Note: Descriptions are shown in the official language in which they were submitted.
DESCRIPTION
STRIPPABLE COATING ~II,M AND COATING METHOD USING S~ME
Technical Field
This invention relates to a novel strippable
coating film and a method of using the same. More
particularly, it relates to a strippable coating (or
masking) film for creating attractively finished
boundaries in multi-color painting of automobiles and
the like, as well as a coating method using the same.
Background Art
Recently, in the field oE automobiles, motor-
cycles and the like, so-called multi-color painting
(i.e., painting in two or more colors) of various parts
(e.g., bumpers, decorative body lines and stripes,
motorcycle gasoline tanks-, motorcycle windshields, and
the like) prevails in the manufacture of new products or
the repair of such vehicles.
In multi-color painting, it is regarded as
important from the viewpoint of commercial value to
prevent the intermingling of colors in boundaries (i.e.,
the regions bounding different colors) and thereby
create sharp boundary lines.
Thus, it has been a conventional practice in
multi-color painting to cover the parts not intended to
be coated with masking tape, used newspaper, film or
the like, protect -the boundaries with masking tape,
apply a coat of paint, and then remove the masking tape
and the like.
However, the use of masking tape has the
disadvantage that the boundaries cannot be finished as
attractively as might have been expected, because (1) it
is difficult to apply masking tape in a straight line
and (2) portions of the applied masking tape may
separate from the substrate and allow the paint to
penetrate into the gaps therebetween.
Disclosure of the Invention
Accordingly, the present inventors studied,
from various angles of vision, the coating method
comprising the step of applying a strippable paint to
an object to be coated, drying the applied strippable
paint, cutting the film so formed with a suitable
cutting tool, stripping off the unnecessary portions of
the film, and then applying a desired coat of paint to
the exposed parts of the object to be coated.
As a result, the use of a knife as the cutting
tool was found to be disadvantageous in that the
precision of the finish may vary according to the
skill of the worker, it is difficult to cut the film
alone without causing damage -to the base material or
substrate comprising the object to be coated, and the
knife edge will soon be worn away and become dull.
~hus, the present inventors made ~urther
studies with their attention focused on the cutting
method usin~ a laser beam.
A carbon dioxide gas laser, which is recently
used in the cutting of materials, makes it possible to
cut metallic and non-metallic materials, glass and the
like easily and to cut wood and the like without
producing noises or swarf. Moreover/ paper, cloth,
leather and the like can also be cut cleanly and rapidly.
~owever, in the cutting of thin plastic films such as
a thin film (e.g., a strippable coating film) used for
protecting a surface of an article temporarily, or a
thin layer forming a part of an article, it has been
found difficult to cut only the thin film or thin layer
(hereinafter referred to simply as thin film~ by means
of a CO2 gas laser without causing damage to the main
body of the article.
On the other hand, a YAG laser beam which is
one type of laser beam may be passed through optical
fibers, so that it is not only useful for purposes of
optical communication, but also now in use for micro-
scopic drilling or other processing of semiconductorsand printed circuit materials. However, few publications
7~3
can be found that report its use for the processing
of a surface layer alone. Experiments using a YAG laser
have revealed ~he intended purpose of cutting a film
cannot be accomplished satisfactorily. Accordingly,
the present inventors have made an investigation on
the type of film used and has found -that, if a strip-
pable paint containing 1 to 20% by weight of carbon
black (based on the resin componant) in the dry film is
applied, only the overlying film can be cut with the
aforesaid laser and, therefore, a method for creating
attractive boundaries can be realized.
Specifi~ly, in one ~pect the p~ent invention provides:
(1) a strippable coating~film containing 1 to 20 parts
by weight of carbon black per 100 parts by weight
of the resin component present therein;
(2) a strippab]e coating film consisting of two layers
of resin coating materials, characterized in that
the undercoating layer in contact with the object
to be coated contains therein 1 to 20 parts by
weight (based on the resin component) of carbon
black and has adhesive power, and the overcoating
layer located on the surface side contains therein
1 to 20 parts by weight (based on the resin compo-
nent) of carbon black, have flexibility and do not
exhibit surface tack;
and
s
~3) a coating method for creating attractively finished
boundaries which comprisas the steps of forming a
coating film as describad above on an object to be
coated, cutting the film with a laser beam ~rom a
YAG laser, stripping of~ the unnecessary portions
of the laser-cut film~ applying a final coat of
paint to the parts from which the film has been
removed, and then stripping off the remaining
portions of the masking film.
Other aspects o~ this invention are as follows:
A strippable coating film containing 1 to 20 parts
by weiqht of carbon black per 100 parts by weight of a
resin component comprising 25 to 40 parts by weight of
acrylonitrile, 65 to 40 parts by weight of butyl
acrylate, and 0.5 to 10 parts by weight of (meth)acrylic
acid present therein, wherein the adhesion of the film
to an object substrate is 20 to 1000 g/inch as expressed
in terms of 180 peeling strength.
A strippable coating film on an object substrate
consisting of two layers of resin coating materials,
characterized in that the undercoating layer in contact
with the object to be coated contains therein 1 to 20
parts by weight (based on the resin component) of carbon
black and has adhesive power, the adhesion to the object
to be coated being 20 to 1000 g/inch as expressed in terms
of 180 peeling strength, and the overcoating layer located
on the surface side contains therein 1 to 20 parts by
weight (based on the resin component) of carbon black, has
flexibility and does not exhibit surface tack.
A coating method for creating attractively finished
boundaries which comprises the steps of applying a
strippable paint containing 1 to 20% by weight (based on
the resin component) of carbon black in the dry film and
having adhesive power to an object to be coated wherein
the adhesion to the object to be coated is 20 to 1000
g/inch as expressed in terms of 180 peeling strength
when dried, to the object to be coated; drying the
applied ~trippable paint; cutting the formed film with
-. ~S
7~
5a
a laser beam from a YAG laser; stripping o:Ef the
unnecessary portions of the laser-cut :film; applying a
final coat of paint to the parts from which the Eilm has
been removed; and then stripping off the remaining
portions ~f the masking film.
~ novel coating method for creating attractively
finished boundaries which comprises the steps of
applying a coating material containing 1 to 20% by
weight (based on the resin component~ of carbon black in
the dry film and having adhesive power to an object to
be coated wherein the adhesion to the object to be
coated is 20 to 1000 g/inch as expressed in tel~s of
180 peeling strength when dried, and thereby forming an
undercoating layer in contact with the object to be
coated; applying a coating material containing 1 to 20~
by weight (based on the resin component) of carbon black
in the dry film; having flexibility, and exhibiting
film-forming properties to the undercoating layer and
thereby forming a surface layer to produce a strippable
coating film composed of two layers both containing
carbon black; cutting only the surface layer of the
coating film with a laser beam from a YAG laser;
stripping off the unnecessary portions of the laser-cut
surface layer together with the underlying adhesive
layer; applying a final coat of paint to the parts from
which the coating film has been removed; and then
stripping off the remaining portions of the strippable
coating film.
Brief Description of the Drawinqs
Fig. 1 is a perspective view for illustrating an
example of practice of the coating method of the present
invention; Fig. 2 is a plan view of a panel suitable for
use in film cutting tests; and Figs. 3 to 10 are graphs
illustrating the optimum output range for film cutting
purposes.
;"
9~
5b
seSt Mode for 5arryin~L_____the Invention
The strippable coating film of the present
invention is formed by applying a so-called strippable
paint to an object to be coated and then drying it.
