U.S. patent application number 12/170903 was filed with the patent office on 2008-10-30 for modified copolyesters and optical films including modified copolyesters.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Bert T. Chien, Martin E. Denker, Kristopher J. Derks, Timothy J. Hebrink, Matthew B. Johnson, Fuming B. Li, William W. Merrill, Richard J. Thompson.
Application Number | 20080268219 12/170903 |
Document ID | / |
Family ID | 35502530 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080268219 |
Kind Code |
A1 |
Hebrink; Timothy J. ; et
al. |
October 30, 2008 |
MODIFIED COPOLYESTERS AND OPTICAL FILMS INCLUDING MODIFIED
COPOLYESTERS
Abstract
Modified copolyesters having relatively low refractive indices
and relatively high glass transition temperatures are disclosed.
These modified copolyesters can be used in forming one or more
layers in an optical film, such as a multilayer polymer film.
Inventors: |
Hebrink; Timothy J.;
(Oakdale, MN) ; Denker; Martin E.; (Vadnais
Heights, MN) ; Chien; Bert T.; (St. Paul, MN)
; Johnson; Matthew B.; (St. Paul, MN) ; Thompson;
Richard J.; (Lino Lakes, MN) ; Derks; Kristopher
J.; (Maplewood, MN) ; Merrill; William W.;
(White Bear Lake, MN) ; Li; Fuming B.; (Woodburry,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
35502530 |
Appl. No.: |
12/170903 |
Filed: |
July 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12036840 |
Feb 25, 2008 |
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12170903 |
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10967582 |
Oct 18, 2004 |
7345137 |
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12036840 |
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Current U.S.
Class: |
428/213 |
Current CPC
Class: |
Y10T 428/31786 20150401;
C08G 63/183 20130101; Y10T 428/2495 20150115; Y10T 428/31507
20150401; C08G 63/181 20130101; B32B 27/36 20130101; Y10T 428/24942
20150115; C08G 63/189 20130101 |
Class at
Publication: |
428/213 |
International
Class: |
B32B 7/02 20060101
B32B007/02 |
Claims
1. A multilayered polymer film, comprising: a plurality of first
optical layers comprising a birefringent first copolyester or
polyester; a plurality of second optical layers comprising a
birefringent second copolyester; and a skin layer disposed on the
plurality of first optical layers or plurality of second optical
layers, the skin layer having a thickness that is at least 10 times
a thickness of an individual first or second optical layer.
2. The multilayered polymer film of claim 1, wherein the plurality
of first and second optical layers are arranged in alternating
pairs.
3. The multilayered polymer film of claim 1 having about 25 to 2000
optical layers.
4. The multilayered polymer film of claim 1, wherein the skin layer
has a thickness of at least 12 micrometers.
5. The multilayered polymer film of claim 1, wherein the skin layer
is not birefringent.
6. The multilayered polymer film of claim 1, wherein the skin layer
has a higher index of refraction than the first and second optical
layers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S. Ser.
No. 12/036,840, filed Feb. 25, 2008, which is a divisional
application of U.S. Ser. No. 10/967,582, filed Oct. 18, 2004, now
issued as U.S. Pat. No. 7,345,157.
BACKGROUND
[0002] The present invention relates to modified copolyester
polymers and optical films including modified copolyester
polymers.
[0003] Polymeric films are used in a wide variety of applications.
One particular use of polymeric films is in mirrors and polarizers
that reflect light of a given polarization or wavelength range.
Such reflective films are used, for example, in conjunction with
backlights in liquid crystal displays to enhance brightness and
reduce glare of the display. A polarizing film may be placed
between the user and the backlight to polarize the light directed
towards the user, thereby reducing the glare. A mirror film may be
placed behind the backlight to reflect light towards the user;
thereby enhancing brightness. Another use of polarizing films is in
articles, such as sunglasses, to reduce light intensity and
glare.
[0004] One type of polymer that is useful in creating polarizer or
mirror films is a polyester. One example of a polyester-based
polarizer includes a stack of polyester layers of differing
composition. One configuration of this stack of layers includes a
first set of birefringent layers and a second set of layers with an
isotropic index of refraction. The second set of layers alternates
with the birefringent layers to form a series of interfaces for
reflecting light.
[0005] Thus, there is a need for the development of polyester films
for use in optical films such as polarizers and mirrors which have
improved properties including physical properties, optical
properties, and lower manufacturing cost.
SUMMARY
[0006] Generally, the present invention relates to modified
copolyesters and optical films including modified copolyesters. One
illustrative embodiment is a co-polyethylene naphthalate copolymer
having carboxylate subunits and glycol subunits and having a
refractive index of 1.58 or less at 632.8 nm and a glass transition
temperature of 90 degree Celsius or greater.
[0007] Another illustrative embodiment is a co-polyethylene
terephthalate copolymer having carboxylate subunits and glycol
subunits having a refractive index of less than 1.54 at 632.8 nm
and a glass transition temperature of 60 degree Celsius or
greater.
[0008] A further illustrative embodiment is a
co-t-butyl-isophthalic acid copolymer having carboxylate subunits
and glycol subunits having a refractive index of 1.53 or less at
632.8 nm and a glass transition temperature of 50 degree Celsius or
greater.
[0009] Another illustrative embodiment is a multilayered polymer
film having a plurality of first layers and a plurality of second
layers. The first layers are made with a first polyester or
copolyester which is birefringent. The second layers are made with
a second copolyester polymer being a co-polyethylene naphthalate
copolymer having carboxylate subunits and glycol subunits and
having a refractive index of 1.58 or less at 632.8 nm and a glass
transition temperature of 90 degree Celsius or greater.
[0010] Another illustrative embodiment is a multilayered polymer
film having a plurality of first layers and a plurality of second
layers. The first layers are made with a first polyester or
copolyester which is birefringent. The second layers are made with
a second copolyester polymer being a co-polyethylene terephthalate
copolymer having carboxylate subunits and glycol subunits having a
refractive index of less than 1.54 at 632.8 nm and a glass
transition temperature of 60 degree Celsius or greater.
[0011] A further illustrative embodiment is a multilayered polymer
film having a plurality of first layers and a plurality of second
layers. The first layers are made with a first polyester or
copolyester which is birefringent. The second layers are made with
a second copolyester polymer being a co-t-butyl-isophthalic acid
copolymer having carboxylate subunits and glycol subunits having a
refractive index of 1.53 or less at 632.8 nm and a glass transition
temperature of 50 degree Celsius or greater.
[0012] Another embodiment is a multilayered polymer film having a
plurality of first optical layers including a birefringent first
copolyester or polyester and a plurality of second optical layers
including a second copolyester being a cycloaliphatic
copolyester/polycarbonate polymer blend and having an in-plane
birefringence of 0.04 or less at 632.8 nm, after the multilayered
polymer film has been formed.
[0013] A further embodiment is a multilayered polymer film
including a plurality of first optical layers including a
birefringent first copolyester or polyester, a plurality of second
optical layers comprising a second copolyester having an in-plane
birefringence of 0.04 or less at 632.8 nm, after the multilayered
polymer film has been formed, and a non-optical skin layer disposed
on the plurality of first optical layers or plurality of second
optical layers, the skin layer including a cycloaliphatic
copolyester/polycarbonate blend.
[0014] In a further embodiment, a multilayered polymer film is
disclosed having a plurality of first layers and a plurality of
second layers. The first layers are made with a first polyester or
copolyester which is birefringent and possesses a nearly truly
uniaxial character in its refractive indices at 632.8 nm. The
second layers are made with a second copolyester polymer being a
co-polyethylene naphthalate copolymer having carboxylate subunits
and glycol subunits and having a glass transition temperature of 90
degree Celsius or greater.
[0015] The above summary of the present invention is not intended
to describe each illustrated embodiment or every implementation of
the present invention. The figures and the detailed description
which follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0017] FIG. 1 is a schematic cross-sectional view of one embodiment
of a multilayered polymer film according to the present
invention;
[0018] FIG. 2 is a schematic cross-sectional view of another
embodiment of a multilayered polymer film according to the present
invention; and
[0019] FIG. 3 is a schematic cross-sectional view of another
embodiment of a multilayered polymer film according to the present
invention.
[0020] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0021] The present invention relates to modified copolyesters and
multilayered polymer films formed from the modified copolyesters
for optical applications and the use of comonomer subunits to
enhance the properties of the polymer films. The properties of a
given polyester are typically determined by the monomer materials
utilized in the preparation of the polyester. A polyester is often
prepared by reactions of one or more different carboxylate monomers
(e.g., compounds with two or more carboxylic acid or ester
functional groups) with one or more different glycol monomers
(e.g., compounds with two or more hydroxy functional groups). Each
set of polyester layers in the stack typically has a different
combination of monomers to generate the desired properties for each
type of layer.
[0022] For the following defined terms, these definitions shall be
applied, unless a different definition is given in the claims or
elsewhere in this specification.
[0023] The term "polymer" will be understood to include polymers,
copolymers (e.g., polymers formed using two or more different
monomers), oligomers and combinations thereof, as well as polymers,
oligomers, or copolymers that can be formed in a miscible blend by,
for example, coextrusion or reaction, including
transesterification. Both block and random copolymers are included,
unless stated otherwise.
[0024] Unless otherwise stated, all numbers expressing quantities
of ingredients, properties such as molecular weight, reaction
conditions, and so forth used in the specification and claims are
to be understood as being modified in all instances by the term
"about." Accordingly, unless stated to the contrary, the numerical
parameters set forth in the foregoing specification and attached
claims are approximations that can vary depending upon the desired
properties sought to be obtained by those skilled in the art
utilizing the teachings of the present invention.
[0025] Mole percent or mol % and the like are synonyms that refer
to the concentration of a substance as the moles of that substance
divided by the moles of the composition and multiplied by 100.
[0026] The recitation of numerical ranges by endpoints includes all
numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2,
2.75, 3, 3.80, 4, and 5) and any range within that range.
[0027] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the content clearly dictates otherwise. Thus, for example,
reference to a composition containing "a polymer" includes a
mixture of two or more polymers. As used in this specification and
the appended claims, the term "or" is generally employed in its
sense including "and/or" unless the content clearly dictates
otherwise.
[0028] FIG. 1 shows a multilayered polymer film 10 which may be
used, for example, as an optical polarizer or mirror. The film 10
includes one or more first optical layers 12, one or more second
optical layers 14, and one or more non-optical layers 18. The first
optical layers 12 are preferably birefringent polymer layers which
are uniaxially- or biaxially-oriented. The second optical layers 14
may also be polymer layers which are birefringent and uniaxially-
or biaxially-oriented. More typically, however, the second optical
layers 14 have an isotropic index of refraction which is different
from at least one of the indices of refraction of the first optical
layers 12 after orientation. The methods of manufacture and use, as
well as design considerations for the multilayered polymer films 10
are described in detail in U.S. Pat. No. 5,882,774 and U.S.
2001/0011779A1, the disclosures of which are incorporated by
reference herein to the extent they are not inconsistent with the
present disclosure. Although, the present invention will be
primarily exemplified by films 10 with second optical layers 14
which have an isotropic index of refraction, the principles and
examples described herein may be applied to multilayered polymer
films with second optical layers 14 that are birefringent, as
described in U.S. Pat. No. 6,113,811, the disclosure of which is
incorporated by reference herein to the extent it is not
inconsistent with the present disclosure.
[0029] Additional sets of optical layers, similar to or different
from the first and second optical layers 12, 14, may also be used
in the multilayered polymer film 10. The design principles
disclosed herein for the sets of first and second optical layers
may be applied to any additional sets of optical layers.
Furthermore, it will be appreciated that, although only a single
stack 16 is illustrated in FIG. 1, the multilayered polymer film 10
may be made from multiple stacks that are subsequently combined to
form the film 10.
