Laminates comprising coextruded liquid crystal polymer films and discardable thermoplastic outside layers

This invention discloses laminates comprising a liquid crystal polymer film inside and non-adherent, non-liquid crystalline polymer film on the outside, prepared by a process of coextrusion. Delamination of the outside layers yields a liquid crystal polymer film of superior surface quality. The invention is particularly suitable for preparing liquid crystal polymer-based polarizers with improved surface quality.

RELATED APPLICATIONS 
The invention disclosed in this application is related to that disclosed in 
copending U.S. patent application Ser. No. 08/761,109, filed of even date 
herewith. 
FIELD OF THE INVENTION 
This invention relates generally to the field of liquid crystal polymers 
("LCPs"). It is also related to polarizers for liquid crystal display 
applications, and specifically to liquid crystal polymer-based polarizers. 
BACKGROUND OF THE INVENTION 
Liquid crystal polymers are well known. Several applications are known for 
LCPs, more recently as components for polarizers in liquid crystal 
displays (LCDs). LCDs are widely used components in applications such as, 
for example, Notebook Personal Computers (PCs), calculators, watches, 
liquid crystal color TVs, word processors, automotive instrument panels, 
anti-glare glasses and the like. A useful review article, for example, is 
"Digital Displays" by in Kirk-Othmer Encyclopedia of Chemical Technology, 
Third edition, Volume 7, page 726 (1979), Wiley-Interscience Publication, 
John Wiley & Sons, New York. Polarizers are important components of liquid 
crystal displays. Typically, Polarizers are used in the form of film, the 
polarizer film (also called polarizing film). In an LCD, the liquid 
crystal elements are generally sandwiched between two layers of polarizing 
films. 
Traditional polarizing films comprise a stretched polymer film such as, for 
example, polyvinyl alcohol (PVA), a dichroic absorber and other optional 
layers. The dichroic absorber is usually iodine or a dichroic dye that is 
absorbed in the polymer film. However, there are several disadvantages 
with such films that make them unsuitable for advanced and sophisticated 
applications. Some such disadvantages include, for example, 
non-uniformity, separation of the absorber over time, susceptibility to 
moisture and the like. For this reason, liquid crystalline polymer-based 
polarizers are being developed for polarizers. The process of molding or 
extrusion generally achieves a high degree of stable orientation in such 
polymers. 
U.S. patent application Ser. No. 08/460,288, filed Jun. 2, 1995, now U.S. 
Pat. No. 5,672,296 discloses novel liquid crystalline polymer compositions 
useful in polarizer applications. Illustrative compositions disclosed 
therein are liquid crystalline polyesters which comprise repeat units 
corresponding to the formula: 
EQU --P.sup.1 !.sub.m --P.sup.2 !.sub.n --P.sup.3 !.sub.q -- 
wherein P.sup.1, P.sup.2 and P.sup.3 represent monomeric moieties with 
P.sup.1 being an aromatic hydroxy carboxylic acid, P.sup.2 being an 
aromatic dicarboxylic acid and P.sup.3 being a phenol; and m, n and q 
represent mole percent of the respective monomers ranging from 5-70 mole 
percent individually. Additional monomers may also be present. A preferred 
composition in the same patent is a film-forming wholly aromatic 
thermotropic liquid crystal polyester which comprises five monomeric 
moieties derived from 4-hydroxybenzoic acid, terephthalic acid, 
4,4'-dihydroxybiphenyl, 6-hydroxy-2-naphthoic acid, and resorcinol in a 
molar ratio 30:20:10:30:10 respectively. Such LCPs are converted to 
polarizing films by combining them with suitable dichroic absorbers and 
then melt extrusion to yield the films. 
There are also LCPs which contain dichroic dyes as covalently linked part 
of the LCP repeat unit. U.S. patent application Ser. No. 08/561,607, filed 
Nov. 21, 1995, discloses some such polymers. These LCPs, which need not be 
combined with dichroic dyes, are also processed by a similar melt 
extrusion to form polarizing films. 
Melt extruded LCP films, however, typically exhibit a degree of machine 
direction-oriented surface texture and therefore need polishing prior to 
further use. In the case of LCPs for polarizers, the films, especially in 
the required thickness of 1 mil (25 .mu.m) or less, easily fibrillate and 
are also damaged easily during slitting and winding operation. It will be 
preferable to have some sheathing layers on the LCP (as a laminate, for 
example) during such operations. The sheaths, however, should be easily 
removable for subsequent steps. 
