U.S. patent application number 10/661522 was filed with the patent office on 2004-04-29 for polyvinyl alcohol polymer film and polarization film.
This patent application is currently assigned to KURARAY CO. LTD.. Invention is credited to Fujiwara, Naoki, Harita, Shigeyuki, Isozaki, Takanori.
Application Number | 20040080825 10/661522 |
Document ID | / |
Family ID | 26591341 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040080825 |
Kind Code |
A1 |
Harita, Shigeyuki ; et
al. |
April 29, 2004 |
Polyvinyl alcohol polymer film and polarization film
Abstract
A polyvinyl alcohol polymer film includes a polyvinyl alcohol
polymer and a plasticizer selected from the group consisting of
ethylene glycol, glycerin, propylene glycol, diethylene glycol,
diglycerin, triethylene glycol, tetraethylene glycol, and
trimethylolpropane. The amount of the polyvinyl alcohol polymer
eluted when a 10 cm square of the polyvinyl alcohol polymer film is
left in 1 liter of water of 50.degree. C. for 4 hours is from 1 to
100 ppm. The film has only a small number of defects and is useful
as raw material for producing a polarization film.
Inventors: |
Harita, Shigeyuki;
(Kurashiki-shi, JP) ; Isozaki, Takanori;
(Kurashiki-shi, JP) ; Fujiwara, Naoki;
(Kurashiki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KURARAY CO. LTD.
Kurashiki-shi
JP
|
Family ID: |
26591341 |
Appl. No.: |
10/661522 |
Filed: |
September 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10661522 |
Sep 15, 2003 |
|
|
|
09842804 |
Apr 27, 2001 |
|
|
|
Current U.S.
Class: |
359/487.02 ;
359/487.06 |
Current CPC
Class: |
C08J 5/18 20130101; Y10S
524/903 20130101; C08J 2329/04 20130101; C08K 5/053 20130101; G02B
5/3033 20130101; C08K 5/053 20130101; C08L 29/04 20130101 |
Class at
Publication: |
359/490 |
International
Class: |
G02B 005/30; G02B
027/28 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2000 |
JP |
2000-132207 |
May 2, 2000 |
JP |
2000-133362 |
Claims
What is claimed is:
1. A polyvinyl alcohol polymer film in which the amount of a
polyvinyl alcohol polymer eluted when a 10 cm square polyvinyl
alcohol polymer film is left in 1 liter of water of 50.degree. C.
for 4 hours is from 1 to 100 ppm.
2. The polyvinyl alcohol polymer film according to claim 1 wherein
the content of an alkali metal compound is 0.5% by weight or less
based on the polyvinyl alcohol polymer.
3. The polyvinyl alcohol polymer film according to claim 2 wherein
the alkali metal compound is sodium acetate.
4. The polyvinyl alcohol polymer film according to claim 1 which is
used for a polarization film.
5. The polyvinyl alcohol polymer film according to claim 2 which is
used for a polarization film.
6. The polyvinyl alcohol polymer film according to claim 3 which is
used for a polarization film.
7. A polarization film made by using a polyvinyl alcohol polymer
film for a polarization film of claim 4.
8. A polarization film made by using a polyvinyl alcohol polymer
film for a polarization film of claim 5.
9. A polarization film made by using a polyvinyl alcohol polymer
film for a polarization film of claim 6.
10. A method of producing a polyvinyl alcohol polymer film of claim
2 comprising film-forming using as a raw material a polyvinyl
alcohol polymer in which the content of an alkali metal compound is
0.5% by weight or less based on the polyvinyl alcohol polymer.
11. The method of producing a polyvinyl alcohol polymer film for a
polarization film according to claim 10 comprising film-forming
using a film formation raw material prepared at temperatures of
150.degree. C. or less containing a polyvinyl alcohol polymer in
which the content of an alkali metal compound is 0.5% by weight or
less based on the polyvinyl alcohol polymer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polyvinyl alcohol polymer
film which has small number of defects and is useful as a
production raw material of a polarization film, and to a
polarization film produced using this.
[0003] 2. Description of the Prior Art
[0004] A polarizer having functions of transmission and shielding
of light is a fundamental constituent element of a liquid crystal
display (LCD), together with a liquid crystal having a function of
switching light. This LCD is applied to portable apparatuses such
as electronic calculators, wristwatches and the like in the initial
period of development of LCD, and recently, to apparatuses in a
wider range such as lap top personal computers, word processors,
liquid crystal color projectors, navigation systems for
automobiles, liquid crystal televisions, personal phones, indoor
and outdoor measuring apparatuses and the like, and there is a need
for polarizer having higher polarization characteristic and smaller
defects than conventional products.
[0005] For obtaining a polarizer having general constitution, a
polyvinyl alcohol polymer film (hereinafter, polyvinyl alcohol
polymer is abbreviated as "PVA", and a polyvinyl alcohol film is
abbreviated as "PVA film", in some cases) is monoaxially stretched
before dyeing, or dyed before monoaxial stretching, and subjected
to fixing treatment with a boron compound (in some cases, dyeing
and fixing treatment are conducted simultaneously, or monoaxial
stretching and fixing treatment are conducted simultaneously),
then, a protection film such as a triacetic cellulose (TAC) film,
cellulose acetate butyrate (CAB) and the like is laminated on the
polarization film.
