Note: Descriptions are shown in the official language in which they were submitted.
CA 02235542 1998-04-22
1
DECORATIVE SHEET
TECHNICAL FIELD
The present invention relates to a decorative
material and particularly to a decorative material, for
building materials, which can impart a desired design to
the surface of furniture, wall surface, and floor covering
and the like and possesses excellent surface protective
properties.
BACKGROUND ART
A decorative sheet comprising a surface protective
layer, constituted by a layer of a resin cured by ionizing
radiation irradiation, provided on the surface of a
decorative sheet for a building material has been proposed
in the art.
Since this conventional surface protective layer is
in a cured state, the layer strength of the surface
protective layer per se is excellent. However, when the
surface protective layer is provided contiguously to other
layer(s), that is, when a solid print layer, a pattern
layer and the like and the surface protective layer are
laminated on a substrate sheet, the adhesive strength
between the solid print layer and the pattern layer and the
surface protective layer is disadvantageously low.
Therefore, the conventional decorative sheet has poor
Hofmann's scratch resistance and, hence, in some cases
cannot be practically used because the decorative sheet
particularly in its horizontal face portion is easily
scratched.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the
above problem of the prior art and to provide a decorative
sheet possessing high adhesive strength between the surface
protective layer and each layer laminated onto the surface
protective layer and, in addition, excellent scratch
resistance.
- CA 02235542 1998-04-22
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According to the present invention, the above
problem can be solved by incorporating a compound having
active hydrogen into any one of a surface protective layer
and a layer contiguous to the surface protective layer,
incorporating an isocyanate compound into the other layer,
and curing these layers.
The present invention specifically includes the
following aspects.
According to one aspect of the present invention,
there is provided a decorative sheet comprising: a
substrate sheet; a contiguous layer provided on the
substrate sheet; and a surface protective layer provided
on the contiguous layer, the surface protective layer
comprising an ionizing radiation-curing resin composition,
the contiguous layer comprising a compound containing
active hydrogen, the surface protective layer further
comprising an isocyanate compound, the contiguous layer and
the surface protective layer being in a cured state.
According to another aspect of the present
invention, there is provided a decorative sheet comprising:
a substrate sheet; a contiguous layer provided on the
substrate sheet; and a surface protective layer provided
on the contiguous layer, the surface protective layer
comprising an ionizing radiation-curing resin composition,
the contiguous layer comprising an isocyanate compound, the
surface protective layer further comprising a compound
having active hydrogen, the contiguous layer and the
surface protective layer being in a cured state.
According to a preferred embodiment of the present
invention, the compound having active hydrogen is a
compound having a group selected from the group consisting
of polyol, COOH, and NHz groups.
According to another embodiment of the present
invention, the contiguous layer further comprises an
isocyanate group-containing acrylate monomer and/or
prepolymer.
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According to the present invention, an ionizing
radiation-curing resin contained in the surface protective
layer is self-reacted and consequently crosslinked or
polymerized, and, in addition, the compound having active
hydrogen, contained in any one of the contiguous layer and
the surface protective layer, and the isocyanate compound
contained in the other layer are chemically reacted with
each other, permitting the contiguous layer and the surface
protective layer to be strongly bonded to each other in the
interface of these layers, which results in markedly
increased ply adhesive strength and improved Hofmann's
scratch resistance of the surface protective layer.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic cross-sectional view showing
the layer construction of a decorative sheet according to
an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
As shown in Fig. 1, the decorative sheet according
to the present invention comprises: a substrate sheet 1;
and a contiguous layer 4 and a surface protective layer 5
which have been formed in that order on the substrate sheet
1 and then cured. In the embodiment shown in Fig. l, the
contiguous layer 4 comprises a solid print layer 2 and a
pattern layer 3.
In the decorative sheet of the present invention,
substrate sheets usable herein include papers, plastics,
metallic foils, and plates. Regarding the form of the
substrate sheets, any of sheets, such as plastic sheets and
nonwoven fabrics, metallic plates, wood plates, and plastic
plates may be used. When a flexible sheet is used as a
roll, a sheet thickness of 5 to 200 um is preferable.
Further, provision of a pattern of irregularities on the
surface of the substrate sheet and a three-dimensional
substrate sheet may also be used.
