Note: Descriptions are shown in the official language in which they were submitted.
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S P E C I F I C A T I 0 N
METHOD FOR BLOW-MOLDING HOLLOW CONTAINER
AND BLOW AIR CYLINDER
Technical Field
This invention reltes to a method for blow-molding hollow
container and to a blow air cylinder and, more particularly, to
a blow-molding method which enables one to shorten the time for
cooling moldings immediately after being blow-molded and to
produce moldings having good dimensional accuracy and to a
blow air cylinder particularly adapted for the blowing method.
Prior Art
In molding hollow container from a thermoplastic resin
according to blow molding technique, it has been well known to
pierce the upper portion of a parison having been melt extruded
through a die head of an extruder with a blow nozzle for
introducing blow air, and blow a compressed air into the
parison through the nozzle to thereby press the parison against
the wall of a metal mold :for shaping and cooling.
The blow nozzle for use in the blow molding is a member
which, upon blow molding, pierces the upper wall of the parison
and which functions to introduce a compressed air through a
blowing inlet or inlets provided at the tip of the nozzle or in
the vicinity thereof, and has a sophisticatedly designed
structure.
For example, Japanese Examined Utility Model No. S52-19033
describes the structure of a blow molding nozzle which has a
pin with a sharp tip, said pin having a passageway for blowing
air formed at its center extending in the direction of central
axis and pores connecting to the passageway almost at a right
angle therewith in the vicinity of the tip of the pin and
having one or more linear grooves outside between the tip and
the pores.
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The form of the nozzle tip for blow molding must be so
designed as to facilitate piercing of the wall of parison
having been extruded in a heated state with the nozzle and
subsequent smooth blowing. The form of the blowing inlets of
the above-described utility model, too, has grooved blowing
inlets toward the tip from this viewpoint.
Japanese Unexamined Utility Model No. 57-169510 discloses
the structure of a blow molding nozzle wherein the tip is of a
shape of closed injection needle with an angular cut of 10 to
45 degrees and which has two air-blowing holes formed on the
way to the tip at a right angle with a blow air passageway. In
this utility model, too, the nozzle tip has a specific
structure which facilitates piercing of the wall of a parison
with even a thick nozzle.
In a horizontally blow molding method, a blow nozle
pierces the wall of a parison having been heat-extruded into a
metal mold and, after closing the metal mold, a compressed air
(blow air) is introduced into the parison to completely press
the soft-state parison against the inside surface of the metal
mold for shaping and cooling, thus one blowing step being
completed.
Problems that the invention is to solve
In the conventional blow molding methods using such known
blow nozzles, however, blow air introduced through the blowing
inlets fills up the bottle at the time when the soft-state
parison is pressed against the wall of the metal mold and,
therefore, flow of the blow air is discontinued. Thus,
subsequent cooling of the blown bottle is mainly conducted by
circulating cooling water in the metal mold in contact with the
bottle.
However, this method requires a considerably long time
for cooling the shaped battle still kept at an elevated
temperature to such a degree that the metal mold can be opened.
Thus, there arises a problem in view of moldng efficiency and,
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in addition, there arises another technical problem that, since
the bottle is not uniform in thickness, uniform cooling can not
be attained.
That is, there are known no blow nozzles of the structure
designed for conducting the step of cooling moldings (bottles)
most effectively, though nozzle structures suited for piercing
the wall of a parison or for introducing the compressed air
have been known.
Objects of the invention
An object of the present invention is to provide a
process f or blow molding hollow container having no molding
deformation and having excellent quality, in which the blow air
introduced into the container (bottle) well circulate therein
even after shaping of the bottle to rapidly cool the bottle.
Another object of the present invention is to provide a
blow air cylinder adapted for the method.
Disclosure of the invention
The present invention is proposed for attaining the
above-described objects and relates to a method for blow
molding hollow container 'using a blow nozzle of a specific
structure and to a blow air cylinder containing the nozzle.
