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BACKGROUND OF THE INVENTION
(1) Field of the Invention:
This invention relates to a foamed base material for a car ceiling member.
(2) Description of the Prior Art:
Car ceiling members have conventionally been produced, each, by pasting a
cushioning material made of polyurethane foam or the like on the
interior-side surface of a molded article, which was obtained by forming a
base material composed principally of a foamed thermoplastic resin into
the shape of the ceiling member, and then pasting a decorative surfacing
made of a synthetic resin sheet, knit or woven fabric or the like on the
cushioning material.
As these base materials for foamed car ceiling members, there have been
used those composed solely of various thermoplastic resin foams, those
constructed by laminating various thermoplastic resin films or sheets on
both sides of such foams (for example, Japanese Patent Laid-Open No.
32514/1978) and the like.
Conventional base materials for car ceiling members are however accompanied
by such problems that in the case of those composed solely of foamed
bodies, their mechanical strength such as compression strength and maximum
bending load is not fully satisfactory and their thermal strength such as
beam span is poor and they undergo deformations during their long-term
application in car interiors where considerable temperature variations
take place; and in the case of those obtained by laminating films or
sheets on both sides of foamed bodies, their production costs are
unexceptionally high although the provision of such surfacings was able to
improve their mechanical strength, thermal strength and the like to
certain extents.
SUMMARY OF THE INVENTION
With the foregoing in view, the present invention has as its object the
provision of a foamed base material for a car ceiling member, which base
material has excellent mechanical and thermal strength and is of an
inexpensive price.
The present inventors have carried out an extensive research with a view
toward developing a foamed base material for a car ceiling member, which
base material has excellent mechanical and thermal strength and is of an
inexpensive price. As a result, it has been found that a foamed body
obtained by forming a foamed cylindrical extrudate, which is made
principally of a thermoplastic resin having a Vicat softening point of
115.degree. C. or higher, into a flattened shape, subjecting the extrudate
to biaxial orientation and then fusion-bonding the resultant
mutually-opposing inner walls to each other is excellent as a foamed base
material for a car ceiling member, leading to completion of this
invention.
In one aspect of this invention, there is thus provided a foamed base
material for a car ceiling member, characterized in that said foamed base
material has been obtained by extruding and foaming a thermoplastic resin
having a Vicat softening point of 115.degree. C. or higher and containing
a blowing agent into a foamed tubular body, subjecting the tubular body to
biaxial orientation, and then pressing the foamed tubular body in
antipodal directions, whereby the foamed tubular body is flattened and
fusion-bonded at the resultant mutually-opposing inner walls thereof.
Owing to the above-mentioned features, the foamed base material of this
invention has not only excellent mechanical strength but also superb
thermal strength. It is therefore free from such a danger that it may
develop deformations during its long-term application in a car interior
which is subject to considerable temperature variations. Since the foamed
base material has sufficient mechanical and thermal strength by itself,
the present invention has brought about a variety of advantageous effects
such that the foamed base material is not required to laminate films,
sheets or the like thereon and is hence provided at a low cost.
The above and other objects, features and advantages of the present
invention will become apparent from the following description and the
appended claims, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings show one embodiment of this invention, in which:
FIG. 1 is a schematic illustration showing a production process of a foamed
base material for a car ceiling member, which pertains the present
invention;
FIG. 2 is a transverse cross-sectional view of the foamed base material of
this invention, taken along line II--II of FIG. 1;
FIG. 3 is a schematic longitudinal cross-sectional view of an illustrative
car ceiling member.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT
As described above, the Vicat softening point of each thermoplastic resin
to be employed in the present invention is required to be 115.degree. C.
or higher. If the Vicat softening point should be lower than 115.degree.