Laminates of LCPs containing other LCPs as surface layers on both sides are 
known. For example, U.S. Pat. No. 5,248,530 discloses such laminates 
prepared by coextrusion. However, the outside LCPs in such laminates 
cannot be delaminated. Therefore, any further processing of such laminate 
has to include the entire laminate and not just the center LCP alone. 
There is a need in the industry for laminates from LCPs and non-liquid 
crystalline polymers, where the non-liquid crystalline polymer can be 
delaminated later for further processing of the LCP for any intended 
application. 
There is also a need in the LCD industry for an improved polarizer film 
with improved surface characteristics. It will be ideal if the polarizer 
comprises LCP moieties. 
It is, therefore, an object of this invention to provide improved quality 
LCP laminates prepared from LCPs and non-liquid crystalline polymers 
wherein the non-liquid crystalline polymer can be delaminated later if so 
desired. 
It is a further object of this invention to provide LCP-based polarizer 
films which contain surface protecting films thereon that may be 
delaminated to provide polarizers with improved surface quality which 
polarizers may be processed further by conventional methods to yield an 
improved device. 
It is a still further objective of this invention to provide polarizers 
containing fewer defects. 
Other objects and advantages of the present invention will be apparent to 
those skilled in the art as well as from the following description and 
Examples. 
SUMMARY OF THE INVENTION 
One or more of the foregoing objectives are achieved by the provision in 
the present invention of improved LCP-containing laminates. The laminates 
comprise an LCP-film in contact with surface layers of a suitable 
non-adherent, non-liquid crystalline polymer sheath on both sides of the 
LCP film. In another embodiment, the present invention also provides 
laminates wherein an LCP-based polarizing film is in contact with surface 
layers of a non-adherent, non-liquid crystalline polymer sheath on both 
sides of the LCP polarizing film. 
The inventive improved laminates are prepared by a process comprising 
lining an LCP on both sides with the non-liquid crystalline polymer by a 
process of coextrusion. In one illustration, a suitable LCP material is 
melted in a suitable extruder. The non-LCP polymer is also converted into 
a melt stream and extrusion is performed such that both the LCP and the 
non-LCP materials form films and that the LCP film is lined on both sides 
by the non-LCP film. In cases, where the LCP material has the dichroic 
absorber already dissolved in it (to make it suitable and processable 
directly to a polarizer film), the same kind of extrusion is performed. In 
this case, the LCP-based polarizer film is directly formed in the middle 
flanked on either side by the sheath polymer film. 
The external layers provide sufficient strength to the LCP film in the 
subsequent steps such as, for example, winding, slitting and transport. 
When needed, the non-liquid crystalline polymer layers are easily 
delaminated to provide LCP films with improved surface quality. If the LCP 
film is suitable to be used for polarizer application, after such 
delamination it may be suitably dyed with a dichroic absorber to form the 
polarizing film. Of course, when the LCP material already had the dye 
dissolved in it, delamination would directly yield a polarizer film. In 
either case, the polarizer film has fewer surface defects than previously 
known, non-coextruded LCP-polarizers and thus yield better devices. 
Preferred non-liquid crystalline polymers for the surface layers are 
thermoplastics. 
DESCRIPTION OF THE INVENTION 
In one embodiment, the present invention discloses improved LCP-containing 
laminates. The laminates comprise an LCP film located between two layers 
of a non-adherent, non-liquid crystalline polymer. The non-liquid 
crystalline polymer (which acts as the cover layer, alternately referred 
to as the glazing layer, sheathing layer or surface layer herein) is 
preferably a thermoplastic polymer. The laminate is prepared by 
coextruding the LCP film with the non-liquid crystalline polymer film. The 
coextrusion process insulates the LCP film from contact with the die 
surface during extrusion and thus leads to a substantially smooth surface. 
Since the outside layers are from a non-adherent film, they are easily 
peeled off prior to any subsequent processing steps. Peeling off the 
surface layer then yields LCP films with significantly improved surface 
quality. 
In another embodiment, the invention provides improved LCP-based polarizer 
films with improved surface quality. An LCP material suitable for 
polarizer use is laminated on both sides with a non-adherent, non-liquid 
crystalline polymer similar to the above. Delaminating the surface films 
then yields an improved LCP film which may be then converted into a 
polarizing film by dyeing it suitably. If the LCP material already has the 
dye dissolved in it, then the inventive coextrusion followed by 
delamination yields the improved quality polarizing film. If the LCP has 
the dye moieties as covalently linked part of the LCP, then also the 
present invention directly yields polarizing LCP films with significantly 
improved surface properties. 
