U.S. patent application number 16/007173 was filed with the patent office on 2018-10-11 for solidification- and extrusion-molded article of polyglycolic acid and method for manufacturing same.
This patent application is currently assigned to Kureha Corporation. The applicant listed for this patent is Kureha Corporation. Invention is credited to Masayuki Okura, Hiroyuki Sato, Takeo Takahashi.
Application Number | 20180291702 16/007173 |
Document ID | / |
Family ID | 50731211 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180291702 |
Kind Code |
A1 |
Okura; Masayuki ; et
al. |
October 11, 2018 |
SOLIDIFICATION- AND EXTRUSION-MOLDED ARTICLE OF POLYGLYCOLIC ACID
AND METHOD FOR MANUFACTURING SAME
Abstract
A solidification- and extrusion-molded article of polyglycolic
acid, which is formed of a resin material containing polyglycolic
acid, the polyglycolic acid having a melt viscosity of 200 to 2,000
Pas, and has a thickness or diameter of greater than 100 mm but not
greater than 500 mm. A downhole tool or a component thereof and a
ball sealer for petroleum excavation are formed by cutting the
solidification- and extrusion-molded article. A method for
manufacturing the solidification- and extrusion-molded article of
polyglycolic acid and a method for manufacturing a ball sealer for
petroleum excavation.
Inventors: |
Okura; Masayuki; (Tokyo,
JP) ; Takahashi; Takeo; (Tokyo, JP) ; Sato;
Hiroyuki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kureha Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Kureha Corporation
Tokyo
JP
|
Family ID: |
50731211 |
Appl. No.: |
16/007173 |
Filed: |
June 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14433490 |
Apr 3, 2015 |
10030465 |
|
|
PCT/JP2013/080751 |
Nov 14, 2013 |
|
|
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16007173 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 48/08 20190201;
Y10T 428/298 20150115; B29K 2033/04 20130101; B29C 48/0022
20190201; E21B 33/1208 20130101; B29L 2031/003 20130101; B29C
48/022 20190201; B29C 48/91 20190201; B29C 48/002 20190201; E21B
33/138 20130101; B29C 48/06 20190201; B29C 48/13 20190201; B29C
48/92 20190201; B29C 2948/92704 20190201; B29C 48/90 20190201; B29C
48/911 20190201; B29C 2948/92695 20190201; B29C 48/12 20190201 |
International
Class: |
E21B 33/12 20060101
E21B033/12; B29C 47/88 20060101 B29C047/88; E21B 33/138 20060101
E21B033/138; B29C 47/92 20060101 B29C047/92 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2012 |
JP |
2012-251670 |
Claims
1. A solidification- and extrusion-molded article of polyglycolic
acid; the solidification- and extrusion-molded article being formed
of a resin material containing polyglycolic acid, the polyglycolic
acid having a melt viscosity of 200 to 2,000 Pas upon being
measured at a temperature of 270.degree. C. under a shearing speed
of 120 sec-1; and having a thickness or diameter of greater than
100 mm but not greater than 500 mm.
2. The solidification- and extrusion-molded article of polyglycolic
acid according to claim 1, wherein the solidification- and
extrusion-molded article has a round bar or plate shape.
3. The solidification- and extrusion-molded article of polyglycolic
acid according to claim 1, wherein the resin material is a
polyglycolic acid composition containing from 0.001 to 5 mass % of
colorant in terms of a total mass.
4. The solidification- and extrusion-molded article of polyglycolic
acid according to claim 1, wherein the resin material is a
polyglycolic acid composition containing from 5 to 70 mass % of
filler in terms of the total mass.
5. The solidification- and extrusion-molded article of polyglycolic
acid according to claim 1, wherein the solidification- and
extrusion-molded article is a stock shape for machining.
6. A downhole tool or component thereof formed by cutting the
solidification- and extrusion-molded article of polyglycolic acid
described in claim 5.
7. A plug for petroleum excavation formed by cutting the
solidification- and extrusion-molded article of polyglycolic acid
described in claim 5.
8. A mandrel of plug for petroleum excavation formed by cutting the
solidification- and extrusion-molded article of polyglycolic acid
described in claim 5.
9. A ball sealer for petroleum excavation having a diameter of 20
to 200 mm formed by cutting the solidification- and
extrusion-molded article of polyglycolic acid described in claim
5.
10. A method for manufacturing a solidification- and
extrusion-molded article of polyglycolic acid, the method
comprising steps 1 to 4 below: a) step 1 of supplying a resin
material containing polyglycolic acid, the polyglycolic acid having
a melt viscosity of 200 to 2,000 Pas upon being measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1, into an extruder, and melt-kneading the resin material
at a cylinder temperature of the extruder of 240 to 285.degree. C.;
b) step 2 of extruding the resin material, melted by the
melt-kneading, from an extrusion die at a tip of the extruder into
a flow path of a forming die comprising cooling means and the flow
path that communicates with a path of melted resin of the extrusion
die and that has a cross-sectional shape of an extrusion molded
article; c) step 3 of solidifying the melted and extruded matter
formed from the resin material by cooling in the flow path of the
forming die, and then extruding the solidified and extruded matter
from the tip of the forming die to outside; and d) step 4 of
pressurizing the solidified and extruded matter, and drawing the
same while applying back pressure thereto in a direction of the
forming die to suppress expansion of the solidified and extruded
matter in a thickness direction or radial direction to obtain a
solidification- and extrusion-molded article of polyglycolic acid
having a thickness or diameter of greater than 100 mm but not
greater than 500 mm.
11. The manufacturing method according to claim 10, wherein, in the
step 3, a forming die having heating means in addition to the
cooling means is used; and the step 3 comprises: first, heating the
melted and extruded matter in the flow path around an extrusion die
outlet to a temperature of 230 to 290.degree. C. by the heating
means, and then cooling the melted and extruded matter in the flow
path to a temperature lower than a crystallization temperature of
the polyglycolic acid to solidify the melted and extruded matter by
the cooling means.
12. The manufacturing method according to claim 10, further
comprising step 5, in which the solidification- and
extrusion-molded article of polyglycolic acid obtained in the step
4 is heat-treated at a temperature of 150 to 230.degree. C. for 3
to 24 hours.
13. The manufacturing method according to claim 10, wherein the
resin material is a polyglycolic acid composition containing from
0.001 to 5 mass % of colorant in terms of a total mass.
14. The manufacturing method according to claim 10, wherein the
resin material is a polyglycolic acid composition containing from 5
to 70 mass % of filler in terms of the total mass.
15. The manufacturing method according to claim 10, wherein, in the
step 4, a solidification- and extrusion-molded article of
polyglycolic acid having a round bar or plate shape is
obtained.
16. A method for manufacturing a downhole tool or component
thereof, the method comprising step 6 of cutting the
solidification- and extrusion-molded article of polyglycolic acid
manufactured by the manufacturing method described in claim 10.
17. A method for manufacturing a ball sealer for petroleum
excavation having a diameter of 20 to 200 mm, the method comprising
step 6 of cutting the solidification- and extrusion-molded article
of polyglycolic acid manufactured by the manufacturing method
described in claim 10.
Description
[0001] This application is a Continuation of copending application
Ser. No. 14/433,490 filed on Apr. 3, 2015, which is the U.S.