C., the thermoplastic resin has poor heat resistance and cannot achieve
the object of the present invention. As exemplary thermoplastic resins,
may be mentioned styrene-acrylic acid copolymer; styrene-methacrylic acid
copolymer; copolymers of styrene and esters of acrylic or methacrylic acid
such as methyl acrylate, ethyl acrylate and methyl methacrylate;
copolymers of styrene and salts or amides of acrylic or methacrylic acid,
such as copolymer of styrene and acrylic amide, acrylic acid and
copolymers of styrene and salts of copolymers of styrene and salts of
methacrylic acid; copolymer of styrene and maleic anhydride; copolymer of
styrene and maleimide; poly-p-methylstyrene polycarbonate; and so on. It
should however be borne in mind that the thermoplastic resin is not
necessarily limited to the above-mentioned resins. Among the
above-described resins, styrene-acrylic acid copolymer and
styrene-methacrylic acid copolymer have excellent heat resistance and
moldability and are thus preferred. Especially, those having Vicat
softening points above 120.degree. C. are preferred. It is also possible
to blend one or more of other resins within the scope of the object of
this invention.
As illustrated in FIG. 1 and FIG. 2, a foamed base material 1 for a car
ceiling member, which pertains to the present invention, is constructed by
mixing and kneading the above-described thermoplastic resin and a blowing
agent in a molten state in an extruder 2, extruding the thus-kneaded mass
through a circular die provided at the free end of the extruder 2 and
causing the thus-extruded mass to foam into a foamed cylindrical body 3,
and then pressing the foamed cylindrical body 3 in antipodal directions by
means of guide rollers 4,4, . . . and pinch rollers 5,5 into a flattened
shape so as to fusion-bond the resultant mutually-opposing inner walls 6
of the foamed body to form a planar plate.
Since the base material 1 of this invention is fusion-bonded at the
flattened inner walls 6, its physical properties such as maximum bending
load and beam span have been improved without need for the lamination of
films, sheets or the like thereon.
The amount of the blowing agent still remaining in the the base material 1
of this invention may preferably range from 0.01 wt. % to 3 wt. %. This
content range is preferred in forming the base material 1 into a final
shape, because the limitation of the remaining blowing agent to the
above-described range will protect the base material 1 from excessive
plasticization upon its heating. As a blowing agent useful in the
production of the base material 1 of this invention, any blowing agent may
be suitably chosen from those employed for usual blowing, foaming or
expanding purposes. Illustrative of such a blowing agent may include
aliphatic hydrocarbons such as propane, butane, n-pentane and isopentane,
halogenated hydrocarbons such as dichlorodifluoromethane,
tetrafluoroethane, trichlorofluoromethane, methyl chloride and ethyl
chloride, ethers such as methyl ether and ethyl ether, and the like. Of
these, a mixture of dichlorodifluoromethane and methyl and/or ethyl
chloride, a mixture of dichlorodifluoromethane and butane or a mixture of
butane and methyl and/or ethyl chloride is preferred from the viewpoint of
the molding performance of the thermoplastic resin. In addition, it is
preferred to use a mixed blowing agent, which has been obtained by mixing
dichlorodifluoromethane and methyl and/or ethyl chloride as blowing agents
at a weight ratio of 5:95-80:20, in an amount of 1-6 parts by weight based
on 100 parts by weight of the resin, because use of such a mixed blowing
agent improves the expansion ratio of the base material 1, allows the
amount of the remaining blowing agent contained in the base material 1 to
fall within the above-described range, and ensures the fusion-bonding of
the inner walls 6 of the foamed body which has been formed with a
flattened shape by pressing the foamed cylindrical body 3 in antipodal
directions.
The base material 1 of this invention has been subjected to biaxial
orientation. Owing to synergistic effects of the biaxial orientation and
the above-described fusion-bonded inner walls 6, the mechanical strength,
especially, the beam span of the base material 1 has been leapingly
improved. The degree of the above orientation may preferably be 5-40% or
especially 15-40%. To control the degree of orientation within the
above-described range, it is preferred to have the foamed cylindrical body
3 expand in such as way that upon extrusion and expansion of the foamed
cylindrical body 3, its blow-up ratio (which is expressed by (L.sub.2
.times.2)/L.sub.1 wherein L.sub.1 is the circumference of a die lip and
L.sub.2 stands for the width of the base material 1) becomes greater than
3, i.e., (L.sub.2 .times.2)/L.sub.1 >3.
