Note: Descriptions are shown in the official language in which they were submitted.
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GLASS BOTTLES AND PROCESS FOR PREPARING THE SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to glass bottles and
lightweight glass bottles having a coating on the
external surface thereof, particularly returnable bottles
which can be recovered and used repeatedly, and a process
for preparation thereof.
2. Description of the Related Art
Hitherto, in the glass bottle industry, a surface of
a one-way bottle was overcoated with an Sn02 or Ti02
coating during the process for preparing the bottle in
order to improve the scuff resistance of the bottle
surface.
More specifically, one-way bottles have on the
external surface thereof a coating comprising Sn02 or
Ti02 and formed by spraying SnCl4 or TiCl4 onto the
bottles which have just been prepared and have not yet
been annealed in an annealing chamber, remaining at a
surface temperature of 400 to 550°C. Such process for
coating is generally called hot end coating method.
The thickness of the coating thus formed is
generally measured by a scale in "C.T.U." with a Hot End
Coating Meter which is manufactured by American Glass
Research Co. While the coating of one-way bottles in the
art has a current standard of 20 to 80 C.T.U., the
thickness of the coating is practically reduced to a
range of 20 to 50 C.T.U. from the viewpoint of cost or
appearance for avoiding the so-called iris phenomenon
which may be caused by alkali washing before bottling.
The unit "C.T.U." herein means a merely optical unit used
for process control and has no physical meaning.
However, 1 C.T.U. may be estimated at about 4 angstroms,
and we have also confirmed the appropriateness of the
value with Elipsometer Model AEP-100 (manufactured by
Shimazu Co.). Therefore, the Sn02 or Ti02 coating of
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one-way bottles prepared by the hot end coating method
may have a thickness of 300 angstroms or less.
Even though such a coating technique is effective as
a method for affording physical properties such as
abrasion resistance or lubricity to the one-way bottle,
the method could not be applied to the returnable bottle
because of the following reason.
The returnable bottle is recovered and used
repeatedly in principle. Bottles recovered from the
market are washed and sterilized every time on recovery
with a high-concentration and hot alkali solution such as
aqueous sodium hydroxide solution in washers in a
bottling factory.
When the bottle having the coating formed by the
method used for the one-way bottle is applied to such an
alkali treatment, the coating will be easily peeled off
and thus loses its effect. For instance, beer bottles
are generally washed with a 4~ aqueous sodium hydroxide
solution at a temperature of up to 80°C. Under such
condition, the coating having a thickness of 20 to 50
C.T.U. formed by the method applied to the one-way bottle
is usually peeled off in a single alkali washing cycle.
If the thickness of the coating is increased to a range
of 50 to 80 C.T.U., the coating may not be completely
peeled off in a single alkali washing cycle. Such a
washing treatment, however, causes iris phenomenon on the
surface of the bottle, and the bottle may lose its
commercial value from the aesthetic standpoint of
packaging. Therefore, even in the case of one-way
bottle, to the bottle is applied a coating which can be
easily peeled off in a single alkali washing cycle before
bottling.
In some literature, the hot end coating method is
carried out at a temperature in the range of 500 to
600°C. However, it can be scarcely supposed that the
treatment would have been practically carried out at a
temperature higher than about 550°C in view of the
CA 02029716 1997-09-29
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position where the hot end coating is carried out, i.e.,
before the annealing process, as well as for fear of
deformation of the glass bottle due to such a high
temperature. Another reason for the temperature
limitation may be the temperature of the glass surface is
measured by a primitive surface thermometer.
It has hitherto been impossible to prepare the
returnable glass bottle having a coating which comprises
SnOz or Ti02 as a main component and resists repeated
alkali treatment.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present
invention to provide a novel process for preparing glass
bottles having a coating which has resistance to repeated
1S alkali treatment.
It is a further object of the present invention to
provide a novel process for preparing glass bottles
having a coating which improves the strength of not only
one-way bottles but returnable bottles.
It is yet another object of the present invention to
provide a glass bottle having a coating which has
resistance to repeated alkali treatment and improves the
strength of the glass bottle.
