Phenolic Plastic

October 8, 2024

wanplas

Industry Knowledge, Plastic Materials

Phenolic plastics, commonly known as Bakelite, are a hard and brittle thermosetting plastic. Plastics based on phenolic resin are generally called phenolic plastics. They are the most important type of thermosetting plastics and are widely used as electrical insulation materials, furniture parts, daily necessities, handicrafts, etc.

Introduction

Phenolic plastic, commonly known as Bakelite, was invented in 1872 and put into industrial production in 1909. It is the oldest plastic in the world, the general name for plastics with phenolic resin as the base material, and the most important type of thermosetting plastic. Generally, it can be divided into two categories: non-laminated phenolic plastic and laminated phenolic plastic. Non-laminated phenolic plastics can be divided into cast phenolic plastics and pressed phenolic plastics. It is widely used as electrical insulation materials, furniture parts, daily necessities, handicrafts, etc. In addition, there are asbestos phenolic plastics mainly used for acid resistance, rubberized paper and rubberized cloth used for insulation, phenolic foam plastics and honeycomb plastics used for thermal insulation and sound insulation, etc.

Basic information

Phenolic plastic : Plastic based on phenolic resin.

Specific gravity: 1.5-2.0 g/cm³

Molding shrinkage: 0.5-1.0%

Molding temperature: 150-170℃

Material properties: Phenolic plastic is a hard and brittle thermosetting plastic, commonly known as bakelite powder. It has high mechanical strength, toughness and wear resistance, dimensional stability, corrosion resistance and excellent electrical insulation properties. Suitable for making insulator components for electrical appliances and instruments, and can be used under hot and humid conditions

Molding performance

1. The formability is good, but the shrinkage and directionality are generally greater than those of aminoplastics, and they contain moisture volatiles. It should be preheated before molding, and the air should be exhausted during the molding process. If not preheated, the mold temperature and molding pressure should be increased.

2. Mold temperature has a great influence on fluidity. Generally, when it exceeds 160℃, fluidity will decrease rapidly.

3. The hardening speed is generally slower than that of aminoplastics, and the heat released during hardening is large. The internal temperature of large thick-walled plastic parts is easily too high, and uneven hardening and overheating are prone to occur.

Processing preheating

Importance

Phenolic plastics are generally preheated using a high-frequency preheater ( high-frequency preheater ). The phenolic molding compound heated by the high-frequency preheater can enhance fluidity, shorten die-casting time, eliminate internal stress in the material, and eliminate product moisture. It can reduce the texture and improve the smoothness of the finished product, save the amount of material and extend the life of the mold. Before electronic components and electrical molding, the molding compound powder (cake) is preheated and softened to improve product quality, insulation performance and mechanical properties.

Machine selection

Select the heating equipment according to the shape of the phenolic molding compound.

Preheating machines are divided according to electrodes: flat electrode type, roller electrode type (drum type, turntable type)

1. Material selection in powdery, granular state, or irregular cake state: Flat electrode type
2. Material selection for preformed cylinder: roller electrode type
3. For powdery and granular materials, the rotating disk electrode type can also be selected (the molding material does not need to be preformed to achieve the roller electrode preheating effect).

Effects of temperature and humidity

Effect on mechanical strength

Comparison of tensile strength and flexural strength of various filled phenolic plastic parts in an environment of 200°C after 1,000 hours: Plastic parts reinforced with glass fiber are minimally affected by temperature. The tensile strength of phenolic plastic parts filled with wood powder decreases rapidly at 90 to 100°C, while that of asbestos filler does not change much.

The water oxygen group in phenolic plastic has a strong affinity for water and is easy to absorb moisture. Plastic parts expand in volume after absorbing moisture, causing internal stress and causing warping and deformation. Generally, moisture absorption is 3%, and the bending strength is reduced by about 25%. As the moisture content increases, the impact strength gradually increases, while the tensile strength and flexural strength decrease significantly.

Effect on electrical properties

The electrical properties of phenolic plastics vary greatly depending on the resin and filler content. When affected by humidity and temperature, the insulation performance changes even more.

The electrical insulation properties of phenolic resin are consistent with the tendency for mechanical strength to decrease. The insulating ability of plastics can indirectly reflect the mechanical strength. However, the volume resistance of plastics does not follow this rule. Often the mechanical strength has been reduced by 50%, but the volume resistance has not yet shown a downward trend. Tests have proven that phenolic plastic parts with asbestos and glass fiber fillers can maintain stable electrical and mechanical properties for a long time at high temperatures above 150°C.

