Note: Descriptions are shown in the official language in which they were submitted.
2102608
1 <TECHNICAL FIELD>
The present invention relates to a cushioning
composite molded article comprising a rigid substrate
and a cushioning material integrally formed on said
rigid substrate and coated with a surface material, and
a process for producing the same. More particularly,
the present invention relates to a cushioning composite
molded article having a rigid substrate for attaining a
certain strength and a surface material-coated cushion-
ing material for att~i n i ng an excellent appearance and asoft feel, which is used, for example, in parts and
products of automotive trims (instrument panel, door
panels, seat back panels, steering wheel, pulls, etc.),
furniture (seating part of chair, etc.), sundries
(shoes, slippers, etc.), and the like.
<BACKGROUND ART>
As processes for producing a cushioning com-
posite molded article, the following processes have
been known.
(1) A process comprising producing a surface
material by vacuum forming of a semirigid vinyl chloride
resin into a semirigid vinyl chloride sheet or by slash
- 2102608
~ - 2 -
l molding of semirigid vinyl chloride resin powder, pro-
ducing rigid substrate by injection-molding a polypro-
pylene, an AS resin, an ABS resin or the like, placing
said surface material and said rigid substrate in a
mold, injecting an expandable polyurethane between the
surface material and the rigid substrate, and expanding
the polyurethane to obtain a cushioning material.
(2) A process in which a laminate of a
surface material and a cushioning material which is
obtained by bonding a semirigid vinyl chloride sheet and
an expanded crosslinked polypropylene sheet to each
other with an adhesive is adhered to a rigid substrate
separately obtained by injection molding, by vacuum
forming.
(3) A process comprising setting in a mold a
laminate of a surface material and a cushioning material
which is obtained by bonding a semirigid vinyl chloride
sheet and an expanded crosslinked polypropylene sheet
to each other with an adhesive; injecting a rigid resin
into a lower mold constituting said mold to mold a rigid
substrate; and thereby uniting the rigid substrate and
the laminate of a surface material and a cushioning
material in a body.
All of the above conventional processes,
however, are disadvantageous in that they involve a
large number of steps for production, require much labor
and entail great cost because in all the processes,
products individually obtained by forming or molding,
210260~
-- 3 --
1 i.e., a surface material made of a non-expandable mate-
rial, a cushioning material obtained by expansion of an
expandable elastomer, and a rigid substrate molded using
a rigid-resin, are united in a body to obtain a product.
For solving these problems, many processes
have been developed but all of them have defects.
Japanese Patent Une~mined Publication No. 1-
249416 discloses a process for producing a molded
article of flexible resin which comprises inserting a
resin insert made of a polyolefin into a mold, injecting
a thermoplastic elastomer material containing a blowing
agent into the mold in an amount smaller than the
capacity of said mold (this operation is hereinafter
referred to as "short shot"), expanding the thermo-
plastic elastomer material- in the mold to form a
non-expanded skin, adhering or heat-fusing a flexible-
resin coat having said skin to said insert, and thereby
producing a flexible-resin molded article (insert-short
shot process).
However, in this process, there cannot be
obtained a molded article having a small thickness, a
high expansion ratio and a correct transcript of the
surface pattern of the mold. The molded article
produced by this process has a markedly rough surface,
that is, characteristic of an expanded molded article
obtained by a short shot process. Thus, there cannot be
obtained a molded article intended according to the
present invention, i.e., a molded article having a
- 2102608
-- 4
l surface similar to that of, for example, natural leather
which can be obtained only by correct transcription of
the surface pattern of a mold.
Japanese Patent Unex~m;ned Publication No. 49-
10967 discloses a process for producing a multilayerstructure having a polyolefin foam layer which is
characterized by placing a strength-maintaining material
previously in a mold for injection molding which has a
cavity capable of increasing its capacity while holding
therein a molten resin, injecting a plastified expand-
able polyolefin resin into said mold cavity, and then
increasing the capacity of said cavity to expand the
polyolefin (insert-space-in-mold enlarging process).
However, since polyolefins do not have a good
rubber-like elasticity which saturated-type styrene-
based substances have, this process characterized by
expanding a polyolefin cannot give a cushioning com-
posite molded article of high quality having a soft and
pleasant feel which is intended according to the present
invention.
Japanese Patent Unexamined Publication No. 63-
227313 discloses an injection-molded article of flexible
resin comprising a resin insert and a flexible-resin
coat,wherein the resin insert is made of a polyolefin
resin, the flexible-resin coat is made of a styrene-
based thermoplastic elastomer having a hardness (JIS
K6301: type A) of 10 to 50 and a compression set (JIS
K6301: 70C x 22 h) of 70% or less, and the thickness of
2102608
-- 5 --
1 the flexible-resin coat is 0.5 mm or more (insert.on-
expanded molded product).
This molded article is obtained by a conven-
tional insert-non-expansion injection molding method.
The conventional insert-non-expansion injection molding
method permits production of a thin molded article hav-
ing a correct transcript of the surface pattern of a
mold but cannot give a cushioning composite molded
article of high quality having a soft and pleasant feel
which is intended according to the present invention.
