[0001] in water to the point of initiation of the dissolution is very short, and since the
dissolution rate is very high, the fiber is dissolved out in a very short time after
dipping in water or the strength of the fiber is lost in a very short time. This time
is ordinarily two hours or shorter. There has been proposed a method in which the
hydrophilic nature of such a water-soluble fiber is modified so that the fiber is
prevented from being completely dissolved.
[0002] In this proposal, the fiber is not dissolved out but the reduction of the strength
is ordinarily controlled to a certain reduction ratio in the range of from 30 to 60%.
Furthermore, this certain reduction ratio is ordinarily reached within 2 hours after
immersion in water. This dissolution time or reduction ratio depends on the temperature,
and the higher the temperature, the shorter the dissolution time and the higher the
strength reduction ratio.
[0003] A water-swelling fiber such as rayon, cellulose or cellulose acetate is not dissolved
out but degradation is stopped at a certain strength reduction ratio, e.g., 20 to
50%, and this certain strength reduction ratio is ordinarily reached within 2 hours.
SUMMARY OF THE INVENTION
[0004] It is a primary object of the present invention to provide a fiber, the strength
of which is gradually reduced with the lapse of time when it is immersed in water
or is wet with water. By the expression "gradually reduced with the lapse of time"
used herein, it is meant that the time required for initiation of degradation after
immersion in water is longer than in a conventional water-soluble or water-swelling
fiber, the dissolution rate is low, and the time required for the dissolution is long.
[0005] In accordance with the present invention, there is provided a wet-degradable fiber
having a covering resin layer, wherein the moisture permeability (R) of a resin
WET-DEGRADABLE FIBERS
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0006] The present invention relates to a wet-degradable fiber. More particularly,'it relates
to a fiber, the strength of which is gradually reduced with the lapse of time when
the fiber is in the wet state or immersed in water.
2. Description of the Prior Art
[0007] As the fiber of which the strength is reduced in water or in the state wet with water,
there are known fibers of water-soluble polymers such as polyvinyl alcohol and polyethylene
glycol and fibers of water-swelling polymers having hydrophilic groups, such as rayon,
cellulose, and cellulose acetate. Reduction of the strength in water or dissolution
in water in these fibers is industrially utilized in various fields.
[0008] For example, because of an excellent water solubility, a polyvinyl alcohol fiber
is used as an adhesive binder, a cracking-preventing agent in a molded article, a
fiber for a crepe fabric, a fiber for a chemical lace fabric, a marking fiber for
a knitted fabric, a selvage curl-preventing fiber for a woven or knitted fabric, a
fiber for preventing extension of an elastic yarn, and a fiber for pressing a strongly
twisted yarn.
[0009] These known fibers, however, are commonly characterized in that degradation of the
strength is manifested in a very short time after immersion in water, or the strength
is reduced to a certain level in a short time after immersion in water and then further
reduction of the strength is halted. The time required for initiation of the reduction
of the strength after immersion in water is very short, and the degradation or dissolution
is completed in a very short time. For example, in the case of a water-soluble fiber
composed of polyvinyl alcohol or polyethylene glycol, the time from the point of immersion
forming the covering layer is at least 2.5 g/m
2.24 hours as determined at a relative humidity difference of 0% - 90% with respect
to a thickness of 0.1 mm, and the strength wet reduction ratio (AS) of the fiber is
within a range satisfying requirements represented by the following formulae:


and

wherein AS
1 represents the strength reduction ratio after two hours' immersion in water at 20°C
and AS
2 represents the strength reduction ratio after fifty hours' immersion in water at
20°C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] The wet-degradable fiber of the present invention has a moisture-permeable covering
resin layer. As the skeleton fiber on which this moisture-permeable covering resin
layer is formed, there can be mentioned a fiber in which reduction of the strength
is advanced in the wet state, such as a water-soluble fiber or a water-swellable fiber,
and a fiber which is hydrolyzed in the wet state in the presence of a hydrolysis promoter
(such as an amine) to advance deterioration or degradation of the fiber, such as a
polyester fiber.
[0011] By the term "water-soluble fiber" used herein is meant a fiber which is dissolved
when it is immersed in water at a temperature higher than 0°C, with the result that
the strength of the fiber is reduced as compared with the strength in air. This fiber
may be composed of a natural polymer, a semi-synthetic polymer, or a synthetic polymer.
