U.S. patent number RE48,098 [Application Number 16/263,547] was granted by the patent office on 2020-07-14 for thermoplastic resin foamed particles.
This patent grant is currently assigned to JSP CORPORATION. The grantee listed for this patent is JSP CORPORATION. Invention is credited to Takuya Chiba, Masaharu Oikawa.
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United States Patent |
RE48,098 |
Chiba , et al. |
July 14, 2020 |
Thermoplastic resin foamed particles
Abstract
Thermoplastic resin foamed particles of the present invention
including .[.more than.]. one .Iadd.or more .Iaddend.functional
additive selected from inorganic powder and inorganic fibers each
includes a core layer formed of a thermoplastic resin and a coating
layer in a foamed state formed of a thermoplastic resin, the mass
ratio of the coating layer to the core layer is 99:1 to 50:50, the
content (X) of the functional additive in the core layer is 5 to
90% by mass, and the content of the functional additive in the
coating layer is smaller than the content (X) of the functional
additive in the core layer. By this way, thermoplastic resin foamed
particles from which a homogeneous foamed particle molding having
excellent dimension stability, fusibility and appearance can be
obtained while containing functional additive are provided.
Inventors: |
Chiba; Takuya (Mie,
JP), Oikawa; Masaharu (Mie, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JSP CORPORATION |
Tokyo |
N/A |
JP |
|
|
Assignee: |
JSP CORPORATION (Tokyo,
JP)
|
Family
ID: |
57504028 |
Appl.
No.: |
16/263,547 |
Filed: |
January 31, 2019 |
PCT
Filed: |
June 03, 2016 |
PCT No.: |
PCT/JP2016/066592 |
371(c)(1),(2),(4) Date: |
December 07, 2017 |
PCT
Pub. No.: |
WO2016/199693 |
PCT
Pub. Date: |
December 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
15580308 |
Jun 3, 2016 |
10106664 |
Oct 23, 2018 |
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Foreign Application Priority Data
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|
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Jun 10, 2015 [JP] |
|
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2015-117688 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J
9/18 (20130101); B29C 44/02 (20130101); C08J
9/232 (20130101); C08J 9/228 (20130101); C08J
9/122 (20130101); C08J 9/16 (20130101); C08J
9/228 (20130101); B32B 27/18 (20130101); B29C
44/3415 (20130101); B32B 5/18 (20130101); B29B
9/06 (20130101); B29C 44/3461 (20130101); C08J
9/0061 (20130101); C08J 9/008 (20130101); B29B
9/12 (20130101); B29C 44/02 (20130101); C08J
9/122 (20130101); C08J 9/16 (20130101); B29B
9/06 (20130101); C08J 9/0061 (20130101); B29C
44/3461 (20130101); B32B 5/18 (20130101); C08J
9/232 (20130101); B29C 44/3415 (20130101); B32B
27/18 (20130101); C08J 9/008 (20130101); C08J
9/18 (20130101); C08J 9/22 (20130101); C08J
9/22 (20130101); C08J 2203/06 (20130101); C08J
2323/12 (20130101); B29K 2995/0011 (20130101); B29K
2105/12 (20130101); C08J 2323/14 (20130101); C08J
2423/14 (20130101); C08J 2201/034 (20130101); C08J
2205/044 (20130101); C08J 2205/052 (20130101); C08J
2207/00 (20130101); B29K 2509/00 (20130101); B29K
2995/0011 (20130101); C08J 2205/044 (20130101); B29K
2105/12 (20130101); C08J 2423/14 (20130101); C08J
2207/00 (20130101); C08J 2323/12 (20130101); C08J
2205/052 (20130101); B29K 2509/00 (20130101); C08J
2203/06 (20130101); C08J 2323/14 (20130101); C08J
2201/034 (20130101) |
Current International
Class: |
C08J
9/16 (20060101); B29B 9/06 (20060101); B29C
44/02 (20060101); C08J 9/22 (20060101); C08J
9/18 (20060101); B32B 27/18 (20060101); B32B
5/18 (20060101); B29C 44/34 (20060101); C08J
9/00 (20060101); C08J 9/12 (20060101); C08J
9/228 (20060101); C08J 9/232 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
58-145739 |
|
Aug 1983 |
|
JP |
|
61-12735 |
|
Jan 1986 |
|
JP |
|
4-056298 |
|
Feb 1992 |
|
JP |
|
2002-003634 |
|
Jan 2002 |
|
JP |
|
2002-3634 |
|
Jan 2002 |
|
JP |
|
2004-115785 |
|
Apr 2004 |
|
JP |
|
2014-115785 |
|
Apr 2004 |
|
JP |
|
2006-232939 |
|
Sep 2006 |
|
JP |
|
Other References
Translation of Table 1 in JP 61-12735 A by USPTO translator (Year:
1986). cited by examiner .
Extended European Search Report dated Oct. 15, 2018 in
corresponding European Patent Application No. 16807400.3. cited by
applicant .
International Search Report dated Jul. 19, 2016 in International
Application No. PCT/JP2016/066592. cited by applicant.
|
Primary Examiner: Diamond; Alan D
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. Thermoplastic resin foamed particles comprising .[.more than.].
one .Iadd.or more .Iaddend.functional additive selected from
inorganic powder and inorganic fibers, wherein each particle
comprises a core layer formed of a thermoplastic resin and a
coating layer in a foamed state formed of a thermoplastic resin,
the mass ratio of the coating layer to the core layer is 99:1 to
50:50, the content (X) of the functional additive in the core layer
is 5 to 90% by mass, and the content of the functional additive in
the coating layer is smaller than the content (X) of the functional
additive in the core layer.
2. The thermoplastic resin foamed particles according to claim 1,
wherein the content of the functional additive in the coating layer
is lower than 20% by mass (including 0).
3. The thermoplastic resin foamed particles according to claim 1,
wherein the functional additive is .[.an.]. .Iadd.a
.Iaddend.conductive carbon.
4. The thermoplastic resin foamed particles according to claim 1,
wherein the thermoplastic resin that forms the core layer and the
thermoplastic resin that forms the coating layer are both
polyolefin-based resins.
5. The thermoplastic resin foamed particles according to claim 2,
wherein the functional additive is .[.an.]. .Iadd.a
.Iaddend.conductive carbon.
6. The thermoplastic resin foamed particles according to claim 2,
wherein the thermoplastic resin that forms the core layer and the
thermoplastic resin that forms the coating layer are both
polyolefin-based resins.
Description
TECHNICAL FIELD
The present invention relates to thermoplastic resin foamed
particles containing functional additive.
BACKGROUND ART
Thermoplastic resin foamed particles can be molded into various
shapes according to use by in-mold molding. Thermoplastic resin
foamed particle molding obtained from said foamed particles by
in-mold molding are used in a wide variety of use such as
dielectric bodies, electric wave shielding bodies, heat insulating
materials, packaging materials for electronic parts, shock
absorbing materials and reusable containers.
For example, Patent Literatures 1 and 2 describe that foamed
particle molding containing functional additive such as inorganic
powder and inorganic fibers are used as dielectric bodies and
electric wave absorbers.
