Title: Method of manufacturing plastic thin-plate article with protrusions on surface thereof
Abstract: A method of manufacturing a diffusion plate for use in a screen plate of projection TV is disclosed. The diffusion plate having a plurality of quadrangular pyramid protrusions almost over one side thereof is manufactured by means of injection molding process of plastic material. This method uses a first molding die having a first molding die surface, a pre-molding die capable of forming a first volume of molding cavity in matching with the first molding die, and a second molding die capable of forming a second volume of molding cavity smaller than the first volume in matching with the first molding die. The molding process comprises; a first step of, with matching the first molding die with the pre-molding die, injecting a molten plastic material from the injection port into the first volume of molding cavity formed between the first molding die and the pre-molding die; and the second step of, after completed the injection in the first step and before curing of the plastic material, releasing the first molding die from the pre-molding die and then matching the first molding die with the second molding die, wherein the plastic material injected in the first step is compressed in the second volume of molding cavity so as to mold the diffusion plate from the plastic material between the first molding die and the second molding die.
Patent Number: 6,858,165 Issued on 02/22/2005 to Hirota, et al.
| Inventors:
|
Hirota; Kashichi (Hachioji, JP);
Fukuda; Junji (Hachioji, JP)
|
| Assignee:
|
Kyowa Electric and Chemical Co. Ltd. (Tokyo, JP)
|
| Appl. No.:
|
760162 |
| Filed:
|
January 12, 2001 |
| Current U.S. Class: |
264/2.2; 264/2.5; 264/319; 264/328.1 |
| Intern'l Class: |
B29D 011//00 |
| Field of Search: |
264/319,320,328.1,328.7,328.8,1.1,2.2,2.5,2.7,1.32
|
References Cited [Referenced By]
| Foreign Patent Documents |
| 59-67008 | Apr., 1984 | JP.
| |
| 60-31930 | Feb., 1985 | JP.
| |
| 01-85010 | Jun., 1989 | JP.
| |
| 02-98416 | Apr., 1990 | JP.
| |
| 05-173253 | Jul., 1993 | JP.
| |
| 06-114860 | Apr., 1994 | JP.
| |
| 10-249898 | Sep., 1998 | JP.
| |
Primary Examiner: Vargot; Mathieu D.
Attorney, Agent or Firm: Cohen, Pontani, Lieberman & Pavane
Parent Case Text
This application is a Continuation Application under 35 USC 371 of
International Application No. PCT/JP98/03507 filed on 6 Aug. 1998.
Claims
What is claimed is:
1. A method of manufacturing a thin-plate article having at least one
surface, with at least a part of the at least one surface of the
thin-plate article being formed into a particular shape, by molding from a
plastic material, said method comprising steps of:
preparing a first molding die having a first molding die surface;
preparing a pre-molding die which is capable of matching with said first
molding die and forming a first volume of molding cavity in matching with
said first molding die, and which has an injection port for injecting a
plastic material into said molding cavity; and
preparing a second molding die which is capable of matching with said first
molding die and forming a second volume of molding cavity smaller than
said first volume in matching with said first molding die, and which has a
second molding die surface facing to said second volume of molding cavity;
with matching said first molding die with said pre-molding die, injecting a
molten plastic material from said injection port into said first volume of
molding cavity formed between said first molding die and said pre-molding
die; and
after completion of said injecting step and before curing of said plastic
material, releasing said first molding die from said pre-molding die and
then matching said first molding die with said second molding die, wherein
said plastic material injected in said injecting step is compressed in
said second volume of molding cavity so as to mold the plastic material
article between said first molding die and said second molding die.