For example, there can be mentioned polyvinyl alcohol, polyethylene oxide, sodium
polyacrylate, and collagen.
[0012] By the term "water-wetting fiber" used herein is meant a fiber which is not dissolved
but swollen when it is immersed in water at a temperature higher than 0°C, with the
result that the strength of the fiber is reduced as compared with the strength in
air. This fiber also may be composed of a natural polymer, a semi-synthetic polymer,
or a synthetic polymer. For example, there can be mentioned rayon, cellulose acetate,
Vinylon, wool, polyvinyl alcohol, polyethylene oxide, sodium polyacrylate, and collagen.
[0013] As the fiber which is hydrolyzed in the wet state in the presence of a hydrolysis
promoter such as an amine, there can be used a polyester fiber, that is, a fiber composed
of a polymer having ester bonds in the main chain. For example, there can be mentioned
a polyester comprising terephthalic acid as the main acid component and at least one
glycol, preferably at least one alkylene glycol selected from ethylene glycol, trimethylene
glycol, tetramethylene glycol, pentamethylene glycol, and hexamethylene glycol, as
the main glycol component.
[0014] A polyester in which a part of the terephthalic acid component is replaced by another
bifunctional carboxylic acid component also can be used, and a polyester in which
a part of the glycol component is substituted by a diol component other than the above-mentioned
glycol also can be used.
[0015] As the bifunctional carboxylic acid other than terephthalic acid, there can be mentioned
aromatic, aliphatic and alicyclic bifunctional carboxylic acids such as isophthalic
acid, napthalene-dicarboxylic acid, diphenyl-dicarboxylic acid, diphenoxyethane-dicarboxylic
acid, 0-hydroxyethoxybenzoic acid, p-hydroxybenzoic acid, 5-sodium-sulfoisophthalic
acid, adipic acid, sebacic acid, and 1,4-cyclohexane-dicarboxylic acid. As the diol
compound other than the above-mentioned glycol, there can be mentioned aliphatic,
alicyclic and aromatic diol compounds such as cyclohexane-l,4-dimethanol, neopentyl
glycol, bisphenol A, and bisphenol S, and polyoxyalkylene glycols.
[0016] A polycarboxylic acid such as trimellitic acid or pyromellitic acid or a polyol such
as glycerol, trimethylolpropane or pentaerythritol may be copolymerized with the polyester,
so far as the polyester is substantially linear (ordinarily, the amount of the comonomer
is up to 1 mole %).
-
[0017] When a fiber composed of a copolycondensate derived from terephthalic acid, 5-sodium-sulfoisophthalic
acid, and ethylene glycol or a fiber composed of a polyester in which 0.1 to 5.0 mole
% of sodium alkylsulfonate or trimethyl phosphate is incorporated is used as the skeleton
fiber, the effect of gradually advancing reduction of the strength in the wet state
with the lapse of time is enhanced. Sodium alkylsulfonate and trimethyl phosphate
may be used alone or in the form of a mixture of both compounds.
[0018] The configuration of the skeleton fiber used in the present invention is not particularly
critical. For example, an unprocessed yarn having a circular or non- circular section
may be used. However, it is preferred that a fiber having a configuration modified
by false twisting, fluid processing, rubbing processing, stuffing processing, asymmetric
structure-forming processing, shrinkage difference-utilizing processing, or raising
processing be used as the skeleton fiber. Moreover, a spun yarn formed by tow spinning,
false twist spinning, or composite spinning can be used. These yarns are effective
for fixing a covering resin tightly to the surfaces of fibers, and the durability
of the applied resin can be increased by the anchoring effect.
[0019] A resin having a moisture permeability (R) of at least 2.5 g/m 2 '24 hours is used
as the resin to be covered on the skeleton fiber in the present invention. The moisture
permeability (R) referred to herein is a value determined according to the method
of JIS Z-0208. Namely, the value of the moisture permeability (R) is expressed by
the amount (g) of water vapor which passes through a film having a thickness of 0.1
mm and an area of 1 m
2 for a period of 24 hours under a relative humidity difference of 90% - 0% (which
means that the atmosphere on one side of the film is maintained at a relative humidity
of 0% and the atmosphere on the other side of the film is maintained at a relative
humidity of 90%).