[0006] By using the above-mentioned polarizer and liquid crystal
having a function of switching light, dichroic display such as
white and black display is enabled, and color display is realized
by combination of a color filter. For improving color
reproducibility of a liquid crystal display, more white hue and
more black hue are required without using color filter, and for
this, smaller unnecessary coloration on a polarizer is
necessary.
[0007] However, when a PVA film is stretched, PVA in the PVA film
may be partially dissolved in a dyeing process and a fixing
treatment process with a boron compound in the case of dry
stretching, and also in a swelling process before stretching and a
stretching process in addition to the dyeing process and fixing
treatment process in the case of wet stretching. The dissolved PVA
is deposited in a vessel and adheres to a PVA film and polarization
film, or deposited on a PVA film and polarization film, providing a
defect, and consequently, decreases the yield of the polarization
film. Further, dissolved PVA which has not been deposited causes
expensive waste water treatment, problematically.
[0008] Furthermore, a conventional PVA film which is a raw material
of a polarization film has a problem that unnecessary coloration
tends to occur by conducting heat treatment in producing a
polarization film. Particularly when a polarizer is made by a dry
stretching method, unnecessary coloration such as yellowing and the
like tends to occur. Therefore, a PVA film causing little
unnecessary coloration even if heat treatment is effected in
producing a polarization film has been desired to be realized.
[0009] Then, an object of the present invention is to provide a PVA
film useful as a raw material for producing a polarization film
having a small number of defects, and a polarization film made by
using this PVA film.
[0010] Further, another object of the present invention is to
provide a PVA film which causes little unnecessary coloration and
is useful as a raw material of a polarization film, and a
polarization film made by using this PVA film.
SUMMARY OF THE INVENTION
[0011] For attaining the above-mentioned objects, in the PVA film
of the present invention, the amount of PVA eluted when a 10 cm
square PVA film is left in 1 liter of water of 50.degree. C. for 4
hours is from 1 to 100 ppm.
[0012] The PVA film of the present invention gives lower amount of
PVA eluted in each process (dyeing, fixing treatment, swelling,
stretching or the like) in producing a polarization film,
therefore, a polarization film having a smaller number of defects
is obtained in high yield by using this PVA film. Also, waste water
treatment becomes easy.
[0013] Further, according to the PVA film of the present invention,
unnecessary coloration can be decreased by controlling the content
of an alkali metal compound to 0.5% by weight or less based on
polyvinyl alcohol.
[0014] The method of producing a PVA film of the present invention
is characterized in that film formation is conducted using a PVA
raw material having a content of an alkali metal compound of 0.5%
by weight or less based on PVA, and further preferably, film
formation is conducted using a film formation raw material prepared
at temperatures of 150.degree. C. or less.
[0015] According to the present invention, the intended PVA film
for a polarization film can be obtained assuredly.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0016] The present invention will be illustrated in detail
below.
[0017] PVA used in the present invention is produced, for example,
by hydrolyzing a polyvinyl ester obtained by polymerizing a vinyl
ester. Further, there are listed modified PVAs obtained by graft
copolymerization of the above-mentioned PVA with unsaturated
carboxylic acids or derivatives thereof, unsaturated sulfonic acids
or derivatives thereof, .alpha.-olefins having 2 to 30 carbon atoms
and the like in a proportion of less than 15 mol %, modified PVAs
produced by hydrolyzing modified polyvinyl esters obtained by
copolymerizing a vinyl ester with unsaturated carboxylic acids or
derivatives thereof, unsaturated sulfonic acids or derivatives
thereof, .alpha.-olefins having 2 to 30 carbon atoms and the like
in a proportion of less than 15 mol %, so-called polyvinyl acetal
resins obtained by partially crosslinking hydroxyl groups of
non-modified or modified PVA with aldehydes such as formalin, butyl
aldehyde, benzaldehyde and the like, and other resin.
[0018] As the above-mentioned vinyl ester, vinyl acetate, vinyl
formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl
versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the
like are listed, and mixtures of two or more of these compounds are
also listed.
[0019] On the other hand, the comonomer used in the modified PVA is
copolymerized mainly for the purpose of modifying PVA, therefore,
used in an amount which does not lose the purpose of the present
invention providing it can be copolymerized with the
above-mentioned vinyl ester. As such comonomer, there are listed,
for example, .alpha.-olefins such as ethylene, propylene, 1-butene,
isobutene and the like; acrylic acid and salts thereof, acrylates
such as methyl acrylate, ethyl acrylate, n-propyl acrylate,
i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl
acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl
acrylate and the like; methacrylic acid and salts thereof,
methacrylates such as methyl methacrylate, ethyl methacrylate,
n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate,
i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl
methacrylate, dodecyl methacrylate, octadecyl methacrylate and the
like; acrylamide derivatives such as acrylamide,
N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide,
diacetoneacrylamide, acrylamidepropanesulfonic acid and salts
thereof, acrylamidepropyldimethylamine and salts thereof,
N-methylolacrylamide and derivatives thereof and the like;
methacrylamide derivatives such as methacrylamide,
N-methylmethacrylamide, N-ethylmethacrylamide,
methacrylamidepropanesulfonic acid and salts thereof,
methacrylamidepropyldimethylamine and salts thereof,
N-methylolmethacrylamide and derivatives thereof and the like;
N-vinylamides such as N-vinylformamide, N-vinylacetamide,
N-vinylpyrolidone and the like; vinyl ethers such as methyl vinyl
ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl
ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl
ether, dodecyl vinyl ether, stearyl vinyl ether and the like;
nitriles such as acrylonitrile, methacrylonitrile and the like;
vinyl halides such as vinyl chloride, vinylidene chloride, vinyl
fluoride, vinylidene fluoride and the like; allyl compounds such as
allyl acetate, allyl chloride and the like; maleic acid and salts
or esters thereof; itaconic acid and salts or esters thereof;
vinylsilyl compounds such as vinyltrimethoxysilane and the like;
isopropenyl acetate, and the like. Among them, .alpha.-olefins are
preferable, and ethylene is particularly preferable.
