U.S. patent application number 11/405430 was filed with the patent office on 2006-08-17 for dispersion stabilizer for suspension polymerization of vinyl compound and method of producing the same.
This patent application is currently assigned to Kuraray Co., Ltd.. Invention is credited to Masako Katayama, Masaki Kato, Yoko Nakano, Kiyohiki Sho, Yoshiko Sho, Yukiko Sho, Kazuyuki Somemiya, Syunji Tago.
Application Number | 20060180956 11/405430 |
Document ID | / |
Family ID | 30447691 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060180956 |
Kind Code |
A1 |
Kato; Masaki ; et
al. |
August 17, 2006 |
Dispersion stabilizer for suspension polymerization of vinyl
compound and method of producing the same
Abstract
The present invention provides a new dispersion stabilizer that
satisfies, at a high level, the performances required for a
dispersion stabilizer used for suspension polymerization. A method
of producing a dispersion stabilizer that is useable for suspension
polymerization of a vinyl compound and contains a vinyl alcohol
polymer (A) includes producing the vinyl alcohol polymer (A) by
heat-treating a vinyl alcohol polymer (B) at a temperature of 90 to
180.degree. C. for 0.5 to 20 hours in an atmosphere in which an
oxygen concentration is 8000 ppm or lower. The vinyl alcohol
polymer (B) has a saponification degree of at least 60 mol % and
contains a residual acetic acid group whose block character is in
the range of 0.3 to 0.6.
Inventors: |
Kato; Masaki;
(Kurashiki-shi, JP) ; Somemiya; Kazuyuki;
(Kitakanbara-gun, JP) ; Tago; Syunji;
(Kitakanbara-gun, JP) ; Sho; Kiyohiki;
(Kurashiki-shi, JP) ; Sho; Yoshiko;
(Kurashiki-shi, JP) ; Sho; Yukiko; (Kurashiki-shi,
JP) ; Katayama; Masako; (Kurashiki-shi, JP) ;
Nakano; Yoko; (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: |
30447691 |
Appl. No.: |
11/405430 |
Filed: |
April 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10732524 |
Dec 11, 2003 |
7070731 |
|
|
11405430 |
Apr 18, 2006 |
|
|
|
Current U.S.
Class: |
264/349 ;
524/557 |
Current CPC
Class: |
C08F 8/00 20130101; C08F
8/12 20130101; C08F 8/12 20130101; C08F 2/20 20130101; C08F 8/00
20130101; C08F 16/06 20130101; C08F 114/06 20130101; C08F 8/06
20130101; C08F 118/08 20130101 |
Class at
Publication: |
264/349 ;
524/557 |
International
Class: |
B29B 15/00 20060101
B29B015/00; B29B 7/00 20060101 B29B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2002 |
JP |
2002-359605 |
Dec 11, 2002 |
JP |
2002-359606 |
Claims
1. A dispersion stabilizer for use in suspension polymerization of
a vinyl compound, the dispersion stabilizer comprising a vinyl
alcohol polymer (A'), wherein in a 0.1-wt. % aqueous solution of
the vinyl alcohol polymer (A'), a ratio (b)/(a) between absorbance
(a) at a wavelength of 280 nm and absorbance (b) at a wavelength of
320 nm is at least 0.7, the 0.1-wt. % aqueous solution has a
transmittance of at least 80% at a wavelength of 500 nm, at
30.degree. C., and a 1-wt. % aqueous solution of the vinyl alcohol
polymer (A') has a yellow index (YI) of 40 or lower.
2. The dispersion stabilizer according to claim 1, wherein a
residual acetic acid group of the vinyl alcohol polymer (A') has a
block character of at least 0.35.
3. The dispersion stabilizer according to claim 1, wherein a
residual acetic acid group of the vinyl alcohol polymer (A') has a
block character of at least 0.37.
4. The dispersion stabilizer according to claim 1, wherein a
residual acetic acid group of the vinyl alcohol polymer (A') has a
block character of at least 0.4.
5. The dispersion stabilizer according to claim 1, wherein a ratio
Mw/Mn between weight-average molecular weight Mw and number-average
molecular weight Mn of the vinyl alcohol polymer (A') is in a range
2.1 to 4.9.
6. The dispersion stabilizer according to claim 1, wherein the
ratio Mw/Mn, of weight-average molecular weight Mw to
number-average molecular weight Mn, of the vinyl alcohol polymer
(A') is in a range 2.2 to 4.7.
7. The dispersion stabilizer according to claim 1, wherein the
ratio Mw/Mn, of weight-average molecular weight Mw to
number-average molecular weight Mn, of the vinyl alcohol polymer
(A') is in a range 2.2 to 4.4.
8. The dispersion stabilizer according to claim 1, wherein the
ratio (b)/(a) between the absorbance (b) and the absorbance (a) is
in the range of 0.7 to 1.5.
9. The dispersion stabilizer according to claim 1, wherein the
absorbance (a) at a wavelength of 280 nm of the 0.1-wt. % aqueous
solution of the vinyl alcohol polymer (A') is at least 0.1.
10. The dispersion stabilizer according to claim 1, wherein the
absorbance (a) at a wavelength of 280 nm of the 0.1-wt. % aqueous
solution of the vinyl alcohol polymer (A') is at least 0.2.
11. The dispersion stabilizer according to claim 1, wherein the
absorbance (a) at a wavelength of 280 nm of the 0.1-wt. % aqueous
solution of the vinyl alcohol polymer (A') is at least 0.25.
12. The dispersion stabilizer according to claim 1, wherein the YI
of the 1-wt. % aqueous solution of the vinyl alcohol polymer (A')
is 35 or lower.
13. The dispersion stabilizer according to claim 1, wherein the YI
of the 1-wt. % aqueous solution of the vinyl alcohol polymer (A')
is 30 or lower.
14. The dispersion stabilizer according to claim 1, wherein the
0.1-wt. % aqueous solution of the vinyl alcohol polymer (A') has a
transmittance of at least 82% at a wavelength of 500 nm, at
30.degree. C.
15. The dispersion stabilizer according to claim 1, wherein the
0.1-wt. % aqueous solution of the vinyl alcohol polymer (A') has a
transmittance of at least 85% at a wavelength of 500 nm, at
30.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/732,524, filed Dec. 11, 2003, now allowed, which claims
priority to Japanese patent application No. 2002-359605, filed Dec.
11, 2002, and Japanese patent application No. 2002-359606, filed
Dec. 11, 2002, all of which are incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a dispersion
stabilizer for use in suspension polymerization of a vinyl compound
and a method of producing the same.
[0004] 2. Related Background Art
[0005] Industrially, vinyl polymers such as vinyl chloride resin
are produced by suspension polymerization. In this suspension
polymerization, a vinyl compound such as vinyl chloride is
dispersed in an aqueous medium containing a dispersion stabilizer,
and polymerization is conducted using an oil-soluble catalyst.
Generally, the factors governing the quality of vinyl polymers
include, for example, the degrees of conversion, the water/monomer
ratio, the polymerization temperature, the type and amount of
catalyst, the type of polymerization vessel, the stirring rate, and
the type of dispersion stabilizer. Among these factors, the type of
dispersion stabilizer has a considerable effect.
[0006] The following properties are important for a dispersion
stabilizer used for suspension polymerization of a vinyl compound.
(1) Addition of a small amount functions to allow vinyl polymer
particles produced therewith to have a narrow particle size
distribution. (2) It functions to make vinyl polymer particles
produced therewith as uniform as possible and making them porous.
This property is required for obtaining, for example, a vinyl
polymer that can be processed easily and has a high rate of
plasticizer absorption, a vinyl polymer that facilitates the
removal of monomers such as vinyl chloride remaining in polymer
particles, and a vinyl polymer that can prevent fish eyes from
being formed in molded articles. (3) It functions to form polymer
particles having a high bulk density. (4) It functions to suppress
the generation of wet foam and dry foam and thereby prevent any
decrease in productivity. (5) It has no harmful effect on the hue
of a vinyl polymer obtained therewith. (6) It does not make an
aqueous solution cloudy during charging for polymerization.