CITATION LIST
Patent Literature
Patent Literature 1: JP 2008-512502 W
Patent Literature 2: JP H04-56298 A
SUMMARY OF INVENTION
Technical Problem
However, as described in Patent Literature 1, in a case where the
thermoplastic resin foamed particles contained functional additive
in a large amount, it was possible that the secondary foamability
of the foamed particles decreases and thus the fusibility and
appearance of a foamed particle molding may decrease. Therefore, in
such case, problems remained in productivity so as to obtain a fine
molding, for example, it was necessary to increase the molding
pressure during the in-mold molding, and it was necessary to
pressurize the foamed particles in advance, and the like.
Furthermore, in the electric wave absorber described in Patent
Literature 2, a foamed particle molding is formed by using foamed
particles to which a dielectric body is adhered and foamed
particles to which a dielectric body is not adhered. However, in
this method, it is difficult to completely and homogeneously mix
these two kinds of foamed particles during the molding of the
foamed particle molding, and thus problems remained in productivity
since there was a possibility that unevenness occurs in the
properties among the foamed particle molding, and the production
control was difficult.
The present invention was made in view of the abovementioned
conventional problems, and aims at providing thermoplastic resin
foamed particles from which a homogeneous foamed particle molding
having excellent dimension stability, fusibility and appearance can
be obtained while containing functional additive.
Solution to Problem
The present invention provides the thermoplastic resin foamed
particles described below. <1> Thermoplastic resin foamed
particles comprising .[.more than.]. one .Iadd.or more
.Iaddend.functional additive selected from inorganic powder and
inorganic fibers, wherein each particle includes a core layer
formed of a thermoplastic resin and a coating layer in a foamed
state formed of a thermoplastic resin, the mass ratio of the
coating layer to the core layer is 99:1 to 50:50, the content (X)
of the functional additive in the core layer is 5 to 90% by mass,
and the content of the functional additive in the coating layer is
smaller than the content (X) of the functional additive in the core
layer. <2> The thermoplastic resin foamed particles according
to <1>, wherein the content of the functional additive in the
coating layer is lower than 20% by mass (including 0). <3>
The thermoplastic resin foamed particles according to <1> or
<2>, wherein the functional additive is .[.an.]. .Iadd.a
.Iaddend.conductive carbon. <4> The thermoplastic resin
foamed particles according to any one of <1> to <3>,
wherein the thermoplastic resin that forms the core layer and the
thermoplastic resin that forms the coating layer are both
polyolefin-based resins.
Advantageous Effects of Invention
According to the thermoplastic resin foamed particles of the
present invention, since the core layer of each foamed particle
including the core layer and a coating layer in a foamed state is
highly filled with the functional additive, the distribution of the
functional additive in the molding is homogenized, and a foamed
particle molding in which the function(s) of the functional
additive is effectively exerted can be obtained. Furthermore, since
the content of the functional additive in the coating layer is
smaller than the content of the functional additive in the core
layer, a homogeneous foamed particle molding that can be
sufficiently secondary-foamed, and have excellent appearance, in
which the fusibility of the foamed particles forming the foamed
particle molding has been improved, can be provided.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic perspective view schematically showing an
embodiment of the thermoplastic resin foamed particle according to
the present invention.
FIG. 2 is an actual electron microscopic photograph of a
cross-sectional surface at A-A of the thermoplastic resin foamed
particle in FIG. 1.
FIG. 3 is an actual electron microscopic photograph of a
cross-sectional surface at B-B of the thermoplastic resin foamed
particle in FIG. 1.
DESCRIPTION OF EMBODIMENTS
The thermoplastic resin foamed particles of the present invention
will further be explained below in detail with referring to the
embodiments for carrying out the invention. FIG. 1 shows a
schematic perspective view schematically showing an embodiment of
the thermoplastic resin foamed particle of the present invention,
FIG. 2 shows an actual electron microscopic photograph of a
cross-sectional surface at A-A of the thermoplastic resin foamed
particle, and FIG. 3 shows an actual electron microscopic
photograph of a cross-sectional surface at B-B of the thermoplastic
resin foamed particle.
[Thermoplastic Resin Foamed Particles 1]
As shown in FIG. 1, the thermoplastic resin foamed particle 1 of
the present embodiment includes a core layer 2 formed of a
thermoplastic resin and a coating layer 3 in a foamed state formed
of a thermoplastic resin.
(Core Layer 2)
The core layer 2 is formed of a thermoplastic resin, and contains
.[.more than.]. one .Iadd.or more .Iaddend.functional additive
selected from inorganic powder and inorganic fibers as essential
component. The structure of the core layer 2 may be in either a
foamed state or a non-foamed state.
(Thermoplastic Resin)
Examples of the thermoplastic resin that forms the core layer 2
include polyolefin-based resins such as polyethylene-based resins
and polypropylene-based resins, polystyrene-based resins,
polycarbonate resins, polyvinylchloride resins,
polymethacrylic-based resins, acrylonitrile-based resins,
polyester-based resins, polyamide-based resins and thermoplastic
polyurethane resins, and blend polymers thereof, and the like.
Among these, the polyolefin-based resins are preferably used.
Furthermore, in a case where a mixed resin of a polyolefin-based
resin and other resin is used, the mixed resin contains the
polyolefin-based resin by preferably 50% by mass or more, more
preferably 70% by mass or more, and further preferably 90% by mass
or more.
Examples of the above-mentioned polyethylene-based resin include
low density polyethylenes, high density polyethylenes, linear low
density polyethylenes, ultra-low density polyethylenes,
ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate
copolymer, ethylene-methacrylic acid copolymer and ionomer-based
resins obtained by crosslinking the molecules thereof with metal
ions.
Furthermore, examples of the above-mentioned polypropylene-based
resins include propylene homopolymers, and propylene-based
copolymers containing structural units derived from propylene by
50% by mass or more. As the copolymers, copolymers of propylene and
ethylene or an .alpha.-olefin having 4 or more carbon atoms such as
an ethylene-propylene copolymer, a propylene-butene copolymer and a
propylene-ethylene-butene copolymer, a propylene-acrylic acid
copolymer and a propylene-maleic anhydride copolymer can be
exemplified. These copolymers may be either block copolymers,
random copolymers or graft copolymers.
As the thermoplastic resin, a non-crosslinked thermoplastic resin
is preferably used in the point that a state in which the
functional additive mentioned below is homogeneously mixed is
easily formed.
