Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CObOUR-PRATCHING OF COATINGS
The present invention relates to the colour matching
of coatings in a process of coating objects with an
undercoat and a pigmented topcoat. In particular, the
invention relates to a process in which the reflectance
of the undercoat and topcoat are matched to improve the
efficiency of the colour matching and in which the
undercoat is white, grey or black, but not otherwise
coloured by pigment. As used herein, '°undercoat'° refers
to the combination of layers of primers, sealers and
other coatings underneath the outer or topcoat on an
object.
The coating of objects, including metal and plastic
objects with pigmented coatings is well known, a major
example being the application of topcoats in the
automotive industry. One or more undercoats e.g. primer
and sealer, are applied to the object, followed by one or
more topcoats. Usually a plurality of coatings of a
topcoat are applied. One of the principal reasons for
the application of a number of coatings of topcoat is to
achieve a' highly uniform coating of the object,
especially with respect to the colour of the object.
This is especially critical in the automotive industry,
where the coatings are subjected to a wide variety of
extreme lighting conditions and consumers demand high
quality in the consistency of colour between different
parts of the automobile.
The problems of differing opacifying power of
topcoats, especially different oolours of topcoats, is
discussed in U.S. Patent 4 876 111 of D. Guyomard et al,
which issued 1959 October 24. Grey was stated to be an
unsatisfactory colour for the undercoat in view of the
poor opacifying characteristics of some colours,
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specifically yellow and red. The method disclosed by D.
Guoyomard et al to overcome the opacifying problem was to
blend a pigmented paste with a neutral primer base to
form a pigmented undercoat, which was then applied to the
object, the pigmented paste being selected on the basis
of a classification of the colour of the topcoat.
Although the use of pigmented undercoats may offer
a solution to poor opacifying power of pigments, the wide
variety of colours of automobiles would require a
substantial inventory of pigmented pastes to enable a
range of colours of undercoat to be produced as demanded
by the colour of the topcoat, as well as a need to select
an appropriate undercoat colour for efficient colour
matching with the topcoat. This would lee especially
critical in automobile repair operations i.e. the
automotive refinish industry. That industry must colour
match refinished objects to remaining sections having the
original colour of the automobile on an individual unit
basis i.e. for each automobile passing through the
refinish operation. Problems of contamination of colours
from one undercoat to the next would also exist.
It has now been found that undercoats that are
white, grey or black in colour, without coloured
pigments, enable efficient colour matching of the topcoat
to be achieved, reducing both inventory and contamination
problems.
Accordingly, the present invention provides a
process for the sequential coating of an object with at
least one undercoat and then at least one pigmented
topcoat, in which the pigmented topcoat has a reflectance
value of "R°', said undercoat and topcoat being comprised
of polymers in carrier liquids, camprising the steps of:
(a) mixing at least two compositions together to form
the undercoat, each of said compositions being comprised
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of polymers in carrier liquids and having different
reflectance values, each of said compositions having a
colour selected from the group consisting of white, grey
and black;
(b) controlling the blending of the compositions under
(a) so that the undercoat composition has a reflectance
value within ~10 units of the reflectance value, "R", of
the topcoat; and
(c) applying the composition of (b) to the object
followed by the composition of the pigmented topcoat.
In a preferred embodiment of the process of the
invention, the compositions used to form the undercoat
composition are different shades of grey.
In another embodiment, the compositions used to form
the undercoat are formed by admixing a black composition
with a white composition.
In yet another embodiment, the compositions used to
form the undercoat are formed by admixing a translucent
sealer with white, grey and/or black tint compositions.
Reflectance is a measure of the amount of light
reflected by a surface, the present invention being
concerned with light in the visible spectrum i.e. light
with wavelengths in the range of approximately 400 to
?OOnm. A coloured material reflects light of its own hue
and absorbs light of other hues. Measurement of
reflectance results in a spectral reflectance curve; as
used herein, reflectance °'R" is the peak value on the
spectral reflectance curve. Apparatus for the
measurement of reflectance are understood to typically
measure the spectral reflectance curve at more than one
angle, although the actual angles used may differ.
