New technology for polyurethane foaming materials in automobiles

Proper use of polyurethane materials can meet the high performance requirements of automobile in power, comfort, appearance, interior softening, lightweight, service life and so on. It is an indispensable important material in modern automobile manufacturing.

1. General situation of application of polyurethane materials

The application of polychloride ester in automotive industry is more and more extensive, and it has become one of the most used plastics in automotive industry. The annual use of polyurethane in global automotive industry exceeds 1 million tons. In 2006, the annual output of China's automobile industry exceeded 7.2 million vehicles, and the total consumption of polyurethane would reach more than 100,000 tons. Polyurethane generally accounts for 15% of automotive plastics. The average usage of polyurethane is 15 kg per vehicle. Most of the products are MDI series.

According to different automobile components, polyurethane can meet different requirements with different morphologies and properties, such as foam plastics, elastomers, adhesives and so on. For example, with the change of formulation, polyurethane foam has the characteristics of light weight, heat insulation, good resilience, good comfort, good low temperature performance, durability, safety and high vibration absorption. Its advantages are incomparable with other materials.

Recycling of waste foam plastics from automobiles and household appliances has attracted more and more attention. Recently, foreign automobile manufacturers have been able to recycle 30% of the waste foam plastics. The production process is cleaning, crushing and drying the waste foam plastics. Finally, the waste foam plastics are bonded together with adhesives, which can be used to produce carpet backing and other cushions.

2. Automotive interiors

2.1 dashboard

(1) Epidermal materials

At present, automobile manufacturers are pursuing to further improve the comfort, safety and beauty of the interior space. It can be said that the interior of automobile is becoming more and more advanced. This kind of high-level first embodies in the use of a variety of materials with different properties (fiber fabrics, leather, wool planting), so that all the surfaces of the car are softened and beautified (deep and thick patterns, wood patterns, color matching). Soft surface materials and internal sound absorption, vibration absorption materials and skeleton materials compounded into car roof, luxury dashboard, steering wheel, seat and so on. This development is actually in contradiction with material recycling and cost reduction. Therefore, it is urgent to develop new materials for interior decoration, which can not only meet the requirements of advanced, soft and individualized interior decoration, but also meet the requirements of lightweight, low cost and material recycling.

BASF has developed a polyurethane elastomer skin material (TPU) Elastoskin for interior decoration of automobiles. It is used for the facing of instrument panel and door panel interior decoration. Its performance is superior to that of PVC and other skin materials currently used. Its cost is lower than that of PVC and other skin materials. It is an ideal substitute for PVC. The material has excellent mechanical properties, excellent leather granularity, flexibility and luxury. It can be used in two-color products. Its excellent durability (weather resistance, high and low temperature resistance, abrasion resistance) makes it the first choice of high-quality skin materials for car interiors above grade C. This material has been used in the dashboard and door inner panel of 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 application of this material in automotive interiors has just begun. The greater significance of the use of aromatic polyurethane to spray the skin is to provide an effective way to produce polyurethane integrated (polyvinyl chloride sprayed epidermis + low density polyurethane foam foam + polyurethane short cut fiber skeleton) recyclable dashboard.

In addition, Bayer's thermoplastic polyurethane is blow moulded for automotive dashboards and door panels. It is said that this process can save 70% of the time compared with casting.

(2) dashboard buffer layer

After vacuum forming, semi-rigid polyurethane foam is filled in the middle of the outer skin of the instrument panel and fixed with metal or plastic skeleton. Semi-rigid polyurethane foam is characterized by high compression load and outstanding vibration reduction performance, and is very suitable for manufacturing protective cushion materials for automotive dashboard, handrails, door posts and other components.

(3) Skeleton materials

A polychloride structure reaction molding (SRlM) technology has been widely used in Europe and America, which can effectively reduce the quality of parts. The technological process is as follows: the skin is pre-formed, the glass felt is put into the mould, then the polychloride resin is injected, and the curing process (micro-foaming) is formed. This process can be used to produce a variety of automotive accessories, such as door interior panel, clothes and hats frame, instrument panel skeleton and ceiling skeleton, etc. SRIM has the advantage of flexible design of wall thickness, radian or reinforcement according to the mechanical properties of parts. Compared with other products such as injection moulding, SRIM has lower endogenous endogenous sound and can improve the physical properties of products, such as lower density, higher elongation, less odor and mildew problems, which can create a comfortable interior environment.