[0020] The modification amount of modified PVA is preferably less
than 15 mol %.
[0021] The degree of hydrolysis of PVA is preferably at least 97
mol %, more preferably at least 98 mol %, further preferably at
least 99 mol %, most preferably at least 99.5 mol %, from
standpoints of elution amount and durcharacteristic.
[0022] The above-mentioned degree of hydrolysis represents a ratio
of units actually hydrolyzed into vinyl alcohol units in units
which can be converted into vinyl alcohol units by hydrolysis. The
degree of hydrolysis of PVA was measured by a method described in
JIS.
[0023] The degree of polymerization of PVA is preferably at least
1000 from the standpoints of reduction in the elution amount of PVA
and the strength of a PVA film, and more preferably at least 1500,
further preferably at least 2000, and particularly, most preferably
at least 2500, from the standpoint of polarization characteristic.
The upper limit of degree of polymerization of PVA is preferably at
least 8000, and more preferably at least 6000.
[0024] The above-mentioned degree of polymerization of PVA is
measured according to JIS K 6726. Namely, PVA is re-hydrolyzed and
purified, then, intrinsic viscosity is measured in water at
30.degree. C. from which the degree of polymerization is
calculated.
[0025] It is important to wash, with water or hot water, PVA in the
form of tip before a process of preparing a PVA solution for film
formation or water-containing PVA described below, to preliminaryly
remove PVA which tends to be eluted. The water or hot water used
for washing may also contain an organic solvent, plasticizer and
surfactant such as acetic acid, methanol, glycerin, and the like,
in an amount which does not lose the object of the present
invention.
[0026] The temperature of the water or hot water used for washing
is preferably from 10 to 90.degree. C., more preferably from 20 to
80.degree. C., further preferably from 25 to 70.degree. C., and
particularly, most preferably from 30 to 60.degree. C. When the
temperature of water is lower than 10.degree. C., washing of an
eluted substance can not be conducted sufficiently, while, when the
temperature of hot water is over 90.degree. C., the elution amount
of PVA in washing is large, increasing loss, and PVAs are stuck
mutually, deteriorating workcharacteristic in the following
solution process and the like, undesirably.
[0027] The bath ratio by weight of water or hot water to PVA tips
is preferably at least 1, more preferably at least 1.5, and
particularly, most preferably at least 2. When the bath ratio is
less than 1, the amount of water or hot water is small,
consequently, washing can not be effected sufficiently, and an
effect to reduce the elution amount of PVA is small. The upper
limit of the bath ratio is 100 or less. Namely, even if the bath
ratio is over 100, there is no corresponding large improvement in
the washing effect, and water or hot water is futile, leading to
diseconomy.
[0028] The time of washing a PVA tip (time from contact of a PVA
tip with water to completion of draining) is preferably at least 30
seconds, more preferably at least 1 minute, further preferably at
least 5 minutes, and particularly, most preferably at least 10
minutes.
[0029] The method of washing a PVA tip is not particularly
restricted, and there are listed a method in which water or hot
water is showered on PVA tips on a net or belt, then, drained, a
method in which water or hot water and PVA tips are placed
batch-wise in a tower or vessel and allowed to stand still or
stirred, then, drained, a method in which water or hot water and
PVA tips are fed continuously in a tower or vessel, and washed in
countercurrent flow or concurrent flow (may be accompanied by
stirring), then, drained, and other methods.
[0030] The draining method after washing is also not particularly
restricted, and there are listed centrifugal separation, vacuum
suction, filter press, compression using rolls and belts,
separation by gravity using a porous plate such as a net, and
cloth, non-woven cloth and the like, decantation, and the like.
[0031] Washing water such as water adhered on surface, releasing
water and the like may remain, in an amount which does not lose the
object of the present invention, on PVA tips after drainage,
however, it is preferable that water used in washing is separated
and removed from PVA tips as completely as possible.
[0032] For producing a PVA film using PVA tips washed
preliminaryly, a PVA solution prepared by dissolving PVA tips in a
solvent is subjected to a casting film formation method, wet film
formation method (discharging into a poor solvent), gel film
formation method (a PVA aqueous solution is once cooled and gelled,
then, water is removed by extraction to obtain a PVA film), and a
combination method thereof, or a melt extrusion film formation
method in which water-containing PVA prepared by allowing PVA tips
to contain water (may also contain an organic solvent and the like)
is melt-extruded, and other methods can be used. Of them, the
casting film formation method and melt extrusion film formation
method are preferable since an excellent polarization film is
obtained.