That is, according to one aspect of the present
invention, there is provided a method for blow molding hollow
container by horizontal blow molding of piercing the wall of a
parison having been extruded through a die head of an extruder
with a blow nozzle, which comprises introducing blow air at
least in the downward direction, i.e., in the direction
opposite to the bottle neck, to form an opening.
Preferably, according .to the present invention,
there is provided a blow molding method, in which a part of a
parison in the vicinity of or above the blow nozzle-piercing
portion is thinned so much, after shaping of the hollow
container, that the part is broken to form an opening through
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which the blow air having circulated inside the hollow
container is discharged.
Preferably, according to the present invention,
there is provided a blow molding method, in which the
amount of air blown in the direction toward the bottom,
i.e., opposite to the bottle neck, is larger than that
blown in other directions.
Preferably, according to the present invention;
there is provided a blow molding method, in which blowing
inlets are formed in the vertical direction, with the
amount of air blown in the direction toward the bottom,
i.e., opposite to the bottle neck, being larger.
Preferably, according to the present invention,
there is provided a blow molding method, in which blowing
inlets are formed in the vertical and horizontal direc-
tions, with the amount of air blown in the direction toward
the bottom, i.e., opposite to the bottle neck, being larger
than that in each of the other three directions.
According to a still further aspect of the
present invention, there is provided a blow air cylinder
comprising, in combination:
a housing having a hollow interior and a guiding
opening;
a blow nozzle having a generally tubular body
which is slidably movable through said guiding opening of
said housing forwardly and backwardly inside a molded body
to be cooled, said molded body having a first end intended
to form a bottle neck and a second end intended to form a
bottom;
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said tubular body of said blow nozzle having a
tip portion including a solid sharp tip for penetrating a
wall of said molded body;
a plurality of blowing inlets, each emitting an
amount of blow air therefrom resulting in a total blow air
amount, said plurality of blowing inlets being located at
spaced locations about a circumference of said tubular body
at a back side of said tip portion in a region of said
tubular body having an outer diameter which is larger than
that at said tip portion;
one of said plurality of blowing inlets being
sized to supply an amount of blow air that is larger than
that of the other blowing inlets, in an amount of at least
300 of the total blow air amount, away from said first end
and toward said bottom of said molded body; and
positioning means on said tubular body of said
blow nozzle cooperating with said guiding opening of said
housing for positioning said blowing inlets inside the
molded body.
Brief description of the drawings
Fig. 1 is a schematic view illustrating the state
of a
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blow nozzle used in the prior art blow molding method.
Fig. 2 is a schematic view illustrating the state of a
blow nozzle used in the blow molding method of the present
invention.
Fig. 3 is a cross-sectional side view of a blow nozzle
used in the prior art blow molding method.
Fig. 4 is a cross-sectional side view of a blow nozzle
used in the blow molding method of the present invention.
Fig. 5 is a cross-sectional f rout view showing one
embodiment of the blow nozzle to be used for the blow molding
method of the present invention.
Fig. 6 is a cross-sectional view of the blow air cylinder
of the present invention before work.
Fig. 7 is a cross-sectional view of the blow air cylinder
of the present invention in the state of initiating
introduction of a blow air for moving forward the blow nozzle
of the blow air cylinder.
Fig. 8 is a cross-sectional view of the blow air cylinder
of the present invention in the state of the blow nozzle being
moved forward by the pressure of the blow air introduced
thereinto.
Fig. 9 is a cross-sectional view of the blow air cylinder
of the present invention i.n the state of initiating
introduction of a blow air for moving backward the blow nozzle.
Fig. 10 is a cross-sectional view of the blow air
cylinder of the present invention in the state of being
restored to the initial position by the pressure of the air.
