U.S. patent application number 14/421560 was filed with the patent office on 2015-10-08 for water-disintegrable composite fiber and method for producing the same.
The applicant listed for this patent is Kureha Corporation. Invention is credited to Yukitoshi Chiba, Hiroyuki Sato, Takeo Takahashi, Masahiro Yamazaki.
Application Number | 20150284879 14/421560 |
Document ID | / |
Family ID | 50278331 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150284879 |
Kind Code |
A1 |
Takahashi; Takeo ; et
al. |
October 8, 2015 |
WATER-DISINTEGRABLE COMPOSITE FIBER AND METHOD FOR PRODUCING THE
SAME
Abstract
A water-disintegrable composite fiber comprising a phase
containing a polyglycolic acid resin and a phase containing a
polylactic acid resin with a D-lactic acid unit ratio of at least
1.0%; the two phases extending continuously in a lengthwise
direction; and the composite fiber having a cross sectional area
formed by the phase containing the polyglycolic acid resin having
an area ration of at most 50%; and the content of the polyglycolic
acid resin being from 2 to 100 parts by mass per 1 part by mass of
the D-lactic acid units in the polylactic acid resin.
Inventors: |
Takahashi; Takeo; (Tokyo,
JP) ; Chiba; Yukitoshi; (Tokyo, JP) ;
Yamazaki; Masahiro; (Tokyo, JP) ; Sato; Hiroyuki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kureha Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
50278331 |
Appl. No.: |
14/421560 |
Filed: |
September 12, 2013 |
PCT Filed: |
September 12, 2013 |
PCT NO: |
PCT/JP2013/074730 |
371 Date: |
February 13, 2015 |
Current U.S.
Class: |
428/374 ;
264/151; 264/173.16; 428/373; 528/361 |
Current CPC
Class: |
D01F 6/625 20130101;
D01D 5/26 20130101; Y10T 428/2931 20150115; D01F 8/14 20130101;
Y10T 428/2929 20150115; C09K 2208/08 20130101; D10B 2331/041
20130101; C09K 8/035 20130101; D01D 5/08 20130101; D01D 5/084
20130101 |
International
Class: |
D01F 8/14 20060101
D01F008/14; D01D 5/26 20060101 D01D005/26; D01D 5/08 20060101
D01D005/08; D01F 6/62 20060101 D01F006/62 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2012 |
JP |
2012-203035 |
Claims
1. A water-disintegrable composite fiber comprising a phase
containing a polyglycolic acid resin and a phase containing a
polylactic acid resin with a D-lactic acid unit ratio of at least
1.0%; the two phases extending continuously in a lengthwise
direction respectively; and the composite fiber having a
cross-sectional area formed by the phase containing the
polyglycolic acid resin having an area ratio of at most 50%; and
the content of the polyglycolic acid resin being from 2 to 100
parts by mass per 1 part by mass of the D-lactic acid units in the
polylactic acid resin.
2. The water-disintegrable composite fiber according to claim 1,
wherein the water-disintegrable composite fiber has a side surface
in which a surface area formed by the phase containing the
polyglycolic acid resin has an area ratio of at most 50%.
3. The water-disintegrable composite fiber according to claim 1,
wherein the water-disintegrable composite fiber has at least one
type of structure selected from a core-sheath type, a multicore
type, a side-by-side type, a multiple-division type, a multilayer
type, and a radial type.
4. The water-disintegrable composite fiber according to claim 1,
wherein the fiber is an undrawn fiber.
5. The water-disintegrable composite fiber according to claim 1,
wherein the fiber is a drawn fiber.
6. The water-disintegrable composite fiber according to claim 5,
wherein a single fiber fineness is 3.0 denier or less.
7. A fiber obtained by removing either the polyglycolic acid resin
or the polylactic acid resin from the water-disintegrable composite
fiber described in claim 5.
8. A water-disintegrable composite staple fiber obtained by cutting
the water-disintegrable composite fiber described in claim 5.
9. The water-disintegrable composite staple fiber according to
claim 8, wherein the staple fiber is used as an additive at a time
of drilling or sompletion of oil or gas recovery.
10. A method for producing a water-disintegrable composite fiber,
the method comprising the steps of: forming a fibrous composite by
continuously discharging a polylactic acid resin having a D-lactic
acid unit ratio of at least 1.0% and from 2 to 100 parts by mass of
a polyglycolic acid resin per 1 part by mass of D-lactic acid units
in the polylactic acid resin from a spinneret for composite fibers,
each of the resins being discharged in a molten state; and cooling
the fibrous composite to obtain an undrawn yarn comprising a phase
containing the polyglycolic acid resin and a phase containing the
polylactic acid resin, the undrawn yarn having a cross section in
which an area formed by the phase containing the polyglycolic acid
resin has an area ratio of at most 50%.
11. A method for producing a water-disintegrable composite fiber,
the method comprising the step of: drawing an undrawn yarn obtained
by the production method described in claim 10 so as to obtain a
drawn yarn comprising the phase containing the polyglycolic acid
resin and the phase containing the polylactic acid resin, the drawn
yarn having a cross section in which an area formed by the phase
containing the polyglycolic acid resin has an area ratio of at most
50%, and the drawn yarn containing from 2 to 100 parts by mass of
the polyglycolic acid resin per 1 part by mass of the D-lactic acid
units in the polylactic acid resin.
12. A method of producing a water-disintegrable composite fiber,
the method comprising the step of cutting a drawn yarn obtained by
the production method described in claim 11 to obtain a
water-disintegrable composite fiber staple fiber.
Description
TECHNICAL FIELD
[0001] The present invention relates to a water-disintegrable
composite fiber and a method for producing the same, and
particularly to a water-disintegrable composite fiber containing a
polyglycolic acid resin and a polylactic acid resin and a method
for producing the same.
BACKGROUND ART
[0002] In drilling techniques such as those used in gas fields or
oil fields, short fibers are added to a well treatment fluid so as
to prevent the backflow of proppants inside the well (for example,
see Japanese Unexamined Patent Application Publication (Translation
of PCT Application) No. 2011-506791 (Patent Document 1)). However,
conventional short fibers added to a well treatment fluid consist
of a resin such as a polyamide or polyolefin which is hardly
decomposed in the ground, resulting in the problem that the short
fibers remain in the ground after well treatment. Therefore, in
recent years, the use of fibers consisting of a biodegradable resin
as short fibers for a well treatment fluid has been investigated
from the perspective of reducing the environmental burden.
[0003] On the other hand, fibers consisting of a polylactic acid
resin or a polyglycolic acid resin are known as fibers having
biodegradability or bioabsorbability and have been conventionally
used as surgical sutures and the like in the medical field. With
the objective of reducing the environmental burden, the
applications of such fibers have been expanded not only to the
medical field but also to a wide range of fields, such as fibers to
be used in industrial materials, sanitary materials, and lifestyle
materials. However, single fibers of a polylactic acid resin or a
polyglycolic acid resin cannot necessarily be considered to have
sufficient water disintegrability or mechanical characteristics,
and the conjugation of single fibers with various resins has been
studied (for example, Japanese Unexamined Patent Application
Publication No. H07-133511 (Patent Document 2), Japanese Unexamined
Patent Application Publication No. 2000-265333 (Patent Document 3),
and Japanese Unexamined Patent Application Publication No.
2007-119928 (Patent Document 4)).
CITATION LIST
Patent Documents
[0004] Patent Document 1: Japanese Unexamined Patent Application
Publication (Translation of PCT Application) No. 2011-506791
[0005] Patent Document 2: Japanese Unexamined Patent Application
Publication No. H07-133511A
[0006] Patent Document 3: Japanese Unexamined Patent Application
Publication No. 2000-265333A
[0007] Patent Document 4: Japanese Unexamined Patent Application
Publication No. 2007-119928A
SUMMARY OF INVENTION
Technical Problem
[0008] Polylactic acid resin fibers exhibit good water
disintegrability at relatively high temperatures of 80.degree. C.
or higher. When short fibers consisting of such a polylactic acid
resin are added to a well treatment fluid, proppants in the well
treatment fluid tend to settle, and it has been difficult to obtain
a well treatment fluid with excellent proppant dispersibility.