Papers used as the substrate sheet may be papers or
fibrous sheets similar to papers. Examples thereof include
papers using natural pulp, such as tissue papers, kraft
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4
papers, titanium papers, linter papers, vinyl wallpaper
sheets, coated papers, paperboards, gypsum liner boards,
and parchment papers; and sheets made of inorganic fibers,
such as glass fibers, asbestos, potassium titanate fibers,
alumina fibers, silica fibers, and carbon fibers, or fibers
of organic polymer compounds, such as polyesters,
polyamides, and acetalated production of polyvinyl alcohol
(trade-mark: Vinylon).
They may be in any of bleached, unbleached, and
colored states which may be selected according to the
contemplated design.
Examples of plastic sheets usable as the substrate
sheet include single layer or laminate sheets of stretched
or unstretched plastic films of: olefinic resins, such as
polyethylene, polypropylene, and polymethylpentene; vinyl
resins, such as polyvinyl chloride, polyvinylidene
chloride, polyvinyl alcohol, vinyl chloride/vinyl acetate
copolymer, ethylene/vinyl acetate copolymer,
ethylene/acrylic acid copolymer, ethylene/acrylic ester
copolymer, ionomer, vinylon, and saponified ethylene/vinyl
acetate copolymer; polyesters, such as polyethylene
terephthalate, polybutyl terephthalate, and polyethylene
naphthalate/isophthalate copolymer; acrylic resins, such
as polymethyl (meth)acrylate, polyethyl (meth)acrylate, and
polybutyl (meth)acrylate; polyamides, such as nylon 6 and
nylon 66; cellulose derivatives, such as cellulose
triacetate and cellophane; polystyrols; polycarbonates;
polyallylates; and polyimides. Metals usable in the
metallic foil include aluminum, stainless steel, iron, and
copper.
Other substrate sheets suitable in the present
invention include: wood plates, such as wood veneers,
laminated woods, particle boards, and medium-density fiber
boards (MDF); gypsum-based boards, such as gypsum boards
and gypsum slag boards; and calcium silicate boards . Other
examples thereof include: fiber cement boards, such as
asbestos cement boards, concrete boards, lightweight gas
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concrete boards, extrusion blown cement boards, pulp cement
boards, asbestos cement boards, and wood chip cement
boards; ceramic boards, such as earthenware plates,
porcelain, stoneware, earthenware, glass, and enamels;
5 metallic sheets or plates, such as steel, galvanized,
polyvinyl chloride sol coated steel, aluminum, copper, and
stainless sheets or plates; thermoplastic resin sheets or
plates, such as polyolefin, acyclic resin, ABS, and
polycarbonate sheets or plates; phenolic resin, urea resin,
unsaturated polyester, and polyurethane sheets or plates;
and the so-called fiber-reinforced plastic (FRP) sheets or
plates prepared by impregnating an epoxy, melamine, or
diallyl phthalate resin, into glass fibers, nonwoven
fabrics, papers, and other various fibrous substrates and
then performing curing; and composite substrate sheets
prepared by laminating two or more of the above various
substrate sheets.
The contiguous layer according to the present
invention may be formed by simply coating or impregnating
the above substrate sheet with a polyol compound or an
isocyanate group-containing acrylate monomer and/or
prepolymer.
In the embodiment shown in Fig. l, the contiguous
layer is constituted by a solid print layer and a pattern
layer. In the present invention, however, the construction
of the contiguous layer is not limited to this.
According to the present invention, a specific
example of the ionizing radiation-curing resin used in the
surface protective layer is a composition, curable with an
ionizing radiation, comprising a suitable mixture of a
prepolymer, an oligomer and/or a monomer having in its
molecule a polymerizable unsaturated bond or an epoxy
group. The term "ionizing radiation" used herein means,
among electromagnetic waves or charged particle beams,
those having energy quantum satisfactory for inducing
polymerization or crosslinking of molecules, and
ultraviolet light or electron beams are generally used.
< CA 02235542 1998-04-22
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Examples of prepolymers and oligomers usable herein
include: unsaturated polyesters which are condensates of
unsaturated dicarboxylic acids with polyhydric alcohols;
(meth)acrylates, such as polyester (meth)acrylate,
polyether (meth)acrylate, epoxy (meth)acrylate, urethane
(meth)acrylate, and melamine (meth)acrylate; and cationic
polymerizable epoxy compounds.
