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Preparation of polypropylene thermoplastic container via thermoforming process
View the table of contents for this issue, or go to the journal homepage for more
2016 IOP Conf. Ser.: Mater. Sci. Eng. 114 012019
(http://iopscience.iop.org/1757-899X/114/1/012019)
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Preparation of polypropylene thermoplastic container via
thermoforming process
Nik Ruqiyah Nik Hassan, Farah Amira Mohd Ghazali, Abdul Aziz Jaafar, Noor
Mazni Ismail
Faculty of Manufacturing Engineering, Universiti Malaysia Pahang, 26600 Pekan,
Malaysia
E-mail: drmazni@ump.edu.my
Abstract. In this study, plastic containers made of polypropylene (PP) sheets were fabricated
via vacuum thermoforming. Thermoforming is a process used in fabricating plastic parts by
changing flat thermoplastic sheet to three dimensional shapes. In preparing these thermoplastic
containers, the design and fabrication of mould were first done by using Catia V5 software and
CNC milling machine, respectively. The thermoforming process was then performed at various
temperatures ranging from 160⁰C until 200⁰C on the PP sheet to form the container. From the
experiment, it can be suggested that the outcomes of final thermoplastic containers are
significantly depends on temperature control during thermoforming process and also the vent
holes design of the mould.
1. Introduction
The thermoplastic material type used in this project is Polypropylene (PP) the propylene used in
many sector, among industries nowadays. Polypropylene is processed into film, rigid packaging,
consumer products, technical parts and also textiles [3]. The properties of this (PP) material are
economical material, good resistance to fatigue and also have a high melting point of temperature.
The most important, polypropylene (PP) is recyclable and has number 5 as its identification.
Polypropylene (PP) is useful for such diverse products as reusable plastic food containers,
microwave and dishwasher safe plastic containers. Thermoforming is the process that used in
industry for plastic part. Thermoforming process is a process of changing flat thermoplastic sheet
to three dimensional shapes [5]. There are three types of thermoforming process which are vacuum
forming, pressure forming and match die forming. Therefore, the design consideration for
thermoplastic container is also important. The design of mould containers needs a practical design
so that the container has a good quality, value and the part can be vacuum during thermoforming.
The type of material used for mould also may affect the thermoforming process.
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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2. METHODOLOGY
2.1 The Design of the Mould
The container was designed by using Catia V5 software. The standard size for mould was less than
130mm width and 200mm length according to the size of the thermoforming plate mould. Draw
ratio = depth of part/width of part. Draw ratio should be less than 2:1 for female moulds or 7:1 for
male mould.
The mould design guidelines for parts need to consider through draft angle. The draft angle for
male mould minimum was three degree, and for female mould draft angle minimum was one
degree. The draft need to consider because of the thermal expansion of the plastic during
thermoforming process. The coefficient of thermal expansion caused it shrink to the plastic part.
The function of draft also to allows for better material distribution by opening up a corner area to
allow clearance for a plug assist to push material or part. The drafted walls have less risk of plug
hitting the sidewall. The larger the draft angle, the better in keeps the end use requirements of
product.
2.2 Preparation of the Mould
The preparation of the mould start with the raw material, the raw material of aluminium block cut
by using band saw for container and for container’s. Figure 1 show the band saw using to cut the
aluminium block. The aluminium block squaring manually by using milling machine before
generates G-code. Figure 2 below shows the milling machine squared the aluminium block. The
size for container size of squaring was 100mm x100mm x50mm and for their cover is 100mm x
100mm x 30mm.
Figure 1. The band saw cutting
the aluminum block.
Figure 2. Squaring an
aluminum block
The next process is machine the shape of mould. The CNC milling machine and some sort of CAD
program used to cut out a solid block of aluminium. The Figure 3 shows the CNC milling machine
the container’s mould.
The mould need to drill the vent holes as the last process in the preparation of mould. The most
important is the vent hole drilled to the mould, the diameter less than the thickness of the PP sheet.
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
2
Vent holes are drilled and placed in all the lower parts of the mould to provide for easy escape of
trapped air. The Figure 4 shows the holes drilled to the mould. The diameter of drill tools used
1mm.
Figure 3. The aluminum block
machine the container’s mould
Figure 4. The drilling process
of vent holes
2.3 Thermoforming Process
The thermoforming process type used in this project is a vacuum forming process as shown in
Figure 5. A vacuum is formed between the mould cavity and the thermoplastic sheet. The basic
processes for this thermoforming operation are, first the flat thermoplastic sheet is clamped.
