One of the main usages of cellulose acetate (CA) is for filter tow as a material for cigarette filters. Filter tow was first introduced in 1952. In 2012, the volume of manufactured filter tow was about 811 000 metric tons.
The major reasons for this growth of filter tow for cigarette filters are;
- the growth of cigarettes with filter tips;
- the substitution of other filtration materials like paper, cotton and
Advantages of Filter tow
Due to the following advantages, CA filters were successfully introduced in more than 90% of the cigarettes in the world;
- as a material CA is non-toxic, tasteless and odorless;
- CA is stable to store under varying conditions of humidity and temperature;
- CA allows the stable and consistent production of filters with uniform, firm structure and a well-defined pressure drop, leading to efficient filtration;
- because of its continuity, filter tow can be converted into filters at rapid speeds and also into individually designed filters;
- filter tow can be hardened with a bonding agent which neither adheres rod making machines nor requires a solvent removal during the formation of the filter rod;
- filter tow has the unique inherent advantage of the selective removal of phenols; nitrosamines, quinolines and other undesired smoke components;
- filter tow plays a significant role in reducing tar yields;
- Charcoal (activated carbon) combined filters have become a great success in some countries in Asia and Europe;
- CA has a preferred – taste “signature”;
Characteristics of Filter Tow
Filter tow is designed by a combination of the following three characters of fiber products.
While DPF and TD are widely used in the industry the official Si-unit is Dtexc.
- DPF – denier per filament: DPF is the thickness of a filament defined by the weight in gram of 9,000 meters of uncrimped fiber. Filter tow is available in a variety of DPF ranging from 1.5 to 9.0s, and DPF from 2.7 to 3.0 is commonly manufactured.
- TD – total denier: TD is the thickness, total mass, of a tow band defined by the weight of 9,000 meters of uncrimped tow. Filter tow is available in a variety of TD ranging from 15,000 to 50,000, and commonly TD from 30,000 to 35,000 are manufactured.
Filter tow grades are expressed by the above three characters. For example, 3.0Y35,000 stands for the tow of DPF=3.0 and TD=35,000 with Y cross section. Crimp structure and moisture content are also important properties which have effects on the productivity and quality of filter rods manufactured.
Filter rod making
Filter tow is processed into filter rods before being cut into cigarette filter tips. On the filter rod making machine, filter tow undergoes stretching and relaxation, called ―blooming to form a web structure of tow. And then it is transformed into filter rods together with wrapping paper strip and paper glue. In the blooming process, glyceryl triacetate, plasticizer of cellulose acetate, is applied onto the surface of tow filaments. Glyceryl triacetate as a bonding agent makes the fibers stick together to form a three-dimensional matrix network to increase the hardness of produced rods.
c Tex is a unit of measure for the linear mass density of fibers and is defined as the mass in grams per 1000 meters. Tex is more likely to be used in Canada and Continental Europe, while denier remains more common in the United States and United Kingdom. The unit code is “tex”. The most commonly used unit is actually the decitex, abbreviated dtex, which is the mass in grams per 10,000 meters. When measuring objects that consist of multiple fibers the term “filament tex” is sometimes used, referring to the mass in grams per 1000 meters of a single filament.
Tex is used for measuring fiber size in many products, including cigarette filters, optical cable, yarn, and fabric.
One can calculate the diameter of a filament yarn using tex with the following formula:
where density in grams per cubic centimeter and the diameter is in mm.