<DISCLOSURE OF THE INV~N'1'10N>
An object of the present invention is to
provide a cushioning composite molded article of high
quality obtained by unitin-g in a body a flexible surface
material composed of an elastomer which is made of a
non-expanded product, a cushioning material formed by
expansion of an elastomer, and a rigid substrate
composed of a molded product of rigid resin. Another
object of the present invention is to provide a process
for producing said composite molded article through a
small number of steps at low cost. More specifically,
the present invention permits the following production:
a cushioning composite molded article comprising a rigid
substrate, a surface material having good appearance and
feel similar to those of, for example, natural leather,
and a cushioning material coated with said surface
material and formed on said rigid substrate is produced
2102608
1 through a small number of steps for production, at a low
production cost by setting a previously produced molded
product of rigid resin as a rigid substrate in a mold
having a space larger than the rigid-resin molded
product, injecting an expandable elastomer into the
space so as to achieve full shot into the mold, forming
a layer of the expandable elastomer integrally on the
rigid substrate, and then enlarging the mold cavity to
expand the layer of the expandable elastomer (insert-
space-in-mold enlarging process); or a cushioning
composite molded article comprising a rigid substrate, a
surface material having good appearance and feel similar
to those of, for example, natural leather, and a
cushioning material coated with said surface material
and formed on said rigid substrate is produced through a
small number of steps for production, at a low produc-
tion cost by injecting a rigid resin into a mold to fill
the mold therewith completely, thereby obt~ining a
molded product of the rigid resin as a rigid substrate,
enlarging the inside of the mold after cooling, inject-
ing an expandable elastomer into the space in the mold
which has been formed by the enlargement, to fill the
mold with said substance completely, forming a layer of
the expandable elastomer integrally on the rigid sub-
strate, and then further enlarging the inside of themold to expand the layer of the expandable elastomer
(two layer molding.space-in-mold enlarging process).
In other words, the present invention relates
2102608
_ - 7 -
1 to a process for producing a cushioning composite moldedarticle comprising a rigid substrate and a cushioning
material integrally formed on said substrate, the
surface of said cushioning material having a correct
transcript of the surface pattern of a mold and having
an excellent appearance and a soft feel, which process
comprises
setting a rigid substrate previously molded in
a desired shape, in a mold having a space larger than
said rigid substrate, or injecting a rigid resin into a
mold of a desired shape to form a rigid substrate,
followed by enlarging the inside of the mold so as to
form a space,
thereafter injecting an expandable elastomer
into the space to form integrally on the rigid substrate
a layer of the expandable elastomer which has been
coated with a surface material formed as a skin layer
having a correct transcript of the surface pattern of
the mold, and
then enlarging the mold cavity to expand the
aforesaid layer of the expandable elastomer, and thereby
forming a cushioning material coated with the above-
mentioned surface material; and a cushioning composite
molded article produced by said production process.
<BRIEF DESCRIPTION OF THE DRAWINGS>
Fig. 1 is an illustration showing the pro-
cedure in the first embodiment of the production process
2102608
- 8 -
1 of the present invention.
Fig. 2 shows cross-sectional views of the
cushioning composite molded article according to the
present invention.
Fig. 3 is an illustration showing the
procedure in the second embodiment of the production
process of the present invention.
The symbols in the drawings have the following
meanings:
1 rigid-resin molded product,
2, 2' molds,
2a, 2a' stationary molds,
2b movable mold,
3 elastomer,
4 skin layer,-
cushioning composite molded article,
6 surface material,
7 expanded elastomer,
8 cushioning material,
9 rigid substrate.
<BEST MODE FOR CARRYING OUT THE INVENTION>
The present invention relates to the above-
mentioned production processes (the insert-space-in-
mold enlarging process and the two-layer molding-space-
in-mold enlarging process) and molded articles produced
by the production processes, and is based on the finding
that a cushioning composite molded article of high
-- 2102608
g
l quality comprising a rigid substrate and a cushioning
material coated with a surface material having good
appearance and feel similar to those of, for example,
natural leather can be produced through a small number
of steps for production, at low cost by the use of a
specified elastomer and proper determination of molding
conditions (the temperature of the inner surface of a
mold, the interval between the completion of injection
and the initiation of the backward movement of a movable
mold, etc.), without employing a dangerous process in
which a high-pressure gas is previously introduced into
the space in a mold (counter pressure process).
The thermoplastic elastomer in the present
invention constitutes the surface material and the
cushioning material. As the elastomer, a saturated-type
styrene-based elastomer is used. As the saturated-type
styrene-based elastomer, there is preferably used a
saturated-type styrene-based elastomer and having an
average molecular weight of not more than 70,000 and
more than 30,000 as measured by a GPC method and an A
hardness according to JIS K6301 of not more than 100 and
more than 50. The saturated-type styrene-based elasto-
mer may be either a saturated-type styrene-butadiene
based elastomer or a saturated-type styrene-isoprene
based elastomer.
A saturated-type styrene-based elastomer and
having an average molecular weight of more than 70,000
is not well expandable when the process of the present
2102608
-- 10 --
1 invention is employed. In the case of a saturated-type
styrene-based elastomer and having an average molecular
weight of 30,000 or less, when the process of the
present invention is employed, no cushioning composite
molded article of high quality can be obtained because
open cells are formed by breakage of cell walls in an
expansion step, huge cells are formed, or cracks or
hollows are formed in the inner part.
In the case of a saturated-type styrenebased
elastomer and having an A hardness according to JIS
K6301 of more than 100, when the process of the present
invention is employed, there cannot be obtained a
cushioning composite molded article of high quality
comprising a cushioning material coated with a surface
material having good appearance and feel similar to
those of, for example, natural leather. In the case of
a saturated-type styrene-based elastomer and having an A
hardness according to JIS K6301 of 50 or less, when the
process of the present invention is employed, said
substance is well expandable, but a cushioning composite
molded article obtained by molding said elastomer has a
sticky surface and is very flexible, namely, no cushion-
ing composite molded article of high quality can be
obtained.
