Resin is a common name, refers to the manufacture of plastic products used in polymer raw materials, where any unprocessed polymer can be called resin. Polyester refers to the dicarboxylic acid and diol polycondensation reaction polymer. Polyester resins fall into two categories: one is a saturated polyester resin that has no non-aromatic unsaturation in its molecular structure, such as poly (ethylene terephthalate). This is a thermoplastic resin that can be injection molded into "polyester" fibers through a spinneret or into a film called a "polyester" film. The other is unsaturated polyester resin, which contains non-aromatic unsaturated bond in its molecular structure. It can be used as a thermosetting plastic by initiating the crosslinking reaction with an appropriate initiator. Unsaturated polyester resins described in this article belong to this category, often referred to as polyester for convenience.
Unsaturated polyester molecules before curing is a long chain of molecules, the relative molecular mass (hereinafter referred to as molecular weight) is generally 100 to 3000, this long chain of molecules with unsaturated monomers can be cross-linked to form a complex Structure of the huge mesh molecules. There are three forms of this network molecule.
1. As a generally uniform continuous network structure;
2. As a non-uniform continuous network structure, low density chain type molecules are connected to each other between dense continuous networks;
3. For discontinuous network structure, a dense continuous network is dispersed in the middle of unbonded components. Unsaturated polyester resin is mainly formed after curing the second network of macromolecules. This configuration can be studied by electron microscopy or observation of the swelling process of the resin. Unsaturated polyesters are the most common resins used in reinforced plastics. In the field of reinforced plastics, the amount of thermosetting resin accounts for about 75%, the amount of thermoplastic resin is increasing.
A variety of thermosetting resins, including unsaturated polyester dosage far more than a variety of other resins, because unsaturated polyester has particularly favorable processing conditions, and the price is cheap. For example, although the price of phenolic resin is lower than that of polyester, it needs to press water and form steam when processing and curing. Therefore, it requires higher forming pressure (usually 8 ~ 30MPa) and heating conditions, thus requiring a larger press to produce. Unsaturated polyesters do not expel water or other byproducts during processing and cure, allowing them to be molded at lower pressures and temperatures. In fact, a large number of unsaturated polyester used at room temperature and contact pressure processed into a variety of products, which is incomparable with other resins. Polyester and two other commonly used thermosetting resin after curing performance comparison in Table 1-1. Unsaturated polyester resin curing although it can become insoluble, non-melting thermosetting material, but its mechanical properties are very low, can not meet most of the requirements. If using glass fiber reinforced it becomes a composite material, commonly known as glass steel. It has many advantages such as light weight, high strength, chemical resistance, electrical insulation, microwave penetration and so on, and its forming method is simple. It can form all kinds of large or complex products at once, becoming a great advantage New Materials.