[0007] Conventionally, as a dispersion stabilizer for suspension
polymerization of a vinyl compound, for instance, cellulose
derivatives such as methylcellulose and carboxymethylcellulose, and
partially saponified polyvinyl alcohol have been used either alone
or in appropriate combinations. Conventional dispersion
stabilizers, however, do not always satisfactorily meet the
performance criteria described in (1) to (6) above.
[0008] For instance, polyvinyl alcohol having a polymerization
degree of 2000 and a saponification degree of 80 mol % and
polyvinyl alcohol having a polymerization degree of 700 to 800 and
a saponification degree of 70 mol % are disclosed as dispersion
stabilizers for suspension polymerization of vinyl chloride (Poval,
Koubunshi Kankoukai, pp. 413-414, issued in 1984). These dispersion
stabilizers, however, do not meet satisfactorily the performance
criteria described in (1) to (3) above.
[0009] Furthermore, JP5(1993)-88251B describes a dispersion
stabilizer that is used for suspension polymerization of a vinyl
compound and is made of polyvinyl alcohol. This polyvinyl alcohol
has a mean degree of polymerization of at least 500 and a ratio
Pw/Pn, between a weight average degree of polymerization Pw and a
number average degree of polymerization Pn, of 3.0 or lower. This
polyvinyl alcohol includes a carbonyl group and a vinylene group
adjacent thereto. Furthermore, a 0.1-% aqueous solution of this
polyvinyl alcohol has absorbances of at least 0.3 and at least 0.15
at wavelengths of 280 nm and 320 nm in the ultraviolet absorption
spectrum, respectively, and a ratio (b)/(a) of the absorbance (b)
at a wavelength of 320 nm to the absorbance (a) at a wavelength of
280 nm of at least 0.30.
[0010] JP5(1993)-105702A describes a dispersion stabilizer that is
used for suspension polymerization of vinyl chloride and is made of
polyvinyl alcohol. This polyvinyl alcohol has a saponification
degree of 75 to 85 mol % and contains 0.01 to 0.15 mol % carboxyl
groups. Its 0.1-wt. % aqueous solution has an absorbance of at
least 0.1 at a wavelength of 280 nm and a clouding point of at
least 50.degree. C. The above-mentioned two stabilizers made of
polyvinyl alcohol, however, also do not always meet the performance
criteria described in (1) to (5).
[0011] Moreover, JP8(1996)-208724 discloses a dispersant used for
suspension polymerization of monomers having an ethylenically
unsaturated double bond. This dispersant is made of a vinyl alcohol
polymer. Its 1-wt. % aqueous solution has an absorbance of at least
2.5 at a wavelength of 280 nm. The vinyl alcohol polymer has a mean
degree of polymerization of at least 500, a saponification degree
of 60 to 90 mol %, a ratio Mw/Mn of weight-average molecular weight
Mw to number-average molecular weight Mn of 2.5 or lower, a block
character with respect to the saponification degree of 0.45 or
lower, and a methanol-soluble portion of 10 wt. % or less. This
dispersant exhibits properties that are balanced relatively well
with respect to the requirements described in (1) to (3). However,
in some cases, it does not perform satisfactorily with respect to
the requirement described in (6).
SUMMARY OF THE INVENTION
[0012] With the foregoing in mind, the present invention intends to
provide a new dispersion stabilizer that satisfies, at a high
level, the performance criteria required for a dispersion
stabilizer for use in suspension polymerization. The present
inventors studied assiduously to solve the above-mentioned problems
and as a result, achieved the present invention described
bellow.
[0013] A production method of the present invention is a method of
producing a dispersion stabilizer that is suitable for use in
suspension polymerization of a vinyl compound and that contains a
vinyl alcohol polymer (A). This method comprises producing the
vinyl alcohol polymer (A) by heat-treating a vinyl alcohol polymer
(B) at a temperature of 90 to 180.degree. C. for 0.5 to 20 hours in
an atmosphere having an oxygen concentration of 8000 ppm or lower.
The vinyl alcohol polymer (B) has a saponification degree of at
least 60 mol %, and contains residual acetic acid groups whose
block character is in a range of 0.3 to 0.6.
[0014] A dispersion stabilizer of the present invention is a
dispersion stabilizer that is suitable for use in suspension
polymerization of a vinyl compound and contains a vinyl alcohol
polymer (A'). In a 0.1-wt. % aqueous solution of the vinyl alcohol
polymer (A'), a ratio (b)/(a) between absorbance (a) at a
wavelength of 280 nm and absorbance (b) at a wavelength of 320 nm
is at least 0.7. The 0.1-wt. % aqueous solution has a transmittance
of at least 80% at a wavelength of 500 nm, at 30.degree. C.
Furthermore, a 1-wt. % aqueous solution of the vinyl alcohol
polymer (A') has a yellow index (YI) of 40 or lower.
[0015] The dispersion stabilizer according to the present invention
provides effects such as, for instance, less polymer scale adhesion
to the inner wall of a polymerization vessel, as compared to
conventional dispersion stabilizers. Hence, the use of the
dispersion stabilizer of the present invention allows suspension
polymerization to be carried out more stably. Furthermore, foaming
caused by polyvinyl alcohol can be suppressed by using this
dispersion stabilizer. Moreover, polymer particles with a high bulk
density can be produced through the suspension polymerization of a
vinyl compound using the dispersion stabilizer. The polymer
particles thus formed are industrially very useful since they have
gelling characteristics and a high plasticizer absorptivity and are
excellent in processability.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Hereinafter, preferred embodiments of the present invention
are described. The present invention relates to a dispersion
stabilizer comprising a vinyl alcohol polymer (hereinafter also
referred to as a vinyl alcohol polymer (A)) and a method of
producing the same. The dispersion stabilizer of the present
invention may contain elements other than the vinyl alcohol polymer
(A) as long as the advantageous of the present invention are
maintained. The dispersion stabilizer of the present invention can
be used as a stabilizer for suspension polymerization of a vinyl
compound.
[0017] The production method of the present invention includes a
step of producing the vinyl alcohol polymer (A) by the heat
treatment of a vinyl alcohol polymer (hereinafter also referred to
as a vinyl alcohol polymer (B)) at a temperature of 90 to
180.degree. C. for 0.5 to 20 hours in an atmosphere having an
oxygen concentration of 8000 ppm or lower. The vinyl alcohol
polymer (B) has a saponification degree of at least 60 mol % and
contains residual acetic acid groups whose block character is 0.3
to 0.6. Furthermore, dispersion stabilizers containing the vinyl
alcohol polymer (A) produced by this method form an another aspect
of the invention.
[0018] In a preferred example of the present invention, the
difference in block character of residual acetic acid groups
between the vinyl alcohol polymer (B) that has not been
heat-treated and the vinyl alcohol polymer (A) that has been
heat-treated is at least 0.02 and the difference in surface tension
between their 0.4-wt. % aqueous solutions is 0.5 mN/m or less.
[0019] In a preferred example of the present invention, a
difference in viscosity between 4-wt. % aqueous solutions of the
vinyl alcohol polymer (B) that has not been heat-treated and the
vinyl alcohol polymer (A) that has been heat-treated is 0.5 mPas or
less.
[0020] The block character of the residual acetic acid groups of
the vinyl alcohol polymer (B) that has not been heat-treated is 0.3
to 0.6, preferably 0.32 to 0.58, and further preferably 0.35 to
0.55. In this specification, the term "residual acetic acid groups
(i.e. residual acetoxyl groups)" denotes acetic acid groups
(acetoxyl groups) that have not been saponified in the production
of the vinyl alcohol polymer carried out by saponification of a
vinyl ester polymer. When the block character of the residual
acetic acid groups of the vinyl alcohol polymer (B) is less than
0.3, aqueous solutions of the vinyl alcohol polymer (A) that has
been heat-treated have a inferior handling properties. On the other
hand, when the block character of the residual acetic acid groups
of the vinyl alcohol polymer (B) exceeds 0.6, a vinyl polymer
obtained by suspension polymerization using the vinyl alcohol
polymer (A) has decreased plasticizer absorptivity. In this
connection, with respect to the block character of the residual
acetic acid groups, details including its measurement and the like
are described in Poval (Koubunshi Kankoukai, issued in 1984, pp.