[0009] The present invention was conceived in light of the problem
of the conventional technology described above, and an objective of
the present invention is to provide a water-disintegrable composite
fiber capable of maintaining high proppant dispersibility in a well
treatment fluid and a method for producing the fiber.
Solution to Problem
[0010] As a result of conducting extensive research in order to
achieve the object described above, the present inventors
discovered that the dispersibility of proppants is reduced in a
well treatment fluid to which short fibers consisting of a
polylactic acid resin have been added, because the diameter of the
polylactic acid resin short fibers is large and the contact area
between fibers and proppants is small. In addition, the present
inventors discovered that polylactic acid resin fibers cannot be
drawn at a high draw ratio and that it is difficult to obtain
polylactic resin fibers with a small diameter. Further, the present
inventors discovered that when the content of D-lactic acid units
(hereafter abbreviated as the "D-form ratio") in the polylactic
acid resin is increased in order to improve the water
disintegrability of the polylactic acid resin short fibers, yarn
breakage occurs more prominently when drawn.
[0011] As a result of conducting further research based on such
knowledge, the present inventors discovered that by including a
prescribed amount of a polyglycolic acid resin with respect to the
D-lactic acid units in a water-disintegrable composite undrawn yarn
comprising a phase containing a polyglycolic acid resin and a phase
containing a polylactic acid resin having D-lactic acid units, it
is possible to draw the composite undrawn yarn at a high draw ratio
and it is possible to obtain a water-disintegrable composite drawn
yarn with a small diameter, and the present inventors thereby
completed the present invention.
[0012] That is, the water-disintegrable composite fiber of the
present invention is an undrawn or a drawn fiber comprising a phase
containing a polyglycolic acid resin and a phase containing a
polylactic acid resin with a D-lactic acid unit ratio of at least
1.0%; the two phases being respectively continuous in the length
direction; a region formed by the phase containing the polyglycolic
acid resin having a cross section with an area ratio of at most
50%; and the content of the polyglycolic acid resin being from 2 to
100 parts by mass per 1 part by mass of the D-lactic acid units in
the polylactic acid resin.
[0013] Such a water-disintegrable composite fiber preferably
further has a side surface in which the region formed by the phase
containing the polyglycolic acid resin has an area ratio of at most
50%. In addition, the fiber structure is preferably at least one
type selected from a core-sheath type, a multicore type, a
side-by-side type, a multiple division type, a multilayer type, and
a radial type structure. Further, the single fiber fineness of the
drawn water-disintegrable composite fiber is preferably at most 3.0
denier.
[0014] In addition, fibers of various structures such as hollow
fibers or ultrafine fibers can be obtained by removing either the
polyglycolic acid resin or the polylactic acid resin from the
water-disintegrable composite fiber of the present invention, and a
water-disintegrable composite staple fiber can be obtained by
cutting the water-disintegrable composite fiber of the present
invention. This water-disintegrable composite staple fiber can be
suitably used as an additive at the time of oil or gas
drilling.
[0015] The method for producing the water-disintegrable composite
fiber of the present invention is a method comprising the steps of
forming a fibrous composite by continuously discharging a
polylactic acid resin having a D-lactic acid unit ratio of at least
1.0% and from 2 to 100 parts by mass of a polyglycolic acid resin
per 1 part by mass of D-lactic acid units in the polylactic acid
resin from a spinneret for composite fibers, each being discharged
in a molten state and cooling the fibrous composite to obtain an
undrawn yarn comprising a phase containing the polyglycolic acid
resin and a phase containing the polylactic acid resin, the undrawn
yarn having a cross section in which the region formed by the phase
containing the polyglycolic acid resin has an area ratio of at most
50%.
[0016] In addition, in the method for producing the
water-disintegrable composite fiber of the present invention, the
undrawn yarn may be drawn so as to obtain a drawn yarn comprising
the phase containing the polyglycolic acid resin and the phase
containing the polylactic acid resin, the drawn yarn having a cross
section in which the region formed by the phase containing the
polyglycolic acid resin has an area ratio of at most 50%, and the
drawn yarn containing from 2 to 100 parts by mass of the
polyglycolic acid resin per 1 part by mass of the D-lactic acid
units in the polylactic acid resin.
[0017] The reason that including a prescribed amount of a
polyglycolic acid resin with respect to the D-lactic acid units in
the polylactic acid resin makes it possible to draw a
water-disintegrable composite undrawn yarn comprising a phase
containing the polyglycolic acid resin and a phase containing the
polylactic acid resin at a high draw ratio is not absolutely
certain, but the present inventors speculate as follows.
Specifically, in a single fiber of a polylactic acid resin with a
high D-form ratio, oriented crystallization caused by drawing is
unlikely to occur due to the crystallization resistant properties
of polylactic acid resins with a high D-form ratio, and it is thus
speculated that the so-called necking phenomenon is unlikely to
occur. When the diameter is reduced by drawing a fiber which is
unlikely to be subjected to the necking phenomenon due to drawing
at a high draw ratio, stress is concentrated in portions where the
fiber diameter is small, in particular, so it is speculated that
fiber breaks when drawing is continued. In addition, such a
phenomenon is speculated to occur more prominently as the D-form
ratio of the polylactic acid resin increases.
[0018] In contrast, in the water-disintegrable composite fiber of
the present invention, the polyglycolic acid resin is easily
subjected to the necking phenomenon due to drawing, so the low
orientation of the polylactic acid resin is compensated by the high
orientation of the polyglycolic acid resin. Therefore, the
concentration of stress is unlikely to occur even when drawn at a
high draw ratio, and it is speculated that this is why fiber is
unlikely to break.
Advantageous Effects of Invention
[0019] With the present invention, it is possible to obtain a
water-disintegrable composite fiber capable of maintaining high
proppant dispersibility in a well treatment fluid.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1A is a schematic view illustrating a preferred
embodiment of the structure of a concentric core-sheath type
water-disintegrable composite fiber of the present invention.
[0021] FIG. 1B is a schematic view illustrating a preferred
embodiment of the structure of an eccentric core-sheath type
water-disintegrable composite fiber of the present invention.
[0022] FIG. 1C is a schematic view illustrating a preferred
embodiment of the structure of a multicore type water-disintegrable
composite fiber of the present invention.
[0023] FIG. 1D is a schematic view illustrating a preferred
embodiment of the structure of a side-by-side type
water-disintegrable composite fiber of the present invention.
[0024] FIG. 1E is a schematic view illustrating a preferred
embodiment of the structure of a multiple-division type
water-disintegrable composite fiber of the present invention.
[0025] FIG. 1F is a schematic view illustrating a preferred
embodiment of the structure of a multilayer type
water-disintegrable composite fiber of the present invention.
[0026] FIG. 1G is a schematic view illustrating a preferred
embodiment of the structure of a radial type water-disintegrable
composite fiber of the present invention.
[0027] FIG. 2 is a schematic view illustrating a melt spinning
device used in the working examples and comparative examples.
[0028] FIG. 3 is a schematic view illustrating a drawing device
used in the working examples and comparative examples.
DESCRIPTION OF EMBODIMENTS
[0029] The present invention will be described in detail hereafter
using preferred embodiments thereof.
[0030] The water-disintegrable composite fiber of the present
invention comprises a phase containing a polyglycolic acid resin
(abbreviated as a "PGA resin phase" hereafter) and a phase
containing a polylactic acid resin with a D-lactic acid unit ratio
(D-form ratio) of at least 1.0% (abbreviated as a "PLA resin phase"
hereafter). First, the polylactic acid resin and the polyglycolic
acid resin used in the present invention will be described.