By the way, each degree of orientation is expressed in terms of its
corresponding degree of heat shrinkage (dimensional changes) when heated
at 150.degree. C. for 100 seconds in an oven.
In order to impart sufficient mechanical strength of the base material 1 of
this invention, it is preferable to form the base material 1 with an
overall thickness in the range of 2-10 mm. It is also preferred that skin
layers are formed respectively on both outer surfaces 7 of the base
material 1. The provision of the skin layers can improve the compression
strength and maximum bending load further. The above-described skin layers
can be formed by cooling the foamed cylindrical body 3, which has been
extruded from an extruder 2 and then caused to expand, at both outer
surfaces thereof or by a like method.
Turning to the basis weight (g/m.sup.2) of the base material 1 of this
invention, a range of 250-600 g/m.sup.2 is preferred. Any basis weights
smaller than 250 g/m.sup.2 may not be able to bring about fully
satisfactory mechanical strength, while any basis weights greater than 600
g/m.sup.2 are unacceptable from the viewpoint of weight reduction and at
the same time result in higher production costs.
After having been formed into the shape of an intended car ceiling member,
the base material 1 of this invention is, as depicted in FIG. 3, applied
with a cushioning material 8 made of polyurethane foam or the like on the
interior-side surface thereof and further with a decorative surfacing 9
made of a synthetic resin sheet such as vinyl chloride, a knit or woven
fabric or the like on the interior-side surface of the cushioning material
8, whereby a car ceiling member 10 is fabricated.
Incidentally, the erm "Vicat softening point" as used herein means a value
measured in accordance with ASTM D-1525.
EXAMPLES
The present invention will hereinafter be described in further detail by
the following Examples.
EXAMPLES 1-3
After mixing and kneading the mixed blowing agent composed of
dichlorodifluoromethane and methyl or ethyl chloride shown in Table 1 with
100 parts by weight of a copolymer of styrene and methacrylic acid (Vicat
softening point: 126.degree. C.) in a molten state in an extruder, a
foamed cylindrical body was extruded through a circular die, followed by
its expansion at its corresponding blow-up ratio given in Table 1. The
foamed cylindrical body was then pressed in antipodal directions, whereby
the foamed tubular body was flattened and fusion-bonded at the resultant
mutually-opposing inner walls thereof to form a planar foamed body (a base
material suitable for the fabrication of a car ceiling member). Properties
of the thus-obtained foamed body are shown in Table 1.
The thus-obtained foamed body was then shaped by means of a
headliner-forming mold. Various properties of the thus-shaped foamed body
were measured. Measurement results are also given in Table 1.
COMPARATIVE EXAMPLE 1
After adding the mixed blowing agent given in Table 1 to 100 parts by
weight of the same resin as that employed in Examples 1-3 and then mixing
and kneading the resultant mixture in a molten state in an extruder, the
resin was extruded into a cylindrical shape through a circular die.
Without pressing it in antipodal directions, it was cut open
longitudinally and then allowed to expand into a planar shape. Properties
of the planar foamed body are shown in Table 1. Thereafter, it was shaped
by using the same headliner-forming mold as that employed in Examples 1-3.
After the shaping, various properties of the resultant foamed body were
measured. Measurement results are also given in Table 1.
EXAMPLE 4
A planar foamed body was obtained by conducting an extrusion and expansion
operation under the same conditions as in Example 2 except that a
copolymer of styrene and maleic anhydride (Vicat softening point:
120.degree. C.) was employed as a base resin. Properties of the foamed
body are shown in Table 1. Then, the foamed body was shaped by means of
the same headliner-forming mold as that employed in Examples 1-3.
Properties of the thus-shaped foamed body are also shown in Table 1.
COMPARATIVE EXAMPLE 2
A planar foamed body was obtained by conducting an extrusion and expansion
operation under the same conditions as in Example 2 except that
polystyrene (Vicat softening point: 105.degree. C.) was employed as a base
resin. Properties of the foamed body are shown in Table 1. Then, the
foamed body was shaped by means of the same headliner-forming mold as that
employed in Examples 1-4. Properties of the thus-shaped foamed body are
also shown in Table 1.
