Note: Descriptions are shown in the official language in which they were submitted.
CA 02798038 2012-12-04
THERMAL TRANSFER LAMINATING METHOD
Field of the Invention
The present invention relates to a thermal transfer laminating method.
Particularly, the
present invention relates to a one-step vacuum thermoforming method combined
with a thermal
transfer printing process.
Background of the Invention
Currently, expanded plastics have been widely applied in the fields of
commodities, traffics,
In the manufacture of helmets such as those for bicycle, skiing/skating, ice
hockey, mountain
climbing, horse riding, aquatics, industrial uses, and the like, a vacuum
thermoforming process is
Currently, a secondary molding method is adopted for combining the plastic-
expanding
process with the vacuum-hermoforming process, which involves vacuum-forming a
thermoformed
part with specific shape by using a vacuum-thermoforming mold, and then
subjecting said
In view of the above problems in the prior art, the present inventor developed
a one-step
molding method for producing an expanded polypropylene vacuum-thermoformed
product
(Chinese patent application No. 201010568086.X), which comprises silk-screen
printing on a
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vacuum-thermoformed part; and foaming expandable polypropylene materials and
integratedly
molding the expanded polypropylene part with the vacuum thermoformed part. In
accordance with
the method, the expanded polypropylene vacuum-thermoformed product exhibits
improved impact
resistance, and that the production process is also improved.
However, silk-screen printing or ink-jet printing of a molded plastic sheet
involves a procedure
of printing a single color and then drying before printing another color. The
identical procedure has
to be repeated 5-6 times to achieve the semi-product having a colored pattern,
and that the product
thus prepared usually has poor quality.
Similarly, the current water-transfer printing process involves firstly
immersing a
water-transfer printing film with a desired pattern in water, followed by
adhering the immersed film
onto a target substrate, removing the bubbles and water present in between the
film and the
substrate. Once the film adheres completely onto the substrate, it is
subjected to drying process at
45 to 50 C for 2 to 5 hours. After complete drying, the film layer is removed
to obtain the product
having the desired pattern. However, the bubble or water in between the film
and the substrate
cannot be entirely removed, resulting in insufficient adhesion. The quality of
products thus
obtained is not promised with scratch, peeling or even cracking occurred
frequently.
Accordingly, novel methods are still required for producing expanded plastic
products
exhibiting resistance to scratching and peeling.
Summary of the Invention
In order to overcome the problems present in the prior art, the objective of
the present
invention is to provide a method for producing expanded plastic products
exhibiting resistance to
scratching and peeling.
To achieve the objective of the present invention, the present invention
provides a thermal
transfer laminating method, which comprises the following steps:
1) subjecting a plastic sheet to thermal transfer printing process;
2) subjecting the plastic sheet obtained from step 1) to vacuum thermoforming
process to
provide a vacuum-thermoformed part; and
3) foaming an expandable plastic material to provide an expanded part and
laminating the
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expanded part with the vacuum-thermoformed part.
In the above thermal transfer printing process, a plastic sheet is subjected
to thermal transfer
printing instead of skin screen printing, ink-jet printing or water transfer
printing.
The thermal transfer printing process can also be conducted following the
laminating process
in step 3), or conducted once prior to step 2) and once after step 3), under
the requirement.
Thus, in an embodiment, the thermal transfer laminating method of the present
invention may
comprise the following steps:
2) subjecting a plastic sheet to vacuum-thermoforming process to provide a
vacuum-thermoformed part;
3) foaming an expandable plastic material to provide an expanded part and
laminating the
expanded part with the vacuum-thermoformed part; and
4) subjecting the laminated part to thermal transfer printing process.
In another embodiment, the thermal-transfer laminating method of the present
invention may
comprise the following steps:
1) subjecting a plastic sheet to thermal transfer printing process;
2) subjecting the plastic sheet obtained from step 1) to vacuum thermoforming
process to
provide a vacuum-thermoformed part;
3) foaming expandable plastic materials to provide an expanded part and
laminating the
expanded part with the vacuum-thermoformed part; and
4) subjecting the laminated part to thermal transfer printing process.
