U.S. patent application number 13/688181 was filed with the patent office on 2013-04-11 for non-iridescent film with polymeric particles in primer layer.
The applicant listed for this patent is John Fitch, Tracy Paolilli. Invention is credited to John Fitch, Tracy Paolilli.
Application Number | 20130089721 13/688181 |
Document ID | / |
Family ID | 48042277 |
Filed Date | 2013-04-11 |
United States Patent
Application |
20130089721 |
Kind Code |
A1 |
Paolilli; Tracy ; et
al. |
April 11, 2013 |
NON-IRIDESCENT FILM WITH POLYMERIC PARTICLES IN PRIMER LAYER
Abstract
This invention relates to an optically clear film of
predominantly thermoplastic polyester base layer and a
carbodiimide-crosslinked, polyester and polymethylmethacrylate
blend primer layer. The base layer preferably has a particle-free
core layer and outer layers containing nonpolyester, organic and/or
inorganic particles. The primer layer is preferably applied to the
base layer from solution that is organic solvent-free. The primer
layer and base layer composite can be laminated with a protective
layer of primarily acrylic polymer to form a solar control film.
Functional additives, such as UV light blockers, can be present in
various layers of the solar control film. Polymethylmethacrylate in
the primer, especially in combination with crosslinking by the
carbodiimide, provides the acrylic coated polyester base solar
control film with notably reduced iridescence. Adhesion between the
acrylic layer applied from organic solvent solutions and the
polyester layers is durable in moist and warm service
conditions.
Inventors: |
Paolilli; Tracy; (East
Greenwich, RI) ; Fitch; John; (Middletown,
RI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Paolilli; Tracy
Fitch; John |
East Greenwich
Middletown |
RI
RI |
US
US |
|
|
Family ID: |
48042277 |
Appl. No.: |
13/688181 |
Filed: |
November 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13337144 |
Dec 25, 2011 |
|
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13688181 |
|
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61514280 |
Aug 2, 2011 |
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Current U.S.
Class: |
428/216 ;
427/162 |
Current CPC
Class: |
B32B 7/12 20130101; B32B
27/308 20130101; C09D 175/04 20130101; B32B 27/20 20130101; B32B
2264/0278 20130101; B32B 2307/702 20130101; B32B 2264/0292
20130101; B32B 2307/71 20130101; C09D 167/00 20130101; C08G 18/0866
20130101; C08G 18/797 20130101; Y10T 428/24975 20150115; B05D 3/007
20130101; B32B 7/02 20130101; B32B 2307/518 20130101; C09D 5/002
20130101; C09D 133/12 20130101; G02B 1/14 20150115; B32B 2264/025
20130101; B32B 27/36 20130101; B32B 2264/102 20130101; B32B 27/08
20130101; B32B 2255/10 20130101 |
Class at
Publication: |
428/216 ;
427/162 |
International
Class: |
C09D 133/12 20060101
C09D133/12 |
Claims
1. A composite film comprising (a) a core layer of substantially
particle-free and optically clear polyester, (b) a first outer
layer in direct contact with one side of the core layer, (c) an
optically clear primer layer in direct contact with a side of the
first outer layer opposite the core layer, and (d) optionally, a
second outer layer in direct contact with a side of the core layer
opposite the first outer layer, in which each outer layer is
optically clear, is independently about 0.1 .mu.m-5 .mu.m thick and
independently comprises inorganic particles dispersed uniformly in
a polyester matrix, and in which the primer layer comprises an
iridescence reducing agent selected from the group consisting of
inversely synthesized aliphatic polyurethane particles and
polymethylmethacrylate particles uniformly dispersed in a matrix of
polyester crosslinked by a carbodiimide crosslinking agent.
2. The composite film of claim 1 in which the iridescence reducing
agent is polymethylmethacrylate particles.
3. The composite film of claim 2 in which both of the first outer
layer and the second outer layer are present.
4. The composite of claim 2 which further comprises an optically
clear protective layer in direct contact with a side of the primer
layer opposite the first outer layer.
5. The composite of claim 4 in which the protective layer comprises
greater than 50 wt. % of an acrylic polymer.
6. The composite of claim 5 in which the protective layer is a
devolatized residue of a solution of the acrylic polymer dissolved
in an organic solvent from which solution the organic solvent has
been substantially removed.
7. The composite of claim 6 in which the protective layer comprises
a trace amount of the organic solvent.
8. The composite of claim 7 in which the organic solvent is methyl
ethyl ketone.
9. The composite of claim 6 in which the polymethylmethacrylate
particles are present in the primer layer at a concentration such
that the composite exhibits haze of at most about 3%.
10. The composite of claim 9 in which thickness of the primer layer
is about 0.03-0.15 .mu.m.
11. The composite of claim 4 which is substantially non-iridescent
under fluorescent illumination.
12. The composite of claim 2 in which the polymethylmethacrylate
particles are microspheres of diameter in the range of about 1
.mu.m-10 .mu.m.
13. The composite of claim 12 in which polymethylmethacrylate
particles are solid microspheres.
14. The composite of claim 12 in which polymethylmethacrylate
particles have a particle size distribution defining a median
particle size and the particle size distribution is narrow such
that at least 80 wt. % of the particles have a diameter within a
range from about +4 .mu.m to -4 .mu.m of the median particle
size.
15. A method of making an optically clear non-iridescent composite
film comprising the steps of (A) providing a mixture comprising an
iridescence reducing agent selected from the group consisting of
inversely synthesized aliphatic polyurethane particles and
polymethylmethacrylate particles and polyester binder particles of
a polyester resin having a softening point lower than 100.degree.
C. uniformly dispersed in a predominantly aqueous medium comprising
carbodiimide crosslinking agent dissolved in water, (B) providing a
base layer comprising a core layer of polyester film of thickness
in the range of about 1-500 .mu.m and optionally comprising about
0.1 to 2 wt % of a UV light absorber composition, (C) depositing a
wet coating of the mixture onto one side of the base layer, (D)
heating the base layer and wet coating effectively to (i) soften
the polyester binder, (ii) evaporate substantially all volatile
components of the predominantly aqueous medium, and (iii), and
activate the crosslinking agent, thereby creating an optically
clear film of solidified primer layer in contact with the one side
of the base layer, in which the wet coating on the base layer is
present in an amount effective to produce a thickness of the
solidified primer layer in the range of about 0.03-0.15 .mu.m.
16. The method of claim 15 in which the iridescence reducing agent
is polymethylmethacrylate particles.
17. The method of claim 16 in which the polymethylmethacrylate
particles are present in the primer layer at a concentration
effective to make the optically clear non-iridescent composite film
have a haze value of at most about 3%.
18. The method of claim 16 in which the step of providing the base
layer further comprises the step of providing a first outer layer
about 0.1-5 .mu.m thick and comprising inorganic particles
uniformly dispersed in a polyester matrix, in which the first outer
layer is in direct contact with a side of the core layer opposite
the one side of the base layer bearing the primer layer, such that
the core layer and the first outer layer collectively define the
base layer.
19. The method of claim 18 in which the step of providing the base
layer further comprises the step of providing a second outer layer
about 0.1-5 .mu.m thick and optionally comprising inorganic
particles uniformly dispersed in a polyester matrix, in which the
second outer layer is in direct contact with a side of the core
layer opposite the first outer layer, such that the core layer,
first outer layer and second outer layer collectively define the
base layer.
20. The method of claim 18 which further comprises the steps of (E)
providing a solution comprising acrylic polymer, a cure initiator,
and an amount of organic solvent effective to dissolve the acrylic
polymer, (F) placing a uniformly thick solvent-wet coating of the
solution onto a side of the primer layer opposite the base layer,
(G) heating solvent-wet coating effectively to evaporate
substantially all volatile components of the organic solvent,
thereby creating an optically clear film having a protective layer
of solidified acrylic polymer in contact with the primer layer, in
which acrylic polymer comprises greater than 50 wt. % of the primer
layer.