[0033] Examples of the solvent for dissolving PVA tips washed
preliminaryly used in producing a PVA film include
dimethylsulfoxide, dimethylformamide, dimethylacetamide,
N-methylpyrolidone, ethylene glycol, glycerin, diglycerin,
propylene glycol, diethylene glycol, triethylene glycol,
tetraethylene glycol, trimethylolpropane, ethylenediamine,
diethylenetriamine, water and the like, and one or more of them can
be used. Among them, water, dimethylsulfoxide, or a mixed solvent
of water and dimethylsulfoxide is suitably used.
[0034] The PVA concentration of a PVA solution or water-containing
PVA used in producing a PVA film is preferably from 3 to 70% by
weight, more preferably from 10 to 60% by weight, further
preferably from 13 to 55% by weight, an particularly, most
preferably from 15 to 50% by weight. This PVA solution or
water-containing PVA may also contain a plasticizer, surfactant,
dichroic dye and the like, if necessary.
[0035] As the plasticizer used in producing a PVA film, a
polyhydric alcohol is preferably added. Examples of the polyhydric
alcohol include ethylene glycol, glycerin, propylene glycol,
diethylene glycol, diglycerin, triethylene glycol, tetraethylene
glycol, trimethylolpropane and the like, and one or more of them
can be used. Among them, diglycerin, ethylene glycol and glycerin
are suitably used for improving stretching property.
[0036] The amount of polyhydric alcohol used is preferably from 1
to 30 parts by weight, more preferably from 3 to 25 parts by
weight, and particularly, most preferably from 5 to 20 parts by
weight, based on 100 parts by weight of PVA. When the use amount is
less than 1 part by weight, dyeing property and stretching property
may decrease, and when over 30 parts by weight, a PVA film may
become too soft, leading to reduction in handling.
[0037] In producing a PVA film, it is preferable to add a
surfactant. The kind of the surfactant is not particularly
restricted, and anionic surfactants or nonionic surfactants are
preferable. As the anionic surfactant, for example, carboxylic
acid-type anionic surfactants such as potassium laurate,
sulfate-type anionic surfactants such as octyl sulfate and the
like, and sulfonic acid-type anionic surfactants such as
dodecylbenzenesulfonate and the like, are suitable. As the nonionic
surfactant, for example, alkyl ether-type nonionic surfactants such
as polyoxyethylene oleyl ether and the like, alkylphenyl ether-type
nonionic surfactants such as polyoxyethylene octylphenyl ether and
the like, alkyl ester-type nonionic surfactants such as
polyoxyethylene laurate and the like, alkylamine-type nonionic
surfactants such as polyoxyethylene laurylamino ether and the like,
alkylamide-type nonionic surfactants such as polyoxyethylene lauric
amide and the like, polypropylene glycol ether-type nonionic
surfactants such as polyoxyethylene polyoxypropylene ether and the
like, alkanolamide-type nonionic surfactants such as oleic acid
diethanol amide and the like, allylphenyl ether-type nonionic
surfactants such as polyoxyalkylene allylphenyl ether and the like,
are suitable. These surfactants can be used alone or in combination
of two or more.
[0038] The amount of the surfactant added is preferably from 0.01
to 1 part by weight, more preferably from 0.02 to 0.5 parts by
weight, and particularly, most preferably from 0.05 to 0.3 parts by
weight, based on 100 parts by weight of PVA. When the addition
amount is less than 0.01 part by weight, effects of improving
stretching property and improving dyeing property are not
manifested easily, and when over 1 part by weight, the surfactant
may be eluted on the surface of a PVA film and cause blocking,
leading to reduction in handling.
[0039] In producing a PVA film, it is preferable to effect drying
sufficiently after film formation, for reducing the elution amount
of PVA, in addition to the above-mentioned washing.
[0040] It is important for the PVA film of the present invention
that the amount of PVA eluted when a 10 cm square PVA film is left
in 1 liter of water of 50.degree. C. for 4 hours is from 1 to 100
ppm. Preferably, this elution amount is from 5 to 80 ppm, and
particularly, most preferably from 10 to 60 ppm. When the elution
amount of PVA is over 100 ppm, the elution amount of PVA into a
vessel increases and the amount of PVA deposited on a PVA film and
a polarization film increases, obtaining a polarization film having
a smaller number of defects becomes difficult, and problems occur
in waste water treatment. For realizing an elution amount of PVA of
less than 1 ppm, an extremely large amount of preliminary washing
water is necessary expensively, and in addition, high degree of
heat treatment after film formation and drying is necessary,
leading to deterioration in monoaxial stretching property, and
resultantly, an excellent polarization film is not obtained
easily.
[0041] The method for measuring the elution amount of PVA is as
follows. A 10 cm square PVA film is left in 1 liter of distilled
water of 50.degree. C. for 4 hours, and the eluted liquid thereof
is colored with an iodine-potassium iodide solution, and within 10
minutes, the absorbancy of a peak showing the maximum absorption is
measured by a spectrophotometer, UV1200 manufactured by Shimadzu
Corp. Since the wavelength of a peak showing the maximum absorption
differs depending on the degree of polymerization and degree of
hydrolysis of PVA (generally, existing around 650 to 700 nm), raw
PVA or PVA obtained by preliminaryly removing and purifying
additives and the like from a PVA film is used to make a
calibration curve, and the elution amount of PVA (PVA concentration
in eluted liquid) is quantified from absorbancy obtained from a
sample.