[0020] When moisture permeability is lower than 2.5 g/m
2.24 hours, the amount of water vapor passing through the covering resin layer is limited
and no substantial wet degradation is attained. If the moisture permeability is very
high, for example, 500 to 1000 g/m
2.24 hours, the degradation rate is too high and the thickness of the covering layer
has to be increased, and the resulting fiber has a thick covering layer such that
it is of almost no practical use.
[0021] Among resins having a moisture permeability (R) of at least 2.5 g/m
2·24 hours, a resin having a flexibility but being not water-soluble or water-swellable
is used. For example, there may be used vinyl and vinylidene resins such as polyacrylic
acid, polymethyl methacrylate, polyacrylonitrile, polyvinyl chloride, polyvinyl acetate,
polyvinylidene chloride, polyethylene, polypropylene, and polybutene, acetal resins
such as a formal resin and polyvinyl butyral, polyamide resins such as nylon 6 and
nylon 66, unsaturated polyester resins, polyurethane resins such as other type polyurethane
and ester type polyurethane, diene type rubbers such as polybutadiene, styrene-butadiene
rubber, acrylonitrile-butadiene rubber, polyisobutylene, and butyl rubber, olefin
rubbers such as ethylene-propylene rubber and polyisobutylether, polysulfide rubbers
such as Thiokol rubber, silicone rubbers, fluorine resins such as polytetrafluoroethylene
and polytrifluoroethylene, and cellulose derivatives such as methyl cellulose and
othyl cellulose.
[0022] The thickness of the covering resin layer is appropriately determined according to
the desired strength wet reduction ratio of the wet-degradable fiber. Ordinarily,
the thickness is varied according to the kind of resin, but it is preferred that the
thickness of the covering resin layer be 0.05 to 5 mm, more preferably 0.1 to 2 mm.
If the thickness of the covering resin layer is smaller than 0.05 mm; a uniform covering
is hardly formed and the permeability of the covering layer becomes uneven. If the
thickness exceeds 5 mm, the contribution of the covering resin layer to the strength
becomes excessive, and control of the strength wet reduction ratio becomes difficult.
[0023] When the skeleton fiber is a polyester fiber, an amine is incorporated in the covering
resin. In this case, the resin not only shows a moisture permeability but also exerts
a function of fixing the amine to the surface of the fiber, preventing falling of
the amine by rubbing or shock and preventing scattering of the amine into air, dissolution
of the amine in water, or adhesion of the amine to the finger or skin.
[0024] By the term "amine" used herein is meant an aliphatic, aromatic or alicyclic hydrocarbon
compound in which an organic group (inclusive of hydrogen) is substituted with ammonia,
a primary amine (RNH
2) or a secondary amine (R
2NH). The number of nitrogen atoms contained in one molecule is not particularly critical,
and one or more of nitrogen atoms may be contained. It is preferred that an amine
which provides a hydrogen ion concentration (pH) of at least 9.0 when dissolved at
a concentration of 5% by weight in water or a solvent having a largest solubility
to the amine be used.
[0025] As specific examples of the amine used in the present invention, there can be mentioned
o-tolylbiguanide, piperazine anhydride, N-methylethanolamine, guanidine carbonate,
hexamethylenediamine carbamate, sodium diethyldithiocarbamate, N-methyl-D-glucamine,
L-alginine, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-l,3-propanediol, 2-amino-2-methyl-l-propanol,
N-methyldiethanolamine, 2,4,6-tris(dimethylaminomethyl) phenol, tetraethylammonium
hydroxide, polyethylene-imine, 2-methylimidazole, 2-ethyl-4-methylimidazole, modified
aliphatic polyamines, modified aliphatic polyamine adducts, and ketimine.
[0026] It is preferred that the-content of the amine in the covering resin be 2 to 100%
by weight, more preferably 10 to 70% by weight, based on the resin. If the content
of the amine is lower than 2% by weight, the hydrolysis-promoting action is insufficient.
If the content of the amine exceeds 100% by weight, the hydrolysis-promoting action
is too violent and desirable strength wet reduction cannot be obtained.
[0027] Any known methods may be adopted for covering the moisture-permeable resin on the
skeleton fiber. For example, there may be adopted a hot melt extrusion coating method,
a method in which the fiber is dipped in a dope of the resin and is squeezed by a
mangle, a method in which the fiber is dipped in a dope of the resin and passed through
a fine hole, and a method in which the fiber is sprayed with a solution of the resin
and is then heated and dried. When an amine is incorporated in the resin, use of the
resin in the form of an aqueous liquid such as an aqueous emulsion or an aqueous suspension
should be avoided.