The saturated-type styrene-based elastomer
may be used alone or as a compound with other elasto-
mers, synthetic resins, fillers, etc. Particularly when
the saturated-type styrene-based elastomer is in the
2lo26o8
l form of a compound of the above-mentioned specified
saturated-type styrene-based elastomer and a polyolefin,
a cushioning composite molded article of high quality
can very easily be obtained.
The polyolefin usable in the compound of the
specified saturated-type styrene-based elastomer and the
polyolefin includes, for example, polyolefins such as
low-density polyethylenes, linear low-density poly-
ethylenes, high-density polyethylenes, polypropylenes,
polybutenes, etc.; ethylene-based copolymers of ethylene
and other olefin monomers; ethylene-based copolymers of
ethylene and other vinyl monomers; propylene-based
copolymers of propylene and other olefin monomers; and
olefin-based elastomer, such as ethylene-propylene
based elastomer.
Particularly when the saturated-type styrene-
based elastomer is in the form of a compound of the
above specified saturated-type styrene-based elastomer
and the polyolefin, the A hardness according to JIS
K6301 of this compound should be in the range of not
more than 100 and more than 50. When the A hardness is
outside this range, no flexible cushioning composite
molded article of high quality comprising a cushioning
material coated with a surface material having good
appearance and feel similar to those of, for example,
natural leather can be obtained by the process of the
present invention.
The melt viscosity of said compound at a
~ 2102608
- 12 -
l temperature at which said compound is injected in the
process of the present invention should be in the range
of not more than 3,000 poise and not less than 300 poise
at a shear rate of 1,000/sec and in the range of not
more than 50,000 poise and not less than 5,000 poise at
a shear rate of 10/sec. When the melt viscosity is
outside these ranges, no cushioning composite molded
article of high quality comprising a cushioning material
coated with a surface material having good appearance
and feel similar to those of, for example, natural
leather can be obtained by the process of the present
invention. Particularly when the melt viscosity at a
shear rate of 1,000/sec exceeds 3,000 poise and the melt
viscosity at a shear rate of 10/sec exceeds 50,000
poise, the process of the present invention does not
permit satisfactory molding of said compound and its
expansion.
The present invention is explained below in
further detail.
In the insert-space-in-mold enlarging process,
i.e., the first embodiment of production of the compo-
site molded article of the present invention, and the
two-layer molding-space-in-mold enlarging process, i.e.,
the second embodiment, the most preferable average
molecular weight of the expandable elastomer for the
most important step therein, the step of forming a
surface material and a cushioning material is not more
than 60,000 and not less than 40,000. A method using a
2102608
_ 13 -
l thermoplastic elastomer having a relatively high
molecular weight and a thermoplastic elastomer having a
relatively low molecular weight by mixing said twos in
such a manner that an average molecular weight of the
resultant mixture becomes not less than 40,000 but not
more than 60,000, is also a preferable method. The
resultant mixture has both the characteristics of the
thermoplastic elastomer having a relatively high mole-
cular weight and those of the thermoplastic elastomer
having a relatively low molecular weight, and thus can
be free from the defects of the two thermoplastic elas-
tomers. When the average molecular weight of thermo-
plastic elastomer is increased, the melt viscosity of
the thermoplastic elastomer at the time of molding is
increased, so that the strength and heat resistance of a
molded article are improved, but production of a thin
and large molded article and the expansion become
difficult. On the other hand, when the average mole-
cular weight of thermoplastic elastomer is decreased,
the melt viscosity of the thermoplastic elastomer at the
time of molding is decreased, so that the production of
a thin and large molded article and the expansion become
easy, but the strength and heat resistance of a molded
article are deteriorated. Therefore, it is most prefer-
able to choose the most suitable average molecularweight of thermoplastic elastomer in the range of not
more than 60,000 and not less than 40,000 depending on
the shape, dimensions and required characteristics of
- 2102608
- 14 -
1 a molded article.
According to the process of the present
invention, the thickness of the surface material and
the expansion ratio of the cushioning material can be
optionally determined by proper determination of molding
conditions, and hence a flexible cushioning composite
molded article of high quality can be obtained by
adjusting the thickness of the surface material to a
small thickness and the expansion ratio of the cushion-
ing material to a high ratio, even when the A hardnessaccording to JIS K6301 of the saturated-type styrene-
based elastomer is relatively high. However, when the A
hardness according to JIS K6301 exceeds 100, the result-
ing cushioning composite molded article is too rigid and
there cannot be obtained a-flexible cushioning composite
molded article of high quality which is intended accord-
ing to the present invention. A flexible cushioning
composite molded article of high quality can be obtained
by adjusting the thickness of the surface material to a
large thickness and the expansion ratio of the cushion-
ing material to a low ratio, even when the A hardness
according to JIS K6301 of the saturated-type styrene-
based elastomer is relatively low. However, when the A
hardness according to JIS K6301 is 50 or less, the
resulting cushioning composite molded article has a
sticky surface and is markedly flexible, namely, it is
not a cushioning composite molded article of high
quality which is intended according to the present
2102608
.
l invention.