Best mode for practicing t:he invention
As is described hereinbefore, a first technical feature
of the present invention is to form blowing inlets of the blow
nozzle so that the amount of blow air in the downward
direction, i.e., in the direction opposite to the bottle neck,
be at least 30 ~, preferably at least 50 $, more preferably at
least 70 ~, of the whole blow air amount.
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The present invention has been described referring to the
case where the parison is held with the bottle neck directed
upward. However, it can easily be understood that, where the
parison is held with the bottle neck directed downward, the
blow air should be introduced in the upward direction.
Another technical feature of the present invention is
that, after shaping of a bottle by ffilling the inside of a
metal mold with the blow air, part of the parison in the
vicinity of or above the blow nozzle-pierced portion be thinned
and broken to form an opening through which blow air having
circulated in the interior of the bottle is discharged.
That is, the opening is formed, after shaping of the
battle, by the pressure o:E the blow air, and this opening
serves to adjust discharge of the blow air filling the bottle.
Hence, the blow air does not stagnate in the metal mold after
shaping of the bottle but circulates within the bottle to
rapidly cool the hot bottle.
Combination of the above-described two technical features
enables one to markedly effectively cool the bottle.
To describe this in more detail, the blow nozzle to be
used in this invention allows most of the introduced blow air
to rapidly proceed downward to the bottom of the bottle due to
the specific structure thereof as has been described
hereinbefore. When the b:Low air reaches the bottom of the
bottle, the parison in a softened state is instantly shaped to
the form of the metal mold and, at this point after shaping of
the bottle, part of the wall of parison in the vicinity of or
above the nozzle-pierced portion is thinned and broken to form
an opening, thus the blow air circulating inside of the bottle
to effectively cool it. '.rhe blow air filling the metal mold is
discharged through the formed opening to ensure subsequent
circulation of blow air.
Thinning of part of the parison wall is conducted by
forming in a corresponding portion an opening communicating
with outside of the metal mold, and pressing the softened
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parison against the opening by the pressure of blow air to form
a thin concavity. The thinned portion is broken by further
introducing blow air.
Alternatively, the above-described opening may be formed
by piercing the wall of said parison with a needle-like member
from outside. The needle-like member has a tip portion of
injection needle form which may be hollow or solid. That is,
as to a hollow needle-like member, it suffices to pierce the
parison wall with it because blow air is discharged through the
hollow
portion and, as to a solid needle-like member, an
opening for discharging,the blow air is formed by piercing the
wall of~a parison with the needle and rapidly drawing it out.
In blow molding bottles, the pinch-off portion at the
bottom is formed in a thickness slightly thicker than other
portions. If the bottom portion is not sufficiently cooled,
there result moldings with deteriorated dimensional accuracy.
According to the present invention, however, the
pinch-off portion having a greater thickness is extremely
effectively cooled and there result bottles with excellent
dimensional accuracy in a short time, because a large amount of
blow air is introduced in the direction toward the botom, i.e.,
opposite to the botle neck, through the blow nozzle, and the
blow air curculates inside the bottle and is then discharged
through an opening formed in part of the parison by the
pressure of the blow air.
As has been described hereinbefore, the blow nozzle used
in the present invention must be so constructed as to allow the
blow air to be introduced into a parison in at least the
direction toward the bottom, i.e., opposite to the bottle neck.
That is, the blow nozzle to be used in the blow molding
method of the present invention must have a blowing inlet or
inlets facing the bottom. The nozzle may have one blowing
inlet facing the bottom, or may have additional inlets facing
any direction. In forming a plurality of blowing inlets, they
must be constituted so that blow air can be introduced in more
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amount through the blowing inlet facing the bottom than that
through other inlets.
Specifically, the amount of blow air introduced in the
direction toward the bottom is more than 30 $, preferably more
than 50 ~, and more preferably more than 70 ~, of the whole
blow air.
In the present invention, "direction toward the bottom"
means not only the direction right under or above the nozzle
but obliquely downward or upward directions in which the blow
air is introduced against the inside of the bottle body.