(Polylactic Acid Resin)
[0031] The polylactic acid resin (abbreviated as the "PLA resin"
hereafter) used in the present invention contains D-lactic acid
units in an amount of at least 1.0%. Specific examples include
poly-DL lactic acids with a D-form ratio of at least 1.0%
(copolymers of D-lactic acid and L-lactic acid (including
ring-opened polymers of D/L-lactides, which are bimolecular cyclic
esters of D-lactic acid and L-lactic acid), abbreviated as "PDLLA
resins" hereafter) and poly-D lactic acids (homopolymers of
D-lactic acid (including ring-opened polymers of D-lactides, which
are bimolecular cyclic esters of D-lactic acid), abbreviated as
"PDLA resins" hereafter) and the like.
[0032] When the D-form ratio of the PLA resin is less than 1.0%,
the water disintegrability (mass loss) of the PLA resin phase
decreases, and the water disintegrability (mass loss) of the
composite fiber also decreases. In the present invention, the
D-form ratio of the PLA resin is preferably at least 1.2% from the
perspective that the water disintegrability of the PLA resin phase
increases. In addition, the upper limit of the D-form ratio of the
PLA resin is not particularly limited but is preferably at most 30%
and more preferably at most 15% from the perspective of ensuring
that the action due to the polyglycolic acid resin described below
is sufficiently expressed.
[0033] Further, the melt viscosity of the PLA resin (temperature:
240.degree. C., shear rate: 122 sec) is preferably from 1 to 10,000
Pas, more preferably from 20 to 6,000 Pas, and particularly
preferably from 50 to 4,000 Pas. When the melt viscosity is less
than the lower limit described above, the spinnability is
diminished and the fiber tends to have break in some parts, whereas
when the melt viscosity exceeds the upper limit described above, it
tends to become difficult to discharge the PLA resin in a molten
state.
[0034] In the present invention, such a PLA resin may be used
alone, and various additives such as thermal stabilizers,
end-capping agents, plasticizers, and UV absorbers or other
thermoplastic resins may be added as necessary and used as a PLA
resin composition.
(Polyglycolic Acid Resin)
[0035] The polyglycolic acid resin (abbreviated as "PGA resin"
hereafter) used in the present invention is a glycolic acid
homopolymer consisting of repeating units of a glycolic acid
represented by the following formula (1) (abbreviated as "PGA
homopolymer" hereafter; including glycolide ring-opened polymers,
which are bimolecular cyclic esters of glycolic acids):
--[O--CH.sub.2--(.dbd.)]-- (1)
[0036] Such a PGA resin can be synthesized by the dehydration
polycondensation of a glycolic acid, de-alcohol polycondensation of
a glycolic acid alkyl ester, the ring-opening polymerization of a
glycolide, or the like. Of these, the PGA homopolymer is preferably
synthesized by the ring-opening polymerization of a glycolide. In
addition, such ring-opening polymerization can be performed by bulk
polymerization or solution polymerization.
[0037] Examples of catalysts used when producing the PGA resin by
the ring-opening polymerization of a glycolide include publicly
known ring-opening polymerization catalysts such as tin compounds
such as tin halide and organic tin carboxylate; titanium compounds
such as alkoxy titanate; aluminum compounds such as alkoxyaluminum;
zirconium compounds such as zirconium acetyl acetone; and antimony
compounds such as antimony halide and antimony oxide.
[0038] The PGA resin can be produced by a conventionally known
polymerization method, but the polymerization temperature is
preferably from 120 to 300.degree. C., more preferably from 130 to
250.degree. C., and particularly preferably from 140 to 220.degree.
C. When the polymerization temperature is less than the lower limit
described above, polymerization tends to not progress sufficiently,
whereas when the polymerization temperature exceeds the upper limit
described above, the resin that is produced tends to be
pyrolyzed.
[0039] The polymerization time of the PGA resin is preferably from
2 minutes to 50 hours, more preferably from 3 minutes to 30 hours,
and particularly preferably from 5 minutes to 18 hours. When the
polymerization time is less than the lower limit described above,
polymerization tends to not progress sufficiently, whereas when the
polymerization time exceeds the upper limit described above, the
resin that is produced tends to be discolored.
[0040] The weight average molecular weight of such a PGA resin is
preferably from 50,000 to 800,000, and more preferably from 80,000
to 500,000. When the weight average molecular weight of the PGA
resin is less than the lower limit described above, the mechanical
strength of the resulting composite fiber tends to be diminished,
whereas when the weight average molecular weight exceeds the upper
limit described above, it tends to become difficult to discharge
the PGA resin in a molten state. The weight average molecular
weight is a value in terms of polymethyl methacrylate measured by
gel permeation chromatography (GPC).
[0041] In addition, the melt viscosity of the PGA resin
(temperature: 240.degree. C., shear rate: 122 sec) is preferably
from 1 to 10,000 Pas, more preferably from 50 to 6,000 Pas, and
particularly preferably from 100 to 4,000 Pas. When the melt
viscosity is less than the lower limit described above, the
spinnability is diminished and the fiber tends to break in some
parts, whereas when the melt viscosity exceeds the upper limit
described above, it tends to become difficult to discharge the PGA
resin in a molten state.
[0042] In the present invention, such a PGA resin may be used
alone, and various additives such as thermal stabilizers,
end-capping agents, plasticizers, and UV absorbers or other
thermoplastic resins may be added as necessary and used as a PGA
resin composition.
[0043] In addition, in the present invention, a polyglycolic acid
copolymer comprising repeating units of a glycolic acid represented
by the aforesaid formula (1) (abbreviated as a "PGA copolymer"
hereafter) may also be used instead of such a polyglycolic acid
resin.
[0044] The PGA copolymer described above can be synthesized by
using a comonomer in a polycondensation reaction or ring-opening
polymerization reaction for synthesizing a PGA homopolymer.
Examples of such a comonomer include cyclic monomers such as
ethylene oxalate (i.e. 1,4-dioxane-2,3-dione), lactides, lactones
(e.g. .beta.-propiolactone, .beta.-butyrolactone,
.beta.-pivalolactone, .gamma.-butyrolactone, .delta.-valerolactone,
.beta.-methyl-.delta.-valerolactone, .epsilon.-caprolactone, and
the like), carbonates (e.g. trimethylene carbonate and the like),
ethers (e.g. 1,3-dioxane and the like), ether esters (e.g.
dioxanone and the like), and amides (e.g. .epsilon.-caprolactam and
the like); hydroxycarboxylic acids such as lactic acid,
3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic
acid, 6-hydroxycaproic acid, and the alkylesters thereof; mixtures
containing substantially equimolar amounts of aliphatic diols, such
as ethylene glycol and 1,4-butanediol, and aliphatic dicarboxylic
acids, such as succinic acid and adipic acid, or the alkyl esters
thereof. One type of these comonomers may be used alone or two or
more types of these comonomers may be used in combination.
<Water-Disintegrable Composite Fiber>
[0045] Next, the water-disintegrable composite fiber of the present
invention will be described. The water-disintegrable composite
fiber of the present invention is an undrawn or a drawn yarn
comprising a phase containing a PGA resin (PGA resin phase) and a
phase containing a PLA resin with a D-form ratio of at least 1.0%
(PLA resin phase); the two phases being respectively continuous in
the length direction of the fiber; the composite fiber having a
cross sectional area partly formed by the PGA resin phase with an
area ratio of at most 50%; and the fiber containing from 2 to 100
parts by mass of the PGA resin per 1 part by mass of the D-lactic
acid units in the PLA resin.
