U.S. patent application number 15/487122 was filed with the patent office on 2017-08-03 for polypropylene resin foamed particles, in-mold foam molded body of polypropylene resin, and method for manufacturing same.
This patent application is currently assigned to Kaneka Corporation. The applicant listed for this patent is Kaneka Corporation. Invention is credited to Shintaro Miura, Toru Yoshida.
Application Number | 20170218158 15/487122 |
Document ID | / |
Family ID | 55746704 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170218158 |
Kind Code |
A1 |
Yoshida; Toru ; et
al. |
August 3, 2017 |
POLYPROPYLENE RESIN FOAMED PARTICLES, IN-MOLD FOAM MOLDED BODY OF
POLYPROPYLENE RESIN, AND METHOD FOR MANUFACTURING SAME
Abstract
An expanded polypropylene resin particle is obtained from a base
material resin having a melting point of 140.degree. C. to
150.degree. C., wherein the base material resin includes a
polypropylene resin A including 3 weight % to 15 weight % of
1-butene and having a melting point of 130.degree. C. to
140.degree. C.; and a polypropylene resin B having a melting point
of 145.degree. C. to 165.degree. C., and wherein the expanded
polypropylene resin particle has an average cell diameter of 100
.mu.m to 340 .mu.m.
Inventors: |
Yoshida; Toru; (Osaka,
JP) ; Miura; Shintaro; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaneka Corporation |
Osaka |
|
JP |
|
|
Assignee: |
Kaneka Corporation
Osaka
JP
|
Family ID: |
55746704 |
Appl. No.: |
15/487122 |
Filed: |
April 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2015/079035 |
Oct 14, 2015 |
|
|
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15487122 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29K 2995/0063 20130101;
C08J 9/224 20130101; C08J 2323/14 20130101; C08J 9/0061 20130101;
C08J 9/232 20130101; C08J 2423/16 20130101; C08L 23/14 20130101;
C08L 23/14 20130101; C08J 2205/04 20130101; C08L 23/14 20130101;
B29K 2105/048 20130101; B29C 44/3461 20130101; B29K 2105/041
20130101; C08J 9/18 20130101; B29K 2023/12 20130101; C08L 23/16
20130101; B29C 44/02 20130101; C08L 23/16 20130101; B29C 44/445
20130101; C08J 2203/06 20130101; C08J 2201/03 20130101; C08L
2314/02 20130101; C08L 23/16 20130101; C08J 2423/14 20130101; B29K
2105/0014 20130101 |
International
Class: |
C08J 9/18 20060101
C08J009/18; C08J 9/232 20060101 C08J009/232 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 15, 2014 |
JP |
2014-210753 |
Claims
1. An expanded polypropylene resin particle, obtained from a base
material resin having a melting point of 140.degree. C. to
150.degree. C., wherein the base material resin comprises: a
polypropylene resin A comprising 3 weight % to 15 weight % of
1-butene and having a melting point of 130.degree. C. to
140.degree. C.; and a polypropylene resin B having a melting point
of 145.degree. C. to 165.degree. C., and wherein the expanded
polypropylene resin particle has an average cell diameter of 100
.mu.m to 340 .mu.m.
2. The expanded polypropylene resin particle according to claim 1,
wherein the polypropylene resin A further comprises 2 weight % to
10 weight % of ethylene.
3. The expanded polypropylene resin particle according to claim 1,
wherein the base material resin comprises: 50 weight % to 70 weight
% of the polypropylene resin A; and 30 weight % to 50 weight % of
the polypropylene resin B, wherein the polypropylene resin A and
the polypropylene resin B together account for 100 weight %.
4. The expanded polypropylene resin particle according to claim 1,
wherein the average cell diameter is 120 .mu.m to 250 .mu.m.
5. The expanded polypropylene resin particle according to claim 1,
wherein the melting point of the base material resin is 145.degree.
C. to 150.degree. C.
6. The expanded polypropylene resin particle according to claim 1,
wherein the melting point of the base material resin is 146.degree.
C. to 148.degree. C.
7. The expanded polypropylene resin particle according to claim 1,
wherein the polypropylene resin B is a propylene-ethylene random
copolymer or a propylene-ethylene-1-butene random copolymer.
8. The expanded polypropylene resin particle according to claim 1,
wherein the polypropylene resin A is obtained using a Ziegler
catalyst.
9. The expanded polypropylene resin particle according to claim 1,
wherein the expanded polypropylene resin particle is an expanded
composite particle comprising an expanded polypropylene resin core
layer covered with a polypropylene resin covering layer, the
expanded polypropylene resin core layer is obtained from a base
material resin comprising the polypropylene resin A and the
polypropylene resin B; and the polypropylene resin covering layer
comprises the polypropylene resin A.
10. A polypropylene resin in-mold expanded molded product formed by
subjecting the expanded polypropylene resin particles according to
claim 1 to in-mold foaming molding.
11. The polypropylene resin in-mold expanded molded product
according to claim 10, wherein the polypropylene resin in-mold
expanded molded product has a density and a 50%-strained
compressive strength satisfying the following: [50%-strained
compressive strength (MPa)].gtoreq.0.0069.times.[Molded product
density (g/L)]+0.018.
12. The polypropylene resin in-mold expanded molded product
according to claim 10, wherein the polypropylene resin in-mold
expanded molded product has a density of 20 g/L to 40 g/L.
13. A method of producing a polypropylene resin in-mold expanded
molded product, comprising: placing polypropylene resin particles,
water, and an inorganic gas foaming agent in a pressure-resistant
container, forming a mixture, wherein the polypropylene resin
particles is obtained from a base material resin having a melting
point of 140.degree. C. to 150.degree. C., the base material resin
comprising: a polypropylene resin A comprising 3 weight % to 15
weight % of 1-butene and having a melting point of 130.degree. C.
to 140.degree. C.; and a polypropylene resin B having a melting
point of 145.degree. C. to 165.degree. C., dispersing the
polypropylene resin particles while stirring the mixture, obtaining
a dispersion liquid, increasing a temperature and a pressure in the
pressure-resistant container, releasing the dispersion liquid from
the pressure-resistant container into a region having a pressure
lower than the pressure in the pressure-resistant container,
producing expanded polypropylene resin particles each having an
average cell diameter of 100 .mu.m to 340 .mu.m; and obtaining the
polypropylene resin in-mold expanded molded product by filling a
mold with the expanded polypropylene resin particles, and then
heating the expanded polypropylene resin particles.
14. The method according to claim 13, wherein the polypropylene
resin A comprises 2 weight % to 10 weight % of ethylene.
15. The method according to claim 13, further comprising: melting
and kneading the polypropylene resin A and the polypropylene resin
B in an extruder and obtaining the polypropylene resin
particles.
16. The method according to claim 13, further comprising: obtaining
the polypropylene resin A by polymerization using a Ziegler
catalyst.
17. The method according to claim 13, wherein the expanded
polypropylene resin particles are each an expanded composite
particle comprising an expanded polypropylene resin core layer
covered with a polypropylene resin covering layer, the expanded
polypropylene resin core layer is obtained from a base material
resin comprising the polypropylene resin A and the polypropylene
resin B; and the polypropylene resin covering layer comprises the
polypropylene resin A.
18. The method according to claim 13, wherein the expanded
polypropylene resin particles are heated with steam having a
pressure of 0.22 MPa (gauge pressure) or less, and the
polypropylene resin in-mold expanded molded product has a density
and a 50%-strained compressive strength satisfying the following:
[50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Molded product density (g/L)]+0.018.
Description
TECHNICAL FIELD
[0001] One or more embodiments of the present invention relate to
(i) an expanded polypropylene resin particle, (ii) a polypropylene
resin in-mold expanded molded product obtained from expanded
polypropylene resin particles, (iii) a method of producing the
expanded polypropylene resin particle, and (iv) a method of
producing the polypropylene resin in-mold expanded molded
product.
BACKGROUND
[0002] A polypropylene resin in-mold expanded molded product, which
is obtained with the use of expanded polypropylene resin particles
obtained from a polypropylene resin, has characteristics such as
being easily shaped, being light in weight, and being heat
insulating, which are advantages of an in-mold expanded molded
product. In comparison with a polystyrene resin in-mold expanded
molded product which is obtained with the use of expanded
polystyrene resin particles, a polypropylene resin in-mold expanded
molded product is superior in terms of chemical resistance, heat
resistance, strain recovery rate after compression, and the like.
In comparison with a polyethylene resin in-mold expanded molded
product which is obtained with the use of expanded polyethylene
resin particles, a polypropylene resin in-mold expanded molded
product is superior in terms of dimension accuracy, heat
resistance, compressive strength, and the like. Because of these
characteristics, a polypropylene resin in-mold expanded molded
product is put to a wide range of use such as not only automobile
interior materials and automobile bumper core materials but also
heat insulating materials, shock-absorbing packing materials, and
returnable containers.
[0003] As described above, a polypropylene resin in-mold expanded
molded product is superior to a polyethylene resin in-mold expanded
molded product in terms of heat resistance and compressive
strength. However, with a polypropylene resin in-mold expanded
molded product, a molding temperature during in-mold foaming
molding becomes high. Therefore, a high steam pressure is necessary
during, for example, in-mold foaming molding with the use of steam.
This tends to cause utility costs to be high.
[0004] Certain techniques have been proposed, examples of which
encompass: (i) techniques in which a low-melting polypropylene
resin having a melting point of 140.degree. C. or lower is used
(e.g. Patent Literature 1), (ii) techniques in which a mixture of a
low-melting polypropylene resin and a high-melting polypropylene
resin is used (e.g. Patent Literatures 2 and 4-8), and (iii)
techniques in which a low-melting metallocene polypropylene resin,
which is polymerized by use of a metallocene catalyst, is used
(e.g. Patent Literature 3). In addition to the literatures above,
Patent Literatures 1 and 12 can be listed as literatures each of
which discloses a technique for producing an expanded polypropylene
resin particle that is excellent in characteristics such as heat
resistance.
[0005] However, even though a molding temperature can be reduced
with these techniques, the amount of decrease in compressive
strength is excessively large in comparison with conventional
in-mold expanded molded products. Specifically, for example, in a
case where a polypropylene resin in-mold expanded molded product
for an automobile bumper has a density of 30 g/L, a strength of
approximately 0.23 MPa is required as compressive strength when the
polypropylene resin in-mold expanded molded product is strained by
50% (hereinafter referred to as "50%-strained compressive
strength"). With conventional technologies, a pressure of 0.26 MPa
(gage pressure) or more (i.e. high molding temperature) as in-mold
foaming molding pressure is necessary in order to obtain
polypropylene resin in-mold expanded molded product having the
strength above.
[0006] Meanwhile, in a case where (i) a low-melting polypropylene
resin is used, (ii) a mixture of a low-melting polypropylene resin
and a high-melting polypropylene resin is used, or (iii) a
metallocene polypropylene resin, which is polymerized by use of a
metallocene catalyst, is used, an in-mold expanded molded product
can be molded at an in-mold foaming molding pressure of 0.20 MPa
(gage pressure) or less. However, a 50%-strained compressive
strength becomes considerably below 0.23 MPa. The decrease in
compressive strength in a case where a polypropylene resin can be
molded with such low molding pressure (low molding temperature) is
remarkable when density of a molded product is 40 g/L or less.
[0007] A metallocene polypropylene resin poses a high production
costs in comparison with a Ziegler polypropylene resin which is
polymerized with the use of a Ziegler catalyst. Therefore, even if
utility costs of in-mold foaming molding can be reduced as a result
of a low molding temperature, material costs are still high. This
is not necessarily advantageous from an industrial perspective.
[0008] Under the circumstances, there are still demands for a
technique for achieving a high-compressive-strength polypropylene
resin in-mold expanded molded product while a molding temperature
during in-mold foaming molding is reduced.
[0009] As examples of a technique in which a molding temperature
during in-mold foaming molding is lowered (i.e. molding at low
steam pressure is enabled), there are known techniques of using
expanded composite particles each including an expanded
polypropylene resin core layer and a polypropylene resin covering
layer that covers the polypropylene resin foamed core layer (e.g.
Patent Literatures 9-10). However, these techniques tend to cause
adhesiveness of an interface between an expanded polypropylene
resin core layer and a polypropylene resin covering layer to be
weak.
CITATION LIST
Patent Literature
[0010] [Patent Literature 1]
[0011] PCT International Publication, No. WO2008/139822
(Publication Date: Nov. 20, 2008)
[0012] [Patent Literature 2]
[0013] PCT International Publication, No. WO2009/001626
(Publication Date: Dec. 31, 2008)
[0014] [Patent Literature 3]
[0015] Japanese Patent Application Publication, Tokukai, No.
2009-144096 (Publication Date: Jul. 2, 2009)
[0016] [Patent Literature 4]
[0017] Japanese Patent Application Publication, Tokukai, No.
2010-144078 (Publication Date: Jul. 1, 2010)
[0018] [Patent Literature 5]
[0019] Chinese Patent Publication, No. CN103509203 (Publication
Date: Jan. 15, 2014).
[0020] [Patent Literature 6]
[0021] PCT International Publication, No. WO2006/054727
(Publication Date: May 26, 2006)
[0022] [Patent Literature 7]
[0023] PCT International Publication, No. WO2009/051035
(Publication Date: Apr. 23, 2009)
[0024] [Patent Literature 8]
[0025] Japanese Patent Application Publication, Tokukai, No.
2008-106150 (Publication Date: May 8, 2008)
[0026] [Patent Literature 9]
[0027] Japanese Patent Application Publication, Tokukai, No.
2004-176047 (Publication Date: Jun. 24, 2004)
[0028] [Patent Literature 10]
[0029] PCT International Publication, No. WO2010/150466
(Publication Date: Dec. 29, 2010)
[0030] [Patent Literature 11]
[0031] Japanese Patent Application Publication, Tokukai, No.