(Kinds of Functional Additives)
The functional additive to be incorporated in the core layer 2
is/are one or more selected from inorganic powder and inorganic
fibers. Specific examples include particulate material and fibers
of metals, minerals, metal compounds and other inorganic
substances, and examples can include carbons such as carbon black,
graphite, graphene, carbon nanotube, carbon nanofibers, carbon
microfibers, carbon microcoils and carbon nanocoils, fibers such as
glass fibers, metal fibers and carbon fibers, metal carbonates such
as calcium carbonate, magnesium carbonate and barium carbonate,
metal sulfates such as calcium sulfate, magnesium sulfate and
aluminum sulfate, metal oxides such as iron oxide, ferrite,
aluminum oxide, zinc oxide, silicon oxide, lead oxide, magnesium
oxide, cobalt oxide, titanium oxide and calcium oxide, and other
clays or natural minerals such as clay, kaolin and zeolite, and the
like. Among these, carbons and metal oxides are preferable as the
functional additives, and specifically, carbons can be preferably
used in that they are excellent in homogeneous dispersibility in
the resin, and the like. As the carbons, conductive carbons are
preferably used, and it is more preferable to use a conductive
carbon having a DBP absorption amount of 150 to 700 cm.sup.3/100
g.
Furthermore, a finer particle size is more preferable for the
above-mentioned functional additives in view of dispersibility in
the resin, and the particle size is preferably 0.001 to 500 .mu.m,
and more preferably 0.01 to 100 .mu.m.
(Content of Functional Additive)
From the viewpoint that higher functions are imparted to the foamed
particles, the lower limit of the content of the functional
additive in the core layer 2 is 5% by mass, preferably 8% by mass,
and more preferably 10% by mass in the thermoplastic resin that
constitutes the core layer 2. On the other hand, the upper limit is
90% by mass, and is preferably 70% by mass, more preferably 60% by
mass, and further preferably 30% by mass in view of
productivity.
In a case where the core layer 2 contains two or more kinds of
functional additives, the total amount of these functional
additives is deemed as the content of the functional additives in
the core layer 2.
(Coating Layer 3)
It is necessary that the coating layer 3 is present in a foamed
state. The structure of the coating layer 3 is formed by foaming
the thermoplastic resin. In a case where a function was exerted by
incorporating a large amount of functional additive in the foamed
particles, there was a possibility that the secondary foamability
of the foamed particles was lowered, and the fusibility of the
resin itself of the foamed particles was lowered. In this case,
there was a possibility that the fusion rate, dimension stability
and appearance of a foamed particle molding obtained by in-mold
molding of the foamed particles containing a large amount of
functional additive were lowered. On the other hand, in order to
improve the fusibility of the foamed particles, it was necessary to
conduct operations such as increasing the molding pressure during
the in-mold molding of the foamed particles, and pressurizing the
foamed particles in advance. However, if the molding pressure is
increased, the shrinkage rate of the molding increases, and thus
the dimension stability and appearance of the molding are easily
lowered. Furthermore, a problem remained in view of productivity
since a pressurization step is required for pressurizing the foamed
particles.
On the other hand, in the present invention, each foamed particle
is formed of a core layer and a coating layer, and these layers are
present at a specific mass ratio. Furthermore, the core layer
contains the functional additive, whereas the coating layer 3
contains the functional additive at a smaller content than that in
the core layer. Furthermore, the coating layer 3 is in a foamed
state. By these facts, the coating layer 3 is sufficiently
secondary-foamed during in-mold molding, and the lowering of the
fusibility of the resin itself that constitutes the coating layer 3
is suppressed in said foamed particles, and thus the foamed
particles can be sufficiently fused each other and a fine foamed
particle molding can be formed. Therefore, the foamed particle
molding obtained from the foamed particles of the present invention
is a foamed particle molding having excellent dimensional accuracy
and appearance without lowering of a fusion rate, irrespective of
incorporation of the functional additive.
(Thermoplastic Resin)
As the thermoplastic resin for forming the coating layer 3, a
similar thermoplastic resin to that constitutes the above-mentioned
core layer 2 can be used.
(Presence or Absence of Functional Additive in Coating Layer 3)
The functional additive may be contained or not contained in the
coating layer 3, and the content of the functional additive in the
coating layer 3 is smaller than that in the core layer 2. From the
viewpoint of improving the foamability of the coating layer 3, the
content of the functional additive in the coating layer 3 is
preferably lower than 20% by mass (including 0), more preferably
lower than 10% by mass (including 0), and further preferably lower
than 5% by mass (including 0) in the thermoplastic resin that
constitutes the coating layer 3. Furthermore, different functional
additives may be added to the core layer 2 and the coating layer 3.
Furthermore, in a case where the coating layer 3 contains two or
more kinds of functional additives, the total amount of these
additives is set as the content of the functional additives in the
coating layer 3.
(Other Additives and the Like)
The core layer 2 and the coating layer 3 in the thermoplastic resin
foamed particles 1 of the present invention can contain other
additives as necessary in the scope in which the effect of the
present invention is not inhibited. Examples of the other additives
include antioxidants, ultraviolet blockers, antistatic agents,
metal inactivators, flame retarders, flame retardant aids, dyes,
pigments, nucleating agents, lubricants, affinity improvers and the
like.
Examples of the above-mentioned antistatic agents include polymeric
antistatic agents such as a block copolymer of a polyether and a
polyolefin. Furthermore, examples of the above-mentioned flame
retarders include brominated organic compounds such as brominated
bisphenol-based compounds, brominated polymers such as brominated
butadiene-based polymers and brominated polystyrenes, and the
like.
(Mass Ratio of Core Layer 2 and Coating Layer 3)
In the thermoplastic resin foamed particles 1 of the present
invention, the mass ratio of the core layer 2 to the coating layer
3 is 1:99 to 50:50, preferably 2:98 to 40:60, more preferably 3:97
to 20:80. By setting such mass ratio, the core layer containing the
functional additive at a large content is surely coated with the
coating layer, the coating layer 3 becomes foamable, and the
secondary foamability of the foamed particles is also ensured;
therefore, foamed particles having excellent fusibility during
in-mold molding while containing the functional additive at an
increased content can be obtained. The masses in the
above-mentioned mass ratio include the masses of the thermoplastic
resin and of the functional additive and the other additive
contained in the thermoplastic resin.
Meanwhile, the foamed particles of the present invention can have a
structure in which an outermost layer is formed and/or other layer
is formed between the core layer and the coating layer besides the
core layer 2 and the coating layer 3.
[Functions of Thermoplastic Resin Foamed Particles 1]
In the thermoplastic resin foamed particles 1 of the present
invention, the core layer 2 contains functional additive at a
specific incorporation ratio as an essential condition.
Furthermore, in the thermoplastic resin foamed particles 1, the
core layer 2 is a layer in which a larger amount of functional
additive is distributed, and the coating layer 3 is a layer that
contains the functional additive at a small amount or contains no
functional additive. According to the thermoplastic resin foamed
particles 1 having such conditions, even when the entirety of the
foamed particles contains functional additive in a large amount,
the secondary foamability of the thermoplastic resin foamed
particles 1 is not inhibited, and thus the fusibility of the foamed
particle molding can be maintained. Therefore, a foamed particle
molding having a high fusion rate and excellent dimension stability
and appearance while containing functional additive in a large
amount can be obtained without conducing operations such as
increasing of a molding pressure and pressurization of the foamed
particles in advance during the in-mold molding of the foamed
particles. Furthermore, since the kinds and addition amounts of the
functional additive can be adjusted for the thermoplastic resin
foamed particle molding obtained by using the thermoplastic resin
foamed particles 1, a foamed particle molding to which various
functions have been imparted can be obtained.