246-249) and Macromolecules, 10, 532 (1977).
[0021] The assessment of block character is described briefly
herein. The block character .eta. is expressed by the following
formula. .eta.=(OH, OAc)/[2(OH)(OAc)]
[0022] In the above-mentioned formula, (OH) and (OAc) indicate the
mole fraction of the vinyl alcohol unit and the mole fraction of
the vinyl acetate unit, respectively. Furthermore, (OH, OAc)
denotes the mole fraction of the structure with a vinyl alcohol
unit and a vinyl acetate unit being in succession. When the vinyl
alcohol unit and the vinyl acetate unit are sequenced always
alternately, (OH, OAc)=1 and (OH)=(OAc)=0.5, resulting in .eta.=2.
When the vinyl alcohol unit and the vinyl acetate unit are
sequenced at random, .eta.=1. Moreover, when the vinyl alcohol
units and the vinyl acetate unit are separated completely from each
other into respective blocks, .eta.=0. That is, the larger the
block character .eta., the lower the rate at which they are
separated into blocks is.
[0023] The block character of the residual acetic acid groups of
the vinyl alcohol polymer can be adjusted by, for example, suitably
selecting a saponification catalyst and a solvent that are used in
producing the vinyl alcohol polymer through the saponification of a
vinyl ester polymer. As compared to alkaline saponification using
an alkaline compound for the saponification catalyst, acidic
saponification using an acidic compound for the saponification
catalyst generally allows a vinyl alcohol polymer having a higher
block character to be obtained.
[0024] The oxygen concentration in the atmosphere in which the
vinyl alcohol polymer (B) is heat-treated is 8000 ppm or lower,
preferably 5000 ppm or lower, and more preferably 2000 ppm or
lower. When the oxygen concentration exceeds 8000 ppm, the vinyl
alcohol polymer that has been heat-treated is colored, which
adversely affects the hue of the vinyl polymer obtained by the
suspension polymerization using this vinyl alcohol polymer that has
been heat-treated. Furthermore, an oxygen concentration exceeding
8000 ppm decreases the plasticizer absorptivity of the vinyl
polymer obtained by suspension polymerization using this vinyl
alcohol polymer that has been heat-treated. The oxygen
concentration in the atmosphere in which the heat treatment is
carried out is preferably at least 5 ppm, more preferably at least
10 ppm, particularly preferably at least 20 ppm. The atmosphere in
which the heat treatment is carried out may contains a gas other
than oxygen that substantially does not react with the vinyl
alcohol polymer at a temperature of 180.degree. C. or lower.
Examples of such gases include rare gases typified by argon and
helium, nitrogen, etc. Among these, nitrogen is industrially
preferable.
[0025] The temperature at which the vinyl alcohol polymer (B) is
heat-treated is 90 to 180.degree. C., preferably 95 to 170.degree.
C., and more preferably 100 to 160.degree. C. When the heat
treatment temperature is lower than 90.degree. C., certain effects
(for instance, the increase in stability during the suspension
polymerization) to be provided by the heat treatment cannot be
obtained satisfactorily in some cases. On the other hand, when the
heat treatment temperature exceeds 180.degree. C., the vinyl
alcohol polymer may be cross-linked through the heat treatment in
some cases. As a result of such cross-linking, the vinyl polymer
obtained by the suspension polymerization using the vinyl alcohol
polymer (A) may contain a larger amount of insoluble substances and
this causes fish eyes.
[0026] The vinyl alcohol polymer (B) is heat-treated for 0.5 to 20
hours, preferably 1 to 18 hours, and more preferably 1 to 16 hours.
When the heat treatment time is less than 0.5 hour, the aqueous
solution of the resulting vinyl alcohol polymer has inferior
handling properties. Furthermore, in a continuous production
process, from the viewpoint of attaching importance to the quality
of the vinyl alcohol polymer (A) to be obtained after the heat
treatment, it is more preferable that the heat treatment time
exceeds five hours. When the heat treatment time exceeds 20 hours,
the vinyl polymer obtained by the suspension polymerization using
the vinyl alcohol polymer (A) has lower plasticizer
absorptivity.
[0027] The vinyl alcohol polymer (B) that has not been heat-treated
and the vinyl alcohol polymer (A) that has been heat-treated both
have a saponification degree of at least 60 mol %, preferably 65 to
95 mol %, and more preferably 68 to 90 mol %. When the vinyl
alcohol polymer has a saponification degree lower than 60 mol %,
this has lower solubility and thereby has a inferior handling
properties.
[0028] It is preferable that the vinyl alcohol polymer (B) that has
not been heat-treated and the vinyl alcohol polymer (A) that has
been heat-treated both contain 3.0 wt. % or less of sodium acetate.
In this connection, the lower limit of the amount of sodium acetate
contained therein is not particularly restricted but preferably is
at least 0.01 wt. %.
[0029] The difference in block character of the residual acetic
acid group between the vinyl alcohol polymer (B) that has not been
heat-treated and the vinyl alcohol polymer (A) that has been
heat-treated is preferably at least 0.02, more preferably at least
0.025, and more preferably at least 0.03. When the difference in
block character of the residual acetic acid groups is less than
0.02, the improvement of the stability during the suspension
polymerization provided by the heat treatment cannot be exhibited
sufficiently in some cases.
[0030] The difference in surface tension between 0.4-wt. % aqueous
solutions of the vinyl alcohol polymer (B) that has not been
heat-treated and the vinyl alcohol polymer (A) that has been
heat-treated is preferably 0.5 mN/m or less, more preferably 0.45
mN/m or less, and more preferably 0.4 mN/m or less. When the
difference in surface tension between the 0.4-wt. % aqueous
solutions exceeds 0.5 mN/m, the vinyl polymer obtained by the
suspension polymerization using the vinyl alcohol polymer (A) may
have lower plasticizer absorptivity.
[0031] The difference in viscosity between 4-wt. % aqueous
solutions of the vinyl alcohol polymer (B) that has not been
heat-treated and the vinyl alcohol polymer (A) that has been
heat-treated is preferably 0.5 mPas or less, more preferably 0.45
mPas or less, and further preferably 0.4 mPas or less. When the
difference in viscosity between the 4-wt. % aqueous solutions
exceeds 0.5 mPas, the vinyl polymer obtained by the suspension
polymerization using the vinyl alcohol polymer (A) may have lower
plasticizer absorptivity.
[0032] The mean degrees of polymerization of the vinyl alcohol
polymers (A) and (B) are both preferably 500 to 4000, more
preferably 600 to 3500, and most preferably 650 to 3000. When the
mean degrees of polymerization of the vinyl alcohol polymers are
lower than 500, the polymerization stability in the suspension
polymerization of a vinyl compound may decrease. On the other hand,
when the mean degrees of polymerization of the vinyl alcohol
polymers exceed 4000, the vinyl alcohol polymers may have inferior
handling properties or their productivity may decrease.
[0033] The method of producing the vinyl alcohol polymer (B) is not
particularly limited. Generally, it is produced using a method
comprising saponifying a vinyl ester polymer obtained by the
polymerization of vinyl ester monomers. As the method of
polymerizing vinyl ester monomers, such methods include solution
polymerization, block polymerization, suspension polymerization,
emulsion polymerization, etc.
[0034] As a polymerization initiator used for polymerizing the
vinyl ester monomers, for example, a well-known azo initiator,
peroxide initiator, or redox initiator maybe used. The initiator is
suitably selected depending on the polymerization method. Examples
of azo initiators include 2,2'-azobisisobutyronitrile,
2,2'-azobis(2,4-dimethylvaleronitrile), and
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of
peroxide initiators include percarbonate compounds such as
diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate,
and diethoxyethyl peroxydicarbonate; perester compounds such as
t-butyl peroxyneodecanate, .alpha.-cumyl peroxyneodecanate, and
t-butyl peroxydecanate; acetylcyclohexylsulfonyl peroxide; and
2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Further, combinations
of the above-mentioned initiators with, for example, potassium
persulfate, ammonium persulfate, or hydrogen peroxide also can be
used as an initiator. Examples of redox initiators include
combinations of the above mentioned peroxides with a reductant such
as sodium hydrogensulfite, sodium hydrogencarbonate, tartaric acid,
L-ascorbic acid, Rongalit, etc. The polymerization temperature
usually is selected from the range of 0 to 180.degree. C.