The existing production technology of car door panels in our country is to lay glass fibre in the mould beforehand, then inject the composite material, after closing the mould, ripen and mold the required interior decorations such as automobile dashboard, door panels, air conditioning cover and so on. Another technology is spray forming of chopped glass fibers.

Polyurethane products formed by RIM and RRIM technology are mainly used in steering wheel, bumper, body panel, engine hood, trunk cover, radiator grille, fender, spoiler and so on. The quality of RRIM products is only 55% of that of steel products, but the surface quality and dimensional stability of parts need to be further improved, and the dosage is not very large.

2.2 Car cushions, backrest and headrest

Seat cushion, backrest and headrest are parts of polyurethane foam plastics which are used widely in automobiles. They are also the most sensitive places for people to ride comfortably. Therefore, the performance requirements of products are also very strict. At present, the polychlorinated foam cushion used for automobiles in China is mostly the uniform density of cold curing products. In recent years, a new type of automobile seat cushion developed is double hardness or multi hardness foam. The production of the double hardness seat cushion can be realized by injection of polyether polyols and isocyanates through a double head or multi head mixing head. The whole MDI cold molding process can also be used. The hardness of different parts of the cushion can be accurately controlled by changing the isocyanate index. The middle part of the cushion is soft. Harder on both sides. Soft foam gives comfort to people. The hard part on both sides provides support performance. When the car is running or turning at high speed, it helps to maintain the stability of the driver and passengers and improve the safety of the ride. FAW Group's FAO company has produced 3 hardness and multi hardness foam technology by using the technology of mixture of components, and technology occupies the leading position in China.

2.3 Door Handrails

The structure of the armrest is a semi-rigid polyurethane foam with steel frame fixed in the middle and door plate covered with self-crusting outer layer. The surface of the armrest has decorative patterns, which makes people feel comfortable and safe when riding. There are also shelves on the inner guard boards of the left and right doors of cars, which are made of self-crusting semi-rigid polyurethane foam plastics, as well as foam plastics filled in the enameled epidermis. The material used in this part should be good in sweat resistance, odorless, hardness index, high and low temperature performance.

2.4 Steering Wheel Assembly

The steering wheel of passenger cars in our country is basically made of semi-rigid self-crusting polyurethane foam plastic as the outer coating, and the inner part is welded by steel skeleton. Now it has gradually turned to die casting of Al-Mg alloy as a whole. The hardness of the coating is generally in the hore A60-80.

2.5 Foam Plastics for Sound and Heat Insulation

(1) Automotive roof and door inner panel

The interior roof is a kind of product which is processed and moulded with various materials. It is required to have many functions such as heat insulation, sound absorption, sound insulation, vibration absorption and so on. The soft ceiling is made of polyurethane foam composite fiber fabric, non-woven fabric and artificial leather. The hard ceiling is made of fabric fiber, glass fiber, cardboard and polyurethane foam by laminating.

There are also many places where polyurethane foam sheets are used in automobiles. For example, the fabric of seat is mainly textile + PU + knitted synthetic fibers. The top interior is made of PVC film and PU, then punched with small holes on its surface, and then pasted with adhesives on the cab roof.

PP and PPO are often used as decorative materials for door posts. Considering the cost of materials, PP materials with high fluidity, high rigidity and good impact resistance will have certain advantages in the future. The surface color of decorative panel for door and column must match the overall color of the car, which requires anti-static, anti-scratch and beautiful appearance. Therefore, the development of vacuum forming or hot pressing technology for the integration of propylene plate and surface decorative material can meet the needs of car production with a small batch.

(2) Polyurethane foam for sealing

There are some rectangular soft polyurethane foam sealing blocks in the automobile heating and air conditioning system, instrument panel assembly, electrical parts or other parts. The A and B columns of the car body are filled with cavity foam, some of them are used to reduce the vibration and noise of the body.

3 Microporous Polyurethane Used as Vibration Absorbing Pad for Vehicle Bottom

Microporous polyurethane foams are expected to replace rubber materials in most car bodies as shock absorber pads for body panels. North American automobile manufacturers are trying to make cars more quiet and comfortable. The shock absorber pad is mounted on the chassis of the car to isolate the body and frame so as to improve the riding and driving quality. Microporous polyurethane is a unique innovative material for sound insulation and vibration attenuation (NVH).

Microporous polychloride is a competitive price as a substitute for rubber body assembly. It can effectively improve the vibration absorption performance, prolong the material performance retention time, reduce the mass, and improve the assembly process. Another advantage of using microporous polyurethane is that by changing the material density, it is convenient to optimize the anti-vibration rubber pad of the body chassis, rather than adjusting it by changing the material production formula or product geometry, as in the traditional process. The latter requires prototyping, which is costly and time-consuming.