[0028] In order to gradually reduce the strength in the wet state with the lapse of time,
the strength wet reduction ratio (AS) of the wet-degradable fiber of the present invention
should satisfy requirements represented by the following formulae:


and

[0029] Supposing that the tensile strength of the wet-degradable fiber in the normal state
is Sa and the tensile strength of the fiber, measured in the wet state when the fiber
is dipped in water at 20°C and is taken out after the lapse of a certain time, is
S B , the strength wet reduction ratio (AS) is represented as follows:

[0030] Incidentally, in the above formulae, ΔS
1 represents the strength wet reduction ratio after 2 hours' immersion in water at
20°C, and àS
2 represents the strength wet reduction ratio after 50 hours' immersion in water at
20°C.
[0031] The wet-degradable fiber of the present invention can be used for engineering work
and ocean engineering work. Especially, the wet-degradable fiber of the present invention
is preferably used for a diameter-expansion type sand bag (pack drain) for solidifying
soft ground, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-143010.
Namely, the wet-degradable fiber of the present invention is suitable as a fiber manifesting
the expansion of diameter required for this diameter-expansion type pack drain.
[0032] The present invention will now be described in detail with reference to the following
examples. These examples by no means limit the scope of the invention.
[0033] In the examples, the tensile strength was measured according to the tensile test
method for filamentary yarns stipulated in JIS L-1070. A constant-speed stretching
type tensile tester was used for the measurement. The measurement conditions are as
follows.
Grip distance: 20 cm
Drawing speed: 100%/min
Example 1
[0034] Three filament yarns of a polyvinyl alcohol fiber (300 denier/50 filaments) (Solubron®
SX supplied by Nichibi K.K.) were doubled and twisted in the Z direction at 200 T/m.
The twists were set by dry heat-setting at 170°C for 2 minutes under tension. The
thus obtained yarn was coated with a resin by using an extrusion coating machine.
The resin used was an ethylene-vinyl acetate copolymer resin having a moisture permeability
R of 140 g/m
2.24 hours (Ultrathene® UE 722 supplied by Toyo Soda Manufacturing Co.). The thickness
of the covering layer was 0.6 mm and the amount of the coated resin was 1850% by weight
based on the fiber.
[0035] When this wet-degradable fiber was immersed in water at 20°C and the strength wet
reduction ratio was determined, it was found that ΔS
1 was 3.8, AS
2 was 60.1, and AS
2/AS
1 was 15.82, and it was confirmed that the fiber had an excellent wet degradability
(see Table 1).
Example 2
[0036] Nine filament yarns of a cellulose acetate fiber (100 denier/25 filaments) (Rosel®
supplied by Teijin Ltd.) were doubled and twisted in the Z direction at 200 T/m. The
twists were set by wet heat-setting at 70°C under tension for 30 minutes. The fiber
was then dried at 100°C for 30 minutes. The thus obtained fiber was covered with a
resin by using an extrusion coating machine. The resin used was the same as the resin
used in Example 1. The thickness of the covering layer was 0.5 mm and the amount of
the coated resin was 1290% by weight based on the fiber.
[0037] When this wet-degradable fiber was immersed in water at 20°C and the strength wet
reduction ratio was determined, it was found that ΔS
1 was 2.5, Δ5
2 was 37.5, and ΔS
2/ΔS
1 was 15.00, and it was confirmed that the fiber had an excellent wet degradability
(see table 1).
Example 3
[0038] A twisted filament yarn having a twist number of 200 T/m (900 denier/150 filaments)
was prepared from the same polyvinyl alcohol fiber as used in Example 1. The obtained
yarn was immersed in a cyclohexane solution containing 10% by weight of 1,2-polybutadiene
having a moisture permeability R of 70 g/m
2·24 hours (JSR-
RB830 supplied by the Nippon Synthetic Chemical Industry Co.) and then the immersed
yarn was passed through a small hole of a polytetrafluoroethylene plate along the
center line of the hole, whereby a uniform covering resin layer was formed on the
surface of each fiber. The coated fiber was then dried at 100°C for 80 seconds. This
resin processing was repeated 8 times. In the obtained fiber, the thickness of the
covering-layer was 0.30 mm and the amount of the coated resin was 541% by weight based
on the fiber.