Since this film is used for the purpose of covering and
protecting a surface of the article tor the object to be
coated) temporarily, it must have a certain level of
adhesive power and a sufficient level of strength
~2~g~
to permit it to be stripped ofE without gettincJ torrl.
Typical strippable paints meeting these
requirements include water-based paints comprising
acrylic emulsions, vinyl acetate emulsions, ethylene-
vinyl acetate, polyurethane and the like, as well assolvent-based paints comprising vinyl chloride sol,
polyvinyl butyral, vinyl acetate, polyurethane and the
like.
The adhesion of the film to the substrate (or
the object to be coated) should preferably be in the
range of 20 to 1000 g/inch as expressed in terms of
180 peeling strength. If the adhesion is less than
20 g/inch, the film will adhere insufficiently and will
tend to peel off during operation. If the adhesion is
greater than 1000 g/inch, the film will adhere so closely
that an unduly great force will be required to strip
off the film, possibly resulting in its tearing.
In addition, the film must contain therein 1
to 20 parts by weight, based on the resin component,
of carbon black so that it may be easily cut with a
low-power YAG laser as described above. If the amount
of carbon balck is less than 1 part by weight, the
laser cutting cannot be achieved smoothly, while if it
is greater than 20 parts by weight, the film will become
hard and, moreover, will exhibit an undesirable tendency
to release powdery carbon black.
~ ~g~7~3
No particular limi-ta-tion is placed on the
type oE carbon black which is incorporated in the
aforesaid strippable paint. That is, there may be
used various commercially available types of carbon
black including furnace black, lamp black, thermal
black, acetylene black, German furnace blac]~ and the
like. Where carbon black is to be incorporated in an
emulsion paint, it is preferable to disperse the carbon
black in water beforehand and use the resulting aqueous-
dispersion.
In order to obtain a paint which, thoughcontaining 1 to 20 parts by weight of carbon black,
gives a coating film having flexibility and not exhibit-
ing surface tack, it is especially preferable to use,
among the aforesaid water-based paints, a coating
composition comprising the following ingredients:
Acrylonitrile 25 to 40 parts by weight
Butyl acrylate 65 to 40 parts by weight
(Meth)acrylic acid 0.5 to 10 parts by weight
In this composition, if the amount of acrylo-
nitrile is less than 25 parts by weight, the formed
film will have insufficient s-trength, while it is
greater than 40 parts by weight, the film will be so
hard and so apt to crack that its stripping operation
may be difficult.
Butyl acrylate in an amoun-t of 65 to ~0 parts
by weight is required to adjust the flexibility of the
film properly.
(Meth)acrylic acid contributes to the stability
of particles in the emulsion. If the amount of (meth)-
acrylic acid is less than 0.5 parts by weight, the
particles will tend to agglomerate and the emulsion
may be hard to handle, while if it i9 greater than 20
parts by weight, the emulsion will show an incxease in
viscosity and may be hard to handle again.
Among the solvent-based paints, a vinyl
chloride resin is preferred~ The plasticizers which
may suitably be used in the vinyl chloride resin
include phthalic acid alkyl esters such as dioctyl
phthalate, dibutyl phthalate t etc; straight-chain dibasic
acid alkyl esters such as dioctyl adipate r etc.; and
phosphoric acid esters such as tricresyl phosphate, etc.
The plasticizer is used in an amount of 25 to 150 parts,
preferably 30 to 100 parts, per 100 parts of the vinyl
chloride resin.
The strippable paint may be applied according
to any o~ various conventional techniques including
spray coating, curtain flo~ coating, roll coating, brush-
ing and dipping. It is desirable to apply the paint as
evenly as possible.
The thickness of the applied paint should be
~2~7g~
such that the resulting dry film has sufEicient strength
to be strippable and does not have discontinuities or
pinholes causing the substrate -to be exposed. Generally,
the dry film thickness may suitably be of the order of
10 to 100 ~. If the thickness is less than 10 ~, the
film will generally be weak, will be liable to get torn
and hence hard to strip, and will tend to produce pin-
holes and discontinuities. If the thickness is greater
than 100 ~, it will be difficult to form a film having
smooth surfaces because cracking or shrinkage may occur
on drying. Moreover, a thickness of 100 ~ would be
amply sufficient for making purposes and greater thick-
nesses are wasteful because such a film requires an
unduly large amount of paint and much time to dry it.
The applied strippable paint may be dried to
such a degree as to form a film. The drying conditions
may be determined according to the type of strippable
paint used. Generally, the drying is carried out at a
temperature ranging from room temperature to about 200C
for a period of time ranging from 0.5 minute to 12
hours.
Now, the present coating method for creating
attractively finished boundaries will be described
hereinbelow.
The present invention is concerned with a
coating method using a strippable paint for masking
~9~9~3
-- 10 --
purposes and the strippable paint is used to form a
protective coat on a substrate comprising an object to
be coated. Typical examples of the substrate include,
but are not limi~ed to, molded articles made of plastic
materials such as polypropylene, polyethylene, vinyl
chloride resins, polystyrene, ABS, polycarbonates, etc.;
metal plates such as stainless steel plates, aluminum
plates, steel plates, etc.; coated plates such as coated
steel plates, etc.; decorative plywood panels; and the
like.
A carbon black-containing strippable coating
film as described above is formed on such an object to
be coated and the resulting film is then cut. In
accordance with the present invention, a laser is used
as the cutting means. Useful lasers are laser oscillators
emitting light of wavelengths ranging from the ~isible
to the near infrared region. A CO2 gas laser emitting
light of wavelengths in the infrared region is not
desirable because the laser light has a strong tendency
to cut not only the superficial strippale film but also
almost all types of plastic materials and coatings which
may be used in the substrate.
It is preferable to use a YAG laæer (emitting
light of wavelengths in the near infrared region) or a
dye laser (emitting light of wavelengths in the visible
region). Especially preferred is a YAG laser. The YAG
:~2~
laser only needs to have an output power of 1 to 20 W
in the single mode.
A dye laser permits its output energy to be
efficiently absorbed in the strippable film, because it
emits light of wavelengths in the visible region. The
dye laser only needs to have an output power sufficient
to cut the strippable film by melting.
More preferably, a YAG laser equipped with a
Q-switch is used. In this case, the strippable film
can be most cleanly cut in a pulse repetition frequency
range of 500 Hz to 5 kHz. Although the strippable film
can also be cut cleanly enough in a pulse repetition
frequency range o* 5 kHz to 50 kHz, not onl~ the strip-
pable film is cut but also the plastic substrate may
often be damaged unless the focus of the laser beam is
moved quickly. This is because, in most cases, the
plastic molded article constituting the substrate
contains carbon black in order to improve its performance.
However, this is not true of plastic molded articles
containing no carbon black, and attractive boundaries
can be created even in the pulse repetition frequency
range o~ 5 kHz to 50 kHz. At pulse repetiton frequencies
lower than 500 Hz, the strippable film may not be cut
if the focus of the laser beam is moved quickly. Al-
though good results can be obtained by moving the laserbeam slowly, this would not be suitable for the operation
~9g7~3
whose purpose is to create boundaries in a masking
film.
In this manner, khe s-trippable film is cut
with a laser beam and the unnecessary portions of the
film are stripped off. Thereafter, a final coat of
paint is applied to the parts from which the film has
been removed.
The paint used in final coating may be selected
according to the intended purpose. Where a solvent-based
paint is to be applied, the strippable paint used for
masking purposes should desirably be a water-based one
(in particular, one prepared by emulsion polymerization).
