Resin usually refers to the softening or melting range after being heated. When softened, it tends to flow under the action of external force. It is a solid, semi-solid or sometimes liquid organic polymer at room temperature. In a broad sense, any polymer that can be used as raw material for plastic products processing is called resin. There are two kinds of resins: natural resin and synthetic resin. Natural resin refers to the amorphous organic substances obtained from animal and plant secretions in nature, such as rosin, amber, shellac, etc. Synthetic resin refers to the resin product obtained by chemical synthesis of simple organic matter or chemical reaction of some natural products. Natural resins can be classified according to resin composition and resin formation history.
According to the basic components of resin, it can be divided into three categories:
(1) pure resin, which is composed of terpenes and crude essential oils. Generally insoluble in water, but soluble in organic solvents, such as rosin.
② Gum resin, or gum resin, is composed of polysaccharides, soluble in or swelling with water, but insoluble in alcohol and organic solvents, such as frankincense.
③ Oil containing resin or gum refers to the resin containing more essential oil and soluble in oil. According to the formation history of resin, it can be divided into fossil resin, semi fossil resin and fresh resin. The latter is the most important natural resin source. Some natural resins are named after the port where they were first transported and exported, such as Gemma resin, Koba resin, etc.
Synthetic resin is a viscous liquid or a solid that can be softened by heating. When heated, it usually has a temperature range of melting or softening. Under the action of external force, it can flow in a plastic state. Some properties are similar to those of natural resin. The most important application of synthetic resin is to make plastics. In order to facilitate processing and improve performance, additives are often added and sometimes directly used for processing and forming, so it is often synonymous with plastics.
Resin composite manhole covers are made of glass fiber and its products (glass cloth, tape, felt, yarn, etc.) as reinforcement materials, and synthetic resin as matrix materials. They are mainly composed of unsaturated polyester resin, filler, initiator, thickener, low shrinkage additive, film mold agent, pigment and reinforcement materials. The resin composite manhole covers are divided into BMC and SMC, SMC and BMC materials as composite materials