2. A method of manufacturing a thin-plate article having a at least one
surface, with at least a part of the at least one surface of the
thin-plate article being formed into a particular shape, by molding from a
plastic material, said method comprising steps of:
preparing a first molding die having a first molding die surface; and
preparing a second molding die which is capable of matching with said first
molding die and forming a molding cavity in matching with said first
molding die, and which has a second molding die surface facing to said
molding cavity;
with releasing said second molding die from said first molding die,
supplying a plastic material having flowability onto a plurality of
portions on said first molding die surface of said first molding die to
spread said plastic material over said first molding die surface by the
flowability of said plastic material, said plastic material being supplied
at two portions on each of two crossing diagonal lines whereby the plastic
material is supplied at four portions; and
matching said second molding die with said first molding die to form said
molding cavity, wherein said plastic material filled in said molding
cavity in advance is cured under compression.
3. A method as defined in claim 2, wherein said plastic material is further
supplied to a portion adjacent to a crossed point of said two diagonal
lines.
4. A method as defined in claim 1, wherein said thin-plate article is a
diffusion plate having quadrangular pyramid protrusions.
5. A method as defined in claim 1, wherein said thin-plate article is a
Fresnel lens.
6. A method as defined in claim 2, wherein said thin-plate article is a
diffusion plate having quadrangular pyramid protrusions.
7. A method as defined in claim 2, wherein said thin-plate article is a
Fresnel lens.
Description
TECHNICAL FIELD
The present invention relates to a method of manufacturing a thin-plate
article made of a plastic material. More particularly, the present
invention relates, but is not limited, to a method suitable for
manufacturing a Fresnel lens or a diffusion plate fit to use in a
projection TV screen plate.
BACKGROUND ART
A conventional projection TV includes a structure shown in FIG. 1. More
specifically, a projected image from an image projection tube 1 is
reflected by a mirror 2 and then focused onto a screen plate 3. As shown
in FIG. 2(a), the screen plate 3 is comprised of a Fresnel lens 4, a
diffusion plate 5 and a protecting plate 6. As shown in FIGS. 2(b) and
2(c), the diffusion plate 5 includes a plurality of angle protrusions 7
which are formed in parallel with each other and which extend in the
longitudinal direction of the diffusion plate 5. The protecting plate 6 is
formed of a transparent plastic plate.
In addition to a diffusion function, the angle protrusions 7 of the
diffusion plate 5 have a lens effect by which the projected image is
zoomed in the lateral direction of the diffusion plate 5. The protecting
plate 6 is originally provided to protect a diffusion surface of the
diffusion plate 5 from scratch or dust. However, since the protecting
plate 6 is the transparent plate having a flat surface, surrounding
lighting equipment tends to project with the eventual image, resulting in
visually unclear image. Thus, a surface of the protecting plate 6 exposed
outside is desirable to be a frosted surface having a microscopic
irregularity. A surface of the diffusion plate 5 opposite to the diffusion
surface thereof may also be formed in a frosted surface to expose outside
without providing the protecting plate 6 separately
In view of cost and weight, it is desirable to mold the Fresnel lens 4, the
diffusion plate 5 and the protecting plate 6, all of which are components
of such a screen plate 3, from a plastic material. However, it is not easy
to mold a thin-plate article having a microscopic irregular pattern on the
surface thereof from a plastic material.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of
manufacturing a plastic material thin-plate article with irregularity on a
surface thereof, such as a Fresnel lens, a diffusion plate, or the like,
for used in a screen plate of a projection TV.
In order to achieve the aforementioned object, according to the present
invention, there is provided a method of manufacturing a thin-plate
article having protrusions, which are formed almost over at least one
surface of the thin-plate article, by molding from a plastic material. In
a method according to one aspect of the present invention, the method
comprises a step of firstly preparing: a first molding die having a first
molding die surface; a pre-molding die which is capable of matching with
the first molding die and forming a first volume of molding cavity in
matching with the first molding die, and which has an injection port for
injecting a plastic material into the molding cavity; and a second molding
die which is capable of matching with the first molding die and forming a
second volume of molding cavity smaller than the first volume in matching
with the first molding die, and which has a second molding die surface
facing to the second volume of molding cavity. The molding process
comprises; a first step of, with matching the first molding die with the
pre-molding die, injecting a molten plastic material from the injection
port into the first volume of molding cavity formed between the first
molding die and the pre-molding die; and the second step of, after
completed the injection in the first step and before curing of the plastic
material, releasing the first molding die from the pre-molding die and
then matching the first molding die with the second molding die, wherein
the plastic material injected in the first step is compressed in the
second volume of molding cavity so as to mold a plastic material article
between the first molding die and the second molding die.
