Method of forming a protective film on a coated surface and apparatus for carrying out the same

A coating nozzle (3) movable in a horizontal direction perpendicular to an advancing direction of a vehicle body (1) drops or trickles a strippable paint linearly along one side of the periphery of an area to be protected, and an air blow-off unit (4) blows off air (F) at a predetermined angle against a surface to which the strippable paint is applied, whereby the strippable paint is spread over the area to be protected, and when the thus spread strippable paint becomes dry, it forms a protective film. The strippable paint is prevented from adhering to a portion other than the area to be protected, and the protective film of strippable paint has a uniform thickness.

This is a national stage application of PCT/JP95/02612, filed Dec. 20, 
1995. 
TECHNICAL FIELD 
The present invention relates to a method and apparatus for forming a 
protective film on a coated surface to temporarily protect the same, and 
more particularly to such a method and apparatus in which a liquid 
strippable paint is applied onto a coated surface of an entire car, for 
example, to form a protective film for temporarily protecting the coated 
surface while the entire car is transported. 
BACKGROUND ART 
One known method of temporarily protecting a coated surface of an entire 
car during the delivery or shipping of the entire car is disclosed, for 
example, in Japanese Patent Laid-Open Publication No. 6-142604, entitled 
"Method of Temporarily Protecting a Film of Coating on Vehicle Body". In 
this disclosed method, an area to be protected, such as the hood, roof or 
trunk of a vehicle body is coated along its peripheral edge with a 
strippable paint of a fixed width applied by a roller or a brush, and 
before or after such coating, the strippable paint is coated by spraying 
over an area which is narrower than the area to be coated and hence 
bordered by the roller- or brush-coated strippable paint so that the 
roller- or brush-coated paint layer and the spray-coated paint layer 
overlap with each other. 
According to this method, since the strippable paint is spray-coated on an 
area narrower than the area to be protected, the efficiency of the coating 
work can be improved with the resulting simplification of following or 
subsequent working processes attained. 
In the prior art, however, since dust of the paint being spayed scatters 
widely, the overlapped coating portion formed by coating the strippable 
paint with the roller or the brush must have an increased area which will 
increase the cost. 
Furthermore, since the paint dust scattering about beyond the overlapped 
coating portion may adhere to a portion other than the area to be 
protected, an appropriate masking process and a process for inspection and 
correction or mending become necessary. As a result, an increase in cost 
is not avoidable. 
In the case of an article having a large area to be coated, such as an 
automobile, the strippable paint as it is coated by the roller or the 
brush tends to become irregular in thickness, resulting in rupture or 
removal of a protective film of the strippable paint. 
With the foregoing drawbacks in view, an object of the present invention is 
to provide a method and apparatus for forming a protective film on a 
coated surface with a uniform thickness and at a high coating efficiency 
while preventing a strippable paint from adhering to a portion other than 
an area to be protected. 
DISCLOSURE OF THE INVENTION 
The above object can be achieved, according to the present invention, by a 
method of forming a protective film on a coated surface for temporarily 
protecting the same, characterized by comprising the steps of: trickling 
or dripping a strippable paint onto the coated surface linearly along one 
side of the periphery of an area to be protected; and blowing the air from 
the above obliquely against the surface to which the strippable paint is 
applied, for causing the strippable paint to spread over the area to be 
protected and then eventually become dry to form a protective film. 
In the case where the strippable paint has a high viscosity or is quick at 
dry, the blow-off air is preferably humidified air. 
It is further preferable that dehumidified air is blown against the 
strippable paint after it is spread over the area to be protected. The 
dehumidified air thus blown after the humidified air ensures further 
spreading of the strippable paint and accelerated drying of the strippable 
paint. 
The angle at which air is blown is in the range of 55.degree. to 
65.degree., and preferably 60.degree.. 
It is preferable that the method further includes the step of coating the 
strippable paint on with a roller or a brush along the periphery of the 
area to be protected so as to form an overlap between a coating portion 
formed by this roller- or brush-coating step and a coating portion formed 
by said blowing-step. With the overlapped coating portion thus formed, the 
aesthetical appearance of a visual boundary portion is improved. 
Preferably, the air is blown in such a direction that stream or air blown 
from left and right sides of a central portion are directed inwardly to 
cross streams of air blown from the central portion. This arrangement is 
advantageous because the strippable paint is prevented from flowing 
outward beyond the area to be protected. 