On the other hand, where a water-based paint is to be
applied, the strippable paint used for masking purposes
may be a water-based or a solvent-based one. In either
case, the strippable paint used for masking purposes
should preferably be resistant to the paint used in final
coating. However, these requirements are not essential
provided that the intended masking function is fulfilled
properly.
After a final coat of paint has been applied,
the strippable film used for maksing purposes may be
stripped off before the final coat of paint hardens,
because this creates more attractive boundaries. If the
strippable film is stripped off after the final coat of
paint has been dried, the boundries may become jagged.
1~9~g3
- 13 -
This is especially true in cases where the resul-ting
film is hard (to such an extent that it tends to crack
at room tempera~ure).
Now, in accordance with another feature of
the present invention, a strippable coating film
consisting of two layers of resin coating materials
and a novel coating method for creating attractively
finished boundaries by using such a film will be
described hereinbelow.
The unique resin coating film of two-layer
construction in accordance with the present invention
consists of a surface coat constituting its overcoating
layer and an adhesive resin layer constituting its
undercoating layer, and the substrate or object to be
coated is protected by the surface coat via the adhesive
resin layer.
Accordingly, the coating material used for
forming the surface cGat may be any conventional coating
material that has been used for the formation of a
strippable film. Typical examples of such coat~ng
materials include water-based paints comprising acrylic
emulsions, vinyl acetate emulsions, ethylene-vinyl
acetate and the like, as well as solvent-based paints
comprising vinyl chloride sol, polyvinyl butyral, vinyl
acetate and the like.
This surface coat must contain therein 1 to
~299~g3
- 14 -
20 parts by weight, based on the resin component, of
carbon black so that it may be easily cu-t with a low~
power ~AG laser as described above. If the amount of
carbon black is less than 1 part by weight, the laser
S cutting cannot be achieved smoothly, while if it is
greater than 20 parts by weight, the film will become
hard and, moreover, will exhibit an undesirable tendency
to release powdery carbon black. The type and particle
size of carbon black may be the same as previously
described.
In order to obtain a coating material which,
though containing 1 to 20 parts by weight of carbon
black, gives a surface coat having flexibility and not
exhibiting surface tack, it is especially preferable to
use, among the aforesaid coating materials, a coating
composition comprising the following ingredients:
Acrylonitrile 25 to 40 parts by weight
Butyl acrylate 65 to 40 parts by weight
(Meth)acrylic acid 0.5 to 10 parts by weight
In this composition, if the amount of acrylo-
nitrile is less than 25 parts by weight, the formed
film will have insufficient strength, while it is greater
than 40 parts by weight, the film will be so hard and
so apt to crack that its stripping operation may be
difficult.
9;~
- 15 -
sutyl acrylate in an amount of 65 to ~0 parts
by weight ls required to adjust the flexibility of the
film properly.
(Meth)acrylic acid contributes to the stability
of particles in the emulsion. If the amount of (meth)~
acrylic acid is less than 0.5 parts by weight, the
particles will tend to agglomerate and the emulsion may
be hard to handle, while if it is greater than 10 parts
by weight, the emulsion will show an increase in viscosity
and may be hard to handle again.
The overcoating layer should preferably have
a dry film thickness of 10 to 100 ~ from the viewpoint
of substrate protection and peeling strength~
The undercoating layer in contact with the
substrate comprising the object to be coated should have
proper levels of adhesive power and strippability
relative to the substrate, act as a buffer zone for
preventing the laser beam from reaching the substrate
during the cutting operation, and adhere closely to the
aforesaid surface coat so as to form an integral film
which can be stripped off after the surface coat has
been cut.
Accordingly, the coating material used for
forming the undercoating layer should desirably have
adhesive properties. For example, aqueous emulsions
such as acrylic emulsions, vinyl acetate emulsions and
7~3
- 16 -
ethylene-vinyl aceta-te emulsions may be used. ~specially
preferred are aqueous acrylic, vinyl acetate or ethylene-
vinyl acetate emulsions forming a film whose adhesion
to the substrate is 20 to 1000 g/inch, more preferably
30 to 600 g/inch, as expressed in terms of 180 peeling
strength. Useful acrylic resins include homopolymers
and copolymers of butyl acrylate or 2~ethylhexyl (meth)-
acrylate; copolymers of these monomers; copolymers of
butyl acrylate or 2-ethylhexyl (meth)acrylate and
copolymerizable monomers such as acrylates (acrylic
esters), methacrylates, styrene, ~-methylstyrene,
acrylonitrile, divinylbenzene, ethylene glycol di(meth)-
acrylate, etc.; and the like.
The undercoating layer must also contain the
same type of carbon black as used in the overcoating
layer, in an amount of 1 to 20 parts by weight based
on the resin component. Provided that the carbon black
content is in this range, the laser beam which may
reach the undercoating layer during the cutting of the
overcoating layer will be absorbed and cause no damage
to the substrate. If the carbon black content is greater
than 20 parts by weight, the film will become hard and
lose its adhesive power and strippability.
The undercoating layer performing the aforesaid
functions only needs to have a dry film thickness of 10
to 100 ~. Thus, imperfect cutting of -the film and damage
7~
to -the substrate can be prevented in spi-te oE variation
in ~he thickness of th~ overcoatin~ layer and ~ariation
in the output or operating conditions of the laser.
Consequently, cut-ting and stripping of the coating
film can be consistently and cleanly achieved to create
attratively finished boundaries.
Furthermore, by incorporating an inorgani~
filler into the overcoating or the undercoating layer,
a coating film having better cuttability with a laser
can be obtained and the allowable range of laser output
can be widened. Useful inorganic fillers include heavy
calcium carbonate, light calcium carbonate, talc, clay,
silica and the like. Among others, heavy calcium
carbonate is preferred. The inorganic filler should
preferably have an average particle diameter of the
order of 0.1 to 10 ~ so that it may be evenly dispersed
in the coating layer. The inorganic filler may be used
in an amount of 5 to 50 parts by weight, preferably 20
to 40 parts by weight, based on the resin component.
If the amount of inorganic filler used is less than 5
parts by weight, the desired effect will not be produced,
while if it is greater than 50 parts by weight, the
coating paint will have an extremely high viscosity,
exhibit poor application properties, and give a brittle
film.
The laser cut-tability of the coating film can
~g~
- 18 -
be enhanced by incorpora-ting the inorganic filler into
the overcoating layer, but a similar effect will also
be produced by incorporating it into the undercoatiny
layer. That is, where the inorganic filler is
incorporated into the undercoating layer, it acts
effectively as a buffer for the laser beam attenuated by
the overcoating layer.
This buffering effect can further be enhanced
by adding aluminum powder to the undercoating layer.
Thus, the laser beam shows a decreased penetrating power
to the substrate and causes little damage to the
substrate. The reason for this seems to be that the
laser beam is irregularly reflected by the aluminum
powder and diffused or absorbed in the undercoating
layer.
The type of aluminum powder used may be of
paint grade. The aluminum powder is used in an amount
of 1 to 40 parts by weight, preferably 5 to 30 parts
by weight, based on the resin component. If the amount
of aluminum powder used is less than 1 part by weight,
the desired effect will not be produced, while if it
is greater than 40 parts by weight, the effect will
reach a maximum level.
Now, the novel coating method for creating
attractively finished boundaries by using the aforesaid
resin coating film of two-layer construction will be
7g~1
-- 19 --
described hereinbelow.