According to an embodiment of the present invention, a thermal-transfer
printing film is
printed a pattern with ink in the thermal transfer printing process. The ink
is preferably a
commercially available thermal-resistant ink that typically comprises
polyvinyl chloride acrylic
resin as well as solvents and pigments commonly employed in the art. Suitable
ink can be
obtained, for example, from Kenbang Printing Material Factory (Dongguan,
China), which can be
suitably selected by a person skilled in the art according to the actual
requirements for printing.
In a specific embodiment, upon ink-printing, the thermal transfer printing
film with printed
pattern is dried by heating. In an embodiment, after printing with the ink,
the thermal transfer
printing plastic film is subjected to transient heating at about 50 C for
drying.
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The thermal transfer printing film is commercially available. In a specific
embodiment, the
thermal transfer printing film may be a polyethylene terephthalate (PET) film
or a polypropylene
(Oriented Polypropylene, OPP) film.
In the method of the present invention, the pattern printed on said thermal
transfer printing
film is transferred to a plastic sheet by heating. The heating temperature may
range from 150 to
200 C, preferably 160 C. The heating period may from 1 second to 30 seconds.
It should be understood that the plastic sheet employed for the method of the
present invention
may be any materials suitable for thermoforming, including but not limited to
polyvinyl chloride
(PVC) sheets, polycarbonate (PC) sheets and acrylonitrile-butadiene-styrene
(ABS) sheets.
In the method of the present invention, the expandable plastic material
employed in step 3)
may be, but not limited to, expandable polypropylene (EPP), modified
expandable polypropylene,
expandable polystyrene (EPS), modified expandable polystyrene or any
combinations thereof
In the method of the present invention, the laminating process in step 3) may
preferably be
conducted under a pressure ranging from 80kPa to 120kPa.
In the method of the present invention, the laminating process in step 3) may
preferably be
conducted at a temperature ranging from 125 C to 150 C.
In the method of the present invention, the laminating process in step 3) may
preferably be
conducted by heating for 25 seconds to 60 seconds. In a specific embodiment,
the laminating
process in step 3) may involve, for example, steam heating. The time for steam
heating can be
suitably determined by a person skilled in the art according to the properties
desired for the
products such as quality, thickness, and the like.
According to the present invention, said expanded part may be prepared by any
methods
commonly known in the art, for example, injection foaming molding, extrusion
molding or
compression molding. In a preferable embodiment, said expanded part is
prepared by injection
foaming molding. In another embodiment, said expanded part is prepared by
extrusion molding or
compression molding.
The advantages and beneficial effects of the one-step method of the present
invention lie in
that the thus produced vacuum-thermoformed products exhibit an improved
resistance to scratch,
and the production process is more superior.
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Brief Description of the Drawings
Figure 1 is a flow chart showing the thermal transfer laminating method of the
present
invention.
It should be understood that merely the basic steps of the preferable
technical solution of the
present invention are shown in the drawing. Other process steps and
examination procedure can
also be included.
Detailed Description of the Invention
In order to further describe the principle and the structure of the present
invention, detailed
description of the preferred examples of the present invention will be made in
reference to the
accompanying drawing. However, the examples are only provided for illustration
and explanation,
which cannot be construed as a limitation of the protection scope of the
present application.
Example 1
Step 1: Thermal Transfer Printing of Plastic Sheet
1) Transferring the pattern on a thermal transfer printing film (PET film) to
a plastic sheet
by heating at 160 C in a thermal transfer printer (Xingiiarun Printing
Machinery Co., Ltd,
China).
Step 2: Vacuum-Thermoforming and Processing of the Plastic Sheet
1) Baking the plastic sheet obtained from Step 1 at about 95 C for 90
minutes;
2) Adjusting the parameters of a vacuum-thermoforming machine (heating
temperature:
about 500 C; heating period: 18 seconds; cooling period: 10 seconds);
3) Vacuum-thermoforming the baked plastic sheet with a vacuum thermoforming
mold to
obtain a vacuum-thermoformed part with specific shape;
4) Processing the vacuum-thermoformed part, including punching and trimming so
as to
finish the specific shape.