An apparatus of the invention for carrying out the method comprises: a 
coating nozzle movable in a horizontal direction perpendicular to an 
advancing direction of an article to be coated for delivering a strippable 
paint onto the article; an air blow-off unit for blowing air at a 
predetermined ejection angle in the range of 55.degree. to 65.degree., and 
preferably 60.degree., against the article; a longitudinally movable frame 
structure carrying thereon the coating nozzle and the air blow-off unit 
and movable in a direction parallel to the advancing direction of the 
article; and a vertically movable frame structure carrying thereon the 
longitudinally movable frame structure and movable in a direction of the 
height of the article. 
It is preferable that the air blow-off unit is composed of a central block, 
a left block and a right block each having at its bottom a plurality of 
air nozzles, and that streams of air blown from the left and right blocks 
are directed inwardly to cross streams of air blown from the central 
block. 
The air blow-off unit has an open delivery end preferably composed of a 
multiplicity of aligned holes. 
The coating nozzle moves in the horizontal direction perpendicular to the 
advancing direction of the article to be coated while trickling or 
dripping the strippable paint linearly onto a coated surface. The air 
blow-off unit ejects or blows air in a direction opposite to the advancing 
direction of the article and at the predetermined ejection angle with 
respect to a coated surface to spread out the trickled paint within the 
area to be protected. 
Then, the longitudinally movable frame structure carrying thereon the 
coating nozzle and the air blow-off unit is moved in the direction 
opposite to the advancing direction of the article. Thereafter, the 
coating nozzle moves again in the horizontal direction while trickling the 
strippable paint on the coated surface. The trickled paint is subsequently 
spread out within the area to be protected by blowing air from the air 
blow-off unit onto the coated surface at the predetermined angle and in 
the direction opposite to the advancing direction of the article. 
The foregoing cycle of operations is repeated until the strippable paint is 
coated uniformly over the entire area to be coated. 
In the case of an air blow-off unit which is composed of an air nozzle for 
ejecting or blowing humidified air and an air nozzle for ejecting or 
blowing dehumidified air, even when the strippable paint used is of the 
type having a high viscosity or becomes dry easily, the humidified air 
forces the trickled paint to spread over the coated surface within the 
area to be protected, and subsequently the dehumidified air effects 
further spreading and thinning of the strippable paint while promoting 
drying of the strippable paint.

BEST BODE FOR CARRYING OUT THE INVENTION 
The present invention will now be described below in greater detail with 
respect to one embodiment shown in the accompanying sheets of drawings. 
A protective film forming apparatus for carrying out a method of forming a 
protective film on a coated surface according to the present invention is 
shown in FIGS. 1 through 3. The protective film forming apparatus 
comprises a portal or gantry-like framework 2 of a size large enough to 
permit passage therethrough of a vehicle body 1 while being conveyed by a 
conveyor (not shown), a coating nozzle 3 for dropping or trickling a 
strippable paint down onto a coated surface of the vehicle body 1 to be 
protected, and an air blow-off unit 4 for blowing or ejecting air against 
the strippable paint trickled from the coating nozzle to spread the 
strippable paint over an area to be protected. In FIGS. 1-3, an orthogonal 
coordinates system (X, Y, Z) is shown. 
The coated surface of the vehicle body 1 includes areas or portions over 
which a protective film is to be formed, these portions being composed, 
for example, of a hood A, a roof B and a trunk lid C, as shown in FIG. 4. 
The strippable paint is preferably of the type which, after it is formed 
into a coated film (protective film), can exhibit excellent impact 
resistance and abrasion resistance and possess a water resistance and an 
oil resistance, and which, when it is to be removed, can be readily 
stripped or peeled off as a single sheet of film. The strippable paint is 
selected, for example, from a polyvinyl chloride paint, a vinyl emulsion 
paint, a water-based emulsion paint and a synthetic latex. 
The portal framework 2 is composed of four rectangular column-like vertical 
frames 5 upstanding from a floor 6, two horizontal side frames 8 extending 
along an advancing direction (X-axis direction) of the vehicle body 1 and 
each attached to the upper ends of two adjacent ones of the vertical 
frames 5 via attachment members or brackets 7, and four horizontal cross 
frames 9 extending in a direction (Y-axis direction) perpendicular to the 
advancing direction (X-axis direction) of the vehicle body 1 and provided 
such that two of the cross frames 9 are each attached to the upper ends of 
two adjacent ones of the vertical frames 5 and the remaining two cross 
frames 9 are each attached to the front ends or the rear ends of the side 
frames 8. As shown in FIG. 3, two additional side frames 11 extending 
horizontally in the X-axis direction are attached to respective lower 
portions of the vertical frames 5 via attachment members or brackets 10 so 
as to reinforce the vertical frames 5. 