2006-096805 (Publication Date: Apr. 13, 2006)
[0032] [Patent Literature 12]
[0033] Japanese Patent Application Publication, Tokukaihei, No.
10-251437 (Publication Date: Sep. 22, 1998)
SUMMARY
[0034] One or more embodiments of the present invention provide a
high-compressive-strength polypropylene resin in-mold expanded
molded product while a molding temperature (steam pressure) during
in-mold foaming molding is reduced.
[0035] The inventors of the present invention found that with the
use of expanded polypropylene resin particles obtained from a base
material resin including (i) a low-melting polypropylene resin
having a structure in which a certain amount of certain comonomers
is contained and (ii) a polypropylene resin having a melting point
higher than that of the low-melting polypropylene resin, it may be
possible to reduce a molding temperature during in-mold foaming
molding to a low temperature and it may also be possible to
maintain, at a level not inferior to those of conventional molded
products, a compressive strength of a polypropylene resin in-mold
expanded molded product to be obtained.
[0036] <1> An expanded polypropylene resin particle which has
an average cell diameter of 100 .mu.m or more to 340 .mu.m or less
and which is obtained from a base material resin, the base material
resin having a melting point of 140.degree. C. or higher to
150.degree. C. or lower and including a polypropylene resin A
satisfying the following condition (a) and having a melting point
of 130.degree. C. or higher to 140.degree. C. or lower and a
polypropylene resin B having a melting point of 145.degree. C. or
higher to 165.degree. C. or lower:
(a) a structural unit of 1-butene is present in an amount of 3
weight % or more to 15 weight % or less with respect to 100 weight
% entire structural units.
[0037] <2> The expanded polypropylene resin particle as set
forth in <1>, configured such that the polypropylene resin A
further satisfies the following condition (b):
(b) a structural unit of ethylene is present in amount of 2 weight
% or more to 10 weight % or less with respect to 100 weight %
entire structural units.
[0038] <3> The expanded polypropylene resin particle as set
forth in <1> or <2>, configured such that: the base
material resin includes the polypropylene resin A in an amount of
50 weight % or more to 70 weight % or less and the polypropylene
resin B in an amount of 30 weight % or more to 50 weight % or less;
and the polypropylene resin A and the polypropylene resin B
together account for 100 weight %.
[0039] <4> The expanded polypropylene resin particle as set
forth in any one of <1> through <3>, configured such
that the average cell diameter is 120 .mu.m or more to 250 .mu.m or
less.
[0040] <5> The expanded polypropylene resin particle as set
forth in any one of <1> through <4>, configured such
that the melting point of the base material resin is 145.degree. C.
or higher to 150.degree. C. or lower.
[0041] <6> The expanded polypropylene resin particle as set
forth in any one of <1> through <5>, configured such
that the melting point of the base material resin is 146.degree. C.
or higher to 148.degree. C. or lower.
[0042] <7> The expanded polypropylene resin particle as set
forth in any one of <1> through <6>, configured such
that the polypropylene resin B is a propylene-ethylene random
copolymer or a propylene-ethylene-1-butene random copolymer.
[0043] <8> The expanded polypropylene resin particle as set
forth in any one of <1> through <7>, configured such
that the polypropylene resin A is obtained with use of a Ziegler
catalyst.
[0044] <9> The expanded polypropylene resin particle as set
forth in any one of <1> through <8>, configured such
that:
[0045] the expanded polypropylene resin particle is an expanded
composite particle in which an expanded polypropylene resin core
layer is covered with a polypropylene resin covering layer
[0046] the expanded polypropylene resin core layer is obtained from
a base material resin including the polypropylene resin A and the
polypropylene resin B; and the polypropylene resin covering layer
includes the polypropylene resin A.
[0047] <10> A polypropylene resin in-mold expanded molded
product obtained by subjecting, to in-mold foaming molding,
expanded polypropylene resin particles recited in any one of
<1> through <9>.
[0048] <11> The polypropylene resin in-mold expanded molded
product as set forth in <10>, configured such that the
polypropylene resin in-mold expanded molded product has a density
and a 50%-strained compressive strength which are related so as to
satisfy the following Formula (1):
[50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Molded product density (g/L)]+0.018
(1)
[0049] <12> The polypropylene resin in-mold expanded molded
product as set forth in <10> or <11>, configured such
that the polypropylene resin in-mold expanded molded product has a
density of 20 g/L or more to 40 g/L or less.
[0050] <13> A method of producing a polypropylene resin
in-mold expanded molded product, including the steps of:
[0051] (A) obtaining expanded polypropylene resin particles each
having an average cell diameter of 100 .mu.m or more to 340 .mu.m
or less, the expanded polypropylene resin particles being obtained
by [0052] (i) placing polypropylene resin particles, water, and an
inorganic gas foaming agent in a pressure-resistant container, so
that a mixture is obtained, the polypropylene resin particles
having been obtained from a base material resin, the base material
resin having a melting point of 140.degree. C. or higher to
150.degree. C. or lower and including [0053] a polypropylene resin
A satisfying the following condition (a) and having a melting point
of 130.degree. C. or higher to 140.degree. C. or lower and [0054] a
polypropylene resin B having a melting point of 145.degree. C. or
higher to 165.degree. C. or lower, [0055] (ii) dispersing the
polypropylene resin particles while the mixture is stirred, so that
a dispersion liquid is obtained, [0056] (iii) increasing a
temperature and a pressure in the pressure-resistant container, and
then [0057] (iv) releasing the dispersion liquid from the
pressure-resistant container into a region having a pressure lower
than an internal pressure of the pressure-resistant container, so
that the polypropylene resin particles are foamed; and
[0058] (B) obtaining the polypropylene resin in-mold expanded
molded product by [0059] (i) filling a mold with the expanded
polypropylene resin particles, and then [0060] (ii) heating the
expanded polypropylene resin particles: (a) a structural unit of
1-butene is present in an amount of 3 weight % or more to 15 weight
% or less with respect to 100 weight % entire structural units.
[0061] <14> The method as set forth in <13>, configured
such that the polypropylene resin A satisfies the following
condition (b):
(b) a structural unit of ethylene is present in amount of 2 weight
% or more to 10 weight % or less with respect to 100 weight %
entire structural units.
[0062] <15> The method as set forth in <13> or
<14>, further including the step of: melting and kneading the
polypropylene resin A and the polypropylene resin B in an extruder
and then obtaining the polypropylene resin particles.
[0063] <16> The method as set forth in any one of <13>
through <15>, further including the step of: obtaining the
polypropylene resin A by carrying out polymerization with use of a
Ziegler catalyst.
[0064] <17> The method as set forth in any one of <13>
through <16>, configured such that:
[0065] the expanded polypropylene resin particles are each an
expanded composite particle in which an expanded polypropylene
resin core layer is covered with a polypropylene resin covering
layer;
[0066] the expanded polypropylene resin core layer is obtained from
a base material resin including [0067] the polypropylene resin A
and [0068] the polypropylene resin B; and
[0069] the polypropylene resin covering layer includes the
polypropylene resin A.
[0070] <18> The method as set forth in any one of <13>
through <17>, configured such that
[0071] in the step (B), [0072] the expanded polypropylene resin
particles are heated with use of steam having a pressure of 0.22
MPa (gage pressure) or less and [0073] the polypropylene resin
in-mold expanded molded product has a density and a 50%-strained
compressive strength which are related so as to satisfy the
following Formula (1):
[0073] [50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Molded product density (g/L)]+0.018
(1)
[0074] According to one or more embodiments of the present
invention, it is possible to (i) reduce a molding temperature
during in-mold foaming molding to a low temperature and (ii)
maintain, at a level not inferior to those of conventional molded
products, a compressive strength of a polypropylene resin in-mold
expanded molded product to be obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0075] FIG. 1 is a view illustrating a DSC curve of second
temperature rise obtained when, in differential scanning
calorimetry (DSC), (i) a temperature of a polypropylene resin is
raised from 40.degree. C. to 220.degree. C. at a heating rate of
10.degree. C./min., (ii) the temperature is cooled from 220.degree.
C. to 40.degree. C. at a rate of 10.degree. C./min., and (iii) the
temperature is raised again from 40.degree. C. to 220.degree. C. at
a rate of 10.degree. C./min. t.sub.m is a melting point.
[0076] FIG. 2 is a view illustrating a DSC curve (temperature vs
heat absorption quantity) obtained by a differential scanning
calorimetry (DSC) in which a temperature of an expanded
polypropylene resin particle is raised from 40.degree. C. to
220.degree. C. at a heating rate of 10.degree. C./min. The DSC
curve shows two melting peaks and two melting heat quantity
regions. The two melting heat quantity regions are a low
temperature-side melting heat quantity region Ql and a high
temperature-side melting heat quantity region Qh.
DESCRIPTION OF EMBODIMENTS
[0077] The following description will discuss one or more
embodiments of the present invention. However, the present
invention is not limited to these embodiments. The present
invention is not limited to any of configurations described below,
but can be altered in many ways within the scope of the claims. An
embodiment and/or an example derived from a proper combination of
technical means disclosed in different embodiments and/or examples
are/is also encompassed in the technical scope of the present
invention. In addition, all of the academic documents and patent
literature listed herein are incorporated by reference herein.
[0078] In one or more embodiments of the present invention, the
expanded polypropylene resin particles is obtained from a base
material resin containing a polypropylene resin A and a
polypropylene resin B.
[0079] The polypropylene resin A used in one or more embodiments of
the present invention is a polypropylene resin which satisfies the
following condition (a) and which has a melting point in a range of
130.degree. C. or higher to 140.degree. C. or lower: (a) a
structural unit(s) of 1-butene is present in an amount of 3 weight
% or more to 15 weight % or less with respect to 100 weight %
entire structural units.
[0080] The polypropylene resin A used in one or more embodiments of
the present invention has a structural unit(s) of 1-butene in an
amount of 3 weight % or more to 15 weight % or less with respect to
100 weight % entire structural units. If a structural unit of
1-butene is less than 3 weight %, then a molding temperature during
in-mold foaming molding tends not to decrease. If a structural unit
of 1-butene is more than 15 weight %, then a compressive strength
of an in-mold expanded molded product to be obtained tends to
decrease.
[0081] The polypropylene resin A can contain, in addition to
1-butene, a structural unit of a comonomer which is copolymerizable
with propylene. Examples of the comonomer encompass at least one
type of .alpha.-olefin, such as ethylene, 1-pentene, 1-hexene, and
4-methyl-1-butene, any of which has 2 carbon atoms or any of 4
carbon atoms through 12 carbon atoms. Among these, the comonomer
may be ethylene.
[0082] The polypropylene resin A may further satisfy the following
condition (b) in regard to ethylene.
(b) A structural unit of ethylene is present in amount of 2 weight
% or more to 10 weight % or less with respect to 100 weight %
entire structural units.
[0083] The polypropylene resin A may satisfy both the condition (a)
and condition (b), because, with such a polypropylene resin A, (i)
a molding temperature during in-mold foaming molding can be easily
made low and (ii) compressive strength of an in-mold expanded
molded product to be obtained does not decrease but can be kept
high. Note that "100 weight % entire structural units" means that
the sum of a structural unit obtained from propylene, a structural
unit obtained from 1-butene, and a structural unit obtained from
another/other comonomer(s) such as ethylene accounts for 100 weight
%.
[0084] Hence, the polypropylene resin A may be at least one
selected from the group consisting of (i) a propylene-1-butene
random copolymer and (ii) a propylene-ethylene-1-butene random
copolymer. In addition, the polypropylene resin A may (i) have a
structural unit obtained from 1-butene in an amount of 4 weight %
or more to 9 weight % or less and/or (ii) have a structural unit
obtained from ethylene in an amount of 2.5 weight % or more to 6
weight % or less.
[0085] The polypropylene resin A may have a melting point of
130.degree. C. or higher to 140.degree. C. or lower, such as
132.degree. C. or higher to 138.degree. C. or lower, or such as
134.degree. C. or higher to 138.degree. C. or lower. If the melting
point of the polypropylene resin A is lower than 130.degree. C.,
then compressive strength of an in-mold expanded molded product to
be obtained tends to decrease. If the melting point is more than
140.degree. C., then a molding temperature during in-mold foaming
molding tends not to decrease.
[0086] A catalyst for use in polymerization of the polypropylene
resin A in accordance with one or more embodiments of the present
invention is not limited to any particular one. Examples of the
catalyst encompass a Ziegler catalyst and metallocene catalyst.
[0087] In general, in comparison with a polypropylene resin
polymerized with the use of a metallocene catalyst (hereinafter
also referred to as "metallocene polypropylene resin"), a
polypropylene resin polymerized with the use of a Ziegler catalyst
(hereinafter also referred to as "Ziegler polypropylene resin") has
lower rigidity by melting point matching. Specifically, a
comparison of rigidity of a Ziegler polypropylene resin and
rigidity of a metallocene polypropylene resin having an identical
melting point shows that the rigidity of the Ziegler polypropylene
resin is lower. Therefore, the use of a Ziegler catalyst may
conventionally be disadvantageous in order to obtain (i) reducing a
molding temperature during in-mold foaming molding to a low
temperature and (ii) maintaining compressive strength of a
polypropylene resin in-mold expanded molded product to be obtained.
However, with one or more embodiments of the present invention in
which not only the condition (a) but also the condition (b) are
defined, it may be possible to easily obtain the product according
to one or more embodiments of the present invention, even in a case
where a polypropylene resin polymerized with the use of a Ziegler
catalyst is used.