[0035] Examples of the vinyl ester monomers include vinyl formate,
vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate,
vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate,
vinyl laurylate, vinyl palmitate, vinyl stearate, vinyl oleate, and
vinyl benzoate. Among them, vinyl acetate is most preferable. When
using vinyl acetate by itself, it is also is possible to obtain a
vinyl alcohol polymer (B) by polymerizing vinyl acetate to produce
polyvinyl acetate and then saponifying the polyvinyl acetate. The
vinyl alcohol polymer (B) may contain substantially no ethylene
units. In this connection, the phrase "contain substantially no
ethylene units" denotes that the content of ethylene units is less
than 0.5 mol %.
[0036] In the polymerization of vinyl ester monomers, other
monomers may be copolymerized without parting from the scope of the
present invention. Examples of the monomers to be copolymerized
include .alpha.-olefins such as ethylene, propylene, n-butene, and
isobutylene; acrylic acid and salts thereof; acrylic acid esters
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, and octadecyl
acrylate; methacrylic acid and salts thereof; methacrylic acid
esters 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, and octadecyl methacrylate; acrylamide;
acrylamide derivatives such as N-methylacrylamide,
N-ethylacrylamide, N,N-dimethylacrylamide, diacetonacrylamide,
acrylamide propanesulfonic acid and salts thereof, acrylamide
propyl dimethylamine and salts or quaternary salts thereof, and
N-methylolacrylamide and derivatives thereof; methacrylamide;
methacrylamide derivatives such as N-methylmethacrylamide,
N-ethylmethacrylamide, methacrylamide propanesulfonic acid and
salts thereof, methacrylamide propyl dimethylamine and salts or
quaternary salts thereof, and N-methylolmethacrylamide and
derivatives thereof; vinyl ethers such as methylvinyl ether,
ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether,
n-butylvinyl ether, i-butylvinyl ether, t-butylvinyl ether,
dodecylvinyl ether, and stearylvinyl ether; nitriles such as
acrylonitrile and methacrylonitrile; vinyl halides such as vinyl
chloride and vinyl fluoride; vinylidene halides such as vinylidene
chloride and vinylidene fluoride; allyl compounds such as allyl
acetate and allyl chloride; unsaturated dicarboxylic acids such as
maleic acid, itaconic acid, and fumaric acid, and salts or esters
thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and
isopropenyl acetate. In addition, combinations of different types
of monomers mentioned above may be used.
[0037] In the polymerization of vinyl ester monomers, the vinyl
ester monomers may be polymerized in the presence of a chain
transfer agent for the purposes of, for example, adjusting the
polymerization degree of the resulting vinyl ester polymers.
Examples of chain transfer agents include aldehydes such as
acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde;
ketones such as acetone, methyl ethyl ketone, hexanone, and
cyclohexanone; mercaptans such as 2-hydroxy ethanethiol and
dodecylmercaptan; and hydrocarbon halides such as trichloroethylene
and perchloroethylene. Among these, aldehydes and ketones are used
suitably. The amount of the chain transfer agent to be added
depends on the chain transfer constant of the chain transfer agent
and the polymerization degree of the vinyl ester polymer to be
obtained. Generally, the amount of the chain transfer agent is
desirably 0.1 to 10 wt. % with respect to the amount of vinyl ester
monomers.
[0038] The saponification of the vinyl ester polymer can be carried
out by well-known methods, for example, alcoholysis or hydrolysis
using a basic catalyst such as sodium hydroxide, potassium
hydroxide, and sodium methoxide, or an acid catalyst such as
p-toluenesulfonic acid. The solvent can be, for example, alcohols
such as methanol and ethanol; esters such as methyl acetate and
ethyl acetate; ketones such as acetone and methyl ethyl ketone; and
aromatic hydrocarbons such as benzene and toluene. These solvents
can be used individually, or as combinations of two types or more
types. Particularly, a saponification reaction using methanol or a
methanol/methyl acetate mixture as solvent and sodium hydroxide as
catalyst can be carried out easily.
[0039] In a preferred example of the method of producing the vinyl
alcohol polymer (B), first vinyl ester monomers are polymerized in
the presence of an initiator and a compound (for instance,
aldehydes or ketones) having a carbonyl group in its molecule and
thereby a vinyl ester polymer is produced. Thereafter, the vinyl
ester polymer thus obtained is saponified to produce a vinyl
alcohol polymer.
[0040] Next, the description is directed to a dispersion stabilizer
of the present invention that is usable for suspension
polymerization of a vinyl compound. This dispersion stabilizer is
composed of a vinyl alcohol polymer (hereinafter referred to as a
"vinyl alcohol polymer (A')" in some cases). This vinyl alcohol
polymer (A') can be produced by the above-mentioned method of the
present invention. The dispersion stabilizer of the present
invention may also comprise components other than the vinyl alcohol
polymer (A') as long as they do not contravene the intention of the
present invention.
[0041] The vinyl alcohol polymer (A') is described as follows. In a
0.1-wt. % aqueous solution of the vinyl alcohol polymer (A'), the
ratio (b)/(a) between the absorbance (a) at a wavelength of 280 nm
and the absorbance (b) at a wavelength of 320 nm is at least 0.7.
The 0.1-wt. % aqueous solution of the vinyl alcohol polymer (A')
has a transmittance of at least 80% at a wavelength of 500 nm, at
30.degree. C. Furthermore, a 1-wt. % aqueous solution of the vinyl
alcohol polymer (A') has a YI of 40 or lower.
[0042] Moreover, it is preferable that the residual acetic acid
groups of the vinyl alcohol polymer (A') have a block character of
at least 0.35. In the vinyl alcohol polymer (A'), it is preferable
that the ratio Mw/Mn between weight-average molecular weight Mw and
number-average molecular weight Mn is in the range of 2.1 to
4.9.
[0043] The absorbance (a) at a wavelength of 280 nm of the 0.1-wt.
% aqueous solution of the vinyl alcohol polymer (A') is preferably
at least 0.1, more preferably at least 0.2, and most preferably at
least 0.25. The upper limit of the absorbance (a) is not
particularly restricted, but is, for example, 0.8 or lower. On the
other hand, the absorbance (b) at a wavelength of 320 nm of the
above-mentioned aqueous solution is preferably at least 0.07, more
preferably at least 0.09, and most preferably at least 0.1. The
upper limit of the absorbance (b) is not particularly restricted,
but is, for example, 0.6 or lower. The ratio (b)/(a) between the
absorbance (b) and the absorbance (a) is at least 0.7, preferably
in the range of 0.7 to 1.5. When the ratio (b)/(a) is lower than
0.7, the polymerization stability in the suspension polymerization
of a vinyl compound may deteriorate in some cases. The absorbance
mentioned above can be measured by the method described in the
accompanying Examples.
[0044] Examples of the method of adjusting the above-mentioned
ratio (b)/(a) to at least 0.7 include a method of treating the
vinyl alcohol polymer with acid or alkali and a method of
heat-treating the vinyl alcohol polymer.
[0045] The YI of the 1-wt. % aqueous solution of the vinyl alcohol
polymer (A') is 40 or lower, preferably 35 or lower, and further
preferably 30 or lower. In the case where the YI of the 1-wt. %
aqueous solution of the vinyl alcohol polymer (A') exceeds 40,
while the polymer obtained by the suspension polymerization is
processed, the polymer is colored. The case therefore is not
preferable. The YI (yellow index) is a value indicating yellowness
and is expressed as a positive amount corresponding to the degree
to which the hue departs from a transparent or white color toward
yellowish colors. A smaller value of YI means that the hue is
closer to the transparent or white color.
[0046] The 0.1-wt. % aqueous solution of the vinyl alcohol polymer
(A') has a transmittance of at least 80%, preferably at least 82%,
and more preferably at least 85% at a wavelength of 500 nm, at
30.degree. C. When the 0.1-wt. % aqueous solution of the vinyl
alcohol polymer has a transmittance lower than 80%, at 30.degree.
