Note: Descriptions are shown in the official language in which they were submitted.
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- METHOD OF JOINING ~ATERPROOF
VULCANIZED SYNTHETIC RUBBER SHEETS
.:
-~ FIELD OF THE INVENTION
This invention relates to a method of joining
waterproof vulcanized synthetic rubber sheets. ~ore
~~ particularly, this invention relates to a method of join-
ing waterproof vulcanized synthetic rubber sheets which
can be used on the job site, e.g., in civil engineering
for preventing-water leakage from reservoirs, irrigation
ponds, tanks for treating industrial wastes, irrigation
channels, and other water courses, as well as for various
community structures, such as indoor structures (e.g.,
lavatories and baths), roofs, subways, ditches, and
~ overpasses. The method comprises joining such sheets by
cold-vulcanizing a cold-vulcanizable adhesive tape between
overlapped areas of the sheets, without the necessity of
applying elther heat or high pressure.
BACKGROUND OF THE INVENTION
Concrete and asphalt have been commonly used
as lining materials for preventing water leakage from
reservoirs, but recently, it is more common to use
vulcanized rubber sheeting that withstands large deforma-
: tions, has high weatherability, and which is flexible
enough to absorb the subsequent movement of the lined
area ~e.g., river bed). But the nature OI the process
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for manufacturing vulcanized rubber sheeting imposes
dimensional limitations on the production equipment,
and although sheeting as long as about 200 m can be made
without great difficulty, its width is usually about
1.0 m, and making sheeting wider than 10 m is practical-
ly impossible. Therefore, the current practice is to
transport vulcanized rubber sheets to the installation
site, where they are then joined together.
Several methods have been proposed to make the
overlapped areas of the joined sheets resistant against
water leakage. The two most common methods are to use
an adhesive agent, and to use an unvulcanized rubber tape.
However, neither method is completely satisfactory. In
the first method, bonding had a tendency to become uneven
because a uniform film of the adhesive cannot easily be
obtained. In addition, the adhesion strength varies
greatly with the length of open time. The open time is
alternatively called "open assembly time" and means the
time which gives an appropriate tackiness to an adhesive
by coating an adhesive to a material and allowing to
stand the coated surface thereof to volatilize a solvent
contained in the adhesive. The greatest defect of this
method is that no matter how good the quality of the
vulcanized sheets and adhesive tape are, poor adhesion
may result unless the persons applying the tape are very
1~'7ZS51
skilled. If a strong wind blows during open time, dust
sticks on the surface and prevents strong adhesion. If
the temperature is high, even a short open time will
result in overdrying of the adhesive to cause poor
adhesion. If the humidity is high, dew is formed on
the joining surfaces, also causing poor adhesion. If
the temperature is too low, a long open time reduces the
joining efficiency. Thus, the sheet-joining workers must
have adequate knowledge on the various environments under
which the work may be executed. Therefore, with the
first method, it is very difficult to join the waterproof
vulcanized rubber sheets securely enough to ensure that
there will be no water leaks.
An example of the second method that uses an
unvulcanized rubber tape comprises sandwiching the
unvulcanized rubber tape between vulcanized rubber sheets
and spot-vulcanizing them by applying heat (150-200C)
and pressure (100-150 kg/cm2) to both obverse and reverse
sides of the sheets. But this method requires a vulcan-
izing press on the job site. In addition, the desiredbond strength is not obtained unless high vulcanization
temperature and pressure are used, and this results in
prolonged joining time, and reduced joining efficiency.
.... .. . . . . . . .. . . . .. . . . . . . . . .
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The conventional unvulcanized rubber tape
has Mooney viscosity [MLl+5 ~100C)] of 23 and .
comprises the following compositions ~parts by
weight).
EPT (third componçnt: dicyclopenta-70 ~.
diene, iodine value: 20)
IIR 30
ZnO 5
SRF carbon~ 40
E~cor~ot~ (product of Esso Chemical Co.) 15
Paraffinic process oil (product of20
Maruzen Oil Co.)
S 1.5
Dipentamethylenehexasulfide 5.5
--4--
.. .. ... . .. . .
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-.~ SUMMARY OF THE INVENTION
~ Therefore, one object of this invention is to
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provide an efficient method of joining waterproof vulcan-
.
. ized rubber sheets without a vulcanizing press.