Second the sheet heated to its softening temperature (the temperature depends on the type of
material used). Next, the force against the shape of mould form of vacuum pressure. The pressure
used in this process is constant at 20 kPa. There are few stages involved in the vacuum forming
process. Firstly, the mould was made from an aluminium material machine with the shape of
container. Secondly, the mould shape placed in vacuum former. Thirdly, a sheet of polypropylene
is clamped in the frame. Next, the polypropylene sheet heated and sealed to the container mould.
Then, the vacuum is turned on and pumps out all the air. At this stage the shape of mould can be
clearly seen through the plastic sheet. The plastic has cooled sufficiently the vacuum pumps switch
off. After that, the plastic sheet removed from the vacuum part and the sheet has the shape as
mould shape. Lastly, the excess plastic is trimmed so that the plastic container remains.
Figure 5. Thermoforming machine used
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IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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2.4 Parameter setting
The parameter setting is the guideline setting for thermoforming process that must be following to
prevent shrinkage. The temperature of the thermoforming depends on the material used. For the
polypropylene material, the recommendation temperature for PP formed is 165˚ C to 180˚C.
Sometimes, the temperature depend on the thickness of the plastic sheet itself, the machine used
and also the type of mould. In this project, the experimental parameter of temperature set start
form 160⁰C until 200⁰C. The temperature controlled start from 160˚C, 165˚ C, 170˚ C, 175˚ C,
180˚ C, 185˚ C, 190˚ C, 195˚ C, and 200˚ C. The temperature sensor used to as the equipment to
control temperature as shows in Figure 6. The vacuum pressure use is constant at 20psi. The
vacuum pressure forces the sheet to forming to the mould and form the desired shape of the part.
Then, the thermoformed part shape cooled.
Figure 6. The temperature sensor used
3. RESULT AND DISCUSSION
3.1The Design
The container successfully design by using Catia V5 software, in detail dimension for mould are in
Figure4.1 below, the type of mould designed was female mould in square shape. Figure 7 and
Figure 8 show the container design by Catia V5 software. The type of mould for container is
cavity mould or female mould.
Figure 7. The details
dimension
Figure 8. The mould
designed by Catia V5
software
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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3.2 The Mould
The aluminium block machined using CNC milling machine and some short of g-cod program to
follow the design of mould in Catia software. The Figure 9 showed the machine aluminium mould.
Figure 9. The aluminum mould
3.3 Thermoforming Process Result
This thermoforming process started with clamp a thermoplastic sheet in a frame. The plastic sheet
is clamped in a frame as shown in Figure 10. Then, the PP sheet heated until it achieved sag point
as shows in figure 11.
The heat time for PP with 1 millimeter (mm) thickness was recommend 50 seconds in theory but
sometimes it depend on the machine thermoforming itself. In this experiment the time to reach sag
point is 2minutes 20 seconds is the best.
Next, the constant vacuum pressure at 20 kPa is applied to the plastic to the mould so that the
vacuum can be applied. Then the shape of the container form as shows in Figure 12.
After that the part of the container need to eject and the excess plastic is trimmed off. Figure 13
shows the excess plastic that need to trim off after ejection process. Lastly, the thermoplastic
container part is successfully form by thermoforming process as shows in Figure 14.
Figure 10. The pp sheet is clamped in the
frame
Figure 11. The plastic sheet at sag point
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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Figure 12. The PP sheet form by applied
vacuum
Figure 13. The excess plastic trimmed
off
Figure 14. The container
3.4 The Result for Temperature Parameters Used
The temperature used to heat PP sheet at 160⁰c to 200⁰c to identify which temperature is the best
in this experiment. In this range temperature, the result shown the temperature in range 165⁰c to
175⁰c is good temperature compare to other temperature during the thermoforming process but
175⁰c is the perfect surface. Table 1 below shows the result of container with different temperature
used.
The data was record during thermoforming process shows in Table 2. Based on the table below it
shows that the increasing the value of temperature, the time taken become longer and the plastic
part closed to melting molten plastic which it cannot form good shape of the container.
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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Table 1. The effect of different temperature used
TEMPERATURE
USED
RESULT
DESCRIPTION
160⁰c
At this temperature the container shape
follow the mould design but the bottom
thickness of the container not uniform.
156⁰c
The container form is good.
170⁰c
At this temperature of PP sheet heating
form good surface of container.
175⁰c
This temperature is better than 170⁰c and
165⁰c
180⁰c
180⁰c cannot be recommended as
temperature of forming because at this
point the PP sheet started wrinkle at the
side wall part.
185⁰c
This temperature produced bad surface of
container.
iMEC-APCOMS 2015 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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190⁰c
The plastic container wrinkle at the top
side wall of the container.
195⁰c
The wrinkle increases at high
temperature.