Thus, the present invention provides, in its
principal aspect, a process for preparing a coating f_-or
glass bottles, which comprises the step of bringing a
glass bottle having an external surface temperature of
550 to 700°C into contact with a material which can form
a coating comprising Sn02 or Ti02 thereby to form a
coating predominantly comprising Snot or Ti0? at a
thickness of 900 to 1000 angstroms.
In another aspect, the present invention provides a
glass bottle having on an external surface thereof a
metal oxide coating predominantly comprising SnO~ or
,TiOz, the coating not being pee1ed off within E3 hours
upon dipping into a 4$ by weight of an aqueous sodium
hydroxide solution at 80°C.
20375-677
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The glass bottle having the coating according to the
present invention is excellent in resistance to abrasion
and resistance to alkali and can be used repeatedly as a
returnable glass bottle.
Further, the strength of the glass bottle having the
coating according to the present invention can be
improved, so that the weight of the glass bottle can be
reduced.
Still further, the coating has a comparatively large
refractive index and thus the reflection of light on the
glass surface may increase, so that the discoloration of
a content or other troubles can be prevented.
Particularly, when the content is beer, the so-called
"sun-struck" flavour which may be caused by the invasion
of light can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are graphs which show the
relationship between the surface temperature of a glass
bottle and the time required for peeling the coating,
respectively;
Figures 3 and 4 are graphs which show the
relationship between the thickness of the coating and the
time required for peeling the coating, respectively;
Figure 5 is~a graph which shows the relationship
between the internal pressure strength of bottles and the
frequency of passing the bottle through a bottling step
including an alkali washing;
Figure 6 is a graph which shows the relationship
between the impact strength of bottles and the frequency
of passing the bottle through a bottling step including
an alkali washing;
Figure 7 is a photomicrograph of the surface of the
coating comprising Sn02 according to the present
invention at a thickness of 600 angstroms after dipping
into 4~ by weight aqueous sodium hydroxide solution
(2,000 x magnification); and
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Figure 8 is a photomicrograph of the surface of the
coating comprising Sn02 according to the hot end coating
method at a thickness of 600 angstroms after dipping into
4% by weight aqueous sodium hydroxide solution (2,000 x
magnification).
DESCRIPTION OF THE PREFERRED EMBODIMENT
Glass Bottle
A glass bottle to which the present invention can be
applied, i.e., a glass bottle as a base is a returnable
glass bottle which is used repeatedly. Such a returnable
glass bottle includes glass bottles for alcoholic drinks
such as beer, whiskey or sake, seasonings such as soy
sauce or vinegar, refreshing drinks such as cola, lemon
pop or juice, milk or the like.
Glass bottles which can enjoy the effect of the
present invention include returnable bottles for liquid
carbonate drinks such as beer, cola or lemon pop in which
carbonate gas is dissolved to an internal pressure of 1.0
to 4.0 kg/cm2, preferably 1.2 to 2.5 kg/cm2 at room
temperature.
The returnable glass bottles may include glass
bottles comprising soda lime glass or borosilicate glass,
preferably soda lime glass.
Preparation of Coating
(1) -Coating Conditions
The process for preparing the coating of the present
invention comprises the step of bringing a glass bottle
having a specific external surface temperature into
contact with a material which can form a coating
comprising Sn02 or Ti02 so as to form a coating
comprising Sn02 or Ti02 as the main component.
The process for preparing a coating of the present
invention requires an external surface temperature of the
glass bottle at 550 to 700°C, preferably higher than
600°C in the case of the coating predominantly comprising
Sn02 and higher than 630°C in the case of the coating
predominantly comprising Ti02. If the external surface
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temperature of the glass bottle is less than 550°C, the
coating is inevitably peeled off within 8 hours upon
dipping the bottle into a 4~ by weight aqueous sodium
hydroxide solution at 80°C even if the coating has a
thickness in the range of 400 to 1,000 angstroms, which
is the same range of the present invention. It is not
preferable that the bottle thus treated has iris
phenomenon. The temperature exceeding 700°C is
undesirable because the glass bottle tends to be deformed
by such a high temperature and .to be cracked due to the
difference of coefficients of thermal expansion between
the bottle and the coating.