National Phase of PCT/JP2013/080751, filed Nov. 14, 2013, and which
claims priority under 35 U.S.C. .sctn. 119(a) to Application No.
2012-251670 filed in Japan, on Nov. 15, 2012. The above
applications are hereby expressly incorporated by reference, in
their entirety, into the present application.
TECHNICAL FIELD
[0002] The present invention relates to a solidification- and
extrusion-molded article of polyglycolic acid and a method for
manufacturing the same. More particularly, the present invention
relates to a solidification- and extrusion-molded article of
polyglycolic acid that is thick or has a large diameter and that
can be formed into a secondarily molded product of a desired shape
by machining such as cutting, drilling, and shearing, and a method
for manufacturing the same.
BACKGROUND ART
[0003] Resin molded articles having a three-dimensional shape or
complex shape are molded typically by injection molding. Injection
molding can mass-produce molded articles having a desired shape.
However, in order to manufacture molded articles that are required
to have a high dimensional precision by injection molding, an
expensive die having a high dimensional precision is required.
Furthermore, since injection-molded articles are readily deformed
by shrinkage and/or residual stress after the injection molding,
the shape of the die needs to be adjusted precisely depending on
the shape of the molded article and properties of the resin
material. Since fraction defective is high in injection molding,
product cost thereby is often high. Furthermore, injection molding
of a molded article having a large thickness is difficult due to
shrinkage and/or residual stress.
[0004] In order to obtain molded articles having a
three-dimensional shape or complex shape, a method for molding a
secondarily molded article having a desired shape, the method
comprising: extruding and solidifying a resin material; producing a
stock shape for machining (also referred to as "stock shape for
cutting") having a shape, such as a plate, round bar, pipe, special
shape, or another shape; and subjecting the stock shape for
machining to machining, such as cutting, drilling, and shearing,
has been known. The method of machining the stock shape for
machining has advantages, including that a molded articles can be
produced in small quantities at a relatively low cost because an
expensive die is not required, that frequent modifications in
molded article specifications can be accommodated, that molded
articles with high dimensional precision can be obtained, that
molded articles having a complex shape or large thickness, which is
not suitable for production using injection molding, can be
produced, and the like.
[0005] However, not all resin materials and/or extrusion molded
articles are suitable as stock shapes for machining. A stock shape
for machining needs to satisfy high levels of required properties,
such as having a large thickness and excellent machinability,
having low residual stress, being capable of avoiding excessive
heat generation that leads to deformation and/or discoloration due
to heat of friction generated during machining, being capable of
being machined with high precision, and the like.
[0006] In general, most of processing methods used in metallic
materials are utilized in machining of polymeric stock shapes as
is. Even among extrusion molded products, an extrusion molded
product that is thin and has great flexibility, such as a typical
film, sheet, or tube, is unsuitable for machining such as cutting.
Even among extrusion molded products having shapes, such as plate
or round bar, with a large thickness or large diameter, if the
extrusion molded product has excessively large residual stress
during extrusion molding, the extrusion molded product readily
deforms during or after machining, and it is difficult to obtain a
secondarily molded article having high dimensional precision. Even
among extrusion molded products having reduced residual stress, the
extrusion molded product that readily breaks or cracks during
machining, such as cutting, drilling, and shearing, is not suitable
as stock shape for machining.
[0007] In order to obtain, via extrusion molding, a stock shape for
machining having properties suitable for machining, selection of
resin materials, method of extrusion molding, or the like needs to
be devised. Therefore, various extrusion molding methods for
producing extrusion molded articles suitable as stock shapes for
machining, the method using resin materials that contain
general-purpose resins and/or engineering plastics, have been
proposed so far.
[0008] For example, Japanese Unexamined Patent Application
Publication No. 2005-226031A (Patent Document 1) discloses a method
for producing a stock shape for machining having a thickness or
diameter exceeding 3 mm, the method comprising solidification- and
extrusion-molding a resin composition containing an engineering
plastic such as a polyether ether ketone, polyetherimide,
polyphenylene sulfide, polysulfone, polyether sulfone, or
polycarbonate.
[0009] On the other hand, biodegradable plastics have drawn
attention as polymer materials that have little adverse effect on
the environment, and have been used in applications including
extrusion molded articles such as films and sheets, blow molded
articles such as bottles, injection molded articles, and the like.
Recently, application of biodegradable plastics in stock shapes for
machining has been increasingly demanded.
[0010] Polyglycolic acid is a crystalline resin having superior
tensile strength, tensile elongation, bending strength, elastic
modulus in bending, hardness, flexibility, heat resistance, and the
like compared to other biodegradable plastics such as polylactic
acid, and the polyglycolic acid is also a biodegradable plastic
having greater or equal gas barrier properties to general-purpose
gas barrier resins. Polyglycolic acid can be molded into films
and/or sheets via extrusion molding. For example, Japanese Patent
No. 4073052B (Patent Document 2) discloses a method for molding
polyglycolic acid into a sheet via extrusion molding. In the
disclosure, various sheet molded articles are produced using the
sheet, having a thickness of 0.01 to 5 mm, utilizing its toughness,
heat resistance, transparency, and other characteristics.
[0011] Furthermore, Japanese Unexamined Patent Application
Publication No. 2010-069718B (Patent Document 3) discloses a
solidification- and extrusion-molded article of polyglycolic acid,
having a thickness or diameter of 5 to 100 mm, that is produced by
subjecting polyglycolic acid to solidification- and
extrusion-molding. Specifically, a solidification- and
extrusion-molded article of polyglycolic acid having a density of
1.575 to 1.625 g/cm.sup.3 and a thickness or diameter of 5 mm or
greater but 100 mm or less, the solidification- and
extrusion-molded article of polyglycolic acid being formed of a
resin material containing polyglycolic acid having a melt viscosity
of 10 to 1,500 Pas, particularly preferably 70 to 900 Pas, measured
at a temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1, has been disclosed. Patent Document 3 describes that,
if the thickness or diameter is too large (i.e. the thickness or
diameter exceeds 100 mm), it will be difficult to sufficiently
remove or reduce residual stress even when the solidification- and
extrusion-molded article is heat-treated, and machining a
solidification- and extrusion-molded article having a large
residual stress tends to cause deformation in the obtained
secondarily molded product.
[0012] If an extrusion molded article that is thicker and suitable
as a stock shape for machining such as cutting can be obtained by
using polyglycolic acid, which is a degradable plastic, it will be
possible to provide a secondarily molded article having excellent
properties, leading to development of new applications of
polyglycolic acid.
[0013] To retrieve hydrocarbon resources (in the present invention,
also simply referred to as "petroleum") from ground containing
hydrocarbon resources such as petroleum (e.g. shale oil) and gas
(e.g. shale gas), a downhole (underground bore hole) is provided.
Use of degradable plastic in downhole tools or components thereof
(i.e. downhole tool components; e.g. mandrel of a plug for
petroleum excavation or the like is well known), which are
components used to form or maintain the downhole or to promote the
retrieval of the resources, is expected since degradable plastic
can be disintegrated in the downhole without collecting it on the
ground after use.
