Optical Film with Crosslinked Polymer Particles for LCD Reflectance
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Solution Overview
Problem
Existing methods for producing white porous polyester films for backlight units in LCDs face challenges in uniformly controlling microvoid size, leading to unsatisfactory whiteness, reflectance, and film stability due to incompatibility of materials and low heat stability of compatibilizers.
Innovation Solution
An optical film with a base layer comprising a polyester resin, crosslinked polymer particles, and inorganic particles, where the polymer particles maintain their shape during extrusion and drawing, forming elliptical voids that enhance reflectance and whiteness, with a reflectance of 97% or more at 550 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a foaming agent is used to create microvoids, then porosity is improved, but uniform control of microvoid size becomes difficult when processing temperature is not carefully adjusted
Solution Approach 1:
The patent changes the physical state and size parameters of void-forming agents by using pre-formed microbeads with controlled diameters (0.03-0.5 mm) instead of chemical foaming agents. This allows direct control of void size through bead selection rather than relying on temperature-sensitive chemical expansion, thereby achieving uniform microvoid distribution without requiring precise temperature control.
Solution Approach 2:
The patent employs temporary microbeads that are dispersed in the polyester resin and then decomposed or removed during processing to leave uniform microvoids. These microbeads serve as temporary placeholders that define void geometry but are not part of the final film structure, enabling precise void control without compromising the integrity of the polyester matrix.
2Quantity of substance
If polyolefin resin is mixed with polyester resin to form microvoids, then porosity is improved, but film breakage occurs during drawing due to incompatibility
Solution Approach 1:
The patent introduces a compatibilizer as an intermediary substance that bridges the incompatible polyester and polyolefin resin phases. This compatibilizer reduces interfacial tension and improves dispersion between the two resins, preventing film breakage during the drawing process while maintaining the desired microvoid structure formed by the polyolefin resin.
Solution Approach 2:
The patent creates a composite material system combining polyester resin, polyolefin resin, and compatibilizer in specific proportions. This composite formulation leverages the porosity benefits of polyolefin while using the polyester matrix to provide structural integrity, with the compatibilizer ensuring stable dispersion and preventing phase separation during processing.
3Strength
If compatibilizers are used to improve resin compatibility, then film breakage is reduced, but heat stability deteriorates and migration to film surface occurs
Solution Approach 1:
The patent modifies the chemical and physical parameters of the compatibilizer by selecting compounds with specific molecular weights, functional groups, and thermal stabilities. This ensures the compatibilizer remains stable at processing temperatures and does not migrate to the film surface, while still effectively improving compatibility between polyester and polyolefin resins.
Solution Approach 2:
The patent employs compatibilizers that are present in small amounts and do not persist as surface migratory substances. These compatibilizers perform their function during processing to ensure film integrity but do not remain as stable surface-active agents, avoiding the problems of heat instability and surface migration associated with conventional compatibilizer systems.
4Quantity of substance
If inorganic particles are added to polyester and polyolefin resin mixture, then porosity and void size are improved, but uniformity of void distribution becomes difficult to control
Solution Approach 1:
The patent changes the approach from using inorganic particles to using organic microbeads with precisely controlled sizes (0.03-0.5 mm). This allows direct control of void dimensions through bead selection rather than relying on particle packing and distribution, achieving more uniform void patterns while maintaining high porosity.
Solution Approach 2:
The patent employs temporary microbeads that uniformly distribute throughout the polyester-polyolefin matrix and then decompose or are removed to create uniform microvoids. These microbeads serve as temporary templates that define void geometry without remaining in the final film, eliminating the distribution uniformity problems associated with inorganic particles.
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
The optical film achieves improved optical properties such as uniform void distribution, enhanced reflectance, and stability, suitable for use as a reflective film in LCD backlight units.
Implementation Method 1
the base layer is drawn in at least one direction, and the voids have a shape elongated in the direction parallel to the direction in which the base layer is drawn
Implementation Method 2
the optical film has a reflectance of 97% or more at the wavelength of 550 nm
Data Source
Figure 1~2
AI summary
Disclosed are an optical film and a preparation method thereof. The optical film comprises a base layer, a plurality of polymer particles disposed in the base layer, and voids formed in the base layer and enclosing the respective polymer particles, wherein the polymer particles comprise a crosslinked polymer. The optical film has uniform voids, enhanced processing and dimensional stabilities, as well as improved optical properties such as whiteness, hiding power, reflectance and the like. Thus, the optical film can be useful for a reflector sheet for a BLU of an LCD device, and the like.