Asahi Chemical has developed a new plastic
molding technology which enables precision mass production
of thin-walled parts and moldings with fine surface
patterns by using CO2 gas to improve melt
flowability and mold surface transfer during injection
molding. Used with engineering resins, this technology
enables reduced molding wall thickness for lighter-weight
mobile electronics devices. AMOTEC is also an environment-friendly
technology, as the improved surface appearance made
possible in general-purpose moldings eliminates the
need for painting and makes parts more easily recyclable.
Commercial sale of specialized apparatus which utilizes
this technology is scheduled to begin in April 2001,
through agreements with major molding machine manufacturers.
Background
With many outstanding characteristics, injection molding
is the most common method of plastic processing. However,
improvement has been sought regarding certain aspects
of processing by injection molding.
- Resin flowability
Because resin melt has a high viscosity, high pressure
is necessary when filling the mold cavity. It is sometimes
difficult to completely fill the cavity when molding
thin-walled parts.
- Mold surface transfer
Because the resin begins hardening the moment it contacts
the mold surface, it is difficult to faithfully reproduce
fine mold surface patterns.
- Resin shrinkage
While the molded resin cools to room temperature after
hardening inside the mold, shrinkage often causes
indentations to form in some portions of the molding,
and the overall shape of the molding to become deformed.
A variety of technologies have been developed
to mitigate these problems. Asahi Chemical has developed
several technologies, including Asahi Gas Injection and
Clear Surface Molding, which are well reputed and used
by molders in a wide range of applications. However, these
technologies have mainly been effective in mitigating
problems of mold surface transfer and resin shrinkage;
until now, no technology which fundamentally mitigates
problems of resin flowability has been successfully developed.
The newly developed technology
AMOTEC utilizes the plasticizing effect of CO2 gas on resins to improve both resin flowability and
mold surface transfer. Potentially beneficial in nearly
all injection molding applications, it is a 21st century
technology which opens the path to a new era in injection
molding.
The trademark AMOTEC
The name of this technology comes from Asahi Molding Technology with CO2.
AMOTEC technology in brief
CO2 is dissolved in the resin melt inside
the heating cylinder of the injection molding machine.
In some cases, the mold cavity is also charged with
CO2 prior to injection. Resin flowability
is dramatically improved due to the plasticizing effect
of CO2, enabling thin-walled molding cavities
to be more easily filled with resin melt. Also, because
the resin surface which contacts the mold surface hardens
more slowly, fine patterns on the mold surface are faithfully
transferred to the molded part.
Advantages of AMOTEC
- For mobile electronic devices: Enables
thin-walled moldings with resin materials such as
engineering plastics which have outstanding physical
properties but poor moldability.
- For light-conducting plates, lenses,
optical discs: Enables precise transfer of the mold
surface.
- For other molded parts: Improves
surface appearance so painting is unnecessary, making
parts easily recyclable.
Merits of using CO2 as
plasticizer
Ordinarily, oils are used as plasticizer for synthetic
resins. While raising resin flowability and lowering
melt temperature, such plasticizers also adversely affect
basic properties such as hardness and strength. CO2 in contrast, while displaying an excellent plasticizing
effect during molding, has no effect on the physical
properties of the molded part because it effuses from
the resin after molding. The plasticizing effect of
CO2 has been known since the 1980s, but AMOTEC,
incorporating CO2 gas supply equipment and
related apparatus, is the first practical implementation
of this principle.
AMOTEC apparatus
In addition to an ordinary injection molding machine,
the following apparatus are required for the use of
AMOTEC:
- CO2 supply equipment.
Equipment to supply CO2 gas at elevated
pressure to the heating cylinder and mold.
- Specialized screw. A modified
screw is necessary to evenly dissolve CO2 gas in the resin as it is melted.
Users will be able to purchase the needed
apparatus from molding machine manufacturers when license
arrangements between these manufacturers and Asahi Chemical
have been agreed.
Further developments
- Agreements will be established with
molding machine manufacturers, and the market for
AMOTEC will be developed.
- Concurrently, AMOTEC applications
development will be advanced, primarily by the plastics-related
business divisions of Asahi Chemical.
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