[0014] For example, relatively small ball sealers that have a
diameter of 16 to 32 mm and that are formed from non-degradable
materials such as aluminum and/or non-degradable resins such as
nylon and phenol resins which are coated, as necessary, with rubber
to improve sealing properties has been conventionally used as ball
sealers (which is an example of a downhole tool) used to fill bore
holes. However, in recent years, demands for ball sealers or the
like having a larger diameter (e.g. diameter of 25 to 100 mm or
even greater) have been increasing as a part of components
constituting a downhole tool (downhole tool component), such as
plugs, including frac plugs and the like, and frac sleeves (tube
and plug for hydraulic fracture), used in hydraulic fracturing.
When a ball sealer or the like having such a large diameter is
produced by injection molding or compression molding using a
degradable resin, which is often a crystalline resin, sink marks
and/or voids are caused due to thermal shrinkage after the
production or shrinkage associated with crystallization, and
dimensional precision required for ball sealers, which is a filling
component, or the like is not obtained. In order to obtain a ball
sealer or the like having a relatively large diameter, production
of a ball sealer or the like by cutting a solidification- and
extrusion-molded article having a large thickness or diameter
formed of degradable resin, for example, has been attempted.
However, as described above, when the thickness or diameter of the
solidification- and extrusion-molded article of polyglycolic acid,
which is a degradable resin, exceeds 100 mm, it is difficult to
sufficiently remove or reduce residual stress, the obtained
secondarily molded product tends to be deformed, and, in some
cases, breaks or cracks readily occur. Therefore, a solidification-
and extrusion-molded article of degradable resin having excellent
strength, processability, and the like as well as having a
sufficiently large thickness or diameter to obtain a ball sealer or
the like having a relatively large diameter has been demanded.
CITATION LISTS
Patent Documents
[0015] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2005-226031A (corresponding to US Patent
Application Publication No. 2008/0038517 specification)
[0016] Patent Document 2: Japanese Patent No. 4073052B (U.S. Pat.
No. 5,908,917 specification)
[0017] Patent Document 3: Japanese Unexamined Patent Application
Publication No. 2010-069718A
SUMMARY OF INVENTION
Technical Problem
[0018] An object of the present invention is to provide a
solidification- and extrusion-molded article of degradable resin
that can be molded into secondarily molded products such as, in
particular, a ball sealer for petroleum excavation which is a
downhole tool or component thereof, having various desired shapes
by machining, such as cutting, drilling, and shearing; and to
provide a method for manufacturing the same.
Solution to Problem
[0019] As a result of diligent research to solve the above
problems, the present inventors have found that a solidification-
and extrusion-molded article of degradable resin, specifically a
solidification- and extrusion-molded article of polyglycolic acid,
having a thickness or diameter exceeding 100 mm can be obtained by
optimizing the melt viscosity of polyglycolic acid, conditions for
solidification- and extrusion-molding, and the like, and, in
particular, by controlling the expansion of the solidified and
extruded matter in a thickness direction or radial direction via
pressurizing the solidified and extruded matter, and thus completed
the present invention.
[0020] According to the present invention, a solidification- and
extrusion-molded article of polyglycolic acid that is formed of a
resin material containing polyglycolic acid, the polyglycolic acid
having a melt viscosity of 200 to 2,000 Pas upon being measured at
a temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1; and having a thickness or diameter of greater than 100
mm but not greater than 500 mm is provided.
[0021] As embodiments according to the present invention,
solidification- and extrusion-molded articles of polyglycolic acid
described below (1) to (4) are provided. [0022] (1) The
solidification- and extrusion-molded article of polyglycolic acid
described above, wherein the solidification- and extrusion-molded
article has a round bar or plate shape. [0023] (2) The
solidification- and extrusion-molded article of polyglycolic acid
described above, wherein the resin material is a polyglycolic acid
composition containing from 0.001 to 5 mass % of colorant in terms
of a total mass. [0024] (3) The solidification- and
extrusion-molded article of polyglycolic acid described above,
wherein the resin material is a polyglycolic acid composition
containing from 5 to 70 mass % of filler in terms of a total mass.
[0025] (4) The solidification- and extrusion-molded article of
polyglycolic acid described above, wherein the solidification- and
extrusion-molded article is a stock shape for machining.
[0026] Furthermore, according to the present invention, a method
for manufacturing a solidification- and extrusion-molded article of
polyglycolic acid is provided; the method comprising steps 1 to 4
below: [0027] a) step 1 of supplying a resin material containing
polyglycolic acid, the polyglycolic acid having a melt viscosity of
200 to 2,000 Pas upon being measured at a temperature of
270.degree. C. under a shearing speed of 120 sec.sup.-1, into an
extruder, and melt-kneading the resin material at a cylinder
temperature of the extruder of 240 to 285.degree. C.; [0028] b)
step 2 of extruding the resin material, melted by melt-kneading,
from an extrusion die at a tip of the extruder into a flow path of
a forming die comprising cooling means and the flow path that
communicates with a path of melted resin of the extrusion die and
that has a cross-sectional shape of an extrusion molded article;
[0029] c) step 3 of solidifying the melted and extruded matter
formed from the resin material by cooling in the flow path of the
forming die, and then extruding the solidified and extruded matter
from the tip of the forming die to outside; and [0030] d) step 4 of
pressurizing the solidified and extruded matter, and drawing the
same while applying back pressure thereto in a direction of the
forming die to suppress expansion of the solidified and extruded
matter in a thickness direction or radial direction to obtain a
solidification- and extrusion-molded article of polyglycolic acid
having a thickness or diameter of greater than 100 mm but not
greater than 500 mm.
[0031] As embodiments according to the present invention, methods
for manufacturing a solidification- and extrusion-molded article of
polyglycolic acid described below (i) to (v) are provided. [0032]
(i) The manufacturing method described above, wherein, in the step
3, a forming die having heating means in addition to the cooling
means is used; and the step 3 comprises: first, heating the melted
and extruded matter in the flow path around an extrusion die outlet
to a temperature of 230 to 290.degree. C. by the heating means, and
then cooling the melted and extruded matter in the flow path to a
temperature lower than a crystallization temperature of the
polyglycolic acid to solidify the melted and extruded matter by the
cooling means. [0033] (ii) The manufacturing method described
above, further comprising step 5, in which the solidification- and
extrusion-molded article of polyglycolic acid obtained in the step
4 is heat-treated at a temperature of 150 to 230.degree. C. for 3
to 24 hours. [0034] (iii) The manufacturing method described above,
wherein the resin material is a polyglycolic acid composition
containing from 0.001 to 5 mass % of colorant in terms of a total
mass. [0035] (iv) The manufacturing method described above, wherein
the resin material is a polyglycolic acid composition containing
from 5 to 70 mass % of filler in terms of a total mass. [0036] (v)
The manufacturing method described above, wherein, in the step 4, a
solidification- and extrusion-molded article of polyglycolic acid
having a round bar or plate shape is obtained.
[0037] Furthermore, a downhole tool or component thereof,
particularly a plug for petroleum excavation or a mandrel of the
plug and a ball sealer for petroleum excavation having a diameter
of 20 to 200 mm, that is formed by cutting the solidification- and
extrusion-molded article of polyglycolic acid described above is
provided according to the present invention. A method for
manufacturing a downhole tool or component thereof, particularly a
ball sealer for petroleum excavation having a diameter of 20 to 200
mm, the method comprising step 6 of cutting the solidification- and
extrusion-molded article of polyglycolic acid manufactured by the
manufacturing method described above is also provided according to
the present invention.
