Note: Descriptions are shown in the official language in which they were submitted.
129649~
PROCESS FOR PRODUCING
STRETCH BLOW-MOLDED BOTTLE WITH A HANDLE
FIELD OF THE INVENTI~N
The present invention relates to a process for pro-
ducing a stretch blow-molded bottle with a handle from a
thermoplastic resin.
5BACKGROUND OF THE INVENTION
Modern plastic bottles with large inner capacities
are usually furnished with a handle that render them easy to
carry.
A common process for producing a plastic bottle with
10a handle by blow molding requires the following basic steps:
extruding a hollow parison from an extruder; fitting the
parison with a bottom; blowing air into the bottomed parison
so that it expands to a preblown article; holding the pre-
blown article between a pair of split mold halves having
15handle forming projections; and blowing air so that the
article is expanded to conform to the shape of the molds.
In this process, the area of the preblown article where a
handle-defining hole is to be made is closed with the pro-
jections on the molds so as to form a bottle where the
20peripheral edges of said hole are used, and the fused edges
(i.e., burrs) are then removed by boring. A method for
making pinched-shut, non-blown portions of a blown plastic
jug with a blow mold projection is disclosed in U.S. Patent
- 1 - ~
æ96495
3,983,199.
This conventional process for making a handle on a
bottle by holding a preblown article between projections on
molds has the following major disadvantage: the handle is
usually situated in the neighborhood of the shoulder of the
bottle, so the area around the top opening of the preblown
article inevitably becomes large but since the neck required
for the blow-molded bottle is small, burrs are unavoidably
formed around the neck of the bottle. The formation of
burrs is extensive in large bottles. See, e.g., Szajna,
"The Plastic Bottle-i~krketing/ Engineering and Economics: A
Supplement to 1980 ANTEC Paper 'Functions vs. Economics vs.
Aesthetics'," SocietY of Plastics En~ineers Annual Technical
Conference 40 (1982), page 707. Another problem is that the
formation of burrs on tbe bottom is too extensive to neglect
in the conventional process.
While direct blow molding has been the most common
of the conventional blow molding techniques, it has recently
become possible to produce blow-molded articles that are
better than the direct blow-molded products in such aspects
as mechanical strength, clarity and gas barrier properties.
Such superior products can be obtained by a new technique
called stretch blow molding, which is already in commercial
use. In the stretch blow-molding technique, air is injected
into a parison emerging from an extruder ~preblowing step),
1296495
1 and the resulting preform (or an injection-molded preform)
is transferred to a blow mold, where it is stretched bi-
directionally at an optimum stretching temperature not lower
than the glass transition point of the resin but less than
its molding temperature, with a stretch pin being inserted
to effect axial stretching and air being blown to cause
transverse stretching. This bidrectional stretching causes
molecular orientation of the polymer chains in the thermo-
plastic resin of which the preform is made, thereby yielding
1~ blow molded articles having the improved properties de-
scribed above. See, Szajna, "The Plastic Bottle - Market-
ing, Engineering and Economics," supra, at pages 705-706;
U.S. Patent Re. 29,045.
There has been a need in the packaging industry to
l~ apply the stretch blow molding technique to the manufacture
of plastic bottles with handles. However, in the stretch
blow molding method, the preform is heated in the mold at a
temperature not lower than the glass transition point of the
thermoplastic resin being molded and which is less than the
2n molding temperature of the resin. If a polyvinyl chloride
bottle is to be made, the preform is typically heated at a
temperature from about 90C to 140C, preferably from 100C
to 120C. In this regard, the glass transition point of
polyvinyl chloride is from about 70C to 80C and the
2~ molding temperature is from about 160C to 220C.
-- 3 --
~2964~S
l Therefore, even if the method of using a pair of split mold
halves having projections for forming a handle-defining hole
is applied to the air and pin stretched preblown article
with a veiw to forming both the handle and the bottle body
5 from a single preform, the neck portion cannot be fused and
the area left after deburring cannot be sealed to provide a
commercially acceptable bottle.
When the handle portion of the thermoplastic resin
is heated at a temperature higher than the molding tempera-
1~ ture of the resin using a mold equipped with a heater so asto avoid the above problem, the effect due to stretching is
lost at the heated portion of the resin so that the mechani-
cal strength markedly decreases~ Particularly, use of crys-
talline resins such as polyethylene terephthalate suffers,
1~ in addition, other problems, e.g., the resin becomes white
as crystallization proceeds by heat, and the molded resin is
easily broken due to distortion generated by the difference
in crystallinity between the handle portion and other por-
tions.
