Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
ELASTOMER SHEET LAMINATE AND WATERPROOFING
WATER-BARRIER SHEET OF THE LAMINATE
TECHNICAL FIELD
The present invention relates to an elastomer sheet
laminate used in applications, e.g., an exterior material to be
exposed to the environment over long, and which is required to
have excellent weatherability and insusceptibility to
discoloration. The present invention further relates to use of
the elastomer sheet laminate as a waterproofing water-barrier
sheet which is laid on a roof, floor, or wall of a building or
the bed of an irrigation pond, an industrial waste disposal
field, etc., and which is highly aesthetic, has excellent
weatherability, and is free from a discoloration problem.
BACKGROUND ART
Sheets for use in applications such as exterior
materials to be exposed to the environment for long, e.g.,
waterproofing water-barrier sheets tc~be laid in roofs, floors,
or walls of buildings or the beds of irrigation ponds,
industrial waste disposal fields, etc., are generally intended
primarily to prevent rainwater from penetrating into buildings
or prevent the water in irrigation ponds from permeating into
the ground. A technique currently employed frequently for
waterproofing the roofs of buildings or for waterproofing
irrigation ponds or the lik~e is to lay an elastomer sheet
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generally made of a rubber, poly(vinyl chloride), polyethylene,
ethylene/vinyl acetate, chlorinated polyethylene, modified
asphalt, or the like.
Among such sheets, the rubber sheets can withstand
long-term use because of the relatively high weatherability of
the material itself. However, other sheets such as poly(vinyl
chloride) and polyethylene sheets have insufficient
weatherability in spite of excellence in functions such as
initial properties and impact resistance, and an improvement in
weatherability has been desired.
It was hence proposed, as disclosed in Unexamined
Japanese Utility Model Publication No. Hei. 3-92228, to
laminate a fluororesin layer, having excellent weatherability,
on a sheet to thereby improve the weatherability of the sheet.
With respect to the waterproofing water-barrier sheets
to be laid on roofs, floors, or walls of buildings or the beds
of irrigation ponds or the like, colored elastomer sheets have
come to be desired from t;he standpoint of attaining an
aesthetic appearance as well as waterproofing performance and
weatherability.
A colored elastomer sheet formed from an elastomer
material which contains a colorant and a laminated sheet
produced by laminating a colored rubber sheet to a conventional
black rubber sheet and vulcanizing the rubbers to obtain a
united sheet are recently being used as the waterproofing
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water-barrier sheets because of the desire for an aesthetic
appearance.
Laminating a colored Tedlar (poly(vinyl fluoride)
manufactured by E.I. du Pont de Nemours & Co.) film to a rubber
sheet is also being conducted.
However, the aforementioned laminated sheet formed by
laminating a fluororesin -to a sheet made of a rubber,
poly(vinyl chloride), polyethylene, chlorosulfonated
polyethylene, or the like has a problem that it warps because
the fluororesin layer diIfers from the base sheet in
expansion/contraction properties.
On the other hand, t:he colored elastomer sheets have
the following problems besides the problem of warpage caused by
property differences between the two constituent layers.
For example, the colored rubber sheet made of a rubber
containing a colorant incorporated therein is inferior in
weatherability to the convent:ional black rubber sheet although
undoubtedly superior in appearance to the black sheet. The
color tones which have been obtained have a low lightness and
are anything but a delicate color tone. The colored rubber
sheet has other problems that the color differs considerably
from lot to lot, and that the colored rubber sheet has poor
weatherability and discolor-, with the lapse of time. The
colored rubber sheet therefore does not satisfy the
requirements.
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The colored sheet comprising poly(vinyl chloride), that
comprising chlorosulfonated polyethylene, and that comprising
polyethylene each itself has poor weatherability and is
unsuitable for long-term outdoor use. Furthermore, a sheet
formed by laminating a poly(vinyl chloride) film to a
vulcanized rubber sheet has a problem that it warps due to
property differences between the two constituent layers.
Poly(vinyl fluoride) (Tedlar) has excellent
weatherability and, hence, the waterproofing water-barrier
sheet formed by laminating a film of the polymer to a rubber
sheet has improved properties with respect to the inhibition of
natural deterioration or discoloration. However, this
laminated sheet still has the problem of warpage caused by
differences in expansion/con1raction properties.
An object of the present invention, which copes with
the circumstances described above, is to provide an elastomer
sheet, including a rubber sheet, which has a delicate color
tone with reduced unevenness of color, does not warp, has
excellent weatherability, and is free from the problem of
discoloration even when the sheet is a colored one, especially
by using an expanded porous polytetrafluoroethylene
(hereinafter referred to also as "ePTFE") film.
