Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Reexamination Certificate
2001-02-21
2004-07-06
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C264S540000, C425S531000, C425S532000, C425S545000, C215S371000, C220S604000
Reexamination Certificate
active
06759003
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a blow-molding method for molding a molding product by introducing a parison extruded from a die into a mold and clamping the parison, a blow-molded product obtained by the blow-molding method and a blow-molding mold used for the blow-molding method.
BACKGROUND
Conventionally, resin-made container such as a bottle or a tank has been molded by a blow-molding method where a gas is blown into an inside of a parison introduced in a mold to render shape thereof.
In the blow-molding process, cylindrical parison is generally prepared by extruding molten resin from a die and the parison is sandwiched by a mold (split die) to render shape.
Thus molded blow-molded product weighs light because of hollow construction and is superior in shock resistance and soundproofness. Further, the blow-molding can be conducted by a low pressure so that production cost can be reduced and the containers etc. manufactured by the blow-molding often has simple structure, so that the molding die can be inexpensively made because of the simple structure of the mold.
In view of the above advantages, in recent years, blow-molded product has been widely used in various industrial fields such as automobile components, housing facilities and building materials.
For instance, bumpers and spoilers in the automobile field, door panel and components attached to bath units and lavatory units in the housing facilities field, and table top and various panels in the building materials in the building material field can be cited as a typical example.
The blow-molded product is manufactured by the blow-molding generally after following four steps as shown in FIG.
6
.
(a)
During a parison injection step, a cylindrical parison
99
is extruded from a mold
90
of a blow-molding machine to be introduced between a first mold
91
and a second mold
92
as the blow-molding molds.
Incidentally, a die design surface
91
A is formed on the first mold
91
, the die design surface
91
A having a pre-contact portion
93
as a convex portion protruding toward the parison
99
and a molding portion (blow-up portion)
94
as a deeply carved concave portion.
(b)
During a mold clamping step, the first mold
91
and the second mold
92
are closed to pinch the parison
99
by land portions
91
B and
92
B (burr portions) located on a periphery of the blow-molding molds
91
and
92
. At this time, a space between the molds
91
and
92
is an open space opening toward the outside before the molds
91
and
92
are closed. Accordingly, since a part of the parison
99
inflates toward outside of the molds
91
and
92
when the molds
91
and
92
are closed, though the parison
99
touches the pre-contact portion
93
, the parison
99
does not touch the whole of the molding portion
94
.
(c)
Air is blown into the parison
99
from a pin
95
during an air blowing step, so that the parison
99
touches the whole of the molding portion
94
.
(d)
Subsequently, the parison
99
is cooled and solidified to obtain the blow-molded products.
The Applicant of the present application has studied and found that the appearance of the blow-molded product is impaired by streaks and wrinkles on borders of respective portions of parison in contact with the pre-contact portion
93
and the molding portion
94
and uneven transfer of grain pattern. Specifically, after touching the pre-contact portion
93
during the mold clamping step as shown in FIG.
6
(
b
), the parison
99
touches the molding portion
94
of the first mold
91
during the air blowing step as shown FIG.
6
(
c
). Thus, the movement of the contact portion of the parison
99
to be in contact with the die design surface becomes stagnant between the part of the parison
99
to be in contact with the pre-contact portion
93
and another part of the parison
99
to be in contact with the molding portion
94
. The above-described streaks and wrinkles are generated and grain pattern was transferred uneven on account of the stagnation of the contact portion.
Conventionally, even when the streaks and wrinkles were generated on the surface of the blow-molded product, the surface was painted to hide the streaks and wrinkles or, alternatively, the grain pattern was used on the surface design to make the streaks and wrinkles less prominent.
However, since cost reduction, recycling, and solvent regulation have been required for the blow-molded products, non-coating and specular appearance have been desired.
Accordingly, various techniques has been proposed for improving appearance design not generating the streaks, wrinkles and uneven pattern transfer and for enhancing transferability to enable decoration with minute complicated patterns to achieve non-coating and mirror-finished appearance.
For instance, a molding die having a heat insulator on a mold body and a space at the back of the die design surface for introducing and discharging heated gas or cooled liquid (Japanese Patent Application Laid-Open Publication No. Hei 07-108534) and a blow-molding method where a parison is forced against a die design surface of a mold covered with a heat insulation layer by a blow gas, the method using a mold capable of accurately transferring the die design surface while keeping the parison at a high temperature (Japanese Patent Application Laid-Open Publication No. Hei 06-328549) have been proposed.
Further, a non-coating molding product having glossy smooth surface made of a thermoplastic resin having specific melt index and flexure modulus of elasticity (Japanese Patent Application Laid-Open Publication No. Hei 08-119043) and a molding product made of polypropylene having high surface glossiness (Japanese Patent Application Laid-Open Publication No. Hei 10-138324) have also been proposed as example of modifying the material of the blow-molded product.
In such technique, the streaks and wrinkles or the uneven transfer on the molding product are prevented by modifying basic molding condition such as a timing for clamping the mold or blowing the air, by controlling the mold temperature during heating and cooling, or by providing vent port or porous electroform to efficiently discharge the gas inside the mold.
However, in a multi-layer blow-molding for not coating the molding product, when a transparent material is used as a surface layer of the molding product, the streaks and wrinkles are prominently generated on the molding product even when the blow-molding mold is heated to a high temperature or when the gas inside the die is efficiently discharged.
Further, when the manufacture thereof cannot be conducted at so high temperature for the convenience of molding cycle, it is found that the above techniques cannot be used for manufacturing a molding product requiring graining for applying pattern of imitation leather or texture.
This is because, though the mold temperature generally is preferably as high as possible for applying flowability to the parison, the molding cycle can be too lengthened since much time is required for raising and cooling the mold temperature when the mold temperature is set so high, so that the productivity can be lowered as a result.
Accordingly, a blow-molding method capable of obtaining molding product having good appearance without streaks, wrinkles and uneven pattern transfer without relying on mold temperature control has been desired.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a blow-molded product having good appearance, a blow-molding method for producing the molding product and a blow-molding mold therefor.
A blow-molding method according to the present invention is for molding a molding product by introducing a parison extruded from a die into a mold, the method being characterized in having the steps of: providing the mold with a parison shutter for shutting the parison to keep the parison from inflating out of the mold; opening the mold; introducing the parison into the mold; shutting the parison by the parison shutter without bringing the parison into contact with the inner surface of the
Kumazaki Shigekazu
Miura Shoichi
Obara Tomoyuki
Sugawara Sueki
Tada Katsuhiko
Flynn ,Thiel, Boutell & Tanis, P.C.
Idemitsu Petrochemical Co. Ltd.
McDowell Suzanne E.
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