[0046] When the content of the PGA resin per 1 part by mass of the
D-lactic acid units in the PLA resin is less than 2 parts by mass,
the undrawn yarn cannot be drawn at a high draw ratio, which makes
it difficult to form a drawn yarn with a small single fiber
fineness and reduces the proppant dispersibility by the drawn
composite fiber. On the other hand, when the PGA resin content
exceeds 100 parts by mass, the proportion of the PLA resin is
small, so the characteristics of the PLA resin cannot be
sufficiently expressed. Moreover, at a relatively high temperature,
specifically 60.degree. C. or higher, the rate of water
disintegration of the composite fiber becomes very high, and the
use of the fiber becomes difficult. In the present invention, the
PGA resin content is preferably from 3 to 100 parts by mass and
more preferably from 5 to 80 parts by mass per 1 part by mass of
the D-lactic acid units in the PLA resin from the perspective of
obtaining a drawn composite fiber with a small single fiber
fineness when the undrawn yarn is drawn at a high draw ratio,
excellent proppant dispersibility, and excellent water
disintegrability at a relatively high temperature of 60.degree. C.
or higher.
[0047] The content of the PGA resin in the component constituting
the PGA resin phase is preferably at least 60 mass %, more
preferably at least 80 mass %, even more preferably at least 95
mass %, and particularly preferably 100%. In addition, the content
of the PLA resin in the component constituting the PLA resin phase
is preferably at least 60 mass %, more preferably at least 80 mass
%, even more preferably at least 95 mass %, and particularly
preferably 100%.
[0048] In the cross section of the water-disintegrable composite
fiber of the present invention, the area formed from the PGA resin
phase is 50% or less in terms of area ratio. When the area ratio of
the region formed by the PGA resin phase in the cross section
exceeds 50%, the proportion of the PLA resin is small, so the
characteristics of the PLA resin cannot be sufficiently expressed,
and the water disintegrability (mass loss) of the composite fiber
at a relatively high temperature of 60.degree. C. or higher
decreases. In the present invention, the area ratio of the region
formed by the PGA resin phase in the cross section is preferably at
most 40% from the perspective that the water disintegrability (mass
loss) of the composite fiber at a relatively high temperature of
60.degree. C. or higher improves. In addition, the lower limit of
the area ratio of the region formed by the PGA resin phase in the
cross section of the water-disintegrable composite fiber of the
present invention is preferably at least 1%, more preferably at
least 5%, even more preferably at least 10%, and particularly
preferably at least 15%. When the area ratio of the region formed
by the PGA resin phase in the cross section is less than the lower
limit described above, the characteristics of the PGA resin cannot
be sufficiently expressed, so the undrawn yarn cannot be drawn at a
high draw ratio, which makes it difficult to form a drawn yarn with
a small single fiber fineness and tends to diminish the proppant
dispersibility of the composite fiber (drawn yarn). Further, the
water disintegrability (mass loss) of the composite fiber at around
60.degree. C. tends to decrease.
[0049] In addition, the area ratio of the region formed by the PGA
resin phase on the side surface of the water-disintegrable
composite fiber of the present invention is preferably at most 50%,
more preferably at most 30%, even more preferably at most 15%, and
particularly preferably at most 10%. When the area ratio of the
region formed by the PGA resin phase on the side surface exceeds
the upper limit described above, the undrawn yarn is prone to
agglutination, and the unwindability after storage, particularly at
high temperature and high humidity (for example, at a temperature
of 40.degree. C. and relative humidity of 80% RH), tends to be
diminished. In addition, it is particularly preferable for the
region formed from the PGA resin phase not to be exposed to the
side surface of the water-disintegrable composite fiber of the
present invention, so the lower limit of the area ratio is
particularly preferably 0% or higher.
[0050] Specific examples of fiber structures of the
water-disintegrable composite fiber of the present invention
include a concentric core-sheath type structure (see FIG. 1A), an
eccentric core-sheath type structure (see FIG. 1B), a multicore
type structure (see FIG. 1C), a side-by-side type structure (see
FIG. 1D), a multiple-division type structure (see FIG. 1E), a
multilayer type structure (see FIG. 1F), a radial type structure
(see FIG. 1G), and composite structures combining two or more types
thereof. In FIGS. 1A to 1G, the left figure is a schematic view of
the cross section of the composite fiber, and the right figure is a
schematic view of the side surface. In addition, in FIGS. 1A to 1G,
A represents the PGA resin phase, and B represents the PLA resin
phase. Of these fiber structures, a concentric core-sheath
structure, an eccentric core-sheath structure, or a multicore
structure is preferable from the perspective that the undrawn yarn
has excellent unwindability, the fiber is unlikely to break when
drawn and that the drawn yarn has a small single fiber fineness and
excellent proppant dispersibility.
[0051] In such a water-disintegrable composite fiber of the present
invention, the mass loss of the drawn yarn when immersed for 14
days in water at 60.degree. C. and 80.degree. C. is preferably at
least 10%, more preferably at least 15%, even more preferably at
least 20%, yet even more preferably at least 25%, and particularly
preferably at least 30%. When the mass loss is less than the lower
limit described above, the fiber is not sufficiently hydrolyzed and
may remain in the ground after well treatment when added to a well
treatment fluid as a short fiber. The upper limit of the mass loss
described above is not particularly limited and is preferably 100%
or less, but the upper limit may also be 95% or less.
[0052] In addition, as described above, since the undrawn yarn can
be drawn at a high draw ratio, this can be drawn to obtain a drawn
yarn with a single fiber fineness of preferably at most 3.0 denier,
more preferably at most 2.0 denier, and particularly preferably at
most 1.5 denier. Such a draw yarn has a very small diameter and
thus excellent proppant dispersibility.
<Method of Producing the Water-Disintegrable Composite
Fiber>
[0053] Next, a preferred embodiment of the method of producing the
water-disintegrable composite fiber of the present invention will
be described with reference to the drawings, but the method of
producing the water-disintegrable composite fiber of the present
invention is not limited to these drawings. In the following
explanations and drawings, elements that are identical or
equivalent are labeled with the same symbols, and duplicate
explanations will be omitted.
[0054] In the method for producing the water-disintegrable
composite fiber of the present invention, a PGA resin in a molten
state and a PLA resin in a molten state (having a prescribed D-form
ratio) are continuously discharged from a spinneret for composite
fibers at a prescribed ratio so as to form a fibrous composite
(discharge step). At this time, the resulting fibrous composite may
be held in an atmosphere at a prescribed temperature for a
prescribed amount of time after being discharged as necessary (heat
retaining step). The fibrous composite is then cooled by a known
cooling method such as air cooling to obtain an undrawn yarn
(cooling step). In the method of producing the water-disintegrable
composite fiber of the present invention, the undrawn yarn may be
mass-produced and stored (storage step) and subjected to drawing
processing as necessary to obtain a drawn yarn (drawing step).
[0055] The PGA resin and the PLA resin in the molten state can be
prepared by melt-kneading using an extruder or the like. For
example, when producing an undrawn yarn using the melt spinning
device illustrated in FIG. 2, the PGA resin and the PLA resin, in a
pellet form or the like, are each independently loaded into
extruders 2a and 2b from raw material hoppers 1a and 1b, and the
PGA resin and the PLA resin are melt-kneaded.
[0056] The melt temperature of the PGA resin is preferably from 200
to 300.degree. C. and more preferably from 210 to 270.degree. C.
When the melt temperature of the PGA resin is less than the lower
limit described above, the fluidity of the PGA resin is diminished,
and the PGA resin is not discharged from the spinneret, which makes
it difficult to form a fibrous composite. On the other hand, when
the melt temperature exceeds the upper limit described above, the
PGA resin tends to be discolored or pyrolyzed.