[0088] That is, it is possible to use a polypropylene resin A which
is polymerized with the use of a Ziegler catalyst. A polypropylene
resin polymerized with the use of a Ziegler catalyst may also be
used in view of the fact that (i) such a polypropylene resin is
industrially more available than a polypropylene resin polymerized
with the use of a metallocene catalyst and (ii) such a
polypropylene resin can be put to a wider range of use.
[0089] Although usable also as a polypropylene resin B described
later, a polypropylene resin polymerized with the use of a Ziegler
catalyst may be used in one or more embodiments of the present
invention by being used as a polypropylene resin A.
[0090] Examples of the polypropylene resin B used in one or more
embodiments of the present invention encompass (i) a propylene
homopolymer and (ii) a copolymer including: propylene; and a
comonomer which is copolymerizable with propylene.
[0091] The polypropylene resin B may be a copolymer including
propylene and a comonomer copolymerizable with the propylene in
view of the fact that such a polypropylene resin B allows a molding
temperature during in-mold foaming molding to be easily made low.
Examples of such a comonomer which is copolymerizable with
propylene encompass .alpha.-olefin, such as ethylene, 1-butene,
1-pentene, 1-hexene, and 4-methyl-1-butene, any of which has 2
carbon atoms or any of 4 carbon atoms through 12 carbon atoms.
Among these, ethylene may be used. These comonomers can be
individually copolymerized with propylene, or these comonomers in
combination can be copolymerized with propylene.
[0092] The polypropylene resin B may be a propylene-ethylene random
copolymer or a propylene-ethylene-1-butene random copolymer in view
of the fact that such a polypropylene resin B allows a molding
temperature during in-mold foaming molding to be easily made low
and makes it possible to maintain high compressive strength of an
in-mold expanded molded product to be obtained without causing the
compressive strength to decrease.
[0093] A melting point of the polypropylene resin B in accordance
with one or more embodiments of the present invention may be
145.degree. C. or higher to 165.degree. C. or lower, such as
147.degree. C. or higher to 160.degree. C. or lower, or such as
148.degree. C. or higher to 153.degree. C. or lower. If the melting
point of the polypropylene resin B is lower than 145.degree. C.,
then compressive strength of an in-mold expanded molded product to
be obtained tends to decrease. If the melting point is more than
165.degree. C., then a molding temperature during in-mold foaming
molding tends to be high.
[0094] A catalyst for use in polymerization of the polypropylene
resin B is not limited to any particular one. Examples of the
catalyst encompass a Ziegler catalyst and metallocene catalyst.
Note, however, that a polypropylene resin B polymerized with the
use of a Ziegler catalyst may be used in view of the fact that such
as polypropylene resin B is easily available industrially and can
be put to a wider range of use.
[0095] A melt flow rate (hereinafter referred to as "MFR") of each
of the polypropylene resin A and the polypropylene resin B is not
particularly limited, but may be more than 3 g/10 min. and less
than 10 g/10 min., such as 5 g/10 min. or more to 9 g/10 min. or
less.
If the MFR of each of the polypropylene resin A and polypropylene
resin B is more than 3 g/10 min. and less than 10 g/10 min., then
(i) an in-mold expanded molded product tends to have a good surface
appearance and (ii) a molding cycle during molding tends to be
short. Note that the MFR of the polypropylene resin according to
one or more embodiments of the present invention is measured with
the use of an MFR measuring instrument described in JIS-K7210 and
under conditions involving (i) an orifice having a diameter of
2.0959.+-.0.005 mm and a length of 8.000.+-.0.025 mm, (ii) a load
of 2160 g, and (iii) a temperature of 230.degree. C..+-.0.2.degree.
C.
[0096] In one or more embodiments of the present invention, a ratio
at which the polypropylene resin A and the polypropylene resin B
are mixed is not particularly limited. Note, however, that in view
of allowing a molding temperature during in-mold foaming molding to
be easily made low and maintaining high compressive strength of an
in-mold expanded molded product to be obtained without causing the
compressive strength to decrease, it may be possible to mix the
polypropylene resin A and the polypropylene resin B such that the
polypropylene resin A accounts for 50 weight % or more to 70 weight
% or less and the polypropylene resin B accounts for 30 weight % or
more to 50 weight % or less with respect to a total amount of both
the polypropylene resins as 100 weight %.
[0097] In one or more embodiments of the present invention, it is
possible to use an additive as necessary in addition to the
polypropylene resin A and the polypropylene resin B. Examples of
the additive encompass: a resin other than a polypropylene resin
(described later); an expansion nucleating agent; a hydrophilic
compound; a colorant; an antistatic agent; a flame retarder; an
antioxidant; and electrically conductive agent. In such a case, a
base material resin is constituted by a mixture of the
polypropylene resin A, the polypropylene resin B, and the
additive.
[0098] Examples of other resins which can be mixed encompass
polyethylene resins such as a high-density polyethylene resin, a
medium-density polyethylene resin, a low-density polyethylene
resin, and a linear low-density polyethylene resin. In a case where
the polyethylene resin is to be mixed, mixing equal to or less than
20 parts by weight of the polyethylene resin in 100 parts by weight
of the polypropylene resin A and the polypropylene resin B combined
may (i) allow an expansion ratio to easily increase or (ii) allow a
molding temperature during in-mold foaming molding to be easily
made low.
[0099] In one or more embodiments of the present invention, it may
be possible to add, to a base material resin, an expansion
nucleating agent which is to become an expansion nucleus during
expansion of the base material resin. Specific examples of the
expansion nucleating agent for use in one or more embodiments of
the present invention encompass silica (silicon dioxide), silicate,
alumina, diatomaceous earth, calcium carbonate, magnesium
carbonate, calcium phosphate, feldspar, apatite, and barium
sulfate. Examples of silicate encompass talc, magnesium silicate,
kaolin, halloysite, dickite, aluminum silicate, and zeolite. These
expansion nucleating agents can be used individually or in
combination.
[0100] In view of uniformity of cell diameters, an amount of the
expansion nucleating agent contained in the base material resin
used in one or more embodiments of the present invention may be
equal to or greater than 0.005 parts by weight and equal to or less
than 2 parts by weight, such as equal to or greater than 0.01 parts
by weight and equal to or less than 1 part by weight, or such as
equal to or greater than 0.03 parts by weight and equal to or less
than 0.5 parts by weight with respect to 100 parts by weight of the
polypropylene resin A and the polypropylene resin B combined.
[0101] Adding a hydrophilic compound to a base material resin may
bring about the effect of promoting an increase in expansion ratio
of expanded polypropylene resin particles.
[0102] Specific examples of a hydrophilic compound for use in one
or more embodiments of the present invention encompass
water-absorbing organic matters such as glycerin, polyethylene
glycol, glycerin fatty acid ester, melamine, isocyanuric acid, and
a melamine-isocyanuric acid condensate.
[0103] An amount of the hydrophilic compound contained in the base
material resin in accordance with one or more embodiments of the
present invention may be equal to or greater than 0.01 parts by
weight and equal to or less than 5 parts by weight, such as equal
to or greater than 0.1 parts by weight and equal to or less than 2
parts by weight with respect to 100 parts by weight of the
polypropylene resin A and the polypropylene resin B combined. If
the amount of the hydrophilic compound contained is less than 0.01
parts by weight, then the effect of increasing an expansion ratio
and the effect of enlarging a cell diameter are difficult to be
obtained. If the amount of the hydrophilic compound contained is
more than 5 parts by weight, then the hydrophilic compound becomes
unlikely to be uniformly dispersed in a polypropylene resin.
[0104] Examples of the colorant encompass carbon black, ultramarine
blue, cyanine pigment, azo pigment, quinacridone pigment cadmium
yellow, chrome oxide, iron oxide, perylene pigment, and
Anthraquinone pigment. These colorants can be used individually or
in combination.
[0105] An amount of the colorant contained in the base material
resin may be equal to or greater than 0.001 parts by weight and
equal to or less than 10 parts by weight, such as equal to or
greater than 0.01 parts by weight and equal to or less than 8 parts
by weight with respect to 100 parts by weight of the polypropylene
resin A and the polypropylene resin B combined. In a case where
blackening is intended with the use of carbon black, in particular,
the carbon black may be equal to or greater than 1 part by weight
and equal to or less than 10 parts by weight with respect to 100
parts by weight of the polypropylene resin A and the polypropylene
resin B combined.
[0106] In one or more embodiments of the present invention, a
melting point of the base material resin including the
polypropylene resin A and the polypropylene resin B is
approximately 130.degree. C. or higher to 165.degree. C. or lower,
based on the respective melting points of the polypropylene resin A
and of the polypropylene resin B. In view of allowing a molding
temperature during in-mold foaming molding to be easily made low
and maintaining high compressive strength of an in-mold expanded
molded product to be obtained without causing the compressive
strength to decrease, the melting point of the base material resin
may be 140.degree. C. or higher to 150.degree. C. or lower, such as
145.degree. C. or higher to 150.degree. C. or lower, such as
145.degree. C. or higher to 149.degree. C. or lower, such as
145.degree. C. or higher to 148.degree. C. or lower, or such as
146.degree. C. or higher to 148.degree. C. or lower.
[0107] Note that, as illustrated in FIG. 1, a melting point t.sub.m
of a polypropylene resin (polypropylene resin A, polypropylene
resin B, or base material resin) is a melting peak temperature in a
second temperature rise (t.sub.m in FIG. 1) in a DSC curve which is
obtained when, in differential scanning calorimetry (DSC), 1 mg or
more to 10 mg or less of polypropylene resin is (i) heated from
40.degree. C. to 220.degree. C. at a heating rate of 10.degree.
C./min., (ii) cooled from 220.degree. C. to 40.degree. C. at a
cooling rate of 10.degree. C./min., and then (iii) heated again
from 40.degree. C. to 220.degree. C. at a heating rate of
10.degree. C./min.
[0108] FIG. 1 shows an example in which a single melting peak
appears. Note, however, that in a case where a plurality of resins
are mixed, a plurality of melting peaks may appear. For example, as
described earlier, a resin other than a polypropylene resin can be
mixed in one or more embodiments of the present invention. In such
a case, if a polyethylene resin is mixed in a high-melting
polypropylene resin such as the polypropylene resin B, then not
only the single melting peak in FIG. 1 but also a melting peak (or
shoulder) based on the polyethylene resin may appear around, for
example, 130.degree. C. That is, the total of two melting peaks may
appear. In a case where a plurality of melting peaks appear in a
DSC curve in a second temperature rise, a temperature of a melting
peak having a largest heat absorption quantity may be used as a
melting point tin.
[0109] Examples of a method of mixing the polypropylene resin A and
the polypropylene resin B encompass (i) a method in which the
polypropylene resin A and the polypropylene resin B are mixed with
the use of a blender or an extruder and (ii) a method in which the
polypropylene resin A and the polypropylene resin B are blended by
multi-stage polymerization during polymerization. Note that the
method in which a blender or an extruder is used can also be used
as a method of mixing the additive in the polypropylene resin. Note
also that the additive can be directly added to the polypropylene
resin. Alternatively, it is possible to (i) prepare a masterbatch
by including, at a high concentration, the additive in another
resin and then (ii) add the masterbatch to the polypropylene
resin.
[0110] A resin to be used for production of a masterbatch may be a
polyolefin resin, such as the polypropylene resin A and/or the
polypropylene resin B, or such as a mixture of the polypropylene
resin A and the polypropylene resin B.
[0111] As described later, expanded polypropylene resin particles
may be expanded composite particles obtained by covering an
expanded polypropylene resin core layer with a polypropylene resin
covering layer because, with such expanded polypropylene resin
particles, (i) a molding temperature in a case of obtaining a
polypropylene resin in-mold expanded molded product to can be made
lower and (ii) high compressive strength of the polypropylene resin
in-mold expanded molded product can be maintained.
[0112] Among such expanded composite particles, (i) a resin of an
expanded polypropylene resin core layer is made of a base material
resin containing a polypropylene resin A and a polypropylene resin
B and (ii) a polypropylene resin covering layer is made of a
polypropylene resin A may be used. This is because, with such
expanded composite particles, (i) adhesiveness of an interface
between the expanded polypropylene resin core layer and the
polypropylene resin covering layer can increase and (ii) fusibility
of an in-mold expanded molded product can easily be good.
[0113] With conventional expanded composite particles, fusibility
between the expanded composite particles during in-mold foaming
molding is increased. However, the conventional expanded composite
particles tend to cause adhesiveness of an interface between an
expanded polypropylene resin core layer and a polypropylene resin
covering layer to be weak. In one or more embodiments of the
present invention, adhesiveness of an interface between an expanded
polypropylene resin core layer and a polypropylene resin covering
layer tends to improve.
[0114] Such a characteristic is assumed to be derived from the
following considerations: (i) Since a polypropylene resin A
included in the expanded polypropylene resin core layer and a
polypropylene resin A included in the polypropylene resin covering
layer are identical polypropylene resins, adhesive strength of an
interface between the expanded polypropylene resin core layer and
the polypropylene resin covering layer becomes strong; and (ii)
Since the polypropylene resin covering layer is made of a
low-melting polypropylene resin A, expanded composite particles can
be fused to each other at a lower molding temperature.
[0115] In production of expanded polypropylene resin particles in
accordance with one or more embodiments of the present invention, a
step (granulation step) of producing polypropylene resin particles,
which are made of a base material resin, can be first carried
out.
[0116] Examples of the method of producing polypropylene resin
particles encompass a method in which an extruder is used.