~ s to the object -to be coated wi-th the strip-
pable coating film of the present invention, typical
examples thereof include, but are not limited ~o,
molded articles made of plastic ma-terials such as
polypropylene, polyethylene, vinyl chloride resins,
polystyrene, AsS, polycarbonates, etc.; metal plates
such as stainless steel plates, aluminum plates, steel
plates, etc.; coated plates such as coated steel plates,
etc.; decorative plywood panels; and the like.
The coating materials used for forming the
overcoating and undercoating layers may be applied
according to any of various conventional techniques
including spray coating, curtain flow coating, roll
coating, brushing and dipping. It is desirable to apply
the coating materials as evenly as possible.
The -thickness of the applied coating materials
should be such that the resulting dry film has sufficient
s-trength to be strippable and does not have discontinuities
or pinholes causiny the substrate to be exposed.
Generally, the combined dry film thickness of -the over-
ocating and undercoating layers may suitably be in the
range of 20 to 300 ~. If the thickness is less -than 20
~, the film will generally be weak, will be liable to
get torn and may be hard to peel off, and will tend to
produce pinholes and discontinuities. If the thickness
~L~9~793
- 20 -
is yreater than 100 1.l with a single coatillg operation,
it will be difficul-t -to form a film having srnooth
surfaces because cracking or shrinkage may occur on
drying. Moreover, a thickness of 300 ~ would be amply
sufficient for making purposes and greater thicknesses
are wasteful because such a film requires an unduly
large amount of coating materials and much time to dry
them.
The applied coating materials may be dried
in such a way that the undercoating material is first
applied and dried, and the overcoating materials is then
applied and dried. Alternatively, this may be by
applying the undercoating and overcoating materials
successively and then drying them simultaneously. The
drying conditions may be determined according to the
type of coating materials used. Generally, the drying
is carried out at a temperature ranging from room
temperature to about 200C for a period of time ranging
from 0.5 minute to 12 hours.
As the means for cutting the film so formed,
a laser is used as described above. Useful lasers are
laser oscillators emitting light of wavelengths ranging
from the visible to the near infrared region. A CO2 gas
laser emitting light of wavelengths in the infrared
region is not desirable because the laser light has a
strong tendency to cut not only the superficial strippable
ILZ9~37~3
- 21
film but also almost all types of plastic materials
and coatings which may be used in the substrate.
It is preferable -to use a YAG laser (emit-ting
light of wavelengths in the near infrared re~ion) or a
dye laser (emitting light of wavelengths in the visible
region). Especially preferred is a YAG laser~ The YAG
laser only needs to have an output power of 1 to 20 W
in the single mode.
A dye laser permits its output energy to be
efficiently absorbed in the coating film, because it
emits light of wavelengths in the visible region. The
dye laser only needs to have an output power sufficien-t
to cut the overcoating layer by melting.
~ore preferably, a YAG laser equipped with a
Q-switch is used. In this case, the coating film can
be most cleanly cut in a pulse repetition frequency
range of 500 Hz to 30 kHz and preferably 1 to 20 kHz.
Although the coating film can also be cut cleanly enough
at pulse repetition frequencies higher than 30 kHz and
up to 50 kHz, not only the strippable film is cut but
also the plastic substrate may often be damaged unless
the focus of the laser beam is moved quickly. This
is because, in most cases, the plastic molded article
constituting the substrate contains carbon black in
order to improve its performance. However, this is not
true of plastic molded articles containing no carbon
~97~3
black, and at-tractive boundaries can be crea-ted even at
pulse repetition frequencies higher than 30 kHz and
up to 50 kHz. ~t pulse repetition frequencies lower
than 500 Hz, the film may not be cut if the focus of
the laser beam is moved quickly. Although good results
can be obtained by moving the laser beam slowly, this
would not be suitable for the operation whose purpose
is to create boundaries in a masking film.
In this manner, the overcoating layer is cut
with a laser beam and then stripped off, so that the
overcoating and undercoating layers are cleanly removed
as an integral film along the cutting line. After the
unnecessary portions of the film are stripped off, a
final coat of paint is applied to the parts from which
the film has been removed.
The paint used in final coating may be
selected according to the intended purpose. Where a
solvent~based paint is to be applied, the overcoating
material used for masking purposes should desirably be
a water-based one (in particular, one prepared by
emulsion polymerization). On the other hand, where a
water-based paint is to be applied, the overcoating
material used for masking purposes may be a water-based
or a solvent-based one. In either case, the overcoating
material used for masking purposes should preferably be
resistant to the paint used in final coating. However,
~;~9~
these requirements are not essential provided that the
intended masking Eunc-tion is Eulfllled properly.
After a final coat of paint has been applied,
the film used for masking purposes may be stripped off
before -the final coat of paint hardens, because this
creates more attractive boundaries. If the film is
stripped off after the final coat of paint has been
dried, the boundries may become jagged. This is
especially true in cases where the resulting film is
hard (to such an extent that it tends to cxack at room
temperature~.
The present invention is further illustrated
by the following examples.
The symbols used in the examples and comparative
examples given below are as follows:
2EHA ... 2-ethylhexyl acrylate; BA ... butyl
acrylate; AN ... acrylonitrile; AA ... acrylic acid;
MMA ... methyl methacrylate; DVB ... divinylbenzene;
MAc ... methacrylic acid; AM .O~ acrylamide; HEMA ...
hydroxyethyl methacrylate; CB ... carbon black; BMA ...
butyl methacrylate.
In these examples, parts are by weight.
Example 1
This example illustrates the preparation of
typical acrylic emulsion type strippable paints for use
~g~9~
- 24 -
in -the formation of coating films in accordance with
the present invention (the overcoating layer in -the
case of coating films of two-layer construc-tion), the
workability and application thereof, the adhesion of
coating films formed of acrylic strippable paints
containing various resin components, the laser cuttability
thereof, and the like.
l Preparation of an acrylic emulsion and a strippable
paint
Into a 2-liter four-necked flask fitted with
a reflux condenser, a thermometer and a stirrer were
charged 1000 g of purified water and 2 g of sodium
dodecylbenzenesulfonate (hereinafter abbreviated as DBS).
While nitrogen gas was being passed through the flask,
its contents were heated to 70C. On the other hand,
350 g of AN, 580 g of BA, 20 g of MAc, 20 g of AM,
and 30 g of HEMA were mixed and a 5/100 portion of the
resulting mixture was reserved in another vessel. 3 g
of DBS was added to and mixed with the remaining
portion of the mixture. To the aforesaid 2-liter flask
containing warm water were added 5 g of potassium
persulfate and then the previously reserved 5/100 portion
of the monomer mixture. After polymerization was carried
out for an hour, the remaining 95/100 portion was added
over a period of 5 hours and the reaction mixture was
9~7~3
25 -
then polymerized for an additional 4 houxs. The
reaction mix-tuxe was cooled to 45C or below and
neutralized with 14~ aqueous ammonia to obtain an acrylic
emulsion (having a resin content of 49.5~). To this
emulsion were added 20 g of dioctyl phthalate (herein-
after abbreviated as DOP), 40 g of a wetting agent
(commercially available from Air Products C~., Ltd. under
the trade name of Surfynol 104~ and 100 g of an aqueous
dispersion of carbon black (commercially available from
Dainichi Seika Co., Ltd. under the trade name of EP 510BR
and having a carbon black content of 37% by weight~.
