Method for producing a decorative sheet having an adhesive layer on its back surface

A method for producing a decorative sheet having an adhesive layer on its back surface, which comprises coating the back surface of a decorative sheet comprising a printed pattern paper with a resin liquid which is liquid at room temperature according to a direct method, and then drying the coating of said resin to form an adhesive layer.

BACKGROUND OF THE INVENTION 
This invention relates to decorative sheets which are utilized in the step 
of finishing the surfaces of furniture and like articles and to a method 
for producing the same. More particularly, the present invention relates 
to a decorative sheet having an adhesive layer which can be adhered to a 
base material for a decorative plate only by hot pressing, that is, which 
can exhibit adhesiveness by hot pressing on the back surface, and to a 
method for obtaining the decorative sheet. 
As a method for obtaining a decorative plate which exhibits excellent 
effect in design characteristics by causing a decorative sheet to adhere 
to a base material for a decorative plate, there are: 
1) a method in which, during adhesion of a decorative sheet to a base 
material for a decorative plate, an adhesive is applied as a coating on 
the back surface of the decorative sheet or on the surface of the base 
material for the decorative plate, and subsequently heat and pressure are 
applied to obtain a decorative plate, and 
2) a method in which a resin layer extruded into a film by an extruder is 
laminated on the back surface of a decorative sheet to obtain a decorative 
sheet having an adhesive layer on the back surface, and then this is 
adhered under heat and pressure onto a base plate for a decorative plate 
to obtain a decorative plate. 
In the method for producing a decorative plate comprising a laminated 
product of a decorative sheet and a base material for a decorative plate 
of the prior art as described above, the method 1) requires a coating 
machine for an adhesive during production of the decorative plate, and 
therefore the production steps will become large in scale and time, 
because curing of the adhesive will be required during production of the 
decorative plate, whereby the production efficiency of the decorative 
plate will be poor. Furthermore, wrinkles, swelling, etc. caused by 
defective adhesion on the decorative plate obtained occur and give rise to 
defects such as poor appearance of the decorative plate. 
On the other hand, the decorative plate obtained by the method 2) has an 
adhesive layer formed on the back surface of the decorative sheet which is 
obtained by causing a resin layer once formed into a film to adhere to the 
back surface of the decorative sheet and therefore has the drawback of 
weak adhesive force between the decorative sheet and the adhesive layer. 
Another drawback is that since the adhesive layer on the back surface of 
the decorative sheet is constituted of a resin having extrusion 
adaptability, that is, a resin having a high melting temperature, a high 
temperature is required during bonding of the decorative sheet onto the 
base material for a decorative plate by utilizing the hot-melting 
fusibility possessed by the adhesive layer through the resin, which is 
uneconomical and also entails a cumbersome temperature management. Also, 
since the adhesive layer on the back surface of the decorative sheet 
comprises a resin once rendered into a film laminated on the decorative 
sheet, the adhesive layer cannot be made thin, whereby a decorative sheet 
having an adhesive layer with desired physical properties cannot be 
obtained. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a decorative sheet with 
which a decorative plate with good appearance can be easily produced 
without the accompaniment of the drawbacks in obtaining a decorative plate 
of the prior art described above, and a method for producing the 
decorative sheet. 
The method for producing a decorative sheet having an adhesive layer on the 
back surface according to a first embodiment of the present invention 
comprises coating the back surface of a decorative sheet comprising a 
printed pattern paper with a resin liquid which is liquid at room 
temperature for formation of an adhesive layer according to the direct 
method, and subsequently heating and drying the coating to form an 
adhesive layer. 
According to this invention there is provided a method for producing a 
decorative sheet having an adhesive layer on its back surface which, 
according to another embodiment of the invention, comprises coating the 
back surface of the decorative sheet comprising a printed pattern paper 
directly with a thermoplastic resin in a thermally molten state, and then 
cooling the resin to form an adhesive layer. 
According to this invention in another aspect thereof, there is provided a 
decorative sheet having an adhesive layer on its back surface, comprising 
a decorative paper and an adhesive layer formed on the back surface of the 
decorative paper, wherein the adhesive layer contain a colorant. 
The nature, utility, and further features of this invention will be more 
clearly apparent from the following detailed description beginning with 
general considerations and concluding with specific examples of practice. 
DETAILED DESCRIPTION OF THE INVENTION 
In the method for producing the decorative sheet having an adhesive layer 
on the back surface of the present invention comprising the above 
constitution, as the decorative sheet to which the adhesive layer is to be 
secured, use can be made of a decorative sheet comprising a printed 
pattern paper having printing with a printing ink using a vehicle of, for 
example, oils and fats, synthetic resins, cellulose derivatives, or rubber 
derivatives. The decorative sheet is formed according to a printing 
process such as gravure, offset, letterpress, ink jet, or silk screen, on 
a base paper for decorative sheet comprising, for example, print base 
paper for construction material of about 20 to 70 g/m.sup.2, an interpaper 
reinforced paper which is an impregnated resin filled-in paper of about 20 
to 70 g/m.sup.2, a print paper for synthetic resin impregnated 
construction material of about 60 to 200 g/m.sup.2, or a sheet having a 
surface protective layer with a resin layer formed on said printed pattern 
paper, namely, a decorative sheet of the prior art per se. 