[Method for Preparing Thermoplastic Resin Foamed Particles 1]
The thermoplastic resin foamed particles 1 can be prepared by, for
example, the following method. Specifically, two extruders are
prepared, a thermoplastic resin composition for forming a core
layer 2 is kneaded in one extruder, and a thermoplastic resin
composition for forming a coating layer 3 is kneaded in the other
extruder. Subsequently, co-extrusion is conducted from dies each
having a predetermined shape, which are attached to the outlet
sides of the extruders, to give a sheath-core type string-shaped
composite formed of a core layer (R) and a coating layer (R)
coating the core layer (R). Secondly, the co-extruded string-shaped
composite is cut by means of a cutter equipped with a taking back
machine into a predetermined mass or size, whereby columnar
composite resin particles each having a non-foamed core layer (R)
and a coating layer (R) can be obtained. In addition, the weight of
each resin particle is preferably 0.1 to 10 mg.
Examples of the foaming agent can include organic physical foaming
agents and inorganic physical foaming agents. Examples of the
organic physical foaming agents include aliphatic hydrocarbons, and
propane, butane, pentane, hexane, heptane, cyclobutane,
cyclopentane, cyclohexane and the like are exemplified. As the
inorganic physical foaming agents, air, nitrogen, carbon dioxide,
oxygen, argon, water and the like are exemplified.
The foamed particles of the present invention can be obtained by
the following method. Firstly, the resin particles each formed of
the above-mentioned core layer (R) and the above-mentioned coating
layer (R), which are dispersed together with a dispersant in an
aqueous medium (generally water) in a pressurizable sealable
container (for example, an autoclave), are impregnated with a
foaming agent under predetermined pressurization and heating to
give foamable resin particles. Thereafter the contents in the
container are released together with the aqueous medium into an
area at a pressure lower than the pressure in the container under a
temperature condition suitable for expansion to allow the foamable
resin particles to foam, whereby foamed particles can be
obtained.
Furthermore, foamed particles having a higher expansion rate can be
obtained by subjecting the obtained foamed particles to a
pressurization treatment with a gas such as air to increase the
pressure in cells of the foamed particles, and heating them with
steam or the like (two-step foaming).
Examples of the above-mentioned dispersant include water-insoluble
inorganic substances such as aluminum oxide, calcium triphosphate,
magnesium pyrophosphate, zinc oxide, kaolin and mica, and
water-soluble polymeric protective colloidal agents such as
polyvinyl pyrrolidone, polyvinyl alcohol and methylcellulose.
Furthermore, anionic surfactants such as sodium dodecylbenzene
sulfonate and sodium alkane sulfonates, and the like can also be
used.
(Bulk Density)
The bulk density of the above-mentioned foamed particles is
preferably 0.3 g/cm.sup.3 or less in view of light weight. Even
when the above-mentioned foamed particles have a bulk density of
0.3 g/cm.sup.3 or less, excellent secondary foamability can be
obtained, and the foamed particles also have excellent in-mold
moldability. The above-mentioned bulk density is more preferably
0.01 to 0.25 g/cm.sup.3, and further preferably 0.02 to 0.2
g/cm.sup.3.
(Average Air Bubble Diameter)
The average cell diameter of the coating layer 3 of the foamed
particles of the present invention is 40 to 300 .mu.m. In a case
where the average cell diameter is lower than 40 .mu.m, it is
possible that the physical properties such as compression permanent
strain and modulus of impact resilience of the foamed particle
molding are lowered. On the other hand, in a case where the average
cell diameter goes beyond 300 .mu.m, it is possible that it becomes
difficult to obtain a fine foamed particle molding. From the
above-mentioned view-points, the above-mentioned average cell
diameter is preferably 40 to 280 .mu.m, and more preferably 50 to
250 .mu.m.
(Closed Cell Rate)
The above-mentioned foamed particles have a closed cell rate of
preferably 70% or more, more preferably 80% or more, and further
preferably 90% or more in view of in-mold moldability.
The average cell diameter, the bulk density and the closed cell
rate can be obtained by the methods described in Examples mentioned
below.
In a case where the foamed particles of present invention are
polypropylene-based resin foamed particles, it is preferable that
the foamed particles have a secondary crystal, and said secondary
crystal has a heat of fusion by a differential thermal analysis of
1 to 30 J/g.
That is, it is preferable that, when 2 to 10 mg of the
above-mentioned polypropylene-based resin foamed particles are
heated by a heat-flux differential scanning calorimetry at a
temperature rising rate of 10.degree. C./min from 23.degree. C. to
220.degree. C., the obtained DSC curve (the DSC curve of the first
heating) has an endothermic peak A inherent to the
polypropylene-based resin (hereinafter simply referred to as
"inherent peak") and more than one endothermic peak B derived from
the above-mentioned secondary crystalline at the high temperature
side of the said inherent peak (hereinafter simply referred to as
"high temperature peak"), and said high temperature peak has a heat
of fusion (hereinafter simply referred to as a high temperature
peak heat of fusion) of 1 to 30 J/g. By setting said high
temperature peak heat of fusion to be within the above-mentioned
range, a foamed particle molding having excellent molding
fusibility can be obtained.
As the method for obtaining foamed particles having a high
temperature peak in the above-mentioned DSC curve includes, in the
above-mentioned step for producing foamed particles, firstly
retaining a sealable container at an optional temperature (Ta)
within a range of a temperature that is 20.degree. C. lower than
the melting point (Tm) of the polyolefin-based resin
(Tm-20.degree.) C. or more and lower than the melting finishing
temperature (T) of the polyolefin-based resin, for a sufficient
time, preferably for about 10 to 60 minutes (a first stage
retention step). Secondly, the sealable container is adjusted to an
optional temperature (Tb) from a temperature that is 15.degree. C.
lower than the melting point (Tm) to the melting finishing
temperature (T)+10.degree. C. At this time, where necessary, the
sealable container may further be retained at said temperature for
a sufficient time, preferably about 10 to 60 minutes (a second
stage retention step). Subsequently, the foamable resin particles
are foamed by releasing the particles from the inside of the
sealable container to a low pressure area. By this method, foamed
particles having a high temperature peak can be obtained.
(Thermoplastic Resin Foamed Particle Molding)
The thermoplastic resin foamed particle molding according to the
present invention is molded by in-mold molding by using the
thermoplastic resin foamed particles 1. Furthermore, the
thermoplastic resin foamed particle molding may also be molded by
using the thermoplastic resin foamed particles 1 of the present
invention and known thermoplastic resin foamed particles in
combination. The shape of the thermoplastic resin foamed particle
molding is not specifically limited, and can be appropriately
preset to be a plate shape, a columnar shape, and various steric
shapes.
[Method for Molding Thermoplastic Resin Foamed Particle
Molding]
The thermoplastic resin foamed particle molding can be prepared by
using, for example, an in-mold molding process. Specifically,
firstly, a mold designed to have a desired shape is prepared.