Thus, there was obtained a strippable paint suitable for
the formation of a coating film in accordance with the
present invention.
l-B Formation of a coating film, i nce
characteristics, and an instance of multi-color
.
paintin~
Using the strippable paint prepared as above,
a bumper consisting essentially of polypropylene and
illustrated in Fig. 1 was painted in such a way that
the color (black) of tha substrate was exposed in the
part E and the same color (e.g., a metallic silver
color) as that of the body was imparted to the part F.
Specifically, the strippable paint prepared as
above was applied to a molded bumper by means of a spray
~g7~3~
- 26 -
gun and then dried in a large-sized dryer at 80C for
10 minutes to form a dry film. This film had an average
thickness of 40 ~.
Subsequently, an optical fiber scope was
connected with a YAG laser (manufactured by NEC and
having a multi-output power of 2 W), and the boundary
line D between the parts E and F of the bumper was cut ~ith
a laser beam. For this purpose, the laser was equipped
with a Q-switch and operated at a pulse repetition
frequency of 3 kHz. The cutting speed was 100 mm/min
and the laser output was 3 W.
After the strippable film was stripped from
the part F, the surface of the bumper was cleaned by
exposing it to trichloroethane vapor for 30 seconds.
A solvent-based primer coat consisting
essentially of chlorinated polypropylene was applied to
the uncoated part F so as to give an average dry film
thickness of 15 ~ and ~hen dried at 80C for 30 minutes.
Thereafter, a solvent-based finishing coat of acrylic
urethane type was applied thereto so as to give an
average dry film thickness of 30 ~ and then dried at
80C for 45 minutes.
When the strippable film was stripped from the
part E, there was obtained a colored bumper having an
attractive boundary between the parts E and F.
On the other hand, a 10 cm x 20 cm flat plate
~Z9~7~
- 27 -
was cut ou-t of the material used for the formatiorl of
the bumper, and -the strippable paint was applied thereto
under the same conditions as described above. Using
a cutting knife, two parallel cuts with a distance of
1 inch were made in the film so that a strip of film
might be peeled off. Then, i-ts 180 peeling strength
was measured with a tensile tester.
The average peeling strength of three measure-
ments was 80 g/inch.
l-C Performance of paints and coating films having
various resin com~ositions
Strippable paints having the respective resin
compositions shown in Tables 1-1 to 1-3 were prepared
in the same manner as described in l-A. Each of the
strippable paints was applied with a spray gun to a
polypropylene test panel (100 x 100 x 3 mm) as illustrated
in Fig. 2, and then dried at 80C for 30 minutes to
obtain a film having an average thickness of 80 - 120 ~.
By using a YAG laser (SL-114F; manufactured
by N~C) combined with a Q-switch, the film was cut under
varying oscillation conditions (as shown at 1) r 2) ~ 3) ~
... in Fig. 2). After the cutting operation, the degree
of cutting of the strippable film and the degree of
damage to the PP panel substrate were examined. Then,
the cuttability oE the film was synthetically judged on
:L2997~3
- 28 -
the basis of the results thus obtained.
Laser cutting conditions:
Laser : SL-114 (manufactured by NEC and having
an output power of 20 W)
Q-switch: SL-231B
~lode : Single mode
The adhesion of the films was evaluated by
measuring their 180 peeling strength in the same manner
as described in l-B.
10 The workability of the strippable paints was
judged on the basis o~ the occurrence of agglomeration
or viscosity increase during its preparation.
Table 1-1
~ _ AN-l AN-2 AN-3 AN-4* AN-5 AN-6
AN 20 25 30 35 40 45
BA 73 68 63 58 53 48
Proportions
o~ MAc 2 2 2 2 2 2
AM 2 2 2 2 2 2
Components
HE~ 3 3 3 3 3 3
CB 3.7 3.7 3.7 3.7 3.7 3.7
Workability O O O O O O
Adhesion (g/inch) Unstrip- 1200 150 80 45 18
pable
Laser Cuttability ~ O O O O O
* Details were given in l-A.
7~3
- 29 -
Table 1-2
BA-l BA-2 BA-3 BA-4 BA-5
AN 40 35 35 33 23
MMA 18 18 8
Proportions BA 35 40 50 60 70
of MAc 2 2 2 2 2
Components AM 2 2 2 2 2
HEMA 3 3 3 3 3
~ 10 CB 4 4 4 4 4
Workability O O O O
Adhesion (g/inch) 9 25 75 110 1300
Laser Cuttability O O O O O
~L2~ 3
- 30 -
Table 1-3
MAc-l M~c-2 MAc-3 MAc-4 MAc-5 MAc-6
; AN 35 35 35 35 32 31
BA 59.7 59.5 59 55 53 52
Proportions
of MAc 0.3 0.5 1.0 5.010.0 12.0
AM 2 2 2 2 2 2
Components
HEMA 3 3 3 3 3 3
CB 5 5 5 5 5 5
10Workability Xl) O O O ~2) x2)
Adhesion (g/inch) 120 110 80 75 60 60
Laser Cuttability O O O O O O
1) Agglomerated on addition of carbon black.
2) Showed an increase in viscosity.
Example 2
Strippable coating films containing varying
amounts of carbon black were comparatively evaluated.
Strippable paints were prepared in the same
manner as described in Example 1, l-A except that the
amount of carbon black was changed to 3 parts, 5 parts,
10 parts, 20 parts or 25 parts.
Each of the aforesaid aqueous acrylic emulsion
type strippable paints containing carbon black was
""` ~2~g~3
- 31
applied with a spray gun -to a PP -test panel (100 x 100 x
3 mm) similar to that used in Examp]e 1, and -then dried
at 80C for 3 minutes to obtain a film having an average
thickness of 80 - 120 ~. The films so formed are
hereinafter referred to as C-3, C-5, C-10, C-20 and C-25
according to their respective carbon black contents.
By using a YAG laser (SL-114F; manufactured
by NEC) combined with a Q-switch (SL-231B), each of
these strippable films was cut under varying oscillation
conditions.
After the cutting operation, the degree of
cutting of the strippable film and -the degree of damage
to the PP panel substrate were examined.
Moreover, their 180 peeling strength was
measured in the same manner as described in Example 1.
For purposes of comparison, the same procedure
was repeated with a film containing no carbon black
(hereinafter referred to as C-0).
The results of the cutting tests were as
follows:
"`` ~2~793
- 32 -
Run No. 1 2 3 4 5 6 7
Modulation pulse repe- 0.3 O.S 1 5 10 20 30
Degree of cutting of X *l ~ O _ O
strippable filmO O
substrate_ O O O ~ Z X X
Exciter lamp input: 17 A
(Average output at a modulation pulse repetition
frequency of 3 kHz: 2.9 W)
*l The film was not completely cut, but was rated
as good (O') because it could be cleanly peeled
off along the cutting line.
*2 The substrate showed a slight trace of laser
light, but was rated as good (~) because no
change in physical properties was noted.
C-5
. Run No. 8 9 10 11 12 13 14
Modulation pulse repe- 0.3 0.5 1 5 10 20 30
. _ _
2 Degree of cutting of *2
0 strippable filmX O O O O O O
substrateO O O O ~3 X X
Exciter lamp input: lSA
(Average output at a modulation pulse repetltion
frequency of 3 kHz: 2.3 W)
*2 The film was not completely cut, but was rated as
good (O') because it could be cleanly peeled off
along the cutting line.
*3 The substrate showed a slight trace of laser light,
but was rated as good (~) because no changes in
physical properties were noted.