200⁰c
Too hot temperature at 200⁰C, causes the
result of container fail to forming
perfectly at this temperature.
Table 2. The data record during thermoforming process
No
Room
Temperature
Temperature of
Mould
Temperature of
PP Sheet
Time Taken For
PP Sheet
Vacuum
Pressure Applied
(Kpa)
1
27 ⁰ c
40⁰ c
160⁰ c
1min 40 second
20
2
27 ⁰ c
40⁰ c
165⁰ c
2 min
20
3
27 ⁰ c
40⁰ c
170⁰ c
2 min
20
4
27 ⁰ c
40⁰ c
175⁰ c
2min 20 second
20
5
27 ⁰ c
40⁰ c
180⁰ c
2 min 30 second
20
6
27 ⁰ c
40⁰ c
185⁰ c
2 min 50 second
20
7
27 ⁰ c
40⁰ c
190⁰ c
3 min 30 second
20
8
27 ⁰ c
40⁰ c
195⁰ c
3min 50 second
20
9
27 ⁰ c
40⁰ c
200⁰ c
4 min
20
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IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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4. DISCUSSION
4.1 Mould Effect
This grid ink was placed on the top of the plastic sheet to see the stretch mark area and the
thickness of plastic part form. Figure 15 shows the stretch mark for temperature 170⁰c outside
mould wall area which has a lower thickness than the bottom area. This caused by the hot sheet
contacts with the outside wall area of the mould at first step in the female mould and consequently
the sheet sticks to the mould.
Figure 15. The stretch mark (170⁰c)
The stretch mark area shows in Figure 16 below is for 200⁰c heating temperature. This
temperature is too hot and causes the stretch area tears.
Figure 16. The stretch mark (200⁰c)
This discussion proved based on the previous research about Numerical and Experimental
Analysis of HIPS Sheets in Thermoforming Process by author Mohammad Ghobadnam Peiman
Mosaddegh & Masood Rezaei Rejani & Hosein Amirabadi &Abbas Ghaei. Published 13
September 2014 [10]
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IOP Conf. Series: Materials Science and Engineering 114 (2016) 012019 doi:10.1088/1757-899X/114/1/012019
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5.0 CONCLUSION
This research study is basically an application of thermoforming process where the main study of
plastic process in industry nowadays, and to identify the main advantage of thermoforming process
compare to other plastic part process in industry today. The main of this experiment also, to test
the process of thermoforming process based the mould design for the container.
This experiment also to identify the suitable temperature and time range used for heating
temperature Polypropylene (PP) sheet during process of thermoforming.
Based on these experiments that were done, it can be concluded that the experiment successfully
fulfils the first objective that was to design and fabricate the mould. The female mould was the
best design for vacuum forming process.
There are some PP sheets not form perfectly during the process because the temperature not
suitable and the pressure was released on two earlier causes the plastic soul before it form. This
experiment proves that the different temperature used during these thermoforming will get
different result either on the surface uniformity or the thickness. Based on the result, the suitable
parameter temperature used for this thermoplastic PP container is in range 165⁰c to 175⁰c. As for
the conclusion, the factors that affect thermoforming process is the mould design, vent holes and
heating temperature for thermoplastic.
6.0 REFERENCES
[1] Morris, Peter J. T. (2005). PolymerPioneers: A Popular History of the Science and
Technology of Large Molecules. Chemical Heritage Foundation. p. 76. ISBN 0-941901-03-3.Jump
up.
[2] Tong Wei Liat, Design validation and development of plastic injection moulding core for
container plastic product, 2008.
[3] CIEC Promoting Science at the University of York, York, UK (January 2014). Retrieved from
http://www.essentialchemicalindustry.org/polymers/polypropene.html
[4] Zhen-Zhe Li1, Guang Ma1, Dong-Ji Xuan1, Seoung-Yun Seol2 and Yun-De Shen (2010) A
Study on Control of Heater Power and Heating Time for Thermoforming; international journal of
precision engineering and manufacturing Vol. 11, No. 6, pp. 873-878.
[5] Donald V.Rosato, Marlene G.Rosato, Nick R.Schott. (2010) Plastic Technology Hanbook
(volume 1); Momentum Press.
[6] J.L. Throne and P.J. Mooney, Thermoforming Quarterly, 2005, 24, 2, 19.
[7] C. Celata, Popular Plastics and Packaging, 2007, 52, 12, 49.
[9] LOTTE CHEMICAL TITAN. Retrieved from (2015) http://www.lottechem.my/Products/pdf
[10] Mohammad Ghobadnam Peiman Mosaddegh & Masood Rezaei Rejani & Hosein Amirabadi
&Abbas Ghaei. Published 13 September 2014.
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