Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1170513
PROCESS FOR THE MANUFACTU~E OF DECORATIVE LAMINATES
This invention relates to a process for the manufacture
oi' decorative laminates, to the laminates so made and to
a paper for use in the process.
Decorative laminates are used, i'or example, for surfacing
furniture, particularly kitchen or other furniture where
it is desirable to have a water-resistant, easily-wipeable
sur~ace, for counter tops-in s~ops ~nd cafes and ~or
building panels. They may be white or coloured, and may
be plain or printed, for example with a woodgrain or other
pattern Printing may be in several colours, and is
usually ei'~ected by a rotogravure technique.
One well-known type of decorative laminate (usually known
as a high-pressure laminate) consists oi' several so-called
core~ sheets ior imparting strength to the laminate, a
decorative sheet serving to mask the uppermost core sheet
and to ai~ord the laminate an attractive surface, and an
overlay sheet on top oi the decoratlve sheet (the overlay
sheet becomes transparent during manuiacture oi' the
lam$nate, and so does not mask the decorative sheet). A
so-called barrier sheet can be provided between the
decorative sheet and the uppermost core sheet to ai~ord an
additional maæking ei'i'ect. All the sheets i'orming the
laminate are impregnated with a thermo-setting resin, for
example a phenolic resin or a melam~ne-i'ormaldehyde or
; 25 other aminoplast resin (the various sheets making up the
laminate are not usually all impregnated with the same
resin). The impregnating resin in the case oi' the
decorative sheet is most commonly a melamine i'ormaldehyde
resin. In the ~inal impregnated sheet, the resin is
usually present in an amount o~ the order of lOO~o W/W.
1170~1 3
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If the decorative laminate is to be of a printed design,
the decorative sheet normally carries the print. Alter-
natively, however, the overlay sheet may carry the print
on its surface which contacts the decorative sheet.
The core sheet3 are normally of strong, relatively in-
expensive paper, for example unbleached softwood kraft
paper. Such paper is not of uniform or particularly
attractive appearance, and is not suitable for high quality
printing. For this reason, it is necessary for the
10 decorative sheet to be sufficientlv opaque to mask the
unattractive and non-uni~orm appearance of the uppermost
core sheet, and for it to be suitable for high quality
printing.
In another type o~ decorative laminate (usually known as a
15 low-pressure laminate), a sheet of chipboard or similar
material is used directly as a support Por the decorative
sheet, instead of the core sheets. The decorative sheet
ln such a laminate serves to mask the chipboard rather than
the core sheets. Again, it is necessary for the decora-
20 tive sheet to be opaque and to be suitable ~or high qualityprintlng. Barrier sheets are not normally used in this
type oi laminate since chipboard is normally o~ a lighter
shade than core sheets and hence is more easily masked.
The paper which is used ~or making decorative sheets is
25 known as plastic base surface paper. In addition to being
opaque and huitable for printing, it must be absorbent so
that it may easily be impregnat~d with resin during a single
pass through an impregnating bath, wh.ich typically takes
about 20sec. The same applies to the overlay sheet if it is
30 to be printed. The absorbency o~ plastic base sur~ace
paper, as measured by the Klemm method, is typically in
the range 30 to 65 mm/10 min i~ ~or use in a high-pressure
1170513
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laminate, or in the range 25 to 45 mm/10 min i~ ~or use
` in a low-pressure laminate (in the Klemm method a strip
o~ paper 15 mm wide is suspended vertically with one end
in a dish of the liquid concerned and the distance the
liquid soaks up the paper in ten minutes is measured).
The absorbency of an overlay sheet is typically in the
higher part of the range quoted for plastic base surface
paper for use in a high-pressure laminate. The absorbency
oi' plastic base surface paper may also be quoted in terms
o~ porosity as measured by a Gurley porosity tester, siJIce - , - -
porosity i~ related to speed of absorbency in this instance.
Plastic base surface ~aper typically has a Gurley porosity
- (20 oz) in the range 10 to 25 sec/100 ml prei'erably 20
to 25 sec/100 ml, if ~or use in a high-prsssure laminate,
or in the range 15 to 50 sec/100 ~1 i~ ~or use in a low-
pressure laminate, although values of 70 sec/100 ml or
more are acceptable,
The requirement ~or plastic base sur~ace paper and overlay
paper to be absorbent results in a relatively rough paper
sur~ace which is not particùlarly suitable ~or high quality
gravure printing. There are two main problems, First,
the rough sur~ace makes it di~i'icult to obtain complete
prlnt coverage ~rom every gravure cell. Second, the
absorbent nature o~ the paper allows ink to penetrate into
25 the sheet and print intensity is there~ore reduced. -
Despite these problems, plastic base surface and overlay
paper can be printed to a high standard, provided larger
quantities oi' ink are used than would be needed on a
good printing sur~ace or provided a lower absorbency is
ac~,eptable.