Further, according to the process of the present
invention, the coating comprising Sn02 or Ti02 as the
main component must be prepared at a thickness of 400 to
1,000 angstroms under the above temperature condition.
The coating having a thickness of less than 400 angstroms
is not preferred because it has a poor durability and is
inevitably peeled off ..within 3 hours upon dipping into a
4~ by weight aqueous sodium hydroxide solution at 80°C.
The coating having a thickness exceeding 1,000 angstroms
is not preferred either because it causes interference
phenomenon which impairs the aesthetic appearance of the
bottle and because it tends to be cracked due to the
difference of coefficients of thermal expansion between
the bottle and the coating.
(2) Material for Forming the Coating
In the process for preparing the coating according
to the present invention, a coating comprising Sn02 or
Ti02 as the main component is prepared on the glass
bottle having a specific external surface temperature.
As a material which can form the coating comprising Sn02
or Ti02, any material which produces Sn02 or Ti02 upon
pyrolysis can be used. For example, the material
includes SnClQ, TiCl4, organometallic compounds of Sn or
Ti such as (CH3)2SnC12, metal alcolates and the like.
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It is also possible to improve the properties of the
coating by incorporating other metal oxides or the like
within the scope of the purpose of the present invention.
(3) Preparation of the Coating
In the process for preparing the coating according
to the present invention, the glass bottle having a
specific external surface temperature and the material
for forming the coating can be contacted by any method
without limitation with the proviso that the method can
perform the formulation of the coating on the surface of
the glass bottle. The coating can be formed-by the
methods such as chemical deposition or spraying method.
The chemical deposition method indicates a method for
preparing a coating of Sn02 or Ti02 on the external
surface of the bottle comprising the steps of vaporizing
the above-mentioned material by heating, transferring the
vaporized material into a coating chamber by means of a
dry gas such as air, oxygen or an inert gas, and reacting
the material with oxygen or water which exists in the
atmosphere or on the surface of the bottle. The spraying
method refers to a method comprising the steps of
dissolving the material in an organic solvent, spraying
it on the surface of the bottle, and pyrolytically
decomposing it to form the coating.
Coating
The glass bottle having the coating according to the
present invention generally exhibits a silvery white
appearance. It forms a contrast with the fact that the
appearance of the glass bottle having the coating
according to the hot end coating method is the same
appearance of an uncoated glass bottle.
The coating obtained by the process according to the
present invention is supposed to be attached securely by
the so-called "anchor effect" which is caused by the
transfer of the coating component to the glass phase of
the bottle to some degree. As a result, it is supposed
that the coating hardly peels off even in the case of an
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alkali treatment at a high temperature and a high
concentration. We have confirmed the following fact. It
was observed by a microscope (2,000 x magnification) that
peeled portions on the surface of the coating comprising
Sn02 at a thickness of 600 angstroms according to the
present invention formed like dots upon dipping into a 4~
by weight aqueous sodium hydroxide solution. On the
other hand, it was observed by a microscope (2,000 x
magnification) that peeled portions on the surface of the
coating comprising Sn02 at a thickness of 600 angstroms
according to the hot end coating method spread
continuously over almost all the surface after the alkali
treatment as mentioned above.
The coating obtained by the present invention has an
indication that the coating is not peeled off within 8
hours upon dipping into a 4~ by weight aqueous sodium
hydroxide solution at 80°C. The wording "the coating is
not peeled off within 8 hours" means that no peeling of
the coating is visually observed after the above alkali
treatment.
Lightweight Glass Bottle
The glass bottle having the coating according to the
present invention can be improved in strength. In
particular, the impact strength and the internal pressure
resistance can be improved. As a result, it is possible
for the bottle having the coating of the present
invention to possess a strength equal to or higher than
that of an untreated glass bottle, even if the base glass
bottle has a thin glass thickness. In other words, the
process for preparing the coating according to the
present invention enables the preparation of a reduced
weight glass bottle, i.e., a lightweight glass bottle.