Advantageous Effects of Invention
[0038] According to the present invention, since a solidification-
and extrusion-molded article of polyglycolic acid is formed of a
resin material containing polyglycolic acid, the polyglycolic acid
having a melt viscosity of 200 to 2,000 Pas when measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1, and has a thickness or diameter of greater than 100 mm
but not greater than 500 mm, a solidification- and extrusion-molded
article of polyglycolic acid that can be formed into a secondarily
molded product such as, in particular, a ball sealer for petroleum
excavation, can be provided via machining, such as cutting,
drilling, and shearing; and a ball sealer for petroleum excavation
or the like can be provided. Furthermore, according to the
manufacturing method of the present invention, it is possible to
provide a solidification- and extrusion-molded article of
polyglycolic acid having properties suitable for machining to form
a secondarily molded product, particularly a ball sealer for
petroleum excavation or the like, that has reduced residual stress
and excellent hardness, strength, and flexibility.
DESCRIPTION OF EMBODIMENTS
1. Solidification- and Extrusion-Molded Article of Polyglycolic
Acid
[0039] The solidification- and extrusion-molded article of
polyglycolic acid of the present invention is a solidification- and
extrusion-molded article of polyglycolic acid that is formed of a
resin material containing polyglycolic acid, the polyglycolic acid
having a melt viscosity of 200 to 2,000 Pa's when measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1; and having a thickness or diameter of greater than 100
mm but not greater than 500 mm.
[0040] The polyglycolic acid used in the present invention is a
polymer containing a repeating unit represented by formula 1:
--(--O--CH.sub.2--CO--)--. The proportion of the repeating unit
represented by formula 1 in the polymer is typically 50 mass % or
greater, preferably 70 mass % or greater, more preferably 80 mass %
or greater, even more preferably 90 mass % or greater, particularly
preferably 95 mass % or greater, and most preferably 99 mass % or
greater. If the proportion of the repeating unit represented by
formula 1 is less than 70 mass %, toughness, crystallizability,
heat resistance, hardness, gas barrier properties, and the like
tend to be decreased. In many cases, use of homopolymer of
polyglycolic acid, where the proportion of the repeating unit
represented by formula 1 is 100 mass %, is the most preferable.
[0041] The polyglycolic acid can be produced by condensation
polymerization of glycolic acid or ring-opening polymerization of
glycolide. Preferable repeating units other than the repeating unit
represented by formula 1 include, for example, repeating units
derived from cyclic monomers such as ethylene oxalate, lactide,
lactones, trimethylene carbonate, and 1,3-dioxane; however, the
repeating unit is not limited to these.
[0042] By introducing the cyclic monomer-derived repeating unit at
a proportion of 1 mass % or greater, processing temperature can be
lowered by lowering the melting point of the polyglycolic acid, and
thus thermal decomposition during melt processing can be reduced.
Extrusion moldability can be also enhanced by controlling the rate
of crystallization of the polyglycolic acid by means of
copolymerization. On the other hand, if the amount of the cyclic
monomer-derived repeating unit is too large, intrinsic
crystallizability of polyglycolic acid will be lost, and the
toughness, heat resistance, and the like of the obtained
solidification- and extrusion-molded article may be significantly
lowered.
[0043] The polyglycolic acid used in the present invention is
preferably a high-molecular weight polymer. The melt viscosity of
the polyglycolic acid used in the present invention measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1 is from 200 to 2,000 Pas, preferably from 450 to 1,600
Pas, more preferably from 700 to 1,400 Pas, particularly preferably
from 850 to 1,300 Pas, and most preferably from 910 to 1,200
Pas.
[0044] If the melt viscosity of the polyglycolic acid is too low,
melt extrusion and/or solidification- and extrusion-molding will be
difficult, the flexibility and toughness of the obtained
solidification- and extrusion-molded article will be reduced, and
the solidification- and extrusion-molded article will be easily
cracked during machining. Furthermore, if the melt viscosity of the
polyglycolic acid is too low, the solidification- and
extrusion-molded article may be cracked during heat treatment
(annealing) of the solidification- and extrusion-molded article. If
the melt viscosity of the polyglycolic acid is too high, thermal
degradation of the polyglycolic acid will easily occur since the
polyglycolic acid has to be heated to a high temperature during
melt extrusion.
[0045] The resin material used in the present invention is a resin
composition containing polyglycolic acid as a main component. The
word "main component" represents that the contained proportion of
the polyglycolic acid in the resin component is typically 50 mass %
or greater, preferably 70 mass % or greater, more preferably 80
mass % or greater, and even more preferably 90 mass % or greater.
Examples of other resin components include thermoplastic resins
other than polyglycolic acid, such as polylactic acid and other
biodegradable resins. Obviously, a resin composition in which the
contained proportion of the polyglycolic acid in the resin
component is 100 mass % can be used.
[0046] The resin material used in the present invention may contain
a colorant such as a dye or pigment. By using a colorant, a
solidification- and extrusion-molded article of polyglycolic acid
that is high quality and that can be easily cut can be obtained. As
the colorant, a pigment is preferable from the perspective of
having excellent heat resistance. As the pigment, pigments of
various color tones, such as yellow pigments, red pigments, white
pigments, and black pigments, that are used in the technical field
of synthetic resin can be used. Among these pigments, carbon black
is particularly preferable. Examples of the carbon black include
acetylene black, oil furnace black, thermal black, channel black,
and the like.
[0047] The resin material used in the present invention is
preferably a polyglycolic acid composition containing from 0.001 to
5 mass % of colorant in terms of the total mass. The contained
proportion of the colorant is preferably from 0.01 to 3 mass %, and
more preferably from 0.05 to 2 mass %. Although the colorant can be
melt-kneaded with the polyglycolic acid, optionally, it is also
possible to prepare a resin material having a desired colorant
concentration by producing a polyglycolic acid composition having a
high colorant concentration (masterbatch) and then diluting the
masterbatch with polyglycolic acid. From the perspective of uniform
dispersibility of the colorant, it is preferable to prepare a resin
material that is formed into a pellet by melt-kneading the
polyglycolic acid and the colorant.
[0048] The resin material used in the present invention can contain
filler in order to enhance mechanical strength and heat resistance.
As the filler, fibrous fillers and granular or powdered fillers can
be used; however, fibrous fillers are preferable.
[0049] Examples of fibrous filler include inorganic fibrous
substances such as glass fibers, carbon fibers, asbestos fibers,
silica fibers, alumina fibers, zirconia fibers, boron nitride
fibers, silicon nitride fibers, boron fibers, and potassium
titanate fibers; metal fibrous substances such as stainless steel,
aluminum, titanium, steel, and brass; and organic fibrous
substances with a high melting point such as polyamides, fluorine
resins, polyester resins, and acrylic resins; and the like. Short
fibers having a length of 10 mm or less, more preferably 1 to 6 mm,
and even more preferably 1.5 to 4 mm are preferable as the fibrous
fillers. Furthermore, inorganic fibrous substances are preferably
used, and glass fibers are particularly preferable.