DISCLOSURE OF THE INVENTION
As a result of intensive studies made by the present
inventors, they have found that laminating an ePTFE film on an
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elastomer sheet, either with or without using a thermoplastic
resin film, to constitute a composite sheet is effective in
accomplishing the above object. The present invention has been
completed based on this finding.
The present invention, which is based on the above
standpoint, first is characterized by an elastomer sheet
laminate basically comprising an elastomer sheet and an ePTFE
film laminated thereto. Advantageous constitutions include to
a thermoplastic resin film interposed between the elastomer
sheet and the ePTFE film, a colored ePTFE film used as the
ePTFE film, a rubber sheet used as the elastomer sheet, and a
colored film used as the thermoplastic resin film. These
constitutions are features of the present invention.
The present invention is further characterized by a
waterproofing water-barrier sheet to be laid especially on a
roof, floor, or wall of a bui:lding or the bed of an irrigation
pond, an industrial waste disposal field, etc., and which has
the basic constitution described above, comprising an elastomer
sheet and an ePTFE film laminated thereto.
Combinations of the above constitution with each of
interposing a thermoplastic resin film between the elastomer
sheet and the ePTFE film, using a colored ePTFE film as the
ePTFE film, using a rubber sheet as the elastomer sheet, and
using a colored film as the thermoplastic resin film are also
features of the present invention.
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The elastomer sheet laminate and waterproofing water-
barrier sheet according to the present invention have greatly
improved weatherability because an ePTFE film, which is not
deteriorated by ultraviolet and has exceedingly high
weatherability, has been laminated on an elastomer sheet
surface. Consequently, it is possible to use even an elastomer
material which has excellent initial properties but
insufficient weatherability and hence has hitherto been
unusable in forming sheets to be subjected to long-term
exposure. Furthermore, since an ePTFE film is flexible and
plastic and has the unique property of coming into close
contact with any shape, it can freely change to shape according
to that of a flexible elastomer material, such as a rubber on
which it is laminated. Therefore, the ePTFE film laminated on
an elastomer sheet neither suffers the peeling caused by the
insufficient flexibility in responding to the shape change of
the elastomer sheet nor warps the elastomer sheet.
In the case where a thermoplastic resin film is
disposed on the surface of an elastomer sheet on which an ePTFE
film is to be laminated, the thermoplastic resin film can be
melted by heating and the molten thermoplastic resin can thus
penetrate into pores of the ePTFE film. Consequently, even a
polytetrafluoroethylene (PTFE) film, which is a fluororesin
film usually unable to be tenaciously bonded by heat fusion,
can be fusion-bonded to the elastomer sheet so as to have a
sufficient strength, whereby a waterproofing water-barrier
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sheet excellent in color tone and weatherability and free from
the problems of discoloration, delamination of the laminated
sheet, warpage, etc. can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view illustrating one embodiment
of the elastomer sheet laminate according to the present
invention and of the wat:erproofing water-barrier sheet
comprising the laminate.
Fig. 2 is a sectional view illustrating another
embodiment of the elastomer sheet laminate according to the
present invention and of the waterproofing water-barrier sheet
comprising the laminate.
Fig. 3 is a view illustrating a vulcanization step and
a step of film contact bonding in a process for producing an
elastomer sheet laminate according to the present invention and
for producing a waterproofing water-barrier sheet comprising
the laminate.
[Description of the Symbols]
1 elastomer sheet laminate (waterproofing water-barrier sheet);
2, 15 elastomer sheet (vulcanized rubber sheet); 3, 17
thermoplastic resin film; 4 ePTFE film; 10 unvulcanized rubber
sheet
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The elastomer sheet laminate according to the present
invention and the waterproofing water-barrier sheet comprising
the laminate will be explained below in more detail.
The laminated sheet 1 shown in Fig. 1, which is an
elastomer sheet laminate according to the present invention or
a waterproofing water-barrier sheet comprising the laminate,
has a three-layer structure consisting of an elastomer sheet 2,
e.g., a vulcanized rubber sheet, and an ePTFE film 4 laminated
thereon on one side through a thermoplastic resin film 3.
Another embodiment has a two-layer structure consisting of an
elastomer sheet 2 and an ePTFE film 4 directly laminated
thereon, as shown in Fig. 2. This two-layer embodiment has an
advantage that the laminated sheet 1 as a whole has a weight
less than the three-layer structure described above.
In the present invention, an ePTFE film 4 colored in a
desired tint is used as the ePTFE film 4 in order to color the
elastomer sheet 2 or the waterproofing water-barrier sheet 1.
Alternatively, an uncolored ePTFE film, which has the white
color inherent in ePTFE, is used.