[0042] The coloration method with an iodine-potassium iodide
solution is as follows. 450 ml of a boric acid aqueous solution
prepared by dissolving 40 g of boric acid in 1000 ml of
ion-exchange water, and 90 ml of an iodine-potassium iodide aqueous
solution prepared by dissolving 12.7 g of potassium iodide and 25 g
of iodine in 100 ml of ion exchange water are mixed, and to the
resulted mixture is added 300 ml of ion exchange water for
dilution, and the temperature of this mixture is controlled to
20.degree. C. to give a coloration reagent. In an Erlenmeyer flask
equipped with a plug, to 10 ml of the extracted liquid cooled to
20.degree. C. is added 10 ml of the coloration reagent to give a
mixture which was left for 15 minutes at 20.degree. C. When the PVA
concentration in the extracted liquid is too high, the extracted
liquid may be diluted with ion exchange water, if necessary.
[0043] The content of an alkali metal compound in the PVA film of
the present invention is preferably 0.5% by weight or less, more
preferably 0.3% by weight or less, more further preferably 0.1% by
weight or less, based on PVA. When the content of an alkali metal
compound is over 0.5% by weight, coloration occurs on a
polarization film, when heated in a process of dry heat stretching,
and the like. From the standpoint of coloration, lower
concentration of an alkali metal compound in PVA is more
preferable, and from the industrial standpoint, the lower limit is
preferably 0.001% by weight.
[0044] In the PVA film of the present invention, the alkali metal
compound means a compound containing an alkali metal such as
lithium, sodium, potassium and the like, and for example, lithium
acetate, sodium acetate, potassium acetate, sodium hydroxide,
potassium hydroxide, sodium tartarate, sodium lactate, sodium
phosphate and the like are listed. Among them, it is preferable to
control the content of sodium acetate since sodium acetate tends to
exert an influence on coloration of a PVA film.
[0045] To control the content of an alkali metal compound in the
PVA film of the present invention to 0.5% by weight or less,
preferably 0.3% by weight or less, further preferably 0.1% by
weight or less, it is necessary that the content of an alkali metal
compound in a PVA raw material used as a film formation raw
material is 0.5% by weight or less, preferably 0.3% by weight or
less, further preferably 0.1% by weight or less. To reduce the
content of an alkali metal compound in a PVA raw material, it is
preferable, for example, to wash a PVA raw material sufficiently
with an acidic aqueous solution such as an acetic acid aqueous
solution and the like, then, with a solvent such as water and the
like, sufficiently.
[0046] In the present invention, it is preferable to form a PVA
film using a film formation raw material containing PVA prepared at
temperatures of 150.degree. C. or less. The reason for this is that
treating temperature in preparing a film formation raw material
(temperature in dissolving a PVA raw material in solvent or in
melting water-containing PVA) exerts an influence on the hue of the
resulting polarization film. When the treating temperature in
preparing a film formation raw material is over 150.degree. C., the
resultant PVA film may manifest yellowish color, further, a
polarization film produced from this PVA film may also manifest
yellowish color. The treating temperature in preparing a film
formation raw material is preferably 150.degree. C. or less,
further preferably 140.degree. C. or less.
[0047] The drying temperature in a process of drying a PVA film is
preferably 150.degree. C. or less, further preferably 140.degree.
C. or less. When the drying temperature is over 150.degree. C., the
resultant PVA film may manifest yellowish color.
[0048] The thickness of a PVA film is preferably from 5 to 150
.mu.m, more preferably from 20 to 100 .mu.m, further preferably
from 30 to 90 .mu.m, most preferably from 35 to 80 .mu.m.
[0049] For producing a polarization film from the PVA film of the
present invention, for example, the PVA film may advantageously be
subjected to dyeing, monoaxial stretching, fixing treatment, drying
treatment, further if necessary, heat treatment, and the operation
order of dyeing, monoaxial stretching and fixing treatment is not
particularly restricted. Further, monoaxial stretching may also be
conducted twice or more times.
[0050] The dyeing can be effected at any period before monoaxial
stretching, in monoaxial stretching and after monoaxial stretching.
As the dye used in the dying, dichroic dyes such as
iodine-potassium iodide; Direct Black 17, 19, 154; Direct Brown 44,
106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240,
242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236,
249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct
Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, and the
like can be used alone or in combination of two or more. Generally,
dyeing is conducted, usually, by immersing a PVA film in a solution
containing the above-mentioned dye, however, treatment conditions
and treatment methods thereof such as mixing of a dye with a PVA
film before film formation, and the like, are not particularly
restricted.
[0051] For the monoaxial stretching, a wet stretching method or dry
heat stretching method can be used, and it can be conducted in hot
water (may also in a solution containing the above-mentioned dye or
a fixing treatment bath described below) or in air using a PVA film
after water absorption. The hot water used in the monoaxial
stretching is preferably a boric acid aqueous solution. The
stretching temperature is not particularly restricted, and when a
PVA film is stretched in hot water (wet stretching), temperatures
from 30 to 90.degree. C. are suitable, and when dry heat stretching
is conducted, temperatures from 50 to 180.degree. C. are suitable.
The stretching ratio in monoaxial stretching (in the case of
multi-stage stretching, the total stretching ratio) is preferably
at least 4-fold, and particularly, most preferably at least 5-fold,
from the standpoint of polarization characteristic. The upper limit
of the stretching is not particularly restricted, and ratios of
8-fold or less are preferable since then uniform stretching is
obtained. The thickness of a film after stretching is preferably
from 3 to 75 .mu.m, more preferably from 5 to 50 .mu.m.