Reflectance is measured on a scale of 0-1.00, with white
having a value of 100 and black a value of 0; values
above 100 may be obtained at some angles of measurement
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i.e. at or near the specular angle (the specular angle
being 90° to the incident light source of the measuring
device), due to presence of aluminum flakes in some
topcoats, and such angles should not be used in
reflectance measurements pertaining to the present
invention.
The reflectance values may be determined on a colour
analyzing apparatus; an example of commercially available
apparatus is a Macbeth Color-Eye~ 5010
Goniospectrophotometer. Techniques of coating undercoats
and especially topcoats onto test panels to a consistent
colour are well known and frequently used in test
laboratories.
The process of the present invention relates to 'the
colour matching of undercoats and topcoats on coated
objects, and especially to a simple and practical method
of achieving matched colours. The process requires the
use of undercoats that are white or various shades of
grey, including very dark grey, or black, regardless of
the colour of the topcoat. This is achieved by matching
the reflectance of the undercoat to that of the topcoat.
The preparation of undercoats having a range of
reflectance values may be illustrated by the following
procedure, using three undercoat compositions. In this
illustration, the first undercoat is white, the second
undercoat is medium grey and the 'third undercaat is a
very dark grey. To prepare the range of undercoats, the
first and second undercoats are mixed in two differing
proportions e.g. 2:1 and 1:2. Likewise, the second and
third undercoats are mixed in two differing proportions
e.g. 2:1 and 1:2. The reflectance values are then
measured on the resultant seven underc~at compositions;
the reflectance values would range from low values e.g.
approximately 10, to high values e.g. approximately 90,
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the actual values depending on the three undercoat
compositions originally selected and the mixing
proportions. A plurality of panels of a material
appropriately similar to 'the object to be coated are
coated with each of the undercoat compositions, and
dried.
To further illustrate the invention, a series of
panels coated with the topcoat composition may be
prepared: the series involves coating panels that have
been coated with an undercoat composition with different
numbers of coatings of a selected topcoat, so that for a
particular undercoat a series of panels coated with one
coating of topcoat, two coatings of topcoat, three
coatings of topcoat etc. are obtained. Each topcoat is
air dried before application of the next top coat. L,a,b
measurements are made on all panels; persons skilled in
the art will appreciate that other valour measurement
classifications may be used. For each undercoat, the
L,a,b values will vary with increasing number of coatings
of the topcoat, and tend towards a constant L,a,b value.
The constant L,a,b value indicates the minimum number of
topcoats required for that particular undercoat in order
to achieve an acceptable coating. Repeating the process
for the different undercoats will reveal the preferred
undercoat i.e. the one giving an acceptable topcoat with
the minimum number of coats i.e. minimum film build, of
the topcoat. While this illustration has been described
with reference to L,a,b measurements, it should be
understood that some skilled persons may be able to
achieve the same result through visual observations.
2n practice, the full procedure described above as
an illustration would not be necessary. The reflectance
of the topcoat is predetermined, either because the
topcoat being applied must match adjacent coatings on the
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object, or because a customer has selected a particular
topcoat for the object. The requirement then becomes a
matter of matching of the reflectance "R" of the topcoat
to that of the undercoat. The reflectance of the
undercoat and topcoat should be within ~10 reflectance
units, especially within ~5 reflectance units, on the 0-
100 scale described above; if the undercoat and topcoat
have differing reflectance values, it is preferred that
the undercoat have the lower reflectance value.
The supplier of the topcoat could provide a
reflectance value, "R", for the topcoat, or a node
related to the reflectance value fox the topcoat, based
on laboratory testing prior to shipment to the customer.
Using mixing apparatus and guidelines provided by the
supplier of the undercoat, the customer that is applying
the topcoat could then select or mix the undercoat
composition to provide an undercoat that enables an
efficient colour match of the topcoat. Such mixing could
be from two undercoat compositions, of very high and very
low relectance characteristics e.g. a white and a very
dark grey or black undercoat composition, but is more
conveniently carried out by mixing two undercoat
compositions from a selection of two or more undercoat
compositions that cover the range of reflectance values.
Alternatively, the procedure illustrated above could be
conducted on a relatively small selection of undercoats,
based on the nature of the topcoat being applied, to give
the undercoat requiring the minimum number of coatings of
topcoat.