In the conventional blow molding method, a blow air is
introduced through the upper portion of a parison (in the case
of holding the parison with its bottom directed downward) using
a blow nozzle as shown in Fig. 1, and hence most of the blow
air is once blown against the wall opposite to the blowing
inlet, then circulates in both downward and upward directions.
However, since the amount of the blow air in the downward
direction is the same as 'that in the upward direction, blow air
not having circulated the inside of the bottle will be
discharged together with blow air having circulated the inside
if an opening is-formed by breaking upper part of the parison
by the pressure of blow a:ir, thus the amount of blow air
circulating downward becoming extremely small.
In addition to the blow nozzle shown in Fig. 3, there
have also been known those nozzles in which blowing inlets are
formed on the way to the tip portion in two directions at a
right angle with a blow a.ir passageway, as disclosed in the
foregoing Japanese Unexamined Utility Model Publication No.
S57-169510. In this type of nozzles, too, blow air is
introduced into a parison merely in the upward and downward
directions, and it has not been disclosed that, as in the
present invention, a large amount of blow air is introduced
into a shaped bottle at least in the direction toward the
bottom to thereby instantly cool the lower part of the bottle.
On the other hand, in the present invention, a blow
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nozzle of a specific structure as shown in Fig. 4 or 5 is
used. When a blowing inlet: or inlets of this nozzle are
located at a position above: about the center of the parison and
a blow air is introduced in a right downward direction (in the
case of holding the parison with its bottom directed downward),
the blow air uniformly circulates along the inside surface of
the bottle wall after reaching the bottom and, when a blow air
is introduced in an obliquely downward direction, it travels
downward along the opposite inside surface of the bottle wall
while cooling the surface <~nd, after reaching the bottom,
travels upward along the other inside surface. Thus, the blow
air circulates inside the bottle to effectively cool the
molding.
A blow nozzle genera:Lly designated by numeral 1 in Figs.
4 and 5, which is one embodiment of the present invention, has
a first feature that, though front cross-section of the blowing
inlets is almost circular, piston 9 sliding inside the body of
the blow cylinder is of tha_ form of almost ellipse in front
cross-section with the major axis being in a horizontal
direction. This elliptical portion functions to resister the
nozzle so that at least one of blowing inlets 2 is always
positioned downward. In this embodiment, four blowing inlets 2
are formed at the slight rear position 5 of the tip 3 of blow
nozzle 1 in horizontal and vertical four directions almost at a
right angle with each other. The passageway of the blow nozzle
1 in the rear of the blowing inlets 2 forms a hollow portion 6,
through which blow air is introduced and which also functions
as a passageway for discharging blow air after completion of
the molding.
The blow nozzle 1 shown in Fig. 5 has four blowing inlets
capable of blowing air in the upward, downward, leftward and
rightward directions, respectively. Of the four blowing
inlets, blowing inlet 2a capable of blowing air in the downward
direction has a larger cross-section than that of other blowing
inlets 2b, 2c and 2d and allows air to be blown therethrough in
CA 02235450 1998-OS-14
an amount of at least 30 $., preferably at least 50 ~, more
preferably at least 70 $, of the whole blow air amount. The
blowing angle ( B 1) of they blowing inlet 2a is designed to be
10 to 20 degrees, preferably 13 to 17 degrees, particularly
preferably about 15 degrees, which ensures effective
circulation of the blown air inside the bottle.
The angle ( ~ z) of t:he tip of nozzle is preferably 55 to
65 degrees, with about 60 degrees being most preferable.
Further, the slope angle ( ~ 3) of from the thin-diameter
10 portion of the nozzle tip to the blowing inlets 2 is preferably
to 25 degrees, with about 20 degrees being most preferred.