_ .
~t might be thought that the above-described problems
' could be simply overcome by the application o~ a pigment
1170513
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coating such as is commonly used in the manuiacture o~
high quality printing papers. Eowever, such coatings
enhance printability not only by increasing surface
smoothness, which would be acceptable in plastic base
surface and overlay papers, but also by decreasing absor-
bency to an extent which would not be ~-cceptable in such
papers. Pigment-coated art papers, for example, typically
bave a Klemm absorbency below 5 mm/10 minutes, which is
well below that required in plastic bæse surface and
10 overlay papers.
However, it has now been found that, contrary to previous
expectations in the art, the printability of plastic base
suriace and overlay papers can be improved without unaccept-
ably reducing the capacity oi the paper to absorb impreg-
15 nating resins by applying to the paper a coating containinga pigment and a binder.
Accordingly, the present invention provides in a first
aspect a process ior the manuiacture oi a decorative
laminate comprising the steps o~ applying a liquid coating
20 composition comprising a pigment and a binder to a surface
oi a previously ~ormed and dried decorative laminate sur~ace
or overlay paper to give a coatwelght when dry o~ up to
lOgm 2 on said sur~ace, the resulting coated paper having
a Gurley porosity (20 oz) o~ about 10 to ~0 sec/100 ml,
25 printing a desired pattern on said coated sur~ace o~ said
paper, impregnating the resulting printed paper with a
thermo-setting resin and laminating the impregnated paper
to a support therefor under conditions e~iective to cure
the resin, thereby to produce said decorative laminate.
30 In a second aspect, the present invention provides a
decorative laminate suriace or overlay paper carrying a
coating composition comprising a pigment and a binder on a
suriace thereoi' at a coatweight oi up to lOgm~2, said paper
,; .
117051 3
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having a Gurley porosity of about 10 to 70 sec/100 ml and
said pigment being kaolin, calcium carbonate, titanium
dioxide or barium sulphate.
In order to ensure that the absorbency of the present
plastic base ~urface or overlay paper is at a suitable
level and that the surface smoothness of the coating is
at an optimum level, the coatweight and the weight ratio
oi' pigment to binder must be chosen carefully. The
- preferred dry coatweight is in the range of from 2.5 to
3gm ~, The weight ratio oi' pig~l~nt to binder in the
coating is preferably in the range 5:1 to l:l, more
preferably from 2.5:1 to 3.5:1. The Gurley poroslty
(20 oz ) of the coated pa?er is preferably in the range
20 to 50 sec/100 ml.
15 The pigment is preferably one having a ~8' h~rdness of
less than 7, ~or example kaolin, calci~m carbonate in
~recipitated or ground iorm, titanium dioxide or barium
sulphate. ~igments having a Mohs'hardness greater than 7,
such as alumina or hydrated alumina, various natural or
20 synthetic alumino-silicates or silica or silica gel may
however be used. The binder may be starch, casein,
latex, polyvinyl alcohol or an aminoplast or other cross-
linking resin.
Pre~erably the liquid coating composition comprising the
25 pigment and binder is appliéd by size press treatment,
although other coating techniques may be used, ior example
alr-kniie coating, It will be appreciated that size
press treatment normally results in a coating being applied
to both sur~?.cés o~ the paper web.
30 Once the decorative laminate sur~ace or overlay paper has
; been coated it may be calendered be~ore being impregnated.
117~513
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The present plastic base suriace or overlay paper enables
an improvement in print quality to be obtained as a result
oi more complete ink transfer from the gravure cells and
oi' less ink absorption. It also permits a reduction in
ink usage for a print of speci~ied quality, or, for the
same ink usage, affords a better print than would be
obtained on the same paper if it were not coated.
