products.


          According to different automobile components, polyurethane adapts to different requirements with different forms and properties such as foam plastics, elastomers, and adhesives. For example, with the change of formula, polyurethane foam has the characteristics of light weight, heat insulation, good resilience, good comfort, good low temperature performance, durability, safety and high vibration absorption, and its superiority is unmatched by other materials.

          People pay more and more attention to the recycling of waste foam plastics from automobiles and home appliances. Recently, foreign automobile manufacturers have been able to recycle 30% of waste foam. The production process is to wash, smash, and dry the waste foam, and finally glue the waste foam together with an adhesive to be used in production. Carpet backing and other cushion materials.

          2 Automotive interior parts
          2.1 Dashboard
          (1) Skin material
          At present, automobile manufacturers are pursuing further improvement of the comfort, safety and beauty of the interior space of the car in terms of car interiors. It can be said that the car interiors are becoming more and more advanced. This advanced level is first reflected in the use of a variety of materials with different properties (fiber fabric, real leather, flocking) to soften all surfaces in the car and strive to beautify (the pattern is dark and thick, wood grain, color matching). The soft decorative surface materials are combined with internal sound-absorbing, vibration-absorbing materials and framework materials to form the interior ceiling, luxurious instrument panel, steering wheel, seat, etc. This development actually contradicts material recycling and cost reduction. Therefore, it is an urgent task to develop new interior materials that can not only meet the advanced, soft and personalized interior, but also meet the requirements of lightweight, low-cost, and material recycling.

          BASF company has developed a polyurethane elastomer skin material (TPU) Elastoskin for automobile interior decoration, which is used for dashboard and door panel interior parts. Its performance is better than the currently used polyvinyl chloride (PVC) and others. The cost of skin material is lower than that of PVC and other skin materials, and it is an ideal substitute for PVC. The material has excellent mechanical properties, very good leather grain, flexibility and luxury, and can be used in two-color products; excellent durability (weather resistance, high and low temperature resistance, scratch resistance) makes it a high-quality C-level The first choice for the surface skin materials of the above car interior parts. The material has been used in the dashboard and door inner panels of cars such as Bujck Park Avenue, OIdsmobiie Aurora and Cadillac CTS. It will also be used in new models such as Cadillac Seville and Cadillac Deville. In short, the material is only used in automotive interior parts. just started. The greater significance of using aromatic polyurethane spray molding skin is to provide an effective way for the production of polyurethane integrated (polyurethane spray skin + low-density polyurethane cushioning foam + polyurethane chopped fiber skeleton) recyclable instrument panel.

          In addition, Bayer's thermoplastic polyurethane is blow-molded for use in automobile dashboards and door panels. It is said that this process can save 70% of the time compared to casting.

          (2) Dashboard buffer layer

          After the outer skin of the instrument panel is vacuum formed, the middle is filled with semi-rigid polyurethane foam and fixed with a metal or plastic frame. Semi-rigid polyurethane foam is characterized by high compressive load and outstanding vibration damping performance, which is very suitable for the manufacture of protective cushion materials for automobile instrument panels, armrests, door posts and other components.

          (3) Frame material
          A kind of polyurethane structure reactive molding (SRlM) technology has been widely used in Europe and America, which can effectively reduce the quality of parts. The process is as follows: first pre-form the skin, put the glass fiber felt into the mold, and then inject the polychloride resin, and mature and shape (micro-foaming). A variety of automotive trim parts can be produced by this process, such as door trim panels, coat racks, instrument panel frames and ceiling frames. The advantage of SRIM is that it can flexibly design wall thickness, curvature or ribs according to the different mechanical properties of parts. Compared with products such as injection molding, SRIM has lower in-car noise and can also improve the physical properties of the product, such as lower density, higher elongation, less odor and mildew problems, etc., which can create a comfortable The environment in the car.

          The existing domestic production technology of door panels is to pour glass fiber into the mold in advance, then inject the composite material, and then cure and mold the required interior parts such as automobile instrument panels, door panels, and air-conditioning covers. Another technique is chopped glass fiber injection molding.

          Polyurethane products formed by RIM and RRIM technology are mainly used in automobiles for steering wheels, bumpers, body panels, engine hoods, trunk covers, radiator grilles, fenders, spoilers, etc. The quality of RRIM products is only 55% of steel, but the surface quality and dimensional stability of the parts need to be further improved, and the amount is not very large.