As to conditions of the injection molding of
the expandable elastomer in the step of forming the
surface material and the cushioning layer, it is most
important to determine properly the temperature of
molten elastomer in an injection cylinder, the pressure
of the molten elastomer in the injection cylinder until
the initiation of injection (the back pressure), the
pressure of the molten elastomer in the injection
cylinder at the time of the injection (the injection
pressure), the temperature of the inner surface of a
mold, the thermal conductivity of the mold, the period
between the initiation and completion of the injection
(the injection time), the interval between the comple-
tion of the injection and the initiation of backwardmovement of a movable mold (the initiation of primary
mold opening) (the interval to the initiation of mold
opening), the period between the initiation and
completion of the backward movement of the movable mold
(the time required for the mold opening), and the
interval between the completion of backward movement of
the movable mold and the initiation of mold opening (the
initiation of secondary mold opening) (the cooling
time).
The temperature of the molten elastomer in an
injection cylinder is set in the range of l90 - 270C.
The pressure of the molten elastomer in the
injection cylinder until the initiation of the injection
210260~
- 16 -
1 (the back pressure) is set in the range of 10 kg/cm2 to
500 kg/cm2. A gas for expansion generated by the decom-
position of a chemical blowing agent should be com-
pletely dissolved in the molten elastomer, and hence
the pressure should be set at a pressure at which the
chemical blowing agent is completely dissolved.
Usually, the pressure is preferably set in the range of
20 kg/cm2 to 100 kg/cm2.
The pressure of the molten elastomer in the
injection cylinder at the time of the injection (the
injection pressure) is set in the range of 100 kg/cm2 to
1,500 kg/cm2. Usually, it is preferably set in the
range of 300 kg/cm2 to 1,000 kg/cm2.
The temperature of the inner surface of the
mold is set in the range of 0 - 80C. Although it is
usually sufficient that the temperature is set in the
range of 10 - 30C, the temperature is preferably set at
a relatively high temperature when an elastomer high
molecular weight is used or when a compound comprising
an elastomer having a high melt viscosity is used. When
the temperature of the inner surface of the mold is set
at a relatively high temperature, it becomes necessary
to adjust the interval between the completion of the
injection and the initiation of backward movement of the
movable mold (the initiation of primary mold opening) to
a long time or adjust the period between the initiation
and completion of the backward movement of the movable
- 2102608
- 17 -
l mold to a long time.
A material for the mold is not particularly
limited and all of generally used metals can be suitably
used. For improving the transcription of the surface
pattern of the mold, it is possible to coat the surface
of the mold with a highly heat insulating material or
use a mold made of a material having a low thermal
conductivity, such as a resin mold or a ceramic mold.
When the surface of the mold is coated with a highly
heat insulating material or when a mold made of a
material having a low thermal conductivity, such as a
resin mold or a ceramic mold is used, it becomes neces-
sary to adjust the interval between the completion of
the injection and the initiation of backward movement of
the movable mold (the initiation of primary mold open-
ing) to a long time or adjust the period between the
initiation and completion of the backward movement of
the movable mold to a long time. A leather pattern or
other patterns may be formed on the surface of the mold
which comes into direct contact with the surface
material, so as to make it possible to transfer the
pattern to the surface material, depending on
application purposes of the composite molded article.
The period between the initiation and com-
pletion of the injection (the injection time) should be
adjusted to as short a time as possible. Usually, it is
adjusted to preferably 5 seconds or less, more prefer-
ably 1 second or less, most preferably 0.5 second or
- 2102608
- 18 -
l less. When the period between the initiation and com-
pletion of the injection is too long, expansion begins
before the completion of the injection, so that no
satisfactory molded article can be produced. Although
it is difficult in some cases to adjust the period to a
very short time in the case of a large-sized molded
article, the period should be adjusted to as short a
time as possible.
The adjustment of the interval between the
completion of the injection and the initiation of
backward movement of the movable mold (the initiation of
primary mold opening) (the interval to the initiation of
mold opening) is very important, and the interval should
be adjusted to as short a time as possible. Usually,
the interval is adjusted to preferably 30 seconds or
less, more preferably 5 seconds or less. It is often
preferable to adjust the interval to 1 second or less.
The thickness of the surface material can be reduced by
adjusting the interval to a short time, and it can be
increased by adjusting the interval to a long time.
When the A hardness according to JIS K6301 of the
elastomer is relatively high, a molded article of good
quality can be obtained by reducing the thickness of the
surface material by adjusting the interval to a rela-
tively short time. When the A hardness according to JISK6301 of the elastomer is relatively low, a molded
article of good quality can be obtained by increasing
the thickness of the surface material by adjusting the
21026~38
-- 19 --
l interval to a relatively long time. When the interval
is too long, the elastomer is not expanded. When the
interval is too short, no satisfactory surface material
is formed.
The adjustment of the period between the
initiation and completion of the backward movement of
the movable mold (the time required for the mold
opening) is very important, and the period should be
properly adjusted.Usually, the period is preferably
adjusted to 30 seconds or less. The thickness of the
surface material can be reduced by adjusting the period
to a short time, and it can be increased by adjusting
the period to a long time. When the A hardness accord-
ing to JIS K6301 of the elastomer is relatively high, a
molded article of good quality can be obtained by reduc-
ing the thickness of the surface material by adjusting
the interval to a relatively short time. When the A
hardness according to JIS K6301 of the elastomer is
relatively low, a molded article of good quality can be
obtained by increasing the thickness of the surface
material by adjusting the interval to a relatively long
time. When the period is too long, the elastomer is
not expanded. When the period is too short, no satis-
factory surface material is formed.
The interval (the cooling time) between the
completion of backward movement of the movable mold and
the initiation of mold opening (the initiation of
secondary mold opening) is preferably adjusted to a
`- 210261)8
- 20 -
1 somewhat long time. Usually, the interval is preferably
adjusted to 30 seconds or more. When the interval is
too short, expansion continues till after the initiation
of mold opening (the initiation of secondary mold
opening), so that no molded article of good quality can
be obtained in some cases.