In the present invention, the solubility parameter
(SP value) of the ionizing radiation-curing resin is
usually 9.7 to 11.0, preferably 9.9 to 10.5. An SP value
of less than 9.7 results in unsatisfactory strength of
bonding to the substrate sheet, unsatisfactory power for
holding spherical particles used in the regulation of gloss
on the surface, and poor scratch resistance. On the other
hand, an SP value exceeding 11.0 in some cases makes it
impossible to meet the requirement for the strength of
bonding to the substrate sheet when the resin is coated
onto paper or a plastic film.
The SP value referred to herein is calculated as
described in "POLYMER ENGINEERING AND SCIENCE, Vol. 14, 174
(1974)." When two or more ionizing radiation-curing resins
are used as a mixture, the SP value is the weighted average
of the SP values of respective ionizing radiation-curing
resins.
Isocyanate compounds usable in the surface
protective layer and/or the contiguous layer according to
the present invention include: aliphatic, alicyclic, or
aromatic di- or triisocyanate compounds, such as 2,4-
tolylene diisocyanate, 2,6-tolylene diisocyanate,
diphenylmethane-4,4'-diisocyanate, polyphenylmethane
polyisocyanate called "crude MDI," xylylene diisocyanate,
isophorone diisocyanate, hexamethylene diisocyanate,
dicyclohexylmethane-4,4'-diisocyanate, and triphenylmethane
triisocyanate; and isocyanate-terminated, low-molecular
weight adducts prepared by reacting a polyisocyanate
compound with a low-molecular weight glycol or triol, for
example, dipropylene glycol, 1,6-hexanediol, 1,2,6-
CA 02235542 1998-04-22
hexanetriol, or trimethylolpropane.
A compound having a group selected from the group
consisting of polyol, COOH, and NHZ groups may be
preferably used as the compound having active hydrogen
contained in the surface protective layer or the contiguous
layer according to the present invention. It is also
possible to use a urethane resin with an excess of polyol
being added thereto.
Preferred polyol compounds usable herein include
monomer diol and triol and polymer diol and triol
containing mainly a repeating unit chain of an alkylene
contributing to the molecular weight. A typical polymer
polyol include a monomer polyol consisting essentially of
any one of a straight chain terminated with a hydroxyl
group and a branched chain and preferably has 2, 3, 4 or
more hydroxyl groups. For example, those comprising
ethylene glycol, propylene glycol, glycerin,
trimethylolpropane, 1,2,6-hexanetriol, butenediol, sucrose,
glucose, sorbitol pentaerythritol, mannitol,
triethanolamine, n-methyldimethanolamine, and cyclic
aromatic and aliphatic and triols. Preferred are polyester
polyol, polyether polyol, acrylic polyol, and epoxy polyol.
In the present invention, an acrylate monomer
and/or a prepolymer having an isocyanate group may further
be added to the surface protective layer and/or the
contiguous layer. A compound having one or more acryloyl
groups in its molecule and one or more isocyanate groups
in its terminal and/or side chain is preferred as the
acrylate monomer and/or prepolymer having an isocyanate
group.
Further, fillers, such as calcium carbonate,
silica, and alumina, viscosity depressants, levelling
agents, colorants, and sheeny pigments may also be added
to the surface protective layer from the viewpoints of
imparting suitability for coating and imparting features
to the surface state.
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Spherical particles may be used as an additive for
improving the abrasion resistance of the surface protective
layer. Spherical particles may be those having a surface
surrounded by a smooth curved surface, such as those having
a spherical shape and a shape close to a sphere, such as
a flattened, elliptical shape. Preferably., the spherical
particles are free from a protrusion or a corner
particularly on the surface of the particles, that is, free
from cutting edges. As compared with irregular particles
made of an identical material, the spherical particles
function to improve the abrasion resistance of the surface
protective layer. Further, they have features including
that they do not abrade a coating device and, even after
curing of the coating, do not abrade other material which
comes into contact therewith, and the transparency can be
improved. The above effect is significant particularly
when there is no cutting edge.
The content of the spherical particles contained in
the surface protective layer according to the present
invention is usually 5 to 30o by weight, preferably 5 to
25% by weight, particularly preferably 5 to 15o by weight.