~n As described above, the method commonly employed in
the conventional blow molding technique (i.e., direct blow
molding) cannot be satisfactorily applied to the stretch
blow molding technique, and therefore, various other methods
have been proposed for producing blow-molding bottles with a
handle by the stretch blow molding technique. A method
which is typical of these proposals is described in Japanese
~296~95
Patent Pubiication No. 11218/88 and consists of furnishing a
stretch blow-molded bottle body with a separately fabricated
handle by a suitable method such as tight fitting.
However, the bottle fabricated by this process is
not a unitary assembly prepared from a single preform con-
sisting of the bottle body and a handle, so it lacks secure
attachment of the handle to the bottle body. In addition,
the fabrication process involves complicated steps.
SUMMARY OF THE INVF~NTION
An object, therefore, of the present invention is to
provide an improved process for producing a bottle with a
handle by the stretch blow molding technique.
As a result of studies conducted in order to attain
this and other objects of the present invention, the present
inventors have now found that a stretch blow-molded bottle
with a handle can be readily produced if, in the process of
stretch blow-molding a preform at a temperature not lower
than its glass transition point but below its molding tem-
perature, a blow mold furnished with a pair of opposed mova-
ble projectlng parts, is used and if the projections arepushed into the preform after it has expanded to the stage
where the formation of a handle portion becomes possible
(i.e., the preform has expanded to at least about 80% of the
inner capacity of the blow mold) and before the preform
cools to a temperature below the glass transition point,
1 2964~5
preferably before the preform expands completely (until its
volume becomes equal to the inner capacity of the blow mold)
and cools upon contact with the inside walls of the blow
mold, thereby pressing and holding the area where a handle-
defining hole is to be formed until cavities in a shapecorresponding to the handle-defining hole form.
If desired, the peripheral edges of the thus-formed
cavities may be fused with heat, followed by boring the
resin in the cavities to form a handle-defining portion.
Accordingly, in one aspect the present invention
relates to a process for producing a stretch blow-molded
bottle with a handle, by the steps of (a) stretching an
injection-molded or blow-molded thermoplastic resin preform
within a blow mold by axial stretching with a stretch pin
and transverse stretching with blown air at a temperature at
least equal to the glass transition point of the resin but
below its molding temperature, (b) pressing and holding an
area of the stretched preform between a pair of opposed
movable projecting members provided within the blow mold,
after the preform is expanded to substantially fill the
volume blow mold and before the preform is cooled to a tem-
perature below the glass transition point of the resin; and
(c) cooling the expanded preform by contact with the inner
walls of the blow mold to form a stretch blow-molded bottle
having opposing depressions defining a handle.
-- 6 --
129649S
In another-aspect, the present invention relates to
a process for producing a stretch blow-molded bottle by the
further step of thermally fusing the peripheral edges of the
opposing depressions and removing the resin inside the
peripheral edges to form a handle hole surrounded by the
stretch blow-molded bottle.
BRIEF DESCRIPTION OF THE DR WINGS
Fig. 1 is a longitudinal section of a mold with a
pair of movable projecting parts 2 in which a preform 1 is
placed in position;
Fig. 2 is a cross section taken on line A-A' of Fig.
1 and which shows the state where the projecting parts 2 are
pushed into the preform 1 that has been expanded by stretch-
ing with air blown through a bl~w pin 5 and by axial move-
ment of a stretch pin 4;
Fig. 3A is a front view of a stretch blow-molded
bottle 7 with cavities 6;
Fig. 3B is a longitudinal section of the same bot-
tle; and
Fig. 4 shows schematically how the peripheral edges
of the cavities 6 in the bottle 7 are fused under pressure
with a high-frequency dielectric heater.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is hereinafter described in
detail with reference to the accompanying drawings.
- 7 -
As shown in Fig. 1, a preform l of a thermoplastic
resin kept at an optimum stretching temperature is placed in
position in a mold 3 having a pair of projecting parts 2
that are moved by suitable means such as hydraulic or
5pnematic pressure, the mold being preferably cooled with a
refrigerant such as water. Then, a stretch pin 4 is pushed
downward to press the bottom of the preform 1. Simultane-
ously or immediately thereafter, air is injected through a
blow pin 5 to expand the preform l toward the inside walls
lOof the mold 3. After the preform 1 has expanded to the
stage where the formation of a handle portion becomes possi-
ble ~i.e., the preform has expanded to at least about 80% of
the inner capacity of the m~ld 3) and before the preform cools at a
temperature below the glass transition point of the resin,
15preferably before the preform expands completely (until its
volume becomes equal to the inner capacity of the mold 3)
and cools upon contact with the inside walls of the mold 3,
the projecting parts 2 are pushed into the preform as shown
in Fig. 2 which is a cross section taken on line A-A' of
20Fig. 1. As a result, a bottle 7 having the shape shown in
Fig. 3 is formed in the mold 3 (this bottle is hereinafter
referred to as an intermediate bottle).