The elastomer used in the present invention is
one which is expandable and contains a blowing agent.
As the blowing agent, any blowing agent may be used so
long as it makes it possible to expand and mold the
elastomer by injection molding. There can be used, for
example, organic chemical blowing agents such as azo
compounds (e.g. azodicarbonamide), nitroso compounds
(e.g. N,N'-dinitrosopentamethylenetetramine), etc., and
inorganic chemical blowing agents such as sodium
carbonate, sodium bicarbonate, etc. Simultaneous use of
the organic chemical blowing agents and the inorganic
chemical blowing agents is also a good method.
When the expansion and molding are carried out
at a relatively high temperature, azodicarbonamide and
sodium bicarbonate are preferable though there can also
be used compounds such as p,p'--oxybis(benzene sulfonyl
semicarbazide), p-toluenesulfonyl semicarbazide,
trihydrazinotriazine, barium azodicarboxylate, etc.
Needless to say, these blowing agents may
contain various expansion assistants.
As the rigid resin which constitutes the
insert substrate or the rigid substrate formed by
- - ` 2102608
- 21 -
1 two-layer molding in the present invention, there may be
used any rigid thermoplastic resin which can be
injection-molded. There can be used, for example,
polyolefin resins such as polyethylenes, polypropylenes,
etc.; polystyrene resins such as polystyrenes,
acrylonitrile-styrene copolymer resins, acrylonitrile-
butadienestyrene copolymer resins, etc.; modified
polyphenylene ether resins.; polyamide resins such as
polyamide 6, polyamide 6,6, etc.; polyester resins such
as poly(ethyleneterephthalate) resins, poly(butylene
terephthalate) resins, etc.; polyoxymethylene resins
such as polyoxymethylene homopolymers, polyoxymethylene
copolymers, etc.; and poly(methylmethacrylate) resins.
As the rigid resin used, there may be used
either a single rigid resin or a blend of a plurality of
rigid resins. In addition, there may be used compounds
of rigid resins and other synthetic resins, elastomers,
fillers, reinforcing materials, etc.
The rigid resin preferably has a low specific
gravity for the reduction of the weight of a cushioning
composite molded article to be obtained. From this
point of view, the polyolefin resins and the polystyrene
resins are preferable.
The elastomer which constitutes the above-
mentioned surface material and cushioning material and
the rigid resin which constitutes the aforesaid rigid
substrate are preferably materials which are compatible
with each other and are similar in kind if possible, for
- ~ 2102608
-
l recycling the elastomer and the rigid resin together
without separating them. However, in general, even if
there are used an elastomer and a rigid resin which are
not compatible with each other, they can be recycled
after being compatibilized by the use of a compatibiliz-
ing agent at the time of recycling.
Next, procedures according to the present
invention are explained below.
(1) As to the invention of the insert-space-
in-mold enlarging process (the first embodiment).
The procedure in the insert.space-in-mold
enlarging process is explained below with reference to
Fig. 1.
An injection molding machine used in the
insert-space-in-mold enlarging process is the most
conventional injection molding machine having one
injection unit.
First, as shown in (a), a rigid-resin molded
product 1 is set in a mold 2. The rigid-resin molded
product 1 constitutes the rigid substrate 9 of the
cushioning composite molded article 5 shown in Fig. 2.
It is sufficient that the rigid-resin molded product 1
is produced so as to have a shape required of the rigid
substrate 9, by a molding method using the rigid resin.
In general, an injection-molded product is used as the
rigid-resin molded product 1, and also a pressure-molded
product, a vacuum-formed product or the like may be
substituted therefor.
- ` 2102608
- - 23 -
l The setting of the rigid-resin molded product
1 in the mold 2 is carried out along a stationary mold
2a or a movable mold 2b. In the drawing, the setting is
carried out along the movable mold 2b.
Then, as shown in (b), an expandable elastomer
3 is injected into the space in the mold 2 equipped with
the aforesaid rigid-resin molded article 1, to fill the
space in the mold 2 completely. That is, full shot of
the expandable elastomer 3 is carried out.
The thickness of the space in the mold 2 which
is to be filled with the expandable elastomer 3 is
preferably in the range of 0.5 to 4 mm, more preferably
in the range of 1 to 3 mm. When the thickness is too
small, the expansion of the expandable elastomer 3
becomes difficult. When the thickness is too large, the
expandable elastomer 3 can be well expanded but the
resulting molded article is unnecessarily heavy and not
economical. Therefore, it is not desirable. For
uniform expansion of the whole expandable elastomer 3,
it is preferable that the thickness of the space in the
mold 2 which is to be filled with the expandable
elastomer 3 is uniform. However, depending on applica-
tion purposes of a cushioning composite molded article 5
to be obtained (see Fig. 2), it is preferable in some
cases to cause nonuniform expansion intentionally by
making the thickness of the space nonuniform purposely.
What is important in the step (b) is the full
shot of the expandable elastomer 3 into the space. When
- ` 21026~8
-
- 24 -
1 the full shot is carried out, the elastomer 3 is in a
substantially non-expanded state in this step because
its expansion is prevented by a pressure accompanying
the injection though the substance is expandable. And
owing to the full shot, the elastomer 3 comes into close
contact with the inner surface of the mold 2, so that
the surface portion of the elastomer 3 in contact with
the inner surface of the mold 2 is cooled, is hardly
expanded in subsequent steps, and constitutes a so-
called skin layer 4 (a non-expanded surface material).
