Film Drawing
“Drawing”film refers to stretching film to change its structure and properties. There are three common ways to stretch thermoplastic films. (1) Machine direction orientation (MDO) involves two pairs of rollers. The film is pinched by the first pair running at a slow speed and then stretched by the second set,which is running at a faster speed. The ratio of the roller speeds determines the amount of stretching. This method is used to create an oriented film or a microporous film in the case of a filled film. The film is stretched only in the machine direction. (2) Tentering involves grabbing the sides of the film and stretching from side to side or in the cross direction. This method can form biaxial oriented film as well as a microporous film for filled films. (3) Incremental stretching involves running the film between grooved or toothed rollers. The grooves or teeth intermesh but do not touch. The result is orientation in the machine direction, cross machine direction,or any combination of the three perpendicular directions. The depth of the intermeshing teeth controls the degree of stretching. (RDC 9/14/2010)
(Cancio, Mushaben, Mortellite and Wu, US Patent 7,740,469, 6/22/2010)
Recent US Patents
11/2/2011
7,824,169
Stretching apparatus for web of thermoplastic synthetic resin
Akaki and Matsumoto of Uni-Charm Corporation, Japan, have developed a stretching apparatus for thermoplastic sheets so that a web can be easily stretched over its entire width. It consists of stretching members L arranged in a circumferential direction on a peripheral surface of a drum 6 rotating in a machine direction M. Rotatable members have second stretching members associated with the first stretching members. (RDC 2/22/2011)
10/5/2010
7,806,679
Drawing apparatus and drawing method
Murata of Nihon Spindle Mfg Co., Japan has developed a drawing apparatus consisting a mold at the tip of a spindle and a squeezing roller for forming a material into a shape along the surface shape of the mold where the mold is a split structure having a concavo-convex surface shape and contractible in diameter after the forming of the material. (RDC 12/19/2010)
6/22/2010
7,740,469
Method and Apparatus for Uniformly Stretching Thermoplastic Film and Products Produced Thereby
Cancio et al developed a process for oriented film by extruding a molten web onto differential speed rollers to chill and orient the film. The can also be combined with incremental rollers for further film treatment.
7/8/1979
4,153,751
Process for Stretching and Impregnated Film of Material and the Microporous Product Produced Thereby
Schwarz produced a microporous film by rolling the film between sets of rollers with parallel grooves, perpendicular grooves or alternating parallel and perpendicular groove. One example was a polyproplene film filled with 15 wt% clay coated with a wetting agent.
Recent Journal Articles
Stretching-induced percolation in polyvinylidene fluoride and nickel composites
(2368–2373) Journal of Applied Polymer Science 120 #4 (2011)
Yu and Li of Ningbo University, China, stretched polyvinylidene fluoride (PVDF) and nickel (Ni) composites at 120°C. There was an abrupt increase in dielectric constants and conductivities with stretching ratio called the stretching-induced percolation. When SR was near the threshold, dielectric constants showed 17 times improvement and conductivities displayed four to five orders of magnitude enhancement at 100 Hz in low Ni fraction composites. (RDC 3/21/2011)