In an illustrative case, laminates were prepared with an LCP film in the 
middle and a non-adherent polyethylene terephthalate ("PET") film layer on 
both surfaces of the LCP by coextrusion. The laminates had an ABA 
arrangement, where A refers to the PET layers and B refers to the middle 
LCP layer. Afterwards, the PET layers were peeled off, and the resulting 
LCP film was optically examined. For comparison, the same LCP was extruded 
as a monolayer by conventional melt extrusion method (without the PET 
surface layers). Both the inventive and the comparative LCP film were 
checked for surface quality. Surface roughness was measured by a Feinpruf 
Perthometer (Model 55P from Mahr Corporation, Cincinnati, Ohio) as well as 
high magnification micrographs. Significantly improved and smoother 
surface was noticed in the inventive LCP as compared to the monolayer 
extruded LCP. Since, as skilled practioners know, surface roughness has 
deleterious effects in a film which is to be used in optical applications, 
the coextruded laminates of the present invention offer substantial 
benefit in the preparation of improved LCP films generally and LCP-based 
polarizer films particularly. 
The invention is particularly suitable for LCP-based polarizers. Many such 
polarizers are generally prepared from suitable LCP materials which are 
then combined suitably with a suitable dichroic absorber and melt extruded 
suitably to prepare the dye-containing LCP-based polarizer film. 
Alternately, the LCP material may already contain the dye dissolved in it. 
The dichroic absorber may be organic or inorganic. Examples of LCP 
materials suitable for polarizing film as well as process of dyeing them 
with a suitable dichroic absorber are disclosed in the above-mentioned 
pending patent application Ser. No. 08/460,288. The liquid crystal 
polymers therein may be liquid crystalline polyester, polyamide, 
polyesteramide, polyketone, polyether and the like. Liquid crystalline 
polyesters are generally preferred. A suitable LCP disclosed in the '288 
application comprises repeat units corresponding to the formula: 
EQU --P.sup.1 !.sub.m --P.sup.2 !.sub.n --P.sup.3 !.sub.q --P.sup.4 !.sub.r 
--P.sup.5 !.sub.s -- 
wherein P.sup.1, P.sup.2, P.sup.3, P.sup.4 and P.sup.5 represent monomeric 
moieties with P.sup.1 being an aromatic hydroxy carboxylic acid, P.sup.2 
being an aromatic dicarboxylic acid, P.sup.3 being a phenol, P.sup.4 being 
a second aromatic hydroxy carboxylic acid and P.sup.5 being a second 
phenol; and m, n, q, r and s represent mole percent of the respective 
monomers with m, n and q ranging from 5-70 mole percent individually, 
while r and s range from 5-20 mole percent individually. Alternately, the 
dye may be a covalently linked part of the liquid crystal polymeric chain. 
Examples of the latter are disclosed in pending patent application Ser. 
No. 08/561,607 noted earlier. Whether covalently dyed, dye-dissolved-in, 
or dyed later, the LCP film has preferred thickness in the range 4-25 
.mu.m for polarizer applications. 
Suitable non-liquid crystalline polymers which form the cover layers for 
the inventive laminates are non-adherent, non-liquid crystalline polymers, 
preferably thermoplastics. Suitable thermoplastics include, for example, 
polyesters, polycarbonates, polyolefins, polyacrylates, 
polyestercarbonates, polyamides, polyketones, polyethers, cyclic olefin 
polymers and copolymers ("COC") and the like. Important criteria for their 
selection include their optical clarity as well as their thermal and 
mechanical properties. Preferred are the polyesters, many of which are 
well-known thermoplastics. Examples are polyethylene terephthalate ("PET") 
and polybutylene terephthalate ("PBT"). The cover layer is in the 0.5 mil 
to 2 mil (2.5-50 .mu.m) thickness range in the practice of the present 
invention. The cover layer polymer on either side of the LCP may be the 
same or different polymer provided they have suitable optical, thermal and 
the like properties as noted above. 
It is important that the surface polymer is non-adherent to the liquid 
crystal polymer film in the laminate. In such a case, after coextrusion, 
the cover layers may be easily delaminated. Delamination may be done by 
any suitable means, including, for example, manual peeling off. 
The process of preparing an inventive laminate is illustrated in the 
Examples section below. The invention is illustrated with PET as the 
surface layers (same on both sides) and an LCP material disclosed in the 
'288 application and referred to as COTBPR therein as the middle layer. 