[0050] As the granular or powdered filler, mica, silica, talc,
alumina, kaolin, calcium sulfate, calcium carbonate, titanium
oxide, ferrite, clay, glass powder, zinc oxide, nickel carbonate,
iron oxide, quartz powder, magnesium carbonate, barium sulfate, and
the like can be used.
[0051] These fillers can be used alone, or two or more types
thereof can be combined for use. The filler may be treated with a
sizing agent or surface treatment agent as necessary. Examples of
the sizing agent or surface treatment agent include functional
compounds such as epoxy-based compounds, isocyanate-based
compounds, silane-based compounds, and titanate-based compounds.
These compounds may be used to perform surface treatment or sizing
treatment on the filler in advance or may be added at the same time
as the preparation of the resin composition.
[0052] The resin material used in the present invention is
preferably a polyglycolic acid composition containing from 5 to 70
mass % of filler in terms of the total mass. The contained
proportion of the filler is preferably from 10 to 60 mass %, more
preferably from 15 to 50 mass %, and even more preferably from 20
to 40 mass %. Although the filler can be melt-kneaded with the
polyglycolic acid, optionally, it is also possible to prepare a
resin material having a desired filler concentration by producing a
polyglycolic acid composition having a high filler concentration
(masterbatch) and then diluting the masterbatch with polyglycolic
acid. From the perspective of uniform dispersibility of the filler,
it is preferable to prepare a resin material that is formed into a
pellet by melt-kneading the polyglycolic acid and the filler.
[0053] In the resin material used in the present invention, as
other additives other than those described above, for example,
impact modifiers, resin-modifying agents, corrosion inhibitors for
die such as zinc carbonate and nickel carbonate, lubricants,
thermosetting resins, antioxidants, ultraviolet absorbents,
nucleating agents such as boron nitride, flame retardants, and the
like can be suitably added.
[0054] The density ("density" refers to the density of resin part
excluding the filler part) of the solidification- and
extrusion-molded article of polyglycolic acid of the present
invention is not particularly limited as long as the
solidification- and extrusion-molded article of polyglycolic acid
is a solidification- and extrusion-molded article of polyglycolic
acid that is formed of a resin material containing the polyglycolic
acid and has a thickness or diameter of greater than 100 mm but not
greater than 500 mm. However, the density is preferably from 1,570
to 1,610 kg/m.sup.3, more preferably from 1,575 to 1,605
kg/m.sup.3, even more preferably 1,577 to 1,603 kg/m.sup.3, and
particularly preferably from 1,580 to 1,600 kg/m.sup.3. If the
density of the solidification- and extrusion-molded article of
polyglycolic acid is too low, cracking will readily occur during
machining such as cutting, drilling, and shearing, due to decrease
in strength, hardness, toughness, flexibility, and the like. If the
density of the solidification- and extrusion-molded article of
polyglycolic acid is too high, production will be difficult.
[0055] The thickness or diameter of the solidification- and
extrusion-molded article of polyglycolic acid is greater than 100
mm but not greater than 500 mm, preferably from 102 to 400 mm, more
preferably from 103 to 350 mm, even more preferably from 105 to 300
mm, and particularly preferably from 106 to 250 mm. In many cases,
a solidification- and extrusion-molded article having satisfactory
machinability can be obtained when the thickness or diameter is in
a range of 107 to 200 mm, and most preferably the thickness or
diameter is in a range of 108 to 150 mm.
[0056] If the thickness or diameter is too small, it will be
difficult to mold a secondarily molded article having a desired
shape via machining such as cutting. That is, because of
flexibility and low toughness, it will be difficult or practically
impossible to perform cutting or mechanical drilling using a drill
or the like. Furthermore, if the thickness or diameter is too
large, even when the solidification- and extrusion-molded article
is heat-treated, it will be difficult to sufficiently remove or
reduce residual stress. If a solidification- and extrusion-molded
article having a large residual stress is subjected to machining,
the obtained secondarily molded product will be readily
deformed.
[0057] The solidification- and extrusion-molded article of
polyglycolic acid of the present invention include solidification-
and extrusion-molded articles having various shapes such as round
bar, plate, pipe, or special shapes. However, from the perspective
of easy solidification- and extrusion-molding and subsequently
performed densification processing, and from the perspective of
having many qualities suitable as a solidification- and
extrusion-molded article, which is a stock shape for machining, the
solidification- and extrusion-molded article preferably has a round
bar or plate shape. Round bar shape is more preferable for forming
a ball sealer for petroleum excavation described below.
[0058] The solidification- and extrusion-molded article of
polyglycolic acid of the present invention may be a solidification-
and extrusion-molded article such that the densities of a surface
part and a center part of the molded article are different from
each other. The difference between the density of the surface part
and the density of the center part is preferably in a range of 0.5
to 50 kg/m.sup.3, more preferably 1.5 to 20 kg/m.sup.3, even more
preferably 2.0 to 10 kg/m.sup.3, and particularly preferably 2.5 to
5 kg/m.sup.3. If the difference between the density of the surface
part and the density of the center part of the solidification- and
extrusion-molded article of polyglycolic acid is in the range
described above, a stock shape for machining having excellent
machinability can be obtained, and it will be possible to precisely
control the shape of a secondarily molded product that is formed by
cutting. Therefore, the above-described range is preferable.
2. Manufacturing Method for Solidification- and Extrusion-Molded
Article of Polyglycolic Acid
[0059] The solidification- and extrusion-molded article of
polyglycolic acid of the present invention can be manufactured by
the manufacturing method comprising the following steps 1 to 4.
[0060] a) step 1 of supplying a resin material containing
polyglycolic acid, the polyglycolic acid having a melt viscosity of
200 to 2,000 Pas upon being measured at a temperature of
270.degree. C. under a shearing speed of 120 sec.sup.-1, into an
extruder, and melt-kneading the resin material at a cylinder
temperature of the extruder of 240 to 285.degree. C.; [0061] b)
step 2 of extruding the resin material, melted by melt-kneading,
from an extrusion die at a tip of the extruder into a flow path of
a forming die comprising cooling means and the flow path that
communicates with a path of melted resin of the extrusion die and
that has a cross-sectional shape of an extrusion molded article;
[0062] c) step 3 of solidifying the melted and extruded matter
formed from the resin material by cooling in the flow path of the
forming die, and then extruding the solidified and extruded matter
from the tip of the forming die to outside; and [0063] d) step 4 of
pressurizing the solidified and extruded matter, and drawing the
same while applying back pressure thereto in a direction of the
forming die to suppress expansion of the solidified and extruded
matter in a thickness direction or radial direction to obtain a
solidification- and extrusion-molded article of polyglycolic acid
having a thickness or diameter of greater than 100 mm but not
greater than 500 mm.
[0064] Manufacturing steps for cases where a solidification- and
extrusion-molded article of polyglycolic acid of the present
invention has round bar or plate shape will be described. In the
step 1, a resin material containing polyglycolic acid is placed in
a hopper of an extruder. As the resin material, pellet is
preferably used. The resin material is preferably sufficiently
dried and dehumidified prior to molding. Conditions for
dehumidification and drying is not particularly limited; however,
for example, a method of leaving the pellet in a dry atmosphere at
100 to 160.degree. C. for 1 to 24 hours is preferably employed.