[0030] The optical layers 12, 14 and, optionally, one or more of
the non-optical layers 18 are typically placed one on top of the
other to form a stack 16 of layers. Usually the optical layers 12,
14 are arranged as alternating pairs, as shown in FIG. 1, to form a
series of interfaces between layers with different optical
properties. The optical layers 12, 14 can be less than 1 .mu.m
thick, although thicker layers may be used. Furthermore, although
FIG. 1 shows only six optical layers 12, 14, many multilayered
polymer films 10 have a large number of optical layers. In some
embodiments, multilayered polymer films have about 2 to 5000
optical layers, or about 25 to 2000 optical layers, or about 50 to
1500 optical layers, or about 75 to 1000 optical layers, as
desired.
[0031] The non-optical layers 18 can be polymer layers that are
disposed within (see FIG. 2) and/or over (see FIG. 1) the stack 16
to protect the optical layers 12, 14 from damage, to aid in the
co-extrusion processing, and/or to enhance post-processing
mechanical properties. The non-optical layers 18 can be thicker
than the optical layers 12, 14. The thickness of the non-optical
layers 18 can be at least two times, or at least four times, or at
least ten times, the thickness of the individual optical layers 12,
14, but it can also be any thickness suitable for a particular
application. For example, the thickness of the non-optical layers
18 may be varied to make a multilayer polymer film 10 having a
particular thickness. In some embodiments, one or more of the
non-optical layers 18 are placed so that at least a portion of the
light to be transmitted, polarized, and/or reflected by the optical
layers 12, 14, also travels through the non-optical layers (i.e.,
the non-optical layers are placed in the path of light which
travels through or is reflected by the optical layers 12, 14).
[0032] The optical layers 12, 14 and the non-optical layers 18 of
the multilayered polymer film 10 can be composed of polymers such
as polyesters. Polyesters include carboxylate and glycol subunits
and are generated by reactions of carboxylate monomer molecules
with glycol monomer molecules. Each carboxylate monomer molecule
has two or more carboxylic acid or ester functional groups and each
glycol monomer molecule has two or more hydroxy functional groups.
The carboxylate monomer molecules may all be the same or there may
be two or more different types of molecules. The same applies to
the glycol monomer molecules. The term "polymer" will be understood
to include both polymers and copolymers, as well as polymers or
copolymers which may be formed in a miscible blend, for example, by
coextrusion or by reaction, including, for example,
transesterification.
[0033] Suitable carboxylate monomer molecules for use in forming
the carboxylate subunits of the polyester layers include, for
example, 2,6-naphthalene dicarboxylic acid and isomers thereof,
terephthalic acid; isophthalic acid; phthalic acid; azelaic acid;
adipic acid; sebacic acid; norbornene dicarboxylic acid;
bi-cyclooctane dicarboxylic acid; 1,6-cyclohexane dicarboxylic acid
and isomers thereof, t-butyl isophthalic acid, tri-mellitic acid,
sodium sulfonated isophthalic acid; 4,4-biphenyl dicarboxylic acid
and isomers thereof, and lower alkyl esters of these acids, such as
methyl or ethyl esters. The term "lower alkyl" refers, in this
context, to C.sub.1-C.sub.10 straight-chained or branched alkyl
groups. Also included within the term "polyester" are
polycarbonates which are derived from the reaction of glycol
monomer molecules with esters of carbonic acid, and blends of
polycarbonates with copolyesters made from the above
comonomers.
[0034] Tertiary butyl isophthalate (tbia) has surprisingly been
found useful for some exemplary embodiments of the present
disclosure due to the inverse effect it has on the polymer
properties of glass transition temperature and refractive index.
Increasing the mol portion of tbia can increase the glass
transition temperature of the copolymer while at the same time
decrease its refractive index.
[0035] Suitable glycol monomer molecules for use in forming glycol
subunits of the polyester layers include ethylene glycol; propylene
glycol; 1,4-butanediol and isomers thereof, 1,6-hexanediol;
neopentyl glycol; polyethylene glycol; diethylene glycol;
tricyclodecanediol; 1,4-cyclohexanedimethanol and isomers thereof;
2-butyl-2-ethyl-1,3-propane diol; 2,2,4-triethyl-1,3-pentane diol;
norbornanediol; bicyclo-octanediol; trimethylol propane;
pentaerythritol; 1,4-benzenedimethanol and isomers thereof,
bisphenol A; 1,8-dihydroxy biphenyl and isomers thereof, and
1,3-bis(2-hydroxyethoxy)benzene.
[0036] 1,4-cyclohexane dimethanol (chdm) also has been found useful
for some exemplary embodiments of the present disclosure due to the
inverse effect it has on the polymer properties of glass transition
temperature and refractive index. Increasing the mol portion of
chdm can increase the glass transition temperature of the copolymer
while at the same time decrease its refractive index. In
particular, copolyesters containing both tbia and chdm were found
to have relatively high glass transition temperatures for their
respective refractive indices.
[0037] The first optical layers 12 can be orientable polymer films,
such as polyester films, which may be made birefringent by, for
example, stretching the first optical layers 12 in a desired
direction or directions. The term "birefringent" means that the
indices of refraction in orthogonal x, y, and z directions are not
all the same. For films or layers in a film, a convenient choice of
x, y, and z axes is shown in FIG. 1 in which the x and y axes
correspond to the length and width of the film or layer and the z
axis corresponds to the thickness of the layer or film. In the
embodiment illustrated in FIG. 1, the film 10 has several optical
layers 12, 14 which are stacked one on top of the other in the
z-direction.
[0038] The first optical layers 12 may be uniaxially-oriented, for
example, by stretching in a single direction. Typically, stretching
in one film in-plane direction causes drawdown in at least one
other orthogonal direction, usually the thickness direction of the
film, to preserve approximate volume conservation (as corrected by
density changes, e.g. due to crystallization) upon stretching. In
one embodiment, the direction of stretching substantially
corresponds to either the x or y in-plane axis shown in FIG. 1.
However, other directions may be chosen. In one illustrative
embodiment of a uniaxial stretch, the film is stretched in one
direction and the film contracts in two orthogonal directions to
this stretch direction, e.g. in the non-drawn (or non-stretched)
in-plane direction and the thickness direction. When the relative
amount of contraction is similar in these directions, the first
optical layers 12 attain relatively similar refractive indices in
these directions perpendicular to stretch. Likewise, the maximum
birefringence of the first optical layers 12 measured in this plane
normal to the stretch direction is small relative to the main
in-plane birefringence of these same first optical layers 12. The
first optical layers 12 are then truly or nearly truly uniaxially
oriented. One useful method to achieve such orientation is
described in U.S. Patent Application Publications US2004/0099992
and US2002/0190406, the disclosures of which are incorporated by
reference herein to the extent they are not inconsistent with the
present disclosure. Another useful method is described in U.S. Pat.
No. 6,609,795, the disclosure of which is incorporated by reference
herein to the extent it is not inconsistent with the present
disclosure. In any case, a birefringent, uniaxially-oriented layer
typically exhibits a difference between the transmission and/or
reflection of incident light rays having a plane of polarization
parallel to the oriented direction (i.e., stretch direction) and
light rays having a plane of polarization parallel to a transverse
direction (i.e., a direction orthogonal to the stretch direction).
For example, when an orientable polyester film is stretched along
the x axis, the typical result is that n.sub.x.noteq.n.sub.y, or
n.sub.x.noteq.n.sub.z where n.sub.x, n.sub.z, and n.sub.y are the
indices of refraction for light polarized in a plane parallel to
the "x," "z" and "y" axes, respectively. The degree of alteration
in the index of refraction along the stretch direction will depend
on factors such as the amount of stretching, the stretch rate, the
temperature of the film during stretching, the thickness of the
film, the variation in the film thickness, and the composition of
the film. In some embodiments, the first optical layers 12 have a
maximum in-plane birefringence (e.g., the absolute value of
n.sub.x-n.sub.y in the absence of shearing rotation or bowing
during stretching) after orientation of 0.04 or greater at 632.8
nm, or about 0.1 or greater, or about 0.2 or greater. In some
embodiments of nearly truly uniaxially oriented films, the maximum
birefringence in the plane normal to the stretch (the absolute
value of n.sub.y-n.sub.z) of the first optical layers 12 is 0.03 or
less at 632.8 nm, 0.02 or less or even 0.01 or less. For a nearly
truly uniaxial orientation, the ratio of the maximum birefringence
in the plane normal to the stretch to the maximum in-plane
birefringence is 0.2 or less, or 0.15 or less, although values of
0.1 or less, or even 0.05 or less, can be achieved. All
birefringence and index of refraction values herein are reported
for 632.8 nm light unless otherwise indicated.
[0039] The birefringence of a material can be increased by
increasing the molecular orientation. Many birefringent materials
are crystalline or semicrystalline. The term "crystalline" will be
used herein to refer to both crystalline and semicrystalline
materials. PEN and other crystalline polyesters, such as
polybutylene naphthalate (PBN), polypropylene naphthalate (PPN),
polyhexamethylene naphthalate (PHN), polyethylene terephthalate
(PET), polybutylene terephthalate (PBT), polypropylene
terephthalate (PPT), and polyhexamethylene terephthalate (PHT) are
examples of crystalline materials useful in the construction of
birefringent film layers, such as is often the case for the first
optical layers 12. In addition, some copolymers of PEN, PPN, PBN,
PHN, PET, PPT, PBT, and PHT are also crystalline or
semicrystalline. The addition of a comonomer to PEN, PPN, PBN, PHN,
PET, PPT, PBT, or PHT may enhance other properties of the material
including, for example, adhesion to the second optical layers 14 or
the non-optical layers 18 and/or the lowering of the working
temperature (i.e., the temperature for extrusion and/or stretching
the film), as desired.
[0040] In some embodiments, the first optical layers 12 are made
from a semicrystalline, birefringent polyester or copolyester
which, in some exemplary embodiments, can include 70 to 100 mol %
of a first carboxylate subunit and 0 to 30 mol % of comonomer
carboxylate subunits. The comonomer carboxylate subunits may be one
or more of the subunits indicated hereinabove. In some embodiments,
first carboxylate subunits include naphthalate and
terephthalate.
[0041] If the polyester material of the first optical layers 12
contains more than one type of carboxylate subunit, then the
polyester may be a block copolyester to enhance adhesion to other
layers (e.g., the second optical layers 14 or non-optical layers
18) made from block copolymers having similar blocks. Random
copolyesters may also be used.
[0042] In other embodiments, the first optical layers 12 are made
from a semicrystalline, birefringent polyester or copolyester which
includes 70 to 100 mol % of a first glycol subunit and 0 to 30 mol
% of comonomer glycol subunits. The comonomer glycol subunits may
be one or more of the subunits indicated hereinabove. In some
embodiments, first glycol subunits are derived from C.sub.2-C.sub.8
diols.
[0043] Yet other embodiments include first optical layers 12 where
both of the carboxylate and glycol subunits include comonomer
subunits. For these embodiments, at least 0.5 mol %, or at least
2.5 mol %, of the combined carboxylate and glycol subunits are
comonomer carboxylate subunits, comonomer glycol subunits, or a
combination thereof.
[0044] In some embodiments, a multilayered polymer film 10 may be
formed using first optical layers 12 that are made from a coPEN
which has the same in-plane birefringence for a given draw ratio
(i.e., the ratio of the length of the film in the stretch direction
after stretching and before stretching) as a similar multilayered
polymer film formed using PEN for the first optical layers. The
matching of birefringence values may be accomplished by the
adjustment of processing parameters, such as the processing or
stretch temperatures or the processing or stretch rates. Often
coPEN optical layers have an index of refraction in the draw
direction which is at least 0.02 units less than the index of
refraction of the PEN optical layers in the draw direction. The
birefringence is maintained because there is a decrease in the
index of refraction in a non-draw direction.
[0045] In some embodiments, PEN often has an in-plane index of
refraction that is 1.84 or higher and the difference between the
in-plane indices of refraction is about 0.22 to 0.24 or more when
measured using 632.8 nm light. The in-plane refractive index
differences, or birefringence, of the first optical layers, whether
they be PEN or coPEN, may be reduced to less than 0.2 to improve
properties, such as interlayer adhesion. Similar comparisons
between suitable coPBN and coPET polymers for the first layers can
be made with PBN and PET.
