Phenolic resin plastic(bakelite) is a hard and brittle thermosetting material.
The characteristics of bakelite are non-absorbent, non-conductive, high temperature resistant and high strength. They are mostly used in electrical appliances. They are called “bakelite” because of their high insulation and plasticity like wood. Bakelite is made of powdered phenolic resin, which is mixed with sawdust, asbestos, or clay, and then pressed into a finished product at a high temperature. Among them, phenolic resin is the world’s first synthetic resin.
Bakelite phenolic plastic: the surface is hard, brittle and fragile, there is a sound of wood when struck, and it is mostly opaque and dark (brown or black), which does not become soft in hot water. It is an insulator, its main component is phenolic resin.
- Good formability, but shrinkage and directionality are generally greater than amino plastics, and contain water volatiles. It should be preheated before molding, and should be exhausted during molding. If it is not preheated, the mold temperature and molding pressure should be increased.
- The mold temperature has a great influence on the fluidity. Generally, when the temperature exceeds 160 degrees, the fluidity will drop rapidly.
- The curing speed is generally slower than amino plastics, and the heat released during curing is large. The internal temperature of large thick-walled plastic parts tends to be too high, which is prone to uneven hardening and overheating.
When the formaldehyde/phenol (molar ratio) is less than 1, a thermoplastic product can be obtained, called a thermoplastic phenolic resin, that is, a novolak phenolic resin, which does not contain further polycondensation groups, and can be cured by adding a curing agent and heating. If hexamethylenetetramine is used as curing agent, the curing temperature is 150 ℃, and the molding powder mixed with filler is commonly known as bakelite powder. When the formaldehyde/phenol (molar ratio) is greater than 1, first-stage resin, ie thermosetting phenolic resin, can be obtained under alkali catalysis and can be dissolved in organic solvents. The first-stage resin contains hydroxymethyl which can be further polycondensed, so it is not necessary It can be cured by adding a curing agent: the B-stage resin is obtained by reaction under heating, also known as semi-soluble phenolic resin, which is insoluble and infusible but can swell and soften. After further reaction, an insoluble and infusible body structure C-stage resin, also known as insoluble phenolic resin, is obtained. The resin in stage A can also be cured by itself for a long time.
The curing form of thermosetting phenolic resin is divided into two types: normal temperature curing and thermal curing. Normal temperature curing can use non-toxic normal temperature curing agent NL, benzenesulfonyl chloride or petroleum sulfonic acid can also be used, but the latter two materials are more toxic and irritating.