21. The method of claim 19 in which the protective layer is
effective to make the optically clear non-iridescent composite film
have a haze value of at most about 3%.
22. The method of claim 16 in which the polymethylmethacrylate
particles are microspheres of diameter in the range of about 1
.mu.m to about 10 .mu.m and in which polymethylmethacrylate
particles have a particle size distribution defining a median
particle size and the particle size distribution is narrow such
that at least 80 wt. % of the particles have a diameter within a
range from about +4 .mu.m to -4 .mu.m of the median particle size.
Description
FIELD OF THE INVENTION
[0001] The invention relates to optically clear biaxially oriented
polyester film with at least one primer layer, having excellent
adhesive properties to acrylic coating material over the primer
layer even under harsh conditions, such as a high moisture
environment. The polyester film coated with an acrylic hard coat,
has reduced iridescence due to dispersion of particles of certain
polyurethane or polymethylmethacrylate within a primer layer
between the polyester and the acrylic hard coat. The polyester film
may have UV blocking and weatherable properties and may be
preferably used for window film, display film, outside clear label,
outside signage and photo voltaic applications.
BACKGROUND OF THE INVENTION
[0002] A commercially and technically important utility for
biaxially oriented polyester films is to serve as a component of
many articles such as food packaging, printing media, electrical
insulation, optical and the other industrial uses. The thermal
stability, dimensional stability, chemical resistance, relative
high surface energy, optical clarity as well as cost effectiveness
of biaxially oriented polyester films are beneficial for typical
end use applications. Regarding optical clarity, biaxially oriented
polyster films can be used for instance as a substrate of optical
products such as window films, display parts, touch screen,
eyewear, including visors, goggles, and spectacles, lenses,
sunscreens, labels and photovoltaic materials. Typically
applications will involve placing optically clear acrylic coating
material onto the biaxially oriented polyester films.
[0003] Although, biaxially oriented polyester film and acrylic
coating each are optically clear, the composite film of biaxially
oriented polyester film coated with acrylic materal can have
adverse optical properties. For example, the film can exhibit
excessive iridescence. The refractive index ("RI") of an acrylic
coating material can be different from the RI of a biaxially
oriented polyester film, e.g. polyethylene terephthalate (PET) film
that is about 1.66. The difference between these refractive indices
causes optical interference of light rays reflected from the
surface between the acrylic layer and the polyester layer. This
interference produces a rippled iridescent appearance through the
spectral reflectance of the acrylic material-coated polyester film.
Iridescence on the acrylic material coated polyester film is very
evident under spectral light of fluorescent lamps because such
light has a sharp distribution of luminescence that interferes with
the rippled spectral reflectance of the acrylic material coated
polyester film.
[0004] Iridescence is reduced or does not occur if the film is hazy
because light is scattered. Hazy film is not desirable for many
optically clear end use applications. Furthermore, the use of
fluorescent lighting in place of incandescent lighting is
increasing due to energy conservation efforts. Consequently, the
iridescence of the acrylic material-coated polyester film can
distort or block the view through the film or detract from the
desired aesthetic appearance of the article comprising the film.
Accordingly, the ability to reduce iridescence is gaining
importance.
[0005] Another problem with the acrylic material-coated polyester
films is adhesion between layers of acrylic material and the
polyester layer. In general, biaxially oriented polyester film has
a highly crystallized surface that makes the polyester difficult to
adhere to an acrylic material coating layer. To overcome this
drawback, a primer layer is sometimes used between polyester and
acrylic polymer layers to improve adhesion.
[0006] Japanese Patent Publication Number JP 2004-299101 of YOKOTA
SUNAO et al., entitled "Transparent Laminated Film for Surface
Protection" is directed to a transparent composite film with a
10-250 .mu.m thick base layer of biaxially stretched polyester and
a 3-20 .mu.m thick hard coat layer of acrylic polymer providing at
least 90% light transmission. The film is for laminating to a
surface of an article, such as a flat panel display member, a
nameplate, a window and the like, to protect the article from
scratching or other damage.
[0007] US patent application 2008/0038539 of Yokota et al.
discloses a composite film having a core layer sandwiched between
outer layers to form a base polyester layer. A coating layer
containing anti-iridescent material covers one side of the base
polyester layer and an acrylic coating is disposed over the
anti-iridescent coating layer. US '539 discloses the effect
achieving anti-iridescence by optimizing RI and the coating layer
thickness to minimize infringement of reflection light which causes
ripples of the spectral reflectance.
[0008] However, the products disclosed by these references do not
fulfill the needs of modern industries for less or no iridescence,
and for more robust adhesion under very harsh condition such as
moisture exposure. The disclosed films above have been found to
provide a hard coat with only moderate adhesion to the base layer,
especially after exposure to heat and moisture.
SUMMARY OF THE INVENTION
[0009] In one aspect this invention relates to a highly optically
clear, composite film having a predominantly thermoplastic
polyester base layer and a primer layer of a polyester and
polyurethane blend composition. The base layer preferably has an
A/B/C layered structure with a substantially particle-free core
layer B of polyester and outer layers A and C of polyester
containing non-polyester, organic and/or inorganic particles. The
primer layer is preferably applied to the base layer from solution
that is organic solvent-free and is crosslinked using a
carbodiimide crosslinking agent. The primer layer and base layer
composite can be laminated with a protective layer of primarily
acrylic polymer, for example to obtain a solar control film.
Various layers of the composite and solar control films can contain
effective amounts of functional additives, such as UV light
blockers. Polyurethane in the primer, especially in combination
with crosslinking by the carbodiimide, provides the acrylic coated
polyester base solar control film with notably reduced iridescence
and durable adhesion between polyester and acrylic layers in moist
and warm service conditions.
[0010] It has also been discovered that polymethylmethacrylate
("PMMA") particles of preselected particle size in the primer
composition in place of polyurethane is very highly effective to
reduce the iridescence of a PET/primer/acrylic polymer
composite.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an elevation cross section view of a composite
film according to an embodiment of this invention.
[0012] FIG. 2 is an elevation cross section view of a solar control
film including the composite film of FIG. 1 and a protective layer
according to another embodiment of this invention.
[0013] FIG. 3 is a graphical plot showing hemispherical reflectance
(% R) vs wavelength (nm), for a comparative example and for
selected operative examples described in greater detail, below.
DETAILED DESCRIPTION OF THE INVENTION
[0014] A basic embodiment of this invention is understood with
reference to FIG. 1 showing a cross section of novel composite film
10. This composite film includes a base layer 5 and a primer layer
2. The base layer is preferably formed of three sublayers, namely
core layer 6, and outer layers 4 and 8. Each of the core and outer
layers is predominantly polyester and can include other components,
such as "UV" (ultraviolet light) blocking additives and particles.
In another embodiment shown in FIG. 2, a solar film 20 includes a
protective layer 9 primarily of preferably an acrylic polymer. The
protective layer 9 is positioned on the composite film in contact
with the primer layer 2.
[0015] In the present invention, the primer layer contains
polymeric binder as a major component of the primer layer. The
polymeric binder may be selected from, but not limited to,
polyester, acrylic, polyurethane or the mixture thereof. It is
preferred to select a polyester binder because its RI is similar to
that of the polyester base layer and thus is helpful to reduce
iridescence in the manner as described in US 2008/0038539. Also the
polyester binder is very compatible with the base polyester layer
to provide preferred adhesion, in general. A preferred raw material
for the polyester binder is a 30% solids dispersion, in 2%
propanol, aqueous solution commercially available under the name
Eastek.RTM. 1200 (Eastman Chemicals Company, Kingsport, Tenn.).