          2.2 Car seat cushion, backrest and headrest
          Seat cushions, backrests and headrests are the places where polyurethane foam is used in a large amount in automobiles, and they are also the most sensitive places for people to ride comfort. Therefore, the performance requirements of the products are also very strict. At present, most of the polyurethane foam seat cushions used in domestic automobiles are cold-cured products with uniform density. The new type of car seat cushion developed in recent years uses dual-hardness or multi-hardness foam. The production of this dual-hardness seat cushion can be achieved by injecting polyether polyol and isocyanate into the mold through a double-head or multi-head mixing head, or Using the full MDI cold molding process, the hardness of different parts of the seat cushion can be accurately controlled by changing the isocyanate index-the middle of the seat cushion is soft and the sides are hard. The soft foam gives people a sense of comfort. The hard parts on both sides provide support performance. When the car is driving or turning at high speed, it helps to keep the body of the driver and passengers stable and improve the safety of the ride. FAW Group Fawer Company has adopted 3-component mixing technology to produce dual-hardness and multi-hardness foams, and the technology is in a leading position in China.

          2.3 Door armrests

           The structure of the armrest is fixed with the door panel with a steel frame in the middle, and the outer layer is covered with self-skinned semi-rigid polyurethane foam. The surface has a decorative pattern, which makes people feel comfortable and safe when riding. There are also hand rests on the inner guard plates of the left and right doors of the car. The material is made of self-skinned semi-rigid polyurethane foam, and there is also a slush-plastic skin filled with foam. The material used in this part should be resistant to sweat, odorless, hardness index and high and low temperature performance.


          2.4 Steering wheel assembly
          The steering wheels of passenger cars in my country are basically made of semi-rigid self-skinning polyurethane foam as the outer covering layer, and the inner part is welded by a steel frame. It has gradually turned to aluminum-magnesium alloy integral die-casting. The hardness of the covering layer is generally Shore A60-80.

          2.5 Foam plastic for sound insulation and heat insulation
          (1) Car roof and door inner panel

          The ceiling of the car is a product formed by composite processing of various materials, which requires multiple functions such as heat insulation, sound absorption, sound insulation, and vibration absorption. The soft ceiling is made of polyurethane foam plastic composite fiber fabric, non-woven fabric and artificial leather. The hard ceiling is made of fabric fiber, glass fiber, cardboard and polyurethane foam through laminating and pressing.

          There are also many places where polyurethane foam sheets are used in automobiles. For example, the seat fabrics currently use textile + PU + knitted synthetic fibers. After the roof trim is made of PVC film + PU compound, small holes are punched on the surface, and then glued on the roof of the cab.

          PP and PPO are often used for door pillar decorative panels. Considering the material cost, PP materials with high fluidity, high rigidity and good impact resistance will have certain advantages in the future. The surface color of the door pillar decorative panel must match the overall color of the car, and it is required to be anti-static, scratch-resistant, and beautiful. Therefore, the development of the production technology of integrated vacuum forming or hot pressing of acrylic board and surface decorative materials can meet the large number of batches. Demand for car production.

          (2) Polyurethane foam for sealing
          There are some rectangular flexible polyurethane foam sealing blocks in the heating and air conditioning system, dashboard assembly, electrical parts or other parts of the car. The A and B pillars of the car body are filled with foam in the cavity, and some are made of vibration damping expansion film to reduce the vibration and noise of the car body.

          3 Microcellular polyurethane is used as a vehicle floor damping pad
          Microcellular polyurethane foam is expected to replace rubber materials as underbody damping pads in most car bodies. North American automakers are working hard to make cars more quiet and comfortable. The damping pad is installed on the chassis of the car to isolate the car body and the frame to improve the ride and driving quality. Microcellular polyurethane is a unique innovative material for sound insulation and vibration reduction (NVH).
          As a substitute for rubber car body assembly, microporous polyurethane has a competitive price. It can effectively improve the damping performance, prolong the retention time of material properties, reduce the quality, and improve the assembly process. Another advantage of using microcellular polyurethane is that by changing the material density, it is convenient to optimize the vehicle chassis anti-vibration rubber pad, instead of changing the material production formula or product geometry as in the traditional process. The latter requires prototype production, which is costly and time-consuming.

