Substantially proportional drawing die for polymer compositions
An inventive solid state drawing die has shaping walls that define a shaping channel and that, in the course of solid state drawing, direct polymer composition along a drawing path. Each cross section of the drawing path (and, hence, polymer composition in the drawing path) is non-circular, substantially proportional to one another, contains a centroid that lies on a substantially straight line parallel to the drawing direction and all cross sectional dimensions are 1.5 millimeters or more.
1. A process for solid state drawing of a polymer composition, the process comprising the steps of:
(a) providing a polymer composition containing an orientable polymer and having a softening temperature;
(b) conditioning the polymer composition to a drawing temperature at or below the polymer composition's softening temperature; and
(c) drawing the polymer composition through a drawing die;
wherein the drawing die is a solid state drawing die for drawing a polymer composition, the die comprising a body having opposing ends and defining a shaping channel that provides fluid communication through the body from one end to the opposing end, the shaping channel begins at one end as an entrance opening and ends at the opposing end of the body as an exit opening, the die having shaping channel walls exposed within the shaping channel and defining the shaping channel, the shaping channel having an non-circular cross sectional shape and having a drawing direction extending in a straight line through the shaping channel, wherein: (i) the shaping channel walls define a polymer composition drawing path extending from the entrance opening to the exit opening substantially proportional non-circular cross section shape and have a centroid lying on a substantially straight line, a centroid line, parallel to the drawing direction; and (ii) all shaping channel cross section dimensions are at least 1.5 millimeters; and where the polymer composition follows the polymer composition drawing path through the shaping channel and experiences free drawing after exiting the drawing die, wherein the die induces polymer movement that applies a substantially balanced force about the centroid line.
2. The process of claim 1 , wherein any cross section of the polymer composition drawing path has a larger area than any cross section of the polymer composition drawing path that is closer to the exit opening.
3. The process of claim 1 , wherein the polymer composition prior to entering the drawing die and after exiting the drawing die has substantially proportional non-circular cross section shapes.
4. The process of claim 1 , wherein the polymer composition initially contacts the shaping channel walls within the shaping channel at any point on the polymer composition's cross sectional perimeter within five millimeters along the drawing direction of any other point on the polymer composition's cross sectional perimeter.
5. The process of claim 1 , wherein the shaping channel walls define one or more gaps or spaces that extend 2.5 centimeters or less along the die drawing direction and wherein the polymer composition prior to entering the drawing die has a cross sectional shape proportion to the entrance and exit openings.
6. The process of claim 1 , wherein the drawing temperature is from ten to forty degrees Celsius below the polymer composition melt temperature.
7. The process of claim 1 , wherein the polymer composition comprises a polymer selected from polypropylene-based polymers and high density polyethylene.