This polyester has inherent viscosity of 0.34-0.42, glass
transition temperature (Tg) of 63.degree. C. and softening point
65.degree. C.
[0016] It now has been discovered that very small polyurethane
particles, particularly inversely synthesized aliphatic type
polyurethane, in the primer layer 2 provide excellent iridescence
canceling. Without wishing to be bound by a particular theory it is
thought that the polyurethane particle anti-iridescent component
scatters light impinging on the film. The iridescence canceling
performance is highly effective. Hence, without significantly
increasing haze, iridescence normally observed with an acrylic
polymer coated polyester film is reduced or substantially
completely prevented. Consequently, use of polyurethane particles
in the primer layer controls iridescence and maintains excellent
optical clarity and thus is different from conventional
anti-iridescent techniques described in the prior art such as US
2008/0038539.
[0017] A traditional approach to reducing iridescence in composite
film utilizes refractive index matching techniques. The refractive
indices of the acrylic material layer and the base biaxially
oriented polyester film layer are distinctly different. The
refractive index difference generates iridescence, as mentioned
above. Selecting a primer composition having a RI that matches and
complements those of the two layers could reduce iridescence by
canceling the effect of disparate refractive indices.
[0018] It is contemplated that low iridescence from the
polyurethane according to this invention is caused by a light
scattering phenomenon (without increasing haze) rather than or in
combination with refractive index matching. This is remarkable
because the polyurethane can be utilized at a particle size and
concentration low enough to allow excellent optical clarity of the
overall film yet provide good anti-iridescence performance. The
implications of this theory include that a polyurethane fine
particle dispersion in a primer layer can be utilized to reduce
iridescence in a wide variety combinations of base layer and the
over coating layer materials. Moreover, low iridescence can be
obtained without constraining the primer layer to have a particular
refractive index that complements the refractive indices of the
other composite film layers, although the combination of the
refractive index matching may be preferred.
[0019] The preferred iridescence-reducing component polyurethane
particle is an inversely synthesized aliphatic polyurethane. The
term "inversely synthesized aliphatic polyurethane" means that the
polyurethane is formed by a process in which (i) non-aromatic
organic polyisocyanate and non-aromatic organic polyol are reacted
to form a polyurethane polymer, (ii) a neutralizing agent, such as
a tertiary amine, is added to water to form an aqueous solution,
and then (iii) the polyurethane polymer is added to and dispersed
in the aqueous neutralizing agent solution. A preferred inversely
produced polyurethane material is commercially available under the
name Neorez R1010 (DSM NeoResins B.V., Waalwijk, Netherlands). It
should be understood that use of inversely synthesized aliphatic
polyurethane particles interrelates successfully with several
important performance parameters of optically clear and solar
control films. In addition to exhibiting little or no iridescence,
these films are called upon to have high cohesive strength for
durability and to be highly transparent with controlled refractive
indices. All of these properties can be achieved by these
polyurethane particles employed in a primer layer together with
polymeric binder and a carbodiimide crosslinking agent in proper
proportions. The polymeric binder provides structural integrity and
serves as a matrix for the dispersed phase of polyurethane
particles. The crosslinking agent transforms the binder to a rigid
network. If too little binder or crosslinking agent is present, the
primer will be too weak to durably hold the protective layer to the
base layer. Delamination can occur. The polyurethane particles
cancel undesirable iridescence. If too little inversely synthesized
aliphatic polyurethane particles are present, iridescence can
occur. Conversely, if there is too much of binder, polyurethane or
crosslinking agent, or the primer layer is too thick, the film can
become excessively hazy and thus unsuitable for optical or solar
control film utilities. The description and examples of this
disclosure provide guidance for selecting relative amounts of the
primer components for successful practice of this invention. The
artisan of ordinary skill will be able to adjust proportions of
primer components and primer layer thickness according to the
principles set forth herein to effectively apply the invention
without undue experimentation.
[0020] The desired particle size of the polyurethane particles
within the primer layer is about 1 .mu.m to about 100 .mu.m,
preferably about 1 .mu.m to about 60 .mu.m and more preferably
about 1 .mu.m to about 25 .mu.m. If the particle size is larger
than 100 .mu.m, the coated film surface can develop a grainy
appearance. Additionally, the haze value can exceed the less than
3% desired limit for the coated polyester film (i.e., the base
layer/primer/acrylic polymer layer composite), thereby reducing the
optical clarity. If the particle size is smaller than 1 .mu.m, the
anti-iridescing properties may not be achieved.
[0021] The content of the polyurethane particles in the primer
layer can be at least about 0.2 wt % preferably at least about 0.25
wt %, and more preferably about 0.3 wt %. If the content is less
than about 0.2 wt % there may not be enough particles to
effectively reduce or eliminate iridescence. There can be at most
about 2.5 wt % polyurethane particles in the primer layer,
preferably at most about 2 wt %, and more preferably at most about
1.5 wt %. If the content is more than about 2.5 wt %, the coated
film surface may exceed a less than 3% haze value, thereby reducing
optical clarity. The urethane particles are preferably uniformly
dispersed within the primer layer. The primer layer should be of a
consistent dry coating weight and thickness with adequate
unagglomerated dispersed particles to sufficiently provide an
optically clear coating with a haze value. Primer layer-coated base
layer (i.e., without an acrylic polymer hard coat layer) of this
invention has a haze value of less than 4%. The preferred thickness
of the primer layer is about 0.03 to 0.15 .mu.m, more preferably,
0.07 to 0.12 .mu.m. If the thickness is less than 0.03 .mu.m, the
desired adhesiveness and anti-iridescence effect may not be
achieved. If the thickness is more than 0.15 .mu.m, then presence
of the primer can detract from overall optical clarity and the
desired anti-iridescence effect may not be achieved.
[0022] As another embodiment of this invention, great preference is
given to strengthening the primer layer and the bond between
polyester film layer and the acrylic polymer layer by crosslinking
the primer layer. Crosslinking strengthens the primer layer by
forming the polymeric binder component of the primer layer into a
permanent, rigid, network structure. It also produces chemical
links between the polymeric binder and the polyester base layer.
Crosslinking can be accomplished during and/or after drying solvent
from the wet primer layer. Typically a crosslinking agent is added
to the primer composition to catalyze the reaction. Many
conventional crosslinking agents for reacting polyurethane and
polyester may be used, such as carbodiimide, melamine, aziridine,
glyoxal, oxazoline and mixtures thereof.
[0023] It has been found that a carbodiimide crosslinking agent
provides excellent adhesive strength while very effectively
preserving the anti-iridescence property afforded by the
polyurethane/polyester binder blend. Carbodiimides have the
chemical formula R.sub.1N.dbd.C.dbd.NR.sub.2 in which R.sub.1 and
R.sub.2 are hydrogen or hydrocarbon radicals. Additional benefits
of using carbdimide crosslinker include improved adhesive bonding
of film layers, useful potlife, low toxicity, improved chemical
resistance and crosslinking at ambient conditions. A preferred
carbodiimide crosslinking agent is Solucote.RTM. XL1 (DSM NeoResins
B.V., Waalwijk, Netherlands). Preferably the crosslinking agent is
added to the primer coating liquid and mixed to uniform
concentration. The preferred content of the crosslinking agent in
the primer layer is about 1 wt % to 5 wt %, more preferably, about
2 to 3 wt %. If the content is less than 1 wt %, the organic
solvent resistance properties, the inorganic solvent resistance
properties and the required adhesive strength of the primer layer
will not be achieved. If the content is more than 5 wt %, excessive
crosslinking can produce haze value of the base layer/primer layer
film greater than 4%, thereby reducing optical clarity.