Another object of this invention is to provide
a method of joining waterproof vulcanized rubber sheets
strongly enough by cold vulcanization to ensure security
from water leaks.
A further object of this invention is to
provide a method of joining waterproof vulcanized rubber
sheets that can be used on a job site.
According to the method of this invention, a
cold-vulcanizable adhesive tape having Mooney viscosity
[MLl+5 (100C)] of from 5 to 25 and an autoadhesion
lS property and containing (1) a rubbery polymer, (2) a
, vulcanizing agent, (3) a vulcanization accelerator, (4)
an adhesive agent, and (5) a softening agent is placed
between overlapped areas of waterproof vulcanized
synthetic rubber sheets, and said adhesive tape is
vulcanized to thereby join the sheets.
BRIEF DESCRI~TION OF THE DRAI~INGS
Figure l is a cross sectional view of over-
lapped areas of waterproof sheets that are joined in one
embodiment of the method of this invention.
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Figures 2 to 5 are cross sectional views of
overlapped areas of waterproof sheets that are joined in
other embodiments of the method of this invention.
- Figure 6 is a graph showing the time-dependent
change in the peel strength of joined waterproof sheets
prepared according to Example 1 that were stored in
, either a Gear oven (Gear system ageing tester) at 80C
or in hot water at 70C.
Figure 7 is a graph showing the time-dependent
change in the peel strength of the joined waterproof
sheets of Example 1 that were subjected to weathering.
Figure 8 is a perspective view of the joined
waterproof sheets of Example 1 that were applied to a
corner portion of another object.
DETAILED DESCRIPTION OF THE INVENTION
,
Specific embodiments of the method of this
invention are now described in detail by reference to
the accompanying drawings. Figure 1 is a cross sectional
view of overlapped areas of waterproof sheets 1 and 1'-
joined according to one embodiment of this invention.
In Figure 1, a cold-vulcanizable adhesive tape (2) of the
same width as the overlapped areas is sandwiched between
these areas, and the overlapped areas of the waterproof
sheets existing the adhesive tape are pressed with a
roller or other suitable means for the purpose of
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increasing a self-adhesion between rubber sheets and
.. also removing air present between rubber sheets. The
pressure is from about 0.3 to 1 kg/cm .
. The adhesive tape used in this invention can
, 5 be placed between the overlapped areas of waterproof
- sheets by several techniques. Three useful techniques
are described below.
- ~1) A pre-formed rubber compound (A) having
- a vulcanizing agent, an adhesive, a softening agent, etc.,
incorporated therein, and a pre-formed rubber compound
(B) having incorporated therein a vulcanization accelera-
tor, an adhesive, a softening agent, etc., are separately
-- charged into a mixing extruder on the job-site-where
; they are mixed and extruded in the form of a tape, and
~r 15 the resulting adhesive tape is placed between the over-
lapped areas of the sheets. In this method, the adhesive
agent or softening agent may be incorporatèd in either
. or both of rubber compounds (A) and ~B).
(2) A pre-formed rubber compound (A) having
a vulcanizing agent, an adhesive agent, and a softening
agent incorporated therein, and a pre-formed rubber
compound (B) having a vulcanization accelerator, an
adhesive agent, and a softening agent incorporated there-
in are charged into a portable extruderJ such as a
portable applicator extruder on the job site, from which
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an adhesive tape is extruded directly between the over-
lapped areas of the sheets. In this technique, the
adhesive agent or softening agent may be incorporated
in either or both of rubber compounds ~A) and ~B).
(3) A pre-formed adhesive tape having incorpo-
rated therein a vulcanizing agent, a vulcanization
accelerator, an adhesive agent, and a softening agent
is placed be~ween the overlapped areas of the sheets on
the job site.
The first two techniques are suitable for
making an adhesive tape which vulcanizes quickly. Due
to the quick vulcanization, such a tape thus obtained
has poor storage stability. On the other hand, the third
technique is suitable for making an adhesive tape which
vulcanizes slowly. Such a tape thus obtained has good
storage stability.
The cold-vulcanizable adhesive tape used in
; this invention is preferably made of a weather-resistant
material such as an ethylene-propylene terpolymer (EPT),
butyl rubber (IIR) or a blend of EPT and IIR. The third
component in the EPT is optional, but the preferred
examples thereof are dicyclopentadiene (iodine value
20), ethylidene norbornene (iodine value 24), etc. The
tape may contain suitable amounts of a vulcanizing agent,
a vulcanization accelerator, an adhesive agent, and a
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~ softening agent, as well as other additives such as
stearic acid, carbon black, inorganic filler, and ZnO.