:~lZ~g~7~93
C-10
Run No.15 16 17 18 19 2021
_ ~ _ ._
Modulation pulse rep~-0.3 0.5 1 5 1020 30
Degree of cutting of X
strippable film O ~ O O O O
~ _ _
Degree of damage ~o PP O O O O O ~ X
Exciter lamp input: 17 A
C-15
Run No. 22 23 24 25 26 2728
Modulation pulse repe- 0.30.5 1 5 1020 30
tition frequency (kHz)
_
Degree of cutting of X
strippable film O O O O O O
substrate O O O O O A x
Exciter lamp input: 17 A
C-20
Run No. 29 30 31 32 33 3435
Modulation pulse repe- 0.30.5 l 5 lO20 30
tltlon frequency (kHz)
Degree of cutting of X r~
strippable film O O O ~J O O
_ _
Degree of damage to PP O O O O O ~ X
Exciter lamp input: 17 A
The film had a considerable degree of hardness.
99793
- 3~ -
C-2~
The f.ilm was harcl and released powdery carbon
black, so that it was unsuitable for use as a strippable
film.
C 0 (Comparative Example)
Run No. ¦ 36 37 3839l 40 41 42
Modulation pulse repe- 0 3 0 5 1 5 lO 20 30
tition frequency (kHz) . .
_ _ .
Degree of cutting of
strippable film XX X X X X X
Degree of damage to PP O ~ X X X X X
substrate _
The laser light not only failed to cut the strippable
film, but also caused damage to the substrate
comprising the test panel.
Adhesion
~anD.e (g/inch)
C-3 80
C-5 80
C-10 75
C-15 73
C-20 70
C-25 55
C-0 80
~99793
- 35 -
Exam~le 3
25 parts of vinyl chloride and 25 p~rts of
dioctyl phthalate were dissolved in lO0 parts of a
mixture of equal amounts of butyl acetate and isopropyl
alcohol, followed by the addition of 0.1 part azobis-
isobutyronitrile. The resulting mixture was polymeri7ed
at 50-60C for 15 hours. Then, carbon black (commercial-
ly available from BASF A.G. under the trade name of
Mikrolith Blac~ was added to and mixed with the mixture
in an amount of 3 parts as solid carbon black. Thus,
there obtained a vinyl chloride sol. This vinyl
chloride sol was spray coated on a PP test panel similar
to that used in Example l and then dried at 80C for 3
minutes to form a strippable coating film in accordance
with the present invention having an average thickness
of 100-150 ~. (The carbon black content based on the
resin component was 6~.)
The film was cut in the same manner as
described in Example 2. The results thus obtained were
as follows.
,i"
g~3
Run No. = 1 2 3 __ 5 6 7
Modulat on pulse repe-0.3 0.5 1 5 10 20 30
_ __ _ _
strippable film X~ 2 O O O _
substrate OO O ~ O ~ X
Exciter lamp inpu-t: 17 A
*2 The film was cut by only 70%, but was rated as
good (~) because the film could be cleanly
peeled off along the cutting line.
The 180 peeling strength was 150 g/inch.
Example 4
This example illustrates a strippable coating
film of two-layer construction in which both the over-
coating layer and the undercoating layer are formed
of acrylic emulsions.
Into a 2-liter four-necked flask fitted with
a reflux condenser, a thermometer and a stirrer were
charged 600 g of purified water and 2 g of DBS. While
N2 gas was being passed through the flask, its contents
were heated to 70C.
500 g of 2EHA, 400 g of BA, 30 g of AA, and
70 g of AN were mixed and a 1/10 portion of the result-
ing mixture was reserved in ano-ther vessel. Then, a
monomer emulsion was prepared by adding the remaining
37~
- 37 -
portion of the monomer mix-ture, drop by drop, tu 400 g
of purified wa~er having 3 g of DBS dissolved therein.
To the aforesaid 2-liter flask containing warm wa-ter
were added 5 g of potassium persulfate and then the
previously reserved 1/10 portion of the monomer mixture.
After polymerization was carried out for an hour, the
monomer emulsion prepared as above was added over a
period of 4 hours and the reaction mixture was then
polymerized for an additional 4 hours. A~ter completion
of the polymerization, the reaction mixture was cooled
to 45C or below and neutralized to pH 7.5 with 1~
aqueous ammonia to obtain an aqueous acrylic emulsion.
To this aqueous acrylic emulsion was added
Carbon Black AM-9700 (manufactured by Dainichi Seika
Co., Ltd.) in an amount of 30 g as solid carbon black.
Thus, there was obtained a coating material (undercoating
material) having the adhesive power required for the
purpose of the present invention.
First, an undercoating material prepared by
adding 3 parts of carbon black to the aforesaid aqueous
acrylic emulsion (containing 50 parts of 2E~IA, 40 parts
of BA, 7 parts of AN, and 3 parts of AA and having a
resin content of 50%) was applied to a test panel (100 x
100 x 3 mm) made of PP, and then dried (the resulting
undercoating layer had an average thickness of 40-50 ~).
Subsequently, an overcoating material prepared
~979~
- 3~ -
by adding 5 par-ts of car~on black to an aqueous acrylic
emulsion formed in the manner described in Example 1
(containing 10 parts of MMA, 55 parts of BA, 33 parts
of AN, and 2 par-ts of AA and having a resin content of
50~) was applied thereto and then dried (the resulting
overcoating layer had an average thickness of 50-70 ~).
Thus, there was obtained a coating film of two-layer
construction.
Using a YAG laser (SL-114F; manufactured by
NEC) combined with a Q-switch (SL-231B), this film was
cut under varying oscillation conditions.
After the cutting operation, the degxee of
cutting of the overcoating layer and the degree of
damage to the PP panel substrate were examined.
(1) Coating conditions
(a) Spray coating
(b) Drying at ~0C for 5 minutes (for each of the
undercoating and overcoating layers)
(2) Laser cutting conditions
(a) Laser: SL-114F (with an output power of 20 W)
and SL-231B (manufactured by NEC)
(b) Exciter lamp input: 17 A (Average output at a
modulation pulse repetition frequency of
3 kHz: 2.9 W)
(c) Mode: Single mode
(d) Cutting speed: 50 mm/sec
~99793
- 39 -
_._ _ _____ _ _
.Run No. 1 2 3 4 5 6 7
. ._ _ , _.
tition frequency (kHz) 0.3 0.5 1 5 10 20 30
. . _. .__ __
Degree of cut-ting of X ~
overcoating layer O O O O O
S-trippability of film _ A O O O O O
_
Degree of damage to PP O O O O O O
At a modulation pulse repetition frequency of
500 Hz or lower, the film was not cut satisfactorily.
At a modulation pulse repetition frequency of 30 kHz or
higher, the film was excessively cut to cause damage to
the panel constituting the substrate.
In a modulation pulse repetition frequency
range of 1 to 20 kHz, the film was clearly cut without
causing damage to the substrate, and could be stripped
off to create an attractive boundary line.
The adhesion of the film to the substrate was
300 g/inch as expressed in terms of 180 peeling strength.
Example 5
This example illustrates a s-trippable coating
film consisting of two layers of resin coating materials
in which the adhesive undercoating material is an acrylic
emulsion and the overcoating material is a vinyl chloride
sol.
37~3
-- ~o --
~dhesive undercoating material (aqueous emulsion havincJ
a resin content of 47.5%)
BMA 42 parts
BA 55 parts
AA 3 parts
Carbon black3 parts (added later)
Overcoating material
Vinyl chloride sol 100 parts
(formulated in the same manner as in Example 3)
Carbon black3 parts
. ...