The moisture absorption of phenolic plastics is directly related to the type of filler. Dip various phenolic plastic parts in water at 24°C. The water absorption amounts are: 1.2% for asbestos filler, 5.4% for short fiber filler, 6.8% for cloth scrap filler, and 8.4% for wood powder filler. When the moisture content is between 2 and 3%, the electrical properties do not change much. If it reaches above 5%, the electrical properties decline rapidly.

Effect on dimensional stability

Although phenolic plastic parts have good dimensional stability and minimal creep, this is only in comparison with other plastics. However, it will also undergo some dimensional changes after being affected by humidity and temperature. For high-precision mechanical parts, it is necessary to understand the relationship between its use environment and dimensional changes.

The shrinkage is more severe in the low-temperature and dry winter, and the shrinkage is less or even expanded in the hot and humid summer. This phenomenon is called the breathing of plastic parts. The breathing of phenolic plastic parts is closely related to the discharge of moisture from the plastic or the absorption of moisture from the outside. Under hot and humid conditions with a relative humidity of 100% and a temperature of 50°C, the time it takes for the size of the plastic part to reach equilibrium is only half that of room temperature. Plastics molded from materials with a moisture content of 0.1% have poor dimensional stability. When the temperature reaches 150°C, the shrinkage of phenolic plastic parts tends to be balanced. When the temperature rises further, the plastic parts will continue to shrink.

Corrosion resistance

Pure phenolic resin without fillers is almost immune to attack by inorganic acids, insoluble in most hydrocarbons and chlorides, and insoluble in ketones and ethanol. But it is not resistant to corrosion such as concentrated sulfuric acid, nitric acid, high temperature chromic acid, fuming sulfuric acid, alkali and oxidants. Phenolic plastic also has the above characteristics, but when studying its corrosion resistance, the corrosion resistance of the filler must also be taken into consideration.

Performance of different filler phenolic plastics (PF)

Modified

The main disadvantages of phenolic plastics are brittleness, poor arc resistance, and dielectric properties that change with frequency. Therefore, in production applications, modification methods are used to make up for the shortcomings of phenolic resins. The performance of phenolic plastics can be improved by mixing phenolic resins (mainly thermoplastics) with other types of polymers. Commonly used polymer compounds include: polyamide resin, polyvinyl chloride resin, nitrile rubber, polypropylene resin, etc. For example, after being mixed with polyvinyl chloride, its mechanical strength, heat resistance, dielectric properties, acid resistance, water resistance, etc. can be improved, and it has better colorability. Bakelite powder based on phenolic resin and nitrile rubber can greatly improve the impact strength of parts. Bakelite powder made from a mixture of phenolic resin, polyamide resin and inorganic fillers (such as mica and feldspar) has higher dielectric properties, and its products can be used under high temperature, high frequency, and high pressure conditions.

Uses

Phenolic plastics are widely used as electrical insulation materials, furniture parts, daily necessities, handicrafts, etc. In addition, it is also used as acid-resistant asbestos phenolic plastic, rubber-coated paper and tape for insulation, phenolic foam plastic and honeycomb plastic for insulation and sound insulation, etc.

Phenolic laminated plastic is made of sheet fillers impregnated with phenolic resin solution and can be made into various profiles and plates. Depending on the filler used, there are various laminated plastics such as paper, cloth, wood, asbestos and glass cloth. Cloth and glass cloth phenolic laminated plastics have excellent mechanical properties, oil resistance and certain dielectric properties. They are used to manufacture gears, bearing bushes, guide wheels, silent gears, bearings and electrical structural materials, electrical insulation materials and wooden layers. Compressed plastic is suitable for bearings and gears under water lubrication and cooling. Asbestos cloth laminated plastic is mainly used for parts that work at high temperatures.

Phenolic fibrous pressed plastic can be heated and molded into various complex mechanical parts and electrical parts. It has excellent electrical insulation properties, heat resistance, water resistance, and wear resistance. It can produce various coil frames, wiring boards, power tool casings, fan blades, acid-resistant pump impellers, gears, cams, etc.