[0024] Inversely synthesized aliphatic polyurethane dispersion and
the crosslinking agent are mixed with the polymeric binder
dispersion in appropriate preselected ratios to form a primer
coating liquid. The coating liquid can be applied to a surface of
the base layer by conventional coating methods such as dip coating,
doctoring, spraying, rod coating and the like. Rod coating is
preferred. Following application, the primer coating liquid is
dried by heating and low humidity ventilation to remove liquid
dispersing medium (mainly water), and leave a solid content of the
primer layer on the base polyester layer. Such coating processes
can be done after the biaxially oriented polyester film is made, or
continuously (i.e., in line) with the biaxially oriented polyester
film fabrication. The in line method is preferred to reduce the
number of steps and cost of coating.
[0025] Examples of polyester suitable to form the base of the
biaxially oriented polyester film are, polyethylene terephthalate
(PET), polyethylene naphthalate (PEN), polybutylene terephthalate
(PBT), polyethylene isophthalate (IPET) and blends or co-polymers
thereof. A preferred polyester is PET because of its good balance
of cost and performance.
[0026] The base layer of biaxially oriented polyester film may have
a mono layer structure or a multi layer structure such as A/B,
A/B/A or A/B/C. A/B/A or A/B/C structures are preferred in which
wherein the core layer B is a polymer layer substantially free of
particles and layers A and C each independently can contain organic
and/or inorganic particles. Core layer B should contain no
particles to achieve the preferred optical clarity of at most about
3% haze value and more preferably at most 2%. The outer layers A
and C may have desired slip agents such as organic and/or inorganic
particles, as disclosed in US patent application 2008/0038539
hereby incorporated herein.
[0027] The biaxially oriented polyester film generally has a
thickness of from 1 to 500 .mu.m, preferably from 5 to 350 .mu.m. A
film thickness of 10 to 50 .mu.m may be preferred for some
applications, such as for solar window film use.
[0028] The biaxially oriented polyester film can be produced by any
conventional method, such as sequential stretching or simultaneous
stretching. In an example of the fabrication process, raw material
polyester pellets and additives are fed to a melt processor, such
as a mixing extruder. The molten material, including the additives,
is extruded through a slot die and quenched on a chill roll, in the
form of a substantively amorphous film. The film may then be
reheated and stretched longitudinally and transversely or
transversely and longitudinally, or longitudinally, transversely,
and again longitudinally and/or transversely. Temperatures during
stretching are generally above the Tg of the film polymer by about
10 to 60.degree. C. Preferably, the longitudinal stretching ratio
is from 2 to 6, more preferably from 3 to 4.5. Preferably, the
transverse stretching ratio is from 2 to 5, more preferably from 3
to 4.5. Preferably, any second longitudinal or transverse
stretching is carried out at a ratio of from 1.1 to 5. The first
longitudinal stretching may also be carried out at the same time as
the transverse stretching (simultaneous stretching). Heat setting
of the film may follow at an oven temperature of about 180 to
260.degree. C., preferably about 220.degree. C. to 250.degree. C.
The film may then be cooled and wound up.
[0029] The biaxially oriented polyester film may contain other
additives such as, but not limited to, UV stabilizer, hydrolysis
resistant agent, optical brightener, frame retardant agent,
anti-oxidation agent. Especially for outdoor applications such as
solar window film or photo voltaic application, it is preferable
that the polyester film contains UV stabilizer to protect the film
itself and/or protect article behind the film from UV light.
Various terms such as "UV light blocker" "UV blocking additive",
"UV stabilizer", "UV absorber", "UV agent" and the like used herein
are to be construed interchangeably as referring to components
included in the base layer to control the effect of ultraviolet
light incident thereon.
[0030] Preferred UV absorbers include 2-hydroxybenzotriazoles,
benzoxazinones and the triazines. A more preferred UV absorber is
2,4-bis-biphenyl-6-[2-hydroxy-4-(2-ethyl-hexyloxy)phenyl]-1,3,5-triazine
in terms of the weatherability and UV resistance performance. The
content of UV absorber may be 0.1 to 2 wt. %. Less than 0.1 wt. %
is not enough to be effective, more than 2 wt. % may increase haze,
yellow color, affect the mechanical properties of the film, and may
create processing issues such as generating undesirable gaseous
byproducts and causing migration to the surface (i.e., "blooming")
of the UV absorber. Preferably, the polyester film includes 0.1 to
2 wt. % UV absorber; more preferably in the range of 0.5 to
1.5%.
[0031] The biaxially oriented polyester film with primer of this
invention can be used as a substrate on which is deposited a
coating of acrylic polymer as mentioned above and seen in FIG. 2.
The acrylic polymer layer is preferred to be optically clear and
primarily to provide a hard, strong, impact resistant barrier
against physical and chemical attack from environmental conditions
to which the desired application of this invention can be exposed
in service. That is, such protective layer reduces damage to the
film from scratching, denting, moisture, atmospheric-borne
contaminants, dirt and permits wash-and-wipe cleaning of the
exposed film surface. The preferred thickness of the acrylic
polymer layer is 2 to 5 .mu.m. Coating layer thickness exceeding 5
.mu.m can adversely affect the refractive index and cause
iridescence. If the thickness is less than 2 .mu.m, the chemical
resistance properties of the acrylic polymer layer can be
diminished.
[0032] Acrylic polymers for the protective layer of this invention
have repeat units that are derivatives of acrylic acid or
substituted acrylic acid. That is, the acrylic polymer is a polymer
comprising polymerized units of the following formula (I)
(I)
##STR00001##
[0034] in which X.dbd.H, for an acrylic acid derivative, or an
alkyl group for an alkyl acrylic acid derivative, such as CH.sub.3
for a methacrylic acid derivative. Typically R is an alkyl group, a
glycidyl group or a hydroxyalkyl group. Representative acrylic
polymers include polymethyl methacrylate, polyethyl methacrylate,
polybutyl methacrylate, polyglycidyl methacrylate, polyhydroxyethyl
methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl
acrylate, polyglycidyl acrylate, polyhydroxyethyl acrylate and
mixtures of these. A protective layer of predominantly acrylic
polymer typically has a refractive index of at most about 1.54, and
frequently about 1.48 to about 1.54.
[0035] The acrylic polymer layer can include functional additives
for specific purposes. Typical additives include antioxidants,
impact resistance modifiers, surfactants, light blocking additives
and the like. Preferably, the acrylic layer for the desired
application such as solar control films contain light blocking
additives, particularly UV light blocking materials. The additives
are usually present in minor quantities to avoid degrading optical
clarity of the acrylic polymer layer. Typically the acrylic polymer
layer contains a total of less than about 1 wt % of additives.
[0036] Frequently, coated polyester films are placed on products to
provide a solar control function by blocking, absorbing and/or
otherwise resisting the transmission of selective wavelengths of
light. These phenomena are sometimes hereinafter collectively
referred to as "light blocking". Ultraviolet light blocking is a
significant utility for coated polyester base solar control films.
PET, which is a most desired polyester, alone does not resist
transmission of ultraviolet ("UV") light very well. UV light
blocking is typically improved by placing a coat of an effective UV
light blocking material on a PET core layer of a composite film. An
example of such a material is a polymeric coating, for example, a
hard coat such as an acrylic polymer that contains a uniformly
dispersed UV light blocking composition. The hard coat also
physically protects the PET base layer with enhanced impact
resistance, abrasion resistance and like properties that lower the
risk of damage from denting, scratching and similar other
environmental assaults.
[0037] In one embodiment of the invention, the acrylic polymer
layer includes UV light blocking materials. In that case, the
acrylic polymer layer generally comprises greater than about 60 wt.
%, preferably greater than about 80 wt. %, more preferably, greater
than about 95 wt. %, and most preferably greater than about 98 wt.
% of an acrylic polymer and 0 to about 2 wt. % preferably about
0.05-1 wt. %, more preferably about 0.1-0.5 wt. %, and most
preferably about 0.2-0.4 wt. % of ultraviolet light blocking
component.
