Low refractive index fluoropolymer compositions having improved coating and durability properties

Abstract

A low refractive index composition that forms a low refractive index layer on an optical display is formed having a co-crosslinked interpenetrating polymer network of a fluoropolymer phase and an acrylate phase. The fluoropolymer phase is preferably formed from fluoropolymers based on THV or FKM and having either a degree of unsaturation and / or containing a reactive cure site monomer in its polymer backbone. The acrylate phase includes a multifunctional acrylate crosslinker, and more preferably includes a perfluoropolyether acrylate crosslinker. The formed low refractive index layer has improved interfacial adhesion to other layers or substrates contained in the optical display. Further, the mechanical strength and scratch resistance of the either of above low refractive index compositions can be further enhanced through the incorporation of surface functionalized inorganic particle into the formed layer.

Description

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION [0001] The present invention relates to antireflection films and more specifically to low refractive index fluoropolymer compositions for use in antireflection films. BACKGROUND OF THE INVENTION [0002] Antireflective polymer films (“AR films”) are becoming increasingly important in the display industry. New applications are being developed for low reflective films applied to substrates of articles used in the computer, television, appliance, mobile phone, aerospace and automotive industries. [0003] The physical principles by which anti-reflection films and coatings function are well known. Several overviews can be found, for example, in Optical Engineering, S. Muskiant Ed, Vol. 6., Optical Materials, Chap. 7, p 161, 1985 and as shown in U.S. Pat. No. 3,833,368 to Land, et al. AR films are preferably constructed of alternating high and low refractive index (“RI”) polymer layers of the correct optical thickness. With regard...

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Benefits of technology

[0009] The low refractive index fluoropolymer compositions of the AR films described in this invention are derived from an interpenetrating polymer network or semi-interpenetrating polymer network which comprises a reactive fluoroplastic and / or a fluoroelastomer (i.e. the functional fluoropolymer phase) blended with multi-functional acrylates (i.e. the acrylate phase) such as trimethylolpropane triacrylate (TMPTA) and optionally additional fluorinated mono-functional acrylates or multi-functional fluorinated acrylates which can be coated and cured by ultraviolet light or by thermal means. The presence of an acrylate crosslinker provides a composition with both low refractive index and improved adhesion to high index polymer substrates such as polyethylene terephthalate (“PET”) or hard coated PET films.

[0010] The coating mixture describe herein comprises a reactive high molecular weight fluoropolymers which can participate in the crosslinking reactions between the monomeric multi-functional acrylates. This enhances the crosslinkability of the fluoropolymer phase to the forming polyacrylate phase and produces a co-crosslinked, interpenetrating or semi-interpenetrating polymer network with enhanced interfacial contact between the high index layer and the low index layer and thereby improved durability and low refractive index.

[0011] Further, improvements in the mechanical strength and scratch resistance of the low refractive index compositions can be enhanced through the incorporation of surface functionalized nanoparticles into the fluoropolymer compositions. Providing functionality to the nanoparticles further enhances the interactions between the fluoropolymers and such functionalized particles.

Problems solved by technology

Although inorganic materials, such as indium tin oxide (“ITO”), possess both high index and hardness, they are difficult and expensive to process into continuous films.

Moreover such metalized surfaces often reflect blue light and therefore optical substrates with such materials are slightly colored and therefore have compromised viewing cosmetics.

However, fluoropolymers tend to have relatively low hardness and poor abrasion and wear resistance properties compared to hydrocarbon polymers such as polymethylmethacrylate (“PMMA”).

Although it is desirable to increase the fluorine content of the low refractive index coating in order to decrease the refractive index, an increase in fluorine content of the low index coating composition tends to decrease the surface energy of the polymer, which in turn can result in poor coating and optical cosmetic properties.

A loss in interfacial adhesion between these layers will compromise the AR film durability.

While these coatings are ideally suited for floor coatings, they have never been investigated for use in antireflection film layers.

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