Therefore, it suffices to form blowing inlets 2 in the
blow nozzle 1 at a position slightly at the rear of the tip 3,
at. which the diameter is 7_arger than that of the tip 3 and
smaller than the outer diameter of the central portion 4, and
at which the blowing inlets 2 can blow air at the
above-described direction so as to effectively circulate
downward.
That is, in the present invention, the aforementioned
blow nozzle 1 with a specific form pierces the upper wall of a
parison, and blowing inleta 2 are located at about the center
of the parison, thus a large amount of blow air being blown
through the blow nozzle 1 against the inside wall of the bottle
or in the right downward direction. When this blow air is
introduced into the bottle, the parison in a softened state is
instantly shaped into a battle in conformity with the form of
the metal mold and, at the' point, the blow air migrates upward
within the bottle to thin and break part of the bottle in the
vicinity of or above the nozzle-pierced portion 7 shown in Fig.
2 and form an opening 8, through which part of the blow air is
discharged out of the bott:le. In addition, the opening 8
serves for the blow air to uniformly circulate in a short time,
thus the inside wall of the bottle being rapidly cooled.
However, this discharge opening is not designed to
discharge the whole blow air introduced through the blow nozzle
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1 :but to discharge only part of the blow air, and most of the
air within the bottle is discharged through the hole formed,
after completion of the blowing, by rapidly moving backward the
blow nozzle 1, then through a discharge outlet 13 formed in the
vicinity of further backward moved blow nozzle and
communicating to the outside of the body. That is, a large
hole formed in the wall by the backward movement of the blow
nozzle 1 functions as a discharge outlet for the inside air,
and hence inside pressure of the bottle is instantly reduced to
the atmospheric pressure.
Therefore, a blow nozzle having a large diameter can form
a large-diameter discharge outlet, which serves to shorten the
time necessary for discharging the inside air.
Structure of a blow air cylinder in accordance with the
present invention is described below.
As is shown in Figs. 6 to 10, the blow air cylinder of
the present invention is constituted by a blow nozzle 1 which
can freely slide forward and backward in the body 11, which has
a mechanism of positioning blowing inlets at least at part of
the nozzle, which has a closed tip portion 3 having a
diameter smaller than the outer diameter of the central portion
4, and which has blowing inlets 2 at the slight rear of the tip
portion 3 and at a position having a diameter larger than that
of the tip portion 3 and smaller than the outer diameter of the
central portion 4, said b7.owing inlets 2 enabling one to
introduce blow air in the downward direction in an amount of at
least 30 ~ of the whole blow air amount; and a body 11 disposed
outside said blow nozzle ~. in a state of being at least partly
in contact with the nozzle.
In the wall in the vicinity of the tip of the body 11 is
formed a discharge outlet 13 through which the blow air filling
the metal mold is effectively discharged upon the blow nozzle 1
being moved backward. In the outer wall of the body 11 are
formed a blow air-feeding inlet lla for moving forward the blow
nozzle and a blow air-feeiiing inlet 12a for moving backward the
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blow nozzle. The blow nozzle 1 having a piston 9 being freely
moved forward and backward by the pressure of blow air is
provided inside the body 11.
At least part of the blow nozzle 1 has an about
elliptical cross-section with the major axis being horizontal.
In Fig. 5, piston 9 has such structure. That is, the blow
nozzle 1 does not have a circular cross-section over the full
length, but at least part of the nozzle 1 has an about
ellipticaal cross-section with the major axis being horizontal,
and hence the blow nozzle 1 is prohibited to rotate and,
therefore, blowing inlets 2 of the nozzle can be directed
always in definite directions, thus functioning as a mechanism
of positioning the blow nozzle 1.
The way how to work the blow air cylinder of the present
invention is described below by reference to cross-sectional
views of one embodiment of the cylinder. Fig. 6 shows a blow
air cylinder before work, Fig. 7 the blow air cylinder in a
state wherein introduction of blow air for moving forward a
blow nozzle is initiated, Fig. 8 the blow air cylinder in a
state wherein the blow nozzle has been moved forward by the
pressure of blow air, Fig. 9 the blow air cylinder in a state
wherein introduction of blow air f or moving backward the blow
nozzle, and Fig. 10 the blow air cylinder in a state wherein
the blow nozzle has been i:estored to its original position by
the pressure of air.