[0038] The acrylic polymer can be applied to the primer layer from
a solution of the acrylic polymer dissolved in organic solvent.
Although the organic solvent is substantially completely removed
from the acrylic polymer after lamination, trace amounts of solvent
can remain in the acrylic polymer layer. By "trace amounts" is
meant a minute amount very much less than 1 wt %, and barely
detectible by rudimentary chemical analytical methods. Not
uncommonly, the compositions in the primer layer are soluble in
organic media. Over time, the very slight but finite residual
solvent in adjacent acrylic polymer layer can weaken the primer
layer. After exposure to heat and moisture under environmental
service conditions, cracking and flaking off of the weakened
acrylic polymer layer can occur. A system for adhering acrylic
polymer layer applied from organic solvent media onto optically
clear solar control films is much needed in the industry.
Therefore, superior organic solvent resistance of the primer layer
is also desired and is achieved by crosslinking agent mentioned
above.
[0039] The acrylic polymer layer can be laminated to the biaxially
oriented polyester film by various known methods. The term
"laminate" is used herein to mean the generic permanent joining of
layers to form a composite structure and is not limited to any
specific method. For example, the acrylic polymer layer can be
preformed as a sheet and laminated onto the primer layer using heat
and pressure. Acrylic polymer can also be extruded onto the primer
layer. Preferably, the acrylic polymer can be deposited onto the
primer layer from a solution. Examples of solution application
methods include doctoring, spraying, painting, dipping, and rod
coating techniques. Following application of solution, the solvent
is removed by conventional techniques such as heat and/or vacuum
treatments. A preferred material for making the acrylic polymer
layer of this invention is an acrylic polymer with a UV cure
initiator solution in methyl ethyl ketone and isopropyl alcohol
solvent. The cure initiator is one which can be activated by
exposure to UV radiation.
[0040] Ideally, all of the solvent is removed to leave a dry, e.g.
hard coat of the acrylic polymer for the solar control film or
display film such as touch screen. After the solvent removal step,
it is not unusual for trace amount of the solvent to remain in the
seemingly dry acrylic polymer layer. The primer according to this
invention can withstand the solubilizing effect of the presence of
such trace residual solvent. It is thus able to create a durable
and strong bond between the acrylic polymer layer and the polyester
base layer. Consequently, the acrylic polymer layer will resist
cracking, chipping, flaking and peeling from the base layer for
extended duration.
[0041] Among the contemplated embodiments of this invention are
included the following.
[0042] 1. Optically clear biaxially oriented polyester film
comprising an anti-iridescent primer layer comprising, (A)
polymeric binder as a major component of the primer layer, (B)
0.1-1.5 wt. % of inversely synthesized aliphatic polyurethane
particle as iridescent reducing component, and (C) at least one
crosslinking agent, wherein, the haze of the polyester film is 4%
or less.
[0043] 2. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. wherein the polymeric binder is
polyester.
[0044] 3. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. wherein thickness of the primer layer is
0.03-0.15 micrometer.
[0045] 4. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. wherein the crosslinking agent is
selected from carbodiimide, melamine, aziridine, glyoxal, oxazoline
or mixture thereof.
[0046] 5. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. wherein the crosslinking agent is
carbodiimide.
[0047] 6. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. which further comprises at least one UV
absorber.
[0048] 7. The optically clear biaxially oriented polyester film of
contemplated embodiment 6. wherein the UV absorber is selected from
2-hydroxybenzotriazoles, benzoxazinones, triazines and mixture
thereof.
[0049] 8. The optically clear biaxially oriented polyester film of
contemplated embodiment 6. wherein the UV absorber is
2,4-bis-biphenyl-6-[2-hydroxy-4-(2-ethyl-hexyloxy)phenyl]-1,3,5-triazine.
[0050] 9. The optically clear biaxially oriented polyester film of
contemplated embodiment 1. for a window film, optical, display,
label or photo voltaic application.
[0051] In another embodiment, certain polymethyl methacrylate
("PMMA") particles can be dispersed within the primer layer in
place of polyurethane particles. Polyester film having PMMA
particles in the primer layer has been found to have generally
equivalent or better film quality and typically superior
iridescence-reducing performance than that of film with
polyurethane particles.
[0052] It has been discovered that dispersing within the primer
layer, highly crosslinked PMMA particles of a particular particle
size range gives a low haze, oriented polyester film with secure
and durable bonding to an acrylic polymer protective coating and
excellent iridescense canceling, With differences now being
explained, the amount, and the methods and conditions for
incorporating the PMMA into the primer layer are generally the same
as for polyurethane particles as previously described.
[0053] Preference is given to using spherical PMMA particles.
Particle diameters that are suitable in this invention are in the
micron range and are sometimes referred to herein as
"microspheres". Hollow microspheres can be used, however, solid
PMMA microspheres are preferred. The nominal particle size of the
PMMA is generally diameter of about 1 .mu.m-10 .mu.m, preferably
about 2 .mu.m-8 .mu.m, and more preferably about 2 .mu.m-5 .mu.m.
Moreover, the particle size distribution of the PMMA is preferably
narrow. Typically greater than 50 wt. % and preferably greater than
80 wt. % of the PMMA particles have a diameter within a range of
about +4 .mu.m to -4 .mu.m of the median particle size, more
preferably within about +2 .mu.m to -2 .mu.m of the median particle
size, and most preferably within about +1 .mu.m to =1 .mu.m of the
median particle size. Because the particle size distribution of the
PMMA is so narrow, and the particles are so small, it is possible
to provide a highly uniform light scattering effect across the
extent of the film such that negation of iridescence is uniform
effective over broad areas. It is also possible to control the
degree of iridescence canceling while maintaining excellent optical
clarity (i.e., low haze).
[0054] Preferred PMMA particles are commercially available under
the name Techpolymer SSX (Sekisui Plastics Co., Tokyo, Japan). This
material is understood to be a cross-linked polymethylmethacrylate
in spherical particle form with small particle size distributions.
This characteristic makes them well-suited for applications having
uniform coating thickness and surface coverage specifications. In
contrast, inversely produced polyurethane particles suitable for
use in this invention as described above can have slightly more
variable particle size distribution. Particle size variability over
the area of the primer layer can produce subtle iridescent effects.
Use of PMMA particles allows greater control over uniformity of
particle size within the primer layer. While polyurethane particles
as set out above can achieve good quality optical films with
reduced iridescence, PMMA particles in the primer layer provide
more consistent iridescence reduction.
[0055] Additionally, the PMMA particles preferred for use in this
invention provide a smaller particle size than the preferred
polyurethane particles in the range of at most about 60 .mu.m
nominal particle size. Smaller particle size coupled with precise
particle size distribution of PMMA particles contributes to lower
haze across the primer coated PET web.
[0056] It is contemplated that low iridescence from the PMMA
according to this invention is caused by a light scattering
phenomenon (without increasing haze) rather than or in combination
with refractive index matching. This is remarkable because the PMMA
can be utilized at a particle size and concentration low enough to
allow excellent optical clarity of the overall film yet provide
good anti-iridescence performance. The implications of this theory
includes that a PMMA particle dispersion in a primer layer can be
utilized to reduce iridescence in a wide variety combinations of
base layer and the over coating layer materials. Moreover, low
iridescence can be obtained without constraining the primer layer
to have a particular refractive index that complements the
refractive indices of the other composite film layers, although the
combination of the refractive index matching may be employed.