          The composite structure of low-foaming PVC material + PU foaming material + porous material is mostly used in light passenger cars. The low-foaming PVC material is shaped by vacuum blister, the foamed PU material is filled in the part, and the porous part is pasted on the back. material. The structure is flexible and relatively firm, and has good foot sensitivity, sound insulation and heat insulation performance.

          4 Insulation layer of refrigerated truck
          In order to effectively ensure the effect of sound insulation and heat insulation of the body interior, in addition to the use of rigid polyurethane foam in the middle of the refrigerated vehicle, the van also uses on-site spray foam to expand the application of rigid polyurethane foam-in The top of the car body and the inside on both sides are sprayed with rigid polyurethane foam on-site and bonded with the inner and outer skins of the car body to form an organic whole. Thereby effectively improving the heat insulation, heat preservation and sealing performance of the car body, preventing body corrosion, reducing body vibration, and reducing internal noise. The estimated usage of each car is about 20 kg.

          The engine heat shield made of rigid polyurethane foam is made by composite pressing of polyurethane foam, glass fiber felt, nylon fabric layer or aluminum film, which has the characteristics of light weight and good heat insulation.

          The application of glass fiber reinforced polyurethane foam in automobile parts is also gradually expanding. For example, the parts for automobile integral roof interiors are made of textiles and glass fiber reinforced PU. Another example is wheel cover fenders, oil pan fenders and other parts that are light and thin, with complex shapes, which require high technological requirements, and require stone splash resistance, impact resistance, and high and low temperature performance.

          5 Application technology outlook
          Recently, many automotive interior parts have shown a development trend of replacing polyurethane (PUR) materials with polyolefin (PO) foam. Several polyolefin foams are constantly challenging the application of polyurethane foam in many aspects, including automotive interior decoration parts. Surface layer, foam, coated fiber. Fabric and sound insulation system. The driving force for foamed polyolefins to replace polyurethane foams lies in the cost of the product, as well as the recyclability of the product and whether it can reduce the emission of toxic gases, because toxic gases are generated during the process of heating the laminated fabric of the PUR foam.

          Automobile dashboards have multiple functions, parts, and complex structures. The recycling of automotive interior materials should first consider the dashboard. The current instrument panels are mostly composed of PVC skin + semi-rigid foamed PU + skeleton, and the recycling of materials is very difficult. The development trend of the instrument panel is that it is easy to disassemble and assemble in design, meet the design requirements in material selection, and consider the possibility of recycling, so as to be as beautiful and low-cost as possible. This may promote the development of thermoplastic instrument panels and single-variety plastic instrument panels, but they should meet the requirements of safety and beauty.

          The interior ceiling of a car is generally formed of glass fiber + foamed polyurethane + surface decorative fabric, etc., and the truck generally uses a foam sheet adhesive ceiling with artificial leather or fiber fabric on the surface. Taking into account the requirements of function and recycling, the future development trend is to use the same kind of materials as possible for the framework, sound absorption, heat insulation and skin materials, or use reinforced composite materials that do not need to be separated and can be recycled directly.

          PU leather is gradually replacing PVC artificial leather. As the first-generation artificial leather product, PVC artificial leather has the characteristics of similar natural leather, bright appearance, soft texture, abrasion resistance, folding resistance, acid and alkali resistance, and has developed on a considerable scale since the 1970s. However, due to poor air permeability and hygroscopicity, the development in recent years has been restricted. At present, wherever PVC is used, PU can become its substitute. PU not only has excellent high strength and toughness, but also is resistant to aging, air permeability, moisture permeability, water impermeability, and oil resistance. It is a mature environmental protection material.

          Fawer Johnson FAW Group is a backbone factory in the automotive interior products industry. It consumes more than 10,000 tons of polyurethane raw materials for softened products such as seats and instrument panels every year, and Changchun alone needs 4,000 tons. There are more than 100 varieties of softened products such as seats and dashboards for Jetta, Audi, Mazda and Jiefang Auto, and more than 3,000 tons of polyurethane raw materials are consumed each year.


          The main technical problems of polyurethane foam and products include: the storage stability of MDI, TDI and additive mixtures, the product's resistance to damp and heat aging, and product cavitation and cracking due to the unstable foaming process.


          The development needs of polyurethane foam and products mainly include: lightweight, multiple hardness, low odor, low haze, aging resistance, storage stability, environmental protection, such as the replacement of foaming agents.


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