[0046] The second optical layers 14 may be made from a variety of
polymers. The second optical layers 14 can be made from a variety
of copolymers of polyesters (i.e., copolyesters.) Illustrative
copolyesters useful in the second optical layers 14 include, coPEN,
coPET and co-TBIA copolymers, for example.
[0047] In some embodiments, the second optical layers 14 are
uniaxially or biaxially orientable. However, more typically the
second optical layers 14 are not oriented under the processing
conditions used to orient the first optical layers 12. These second
optical layers 14 typically retain a relatively isotropic index of
refraction, even when stretched. Preferably, the second optical
layers have a birefringence (e.g., |n.sub.x-n.sub.y| or
|n.sub.x-n.sub.y|) of less than about 0.04 or less than about 0.02
at 632.8 nm.
[0048] One illustrative copolyester useful for forming the second
optical layers is a coPEN polymer. The coPEN polymers of the
present disclosure have low in-plane indices of refraction (e.g.,
n.sub.x or n.sub.y or both) while maintaining relatively high glass
transition temperatures. Some illustrative coPEN polymers have
in-plane indices of refraction that are less than 1.59, for
example, 1.58 or less, with a glass transition temperature of 90
degrees Celsius or greater, 100 degrees Celsius or greater, or 102
degrees Celsius or greater. Other illustrative coPEN polymers have
in-plane indices of refraction of 1.57 or less with a glass
transition temperature of 90 degrees Celsius or greater, or 1.56 or
less with a glass transition temperature values of 80 degrees
Celsius or greater.
[0049] In some embodiments, these coPEN copolymers include
carboxylate subunits which are derived from 10 to 50 mol %
naphthalate dicarboxylate and 30 to 90 mol % t-butyl-isophthalic
acid (TBIA) or an ester thereof and terephthalate may optionally be
present up to 50 mol % or 0 to 50 mol %. Higher refractive indices
and higher glass transition temperature can be achieved by
increasing the naphthalate dicarboxylate content.
[0050] The coPEN copolymers also include glycol subunits which are
derived from, in some embodiments, 10 to 90 mol % cycloaliphatic
diol, and 10 to 90 mol % branching diol and 1,2 ethane diol may be
optionally present up to 10 mol % or 1-10 mol %. Branching diols
include, for example, neopentyl glycol, 2-butyl-2-ethyl-1,3-propane
diol, 2,2,4-triethyl pentane diol, and bisphenol A. In some
embodiments, these coPEN copolymers include glycol subunits which
are derived from 15 to 85 mol % cycloaliphatic diol, and 15 to 85
mol % branching diol. Cycloaliphatic diol refers to an alicyclic
diol. Examples include, cyclohexane diols, and cyclopentane diols.
One illustrative cycloaliphatic diol is 1,4-cyclohexane
dimethanol.
[0051] The coPEN copolymers also can include carboxylate or glycol
subunits that have more than two functional groups. In some
embodiments, the coPEN includes 0.01 to 2.5 mol % of carboxylate or
glycol subunits derived from compounds having three or more
carboxylate or ester functionalities, three or more hydroxyl
functionalities, or a combination thereof. These comonomer
materials include, for example, trimethylol propane, tri-mellitic
acid, and pentaerythritol. These comonomers may be distributed
randomly in the coPEN polyester or they may form one or more blocks
in a block copolymer. The addition of these comonomer subunits
derived from compounds with three or more carboxylate, ester, or
hydroxy functionalities may also decrease the birefringence of the
copolyester of the second layers. These compounds can crosslink
with other polymer molecules. In some embodiments of the invention,
the copolyester of the second layer includes 0.01 to 5 mol %, or
0.1 to 2.5 mol %, of these compounds.
[0052] One illustrative example of a coPEN has carboxylate subunits
derived from 35 to 45 mol % naphthalate dicarboxylate and 40 to 50
mol % TBIA, and 10-20 mol % terephthalate; and glycol subunits
derived from 50 to 70 mol % 1,4-cyclohexane dimethanol and 20 to 40
mol % neopentyl glycol, and 5-30 mol % 1,2 ethane diol. This
illustrative coPEN has a refractive index of 1.56-1.58 and a glass
transition temperature (Tg) of 100 to 105 degrees Celsius. Other
exemplary coPEN polymers can be produced with a Tg of 106 to 107
degrees Celsius that have a refractive index of about 1.58. Such
higher Tgs can be achieved, for example, by increasing the
naphthalate dicarboxylate content.
[0053] Another illustrative copolyester useful for forming the
second optical layers is a coPET polymer. These coPET polymers have
low in-plane indices of refraction (e.g., n.sub.x or n.sub.y or
both) with relatively high glass transition temperature values.
Some illustrative coPET polymers has in-plane indices of refraction
that are 1.55 or less with a Tg of 80 degrees Celsius or greater,
or 1.54 or less with a Tg of 70 degrees Celsius or greater, or 1.53
or less with a glass transition temperature values of 60 degrees
Celsius or greater. For example, illustrative coPET polymers of the
present disclosure can be produced with a Tg of about 75 degrees
Celsius that have a refractive index of about 1.53. Such higher Tgs
can be achieved, for example, by increasing the TBIA content.
Increasing terephthalate content also increases Tg while also
increasing the refractive index.
[0054] In some embodiments, these coPET copolymers include
carboxylate subunits which are derived from 10 to 50 mol % dimethyl
terephthalate, 20 to 50 mol % cycloaliphatic dicarboxylate, and 20
to 60 mol % t-butyl-isophthalic acid (TBIA) or an ester thereof. In
other embodiments, these coPET copolymers include carboxylate
subunits which are derived from 15 to 45 mol % dimethyl
terephthalate, 25 to 45 mol % cycloaliphatic dicarboxylate, and 25
to 55 mol % TBIA or an ester thereof.
[0055] The coPET copolymers also include glycol subunits which are
derived from, in some embodiments, 10 to 90 mol % cycloaliphatic
diol, and 10 to 90 mol % branching diol and 1,2 ethane diol may be
optionally present up to 10 mol % or 1-10 mol %. Branching diols
include, for example, neopentyl glycol, 2-butyl-2-ethyl-1,3-propane
diol, 2,2,4-triethyl pentane diol, and bisphenol A. In other
embodiments, these coPEN copolymers include glycol subunits which
are derived from 15 to 85 mol % cycloaliphatic diol, and 15 to 85
mol % branching diol. Cycloaliphatic diol refers to an alicyclic
diol. Examples include, cyclohexane diol, and cyclopentane diol.
One illustrative cycloaliphatic diol is dimethyl cyclohexane
diol.
[0056] The coPET copolymers also can include carboxylate or glycol
subunits that have more than two functional groups. In some
embodiments, the coPET includes 0.01 to 2.5 mol % of carboxylate or
glycol subunits derived from compounds having three or more
carboxylate or ester functionalities, three or more hydroxyl
functionalities, or a combination thereof. These comonomer
materials include, for example, trimethylol propane, trimellitic
acid, and pentaerythritol. These comonomers may be distributed
randomly in the coPET polyester or they may form one or more blocks
in a block copolymer. The addition of these comonomer subunits
derived from compounds with three or more carboxylate, ester, or
hydroxy functionalities may also decrease the birefringence of the
copolyester of the second layers. These compounds can crosslink
with other polymer molecules. In some embodiments of the invention,
the copolyester of the second layer includes 0.01 to 5 mol %, or
0.1 to 2.5 mol %, of these compounds.
[0057] One illustrative example of a coPET has carboxylate subunits
derived from 10 to 40 mol % dimethyl terephthalate, 30 to 45 mol %
cycloaliphatic dicarboxylate, and 30 to 45 mol % TBIA; and glycol
subunits derived from 20 to 80 mol % 1,4-cyclohexane dimethanol and
20 to 80 mol % neopentyl glycol, and 5-50 mol % 1,2 ethane diol.
This illustrative coPET has a refractive index of 1.53 to 1.54 and
a glass transition temperature of 60 to 70 degrees Celsius. Other
illustrative coPET polymers of the present disclosure can be
produced, for example, with a Tg of about 75 degrees Celsius that
have a refractive index of about 1.53. Such higher Tgs can be
achieved, for example, by increasing the TBIA content. Increasing
terephthalate content also increases Tg while also increasing the
refractive index.
[0058] Another type of useful copolyester for forming the second
optical layers is a copolyester having cyclohexane dicarboxylate
subunits and TBIA subunits and is referred to as "coTBIA." These
coTBIA polymers have low in-plane indices of refraction (e.g.,
n.sub.x or n.sub.y or both) that are 1.53 or less with a glass
transition temperature (Tg) of greater than 60 degrees Celsius, or
1.52 or less with a glass transition temperature of 55 degrees
Celsius, or 1.51 or less with a glass transition temperature value
of 50 degrees Celsius or greater.
[0059] In some embodiments, these coTBIA copolymers include
carboxylate subunits which are derived from 30 to 70 mol %
cycloaliphatic dicarboxylate, and 30 to 70 mol % TBIA or an ester
thereof. In other embodiments, these coTBIA copolymers include
carboxylate subunits which are derived from 40 to 60 mol %
cycloaliphatic dicarboxylate, and 40 to 60 mol % TBIA or an ester
thereof.
[0060] The coTBIA copolymers also include glycol subunits which are
derived from, in some embodiments, 10 to 90 mol % cycloaliphatic
diol, and 10 to 90 mol % branching diol and 1,2 ethane diol may be
optionally present up to 10 mol % or 1-10 mol %. Branching diols
include, for example, neopentyl glycol, 2-butyl-2-ethyl-1,3-propane
diol, 2,2,4-triethyl pentane diol. In other embodiments, these
coTBIA copolymers include glycol subunits which are derived from 20
to 80 mol % cycloaliphatic diol, and 20 to 80 mol % branching diol.
Cycloaliphatic diol refers to an alicyclic diol. Examples include,
cyclohexane diol, and cyclopentane diols. One illustrative
cycloaliphatic diol is 1,4-dimethyl cyclohexane dimethanol.
[0061] The coTBIA copolymers also can include carboxylate or glycol
subunits that have more than two functional groups. In some
embodiments, the coTBIA copolymers include 0.01 to 2.5 mol % of
carboxylate or glycol subunits derived from compounds having three
or more carboxylate or ester functionalities, three or more
hydroxyl functionalities, or a combination thereof. These comonomer
materials include, for example, trimethylol propane, trimellitic
acid, and pentaerythritol. These comonomers may be distributed
randomly in the coPEN polyester or they may form one or more blocks
in a block copolymer. The addition of these comonomer subunits
derived from compounds with three or more carboxylate, ester, or
hydroxy functionalities may also decrease the birefringence of the
copolyester of the second layers. These compounds crosslink with
other polymer molecules. In some embodiments of the invention, the
copolyester of the second layer includes 0.01 to 5 mol %, or 0.1 to
2.5 mol %, of these compounds.
[0062] One illustrative example of a coTBIA copolymer has
carboxylate subunits derived from 40 to 60 mol % dimethyl
cyclohexane dicarboxylate, and 40 to 60 mol % TBIA; and glycol
subunits derived from 30 to 70 mol % 1,4-cyclohexane dimethanol and
30 to 70 mol % branching diol. This illustrative coTBIA has a
relatively low refractive index of 1.51-1.52 and a relatively high
glass transition temperature of 60 to 70 degrees Celsius. Other
illustrative coTBIA polymers of the present disclosure can be
produced, for example, with a Tg of about 73 degrees Celsius that
have a refractive index of about 1.53 or with a Tg of about 67
degrees Celsius that have a refractive index of about 1.52. Such
higher Tgs can be achieved, for example, by increasing the TBIA
content.