[0057] It should be understood that use of PMMA particles also
influences several important performance parameters of optically
clear and solar control films in addition to exhibiting little or
no iridescence. Optically clear, solar control films are called
upon to have high cohesive strength for durability and to be highly
transparent with controlled refractive indices. All of these
properties can be achieved by these PMMA particles employed in a
primer layer together with polymeric binder and a carbodiimide
crosslinking agent in proper proportions. The polymeric binder
provides structural integrity and serves as a matrix for the
dispersed PMMA particles. The crosslinking agent transforms the
binder to a rigid network. If too little binder or crosslinking
agent is present, the primer will be too weak to durably hold the
protective layer to the base layer. Delamination can occur. The
PMMA particles cancel undesirable iridescence. If too little PMMA
particles are present, iridescence can occur. Conversely, if there
is too much of binder, PMMA or crosslinking agent, or the primer
layer is too thick, the film can become excessively hazy and thus
unsuitable for optical or solar control film utilities. The
description and examples of this disclosure provide guidance for
selecting relative amounts of the primer components for successful
practice of this invention. The artisan of ordinary skill will be
able to adjust proportions of primer components and primer layer
thickness according to the principles set forth herein to
effectively apply the invention without undue experimentation.
[0058] The content of the PMMA particles in the primer layer can be
at least about 0.2 wt % preferably at least about 0.25 wt %, and
more preferably about 0.3 wt %. If the content is less than about
0.2 wt % there may not be enough particles to effectively reduce or
eliminate iridescence. There can be at most about 2.5 wt %
polyurethane particles in the primer layer, preferably at most
about 2 wt %, and more preferably at most about 1.5 wt %. If the
content is more than about 2.5 wt %, the coated film surface may
exceed a less than 3% haze value, thereby reducing optical clarity.
The PMMA particles are preferably uniformly dispersed within the
primer layer.
[0059] This invention will be better understood with reference to
the following examples, which are intended to illustrate specific
embodiments within the overall scope of the invention.
[0060] Optically clear biaxially oriented polyester film comprising
an anti-iridescent primer layer comprising, (A) polymeric binder as
a major component of the primer layer, (B) 0.1-1.5 wt. % of PMMA
particles (C)
[0061] Test Methods
[0062] Haze: Haze of films was measured according to ASTM D1003
that determines the percent of transmitted light scattered at more
than 2.5.degree. from the incident light. A suitable instrument to
measure haze is GARDNER HAZE-GARD PLUS No. 4725 hazemeter
(BYK-Gardner USA). A haze value of 3% or less is considered
acceptable, and 2% or less is preferred.
[0063] Iridescent appearance test: Samples of primer layer-coated
base layer composite films were coated with an acrylic polymer
layer. A solution of acrylic polymer composition with a UV cure
initiator in methyl ethyl ketone was drawn onto the composite film
sample with a No. 2.5 mayer coating rod. The solution coated
composite film was passed at a rate of 0.25 m/s (50 ft/min.)
through a field of ultraviolet light radiation of 620,000
Watts/m.sup.2 (400 Watts per square inch) to cure and thereby
solidify the acrylic polymer composition. The coated film was taped
to a black & white lanetta card (9A). Then the surface of the
hard coating was visually inspected under fluorescent lamp
illumination and rated according to the scale below. [0064] Rating
1 (Good): No iridescence observed. [0065] Rating 2 (Acceptable):
Weak iridescence observed. [0066] Rating 3 (Unacceptable): Strong
iridescence observed.
[0067] Acrylic polymer layer (hard coat) adhesion test (Spray
Test): A 12.7 cm.times.25.4 cm sample of composite film coated with
an acrylic polymer layer as described in the Anti-Iridescent
Appearance test method, above, was rolled up in a cylinder of
approximately 2.5 cm diameter and secured with a paper clip. The
rolled up film was exposed to temperature of 66.degree. C.
(150.degree. F.) for 5 minutes. Thereafter the cylinder was
unrolled and the surface of the film was visually inspected and
rated according to the scale below.
[0068] Rating 1 (Good): No discoloration and no separation of
acrylic polymer layer from composite film observed
[0069] Rating 2 (Acceptable): Discoloration but no separation of
acrylic polymer layer from composite film observed
[0070] Rating 3 (Unacceptable): Discoloration and separation of
acrylic polymer layer from composite film observed
[0071] Acrylic polymer layer (hard coat) adhesion test (Boil Test):
A 12.7 cm.times.25.4 cm sample of composite film was coated with an
acrylic polymer layer as described in the Anti-Iridescent
Appearance test method, above. The acrylic polymer layer-coated
sample was submerged in boiling water (100.degree. C.) for 5
minutes. Thereafter the surface of the film was visually inspected
and rated according to the same scale as in the Spray Test for
Acrylic polymer layer adhesion.
[0072] Acrylic polymer layer (hard coat) adhesion test (Tape
Test):
[0073] A 12.7 cm.times.25.4 cm sample of composite film was coated
with an acrylic polymer layer as described in the Anti-Iridescent
Appearance test method, above. The acrylic polymer layer surface of
the sample was pressed against Scotch Brand 810 adhesive tape to
adhere the sample to the tape. The tape was peeled away rapidly
from the tape in directions perpendicular and parallel to the tape.
The sample and tape were visually inspected for transfer of hard
coat acrylic polymer layer to the tape. The sample failed the test
if any of the acrylic polymer layer transferred to the tape.
EXAMPLES
[0074] This invention is now illustrated by examples of certain
representative embodiments thereof, wherein all parts, proportions
and percentages are by weight unless otherwise indicated. All units
of weight and measure not originally obtained in SI units have been
converted to SI units.
Comparative Example 1
[0075] Making biaxially oriented polyester film with a primer layer
(in line coating method): Four masterbatch compositions, MB-A
through MB-D, of additives were prepared by individually blending
additive components with polyethylene terephthalate in the
proportions shown in Table 1. MB-A, MB-B and MB-C were produced by
adding the additive components to the reaction mass during
polymerization of the PET. After synthesis, the PET with additive
masterbatch compositions were pelletized. MB-D was made by charging
the additive with PET pellets (0.65 inherent viscosity) to a twin
screw extruder in which the masterbatch composition was melt
blended and then pelletized.
TABLE-US-00001 TABLE 1 Average additive Additive particle size
Concentration Additive (.mu.m) (wt %) MB-A CaCO.sub.3 1.1 1.0 MB-B
AlO.sub.2 0.1 1.5 MB-C SiO.sub.2 2.0 1.0 MB-D UVA(*) Not
applicable* 20 *ultraviolet light absorber
2,4-bis-biphenyl-6-[2-hydroxy-4-(2-ethyl-hexyloxy)phenyl]-1,3,5-triazine
[0076] An outer layer composition for a polyester base layer film
was made by mixing the masterbatch pellets with PET pellets of
inherent viscosity 0.6 in the proportions shown in Table 2. The
combination of pellets was dried to less than 100 ppm moisture
content then melt-blended in an extruder.
TABLE-US-00002 TABLE 2 Component (wt %) PET 65 MB-A 22 MB-B 7 MB-C
2 MB-D 4
[0077] A core layer was formed by mixing 4 wt. % of MB-D pellets
and 96 wt. % PET (inherent viscosity 0.65) pellets, drying the
mixture to less than 100 ppm moisture content, then melt-blending
the dried pellet mixture in an extruder. The outer layer and core
layer melt streams were then continuously co-extruded at a
temperature of 285.degree. C. through a rectangular joining zone to
form an A/B/A multi-layered melt structure. The multi-layered melt
curtain was quenched on a casting drum at 20.degree. C. to form a
base layer film. The film was oriented in the machine direction by
stretching to 3.3 times original length at 95.degree. C. with a
roller stretcher.
[0078] Formulation of the Primer Layer Composition:
[0079] A liquid primer composition was formed by combining and
blending to uniform composition 19.3 parts weight per hundred
("pph") of a polyester binder dispersion, 0.04 pph of a leveling
surfactant, 0.08 pph of an antifoam/leveling surfactant, 0.14 pph
of an aqueous silica particle dispersion, and 2.62 pph of an
aqueous crosslinking agent dispersion with 76.7 pph deionized
water. The polyester binder dispersion was a 30 wt % solids
polyester particle dispersion in 2% propanol, aqueous solution
(Eastek.RTM. 1200, Eastman Chemicals Company, Kingsport, Tenn.).