[0052] The fixing treatment is often conducted for the purpose of
rendering adsorption of the above-mentioned dye onto a PVA film
stronger. Into a treating bath used for the fixing treatment, boric
acid and/or boron compound is usually added. If necessary, an
iodine compound may also be added into the treating bath.
[0053] The drying treatment (heat treatment) of the above-mentioned
PVA film is conducted at a temperature preferably from 30 to
150.degree. C., more preferably from 50 to 150.degree. C.
[0054] On a polarization film obtained as described above, a
protective film having optically transparent and having mechanical
strength is laminated on each surface or on one surface thereof to
provide a polarizer to be used. As the protective film, a triacetic
cellulose (TAC) film, cellulose acetate butyrate (CAB) film,
acrylic film, polyester film and the like are used. As the adhesive
for lamination, PVA adhesives and urethane adhesives are listed,
and of them, PVA adhesives are suitable.
[0055] Regarding the hue of a polarization film obtained from the
PVA film of the present invention, when the hue of a single body is
measured according to JIS Z 8719 (light source: C, field of view:
2.degree.), a* value is preferably from -1.6 to +1.6, further
preferably from -1.5 to +1.5. b* value is preferably from -3.0 to
+3.0, further preferably from -1.5 to +1.5.
EXAMPLES
[0056] The following examples illustrate the present invention
specifically, but dot not limit the scope of the present invention.
Dichroic ratio and hue in the examples were evaluated by the
following methods.
[0057] Dichroic Ratio
[0058] Dichroic ratio was used as an index for evaluating
polarization characteristic of the resulted polarization film. This
dichroic ratio was obtained from the following formula using
transmittance Ts (%) and degree of polarization P (%) obtained by
calculation and measurement at 2.degree. field of view and C light
souce using a spectrophotometer according to Standards of
Electronic Industries Association of Japan (EIAJ) LD-201-1983.
Dichroic ratio=log (Ts/100-Ts/100.times.P/100)/log
(Ts/100+Ts/100.times.P/- 100)
[0059] Hue:
[0060] Hue was measured according to JIS Z 8719 (light source: C,
field of view: 2.degree.).
Example 1
[0061] PVA tips were washed with hot water having a temperature of
40.degree. C. for 15 minutes at a bath ratio by weight of 3. This
PVA had a degree of hydrolysis of 99.9 mol % and a degree of
polymerization of 1750. An aqueous solution was prepared having a
PVA concentration of 15% by weight containing 100 parts by weight
of this PVA and 10 parts by weight of glycerin. Then, this aqueous
solution was cast on a metal roll of 90.degree. C. to form a film
which was dried, and the film was further dried on a metal roll of
100.degree. C., to obtain a PVA film having a thickness of 75
.mu.m.
[0062] A 10 cm square PVA film cut out from this PVA film was left
in 1 liter of water of 50.degree. C. for 4 hours, and the amount of
PVA eluted was 50 ppm at this point.
[0063] The above-mentioned PVA film was subjected to preliminary
swelling, dyeing, monoaxial stretching, fixing treatment, drying
and heat treatment in this order, to produce a polarization film.
Namely, this PVA film was immersed in water of 30.degree. C. for 5
minutes to effect preliminary swelling, and immersed in an aqueous
solution of 35.degree. C. having an iodine concentration of 0.4
g/liter and a potassium iodide concentration of 40 g/liter for 3
minutes. Subsequently, monoaxial stretching was conducted at 5.3
times in an aqueous solution of 40.degree. C. having a boric acid
concentration of 4%, then the stretched film was immersed in an
aqueous solution of 30.degree. C. having a potassium iodide
concentration of 40 g/liter, a boric acid concentration of 40
g/liter and a zinc chloride concentration of 10 g/liter for 5
minutes to effect fixing treatment. Then, the PVA film was removed,
and dried with hot air of 40.degree. C. and further, heat-treated
at 100.degree. C. for 5 minutes, while maintaining the length
constant.
[0064] Thus obtained polarization film had a thickness of 22 .mu.m,
a transmittance of 43.3%, a degree of polarization of 98.5%, and a
dichroic ratio of 33.3. Further, defects due to deposition of PVA
was not found even when a polarization film was produced
continuously using the above-mentioned PVA film.
Example 2
[0065] PVA tips were washed with hot water having a temperature of
35.degree. C. for 2 hours at a bath ratio by weight of 4. This PVA
had a degree of hydrolysis of 99.9 mol % and a degree of
polymerization of 4000. To 100 parts by weight of this PVA and 10
parts by weight of glycerin was added water so as to give a PVA
concentration of 40% by weight and the mixture was melt-kneaded in
an extruder, and melt-extruded through a dice onto a metal roll of
90.degree. C. and dried thereon, to obtain a PVA film having a
thickness of 75 .mu.m.
[0066] A 10 cm square PVA film cut out from this PVA film was left
in 1 liter of water of 50.degree. C. for 4 hours, and the amount of
PVA eluted was 40 ppm at this point.
[0067] The above-mentioned PVA film was subjected to preliminary
swelling, dyeing, monoaxial stretching, fixing treatment, drying
and heat treatment in this order, to produce a polarization film.