COTBPR comprises repeat units from 4-hydroxybenzoic acid, terephthalic 
acid, resorcinol, 4,4'-biphenol and 6-hydroxy-2-naphthoic acid. As stated 
above, after preparation of the PET/LCP/PET coextruded laminate, the cover 
layers may be peeled off to expose the improved LCP film which may be then 
dyed suitably. Alternately, if the LCP material already had the dye 
dissolved in it, the film need not be dyed again. The polarizer film may 
then be further processed suitably by conventional methods to make devices 
such as, for example, liquid crystal display devices. 
The present invention has several key advantages over prior known laminates 
and processes for preparing them. The advantages include ease of 
operation, cost advantages as well as improved surface quality in the 
resulting delaminated film. For polarizer films, they are particularly 
attractive since the coextrusion process yields better surface quality in 
the film and hence better optical suitability. 
The following Examples are provided to further illustrate the present 
invention, but the invention is not to be construed as being limited 
thereto.

EXAMPLES 
Example 1 
Preparation of COTBPR: This example illustrates the preparation of COTBPR 
polyester from a 1 mole reaction mixture of 4-hydroxybenzoic acid ("HBA"), 
6-hydroxy-2-naphthoic acid ("HNA"), terephthalic acid ("TA"), 
4,4'-biphenol ("BP"), and resorcinol ("R") in the ratio 30:30:20:10:10. 
To a 500 ml 3-neck flask equipped with a half-moon shaped TEFLON.RTM. 
stirrer blade, gas inlet tube, thermocouple, a Vigreux column attached to 
a condenser and receiver were added the following: 
a) 41.440 grams of 4-hydroxybenzoic acid (0.3 moles); 
b) 56.456 grams of 6-hydroxy-2-naphthoic acid (0.3 moles); 
c) 33.226 grams of terephthalic acid (0.2 moles); 
d) 18.600 grams of 4,4-biphenol (0.1 moles); 
e) 11.012 grams of resorcinol (0.1 moles); 
the flask was immersed in an oil bath and provided with means to accurately 
control the temperature. The flask was thoroughly purged of oxygen by 
evacuation and then flushed with nitrogen three times, and slowly heated 
in the oil bath; and 
f) 0.02 grams of potassium acetate was added as a catalyst along with 
105.48 grams of acetic anhydride (2.5% excess). Acetic acid began to 
distill over and was collected in a graduated cylinder. 
The contents of the flask were heated while stirring at a rate of 2000 rpm 
to 200.degree. C. over a period of 60 minutes at which time 10 ml of 
acetic acid had been collected. The reaction temperature was then 
gradually raised at a rate of about 1.degree. C./min to 320.degree. C. at 
which time 96 ml of acetic acid had been collected. The flask was heated 
at 320.degree. C. for another 60 min. A total of 110.5 ml of acetic acid 
had been collected. The flask was then evacuated to a pressure of 1.0 mbar 
at 320.degree. C. while stirring. During this period the polymer melt 
continued to increase in viscosity while the remaining acetic acid was 
removed from the flask. The flask and its contents were removed from the 
oil bath and were allowed to cool to the ambient temperature. Polymer was 
then removed from the flask and a total of 120 grams of polymer was 
obtained. 
The resulting polyester had an inherent viscosity (IV) of 2.0-2.4 dl/g as 
determined in a pentafluorophenol solution of 0.1 percent by weight 
concentration at 60.degree. C. and a melt viscosity (MV) of 550 poise at a 
shear rate of 10.sup.3 sec.sup.-1 measured at 230.degree. C. in a 
capillary rheometer using an orifice of 1 mm diameter and 30 mm length. 
When the polymer was subjected to differential scanning calorimetry 
(10.degree. C./min heating rate), it exhibited a glass transition 
temperature (Tg) of 106.degree. C. When the polymer was examined by 
hot-stage cross-polarized optical microscopy, it has a transition 
temperature from solid to liquid crystalline (T.sub.s-&gt;lc) at 170.degree. 
C. The polymer melt was optically anisotropic. 
Example 2 
Coextrusion Experiments: COTBPR (melt stream B) was extruded from a 2" 
single screw extruder at the conditions shown in Table 1. Bottle resin 
grade PET from Hoechst Celanese Corporation (melt stream A) was extruded 
from a 31/2 inch Egan single screw extruder (from Egan Davis Standard, 
Somerville, N.J.) at the conditions shown in Table 1. The two melt streams 
were combined in a commercial "ABA" structure combining block (from 
Cloeren, Inc., Orange, Tex.) and the combined melt streams were extruded 
from a commercial 24 inch wide coat hanger style film die (from Extrusion 
Dies, Inc., Chippewa Falls, Wis.) into the nip between a rubber roll and a 
steel roll where the melt was cooled and solidified. The film laminate 
produced had the structure of 2 mil PET/1 mil COTBPR/2 mil PET. After 
production the PET layers were delaminated manually from the COTBPR layer 
to produce free-standing COTBPR film. A 2 mil PET/0.6 mil COTBPR/2 mil PET 
structure was similarly produced and separated to produce a 0.6 mil COTBPR 
film. 