[0063] Another copolyester useful for forming the second optical
layers and non-optical skin layers is a blend of a copolyester and
polycarbonate such as, for example, a cyclo-aliphatic copolyester
(such as, coPET) and polycarbonate which can transesterify into a
new cyclo-aliphatic copolyester containing bisphenol A. These
copolyester-carbonates have low in-plane indices of refraction
(i.e., n.sub.x or n.sub.y or both) that are 1.57 or less with a Tg
greater than 100 degrees Celsius, or greater than 105 degrees
Celsius, or greater than 110 degrees Celsius. One such copolyester
is commercially available from GE Plastics under the trademark
Xylex, and another is commercially available from Eastman Chemical
under the trademark SA115. In some embodiments, additional
polycarbonate can be blended with either Xylex or SA115 to increase
the polymer blend Tg for improved dimensional stability.
[0064] Still another useful copolyester useful for forming the
second optical layers and non-optical skin layers is a blend of a
cyclo-aliphatic CoPEN and polycarbonate which can transesterify
into a new cyclo-aliphatic copolyester containing bisphenol A.
These coPEN polymers have low in-plane indices of refraction (i.e.,
n.sub.x or n.sub.y or both) that are 1.64 or less with a Tg greater
than 110 degrees Celsius. In some embodiments, the polymer blend of
a copolyester and polycarbonate contains at least 20 mol %
polycarbonate.
[0065] The non-optical layers 18 may also be made from copolyesters
similar to the first or second optical layers 12, 14 using similar
materials and similar amounts of each material. The polyesters of
the first optical layers 12, the second optical layers 14, and the
non-optical layers 18 can be chosen to have similar rheological
properties (e.g., melt viscosities) so that they can be
co-extruded. The second optical layers 14 and the non-optical
layers 18 can have a glass transition temperature, T.sub.g, that is
either below or no greater than about 40.degree. C. above the glass
transition temperature of the first optical layers 12. Preferably,
the glass transition temperature of the second optical layers 14
and the non-optical layers 18 is below the glass transition
temperature of the first optical layers 12.
[0066] FIG. 3 shows one illustrative embodiment having non-optical
skin layers 20 disposed on the non-optical layers 18. Non-optical
skin layers 20 can comprise blends of cyclo-aliphatic
copolyester/polycarbonates and immiscible polymers which form
discrete minor phase particles to create haze or light scattering
centers for hiding cosmetic defects in the optical film. The
immiscible polymer minor phase particles can have a refractive
index match with the cyclo-aliphatic/polycarbonate major phase, in
which case they create haze by generating surface roughness in the
non-optical skin layers. Examples of immiscible polymer minor phase
particles having a similar refractive index to the cyclo-aliphatic
copolyesters include; polystyrene and styrene acrylo-nitrile,
styrene-acrylate copolymers, and other styrene copolymers;
copolyesters such as CoPEN-tbia and PETG. Alternatively, the
refractive index of the immiscible polymer minor phase particles
can differ from the refractive index of the major phase
cyclo-aliphatic copolyester/polycarbonate and thus generate bulk
light scattering or diffusion in the non-optical skin layers 20.
Examples of immiscible polymer minor phase particles include;
polymethyl methacrylate (PMMA), acyrilonitrile butadiene styrene
(ABS), polyamides, polyimides, and olefins such as polyethylene,
polyethylene copolymer, polypropylene, and polypropylene
copolymers.
[0067] A polarizer may be made by combining a uniaxially-oriented
first optical layer 12 with a second optical layer 14 having an
isotropic index of refraction that is approximately equal to one of
the in-plane indices of the oriented layer. Alternatively, both
optical layers 12, 14 can be formed from birefringent polymers and
are oriented in a multiple draw process so that the indices of
refraction in a single in-plane direction are approximately equal.
The interface between the two optical layers 12,14, in either case,
forms a light reflection plane. Light polarized in a plane parallel
to the direction in which the indices of refraction of the two
layers are approximately equal will be substantially transmitted.
Light polarized in a plane parallel to the direction in which the
two layers have different indices will be at least partially
reflected. The reflectivity can be increased by increasing the
number of layers or by increasing the difference in the indices of
refraction between the first and second layers 12, 14.
[0068] Typically, the highest reflectivity for a particular
interface occurs at a wavelength corresponding to twice the
combined optical thickness of the pair of optical layers 12, 14
which form the interface. The optical thickness of the two layers
is n.sub.1d.sub.1+n.sub.2d.sub.2 where n.sub.1, n.sub.2 are the
indices of refraction of the two layers and d.sub.1, d.sub.2 are
the thicknesses of the layers. The layers 12, 14 may each be a
quarter wavelength thick or the layers 12, 14 may have different
optical thicknesses, so long as the sum of the optical thicknesses
is half of a wavelength (or a multiple thereof). A film having a
plurality of layers may include layers with different optical
thicknesses to increase the reflectivity of the film over a range
of wavelengths. For example, a film may include pairs of layers
which are individually tuned to achieve optimal reflection of light
having particular wavelengths.
[0069] Alternatively, the first optical layers 12 may be
biaxially-oriented by stretching in two different directions. The
stretching of optical layers 12 in the two directions may result in
a net symmetrical or asymmetrical stretch in the two chosen
orthogonal axes.
[0070] One example of the formation of a mirror is the combination
of a biaxially-oriented optical layer 22 with a second optical
layer 24 having indices of refraction which differ from both the
in-plane indices of the biaxially-oriented layer. The mirror
operates by reflecting light having either polarization because of
the index of refraction mismatch between the two optical layers 12,
14. Mirrors may also be made using a combination of
uniaxially-oriented layers with in-plane indices of refraction
which differ significantly. In another embodiment, the first
optical layers 12 are not birefringent and a mirror is formed by
combining first and second optical layers 12, 14 which have
significantly different indices of refraction. Reflection occurs
without orientation of the layers. There are other methods and
combinations of layers that are known for producing both mirrors
and polarizers and which may be used. Those particular combinations
discussed above are merely exemplary.
[0071] The second optical layers 14 may be prepared with a variety
of optical properties depending, at least in part, on the desired
operation of the film 10. In one embodiment, the second optical
layers 14 are made of a polymer material that does not appreciably
optically orient when stretched under conditions which are used to
orient the first optical layers 12. Such layers are particularly
useful in the formation of reflective polarizing films, because
they allow the formation of a stack 16 of layers by, for example,
coextrusion, which can then be stretched to orient the first
optical layers 12 while the second optical layers 14 remain
relatively isotropic. Typically, the index of refraction of the
second optical layers 14 is approximately equal to one of the
indices of the oriented first optical layers 12 to allow
transmission of light with a polarization in a plane parallel to
the direction of the matched indices. Preferably, the two
approximately equal indices of refraction differ by about 0.05 or
less, and more preferably by about 0.02 or less, at 632.8 nm. In
one embodiment, the index of refraction of the second optical
layers 14 is approximately equal to the index of refraction of the
first optical layers 12 prior to stretching.
[0072] In other embodiments, the second optical layers 14 are
orientable. In some cases, the second optical layers 14 have one
in-plane index of refraction that is substantially the same as the
corresponding index of refraction of the first optical layers 12
after orientation of the two sets of layers 12, 14, while the other
in-plane index of refraction is substantially different than that
of the first optical layers 12. In other cases, particularly for
mirror applications, both in-plane indices of refraction of the
optical layers 12, 14 are substantially different after
orientation.
[0073] Referring again to FIGS. 1 and 2, one or more of the
non-optical layers 18 may be formed as a skin layer over at least
one surface of stack 16 as illustrated in FIG. 1, to, for example,
protect the optical layers 12, 14 from physical damage during
processing and/or afterwards. In addition, one or more of
non-optical layers 18 may be formed within the stack 16 of layers,
as illustrated in FIG. 2, to, for example, provide greater
mechanical strength to the stack or to protect the stack during
processing.
[0074] One or more strippable skin layers can be provided over the
non-optical layers 18 and/or non-optical skin layers 20. These
strippable skin layers can be used to protect the underlying
optical body during storage and shipping. The strippable skin
layers can be removed prior to use of the multilayer film. The
strippable skin layers can be disposed onto the multilayer film by
coating, extrusion, or other suitable methods or can be formed by
coextrusion or other suitable methods with the multilayer film. The
strippable skin layer can be adhered to the multilayer film using
an adhesive, although in some embodiments, no adhesive is
necessary. The strippable skin layers can be formed using any
protective polymer material than has sufficient adherence (with or
without adhesive as desired) to the multilayer film so that the
strippable skin layer will remain in place until the strippable
skin layer is removed manually or mechanically. Suitable materials
include, for example, low melting and low crystallinity polyolefins
such as copolymers of syndiotactic polypropylene (for example,
Finaplas 1571 from Atofina), copolymers of propylene and ethylene
(for example, PP8650 from Atofina), or ethylene octene copolymers
(for example, Affinity PT 1451 from Dow). Optionally, a mixture of
polyolefin materials can be utilized for the strippable skin layer.
Preferably, when the strippable skin layer is removed there will be
no remaining material from the strippable skin layer or any
associated adhesive, if used. In some embodiments, the strippable
skin layer can have a thickness of at least 12 micrometers.
[0075] The non-optical layers 18 ideally do not significantly
participate in the determination of optical properties of the
multilayered polymer film 10, other than haze generation, at least
across the wavelength region of interest. The non-optical layers 18
are typically not birefringent or orientable but in some cases this
may not be true. Typically, when the non-optical layers 18 are used
as skin layers there will be at least some surface reflection. If
the multilayered polymer film 10 is to be a polarizer, the
non-optical layers preferably have an index of refraction which is
relatively low. This decreases the amount of surface reflection. If
the multilayered polymer film 10 is to be a mirror, the non-optical
layers 18 preferably have an index of refraction which is high, to
increase the reflection of light.
[0076] When the non-optical layers 18 are found within the stack
16, there will typically be at least some polarization or
reflection of light by the non-optical layers 18 in combination
with the optical layers 12, 14 adjacent to the non-optical layers
18. Typically, however, the non-optical layers 18 have a thickness
which dictates that light reflected by the non-optical layers 18
within the stack 16 has a wavelength outside the region of
interest, for example, in the infrared region for visible light
polarizers or mirrors.
[0077] A brief description of one method for forming multilayer
polymer films is provided below. A fuller description of other
exemplary process conditions and considerations can be found in
U.S. patent application Ser. No. 09/006,288 entitled "Process for
Making Multilayer Optical Film." The multilayer polymer films are
formed by extrusion of polymers to be used in the first and second
optical layers, as well as the non-optical layers. Extrusion
conditions are chosen to adequately feed, melt, mix and pump the
polymer resin feed streams in a continuous and stable manner. Final
melt stream temperatures are chosen to be within a range which
reduces freezing, crystallization or unduly high pressure drops at
the low end of the range and which reduces degradation at the high
end of the range. The entire melt stream processing of more than
one polymer, up to and including film casting on a chill roll, is
often referred to as co-extrusion.
[0078] Following extrusion, each melt stream is conveyed through a
neck tube into a gear pump used to regulate the continuous and
uniform rate of polymer flow. A static mixing unit may be placed at
the end of the neck tube to carry the polymer melt stream from the
gear pump into a multilayer feedblock with uniform melt stream
temperature. The entire melt stream is typically heated as
uniformly as possible to enhance both uniform flow of the melt
stream and reduce degradation during melt processing.
[0079] Multilayer feedblocks divide each of two or more polymer
melt streams into many layers, interleave these layers, and combine
the many layers into a single multilayer stream. The layers from
any given melt stream are created by sequentially bleeding off part
of the stream from a main flow channel into side channel tubes
which lead to layer slots in the feed block manifold. The layer
flow is often controlled by choices made in machinery, as well as
the shape and physical dimensions of the individual side channel
tubes and layer slots.
[0080] The side channel tubes and layer slots of the two or more
melt streams are often interleaved to, for example, form
alternating layers. The feedblock's downstream-side manifold is
often shaped to compress and uniformly spread the layers of the
combined multilayer stack transversely. Thick, non-optical layers,
known as protective boundary layers (PBLs), may be fed near the
manifold walls using the melt streams of the optical multilayer
stack, or by a separate melt stream. As described above, these
non-optical layers may be used to protect the thinner optical
layers from the effects of wall stress and possible resulting flow
instabilities.