In Figs. 6 through 10, air flow is shown by dotted band.
Numeral 11 designates a body, and 1 a blow nozzle having a
structure capable of being moved backward andforward inside the
blow air cylinder and hav:Lng a piston.
In the outer wall of the body 11 are formed air-feeding
inlet lla for moving foreward the blow nozzle and air-feeding
inlet 12a for moving backward the blow nozzle after completion
of the blow-molding. The air-feeding inlet lla is connected to
the inside of the body 11 at a portion 11b at the slight rear
of the center of the body 11, whereas the air-feeding inlet 12a
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is connected to the insidE: of the cylinder at a top portion 12b
of the hollow portion 14 of the body.
In Fig. 7, the air blown through the air-feeding inlet
lla presses piston 9 capable of being moved forward and
backward in contact with the inside wall of the body 11 to
thereby move forward the blow nozzle. At the point when the
piston 9 reaches the top end of the hollow portion of the body
11, blow air-feeding inlet 21 formed at about the end of the
nozzle 2 is laid bare in the hollow portion of the body ll, and
the subsequently introduced blow air travels through the blow
ai.r-feeding inlet 21, hol:Low portion 6, and the air-blowing
inlets 2a, 2b, ....formed at a slight rear of the tip portion 3
of the blow nozzle, finally into the inside of the blow molding
(See Fig. 5).
Upon completion of the blowing, an automatic changing
apparatus (not shown)) provided in the air-feeding equipment is
actuated, and now introduction of .air through the air-feeding
inlet 12a is initiated as shown in Fig. 9. At this point,
air-feeding inlet 12b is in the state of connecting to the
space enclosed with the piston 9, the blow nozzle land the
body 11, and the air fed through the air-feeding inlet 12a is
introduced into the inside of the body 11 through the
air-feeding inlet 12b, thus the piston 9 being pressed in the
backward direction till the blow nozzle 1 is restored to its
original position (Fig. 10).
Upon the blow nozzle is moved backward to leave the
parison, the blow air filling the cavity of the metal mold is
vigorously discharged through the largish hole in the wall of
the parison having been formed by the blow nozzle 1, then
through a discharging ho7.e 13 formed in the wall of the body 11
at a position in the vicinity of the top of the body 11.~
Part of the blow ai.r can also be discharged through the
blowing inlets 2a, 2b, ... formed in the blow nozle 1, migrates
backward through the hollow portion 6 of the blow nozzle as
well as through the aforesaid discharge outlet 13.
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In the blow molding method of the present invention, the
use of such specif is blow nozzle enables one to instantly blow
a large amount of blow air having been fed through the
ai.r-blowng inlet in the downward direction and, after
completion of the molding, instantly discharge outside the blow
air filling the cavity of the metal mold.
According to the present invention, blow air can be
effectively circulated in the bottle and, since the hole formed
after the blow nozzle being moved backward and the discharge
outlet 13 formed in the wall of the body in the vicinity of the
tip of the body function as discharge holes to instantly
discharge a large amount crf blow air out of the body, the blow
molding cycle is markedly shortened. This advantage can be
obtained only by the combination of formation of an opening in
the vicinity of or above t:he blow nozzle-pierced portion of a
parison by thinning and bi:eaking the portion by the blow air or
by piercing with a needle--like member and the blow air cylinder
having the above-described specific structure.
Ex:amp 1 a
Advantages of the present invention are now described in
more detail by reference t:o the following example.
Additionally, conditions under which the average
temperature in thicknesswise direction becomes 108°C.when blow
molding conditions of 26°(: in blow air temperature, 15°C in the
surface temperature of the metal mold, and 13 seconds in
cooling time are employed as in the conventional blow molding
are taken as standard conditions.
