Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
: ~O 92/06243 2 0 ~ 3 1~ ~ PCl/AU91/00451
VACUUM MErALLlZATION OF SUPSTRATES
This invention relates to the vacuum metallization of substrates and more
particularly to an apparatus for use in the vacuum metallization of substrates such as
paper.
Various processes have been employed for the metal cladding of web or sheet
substrates. The traditional process involves adhering a thin metal foil to a paper or
board substrate, aluminium foil being most commonly used. This process has proved to
be uncertain from an economy viewpoint since the cost of metal foil is a fluctuating
commodity-sensitive item and because a relatively thick foil was necessary.
Another commonly used, and superlor process is that known as vacuum
metallization, in which a vaporized metal is condensed onto a substrate to be metallized.
Other prior art processes have included so-called ~transfer metallization~
as described in U.S. Patent No. 4,215,170 (OLIVA), involving coating a substrate or a
. transfer agent with a varnish, laminating substrate and transfer agent~ drying the
15 varnish and stripping the transfer agent from the substrate. Curing time for the varnish
may be form 24 to 26 hours, which period seriously interferes with inspection and
. subsequent treatment. This "time lag" problem was solved by radiation curing, that is to
' say, electron beam curing, of coatings and adhesives in the process of the metalliza~ion of
`f paper substrates. Such a process including curing the varnish substantially
2 0 instantaneously wlth electron radiation is disclosed in lapsed Australian Patent
Application No. 23174/84.
Two different paper me~alllzation process systems are currently is use, viz,
direct metallizatlon and transfer metal!lzation.
This specification is concerned with direct metallization.
2 5 The process of transfer vacuum metallization is practised by the~deposition of
metal, usually aluminium, (but not exclusively, as silver, gold, copper, ~in, platinum
~ etc. may be contemplated) in a vacuum chamber onto a plastic carrier web, and by the
- subsequent transfer of the metai layer from the carrier web to the chossn paper
- substrate by an adhesive laminating process. Finally, the carrier web is stripped by
3 0 delamination of the plastic.carrier web from the metal clad paper substrate.This process normally provides a metal clad paper surface which is a replica
-~ of the surface condition of the carrier web on which the metal was originally deposited.
The stripping of the carrier web from the laminated paper structure is intended to occur
without damage, thus enabling the carrier web to be eventually recycled.
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The economic viability of the above metallizing process for paper is
tcritically dependant on the number of process cycles through which the carrier web can
be re-used.
When carried out in an effective manner, the visual quality of transfer
5 metallized paper is superior to the appearance of direct metallized paper. However,
because of the unpredictable cost factor of carrier web re-cycling, the cost predicability
and the relative cost of the direct process are, respectively, significantly higher and
consis~ently lower than the transfer process.
Thus it will be appreciated that i~ is an object of the present invention to
10 overcome at least one disadvantage by the provision of a metallization process which
glves the finished product substrate a visual quality advantage; the direct process being
of a lower, more predictable cost.
According to one aspect of the present invention there is disclosed a
premetallization process comprising the steps of:
1 5 ( a) coating a drum with a liquid coating, said coating being performed
by said drum contacting at least one roller to supply said coating;
(b) passing a paper substrate over said drum, in contact with said
coating;
( c ) electron curing said coating onto said substrate; and
2 0 ( d ) removing the coated and cured substrate by peeling from the drum
surface .
This product can then be taken to the metallising process, after the
application of which it is given a final top coating.
According to another aspect of the present invention there is disclosed a
25 metallization process wherein pressure is applied to said substrate to initiate contact
said roller.
: - According to another aspect of the present invention there is disclosed a
metallized paper product produced by a process having after final top coating a specular
reflectance value of with the range of 45 units to 100 units, said value being determined
3 0 by illumination at an angle of 60 with- the reflection being received by a Dr. Lange gloss
meter model RB60M. ~ 3-
-In order that a better understanding of the invention may be gained, preferred
embodiments thereof will now be described, by way of example only and with reference to
the accompanying drawings in which:- - - ,
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~VO 9~/06243 2 ~ ~ ~13 ~ PCI`~AU91/00451
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Figure 1 illustrates schematically, a "state of the art" transfer vacuum
metallization apparatus;
Figure 2 illustrates also schematically, a drum transfer or casting apparatus
according ! the present invention; and
Figure 3 illustrates a drum transfer process according to a further
' embodiment of the present invention.
It will be understood that the coating of films or coatings from cylindrical or
drum-like surfaces, usually of polished or engraved metal, is a well-established art and
has been commercially practised for both the coating of paper and the printing of
10 textiles, to name but two examples.
' This invention involves the employment of a somewhat similar drum adapted
' to supply high velocity electrons from an electron generator and for the drum to receive
' an electron-curable coating applied either directly to the drum surface or to the paper
~' web immediately prior to its contact with the drum surface, such coating being
;' 15 specifically formulated for later metallization.
The prior art transfer vacuum apparatus shown in Figure 1 comprises a
' vacuum metallized carrier web 1 - usually a plastic film - feeds from a carrier storage
' reel 2 to a coating station comprising an assembly of coating rollers 3, 4 and 5, the
lowermost roller 5 rotating in a tank 6 of a suitable laminating adhesive. From the
2 0 coating station carrier web 1 with its adhesive coating 6 passes to a pair of laminating
nip rollers 7 and 8 where it is "nip laminated~ with a paper substrate 9 wnich is fed
from a paper storage reel 10. The completed web, that is to say the carrier web 1,
adhesive coating 6 and paper substrate 9, then travel through a chamber 11 of anelectron-curing apparatus 12 where the adhesive coating layer 6 is substantially: 25 instantaneously cured.
The completed and cured web then pass between a pair of release nip rollers
- 13 and 14 where the carrier web is stripped from the cured web and fed to a carrier
storage reel 15 for re-use. The finished product 16 is fed to another storage reel 17 to
.u await usage.
3 0 At this point it should be observed that such an- electron-curing apparatus as
12 utilizes either a heated filament or a gas plasma/cold cathode system-to generate a
curtainn of electrons which penetrate the adhesive coating on the substrate web, which
travels normal to-the longitudinal axis of the linear filament. The system. is self-
shielded and its accelerating voltage limited to, say, 350 kv. ~ -
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This invention therefore enables the manufacture of a mirror-like metallized
paper or paperboard or alternatively an engraved or embossed surface finish is
achievable or a combination of both could be applied by changing cylinders between pre-
coating and post coating.
6 This process eliminates the recycled carrier web of the transfer
metallization process, with the obvious benefit of cost predictably of this new version of
the direct process of metallization.
Coatings of the free-radical polymerisation reactive type or of the cationic
cure type, both involvlng electron irradiatlon for cure are essential in order to solidify
; 10 the liquid coatings more or less instantly (within 500 milliseconds) prior to their peel
-~ removal from the drum surface.
From the above it will be realised by those who are skilled in the art that
numerous variations and modifications may be made to the invention without departing
from ~he spirit and scope thereof as described and illustrated hereinbefore.
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