[0081] The multilayer stack exiting the feedblock manifold may then
enter a final shaping unit such as a die. Alternatively, the stream
may be split, preferably normal to the layers in the stack, to form
two or more multilayer streams that may be recombined by stacking.
The stream may also be split at an angle other than normal to the
layers. A flow channeling system that splits and stacks the streams
is called a multiplier. The width of the split streams (i.e., the
sum of the thicknesses of the individual layers) can be equal or
unequal. The multiplier ratio is defined as the ratio of the wider
to narrower stream widths. Unequal streams widths (i.e., multiplier
ratios greater than unity) can be useful in creating layer
thickness gradients. In the case of unequal stream widths, the
multiplier may spread the narrower stream and/or compress the wider
stream transversely to the thickness and flow directions to ensure
matching layer widths upon stacking.
[0082] Prior to multiplication, additional non-optical layers can
be added to the multilayer stack. These non-optical layers may
perform as PBLs within the multiplier. After multiplication and
stacking, some of these layers may form internal boundary layers
between optical layers, while others form skin layers.
[0083] After multiplication, the web is directed to the final
shaping unit. The web is then cast onto a chill roll, sometimes
also referred to as a casting wheel or casting drum. This casting
is often assisted by electrostatic pinning, the details of which
are well-known in the art of polymer film manufacture. The web may
be cast to a uniform thickness across the web or a deliberate
profiling of the web thickness may be induced using die lip
controls.
[0084] The multilayer web is then drawn to produce the final
multilayer optical film. In one exemplary method for making a
multilayer optical polarizer, a single drawing step is used. This
process may be performed in a tenter or a length orienter. Typical
tenters draw transversely (TD) to the web path, although certain
tenters are equipped with mechanisms to draw or relax (shrink) the
film dimensionally in the web path or machine direction (MD). Thus,
in this exemplary method, a film is drawn in one in-plane
direction. The second in-plane dimension is either held constant as
in a conventional tenter, or is allowed to neck in to a smaller
width as in a length orienter. Such necking in may be substantial
and increase with draw ratio.
[0085] In one exemplary method for making a multilayer mirror, a
two step drawing process is used to orient the birefringent
material in both in-plane directions. The draw processes may be any
combination of the single step processes described that allow
drawing in two in-plane directions. In addition, a tenter that
allows drawing along MD, e.g. a biaxial tenter which can draw in
two directions sequentially or simultaneously, may be used. In this
latter case, a single biaxial draw process may be used.
[0086] In still another method for making a multilayer polarizer, a
multiple drawing process is used that exploits the different
behavior of the various materials to the individual drawing steps
to make the different layers comprising the different materials
within a single coextruded multilayer film possess different
degrees and types of orientation relative to each other. Mirrors
can also be formed in this manner.
[0087] The intrinsic viscosity of the polyesters used in these
layers and films is related to the molecular weight (in the absence
of branching monomers) of the polymer. In some embodiments, the
polyesters have an intrinsic viscosity of greater than about 0.4
dL/g, or between about 0.4 to 0.9 dL/g. Intrinsic viscosity, for
purposes of this disclosure, is measured in a 60/40 wt. %
phenol/o-dichlorobenzene solvent at 30.degree. C. unless otherwise
indicated.
[0088] The following examples demonstrate the manufacture and uses
of multilayered polymer films of the invention. It is to be
understood that these examples are merely illustrative and are in
no way to be interpreted as limiting the scope of the
invention.
EXAMPLES
Test Methods
[0089] To test for film microwrinkling, a sample of multilayer film
was taken and any outer propylene polymer skin layers were removed
from the film. The sample was then adhered to the non-adhesive side
of a sample of adhesive-backed polarizer film (Sanritz
adhesive-backed polarizer film (available from Set (HK) Ltd. of
Hong Kong, People's Republic of China) using a commercially
available adhesive (Soken 1885 adhesive available from Soken
Chemical & Engineering Company, Ltd. of Saitama Prefecture,
Japan). The construction was then applied to a piece of glass using
the adhesive of the adhesive-backed polarizer to adhere the
polarizer to the glass. The finished construction comprised the
following layers, in order: the multilayer optical film, a layer of
Soken 1885 pressure-sensitive adhesive (PSA), the polarizer film,
an adhesive layer and the glass plate. This construction was heated
at 85.degree. C. and examined periodically for microwrinkling. The
construction was heated at 85.degree. C. until microwrinkling was
observed or for up to 1,000 hours if microwrinkling was not
observed. Microwrinkling manifests itself as objectionable haze or
iridescence in the films, and when examined under a microscope at a
magnification of between 50 and 200 times is observed to be a
permanent deformation of optical layers or any protective outer
layers. This appears as wrinkles under the surface layers or rough
texture on the surface of the multilayer film.
[0090] The test for warp: Clean two 9.5''.times.12.5''
(24.1.times.31.8 cm) flat pieces of double strength glass with
isopropyl alcohol. A 9''.times.12'' (22.9.times.30.5 cm) piece of
the optical body is attached to one piece of glass on two short
sides and one of the long sides, leaving the remaining long side
unconstrained. To attach the optical body, first attach Double
Stick Tape (3M, St. Paul, Minn.) to a piece of glass such that the
tape is 0.5'' (1.3 cm) from three edges of the glass and will be
exactly covered by 3 sides of the optical body. Avoid overlapping
the ends of the tape. Place the optical body on the tape such that
the optical body is tensioned across the tape and is held above the
glass surface by the thickness of the tape (about 0.1 mm). Roll the
optical body down to the tape with a 4.5 lb. (2 kg) roller once in
each direction, avoiding extra force.
[0091] Place three 0.1 mm thick, 0.5'' (1.3 cm) wide polyethylene
terephthalate (PET) shims onto the rolled optical body, the shims
being exactly above the tape and of the same lengths, but on the
opposite side of the optical body. Avoid overlapping the shims.
Place the top piece of glass on top of the shims and exactly
aligned with the bottom piece of glass.
[0092] This completes a sandwiched construction of
glass-tape-optical film-shim-glass, in which the optical body is
constrained at three edges and substantially free floating in the
center. This construction is attached together with 4 binder clips
as are commonly used to hold stacks of paper together (Binder
Clips, Officemate International Corporation, Edison, N.J.). The
clips should be of an appropriate size to apply pressure to the
center of the tape (approximately 0.75'' (1.9 cm) from the edge of
the glass) and are positioned two each on the short sides of the
construction, each about 0.75'' (1.9 cm) away from the bottom and
top of the optical body.
[0093] This completed construction is placed in a thermal shock
chamber (Model SV4-2-2-15 Environmental Test Chamber,
Envirotronics, Inc., Grand Rapids, Mich.) and subjected to 96
cycles, a cycle consisting of one hour at 85.degree. C. followed by
one hour at -35.degree. C. The film is then removed from the
chamber and inspected for warp. Warp is considered unacceptable
when there are many deep wrinkles across the surface of the film.
When there are few shallow wrinkles or the film appears smooth,
warp is generally considered acceptable.
[0094] Intrinsic viscosity (IV) was measured according to ASTM
D5225.
[0095] Refractive index was measured with a Metricon refractometer
at a wavelength of 632 nanometers.
Materials
[0096] Monomers, catalysts and stabilizers utilized in creating
polymers for these examples are commercially available from the
following exemplary suppliers: dimethyl
2,6-naphthalenedicarboxylate from Amoco (Decatur, Ala.); dimethyl
terephthalate from Hoechst Celanese (Dallas, Tex.); 1,4-cyclohexane
dimethanol from Sigma-Aldrich (St. Louis, Mo.); neopentyl glycol
from Sigma-Aldrich (St. Louis, Mo.); ethylene glycol from Union
Carbide (Charleston, W.V.); trimethylolpropane from Sigma-Aldrich;
anhydrous cobalt (II) acetate from Hall Chemical (Wickliffe, Ohio);
anhydrous zinc acetate from Sigma-Aldrich; antimony (III) acetate
available as antimony triacetate from Elf Atochem (Philadelphia,
Pa.); triethyl phosphonoacetate from Albright & Wilson (Glen
Allen, Va.); tertiary butyl isophthalate from Noetic Technologies,
Inc. (Hattiesburg, Miss.); phenol from Sigma-Aldrich;
o-chlorophenol available as 2-chlorophenol from Sigma-Aldrich;
poly(methyl methacrylate) available under the trade name of V044
from Atofina Chemicals (Philadelphia, Pa.); propylene polymer
available as PP 6671 from Atofina Chemicals; propylene polymer
available as PP1024 from Exxon Mobil (Houston, Tex.); polyethylene
cyclohexamethylene terephthalate (PETG) is available under the
trade name Eastar 6763 from Eastman Chemical Company (Kingsport,
Tenn.); manganese (II) acetate from Hall Chemical; dimethyl
cyclohexane dicarboxylate from Eastman Chemical Co.; PCTG is
available under the trade name of ESTAR6763 from Eastman Chemical
Co. A thermoplastic polyester is available under the trade name of
ECDEL from Eastman Chemical Company.
Example 1
Synthesis of Polyethylene Naphthalate (PEN)
[0097] The polyethylene naphthalate (PEN) used to form the first
optical layers was synthesized in a batch reactor with the
following raw material charge: dimethyl naphthalene dicarboxylate
(136 kg), ethylene glycol (73 kg), manganese (II) acetate (27 g),
cobalt (II) acetate (27 g) and antimony (III) acetate (48 g). Under
a pressure of 2 atmospheres (1520 torr or 2.times.10.sup.5
N/m.sup.2), this mixture was heated to 254.degree. C. while
removing methanol (a transesterification reaction by-product).
After 35 kg of methanol was removed, 49 g of triethyl
phosphonoacetate (49 g) was charged to the reactor and the pressure
was gradually reduced to 1 torr (131 N/m.sup.2) while heating to
290.degree. C. The condensation reaction by-product, ethylene
glycol, was continuously removed until a polymer with an intrinsic
viscosity of 0.48 dL/g (as measured in 60/40 wt. %
phenol/o-dichlorobenzene) was produced.
Synthesis of Ethylene Naphthalate t-Butyl Isophthalate Polymer
(CoPEN-tbia)
[0098] The synthesis of the CoPEN-tbia polymer was carried out in a
batch reactor which was charged with the following materials:
dimethyl 2,6-naphthalenedicarboxylate (47.3 kg), dimethyl
terephthalate (18.6 kg), 1,4-cyclohexane dimethanol (40.5 kg),
neopentyl glycol (15 kg), ethylene glycol (41.8 kg), trimethylol
propane (2 kg), cobalt (II) acetate (36.3 g), zinc acetate (50 g),
and antimony (III) acetate (65 g). The mixture was heated to a
temperature of 254.degree. C. at a pressure of two atmospheres
(2.times.10.sup.5 N/m.sup.2) and the mixture allowed to react while
removing the methanol reaction product.
[0099] After completing the reaction and removing all of the
methanol (approximately 13.1 kg) the reaction vessel was charged
with tertiary-butyl isophthalate (43.2 kg). The reaction was
continued at 254.degree. C. until approximately 7.4 kg of water was
removed and the reaction was complete.
[0100] The reaction vessel was charged with triethyl
phosphonoacetate (70 g) and the pressure was reduced to one torr
(263 N/m.sup.2) while heating to 290.degree. C. The condensation
by-product, ethylene glycol, was continuously removed until a
polymer with intrinsic viscosity 0.632 dl/g as measured in a 60/40
weight percent mixture of phenol and o-dichlorobenzene is produced.
The CoPEN-tbia polymer produced by this method had a glass
transition temperature (Tg) of 102.degree. C. as measured by
differential scanning calorimetry at a temperature ramp rate of
20.degree. C. per minute. The CoPEN-tbia polymer had a refractive
index of 1.567.