When the content of the spherical particles is less
than 5o by weight, the scratch resistance is
unsatisfactory. On the other hand, when it exceeds 30o by
weight, the binder effect exerted by the ionizing
radiation-curing resin is deteriorated, raising a problem
such as lowered flexibility.
In general, the diameter of the spherical particles
is preferably 5 to 100 um. When it is less than 5 um,
there is a possibility that the coating becomes opaque.
On the other hand, when the average particle diameter
exceeds 100 um, the surface smoothness of the coating is
likely to lower. The smaller the diameter of the spherical
particles, the lower the abrasion resistance. On the other
hand, the abrasion resistance improves with increasing the
diameter of the spherical particles. In this case,
however, for some thickness, uniform coating becomes
CA 02235542 1998-04-22
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difficult. For example, a surface protective layer
thickness of 10 to 30 ~.m is contemplated, the particle
diameter of the spherical particles is preferably 10 to 50
um.
More preferably, the average particle diameter of
the spherical particles is selected according to the
thickness of the surface protective layer. In particular,
when the average thickness of the surface protective layer
is t (mm) with the average particle diameter of the
spherical particles being d ( mm ) , it is preferred to select
spherical particles so as to satisfy the following formula
(1). When the average particle diameter d (mm) of the
spherical particles exceeds 2.0t, the spherical particles
are exposed on the surface of the surface protective layer,
often leading to deteriorated appearance. On the other
hand, when the average particle diameter d ( mm ) is less
than 0.3 t, the abrasion resistance is likely to be
unsatisfactory.
0.3t S d S 2.0t ........ (1)
Any material may be used for the spherical
particles so far as the hardness is higher than the
ionizing radiation-cured resin, and inorganic particles
and/or organic particles may be used. The difference in
hardness between the spherical particles and the ionizing
radiation-cured resin may be measured in terms of Mohs
hardness, Vickers hardness and the like. For example, the
hardness in terms of Mohs hardness is preferably not less
than 1, and the Knoop hardness is preferably not less than
1300 g/mmZ, more preferably not less than 1800 g/mm2.
The Knoop hardness referred to herein is a micro
indentation hardness measured with a Knoop indenter and is
a numerical value expressed by the quotient determined by
dividing a load used for creating a diamond-shaped dent
before the test by the projected area of indentation
determined from the length of the longer diagonal of
permanent indentation. This testing method is described
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in ASTM C-849.
Materials for spherical particles include inorganic
particles of a-alumina, silica, chromium oxide, iron oxide,
diamond, and graphite, and organic resin particles, such
5 as synthetic resin beads of crosslinked acrylic resins.
a-Alumina may be fused alumina, alumina produced by Bayer's
process or the like. Other inorganic particle usable
herein include zirconia, titania, and an eutectic mixture
thereof with fused alumina or alumina produced by Bayer's
10 process.
An example of a method for bringing the shape of
these inorganic particles to a spherical one is to spray
a melt prepared by heating a pulverized irregular inorganic
compound of the above type at a high temperature above the
melting point.
Particularly preferred spherical particles are
spherical a-alumina because it has very high hardness and
is very effective in imparting abrasion resistance and
spherical particles can be relatively easily obtained. The
spherical a-alumina is described in Japanese Patent Laid-
Open No. 56269/1990 published Feb. 26/90. Specifically, a
curing agent, such as alumina hydrate, halide compound, or boron
compound, or a crystallizing agent is added in a small amount to
a pulverized product of fused alumina or sintered alumina, and
the mixture is heat treated at a high temperature of 1400°C for
2 hr or more. This reduces cutting edges of the alumina and, at
the same time, provides spherodized alumina. Such spherical
alumina is commercially available in various average particle
diameters as "Spherical Alumina AS-10, AS-20, AS-30, AS-40, and
AS-5""" from Showa Denko K.K.
The spherical particles may be surface treated to
enhance the adhesion to the binder or to improve the
dispersibility. For example, treatment with a fatty acid,
such as stearic acid, results in improved dispersibility.