[0057] In addition, the melt temperature of the PLA resin is
preferably from 170 to 280.degree. C. and more preferably from 210
to 240.degree. C. When the melt temperature of the PLA resin is
less than the lower limit described above, the fluidity of the PLA
resin is diminished, and the PLA resin is not discharged from the
spinneret, which makes it difficult to form a fibrous composite. On
the other hand, when the melt temperature exceeds the upper limit
described above, the PLA resin tends to be pyrolyzed.
[0058] In such a melt-kneading process, a stirrer, a continuous
kneader, or the like can be used instead of an extruder, but it is
preferable to use an extruder from the perspective that processing
can be accomplished in a short period of time and that a smooth
transition can be made to the subsequent discharge step.
(Discharge Step)
[0059] In the discharge step of the present invention, the PLA
resin in the molten state prepared as described above and the PGA
resin in a molten state in an amount of 2 to 100 parts (preferably
3 to 100 parts and more preferably 5 to 80 parts) by mass per 1
part by mass of the D-lactic acid units in the PLA resin are
discharged from a spinneret for composite fibers so as to form a
fibrous composite comprising a phase containing the PGA resin in a
molten state (called the "molten PGA resin phase" hereafter) and a
phase containing the PLA resin in a molten state (called the
"molten PLA resin phase" hereafter); the region formed by the
molten PGA resin phase having a cross section with an area ratio of
at most 50% (preferably at most 40%) (the region formed by the
molten PGA resin phase more preferably has an area ratio of at most
50% (preferably at most 30%, more preferably at most 15%, and
particularly preferably at most 10%)). For example, in the melt
spinning device illustrated in FIG. 2, the PGA resin in a molten
state is transferred to a spinneret 4 from the extruder 2a while
regulating the volume using a gear pump 3a, and the PLA resin in a
molten state is transferred to the spinneret 4 from the extruder 2b
while regulating the volume using a gear pump 3b. The PGA resin and
the PLA resin are then discharged from the hole of the spinneret 4
at a prescribed ratio and in an incompatible state to form a
fibrous composite having the cross section and the side surface
described above.
[0060] In a fibrous composite obtained in this way, the content of
the PGA resin in the component constituting the molten PGA resin
phase is preferably at least 60 mass %, more preferably at least 80
mass %, even more preferably at least 95 mass %, and particularly
preferably 100%. In addition, the content of the molten PLA resin
in the component constituting the PLA resin phase is preferably at
least 60 mass %, more preferably at least 80 mass %, even more
preferably at least 95 mass %, and particularly preferably
100%.
[0061] A conventionally known spinneret for composite fibers can be
used as the spinneret 4 as long as a fibrous composite having the
cross section and the side surface described above can be formed.
For example, a concentric core-sheath type, an eccentric
core-sheath type, a multicore type, a side-by-side type, a
multiple-division type, a multilayer type, a radial type, or a
composite type spinneret for composite fibers comprising two or
more types thereof may be used as long as the region where the PGA
resin in a molten state is discharged accounts for at most 50% in
terms of area ratio (preferably at most 40%) in a hole. In
addition, in the present invention, the number of holes and the
hole diameter of such a spinneret for composite fibers are not
particularly limited.
[0062] The discharge temperature of the PGA resin and the PLA resin
in a molten state, that is, the discharge temperature of the
composite in a molten state (spinneret temperature), is preferably
from 210 to 280.degree. C., and more preferably from 235 to
268.degree. C. When the discharge temperature is less than the
lower limit described above, the fluidity of the PGA resin and the
PLA resin is diminished, and the resins are not discharged from the
spinneret, which makes it difficult to form the fibrous composite.
On the other hand, when the discharge temperature exceeds the upper
limit described above, these resins tend to be prone to
pyrolysis.
(Heat Retaining Step)
[0063] In the method for producing the water-disintegrable
composite fiber of the present invention, the fibrous composite
discharged from the spinneret is preferably retained in a heat
sleeve 5 set to a temperature of 110.degree. C. or higher
(preferably 120.degree. C. or higher) as necessary. Consequently,
an undrawn yarn with low orientation is obtained, which enables
drawing at a high draw ratio. As a result, the single fiber
fineness of the drawn yarn becomes low, which tends to result in a
composite fiber with an even higher tensile strength. In addition,
the temperature inside the heat sleeve is preferably at most the
melting point of the PGA resin. When the fibrous composite that is
discharged from the spinneret is held in an atmosphere at a
temperature exceeding the melting point of the PGA resin
immediately after being discharged, the fibrous composite tends to
be prone to break in some parts during being taken up, which tends
to lead to a lack of productivity.
[0064] Inside the heat sleeve, it is not absolutely necessary for
the temperature to be constant, and the atmosphere may have a
temperature distribution. The temperature (temperature
distribution) inside such a heat sleeve can be measured using an
infrared laser thermometer or the like.
[0065] In the heat retaining step of the present invention, the
fibrous composite formed in the discharge step is typically held in
the heat sleeve 5 set to a prescribed temperature while being taken
up. The take-up rate (spinning rate) of the fibrous composite is
not particularly limited, but it is particularly preferable to take
up the fibrous composite at a take-up rate such that the mass per
unit length of a single fiber constituting an undrawn yarn
(hereafter called an "undrawn single fiber") is 6.times.10.sup.-4
g/m or greater (and more preferably 13.times.10.sup.-4 g/m or
greater). As a result, a composite fiber (undrawn yarn) which is
not prone to break when drawn tends to be obtained. The mass per
unit length of the undrawn single fiber changes depending on
factors such as the hole diameter of the spinneret and the
discharge volume per hole of the spinneret, so the take-up rate is
set while taking these factors into consideration so as to achieve
the desired mass per unit length of the undrawn single fiber.
(Storage Step)
[0066] Since the water-disintegrable composite fiber of the present
invention having the side surface described above demonstrates
excellent unwindability in the undrawn yarn, the fiber can be wound
around a bobbin or the like or housed in a tow can for storage. As
a result, the undrawn yarn can be produced and stored in large
quantities and can also be supplied stably, which enables the
adjustment of the production of a drawn yarn.
[0067] The storage temperature is not particularly limited, but the
undrawn yarn can be stably stored at 25 to 40.degree. C. When
stored at a temperature less than the lower limit described above,
a cooling device is necessary, which is not preferable from an
economic standpoint. That is, in the method of producing the
water-disintegrable composite fiber of the present invention,
low-temperature storage is unnecessary, so it is possible to cut
the production cost (storage cost) when producing a drawn yarn. On
the other hand, when stored at a temperature exceeding the upper
limit described above, the agglutination of the undrawn composite
fiber, which the PGA resin is exposed to the side surface of, may
occur, and it is not preferable for such composite fiber.
[0068] The storage time in the method for producing the
water-disintegrable composite fiber of the present invention is not
particularly limited, but the fiber can be stored, for example, for
24 hours or longer in an environment with a temperature of
30.degree. C. and a relative humidity of 80% RH.
(Drawing Step)
[0069] Since the water-disintegrable composite fiber of the present
invention demonstrates excellent unwindability in the undrawn yarn,
the undrawn yarn that is wound around a bobbin or the like or
housed in a tow can for storage as described above can be drawn
after being pulled out while being unwound. As a result, it is
possible to obtain a drawn yarn comprising a PGA resin phase and a
PLA resin phase; the region formed by the PGA resin phase having a
cross section with an area ratio of at most 50% (preferably at most
40%) (the region formed by the PGA resin phase more preferably has
an area ratio of at most 50% (preferably at most 30%, more
preferably at most 15%, and particularly preferably at most 10%);
and the drawn yarn containing the PGA resin in an amount of from 2
to 100 parts by mass (preferably from 30 to 100 parts by mass and
more preferably from 5 to 80 parts by mass) per 1 part by mass of
the D-lactic acid units in the PLA resin.