In the case where a :Laminated sheet 1 colored on both
sides is desired from the standpoint of an aesthetic
appearance, a colored ePTFE film 4 may be disposed on each side
of an elastomer sheet 2.
The elastomer sheet used in the present invention has
the same functions (waterproofing water-barrier performance,
mechanical strength, and other physical and chemical properties
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required of waterproofing water-barrier sheets) as the
conventional waterproofing water-barrier sheets consisting of
an elastomer, e.g., a vulcanized rubber or poly(vinyl
chloride). Consequently, the ePTFE film 4 functions only as a
supplement to the elastomer sheet by shutting off ultraviolet
to thereby improve weatherability and other functions without
warping the waterproofing wat:er-barrier sheet and by imparting
an excellent color tone.
Examples of the elastomer constituting the elastomer
sheet 2 include rubbers such as natural rubber, polybutadiene
rubber, polyisoprene rubber, butyl rubber, chloroprene rubber,
fluororubbers, styrene/butadiene copolymer rubbers, and
ethylene/propylene terpolymers (examples of the other monomer
include ethylidenenorbornene, dicyclopentadiene, and 1,4-
hexadiene); thermoplastic elastomers such as olefin elastomers,
e.g., ethylene/vinyl acetate copolymers, polyethylene, and
polypropylene, thermoplastic olefin elastomers, thermoplastic
urethane elastomers, and thermoplastic styrene/butadiene
copolymer elastomers; and blends thereof. Those rubbers may be
vulcanized rubbers obtained through vulcanization using a
vulcanizing agent, a vulcanization accelerator, etc., or may be
unvulcanized rubbers. The thermoplastic olefin elastomers and
the thermoplastic urethane elastomers include wholly
crosslinked elastomers and half-crosslinked elastomers. Most
preferred among those materials are ethylene/propylene
terpolymers and blends thereof with butyl rubber. The reasons
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for the preference of ethylene/propylene terpolymers include
that the terpolymers have the highest weatherability among the
currently known rubber materials, and that the terpolymers are
easily fusion-bonded to thermoplastic resins because they
contain ethylene. The reasons for the preference of the blends
with butyl rubber include that these materials have improved
processability and improved adhesive properties.
The thickness of the elastomer sheet 2 is preferably
from 0.3 to 3.0 mm, more preferably from 1.0 to 2.0 mm.
Thicknesses thereof larger than 3.0 mm are undesirable in that
such a thick sheet has impaired flexibility and is less apt to
come into close contact with the substrate. The reasons for
the more preferred range of from 1.0 to 2.0 mm are as follows.
If the thickness of the elastomer sheet is smaller than 1.0 mm,
the resultant laminated sheet considerably warps because of a
difference in the coefficient of thermal expansion between the
ePTFE film and the elastomer sheet. If the thickness thereof
is larger than 2.0 mm, joints between sheets have a large
difference in level and this results in a poor appearance or
impaired suitability for walking thereon. The thermoplastic
resin film 3, which is a constituent element in the present
invention, is an interposition for laminating the elastomer
sheet 2 to the ePTFE film 4 through heat fusion. Any
thermoplastic resin film may be used for producing a sheet of
the three-layer structure, as long as it is made of a material
capable of being fused to both the elastomer sheet 2 and the
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CA 02232617 1998-03-18
ePTFE film 4. However, preferred materials include
polyethylene, ethylene/vinyl acetate copolymers, and
ethylene/methyl methacrylate. Among these, polyethylene is
most preferred from the standpoints of processability, adhesive
properties, chemical stability after processing, etc. The
thickness of the thermoplastic resin film 3 is preferably 10 ~m
or larger, more preferably 20 ~m or larger. Thicknesses
thereof smaller than 10 ~m are undesirable in that not only
such a thin film has poor processability but use thereof
results in a reduced fusion bonding region to cause fusion
bonding failure.
It is preferred to use a colored thermoplastic resin
film 3 for the following reason. There are cases where the
color of the elastomer sheet 2 in a laminated sheet of the
present invention is visible on the surface through the ePTFE
film 4 depending on the thickness of the film 4. This
phenomenon is severe especially when an excellent appearance is
to be imparted to the laminated sheet using a colored ePTFE
film. By using a thermoplastic resin film 3 which has been
colored, the color of the elastomer sheet 2 can be prevented
from being seen from the surface, whereby the resultant
laminated sheet can have a brighter color. The color of the
thermoplastic resin film 3 may be the same as or different from
that of the ePTFE film 4 as the surface layer.