Further, surface treatment with a silane coupling agent can
improve the adhesion between the spherical particles and
the ionizing radiation-curing resin used as the binder and,
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in addition, can improve the dispersibility of the
particles in the coating liquid composition. Silane
coupling agents usable herein include an alkoxysilane
having in its molecule a radical polymerizable unsaturated
bond, such as methacryl, and an alkoxysilane having in its
molecule a functional group, such as epoxy, amino, or
mercapto. For the silane coupling agent, preferably, the
type of the radical polymerizable unsaturated bond or the
functional group is selected according to the type of the
crosslinking resin used with the spherical particles, for
example, in such a manner that an alkoxysilane having a
radical polymerizable unsaturated bond is used in the case
of an ionizing radiation-curing resin, such as
(meth)acrylate, and an alkoxysilane having an epoxy or
amino group is used in the case of a two-component curing
type urethane resin.
Any conventional method may be used without
limitation for treating the surface of the spherical
particles with the silane coupling agent. Examples thereof
include a dry method wherein a predetermined amount of the
silane coupling agent is sprayed while vigorously stirring
the spherical particles and a method wherein, after the
spherical particles are dispersed in a solvent, such as
toluene, a predetermined amount of the silane coupling
agent is added followed by a wet reaction. The amount of
the silane coupling agent necessary for the treatment of
the spherical particles is preferably such that the minimum
covering area of the silane coupling agent based on the
specific surface area 100 of the spherical particle is not
less than 10. When the minimum covering area of the
spherical particles is less than 10 based on the specific
surface area 100 of the spherical particles, the
contemplated effect is small.
The surface protective layer according to the
present invention may be formed by directly coating a
coating liquid composition onto the contiguous layer. In
this case, coating methods usable herein include gravure
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coating, roll coating, flow coating, and Komma coating.
Although the viscosity of the ionizing radiation-curing
composition, when coated, is determined by coating method
and coverage, it is preferably not more than 1000 cP. The
composition may be of a non-solvent type not containing a
volatile solvent or a solvent type containing a volatile
solvent. When the non-solvent type is used and coating at
room temperature is difficult due to high viscosity, it is
possible to use a method wherein the ionizing radiation-
curing composition is heated to 40 to 80~C to lower the
viscosity to a suitable value, for example, not more than
1000 cP, and then coated.
The coating thickness is 3 to 100 um, preferably S
to 30 um.
Regarding a device for ionizing radiation
irradiation used for curing the ionizing radiation-curing
composition, light sources, such as ultra-high pressure
mercury lamps, high pressure mercury lamps, low pressure
mercury lamps, carbon arcs, black light lamps, and metal
halide lamps, may be used in the case of ultraviolet
irradiation.
Electron beam sources usable herein include various
electron beam accelerators, such as a Cockcroft-Walton
accelerator, a van de Graaff accelerator, a resonance
transformer accelerator, an insulated core transformer
accelerator, a linear accelerator, a Dynamitron accelerator.
and a high frequency accelerator. The exposure dose of the
electron beam is about 0.1 to 30 Mrad, preferably about 1
to 10 Mrad at an energy of usually 100 to 10000 keV,
preferably 100 to 300 keV.
When the exposure dose is less than 0.1 Mrad, the
curing is likely to be unsatisfactory. On the other hand,
when the exposure dose exceeds 30 Mrad, the cured coating
or the substrate sheet is likely to be damaged.
When the ionizing radiation-curing resin layer is
cured by exposure to ultraviolet light, at least one
photoreaction initiator selected from benzoin, benzoin
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methyl ether, acetophenone, Michler's ketone, diphenyl
sulfite, dibenzyl sulfide, diethyl oxide, triphenyl
biimidazole, and isopropyl-N,N-dimethylaminobenzoate may
be used in an amount of 0.1 to 10 parts by weight based on
100 parts by weight of the ionizing radiation-curing
composition.
The exposure dose of the ultraviolet light is
preferably 50 to 100 mj/cmz. When the exposure dose of the
ultraviolet light is less than 50 mj/cmz, the curing is
likely to be unsatisfactory. On the other hand, when it
exceeds 100 mj/cm2, the cured coating is likely to be
yellowed.
The crosslink-to-crosslink average molecular weight
after the reaction of the ionizing radiation-curing resin
according to the present invention is usually 150 to 1000,
preferably 200 to 1000, particularly preferably 250 to 800.
When crosslink-to-crosslink average molecular weight is
less than 150, the flexibility of the whole resin is
lowered, leading to cracking upon bending of the coating.
