Methods and devices for stretching polymer films
First Claim
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1. An apparatus for stretching a film, the apparatus comprising:
- a plurality of gripping elements to hold opposing ends of a film;
opposing tracks along which the plurality of gripping elements travel, the opposing tracks defining a primary stretching region in which the tracks generally diverge to stretch a film held by the gripping elements, wherein each of the opposing tracks in the primary stretching region comprises at least one continuous rail extending the length of the track through the primary stretching region; and
at least one track shape controller coupled to at least one of the continuous rails within the primary stretching region, wherein the track shape controller is capable of applying a force to the continuous rail to modify a shape of the track in the primary stretching region, said track being generally curvilinear within the primary stretching region.
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Abstract
Stretched polymeric films can be used in a variety of applications, including optical applications. The stretching conditions and shape of the stretching tracks in a stretching apparatus can determine or influence film properties. Methods and stretching apparatuses can include adjustable or zone-defined stretching regions.
67 Citations
21 Claims
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1. An apparatus for stretching a film, the apparatus comprising:
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a plurality of gripping elements to hold opposing ends of a film; opposing tracks along which the plurality of gripping elements travel, the opposing tracks defining a primary stretching region in which the tracks generally diverge to stretch a film held by the gripping elements, wherein each of the opposing tracks in the primary stretching region comprises at least one continuous rail extending the length of the track through the primary stretching region; and at least one track shape controller coupled to at least one of the continuous rails within the primary stretching region, wherein the track shape controller is capable of applying a force to the continuous rail to modify a shape of the track in the primary stretching region, said track being generally curvilinear within the primary stretching region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for stretching a film, the apparatus comprising:
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a plurality of gripping elements to hold opposing ends of a film; opposing tracks along which the plurality of gripping elements travel, the opposing tacks defining a primary stretching region in which the tracks generally diverge to stretch a film held by the gripping elements, wherein the prhnaiy stretching region comprises (i) an initial stretching zone, configured and arranged so that the machine direction draw ratio (MDDR), defined as cosine of a positive included divergence angle θ
between a machine direction and an instantaneous tangent of a track, and the tranaverse direction draw ratio (TDDR), defined as a ratio of a current separation distance of the tracks and an initial separation distance of the tracks, have the following relationship;
MDDR>
(TDDR)−
1/2and TDDR is increased by at least 0.5 in the initial stretching zone; and (ii) a later stretching zone configured and arranged so that MDDR is approximately equal to (TDDR)−
1/2 and TDDR is increased by at least a 5 in the later stretching zone.- View Dependent Claims (12, 13, 14, 15)
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16. An apparatus for stretching a film, the apparatus comprising:
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a plurality of gripping elements to hold opposing ends of a film; opposing tracks along which the plurality of gripping elements travel, the opposing tracks defining a primary stretching region in which the tracks generally diverge to stretch a film held by the gripping elements, wherein each of the opposing tracks in the primary stretching region comprises at least one continuous rail extending the length of the track through the primary stretching region and the rail having a crass-sectional area that varies along a length of the track; and at least one track shape controlkr coupled to at least one of the continuous rails within the primary stretching region, wherein the track shape controller is capable of applying a force to the continuous rail to modify a shape of the track in the primary stretching region. - View Dependent Claims (17, 18)
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19. An apparatus for stretching a film, the apparatus comprising:
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a plurality of gripping elements to hold opposing ends of a film; opposing tracks along which the plurality of gripping elements travel, the opposing tracks defining a primary stretching region in which the tacks generally diverge to stretch a film held by the gripping elements, wherein each of the opposing tracks in the primary stretching region comprises at least one continuous rail extending the length of the track through the primary stretching region; at least one track shape controller coupled to at least one of the continuous rails within the primary stretching region, wherein the track shape controller is capable of applying a force to the continuous rail to modify a shape of the track in the primary stretching region; and a takeaway system used to remove the film directly from the primary stretching region, the takeaway system being independent of the tracks of the primary stretching region. - View Dependent Claims (20, 21)
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Specification