Printing – Stenciling – Processes
Reexamination Certificate
1999-05-26
2001-01-23
Yan, Ren (Department: 2854)
Printing
Stenciling
Processes
C101S123000
Reexamination Certificate
active
06176179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screen printer for screen printing. Particularly, the present invention relates to the screen printer which does not result in uneven printing.
2. Background Art
The drawing of
FIG. 7
illustrates a perspective side view of the actual screen printer.
The drawing of
FIG. 8
outlines a lateral view of the screen printer.
The drawing of
FIG. 9
outlines a plane view of the screen printer.
FIG. 7
illustrates the following elements: a screen printer
101
; a base
102
of the screen printer; a movable table
103
attached to allow for a movement; a guide rail
104
for guiding the movement of movable table
103
; an operating box
105
of the screen printer; an operating switch
107
attached to the operating box; and a printing unit
109
for printing a work placed on the movable table
103
.
FIGS. 8 and 9
illustrate the following elements: a work
110
placed on top of the movable table
103
; a screen plate
200
; a screen frame
201
of the screen plate
200
; a screen
211
affixed to the screen plate
200
; a slider
106
holding a squeegee
111
and a scrapper (not illustrated), for sliding in directions indicated by arrows A and D; and frames
108
for sliding the slider
106
.
The movable table
103
is situated on the guide rail
104
which is laid to the base
102
so that the movable table
103
can move along the guide rail
104
, sliding from side to side. When the movable table
103
moves beneath the printing unit
109
, the movable table
103
is stopped by a stopper which is not illustrated, and then the printing unit
109
performs a screen print on the work
110
.
Suction holes
190
are installed to the movable table
103
. The work
110
is stuck to the movable table
103
by sucking up the air through the suction holes
190
as indicated by the arrows.
The drawing of
FIG. 10
illustrates printing states of the printing unit
109
.
An ink
51
is applied uniformly on top of the screen
211
.
In
FIG. 10
, state (a) illustrates a state before commencing the printing. There is a distance
95
between the screen
211
and the work
110
. In
FIG. 10
, state (b) illustrates a case of starting the printing by applying a pressure P to the squeegee
111
. In
FIG. 10
, state (c) illustrates a case of printing a pattern
52
, pattern
53
and pattern
54
onto the work
110
in accordance to pre-made patterns of the screen
211
. In
FIG. 10
, state (d) illustrates completion of the printing. During the states (b) to (d) of
FIG. 10
which illustrate printing in progress, the pressure P applied to the squeegee
111
is constant as illustrated in graph (e) of FIG.
10
.
While printing as shown in
FIG. 10
, there is a case when a height H
1
of the pattern
52
and a height H
2
of the pattern
54
illustrated in state (d) of
FIG. 10
may become different. Although the screen
211
is firmly affixed to the screen frame
201
, a tension varies in different places of the screen
211
. Therefore, even if a constant pressure P is applied from above to down, the printed heights of the patterns may vary depending on the position printed, or in other words, the heights of printed ink may become different. There is a problem of unevenness in the spread of the ink on the work
110
or a problem of uneven printing.
The drawing of
FIG. 11
illustrates a method to resolve the previously described unevenness in the spread of the ink.
When the printing is in progress, a lifting apparatus (screen detaching apparatus) not illustrated is used to lift the screen plate
200
in a direction of arrow X (H
10
<H
20
<H
30
). By lifting the screen plate
200
from a side where the screen printing is finished, the conventional screen printer offsets a change in the tension on different positions of the screen
211
. As a result of this, the height H
1
of pattern
52
printed at the edge of the work
110
and the height H
2
of pattern
54
printed at the center of the work
110
can be made almost equal.
However, by using this method of lifting one side of the screen plate
200
as illustrated in
FIG. 11
, a pressure is applied to the screen plate
200
more than necessary. Due to this, a position of printing the pattern installed to the screen
211
may be displaced, and a durability of the screen plate
200
may be reduced.
The present invention attempts to solve the problems mentioned above by aiming to achieve a screen printing for even printing to the work
110
without having to use the lifting apparatus.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a screen printer for screen printing using a squeegee comprises: a position detecting unit for detecting a squeegee moving position during the screen printing; a pressure unit for applying a pressure to the squeegee during the screen printing; and a pressure control unit for controlling the pressure of the pressure unit depending on the squeegee moving position detected by the position detecting unit.
According to another aspect of the present invention, the screen printer includes the pressure control unit which reduces a pressure applied to a center area of squeegee movement to be smaller than a pressure applied to edges of the area of squeegee movement.
According to another aspect of the present invention, the screen printer includes the pressure control unit which changes the pressure smoothly.
According to another aspect of the present invention, the screen printer comprises the position detecting unit which includes a sensor which can change its setting position along a direction of the squeegee movement.
According to another aspect of the present invention, the screen printer comprises the pressure unit which includes an air pump for generating a compressed air; a valve for allowing a passage of the compressed air; and an air cylinder for applying the pressure to the squeegee by inputting the compressed air through the valve. The pressure control unit adjusts a degree of opening and closing of the valve.
According to another aspect of the present invention, the screen printer comprises the pressure unit which includes a motor which generates the pressure.
According to another aspect of the present invention, the screen printer comprises the position detecting unit which includes a sensor which detects a number of motor rotations involved in the squeegee movement.
According to another aspect of the present invention, the screen printer comprises the pressure control unit including a program which calculates the pressure based on the squeegee moving position and one of a screen size, a screen tension, a work size, and a distance between work and screen.
According to another aspect of the present invention, a screen printing method for screen printer using a squeegee, comprises steps of: detecting a squeegee moving position during the screen printing; applying a pressure to the squeegee during the screen printing; and controlling the pressure depending on the squeegee moving position detected.
According to another aspect of the present invention, the screen printing method includes the pressure controlling step which reduces a pressure applied to a center area of squeegee movement to be smaller than a pressure applied to edges of the area of squeegee movement.
According to another aspect of the present invention, the screen printing includes the pressure controlling step which changes the pressure smoothly.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5483884 (1996-01-01), Vellanki
patent: 5893325 (1999-04-01), Sakai
patent: 7185429 (1993-12-01), None
Micro-Tec Company Ltd.
Yan Ren
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