Obliquely Stretched Film Two-Stage Process
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Solution Overview
Problem
Existing methods for producing obliquely stretched films with orientation axes at 40° or more and 85° or less from the width direction are prone to wrinkles and twists, making it difficult to achieve uniform thickness and orientation, which hinders mass production of wide and long optical films for liquid crystal display devices.
Innovation Solution
A two-stage stretching process where the film is first longitudinally stretched and then obliquely stretched at a controlled angle, with specific conditions to ensure the average retardation of the obliquely stretched film is smaller than the longitudinally stretched film, allowing for uniform orientation and reduced thickness fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a transparent resin film is stretched longitudinally or laterally to be oriented and then cut in a rectangular shape with a predetermined angle, then a retarder with the desired orientation axis can be obtained, but a cutting loss is generated that lowers use efficiency of the stretched film
Solution Approach 1:
Instead of stretching the film first and then cutting it at an angle (which causes waste), the invention inverts the sequence by cutting the stretched film parallel to its sides. This allows the orientation axis to be at 40-85 degrees relative to the film side while eliminating cutting loss, as the film is now cut in the same direction as its orientation rather than at an angle to it.
2Manufacturing precision
If both side ends of a film are grasped between two rows of chucks running on tenter rails with different traveling distances, then an obliquely stretched film can be obtained, but wrinkles or twists easily occur making it impossible to achieve uniform thickness and orientation
Solution Approach 1:
The invention segments the stretching process into two distinct stages: first longitudinal stretching to achieve initial orientation and uniform thickness, then oblique stretching to achieve the final orientation angle. This segmentation prevents the film defects caused by attempting to achieve both uniformity and oblique orientation in a single stretching step.
3Adaptability or versatility
If stretching is performed with different traveling distances at both side ends to achieve oblique orientation, then an obliquely stretched film can be obtained, but it is substantially impossible to obtain a wide film having uniform thickness and an orientation axis uniformly oriented in an oblique direction at 40° or more and 85° or less
Solution Approach 1:
The invention performs preliminary longitudinal stretching first to establish uniform thickness and basic orientation across the film width. Only after this preliminary action is complete does it perform the oblique stretching to achieve the 40-85 degree orientation angle. This preliminary action ensures that the film has the structural integrity needed to withstand the subsequent oblique stretching without developing defects.
4Manufacturing precision
If the stretching process is repeated several times or performed after advance stretching in longitudinal or lateral direction, then an obliquely stretched film can be obtained, but mass production of long and wide optical film remains difficult due to wrinkles and twists
Solution Approach 1:
The invention changes the key parameter of stretching direction from conventional longitudinal-only or simple oblique stretching to a two-stage process with specific angle ranges (40-85 degrees). By optimizing this parameter along with the sequential process structure, the invention achieves both precise orientation control and mass production capability that were previously incompatible.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the production of wide and long obliquely stretched films with uniform thickness and orientation, suitable for use as retarders in liquid crystal display devices, improving productivity and display quality by reducing waste and enhancing view angles.
Implementation Method 1
a step of longitudinally stretching a long raw material film to obtain a longitudinally stretched film with an average retardation Re 1; and a step of stretching the longitudinally stretched film in a direction with an angle θe oblique to the width direction
Data Source
Figure 1
Figure 2~3
AI summary
A long obliquely stretched film is obtained having an orientation axis in a direction with an angle θs of 45° to 85° from a width direction by grasping both side ends in the width direction of a longitudinally stretched film with an average retardation Re1 by grasping means; stretching the film under a condition that a long obliquely stretched film sample with an average retardation Re2 (Re2 is smaller than Re1) can be obtained and traveling speeds of the grasping means are substantially equal at the film both side ends through a preheating zone, a stretching zone and a fixing zone; releasing the both side ends of the film from the grasping means; and taking it up around a winding core.