Specifically, it is possible, for example, that (i) a polypropylene
resin A, a polypropylene resin B, and, as necessary, an additive
(e.g. another resin, an expansion nucleating agent, a hydrophilic
compound, and a colorant) are blended, so that a blended product is
obtained, (ii) the blended product is introduced into an extruder
and is melted and kneaded, (iii) a resultant product is extruded
through a die provided at a tip of the extruder, and is then
allowed to pass through water so as to be cooled, and (iv) the
resultant product is chopped with the use of a cutter, so that
polypropylene resin particles each having a desired shape, such as
a columnar shape, an ellipsoidal shape, a spherical shape, a cubic
shape, and a rectangular parallelepiped shape, are obtained.
Alternatively, it is possible to (i) directly extrude the resultant
product through the die into water, and immediately cut the
resultant product into a particle shape, so that particles are
obtained, and then (ii) cool the particles. By thus melting and
kneading the resins, the resins are made into a more uniform base
material resin. Alternatively, it is possible to (i) introduce the
polypropylene resin A and the polypropylene resin B into an
extruder, (ii) as necessary, feed an additive (e.g. an expansion
nucleating agent a hydrophilic compound, a colorant) from a middle
part of the extruder so as to be mixed in the extruder, and (iii)
melt and knead a resultant mixture in the extruder.
[0117] A weight of each of the polypropylene resin particles thus
obtained may be 0.2 mg per particle or more to 10 mg per particle
or less, such as 0.5 mg per particle or more to 5 mg per particle
or less. If the weight of each of the polypropylene resin particles
is less than 0.2 mg per particle, then handleability tends to
decrease. If the weight is more than 10 mg per particle, then a
mold-filling property during an in-mold foaming molding step tends
to decrease.
[0118] The expanded polypropylene resin particles in accordance
with one or more embodiments of the present invention may be
expanded composite particles obtained by covering an expanded
polypropylene resin core layer with a polypropylene resin covering
layer. Examples of a method of producing the expanded polypropylene
resin particles encompass a method in which composite resin
particles are first produced, the composite resin particles
including a non-expanded polypropylene resin core layer and a
non-expanded polypropylene resin covering layer. Examples of a
method of producing such composite resin particles encompass a
method in which a die provided at a tip of an extruder is a
core-sheath coextrusion die such as those disclosed in Japanese
Examined Patent Application Publication, Tokukosho, No. 41-16125,
Japanese Examined Patent Application Publication, Tokukosho, No.
43-23858, Japanese Examined Patent Application Publication,
Tokukosho, No. 44-29522, Japanese Patent Application Publication,
Tokukaisho, No. 60-185816, and the like.
[0119] In such a case, two extruders are used such that (i) a
polypropylene resin for forming a polypropylene resin core layer is
melted and kneaded in one of the two extruders, (ii) a
polypropylene resin for constituting a polypropylene resin covering
layer is melted and kneaded in the other one of the two extruders,
(iii) molten resins thus obtained are introduced into a coextrusion
die which is connected to the two extruders, and (iv) a sheath-core
composite, which includes the polypropylene resin core layer and
the polypropylene resin covering layer, is discharged in a strand
shape. After the discharged substance in a strand shape is cooled
by, for example, being allowed to pass through water, the
discharged substance is cut so as to have a certain weight or size
by use of a cutting machine including a drawing machine. This makes
it possible to obtain composite resin particles each including a
polypropylene resin core layer and a polypropylene resin covering
layer. Alternatively, it is possible to (i) directly extrude the
discharged substance in a strand shape through the die into water,
and immediately cut the discharged substance into a particle shape,
so that particles are obtained, and then (ii) cool the
particles.
[0120] A polypropylene resin covering layer which is less in
thickness causes foaming of a polypropylene resin covering layer to
be less likely to occur during foaming of composite resin
particles. However, a polypropylene resin covering layer is
excessively thin, then sufficient covering is difficult. Therefore,
a thickness of a polypropylene resin covering layer before being
produced into expanded polypropylene resin particles (expanded
composite particles) may be 0.1 .mu.m or more to 300 .mu.m or less,
and a thickness of a polypropylene resin covering layer after being
produced into the expanded polypropylene resin particles (expanded
composite particles) may be 0.1 .mu.m or more to 250 .mu.m or
less.
[0121] A weight ratio between the polypropylene resin core layer
and the polypropylene resin covering layer may be 99.5:0.5 to
65:35, such as 99:1 to 70:30, or such as 97:3 to 80:20. The weight
ratio between the polypropylene resin core layer and the
polypropylene resin covering layer can be adjusted by adjusting
respective discharge quantities the two extruders.
[0122] Note that it may be possible that (i) an expansion
nucleating agent, a hydrophilic compound, and/or an antioxidant,
for example, is/are added to the polypropylene resin for forming a
polypropylene resin core layer and (ii) an antistatic agent, a
flame retarder, and/or an electrically conductive agent, for
example, is/are added to the polypropylene resin for constituting a
polypropylene resin covering layer. However, one or more
embodiments of the present invention is not limited to such a
configuration, and such additives can be adjusted as
appropriate.
[0123] Expanded polypropylene resin particles may be produced with
the use of polypropylene resin particles (or composite resin
particles) thus obtained.
[0124] Examples of a method of producing the expanded polypropylene
resin particles in accordance with one or more embodiments of the
present invention encompass a method of producing expanded
polypropylene resin particles in an aqueous dispersion system by
carrying out the following foaming step: (i) polypropylene resin
particles along with a foaming agent such as carbon dioxide are
dispersed into an aqueous dispersion medium in a pressure-resistant
container, (ii) a resultant dispersion liquid is heated to a
temperature equal to or higher than a softening temperature of the
polypropylene resin particles and is subjected to pressure, (iii)
the temperature and the pressure are retained for a certain period
of time, (iv) the dispersion liquid is released to a region having
a pressure lower than an internal pressure of the
pressure-resistant container, so that the expanded polypropylene
resin particles are obtained.
[0125] Specifically,
(1) Polypropylene resin particles, an aqueous dispersion medium,
and, as necessary, a dispersing agent, for example, are placed into
the pressure-resistant container. Then, while a resultant mixture
is stirred, the inside of the pressure-resistant container is
vacuumed as necessary. Then, a foaming agent having a pressure of 1
MPa (gage pressure) or more to 2 MPa (gage pressure) or less is
introduced, and then the mixture is heated to a temperature equal
to or higher than the softening temperature of the polypropylene
resin. By the heating, the internal pressure of the
pressure-resistant container rises to approximately 2 MPa (gage
pressure) or more to 5 MPa (gage pressure) or less. The expanded
polypropylene resin particles can also be obtained by (i) further
adding, as necessary, a foaming agent around a foaming temperature
to adjust a foaming pressure to a desired pressure, (ii) further
adjusting a temperature, (iii) retaining adjusted temperature and
the adjusted pressure for a certain period of time, (iv) releasing,
into a region having a pressure lower than the internal pressure of
the pressure-resistant container, the dispersion liquid in the
pressure-resistant container.
[0126] As another embodiment disclosed herein, the following aspect
is possible: (2) Polypropylene resin particles, an aqueous
dispersion medium, and, as necessary, a dispersing agent, for
example, are placed into the pressure-resistant container. Then,
while a resultant mixture is stirred, the inside of the
pressure-resistant container is vacuumed as necessary. Then, while
the mixture is heated to a temperature equal to or higher than the
softening temperature of the polypropylene resin, a foaming agent
is introduced into the dispersion liquid in the pressure-resistant
container.
[0127] As yet another embodiment disclosed herein, the following
aspect is possible: (3) Polypropylene resin particles, an aqueous
dispersion medium, and, as necessary, a dispersing agent, for
example, are placed into the pressure-resistant container. Then, a
resultant mixture is heated to a temperature around a foaming
temperature. Then, a foaming agent is further introduced into the
dispersion liquid in the pressure-resistant container, and a
resultant mixture is at foaming temperature. Then, the foaming
temperature is retained for a certain period of time. Then, the
dispersion liquid in the pressure-resistant container is released
into a region having a pressure lower than an internal pressure of
the pressure-resistant container, so that expanded polyolefin resin
particles are obtained.
[0128] Note that the expansion ratio can be adjusted by (i)
adjusting a pressure-releasing speed during foaming by increasing
the internal pressure of the pressure-resistant container through
injecting carbon dioxide, nitrogen, air, or a substance used as a
foaming agent, into the pressure-resistant container before the
dispersion liquid in the pressure-resistant container is released
into the low-pressure region and (ii) controlling the pressure
through introducing carbon dioxide, nitrogen, air, or a substance
used as a foaming agent, into the pressure-resistant container also
while the dispersion liquid in the pressure-resistant container is
being released into the low-pressure region.
[0129] In one or more embodiments of the present invention, the
pressure-resistant container into which the polypropylene resin
particles are dispersed is not limited to any particular one,
provided that the pressure-resistant container is capable of
resisting a pressure and temperature inside the container during
production of the expanded particles. Examples of the
pressure-resistant container encompass an autoclave-type
pressure-resistant container.
[0130] An aqueous dispersion medium for use in one or more
embodiments of the present invention may be water. Alternatively,
the aqueous dispersion medium can also be a dispersion medium
obtained by adding methanol, ethanol, ethylene glycol, glycerin, or
the like to water. In a case where the base material resin contains
a hydrophilic compound, water in the aqueous dispersion medium
serves also as a foaming agent. This contributes to an increase in
expansion ratio.
[0131] Examples of the foaming agent for use in one or more
embodiments of the present invention encompass: saturated
hydrocarbons such as propane, butane, and pentane; ethers such as
dimethyl ether, alcohols such as methanol and ethanol; and
inorganic gas such as air, nitrogen, carbon dioxide, and water.
Among these foaming agents, an inorganic gas foaming agent has
particularly small environmental impact and has no dangerous
inflammability, and is therefore may be used. It may also be
possible to use at least one foaming agent selected from the group
consisting of carbon dioxide and water.
[0132] In one or more embodiments of the present invention, it may
be possible to use a dispersing agent and/or a dispersion auxiliary
agent in order to prevent polypropylene resin particles in an
aqueous dispersion medium from adhering to each other.
[0133] Examples of the dispersing agent encompass inorganic
dispersion agents such as tertiary calcium phosphate, tertiary
magnesium phosphate, basic magnesium carbonate, calcium carbonate,
barium sulfate, kaolin, talc, and clay. These inorganic dispersion
agents can be used individually, or two or more of these inorganic
dispersion agents can be used in combination.
[0134] Examples of the dispersion auxiliary agent encompass: (i)
anionic surfactants of carboxylate type, (ii) anionic surfactants
of sulfonate type such as alkylsulfonic acid salt, n-paraffin
sulfonate salt, alkyl benzene sulfonate, alkyl naphthalene
sulfonate, and sulfosuccinate, (iii) anionic surfactants of sulfate
ester type such as sulfonated oil, alkyl sulfate salt, alkyl ether
sulfate, and alkyl amide sulfate, and (iv) anionic surfactants of
phosphate ester type such as alkyl phosphate, polyoxyethylene
phosphate, and alkyl allyl ether sulfate. These dispersion
auxiliary agents can be used individually or two or more of these
dispersion auxiliary agents can be used in combination.
[0135] Of these, the following may be used in combination: (i) at
least one dispersing agent selected from the group consisting of
tertiary calcium phosphate, tertiary magnesium phosphate, barium
sulfate, and kaolin; and (ii) a dispersion auxiliary agent which is
n-paraffin sulfonic acid soda.
[0136] It may be possible to use an aqueous dispersion medium in an
amount of equal to or greater than 100 parts by weight and equal to
or less than 500 parts by weight with respect to 100 parts by
weight of polypropylene resin particles so that dispensability of
the polypropylene resin particles in the aqueous dispersion medium
is good. The respective amounts of dispersing agent and dispersion
auxiliary agent vary, depending on (i) the types of the dispersing
agent and the dispersion auxiliary agent and (ii) the type of and
amount of polypropylene resin particles used. Ordinarily, with
respect to 100 parts by weight of polypropylene resin particles,
the dispersing agent may be used in an amount of 0.2 parts by
weight or more to 3 parts by weight or less, and the dispersion
auxiliary agent may be used in an amount of 0.001 parts by weight
or more to 0.1 parts by weight or less.
[0137] The step of thus obtaining expanded polypropylene resin
particles from polypropylene resin particles may be referred to as
"first-stage foaming step", and the expanded polypropylene resin
particles thus obtained may be referred to as "first-stage expanded
particles".
[0138] An expansion ratio of first-stage expanded particles may not
reach 10 times, depending on foaming conditions such as foaming
temperature, foaming pressure, and the type of foaming agent. In
such a case, expanded polypropylene resin particles whose expansion
ratio is increased in comparison with that of first-stage expanded
particles can be obtained by (i) applying an internal pressure to
the first-stage expanded particles by impregnation of inorganic gas
(e.g. air, nitrogen, carbon dioxide) and then (ii) causing the
first-stage expanded particles to come into contact with steam
having a certain pressure.
[0139] The step of thus further foaming the expanded polypropylene
resin particles so as to obtain expanded polypropylene resin
particles having a high expansion ratio may be referred to as
"second-stage foaming step". Expanded polypropylene resin particles
thus obtained through the second-stage foaming step may be referred
to as "second-stage expanded particles".
[0140] A pressure of steam in the second-stage foaming step may be
adjusted 0.04 MPa (gage pressure) or more to 0.25 MPa (gage
pressure) or less, such as 0.05 MPa (gage pressure) or more to 0.15
MPa (gage pressure) or less, in view of the expansion ratio of the
second-stage expanded particles.
[0141] If the pressure of steam in the second-stage foaming step is
less than 0.04 MPa (gage pressure), then the expansion ratio is
less likely to increase. If the pressure is more than 0.25 MPa
(gage pressure), then second-stage expanded particles to be
obtained tend to adhere to each other, so that it becomes
impossible to use the second-stage expanded particles for
subsequent in-mold foaming molding.