C., the aqueous solution of the vinyl alcohol polymer has a
inferior handling properties.
[0047] The residual acetic acid groups of the vinyl alcohol polymer
(A') preferably have a block character of at least 0.35, more
preferably at last 0.37, and most preferably at least 0.4. When the
residual acetic acid groups of the vinyl alcohol polymer have a
block character lower than 0.35, the aqueous solution of the vinyl
alcohol polymer may have a inferior handling properties.
[0048] The ratio Mw/Mn, of weight-average molecular weight Mw to
number-average molecular weight Mn, of the vinyl alcohol polymer
(A') is preferably 2.1 to 4.9, more preferably 2.2 to 4.7, and most
preferably 2.2 to 4.4. When the value of Mw/Mn is larger than 4.9,
the vinyl polymer particles obtained by suspension polymerization
of a vinyl compound have a broader particle size distribution. In
this connection, the number-average molecular weight Mn and the
weight-average molecular weight Mw of the vinyl alcohol polymer are
values measured by the gel permeation chromatography (GPC) method
described herein.
[0049] The ratio Mw/Mn of the vinyl alcohol polymer can be adjusted
by various methods, for example, by the following methods. A first
method is a method of blending vinyl alcohol polymers having
different polymerization degrees. A second method is a method of
saponifying a blend of vinyl ester polymers having different
polymerization degrees from each other. A third method is a method
of producing a vinyl ester polymer containing a component with a
low polymerization degree using an agent for controlling the
polymerization degree such as aldehydes, hydrocarbon halides or
mercaptans, and then saponifying the vinyl ester polymer thus
obtained. A fourth method is a method of producing a vinyl ester
polymer by carrying out polymerization of vinyl ester monomers in
multiple steps while adjusting their polymerization degree in each
step, and then saponifying the vinyl ester polymer thus obtained.
Furthermore, a fifth method is a method of producing a vinyl ester
polymer while adjusting the rate of polymerization of vinyl ester
monomers and then saponifying the vinyl ester polymer thus
obtained.
[0050] The saponification degree of the vinyl alcohol polymer (A')
is preferably at least 60 mol %, more preferably 65 to 95 mol %,
and most preferably 68 to 90 mol %. When the saponification degree
of the vinyl alcohol polymer is lower than 60 mol %, the vinyl
alcohol polymer has a lower water-solubility and may thus have
inferior handling properties.
[0051] The mean degree of polymerization of the vinyl alcohol
polymer (A') is preferably 500 to 4000, more preferably 600 to
3500, and most preferably 650 to 3000. When the mean degree of
polymerization of the vinyl alcohol polymer is lower than 500, the
polymerization stability in the suspension polymerization of a
vinyl compound may decrease. On the other hand, when the mean
degree of polymerization of the vinyl alcohol polymer is higher
than 4000, the vinyl polymer obtained by the suspension
polymerization of a vinyl compound may have a lower plasticizer
absorptivity or the vinyl polymer particles may have a broader
particle size distribution.
[0052] Next, the description is directed to an example of the
method of producing a vinyl polymer by suspension polymerization of
a vinyl compound using the dispersion stabilizer of the present
invention.
[0053] In the suspension polymerization of a vinyl compound in an
aqueous medium using the dispersion stabilizer of the present
invention, the temperature of the aqueous medium is not
particularly limited. The aqueous medium can be suitably used at,
for example, in a range of 20.degree. C. to 90.degree. C., or at
even high temperature. This aqueous medium can be pure water or an
aqueous medium that contains an aqueous solution containing various
additives, or another organic solvent. The amount of aqueous medium
to be supplied to a polymerization reaction system is not
restricted as long as it allows the polymerization reaction system
to be heated sufficiently. Furthermore, in order to increase heat
removal efficiency, a polymerization vessel fitted with a reflux
condenser is also used suitabe.
[0054] When the suspension polymerization of a vinyl compound is
carried out using the dispersion stabilizer of the present
invention, the amount of the dispersion stabilizer to be used is
not particularly limited, but is preferably 0.01 to 5 parts by
weight, more preferably 0.02 to 2 parts by weight, and most
preferably 0.02 to 1 part by weight with respect to 100 parts by
weight of the vinyl compound.
[0055] The dispersion stabilizer of the present invention may be
used by itself or together with another dispersion stabilizer that
is usually used for suspension polymerization of a vinyl compound
in an aqueous medium. Examples of such dispersion stabilizers
include water-soluble cellulose ethers such as methyl cellulose,
hydroxyethyl cellulose, hydroxypropyl cellulose, and
hydroxypropylmethyl cellulose. In addition, water-soluble polymers
such as vinyl alcohol polymer and gelatin may also be used.
Furthermore, oil-soluble emulsifying agents also may be used
including, for example, sorbitan monolaurate, sorbitan trioleate,
glycerin tristearate, and ethylene oxide/propylene oxide block
copolymers. Moreover, water-soluble emulsifying agents can also be
used including, for example, polyoxyethylenesorbitan monolaurate,
polyoxyethyleneglycerin oleate, and sodium laurate. The amount of a
dispersant added to the polymerization reaction is not particularly
limited, but is preferably 0.01 to 1.0 part by weight per 100 parts
by weight of the vinyl compound.
[0056] In the suspension polymerization of a vinyl compound using
the dispersion stabilizer of the present invention, the
polymerization initiator can be selected from those conventionally
used for polymerizing a vinyl compound. Specifically, the same
initiators as those described as examples in the above-mentioned
method of polymerizing vinyl ester monomers can be used.
[0057] Furthermore, in the suspension polymerization of a vinyl
compound using the dispersion stabilizer of the present invention,
other various additives may be added to the polymerization system
as required. Examples of the additives include agents for
controlling the polymerization degree such as aldehydes,
hydrocarbon halides, and mercaptans; and polymerization inhibitors
such as phenolic compounds, sulfur compounds, and N-oxide
compounds. Further, pH adjustors, scale inhibitors, and
crosslinking agents can also be added as required, and a plurality
of the additives mentioned above may be used together.
[0058] Examples of vinyl compounds that can be subjected to
suspension polymerization using the dispersion stabilizer of the
present invention include vinyl chloride alone, or a monomer
mixture containing vinyl chloride as its main component (vinyl
chloride: at least 50 wt. %). Examples of the comonomers to be
copolymerized with vinyl chloride include vinyl esters such as
vinyl acetate and vinyl propionate; (meth)acrylic acid esters such
as methyl (meth)acrylate and ethyl (meth)acrylate; .alpha.-olefins
such as ethylene and propylene; unsaturated dicarboxylic acids such
as maleic anhydride and itaconic acid; acrylonitrile, styrene,
vinylidene chloride, vinyl ether, and other monomers that can be
copolymerized with vinyl chloride. Furthermore, the dispersion
stabilizer of the present invention can also be used in the case
where the above-mentioned vinyl compound containing no vinyl
chloride is polymerized individually or is copolymerized.
[0059] In the suspension polymerization of the vinyl compound using
the dispersion stabilizer of the invention, the proportion of each
component to be charged, the polymerization temperature, and the
like may be determined according to the conditions employed
conventionally in suspension polymerization of vinyl compounds such
as vinyl chloride. Further, the vinyl compound, the polymerization
initiator, the aqueous medium, and other conditions (for instance,
the order of charging additives or the ratio thereof) are not
limited at all. Moreover, a method also is used suitably in which
hot water is used as the aqueous medium and the vinyl compound is
heated before being charged into a polymerization vessel.
[0060] As described above, according to the present invention, a
dispersion stabilizer can be obtained that allows suspension
polymerization to be carried out stably by providing effects such
as, for example, less polymer scale adhesion to the inner wall of
the polymerization vessel. The use of this dispersion stabilizer
can inhibit foaming caused by vinyl alcohol polymer. Furthermore,
by the suspension polymerization of a vinyl compound carried out
using the dispersion stabilizer, vinyl polymer particles can be
produced that are less colored and have high plasticizer
absorptivity and a high bulk density.
EXAMPLES
[0061] Hereinafter, the present invention is described in further
detail using examples but is not limited to the examples by no
means. In the examples described below, "%" denotes "% by weight
(wt. %)" unless otherwise specified.