The following examples are provided to enable one
skilled in the art to practice the present invention.
However, these examples are merely illustrative of the
invention and are not to be read as limiting the scope of
the invention.
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Example 1
A coating comprising Sn02 or Ti02 as the main
component was formed at a thickness of 600 angstroms on
large-size beer bottles (manufactured by Kirin Beer K.K.,
returnable bottles having a weight of 605 g prepared in a
bottle making machine) at various surface temperatures of
the glass bottles. The bottles thus obtained were dipped
into a 4~ by weight aqueous sodium hydroxide solution at
80°C, and the time required for the peeling of the
coating was measured. The results are shown in Figures 1
and 2.
Example 2
A coating comprising Sn02 or Ti02 as the main
component was formed on the same bottles as in Example 1
at various thicknesses at a glass surface temperature of
630°C. The bottles thus obtained were treated in the
same manner as in Example 1, and the time required for
the peeling of the coating was measured. The results are
shown in Figures 3 and 4.
Example 3 and Comparative Example 1
The same large-size bottles as in Example 1 and
lightweight large-size bottles which had the same profile
as the above large-size bottle but had their weight
reduced by 130 g were provided.
While the external surface temperature of these
bottles was maintained at 600 to 700°C over the entire
surface thereof, an Sn02 coating was formed by spraying
SnCl4 and depositing it on the surface of the bottles at
an average coating thickness of 600 angstroms. The
bottles having the coating thus obtained and uncoated
bottles having a weight of 605 g were passed 30 times
repeatedly through a bottling step in an ordinary beer
factory including an alkali washing (with a 4~ by weight
aqueous sodium hydroxide solution at a maximum
temperature of 80°C for about 10 minutes).
These bottles which had been subjected to the above
test were then estimated for the internal pressure
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resistance and the impact strength. The results are
shown in Figures 5 and 6. Comparing the uncoated bottles
having a weight of 605 g with the coated bottle having a
weight of 605 g, the reduction of the strength of the
coated bottle is lesser than that of the uncoated bottle.
The coated bottle having a weight of 475 g has the same
internal pressure resistance as the 605 g uncoated
bottles. Further, the 475 g coated bottle is superior in
impact strength to the 605 g uncoated bottle. The
results show the fact that. the weight of glass bottles
can be reduced by the coating according to the present
invention.
Ten (10) bottles of each group after passing through
the above bottling step were picked up to estimate the
damage by the scuff marks on the bottles. The results
are shown in Table 1.
Table 1
1 2 3 4 5 6 7 8 9 10
605 g Coated +1 +1 +1 +1 +1 +1 +1 +1 +1 +1
475 g Coated +1 +1 +1 +1 +1 +1 +1 +1 +1 +1
605 g Uncoated +4 +4 +4 +4 +4 +4 +4 +4 +4 +4
Indices to the damage of the samples are as follows.
0 : Intact
+1: Slightly damaged
+2: Damaged
+3: Considerably damaged
+4: Severely damaged
Comparative Example 2
An Sn02 coating was formed at a thickness of 160
angstroms (about 40 C.T.U.) by spraying SnCl4 onto the
same bottles having a weight of 605 g as in Example 3 at
a surface temperature of 400 to 500°C.
The glass bottles thus obtained were passed through
the same bottling step as in Example 3. As a result, the
coating was completely peeled off by one passing.
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Example 4
The formation of a coating was carried out in the
same manner as in Example 3 except that a Ti02 coating
was formed by spraying TiCl4 onto the same bottles having
a weight of 605 g as in Example 3.
The glass bottles thus obtained were passed 15 times
repeatedly through the same bottling step as in Example
3. The results were as good as those in Example 3.
Comparative Example 3
A coating was formed in the same manner as in
Comparative Example 2 except that a Ti02 coating was
formed by spraying TiCl4.
The glass bottles thus obtained were passed through
the same bottling step as in Example 3. As a result, the
coating was completely peeled off by one passing.
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