As described above, the thermoplastic resin film 3
functions as an adhesive for laminating an elastomer sheet 2 to
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an ePTFE film 4, and use of the thermoplastic resin film 3
enables laminating by fusion bonding. PTFE is generally known
as a material which is exceedingly difficult to subject to
fusion bonding processing or bonding processing. In the
present invention, however, an ePTFE film 4 is used as
described above to utilize pores of the stretched porous film.
Specifically, a heated thermoplastic resin in a molten state is
caused to penetrate into the pores to produce an anchoring
effect, whereby the elastomer sheet 2 can be tenaciously
laminated on the ePTFE film 4.
On the other hand, the ePTFE film 4, which is a
constituent element important for the features of the present
invention, functions as a supplement to the elastomer sheet by
shuttering off ultraviolet to thereby improve weatherability
and other functions without warping the waterproofing water-
barrier sheet and by imparting an excellent color tone, as
stated hereinabove.
The ePTFE film 4 can be produced by the known processes
described, e.g., in Examined Japanese Patent Publication Nos.
Sho. 53-39719 and Sho. 51-18991, and the microstructure thereof
is also known. Specifically, the ePTFE film is produced by
preparing a paste consisting basically of a mixture of a fine
PTFE powder and a lubricant, e.g., petroleum naphtha, extruding
the paste through a die to obtain a tape-form extrudate,
heating the extrudate to vaporize and remove the lubricant, and
then stretching the extrudate at least uniaxially at a high
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temperature below the melting point of PTFE. After the
stretching, a sintering may be conducted in which the stretched
sheet is heated to a temperature not lower than the melting
point of PTFE while keeping the stretched state of the sheet
and is then cooled. This treatment is intended to fix the
microstructure formed by the stretching and to thereby enhance
dimensional stability. However, the sintering as the last step
is not essential to the ePTFE film in the present invention.
The ePTFE film thus produced is a flexible film which
is pure-white and marshmallowy to the touch. This film is
permeable to air, showing that the openings called "pores" are
interconnected from the front to the back side of the film. An
examination with an electron microscope reveals that the
microstructure of the film, in both the surface and inner
parts, is a unique fibrous porous structure comprising fibrils
(small fibers) and nodes (knots) which connect the fibrils to
one another. The state of this fibril/node structure varies
depending on stretching direction and stretch ratio. For
example, uniaxial stretching results in a film in which the
fibrils have been uniaxially oriented along the stretching
direction like a reed screen and the nodes connecting the
fibrils are observed as long islands whose major axes have been
oriented perpendicularly to the stretching direction. On the
other hand, biaxial stretching results in a film in which the
fibrils extend radially in the plane including the stretching
directions, and the nodes connecting the fibrils are observed
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as fine particles rather than islands. As the stretch ratio
increases, the fibrils generally become longer and the nodes
become smaller, regardless of stretching direction, finally
resulting in the so-called node-less structure consisting only
of fibrils. The ePTFE films have lower specific gravities than
solid films of pure PTFE, and the specific gravities thereof,
which depend on porosity, are mostly lower than that of water.
An ePTFE film is made of pure PTFE, and the fibrils and
nodes characteristic of the structure thereof are made of the
PTFE. PTFE is a material which is so stable chemically that it
is less susceptible to deterioration or corrosion even when
used for roof waterproofing or as a water barrier in an
irrigation pond, where the polymer is exposed to sunlight and
the atmosphere for long. Since an ePTFE essentially has the
excellent chemical stability of PTFE, it has resistance to
ultraviolet and is not oxidized by air. Furthermore, since
PTFE is not synthesized in the natural world, it undergoes no
degradation by bacteria. Thus, an ePTFE film has excellent
weatherability.
However, ePTFE films have mechanical and physical
properties different from those of solid films of PTFE. Solid
films of PTFE are milk-white like transparent ground glass,
whereas ePTFE films are remarkably pure-white. This pure-white
color is thought to be attributable to the total reflection
phenomenon due to the porous microstructure of the ePTFE films.
Furthermore, in contrast to solid PTFE films, which are
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generally regarded as a rigid material, ePTFE films are
marshmallowy to the touch as stated hereinabove and are so
plastic that they change their shape to hold close contact with
an object of any shape. This property also is thought to be
attributable to the unique fibrous structure thereof. In
addition, ePTFE films show gradual elastic recovery due to
their network structure. Therefore, when an ePTFE film is used
as a lamina in the elastomer sheet laminate of the present
invention, it can easily stretched and contract together with
the elastomer. Although PTFE is thought to be a material which
is incompatible with other substances and exceedingly difficult
to bond, ePTFE films can be easily bonded using the so-called
anchoring effect produced by a porous structure they have. In
particular, since the porous structure is easily permeable to
organic media having a low surface tension, this property is
utilized to conduct processings such as bonding, impregnation,
and coating.