TABLE 1 
______________________________________ 
Extrusion 
Melt Feedblock 
Die Extrusion 
Take up 
Temp. Temp. Temp. Rate Speed 
(.degree.C.) (.degree.C.) 
(.degree.C.) 
(pph) fpm 
______________________________________ 
PET 285 280 260 34 12 
COTBPR 250 280 260 9.8 12 
______________________________________ 
The COTBPR films were analyzed for machine direction surface texture by a 
"Perthometer" contact stylus type surface analyzer and optical DIC 
(differential interference contrast microscopy). The analysis for the 
COTBPR layer is shown in Table 3. The average roughness (Ra) is around 0.1 
microns with a maximum peak to valley (Rt Maximum) distance in the range 
of 2 micron. The DIC photographs (obtained using a Nikon Microphot FX with 
Epi Nomarski, from Nikon, Inc., Melville, N.Y.) show only a very low level 
of the machine direction surface striations. 
Example 3 
Comparative Example: A monolayer COTBPR extruded film was produced using 
the same COTBPR polymer and similar extrusion conditions described in the 
preceding example (see Table 2). The surface analysis of this 1 mil COTBPR 
film shows a Ra of over 0.3 microns and a Rt Maximum of about 3 microns. 
TABLE 2 
______________________________________ 
Extrusion 
Melt Adaptor Extrusion 
Take up 
Temp. Temp. Die Temp. Rate Speed 
(.degree.C.) (.degree.C.) 
(.degree.C.) 
(pph) fpm 
______________________________________ 
COTBPR 250 250 245 10 11 
______________________________________ 
The Rt Maximum shows that in areas where valleys and peaks on opposite side 
of the film reinforce each other the 25 micron thick films thickness on a 
small scale in the range of (0.5 mm) could range from 22.mu. to 28.mu.. 
This .+-.12% small scale thickness nonuniformity is unacceptable for a 
dyed polarizer film. The DIC photographs also show a very pronounced level 
of machine direction striation in the film surface. 
Example 4 
Coextrusion of dyed LCP with a non-LCP plus an LCP: This Example 
illustrates that a dyed LCP may be coextruded with two layers on either 
side: an undyed LCP layer in contact with the dyed LCP, and a non-LCP 
layer in contact with the undyed LCP. In other words, the dyed LCP layer 
is in the middle, while the non-LCP layers are on the outside, with the 
undyed LCP layer in between them. Thus, COTBPR material is dyed with a 
suitable dichroic absorber and this dyed COTBPR is used for melt stream C. 
Melt stream B is undyed COTBPR, while melt stream A is a non-adherent, 
non-liquid crystalline polymer. A coextruded film of the type ABCBA is 
formed using a suitable extruder, as described before. If any dye happens 
to migrate or diffuse from the dyed COTBPR during the coextrusion process, 
it will still be in the oriented LCP layer it is in contact with. Thereby 
orientation stays preserved. 
TABLE 3 
__________________________________________________________________________ 
SURFACE CHARACTERIZATION 
FILM TYPE* 
Ra Average 
Rs Average 
Rz Average 
Rt Maximum 
THICKNESS 
(microns) 
(microns) 
(microns) 
(microns) 
(mils) TD TD TD TD 
__________________________________________________________________________ 
Comparative Example 
COTBPR Monolayer 
1 
Side A 0.381 0.474 2.063 3.337 
Side B 0.338 0.423 1.895 2.561 
Example 1 
COTBPR Coextruded 
1 
Side A 0.1 0.124 0.513 0.849 
Side B 0.074 0.093 0.525 1.107 
COTBPR Coextruded 
0.6 
Side A 0.111 0.146 0.617 1.189 
Side B 0.141 0.182 0.756 1.246 
__________________________________________________________________________ 
*Same polymer used for all films 
Trace Length = 4.8 mm 
Cutoff Wave = 0.25 mm 
Stylus = 5 micron radius 
Ra--Arithmetic average roughness value. 
Rs--Geometric average roughness value. 
Rz--Average roughness depth of the 5 individual Z values. 
Rt--Maximum vertical difference for highest and lowest point