As the resin liquid for formation of the adhesive layer, a resin solution 
of a solvent soluble type resin as represented by, for example, vinyl 
type, acrylic type, polyamide type, epoxy type, rubber type, or urethane 
type, or a resin which is a liquid at room temperature comprising a 
monomer or a prepolymer of the type which is polymerized by heating or 
post-treatment such as UV-ray irradiation or electron beam irradiation can 
be used. Specific examples are adhesives such as unsaturated polyester, 
melamine, polyester (meth)acrylate, urethane (meth)acrylate, epoxy 
(meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine 
(meth)acrylate and silicone (meth)acrylate, or hot melt adhesives, can be 
used. 
Among those mentioned above, a solvent soluble type resin is preferred 
because the resin itself has high tackiness, above all particularly a 
polyamide resin. 
The addition of a tackifier to a hot melt adhesive of the prior art type 
such as ethylne/vinyl acetate type copolymer is indispensable in order to 
augment the tackiness, but the tackifier added tends to separate with 
elapse of time, and therefore it is not suitable for use when the product 
is to be placed for a long time on a shelf in the form of furniture, etc. 
after adhesion as in the case of a decorative sheet. However, in the case 
of a solvent soluble resin, it can be used because no such drawback will 
occur. 
The above resin liquid is applied as a coating on the back surface of the 
decorative sheet at room temperature according to a direct method, for 
example, a coating method such as gravure roll coating, doctor blade 
coating, or reverse coating to about 10 to 50 g (solid component)/m.sup.2, 
preferably about 20 to 30 g (solid component)/m.sup.2, followed by heating 
and drying, to be formed into an adhesive layer. 
The present invention as described above also has a specific feature in the 
application of the coating of a resin liquid according to a direct method. 
The "direct method" in the present invention means application of a resin 
liquid as a coating from the coater to the back surface of the decorative 
sheet directly, that is, substantially without time interval or spatial 
gap. 
The decorative sheet comprising the above printed pattern paper on which an 
adhesive layer is to be formed on the back surface may also have a surface 
protective layer of a resin film as described above. This surface 
protective layer is easily formed by applying a coating on the surface of 
the printed pattern paper of a resin such as, for example, an urethane 
resin such as acryl-modified urethane or polyester-modified urethane, an 
amino alkyd resin, a polyester resin, an acryl-modified resin, a phenol 
resin, a melamine resin, a melamine alkyd resin, an epoxy resin, or a 
diallylphthalate resin, according to a coating method such as natural roll 
coating, gravure coating, air knife coating, reverse roll coating, bar 
coating, flow coating, or spray coating to 2 to 30 g (solid 
component)/m.sup.2, preferably 2 to 10 g (solid component)/m.sup.2, or 
covering the surface with an already formed film. 
The resin liquid to be coated on the back surface of the decorative sheet 
comprising the above printed pattern paper also may be a resin liquid 
containing an inorganic filler, and a resin liquid containing about 1 to 
100 parts by weight of an inorganic filler such as calcium carbonate, 
barium sulfate, titanium dioxide, clay, talc, magnesium oxide, or 
magnesium carbonate per 100 parts by weight of the resin component may be 
utilized. 
The inorganic filler to be added in the above resin liquid is used for the 
purpose of: 
1) improving the handling characteristics of the resin liquid used for 
coating; 
2) adjusting the resin liquid to a suitable viscosity; 
3) causing the adhesive layer formed to have characteristics such as 
slipping characteristic and antiblocking characteristic; 
4) reducing shrinkage of the adhesive layer formed, thereby preventing 
generation of cracks in the adhesive layer; 
5) preventing defective adhesion between the decorative sheet and the 
adhesive layer; 
6) preventing excessive penetration of the coated resin liquid into the 
decorative sheet; and 
7) improving the heat resistance of the adhesive layer formed, etc. 
Particularly when a solvent soluble type resin is used, it has advantages 
such as high tackiness, little change in tackiness with lapse of time, 
while on the other hand it has a narrower melting point range as compared 
with ethylene/vinyl acetate type copolymers, etc., whereby control of the 
heat applied during adhesion of the decorative sheet onto the base plate 
is difficult. By the addition of an inorganic filler as described above, 
the tolerable range of the heat applied during adhesion of the decorative 
sheet can be broadened. 
An example of a preferable resin composition for the adhesive layer in the 
present invention is as follows, all parts being by weight. 