[0039] When this wet-degradable fiber was immersed in water at 20°C and the strength wet
reduction ratio was measured, it was found that ΔS
1 was 9.8, ΔS
2 was 64.7, and ΔS
2/ΔS
1 was 6.60, and it was confirmed that the fiber had an excellent wet degradability
(see Table 1).
Example 4
[0040] A twisted filament yarn having a twist number of 200 T/m (900 denier/150 filaments)
was prepared from the same polyvinyl alcohol fiber as used in Example 1. Low density
polyethylene having a moisture permeability R of 2.5 g/m
2·24 hours (F028 supplied by Ube Industries Ltd.) was dissolved in xylene by heating.
The solution temperature was 95°C and the polyethylene concentration was 8% by weight.
The twisted filament yarn was immersed in the solution while maintaining the solution
temperature at 95°C. The yarn was passed through a polytetrafluoroethylene slit to
remove the excessive solution, and then the yarn was dried at 150°C for 85 seconds.
This resin processing was repeated 9 times. In the obtained yarn, the thickness of
the covering resin layer was 0.4 mm and the amount of the coated resin was 612% by
weight based on the fiber.
[0041] When this wet-degradable fiber was immersed in water at 20°C and the strength wet
reduction ratio was determined, it was found that ΔS
1 was 0.4, AS
2 was 21.8, and ΔS
2/ΔS
1 was 54.5, and it was confirmed that the fiber had an excellent wet degradability
(see table 1).
Comparative Example 1
[0042] A twisted filament yarn having a twist number of 200 T/m (900 denier/150 filaments)
was prepared from the same polyvinyl alcohol fiber as used in Example 1. When this
yarn was directly immersed in water at 20°C, the yarn was dissolved out completely
in about 5 minutes and the strength could not be measured (see Table 1).
Comparative Example 2 -
[0043] A twisted filament yarn having a twist number of 200 T/m (900 denier/225 filaments)
was prepared from the same cellulose acetate fibers as used in Example 2. When the
yarn was directly immersed in water at 20°C and the strength wet reduction ratio was
determined, it was found that AS
1 was 37.4, AS
2 was 37.5, and ΔS
2/ΔS
1 was 1.00, and it was confirmed that wet degradation was caused but it was substantially
completed within 2 hours from the point of immersion in water (see Table 1).
Comparative Example 3
[0044] Three filament yarns of the same polyvinyl alcohol fiber (Solubron® SX, 300 denier/50
filaments) as used in Example 1 were doubled and twisted in the Z direction at 200
T/m. The twists were set by dry heat-setting at 170°C under tension for 2 minutes.
The obtained yarn was immersed in a tetrahydrofuran solution containing 10% by weight
of a polyvinylidene chloride resin having a moisture permeability R of 0.3 g/m
2·24 hours (Saran® F-216 supplied by Asahi Kasei Kogyo K.K.) and was then passed through
a fine hole made on a polytetrafluoroethylene plate to uniformly coat the resin on
each fiber. The coated fiber was heated at 90°C for 60 seconds. This resin processing
was repeated 8 times. In the obtained fiber, the thickness of the covering layer was
0.3 mm and the amount of the coated resin was 583% by weight based on the fiber.
[0045] When this fiber was immersed in water at 20°C and the strength wet reduction ratio
was determined, it was found that ΔS
1 was 0.1, àS
2 was 0.1, and AS
2/
AS
1 was 1.00 (see Table 1).
[0046]

Example 5
[0047] A polyethylene terephthalate filament yarn (75 denier/24 filaments) was subjected
to spindle false twisting at a heater temperature of 220°C, a speed of 120 m/min,
and a twist number of 3305 T/m to prepare a woolly finished yarn having a total crimp
degree (TC) of 37%.
[0048] The twelve woolly filament yarns thus prepared were doubled and twisted in the Z
direction at a twist number of 100 T/m to obtain a woolly yarn (900 denier/288 filaments).
[0049] 25 parts by weight of piperazine anhydride (supplied by Kawaken Fine Chemicals Co.),
25 parts by weight of polyvinyl alcohol having a moisture permeability R of 366 g/m
2·24 hours (Gosefimer® L-7514 supplied by The Nippon Synthetic Chemical Industry Co.),
and 50 parts by weight of methanol (first class chemical) were weighed. At first,
methyl alcohol was stirred and heated on a warm water bath maintained at 60°C, and
polyvinyl alcohol was gradually added thereto with stirring to dissolve the polyvinyl
alcohol in methanol. Then piperazine anhydride was similarly added to the solution
and dissolved therein with stirring. The woolly yarn was immersed in the thus prepared
solution maintained at normal temperature and then the woolly yarn was passed through
the center of a small hole having a diameter of 1.2 mm, which was made through a polytetrafluoroethylene
plate, to uniformly coat the woolly yarn with the resin solution. The yarn was dried
at 100°C for 1 hour. In the dried yarn, the amount of the coated amine-containing
resin was 96% by weight based on the woolly yarn.
