Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
2001-11-13
2004-04-13
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S212000, C428S220000, C428S483000, C252S582000
Reexamination Certificate
active
06720061
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optically active film composites, and in particular but not exclusively to window film of the type adhered to the surfaces of already existing windows of buildings and vehicles.
BACKGROUND AND SUMMARY OF THE INVENTION
Certain block copolymer solutions are known to form distinctive morphologies and may spontaneously separate into microdomains when they are cooled from the melt or solvent is evaporated from solutions of the copolymers. The size, shape, spacing and number of the microdomains can be controlled through the selection of the relative amounts of the various comonomers, their molecular weight, and the thermodynamic incompatibility of the copolymer components. All this is disclosed in U.S. Pat. No. 5656205 and U.S. Pat. No. 5622668. In particular it is known that when the percentage volumes of the two components of the copolymers are substantially 50:50 the block copolymer will segregate into lamellar microdomains of the component polymers.
French Patent 2138 645 discloses a method for making high molecular weight block copolymers having lamellar layers of different refractive indices.
The present invention uses the known properties of block copolymers to produce film composites which are particularly useful for window film.
Accordingly there is provided an optically active layered composite comprising a substrate having thereon at least one layer of block copolymer film comprising at least two polymeric components separated into lamellar microdomains of each polymeric component, which components have different refractive indices.
Optical properties include reflectance properties and light transmission properties.
Typically the block copolymer comprises between 30:70 and 70:30 volume percent of each component of the copolymer, preferably between 40:60 to 60:40 volume percent of each component, and more preferably 50:50 by volume of each component.
Polystyrene:polybutadiene (PS-PB) block copolymers can produce lamellar structures with a styrene butadiene volume ratio of 30:70, and polybutadiene-polyethylene oxide block copolymers will produce lamellar structures with a 30:70 volume ratio of butadiene:ethylene oxide.
The block copolymer film is optically clear, that is essentially haze free, and the difference between the refractive indices of the two components should be at least 0.08. The block copolymer layer preferably reflects at least 50% of incident light of selected wavelengths.
The substrate may be covered in a plurality of layers of block copolymer film, and the repective block copolymer in one layer may be different than the respective copolymer in another layer so that different film layers selectively reflect different wavelegths of incident light.
The preferred substrate is a transparent substrate, preferably a polymeric film, typically polyethylene terephthalate (PET), and preferably the block copolymer layer is sandwiched between two film substrates. The substrate film may have a thickness of about 12-50 microns, as is typically used for window film.
The block copolymer typically contains as one component a high refractive index polymer such as polystyrene and the other component may comprise a lower refractive index polymer such as at least one of the following: polyisoprene, polybutadiene, polymethyl methacrylate, polydimethylsiloxane, polyethylene-butylene (hydrogenated polybutadiene).
The copolymer may be in form of diblock copolymers A-B where A & B are different polymer components, or triblock copolymers A-B-A.
The lamellar microdomains are formed with the two polymers forming alternating domains of components A & B formed from an AB or ABA block copolymer. The thickness of a pair of adjacent domains in lamellar morphology is referred to as the “d” spacing. The “d” spacing is determined by the molecular weight (MW) of the copolymer and will be the same (for a given MW) for AB or ABA copolymer.
The thickness of the lamellae is related to the molecular weight by the equation:
d=K Mn
⅔
where k is a constant for the particular pair of polymers in the block copolymer; and
d is the lamellar thickness of two adjacent domains in nanometer; and
Mn=number average molecular weight of the copolymer in g/mole.
For example, for a styrene:butadiene block copolymer
d
=0.024 Mn
⅔
(Hashimoto et al Macromolecules 1980, 13, 1237)
It is therefore possible to make film composites that reflect light of a particular band width by selection of the molecular weight of the copolymer.
For a PS-PB block copolymer the number average molecular weight (Mn) of the block copolymer is in the range of 200,000 to 2000,000, preferably 250,000-1000000, and more preferably 300,000-600,000.
The “d” spacing is not affected in theory by the thickness of the applied block copolymer layer. Thickness does affect the number of lamellar domain pairs. For example, a 1 micron coating of an AB block copolymer having a molecular weight such that it forms a lamellar morphology with a “d” spacing of 100 nm, will segregate into 10 lamellar domain pairs of A & B, and hence 20 alternating lamellae of A & B.
Reflection is best provided by lamellar domains having a thickness of about ¼ wavelength. The wave length of light varies with the refractive index of the material through which it is passing according to the formula:
λ
material
=
λ
air
η
material
where &lgr;=wavelength, &eegr;= refractive index.
The film composite may be made to reflect particular wave bands of light by selection of the copolymer component to provide “tailored” average thickness lamellae. For example for a block copolymer having a refractive index of between 1.5-1.6 (typical for polymers) a UV light (&lgr;=350 nm) is reflected by lamellae having a thickness of about 60 nm. IR light (&lgr;800-1500 nm) is reflected by lamellae having a thickness of between 140-250 nm, and visible light (&lgr;400-800 nm) is reflected by lamellae having a thickness of between 70-140 nm. In practice, it is believed that the maximum thickness of lamellae that can produced will be about 170 nm.
The “d” spacing may also be increased by the inclusion of a diluent either in the form of a compatible solvent, plasticizer, or homopolymer. Typical solvents are cumene, or chloroform with PS-PB block copolymer, or toluene with the block copolymers of polystyrene/polyisoprene; polystyrene/polybutadiene; polystyrene/polymethyl methacrylate; polystyrene/polydimethylsiloxane. Typical plasticizers may include hydrocarbon oils for use with polybutadiene.
The volume fractions of each copolymer may be made up entirely of the respective copolymer component, or copolymer plus a compatible homopolymer diluent. The compatible homopolymer may comprise the homopolymer of a respective copolymer component. For example polystyrene or polybutadiene may be mixed with PS-PB block copolymer, to achieve a total volume ratio of polystyrene:polybutadiene of about 1:1. Alternatively, or additionally the homopolymer may comprise a different homopolymer, for example poly 2,6 dimethylphenylene oxide may be added to swell the polystyrene phase of a block copolymer.
Homopolymer polystyrene may be added to a PS-PB copolymer consisting of a 30:70 ratio polystyrene:polybutadiene to raise the polystyrene ratio from 30:70 to 60:40 polystyrene:polybutadiene. The diluent homopolymer should have a lower molecular weight than the block copolymer to which it is added. Preferably the molecular weight of the homopolymer should not exceed 40% of the molecular weight of the block copolymer to which it is added.
When a block copolymer is blended with a homopolymer the properties of the lamellar domains are related to the molecular weights of the-various components by a factor &agr;, where:
α
=
(
NaNb
)
Nab
<
0.5
where Na is the number average degree of polymerisation of homopolymer component a, Nb is the number average degree of polymerisation of homopolymer component b, Nab is the number average degree of polymerisation o
Fairclough John P. A.
Port Anthony B.
Ryan Anthony J.
Salou Corrine L. O.
Nixon & Vanderhye P.C.
Pyon Harold
Simone Catherine A.
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