Namely, this PVA film was immersed in water of 30.degree. C. for 5
minutes to effect preliminary swelling, and immersed in an aqueous
solution of 35.degree. C. having an iodine concentration of 0.4
g/liter and a potassium iodide concentration of 40 g/liter for 3
minutes. Subsequently, monoaxial stretching was conducted at 5.5
times in an aqueous solution of 40.degree. C. having a boric acid
concentration of 4%, then the stretched film was immersed in an
aqueous solution of 30.degree. C. having a potassium iodide
concentration of 40 g/liter, a boric acid concentration of 40
g/liter and a zinc chloride concentration of 10 g/liter for 5
minutes to effect fixing treatment. Then, the PVA film was removed,
and dried with hot air of 40.degree. C. and further, heat-treated
at 100.degree. C. for 5 minutes, while maintaining the length
constant.
[0068] Thus obtained polarization film had a thickness of 22 .mu.m,
a transmittance of 43.0%, a degree of polarization of 99.6%, and a
dichroic ratio of 41.7. Further, defects due to deposition of PVA
was not found even when a polarization film was produced
continuously using the above-mentioned PVA film.
Comparative Example 1
[0069] A PVA film was obtained in the same manner as in Example 1
except that PVA tips were not washed.
[0070] A 10 cm square PVA film cut out from this PVA film was left
in 1 liter of water of 50.degree. C. for 4 hours, and the amount of
PVA eluted was 200 ppm at this point.
[0071] The above-mentioned PVA film was treated in the same manner
as in Example 1. The obtained polarization film had a thickness of
23 .mu.m. It had a transmittance of 43.2%, a degree of polarization
of 98.5%, and a dichroic ratio of 32.8, showing no problem on
abilities. Further, at the initial period of producing a
polarization film, the film could be produced without problem,
however, with progress of continuous production of a polarization
film, defects due to deposition of PVA were found on scattered
sites of the polarization film, and the yield of the polarization
film decreased gradually.
Comparative Example 2
[0072] A PVA film was obtained in the same manner as in Example 1
except that glycerin was not added, and heat treatment at
190.degree. C. was conducted instead of drying on a metal roll of
100.degree. C.
[0073] A 10 cm square PVA film cut out from this PVA film was left
in 1 liter of water of 50.degree. C. for 4 hours, and the amount of
PVA eluted was 0.5 ppm at this point.
[0074] The above-mentioned PVA film was tried to be subjected to
the same treatments as in Example 1, however, cutting occurred
frequently during stretching and a polarization film was not
obtained in stable manner.
Comparative Example 3
[0075] PVA tips were washed with water having a temperature of
5.degree. C. for 5 minutes at a bath ratio by weight of 0.8. This
PVA had a degree of hydrolysis of 99.6 mol % and a degree of
polymerization of 4000. A PVA film was obtained in the same manner
as in Example 2 except that to 100 parts by weight of this PVA and
10 parts by weight of glycerin was added water so as to give a PVA
concentration of 50% by weight and the mixture was melt-kneaded in
an extruder.
[0076] A 10 cm square PVA film cut out from this PVA film was left
in 1 liter of water of 50.degree. C. for 4 hours, and the amount of
PVA eluted was 150 ppm at this point.
[0077] The above-mentioned PVA film was treated in the same manner
as in Example 2. The obtained polarization film had a thickness of
22 .mu.m. It had a transmittance of 42.5%, a degree of polarization
degree of 99.7%, and a dichroic ratio of 40.6. Further, at the
initial period of producing a polarization film, the film could be
produced without problem, however, with progress of continuous
production of a polarization film, defects due to deposition of PVA
were found on scattered sites of the polarization film, and the
yield of the polarization film decreased gradually.
Example 3
[0078] 100 parts by weight of PVA tips having a sodium acetate
content of 2.4% by weight (degree of hydrolysis: 99.9 mol %, degree
of polymerization: 4000) were immersed in 2500 parts by weight of
distilled water of 35.degree. C. for 24 hours, then, dehydrated
centrifugally. The resulted PVA tip had a sodium acetate content of
0.1% by weight based on PVA. 200 parts by weight of the
water-containing PVA tips, 15 parts by weight of glycerin and water
were dissolved at 120.degree. C. in a tank to prepare a PVA
solution having a volatile content of 90% by weight. This PVA
solution was cooled to 100.degree. C. by a heat exchanger, then,
cast on a metal drum at 95.degree. C. to form a film which was
subsequently dried, to obtain a PVA film having a width of 1.2 m
and an average thickness of 75 .mu.m and a sodium acetate content
of 0.1% by weight based on PVA. A 10 cm square PVA film cut out
from this PVA film was left in 1 liter of water of 50.degree. C.
for 4 hours, and the amount of PVA eluted was 8 ppm at this
point.
[0079] This PVA film was subjected to monoaxial stretching, dyeing,
fixing treatment, drying and heat treatment in this order, to
produce a polarization film. Namely, this PVA film was monoaxially
stretched at 4.5 times at 110.degree. C. This monoaxially stretched
PVA film was immersed in an aqueous solution of 40.degree. C.
having an iodine concentration of 0.8 g/liter, a potassium iodide
concentration of 50 g/liter and a boric acid concentration of 40
g/liter for 1 minute while maintaining this film under stressed
condition. Subsequently, the film was immersed in an aqueous
solution of 65.degree. C. having a potassium iodide concentration
of 60 g/liter and a boric acid concentration of 70 g/liter for 5
minutes to effect fixing treatment. Then, this was washed with
distilled water of 20.degree. C. for 10 seconds, then, dried with
hot air of 40.degree. C. and further, heat-treated at 100.degree.