The undercoat compositions used in the invention are
intended to be white, a shade of grey or black, without
any coloured pigments that assist in the matching of the
colours of the undercoat end the topcoat. while minor
amounts of a coloured pigment may be added, they may or
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may not assist in the colour matching of the topcoat, and
may have detrimental effects on and increase the
complexity of the colour matching.
The admixing of the compositions that form the
undercoat is carried out to provide a undercoat with the
required degree of reflectance. The admixing may be done
on a batch basis, with appropriate adjustments being made
during the mixing step so as to obtain an undercoat of
the required reflectance. Alternatively, the mixing may
be done on a continuous basis, with tests being conducted
periodically for purposes of monitoring, and adjustment
as required, of the reflectance of the undercoat.
Both the undercoat and topcoat will normally be in
the form of a polymeric component in a carrier liquid.
The polymeric component is also known as resin or binder,
and catalysts and other additives may also be added to
the compositions, as will be appreciated by persons
skilled in the art. The carrier liquid may be an organic
solvent, the polymeric component being in the form of a
solution or dispersed in the liquid. Alternatively, the
carrier liquid may be an aqueous solution, in which event
the polymeric component will normally be in the form of
a dispersion. In another embodiment, the topcoat may be
in the form of a powder. The topcoat will normally also
contain pigments. The undercoat may or may not contain
pigments in minor amounts.
The undercoat and topcoat may be applied using
spraying techniques, as will be understood by persons
skilled in the art. Alternatively, especially fox the
undercoat, the coating may be applied by
electrodeposition techniques. Other coating techniques
may also be used.
The method of the present invention may be used in
the coating of objects in which a undercoat and a topcoat
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are applied. In particular, the process may be used in
the automotive industry, and especially in the refinish
or repair portions of the automotive industry.
The use of the fewest number of topcoats, or minimal
film build, to achieve an acceptable coating has a number
of benefits to the operator of the coating line e.g. in
a repair or refinish coating operation. For instance,
fewer coatings (or less film build) means that less
topcoat is required in order to obtain the acceptable
coating, which is a savings in terms of both the cost of
the topcoat and the time required i.e. the time to apply
the required number of coatings is reduced. The ability
to be able to prepare undercoats from a small number of
undercoat compositions, being two or more but preferably
three, simplifies the inventory and operational problems
for the repair or refinish operator while still
permitting efficient and acceptable use of possibly
hundreds of different topcoats.
The present invention is illustrated by the
embodiments shown in the following examples:
Example I
A series of undercoats were'prepared by admixing two
compositions that were white and medium grey or medium
grey and very dark grey in colour. A total of seven
undercoats were prepared, having reflectance values of
from approximately 10 to 85.
A red metallic automotive topcoat was selected for
testing. When tested for reflectance, this topcoat had a
reflectance '°R" of 20. This value of reflectance was
intermediate between undercoat # 6 having a reflectance
of 15 and undercoat #5 having a reflectance of 25. In
the absence of preparation of another undercoat with a
reflectance more closely matching that of the topcoat, it
would therefore be expected that undercoat #6 would be
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the preferred undercoat.
A series of 21 panels were prepared, in three sets
of seven, from undercoats #5 and 6 above, and from
undercoat #7 which had a reflectance of 10. One panel of
each set was coated with two coats of the red metallic
topcoat. Similarly, one panel from each set was coated
with from three to eight coats of the topcoat, such that
all 21 panels had been coated. Each coating of topcoat
was approximately 25 microns in thickness and was air
dried prior to application of any further coating.
L,a,b measurements were conducted on all panels.
The panels were also inspected visually for colour match
to a standard. In each series, the panels with a colour
match to a standard panel coated with the same topcoat
were determined. It was found that undercoats #5 and #7
required at least 6 coats of the topcoat before a colour
match was obtained, with the grey shade being apparent
after 4 coats with both of these undercoats. However,
undercoat #6 gave a good colour match after 4 coats of
topcoat, confirming the prediction that undercoat #6
would be the preferred undercoat.
Example II
The procedure of Example Z was repeated using 35
topcoats of different colours. In each instance, the
undercoat having the closest match of reflectance to that
of the topcoat was the preferred undercoat, requiring the
least number of coats of topcoat to obtain a colour
match.
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