Multilayer Optical Film--PEN/CoPEN-tbia Reflective Polarizer
Film
[0101] The above described PEN and CoPEN-tbia were coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. The PEN
layers were the first optical layers and the CoPEN-tbia layers were
the second optical layers. In addition to the first and second
optical layers, a set of non-optical layers, also comprised of
CoPEN-tbia were coextruded as PBL (protective boundary layers) on
either side of the optical layer stack. Two sets of skin layers
were also coextruded on the outer side of the PBL non-optical
layers through additional melt ports. Poly(methyl methacrylate) was
used to form the internal set of skin layers. The external skin
layers were made from a blend of propylene polymers (80:20 by
weight respectively of PP6671 and PP1024) were used to form the
external set of coextruded skin layers. The construction was,
therefore, in order of layers: polypropylene mixture outer skin
layer, polymethyl methacrylate inner skin layer, 275 alternating
layers of optical layers one and two, polymethyl methacrylate inner
skin layer, and a further polypropylene outer skin layer.
[0102] The multilayer extruded film was cast onto a chill roll at
23.5 meters per minute (77 feet per minute) and heated in an oven
at 154.degree. C. (310.degree. F.) for 30 seconds, and then nearly
truly uniaxially oriented at a 6:1 draw ratio to produce a
reflective polarizer film of approximately 30 microns (1.2 mils)
thickness.
[0103] This multilayer film was tested for microwrinkling--no
appreciable microwrinkling was observed up to 1000 hours.
Example 2
Synthesis of PET
[0104] The polyethylene terephthalate (PET) used in the examples
was made as follows: A batch reactor was charged with dimethyl
terephthalate (5,000 kg), ethylene glycol (3,502 kg), manganese
(II) acetate (1.2 kg), and antimony (III) acetate (1.6 kg). The
mixture was heated to 254.degree. C. at a pressure of two
atmospheres (1520 torr or 2.times.10.sup.5 N/m.sup.2) while
removing the transesterification by-product methanol. After 1,649
kg of methanol was removed, triethyl phosphonoacetate (2.45 kg) was
added to the reactor and the pressure was gradually reduced to one
torr (131N/m.sup.2) while heating to 280.degree. C. The
condensation by-product, ethylene glycol, was continuously removed
until a polymer with an intrinsic viscosity of 0.60 (measured in a
60/40 phenol/dichlorobenzene mixture) was produced.
Synthesis of Polyethylene Terephthalate t-Butyl Isophthalate
Polymer (CoPET-tbia I)
[0105] The CoPET-tbia I used comprised sub-units derived from
1,4-dimethyl terephthalate (40 mol %), t-butyl dicarboxylate (30
mol %), dimethyl cyclohexane dicarboxylate (30 mol %); and glycol
subunits derived from 1,4-cyclohexane dimethanol (60 mol %),
neopentyl glycol (20 mol %), ethylene glycol (19.5 mol %) and
trimethylolpropane (0.5 mol %).
[0106] The synthesis of the CoPET-tbia I polymer was carried out in
a batch reactor which was charged with the following materials:
dimethyl terephthalate (44 kg), 1,4-dimethyl cyclohexane
dicarboxylate (33.7 kg), 1,4-cyclohexane dimethanol (47.6 kg),
neopentyl glycol (11.8 kg), ethylene glycol (24.6 kg), trimethylol
propane (2 kg), cobalt (II) acetate (36.3 g), zinc acetate (50 g),
and antimony (III) acetate (65 g). The mixture was heated to a
temperature of 254.degree. C. at a pressure of two atmospheres
(2.times.10.sup.5 N/m.sup.2) and the mixture allowed to react while
removing the methanol reaction product.
[0107] After completing the reaction and removing the methanol
(approximately 25.4 kg), the reaction vessel was charged with
tertiary-butyl isophthalate (37.7 kg). The reaction was continued
at 254.degree. C. and at two atmospheres (2.times.10.sup.5
N/m.sup.2) pressure removing the reaction by-product water (a total
of approximately 6.1 kg) until the reaction was complete.
[0108] The reaction vessel was charged with triethyl
phosphonoacetate (70 g) and the pressure was reduced to one torr
(263 N/m.sup.2) while heating to 290.degree. C. The condensation
by-product, ethylene glycol, was continuously removed until a
polymer with intrinsic viscosity 0.65 dl/g as measured in a 60/40
weight percent mixture of phenol and o-dichlorobenzene is produced.
The CoPET-tbia I polymer produced by this method had a glass
transition temperature (Tg) of about 70.degree. C. as measured by
differential scanning calorimetry at a temperature ramp rate of
20.degree. C. per minute. The CoPET-tbia I polymer had a refractive
index of 1.54 as measured with a Metricon refractometer at a
wavelength of 632 nanometers.
Multilayer Optical Film--PET/CoPET-tbia I Reflective Polarizer
Film
[0109] The above described PET and CoPET-tbia I can be coextruded
through a multilayer melt manifold to create a multilayer optical
film with 825 alternating first and second optical layers. The PET
layers can be the first optical layers and the CoPET-tbia I layers
can be the second optical layers. In addition to the first and
second optical layers, a set of non-optical layers, also comprised
of CoPET-tbia were coextruded as PBL (protective boundary layers)
on either side of the optical layer stack. Two sets of skin layers
were also coextruded on the outer side of the PBL non-optical
layers through additional melt ports. PET can be used to form the
internal set of skin layers. The external skin layers can be a
blend of propylene polymers (80:20 by weight respectively of PP8650
and PP1571).
[0110] The multilayer extruded film can be cast onto a chill roll
at 23.5 meters per minute (77 feet per minute) and heated in an
oven at 99.degree. C. (210.degree. F.) for 30 seconds, and then
nearly truly uniaxially oriented at a 6:1 draw ratio to produce a
reflective polarizer film of approximately 30 microns (1.2 mils)
thickness.
[0111] This multilayer film is intended for applications exposed to
environmental conditions up to 60 degrees Celsius, and
microwrinkling is not expected to occur up to that temperature
within 1000 hours.
Example 3
[0112] The PET used in Example 3 was made as described in Example
2.
Synthesis of Polyethylene Terephthalate t-Butyl Isophthalate
Polymer (CoPET-tbia II)
[0113] The CoPET-tbia polymer used in this example, CoPET-tbia II
carboxylate subunits derived from 1,4 dimethyl terephthalate (40
mol %), tertiary butyl dicarboxylic acid (30 mol %), and dimethyl
cyclohexane dicarboxylate (30 mol %); and glycol subunits derived
from 1,4 cyclohexane dimethanol (30 mol %), neopentyl glycol (20
mol %), ethylene glycol (49.5 mol %) and trimethylol propane (0.5
mol %).
[0114] The CoPET-tbia II was synthesized in a batch reactor which
was charged with the following raw materials: 1,4 dimethyl
terephthalate (7.11 kg), 1,4 dimethyl cyclohexane dicarboxylate
(5.45 kg), 1,4 cyclohexane dimethanol (3.85 kg), neopentyl glycol
(1.9 kg), ethylene glycol (11.36 kg), trimethylol propane (0.2 kg),
cobalt (II) acetate (3.6 g), zinc acetate (5.0 g), and antimony
(III) acetate (6.5 g). Under pressure of 2 atmospheres
(2.times.10.sup.5 N/m.sup.2), the mixture was heated to 254.degree.
C. while removing the reaction by-product, methanol. After
completing this reaction and removing the methanol, tertiary butyl
isophthalic acid (6.1 kg) was charged to the reactor. Under
pressure of 2 atm, this mixture was heated to 254.degree. C. until
the reaction by-product, water, is removed. Triethyl
phosphonoacetate (7.0 g) was then charged to the reactor and the
pressure was gradually reduced to 1 torr (263 N/m.sup.2) while
heating to 290.degree. C. The condensation by-product, ethylene
glycol, was continuously removed until a polymer with intrinsic
viscosity of 0.68 dl/g, as measured in 60/40 wt %
phenol/o-dichlorobenzene, was produced. The polymer produced had a
glass transition temperature of about 67.degree. C. as measured by
differential scanning calorimetry (DSC) at a temperature ramp of
20.degree. C./min. This CoPET-tbia II had a refractive index of
1.535 as measured with a Metricon refractometer at 632 nm.
Multilayer Optical Film--PET/CoPET-tbia II Reflective Polarizer
Film
[0115] The above described PET and CoPET-tbia II can be coextruded
through a multi-layer melt manifold to create a multi-layer optical
film with 825 alternating first and second optical layers. The PET
can be used for the first optical layers and the CoPET-tbia II can
be used for the second optical layers. In addition to the first and
second optical layers, a set of skin layers can be coextruded on
the outside of the optical layers through additional melt ports.
PP8650 propylene polymer can be used to form the external pair of
coextruded skin layers. This multilayer cast film can be cast onto
a chilled wheel, and then heated in an oven charged with hot air at
99.degree. C. for about 30 seconds, and then nearly truly
uniaxially oriented, (true uniaxial orientation meaning uniaxial
orientation whereby the film can be allowed to relax in the machine
direction while being oriented in the transverse direction), at a
6:1 draw ratio to produce a reflective polarizer film of
approximately 25 microns in thickness.
[0116] This multilayer film is intended for applications exposed to
environmental conditions up to 60 degrees Celsius, and
microwrinkling is not expected to occur up to that temperature
within 1000 hours.
Example 4
[0117] A multi-layer reflective mirror film is constructed with
first optical layers created from polyethylene terephthalate and
second optical layers created from co-cyclohexane-tbia (CCH-tbia)
having carboxylate subunits derived from tertiary butyl
dicarboxylate (50 mol %) and dimethyl cyclohexane dicarboxylate (50
mol %); and glycol subunits derived from 1,4 cyclohexane dimethanol
(50 mol %), neopentyl glycol (20 mol %), ethylene glycol (29.5 mol
%), and trimethylol propane (0.5 mol %).
[0118] The polyethylene terephthalate (PET) used to form the first
optical layers was synthesized as described for Examples 2 and
3.
Synthesis of Co-Cyclohexane-Tertiary Butyl Isophthalate Polymer
(CCH-tbia) Using DMCD
[0119] Synthesis of the co-cyclohexane-tbia was carried out in a
batch reactor which was charged with the following raw materials:
1,4 dimethyl cyclohexane dicarboxylate (8.45 kg), 1,4 cyclohexane
dimethanol (8.98 kg), neopentyl glycol (1.8 kg), ethylene glycol
(7.95 kg), trimethylol propane (0.2 kg), cobalt (II) acetate (3.6
g), zinc acetate (5.0 g), and antimony (III) acetate (6.5 g). Under
a pressure of 2 atmospheres (2.times.10.sup.5 N/m.sup.2), this
mixture was heated to 254 C while removing the reaction by-product,
methanol. After completing this reaction and removing the methanol,
tertiary butyl isophthalate (9.48 kg) was charged to the reactor.
Under a pressure of 2 atmospheres (2.times.10.sup.5 N/m.sup.2), the
mixture was heated to 254.degree. C. until the reaction by-product,
water, was removed. Triethyl phosphonoacetate (7.0 g) was then
charged to the reactor and the pressure was gradually reduced to 1
torr (263 N/m.sup.2) while heating to 290.degree. C. The
condensation by-product, ethylene glycol, was continuously removed
until a polymer with intrinsic viscosity of 0.72 dl/g, as measured
in 60/40 wt % phenol/o-dichlorobenzene, was produced. The polymer
had a glass transition temperature of about 67.degree. C. as
measured by DSC with a temperature ramp of 20.degree. C./min. This
CCH-tbia had a refractive index of 1.519 as measured with a
Metricon refractometer at 632 nm.
Alternate Synthesis of Co-Cyclohexane-Tertiary Butyl Isophthalate
Polymer (CCH-tbia) Using 1,4 CHDA
[0120] Synthesis of the co-cyclohexane-tbia was carried out in a
batch reactor which was charged with the following raw materials:
1,4 cyclohexane dicarboxylic acid (37 kg), tertiary butyl
isophthalic acid (59.9 kg), 1,4 cyclohexane dimethanol (37.8 kg),
neopentyl glycol (11.2 kg), ethylene glycol (60.3 kg), trimethylol
propane (0.5 kg), and antimony (III) acetate (90 g). Under a
pressure of 2 atmospheres (2.times.10.sup.5 N/m.sup.2), this
mixture was heated to 254 degrees C. while removing the reaction
by-product, water. After completing this reaction and removing the
water, the pressure was gradually reduced to 1 torr (263 N/m.sup.2)
while heating to 290.degree. C. The condensation by-product,
ethylene glycol, was continuously removed until a polymer with
intrinsic viscosity of 0.72 dl/g, as measured in 60/40 wt %
phenol/o-dichlorobenzene, was produced. The polymer had a glass
transition temperature of about 67.degree. C. as measured by DSC
with a temperature ramp of 20.degree. C./min. This CCH-tbia had a
refractive index of 1.519 as measured with a Metricon refractometer
at 632 nm.