[0065] In the step 1, the resin material is melt-kneaded in the
cylinder of the extruder. The cylinder temperature is adjusted to
240 to 285.degree. C., preferably 245 to 275.degree. C., and more
preferably 247 to 273.degree. C. For cases where a plurality of
heating means is arranged, corresponding to a solid phase resin
transportation part, a melting part, a liquid phase resin
transportation part, and the like, in the cylinder of the extruder,
temperature of each heating means may be made different from each
other within the range described above, or the temperature of each
heating means may be controlled to be identical.
[0066] In the step 2, the resin material melted by melt-kneading is
melt-extruded from an extrusion die at a tip of the extruder. The
melted resin material from an extrusion die is extruded into a flow
path of a forming die comprising cooling means and the flow path
that communicates with a path of melted resin of the extrusion die
and that has a cross-sectional shape of an extrusion molded
article. The cross-sectional shape of the extrusion molded article
is rectangular when the extrusion molded article has a plate shape;
and the cross-sectional shape of the extrusion molded article is
circular when the extrusion molded article has a round bar
shape.
[0067] In the step 3, the melted and extruded matter formed from
the resin material is solidified by cooling in the flow path of the
forming die, and then solidified and extruded matter is extruded
from the tip of the forming die to outside. The extrusion rate is
typically from 5 to 27 mm/10 minutes, and preferably from 10 to 25
mm/10 minutes.
[0068] In the step 3, it is preferable to employ a method in which
a forming die having heating means in addition to the cooling means
is used; and the method comprises, first, heating the melted and
extruded matter in the flow path around an extrusion die outlet to
a temperature of 230 to 290.degree. C., and preferably 250 to
285.degree. C., by the heating means, and then cooling the melted
and extruded matter, particularly the surface part thereof, in the
flow path to a temperature lower than a crystallization temperature
of the polyglycolic acid to solidify the melted and extruded matter
by the cooling means. When the temperature around the extrusion die
outlet is lowered rapidly, progress of crystallization of the
polyglycolic acid may be delayed. By cooling the temperature in the
vicinity of the extrusion die to a temperature within the range
described above after heating, it is possible to promote
crystallization of the melted and extruded matter, particularly the
surface part thereof. Also, by setting the extrusion die outlet
temperature to be within the range described above, the temperature
of the melted and extruded matter, particularly the surface part
thereof, that is in the flow path around the extrusion die outlet
can be adjusted to a temperature within the range described
above.
[0069] By cooling means, the extrusion molded article, particularly
the temperature of the surface part thereof, is cooled to a
temperature lower than the crystallization temperature of the
polyglycolic acid to solidify. The crystallization temperature
(crystallization temperature detected when the temperature of the
polyglycolic acid in the melted state is lowered) of the
polyglycolic acid is typically approximately from 130 to
140.degree. C. The cooling temperature of the cooling means is
preferably 100.degree. C. or lower, and more preferably 90.degree.
C. or lower. The lower limit of the cooling temperature is
preferably at 40.degree. C., and more preferably at 50.degree. C.
For cases where the resin material used in the step 1 contains a
filler such as glass fibers, the crystallization temperature of the
polyglycolic acid may be raised due to melt-kneading in the
cylinder of the extruder; however, even in this case, the cooling
temperature is preferably within the range described above.
[0070] The heating means comprise, for example, a heater as a heat
source. The cooling means comprise, for example, a cooling water
pipe that can circulate cooling water as a coolant.
[0071] In the step 4, the solidified and extruded matter is
pressurized and drawn while back pressure is applied in a direction
of the forming die to suppress expansion of the solidified and
extruded matter in a thickness direction or radial direction to
obtain a solidification- and extrusion-molded article of
polyglycolic acid having a thickness or diameter of greater than
100 mm but not greater than 500 mm. The pressurizing means include,
for example, a combination of upper rolls and lower rolls. The
solidified and extruded matter can be pressurized by a method of
placing the lower rolls on a stand and then applying a load on the
upper rolls. The solidified and extruded matter may be also
pressurized by a method of applying a load on the lower rolls in a
direction toward upper part and applying a load on the upper rolls
in a direction toward lower part.
[0072] By applying the pressure, starting from the discharge port
of the forming die, on the solidified and extruded matter extruded
from the forming die by using rolls in which a plurality of rolls
are combined, expansion of the solidified and extruded matter in
the thickness direction or radial direction can be suppressed, and
back pressure can be also applied in the forming die direction.
Also, back pressure can be applied to the solidification- and
extrusion-molded article in the forming die direction by combining
suitable loading means. The amount of back pressure is typically in
a range of 1,500 to 8,500 kg, preferably 1,600 to 8,000 kg, more
preferably 1,800 to 7,000 kg, and even more preferably 2,000 to
6,000 kg. For cases where the diameter or thickness of the
solidification- and extrusion-molded article is large, it is
preferable to increase the back pressure to be applied. This back
pressure can be measured as an external pressure of the die
(pressure applied on the flow path).
[0073] By suppressing expansion of the solidified and extruded
matter in a thickness direction or radial direction by this
pressurization, the thickness or diameter of the finally resulting
solidification- and extrusion-molded article is adjusted to greater
than 100 mm but not greater than 500 mm. After the pressurization,
the solidification- and extrusion-molded article is drawn.
[0074] For cases where the solidification- and extrusion-molded
article is a round bar, other than the method of pressurizing using
a combination of upper rolls and lower rolls described above, a
method of arranging rolls to enclose the round bar-shaped
solidification- and extrusion-molded article and then applying
pressure on the rolls toward the center can be also used. Any
method can be employed as the method of pressurizing the solidified
and extruded matter discharged from the forming die as long as the
method can apply back pressure in the forming die direction, can
suppress expansion of the solidified and extruded matter in a
thickness direction or radial direction by pressurization, and can
adjust the thickness or diameter of the eventually resulting
solidification- and extrusion-molded article to be greater than 100
mm but not greater than 500 mm.
[0075] The extrusion molded article of polyglycolic acid obtained
in the step 4 is preferably annealed by performing step 5 in which
the extrusion molded article is heat-treated at a temperature of
150 to 230.degree. C. for 3 to 24 hours. By this annealing
treatment, it is possible to remove residual stress of the
solidification- and extrusion-molded article and to avoid
inconveniences, such as deformation caused in the solidification-
and extrusion-molded article itself and deformation caused in the
secondarily molded article after machining. The heat treatment
temperature is preferably from 175 to 225.degree. C., and more
preferably from 185 to 215.degree. C. The heat treatment time is
preferably from 4 to 20 hours, and more preferably from 5 to 15
hours.
[0076] Although solidification- and extrusion-molded articles of
polyglycolic acid manufactured by the manufacturing method of the
present invention can have various shapes such as round bar, plate,
pipe, or special shapes, from the perspective of easy
solidification- and extrusion-molding and subsequently performed
densification processing, and from the perspective of having many
qualities suitable as a stock shape for machining, the
solidification- and extrusion-molded article preferably has a round
bar or plate shape, and more preferably a round bar shape.
[0077] Examples of the machining that can be performed on the
solidification- and extrusion-molded article of polyglycolic acid
include cutting, drilling, shearing, and a combination of these.