.
Suitable examples of vulcanizing agents
include sulfur or sulfur compounds, such as morpholine
- 5 disulfide, phosphorus-containing polysulfide and sulfur
chloride; oximes such as p-quinone dioxime and p,p'-
- dibenzoyl quinone dioxime; and peroxides such as ~-cumyl
hydroperoxide, methyl ethyl ketone peroxide, hydrogen
peroxide, acetylacetone peroxide, t-butyl hydroperoxide,
and t-butyl peroxybenzoate. These vulcanizing agents
- are usually included in an amount of from 1 to 6 parts
by weight per 100 parts by weight of the rubbery polymer.
Suitable examples of vulcanization accelerators
include thiazoles such as 2-mercaptobenzothiazole and
dibenzothiazyl disulfide; thiurams such as tetramethyl-
thiuram monosulfide, tetramethylthiuram disulfide, and
dipentamethylenethiuram hexasulfide; dithiocarbamates
- such as Zn-dimethyl dithiocarbamate, Zn-di-n-butyl
dithiocarbamate; and PbO2 and Trimene Base (trademark ~
of Uniroyal Chem. for a reaction product of ethyl
chloride, formaldehyde, and ammonia). These vulcaniza-
tion accelerators are usually included in an amount of
from 2 to 10 parts by weight per 100 parts by weight of
the rubbery polymer.
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.~ Suitable examples of the adhesive agents
-: include petroleum hydrocarbon resins, such as an aromatic
., .
--. hydrocarbon resin (e.g., Petrosin (trademark) of Mitsui Petrochemical Industries, Ltd.) and an alicyclic hydro-
carbon resin (e.g., Hyretz Ctrademark) of Mitsui Petro-
chemical Industries, Ltd.); an unsaturated hydrocarbon
- polymer such as Escoretz (trademark) of Esso Chemical
-- Co.; a hydrocarbon tackifier resin such as Tackace
:.-
(trademark) of Mitsui Petrochemical Industries, Ltd.;
and a phenolic resin, such as phenol-formaldehyde resin.
These adhesive agents are usually used in an amount of
. from 30 to 100 parts by weight per 100 parts by weight
of the rubbery polymer.
: Any known softening agent may be used in
combination with the adhesive agents mentioned above,
and typical examples of the softening agent are process
:~ oil, polybutene, liquid paraffin, pine tar and other
high-boiling petroleum compounds. These softening
agents are usually used in an amount of from 30 to 150 ~
parts by weight per 100 parts by weight of the rubbery
polymer.
A cold-vulcanizable adhesive tape that
vulcanizes in a relatively short time and can be
prepared on the job site can be a blend composed, for
example, of 100 parts by weight of the rubbery polymer,
from 1 to 2 parts by weight of an oxime vulcanizing
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agent (e.g., p-quinone dioxime or p,p'-dibenzoyl quinone
` dioxime), from 3 to 4 parts by weight of a PbO2 vulcani-
-- zation accelerator, from 30 to 100 parts by weight of an
adhesive agent, and from 30 to 150 parts by weight of a
softening agent, such as process oil. A cold-vulcanizable
` adhesive tape that vulcanizes in a relatively long time
~ and can be preformed in a factory can be a blend which
. is composed, for example, of 100 parts by weight of the
rubbery polymer1 from 1 to 3 parts of a vulcanizing
agent selected from sulfur and sulfur-containing
compounds such as morpholine disulfide, phosphorus-
containing polysulfide and sulfur chloride, from 2 to 6
parts by weight of a vulcanization accelerator seleSted
from among thiazoles, thiurams, and dithiocarbamates,
15 from 30 to 100 parts by weight of an adhesive agent,
- and from 30 to 150 parts by weight of a softening agent
such as process oil.