Analysis of Vinyl Alcohol Polymer
[0062] A method of analyzing a vinyl alcohol polymer is described
as follows.
(1) Mean Degree of Polymerization
[0063] The mean degree of polymerization was measured according to
JIS K6726 that is a method specified by Japanese Industrial
Standard (JIS).
(2) Saponification Degree
[0064] The saponification degree was measured according to JIS
K6726.
(3) Block Character
[0065] The block character was determined from the peak in the
methylene region of .sup.13C-NMR according to the measurement
method described in Poval (Koubunshi Kankoukai, issued in 1984, pp.
246-249) and Macromolecules, 10, 532 (1977). Specifically,
.sup.13C-NMR measurements were carried out and the above-mentioned
mole fractions (OH), (OAc) and (OH, OAc) were calculated from the
intensities of resonances corresponding to a methylene group in
"--CHOH--CH.sub.2--CHOH-" structure, a methylene group in
"--CHOH--CH.sub.2--CHOAc--" structure and a methylene group in
"--CHOAc--CH.sub.2--CHOAc--" structure. The block character was
determined from the mole fractions (OH), (OAc) and (OH, OAc).
(4) Surface Tension
[0066] A 0.4-wt. % aqueous solution of a vinyl alcohol polymer was
prepared and its surface tension at 20.degree. C. was measured
using a surface tension balance (manufactured by KYOWA INTERFACE
SCIENCE CO., LTD.; CBUP-A3) by the Wilhelmy method.
(5) Viscosity
[0067] The viscosity was measured according to JIS K6726.
(6) Absorbance
[0068] A 0.1-wt. % aqueous solution of a vinyl alcohol polymer was
prepared as a test portion. With respect to this test portion,
absorbance at wavelengths of 280 nm and 320 nm was measured with
the optical path length being 1 cm. A UV spectrophotometer
(manufactured by Shimadzu Corporation; UV2100) was used for the
measurement.
(7) YI (Yellow Index)
[0069] A 1-wt. % aqueous solution of a vinyl alcohol polymer was
prepared and its YI was measured according to JIS K7103. A
color-difference meter (manufactured by Nihon Denshoku Kogyo Co.,
Ltd.; ZE-200) was used for the measurement.
(8) Transmittance
[0070] With respect to a 0.1-wt. % aqueous solution (30.degree. C.)
of a vinyl alcohol polymer, the transmittance at a wavelength of
500 nm of a test portion was measured with the optical path length
being 1 cm. The UV spectrophotometer (manufactured by Shimadzu
Corporation; UV2100) was used for the measurement.
(9) Calculation of the Ratio Mw/Mn
[0071] Using monodispersed polymethyl methacrylate as a specimen
and hexafluoroisopropanol containing 20 millimole/liter of sodium
trifluoroacetate for the mobile phase, the GPC measurement was
carried out at 40.degree. C. and thereby the weight-average
molecular weight Mw and the number-average molecular weight Mn of
the vinyl alcohol polymer were determined. Subsequently, the ratio
Mw/Mn was calculated from the measured values thus obtained.
Evaluation of Polymerizability of Vinyl Chloride Monomers and
Properties of Vinyl Chloride Polymer Obtained
[0072] The following description is directed to a method of
evaluating the polymerizability of vinyl chloride monomers and
properties of a vinyl chloride polymer obtained.
(10) Mean Particle Diameter
[0073] The particle size distribution was measured by a dry sieve
analysis using a wire mesh that meets the Tailer mesh standard, and
then the mean particle diameter was determined.
(11) Bulk Density
[0074] The bulk density was measured according to JIS K6721.
(12) Cold Plasticizer Absorption (CPA)
[0075] Absorption of dioctyl phthalate at 23.degree. C. was
measured by the method described in ASTM-D3367-75.
(13) Foaming
[0076] The state of foaming that occurred inside a reactor vessel
was observed visually 30 minutes after the start of polymerization
of vinyl chloride, and was evaluated according to the following
criteria. In this case, the liquid level was at a height of 70%
from the bottom face of the reactor vessel. [0077] AA: Almost no
foaming was observed. [0078] A: Foaming was observed up to a height
of 75 to 80% from the bottom face of the reactor vessel. [0079] B:
Foaming was observed up to a height of 80 to 90% from the bottom
face of the reactor vessel. [0080] C: Foaming was observed up to a
height of 90 to 100% from the bottom face of the reactor vessel.
(14) Polymerization Stability
[0081] After a polymer slurry was taken out of the reactor vessel,
the state of scale adhesion inside the reactor vessel was observed
visually. The scale adhesion was evaluated according to the
following criteria. [0082] A: Almost no adhesion of polymer scales
was observed. [0083] B: White polymer scales were observed on the
inner wall of the reactor vessel. [0084] C: A lot of white polymer
scales were observed on the inner wall of the reactor vessel. (15)
Coloration of Vinyl Chloride Polymer
[0085] First, 100 parts by weight of vinyl chloride polymer, 2.5
parts by weight of dibutyltin maleate, and 40 parts by weight of
dioctyl phthalate used as a plasticizer were mixed together. Then
this mixture was kneaded by open rolling at 170.degree. C. for five
minutes to obtain a sheet with a thickness of about 1 mm. The
degree to which the sheet was colored was observed visually and was
determined as follows.
[0086] A: Hardly colored.
[0087] B: Slightly colored.
[0088] C: Greatly colored.
Production Example 1 of Vinyl Alcohol Polymer
[0089] A production example of a vinyl alcohol polymer is described
below. First, 133 kg of vinyl acetate, 7.0 kg of methanol, and 2.7
kg of acetaldehyde were charged into a reactor vessel. Thereafter,
the atmosphere inside the reactor vessel was replaced with nitrogen
by bubbling of nitrogen gas. Separately,
2,2'-azobisisobutyronitrile was dissolved in methanol to prepare an
initiator solution with a concentration of 0.8 g/L. This initiator
solution was flushed with nitrogen by bubbling of nitrogen gas.
[0090] Next, the temperature of the reactor vessel was raised. When
its internal temperature reached 60.degree. C., 420 mL of the
above-mentioned initiator solution was added into the reactor
vessel and thereby polymerization was started. During the
polymerization, the polymerization temperature was maintained at
60.degree. C., and the initiator solution was added continuously at
a rate of 1310 mL/hr. The container was cooled to stop the
polymerization 4 hours after the start of the polymerization. At
that point in time, the conversion was 40%. Subsequently, while
methanol was added at intervals, unreacted vinyl acetate monomers
were removed from the reacted solution under reduced pressure at
30.degree. C. to obtain a methanol solution of polyvinyl acetate
(with a concentration of 50%).
[0091] To a portion sampled from the methanol solution of polyvinyl
acetate was added a methanol solution of sodium hydroxide whose
concentration was 10% so that an alkali molar ratio (the mole ratio
of an alkali compound to a vinyl acetate unit in the polyvinyl
acetate) reached 0.5. This was left at 60.degree. C. for five hours
to allow saponification to proceed. After completion of the
saponification, the Soxhlet extraction was conducted using methanol
for three days and then drying was carried out under reduced
pressure at 80.degree. C. for three days. Thus, purified polyvinyl
alcohol was obtained. The mean degree of polymerization of the
polyvinyl alcohol was measured according to JIS K6726 and was
700.
[0092] To the above-mentioned methanol solution of polyvinyl
acetate whose concentration was 50% were added water, methanol,
methyl acetate, and a methanol solution of sodium hydroxide whose
concentration was 10% so that the amounts of polyvinyl acetate,
water, and methyl acetate were 30%, 1%, and 30%, respectively and
the alkali molar ratio was 0.018. Thus, the polyvinyl acetate was
saponified. Gelling occurred about three minutes after the addition
of alkali. This gelled material was pulverized by a pulverizer,
which was then left at 40.degree. C. for one hour to allow
saponification to proceed. Thereafter, the same volume of a mixed
solution of methyl acetate/water (8/2) as the volume of the
reaction solution was added to the reaction system to neutralize
residual alkali. After completion of the neutralization was
confirmed using a phenolphthalein indicator, polyvinyl alcohol was
obtained through centrifugal deliquoring. This polyvinyl alcohol
was dried at 60.degree. C. for one day and then its saponification
degree was measured according to JIS K6726. The saponification
degree was 70 mol %. This polyvinyl alcohol was heat-treated at
120.degree. C. for 10 hours under a nitrogen atmosphere in which
the oxygen concentration was 400 ppm. Consequently, a vinyl alcohol
polymer (P-1) was obtained.