Experiments of molding the same shaped moldings were
conducted using the same materials and changing part of the
blowing conditions to determine conditions for cooling the
moldings to the average temperature of 108°C in the thickness-
wise direction.
The blow nozzle use~3 in the experiments of the present
invention described in (3) and (4) below has four blowing
CA 02235450 1998-OS-14
inlets f acing upward, downward, leftward and rightward,
respectively, with the blowing inlet facing downward having a
diameter of 3.5 ~ and the blowing inlets facing downward,
leftward and rightward having a diameter of 1.55, and a
passageway having a diameter of 5~ and a cross-sectional area
of 19.6 mmZ, with the inlets having an angle of 15 degrees.
This blow nozzle is so constituted as to blow 64 ~ of blow air
based on the whole blow air through the inlet facing downward.
(1.) When blow molding was conducted under the conditions of
10 26°C in blow air temperature and 5°C in the surface
temperature
of the metal mold, the average temperature became 108°C in 12.5
seconds. Therefore, the molding cycle was shortened by 5 ~ by
changing the surface temperature of the metal mold from 15''C to
5°C.
(2) When blow molding was conducted under the conditions of 0
°C in blow air temperature and 15°C in the surface temperature
of the metal mol, the average temperature became 108°C in 12.7
sE~conds. Theref ore, the molding cycle was shortened by 3 ~ by
changing the blow air temperature from 26°C to 0°C.
(:3) When blow molding was conducted under the conditions of
26°C in blow air temerature and 15°C in the surface temperature
of the metal mold using the blow air cylinder of the present
invention and piercing the parison with the blow nozzle as
shown in Fig. 2, the average temperature became 108'C in 10.5
seconds. Therefore, the molding cycle was shortened by 25 $ in
this case.
(4) When the nozzle was moved backward immediately after
blowing the blow air for about 9 seconds to form a hole in the
blow molding (3), said hole functioning as a discharge hole for
discharging the air inside the bottle, the average temperature
became 108°C in 9.4 seconds. Therefore, the molding cycle was
shortened by 40 ~ in this case.
Additionally, in the above-described (1), it requires to
feed a cooling water of 0°C or lower than that in order to keep
the surf ace temperature of the metal mold at 5°C, which is
CA 02235450 1998-OS-14
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industrially difficult and involves the problem of dropwise
condeensation on the surface of metal mold, thus being
imp>ossible to practice. In the above-described (2), it is
industrially difficult to feed blow air of 0°C. In addition,
both ( 1 ) and ( 2 ) scarcely contribute to shortening of the
blow-molding time. Thus, :~t can be seen that such blow molding
conditions cannot be practically_employed. .
As can be seen from the above-described results on the
experiments, blow molding cycle can be markedly shortened by
instantly introducing blown air particularly in the downward
direction to rapidly circu:Late throughout inside the molding
and by rapidly discharge the blow air introduced in a pressed
state.
Therefore, the structure of the nozzle realizing
theeffective circulation of the blow air inside the moldng has
a great significance.
Industrial utility
As has been described in detail, according to the present
invention, a blow air cylinder of a specific structure is
employed, an opening is formed above the blow nozzle-pierced
portion by the pressure of blow air or by piercing with a
needle-like member from outside, and an upper portion of the
parison is pierced with said blow nozzle to locate it at about
the center of the parison, thus effective circulation of the
blow air being conducted on the inside surface of the molding.
In addition, a hole formed. after the blow nozzle being moved
backward and a discharge hole in the vicinity of the tip of the
body function as air-discraarging outlets, which serve to
instantly discharge the pressed air inside the molding. As a
result, cooling time for the blow molding products is markedly
shortened, which serves to shorten molding cycle and improve
quality of the product such as dimensional accuracy, uniformity
of thickness, etc.