Broadly speaking, the cutting method may include drilling, in
addition to cutting. Examples of the cutting method include
turning, grinding, lathing, boring, and the like performed by using
a single cutter. Examples of the cutting method making use of a
multi-cutter include milling, drilling, thread cutting, gear
cutting, diesinking, filing, and the like. In the present
invention, drilling making use of a drill or the like may be
distinguished from the cutting in some cases. Examples of the
shearing method include shearing by a cutting tool (saw), shearing
by abrasive grains, shearing by heating and melting, and the like.
Besides these, ground finishing methods, plastic working methods
such as punching making use of a knife-like tool and marking-off
shearing, special working methods such as laser beam machining, and
the like may also be applied.
[0078] For cases where the solidification- and extrusion-molded
article of polyglycolic acid (i.e. stock shape for machining) has a
plate or round bar shape having a large thickness, the
solidification- and extrusion-molded article is typically shorn
into a proper size or thickness, the shorn solidification- and
extrusion-molded article is ground to adjust its shape to a desired
shape, and, as necessary, some parts of the solidification- and
extrusion-molded article are further subjected to drilling. The
solidification- and extrusion-molded article is finally subjected
to a finishing operation as necessary. However, the order of the
machining is not limited to this order. When a smooth surface is
hard to form because of melting of the solidification- and
extrusion-molded article due to frictional heat upon the machining,
the machining is desirably performed while cooling a cut surface or
the like. Excessive heat generated on the solidification- and
extrusion-molded article by frictional heat can cause deformation
and discoloration. Therefore, it is preferable to control the
temperature of the solidification- and extrusion-molded article or
surface to be machined to a temperature of 200.degree. C. or lower,
and more preferably to a temperature of 150.degree. C. or
lower.
3. Stock Shape for Machining
[0079] By subjecting the solidification- and extrusion-molded
article of polyglycolic acid of the present invention to machining
such as cutting, drilling, and shearing, the solidification- and
extrusion-molded article can be made into a stock shape for
machining, whereby various secondarily molded articles such as
resin parts can be obtained. Examples of the secondarily molded
article include various components used in a downhole (downhole
tools) that are used in drilling and completion of hydrocarbon
resources (as previously stated, also simply referred to as
"petroleum") such as petroleum and gas. That is, the secondarily
molded article is exemplified by a downhole tool or component
thereof formed from a degradable material, such as plug for
petroleum excavation or mandrel of the plug. In particular, the
secondarily molded article is exemplified by a ball sealer for
petroleum excavation formed from a degradable material. By cutting
the solidification- and extrusion-molded article of polyglycolic
acid of the present invention, a downhole tool or component
thereof, particularly a ball sealer, having a large diameter such
as a diameter of 20 mm or greater, preferably a diameter of 50 mm
or greater, more preferably a diameter of 70 mm or greater, and
particularly preferably a diameter of 90 mm or greater, can be
obtained. The upper limit of the diameter of the ball sealer and
the like is typically 300 mm and, in many cases, 200 mm.
[0080] That is, by comprising the step 6 in which the
solidification- and extrusion-molded article of polyglycolic acid
manufactured by the manufacturing method of the present invention
is subjected to cutting, a ball sealer for petroleum excavation,
that is a downhole tool or component thereof, having a diameter of
20 to 200 mm and the like can be manufactured. The diameter of the
ball sealer for petroleum excavation or the like is more preferably
in a range of 30 to 170 mm, even more preferably 50 to 150 mm, and
particularly preferably 70 to 120 mm.
[0081] The solidification- and extrusion-molded article of
polyglycolic acid of the present invention can be formed into other
secondarily molded articles by subjecting the solidification- and
extrusion-molded article to machining. In electric and electronic
fields, examples thereof include wafer carriers, wafer cassettes,
spin chucks, tote bottles, wafer boards, IC chip trays, IC chip
carriers, IC conveying tubes, IC test sockets, burn-in sockets, pin
grid array sockets, quad flat packages, leadless chip carriers,
dual in-line packages, small outline packages, reel packings,
various cases, storage trays, parts for conveying apparatus,
magnetic card readers, and the like.
[0082] In a field of OA instruments, examples thereof include
various roll components in image forming apparatus such as
electrophotographic copying machines and electrostatic recording
apparatus, transfer drums for recording apparatus, printed circuit
board cassettes, bushings, paper and paper money conveying parts,
paper feed rails, font cartridges, ink ribbon canisters, guide
pins, trays, rollers, gears, sprockets, housings for computers,
modem housings, monitor housings, CD-ROM housings, printer
housings, connectors, computer slots, and the like.
[0083] In a field of communication apparatus, examples thereof
include portable telephone parts, pagers, various kinds of sliding
materials, and the like. In a field of automobiles, examples
thereof include interior materials, underhoods, electronic and
electric instrument housings, gas tank caps, fuel filters, fuel
line connectors, fuel line clips, fuel tanks, instrument bezels,
door handles, other various parts, and the like. In other fields,
examples thereof include electric wire supporters, electromagnetic
wave absorbers, flooring materials, pallet, shoe soles, brushes,
blower fans, flat heaters, polyswitches, and the like.
EXAMPLES
[0084] The present invention will be described in further detail
hereinafter using working examples, a comparative example, and
reference examples; however, the present invention is not limited
by the examples. The measurement methods for the physical
properties and characteristics are as follows.
(1) Melt Viscosity of Polyglycolic Acid
[0085] Using a sample, prepared by crystallizing an amorphous sheet
of polyglycolic acid having a thickness of approximately 0.2 mm by
heating the amorphous sheet at approximately 150.degree. C. for 5
minutes, melt viscosity of the sample was measured by using a
capilograph equipped with a nozzle having a diameter (D) of 0.5 mm
and length (L) of 5 mm (manufactured by Toyo Seiki Seisaku-sho,
Ltd.) at a temperature of 270.degree. C. under a shearing speed of
120 sec*
(2) Density
[0086] A sample cut out from the solidification- and
extrusion-molded article of polyglycolic acid was measured in
accordance with JIS R 7222 (a pycnometer method using
n-butanol).
Working Example 1
[0087] Pellets of polyglycolic acid having a melt viscosity of 920
Pas, measured at a temperature of 270.degree. C. under a shearing
speed of 120 sec.sup.-1, were left at a temperature of 140.degree.
C. for 6 hours to dehumidify and dry. The dehumidified and dried
pellets were supplied to the hopper of a single screw extruder
(L/D=20; diameter: 30 mm), melt-kneaded at a cylinder temperature
of 251.degree. C., melt-extruded into a flow path of a forming die
at an extrusion die outlet temperature of 276.degree. C., and
cooled and solidified at a cooling temperature of 80.degree. C.
Extrusion rate was approximately 18 mm/10 minutes.
[0088] By pressurizing the solidification- and extrusion-molded
article that was solidified in the flow path of the forming die by
passing the solidification- and extrusion-molded article in between
upper rolls and lower rolls, expansion of the solidification- and
extrusion-molded article of polyglycolic acid were suppressed by
adjusting the external pressure (back pressure) of the forming die
to be 3,200 kg. Thereafter, the solidification- and
extrusion-molded article was heat-treated at a temperature of
205.degree. C. for 10 hours to remove residual stress. The heat
treatment did not crack or deform the solidification- and
extrusion-molded article.