If a film made of a material which itself is highly
rigid and poorly flexible, such as a~solid PTFE film, a film of
a fluororesin other than PTFE, a polyester film, or a
poly(vinyl chloride) film, is laminated on an elastomer sheet,
then the resultant laminate warps due to a difference in the
coefficient of expansion or contraction between the constituent
materials or suffers delamination as a result of repetitions of
bending. For example, if a fluororesin film or polyester film
is laminated on an elastomer sheet, the laminated sheet suffers
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warpage or delamination because the fluororesin film or
polyester film is too rigid to follow a shape change of the
elastomer sheet. However, in the case where an ePTFE film 4 is
laminated on an elastomer sheet 2, the laminated sheet is
prevented from warping because the film 4 has a small value of
tensile modulus and excellent flexibility due to the
constitution described above.
In Table 1 are shown the tensile moduli of typical
fluororesin films, a poly(monofluoroethylene) film tPFE), and
an ePTFE film. Table 1 shows that the ePTFE film has an
exceedingly small value of tensile modulus and excellent
flexibility as compared with the general fluororesin films
(poly(vinyl difluoride) film (PVDF) and poly(vinyl fluoride)
film (PVF)).
Table 1
ASTM ePTFE PTFE PFE PVDF PVF
test
method
Tensile D638 360 4100- 3500 10200- 19000
modul~s 5600 30000
(kg/cm )
The thickness of the ePTFE film 4 is preferably from 3
to 300 ~m, more preferably from 20 to 100 ~m, in terms of
average thickness determined with a dial gauge (measurement is
made with a 1/1000 mm dial thickness gauge manufactured by
Tecrock Co., without imposing a load other than the spring load
of the gauge). If the thickness thereof is smaller than 3 ~m,
not only sufficient mechanical durability cannot be obtained
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but also the film is difficult to laminate. On the other hand,
thicknesses thereof exceeding 300 ~m are undesirable from the
standpoint of cost because of the low productivity and an
increased material cost.
With respect to the pore diameter of the ePTFE film 4,
the maximum pore diameter thereof as determined by the bubble
point method (ASTM F-316) is preferably from 0.01 to 10 ~m,
more preferably from 0.05 to 5 ~m. If the mAximum pore
diameter thereof is smaller than 0.01 ~m, the fusion bonding
based on an anchoring effect is difficult. If the maximum pore
diameter thereof exceeds 10 ~m, sufficient mechanical strength
cannot be obtained.
The ePTFE film 4 may be an embossed film. In the case
of a laminated sheet in which the color of the elastomer sheet
2 is visible on the surface through the ePTFE film 4 because of
the small thickness of the film 4, the appearance of the
laminated sheet can be improved by embossing the ePTFE film 4
beforehand to evenly pattern the color which is visible through
the film 4. The embossing of the ePTFE film 4 may be conducted
prior to laminating to the elastomer sheet 2 and the
thermoplastic resin film 3, or may be conducted at the time of
the laminating.
Examples of methods for coloring an ePTFE film include:
a method in which the polymer is compounded with a pigment
during film production to thereby produce a film containing
pigment particles embedded in openings thereof; a method in
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which a film is formed and then coated with a solvent-based
coating composition to thereby embed pigment particles into
openings of the film; and a method in which a film is formed
and then dipped in a coating composition bath to thereby embed
pigment particles in openings of the film.
The method of coloring an ePTFE film by pigment
compounding is explained below.
A PTFE resin is compounded with 0.5 to 30% by weight
inorganic pigment suitable for the desired color tone, e.g.,
carbon black. Although the incorporation amount of the pigment
is regulated according to the desired color tone and the kind
of the pigment, pigment amounts larger than 30% by weight may
result in development of pinholes during film stretching or
lead to a decrease in strength. Examples of methods for the
compounding include: (1) a method in which a sufficiently dried
pigment is added to a PTFE resin to be granulated, and the
mixture is homogenized with a mixer; and (2) a method in which
a pigment is added to a liquid prepared by dispersing primary
PTFE particles into water, which is called a dispersion, and
the mixture is homogenized and granulated. Although either
method is usable, method (2) is preferred in that more
homogeneous pigment dispersion is possible and the colored
ePTFE film to be finally obtained will be less apt to have
unevenness of color. The granulated PTFE is mixed with 17 to
22% by weight hydrocarbon solvent as a lubricant for extrusion,
and the resultant mixture is preformed by paste extrusion. The
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preform is rolled to a given thickness, and the resultant film
is dried to remove the lubricant therefrom. Thereafter, the
dried film is stretched in the width direction at a stretch
ratio of from 50 to 1,500%, preferably from 500 to 1,000%, at
a high temperature below the melting point of PTFE (327~C). If
desired and necessary, the stretched film is heat-treated at a
temperature not lower than the melting point of PTFE. The film
thus obtained has a width of preferably 500 mm or larger, more
preferably 1,200 mm or larger. Widths of the film smaller than
500 mm are undesirable in that the waterproofing water-barrier
sheet to be finally obtained will have a width limited to below
500 mm and hence have reduced in-situ applicability.
