Dry cleaning uses organic solvents such as tetrachloroethylene or fine hydrocarbons to wash clothes, and ordinary washing uses water as a solvent. When washing, special detergent is often added to the solvent to improve the decontamination and stain removal ability in the washing process. In addition, modern detergents can also make clothes have the effect of re-expansion to improve hand feel. The two washing methods are the same, except that the water or solvent in the clothes is dried by high-speed centrifugation before drying. But the difference lies in various processes after clothes are dried.
In the ordinary laundry process, most washing machines need to take out wet clothes after the washing process, or naturally evaporate and dry them, such as drying clothes, or spin them with a drum. However, in dry cleaning, "wet" clothes are actually soaked in dry cleaning agent. The drum spinning method improved by dry cleaning machine is used to remove the residual dry cleaning agent from clothes so that it can be recycled.
In daily life, clothes need to be cleaned because they are dirty. There are two main reasons why clothes need dry cleaning: first, in the washing process of ordinary washing machines, the combined action of water and machinery will cause irreversible deformation of clothing fibers, leading to size shrinkage or other damage; Secondly, the chemical action of water is incompatible with most dyes used in this kind of clothing fabrics, which leads to the diffusion or fading of dyes.
All kinds of dry cleaning agents used for dry cleaning are not water-based solvents and will not "soak" clothes, so their fibers rarely or even will not swell. This is the origin of the word "dry cleaning". In addition, these dry cleaners usually have good chemical compatibility, so they have little influence on the dimensional stability and color characteristics of clothes.
Another reason why clothes need dry cleaning is that organic dry cleaning agents have stronger decontamination ability than water, so dry cleaning is often used.
Most of the dirt on clothes is dust in the air attached to oil or grease, and then attached to fibers. Oil or grease mainly comes from fat secreted by human body, lampblack and automobile exhaust. The function of dry cleaning agent used in dry cleaning is to quickly dissolve the oil or grease that makes dust stick to fibers. Adding a special dry cleaning additive (dry cleaning oil) to the dry cleaning agent can suspend dust and prevent it from depositing on clothes again. Then, the free dirt can be separated from the dry cleaning agent by filtration or distillation.
Water-soluble scale, such as sludge, food and beverage color stains, etc., is not easy to remove only with dry cleaning agent. In order to enhance this decontamination ability, a small amount of mixed liquid of water and dry cleaning additives is usually added in the dry cleaning process. Modern dry cleaning additives generally contain enough water, so there is no need to add water.
The mixture of dry cleaning auxiliaries and water (emulsion) can also be directly used to brush off stains on clothes before dry cleaning. Thus, a small amount of water is introduced into the dry cleaning system in the form of emulsion. This process is usually called pre-decontamination. Because the amount of water added is very small, the dry cleaning machine is basically kept in a "dry cleaning" state, so all the problems that can be avoided with dry cleaning agents such as shrinkage, discoloration and deformation can be minimized.
Modern dry cleaning machines use so-called dry-dry closed-loop technology. It refers to the washing process from putting dry and dirty clothes into the machine to taking clean clothes out of the machine. Compared with the "two-machine transfer" mode 30-40 years ago, this kind of dry cleaning has lower labor intensity and can minimize emissions. The so-called double-machine transfer method means using two machines, one for washing and one for drying. This dry cleaning method is still widely used in some countries in the world, such as Japan and the United States. In the process of transfer dry cleaning, clothes are transferred from one machine to another in the wet state of dry cleaning agent. Following the "transfer method", the first generation of dry cleaning machines adopted the "dry-dry open loop" technology. This dry cleaning technology has great advantages, but after the drying process, the air filled with dry cleaning agent should be exhausted from the machine.