On the other hand, when it exceeds 1000, the resin per se
becomes excessively flexible, so that the power for holding
the spherical particles is unsatisfactory, resulting in
unsatisfactory scratch resistance.
The crosslink-to-crosslink average molecular weight
A referred to herein is a numerical value determined by the
following equation (2).
A = m/[2 X (f - 1)]
wherein f represents the average number of polymerizable
functional groups of the ionizing radiation-curing resin
and m represents the average molecular weight.
A pattern layer may be printed on the substrate
sheet according to the present invention. Printing
methods usable herein include conventional sheet-feed or
rotary printing or offset printing using an intaglio
(including a gravure plate), lithography, relief, or
stencil, and, in addition, electrostatic printing and ink
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jet printing. Among them, gravure rotary printing, flexo
rotary printing, and silk screen printing are preferred.
It is also possible to use a method wherein a
transfer film with a pattern layer formed on a release film
is used to transfer the pattern layer onto a predetermined
substrate sheet.
A printing ink for forming a pattern layer or a
solid print layer is selected from conventional inks
compatible with a printing method used and raising no
problem associated with the adhesion to the substrate sheet
and post-treatment.
The ink is constituted by a composition comprising
a durable pigment, an extender pigment, a thermoplastic
resin, a binder, such as a reaction curable resin, a curing
agent, an additive, a solvent and the like.
For the binder, preferably, in order to react with
the surface protective layer to increase the adhesive
strength, a polyol may be added, and an acrylate monomer
and/or a prepolymer having an isocyanate group may be
incorporated.
The pattern layer may be suitably selected from
reprodudtions of naturally occurring products with
gradation, such as woodgrain, grain, and texture, solid
printing, such as letters, symbols, and line drawing,
abstract patterns and the like.
Irregularities may be created in the surface
protective layer, and embossing utilizing pressing under
heating may be used for this purpose. Specifically, a
solvent type coating liquid composition for a surface
protective layer is coated and dried to form a tack-free
layer which, in an uncured state, is heated at 80 to 180vC,
embossed by means of a cooled embossing roll with a convex
pattern, and cooled followed by irradiation with an
ionizing radiation to form a cured surface protective layer
having a irregular pattern.
A color may be provided in the concave portion
created by the embossing. For example, a wiping method may
CA 02235542 1998-04-22
be used for this purpose. Specifically, an ink is coated
on the whole surface of the sheet including the concave
portions by doctor blade coating, knife coating or the
like, and the ink is removed by means of a squeegee from
5 the surface of the sheet except for the concave portions.
Thus, the concave portions are filled, with the ink
remaining unremoved and hence colored. The ink used for
coloring may be one prepared by dispersing a colored
pigment, such as an inorganic or sheeny pigment, in a
10 vehicle comprising a binder comprised of a thermoplastic
resin, a thermosetting resin, an ionizing radiation-curing
resin, a plasticizer, a lubricant and the like and a water
and/an organic solvent.
The present invention will be described in more detail
with reference to the following examples.
Rxamr~l P 1
As shown in Fig. 1, a paper, with ply reinforcement,
5 having a basis weight of 30 g/m2 (manufactured by Sanko
Paper Manufacturing Corporation) was provided as a
substrate sheet 1, and a contiguous layer 4 constituted by
a solid print layer 2 and a woodgrain pattern layer 3 was
gravure-printed using a gravure ink UE (tradename,
10 manufactured by Showa Ink Ind. Co., Ltd.) containing an
acrylic polyol on one side of the substrate sheet 1.
Subsequently, the following "ionizing radiation-curing
resin composition 1 for a surface protective layer" was
roll-coated on the whole surface of the pattern layer at
15 a coverage of 10 g/m2, followed by irradiation and curing
with an electron beam from an electron beam irradiation
device (manufactured by ESI) under conditions of 175 KeV
and 5 Mrad to form a surface protective layer 5, thereby
preparing a decorative sheet 10 of Example 1.
Ionizing radiation-curing resin composition 1 for a
surface protective layer:
Urethane acrylate oligomer 48 parts by weight
Polyfunctional acrylate monomer 45 parts by weight
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16
Tolylene diisocyanate 5 parts by weight
Silicone acrylate 2 parts by weight
Example 2
As shown in Fig. 1, a paper, with ply reinforcement,
having a basis weight of 30 g/mz (manufactured by Sanko
Paper Manufacturing Corporation) was provided as a
substrate sheet l, and a contiguous layer 4 constituted by
a solid print layer 2 and a woodgrain pattern layer 3 was
gravure-printed using a "gravure ink 1 for a contiguous
layer" having the following composition on one side of the
substrate sheet 1.