If, in the process described above, the projecting
parts 2 are pushed into the preform 1 before it has expanded
; 25to ~he stage where the formation of a handle portion becomes
1296495
possible (i.e., the volume of the preform is less than about
80% of the inner capacity of the mold 3), cavities 6 corre-
sponding to a handle-defining hole will not be formed in a
desired shape. When the preform 1 has expanded completely
S (until its volume becomes equal to the inner capacity of the
mold 3) and cools to a temperature below the glass transi-
tion point upon contact with the inside walls of the mold 3,
the subsequent pressing and holding cannot be performed. If
the projecting parts 2 are pushed into the preform l at this
stage, the preform l may break or the thickness of the walls
between the cavities 6 may become uneven.
The projecting parts 2 are preferably pushed into
the preform 1 at a time that is as close as possible to the
time when the latter has expanded completely (until its
volume becomes equal to the inner capacity of the mold 3)
and cools upon contact with the inside walls of the mold 3.
If this condition is satisfied, better characteristics are
provided for the blow-molded bottle obtained.
The portion corresponding to the cavities 6 is
preferably curved concavely toward the center of the blow-
molded bottle in view of the strength against deformation
and for gripping the bottle formed. For this pùrpose, the
projecting parts 2 preferably have smoothly and convexly
curved surfaces.
The so produced intermediate bottle 7 can be direct-
~ 296495
ly used as a final bottle with a handle. If a large bottle
having an inner capacity of at least 1,000 ml is to be pro-
duced, the cavities 6 are preferably bored through. As will
be stated below, the peri~heral edges of the cavities 6 can
be readily fused with heat, so by boring the inside of the
cavities after thermally fusing their peripheral edges, a
bottle with a handle that is easier to carry can be pro-
duced.
The depressions or cavities 6 in the intermediate
bottle 7 are defined by a pair of opposed plastic walls
spaced apart by a small gap. Since the palr of oppo ~ plastic
wall are formed by pressing the pair of projecting parts 2
in the accordance with the present invention, the gap
between the two plastic walls can be made as small as 0.1 mm
and below or even substantially zero if desired, so the
peripheral edges of the cavities 6 can be readily fused with
heat.
The method for thermally fusing the peripheral edges
of the cavities 6 in the intermediate bottle 7 is described
; 20 in greater detail below.
Typical methods of thermal fusion that can be
employed in the present invention include high-frequency
dielectric heating, ultrasonic bonding, heat sealing and
impulse sealing. An appropriate method can easily be
selected in accordance with the type of thermoplastic resin
-- 10 --
'~. ',
1296~5
of which the bottle is to be made. For example, if the
bottle is made of polyvinyl chloride, high-frequency dielec-
tric bonding is preferably used; if the bottle is made of
polyethylene terephthalate or polypropylene, ultrasonic
bonding or i~pulse sealing is preferably used; and if the
bottle is made of polyacrylonitrile, a preferred method is
high-frequency bonding, heat sealing or impulse sealing.
Thermal fusion of the peripheral edges of the cavi-
ties 6 is described hereinafter more specifically with
reference to the case where the intermediate bottle 7 is
made of polyvinyl chloride and thermal fusion is effected by
high-frequency dielectric heating, but the present invention
is not to be construed as being limited thereto.
The electrodes, or heating terminals, on the high-
frequency dielectric bonding apparatus are preferably madeof brass. The periphery of the working faces of the heating
terminals is preferably slightly smaller than the periphery
of each cavity 6. As shown in Fig. 4, the heating terminals
8 preferably have protruding working faces 8a of about 0.2
to about 2 mm in width provided at their periphery so that
the cavities 6 are thermally fused throughout the periphery
thereof. The width of the protruding working faces 8a is
particularly preferably from about 0.2 to about 0.4 mm,
whereby the cavities 6 after thermal fusion can be removed
more easily and with less burr and moreover the cavities 6
-- 11 --
..
` ~296495
can be removed simultaneously upon thermal fusion. The
heating terminals preferably have a built-in heater that
maintains a temperature of about 45 to 80C during use.
A pair of the heating terminals 8 described above
are held against the peripheral edges of the cavities 6 in
the intermediate bottle 7 as shown in Fig. 4 and an electric
current is applied to the heating terminals so that the
entire portion of the peripheral edges is thermally fused
over a width ranging from about 0.2 to 2 mm. The high-fre-
quency dielectric bonding apparatus typically generates afrequency of the order to 40.46 MHz. The preferred heating
time varies with the wall thickness of the bottle to be
produced but sat$sfactory results are usually attained by
heating for a period of 1 to 4 seconds.
