Modern Mechanical Engineering, 2012, 2, 35-40
http://dx.doi.org/10.4236/mme.2012.22005 Published Online May 2012 (http://www.SciRP.org/journal/mme)
A Novel Extrusion Microns Embossing Method of
Polymer Film
Ying Liu1, Wenlong Liu1, Yajun Zhang1*, Daming Wu1, Xinliang Wang2
1Institute of Plastics Machinery and Engineering, Beijing University of Chemical Technology, Beijing, China
2L.K.Group Ningbo L.K. Technology Co. Ltd., Ningbo, China
Received December 3, 2011; revised February 10, 2012; accepted February 18, 2012
ABSTRACT
A continuous hot embossing method is reported in this paper. The continuous means that the extruder and the hot em-
bossing equipment is used in series, the polymer film is embossed after extrusion immediately. The basic principle of
this method, the key design point and the corresponding operate process of the embossing equipment is described in this
paper. The polymer diffuser with micro-lens matrix on its surface is designed and the optical properties are simulated.
Then, the diffuser is fabricated by the embossing equipment. The optical properties of the diffuser are tested and com-
pared with the results of the simulation to verify the reproducibility of the equipment. By this method, the diffuser with
large area can be fabricated with high precision of graphic replication, high efficiency and low cost.
Keywords: Extrusion Microns Embossing; Hot Embossing Equipment; Diffuser; Reproducibility
1. Introduction
The hot embossing method is proposed by Chou of
Princeton University in the mid of 1990s. Compared with
the traditional lithography technology and the electronic
etching technology, the diffraction phenomenon that oc-
curs during optical exposure, and scattering phenomenon
that occurs during electron-beam exposure are not exist
in this technology. By this technology, the resolution of
the graphic on the films can reach a few nanometers.
Besides, this technology does not need complex equip-
ment, and the cost is low relatively. The mold is used
hundred thousand times in this technology and it is very
suitable for mass production [1].
The hot embossing method is suitable for the produc-
tion with small area, and the process is not continuous.
This limitation on the area size is due to the high pres-
sures needed for those processes, often bigger than 1MPa.
The processes are quite slow, and the equipments and the
molds are usually very complex and expensive [2].
Roll-to-roll nano imprinting lithography has become a
promising method in the production of large area micro
patterns. This process is very similar to the traditional
nano imprinting lithography (NIL). However, in this
method the flat mold used in NIL is wrapped around a
roller. This method has two significant advantages.
Firstly, the contact area of the two rollers is a line; it can
achieve very high pressures with a low applied force.
Secondly, using this method, a small mold is used to cre-
ate a significantly larger patterned area in a continuous
process which can greatly reduce the cost of mould [3-5].
Although the roll-to-roll nano-imprinting lithography
has improved the efficiency and reduced the cost of pro-
duction, there are still some drawbacks. The polymer film
used in this method is bought, it need be heated while the
embossing. In order to improve the efficiency of the pro-
duction, a high heating power system is designed to heat
the polymer film. The thermal deformation of the polymer
film is very likely to occur while heating. And this influ-
ences the thickness uniformity of the polymer film and
lead to uneven distribution of pressure during embossing.
In order to overcome the shortcoming of the roll-to-roll
nano imprinting lithography, a continuous hot embossing
system with pre-flatten system is designed in this paper.
The extrusion machine and the micro embossing equip-
ment are lined in series. In this system, the polymer film
is extruded from the extruder, flattened by the roller and
feed into the micro-embossing equipment directly. By this,
the polymer film does not need be heated to the required
process temperature. This save the heating time and en-
ergy, improve the efficiency of the manufacture, and
eliminate the thermal deformation.
2. The Principle of Extrusion Microns
Embossing
2.1. The Basic Principle of the Method
The rollers used for embossing have temperature control
*Corresponding author.