[0050] When the strength wet reduction ratio of this wet-degradable fiber was determined,
it was found that ΔS
1 was 25.2, àS
2 was 64.8, and ΔS
2/ΔS
1 ratio was 2.57, and it was confirmed that the fiber had an excellent wet degradability
(see Table 2).
Example 6
[0051] A filament yarn (75 denier/24 filaments) of a polyester obtained by copolycondensing
terephthalic acid containing 2.6 mole % of 5-sodium-sulfoisophthalic acid with ethylene
glycol was subjected to spindle false twisting at a heater temperature of 180°C, a
speed of 120 m/min, and a twist number of 3305 T/m to obtain a woolly yarn having
a TC of 35%. Twelve woolly yarns thus prepared were doubled and twisted in the Z direction
at a twist number of 100 T/m to obtain a woolly yarn (900 denier/288 filaments).
[0052] The woolly yarn was processed with the same resin solution as used in Example 5 in
the same manner as in Example 5, and then the yarn was dried at 100°C for 1 minute.
In the obtained covered yarn, the amount of the coated resin was 90% by weight based
on the fiber.
[0053] When the resulting wet-degradable fiber was immersed in water at 20°C and the strength
wet reduction ratio was determined, it was found that ΔS
1 was 28.4, AS
2 was 73.5, and AS
2/AS
1 was 2.59, and it was confirmed that the fiber had an excellent wet degradability
(see Table 2).
Example 7
[0054] 20 parts by weight of o-tolylbiguanide (Nocselar® BG supplied by Ouchi Shinko Kagaku
Kogyo K.K.), 15 parts by weight of ethyl cellulose having a moisture permeability
R of 262 g/m
2.24 hours (N-7 supplied by Hercules K.K.) and 65 parts by weight of ethyl alcohol (first
class chemical) were weighed. At first, ethyl alcohol was heated and stirred at 60°C
on a warm water bath, and then ethyl cellulose was gradually added to ethanol and
dissolved therein with stirring. Then, o-tolylbiguanide was similarly added to the
solution and dissolved therein with stirring. The same woolly yarn as used in Example
6 was processed with the thus-formed solution in the same manner as described in Example
6. The amount of the coated resin containing the amine was 88% by weight based on
the fiber.
[0055] When the strength wet reduction of this wet-degradable fiber was determined, it was
found that AS
1 was 26.1, AS
2 was 66.3, and ΔS
2/ΔS
1 was 2.54, and it was confirmed that the fiber had an excellent wet degrad-. ability
(see Table 2).
Comparative Example 4
[0056] The procedures of Example 5 were repeated in the same manner except that drying was
carried out at 40°C for 3 minutes instead of drying at 100°C for 1 minute. The amount
of the coated resin was 97% by weight based ' on the fiber. The obtained fiber was
characterized by AS
1 of 2.8, AS
2 of 3.0, and ΔS
2/ΔS
1 of 1.07, and it was confirmed that the degradation was low and the fiber had no practical
utility (see Table 2).
Comparative Example 5
[0057] The procedures of Example 6 were repeated in the same manner except that drying was
carried out at 180°C for 1 minute instead of drying at 100°C for 1 minute. The amount
of the coated resin was 54% by weight based on the fiber. When this fiber was immersed
in water at 20°C, the strength was drastically reduced, and it was confirmed that
the fiber had no practical utility (see Table 2).
Comparative Example 6
[0058] A polyvinyl alcohol filament yarn (100 denier/30 filaments) (Solubron® SL supplied
by Nichibi) was dipped in water at 20°C and the strength wet reduction was determined.
It was found that ΔS
1 was 52.7, ΔS
2 was 52.8, and ΔS
2/ΔS
1 was 1.00. The degradation was very fast and the fiber was different from the fiber
of the present invention in which the strength was gradually reduced with the lapse
of time (see Table 2).
[0059]