Multilayer Optical Film--PET/CCH-tbia Mirror Film
[0121] The above described PET and CCH-tbia could be coextruded
through a multi-layer melt manifold to create a multi-layer optical
film with 825 alternating first and second optical layers. The
first optical layers can be formed from PET and the second optical
layers can be formed from the CCH-tbia. In addition to the first
and second optical layers, a set of non-optical layers, comprised
of the same material as the second optical layers can be coextruded
as PBL (protective boundary layers) on either side of the optical
layer stack. Another set of skin layers can also be coextruded on
the outer side of the PBL non-optical layers through additional
melt ports. The skin layers can consist of the same PET material as
the PET material used for the first optical layers. This
multi-layer extruded film can be cast onto a chilled wheel, and
then heated in an oven charged with hot air at 99.degree. C. for
about 30 seconds, and then biaxially oriented at draw ratios of 3.5
in the machine direction and by 3.5 in the transverse direction to
form a multi-layer mirror film.
[0122] This multilayer film is intended for applications exposed to
environmental conditions up to 60 degrees Celsius, and
microwrinkling is not expected to occur up to that temperature
within 1000 hours.
Example 5
Multilayer Optical Film--CoPEN8218/Xylex Reflective Polarizer
Film
[0123] A multilayer reflective polarizer film may be constructed
with first optical layers created from a co(polyethylene
naphthalate) and second optical layers created from cycloaliphatic
polyester/polycarbonate blend commercially available from GE
Plastics under the series tradename "Xylex."
[0124] The co(polyethylene naphthalate) used to form the first
optical layers is synthesized in a batch reactor with the following
raw material charge: 126 kg dimethyl naphthalene dicarboxylate, 11
kg dimethyl terephthalate, 75 kg ethylene glycol, 27 g manganese
acetate, 27 g cobalt acetate, and 48 g antimony triacetate. Under
pressure of 2 atm (2.times.10.sup.5 N/m2), this mixture is heated
to 254.degree. C. while removing methanol. After 36 kg of methanol
is removed, 49 g of triethyl phosphonoacetate is charged to the
reactor and than the pressure is gradually reduced to 1 torr while
heating to 290.degree. C. The condensation reaction by-product,
ethylene glycol, is continuously removed until a polymer with an
intrinsic viscosity of 0.50 dL/g, as measured in 60/40 wt. %
phenol/o-dichlorobenzene, is produced. This co(polyethylene
naphthalate) or "coPEN9010" was blended with 9 wt % PET to form
"coPEN8218"
[0125] CoPEN8218 was coextruded with Xylex 7200 through a
multilayer melt manifold to create a multilayer optical film with
275 alternating first and second optical layers. The CoPEN8218
layers were the first optical layers and the Xylex 7200 layers were
the second optical layers. In addition to the first and second
optical layers, a set of non-optical layers, also comprised of
Xylex 7200 were coextruded as PBL (protective boundary layers) on
either side of the optical layer stack. Two sets of skin layers
were also coextruded on the outer side of the PBL non-optical
layers through additional melt ports. Polypropylene 6671 was used
to form the internal set of skin layers. The external skin layers
were made from a blend of propylene polymers (80:20 by weight
respectively of PP6671 and PP8650) were used to form the external
set of coextruded skin layers. The construction was, therefore, in
order of layers: polypropylene mixture outer skin layer,
polypropylene inner skin layer, 275 alternating layers of optical
layers one and two, polypropylene inner skin layer, and a further
polypropylene mixture outer skin layer.
[0126] The multilayer extruded film was cast onto a chill roll at
22 meters per minute (66 feet per minute) and heated in an oven at
139.degree. C. (283.degree. F.) for 30 seconds, and then nearly
truly uniaxially oriented at a 6:1 draw ratio to produce a
reflective polarizer film of approximately 30 microns (1.2 mils)
thickness after removal of the strippable polypropylene mixture
outer skin layers.
[0127] This multilayer film was tested for microwrinkling--no
appreciable microwrinkling was observed up to 1000 hours.
Example 6
Multilayer Optical Film--PEN/CoPEN5050HH/Xylex 7200 Reflective
Polarizer Film
[0128] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from co(polyethylene naphthalate)
and skin layers or non-optical layers created from a cycloaliphatic
polyester/polycarbonate blend commercially available from GE
Plastics under the series tradename "Xylex."
[0129] The copolyethylene-hexamethylene naphthalate polymer
(CoPEN5050HH) used to form the first optical layers is synthesized
in a batch reactor with the following raw material charge: dimethyl
2,6-naphthalenedicarboxylate (80.9 kg), dimethyl terephthalate
(64.1 kg), 1,6-hexane diol (15.45 kg), ethylene glycol (75.4 kg),
trimethylol propane (2 kg), cobalt (II) acetate (25 g), zinc
acetate (40 g), and antimony (III) acetate (60 g). The mixture was
heated to a temperature of 254 C at a pressure of two atmospheres
(2.times.10.sup.5 N/m2) and the mixture allowed to react while
removing the methanol reaction product. After completing the
reaction and removing the methanol (approximately 42.4 kg) the
reaction vessel was charged with triethyl phosphonoacetate (55 g)
and the pressure was reduced to one torr (263 N/m2) while heating
to 290 C. The condensation by-product, ethylene glycol, was
continuously removed until a polymer with intrinsic viscosity 0.55
dl/g as measured in a 60/40 weight percent mixture of phenol and
o-dichlorobenzene is produced. The CoPEN5050HH polymer produced by
this method had a glass transition temperature (Tg) of 85 C as
measured by differential scanning calorimetry at a temperature ramp
rate of 20 C per minute. The CoPEN5050HH polymer had a refractive
index of 1.601 at 632 nm.
[0130] The above described PEN and CoPEN5050HH were coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. This 275
layer multi-layer stack was divided into 3 parts and stacked to
form 825 layers. The PEN layers were the first optical layers and
the CoPEN5050HH layers were the second optical layers. In addition
to the first and second optical layers, a set of non-optical
layers, also comprised of CoPEN5050HH were coextruded as PBL
(protective boundary layers) on either side of the optical layer
stack. Two sets of skin layers were also coextruded on the outer
side of the PBL non-optical layers through additional melt ports.
Xylex 7200 was used to form the internal set of skin layers. The
external skin layers were made from polypropylene-ethylene
copolymer (PP8650 available from Atofina) blended with 3 wt %
Pelestat 300 (available from Tomen/Sanyo.) The construction was,
therefore, in order of layers: polypropylene mixture outer skin
layer, Xylex 7200 inner skin layer, 825 alternating layers of
optical layers one and two, Xylex 7200 inner skin layer, and a
further polypropylene mixture outer skin layer.
[0131] The multilayer extruded film was cast onto a chill roll at 5
meters per minute (15 feet per minute) and heated in an oven at
150.degree. C. (302.degree. F.) for 30 seconds, and then uniaxially
oriented at a 5.5:1 draw ratio. A reflective polarizer film of
approximately 150 microns (6 mils) thickness was produced after
removal of the strippable polypropylene mixture skins.
[0132] This multilayer film was tested for warping after exposure
to a thermal shock test varying from -30.degree. C. to 85.degree.
C. once per hour and minimal warping was observed after 100
hrs.
Example 7
Multilayer Optical Film--PEN/CoPEN5050HH/SA115 Reflective Polarizer
Film
[0133] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from co(polyethylene naphthalate)
and skin layers or non-optical layers created from a cycloaliphatic
polyester/polycarbonate blend commercially available from Eastman
Chemical CO., under the tradename "SA115."
[0134] The above described PEN and CoPEN5050HH would be coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. This 275
layer multi-layer stack would be divided into 3 parts and stacked
to form 825 layers. The PEN layers would be the first optical
layers and the CoPEN-5050HH layers would be the second optical
layers. In addition to the first and second optical layers, a set
of non-optical layers, also comprised of CoPEN5050HH can be
coextruded as PBL (protective boundary layers) on either side of
the optical layer stack. Two sets of skin layers were also
coextruded on the outer side of the PBL non-optical layers through
additional melt ports. The non-optical layers or internal skin
layers can be formed from a cycloaliphatic polyester/polycarbonate
blend commercially available from Eastman Chemical Co., under the
series tradename "SA115." The external skin layers would be made
from polypropylene-ethylene copolymer (PP8650 available from
Atofina) blended with 3 wt % Pelestat 300 (available from
Tomen/Sanyo.) The construction would be, therefore, in order of
layers: polypropylene mixture outer skin layer, SA115 inner skin
layer, 825 alternating layers of optical layers one and two, SA115
inner skin layer, and a further polypropylene mixture outer skin
layer.
[0135] The multilayer extruded film would be cast onto a chill roll
at 15 meters per minute (45 feet per minute) and heated in an oven
at 150.degree. C. (302.degree. F.) for 30 seconds, and then
uniaxially oriented at a 5.5:1 draw ratio. A reflective polarizer
film of approximately 150 microns (6 mils) thickness was produced
after removal of the strippable polypropylene mixture skins.
[0136] This multilayer film when exposed to the thermal shock test
(warp test) is expected to have an acceptable level of warp after
100 hrs.
Example 8
Multilayer Optical Film --PEN/CoPEN5050HH/Xylex 7200/CoPEN-tbia
Reflective Polarizer Film
[0137] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from co(polyethylene naphthalate)
and skin layers or non-optical layers created from a cycloaliphatic
polyester/polycarbonate blend commercially available from GE
Plastics under the series tradename "Xylex" and additionally
blended with CoPEN-tbia.
[0138] The copolyethylene-hexamethylene naphthalate polymer
(CoPEN5050HH) used to form the first optical layers is synthesized
in a batch reactor with the following raw material charge: dimethyl
2,6-naphthalenedicarboxylate (80.9 kg), dimethyl terephthalate
(64.1 kg), 1,6-hexane diol (15.45 kg), ethylene glycol (75.4 kg),
trimethylol propane (2 kg), cobalt (II) acetate (25 g), zinc
acetate (40 g), and antimony (III) acetate (60 g). The mixture was
heated to a temperature of 254 degrees C. at a pressure of two
atmospheres (2.times.10.sup.5 N/m.sup.2) and the mixture allowed to
react while removing the methanol reaction product. After
completing the reaction and removing the methanol (approximately
42.4 kg) the reaction vessel was charged with triethyl
phosphonoacetate (55 g) and the pressure was reduced to one torr
(263 N/m2) while heating to 290 degrees C. The condensation
by-product, ethylene glycol, was continuously removed until a
polymer with intrinsic viscosity 0.55 dl/g as measured in a 60/40
weight percent mixture of phenol and o-dichlorobenzene is produced.
The CoPEN5050HH polymer produced by this method had a glass
transition temperature (Tg) of 85 degrees C. as measured by
differential scanning calorimetry at a temperature ramp rate of 20
degrees C. per minute. The CoPEN5050HH polymer had a refractive
index of 1.601 at 632 nm.
[0139] The above described PEN and CoPEN5050HH were coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. This 275
layer multi-layer stack was divided into 3 parts and stacked to
form 825 layers. The PEN layers were the first optical layers and
the CoPEN5050HH layers were the second optical layers. In addition
to the first and second optical layers, a set of non-optical
layers, also comprised of CoPEN5050HH were coextruded as PBL
(protective boundary layers) on either side of the optical layer
stack. Two sets of skin layers were also coextruded on the outer
side of the PBL non-optical layers through additional melt ports.