The invention will now be described with reference to the
iollowing examples :
10 - xArlpLE 1
A sheet o~ plastic base surface paper having a grammage of
100gm 2 was size press coated with an aqueous coating
containing a mixture of kaolin (supplied by English China
Clays under the designation "Supreme"), esterified starch
15 and mel'amine-formaldehyde resin in a weight ratio of
3:1:0.001. The coating was then dried, the dry coatweight
being 3gm 2 The absorbency oi' both the coated and the
uncoated paper was i'ound to be 30mm/10 min. The Gurley
porosity (20 oz) oi' the coated paper was ~ound to be 24 sec/
20 100 ml, and that o~ the uncoated paper was 18 sec/100 ml.
Both the coated paper and a sample oi' uncoated plastic base ~ -
sur~ace paper were then printed with the same amount of ink
using a gravure printing process. On examination of the
printed papers, it was i'ound that the optical re~lectivity
25 o~ the uncoated paper (as measured by an Elrepho opacimeter) '~
was 20% whereas that oi the coated paper was 10%. Both
papers absorbed a su~icient amount oi' resin to make
satis~actory laminates and the colour or shade o~ the
unprinted sur~ace oi a laminate containing the coated paper
30 was ~udged to be the same as that o~ a laminate containing
uncoated paper.
~.1
1 ~7051 3
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- EXAMPLE 2
.
A sheet of plastic base surface paper having a grammage of
120gm 2 was size press coated with an aqueous coating
containing a mixture of barium sulphate (precipitated),
esterified starch and melamine formal~e.lyde resin in a
weight ratio of 3:1:0.001. The coating was then dried
and calendered, the dry coatweight being 7gm 2. The
- Gurley porosity (20 oz) of the coated paper was found to
be 26 sec/100 ml, and that oi~;the ~ln~oated paper was
14 sec/100 ml.
Both the coated paper and a sample of uncoated plastic
base surface paper were then printed with the same amount
of ink using a gravure printing process. On examination
of the printed papers, it was found that the optical
reflectivity of the uncoated paper (as measured by an
Elrepho opacimeter) was 20% whereas that oi' the coated
paper was 18~o. Both papers absorbed a sufficient amount
o~ resin to make satisfactory l~minates and the colour or
shade of the unprinted sur~ace of a laminate containing
the coated paper was ~udged to be the same as that o~ a
laminate containing uncoated paper.
EXAMPLE 3
A sheet of plastic base surface paper having a grammage of
120gm 2 was size press coated with an aqueous coating
containing a mixture oi titanium diov~ide (supplied by
British Titan Products, under the designation ALF),
esterified starch and melamine ~ormaldehyde resin in a
weight ratio of 3:1:0.001. The coating was then dried
and calendered, the dry coatweight being 6.6gm 2. The
Gurley porosity (20 oz) of the coated paper was found to
be 69 sec/100 ml, and that of the uncoated paper was
14 sec/100 ml.
1 17051 3
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Both the coated paper and a sample o~ uncoated plastic base
surface paper were then printed with the same amount of ink
using a gravure printing process. On examination of the
printed papers, it was found that the optical reflectivity
of the uncoated paper (as measured by an Elrepho opacimeter)
was 20% whereds that of the coated paper was 17~. Both
papers absorbed a sufficient amount of resin to make
satis~actory laminates and the colour or shade of the
unprinted surface o~ a laminate containing the coated pa~er
10 was j~dged to be the same as that of a laminate containing
uncoated pap~r.
EXAMPLE 4
A sheet of plastic base surface paper having a grammage of
120gm 2 was size press coated with an aqueous coating
15 containing a mixture of calcium carbonate (under the
designation Hydrocarb) esterified starch and melamine
iormaldehyde resin ir. a weight ratio oi' 3:1:0.001. The
coating was then dried and calendered, the dry coatweight
being 5.5gm 2 The Gurley porosity (20 oz) of the coated
20 paper was ~ound to be 50 sec/100 ml, and that of the
uncoated paper was 14 sec/100 ml.
Both the coated paper and a sample of uncoated plastic base
suriace paper wcre then printed with the same amount of ink
using a gravure printing process. On examination of the
25 printed papers, it was found that the optical re~lectivity
oi the uncoated paper (as measured by an Elrepho opacimeter)
was 20~o whereas that of the coated paper was 17%. Both
papers absorbed a sufficient amount oi resin to make
satisfactory laminates and the colour or shade o~ the
30 unprinted sur~ace of a laminate containing the coated paper
was judged to be the same as that of a laminate containing
uncoated paper.
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