Effect
of
decoration
film
on
mold
surface
temperature
during
in-mold
decoration
injection
molding process
鈽?/p>
Shia-Chung Chena, b,
,
,
Hai-Mei Lic,
Shih-Tsun Huanga,
Yi-Chao Wanga
a Department of Mechanical Engineering, Chung Yuan Christian University, Chung-Li, Taiwan
b R&D Center for Membrane Technology, Chung Yuan Christian University, Chung-Li, Taiwan
c
Advanced
Polymer
Processing
Technologies
of
National
Engineering
Research
Center,
Zhengzhou University, Zhengzhou, Henan, China
Available online 4 February 2010.
http://dx.doi.org/10.1016/j.icheatmasstransfer.2010.01.005, How to Cite or Link Using DOI
Permissions & Reprints
Abstract
In-mold
decoration
(IMD)
during
injection
molding
is
a
relatively
new
injection
molding
technique and has been employed for plastic products to improve surface quality and achieving
colorful surface design, etc. During IMD processing, the film is preformed as the shape of mold
cavity and attached to one side of the mold wall (usually cavity surface), then molten polymer is
filled
into
the
cavity.
Heat
transfer
toward
the
mold
cavity
side
during
molding
IMD
part
is
significantly
retarded
because
the
film
is
much
less
thermal
conductive
than
metal
mold.
To
investigate the effect of film on temperature field, polycarbonate (PC) was injection molded under
various
conditions
including
coolant
temperature,
melt
temperature,
film
material
and
film
thickness. Simulations were also conducted to evaluate the melt
鈥?/p>
film interface temperature and its
influence from film initial temperature and film thermal properties. For PC film, it was found that
the
heat
transfer
retardation
results
in
the
mold
temperature
drop
in
cavity
surface
and
the
maximum temperature drop as compared to that of conventional injection molding without film
may be as high as 17.7 掳
C. For PET film, this maximum mold temperature drop is about 13 掳
C. As
PC film thickness increases, the retardation-induced mold temperature difference also increases.
The initial film temperature (30 掳
C and 95 掳
C) may affect the melt
鈥?/p>
film interface temperature at
the contact instant of melt and film by about 12 掳
C to 17 掳
C. When thermal conductivity of film
increases from 0.1 W/(m
鈥?/p>
k) to 0.2 W/(m
鈥?/p>
k), melt
鈥?/p>
film interface temperature may vary by 22.9 掳
C.
The simulated mold temperature field showed reasonable agreement with experimental results.
Keywords
Mold surface temperature;
Film
鈥?/p>
mold and melt
鈥?/p>
film interface temperature;
Heat transfer retardation;
Film-insert;
In-mold decoration injection molding
1. Introduction
Injection
molding
is
one
of
the
most
useful
polymer
processing
methods
because
complex
geometry
products
can
be
manufactured
rapidly
at
relatively
low
cost.
Injection
molding
is
a
cyclic process and can be divided into four stages, namely filling, packing, cooling and ejection,
with
pressure
and
temperature
variations
[1].
In-mold
decoration
injection
molding
(IMD),
or
film-insert
injection
molding,
is
a
relatively
new
injection
molding
technique
in
which
molten
polymer
is
introduced
into
the
cavity
after
a
decorated film
is
attached
to one
side
of
the
mold
walls,
usually
in
cavity
surface.
Recently,
IMD
has
been
employed
for
production
of
various
molded products to improve surface quality such as automotive interior parts, cellular phone cases,
and
logo
imprinted
plastic
products.
IMD's
primary
advantage
is
the
integration
of
several
manufacturing steps (production and decoration of molded part) into one production operation [2].
Since surface quality of plastic parts can be improved with the inserted decorating film during the
injection
molding
process,
the
process
is
designated
as in-mold
decoration
(IMD).
The
relevant
IMD molding also includes in-mold
labeling (IML) and in-mold rolling (IMR) [3].
The surface
quality of film-injection molded parts without any post-processing such as screen printing or spray
painting,
therefore
IMD
is
a
highly
advanced
method
compared
with
the
conventional
injection
molding [1], [2], [3] and [4]. Moreover, the injected hot melt resin may partially join with the film