In a method according to another aspect of the present invention, the
method comprises a step of firstly preparing: a first molding die having a
first molding die surface; and a second molding die which is capable of
matching with the first molding die and forming a molding cavity in
matching with the first molding die, and which has a second molding die
surface facing to the molding cavity. Then, with releasing the second
molding die from the first molding die, supplying a plastic material
having flowability onto a plurality of portions on the first molding die
surface of the first molding die to spread the plastic material over the
first molding die surface by the flowability of the plastic material.
Then, matching the second molding die with the first molding die to form
the molding cavity, wherein the plastic material filled in the molding
cavity in advance is cured with compressed.
In a method according to yet other aspect of the present invention, the
method comprises a step of firstly preparing: a first molding die having a
first molding die surface; and a second molding die which is capable of
matching with the first molding die and forming a molding cavity in
matching with the first molding die, and which has a second molding die
surface facing to the molding cavity. Then, with releasing the second
molding die from the first molding die, linearly supplying a plastic
material having flowability via an elongated nozzle onto the first molding
die surface of the first molding die, and simultaneously moving the nozzle
and the first molding die relatively in the lateral direction each other,
to spread the plastic material over the first molding die surface. Then,
matching the second molding die with the first molding die to form the
molding cavity, wherein the plastic material filled in the molding cavity
in advance is cured with compressed.
In a method of still other aspect of the present invention, the method
comprises a step of preparing: a plastic material supply station; a first
molding station provided adjacently to the plastic material supply
station; a second molding station provided adjacently to the plastic
material supply station in a different position from that of the first
molding station; a first molding die provided respectively in association
with each of the first molding station and the second molding station, the
first molding die being movable between the associated molding station and
the plastic supply station, the first molding die having a first molding
die surface; a second molding die provided at each of the first molding
station and the second molding station, the second molding die being
capable of matching with the first molding die and forming a molding
cavity in matching with the first molding die, the second molding die
having a second molding die surface facing to the molding cavity; and an
elongated nozzle provided at the plastic material supply station. Then,
firstly moving the first molding die associated with the first molding
station to the plastic material supply station; linearly supplying a
plastic material having flowability via an elongated nozzle onto the first
molding die surface of the first molding die, and simultaneously moving
the nozzle and the first molding die relatively in the lateral direction
each other, to spread the plastic material over the first molding die
surface. Then, moving the first molding die associated with the first
molding station to the first molding station; matching the second molding
die provided at the first molding station with the first molding die which
has been moved to the first molding station to form the molding cavity,
wherein the plastic material filled in the molding cavity in advance is
cured with compressed. In this method, during the latter step(s), moving
the first molding die associated with the second molding station to the
plastic material supply station, and performing the same steps mentioned
above to spread the plastic material over the first molding surface of the
first molding die associated with the second molding station.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal-sectional view showing a schematic construction of
a typical conventional projection TV;
FIG. 2 shows a screen plate of the conventional projection TV, wherein FIG.
2(a) is a longitudinal-sectional view showing an overall construction of
the screen plate, FIG. 2(b) is a partial top plan view thereof, and FIG.