The cold-vulcanizable adhesive tape used in
this invention can be vulcanized in air or water at
ambient temperature, and it can be vulcanized on the
job site without application of any heat or high pressure
that has heretofore been necessary. In addition, water-
proof vulcanized rubber sheets can be joined by this
tape very strongly so that adequate prevention of water
leakage can be achieved. This tape is required to
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~ provide a sheet joint with an initial strength of auto-
--. adhesion strength of at least about from 0.5 to 3 kg/25
^l mm, and without such strength, the overlapped areas of
the joined sheets can deform or slip from place when the
sheets are wrapped around something or stretched. There-
- fore, to provide the minimum amount of autoadhesion
strength, typically from 30 to 100 parts of an adhesive
.
agent and from 30 to 150 parts by weight of a softening
agent are incorporated per 100 parts of the rubbery
polymer so that the resulting adhesive tape has Mooney
- viscosity [MLl+5 (100C)] in the range of from 5 to 25.
If the adhesive tape has Mooney viscosity of this range,
foreign particles such as dust or dirt that might adhere
~ to the joined surfaces of waterproof sheets penetrate
into the tape, and as a result, the adhesive strength
between the joined sheets is not significantly affected.
The adhesive tape used in this invention
desirably has a thickness between 0.5 and 2 mm. If the
thickness of adhesive tape is thinner than 0.5 mm or
thicker than 2.0 mm, the adhesive strength decreases.
The waterproof vulcanized synthetic rubber
sheet used in the method of the present invention is
preferably made of an excellent weather-resistant
material such as an ethylene-propylene terpolymer (EPT),
butyl rubber (IIR) or a blend of EPT and IIR.
.
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; After the adhesive tape is placed between the
- overlapped areas of waterproof sheets in the manner
described below, the overlapped areas are pressed
together with a roller or other suitable means. This
is for the purposes of providing increased adhesive
~- strength between the joined sheets and removing any air
~ trapped between the two sheets. As a further advantage,
reliable on the job site joining is achieved by the
method of this invention, because the adhesive tape
further vulcanizes in the course of time to provide an
even s~ronger bonding of the two sheets. The adhesive
tape is flexible and has a substantially uniform thick-
ness, so upon application of pressure, it is brought
into uniform and intimate contact with the overlapped
areas of the waterproof sheets, thus assuring the
desired protection from water leakage.
In the case wherein the overlapped areas of
the waterproof sheets require an initial strength higher
than 3 kg/25 mm, after the adhesive tape is placed -
between the overlapped areas of the waterproof sheets,the overlapped areas are put between two plane plates
and then pressed and heated, or the overlapped areas are
pressed and heated by hot plates placed on the upper
surfaces of the overlapped areas. In this case, the
conditions are pressure of from 10 g/cm2 to 3 kg/cm2,
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temperature of from 120 to 230C and press-heating time
~ of from 1 to 5 minutes.
s; Thus, the adhesive tape present on the over-
lapped areas is semi-vulcanized and the adhesive strength
~ 5 between the waterproof sheets increases within a short
`. period of time.
- The adhesive tape is thereafter cold-vulcanized.
- Figure 2 is a cross section of the overlapped
- areas of waterproof sheets 1, 1' that are joined in
another embodiment of the method of this invention. In
the figure, a cold-vulcanizable adhesive tape 2 of the
. same width as the overlapped areas is positioned between
- those areas in such a manner that one end-of the tape
extends from the overlapped end of the sheet 1'. The
joined surfaces of the sheets are-then pressed together
by a roller or other suitable means. In the embodiment
of Figure 2, there is no great difference in level
between the joined sheets 1, 1' because of the end of
the tape exposed from the overlapped end of the sheet I'.
Consequently, the possibility of subsequent separation
of the overlapped area of the sheet 1' is decreased
while also better assuring security from the penetration
of water.
Figures 3, 4, and 5 are cross sectional views
of overlapped areas of waterproof sheets 3 and 3' that
are joined in still other embodiments of the method of
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i this invention, wherein the adhesive tape is used for
the purpose of providing greater initial adhesive
, strength between two sheets that are joined on the job
; site. In Figure 3, the adhesive tape covers the over-
lapped area of the waterproof sheet 3'. More specifi-
cally, a vulcanized rubber tape 7 with an adhesive tape
which comprises a vulcanized rubber layer 5 laminated
with cold-vulcanizable adhesive tape 6 in such a manner
that both ends of the tape 6 extend from the rubber
layer 5 is attached to cover the overlapped area of the
waterproosf sheet 3', with the adhesive tape 6 facing
down. In the embodiment of Figure 3, the overlapped
areas of the sheets 3 and 3' are joined with an adhesive
agent 8 as in the conventional manner. By so doing,
adequate protection from water leakage can be achieved
because no water will enter from the overlapped area of
the sheet 3'. The arrangement of Figure 3 also has the
advantage of reinforcing the joined areas of waterproof
sheets. Another advantage of the embodiment of Figure ~
3, wherein the adhesive tape 6 is so wide that both of
its ends extend exposed from the vulcanized rubber part
5,is that the force of cohesion between the polymer
particles of the tape is increased while minimizing the
expansion and shrinkage of the rubber part.