Run No. 1 2 3 4 5 6 7
Modulation pulse repe- 0.3 0.5 1 5 10 20 30
. _
5 Degree of cutting of X ~ O O O O O
_
Strippability of film X O O O O O O
......
Degree of damage to PP O O O O O O _
Average thickness of the adhesive 50 70
undercoatlng layer
Average thickness of the , ~0 50
overcoating layer
Adhesion to the substrate 18 / h
(180 peeling strength) 0 g lnc
In a modulation pulse repetition frequency
range of 1 to 20 kHz, the film could be clearly cut
without causing damage to -the substrate.
997~93
- Al -
Compara-tive Examp:Le 1
I`he procedure of Example 4 was repeated
except that the adhesive undercoa-ting layer was a clear
layer containing no carbon black. Specifically, the
formulations used were as follows:
Adhesive undercoating material
2EHA 50 parts
BA 40 parts
AN 7 parts
AA 3 parts
100 parts (resin content 50%)
Overcoating material
MMA 22 parts
BA 50 parts
AN 25 parts
AA 3 parts
Carbon black5 parts (added later)
.
105 parts (resin content 50%)
Run No. 1 2 3 4 5 6 7
Modulation pulse repe-0.3 0.5 1 5 10 20 30
tition frequency (~Hz)
_ _ _
Degree of cutting of
overcoating layer X ~ O O O O O
Strippability of film _ ~ O O O O O
Degree of damage to PP O _ O O X X
7~:3
- 42 -
Average thickness of the adhesive . 60 80
undercoating layer
Average thickness oE the 50 70
overcoating layer
Adhesion to the substrate 310 /inch
(180 peeling strength) g
When the undercoating layer contained no carbon
black, the laser beam caused damage to the PP substrate
if the overcoating layer was cut to a certain extent.
That is, the adhesive layer did not perform its bufEering
function. The boundaries were attractively finished.
~omparative Example 2
The procedure of E~ample 4 was repeated except
that the overcoating layer was a clear layer containing
no carbon black. Specifically, the formulations used
were as follows:
Adhesive undercoating material
2EHA 50 parts
BA ~0 parts
AN 7 parts
AA 3 parts
Carbon black 3 parts (added later)
103 parts (resin content 50%)
~Z9~793
- ~3 -
o coating material
MMA 22 parts
sA 50 parts
AN 25 parts
5 ~A 3 parts
100 parts (resin conten-t 50~)
Run No. 1 2 3 4 5 6 7
. _
10 Moidulation pulse repe-0.3 0.5 1 5 10 20 30
Degree of cutting of
overcoating layer XX X X X X X
_ __
Degree of cutting of
undercoating layer XX ~ O O
. _
Strippability of film _ _ _ _ _ _ _
____ _
Degree of damage to PP
substrate - O A ~ X X X X
(1) Since the overcoating layer was not cut
at all, the film could not be stripped off along the
cutting line and remained continuous all over.
(2) The undercoating layer was cut at modula-
tion pulse repetition frequencies of 3-5 kHz, but re-
fused at 20 kHz (though the re-fused zone was deprived
of carbon black to form a transparent streak).
(3) The PP substrate was damaged in the parts
where the corresponding parts of the adhesive film
~997~33;3
consisting of the overcoating and undercoating layers
were deprived of carbon black. Tha-t is, -the subs-trate
was damaged in the parts where the laser light was not
intercepted by the overcoating layer. Moreover, at
higher modulation pulse repetition frequencies, the
substrate was damaged in spite of re-fusion of the
undercoating layer. The adhesion of the film to the
substrate was 280 g/inch as expressed in terms of 180
peeling strength.
Comparative Example 3
The procedure of Example 4 was repeated
except that the undercoating layer was formed of a
coating material having the same film-forming properties
and film strength as the overcoating material. Speci-
fically, the formulation of the undercoating material
was as follows:
Undercoating material
MMA 22 parts
BA 50 parts
AN 25 parts
AA 3 parts
Carbon black 5 parts (added later)
105 parts (resin content 50~)
~2~
- ~5 -
Average thickness of the undercoating : 30-50
layer
Average thickness oE the overcoating layer : 30-50
Adhesion of the film
(180 peeling s-trength) : 100 g/lnch
Run No. 1 2 3 4 5 6 7
Modulation pulse repe- 0.3 0.5 1 _ _ 10 20 30
tition fre~uency tkHZ) -
Degree of cutting of X
overcoating layer _ O O O O
Degree of cutting of
undercoating layer X X X ~ ~ O O
_ _
Strippability of film X X X ~ O O O
substrate O O O O O O X
(1) Even when the overcoating layer was cut,
the film could not be stripped off if the undercoating
layer was not cut. Thus, the strippability of the film
was poor in such a case.
(2) In the range where both the overcoating
layer and the undercoating layer could be cut, the
substrate was damaged by the laser beam. Thus, the
range where the film could be cut without causing
damage to the substrate was narrow.
Example 6
This example illustrates an inorganic filler-
7~3
- 46 -
containing strippable coating film of two-layer construc-
tion.
An acrylic emulsion having a concentration
of 50% was prepared by copolymerizing 54 parts by
weight of BMA, 42 parts by weight of sA, 2 parts by
weight of methacrylic acid (MAc), and 2 parts by weight
of acrylamide in the usual manner. To this acrylic
emulsion was added an aqueous carbon black pigment
(EP510BR; manufactured by Dainichi Seika Co., Ltd.) in
an amount of 4 parts (as solid carbon black). Thus,
there was obtained the coating material I.
Next, an acrylic emulsion having a concentra-
tion of 50~ was prepared by copolymerizing 30 parts of
AN, 52 parts of BA, 11 parts of MMA, 3 parts of HEMA,
and 2 parts of MAc as in the usual manner. To this
acrylic emulsion was added the aforesaid carbon black
pigment in an amount of 4 parts (as solid carbon black).
Further, calcium carbonate (Calcium Carbonate Super S;
manufactured by Maruo Calcium Co., Ltd.) was incorporated
into the acrylic emulsion in an amount of 40 parts (as
solid calcium carbonate) per 100 parts of the resin.
Thus, there was obtained the coating material II (Run
No. 6-1 in Table 6-1).
Similarly, the coating materials I and II of
Run Nos. 6-2 to 6-5 were prepared according to the
formulations given in Table 6-1. In each run, the
793
- ~7 -
coating material I was appl.ied with a spray gwn to a
test panel (10 cm x 10 cm x 3 cm) made of PP so as to
give a dry film thickness oE about 50 ~, and then
dried at 80C for 3 minutes. Subsequentl.y, the coating
material II was sprayed thereon so as to give a dry film
thickness of about 50 ~, and then dried at 80C for 5
minutes.
9~793
rr~ble 6-1
(Unit: parts by weight)
-- _
6-1 6-2 6-3 6-~ 6--5
AN 30 30 30 30 30
BA 52 52 52 52 52
Overcoating MMA 11 11 11 11 11
Layer HEMA 3 3 3 3 3
(Coating MAc 2 2 2 2 2
Material II) A~ 2 2 2 2 2
CB 4 4 4 4 4
Filler40 - 40
BMA 54 - - - 54
BA 42 - - - 42
Undercoating2-EHA _ 93 93 93
15 Layer MAc 2 1 1 1 2
(Coating ~M 2 1 1 1 2
Material I) DVB - 5 5 5
CB 4 4 4 4 4
Filler - 20 20 60
Allowc ble range
Evalu- of laser output
ation (W) at a pulse 5 4.7 1.9 - 2
repetition fre-
quency of 5 kHz
_ ~9 _
The test panels thus obtaincd we.re laser-cut
under -the following condi-tions. The cuttability of the
strippable coating film and -the degree of damage to the
PP panel substrate were examined.