2(c) is a cross-sectional view thereof;
FIG. 3 shows one example of a diffusion plate for use in a screen plate
according to the present invention, wherein FIG. 3(a) is a partially
enlarged top plan view of the diffusion plate and FIG. 3(b) is a partially
perspective view thereof;
FIG. 4 shows another embodiment of a diffusion plate for use in the screen
plate according to the present invention, wherein FIG. 4(a) is a partially
enlarged top plan view of the diffusion plate and (b) is a partially
perspective view thereof;
FIG. 5 is a longitudinal-sectional view of an embodiment of the screen
plate according to the present invention;
FIG. 6 shows manufacturing steps of the diffusion plate for use in the
screen plate according to the present invention, wherein FIG. 6(a) shows a
first step and FIG. 6(b) shows a second step;
FIG. 7 shows other embodiment of the method according to the present
invention, wherein FIG. 7(a) is a top plan view of the device for use in
the method and FIG. 7(b) is a partially sectional side view thereof;
FIG. 8 is a top plan view showing an example of a device for use in an
alternative method of the embodiment in FIG. 7;
FIG. 9 shows yet other embodiment according to the present invention,
wherein FIG. 9(a) is a top plan view of a device for use in the method and
FIG. 9(b) is a partially sectional side view thereof; and
FIG. 10 is a side view of a molding device showing still other embodiment
according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The embodiments of the present invention will now be described with
reference to the drawings. FIG. 3(a) and FIG. 3(b) show one example of a
diffusion plate manufactured by a method of the present invention. As
shown in the drawings, the diffusion plate 5 includes protrusions 5a, each
of which is formed in quadrangular pyramid and which are arranged in the
longitudinal and lateral directions alongside each other almost over a
surface of the diffusion plate 5. The quadrangular pyramid protrusions 5b
may be arranged at a slant or in the diagonal direction as shown in FIG.
4(a) and FIG. 4(b). In such diffusion plates 5, it is preferable to make
an opposite surface to the surface having the protrusions 5a or 5b into a
frosted surface.
FIG. 5 shows one example of a screen plate using the diffusion plate
manufactured by a method according to the present invention. The diffusion
plate 5 is positioned to make the surface having the protrusions 5a face a
lens surface of a Fresnel lens 4 and is fixed to the Fresnel lens 4 by
means of bonding or the like. The diffusion plate 5 having the protrusions
5b can be positioned and fixed in the same manner. The arrow in FIG. 5
shows the direction of visual observation.
FIG. 6 shows a method according to a first aspect of the present invention
for manufacturing the aforementioned diffusion plate 5 for use in the
screen plate by molding from a plastic material. Dies for use in
manufacturing the diffusion plate 5 comprises an upper die having a
pre-molding recessed portion 6a, i.e. a pre-molding die 6, a lower die 7
having a molding recessed portion 7a formed with a molding surface, and an
upper die 8 having a molding recessed portion 8a formed with a molding
surface. A gate 6b for injecting a molten plastic material therethrough is
formed in the center of the pre-molding die 6. A plastic material
injection cylinder 9 is provided at a gate 6b. The recessed portion 6a of
the pre-molding upper die 6 and the raised portion 7a of the lower die 7
are adapted to form an excess area 10 outside of the molding area for the
diffusion plate. With matching the pre-molding upper die 6 with the lower
die 7, a first volume of pre-molding cavity 11 is formed therebetween.
The molding upper die 8 and the lower die 7 can be moved from the position
shown in FIG. 6(b) downward and upward respectively to match closer with
each other. Thus, with matching the molding upper die 8 with the lower die
7, a smaller volume of molding cavity 11a than that of the first volume is
formed therebetween.
In manufacturing, as shown in FIG. 6(a), the pre-molding upper die 6 and
the lower die 7 are matched with each other and retained to form the
pre-molding cavity 11. Then, a molten or softened plastic material is
injected from the plastic injection cylinder 9 held at the gate 6b. The
plastic material may include methylmethacrylate, polycarbonate,
polystyrene or the like.
When a predetermined amount of the molten or softened plastic material is
injected into the pre-molding cavity 11, the injection is stopped. Then,
the lower die 7 is released from the pre-molding upper die 6 and moved
under the molding upper die 8 as the state shown in FIG. 6(b), with
retaining the injected plastic material within the recessed portion 7a.