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The embodiment of Figure 4 is identical with
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,. that of Figure 3, except that the adhesive tape 6 is
. .
also used between the waterproof sheets 3 and 3'. The
. embodiment of Figure 5 is also ident.ical with that of
. 5 Figure 3 except that the adhesive tape is placed between
the waterproof sheets 3 and 3', and a vulcanized rubber
tape composed of the vulcanized rubber layer 5 having a
~ coating of adhesive agent 8 is placed on the sheets so
- as to cover the overlapped area of the sheet 3'. The
embodiments of Figures 4 and 5 achieve the same result
- as that of the embodiment of Figure 3.
The method of this invention is now described
~ in greater detail by reference to the following examples
which are given here for illustrative purposes only,
lS and are not intended to limit the scope of the invention.
Example 1
Equal weights of p~e-formed rubber compounds
~A) and CB) having the formulations indicated in Table 1
were charged into a conventional mixing extruder on a ~
job site from which a cold-vulcanizable adhesive tape
having a thickness of 1.0 to 1.5 mm, a width of 100 mm,
and Mooney viscosity of 15 was extruded. The tape was
positioned,as shown in Figure 1, between lQ0 mm wide
overlapped edges of two waterproof vulcanized rubber
sheets 1.5 mm thick composed of an EPT/IIR blend, and
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the two sheets were pressed together with a roller at
a linear pressure of 0.5 kg/cm.
Table 1
Formulation of adhesive tape in parts by weight
Compound ~A) Compound (B)
: IIR 35 35
EPT 15 15
ZnO ~~ 5
Stearic acid 0.5 0,5
10 HAF carbon 50
Calcium carbonate -- 50
Olefinic resin ~Escoretz, 30 30
Esso Chemical Co.)
Paraffinic process oil 25 35
15 (Maruzen Oil Co.)
GMF ~p-quinone dioxime) 1 --
PbO2 3 5
In summer, waterproof sheets in service may be
heated by the direct sunshine and the tempera'ure of
their surface may become as high as 70-80C. Therefore-,
the time-dependent change in the peel strength of the
sheets was checked by storing them in a Gear oven at
80C and in hot water at 70C. The results are shown in
Figure 6. The sheets were also subjected to outdoor
weathering for checking the time-dependent change in
their peel strength. The results are shown in Figure 7.
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, The peel tests were conducted by the following procedure:
~r l x 6 inch test pieces cut from the joined sheets were
subjected to a T-peel with a tensile tester (20-25C,
50 mm/min).
The bond strength of the waterproof sheets at
a corner was checked by the following procedure: water-
-; proof sheets indicated at lO in Figure 8 were attached
to a cornered mortar wall 9 with an adhesive tape 12
positioned between the overlapped areas 11 of the sheets,
and the joined sheets were subjected to weathering to
see if the sheets at the corner came apart. The results
- are shown in Table 2.
Table 2
- ~eatheringStarted in April
15 Days 7 15 30 60
-i SeparationNo No No No
Example 2
A pre-formed cold-vulcanizable adhesive tape
having a thickness of 1.0 to 1.5 mm, a width of 100 mm~
and Mooney viscosity of 15 which was prepared from a
rubber compound of the composition indicated in Table 3
was stored for 2 days at 25C before it was brought to
the job site. The tape was positioned as shown in
Figure l between 20-mm wide overlapped areas of two
waterproof sheets of the same material as indicated in
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~;Example 1, and the sheets were pressed together with a
'`r~roller at a linear pressure of 0.5 kg/cm. The joined
.sheets were stored in a Gear oven at 80C to check the
time-dependent change in their peel strength. The
results are shown in Table 4.
, Table 3
~Composition of rubber compound in parts by wei~ht
. _ . ~
EPT 30
IIR 70
ZnO 5
Paraffinic process oil (Maruzen Oil Co.) 60
! ' Calcium carbonate 20
FEF carbon 50
Petroleum resin (Petrosin, Mitsui 60
Petrochemical Ind.)