The skin layer 4 becomes the surface material 6 of the
cushioning composite molded article 5 shown in Fig. 2,
and since it is formed in a substantially non-expanded
state in close contact with the inner surface of the
mold 2, it has a satisfactory surface profile having a
correct transcript of the surface pattern of the mold.
On the other hand, when the expandable
elastomer 3 is injected in an amount insufficient to
fill the space in the mold 2 (short shot) instead of
carrying out the above-mentioned full shot into the
space in the mold, the expandable elastomer 3 is
expanded in this step. The expandable elastomer 3 comes
into close contact with the inner surface of the mold 2
owing to an increase of its volume caused by the
expansion,so that its surface is cooled. The surface
thus obtained is rough because it is a surface cooled
after the expansion, and there is not formed a practical
surface material similar in appearance and feel to, for
210260~
- 25 -
1 example, natural leather, which is intended according to
the present invention.
After the above-mentioned complete injection
into the space in the mold, the inside of the mold 2 is
enlarged by moving the movable mold 2b by removal of the
injection pressure, while the inner part of the
expandable elastomer 3 is in an expand-able state. The
enlargement of the inside of the mold 2 may be carried
out by either a method in which as shown in (c), the
enlargement is carried out in the mold 2 in an unopen
state, without separating the stationary mold 2a and the
movable mold 2b (a core shutting-in method), or a method
in which as shown in (d), the enlargement is carried out
by opening the mold 2 by separating the stationary mold
2a and the movable mold 2b (a core opening method). The
inside of the mold 2 may be partly enlarged by moving a
movable block set in a part of the stationary mold 2a or
the movable mold 2b, without moving the whole movable
mold 2b.
Owing to the enlargement, as shown in (e) and
(f), the expandable elastomer 3 is expanded to become an
expanded elastomer 7. The expanded elastomer 7 consti-
tutes the cushioning material 8 of the cushioning
composite molded article 5 shown in Fig. 2.
In the case of the core opening method (d),
since the expandable elastomer 3 is freely expanded with
its surface apart from the mold 2, the surface becomes a
smooth and curved surface and the expandable elastomer 3
2102608
.
- 26 -
1 becomes an expanded product 7 having a relatively high
expansion ratio. On the other hand, in the case of the
core shutting-in method (c), the expansion can be
carried out while controlling the thickness of the
expanded elastomer 7 to be obtained, by adjusting the
degree of movement of the movable mold 2b.
For obtaining the skin layer 4 tthe surface
material) having a satisfactory surface profile in the
above step (b) and for attAining a good expanded state
of the expandable elastomer 3 in the steps (c) or (d) to
(e) or (f), it is necessary to set the temperature of
the mold 2 in the steps from the above step (b) to the
step (c) or (d) properly.
Although the preset temperature of the mold 2
in the steps from the above step (b) to the step (c) or
(d) is varied depending on the kind of the expandable
elastomer 3 used, the temperature is set in a temper-
ature range in which the expandable elastomer 3 can be
sufficiently solidified. Usually, room temperature or a
temperature close thereto is sufficient. It is also
effective to coat, if necessary, the inner surface of
the mold 2 with a heat insulating layer of a material
having a low thermal conductivity, or make the whole
mold 2 out of a material having a low thermal conduc-
tivity.
It is in some cases effective to heat the mold2 previously in a temperature range in which the expand-
able elastomer 3 can be sufficiently solidified. A
2102608
- 27 -
1 method in which the heating of the mold 2 is conducted
only on the inner surface of the mold 2 by a radio
frequency induction heating method or the like is an
example of preferable method.
S The interval between the completion of
injection of the elastomer 3 into the mold 2 and the
initiation of backward movement of the movable mold 2b
(the interval to the initiation of mold opening) is
preferably adjusted depending on the kind of the
elastomer 3, the temperature of inner surface of the
mold 2 (the temperature of the elastomer 3), etc., for
attaining a good expanded state of the elastomer 3 in
the step (c) or (d).
For example, when the elastomer 3 used is
relatively rigid, the elastomer becomes difficult to
expand even by the backward movement of the movable mold
2b when the skin layer 4 becomes thick. Therefore, it
is preferable to make possible the maintenance of the
inner surface of the mold 2 at a relatively high
temperature and move the movable mold 2b backward soon
after the injection of the expandable elastomer 3. When
the elastomer 3 used is relatively flexible, it is
preferable to move the movable mold 2b backward after a
relatively long interval between the completion of
injection of the expandable elastomer 3 and the initia-
tion of backward movement of the movable mold 2b, for
accelerating the formation of the skin layer 4 having a
satisfactory surface profile.
- 2102608
- 28 -
1 The period between the initiation and comple-
tion of the backward movement of the movable mold 2b is
important for attaining a good expanded state of the
expandable elastomer 3 in the step (c) or (d), and is
preferably properly adjusted like the interval between
the completion of the injection and the initiation of
backward movement of the movable mold 2b.
When the expanded elastomer 7 having the
skin layer 4 is obtained by expanding the expandable
elastomer 3 in the manner described above, sufficiently
cooled and then taken out of the mold, there can be
obtained the cushioning composite molded article 5 in
which as shown in Fig. 2, the cushioning material 8
having the surface material 6 is integrally formed on
the rigid material 9.
(2) As to the invention of the two-layer
molding-space-in-mold enlarging process (the second
embodiment).
The procedure in the two-layer molding-space-
in-mold enlarging process is explained below with
reference to Fig. 3.