Secondly, the mold is filled with the above-mentioned thermoplastic
resin foamed particles 1, and the inside of the mold is heated by
feeding steam into the mold. At this time, the coating layers 3 of
the adjacent thermoplastic resin foamed particles 1 are melt-bonded
to each other, and the thermoplastic resin foamed particles 1 are
secondary-foamed, whereby the gaps among the foamed particles are
filled, and the many thermoplastic resin foamed particles 1 filled
in the mold are integrated. The mold is then cooled, and the
content is taken out of the mold, whereby a thermoplastic resin
foamed particle molding can be obtained.
(Apparent Density)
The apparent density of the thermoplastic resin foamed particle
molding is not specifically limited, and is preferably 0.015 to
0.45 g/cm.sup.3, more preferably 0.02 to 0.3 g/cm.sup.3, and
further preferably 0.03 to 0.2 g/cm.sup.3. The apparent density of
the foamed particle molding can be obtained by dividing the mass of
the molding by the volume of the molding. The volume of the molding
can be obtained from the outside dimension and the like of the
molding.
(Fusion Rate)
From the viewpoint of obtaining an thermoplastic resin foamed
particle molding having excellent dimension stability and excellent
appearance, the fusion rate of the above-mentioned thermoplastic
resin foamed particles 1 that constitute the thermoplastic resin
foamed particle molding is 60% or more, preferably 70% or more, and
more preferably 80% or more.
(Bending Strength)
The bending strength of the above-mentioned foamed particle molding
is measured by the method described in JIS K7221-2 (1999).
Specifically, the bending strength of the molding is measured by
firstly cutting a sample piece having no molding skin surface of
120.times.25.times.20 mm out of the foamed particle molding, and
subsequently conducting a three-point bending test on the sample
piece by using an autograph apparatus manufactured by Shimadzu
Corporation under conditions of a distance between supporting
points of 100 mm and a test rate of 10 mm/min.
(Shrinkage Rate of Molding)
Since the foamed particle molding obtained by the foamed particles
of the present invention has the above-mentioned specific cell
structure, the shrinkage rate of the molding is small. It is
preferable that the shrinkage rate of the molding is 3% or less.
The shrinkage rate of the molding is measured by the method
described below.
(50% Compression Strain)
It is preferable that the foamed particle molding obtained by the
foamed particles of the present invention has a 50% compression
strain of 5 MPa or less. The 50% compression strain of the molding
is measured according to JIS K6767 (1999).
EXAMPLES
The present invention will further be explained below in detail by
Examples.
Raw material master batches (MB) were prepared by using the
following raw materials, and the thermoplastic resin foamed
particles of Examples 1 to 8 and Comparative Examples 1 to 4 shown
in Tables 3 and 4 were obtained.
(Raw Materials)
Thermoplastic resin: polypropylene-based resin shown in Table 1
Functional additive: functional additive shown in Table 2
[Preparation of Raw Material Master Batches (MB)]
The PP in Table 1 and the functional additive in Table 2 were fed
to a biaxial extruder having an inner diameter of 20 mm at the
formulation rate shown in Tables 3 and 4, melt-kneaded at 200 to
220.degree. C., and extruded into a strand shape. Said strand was
cooled and cut to give a master batch for forming a functional
additive-containing core layer and a master batch for forming a
coating layer.
[Production of Thermoplastic Resin Particles (Resin Particles)]
Example 1
An extruder including an extruder for a resin particle-core layer
having an inner diameter of 65 mm and an extruder for a resin
particle-coating layer having an inner diameter of 30 mm in which a
die for forming a multilayer strand had been attached to the outlet
sides of the extruders was prepared. The above-mentioned master
batch for forming a core layer was fed to the extruder for a resin
particle-core layer having an inner diameter of 65 mm, and
simultaneously, the above-mentioned master batch for forming a
coating layer was fed to the extruder for a resin particle-coating
layer having an inner diameter of 30 mm so as to give the
formulation rate shown in Table 3. The respective master batches
were heated at a temperature of 200 to 220.degree. C., melted and
kneaded, fed to the above-mentioned die, and combined in the die.
Furthermore, the master batches were co-extruded as a multilayer
strand including a core layer coated with a coating layer from fine
pores of a cap attached to the tip of the extruder. Subsequently,
the co-extruded strand was cooled with water, and cut with a
pelletizer so as to be 2 mg and have L/D=2.4, whereby the resin
particles described in Table 3 each having a columnar shape formed
into two layers (a sheath-core structure) were obtained. In
addition, zinc borate as a cell adjusting agent was fed to the
extruder for a coating layer so as to contain the agent of 1,000
ppm by mass in the coating layer. Furthermore, the mass ratio of
core layer:coating layer was 10:90.
[Production of Thermoplastic Resin Foamed Particles (Foamed
Particles)]
1 kg of the above-mentioned resin particles were charged together
with 3 L of water as a dispersion medium in a 5 L autoclave, and 3
g of kaolin as a dispersant, 0.04 g of a sodium alkylbenzene
sulfonate as a dispersion aid, and 0.1 g of aluminum sulfate were
each added to the dispersion medium. Carbon dioxide as a foaming
agent was injected into a sealable container with applying a
pressure so that the pressure in the container becomes the pressure
shown in Table 3, and the temperature of the sealable container was
raised by heating up to the foaming temperature while the
dispersion medium was stirred. The sealable container was retained
at a foaming temperature for 15 minutes to adjust the high
temperature peak heat of fusion of the resin particles, and the
content in the autoclave was released together with water under an
atmospheric pressure to give the thermoplastic resin foamed
particles described in Table 3.
[Production of Thermoplastic Resin Foamed Particle Molding (Foamed
Particle Molding)]
A cavity of a flat plate-molding mold having length 250 mm
(longitudinal side).times.width 200 mm.times.thickness 50 mm was
filled with the above-mentioned foamed particles, and subjected to
in-mold molding by steam heating to give a plate-like foamed
molding. At this time, pre-heating (a gas exhausting step) was
firstly conducted by feeding steam into the molding mold for 5
seconds in a state that the drain valves of the molding mold on the
both surfaces were opened, one-direction heating was then conducted
at a pressure of 0.04 MPa (G) lower than molding pressure,
one-direction heating from the opposite direction was then
conducted at a pressure of 0.02 MPa (G) lower than molding
pressure, and heating was then conducted at the molding heating
vapor pressure (molding pressure) shown in Table 3, whereby foamed
particles were formed by in-mold molding.
The molding pressure is the lowest pressure at which a molding
having excellent appearance can be obtained without significant
shrinkage of the molding. After the heating had been completed, the
pressure in the molding mold was released, the molding mold was
cooled with water until the surface pressure by the expansion force
of the molding became 0.04 MPa (G), the molding mold was opened,
and the molding was taken out of the molding mold. The obtained
molding was cured in an oven at 80.degree. C. for 12 hours to give
a foamed particle molding. The physical properties of the obtained
foamed particle molding were shown in Table 3.
Examples 2 to 8
Resin particles, foamed particles and a foamed particle molding
were obtained in similar manners to those of Example 1, except that
the conditions were changed to the conditions shown in Tables 3 and
4.