The composite structure of low foaming PVC material + PU foaming material + porous material is mostly used in light bus. The low foaming PVC material is shaped by vacuum suction, partially filled with foaming PU material, and partially pasted with porous material on the back. The structure is flexible and firm, and has good foot sensibility, sound insulation and heat insulation.

4 Refrigerator Thermal Insulation Layer

In order to effectively guarantee the sound insulation and heat insulation effect of car body interior decoration, besides the use of rigid polyurethane foam in the insulation layer in the middle of refrigerated truck, the van also adopts the method of on-site spraying to expand the application of rigid polyurethane foam plastics-on-site spraying of rigid polyurethane foam plastics on the top and both sides of the car body interior, and bonding with the inside and outside skin of the car body to form an existing one. Machine as a whole. Thus, the heat insulation, heat preservation and sealing performance of the car body are effectively improved, the corrosion of the car body is prevented, the vibration of the car body is reduced, and the noise inside the car is reduced. The estimated consumption of each car is about 20 kg.

The thermal insulation cover made of rigid polyurethane foam is made of polyurethane foam, glass fiber felt, nylon fabric layer or aluminum film, and has the characteristics of light weight and good heat insulation.

The application of fiberglass reinforced polyurethane foam plastics in automotive parts is also gradually expanding. For example, the automotive integral roof interior parts are made of textile and fiberglass reinforced PU. Moreover, such as the wheel shield and oil pan mudguard, which are light and complex in shape, require a higher technological requirement, and require anti-spatter, impact resistance, and can withstand high and low temperature performance.

5. Prospects of Applied Technology

Recently, many automotive interior parts show the development trend of polyolefin (PO) foamed plastics instead of polyurethane (PUR) materials. Several kinds of polyolefin foam plastics are constantly challenging the application of polyurethane foam in many aspects, including surface decoration, foam, coated fiber, fabric and sound insulation system. The driving force of foaming polyolefin instead of polyurethane foam is the cost of products, as well as the recovery of products and whether it can reduce the emission of toxic gases, because toxic gas will be generated in the process of PUR foam laminated fabric.

The automobile dashboard has many functions, many parts and complex structure. The first consideration for the recycling and utilization of automobile interior materials is the dashboard. At present, most dashboards are made of PVC epidermis + semi-rigid foamed PU + bone structure, so it is very difficult to recycle materials. The development trend of dashboards is that they are easy to disassemble and assemble in design, meet the design requirements in material selection and consider the possibility of recycling, so as to achieve beauty and low cost as far as possible. This may promote the development of thermoplastic dashboards and single plastic dashboards, but it should meet the requirements of safety and beauty.

The car interior ceiling is usually made of glass fiber + foam polychlorinated ester + surface decoration fabric, etc. the truck generally adopts the foam sheet pasting ceiling with artificial leather or fiber fabric on the surface. Considering the requirements of function and recycling, the development trend in the future is to use skeleton, sound absorption, heat insulation and skin materials as the same material as possible, or to use reinforced composites which can be directly recycled without separation.

PU leather is gradually replacing PVC artificial leather. As the first generation of artificial leather products, PVC artificial leather has a considerable scale since its development in 1970s because of its similar natural leather, bright appearance, soft texture, wear resistance, flexural resistance, acid and alkali resistance. However, due to the poor permeability and hygroscopicity, the development in recent years has been limited. At present, PU can be used as a substitute for PVC. PU is not only excellent in strength and toughness, but also ageing resistance, air permeability, moisture permeability, water impermeability, oil resistance. It is a mature environmental protection material.

FAW Group Fuo Johnson Company is the backbone of the automotive interior products industry. Every year, more than 10,000 tons of polyurethane raw materials are used for seat, dashboard and other softening products. Changchun alone needs 4,000 tons. For Jetta, Audi, Mazda, Liberation Vehicle, chairs, dashboards and other softening products, up to 100 varieties, more than 3,000 tons of polyurethane raw materials are consumed annually.

The main technical problems of polychlorinated foam and products include storage stability of MDI, TDI and additive mixture, moisture and heat resistance of products, vacuoles and cracking caused by unstable foaming process.

The development needs of polyurethane foam and products include light weight, multi hardness, low odor, low haze, aging resistance, storage stability and environmental protection, such as the replacement of foaming agents.