Step 3: Foaming expandable polystyrene and expanded polypropylene (EPS & EPP)
to provide
an expanded part, and laminating the expanded part with the vacuum-
thermoformed part
1) Adjusting the parameters of a foam-molding machine (steaming pressure: 100
kPa;
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steaming period: 35 seconds; cooling period: 120 seconds; vacuum period: 20
seconds;
temperature in the mold during molding: about 130 C);
2) Placing the finished vacuum-thermoformed part into a polyfoam mold;
3) Turning on the machine, feeding the raw materials of EPS & EPP, and
conducting
foaming of EPS & EPP according to the parameter setting to provide an expanded
EPS & EPP
part and laminate the expanded part closely with the vacuum-thermoformed part,
so as to
achieve a product having the polyfoam laminated with the vacuum-thermoformed
part;
4) Upon de-molding, the polyfoam and the vacuum-thermoformed part are closely
bonded together.
Example 2
In the following example, the method of the present invention is exemplified
with modified
expandable polystyrene (EPS; available from: Polysource, US; Japan JSP EPP
Material; Japan
Kaneka; Austria Sunpor) as the raw material. The method comprises the
following four steps:
thermal transfer printing of a plastic sheet, vacuum-thermoforming and
processing of the plastic
sheet, foaming modified expandable polystyrene to provide an expanded part and
laminating the
expanded part with the vacuum-thermoformed part, and thermal transfer printing
process.
Step 1: Thermal Transfer Printing of Plastic Sheet
1) transferring colored pattern on a thermal transfer printing film (PET film)
to a plastic
sheet at 160 C in a thermal transfer printer (Xingiiarun Printing Machinery
Co., Ltd, China).
Step 2: Vacuum Thermoforming and Processing of the Plastic Sheet
1) Baking the plastic sheet obtained from Step 1 at about 95 C for 90
minutes;
2) Adjusting the parameters of the vacuum-thermoforming machine (heating
temperature:
about 500 C; heating period: 18 seconds; cooling period: 10 seconds);
3) Vacuum-thermoforming the baked plastic sheet with a vacuum-thermoforming
mold to
obtain a vacuum-thermoformed part with specific shape;
4) Processing the vacuum-thermoformed part, including punching and trimming so
as to
finish the specific shape.
Step 3: Foaming modified expandable polystyrene to provide an expanded part,
and laminating
the expanded part with the vacuum-thermoformed part
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1) Adjusting the parameters of a foam-molding machine (steaming pressure: 100
kPa;
steaming period: 35 seconds; cooling period: 120 seconds; vacuum period: 20
seconds;
temperature in the mold during molding: about 150 C);
2) Placing the finished vacuum-thermoformed part into a polyfoam mold;
3) Turning on the machine, feeding the raw materials, and conducting foaming
of the
modified expandable polystyrene according to the parameter setting to provide
an expanded
part and laminate the expanded part closely with the vacuum-thermoformed part,
so as to
achieve a product having the modified expanded polystyrene polyfoam laminated
with the
vacuum-thermoformed part;
4) Upon de-molding, the modified expanded polystyrene and the vacuum-
thermoformed
part are closely bonded together.
Step 4: thermal-transferring the colored pattern on a thermal transfer
printing film (PET film)
onto the molded helmet in a thermal transfer printer (Xingjiarun Printing
Machinery Co., Ltd, China)
at 150 C to 200 C.
In Step 3 of Examples 1 and 2 above, the expandable polystyrene or the
modified expandable
polystyrene is molded by injection foaming process. However, it should be
understood that the
expandable polystyrene and the modified expandable polystyrene can be molded
by any other
methods capable of producing the desired shape, such as extrusion molding,
compression molding
and the like.
The peeling resistance of the products obtained from Examples 1 and 2 were
tested according
to the standard method of National standard GBT9286-1998 or ASTM D3359-09. The
testing
results showed that all the products passed the standard tests and achieved at
least the level of ISO
Classification 2 (or Classification 3B in ASTM D3359-09). That is, the
resistance to peeling of
the product according to the present invention is up to the satisfying level.
In contrast, under the same conditions, the products obtained by replacing the
thermal transfer
printing with water transfer printing process exhibited poor resistance to
peeling, and did not
achieve the level of ISO Classification 2 (or Classification 3B in ASTM D3359-
09). In other
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words, the products obtained with water transfer printing process did not pass
the standard test.
Although the embodiments of the present invention have been described in
details, it should be
understood that various alterations or modifications may be made therein
without departing from
the spirit or scope of the invention, and that all modifications or
alternatives equivalent thereto are
within the spirit and scope of the invention as set forth in the appended
claims.
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