[0089] By the method as described above, a round bar-shaped
solidification- and extrusion-molded article of polyglycolic acid
having a diameter of 120 mm and a length of 1,000 mm was obtained.
Using samples (three samples) that were cut out in the radial
direction from positions located at 5 mm from each of the ends of
the obtained round bar and from a position at the center of the
obtained round bar in the length direction, densities of the outer
surface part and the center part in the radial direction (radius:
10 mm) were measured. The density of the outer surface part was
1,581.1 kg/m.sup.3, and the density of the center part was 1,584.2
kg/m.sup.3 (average values of three samples).
[0090] When the obtained round bar was shorn using a milling
cutter, the round bar was shorn without causing cracks. Shorn
surface thereof had no streak-like flow pattern caused by
insufficient kneading, and the shorn surface was uniform and
beautiful. Furthermore, when this round bar was subjected to
cutting at 495 rotation/minutes using a single-edged HSS tool bit,
nine balls having a diameter of 101.6 mm (4 inches) were produced
without causing cracks.
Working Example 2
[0091] A round bar-shaped solidification- and extrusion-molded
article of polyglycolic acid having a diameter of 120 mm and a
length of 1,000 mm was obtained in the same manner as in Working
Example 1 except for using a raw material that is obtained by
preparing pellets of a resin material via melt-kneading glass
fibers (03JAFT592S, manufactured by Owens Corning; length: 3 mm)
and a polyglycolic acid having a melt viscosity, measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1, of 920 Pas mixed at a mass ratio of 70:30, and then
leaving the pellets at a temperature of 120.degree. C. for 6 hours
to dehumidify and dry the pellets.
[0092] When the obtained round bar was shorn using a milling
cutter, the round bar was shorn without causing cracks. Shorn
surface thereof had no streak-like flow pattern caused by
insufficient kneading, and the shorn surface was uniform and
beautiful. Furthermore, when this round bar was subjected to
cutting in the same manner as in Working Example 1, nine balls
having a diameter of 101.6 mm (4 inches) were produced without
causing cracks.
Comparative Example 1
[0093] A round bar-shaped solidification- and extrusion-molded
article of polyglycolic acid having a diameter of 120 mm and a
length of 1,000 mm was produced in the same manner as in Working
Example 1 except for using, as a raw material, pellets of
polyglycolic acid having a melt viscosity, measured at a
temperature of 270.degree. C. under a shearing speed of 120
sec.sup.-1, of 100 Pas. However, in a step of heat-treating at a
temperature of 205.degree. C. for 10 hours, deformation such as
necking was observed in some parts of the article.
[0094] When the produced round bar was subjected to cutting in the
same manner as in Working Example 1, cracks occurred. Furthermore,
when this round bar was subjected to shearing in the same manner as
in Working Example 1, a streak-like flow pattern was observed on
the shorn surface.
Reference Example 1
[0095] A round bar-shaped solidification- and extrusion-molded
article of polyglycolic acid having a diameter of 30 mm and a
length of 1,000 mm was obtained by performing the same procedure as
in Working Example 1. The heat treatment did not crack or deform
the solidification- and extrusion-molded article.
[0096] When the obtained round bar was shorn using a milling
cutter, the round bar was shorn without causing cracks. Shorn
surface thereof had no streak-like flow pattern caused by
insufficient kneading, and the shorn surface was uniform and
beautiful. Furthermore, when this round bar was subjected to
cutting in the same manner as in Working Example 1, 35 balls having
a diameter of 25.4 mm (1 inch) were produced without causing
cracks.
Reference Example 2
[0097] After a round bar-shaped solidification- and
extrusion-molded article of polyglycolic acid having a diameter of
30 mm and a length of 1,000 mm was obtained by performing the same
procedure as in Comparative Example 1, the obtained round bar was
shorn using a milling cutter. The round bar was shorn without
causing cracks. The heat treatment did not crack or deform the
solidification- and extrusion-molded article. Shorn surface thereof
had no streak-like flow pattern caused by insufficient kneading,
and the shorn surface was uniform and beautiful. Furthermore, when
this round bar was subjected to cutting in the same manner as in
Working Example 1, 35 balls having a diameter of 25.4 mm (1 inch)
were produced without causing cracks.
[0098] From Working Examples 1 and 2, it was found that a
solidification- and extrusion-molded article of polyglycolic acid
that was formed of a resin material containing polyglycolic acid,
the polyglycolic acid having a melt viscosity of 200 to 2,000 Pas
when measured at a temperature of 270.degree. C. under a shearing
speed of 120 sec.sup.-1, and that had a thickness or diameter of
greater than 100 mm but not greater than 500 mm had excellent
machinability and was possible to be formed into a secondarily
molded product, particularly a ball sealer for petroleum
excavation, via machining, such as cutting, drilling, and shearing.
On the other hand, it was found that the solidification- and
extrusion-molded article of polyglycolic acid of Comparative
Example 1 that was formed of a resin material containing
polyglycolic acid, the polyglycolic acid having a melt viscosity of
100 Pas when measured at a temperature of 270.degree. C. under a
shearing speed of 120 sec.sup.-1, and that had a thickness or
diameter of greater than 100 mm but not greater than 500 mm was
deformed by the heat treatment that was performed in order to
reduce stress, was cracked by machining such as cutting or
shearing, and/or failed to provide a beautifully processed
surface.
[0099] Furthermore, from Reference Examples 1 and 2, for the
solidification- and extrusion-molded articles of polyglycolic acid
having a thickness or diameter of 100 mm or less, no significant
differences in machinability and heat resistance were observed due
to difference in materials, i.e. a resin material containing
polyglycolic acid having a melt viscosity of 200 to 2,000 Pas and a
resin material containing polyglycolic acid having the melt
viscosity of 100 Pas when measured at a temperature of 270.degree.
C. under a shearing speed of 120 sec.sup.-1. That is, it was found
that, in order to achieve excellent machinability and heat
resistance that make it possible to produce a ball sealer for
petroleum excavation having a diameter of 20 to 200 mm, for the
solidification- and extrusion-molded article of polyglycolic acid
having a thickness or diameter of greater than 100 mm but not
greater than 500 mm, a resin material containing polyglycolic acid
having a melt viscosity, measured at a temperature of 270.degree.
C. under a shearing speed of 120 sec.sup.-1, of 200 to 2,000 Pas
should be selected, and a particular solidification- and
extrusion-molding step should be employed.
INDUSTRIAL APPLICABILITY
[0100] Since the solidification- and extrusion-molded article of
polyglycolic acid of the present invention is a solidification- and
extrusion-molded article of polyglycolic acid formed of a resin
material containing polyglycolic acid, the polyglycolic acid having
a melt viscosity of 200 to 2,000 Pas when measured at a temperature
of 270.degree. C. under a shearing speed of 120 sec.sup.-1, and has
a thickness or diameter of greater than 100 mm but not greater than
500 mm, the solidification- and extrusion-molded article exhibits
high precision in processing, is suitable for molding a secondarily
molded article, such as various resin parts, via machining, and is
also suitable for molding a downhole tool or component thereof,
particularly a ball sealer for petroleum excavation having a
diameter of 20 to 200 mm or the like. Therefore, the
solidification- and extrusion-molded article of polyglycolic acid
of the present invention has high industrial applicability.
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