[0142] An internal pressure of air to be impregnated into the
first-stage expanded particles may be (i) made to change as
appropriate in view of (a) the expansion ratio of the second-stage
expanded particles and (b) steam pressure in the second-stage
foaming step and (ii) 0.2 MPa or more (absolute pressure) or more
to 0.6 MPa or less (absolute pressure).
[0143] If the internal pressure of air to be impregnated into the
first-stage expanded particles is less than 0.2 MPa (absolute
pressure), then steam having a high pressure is necessary to
increase the expansion ratio, so that the second-stage expanded
particles tend to adhere to each other. If the internal pressure of
air to be impregnated into the first-stage expanded particles is
more than 0.6 MPa (absolute pressure), then the second-stage
expanded particles tend to become an open-cell foam. In such a
case, rigidity, such as compressive strength, of an in-mold
expanded molded product tends to decrease.
[0144] The expansion ratio of the expanded polypropylene resin
particles is not particularly limited, and may be 5 times or more
to 60 times or less. If the expansion ratio of the expanded
polypropylene resin particles is less than 5 times, then reductions
in weights of expanded polypropylene resin particles and of a
polypropylene resin in-mold expanded molded product tend to be
insufficient. If the expansion ratio of the expanded polypropylene
resin particles is more than 60 times, then mechanical strengths of
expanded polypropylene resin particles and of a polypropylene resin
in-mold expanded molded product tend to be impractical.
[0145] An average cell diameter of the expanded polypropylene resin
particles may be 100 .mu.m or more to 340 .mu.m or less, such as
110 .mu.m or more to 330 .mu.m or less, or such as 120 .mu.m or
more to 250 .mu.m or less. If the average cell diameter falls
within these ranges, then the polypropylene resin in-mold expanded
molded product tends to (i) have a good surface appearance and (ii)
have a high compressive strength.
[0146] Note that the average cell diameter of the expanded
polypropylene resin particles can be controlled by adjusting the
amount of an expansion nucleating agent to add. Alternatively, the
average cell diameter can be controlled by, for example, adjusting
a high-temperature heat quantity ratio described later. If the
high-temperature heat quantity ratio is less than 15%, then the
average cell diameter tends to become large. If the
high-temperature heat quantity ratio is more than 50%, then the
average cell diameter tends to become small.
[0147] In a DSC curve which is obtained by differential scanning
calorimetry (DSC) in which a temperature of the expanded
polypropylene resin particles is raised at a heating rate of
10.degree. C./min., as illustrated in FIG. 2, expanded
polypropylene resin particles have (i) at least two melting peaks
and (ii) at least two melting heat quantities of a low
temperature-side melting heat quantity (Ql) and a high
temperature-side melting heat quantity (Qh).
[0148] As described earlier, a resin other than a polypropylene
resin can be mixed. In such a case, if a polyethylene resin is
mixed, then not only the two melting peaks in FIG. 2 but a melting
peak (or shoulder) based on the polyethylene resin may appear in a
DSC curve obtained. That is, the total of three melting peaks may
appear in the DSC curve.
[0149] Expanded polypropylene resin particles having at least two
melting peaks can be easily obtained by, in the earlier-described
method of producing expanded polypropylene resin particles in an
aqueous dispersion system, (i) controlling, as appropriate, a
temperature in the pressure-resistant container during foaming to a
proper value and (ii) retaining the temperature for a certain
period of time. That is, in a case where a melting point of a
polypropylene resin (base material resin) is t.sub.m (.degree. C.),
the temperature in the pressure-resistant container during foaming
may be t.sub.m-8 (.degree. C.) or higher, such as t.sub.m-5
(.degree. C.) or high and t.sub.m+4 (.degree. C.) or lower, or such
as t.sub.m-5 (.degree. C.) or higher and t.sub.m+3 (.degree. C.) or
lower.
[0150] A period of time during which the polypropylene resin
particles are retained at the temperature controlled in the
pressure-resistant container during foaming may be 1 min. or more
to 120 min. or less, such as 5 min. or more to 60 min. or less.
[0151] In one or more embodiments of the present invention, an
entire melting heat quantity (Q), a low temperature-side melting
heat quantity (Ql), and a high temperature-side melting heat
quantity (Qh) of expanded polypropylene resin particles are defined
as follows by use of FIG. 2. In the DSC obtained (FIG. 2), the
entire melting heat quantity (Q=Ql+Qh), which is the sum of the low
temperature-side melting heat quantity (Ql) and the high
temperature-side melting heat quantity (Qh), is indicated by a part
surrounded by a (i) line segment A-B which is drawn so as to
connect a heat absorption quantity (point A) at temperature
80.degree. C. and a heat absorption quantity (point B) at a
temperature at which melting on a high temperature side ends and
(ii) the DSC curve.
[0152] The low temperature-side melting heat quantity (Ql) is
indicated by a part surrounded by a line segment A-D, a line
segment C-D, and the DSC curve, and the high temperature-side
melting heat quantity (Qh) is indicated by a part surrounded by a
line segment B-D, the line segment C-D, and the DSC curve where (i)
a point C is a point at which a heat absorption quantity between
two melting heat quantity regions in the DSC curve is the smallest,
the two melting heat quantity regions being a region of the low
temperature-side melting heat quantity and a region of the high
temperature-side melting heat quantity and (ii) a point D is a
point at which the line segment A-B intersects a line that is drawn
so as to extend, parallel to a Y-axis (axis indicating the heat
absorption quantity), from the point C toward the line segment A-B.
Note that in a case where three melting peaks appear, there appear
two points at which the heat absorption quantity is the smallest
between two adjacent melting heat quantity regions. In such a case,
out of the two points, the point on the high-temperature side is
regarded as the point C.
[0153] The expanded polypropylene resin particles may haves a ratio
of the high temperature-side melting heat quantity (Qh) to the
entire melting heat quantity [={Qh/(Q-Qh)}.times.100(%)]
(hereinafter also referred to as "high-temperature heat quantity
ratio"), which ratio may be 15% or more to 50% or less, such as 15%
or more to 40% or less, or such as 20% or more to 30% or less. In a
case where the high-temperature heat quantity ratio falls within
these ranges, even if a molding temperature (steam pressure) during
production of a polypropylene resin in-mold expanded molded product
is low, it is still easy to obtain a polypropylene resin in-mold
expanded molded product which (i) has a good surface appearance,
(ii) has a high compressive strength, and (iii) has good
fusibility.
[0154] The high-temperature heat quantity ratio of the expanded
polypropylene resin particles can be adjusted as appropriate by,
for example, (i) a retention time at the temperature in the
pressure-resistant container (i.e. a retention time that (a) starts
from a time point at which the polypropylene resin particles reach
a desired temperature in the pressure-resistant container and (b)
ends at time point at which the polypropylene resin particles foam,
(ii) a foaming temperature (which is a temperature during foaming
and which may or may not be identical to the temperature in the
pressure-resistant container), and (iii) foaming pressure (pressure
during foaming). In general, a high-temperature heat quantity ratio
or a heat quantity at the high temperature-side melting peak tends
to become large by extending a retention time, decreasing a foaming
temperature, or decreasing foaming pressure. Because of these
factors, conditions to obtain a desired high-temperature heat
quantity ratio can be easily found by conducting several
experiments in which a retention time, a foaming temperature, or a
foaming pressure is systematically changed. Note that the foaming
pressure can be adjusted by adjusting the amount of a foaming
agent.
[0155] PCT International Publication No. WO2009/001626 discloses an
expanded polypropylene resin particle which has such a crystal
structure that a DSC curve, which is obtained in a first
temperature rise when a temperature of an expanded polypropylene
resin particle is raised from room temperature to 200.degree. C. at
a heating rate of 2.degree. C./min. in heat flux differential
scanning calorimetry, shows (i) a main endothermic peak of
100.degree. C. to 140.degree. C. endothermic peak apex temperature
exhibiting 70% to 95% endothermic peak heat quantity with respect
to an entire endothermic peak heat quantity and (ii) two or more
endothermic peaks appearing on a high-temperature side with respect
to the main endothermic peak.
[0156] In terms used in PCT International Publication No.
WO2009/001626, the expanded polypropylene resin particles are not
limited to any number of endothermic peaks on a high-temperature
side with respect to a main endothermic peak in heat flux
differential scanning calorimetry at a heating rate of 2.degree.
C./min., but may have such a crystal structure that one endothermic
peak appears.
[0157] The expanded polypropylene resin particles having such a
crystal structure that one endothermic peak appears can be easily
obtained by use of a base material resin including (i) a
polypropylene resin A having a melting point of 130.degree. C. or
higher to 140.degree. C. or lower and (ii) a polypropylene resin B
having a melting point higher than that of the polypropylene resin
A by less than 25.degree. C.
[0158] The expanded polypropylene resin particles having such a
crystal structure that one endothermic peak may appear because,
with such expanded polypropylene resin particles, (i) compatibility
between both resins (polypropylene resin A and polypropylene resin
B) when melted and kneaded is good, (ii) a variance in cell
diameter of expanded polypropylene resin particles becomes small,
and (iii) an in-mold expanded molded product has a good surface
appearance.
[0159] The expanded polypropylene resin particles may be made into
a polypropylene resin in-mold expanded molded product by a
conventionally known in-mold foaming molding method.
[0160] Examples of an in-mold foaming molding method encompass:
[0161] i) a method of (a) subjecting expanded polypropylene resin
particles to a pressure treatment with the use of inorganic gas
(e.g. air, nitrogen, carbon dioxide) so that the expanded
polypropylene resin particles, into which the inorganic gas is
impregnated, has a certain internal pressure and (b) filling a mold
with the expanded polypropylene resin particles, and (c) heating
the mold by steam so that the expanded polypropylene resin
particles are fused to each other.
[0162] ii) a method of (a) compressing expanded polypropylene resin
particles by gas pressure, (b) filling a mold with the expanded
polypropylene resin particles, and (c) heating the mold by steam so
that the expanded polypropylene resin particles are fused to each
other by the effect of resilience of the expanded polypropylene
resin particles.
[0163] iii) a method of (a) filling a mold with expanded
polypropylene resin particles without any particular pretreatment
and (b) heating the mold by steam so that the expanded
polypropylene resin particles are fused to each other.
[0164] The polypropylene resin in-mold expanded molded product may
be obtained as a high-compressive-strength polypropylene resin
in-mold expanded molded product by subjecting expanded
polypropylene resin particles to in-mold foaming molding while a
molding temperature (steam pressure) is reduced. The polypropylene
resin in-mold expanded molded product may be used in that a
relationship particularly between a density of the molded product
and a 50%-strained compressive strength satisfies the following
Formula (1):
[50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Density (g/L) of molded product]+0.018
(1)
[0165] Specifically, polypropylene resin in-mold expanded molded
products satisfying Formula (1) have conventionally been used as
highly strong polypropylene resin in-mold expanded molded products
for automobile interior materials and automobile bumper core
materials. However, such conventional polypropylene resin in-mold
expanded molded products require a high molding temperature during
in-mold foaming molding. For example, during in-mold foaming
molding in which steam is used, such a high steam pressure as 0.24
MPa (gage pressure) or more was necessary. However, it may be
possible to produce a polypropylene resin in-mold expanded molded
product satisfying Formula (1) even with such a low steam pressure
as 0.22 MPa (gage pressure) or less.
[0166] The polypropylene resin in-mold expanded molded product in
accordance with one or more embodiments of the present invention is
not limited to any particular density. With the conventional
technologies, a decrease in compressive strength in a case where
molding is possible with a low steam pressure (molding temperature)
tends to be remarkable in a case where a density of molded product
is 40 g/L or less. In view of this, the density of the molded
product may be 40 g/L or less. The density of the molded product
may be 20 g/L or more to 40 g/L or less, such as 20 g/L or more to
35 g/L or less.
[0167] A polypropylene resin in-mold expanded molded product thus
obtained can be put to various applications such as heat insulating
materials, shock-absorbing packing materials, and returnable
containers in addition to automobile interior materials and
automobile bumper core materials.
[0168] In particular, the polypropylene resin in-mold expanded
molded product may be used for automobile materials such as
automobile interior materials and automobile bumper core materials
because such automobile materials obtained from the polypropylene
resin in-mold expanded molded product, which can be molded with a
lower molding temperature (steam pressure), exhibit a compressive
strength similar to those obtained from conventional molded
products molded with a high molding temperature (steam
pressure).
[0169] One or more embodiments of the present invention may be
configured as follows:
[0170] [1] A polypropylene resin in-mold expanded molded product
obtained by subjecting, to in-mold foaming molding, expanded
polypropylene resin particles obtained from a base material resin
which includes (i) a polypropylene resin A satisfying the following
condition (a) and having a melting point of 130.degree. C. or
higher to 140.degree. C. or lower and (ii) a polypropylene resin B
having a melting point of 145.degree. C. or higher to 165.degree.
C. or lower:
(a) a structural unit of 1-butene is present in an amount of 3
weight % or more to 15 weight % or less with respect to 100 weight
% entire structural units.
[0171] [2] The polypropylene resin in-mold expanded molded product
as set forth in [1], configured such that the polypropylene resin A
satisfies the following condition (b): (b) a structural unit of
ethylene is present in amount of 2 weight % or more to 10 weight %
or less with respect to 100 weight % entire structural units.
[0172] [3] The polypropylene resin in-mold expanded molded product
as set forth in [1] or [2], configured such that: the base material
resin includes the polypropylene resin A in an amount of 50 weight
% or more to 70 weight % or less and the polypropylene resin B in
an amount of 30 weight % or more to 50 weight % or less; and the
polypropylene resin A and the polypropylene resin B together
account for 100 weight %.
[0173] [4] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [3], configured such that
the melting point of the base material resin is 140.degree. C. or
higher to 150.degree. C. or lower.