C
opyright © 2012 SciRes. MME

Y. LIU ET AL.
36
system which ensures the precise control of the emboss-
ing temperature. At the same time, by control the gap
between the two embossing rollers, the pressure that ap-
plied on the polymer film can be controlled.
2.2. The Process of the Extrusion Microns
Embossing Method
The main process of the extrusion microns embossing
method is illustrated in Figure 1. The polymer film is
extruded from the extruder through the die. Then it is
flattened to ensure the uniformity of thickness by two
adjusting rollers. At the last, the polymer film is fed into
the pressure roller and the embossing roller. The mold is
wrapped on the embossing roller with micro structure.
Through the pressure effects between these two rollers,
the polymer film is embossed and thus the microstructure
on the mold be transferred to the surface of the polymer
film. After embossing, the polymer film with the micro
structure on its surface need be cooled down.
During this period, the polymer film has to maintain
good contact with the mold that is wrapped around the
embossing roller to ensure the dimensional stability of
the micro structure while cooling. Finally, the polymer
film with the micro structure on its surface is de-molded
by the draught device. The draught device is composed
of two rollers, the top one is wrapped with a layer of soft
materials to prevent the damage of the micro structure
when pulling.
3. The Design of the Microns Embossing
Equipment
The temperature and pressure are two most important
parameters for the embossing process. The temperature
control accuracy and the uniformity of pressure play a
decisive role in the quality of the products. The key points
1. Extruder, 2. Die, 3. Film, 4. Pre-compacted thickness control roll, 5.
Pressure roller, 6. Imprint roller, 7. Draught device
Figure 1. The schematic of the extrusion microns embossing.
of the embossing equipment are focused on the control of
the temperature and pressure. Besides, embossing speed,
plasticizing quality of the polymer film etc. also have an
important impact on the quality of the embossing products.
Figure 2 shows the microns embossing equipment de-
signed in this paper. The main parameters are given in
the next chapter in Table 1.
3.1. Driving System of the Embossing Rollers
If the speeds of the two rollers are inconsistent, it will
lead to a shearing to the polymer film. This will deform
the film and thus influence the microstructure transfer
accuracy as well as the surface quality of the production.
The speed consistency of the pressure roller and em-
bossing roller is very important.
In this paper, the driving system adopts two sets of
servo motor driven gear structure to drive the two rollers
respectively. The speed of the two rollers servo motor is
controlled precisely. The speed consistency of the two
rollers is ensured by the closed loop control system of
servo motor.
3.2. Temperature Control System
The temperature is one of the most important parameters
in hot embossing process. If the temperature of the poly-
mer film is too low, it lead to insufficient liquidity of the
polymer, incomplete filling of the mold and a large elas-
tic recovery of the micro structure after de-molding; On
the contrary, if the temperature of the polymer film is too
high, it may destroy the structure of the polymer chain
and generate much more defects on the micro structure.
Usually, the maximum temperature during embossing
process should be controlled at 50˚C - 100˚C higher than
the Tg of the polymer. The temperature control system is
sensitive to temperature change and has a relatively high
heating power so that it response quickly to the tempera-
ture change.
Here, the heating oil is used to control the temperature
of the two rollers. The oil cycling inside the rollers and
its temperature is controlled by a separate machine. By
control the temperature of the heating oil, the tempera-
ture of the two rollers is controlled. This method has high
1. Extruder, 2. Die, 3. Film, 4. Pre-compacted thickness control roll, 5.
Pressure roller, 6. Imprint roller, 7. Draught device
Figure 2. Hot embossing machine.

Y. LIU ET AL. 37
Table 1. The main parameters of the hot embossing ma-
chine.
Material Alloy steel
Diameter(mm) 140
Rollers
Useful Length(mm) 250
Rough adjustment (mm) 10 - 30
Adjusting range of the
gap between the two
rollers (mm) Accurate adjustment (mm) 0 - 5
Rotate speed range (rpm) 0 - 30
Temperature range of the pressure roller (˚C) 150 - 260
Temperature range of the embossing roller (˚C) 20 - 120
Adjusting range of the pressure (MPa) 0 - 10
Embossing speed range (m/min) 1 - 3
temperature control precision, small temperature fluctua-
tions and a wide range of temperature adjustment.