Gravure ink 1 for a contiguous layer:
Acrylic polyol 20 parts by weight
Acrylate monomer having isocyanate group
5 parts by weight
Pigment 10 parts by weight
Solvent 65 parts by weight
Subsequently, the "ionizing radiation-curing resin
composition 1 for a surface protective layer" used in
Example 1 was roll-coated on the whole surface of the
pattern layer at a coverage of 10 g/m2, followed by
irradiation and curing with an electron beam from an
electron beam irradiation device (manufactured by ESI)
under conditions of 175 KeV and 5 Mrad to form a surface
protective layer 5, thereby preparing a decorative sheet
10 of Example 2.
ExamnlP
As shown in Fig. 1, a paper, with ply reinforcement,
having a basis weight of 30 g/m2 (manufactured by Sanko
Paper Manufacturing Corporation) was provided as a
substrate sheet 1, and a contiguous layer 4 constituted by
a solid print layer 2 and a woodgrain pattern layer 3 was
gravure-printed using the "gravure ink 1 for a contiguous
layer" used in Example 2 on one side of the substrate sheet
1.
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17
Subsequently, the following "ionizing radiation-curing
resin composition 2 for a surface protective layer" was
roll-coated on the whole surface of the pattern layer at
a coverage of 10 g/m2, followed by irradiation and curing
with an electron beam from an electron beam irradiation
device (manufactured by ESI) under conditions of 175 KeV
and 5 Mrad to form a surface protective layer 5, thereby
preparing a decorative sheet 10 of Example 3.
Ionizing radiation-curing resin composition 2 for a
surface protective layer:
Urethane acrylate oligomer 48 parts by weight
Polyfunctional acrylate monomer 20 parts by weight
Tolylene diisocyanate 30 parts by weight
Silicone acrylate 2 parts by weight
Example 4
A contiguous layer 4 constituted by a solid print
layer 2 and a woodgrain pattern layer 3 was formed in the
same manner as in Example 1. T he f o 11 ow i ng
"ionizing radiation-curing resin composition 3 for a
surface protective layer" was then roll-coated on the whole
surface of the pattern layer at a coverage of 10 g/mz,
followed by irradiation and curing (average crosslink-to-
crosslink molecular weight 272) with an electron beam from
an electron beam irradiation device (manufactured by ESI)
under conditions of 175 KeV and 5 Mrad to form a surface
protective layer 5, thereby preparing a decorative sheet
10 of Example 4.
Ionizing radiation-curing resin composition 3 for a
surface protective layer:
Urethane acrylate oligomer 20 parts by weight
(average molecular weight 1700)
Trimethylolpropane acrylate 20 parts by weight
(average molecular weight 296,
number of functional groups 3)
Bisphenol A ethylene oxide 20 parts by weight
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diacrylate
(average molecular weight 500,
number of functional groups 2)
Phenol ethylene oxide diacrylate 20 parts by weight
(average molecular weight 236,
number of functional groups 1)
Tolylene diisocyanate 5 parts by weight
a-Alumina particles 15 parts by weight
(average molecule diameter 30 um,
Knoop hardness 1800 g/mm2)
Example 5
A paper, with ply reinforcement, having a basis weight
of 30 g/m2 (manufactured by Sanko Paper Manufacturing
Corporation) was provided as a substrate sheet, and a
contiguous layer constituted by a solid print layer and a
woodgrain pattern layer was gravure-printed using a gravure
ink containing tolylene diisocyanate on one side of the
substrate sheet.
Subsequently, the following "ionizing radiation-curing
resin composition 5 for a surface protective layer" was
roll-coated on the whole surface of the pattern layer at
a coverage of l0 g/m2, followed by irradiation and curing
with an electron beam from an electron beam irradiation
device (manufactured by ESI) under conditions of 175 KeV
and 5 Mrad to form a surface protective layer 5, thereby
preparing a decorative sheet of Example 5.