Sulfur 2
Dipentamethylenethiuram hexasulfide 5
Table 4
Peel stren~th (kg/25 mm)
Age Peel Strength
. ~
Immediately after joining 1.25
2 hours later 2.0
24 hours later 9.5
7 days later 10.3
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Example 3
Pre-formed rubber compounds (A~ and ~B) having
the formula~ions indicated in Table 5 were charged into
a portable applicator on the site from which a cold-
-5 vulcanizable adhesive tape having a width of 100 mm, a
::.
` thickness of 1.0 mm, and Mooney viscosity of 8 was
- extruded continuously. The tape was sandwiched, as
.~ shown in Figure 1, between the overlapped areas of two
waterproof sheets of the same material as indicated in
Example 1, and the sheets were pressed together with a
roller at a linear pressure of 0.5 kg/cm. The joined
sheets were stored in a Gear oven at 80C to check the
time-dependent change in their peel strength. The
results are shown in Table 6.
Table 5
Formulation of adhesive tape (parts by weight)
Compound (A) Compound (B)
IIR 50 50
ZnO 5
- 20 Stearic acid 0.5 0.5
FEF carbon 50 --
: Calcium carbonate -- 40
Petroleum resin 30 30
Paraffinic process oil 35 25
25 p-Quinone dioxime 1 --
b2 3 5
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Table 6
.- Peel strength (kg/25 mm)
~ _ Age Peel Strength
;~ Immediately after joining2.0
2 hours later 9.8
~ 24 hours later 10.8
:. 7 days later 14.9
Comparative Example - ~
As shown in Figure 1, a coating of a cold-
vulcanizable butyl solvent adhesive having the composi-
` tions, parts by weight, of IIR 100 parts, TiO2 3.5 parts,
~, SRF carbon 25 parts, T ~c~ (product of Mitsui Petro-
chemical Ind.) 30 parts, GMF 3.5 parts, PbO2 2.5 parts,
- toluene 42Z parts and n-hexane 138 parts, was applied in
a thickness of 0.4-0.5 mm between the 100-mm wide over-
lapped areas of waterproof sheets made of the vulcanized
- rubber identified in Example 1, and after an open time
of 30 minutes the joined sheets were pressed together
with a roller at a linear pressure of 0.5 kg/cm. The ~
- 20 sheets were then stored in a Gear oven at 80C to check
- the time-dependent change in their peel strength. The
results are shown in Table 7 together with those of
Examples 1, 2 and 3. The joining efficiency of the
method used in Comparative Example as compared with that
of the method of this invention according to Example 1 is
set forth in Table 8.
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, The joining work was done during a period in
September and October when the outdoor average tempera-
' ture was from about 16.9 to 23.0C. As in the method of
-, Example 1, the adhesive tape was positioned between the
100 mm wide overlapped areas of waterproof sheets.
Table 7
Peel strength (kg/25 mm)
Comparative Example Example Examplè
Age Example _ 1 2 3_
Immediately
after 2,5 1.25 2.0
oining
10 2 hours 8.0 2.0 9.8
6 hours 2 0
later
hours 3.5 9.8 9.5 10.8
later 4.1 12.0 10.314.9
Table 8
Method _ Joining Efficiency
Comparative Example ca. 300 m/5 men-day
using adhesive (by 5 skilled workers)
Example 1 using ca. 600 m/5 men-day
adhesive tape ~by 1 skilled worker and
4 unskilled workers)
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-; As is clear from the above examples, the join-
ing method of this invention that uses a cold-vulcanizable
adhesive tape and which does not require a vulcanizing
. press on the job site achieves an efficient joining
- 5 operation. Since the adhesion strength of the rubber
sheet immediately after joining is as good as that
obtained by the conventional method that uses an
adhesive, the overlapped areas of waterproof sheets
will remain ln place throughout the joining work. In
addition, the adhesion strength increases over a period
of time. As another advantage, the adhesive tape makes
uniform and intimate contact with the overlapped areas
- of waterproof sheets, and so complete security from
water leakage is assured.
l~ile the invention has been described in detail
and with reference to specific embodiments thereof, it
will be apparent to one skilled in the art that various
changes and modifications can be made therein without
departing from the spirit and scope thereof.
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