1. Technical Field
The present invention relates to filter elements and the method and apparatus for fabricating such filter elements. More particularly, the present invention relates to an improved overwrap for a tobacco smoke filter which considerably reduces filter fabrication costs without introducing undesirable side effects.
Although the present invention is primarily concerned with producing filter means for cigarettes, it should be noted that the products of the present invention are generally useful as filters for any tobacco smoking means, whether they be cigarettes, cigars, pipes, etc. Since filters for cigarettes have particular commercial importance, the preferred embodiments described herein relate to the production of filtered cigarettes.
2. The Prior Art
In fabricating filters for use in connection with cigarettes and the like, a number of different properties of the resultant filter must be taken into consideration. While filtration efficiency (i.e., the ability of the filter to remove undesirable constituents from the tobacco smoke) is a very important property of cigarette filters, filtration efficiency must frequently be compromised in order for the filter to possess a commercially acceptable combination of other properties, including pressure drop, taste, hardness, appearance and cost. For example, the most commonly utilized cigarette filter material, cellulose acetate, has a relatively low filtration efficiency; however, this material has a commercially acceptable overall combination of properties.
The relatively poor filtration efficiency of cellulose acetate has resulted in a long but unsuccessful search for an acceptable substitute. A wide variety of different materials have been tried, including paper, polypropylene, and others, but all have been rejected primarily because they introduce an unacceptable taste to the smoker. It has been found that the taste of cigarette smoke is extremely sensitive to the filter material and to foreign substances in or in contact with the filter material. Even in cases where filters have been modified with plastic tubes or other ingredients, the resulting taste has proven to be commercially objectionable.
In spite of the objectionable taste introduced into smoke by paper, it is the most economical and commercially viable material for plug wrap or overwrap material used to circumscribe a cellulose acetate filter rod. The use of paper overwrap is clearly a compromise of the filter taste property. In order to avoid this compromise in taste, attempts have been made to change the filter structure, the filter material, and the overwrap material; all have been commercially unacceptable. Attempts have also been made to eliminate the overwrap entirely; however, these have been unsuccessful because, without an overwrap, the fabrication machines cannot be operated at high speeds.