Example 9
Resin particles and foamed particles were obtained in similar
manners to those of Example 1, except that the conditions were
changed to the conditions shown in Table 4. The obtained foamed
particles were subjected to a pressurization treatment with air to
increase the pressure in the cells of the foamed particles, and
foamed by heating with steam to give two-step foamed particles. The
two-step foamed particles were subjected to in-mold molding under
similar conditions to those of Example 1 to give a foamed particle
molding.
The pressure in the cells applied to the foamed particles was 0.12
MPa, the steam pressure during the second-stage expansion was 0.09
MPa, and the core layer average cell diameter of the foamed
particles was 27 .mu.m. Furthermore, the bulk density of the foamed
particles after the second-stage expansion was shown in Table
4.
Comparative Example 1
PP1 in Table 1, CB1 in Table 2 and zinc borate were fed to a
monoaxial extruder having an inner diameter of 50 mm so that the
PP1 becomes 85.9% by mass, the CB1 becomes 14% by mass and the
content of the zinc borate becomes 1,000 ppm by mass, melt-kneaded
at 200 to 220*C, and extruded into a strand shape. Said strand was
cooled, and cut with a pelletizer so as to be 2 mg and have L/D=2.4
to give the single layer resin particles described in Table 3.
Resin particles, foamed particles and foamed particle molding were
obtained in similar manners to those of Example 1 except for the
above-mentioned points.
Comparative Example 2
Resin particles, foamed particles and foamed particle molding were
obtained in similar manners to those of Example 1, except that the
conditions shown in Table 3 were changed.
Comparative Example 3
PP1 in Table 1, CB1 in Table 2 and zinc borate were fed to a
monoaxial extruder having an inner diameter of 50 mm so that the
PP1 becomes 85.9% by mass, the CB1 becomes 14% by mass and the
content of the zinc borate becomes 1,000 ppm by mass, melt-kneaded
at 200 to 220.degree. C., and extruded into a strand shape. Said
strand was cooled, and cut with a pelletizer so as to be 2 mg and
have L/D=2.4 to give resin particles 1. PP2 in Table 1, CB2 in
Table 2 and zinc borate were fed to a monoaxial extruder having an
inner diameter of 50 mm so that the PP2 becomes 99.4% by mass, the
CB2 becomes 0.5% by mass and the content of the zinc borate becomes
1,000 ppm by mass, melt-kneaded at 200 to 220'C, and extruded into
a strand shape. Said strand was cooled, and cut with a pelletizer
so as to be 2 mg and have L/D=2.4 to give resin particles 2. The
above-mentioned resin particles 1 were foamed under similar
conditions to those of Comparative Example 1 to give foamed
particles 1 having a bulk density of 0.078 g/cm.sup.3. Furthermore,
the resin particles 2 were foamed under similar conditions to those
of Example 1 to give foamed particles 2 having a bulk density of
0.065 g/cm.sup.3. The foamed particles 1 and 2 were mixed in a
tumbler so that the weight ratio becomes 15:85, and subjected to
in-mold molding under similar conditions to those of Example 1 to
give a foamed particle molding.
The obtained foamed particle molding had a fusion rate of 95%, a
bending strength of 498 kPa, a density of 0.054 g/cm.sup.3 and a
shrinkage rate of 2.2%, and a secondary foamability of [Below
average], a surface smoothness of [Below average], a molding
uniformity of [poor] and a 50% compression strain of 468 kPa.
Comparative Example 4
Preparation of resin particles was tried in similar manners to
those of Example 1 except that the conditions shown in Table 4 were
changed. However, the content of the functional additive in the
core layer was excess, and the extrusion pressure became too high,
and thus resin particles were not able to be obtained. Accordingly,
preparation of a foamed particle molding was resigned.
TABLE-US-00001 TABLE 1 Abbreviation PP1 PP2 Polypropylene- Kind of
resin Ethylene- Ethylene-propylene based resin propylene random
random copolymer copolymer Ethylene content (%) 3.6 3.1 Melting
point (.degree. C.) 136 131 Glass transition 3 3 temperature
(.degree. C.) MFR (g/10 min) 8.2 25
TABLE-US-00002 TABLE 2 Abbreviation CB1 CB2 MO1 Functional Kind Oil
furnace Oil furnace Ferrite additive black black Product name
Ketjen Black #650B EC300J DBP absorption 360 114 -- amount
(cm.sup.3/100 g) Particle size (nm) 40 22 5
TABLE-US-00003 TABLE 3 Com- Com- parative parative Example 1
Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Resin
Core PP species PP1 PP1 PP1 PP1 PP1 PP1 PP1 particles layer PP %
86.0 86.0 82.5 86.0 86.0 86.0 86.0 Functional CB CB1 CB1 CB1 CB1
CB1 CB1 CB1 additive species CB % 14 14 17.5 14 14 14 14 Total (%
by mass) 100 100 100 100 100 100 100 Coating PP species PP1 PP1 PP1
PP1 PP1 -- PP1 layer PP % 96 96 96 96 100 -- 100 Functional CB CB2
CB2 CB2 CB2 -- -- -- additive species CB % 4 4 4 4 -- -- -- Total
(% by mass) 100 100 100 100 100 -- 100 Core layer/Coating layer
(mass ratio) 10/90 15/85 10/90 40/60 5/95 100/0 60/40 Mass of resin
particles (mg) 2 2 2 2 2 2 2 Foamed Production Retention
temperature (.degree. C.) 148 148 148 148 148 148 148 particles
conditions Retention time (min) 15 15 15 15 15 15 15 Pressure in
sealable container (MPa (G)) 2.6 2.6 2.6 2.6 2.6 3.4 2.6 Foaming
temperature (.degree. C.) 148 148 148 148 148 148 148 Physical
Apparent density (g/cm.sup.3) 0.071 0.075 0.063 0.074 0.064 0.080
0.071 properties Closed cell rate (%) 98 98 98 98 98 92 95 Average
cell diameter of coating layer 63 68 77 65 63 -- 67 (.mu.m) Average
cell diameter of core layer (.mu.m) 19 18 30 24 18 30 34 High
temperature peak heat of fusion 15.4 15.5 16.4 14.3 15.7 10.6 13.1
(J/g) Molded Physical Molding pressure (MPa (G)) 0.26 0.24 0.26
0.28 0.24 0.38 0.30 body properties Fusion rate (%) 100 100 100 100
100 95 95 Bending strength (kPa) 513 601 448 548 491 504 529
Molding density (g/cm.sup.3) 0.053 0.058 0.050 0.053 0.056 0.058
0.053 Shrinkage rate (%) 2.2 2.2 2.8 2.8 2.2 3.8 3.2 Secondary
foamability Good Good Good Good Good Poor Below Average Surface
smoothness Excellent Excellent Excellent Good Excellent Poor Bel-
ow Average molding uniformity Good Good Good Good Good Good Good
50% compression strain (kPa) 430 476 317 397 461 447 388
TABLE-US-00004 TABLE 4 Comparative Example 6 Example 7 Example 8
Example 4 Example 9 Resin Core PP species PP2 PP2 PP2 PP1 PP1
particles layer PP % 10 60 30 5 86.0 Functional Kind MO1 MO1 MO1
MO1 CB1 additive Formulation 90 40 70 95 14 amount (% by mass)
Total (% by mass) 100 100 100 100 100 Coating PP species PP1 PP1
PP1 PP1 PP1 layer PP % 100 100 100 100 100 Functional Kind -- -- --
-- -- additive Formulation -- -- -- -- -- amount (% by mass) Total
(% by mass) 100 100 100 100 100 Core layer/Coating layer (mass
ratio) 10/90 10/90 10/90 10/90 5/95 Weight of resin particles (mg)
2 2 2 -- 2 Foamed Production Retention temperature (.degree. C.)