A vertically movable frame structure 13 is coupled with the rectangular 
column-like vertical frames 5 so that it is movable in a vertical 
direction (Z-axis direction). 
The vertically movable frame structure 13 is composed of four guide members 
14 vertically movably engaged with corresponding ones of the column-like 
vertical frames 5, two frames 15 spanning in the X-axis direction over 
respective ends of the guide members 14, and two frames 16 each 
interconnecting the front ends or the rear ends of the frame 15 in the 
Y-axis direction. 
One of the frames 15 has a rack 17 longitudinally disposed thereon, as 
shown in FIG. 2, and the other frame 15 has a rail 18 longitudinally 
disposed thereon. 
Thus, the vertically movable frame structure 13 is movable in the vertical 
or Z-axis direction by means of a drive means and a guide means (neither 
shown) while it is held in engagement with the column-like vertical frames 
5. 
The vertically movable frame structure 13 is also engaged with a 
longitudinally movable frame structure 20 which is movable in the X-axis 
direction and equipped with the coating nozzle 3 and the air blow-off unit 
4. 
The longitudinally movable frame structure 20 is composed of two frames 23 
extending in the Y-axis direction and each having a pinion 21, at one end, 
and a roller 22, at the opposite end, two frames 24 interconnecting 
adjacent ends of the frames 23 in the X-axis direction, and a rail member 
25 spanning between the frames 24. 
A motor 27 is fixedly mounted on one of the frames 24 and has a pinion 26 
attached to its rotating shaft. 
The pinions 21, 26 are held in mesh with the rack 17 and the rollers 22 are 
held in rolling engagement with the rail 18, so that when the motor 27 is 
energized, the longitudinally movable frame structure 20 is movable in the 
X-axis direction on and along the vertically movable frame structure 13. 
The coating nozzle 3 is secured to a nozzle base 30 and connected to a 
paint supply device or unit (not shown) provided for supplying a 
strippable paint to the coating nozzle 3, the nozzle base 30 being movable 
horizontally in the Y-axis direction. The nozzle base 30 has a 
self-propelling or mobile structure which is movable at a desired speed on 
and along a portion of the longitudinally movable frame structure 20, 
viz., the rail member 25 by the action of a drive means (not shown) 
equipped with a servo motor and a speed reducer. 
The air blow-off unit 4 is secured to one of the frames 23 and connected to 
an air supply device or unit (not shown) provided for supplying air to the 
air blow-off unit 4 via hoses 34. As shown in FIG. 5, the air blow-off 
unit 4 is composed of three rectangular boxes, namely, a central box 35, a 
left box 36 and a right box 37. The boxes 35, 36, 37 each have at its 
bottom wall a multiplicity of aligned air blow-off holes or nozzles 38 so 
formed as to open in the Z-axis direction. The air blow-off holes 38 have 
a diameter of about 0.6 mm and are able to blow or eject air at a speed of 
about 25 m/sec. 
By virtue of the multiplicity linearly arranged air nozzles 38, the air 
blow-off unit 4 is able to create closely juxtaposed streams of air 
resembling a planar stream of air created by a single slit. 
As shown in FIGS. 5 and 6, the air blow-off holes 38 are open or directed 
at an angle substantially perpendicular to a coated surface S of the 
vehicle body 1. In view of the orientation of the air nozzles, the boxes 
35, 36, 37 are each provided with a plate member 39 which has a setting 
angle .beta. variable to adjust or regulate the air ejection angle .alpha. 
at a desired value. By adjusting the setting angle .beta. of the plate 
member 39, the angle at which streams of air F ejected from the individual 
air blow-off holes 38 hit or impinge against the plate member 39 can be 
changed so as to adjust the air ejection angle .alpha. at the desired 
value. 
The setting angle .beta. of the plate member 39, which is defined between 
the plate member 39 and the bottom wall of the air blow-off unit 4 
including the air blow-off holes 38, is preferably in the range of 
55.degree. to 65.degree.. The setting angle .beta., if greater than 
65.degree., can only provide a narrow visual boundary and, if smaller than 
55.degree., tends to cause a scattering of air. In the illustrated 
embodiment, a setting angle .beta. of 60.degree. is adopted as an 
especially preferable example. 
The blow-off direction of air F ejected from the left and right boxes 36, 
37 is directed inwardly to cross or intersect the blow-off direction of 
air F ejected from the central box 35, as shown in FIG. 5. This 
arrangement is effective to prevent the strippable paint from flowing 
outwardly beyond the area to be protected. 