An injection molding machine used in the
invention of the two-layer molding-space-in-mold
enlarging process is an injection molding machine
having two or more injection units which is generally
called a two-color molding machine or a multi-color
molding machine.
First, as shown in (a), a rigid resin is
- 2102608
1 injected into a mold 2~ composed of a stationary mold
2a' and a movable mold 2b to obtain a rigid-resin molded
product 1. The molding into the rigid-resin molded
product 1 may be carried out until the rigid resin
injected into the mold 2' is sufficiently cooled, or the
molding may be stopped at a cooled state in which the
rigid resin is not deformed at the time of its transfer
to a subsequent step (b).
Then, as shown in (b), the movable mold 2b is
moved backward to be separated from the stationary mold
2a', and is combined with another stationary mold 2a,
whereby the inside of the mold 2 is enlarged to form a
space in the mold 2. The enlargement of inside of the
mold 2 can be carried out also as the enlargement of
inside of the mold 2' shown in (a). For example, the
inside of the mold 2' may be partly enlarged by moving a
movable block set in a part of the stationary mold 2a'
or the movable mold 2b. In addition, the inside of the
mold 2' may be enlarged by moving the movable mold 2b to
such an extent that the mold 2' shown in (a) is not
opened. The step (b) corresponds to the above-mentioned
state shown in Fig. l(a), and subsequent steps (c) to
(g) of the procedure are the same as the steps illus-
trated in Figs. l(b) to (f).
In the insert.space-in-mold enlarging process
previously described, the rigid-resin molded product 1
which becomes the rigid substrate 9 is previously and
separately produced, and the formation of the surface
2102608
- 30 -
l material 6 and the cushioning material 8 and the union
of the cushioning material 8 and the rigid substrate 9
in a body are carried out in one mold, i.e., the mold 2.
On the other hand, the two-layer-space-in-mold enlarging
process can be practiced without taking the rigid-resin
molded article 1 which becomes the rigid substrate 9,
out of the mold 2', and hence is advantageous in that
since an expandable elastomer 3 can be injected while
the rigid-resin molded product 1 has a relatively high
temperature, the state of their joining can easily be
improved. Furthermore, for the same reason, it is
possible to make very thin a skin layer 4 formed during
the injection of the expandable elastomer 3, in a
portion of the substance in which the substance comes
into contact with the rigi-d-resin molded product 1.
[Examples] and [Comparative Examples]
The present invention is concretely illus-
trated below with examples and comparative examples, but
needless to say, the present invention is not limited by
the examples and the comparative examples.
Materials, an equipment and a molding pro-
cedure which were employed in them are as follows.
(1) Materials
Rigid resins
PP : a polypropylene having an MFR at 230C
according to ASTM D1238 of 8 g/10 min and a density
according to ASTM D1505 of 0.90 g/cm2.
- _ 32102 60
1 GPP: a glass fiber-reinforced polypropylene
having an MFR at 230C according to ASTM D1238 of
7 g/10 min and a density according to ASTM D1505 of
1.12 g/cm2.
Elastomers
SB1: a saturated-type styrene-butadiene based
elastomer and having an average molecular weight of
50,000 as measured by a GPC method and an A hardness
according to JIS R6301 of 67, and a styrene content of
20% by weight.
SB2: a saturated-type styrene-butadiene based
elastomer, having an average molecular weight of 40,000
as measured by a GPC method and an A hardness according
to JIS K6301 of 84, and a styrene content of 30~ by
weight.
SB3: a compound of saturated-type styrene-
butadiene based elastomer and polyolefins which has an A
hardness according to JIS K6301 of 74 and melt viscosity
values at 230C of 1,800 poise at a shear rate of
1,000/sec and 18,000 poise at a shear rate of 10/sec,
and consists of 60 parts by weight of a saturated-type
styrene-butadiene based elastomer, having an average
molecular weight of 50,000 as measured by a GPC method
and an A hardness according to JIS K6301 of 67, and a
styrene content of 20% by weight, of 20 parts by weight
of a saturated-type styrene-butadiene based elastomer,
having an average molecular weight of 70,000 as measured
by a GPC method and an A hardness according to JIS K6301
322l268
1 of 67, and a styrene content of 20% by weight of 5 parts
by weight of a linear low-density polyethylene having an
MFR at 190C according to ASTM D1238 of 19 g/10 min and
a density according to ASTM D1505 of 0.93 g/cm2, and of
20 parts by weight of a polypropylene having an MFR at
230C according to ASTM D1238 of 40 g/10 min and a
density according to ASTM D1505 of 0.90 g/cmZ.
Blowing agents
BA1: an azodicarbonamide-based blowing agent
BA2: a sodium bicarbonate-based blowing agent
(2) Molding equipment
A core rotation type, two-color, different-
materials injection molding machine.
(3) Dimensions and outer shape of a molded article
(those before expansion)
A box shape with a width of 74 mm, a length of
100 mm and a height of 10 mm. The thickness of a por-
tion filled with a rigid resin (a rigid-resin molded
product) is 2 mm, and the thickness of a portion filled
with an expandable elastomer is 3 mm or 2 mm.
(4) Molding procedure
A granular rigid resin is put into the resin
feed opening of the first injection unit of the molding
machine, and a mixture of a granular elastomer and a
powdered blowing agent is put into the resin feed
210260~
- 33 -
l opening of the second injection unit.
Using the first injection unit, the rigid
resin is injected into a mold having a space corre-
sponding to a rigid-resin molded article to produce the
rigid-resin molded article.