In Run No. 6-4, the coating material II
containing 60 parts of calcium carbonate had an
excessively high viscosity and could not be dispersed
satisfactorily. Moreover, it had such poor application
properties that no test panel could be ormed.
~1) YAG laser
YAG laser main unit: SL-114F (manufactured by NEC)
Q-switching oscillator: SL-231B (manufactured by
NEC)
(2) Oscillation conditions
Single mode
Mirror controlling method
(3) Cutting conditions
The test panel was cut while the laser output
was changed ~y varying the Q-switching oscillation
conditions (pulse repetition frequency) and the
lamp input current.
a) Pulse repetition frequency range: 1-30 kHz
b) Lamp input current: 14-19 A
Each sample was uct under the aforesaid
conditions and the results thus obtained are shown in
Figs. 3-6.
~Z~97~3
- 50 -
In Figs. 3-6, the abscissa of -the graph
indicates the laser output (W) which vaxies with the
lamp input current and the pulse repetition frequency.
The outpu-t was read in an output meter. The ordinate
of the graph indicates the pulse repetition frequency
of the Q-switching oscillator.
The solid line 1 on the left-hand side of the
graph indicates the borderline of cuttability of the
overcoating layer. That is, the overcoating layer could
not be cut in the area on the left of the solid line 1,
while it could be cut in the area on the right thereof.
The solid line 2 on the right-hand side of the graph
indicates the borderline of damage to the test panel
made of PP. That is, the test panel was not damaged
in the area on the left of the solid line 2, while it
was damaged by the laser beam in the area on the right
thereof.
Accordingly, the desirable results of the
present invention can be expected in the region defined
by overlapping of the area on the right of the left-hand
solid line 1 (where the overcoating layer could be cut)
and the area on the left of the right-hand solid line 2
(where the test panel was not damaged).
The graphs show that the magnitude of the
effect can be evaluated on the basis of "the width of
the overlapping region". In Table 6-1, however, the
~99~793
-- 51 --
allowable range of -the laser outpu-t at a pulse repetition
frequency of 5 kH~ is given as a criterion under the
head of "Evaluation"n
In each pair of data points ( O or X ) shown
in the graphs, the left-hand symbol indicates the
cuttability of the film and the right-hand symbol
indicates the degree of damage to the test panel.
These parameters were rated on the following
basis:
(1) Cuttability of the film
O = The overcoating layer was perfectly cut, and
the film could be cleanly stripped off to
create attractive boundaries.
~ = Part of the overcoating layer was not cut,
but the film could be stripped off along the
cutting line. However, the precision of the
finish of boundaries was similar to that
attainable with the current masking technique.
X = The overcoating layer was not cut.
(2) Degree of damage to the PP panel substrate
O = There was no sign of damage.
= A slight sign of damags was noted in the
surface.
X = A deep flaw was noted in the trace of the
laser beam.
As can be seen from the four graphs so
3L~99~3
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constructed, the laser output range in which the film
could be cut without causing damage to the substrate
was about 2 W in Run Nos. 6-3 (Fig. 5) and 6-5 (Fig. 6).
Howe~er, in Run Nos. 6-1 ~Fig. 3) and 6-2 (Fig. 4)
involving the addition of an appropriate amount of an
inorganic filler, the laser output range was as wide
as 4.5-5 W and indicates a high degree of utility.
The adhesion to the substrate as expressed
in terms of 180 peeling strength was as follow:
I _ 1 6-1 6-2 6-3 6-4 6~5
¦ Adhesion (g/inch) ¦ 350 107 105 105 350
Example 7
This example illustrates an aluminum powder-
containing strippable coating film of two-layer
construction.
An aqueous acrylic emulsion (having a concen-
tration of 50%) was prepared by copolymerizing 93 parts
of 2EHA, 5 parts of DVB, 1 part of MAc and 1 part of
AM according to the usual emulsion polymerization
technique. To this acrylic emulsion were added an
aqueous carbon black pigment (EP 510BR; manufactured by
Dainichi Seika Co., Ltd.) in an amount of 4 parts based
~Z~9~3
- 53 -
on the resin component and paint grade aluminum powder
(manufactured by Toyo Aluminum Co., L-td.) in an amount
of 15%~dry/dry) based on the resin component. Thus,
there was obtained the coating material I having
adhesive power.
On the other hand, an aqueous acrylic emulsion
having a concentration of 50% was prepared by copolymer-
izing 30 parts of AN, 52 parts of BA, 11 parts of MMA,
3 parts of HEMA, and 2 parts of MAc as in the same manner
as described above.
To this acrylic emulsion was added an aqueous
carbon black pigment in an amount of 4% (as solid carbon
black). Thus, there was obtained the coating material
II (Run No. 7-1 in Table 7-1). A film formed of the
coating material II had high strength, could be easily
stripped as a continuous film, and exhibited on adhesive
properties (when tested by the contact method).
Similarly, the coating materials I and II of
Run Nos. 7-2 to 7-4 were prepared according to the
formulations given in Table 7-1.
In each run, the coating material I was applied
with a spray gun to a test panel (100 x 100 x 3 mm) made
of PP so as to give a dry film thickness of 40-50 ~, and
then dried at 80C for 5 minutes. Subsequently, the
coating material II was sprayed thereon so as to give
a dry film thickness of 80-100 ~, and then dried at 80C
- 54 -
for 5 minutes. Thus, there was obtained a test panel
having a coating film of two-layer construction.
The test panels thus obtained were laser-cut
under the same conditions as described in Example 6.
The cuttability of the strippable coating film and the
degree of damage to the PP panel substrate were examined.
The results thus obtained are graphically shown in
Figs. 7 to 10 in the same manner as in Example 6, and
the results of evaluation obtained in the same manner
as in Example 6 are shown in Table 7-1 under the head
of "Evaluation". The adhesion of the films to the
substrate (180 peeling strength) is also shown in
Table 7-1.
~Z~979;~
- 5S -
Table 7-1
7-1 7-2 7-3 7-4
(Fig.7) (Fig.8) ~Fig.9) (Fig.10)
AN 30 30 30 30
MMA 11 11 11 11
Overcoating BA 52 52 52 52
HElYA 3 3 3 3
Layer
(Coating ~c 2 2 2 2
Material II) AM 2 2 2 2
Calcium _ 40
carbonate
CB 4 4 4 4
2-EHA g3 93 93 93
Undercoating MAc
15 Layer AM 1 1~ 1 1
(Coating DVB 5 5 5 5
Material I) Al powderlS 15
CB4 4 4 4
Allowable range
1 of laser output
Eva u-(W) at a pulse 5.5 5.8 2 1.2
repetition fre-
quency of 5 kHz
Adhesion to substrate ¦ 100 90 100 100
17~
- 56 -
Exploitability in Industry
AS described above in detail, the s-trippable
coating film of the present invention has excellent
masking properties and can be easily and consistently
cut with a laser beam, and the coating method o~ the
present invention makes it possible to achieve an
attractive finish of the boundaries. Accordingly, the
present invention can be widely exploited in a variety
of fields involving multi-color painting.