Production Examples 2 to 16 of Vinyl Alcohol Polymers
[0093] Vinyl alcohol polymers (P-2 to P-16) were produced in the
same manner as in Production Example 1 except for the following
points that were changed suitably: the charging amounts of vinyl
acetate monomers, methanol, initiator, and acetaldehyde used in
polymerizing vinyl acetate monomers; the alkali molar ratio and the
solvent composition employed in saponifying polyvinyl acetate; and
the oxygen concentration in the atmosphere and the heat treatment
temperature and time employed in heat-treating the vinyl alcohol
polymer.
Production Example 17 of Vinyl Alcohol Polymer
[0094] In Production Example 17, a vinyl alcohol polymer was
produced using two types of polyvinyl acetate. Specifically, first,
133 kg of vinyl acetate, 7.0 kg of methanol, and 5.8 kg of
acetaldehyde were charged into a reactor vessel. Thereafter, the
atmosphere inside the reactor vessel was replaced with nitrogen by
bubbling of nitrogen gas. Separately, 2,2'-azobisisobutyronitrile
was dissolved in methanol to prepare an initiator solution with a
concentration of 0.8 g/L. This initiator solution was flushed with
nitrogen by bubbling of nitrogen gas.
[0095] Next, the temperature of the reactor vessel was raised. When
its internal temperature reached 60.degree. C., 420 mL of the
above-mentioned initiator solution was added into the reactor
vessel and thereby polymerization was started. During the
polymerization, the polymerization temperature was maintained at
60.degree. C., and the initiator solution was added continuously at
a rate of 1310 mL/hr. The container was cooled to stop the
polymerization 4.5 hours after the start of the polymerization. At
that point in time, the conversion was 40%. Subsequently, while
methanol was added at intervals, unreacted vinyl acetate monomers
were removed from the reacted solution under reduced pressure at
30.degree. C. to obtain a methanol solution of polyvinyl acetate
(with a concentration of 60%).
[0096] To a portion sampled from the methanol solution of polyvinyl
acetate was added a methanol solution of sodium hydroxide whose
concentration was 10% so that the alkali molar ratio (the mole
ratio of an alkali compound to a vinyl acetate unit in the
polyvinyl acetate) reached 0.5. This was left at 60.degree. C. for
five hours to allow saponification to proceed. After completion of
the saponification, the Soxhlet extraction was conducted using
methanol for three days and then drying was carried out under
reduced pressure at 80.degree. C. for three days. Thus, purified
polyvinyl alcohol was obtained. The mean degree of polymerization
of the polyvinyl alcohol was measured according to JIS K6726 and
was 450.
[0097] Furthermore, polyvinyl acetate whose mean degree of
polymerization was 1000 was obtained through polymerization
conducted in the same manner as described above except that the
charging amounts of vinyl acetate monomers, methanol, initiator,
and acetaldehyde were changed.
[0098] The polyvinyl acetate whose mean degree of polymerization
was 450 and the polyvinyl acetate whose mean degree of
polymerization was 1000 were blended in a weight ratio of 55/45. As
a result, a polyvinyl acetate whose mean degree of polymerization
was 700 was obtained. This polyvinyl acetate was dissolved in
methanol to prepare a methanol solution of polyvinyl acetate whose
concentration was 55%. Thereafter, to this methanol solution were
added water, methanol, methyl acetate, and a methanol solution of
sodium hydroxide whose concentration was 10% so that the amounts of
polyvinyl acetate, water, and methyl acetate were 30%, 1%, and 30%,
respectively, and the alkali molar ratio was 0.02. Thus, the
polyvinyl acetate was saponified. Gelling occurred about five
minutes after the addition of alkali. This gelled material was
pulverized by a pulverizer, which was then left at 40.degree. C.
for one hour to allow saponification to proceed. Thereafter, the
same volume of a mixed solution of methyl acetate/water (8/2) as
the volume of the reaction solution was added to the reaction
system to neutralize residual alkali. After completion of the
neutralization was confirmed using a phenolphthalein indicator, a
vinyl alcohol polymer was obtained through centrifugal deliquoring.
This vinyl alcohol polymer was left in a drier at 60.degree. C. for
one day and was then heat-treated at 120.degree. C. for 10 hours
under a nitrogen atmosphere. Consequently, a vinyl alcohol polymer
(P-17) was obtained.
[0099] Tables 1-1, 1-2, 2-1, and 2-2 indicate conditions employed
for producing the vinyl alcohol polymers (P-1 to P-17) described in
the above and results of the analysis of vinyl alcohol polymers
that was carried out before and after the heat treatment.
Production Examples 14 and 15 are examples that were not
heat-treated and are different from each other in the block
character of the acetic acid groups. The evaluation results
indicated in Tables 2-1 and 2-2 are the results of evaluation of
the vinyl alcohol polymers that were heat-treated except for P-14
and P-15. In Tables 2-1 and 2-2, the evaluation results of P-14 and
P-15 are results of evaluation of the vinyl alcohol polymers that
were not heat-treated. TABLE-US-00001 TABLE 1-1 Conditions of Heat
Treatment Saponifi- Oxygen Polymer- cation Concen- Temper- ization
Degree tration Time ature Name Degree (mol %) (ppm) (hr) (.degree.
C.) Prod. P-1 700 70 400 10 120 Ex. 1 Prod. P-2 1700 78 100 18 100
Ex. 2 Prod. P-3 2300 85 5 5 140 Ex. 3 Prod. P-4 700 70 500 1 120
Ex. 4 Prod. P-5 700 70 400 18 120 Ex. 5 Prod. P-6 700 70 2000 10
120 Ex. 6 Prod. P-7 700 70 5000 10 120 Ex. 7 Prod. P-8 700 70 8000
10 120 Ex. 8 Prod. P-9 1700 78 1000 18 190 Ex. 9 Prod. P-10 700 70
400 10 70 Ex. 10 Prod. P-11 700 70 400 25 120 Ex. 11 Prod. P-12 700
70 10000 10 120 Ex. 12 Prod. P-13 700 70 50000 10 120 Ex. 13 Prod.
P-14 2300 85 -- -- -- Ex. 14 Prod. P-15 2300 85 -- -- -- Ex. 15
Prod. P-16 1700 50 1000 18 100 Ex. 16 Prod. P-17 700 72 400 10 120
Ex. 17 Prod. Ex. = production example
[0100] TABLE-US-00002 TABLE 1-2 Before Heat Treatment After Heat
Treatment Block Surface Block Surface Char- Viscosity Tension Char-
Viscosity Tension Name acter (mPa s) (mN/m) acter (mPa s) (mN/m)
Prod. P-1 0.390 7.7 41.7 0.523 7.6 41.7 Ex. 1 Prod. P-2 0.475 19.0
47.2 0.513 19.1 47.3 Ex. 2 Prod. P-3 0.502 45.0 54.0 0.549 45.2
54.0 Ex. 3 Prod. P-4 0.390 7.7 41.7 0.395 7.7 41.7 Ex. 4 Prod. P-5
0.390 7.7 41.7 0.562 8.4 42.0 Ex. 5 Prod. P-6 0.390 7.7 41.7 0.501
8.0 42.2 Ex. 6 Prod. P-7 0.390 7.7 41.7 0.462 8.3 42.1 Ex. 7 Prod.
P-8 0.390 7.7 41.7 0.435 8.3 42.3 Ex. 8 Prod. P-9 0.475 19.0 47.2
0.529 22.0 48.3 Ex. 9 Prod. P-10 0.390 7.7 41.7 0.400 7.6 41.7 Ex.