Then, the lower die 7 is moved upward and matched with the upper die 8 to
form the molding cavity 11a. By virtue of this operation, the injected
plastic material is compressed within the smaller volume of molding cavity
11a than that of the pre-molding cavity 11 shown in FIG. 6(a), and molded
by the molding surfaces of the recessed portions 7a and 8a. In this step,
an excess plastic material in the molding cavity 11a is extruded into the
surrounding excess area 10. Thus, according to this method, the surface
having the quadrangular pyramid protrusions 5a and 5b and the opposite
frosted surface of the diffusion plate surface can be simultaneously
molded.
FIG. 7(a) and FIG. 7(b) show another embodiment of the present invention.
In this embodiment, a lower die 7 has the same structure as that of the
previous embodiment. While not shown in the drawings, the same structure
as the upper die 8 in the previous embodiment is applied as an upper die
of this embodiment. In this embodiment, a nozzle device 12 is provided to
supply a plastic material to the lower die 7. The nozzle device 12 has a
nozzle block 13 in which an X-shaped injection manifold 14 is provided
extending along two crossing diagonal lines 13a and 13b. An injection
nozzle 15 is placed at each end of the X-shaped injection manifold 14. The
injection nozzle 15 is composed of a known structure opened/closed by a
cutoff pin 16 in which the plastic material from the injection manifold 14
is discharged from the nozzle 15 when the cutoff pin 16 is pulled in to
open the nozzle opening. An injection passage 18 extending from a plastic
material injection cylinder 17 is connected to a crossed portion of the
X-shaped injection manifold 14.
In manufacturing a plastic material thin-plate article, firstly, with
releasing the lower die 7 from the upper die (not shown), the lower die 7
is located under the nozzle device 12. Then, the injection cylinder 17 is
activated to supply the molten and fluidic plastic material from the
injection nozzle 15 onto the molding recessed portion 7a of the lower die
7. The plastic material supplied onto the molding recessed portion 7a of
the lower die 7 is spread over the molding surface of the molding recessed
portion 7a of the lower die 7 due to flowability of the plastic material.
Then, the cutoff pin 16 is moved in its closing position to close the
nozzle 15, and the nozzle device 12 is separated from the lower die 7. The
lower die 7 is then moved under the upper die, and the same steps as those
of the previous embodiment are performed to mold between the lower die 7
and the upper die.
FIG. 8 shows an alternative example of the embodiment shown in FIG. 7. In
this embodiment, in addition to four nozzles 15, the X-shaped injection
manifold 14 provided at the nozzle block 13 of the nozzle device 12 is
provided with a further nozzle 15a adjacently to a central portion of the
X-shape, i.e. the crossed portion of the two diagonal lines. Other
construction is same as in the embodiment shown in FIG. 7.
FIG. 9(a) and FIG. 9(b) show yet other embodiment according to the present
invention. In this embodiment, a nozzle device 21 is applied as substitute
for the nozzle device 12 of the embodiment shown in FIG. 7. A molding
lower die 7 and a molding upper die (not shown) are in the same structure
as those of respective the previous embodiments. The nozzle device 21
includes a nozzle 22 having an elongated slit type of discharge opening
22a, and an plastic material extruding cylinder or a plastic material
extruding screw 23 is connected to the nozzle 22. The nozzle device 21 and
the lower die 7 can be moved relatively to each other. In this embodiment,
the lower die 7 is moved laterally with respect to the nozzle device 21 as
shown by the broken line in FIG. 9(b).