C. for 5 minutes, while maintaining the length constant.
[0080] The obtained polarization film had a thickness of 35 .mu.m
at the central part along width direction, a transmittance of
44.0%, a degree of polarization of 99.2%, and a dichroic ratio of
42.8. The hue of a single body was measured according to JIS Z 8719
(light source: C, field of view: 2.degree.), a* was -1.2 and b*
value was +0.8.
Example 4
[0081] 100 parts by weight of PVA having a sodium acetate content
of 1.9% by weight (degree of hydrolysis: 99.9 mol %, degree of
polymerization: 2400) were immersed in 10000 parts by weight of
distilled water of 30.degree. C. for 24 hours, then, dehydrated
centrifugally. The resulted PVA had a sodium acetate content of
0.03% by weight based on PVA. Water-containing tips having a
volatile content of 70% by weight obtained by impregnating 200
parts by weight of the water-containing PVA tips with 15 parts by
weight of glycerin and water were heat-melted in an extruder having
a maximum temperature of 130.degree. C. The melted substance was
cooled to 100.degree. C. by a heat exchanger, then, melt-extruded
on a metal drum at 95.degree. C. to form a film which was
subsequently dried. A PVA film having a width of 1.2 m and an
average thickness of 75 .mu.m and a sodium acetate content of 0.03%
by weight based on PVA was obtained. A 10 cm square PVA film cut
out from this PVA film was left in 1 liter of water of 50.degree.
C. for 4 hours, and the amount of PVA eluted was 2 ppm at this
point.
[0082] This PVA film was subjected to monoaxial stretching, dyeing,
fixing treatment, drying and heat treatment in this order, to
produce a polarization film. Namely, this PVA film was monoaxially
stretched at 4.5 times at 100.degree. C. This monoaxially stretched
PVA film was immersed in an aqueous solution of 40.degree. C.
having an iodine concentration of 0.8 g/liter and a potassium
iodide concentration of 50 g/liter for 1 minute while maintaining
this film under stressed condition. Subsequently, the film was
immersed in an aqueous solution of 65.degree. C. having a potassium
iodide concentration of 60 g/liter and a boric acid concentration
of 70 g/liter for 5 minutes to effect fixing treatment. Then, this
was washed with distilled water of 20.degree. C. for 10 seconds,
then, dried with hot air of 40.degree. C. and further, heat-treated
at 100.degree. C. for 5 minutes, while maintaining the length
constant.
[0083] The obtained polarization film had a thickness of 35 .mu.m
at the central part along width direction, a transmittance of
43.5%, a degree of polarization of 99.1%, and a dichroic ratio of
38.6. The hue of a single body was measured according to JIS Z 8719
(light source: C, field of view: 2.degree.), a* was -1.0 and b*
value was +0.4.
Comparative Example 4
[0084] Water-containing PVA tips having a volatile content of 70%
by weight composed of 100 parts by weight of PVA tips having a
sodium acetate content of 1.9% by weight (degree of hydrolysis:
99.9 mol %, degree of polymerization: 2400), 15 parts by weight of
glycerin and water was heat-melted in an extruder having a maximum
temperature of 130.degree. C. The melted substance was cooled to
100.degree. C. by a heat exchanger, then, melt-extruded on a metal
drum at 95.degree. C. to form a film which was subsequently dried.
A PVA film having a width of 1.2 m and an average thickness of 75
.mu.m and a sodium acetate content of 1.9% by weight based on PVA
was obtained. A 10 cm square PVA film cut out from this PVA film
was left in 1 liter of water of 50.degree. C. for 4 hours, and the
amount of PVA eluted was 180 ppm at this point.
[0085] This PVA film was subjected to monoaxial stretching, dyeing,
fixing treatment, drying and heat treatment in this order, to
produce a polarization film. Namely, this PVA film was monoaxially
stretched at 4.5 times at 110.degree. C. This monoaxially stretched
PVA film was immersed in an aqueous solution of 40.degree. C.
having an iodine concentration of 0.8 g/liter and a potassium
iodide concentration of 50 g/liter for 1 minute while maintaining
this film under stressed condition. Subsequently, the film was
immersed in an aqueous solution of 65.degree. C. having a potassium
iodide concentration of 60 g/liter and a boric acid concentration
of 70 g/liter for 5 minutes to effect fixing treatment. Then, this
was washed with distilled water of 20.degree. C. for 10 seconds,
then, dried with hot air of 40.degree. C. and further, heat-treated
at 100.degree. C. for 5 minutes, while maintaining the length
constant.
[0086] The obtained polarization film had a thickness of 35 .mu.m
at the central part along width direction, a transmittance of
42.8%, a degree of polarization of 98.9%, and a dichroic ratio of
33.3. The hue of a single body was measured according to JIS Z 8719
(light source: C, field of view: 2), a* was -1.8 and b* value was
+3.8.
[0087] Although the present invention has been fully described in
connection with the preferred embodiments thereof, those skilled in
the art will readily conceive of numerous changes and modifications
within the framework of obviousness upon the reading of the
specification herein presented of the present invention.
Accordingly, such changes and modifications are, unless they depart
from the scope of the present invention as delivered from the
claims annexed thereto, to be construed as included therein.
* * * * *