[0070] In the method of producing the water-disintegrable composite
fiber of the present invention, the drawing temperature and draw
ratio are not particularly limited and can be set appropriately in
accordance with the desired physical properties and the like of the
composite fiber, but the drawing temperature is preferably from 40
to 120.degree. C., and the draw ratio is preferably from 2.0 to
6.0, for example. In addition, the drawing method is not
particularly limited, and a conventionally known fiber drawing
method can be employed. For example, when drawing an undrawn yarn
using the drawing device illustrated in FIG. 3, an undrawn yarn is
pulled out from a bobbin 14 via a feed roller 21, and after the
undrawn yarn is drawn using rollers 22 and 23, the resulting drawn
yarn is wound around a bobbin 25.
[0071] The drawn yarn that is obtained in this way may be used
directly as a long fiber or may be cut so as to form a staple
fiber. The cutting method is not particularly limited, and a
publicly known cutting method used in the production method for a
staple fiber can be employed. Such a staple fiber has a small
diameter and a large specific surface area and therefore tends to
exhibit excellent proppant dispersibility when added to a well
treatment fluid.
[0072] In addition, by removing either the PGA resin or the PLA
resin in the water disintegrable composite fiber of the present
invention (in particular, the drawn yarn), it is possible to obtain
fibers of various structures in accordance with the structure of
the composite fiber, and this can be cut to form a staple fiber.
For example, hollow fibers can be obtained by removing the PGA
resin from concentric core-sheath type (FIG. 1A), eccentric
core-sheath type (FIG. 1B), and multicore type (FIG. 1C)
water-disintegrable composite fibers. On the other hand, by
removing the PLA resin, it is possible to obtain a PGA resin single
fiber having a smaller fiber diameter than the water-disintegrable
composite fiber of the present invention. In addition, by removing
either the PLA resin or the PGA resin, a single fiber of the PGA
resin or the PLA resin having a semicircular cross section can be
obtained from a side-by-side type water-disintegrable composite
fiber (FIG. 1D), a single fiber of the PGA resin or the PLA resin
having a fan-shaped cross section can be obtained from a
multiple-division type water-disintegrable composite fiber (FIG.
1E), or a single fiber of the PGA resin or the PLA resin having a
flat cross section can be obtained from a multilayer type
water-disintegrable composite fiber (FIG. 1F). A single fiber of
the PGA resin having a radial cross section can be obtained by
removing the PLA resin from a radial type water-disintegrable
composite fiber (FIG. 1G).
[0073] Examples of methods for removing resins from the
water-disintegrable composite fiber of the present invention
include a method of separating the PGA resin phase and the PLA
resin phase by peeling and a method of dissolving one of the resins
by immersing the water-disintegrable composite fiber in a solvent
that is a good solvent for one of the PGA resin or the PLA resin
and a poor solvent for the other. The solvent used in the
dissolution method is not particularly limited.
EXAMPLES
[0074] The present invention will be described in further detail
hereafter based on working examples and comparative examples, but
the present invention is not limited to the following examples. The
physical properties of the resins and the properties of the undrawn
yarn and staple fiber were measured with the following methods.
<Melting Point and Glass Transition Temperature>
[0075] The melting point and the glass transition temperature of
the resin were measured in a nitrogen atmosphere at a heating rate
of 20.degree. C./min using a differential scanning calorimeter
(DSC; "TC-15" manufactured by Mettler-Toledo International
Inc.).
<Melt Viscosity>
[0076] The melt viscosity of the resin was measured using a
capirograph equipped with capillaries (1 mm in diameter.times.10 mm
in length) ("Capirograph 1-C" manufactured by Toyo Seiki
Seisakusho). Specifically, approximately 20 g of the resin was
introduced into the capirograph set to a measurement temperature of
240.degree. C. and was held for 5 minutes, and measurements were
then performed under conditions with a shear rate of 122
sec.sup.-1.
<Single Fiber Fineness>
[0077] 90 m of a drawn yarn was hanked on a rewinder with a frame
circumference of 1 m, and the absolute dry mass M was measured. The
single fiber fineness was calculated from the following
formula.
Single fiber fineness (denier)=100.times.M/H
[0078] Here, M is the absolute dry mass (g) of the drawn yarn, and
H is the number of holes (=24 holes) of the spinneret.
<Mass Loss>
[0079] A staple fiber and deionized water were mixed in a vial with
a volume of 50 ml so that the solid content concentration of the
staple fiber was 2 mass %, and the resulting mixture was left to
stand for 14 days in a gear oven set to 60.degree. C. or 80.degree.
C. After being left to stand, the mixture was subjected to gravity
filtration using filter paper, and the residue on the filter paper
was dried at 80.degree. C. The mass after drying was measured, and
the mass loss was determined.
<Proppant Dispersibility>
[0080] Pseudo-mud was prepared by adding 0.2 g of xanthan gum
("XCD-Polymer" manufactured by Telnite Co., Ltd.) and 2.0 g of
starch ("Telpolymer DX" manufactured by Telnite Co., Ltd.) to 100
ml of a 10 mass % NaCl aqueous solution and stirring for 1 minute.
Staple fiber-dispersed pseudo-mud was prepared by adding 0.2 g of
the staple fiber to the pseudo-mud and stirring for 1 minute.
Proppant/staple fiber-dispersed pseudo-mud was prepared by adding 6
g of a proppant ("Bauxite 20/40" manufactured by SINTEX Co., Ltd.)
to the staple fiber-dispersed pseudo-mud and stirring for 1
minute.
[0081] Next, 100 ml of the proppant/staple fiber-dispersed
pseudo-mud was placed in a graduated cylinder with a volume of 100
ml, and the mark corresponding to the uppermost part of the
pseudo-mud (mark before being left to stand) was read accurately.
After the solution was left to stand for 1 hour, the mark
corresponding to the uppermost part of the proppant (mark after
being left to stand) was read accurately, and the proppant
dispersibility was assessed in accordance with the following
criteria based on the difference in the marks before and after
being left to stand.
[0082] A (outstanding): mark difference of less than 40 ml.
[0083] B (excellent): mark difference of at least 40 ml and less
than 55 ml.
[0084] C (good): mark difference of at least 55 ml and less than 70
ml.
[0085] D (poor): mark difference of at least 70 ml.
Working Example 1
<Production of a PGA/PLA Composite Underdrawn Yarn>
[0086] A PGA/PLA composite undrawn yarn was produced by using the
melt spinning device illustrated in FIG. 2. A
temperature-controllable heat sleeve 5 with a length of 150 mm and
an inner diameter of 100 mm was mounted beneath a spinneret 4 for
composite fibers of the melt spinning device. In the following
explanations and drawings, elements that are identical or
equivalent are labeled with the same symbols, and duplicate
explanations will be omitted.
[0087] First, a pellet-formed PGA resin (made by the Kureha
Corporation, weight average molecular weight: 180,000, glass
transition temperature: 43.degree. C., melting point: 220.degree.
C., melt viscosity (temperature: 240.degree. C., shear rate: 122
sec.sup.-1: 790 Pas, size: 3 mm in diameter.times.3 mm in length)
was loaded into a single-screw extruder 2a (made by Plagiken Co.,
Ltd., cylinder diameter: 30 mm, L/D=24) from a raw material hopper
la and melted at 215 to 250.degree. C. The cylinder temperature of
the extruder 2a was set to 215 to 250.degree. C., and the adapter
temperature, the gear pump temperature, and the spin pack
temperature were set to 250.degree. C.
[0088] On the other hand, a pellet-formed PLA resin ("6302D" made
by Nature Works Co., Ltd., D-form ratio: 9.5%, glass transition
temperature: 55 to 60.degree. C., melting point: 155 to 170.degree.
C., melt viscosity (temperature: 240.degree. C., shear rate: 122
sec.sup.-1: 290 Pas) was loaded into a single-screw extruder 2b
(made by Plagiken Co., Ltd., cylinder diameter: 25 mm, L/D=24) from
a raw material hopper 1b and melted at 170 to 250.degree. C. The
cylinder temperature of the extruder 2b was set to 170 to
200.degree. C., the adapter temperature and the gear pump
temperature were set to 200.degree. C., and the spin pack
temperature was set to 250.degree. C.