As shown in FIG. 9(a), the nozzle 22 is positioned to allow the slit type
discharge opening 22a to extend in the width direction of the molding
recessed portion 7a of the molding lower die 7. A gear pump 24 is
positioned above the nozzle 22 in communicate with a plastic material
passage within the nozzle 22. In operation, the extruding cylinder or
extruding screw 23 is activated to supply the molten plastic material to
the nozzle 22. The plastic material is then supplied from the discharge
opening 22a of the nozzle 22 onto the molding recessed portion 7a of the
lower die 7. During this operation, the lower die 7 is moved relatively to
the nozzle device 21 as shown by the broken line in FIG. 9(b). Thus, the
plastic material is linearly supplied and spread in the width direction of
the molding recessed portion 7a of the lower die 7 due to flowability of
the plastic material. When the lower die 7 is moved relatively to the
nozzle device 21, the plastic material is supplied and spread almost over
the entire area in the longitudinal direction of the molding recessed
portion 7a of the lower die. Then, the extruding cylinder or extruding
screw 23 is then deactivated, and the gear pump 24 is activated to suck
back a residual molten plastic material in the nozzle 22. This enables to
prevent the plastic material from dropping down from the discharge opening
22a of the nozzle 22. Then, the lower die 7 is moved under the upper die
(not shown) and the same steps as those of the previous embodiments are
performed to mold.
FIG. 10 shows one application of the embodiment of FIG. 9. The device for
use in this method includes a nozzle device 21 similar to that shown in
FIG. 9, in a plastic material supply station S. A first molding station A
is provided adjacently to one side of the plastic material supply station
S, while a second molding station B is provided adjacently to another side
of the plastic material supply station S. Each of the first and second
molding stations A and B is provided with an upper die 8 which is
vertically movable. Each of the molding stations A and B also has a lower
die 7 which is movable between each of the molding stations and the
plastic material supply station S. With respect to the nozzle device 21 of
the plastic material supply station S, a leveling roller 25a rotating in
the direction of the arrow "a" of FIG. 10 is positioned on the side of the
first molding station A, while a leveling roller 25b in the direction of
the arrow "b" is positioned on the side of the second molding station B.
In the method of the present invention applying the device shown in FIG.
10, the lower die 7 associated with the first molding station A is firstly
moved under the nozzle device 21 of the plastic material supply station S.
Then, the molten plastic material is linearly supplied to the molding
surface 7a of the lower die 7 in the same steps as described for FIG. 9.
During these steps, the lower die 7 is moved to the direction of the first
molding station A as shown by the arrow "c" in FIG. 10 and the plastic
material is then supplied onto the almost entire surface of the molding
surface 7a of the lower die 7. The molten plastic material supplied onto
the molding surface 7a of the lower die 7 is leveled by the leveling
roller 25b rotating in the direction of the arrow "a". When the supply of
the plastic material is completed, the extruding cylinder or the extruding
screw 23 is stopped, the molten plastic material in the nozzle 22 is
sucked back by the gear pump 24.
Then, the lower die 7 is moved back to the first molding station A and the
upper die 8 of the first molding station A is moved downward to a position
in which the upper die 8 is matched with the lower die 7. Then, in the
molding cavity formed between the upper die and the molding surface 7a of
the lower die 7, the plastic material is molded. During these steps, the
lower die 7 of the second molding station B is moved to the plastic
material supply station S and the molten plastic material is supplied onto
the molding surface 7a of the lower die 7 in the same operation described
above. This method is effective to enhance the manufacturing efficiency.
According to the method of the present invention, a thin-plate plastic
material article having a microscopic irregular pattern on the surface
thereof can be easily manufactured. When the diffusion plate shown in FIG.
3 is applied, there is no need to provide a protecting plate outside of
the screen plate, resulting in simplified structure. Providing a frosted
surface on the opposite surface to the surface having protrusions of the
diffusion plate enables to solve the problem that the image becomes
visually unclear due to reflected surrounding light. The method of the
present invention has a significant effect on forming the Fresnel lens and
the diffusion plate having irregularity on large and flat surface thereof
without any problems.
While the present invention has been described in connection with specific
embodiments with reference to the drawings, the present invention is not
limited to the illustrated specific embodiments and various modifications
and variations may be made within the scope of the spirit of the present
invention according to the claims. Thus, the present invention is limited
not by the illustrated specific structure but only by the appended claims.
*