TABLE 1
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Example Comp. Example
1 2 3 4 1 2
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Conditions for extrusion and expansion
Blowing agent
(Blowing agent) Composition (wt. %) (added wt. parts)
Dichlorodifluoromethane 15/0.4
50/1.5
80/3.3
50/1.5
50/1.5
50/1.5
Methyl chloride 84/2.0
50/1.5
-- 50/1.5
50/1.5
50/1.5
Ethyl chloride -- -- 20/1.0
-- -- --
Blow-up ratio 3.5 3.5 3.5 3.5 2 2
Foamed body before shaping
Basis weight (g/m.sup.2) 546 552 542 540 541 550
Thickness (mm) 4.7 4.6 4.5 4.5 4.6 4.6
Skin layer formed
formed
formed
formed
formed
formed
Degree of orientation
Longitudinal 28 28 27 25 8 9
Lateral 25 27 25 25 5 6
Foamed body after shaping
Thickness (mm) 6.8 6.8 6.5 6.8 6.8 6.8
Maximum bending load.sup.1 (kg)
Longitudinal 2.5 3.6 3.8 2.0 1.5 1.0
Lateral 2.0 2.7 2.7 1.8 1.3 0.8
25% Compression strength.sup.2 (kg/m.sup.2)
1.7 2.5 2.9 1.4 1.0 0.8
Beam span.sup.3 (mm)
Longitudinal (Lo.) 3 6 7 10 28 35
Lateral (La.) 7 12 15 16 33 40
##STR1## 4.6 8.5 10 13 30 37
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Remarks:
.sup.1 A test piece of 50 mm .times. 150 mm wide was cut out from each
foamed body after its shaping. The test piece was mounted on supports,
which were arranged with an interval of 100 mm, at imaginary lines
extending inwardly of and parellelly with their corresponding 50 mm long
end edges with an interval of 25 mm. A load was applied at a rate of 20 m
per minute to the entire central width of the test piece (i.e., at the
central position between the supports), thereby obtaining a loaddeflectio
curve. The maximum load on the curve was recorded as the maximum bending
load. By the way, each longitudinal maximum load corresponds to a
measurement value of a test piece cut out with its 150 mm long sides
extending in the direction of extrusion of the corresponding foamed body
while each lateral maximum load corresponds to a measurement value of a
test piece cut out with its 150 mm long sides extending in a direction
perpendicular to the direction of extrusion of the corresponding foamed
body.
.sup.2 ASTM-D-1621 was followed substantially. Setting the testing speed
at 10 mm/min. and the size of each test piece as wide as 50 mm .times. 50
mm, the load required to compress the thickness of the test piece by 25%
was measured. The measurement result was recorded as 25% compression
strength.
.sup.3 A test piece of 150 mm .times. 450 mm wide was cut out from each
foamed body after its shaping. The test piece was supported on two
supports, which were arranged with an interval of 300 mm, at imaginary
lines extending inwardly of and parellelly with their corresponding 150 m
long end edges with an interval of 75 mm. After superposing a polyethylen
sheet of 150 mm .times. 450 mm wide and 20 mm thick on the upper surface
of the test piece, the test piece was heated for 6 hours in a
circulatingair drier controlled at 105.degree. C. .+-. 2.degree.C. Its
beam span was expressed in terms of the degree of sagging of the test
piece. By the way, each longitudinal beam span corresponds to a
measurement value of a test piece cut out with its 450 mm long sides
extending in the direction of extrusion of the corresponding foamed body
while each lateral beam span corresponds to a measurement value of a test
piece cut out with its 450 mm long sides extending in a direction
perpendicular to the direction of extrusion of the corresponding foamed
body. In addition to the longitudinal and lateral beam spans, their
geometric mean is also shown.
Having now fully described the invention, it will be apparent to one of
ordinary skill in the art that many changes and modifications can be made
thereto without departing from the spirit or scope of the invention as set
forth herein.
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