In the case where the strippable paint used is of the type having a high 
viscosity or becomes dry easily, an air blow-off unit 42 such as shown in 
FIG. 7 is used, including a humidified air nozzle 40 for ejecting 
humidified air W and a dehumidified air nozzle 41 for ejecting 
dehumidified air D. By the use of humidified air W, the strippable paint P 
trickled on the coated surface S is spread out uniformly within the area 
to be protected and hence is reduced in thickness. Ejection of the 
humidified air W is followed by ejection of the dehumidified air D by 
means of which the strippable paint P is further spread out with an 
additional reduction in thickness and with accelerated drying of the 
strippable paint P, at the same time. 
The protective film forming apparatus of the foregoing construction will 
operate to carry out the method of the invention for forming a protective 
film on a coated surface in a manner described below. 
At first, a vehicle body 1 consisting of a coated entire car while being 
conveyed by the conveyor (not shown) is stopped at a position where only 
the hood A of the vehicle body 1 underlies the vertically movable frame 
structure 13. Upon stopping the vehicle body 1, the vertically movable 
frame structure 13 is lowered by the drive means (not shown) from its 
uppermost original position, as indicated by the chain lines shown in FIG. 
2, while the longitudinally movable frame structure 20 carded on the 
vertically movable frame structure 13 is located at the rear or trailing 
end of the frame structure 13 as viewed from the advancing direction of 
the vehicle body 1. Downward movement of the vertically movable frame 
structure 13 is stopped when it arrives at a position where the coating 
nozzle 3 is located above the front end of the hood A with a predetermined 
space therebetween. 
At this time, the coating nozzle 3 is disposed in its original position 
indicated by the chain lines in FIG. 1 which is in registry with a right 
side edge of the vehicle body 1. Then, the coating nozzle 3 is moved at a 
predetermined speed horizontally in the Y-axis direction toward a left 
side edge of the hood A while it is trickling or dripping the strippable 
paint P at a predetermined amount of discharge onto the hood A along the 
front end edge thereof. Subsequently, the motor 27 is energized to move 
the longitudinally movable frame structure 20 by a predetermined distance 
in a direction (indicated by the arrow shown in FIG. 6) opposite to the 
advancing direction of the vehicle body 1. 
Simultaneously with this movement of the longitudinally movable frame 
structure 20, air F is ejected or blown at a predetermined air ejection 
angle .alpha. from the air blow-off unit 4 onto the coated surface S in a 
manner as shown in FIGS. 5 and 6, so that the strippable paint P trickled 
on the front end edge of the hood A is spread out within a protective-film 
forming area by the force or pressure of the blow-off air. The coating 
nozzle 3 while trickling the strippable paint P onto the left side edge of 
the hood A is then moved at the predetermined speed in the Y-axis 
direction toward the right side edge of the hood A. Subsequently, the 
longitudinally movable frame structure 20 is moved again by the motor 27 
in the direction (indicated by the arrow shown in FIG. 6) opposite to the 
advancing direction of the vehicle body 1 over the predetermined distance. 
Simultaneously with this movement of the longitudinally movable frame 
structure 20, the air blow-off unit 4 blows air F at the predetermined air 
ejection angle .alpha. onto the coated surface S in the manner shown in 
FIGS. 5 and 6 whereby the strippable paint P trickled on the hood A is 
forced to spread out within the protective-film forming area. 
The foregoing cycle of operations is repeated until after the strippable 
paint P is spread over the entire part of the protective-film forming area 
of the hood A, whereupon the discharge of the strippable paint P from the 
coating nozzle 3 is stopped. Thereafter, ejection of air F from the air 
blow-off unit 4 is stopped, and in order to keep the strippable paint P 
from spreading out beyond a boundary of the protective-film forming area, 
the ejection angle of air F is changed such that air F blown from the air 
blow-off unit 4 will not impinge against the boundary of the 
protective-film forming area, 
When the strippable paint P coated on the hood A becomes dry, it forms a 
thin protective film of a uniform thickness extending over the entire area 
of the coated surface of the hood A. 
In the case where the strippable paint P used is of the type having a high 
viscosity or dries easily, the resulting protective film is liable to 
become irregular in thickness or ruptured. To avoid this, humidified air W 
is blown from the humidified air nozzle 40 at a predetermined air ejection 
angle .alpha. relative to the coated surface S, as shown in FIG. 7, 
thereby forcing the strippable paint P to sufficiently spread out within 
the protective-film forming area, with a reduction in thickness. After the 
strippable paint P is spread by the humidified air W, dehumidified air D 
is blown from the dehumidified air nozzle 41 to effect additional 
spreading and thinning of the strippable paint P and thereby ensure 
accelerated drying of the strippable paint P. 