3.3. Pressure and Roller Gap Adjustment System
The pressure is the other important parameter in hot
embossing process. If the pressure is too low, it will lead
to incomplete filling of the mold. On the other hand, if the
pressure is too high, it will generate residual stress in the
final products and deformation of the product will occur
after de-molding. The uneven of the pressure will lead to
poor distribution of the micro structure and make the
mold easily damaged. In this paper, the adjustment of the
pressure is achieved by adjusting the gap between the two
rollers. The roller gap adjustment system includes two
parts, the rough and the accurate adjustment mechanism.
The rough adjustment mechanism is used to adjust the
gap in a wide range, and realize rapid opening and closing
of the two rollers. The accurate adjustment mechanism is
used for adjust the gap in a very small rang, and control
the gap and pressure accurately.
3.4. The Design of the Embossing Mold
The micro structure on the roller’s surface is transferred
to the polymer film directly during the embossing proc-
ess. Therefore, it decides the shape of the micro structure.
In this paper, a chemical etching method is used to pro-
duce an array of micro structure on the stainless steel
plate. Then the plate is wrapped around the roller. This is
illustrated in Figure 3.
The main parameters of this device are given in Table
1.
4. Simulations and Experimental Analysis
4.1. The Simulation of Diffuser’s Optical
Properties
The diffuser is mainly used for converting the point light
source into surface light source and the light distribute on
Figure 3. The photo of the roller mold. (a) 40 times photo of
the mold; (b) 200 times photo of the mold; (c) Photo of the
mold.
its surface uniformly. A key performance of the diffuser
is the light distribution uniformity. Generally speaking,
the diffuser can be roughly divided into two types, the
particle diffusion and surface diffusion. In this paper, the
surface diffusion is used and the micro lens matrix is
made on the surface of polymer film to achieve the effect
of light diffusion. The micro lens matrix is produced by
the method that mentioned above. By the light tools
software, the optical properties of the diffuser are simu-
lated with the micro lens matrix on its surface. And it is
compared with the results without micro structure on its
surface. Also, the properties with different micro lens
matrix on its surface are also compared. The results are
given as follow:
(1) Film without micro structure on its surface. Degree
of uniformity is 69.40% and the Luminousness is 90.44%.
The simulation result of the illumination distribution is
shown in Figure 4(a).
(2) Polypropylene sheet with micro lens matrix on its
surface. Diameter of the micro lens is 175 μm, 400 μm
pitch, and triangle arrangement. Degree of uniformity is
69.67%, Luminousness is 81.33%. The simulation result
of the illumination distribution is shown in Figure 4(b).
(3) The simulation of the Polypropylene sheet with
micro lens matrix on its surface. Diameter of the micro
lens is 270 μm, and pitch is 500 μm, arrangement is tri-
angle. Degree of uniformity is 72.98%, Luminousness is
80.22%. The simulation result of the illumination distri-
bution is shown in Figure 4(c).
From the simulation results and illumination distribu-
tion figures, uniformity of light has improved when the
polypropylene film has micro lens matrix on its surface.
The micro lens matrix on the surface of the polymer film

Y. LIU ET AL.
38
(a)
(b)
(c)
Figure 4. Illumination distribution of PP film. (a) Without micro structure; (b) With micro structure (diameter of 175 μm;
400 μm pitch); (c) With microstructure (diameter of 270 μm; 500 μm pitch).

Y. LIU ET AL. 39
plays an important role in the proliferation of light. Be-
sides, the proliferation of light has a close relationship
with the structure of the microstructure that on the sur-
face of the polymer film.