148 148 148 -- 148 particles conditions Retention time (min) 15 15
15 -- 15 Pressure in sealable container (MPa (G)) 2.6 2.6 2.6 --
2.6 Foaming temperature (.degree. C.) 148 148 148 -- 148 Physical
Apparent density (g/cm.sup.3) 0.078 0.077 0.071 -- 0.026 properties
Closed cell rate (%) 96 96 98 -- 98 Average cell diameter of
coating layer 102 126 118 -- 92 (.mu.m) High temperature peak heat
of fusion 14 14.2 14.8 -- 15.7 (J/g) Molding Physical Molding
pressure (MPa (G)) 0.18 0.22 0.20 -- 0.18 properties Fusion rate
(%) 100 100 100 -- 100 Bending strength (kPa) 405 449 459 -- 191
Molding density (g/cm.sup.3) 0.050 0.051 0.056 -- 0.020 Shrinkage
rate (%) 2.4 2.4 2.4 -- 3.2 Secondary foamability Good Good Good --
Good Surface smoothness Excellent Excellent Excellent -- Excellent
molding uniformity Good Good Good -- Good 50% compression strain
(kPa) 311 376 328 -- 198
In Tables 3 and 4, the mass ratio of coating layer/core layer
represents the ratio (%) of the respective masses of the coating
layer and the core layer to the total mass of the resin
particles.
The physical properties of the foamed particles and the foamed
particle molding were evaluated by the following methods.
[Bulk Density of Foamed Particles]
The bulk density of the foamed particles was obtained as follows. A
1 L measuring cylinder was firstly prepared, and filled with a
group of the foamed particles up to the gauge line of 1 L in the
measuring cylinder. The mass of the filled foamed particles per 1 L
(g/L) was measured, and the unit was converted to obtain the bulk
density (g/cm.sup.3) of the foamed particles.
[Closed Cell Rate of Foamed Particles]
The closed cell rate of the foamed particles was measured as
follows. Using the foamed particles having a bulk volume of about
20 cm.sup.3 that had been left in a thermostat chamber for 10 days
as a measurement sample, an apparent volume Va was measured as
follows according to the submersion method. The measurement sample
for which the apparent volume Va was measured was sufficiently
dried, and according to the procedure C described in ASTM-D2856-70,
the value Vx of the true volume of the measurement sample was
measured by "an air-comparison pycnometer 930" manufactured by
Beckman-Toshiba, Ltd. Furthermore, based on these volume values Va
and Vx, the closed cell rate was calculated according to the
following formula, and an average value of five samples (N=5) was
deemed as the closed cell rate of the foamed particles.
(Mathematical Formula 7) Closed cell rate
(%)=(Vx-W/.rho.).times.100/(Va-Q/.rho.) (6)
In the formula, Vx: the true volume (cm.sup.3) of the foamed
particles measured by the above-mentioned method, i.e., the sum of
the volume of the resin that constitutes the foamed particles and
the total volume of the closed cell parts in the foamed particles
Va: the apparent volume (cm.sup.3) of the foamed particles measured
from the raising of the water level when the foamed particles are
submerged in water in a measuring cylinder W: the weight (g) of the
measurement sample of the foamed particles .rho.: the density
(g/cm.sup.3) of the resin that constitutes the foamed particles
[Average Cell Diameter of Foamed Particles]
The average cell diameter of the foamed particles was measured as
follows. The average cell diameter was obtained as follows based on
an enlarged photograph obtained by photographing under a microscope
a cross-sectional surface obtained by cutting one foamed particle
at the B-B cross-sectional surface in FIG. 1 into approximately
halves as in FIG. 3. Firstly, in the cross-sectional enlarged
photograph of the foamed particle, a perpendicular bisector I with
respect to a line segment having the minimum distance from the
upper end surface to the lower end surface of the foamed particle
was drawn so that the perpendicular bisector runs on the center of
the cross-sectional surface of the foamed particle. Secondly, the
length of the line segment I from the left end surface to the right
end surface of the foamed particle was measured. Subsequently, the
length was set as Lc (.mu.m), the number Nc of the cells
intersecting with the straight line I was obtained, and a value
obtained by dividing Lc by Nc (Lc/Nc) was deemed as the average
cell diameter of the core layer 2 of one foamed particle.
Furthermore, in the cross-sectional enlarged photograph of the
foamed particle, a curve running at 100 .mu.m inwardly away from
the upper end surface of the foamed particle was drawn from the
right end surface to the left end surface. Subsequently, the length
Ls (.mu.m) of the curve and the number of the cells intersecting
with the curve Ns were obtained, and a value obtained by dividing
Ls with Ns (Ls/Ns) was set as an average cell diameter of the
coating layer 3 in one foamed particle. These operations were
conducted on ten foamed particles, and a value obtained by
arithmetically averaging the average cell diameters of the core
layer 2 and the coating layer 3 of each foamed particle was set as
an average cell diameter of the core layer 2 and the coating layer
3 of the foamed particle.
[High Temperature Peak Heat of Fusion of Foamed Particles]
In a DSC curve obtained by heating 1 to 3 mg of the foamed
particles by a thermal flux differential scanning calorimeter from
25.degree. C. to 200.degree. C. at a temperature rising rate of
10.degree. C./min (a DSC curve of first heating), an inherent peak
Pc having a peak temperature PTmc inherent to the thermoplastic
resin appears. Furthermore, more than one endothermic peak Pd
having a peak temperature PTmd appears in the high temperature
region of said inherent peak. Said endothermic peak Pd is/are the
high temperature peak in the present invention, and the surface
area of said endothermic peak Pd corresponds to the melting heat of
fusion (D) of the high temperature peak of the foamed particles. In
addition, the high temperature peak Pd obtained by the retention
operation during the above-mentioned production of the foamed
particles appears in the DSC curve of the first heating of the
foamed particles measured as above, but does not appear in the DSC
curve of the second heating obtained when the foamed particles are
cooled from 200.degree. C. to 25'C at a cooling rate of 10.degree.
C./min after the DSC curve of the first heating is obtained, and
heated again at a temperature rising rate of 10.degree. C./min up
to 200.degree. C. Therefore, since only a similar endothermic peak
to the inherent peak Pc appears in the DSC curve of the second
heating, the inherent peak Pc can be easily distinguished from the
high temperature peak Pd. The average value of the high temperature
peak heat of fusion of five foamed particles (N=5) was deemed as
the high temperature peak heat of fusion of the foamed
particles.