Xylex 7200 blended with 20 wt % CoPEN-tbia was used to form the
internal set of skin layers. The external skin layers were made
from polypropylene-ethylene copolymer (PP8650 available from
Atofina) blended with 3 wt % Pelestat 300 (available from
Tomen/Sanyo.) The construction was, therefore, in order of layers:
polypropylene mixture outer skin layer, Xylex 7200/CoPEN-tbia blend
inner skin layer, 825 alternating layers of optical layers one and
two, Xylex 7200/CoPEN-tbia blend inner skin layer, and a further
polypropylene mixture outer skin layer.
[0140] The multilayer extruded film was cast onto a chill roll at 5
meters per minute (15 feet per minute) and heated in an oven at
150.degree. C. (302.degree. F.) for 30 seconds, and then uniaxially
oriented at a 5.5:1 draw ratio. A reflective polarizer film of
approximately 125 microns (5 mils) thickness was produced after
removal of the strippable polypropylene mixture skins.
[0141] This multilayer film was measured to have a haze level of
21% as measured with a Gardner haze meter. This multilayer film
when exposed to the thermal shock test (warp test) is expected to
have an acceptable level of warp after 100 hrs.
Example 9
Multilayer Optical Film--PEN/CoPEN5050HH/Xylex 7200/ABS Reflective
Polarizer Film
[0142] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from co(polyethylene naphthalate)
and skin layers or non-optical layers created from a cycloaliphatic
polyester/polycarbonate blend commercially available from GE
Plastics under the series tradename "Xylex" and additionally
blended with ABS Toyolac 900 available from Tomen/Sanyo.
[0143] The copolyethylene-hexamethylene naphthalate polymer
(CoPEN5050HH) used to form the first optical layers is synthesized
in a batch reactor with the following raw material charge: dimethyl
2,6-naphthalenedicarboxylate (80.9 kg), dimethyl terephthalate
(64.1 kg), 1,6-hexane diol (15.45 kg), ethylene glycol (75.4 kg),
trimethylol propane (2 kg), cobalt (II) acetate (25 g), zinc
acetate (40 g), and antimony (III) acetate (60 g). The mixture was
heated to a temperature of 254 degrees C. at a pressure of two
atmospheres (2.times.10.sup.5 N/m.sup.2) and the mixture was
allowed to react while removing the methanol reaction product.
After completing the reaction and removing the methanol
(approximately 42.4 kg) the reaction vessel was charged with
triethyl phosphonoacetate (55 g) and the pressure was reduced to
one torr (263 N/m.sup.2) while heating to 290 degrees C. The
condensation by-product, ethylene glycol, was continuously removed
until a polymer with intrinsic viscosity 0.55 dl/g as measured in a
60/40 weight percent mixture of phenol and o-dichlorobenzene is
produced. The CoPEN5050HH polymer produced by this method had a
glass transition temperature (Tg) of 85 degrees C. as measured by
differential scanning calorimetry at a temperature ramp rate of 20
degrees C. per minute. The CoPEN5050HH polymer had a refractive
index of 1.601 at 632 nm.
[0144] The above described PEN and CoPEN5050HH were coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. This 275
layer multi-layer stack was divided into 3 parts and stacked to
form 825 layers. The PEN layers were the first optical layers and
the CoPEN5050HH layers were the second optical layers. In addition
to the first and second optical layers, a set of non-optical
layers, also comprised of CoPEN5050HH were coextruded as PBL
(protective boundary layers) on either side of the optical layer
stacks. Two sets of skin layers were also coextruded on the outer
side of the PBL non-optical layers through additional melt ports.
Xylex 7200 blended with 20 wt % Toyolac 900 was used to form the
internal set of skin layers. The external skin layers were made
from polypropylene-ethylene copolymer (PP8650 available from
Atofina) blended with 3 wt % Pelestat 300 (available from
Tomen/Sanyo.) The construction was, therefore, in order of layers:
polypropylene mixture outer skin layer, Xylex 7200/Toyolac 900
inner skin layer, 825 alternating layers of optical layers one and
two, Xylex 7200/Toyolac 900 blend inner skin layer, and a further
polypropylene mixture outer skin layer.
[0145] The multilayer extruded film was cast onto a chill roll at 5
meters per minute (15 feet per minute) and heated in an oven at
150.degree. C. (302.degree. F.) for 30 seconds, and then uniaxially
oriented at a 5.5:1 draw ratio. A reflective polarizer film of
approximately 125 microns (5 mils) thickness was produced after
removal of the strippable polypropylene mixture skins.
[0146] This multilayer film was measured to have a haze level of
22% as measured with a Gardner haze meter. This multilayer film
when exposed to the thermal shock test (warp test) is expected to
have an acceptable level of warp after 100 hrs.
Example 10
Multilayer Optical Film--CoPEN9010/SA115 Reflective Polarizer
Film
[0147] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from cycloaliphatic
polyester/polycarbonate blend commercially available from Eastman
Chemical under the series tradename "SA115."
[0148] The copolyethylene naphthalate(CoPEN9010) used to form the
first optical layers is synthesized in a batch reactor with the
following raw material charge: 126 kg dimethyl naphthalene
dicarboxylate, 11 kg dimethyl terephthalate, 75 kg ethylene glycol,
27 g manganese acetate, 27 g cobalt acetate, and 48 g antimony
triacetate. Under pressure of 2 atm (2.times.10.sup.5 N/m2), this
mixture is heated to 254.degree. C. while removing methanol. After
36 kg of methanol is removed, 49 g of triethyl phosphonoacetate is
charged to the reactor and than the pressure is gradually reduced
to 1 torr while heating to 290.degree. C. The condensation reaction
by-product, ethylene glycol, is continuously removed until a
polymer with an intrinsic viscosity of 0.50 dL/g, as measured in
60/40 wt. % phenol/o-dichlorobenzene, is produced.
[0149] This CoPEN9010 may be coextruded with SA115 through a
multilayer melt manifold to create a multilayer optical film with
275 alternating first and second optical layers. The CoPEN9010
layers would be the first optical layers and the SA115 layers would
be the second optical layers. In addition to the first and second
optical layers, a set of non-optical layers, also comprised of
SA115 were coextruded as PBL (protective boundary layers) on either
side of the optical layer stack. Two sets of skin layers were also
coextruded on the outer side of the PBL non-optical layers through
additional melt ports. SA115 may be used to form the internal set
of skin layers. The external skin layers could be made from a blend
of propylene polymers (90:10 by weight respectively of PP6671 and
PP8650) to form the external set of coextruded skin layers. The
construction would be, therefore, in order of layers: polypropylene
mixture outer skin layer, polypropylene inner skin layer, 275
alternating layers of optical layers one and two, polypropylene
inner skin layer, and a further polypropylene mixture outer skin
layer.
[0150] The multilayer extruded film may be cast onto a chill roll
at 22 meters per minute (66 feet per minute) and heated in an oven
at 139.degree. C. (283.degree. F.) for 30 seconds, and then nearly
truly uniaxially oriented at a 6:1 draw ratio to produce a
reflective polarizer film of approximately 30 microns (1.2 mils)
thickness after removal of the strippable polypropylene mixture
outer skin layers.
[0151] This multilayer film would be tested for microwrinkling--no
appreciable microwrinkling would be expected up to 1000 hours.
Example 11
Multilayer Optical Film --PEN/CoPEN5050HH/SA115/PC/PS Reflective
Polarizer Film
[0152] A multilayer reflective polarizer film may be constructed
with first optical layers created from a polyethylene naphthalate
and second optical layers created from co(polyethylene naphthalate)
and skin layers or non-optical layers created from a cycloaliphatic
polyester/polycarbonate blend commercially available from Eastman
Chemical CO., under the tradename "SA115" that is further blended
with polycarbonate and polystyrene.
[0153] The above described PEN and CoPEN5050HH would be coextruded
through a multilayer melt manifold to create a multilayer optical
film with 275 alternating first and second optical layers. This 275
layer multi-layer stack would be divided into 3 parts and stacked
to form 825 layers. The PEN layers would be the first optical
layers and the CoPEN-5050HH layers would be the second optical
layers. In addition to the first and second optical layers, a set
of non-optical layers, also comprised of CoPEN5050HH were
coextruded as PBL (protective boundary layers) on either side of
the optical layer stack. Two sets of skin layers were also
coextruded on the outer side of the PBL non-optical layers through
additional melt ports. The non-optical layers or internal skin
layers can be formed from a cycloaliphatic polyester/polycarbonate
blend commercially available from Eastman Chemical Co., under the
series tradename "SA115" that is additionally blended with 10 wt %
polycarbonate available from Bayer as Macrolon 2458 and 20 wt %
polystyrene available from Dow as Styron 685. The external skin
layers would be made from polypropylene-ethylene copolymer (PP8650
available from Atofina) blended with 3 wt % Pelestat 300 (available
from Tomen/Sanyo.) The construction would be, therefore, in order
of layers: polypropylene mixture outer skin layer, SA115/Macrolon
2458/Styron 685 inner skin layer, 825 alternating layers of optical
layers one and two, SA115/Macrolon 2458/Styron 685 inner skin
layer, and a further polypropylene mixture outer skin layer.
[0154] The multilayer extruded film would be cast onto a chill roll
at 15 meters per minute (45 feet per minute) and heated in an oven
at 150.degree. C. (302.degree. F.) for 30 seconds, and then
uniaxially oriented at a 5.5:1 draw ratio. A reflective polarizer
film of approximately 150 microns (6 mils) thickness was produced
after removal of the strippable polypropylene mixture skins. This
film would be expected to have a haze value of approximately
30%.
[0155] This multilayer film when exposed to the thermal shock test
(warp test) is expected to have an acceptable level of warp after
100 hrs.
Comparative Example C1
Multilayer Optical Film--PEN/PETG Reflective Polarizer Film
[0156] A multilayer reflective polarizer film was made with first
optical layers of PEN and second optical layers made from
polyethylene cyclohexamethylene terephthalate (PETG).
[0157] The PEN was synthesized as described in Example 1. The PETG
is commercially available from Eastman Kodak (Kingsport, Tenn.)
under the trade name EASTAR 6763.
[0158] The multilayer reflective polarizer film was made as
described for Example 1 except that the PETG was used for the
second optical layers instead of the CoPEN-tbia that was used for
the second optical layers in Example 1.
[0159] The multilayer film was tested for microwrinkling--the film
was permanently deformed giving very extensive bad microwrinkling
after only 500 hours at 80.degree. C.
Results
[0160] TABLE 1 shows the constructions of the multilayer optical
films made in the above Examples:
TABLE-US-00001 TABLE 1 Multilayer optical film constructions
Microwrinking observed Example First optical layers Second optical
layers at 1,000 hours or less 1 PEN CoPEN-tbia No 2 PET CoPET-tbia
I No 3 PET CoPET-tbia II No 4 PET CCH-tbia No C1 PEN PETG Yes, 500
hours 5 CoPEN8218 Xylex 7200 No Note: As described above, Examples
1, C1, and 5 were tested at 85 degrees Celsius and Examples 2, 3
and 4 were tested at 60 degrees Celsius.
[0161] TABLE 2 shows the refractive indices and glass transition
temperatures of a number of the materials from Examples 1, 2 and 3
and some commercial polyester materials. As can be seen, the tbia
materials show very low refractive indices with relatively high
glass transition temperatures.
TABLE-US-00002 TABLE 2 Glass transition temperatures and refractive
indices Material Tg/.degree. C. Refractive Index Example(s) PEN 123
1.64 1, C1, 6, 7 PET 79 1.57 2, 3, 4 CoPEN-tbia 102 1.567 1
CoPET-tbia I 70 1.540 2 CoPET-tbia II 67 1.535 3 CCH-tbia 67 1.519
4 CoPEN8218 112 1.628 5 CoPEN5050HH 87 1.601 6, 7 PETG 83 1.565 C1
PCTG 88 1.555 -- ECDEL 5 1.54 -- Xylex 7200 113 1.555 5, 6 SA115
115 1.57 7
[0162] The present invention should not be considered limited to
the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the present specification. The claims are intended to
cover such modifications and devices.
* * * * *