In the case where a confined visual boundary is needed, a strippable paint 
may be coated on with a roller (100 mm in width) or a brush (50 mm in 
width) along the periphery of an area to be protected so as to provide an 
overlap or two-ply coating portion between the roll- or brush-coated film 
and the coating film formed by the protective film forming apparatus of 
this invention, thereby improving the aesthetical appearance of the visual 
boundary. 
Likewise the hood A, the roof B and the trunk lid C is coated with a 
protective film of strippable paint, as will be described below. 
When the coating of the hood A is completed, the vertically movable frame 
structure 13 is moved upward to its uppermost original position, and the 
vehicle body 1 is advanced by the conveyor to a position in which only the 
roof B underlies the vertically movable frame structure 13. Then, the 
vertically movable frame structure 13 is lowered by the drive means from 
its uppermost original position and, at the same time, the longitudinally 
movable frame structure 20 is moved in the advancing direction of the 
vehicle body 1. Movement of the frame structures 13, 20 is stopped when 
the coating nozzle 3 is located above the front end of the roof B with a 
predetermined space therebetween. 
At this time, the coating nozzle 3 is disposed in its original position 
which is in registry with a right side edge of the vehicle body 1. Then, 
in the same manner as done with respect to the hood A, the coating nozzle 
3 is moved at a predetermined speed horizontally in the Y-axis direction 
toward a left side edge of the roof B while trickling the strippable paint 
P at a predetermined amount of discharge onto the roof B along the front 
end edge thereof. Subsequently, the motor 27 is energized to move the 
longitudinally movable frame structure 20 in the direction opposite to the 
advancing direction of the vehicle body 1 over the predetermined distance. 
Simultaneously with this movement of the longitudinally movable frame 
structure 20, the air blow-off unit 4 ejects air F at a predetermined air 
ejection angle .alpha. with respect to the coated surface S in the same 
manner as done with respect to the hood A, such as shown in FIGS. 5 and 6, 
so that the strippable paint P trickled on the front end edge of the roof 
B is spread out within a protective-film forming area. 
When the roof B coating process is completed, the vertically movable frame 
structure 13 is moved upward and returns to its uppermost original 
position. Then, the vehicle body 1 is advanced by the conveyor to a 
position in which only the trunk lid C underlies the vertically movable 
frame structure 13. Subsequently, the vertically movable frame structure 
13 is lowered from its uppermost original position by the drive means and, 
at the same time, the longitudinally movable frame structure 20 is moved 
in the advancing direction of the vehicle body 1. Movement of the frame 
structures 13, 20 is stopped when the coating nozzle 3 is located above 
the front end of the trunk lid C with a predetermined space therebetween. 
The coating nozzle 3 and the air blow-off unit 4 cooperate to form a 
protective film of the strippable paint coated over the trunk lid C in the 
same manner as done with respect to the hood A and the roof B. 
When coating of the trunk lid C is completed, the vertically movable frame 
structure 13 returns to its uppermost original position. Thereafter, the 
vehicle body 1 is discharged from the protective film forming apparatus by 
means of the conveyor. In the case where an article to be coated with a 
protective film, that is, the hood A, the roof B or the trunk lid C 
includes a certain degree of irregularity in shape and configuration, the 
coating nozzle 3 and the air blow-off unit 4 may be attached to an 
industrial robot to ensure that a protective film can be formed in 
conformity with the irregular shape and configuration of the article. 
It is further possible to use another industrial robot and attach thereto 
the coating nozzle 3 and the air blow-off unit 4 for enabling that a 
protective film can be formed by two robots cooperating with each other. 
INDUSTRIAL APPLICABILITY 
As described above, according to the present invention, dust of the 
strippable paint is no longer generated, the strippable paint is prevented 
from adhering to a portion other than the area to be protected, and the 
need for a masking process and a process for inspection and correction or 
mending can be obviated. It is therefore possible to form a protective 
film with improved working efficiency and improved coating efficiency. 
By the combination of trickling of the strippable paint by the coating 
nozzle and blowing of air from the air blow-off unit, the strippable paint 
can be uniformly coated over the coated surface without causing 
irregularities in thickness. 
It appears from the foregoing that the present invention is extremely 
useful when applied in the coating industries concerned not only with the 
coating of vehicle bodies but also with the coating of other articles.