[0174] [5] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [4], configured such that
the melting point of the base material resin is 146.degree. C. or
higher to 148.degree. C. or lower.
[0175] [6] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [5], configured such that
the polypropylene resin B is a propylene-ethylene random copolymer
or a propylene-ethylene-1-butene random copolymer.
[0176] [7] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [6], configured such that
the polypropylene resin A is obtained with use of a Ziegler
catalyst.
[0177] [8] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [7], configured such
that:
[0178] the expanded polypropylene resin particles are each an
expanded composite particle in which an expanded polypropylene
resin core layer is covered with a polypropylene resin covering
layer
[0179] the expanded polypropylene resin core layer is obtained from
a base material resin including [0180] a polypropylene resin A and
[0181] a polypropylene resin B;
[0182] the polypropylene resin covering layer includes the
polypropylene resin A.
[0183] [9] The polypropylene resin in-mold expanded molded product
as set forth in any one of [1] through [8], configured such that
the polypropylene resin in-mold expanded molded product has a
density of 20 g/L or more to 40 g/L or less.
[0184] [10] A method of producing a polypropylene resin in-mold
expanded molded product, including the steps of:
[0185] (A) obtaining expanded polypropylene resin particles by
[0186] (i) placing polypropylene resin particles, water, and an
inorganic gas foaming agent in a pressure-resistant container, so
that a mixture is obtained, the polypropylene resin particles
having been obtained from a base material resin including [0187] a
polypropylene resin A satisfying the following condition (a) and
having a melting point of 130.degree. C. or higher to 140.degree.
C. or lower and [0188] a polypropylene resin B having a melting
point of 145.degree. C. or higher to 165.degree. C. or lower,
[0189] (ii) dispersing the polypropylene resin particles while the
mixture is stirred, so that a dispersion liquid is obtained, [0190]
(iii) increasing a temperature and a pressure, and then [0191] (iv)
releasing the dispersion liquid from the pressure-resistant
container into a region having a pressure lower than an internal
pressure of the pressure-resistant container, so that the
polypropylene resin particles are foamed; and
[0192] (B) obtaining the in-mold expanded molded product by [0193]
(i) filling a mold with the expanded polypropylene resin particles,
and then [0194] (ii) heating the expanded polypropylene resin
particles: (a) a structural unit of 1-butene is present in an
amount of 3 weight % or more to 15 weight % or less with respect to
100 weight % entire structural units.
[0195] [11] The method as set forth in [10], configured such that
the polypropylene resin A satisfies the following condition
(b):
(b) a structural unit of ethylene is present in amount of 2 weight
% or more to 10 weight % or less with respect to 100 weight %
entire structural units.
[0196] [12] The method as set forth in [10] or [11], further
including the step of, melting and kneading the polypropylene resin
A and the polypropylene resin B in an extruder and then obtaining
polypropylene resin particles.
[0197] [13] The method as set forth in any one of [10] through
[12], further including the step of: obtaining the polypropylene
resin A by carrying out polymerization with use of a Ziegler
catalyst.
[0198] [14] The method as set forth in any one of [10] through
[13], configured such that:
[0199] the expanded polypropylene resin particles are each an
expanded composite particle in which an expanded polypropylene
resin core layer is covered with a polypropylene resin covering
layer.
[0200] the expanded polypropylene resin core layer is obtained from
a base material resin including [0201] the polypropylene resin A
and [0202] the polypropylene resin B; and
[0203] the polypropylene resin covering layer includes the
polypropylene resin A.
EXAMPLES
[0204] The following description will discuss one or more
embodiments of the present invention in more detail with Examples
and Comparative Examples. Note, however, that the embodiments
disclosed are not limited to these Examples and Comparative
Examples.
[0205] [Polypropylene Resin]
[0206] Table 1 shows polypropylene resins A-1 through A-8,
polypropylene resins B-1 through B-5, and a polypropylene resin C
which were used. Note that a Polypropylene resin B-4 is a propylene
homopolymer, whereas the other polypropylene resins are random
copolymers.
TABLE-US-00001 TABLE 1 Comonomer content (weight %) MFR Type of
catalyst 1-butene Ethylene Melting point (.degree. C.) (g/10 min.)
Polypropylene resin A-1 Ziegler 4.3 2.9 134 7 Polypropylene resin
A-2 Ziegler 7.0 2.5 132 8 Polypropylene resin A-3 Ziegler 8.6 4.3
134 8 Polypropylene resin A-4 Ziegler 9.5 5.1 136 7 Polypropylene
resin A-5 Metallocene 4.5 0.5 136 9 Polypropylene resin A-6 Ziegler
1.9 5.1 132 8 Polypropylene resin A-7 Ziegler 16.2 -- 136 9
Polypropylene resin A-8 Ziegler -- 4.1 139 7 Polypropylene resin
B-1 Ziegler -- 2.5 152 7 Polypropylene resin B-2 Ziegler -- 3.1 151
7 Polypropylene resin B-3 Ziegler 1.9 4.3 145 7 Polypropylene resin
B-4 Ziegler -- -- 164 5 Polypropylene resin B-5 Ziegler -- 3.3 144
8 Polypropylene resin C Metallocene -- 2.8 125 7
[0207] Polypropylene resin B-4 is a propylene homopolymer, and the
other polypropylene resin is a random copolymer.
[0208] <Other Additives>
[0209] Talc: manufactured by Hayashi-Kasei Co., Ltd., Talcan Powder
PK-S
[0210] Polyethylene glycol: manufactured by Lion Corporation,
PEG#300
[0211] Carbon black: manufactured by Mitsubishi Chemical
Corporation, MCF88 (average particle size: 18 nm)
[0212] In Examples and Comparative Examples, evaluations were made
by the following methods:
[0213] (Quantification of Copolymer Composition)
[0214] A polypropylene resin having a known comonomer content was
hot pressed at 180.degree. C., so that a film having a thickness of
approximately 100 .mu.m was produced. The film thus produced was
subjected to IR spectrum measurement so that a propylene-derived
absorbance (I.sub.810) at 810 cm.sup.-1, an ethylene
comonomer-derived absorbance (I.sub.733) at 733 cm.sup.-1, and a
butene comonomer-derived absorbance (I.sub.766) at 766 cm.sup.-1
were read. Then, an absorbance ratio (I.sub.733/I.sub.810) is shown
in a horizontal axis, and an ethylene comonomer content is shown in
a vertical axis, so that a calibration curve indicative of the
ethylene comonomer content was obtained. Likewise, an absorbance
ratio (I.sub.766/I.sub.810) is shown in a horizontal axis, and a
butene comonomer content is shown in a vertical axis, so that a
calibration curve indicative of the butene comonomer content was
obtained. Then, as with the method of preparing a sample during
production of the calibration curves, (i) a polypropylene resin
having an unknown comonomer content was hot pressed, so that a film
having a thickness of approximately 100 .mu.m was produced, (ii)
I.sub.810, I.sub.733, and I.sub.766 were read by IR spectrum
measurement, and (iii) an ethylene comonomer content and a butene
comonomer content were calculated according to the calibration
curves produced earlier.
[0215] (Measurement of Melting Point t.sub.m of Polypropylene Resin
or Base Material Resin)
[0216] A melting point t.sub.m of the polypropylene resin was
measured with the use of a differential scanning calorimeter DSC
(manufactured by Seiko Instruments Inc., model: DSC6200).
Specifically, the melting point t.sub.m was found as a melting peak
temperature in a second temperature rise on a DSC curve obtained by
(i) raising a temperature of 5 mg to 6 mg of the polypropylene
resin (polypropylene resin particles) from 40.degree. C. to
220.degree. C. at a heating rate of 10.degree. C./min. so as to
melt the polypropylene resin, (ii) lowering the temperature from
220.degree. C. to 40.degree. C. at a cooling rate of 10.degree.
C./min. so as to crystallize the polypropylene resin (polypropylene
resin particles), and then (iii) raising the temperature again from
40.degree. C. to 220.degree. C. at a heating rate of 10.degree.
C./min. (see tm1 in FIG. 1). Note that in a case where two melting
peaks appear in the DSC curve of the second temperature rise, a
temperature of a melting peak having a larger heat absorption
quantity was used as a t.sub.m.
[0217] (Expansion Ratio of Expanded Polypropylene Resin
Particles)
[0218] Approximately 3 g or more to 10 g or less of the expanded
polypropylene resin particles obtained was used. Then, the expanded
polypropylene resin particles were dried at 60.degree. C. for 6
hours, and were then subjected to conditioning indoors at
23.degree. C. and at a humidity of 50%. Then, after a weight w(g)
of the expanded polypropylene resin particles was measured, a
volume v(cm.sup.3) of the expanded polypropylene resin particles
was measured by an immersing the resultant particles, so that an
absolute specific gravity (.rho.b=w/v) of the expanded particles
was obtained. Then, based on a ratio of the absolute specific
gravity to a density (.rho.r) of the polypropylene resin particles
before foaming, an expansion ratio (K=.rho.r/.rho.b) was
calculated. Note that in each of Examples and Comparative Examples,
the density (pr) of the polypropylene resin particles before
foaming (polypropylene resin particles) was 0.9 g/cm.sup.3.
[0219] (Average Cell Diameter of Expanded Polypropylene Resin
Particle)
[0220] While caution was exercised so that a foam membrane (cell
membrane) in an expanded polypropylene resin particle obtained
would not be destroyed, the expanded particle was cut substantially
through a center part, and then a cross section was observed with
the use of a microscope (manufactured by Keyence Corporation: VHX
digital microscope). A line segment, a length of which corresponds
to 1000 .mu.m, was drawn on an entire portion of a photograph
captured by the microscope for observation except a portion of a
surface layer of the expanded particle. Then, the number (n) of
cells on which the line segment passes was counted, so that a cell
diameter was calculated in 1000/n (.mu.m). Such operations were
carried out for 10 expanded particles, and an average value of
respective cell diameters of cells calculated in the 10 operations
was regarded as an average cell diameter of the expanded
polypropylene resin particles.
[0221] (Calculation of High-Temperature Heat Quantity Ratio of
Expanded Polypropylene Resin Particles)
[0222] A high-temperature heat quantity ratio
[={Qh/(Ql+Qh)}.times.100(%)] was calculated based on a DSC curve in
a first temperature rise (see FIG. 2) which was obtained with the
use of a differential scanning calorimeter (manufactured by Seiko
Instruments Inc., model: DSC6200) by raising a temperature of 5 mg
to 6 mg of the expanded polypropylene resin particles from
40.degree. C. to 220.degree. C. at a heating rate of 10.degree.
C./min. In the DSC obtained illustrated in FIG. 2, an entire
melting heat quantity (Q=Ql+Qh), which is the sum of a low
temperature-side melting heat quantity (Ql) and a high
temperature-side melting heat quantity (Qh), is indicated by a part
surrounded by a (i) line segment A-B which is drawn so as to
connect a heat absorption quantity (point A) at temperature
80.degree. C. and a heat absorption quantity (point B) at a
temperature at which melting on a high temperature side ends and
(ii) the DSC curve. The low temperature-side melting heat quantity
(Ql) is indicated by a part surrounded by a line segment A-D, a
line segment C-D, and the DSC curve and the high temperature-side
melting heat quantity (Qh) is indicated by a part surrounded by a
line segment B-D, the line segment C-D, and the DSC curve where (i)
a point C is a point at which a heat absorption quantity between
two melting heat quantity regions in the DSC curve is the smallest,
the two melting heat quantity regions being a region of the low
temperature-side melting heat quantity and a region of the high
temperature-side melting heat quantity and (ii) a point D is a
point at which the line segment A-B intersects a line that is drawn
so as to extend, parallel to a Y-axis (axis indicating the heat
absorption quantity), from the point C toward the line segment A-B.
Note that in a case where three melting peaks appear, there appear
two points at which the heat absorption quantity is the smallest
between two adjacent melting heat quantity regions. In such a case,
out of the two points, the point on the high-temperature side was
regarded as the point C.
[0223] (DSC Measurement of Expanded Polypropylene Resin Particles
at Heating Rate of 2.degree. C./min.)
[0224] DSC measurement was carried out with the use of a
differential scanning calorimeter (manufactured by Seiko
Instruments Inc., model: DSC6200) by raising a temperature of 1 mg
to 3 mg of expanded polypropylene resin particles from 40.degree.
C. to 200.degree. C. at a heating rate of 2.degree. C./min.
[0225] (Moldability Evaluation)
[0226] With the use of a polyolefin molding machine (manufactured
by DAISEN Co., Ltd., KD-345), (i) a mold, which allows a plate-like
in-mold expanded molded product having a size of length 300
mm.times.width 400 mm.times.thickness 50 mm to be obtained, was
filled with expanded particles while cracking was 5 mm, which
expanded particles had been prepared in advance so that expanded
polypropylene resin particles would have an internal air pressure
as shown in Table 2 or 3 and (ii) the expanded particles were heat
molded by being compressed by 10% in thicknesswise directions. This
resulted in a plate-like polypropylene resin in-mold expanded
molded product having a size of length 300 mm.times.width 400
mm.times.thickness 50 mm. In so doing, after the mold was filled
with the expanded polypropylene resin particles and the mold was
then completely closed, air in the mold was purged by use of steam
having a pressure of 0.1 MPa (gage pressure) (preheating step), the
expanded polypropylene resin particles were heat molded for 10 sec.
by use of heating steam having a certain molding pressure
(both-surface heating step). This resulted in an in-mold expanded
molded product. The polypropylene resin in-mold expanded molded
product obtained was (i) left at room temperature for 1 hour, (ii)
cured and dried in a thermostatic chamber at 75.degree. C. for 3
hours, and (iii) extracted again and left at room temperature for
24 hours. Then, fusibility and a surface property were evaluated.