In the case where an ePTFE film, which usually is
white, is laminated as such to an elastomer sheet, the
resultant laminate can be used as a white waterproofing water-
barrier sheet. This laminated sheet also is within the scope
of the invention. When an ePTFE film colored in any desired
tint is used, an elastomer sheet can be colored in the desired
tint. Thus, an excellent color tone can be imparted to the
appearance of a waterproofing water-barrier sheet.
By embedding pigment particles in openings of an ePTFE
film, a film colored in any desired tint can be obtained.
Furthermore, an ePTFE film containing no pigment can be used as
such as a pure-white film.
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Processes for producing the elastomer sheet laminate
and colored waterproofing water-barrier sheet of the present
invention will be explained next.
Examples of methods for laminating a vulcanized rubber
sheet 2 such as that described above, employed as an example of
an elastomer sheet, to an ePTFE film 4 through a thermoplastic
resin by heat fusion include: a method which comprises
laminating beforehand a thermoplastic resin film 3 to an ePTFE
film 4, for example, by fusion bonding with a heated roll,
superposing a vulcanized rubber sheet 2 on the resultant
laminate on the side of the thermoplastic resin film 3, and
then heating and pressing the assemblage with, e.g., heated
rolls to laminate the sheet 2; a method which comprises
superposing a thermoplastic resin film 3 on a vulcanized rubber
sheet 2, heating and pressing the assemblage with, e.g., heated
rolls to obtain a laminated sheet, and then laminating an ePTFE
film 4 to the laminated sheet, e.g., by fusion bonding with
heated rolls; and a method which comprises superposing an ePTFE
film 4 on a thermoplastic resin film 3 and a vulcanized rubber
sheet 2 and heating and pressing the assemblage with, e.g.,
heated rolls to thereby laminate the thermoplastic resin film
to the ePTFE film and simultaneously laminate the thermoplastic
resin film 3 on the vulcanized rubber sheet 2. All of these
methods can be used.
As described above, another embodiment of the present
invention is a sheet consisting of a vulcanized rubber sheet 2
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and an ePTFE film 4 laminated thereon without interposing a
thermoplastic resin film 3 therebetween. For producing this
two-layer laminate, laminating can be conducted by the
following method.
An unvulcanized rubber sheet is superposed on an ePTFE
film 4, and the assemblage is heated and pressed with, e.g., a
vulcanizer to thereby vulcanize the rubber and simultaneously
laminate the rubber sheet on the film 4.
In this case, since the rubber in an unvulcanized state
is flowable, it can penetrate into openings of the ePTFE film
4. Thus, an anchoring effect can be obtained to accomplish
laminating, without interposing a thermoplastic resin film 3.
An unvulcanized rubber sheet may, of course, be used
likewise to produce a laminated sheet containing an interposed
thermoplastic resin film 3, which is the three-layer embodiment
described hereinabove. Laminating can be conducted also by
bonding using an adhesive such as a chloroprene rubber, butyl
rubber, epoxy resin, urethane, or cyanoacrylate adhesive.
These adhesives may be used even when the elastomer is a
polymer which is not a rubber.
The following method can be used for efficiently
producing the sheet of the present invention to attain
heightened productivity.
In this efficient method, a rubber sheet 2 which has
undergone vulcanization just before and is hence still hot is
laminated on a thermoplastic resin film 3 or to a thermoplastic
CA 02232617 1998-03-18
resin film 3 which has been laminated on an ePTFE film 4.
Namely, the heat of the vulcanized rubber sheet 2 is utilized
for the laminating. This method is illustrated in Fig. 3. The
apparatus shown in the Figure is used for this method.
