Filter Rod For Filtering The Smoke Of A Cigarette

What is this patent about?

'620 is related to the field of cigarette filters, specifically addressing the problem of improving the filtration efficiency and pressure drop of acetate tow filters while preventing the tow from snagging on the rollers of filter rod making machines. The background highlights the trade-off between achieving adequate crimp recovery for pressure drop and the increased risk of the acetate tow catching on the machinery.

The underlying idea behind '620 is to control the crimping process of the acetate tow by carefully managing the acetone content and temperature of the tow as it exits the stuffing box crimping apparatus. By maintaining these parameters within specific ranges, the acetate tow achieves a high crimp modulus, leading to improved filter performance and reduced processing issues.

The claims of '620 focus on an acetate tow for cigarette filters characterized by a degree of crimping of 1.4 or more measured just downstream of the delivery roller in a filter rod making machine. This crimping is achieved by controlling the acetone content and temperature of the tow during the crimping process within defined limits.

In practice, the invention involves a dry spinning process to create the acetate tow, followed by crimping using a stuffing box type crimping machine. The key is to ensure that the acetone content and temperature of the tow, immediately after crimping, fall within the ranges defined by equations (1) and (2) in the patent. This may involve adjusting the temperature of the air blown into the spinning tube, or heating the tow before or during crimping, for example by using a heated roller.

This approach differentiates itself from prior art by recognizing and controlling the critical relationship between acetone content and temperature during crimping. Earlier methods, such as steam treatment, were prone to inconsistencies and fiber adhesion. By carefully balancing these two factors, the invention achieves a high crimp modulus without causing the acetate tow to stick to the rollers, resulting in a filter rod with both a high pressure drop and efficient manufacturing.