Note that during in-mold foaming molding, the in-mold expanded
molded product was molded while the molding pressure (steam
pressure) in the both-surface heating step was changed in
increments of 0.01 MPa. The lowest molding pressure, at which an
in-mold expanded molded product whose fusibility was evaluated as
"good" or "excellent" in fusibility evaluation (see below) was
obtained, was regarded as a minimum molding pressure. An in-mold
expanded molded product molded with the minimum molding pressure
was subjected to (i) surface appearance evaluation, (ii) molded
product density measurement, and (iii) 50%-strained compressive
strength measurement.
[0227] <Fusibility>
[0228] The in-mold expanded molded product thus obtained was (i)
notched by 5 mm in a thickness-wise direction with the use of a
cutter and (ii) cleaved by hand. A cleaved surface was observed by
visual inspection, and a percentage of clefts in expanded particles
and not clefts in the interfaces of the expanded particles was
obtained. Then, fusibility was judged by the following
criteria:
Excellent: The percentage of clefts in the expanded particles was
80% or more. Good: The percentage of clefts in the expanded
particles was 60% or more to less than 80%. Failed: The percentage
of clefts in the expanded particles was less than 60% (fusibility
was so low that the percentage of clefts appearing in the
interfaces of the expanded particles on the cleaved surface was
more than 40%).
[0229] <Surface Appearance (Surface Part)>
[0230] A surface of having a length of 300 mm and a width of 400 mm
of the in-mold expanded molded product obtained was obtained by
visual inspection, and a surface property was judged by the
following criteria:
E (Excellent): There is hardly any inter-particle space (spaces
between expanded polypropylene resin particles); there is no
noticeable surface unevenness; there is no wrinkle or shrinkage and
the surface is therefore beautiful. G (Good): Some inter-particle
spaces, surface unevenness, shrinkage, or wrinkles are observed. F
(Failed): Inter-particle spaces, surface unevenness, shrinkage, or
wrinkles are noticeable throughout the surface observed.
[0231] <Surface Appearance (Edge Part)>
[0232] An edge part (ridge part), at which two surfaces of the
in-mold expanded molded product obtained intersect, was obtained by
visual inspection, and surface appearance was judged by the
following criteria:
E (Excellent): An edge part (ridge part), at which two surfaces of
the in-mold expanded molded product obtained intersect, had no
unevenness resulting from the expanded polypropylene resin
particles and had a clear ridge formed; mold transferability is
good. Even if the edge part was rubbed with a finger, the expanded
particles were not peeled off. F (Failed): Unevenness resulting
from the expanded polypropylene resin particles was noticeable at
an edge part (ridge part): mold transferability was poor. If the
edge part was rubbed with a finger, then the expanded particles
were easily peeled off.
[0233] (Molded Product Density)
[0234] A test piece, which had a size of length 50 mm.times.width
50 mm.times.thickness 25 mm, was cut out from substantially a
center part of the in-mold expanded molded product obtained. Note
that the test piece had a thickness of 25 mm by cutting off, by
approximately 12.5 mm, each of parts containing respective surface
layers of the in-mold expanded molded product.
A weight W(g) of the test piece was measured, and the length,
width, and thickness of the test piece were measured with the use
of a caliper, so that a volume V(cm.sup.3) of the test piece was
calculated. Then, a molded product density was obtained by W/V. A
conversion was made so that the unit was g/L.
[0235] (50%-Strained Compressive Strength and Evaluation)
[0236] The test piece, whose molded product density was measured,
was subjected to a compressive strength test. Specifically, a
compressive stress of the test piece when the test piece was
compressed by 50% at a rate of 10 mm/min. was measured with the use
of a tension and compression testing machine (manufactured by
Minebea Co., Ltd., TG series) in conformity with NDS Z 0504. In
addition, the 50%-strained compressive strength was evaluated as
follows.
The following Formula (1) is satisfied: A The following Formula (1)
is not satisfied, but the following Formula (2) is satisfied: B The
following Formula (2) is not satisfied: C
[50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Molded product density (g/L)]+0.018
(1)
[50%-strained compressive strength
(MPa)].gtoreq.0.0069.times.[Molded product density (g/L)] (2)
Examples 1 Through 15 and Comparative Examples 1 Through 8
[0237] [Production of Polypropylene Resin Particles]
[0238] Polypropylene resins and additives were mixed in amounts
shown in Tables 2 and 3 with the use of a blender. Each of the
mixtures obtained was melted and kneaded at a resin temperature of
220.degree. C. and extruded in a strand shape with the use of a
twin-screw extruder (manufactured by O. N. Machinery Co., Ltd.,
TEK45). The strand thus extruded was water-cooled in a water tank
having a length of 2 m, and was then cut. This resulted in
polypropylene resin particles (1.2 mg per particle).
[0239] [Production of First-Stage Expanded Particles]
[0240] 100 parts by weight of the polypropylene resin particles
obtained, 300 parts by weight of water, 1.5 parts by weight of
powdered basic tribasic calcium phosphate as a dispersing agent,
0.06 parts by weight of n-paraffin sulfonic acid soda as a
dispersion auxiliary agent, and 7.5 parts by weight of carbon
dioxide as a foaming agent were placed in a 10 L-pressure-resistant
container. While a resultant mixture was stirred, a temperature of
the mixture was raised to a foaming temperature shown in a
corresponding part in Table 2 or 3, and the mixture was retained at
the foaming temperature for 10 min. Then, carbon dioxide was
additionally injected so that a foaming pressure was adjusted to a
value shown in a corresponding part in Table 2 or 3. Then, the
foaming pressure was retained for 30 min.
[0241] Then, a valve at a lower part of the pressure-resistant
container was opened while carbon dioxide was injected such that
the temperature and the pressure in the container were retained. An
aqueous dispersion medium was released from the valve into air
under atmospheric pressure through an orifice plate having an
opening diameter of 3.6 mm.phi., so that expanded polypropylene
resin particles (first-stage expanded particles) were obtained. A
high-temperature heat quantity ratio, a cell diameter, and an
expansion ratio of the first-stage expanded particles thus obtained
were measured. The results are shown in a corresponding part of
Table 2 or 3. The first-stage expanded particles were subjected to
DSC measurement at a heating rate of 10.degree. C./min. to obtain
the high-temperature heat quantity ratio. Then, a DSC curve of a
first temperature rise showed (i) one main endothermic peak and
(ii) one high temperature peak on a high temperature-side of the
main endothermic peak
[0242] In each of Example 9, Comparative Examples 1 through 3, and
Comparative Example 8, the expansion ratio of the first-stage
expanded particles was 14 times. Therefore, (i) the first-stage
expanded particles were dried at 80.degree. C. for 6 hours, (ii)
pressurized air was impregnated in the pressure-resistant
container, so that the internal pressure was 0.21 MPa (absolute
pressure), and then (iii) the first-stage expanded particles were
allowed to come in contact with steam having a pressure of 0.04 MPa
(gage pressure). This subjected the first-stage expanded particles
to second-stage foaming. The expansion ratio of the second-stage
expanded particles thus obtained was 19 times or 20 times. The
second-stage expanded particles were also subjected to DSC
measurement at a heating rate of 10.degree. C./min. Then, a DSC
curve of a first temperature rise showed (i) one main endothermic
peak and (ii) one high temperature peak on a high temperature-side
of the main endothermic peak. An apex temperature of the main
endothermic peak of the second-stage expanded particles was
identical to that of corresponding first-stage expanded particles.
However, a shoulder, which was supposedly derived from heating
during second-stage foaming, appeared around 110.degree. C. on the
DSC curve.
[0243] Note that expanded polypropylene resin particles were
subjected to DSC measurement at a heating rate of 2.degree. C./min.
In each of Examples 1 through 6, Examples 8 through IS, and
Comparative Examples 1 through 8, the DSC curve showed the total of
two endothermic peaks which are (i) one main endothermic peak at
145.degree. C. or lower and (ii) one high temperature peak on a
high temperature-side of the main endothermic peak. In Example 7,
the DSC curve showed the total of three endothermic peaks which are
(i) one main endothermic peak at 145.degree. C. or lower and (ii)
two high temperature peaks on a high temperature-side of the main
endothermic peak.
[0244] [Production of in-Mold Expanded Molded Product]
[0245] The first-stage expanded particles obtained (or second-stage
expanded particles in Example 9, Comparative Examples 1 through 3,
and Comparative Example 8) were introduced into a
pressure-resistant container. Then, pressurized air was impregnated
so that internal pressure of the expanded particles was adjusted in
advance as shown in a corresponding part of Table 2 or 3.
[0246] Then, (i) a mold, which allows a plate-like in-mold expanded
molded product having a size of length 300 mm.times.width 400
mm.times.thickness 50 mm to be obtained, was filled with the
expanded polypropylene resin particles while cracking was 5 mm,
which expanded polypropylene resin particles had the adjusted
internal pressure and (ii) the expanded particles were heat molded
by being compressed by 10% in thicknesswise directions. This
resulted in a plate-like in-mold expanded molded product having a
size of length 300 mm.times.width 400 mm.times.thickness 50 mm.
[0247] In so doing, after the mold was filled with the expanded
polypropylene resin particles having the adjusted internal pressure
and the mold was then completely closed, air in the mold was purged
by use of steam having a pressure of 0.1 MPa (gage pressure)
(preheating step), the expanded polypropylene resin particles were
heat molded for 10 sec. by use of heating steam having a certain
molding pressure (both-surface heating step). This resulted in an
in-mold expanded molded product. Note that (i) the preheating step
was carried out for 10 sec., (ii) the step of heating one side was
carried out for 2 sec., (iii) the step of heating the other side
was carried out for 2 sec., and (iv) the both-surface heating step
was carried out for 10 sec. as described above. Note also that the
in-mold expanded molded product was prepared while a molding
pressure (steam pressure) was changed in 0.01 MPa increments in the
both-surface heating step.
[0248] Tables 2 and 3 show the results of moldability evaluation,
molded product density measurement, and 50%-strained compressive
strength measurement.
TABLE-US-00002 TABLE 2 ("PBW" stands for "Part by weight".)
Examples 1 2 3 4 5 6 7 8 Base Polypropylene Polypropylene PBW 60 60
60 60 50 material resin A resin A-1 resin Polypropylene PBW 60
resin A-2 Polypropylene PBW 60 resin A-3 Polypropylene PBW 60 resin
A-4 Polypropylene PBW resin A-5 Polypropylene PBW resin A-6
Polypropylene PBW resin A-7 Polypropylene PBW resin A-8
Polypropylene Polypropylene PBW 40 40 40 40 50 resin B resin B-1
Polypropylene PBW 40 resin B-2 Polypropylene PBW 40 resin B-3
Polypropylene PBW 40 resin B-4 Polypropylene PBW resin B-5 Other
Polypropylene PBW polypropylene resin C resin Additive Talc PBW
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Polyethylene PBW 0.5 0.5
0.5 0.5 0.5 0.5 0.5 0.5 glycol Carbon black PBW Physical Melting
point .degree. C. 146 146 146 147 146 141 149 146 property First-
Foaming Amount of carbon PBW 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 stage
conditions dioxide foaming Foaming .degree. C. 148 148 148 149 148
142 153 148 temperature Foaming pressure MPa 3.3 3.3 3.3 3.3 3.3
3.3 3.3 3.3 (gage pressure) Physical High-temperature % 22 22 21 21
22 22 20 22 property heat quantity ratio Average cell .mu.m 180 180
180 160 170 190 150 180 diameter Expansion ratio Times 19 20 19 19
19 20 18 19 Second- Foaming Internal pressure MPa -- -- -- -- -- --
-- -- stage conditions (Absolute pressure) foaming Physical
High-temperature % -- -- -- -- -- -- -- -- property heat quantity
ratio Average cell .mu.m -- -- -- -- -- -- -- -- diameter Expansion
ratio Times -- -- -- -- -- -- -- -- In-moid Moldability Expanded
particle MPa 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 expanded internal
pressure molded (Absolute pressure) product Minimum molding MPa
0.20 0.20 0.20 0.21 0.20 0.20 0.22 0.20 pressure (gage pressure)
Surface Surface -- E E E E E E G E appearance part Edge -- E E E E
E E G E part Physical Molded product g/L 30 30 30 30 30 30 32 30
property density 50%-strained MPa 0.23 0.23 0.23 0.23 0.23 0.21
0.23 0.23 compressive strength 50%-strained -- A A A A A B B A
compressive strength evaluation Examples 9 10 11 12 13 14 15 Base
Polypropylene Polypropylene PBW 40 70 80 60 60 60 material resin A
resin A-1 resin Polypropylene PBW resin A-2 Polypropylene PBW resin
A-3 Polypropylene PBW resin A-4 Polypropylene PBW 60 resin A-5
Polypropylene PBW resin A-6 Polypropylene PBW resin A-7
Polypropylene PBW resin A-8 Polypropylene Polypropylene PBW 60 30
20 40 40 40 40 resin B resin B-1 Polypropylene PBW resin B-2
Polypropylene PBW resin B-3 Polypropylene PBW resin B-4
Polypropylene PBW resin B-5 Other Polypropylene PBW polypropylene
resin C resin Additive Talc PBW 0.05 0.05 0.05 0.05 0.05 0.05 0.05
Polyethylene PBW 0.5 0.5 0.5 0.5 0.5 0.5 0.5 glycol Carbon black
PBW 6 Physical Melting point .degree. C. 147 145 145 146 146 146
147 property First- Foaming Amount of carbon PBW 7.5 7.5 7.5 7.5
7.5 7.5 7.5 stage conditions dioxide foaming Foaming .degree. C.