Specifically, an unvulcanized rubber sheet 10 extruded from an
extruder (not shown) is placed on an endless belt 11,
introduced through introduction rolls 12 into a vulcanizer 13
set at a given temperature (150 to 180~C), and then vulcanized
therein. The vulcanized rubber sheet is taken out of the
vulcanizer 13 through withdrawal rolls 14, sent through guide
rolls, and then contact-bonded with pressure rolls 16 to a
thermoplastic resin film 17 or to a thermoplastic resin film 17
which has been laminated on an ePTFE film. The resultant
laminated sheet is sent via a tension roll 18 and wound on a
wind-up roll 19. In this case, since the vulcanized rubber
sheet 15 which was taken out of the vulcanizer 13 just before
has a surface temperature of from 130 to 150~C, the
thermoplastic resin film 17 can be easily fusion-bonded
thereto. This method does not necessitate preheating of the
pressure roll 16, so that it can contribute to a reduction in
production cost coupled with an improvement in productivity.
When an ePTFE film 4 is superposed on the thermoplastic
resin film 3 bonded to a surface of the vulcanized rubber sheet
2 by the method described above and the thermoplastic resin
film 3 is melted by heating, then the molten thermoplastic
resin can penetrate into pores of the porous film. Therefore,
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CA 02232617 1998-03-18
the PTFE resin film, which is a fluororesin film usually unable
to be tenaciously bonded by heat fusion, can be fusion-bonded
to attain a sufficient bonding strength by using the processes
according to the present invention described above. As a
result, a colored rubber sheet laminate and a colored
waterproofing water-barrier sheet 1 can be obtained which is
excellent in color tone and weatherability and free from the
problems of discoloration, delamination, warpage, etc.
BEST MODES FOR CARRYING OUT THE INVENTION
EXAMPLE 1
A sheet laminate consisting of a vulcanized rubber
sheet 2 and an ePTFE film 4 made of PTFE and laminated thereon
through a polyethylene resin film, i.e., having the
constitution shown in Fig. 1, was produced in the following
manner.
The vulcanized rubber sheet 2 used was a sheet formed
from a composition containing an ethylene/propylene terpolymer
(EPT) as the main component and having the makeup shown in
Table 2.
The polyethylene resin film used was a polyethylene
film (thickness, 30 ~m) manufactured by Sanwa Chemical Co.,
Ltd.
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CA 02232617 1998-03-18
Table 2
IngredientAmount (parts by weight)
EPT 100
Stearic acid
Zinc white 3
Process oil 50
Carbon black 50
Calcium carbonate 60
Accelerator TT 1.0
Accelerator DM 1.0
Sulfur 1.5
EXAMPLE 2
A sheet laminate consisting of a polyethylene sheet
(high-density) and an ePTFE film laminated thereon through a
polyethylene resin film, i.e., having the constitution shown in
Fig. 1, was produced. The polyethylene sheet used was a sheet
comprising high-density polyethylene (HDPE) as the main
component and having the makeup shown in Table 3. The
polyethylene resin film was the same as in Example 1.
Table 3
Ingredient Amount (parts by weight)
HDPE 100
Carbon black
The ePTFE film 4 was a film colored gray and produced
by the following method.
As PTFE was used Dispersion Teflon manufactured by Du
Pont-Mitsui Fluorochemicals Co., Ltd.
Ketjen Black manufactured by Mitsubishi Chemical Corp.
was used as a pigment for coloring. The pigment was mixed with
the Dispersion Teflon in an amount of 3% by weight, and the
mixture was granulated. The resultant PTFE granules were mixed
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CA 02232617 1998-03-18
with 18.5% by weight Super Sol, manufactured by Idemitsu
Petrochemical Co., Ltd., as a lubricant for extrusion, and the
mixture was stretched in the width direction at a stretch ratio
of 700% and then heat-treated at 360~C to obtain a light-gray
ePTFE film 4. The ePTFE film 4 obtained had a thickness of 43
~m (as measured with a 1/1000 mm dial thickness gauge
manufactured by Tecrock Co., without imposing a load other than
the spring load of the gauge) and a maximum pore diameter of
0.5 ~m (ASTM F-316).
For producing ePTFE films, the same processing method
as the above was used, except that Ketjen Black was
incorporated in various amounts of 1, 3, 7, 10, and 25% by
weight. As a result, the color tone of the thus-obtained ePTFE
films changed from light-gray to black as the incorporation
amount of Retjen Black increased. The ePTFE film obtained with
3% by weight Ketjen Black had the best gray color.
The laminae described above were laminated in the
following manner in order to obtain a waterproofing water-
barrier sheet.
First, the ePTFE film which had been colored light-gray
was fusion-bonded to the polyethylene film by nipping these
films with a heated roll and a nipping roll in such a manner
that the ePTFE film side came into contact with the heated roll
and the polyethylene film side came into contact with the
nipping roll in order to prevent the polyethylene film from
fusing to the heated roll. This processing was conducted at a
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CA 02232617 1998-03-18
heated-roll temperature of 170~C, a nipping pressure of 7
kg/cm2, and a processing speed of 5 m/min.