[0089] The molten PGA resin and the molten PLA resin were
continuously supplied to the spinneret 4 (for core-sheath type
composite fibers; hole size: 0.40 mm, 24 holes, temperature:
250.degree. C.) while regulating the volume using gear pumps 3a and
3b, respectively, so that the cross-sectional area ratio of the
core part to the sheath part at the discharge port was core
part/sheath part=25/75, and as a result, the core part of the
composite fiber formed the PGA resin phase and the sheath part
formed the PLA resin phase. After the resins were discharged from
the spinneret 4 to form a fibrous PGA/PLA composite, the composite
was passed through a heat sleeve 5 set to 120.degree. C. The
fibrous PGA/PLA composite was then air-cooled, and the resulting
PGA/PLA composite undrawn yarn was coated with an oiling agent for
fibers ("Lurol", made by the GOULSTON). The yarn was taken up with
a first take-up roller 7 at a circumferential speed of 1,000 m/min,
and a core-sheath type PGA/PLA composite undrawn yarn (core part:
PGA resin, sheath part: PLA resin) was wound around a bobbin 14
every 5,000 m via second to seventh take-up rollers 8 to 13. The
content of the PGA resin in the resulting core-sheath type PGA/PLA
composite undrawn yarn is 3.5 parts by mass per 1 part by mass of
the D-lactic acid units in the PLA resin.
<Production and Evaluation of a PGA/PLA Composite Drawn
Yarn>
[0090] A bobbin around which the PGA/PLA composite undrawn yarn was
wound was mounted on the drawing device illustrated in FIG. 3, and
this PGA/PLA composite undrawn yarn was unwound and drawn from the
bobbin 14 via the feed roller 21 using a first heating roller 22
and a second heating roller 23. A core-sheath type PGA/PLA
composite drawn yarn (core part: PGA resin, sheath part: PLA resin)
was wound around a bobbin 25 via a third heating roller 24. The
drawing temperature was set to 65.degree. C., and the draw ratio
was set to 2.2 times by adjusting the circumferential speeds of the
first and second heating rollers. The single fiber fineness of the
resulting PGA/PLA composite drawn yarn was measured in accordance
with the evaluation method described above. The results are shown
in Table 1.
<Production and Evaluation of a PGA/PLA Staple Fiber>
[0091] A PGA/PLA composite drawn yarn was cut using an EC cutter so
as to produce a core-sheath type PGA/PLA staple fiber (core part:
PGA resin, sheath part: PLA resin). The mass loss and proppant
dispersibility of the resulting PGA/PLA staple fiber were measured
in accordance with the evaluation methods described above. These
results are shown in Table 1.
Working Example 2
[0092] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 1 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part of
the discharge port was core part/sheath part=35/65. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 5.7 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin.
[0093] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 1 with the exception of changing the
draw ratio to 2.5 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 1.
Working Example 3
[0094] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 1 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part at
the discharge port was core part/sheath part=50/50. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 10.5 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin.
[0095] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 1 with the exception of changing the
draw ratio to 2.5 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 1.
Working Example 4
[0096] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 1 with the exception of changing the
resin constituting the sheath part to a pellet-formed PLA resin
having a D-form ratio of 1.4% ("4032D" made by Nature Works Co.,
Ltd., glass transition temperature: 57.degree. C., melting point:
160 to 170.degree. C., melt viscosity (temperature: 240.degree. C.,
shear rate: 122 sec.sup.-1: 500 Pas) and regulating the volume of
the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part at
the discharge port was core part/sheath part=20/80. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 17.9 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin.
[0097] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 1 with the exception of changing the
draw ratio to 2.8 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 1.
Working Example 5
[0098] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 4 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part at
the discharge port cross section was core part/sheath part=35/65.
The content of the PGA resin in the resulting core-sheath type
PGA/PLA composite undrawn yarn is 38.5 parts by mass per 1 part by
mass of the D-lactic acid units in the PLA resin.
[0099] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 4 with the exception of changing the
draw ratio to 3.0 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 1.
Working Example 6
[0100] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 4 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part of
the discharge port was core part/sheath part=10/90. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 7.9 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin.
[0101] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 4 with the exception of changing the
draw ratio to 2.3 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 1.
Comparative Example 1
[0102] A PLA resin undrawn yarn was produced in the same manner as
in Working Example 1 with the exception that a PGA resin was not
used and that a spinneret for single fibers (hole size: 0.40 mm, 24
holes) was used as the spinneret 4. An attempt was then made to
produce a PLA resin drawn yarn by changing the draw ratio to 1.5
times, but the yarn broke when the yarn was drawn, and a PLA resin
drawn yarn was not obtained.
Comparative Example 2
[0103] After a PLA resin undrawn yarn was produced in the same
manner as in Comparative Example 1, a PLA resin drawn yarn was
produced in the same manner as in Working Example 1 with the
exception of changing the draw ratio to 1.3 times, and a PLA resin
staple fiber was further produced. The single fiber fineness of the
resulting PLA resin drawn yarn and the mass loss and proppant
dispersibility of the PLA resin staple fiber were measured in
accordance with the evaluation methods described above. These
results are shown in Table 2.
Comparative Example 3
[0104] A PLA resin undrawn yarn was produced in the same manner as
in Working Example 4 with the exception that a PGA resin was not
used and that a spinneret for single fibers (hole size: 0.40 mm, 24
holes) was used as the spinneret 4. An attempt was then made to
produce a PLA resin drawn yarn by changing the draw ratio to 1.7
times, but the yarn broke when the yarn was drawn, and a PLA resin
drawn yarn was not obtained.
Comparative Example 4
[0105] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 1 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part at
the discharge port was core part/sheath part=10/90. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 1.2 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin.
[0106] A core-sheath type PGA/PLA composite drawn yarn (core part:
PGA resin, sheath part: PLA resin) was then produced in the same
manner as in Working Example 1 with the exception of changing the
draw ratio to 1.3 times, and a core-sheath type PGA/PLA staple
fiber (core part: PGA resin, sheath part: PLA resin) was further
produced. The single fiber fineness of the resulting PGA/PLA
composite drawn yarn and the mass loss and proppant dispersibility
of the PGA/PLA staple fiber were measured in accordance with the
evaluation methods described above. These results are shown in
Table 2.
Comparative Example 5
[0107] A core-sheath type PGA/PLA composite undrawn yarn (core
part: PGA resin, sheath part: PLA resin) was produced in the same
manner as in Working Example 4 with the exception of regulating the
volume of the molten PGA resin and the molten PLA resin so that the
cross-sectional area ratio of the core part to the sheath part at
the discharge port was core part/sheath part=2/98. The content of
the PGA resin in the resulting core-sheath type PGA/PLA composite
undrawn yarn is 1.5 parts by mass per 1 part by mass of the
D-lactic acid units in the PLA resin. An attempt was then made to
produce a PGA/PLA resin drawn yarn by changing the draw ratio to
1.7 times, but the yarn broke when the yarn was drawn, and a
PGA/PLA resin drawn yarn was not obtained.