[Apparent Density of Foamed Particle Molding]
The apparent density of the foamed particle molding was obtained by
dividing the mass (g) of the molding by the volume (cm.sup.3)
obtained from the outside dimension of the molding.
[Fusion Rate of Molding]
The fusion rate of the molding was obtained based on the ratio of
the number of the foamed particles that had under-gone material
failure among the foamed particles exposed on a broken
cross-sectional surface when the foamed particle molding was
broken. Specifically, firstly, test pieces were cut out of the
foamed particle molding, a cut of about 5 mm was made by a cutter
knife in each test piece, and the test piece was broken from the
cut part. Secondly, the number (n) of the foamed particles present
on the broken cross-sectional surface of the foamed particle
molding and the number (b) of the foamed particles that had
undergone material failure were measured, and the ratio of (b) to
(n) (b/n) was represented by a percentage and deemed as a fusion
rate (%).
[Shrinkage Rate]
The shrinkage rate [%] of the foamed particle molding was obtained
by ((250 [mm]-the longer side length of the molding [mm])/250
[mm]).times.100. The "250 [mm]" is the size of the longer side of
the molding mold. Furthermore, "the longer side length of the
molding [mm]" is a value obtained by curing the foamed particle
molding obtained in each of Examples and Comparative Examples under
an atmosphere of 80.degree. C. for 12 hours, annealing, and further
curing under an atmosphere of 23.degree. C. for 6 hours, and
thereafter calculating the length of the longer side of the foamed
particle molding.
[Surface Smoothness]
The surface smoothness of the foamed particle molding was evaluated
by an observation of the surface of the molding by the unaided
eyes. Excellent: represents a fine surface state in which no
wrinkles, shrinks, and unevenness due to depression are observed on
the surface of the foamed particle molding. Good: Slight wrinkles,
shrinks, and unevenness due to depression are observed on the
surface of the foamed particle molding. Below average: Clear
wrinkles, shrinks, and unevenness due to depression are observed on
the surface of the foamed particle molding. Poor: Wrinkles,
shrinks, and unevenness due to depression on the surface of the
foamed particle molding are significant. [Secondary
Foamability]
The secondary foamability of the foamed particle molding was
evaluated as follows. Good: The gaps among the foamed particles on
the surface of the molding are completely filled. Below average:
The gaps among the foamed particles on the surface of the molding
are slightly observed. Poor: The gaps among the foamed particles on
the surface of the molding are clearly unfilled. [50% Compression
Strain]
The mechanical strength of the molding was evaluated by measuring
the 50% compression strain of the foamed particle molding. Firstly,
a test piece was cut out of the central part of the molding into
length 50 mm.times.width 50 mm.times.thickness 25 mm so that the
portions except for the skin layer during the molding has a cubic
shape. Secondly, using an AUTOGRAPH AGS-X (manufactured by Shimadzu
Corporation) on this test piece, the load at 50% strain was
obtained at a compression rate of 10 mm/min according to JIS K 6767
(1999). The 50% compression strain [kPa] was obtained by dividing
this load by the pressurized surface area of the test piece.
[Electrostatic Capacity]
The electrostatic capacity of the foamed particles was measured by
using a electrostatic capacity meter CM113N manufactured by
Yamamoto Electric Instruments. A probe having a detection electrode
diameter of 98 mm, a guard electrode outer diameter of 150 mm, an
inner diameter of 100 mm, an electrode width of 50 mm, and an
insulation distance between electrodes of 2 mm (A1407-8065) was
used. Specifically, firstly, a metal plate to be a counter
electrode was put on the horizontal surface, and a cylinder made of
an insulator of inner diameter 100 mm.times.outer diameter 150
mm.times.height 100 mm was put thereon so that the circular part
becomes a bottom surface. Secondly, a measurement probe was
installed on the cylinder so that any gap is not generated between
the guard electrode and the cylinder, and the origin point was
adjusted by measuring the electrostatic capacity. The cylinder on
the counter electrode was then filled to full leveling with the
foamed particles that had been cured under conditions of 23'C and
50% RH for 1 day so that the gaps are minimized, a measurement
probe was then put on the cylinder filled with the foamed
particles, and the electrostatic capacity of the foamed particles
was measured. The measured electrostatic capacity was 0.326 pF in
Example 1, and 0.369 pF in Example 2.
[Molding Uniformity]
Good: The foamed particle molding is evenly constituted since it is
constituted by a single kind of foamed particles. Poor: The foamed
particle molding is unevenly constituted since it is constituted by
two kinds of foamed particles. [Results of Evaluation]
In the foamed bodies of Examples 1 to 9, the core layers of the
foamed particles were highly filled with the functional additives.
Furthermore, since the coating layers of the foamed particles were
foamed, and the coating layers did not contain the functional
additives in a large amount with respect to the core layers, the
foamed particles were excellent in the secondary foamability during
the in-mold molding. Therefore, it was confirmed that a molding
being excellent in fusibility and dimension stability while
containing functional additives in a large amount, and also being
excellent in appearance, in which the gaps of the foamed particles
are filled, and no wrinkles, shrinks and depressions are seen on
the surface, was able to be obtained. Accordingly, it can be said
that a foamed particle molding having a low shrinkage rate and
being excellent in dimension stability can be obtained while
utilizing the properties of various functional additives, by using
the foamed particles of the present invention in which the
functional additives are incorporated.
On the other hand, Comparative Example 1 is an example of a foamed
particle molding having a single layer, in which the core layers of
the foamed particles are highly filled with the functional
additives. Therefore, problems remained in the secondary
foamability of the foamed particles and the appearance of the
molding, the shrinkage rate of the molding was high, and the
molding was poor in dimension stability.
In Comparative Example 2, since the mass ratio of the core layers,
which were highly filled with the functional additives, in the
foamed particles was high, the foamed particles were poor in
secondary foamability, the shrinkage rate of the molding was high,
and the molding was poor in dimension stability and appearance.
In Comparative Example 3, the foamed particle molding was formed
from the foamed particles formed by mixing the foamed particles 1
and 2 having different functional additive contents. The foamed
particles 1, which have a large functional additive content and a
dark color, are different in appearance from the foamed particles
2, which have a light color, and thus these foamed particles can be
identified. In Comparative Example 3, it was confirmed by a visual
observation that the foamed particles 1 were interspersed in the
molding, and the molding was heterogeneously constituted.
Furthermore, differences were seen in the degrees of dispersion of
the foamed particles 1 in the moldings among the plural foamed
particle molding prepared by the production method of Comparative
Example 3. Moreover, since the difference in molding shrinkage rate
and the difference in secondary foamability were significant
between the part formed of the foamed particles containing carbon
black at a large amount and the part formed of the foamed particles
containing carbon black at a small amount in the molding, the
obtained molding was poor in secondary foamability and surface
smoothness.
Furthermore, since the concentration of the filler material added
to the core layers was very high in Comparative Example 4, resin
particles were not able to be made, and thus a foamed body was not
able to be obtained.
* * * * *