Using an apparatus such as that shown in Fig. 3, the
thus-obtained two-layer laminate consisting of an ePTFE film
and a polyethylene film was fusion-bonded to a vulcanized
rubber sheet with a pressure roll immediately after the rubber
sheet was taken out of the vulcanizer. The processing
conditions included a surface temperature of the vulcanized
rubber sheet of 153~C, a nipping pressure of 5 kg/cm2, and a
processing speed of 5 m/min. Thus, a three-layer laminate
consisting of an ePTFE film, a polyethylene film, and a
vulcanized rubber sheet was obtained.
COMPARATIVE EXAMPLE 1
A colored sheet of Comparative Example 1 was produced
by laminating a colored rubber sheet (0.3 mm thick) made from
a composition containing an ethylene/propylene terpolymer and
butyl rubber (IIR) as the main components and having the makeup
shown in Table 4 to a black rubber sheet (1.2 mm) made from a
composition containing an ethylene/propylene terpolymer as the
main component and having the makeup shown in Table 2.
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CA 02232617 1998-03-18
Table 4
Ingredient Amount (parts by weight)
ERT 70
IIR 30
Zinc white 5
Stearic acid
Talc SW 40
Heavy calcium carbonate 30
Silica 20
Paraffin oil 30
Carbon black
Vulcanizing agent TMTD
MBT 0.5
Sulfur
COMPARATIVE EXAMPLE 2
A sheet laminate of Comparative Example 2 was produced
by conducting the same procedure as in Example 1, except that
a film obtained by coloring a 30 ~m-thick Tedlar (poly(vinyl
fluoride) manufactured by E.I. du Pont de Nemours & Co., Inc.)
film green was used in place of the ePTFE film used in Example
1.
COMPARATIVE EXAMPLE 3
A sheet laminate of Comparative Example 3 was produced
by conducting the same procedure as in Example 2, except that
the ePTFE film used in Example 2 was omitted.
Data for the Examples and Comparative Examples given
above are shown in Table 5 for comparison.
The weatherometer and outdoor exposure tests given in
the Table were conducted under the following conditions.
~eatherometer: after 1,000 hours, in accordance with JIS A
1415
Outdoor exposure test: after a half year
Table 5
Example 1 Example 2 Comparative Comparative Comparative
Example 1 Example 2 Example 3
Color tone (gray) good good good good good
Unevenness of color uneven from
tone none none lot to lot none none
Color fading none none fading none fading
colored- film
Peeling film film rubber breakage none
Weathero- breakage breakage breakage delamination
meter +15 mm D
Warpage almost none none none warpage on none
film side
Surface
cracking none none none none cracking
Color fading none none slight
fading none fading
colored- film
Outdoor Peeling fiim film rubber breakage none
exposure breakage breakage breakage delamination
test +12 mm
Warpage almost none none none warpage on none
film side
Surface cracking
cracking none none none none
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CA 02232617 1998-03-18
Table S shows the following. The colored rubber sheet
of Comparative Example 1 had unevenness of color from lot of
lot and suffered considerable color fading through the
weatherometer test and the outdoor exposure test, although the
initial color tone of the sheet was safisfactory. The
poly(vinyl fluoride) laminated sheet of Comparative Example 2
warped due to a difference in the coefficient of thermal
expansion between the rubber and the poly(vinyl fluoride),
although it underwent no color fading through the weatherometer
test and the outdoor exposure test. In addition, in the
peeling test, the sheet of Comparative Example 2 underwent
partial film breakage and partial delamination. The sheet of
Comparative Example 3 suffered color fading, although its
initial color tone satisfactory.
In contrast, the sheets of the Examples according to
the present invention each had a satisfactory color tone and
underwent neither color fading, ePTFE film peeling, nor warpage
even through the test for exposure to various lights. Thus,
the sheets of the Examples gave highly satisfactory results as
compared with the sheets of Comparative Examples 1, 2, and 3.
POSSIBILITY OF INDUSTRIAL APPLICATION
As described above, the sheets of the present
invention, each of which comprises an ePTFE film and an
elastomer sheet laminated thereon, not only have a delicate
color tone with reduced unevenness of color, but suffers no
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CA 02232617 1998-03-18
warpage. In addition, sufficient weatherability can be
imparted to an elastomer material which has hitherto been
unusable because of its poor weatherability. Namely, the
conventional waterproofing water-barrier sheets of various
kinds, each having both merits and demerits, are improved in
their unsatisfactory properties not always sufficient. Thus,
the present invention produces the remarkable effect of
providing a waterproofing water-barrier sheet free from the
problems of discoloration and delamination.
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