The peripheral edges of the cavities 6 in the bottle
7 may be thermally fused by high-frequency dielectric heat-
ing in the manner described above after the bottle 7 is
removed from the blow mold. Alternatively, thermal fusion
may be conducted within the mold 3 if it is furnished with
movable plugs incorporating in its tips the heating termi-
nals of-the high-frequency dielectric bonding apparatus.
After thermally fusing the peripheral edges of the
area of the intermediate bottle 7 where the handle-defining
hole is to be formed, the inside of the cavities 7 may be
2~ bored through by the following method.
- 12 -
, .
~296495
If thermal fusion of the peripheral edges of the
cavities 6 is performed by high-frequency dielectric heat-
ing, the inside of the cavities 6 can be readily bored
through the pushing one of the two heating terminals into
the fixed bottle 7 while pulling the other heating terminal
away from the bottle immediately after the thermal fusion,
or at the time when the bonded areas are still in the molten
state. Another method that can be employed to bore the
inside of the cavities 6 is to use a punching machine.
Thermoplastic resins from which a bottle with a han-
dle can be produced in the present invention include those
which are capable of undergoing orientation of the polymer
chains upon stretch blow molding~ Suitable examples include
polyvinyl chloride, polypropylene, polyethylene terephthal-
ate, polyacrylonitrile and polyethylene. From the view-
points of moldability and mechanical strength of the bottle
produced, polyvinyl chloride having a degree of polymeriza-
tion in the range of about 600 to 1100 and polyethylene
terephthalate are preferred, and polyvinyl chloride which
can be stretched within a wide range of temperature and be
thermally fused by the high-frequency dielectric bonding
method is particularly suitable for the process of the
present invention.
One embodiment of the process of the present inven-
tion is illustrated in greater detail with reference to the
- 13 -
~649~;
following example, which is not to be construed as limiting
the scope of the present invention.
EXAMPLE
A stretch blow-molded bottle with a handle was pro-
duced with a biaxial stretching blow-molding machine (BM04,
manufactured by Bekumu Co.) using a commercially available
PVC compound for blow-molding, mainly composed of PVC (de-
gree of polymerization 700) stabilized with octyl-tin-
mercato octyl (Aron Compound BL 2H-8VIP, produced by Toa
Gosei Chemical Industry Co., Ltd.).
The PVC compound was molded into a cylindrical pari-
son by an extruder wherein the temperature of the cylinder,
adapter and die portions were controlled to 170 to 180C.
The parison was then put into a preform mold of beryllium-
copper alloy kept at 10 to 70C with a heat-control jacket
capable of controlling temperatures in seven divided por-
tions independently and the parison was cut at the top of
the mold through which a blow pin was inserted, followed by
blowing compressed air thereto to obtain a preform which was
then properly cooled to 100 to 120C with the thermally
controlled mold, to produce a molded preform having a dia-
meter of 45 mm, a height of 250 mm and a round bottom.
The thus obtained preform which was thermally con-
trolled at 100 to 120C was placed in a finish mold ~for a
bottle of 1,800 ml) provided with a pair of movable project-
lZ96495
ing parts for forming a handle and was stretched downward to
the bottom of the mold with a stretch pin while blowing air
from the upper portion of the preform. When the volume of
the preform was almost the same as that of the mold, the
preform was pressed with the pair of projecting parts to
form the handle, and then the air-blowing was completed to
fill the mold with the molded product.
After removing the molded product from the mold, it
was then subjected to thermal fusion at the peripheral edge
of the pressed portions with a pair of heating terminals
having protruding working faces of high-frequency welder
(3kw) in conformity with the periphery of the pressed por-
tions to fuse the opposing pressed portions at their edges,
and then one of the heating terminals was pushed into the
fused pressed portion of the bottle while withdrawing the
other terminal, whereby the pressed portion was removed with
burr and the thus formed handle was smoothed with the side
of the heating terminal inserted.
In accordance with the present invention, a bottle
with a handle can be easily stretch blow-molded from a
single preform as a unitary assembly of the handle and the
bottle body. The molded bottle has good aesthetic appeal
because of its high clarity. In addition, it has sufficient
gas barrier properties to ensure prolonged storage of the
contents. As a further advantage, the bottle can be pro-
- 15 -
1296495
duced from a small charge of resin without sacrificing its
mechanical strength.
Whlle 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.
- 16 -