Ionizing radiation-curing resin composition 5 for a
surface protective layer:
Urethane acrylate oligomer 40 parts by weight
Polyfunctional acrylate monomer 45 parts by weight
Acrylic polyol 13 parts by weight
Silicone acrylate 2 parts by weight
Comparative Example 1
A contiguous layer 4 constituted by a solid print
layer 2 and a woodgrain pattern layer 3 was formed in the
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same manner as in Example 1 . T h a f o 11 o w i n g
"ionizing radiation-curing resin composition 4 for a
surface protective layer" was then roll-coated on the whole
surface of the pattern layer at a coverage of 10 g/mz,
followed by irradiation and curing (average crosslink-to-
crosslink molecular weight 272) with an electron beam from
an electron beam irradiation device (manufactured by ESI)
under conditions of 175 KeV and 5 Mrad to form a surface
protective layer 5, thereby preparing a decorative sheet
10 of Comparative Example 1.
Ionizing radiation-curing resin composition 4 for a
surface protective layer:
Urethane acrylate oligomer 49 parts by weight
Polyfunctional acrylate monomer 49 parts by weight
Silicone acrylate 2 parts by weight
Comparative Example 2
As shown in Fig. 1, a paper, with ply reinforcement,
having a basis weight of 30 g/mz (manufactured by Sanko
Paper Manufacturing Corporation) was provided as a
substrate sheet 1, and a contiguous layer 4 constituted by
a solid print layer 2 and a woodgrain pattern layer 3 was
gravure-printed using the following "gravure ink 2 for a
contiguous layer" on one side of the substrate sheet 1.
Gravure ink 2 for a contiguous layer:
Acrylic polyol 20 parts by weight
Tolylene diisocyanate 5 parts by weight
Pigment 10 parts by weight
Solvent 65 parts by weight
Subsequently, an "ionizing radiation-curing resin
composition 5 for a surface protective layer" having the
following composition was roll-coated on the whole surface
of the pattern layer at a coverage of 10 g/mz, followed by
irradiation and curing with an electron beam from an
electron beam irradiation device (manufactured by ESI)
under conditions of 175 KeV and 5 Mrad to form a surface
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protective layer 5, thereby preparing a decorative sheet
10 of Comparative Example 2.
Ionizing radiation-curing resin composition 5 for a
surface protective layer:
5 Urethane acrylate oligomer 49 parts by weight
Polyfunctional acrylate monomer 49 parts by weiaht
Tolylene diisocyanate 5 parts by weight
Silicone acrylate 2 parts by weight
The samples prepared in Examples 1 to 4 and
10 Comparative Examples 1 and 2 were aged at 40vC for 3 days
and tested for adhesion and Hofmann' s scratch test, and the
results are summarized in Table 1.
(Adhesion test)
Cross-cuts each having a size of 1 mm square were
15 provided in an area of 10 x 10 mm from the surface
protective layer side, and a pressure-sensitive adhesive
tape was adhered to the whole face of the surface
protective layer and then rapidly separated to measure the
number of cross-cuts remaining unremoved on the sample.
20 For samples having strong adhesion, the test was repeated
ten times.
(Hofmann's scratch test)
This test was performed using a tester manufactured
by BYK Gardner Inc.
Table 1
Sample Adhesion Hofmann's scratch test
Ex. 1 10 times 100/100 350 g
Ex. 2 10 times 100/100 400 g
Ex. 3 10 times 100/100 500 g
Ex. 4 10 times 100/100 500 g
Ex. 5 10 times 100/100 300 g
Comp.Ex. 1 3 times 50/100 100 g
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Comp.Ex. 2 5 times 50/100 200 g
In the decorative sheet of the present invention, any
one of a contiguous layer and a surface protective layer
provided on a substrate layer contains a compound having
active hydrogen with the other layer containing an
isocyanate compound. Therefore, according to the present
invention, an ionizing radiation-curing resin contained in
the surface protective layer is self-reacted and
consequently crosslinked or polymerized, and, in addition,
the compound having active hydrogen, contained in any one
of the contiguous layer and the surface protective layer,
and the isocyanate compound contained in the other layer
are chemically reacted with each other, permitting the
contiguous layer and the surface protective layer to be
strongly bonded to each other in the interface of these
layers, which results in markedly increased ply adhesive
strength and improved Hofmann's scratch resistance of the
surface protective layer.