4.2. Experimental Materials and Equipment
The Materials used in the experiment is Polypropylene
(T4802) of Sinopec Beijing Yanshan Company. The
Precision single screw extruder used in the experiment is
PSJ-32-28A which is made by Plastic Machinery Research
Institute of Beijing University of Chemical Technology.
The optical microscope is SZM-B2 which is made by
Yongfeng electro mechanical technology company. Light
transmittance haze Tester is WGT-S which is made by
Shanghai precision scientific instrument Company. Illu-
mination meter is ST-80C which is made by photo electric
instrumental Company.
4.3. Experiments
First, the parameters of the extruder are adjusted to the
required value. At the same time, the hot embossing
equipment is started and the embossing parameters are
adjusted to ensure the quality of the polymer film. After
the extrusion of the film and all the parameters are stable,
the polymer film is extruded from the extruder, and fed
into the embossing equipment. In this stage, the polymer
film is embossing at a low pressure. The polymer film is
embossing at a relative large roller gap, so the parameters
are adjusted easily. After the embossing process, the pa-
rameters are adjusted to the desired value and begin the
experiment.
4.4. Results and Discussion
4.4.1. Preparation of Diffuser
The experimental process condition for the preparation of
the diffuser is as follow. The temperature of each section
of the extruder is 175˚C, 190˚C, 200˚C, 205˚C and 210˚C.
The temperature of the die is 210˚C. The speed of the
embossing roller is 2 rpm. The embossing force is 8.2
KN. The temperature of the embossing roller is 60˚C.
The temperature of the pressure roller is 165˚C. The di-
ameter of the micro structure on the molds is 150 μm and
250 μm, 400 pitches and 500 pitches respectively. The
micro structure is all through-hole and present triangle
arrangement on the molds. Because the mold is made by
the method of chemical etching, there are some devia-
tions between actual size and design size. The diameter
of the actual size of the micro structure is 175 μm and
270 μm, 400 μm pitches and 500 pitches respectively.
The diffuser made by this method is shown in Figure 5.
From the picture, we can see that the micro structure on
the mold has been successfully transferred to the surface
of the polymer film.

(a) (b)
Figure 5. The photo of polymer diffuser.
4.4.2. The Experimental Test of Diffuser’s Optical
Properties
The optical properties of the diffuser are tested by light
transmittance/haze Tester and illumination meter. The
diffuser has the micro lens matrix on its surface which is
made by the method that mentioned above. The test re-
sults are shown in Table 2.
An optical test platform is used to test the diffuser’s
effect on the proliferation of light. This optical test plat-
form include a laser pointer light, a support frame used
for fixing laser pointer light and diffuser, a white screen
used to receive and display the effect of proliferation of
light. The experimental results are shown in Figure 6.
From the experimental results, the proliferation and uni-
formity of light is improved by the micro lens matrix on
its surface.
5. Conclusion
A continuous polymer micro embossing method and its
principle are introduced in this paper. The critical pa-
rameters during the embossing process and the influence
of these parameters on the accuracy of graph transfer are
analyzed. Then, hot embossing equipment is designed to
meet the requirement of the process conditions. Using
this hot embossing machine and a precision single screw
extruder, the polymer diffuser with micro lens matrix on
Table 2. The optical properties of the diffuser.
Luminousness Uniformity Haze
PP film 88.1 65.9 26.0
PP 0.175 82.5 69.6 34.6
PP 0.27 85.7 73.6 37.3
Figure 6. The diffusion effect chart of the diffuser.

Y. LIU ET AL.
40
its surface is produced successfully. The optical proper-
ties of the polymer diffuser are analyzed though simula-
tions and experiments. The results show that the micro
structure on the mold was perfectly transferred to the
polymer film and the diffuser’s light uniformity simula-
tion results are consistent with the experimental results.
This is a feasible method for producing polymer diffuser
with micro structure on the surface. This is a very prom-
ising method in the field of making micro structure. It
has the advantage of high precision, simple process, easy
to operate, high production efficiency and low cost.
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