New trends in the application of modified PP plastics in the field of household appliances

As one of the four general plastic materials, PP has excellent comprehensive performance, good chemical stability, good molding processing performance and relatively low price; but it also has low strength, modulus, low hardness and low temperature impact resistance. Poor strength, large shrinkage, easy to age and other shortcomings. Therefore, it must be modified to adapt to the needs of the product. The modification of PP materials is generally through several ways of adding minerals to enhance toughening, weathering modification, glass fiber reinforcement, flame retardant modification and super toughness modification. Each modified PP has its own in the field of household appliances. A large number of applications.

Mineral filled modified PP

Mineral filling modification is the most widely used modification route. Minerals such as calcium carbonate, talc, wollastonite, glass microspheres, and mica powder are added to the PP raw material. These minerals can not only improve the mechanical properties and impact toughness of PP materials to a certain extent, reduce the molding shrinkage of PP materials to enhance their dimensional stability, and can greatly increase the cost difference between minerals and PP matrix. Reduce the cost of PP materials.

At present, the application of mineral-filled modified PP in household appliances mainly includes: inner barrel of pulsator washing machine and drum washing machine, pulsator and clothes taking port, etc.; sealing strip of microwave oven, speaker bell mouth, horn bracket; refrigerator shelf Rack; the outer casing and base of the rice cooker.

Many parts of the microwave oven are also made of mineral-reinforced, toughened PP materials. For example, the sealing strip of the door of the microwave oven, the speaker bell of the microwave oven, the horn bracket, and the like. Due to the addition of minerals, the heat-resistant temperature of the PP material itself can be further improved on the basis of the higher heat-resistant temperature of the PP material to meet the high temperature requirements of the microwave oven.

In recent years, the price of raw materials has soared. Due to cost pressure, many injection molding manufacturers are considering replacing polystyrene with ABS or replacing polystyrene products with modified PP products to reduce costs. Therefore, a large number of PP materials have emerged. An alternative to polystyrene. For example, after using mineral reinforcement and toughening PP material to replace the original polystyrene material injection refrigerator drawer, the cost per ton of raw materials can be 1,500~2000 yuan. Due to the large amount of use, only Haier Group will consume about 1,000 tons of this PP modified material in one year. In addition, many refrigerator companies' refrigerator countertops have also been replaced with mineral-reinforced and toughened PP materials, such as Kelon Electric, Meiling Electric and other companies. Although the mechanical properties of PP modified materials are slightly worse than polystyrene, there are problems such as distortion, shrinkage, and poor rigidity. The PP material has good toughness and high MFR characteristics, and the product is redesigned on the side and top surface of the product. The physical rib is added to the intersection of the joint, so that the problem of poor rigidity of the product is basically solved, so that material cost can be saved in a large amount.

The PP modified materials used for the plastic parts on the rice cooker are mainly classified into high gloss type and heat resistant type, the rice cooker outer shell is required to have high glossiness, and the base requires high heat resistance of the material. The outer casing of the rice cooker was mainly made of ABS. Due to cost pressure, modified PP is now mainly used instead of ABS. The rice cooker shell material is required to have high gloss and low shrinkage properties, and can be improved by mineral filling method. However, in the selection of minerals, glass beads, barium sulfate, calcium carbonate, etc., which have little influence on surface gloss, should be selected, if necessary. The surface gloss can be improved by a nucleating agent, a lubricant, a fluorescent agent or the like.

Weathering modified PP

Since PP contains unstable tertiary carbon groups, it is prone to aging degradation after light, heat and oxygen, resulting in problems such as discoloration and strength reduction, thereby limiting its application in outdoor products. Therefore, by modifying the weathering of PP, the service life of PP materials in outdoor harsh weather conditions can be greatly improved. The modified material is mainly used for manufacturing household appliances that are used in the open air all year round, especially for manufacturing an outdoor main casing of an air conditioner to replace the traditional metal sprayed outer casing.

The outdoor unit of the air conditioner is to withstand the test of different climatic conditions such as sun, rain, and cold, and it must meet the requirements for long-term use. The use of plastic instead of metal spray technology was first developed and put into use by Sumitomo and Mitsubishi Chemical Co., Ltd. in the early 1990s. This technology overcomes the complicated manufacturing process and cost of the original metal spray molded casing. High and heavy weight, easy to rust (can affect the performance and service life of the whole machine) and other shortcomings, ultimately reducing the labor intensity of workers, reducing energy consumption and extending service life. Weatherproof PP is also used in addition to the outdoor unit casing of the air conditioner, the axial flow vane of the air conditioner outdoor unit, and the air outlet of the heater. In recent years, with the increase in the output of air conditioners, the application of modified weathering PP in the market of this product has gradually increased.

Flame retardant modified PP

In order to avoid fires, many countries now require materials used in electronic and electrical components in household appliances to be flame retardant. Among the flame retardant PP, 63% require UL94V-0, 23% require UL94V-2, 12% DIN4102B1, and 1% other flame retardant. The high crystallization and flammability of PP make it difficult to achieve high flame retardant levels in electrical and other industries, and the cost increases. However, as the society's requirements for flame retardant of plastic products increase, the proportion of flame retardant PP will follow. Increased, the current annual growth rate of flame retardant PP is 8%.

Since PP is a flammable material, it is generally used in the market for the flame retardant modification of the Br/Sb composite flame retardant. Through flame retardant modification, PP products can reach UL94V-0 grade, and can withstand 650 ° C or even 750 ° C glow wire without burning. Such flame retardant modified PP materials are commonly used to make parts with potential fire hazards such as television housings, washing machine control trays, wire controller housings, refrigerator evaporating dishes, air ducts, and the like.

Glass fiber reinforced modified PP

Generally, the tensile strength of PP material is between 20M and 30MPa, the bending strength is between 25M and 50MPa, and the flexural modulus is between 800M and 1500MPa. If you want to use PP on engineering structural parts, you must use glass fiber for reinforcement.

In general, the mechanical properties of glass-reinforced PP products can be doubled or even multiplied. Specifically, the tensile strength reaches 65MPa~90MPa, the bending strength reaches 70MPa~120MPa, and the flexural modulus reaches 3000MPa~4500MPa. Such mechanical strength can be comparable to ABS and reinforced ABS products, and is more resistant to heat. Generally, the heat resistance temperature of ABS and reinforced ABS is between 80 ° C and 98 ° C, while the heat resistance temperature of glass fiber reinforced PP material can reach 135 ° C to 145 ° C. It can be used to make axial fans and cross-flow fans in refrigeration machines such as refrigerators and air conditioners, which are much less expensive than ABS-reinforced products. In addition, it can also be used to manufacture the inner barrel and pulley of high-speed washing machine to meet its high mechanical performance requirements, and is used in places with high temperature resistance such as rice cooker base and handle, electronic microwave oven.