After the rigid-resin molded article is cooled
to such an extent that it can be taken out, the movable
mold of the mold is moved backward, rotated, and then
connected to a stationary mold for the second injection
unit to form a space into which the expandable elastomer
is to be injected. Using the second injection unit, the
expandable elastomer is injected into the space in the
mold.
After the surface layer of the injected
expandable elastomer is solidified and while the inner
part is in a molten state and is expandable, the movable
mold is moved backward to expand the inner part of the
elastomer. The enlargement of the inside of the mold by
the backward movement of the movable mold is carried out
by the core opening method in Example 1, Comparative
Example 1, Example 2 and Comparative Example 2, or the
core shutting-in method in Example 3.
After an expanded elastomer formed by the
expansion of the expandable elastomer is sufficiently
cooled, the cushioning composite molded article thus
produced is taken out of the mold.
2102608
-
- 34 -
1 Example 1
Molding was conducted by carrying out the
enlargement of the inside of the mold by the backward
movement of the movable mold according to the core
opening method, and varying the kind of rigid resin,
the kind of elastomer and the kind of blowing agent.
The injection of an expandable elastomer was full shot
in all the cases. Conditions and the results are shown
in Table l.
Cushioning composite molded articles having an
excellent appearance and proper cushioning properties
could be produced even when the kind of rigid resin was
varied.
In addition, cushioning composite molded
articles having an excellent appearance and proper
cushioning properties could be produced even when the
kind of elastomer was varied. However, the molded state
varied depending on the kind of elastomer. In particu-
lar, the cushioning properties of the obtained cushion-
ing composite molded articles varied depending on therigidity of the elastomer.
Furthermore, when the kind of blowing agent
was varied, both of the blowing agents could be
advantageously used.
2S Comparative Example 1
A cushioning composite molded article was
produced by injecting an expandable elastomer in a short
2102608
- 35 -
1 shot manner. Conditions and the results are shown in
Table 1.
No satisfactory molded article could be
produced.
Example 2
Molding was conducted by carrying out the
enlargement of the inside of the mold by the backward
movement of the movable mold according to the core
opening method, and varying the amount of a blowing
agent added. The injection of an expandable elastomer
was full shot in all the cases. Conditions and the
results are shown in Table 2.
The cushioning properties of the resulting
cushioning composite molded articles varied depending on
lS the amount of the blowing agent added.
In addition, molding was conducted by carrying
out the enlargement of the inside of the mold by the
backward movement of the movable mold according to the
core opening method, and varying the mold temperature
and the interval between the completion of injection of
the elastomer and the initiation of backward movement of
the movable mold (the interval to the initiation of mold
opening). The injection of the expandable elastomer
was full shot in all the cases. Conditions and the
results are shown in Table 2.
A proper interval to the initiation of mold
opening varied owing to the variation of the mold
2102608
- 36 -
l temperature. In detail, when the mold temperature was
raised, a satisfactory cushioning composite molded
article could be obtained even when the interval to the
initiation of mold opening was extended.
Comparative Example 2
Molding was carried out by varying the
interval to the initiation of mold opening greatly.
When the interval to the initiation of mold
opening was beyond its proper range, no satisfactory
molded article could be produced.
Example 3
Molding was conducted by carrying out the
enlargement of the inside-of the mold by the backward
movement of the movable mold according to the core
shutting-in method, and varying the kind of blowing
agent, the thickness of a portion filled with an
expandable elastomer, and the kind of elastomer. The
injection of the expandable elastomer was full shot in
all the cases. Conditions and the results are shown in
Table 3.
Even in the case of the core shutting-in
method, a good expanded state could be attained even
when there were varied the kind of blowing agent, the
thickness of the portion filled with the expandable
elastomer, and the kind of elastomer.
Physical properties of molded articles were
3~l02608
l evaluated according to the following criteria.
State of expansion
Good: a state in which a non-expanded surface
material was uniformly formed on the surface of a molded
article to a uniform thickness, and a cushioning mate-
rial having a large number of uniform and fine closed
cells was uniformly formed in the inside.
Bad: an expanded state of a molded article which
is different from the above state.
Appearance
Good: a state in which the surface pattern of the
mold was correctly transferred to the surface of a
molded article.
Poor: a state in which a pattern different from the
surface pattern of the mold, such as depressions and
protuberances, a flow mark or the like was formed on the
surface of a molded article.
Feel
Good: a feel similar to the good feel of a cushion-
ing composite molded article composed of a surface
material made of smooth natural leather of adult cattle
obtained by chromium tAnning, a cushioning material made
of a flexible closed-cell polyurethane foam, and a rigid
substrate.
Unpleasant:
a feel different from the above good feel.
2102608
-- 38 --
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2102608
-- 39 --
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- 2102608
-- 40 --
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- 41 2102608
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2102608
-- 42 --
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- 2102608
-- 43 ~
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442lO2608
< INDUSTRIAL APPLICABILITY>
The present invention is as explained above
and has the following effects.
That is, in the first embodiment of the
process for producing a composite molded article of the
present invention, molding of a surface material, mold-
ing of a cushioning material, and union of the cushion-
ing material and a rigid substrate in a body can be
carried out in one mold, so that a saving in labor and a
reduction in the production cost can be achieved in the
production of a cushioning composite molded article. In
the second embodiment of said process, since not only
the above operations but also molding of a rigid sub-
strate can be carried out in the same mold in succes-
sion, there can be achieved a greater saving in laborand a sharper reduction in the production cost than in
the first embodiment.
A cushioning composite molded article obtained
by said process gives an excellent appearance and a soft
feel and hence is very useful as a material for various
internal trims.