TABLE-US-00001 TABLE 1 Working Working Working Example 1 Example 2
Example 3 D-form ratio 9.5 9.5 9.5 (%) of PLA Fiber structure
Core-sheath Core-sheath Core-sheath type type type Core part: PGA
Core part: PGA Core part: PGA Sheath part: Sheath part: Sheath
part: PLA PLA PLA Area ratio (%) 25 35 50 of the PGA phase of the
cross section Area ratio (%) 0 0 0 of the PGA phase of the side
surface D-form content 7.1 6.2 4.8 (mass %) in the composite fiber
PGA content 3.5 5.7 10.5 (parts by mass) per 1 part by mass of the
D-lactic acid units in the PLA resin of the composite fiber Draw
ratio 2.2 2.5 2.5 (times) Single fiber 2.0 1.3 1.4 fineness
(denier) 60.degree. C. mass 25.0 27.4 34.2 loss (%) 80.degree. C.
mass 90.9 92.3 96.0 loss (%) Proppant B A A dispersibility Working
Working Working Example 4 Example 5 Example 6 D-form ratio 1.4 1.4
1.4 (%) of PLA Fiber structure Core-sheath Core-sheath Core-sheath
type type type Core part: PGA Core part: PGA Core part: PGA Sheath
part: Sheath part: Sheath part: PLA PLA PLA Area ratio (%) 20 35 10
of the PGA phase of the cross section Area ratio 0 0 0 (%) of the
PGA phase of the side surface D-form content 1.1 0.9 1.3 (mass %)
in the composite fiber PGA content 17.9 38.5 7.9 (parts by mass)
per 1 part by mass of the D-lactic acid units in the PLA resin of
the composite fiber Draw ratio 2.8 3.0 2.3 (times) Single fiber 1.5
1.5 1.9 fineness (denier) 60.degree. C. mass 18.3 26.6 14.3 loss
(%) 80.degree. C. mass 88.5 91.4 81.5 loss (%) Proppant A A B
dispersibility
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example
1 Example 2 Example 3 D-form ratio (%) of 9.5 9.5 1.4 PLA Fiber
structure PLA PLA PLA Single fiber Single fiber Single fiber Area
ratio (%) of the 0 0 0 PGA phase of the cross section Area ratio
(%) of the 0 0 0 PGA phase of the side surface D-form content 9.5
9.5 1.4 (mass %) in the composite fiber PGA content (parts by 0 0 0
mass) per 1 part by mass of the D-lactic acid units in the PLA
resin of the composite fiber Draw ratio (times) 1.5 1.3 1.7 Single
fiber fineness (denier) -- 3.5 -- 60.degree. C. mass loss (%) --
12.4 -- 80.degree. C. mass loss (%) -- 76.5 -- Proppant -- D --
dispersibility Comparative Comparative Example 4 Example 5 D-form
ratio (%) of 9.5 1.4 PLA Fiber structure Core-sheath type
Core-sheath type Core part: PGA Core part: PGA Sheath part: PLA
Sheath part: PLA Area ratio (%) of the 10 2 PGA phase of the cross
section Area ratio (%) of the 0 0 PGA phase of the side surface
D-form content 8.6 1.4 (mass %) in the composite fiber PGA content
(parts by 1.2 1.5 mass) per 1 part by mass of the D-lactic acid
units in the PLA resin of the composite fiber Draw ratio (times)
1.3 1.7 Single fiber fineness 3.5 -- (denier) 60.degree. C. mass
loss (%) 14.9 -- 80.degree. C. mass loss (%) 80.1 -- Proppant D --
dispersibility
[0108] As is clear from the results shown in Table 1, it can be
seen that a core-sheath type composite undrawn yarn (core part: PGA
resin, sheath part: PLA resin) containing a prescribed amount of a
PGA resin with respect to the D-lactic acid units in the PLA resin
can be drawn at a ratio of 2 or more times and that the single
fiber fineness of the core-sheath type composite drawn yarn (core
part: PGA resin, sheath part: PLA resin) can be controlled to 2.0
denier or lower. In addition, it was confirmed that a core-sheath
composite drawn yarn with such low fineness has excellent proppant
dispersibility.
[0109] On the other hand, as is clear from the results shown in
Table 2, it can be seen that an undrawn yarn formed from a PLA
resin alone is prone to break even when drawn at a low ratio of 1.7
times or lower (Comparative Examples 1 and 3). Further, it can be
seen that when the draw ratio is reduced so that fibers of the yarn
do not break, it is difficult to control the single fiber fineness
to 3.0 denier or lower (Comparative Example 2). In addition, even
in the case of a core-sheath type composite undrawn yarn in which
the core part is formed from a PGA resin and the sheath part is
formed from a PLA resin, when the content of the PGA resin with
respect to the D-lactic acid units in the PLA resin is low, it is
difficult to draw the yarn at a high ratio, and it was difficult to
obtain a core-sheath type composite drawn yarn (core part: PGA
resin, sheath part: PLA resin) with excellent proppant
dispersibility.
INDUSTRIAL APPLICABILITY
[0110] As described above, with the present invention, it is
possible to obtain a water-disintegrable composite undrawn yarn
which can be drawn at a high ratio. Accordingly, by drawing the
water-disintegrable composite undrawn fiber of the present
invention at a high ratio, it is possible to obtain a
water-disintegrable drawn yarn with a small single fiber fineness
(that is, a small diameter). Further, a the water-disintegrable
composite staple fiber of the present invention formed by cutting
the water-disintegrable drawn yarn of the present invention has a
small diameter and a large specific surface area and therefore
demonstrates excellent proppant dispersibility when added to a well
treatment fluid.
[0111] The water-disintegrable composite staple fiber of the
present invention is useful for applications to the drilling or
completion field of oil and gas recovery from the perspective of
productivity improvement, drilling cost reduction, reduction in
damage to subterranean formation, and reduction in environmental
burden. For example, the fiber is useful as an additive for
improving the productivity of a subterranean formation with low
permeability. One method used for shale gas or shale oil recovery
is hydraulic fracturing, and this fiber is useful at the time of
hydraulic fracturing as an auxiliary material for efficiently
transporting proppants such as sand or for efficiently refluxing a
fluid containing proppants such as sand.
[0112] Furthermore, the fiber is useful as an auxiliary material
for uniformly treating subterranean formation in acid treatment
using hydrochloric acid or the like, which is typically used in
drilling or completion of oil and gas recovery. Specifically, by
using a water-disintegrable composite staple fiber, it is possible
to seal the subterranean formation through which fluids flow easily
and to adjust the formation so that fluids flow at locations where
fluid flow is desirable, and since the material decomposes at the
time of production, this means that the productivity is not
inhibited. Such a sealing function can also be applied to improve
the product recovery efficiency by temporarily sealing holes
intentionally formed in subterranean formation, in particular, in
production layers from which petroleum or gas can be obtained.
[0113] Other related applications for which the fiber is useful
include applications for preventing the clogging of screens using
disintegrability by utilizing the water-disintegrable composite
fiber to form the cake layer formed during drilling, and
applications for preventing lost circulation of water or mud into
subterranean formation with high permeability or natural holes by
adding a water-disintegrable composite fiber staple fiber to mud
water for drilling. In applications in which the fiber is added to
mud for drilling, it has the effect of reducing the viscosity of
mud and increasing the fluidity, by the releasing effect of acids
released after decomposition of the fiber. Furthermore, by adding
the water-disintegrable composite fiber to mud for drilling or
completion, it is possible to reduce the amount of water or sand
used, which makes it possible to reduce the drilling cost. In all
of these applications, the water-disintegrable composite staple
fiber has a disintegrating property, which yields the advantage
that there is no damage to subterranean formation.
REFERENCE SIGNS LIST
[0114] A: PGA resin phase [0115] B: PLA resin phase [0116] 1a, 1b:
Raw material hoppers [0117] 2a, 2b: Extruders [0118] 3a, 3b: Gear
pumps [0119] 4: Spinneret (spinning nozzle) [0120] 5: Heat sleeve
[0121] 6: Oiling agent application device [0122] 7-13: First
through seventh take-up rollers [0123] 14: Undrawn yarn bobbin
[0124] 21: Feed roller [0125] 22: First heating roller [0126] 23:
Second heating roller [0127] 24: Third heating roller [0128] 25:
Drawn yarn bobbin
* * * * *