10 Prod. P-11 0.390 7.7 41.7 0.540 7.9 42.8 Ex. 11 Prod. P-12 0.390
7.7 41.7 0.420 8.6 42.8 Ex. 12 Prod. P-13 0.390 7.7 41.7 0.410 8.8
42.9 Ex. 13 Prod. P-14 0.502 45.0 54.0 -- -- -- Ex. 14 Prod. P-15
0.544 46.0 55.2 -- -- -- Ex. 15 Prod. P-16 0.500 * * 0.511 * * Ex.
16 Prod. P-17 0.391 7.7 41.4 0.500 7.7 41.5 Ex. 17 Prod. Ex. =
production example
[0101] In Table 1-2, the mark "*" indicates that no measurement was
possible due to phase separation. TABLE-US-00003 TABLE 2-1
Saponifi- Absor- Absor- Polymer- cation bance bance ization Degree
at 280 at 320 Name Degree (mol %) nm (a) nm (b) (b)/(a) Prod. Ex. 1
P-1 700 70 0.274 0.313 1.14 Prod. Ex. 2 P-2 1700 78 0.020 0.030
1.50 Prod. Ex. 3 P-3 2300 85 0.011 0.013 1.18 Prod. Ex. 4 P-4 700
70 0.453 0.060 0.13 Prod. Ex. 5 P-5 700 70 0.243 0.350 1.44 Prod.
Ex. 6 P-6 700 70 0.277 0.305 1.10 Prod. Ex. 7 P-7 700 70 0.300
0.301 1.00 Prod. Ex. 8 P-8 700 70 0.335 0.277 0.83 Prod. Ex. 9 P-9
1700 78 0.032 0.019 0.59 Prod. Ex. 10 P-10 700 70 0.453 0.070 0.15
Prod. Ex. 11 P-11 700 70 0.256 0.363 1.41 Prod. Ex. 12 P-12 700 70
0.357 0.227 0.66 Prod. Ex. 13 P-13 700 70 0.412 0.216 0.52 Prod.
Ex. 14 P-14 2300 85 0.021 0.001 0.05 Prod. Ex. 15 P-15 2300 85
0.020 0.001 0.05 Prod. Ex. 16 P-16 1700 50 0.028 0.023 1.46 Prod.
Ex. 17 P-17 700 72 0.315 0.319 1.01 Prod. Ex. = production
example
[0102] TABLE-US-00004 TABLE 2-2 Trans- Block Character mittance
After Heat Name YI (%) Treatment Mw/Mn Prod. Ex. 1 P-1 10.2 97.5
0.523 2.1 Prod. Ex. 2 P-2 11.1 98.9 0.513 2.2 Prod. Ex. 3 P-3 12.2
99.3 0.549 2.1 Prod. Ex. 4 P-4 7.1 82.5 0.395 2.1 Prod. Ex. 5 P-5
20.5 98.7 0.562 2.1 Prod. Ex. 6 P-6 16.4 95.3 0.501 2.2 Prod. Ex. 7
P-7 25.3 94.5 0.462 2.2 Prod. Ex. 8 P-8 38.6 94.0 0.435 2.4 Prod.
Ex. 9 P-9 35.3 94.2 0.529 2.2 Prod. Ex. 10 P-10 8.2 72.1 0.400 2.1
Prod. Ex. 11 P-11 45.1 99.2 0.540 2.1 Prod. Ex. 12 P-12 50.2 93.2
0.420 2.5 Prod. Ex. 13 P-13 61.8 92.0 0.410 2.7 Prod. Ex. 14 P-14
8.2 93.2 0.502 2.1 Prod. Ex. 15 P-15 8.3 93.2 0.544 2.1 Prod. Ex.
16 P-16 12.5 53.2 0.511 2.2 Prod. Ex. 17 P-17 9.4 97.0 0.500 2.2
Prod. Ex. = production example
[0103] As is clear from Tables 1-1, 1-2, 2-1, and 2-2, the heat
treatment changed the block characters of the vinyl alcohol
polymers. In the examples mentioned above, the value of block
character increased considerably when the heat treatment was
carried out under the conditions in which the oxygen concentration
was 5 ppm to 8000 ppm, the temperature was 100.degree. C. to
140.degree. C., and the heat treatment time was 5 to 18 hours. By
such a heat treatment carried out under the atmosphere in which an
oxygen concentration is in a certain range, vinyl alcohol polymers
can be obtained that exhibit excellent surface tension and
viscosity when they are prepared as aqueous solutions. Thus, less
coloration is caused and excellent handling properties are
provided.
Polymerization of Polyvinyl Chloride
Examples 1 to 9 and Comparative Examples 1 to 8
[0104] Suspension polymerization of polyvinyl chloride was carried
out using the above-mentioned vinyl alcohol polymers (P-1 to P-17)
as dispersion stabilizers.
[0105] First, an autoclave with glass lining was charged with 40
parts by weight of deionized water containing a dispersion
stabilizer (P-1 to P-17) dissolved therein and 0.04 parts by weight
of a 70% toluene solution of diisopropyl peroxydicarbonate. The
inside of the autoclave was evacuated until its internal pressure
reached 0.0067 MPa and thereby oxygen was removed. Then, 30 parts
by weight of vinyl chloride monomers were charged therein and the
reaction solution was heated to 57.degree. C., while being stirred
to conduct polymerization. At the start of the polymerization, the
pressure inside the autoclave was 0.83 MPa. This pressure reached
0.44 MPa 7 hours after the start of the polymerization, at which
time the polymerization was stopped. The unreacted vinyl chloride
monomers were purged, and the content was taken out and dehydrated
to dryness. The yield of the vinyl chloride polymer was 85%. The
mean degree of polymerization thereof was 1050. Polymerizability of
vinyl chloride and properties of the vinyl chloride polymers thus
obtained were evaluated. Results of the evaluation are indicated in
Tables 3-1 and 3-2. TABLE-US-00005 TABLE 3-1 Dispersion Stabilizer
Evaluation of Polymerization Quantity Polymerization PVA
(%/monomer) Stability Foaming Example 1 P-1 0.10 A AA Example 2 P-2
0.12 A AA Example 3 P-3 0.14 A AA Example 4 P-4 0.10 B A Example 5
P-5 0.10 A A Example 6 P-6 0.10 A A Example 7 P-7 0.10 A A Example
8 P-8 0.10 A A Comp. Ex. 1 P-9 0.12 C B Comp. Ex. 2 P-10 0.10 C C
Comp. Ex. 3 P-11 0.10 B B Comp. Ex. 4 P-12 0.10 B C Comp. Ex. 5
P-13 0.10 B C Comp. Ex. 6 P-14 0.10 C C Comp. Ex. 7 P-15 0.10 C C
Comp. Ex. 8 P-16 0.12 C C Example 9 P-17 0.10 A AA Comp. Ex. =
Comparative Example
[0106] TABLE-US-00006 TABLE 3-2 Evaluation of Polyvinyl Chloride
Mean Particle Plasticizer Diameter Absorptivity Bulk Density
(.mu.m) (%) (g/cm.sup.3) Coloration Example 1 143 30.5 0.502 A
Example 2 131 27.2 0.523 A Example 3 125 25.1 0.555 A Example 4 172
29.2 0.451 A Example 5 145 27.5 0.499 B Example 6 148 29.9 0.503 A
Example 7 150 29.3 0.503 B Example 8 161 28.5 0.462 B Comp. Ex. 1
150 22.1 0.501 B Comp. Ex. 2 199 30.1 0.459 A Comp. Ex. 3 160 26.1
0.477 C Comp. Ex. 4 161 26.3 0.460 C Comp. Ex. 5 158 26.2 0.481 C
Comp. Ex. 6 167 23.4 0.502 A Comp. Ex. 7 160 20.1 0.509 A Comp. Ex.
8 284 16.1 0.443 A Example 9 136 31.3 0.496 A Comp. Ex. =
Comparative Example
[0107] As is apparent from Tables 3-1 and 3-2, polyvinyl chloride
with excellent properties was produced stably using vinyl alcohol
polymers of P-1 to P-8 and P-17 as dispersion stabilizers.
[0108] The invention may be embodied in other forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not limiting. The scope of the
invention is indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are intended to be
embraced therein.
* * * * *