149 147 147 148 149 146 149 temperature Foaming pressure MPa 3.3
3.3 3.3 3.3 3.3 3.3 3.3 (gage pressure) Physical High-temperature %
21 22 21 22 16 27 21 property heat quantity ratio Average cell
.mu.m 120 180 190 130 220 150 170 diameter Expansion ratio Times 14
20 20 21 23 15 20 Second- Foaming Internal pressure MPa 0.21 -- --
-- -- -- -- stage conditions (Absolute pressure) foaming Physical
High-temperature % 21 -- -- -- -- -- -- property heat quantity
ratio Average cell .mu.m 170 -- -- -- -- -- -- diameter Expansion
ratio Times 19 -- -- -- -- -- -- In-moid Moldability Expanded
particle MPa 0.2 0.2 0.2 0.2 0.2 0.2 0.2 expanded internal pressure
molded (Absolute pressure) product Minimum molding MPa 0.21 0.20
0.19 0.20 0.20 0.20 0.21 pressure (gage pressure) Surface Surface
-- E E E E E E E appearance part Edge -- E E E E E E E part
Physical Molded product g/L 30 29 30 29 25 40 30 property density
50%-strained MPa 0.23 0.22 0.21 0.23 0.20 0.33 0.23 compressive
strength 50%-strained -- A A B A A A A compressive strength
evaluation
TABLE-US-00003 TABLE 3 ("PBW" stands for "Part by weight".)
Comparative Examples 1 2 3 4 5 6 7 8 9 Base Poly- Polypropylene
resin A-1 PBW 60 100 material propylene Polypropylene resin A-2 PBW
resin resin A Polypropylene resin A-3 PBW Polypropylene resin A-4
PBW Polypropylene resin A-5 PBW Polypropylene resin A-6 PBW 100 60
Polypropylene resin A-7 PBW 100 60 Polypropylene resin A-8 PBW 90
Poly- Polypropylene resin B-1 PBW 40 40 propylene Polypropylene
resin B-2 PBW resin B Polypropylene resin B-3 PBW Polypropylene
resin B-4 PBW 10 Polypropylene resin B-5 PBW 100 40 Other
Polypropylene resin C PBW 100 poly- propylene resin Additive Talc
PBW 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.005 Polyethylene
glycol PBW 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Carbon black PBW
Physical Melting point .degree. C. 144 132 125 140 141 136 144 134
145 property First-stage Foaming Amount of carbon PBW 7.5 7.5 7.5
7.5 7.5 7.5 7.5 7.5 15 foaming conditions dioxide (Isobutane)
Foaming temperature .degree. C. 146 132 128 143 143 139 146 136 142
Foaming pressure MPa 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 2.0 (gage
pressure) Physical High-temperature % 22 21 21 21 21 21 22 22 26
property heat quantity ratio Average cell diameter .mu.m 130 145
130 180 180 210 190 140 350 Expansion ratio Times 14 14 14 19 19 20
20 14 22 Second- Foaming Internal pressure MPa 0.21 0.21 0.21 -- --
-- -- 0.21 -- stage conditions (Absolute pressure) foaming Physical
High-temperature % 22 21 21 -- -- -- -- 22 -- property heat
quantity ratio Average cell diameter .mu.m 180 210 180 -- -- -- --
200 -- Expansion ratio Times 19 20 19 -- -- -- -- 20 -- In-mold
Mold- Expanded particle MPa 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
expanded ability internal pressure molded (Absolute pressure)
product Minimum molding MPa 0.26 0.16 0.14 0.20 0.20 0.23 0.24 0.18
0.20 pressure (gage pressure) Surface Surface -- E G G E E E E E E
appearance part Edge part -- E E E E E E E E E Physical Molded
product density g/L 30 30 30 30 30 30 30 30 30 property
50%-strained MPa 0.23 0.19 0.18 0.20 0.20 0.20 0.22 0.20 0.20
compressive strength 50%-strained -- A C C C C C B C C compressive
strength evaluation
[0249] Comparisons between the molded products having substantially
identical molded product densities indicate that (i) those in
Examples can be molded with a low molding pressure and exhibit
higher 50%-strained compressive strength and (ii) those in
Comparative Examples exhibit decreased 50%-strained compressive
strength with a low molding pressure and demand a higher molding
pressure for high 50%-strained compressive strength.
Comparative Example 9
[0250] A polypropylene resin A-8 (which is an ethylene-propylene
random copolymer), a polypropylene resin B-4 (which is a
homopolypropylene), and talc were mixed in amounts shown in Table 3
with the use of a blender.
[0251] The mixture obtained was melted and kneaded at a resin
temperature of 220.degree. C. and extruded in a strand shape with
the use of a twin-screw extruder (manufactured by O. N. Machinery
Co., Ltd., TEK45). The strand thus extruded was water-cooled in a
water tank having a length of 2 m, and was then cut. This resulted
in polypropylene resin particles (1.3 mg per particle).
[0252] 100 parts by weight of the polypropylene resin particles,
300 parts by weight of water, 3.0 parts by weight of tribasic
calcium phosphate as a dispersing agent, and 0.075 parts by weight
of sodium normal paraffin sulfonate were placed into a 10
L-pressure-resistant container. Then, while a resultant aqueous
dispersion was stirred, 15 parts by weight of isobutane was added
as a foaming agent, a temperature of a resultant mixture was raised
to the foaming temperature shown in Table 3.
[0253] Then, gaseous isobutane was added so that the internal
pressure of the container was adjusted to the foaming pressure
shown in Table 3. Then, the temperature was retained for 30 min.
Then, a valve at a lower part of the pressure-resistant container
was opened while nitrogen gas was injected such that the
temperature and the pressure in the container were retained. An
aqueous dispersion medium was released from the valve into air
under atmospheric pressure through an orifice plate having an
opening diameter of 4 mm.phi., so that expanded polypropylene resin
particles having the high-temperature heat quantity ratio, the
average cell diameter, and expansion ratio shown in Table 3 were
obtained.
[0254] Subsequent production and evaluation of an in-mold expanded
molded product were carried out as in Example 1. Table 3 shows the
results of moldability evaluation, molded product density
measurement, and 50%-strained compressive strength measurement.
[0255] In this case, while the minimum molding pressure was 0.20
MPa (gage pressure), 50%-strained compressive strength was 0.20 MPa
which is lower than those in Examples.
Examples 16 and 17 and Comparative Examples 10 and 11
[0256] [Production of Composite Polypropylene Resin Particle]
[0257] As core layer base material resins, polypropylene resins and
additives were mixed in amounts shown in Table 4 with the use of a
blender so that mixtures serve as core layer base material
resins.
[0258] Meanwhile, as a covering layer resin, (i) a polypropylene
resin A-1 was prepared in Example 16, (ii) a polypropylene resin
A-2 was prepared in Example 17, (iii) a polypropylene resin A-6 was
prepared in Comparative Example 9, and (iv) a polypropylene resin
A-1 was prepared in Comparative Example 10.
[0259] With the use of a 50 mm single-screw extruder (manufactured
by Osaka Seiki Kousaku K. K., model: 20VSE-50-28), a mixture
prepared as a core layer base material resin was melted and kneaded
at a resin temperature of 220.degree. C. Meanwhile, with the use of
a 30 mm twin-screw extruder (manufactured by Ikegai Corporation,
PCM30), a mixture prepared as a covering layer resin was melted and
kneaded at a resin temperature of 220.degree. C.
[0260] On outlet sides of the 50 mm single-screw extruder and the
30 mm twin-screw extruder, a co-extrusion die was provided. The
molten resins were supplied from the extruders to the die, so that
the molten resins were joined in the die. Then, a multi-layer
strand, in which the core layer base material resin was covered
with the covering layer resin, was extruded. Note that a ratio of a
discharge quantity of the core layer base material resin extruded
from the 50 mm single-screw extruder to a discharge quantity of the
covering layer resin extruded from the 30 mm twin-screw extruder
was adjusted to 95/5.
[0261] The strand thus extruded was water-cooled in a water tank
having a length of 2 m, and was then cut. This resulted in
composite resin particles (1.2 mg per particle).
[0262] [Production of First-Stage Expanded Particles] [Production
of in-Mold Expanded Molded Product]
[0263] Subsequent production of first-stage expanded particles and
of an in-mold expanded molded product was carried out as in Example
1 except the conditions shown in Table 4 were met. Table 4 shows
the results of moldability evaluation, molded product density
measurement, and 50%-strained compressive strength measurement.
Note that expanded polypropylene resin particles were subjected to
DSC measurement at a heating rate of 2.degree. C./min. In each of
Examples 16 and 17 and Comparative Examples 9 and 10 also, the DSC
curve showed the total of two endothermic peaks which are (i) one
main endothermic peak at 145.degree. C. or lower and (ii) one high
temperature peak on a high temperature-side of the main endothermic
peak.
TABLE-US-00004 TABLE 4 ("PBW" stands for "Part by weight".)
Examples Comparative Examples 16 17 10 11 Base Polypropylene
Polypropylene resin A-1 PBW 60 material resin A Polypropylene resin
A-2 PBW 60 resin Polypropylene resin A-3 PBW Polypropylene resin
A-4 PBW Polypropylene resin A-5 PBW Polypropylene resin A-6 PBW 60
Polypropylene resin A-7 PBW Polypropylene Polypropylene resin B-1
PBW 40 40 40 resin B Polypropylene resin B-2 PBW Polypropylene
resin B-3 PBW Polypropylene resin B-4 PBW Polypropylene resin B-5
PBW 100 Other Polypropylene resin C PBW polypropylene resin
Additive Talc PBW 0.05 0.05 0.05 0.05 Polyethylene glycol PBW 0.5
0.5 0.5 0.5 Carbon black PBW Physical property Melting point
.degree. C. 146 146 141 144 Covering Polypropylene resin
Polypropylene Polypropylene Polypropylene Polypropylene layer resin
resin A-1 resin A-2 resin A-6 resin A-1 First-stage Foaming
conditions Amount of carbon dioxide PBW 7.5 7.5 7.5 7.5 foaming
Foaming temperature .degree. C. 148 148 143 146 Foaming pressure
MPa 3.3 3.3 3.3 3.3 (gage pressure) Physical property
High-temperature % 22 22 21 22 heat quantity ratio Average cell
diameter .mu.m 180 180 180 180 Expansion ratio Times 19 19 19 19
In-mold Moldability Expanded particle internal MPa 0.2 0.2 0.2 0.2
expanded pressure (Absolute molded pressure) product Minimum
molding MPa 0.19 0.19 0.19 0.25 pressure (gage pressure) Surface
Surface part -- E E E E appearance Edge part -- E E E E Physical
property Molded product density g/L 30 30 30 30 50%-strained
compressive MPa 0.23 0.23 0.20 0.23 strength 50%-strained
compressive -- A A C A strength evaluation
[0264] Note that observation, by a microscope, of cleaved surfaces
of molded products whose fusibility was evaluated as "excellent" in
fusibility evaluation confirmed that in Comparative Example 1, (i)
expanded composite particle interfaces (interfaces between the
expanded composite particles) were not cleaved and (ii) the
percentage of clefts in the expanded composite particles was 80% or
more. However, it was also confirmed that the expanded
polypropylene resin core layer and the polypropylene resin covering
layer were partially peeled from each other at the interface.
Meanwhile, in Example 16, Example 17, and Comparative Example 10,
peeling of an expanded polypropylene resin core layer and a
polypropylene resin covering layer from each other at an interface
therebetween in each of expanded composite particles was hardly
confirmed.
[0265] Any of a comparison between Example 1 and Example 16 and a
comparison between Example 2 and Example 17 indicates that expanded
composite particles may be molded with a low molding pressure. Any
of a comparison between Example 16 and Comparative Example 10 and a
comparison between Example 17 and Comparative Example 10 indicates
that one or more embodiments of the present invention may be molded
with a low molding pressure and exhibits high 50%-strained
compressive strength. A comparison of Example 16 or Example 17 with
Comparative Example 11 indicates that adhesiveness of an interface
between an expanded polypropylene resin core layer and a
polypropylene resin covering layer is increased in each expanded
composite particle.
[0266] One or more embodiments of the present invention can be used
for various purposes such as automobile interior materials,
automobile bumper core materials, heat insulating materials,
shock-absorbing packing materials, and returnable containers.
REFERENCE SIGNS LIST
[0267] t.sub.m: Melting peak temperature of polypropylene resin (or
base material resin) in DSC curve of second temperature rise
[0268] Point A: Heat absorption quantity of expanded polypropylene
resin particles at 80.degree. C. in DSC curve of first temperature
rise
[0269] Point B: Heat absorption quantity of expanded polypropylene
resin particles at temperature at which melting on high temperature
side ends in DSC curve of first temperature rise
[0270] Point C: Point at which heat absorption quantity of expanded
polypropylene resin particles becomes small between two melting
heat quantity regions in DSC curve of first temperature rise, the
two melting heat quantity regions being region of low
temperature-side melting heat quantity and region of high
temperature-side melting heat quantity
[0271] Point D: Point at which line segment A-B intersects line
that is drawn so as to extend, parallel to Y-axis, from point C
toward line segment A-B in DSC curve of first temperature rise of
expanded polypropylene resin particles
[0272] Qh: High temperature-side melting heat quantity of expanded
polypropylene resin particles in DSC curve of first temperature
rise
[0273] Ql: Low temperature-side melting heat quantity of expanded
polypropylene resin particles in DSC curve of first temperature
rise
[0274] Although the disclosure has been described with respect to
only a limited number of embodiments, those skilled in the art,
having benefit of this disclosure, will appreciate that various
other embodiments may be devised without departing from the scope
of the present invention. Accordingly, the scope of the present
invention should be limited only by the attached claims.
* * * * *