Performance

Molding shrinkage

The molding shrinkage of phenolic resin is determined by many factors, such as resin composition, filler type, moisture content, molding conditions, etc.

Heat resistance

From a practical point of view, the use temperatures of phenolic plastics with various fillers are: 160°C for inorganic fillers; 140°C for organic fillers; the highest use temperatures for glass fiber and asbestos fillers are 170~180°C.

Current situation analysis

Due to its excellent heat resistance and good cost performance, phenolic plastic still has advantages that other general-purpose plastics cannot match. As China has become a major producer of electronic and electrical products and cookware in the world, a large number of products are exported every year, which has driven the rapid growth of phenolic plastic production. China’s phenolic plastic production volume ranks among the top in the world, and domestic market consumption accounts for 1/2 of the global market.

There are more than 40 phenolic plastic raw powder manufacturers in China. The major companies with larger output and product specifications include Shanghai Eurasian Synthetic Materials Company, Shanghai Shuangshu Plastic Factory, Wenzhou South China Chemical Company, etc. There are nearly 10,000 downstream manufacturers of various types of phenolic plastic products, mainly distributed in the fields of circuit boards and heat-resistant resistive accessories for various electronic and electrical products, cookware handles, automobile brake pads and heat-resistant plastic accessories, fiberglass products and other fields. According to the survey statistics of the National Phenolic Resin and Plastics Industry Collaboration Group, china’s phenolic plastic production was 180,000 tons in 2001, of which injection plastics accounted for 30%. The output of phenolic plastics in 2002 was basically the same as that in 2001. In 2002, 27,872 tons of phenolic resin and plastics were exported, an increase of 42% over the previous year; 94,464 tons were imported, an increase of 18.8% over the previous year. In 2002, the china’s market consumption of phenolic plastics was about 250,000 tons, with a growth rate of 3%.

With economic development, many new application fields of phenolic resins and plastics are constantly being developed. Experiments have found that phenolic resin and plastic products not only have good heat resistance and flame retardant properties, but also produce less toxic smoke after burning. The number one cause of death in urban fires is the toxic smoke generated by the burning of chemical building materials in buildings. With the increasing development of tunnel traffic and the increasing number of high-rise buildings, phenolic plastics are particularly suitable for applications with strict fire protection requirements. Plastic products in urban subway vehicles and high-rise building materials are increasingly using various types of phenolic plastic composite materials.

Although phenolic plastics have poor impact resistance, the continuously developing enhancement modification technology has improved this defect. According to the latest research results of scientific research institutes, modification with nitrile rubber can significantly improve the impact strength of phenolic plastics. When the amount of nitrile rubber is only 2%, the impact strength of phenolic plastic can be increased by 100%. As the amount of nitrile rubber increases, the impact strength of phenolic plastics further increases, while the softening point increases and the gel time shortens.

The current difficulty faced by the phenolic resin and plastics industries is the tight supply of raw material phenol and the sharp rise in prices. The price of phenol has increased from 6,500 yuan (ton price, the same below) a month ago to about 9,000 yuan. This is mainly because china’s phenol production can only meet 50% of demand, and imports account for a large proportion. China has implemented anti-dumping measures on imported phenol, which will reduce imports and cause the price of phenol to rise sharply. On July 18, 2012, at the phenolic resin and plastic industry conference held in Chun’an, Zhejiang, the participating companies unanimously believed that production at the current 2013 phenol price would cause industry-wide losses.

Experimental part

Experimental raw materials

Thermoplastic phenolic resin (novolak): brand number 2123,

Thermosetting phenolic resin (resol): brand number 2124,

Chopped alkali-free glass fiber: length, 1~6mm, diameter, 1~3μm, produced by Zhejiang Jushi Group,

Other additives are industrial products.

Injection plastic formula

Injection plastic performance characterization

1. High appearance and thermal stability

The test sample (120×15×10mm) was placed in an oven at 200°C for 3 hours, then the temperature was raised to 250°C, kept for 1 hour, continued to increase the temperature to 300°C, kept for 2 hours, and continued to increase the temperature to 370°C for 1 hour., take out the sample and observe the surface of the sample. If there is no blistering, cracking, or bending deformation, it means that the sample has passed the appearance thermal stability test within this temperature time, and vice versa.

2. The mechanical properties, thermal properties, and electrical properties of injection molded products are tested according to the china’s standard GB1404-95 for phenolic molding compounds.