The leveling surfactant was an ethoxylated acetylenic diol
(Surfonyl 440), and the antifoam/leveling surfactant was an
ethoxylated acetylenic diol (Surfonyl 420). The silica particle
dispersion was a 20 wt % aqueous dispersion of synthetic amorphous
silica particles (Grace 703A, W. R. Grace Co.). The crosslinking
agent was a 45 wt % aqueous dispersion of polycarbodiimide
(Solucote XL1, (DSM NeoResins B.V., Waalwijk, Netherlands).
[0080] The liquid primer composition was coated with a Mayer rod
coater onto one side of the base layer film. The primer solution
was deposited at a rate of about 1.4 g/m.sup.2 of base layer area
that was calculated as effective to produce a primer layer of basis
weight of 0.10 g/m.sup.2, 0.1 .mu.m thickness and 97.9 wt. %
crosslinked polyester after drying. The wet coated film was
transported through an oven, preheated at 110.degree. C., and
oriented in the transverse direction to 4.0 times original width at
110.degree. C. The composite film was heat-set at 236.degree. C.
and relaxed (5%) using a chain driven stretcher. The completed film
was then wound up. The biaxially oriented polyester film had an
A/B/A thickness of 1.5/47/1.5 .mu.m. The film was aged seven days
at ambient temperature for full crosslinking to occur.
[0081] Application of an acrylic polymer layer on the primed
polyester composite film, above:
[0082] A methyl ethyl ketone (MEK) based, acrylic hard coat
containing a UV cure initiator was drawn onto the primed surface of
the substrate polyester composite film above with a size No. 2.5
Mayer coating rod. The solution coated composite film was passed at
a rate of 0.25 m/s (50 ft/min.) through a field of ultraviolet
light radiation of 620,000 Watts/m.sup.2 (400 Watts per square
inch). The radiation exposure caused the crosslinking agent to
crosslink the polyester binder while volatizing the MEK from the
solution to produce an acrylic polymer coated polyester film
(having a dry hard coat of acrylic polymer laminated onto the base
polyester film above).
[0083] Samples of the above coated film were subjected to adhesion,
haze and anti-iridescence appearance testing. Analytical results
are presented in Table 3, below. The product did not meet low
iridescence specification.
Example 2
[0084] The procedure of Comparative Example 1 was repeated except
that the liquid mixture composition for the primer layer consisted
of 19.267 pph polyester primer dispersion, 0.04 pph of leveling
surfactant, 0.081 pph of antifoam/leveling surfactant, 0.144 pph of
aqueous silica particle dispersion, 2.615 pph of aqueous
crosslinking agent dispersion and 0.329 pph aqueous polyurethane
particle dispersion combined with 76.455 pph deionized water. The
aqueous polyurethane dispersion was a 32 wt % solids dispersion of
particles less than about 100 .mu.m size of inversely synthesized
aliphatic polyurethane (Neorez R1010, DSM NeoResins B.V., Waalwijk,
Netherlands). The primer layer drying conditions were same as in
Comparative Example 1. The dry primer layer basis weight was again
about 0.10 g/m.sup.2 and dry primer layer thickness was about 0.1
.mu.m. Composition of the dry primer layer was about 96.5 wt %
crosslinked polyester and about 1.5 wt % of the inversely
synthesized aliphatic polyurethane particles dispersed therein.
[0085] Samples of the above acrylic polymer coated polyester film
were subjected to adhesion, haze value and anti-iridescence
appearance testing. Analytical results shown in Table 3 indicate
that the iridescent rating value of 1 to 2 was acceptable to good
and adhesion and haze specifications were satisfied.
Comparative Examples 3 and 4
[0086] In Comp. Ex. 3, the procedure of Example 2 was repeated
except that the content of the polyurethane particle in the primer
layer was 9.0 wt %. In Comp. Ex. 4, the procedure of Example 2 was
again repeated except that the content of the polyurethane particle
in the primer layer was 0.22 wt %.
[0087] Evaluation of Results
[0088] Analytical results are shown in Table 3. These examples show
that excessive amounts of polyurethane particles can detract from
optical clarity of the film (Comp. Ex. 3) and that insufficient
polyurethane particles do not provide adequate iridescence
canceling power (Comp. Ex. 4).
Comparative Example 5
[0089] The procedure of Example 2 was repeated except that primer
solution was deposited onto the base layer at about 2.8 g/m.sup.2
rate such that the primer thickness after drying was 0.2 .mu.m.
Analytical results shown in Table 3 indicate that excessive
thickness of the primer layer adversely affects optical clarity
although iridescence was canceled.
Comparative Examples 6 and 7
[0090] For Comp. Ex. 6, the procedure of Example 2 was repeated
except that a glyoxal crosslinking agent (Freechem.RTM.
40.quadrature.L from Emerald Performance Materials) was substituted
for the carbodiimide crosslinking agent. Freechem 40DL is an
aqueous solution of ethanedial which containing less than 0.2%
residual acid. For Comp. Ex. 7 the same procedure as Ex. 2 was
repeated except that melamine formaldehyde resin crosslinking agent
(Cymel.RTM. 385 Cytec Industries, Woodland Park, N.J.) replaced the
carbodiimide crosslinking agent. The amounts of crosslinking agent
was the same as in Example 2. Analytical results are shown in Table
3. They reveal that the inversely synthesized aliphatic
polyurethane and primer proportions as in Ex. 2 gave satisfactory
iridescence and haze properties. However, replacement of
carbodiimide by other crosslinking agents gave inferior Spray and
Boil adhesion performance.
TABLE-US-00003 TABLE 3 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1
Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Spray Adhesion 1 1 1 1 1 2 3
Boil Adhesion 1 1 1 1 1 2 3 Tape Adhesion Pass Pass Pass Pass Pass
Pass Pass parallel Tape Adhesion Pass Pass Pass Pass Pass Pass Pass
perpendicular Iridescence 3 1-2 1-2 3 1-2 1-2 1-2 Haze % 1.37 1.7
3.53 0.85 6.5 1.22 1.35
Examples 8-11
[0091] For Examples 8-10, the procedure of Ex. 2 was repeated
substantially identically except that 0.40 pph of PMMA particles
was charged into the liquid mixture composition for the primer
layer in place of polyurethane. In Ex. 8 a mixture of 50 wt. %
Techpolymer SSX-102 and 50 wt. % Techpolymer SSX-104 microspheres
was dispersed in the primer layer coating composition. Both of
these Techpolymer materiasl from Sekisui are solid microsphers.
SSX-102 particles had a nominal diameter of 2 .mu.m. Mean diameter
was 2.51 .mu.m, median diameter was 2.46 .mu.m, standard deviation
of diameter was 0.25 .mu.m and 97.6% of the particles had diameter
between 2.00 and 3.17 .mu.m. SSX-104 particles had a nominal
diameter of 4 .mu.m. Mean diameter was 4.298 .mu.m, median diameter
was 4.239 .mu.m, standard deviation of diameter was 0.504 .mu.m and
89.4% of the particles had diameter between 4.00 and 5.04 .mu.m.
For Ex. 9, the PMMA particles were Techpolymer SSX-103DXE and had a
nominal diameter of 3 .mu.m, however these were hollow
microspheres. Mean diameter was 3.17 .mu.m, median diameter was
3.07 .mu.m, standard deviation of diameter was 0.40 .mu.m and 94.7%
of the particles had diameter between 2.52 and 4.00 .mu.m. Thus
overall particle sizes for Exs. 8 and 9 were very similar. The main
difference between these examples was the solid particle structure
of Ex. 8 compared to hollow sphere structure of Ex. 9. In Ex. 10
the PMMA nominal particles size was 7 .mu.m. Mean diameter was 6.77
.mu.m, median diameter was 6.51 .mu.m, standard deviation of
diameter was 2.56 .mu.m and 59.0% of the particles had diameter
between 4.00 .mu.m and 8.00 .mu.m. The microspheres were solid and
the particle size distribution about the mean was slightly broader
than in Exs. 8 and 9. In Example 11 the same aqueous polyurethane
dispersion was used again to essentially repeat Ex. 2 within the
range of experimental accuracy. Resulting samples were tested
together with samples of Comp. Ex. 1 for adhesion, haze and
iridescence, as above. Additional iridescence testing was
performed. Analytical methods are described and results are
presented in Table 4 below.
[0092] Every one of Comp. Ex. 1 and Exs. 8-11 yielded values of 1
("good") in the Spray Test and Boil Test for adhesion and passed
the perpendicular and parallel Tape Peel test. Additional
iridescence measurements were made as follows. Rectangular sheet
samples 14 cm wide.times.22.9 cm high (5.5 inch.times.9 inch) of
primer coated base layer film from Comp. Ex. 1, Exs. 8-11 were
taken from positions at the left side (A), center (B) and right
side (C) of a single, 6 meter wide web for each example. The three
samples (A, B and C) were coated with an acrylic polymer coat as
described above. A 2.5 cm.times.2.5 cm (1 inch.times.1 inch) square
hole was cut out near the center of an opaque 21.6.times.27.9 cm
(8.5 inch.times.11 inch) cardboard sheet to form a mask. In turn,
the mask was laid over the three sample sheets at four observation
positions along a corner-to-corner diagonal line of the sheets. The
diagonal line was oriented with the same orientation for all the
sheets (i.e., top left corner to bottom right corner). The line was
divided into five equal length segments and the four observation
positions, OP1-OP4 were located at the interior junctions of the
segments.
[0093] Iridescence assessments and haze measurements were obtained
at each observation point of the three sheets. Results are shown in
Table 4. The average value of iridescence and haze and the standard
deviation of the haze from average were calculated. Results show
that the iridescence canceling with both PMMA (Exs. 8-10) and
polyurethane (Ex. 11) in the primer layer was better than when
neither of these materials was present (Comp. Ex. 1). Iridescence
canceling performance was very good for the polyurethane sample and
even better for Ex. 8 with nominal 2 .mu.m and 4 .mu.m particle
size, solid PMMA microspheres. Iridescence performance of the
larger solid microspheres of Ex. 10 was less effective but
acceptable. Ex. 9 shows that hollow PMMA microspheres had even less
effective iridescence canceling ability than solid microspheres of
about the same size in Ex. 8. Haze values for all examples were
acceptable. For Comp. Ex. 1 this can be attributed to the absence
of light scattering particles that could increase haze if present
as in the operative examples. The combination of haze with the
small PMMA iridescence reducing particles in Ex. 8 was excellent
with an average of 1.50% and a very uniform performance over the
areas of samples tested. All of the PMMA samples demonstrated that
the microspheres did not significantly degrade optical clarity
although the variability in haze value for the hollow microspheres
was the highest of the PMMA samples. The combination of iridescence
and haze analyses suggest that smaller and solid PMMA microspheres
perform better than hollow microspheres. Ex. 11 with polyurethane
particles also had acceptable haze but was more hazy and had higher
haze variability than all other examples.
[0094] Samples of Comp. Ex. 1, Ex. 8 and Ex. 11 were subjected to
total hemispherical reflectance analysis using a Hitachi high
technology U-3900-H UV-Vis-NIR Spectrophotometer. The instrument
was set up in total hemispherical reflectance geometry
(8.degree./t) using a high technology 60 mm integrating sphere
accessory with the measurement beam focused at the center of the
sphere. The reflectance factor measurements were relative to barium
sulfate instrument calibration standard material E259-98 and CIE
15.2 at ambient temperature (22.degree..+-.1.degree. C.). The
calibration of the sample was performed at 1.0 nm intervals over
the wavelength range from 250 nm to 900 nm for
8.degree./hemispherical geometry. In the 250-320 nm wavelength
range a deuterium source was used. A tungsten-halogen source was
used in the 340-900 nm wavelength range. A photomultiplier detector
in the UV-Vis (ultraviolet-visual wavelength range) and a lead
sulfide detector in the NIR (near infrared wavelength range) were
also used. Other settings for these analyses were: integrating
sphere 60 mm diameter, data mode % reflectance (R), scan speed 300
nm/min., delay 0 second, cycle time 0 min., auto zero before each
run off, PMT voltage auto, slit width 4 nm, lamp change mode auto,
base line correction user1, high resolution off, D2 lamp on, WI
lamp on and R/S on. Spectral scans were obtained with each sample
in 0.degree. and 90.degree. (mutually orthogonal) orientations and
the arithmetical average of the two analyses were used for plots of
results.
[0095] Plots of % R vs. wavelength .lamda. (nm) obtained from the
hemispherical reflectance analysis are shown in FIG. 3. The visible
wavelength spectrum extends from about 390 to 750 nm. FIG. 3 shows
that for Comp. Ex. 1, % R fluctuates significantly in the visible
wavelength range and thus iridescence is significant. Ex. 11
utilized particles of inversely synthesized polyurethane as the
iridescence reducing agent in the primer. The reflectance plot
shows much less variability of reflectance in the visual range.
This indicates that the polyurethane particles were very effective
at reducing iridescence. The plot for Ex. 8 that used PMMA
particles in the primer was extremely constant in the visible
range. This performance demonstates the superior ability of PMMA
particles to cancel iridescence.
TABLE-US-00004 TABLE 4 Comp Ex. 1 Comp Ex. 1 Ex. 8 Ex. 8 Ex. 9 Ex.
9 Ex. 10 Ex. 10 Ex. 11 Ex. 11 Iridescence Haze Iridescence Haze
Iridescence Haze Iridescence Haze Iridescence Haze Location rating
(%) rating (%) rating (%) rating (%) rating (%) A/OP1 2 1.18 1 1.49
3 1.45 3 1.64 1 2.57 A/OP2 3 1.50 2 1.46 2 1.30 2 1.48 1 2.59 A/OP3
2 1.20 1 1.44 3 1.22 3 1.53 1 2.51 A/OP4 3 1.49 1 1.48 3 1.46 3
1.46 1 3.00 B/OP1 3 1.32 1 1.42 2 1.39 3 1.49 1 2.57 B/OP2 2 1.27 1
1.48 3 1.46 2 1.62 2 2.36 B/OP3 3 1.38 2 1.58 2 1.29 3 1.49 2 2.46
B/OP4 3 1.36 1 1.52 3 1.23 2 1.52 2 2.40 C/OP1 3 1.35 2 1.52 2 1.21
2 1.45 1 2.55 C/OP2 3 1.36 1 1.51 3 1.47 2 1.66 2 2.44 C/OP3 3 1.38
1 1.56 2 1.38 1 1.48 2 2.44 C/OP4 3 1.35 1 1.48 3 1.20 2 1.55 1
2.64 average 2.75 1.35 1.25 1.50 2.58 1.36 2.33 1.53 1.42 2.54 std.
dev. 0.097 0.046 .108 .072 0.167
[0096] Although specific forms of the invention have been selected
in the preceding disclosure for illustration in specific terms for
the purpose of describing these forms of the invention fully and
amply for one of average skill in the pertinent art, it should be
understood that various substitutions and modifications which bring
about substantially equivalent or superior results and/or
performance are deemed to be within the scope and spirit of the
following claims. The entire disclosure of the US patents and
patent applications referred in this application are hereby
incorporated herein by reference.
* * * * *