Dimer acid base polyamide resin 40 parts 
N-ethylorthoparatoluenesulfonamide 3 parts 
Microsilica 1 part 
Calcium carbonate 20 parts 
Toluene/xylene/isopropanol (1/1/1) 60 parts 
The method for producing the decorative sheet having an adhesive layer on 
its back surface according to a second embodiment of the present invention 
comprises forming a coated layer by direct coating of a thermoplastic 
resin in a thermally molten state by, for example, a slot orifice coater 
or a roll coater, and then solidifying by cooling the above coated layer 
to form an adhesive layer. 
Examples of the thermoplastic resin for formation of the adhesive layer to 
be used in thermally molten state are thermoplastic resins as represented 
by ethylene-vinyl acetate copolymer, polyethylene, low molecular weight 
polyethylene, atactic polypropylene, polyamide, polyester, 
styrene-butadiene block copolymer, styrene-isopropylene block copolymer, 
polyvinyl acetate, ethylene-ethyl acrylate, EVA-azide terpolymer, 
polycarbonate, polyvinyl ether, polyurethane, polyacetal, polyisobutylene, 
and butyl rubber. It is possible to add an inorganic filler similarly as 
in the resin liquid. 
In the method for producing the decorative sheet having an adhesive layer 
of its back surface of the present invention, the thermoplastic resin in a 
thermally molten state is coated by direct coating by means of an 
applicator such as a slot orifice, or a roll coater. That is, the 
thermoplastic resin is directly coated onto the back surface of the 
decorative sheet in a molten state without film formation while 
maintaining the thermally molten state, and an adhesive layer is formed by 
coating generally to about 10 to 50 g (dry)/m.sup.2, preferably 20 to 30 g 
(dry)/m.sup.2, followed by cooling and solidification. 
The decorative sheet having an adhesive layer on its back surface of the 
present invention comprises a decorative sheet and an adhesive layer 
formed on the back surface of the decorative sheet, and moreover the 
adhesive layer may contain a colorant. 
For the base paper for a decorative sheet, a colored base paper also can be 
used, and if the shielding characteristic of the decorative sheet on which 
the adhesive layer is provided is inadequate or if the decorative sheet 
has a portion with inadequate shielding characteristics since, in the 
decorative sheet of the present invention, coloration caused by the 
colorant in the adhesive layer is visually recognized through the above 
portion with inadequate shielding characteristics, the decorative sheet 
exhibits excellent effects of design characteristic of a rich solid 
feeling. 
The adhesive layer on the back surface of the above decorative sheet is a 
resin layer containing a colorant such as an organic pigment, an inorganic 
pigment or a dye. 
The colorant in the adhesive is a dye, an organic pigment, an inorganic 
pigment, metal powder or the like. Among these from the standpoint of 
shielding performance fulfilled by the adhesive layer or inhibition of 
generation of migration of the colorant during formation of the adhesive 
layer, an inorganic pigment is most suitable. 
These colorants are dispersed or dissolved in the resin for formation of 
the adhesive layer in the conventional manner and coated on the back 
surface of the decorative sheet. When the resin for formation of the 
adhesive layer is used as a solution in a solvent, the colorant can be 
dispersed or dissolved merely by adding a colorant in the resin solution 
and stirring or kneading the mixture, whereby coloration can be effected 
simply. 
The mixing ratio of the resin and the colorant in the adhesive layer is 10 
to 200 parts by weight of the colorant per 100 parts by weight of the 
resin when the colorant is a pigment. If the colorant is less than 10 
parts by weight, the coloration effect is insufficient, while if it 
exceeds 200 parts by weight, not only the adhesive performance of the 
adhesive layer is lowered, but also working efficiency accompanied with 
elevation of dissolving viscosity will be lowered. A more preferable 
amount to be added is 10 to 100 parts by weight. 
As the colorant in the adhesive layer, it is most preferable to utilize the 
colorant with a tone such that the above mentioned adhesive layer will 
exhibit a tone which is the same as or similar to the whole tone in the 
decorative paper. 
The decorative sheet of the present invention can be formed by coating the 
back surface of a decorative sheet comprising a printed pattern paper with 
a resin liquid containing a colorant by the direct method. 
When the resin liquid for formation of the adhesive layer is a 
thermoplastic resin liquid in a thermally molten state, the decorative 
sheet back surface is coated with the above resin liquid by a slot orifice 
coater or a roll coater, that is, the decorative sheet back surface is 
coated with the above thermoplastic resin from molten state without film 
formation, while maintaining the thermally molten state, and generally an 
adhesive layer is formed by coating to 10 to 50 g (dry)/m.sup.2, 
preferably about 20 to 30 g (dry)/m.sup.2, followed by cooling and 
solidification. On the other hand, when the resin liquid for formation of 
adhesive layer is a solvent soluble resin, an adhesive layer is formed by 
coating the solution by such coating methods as gravure roll coating, 
doctor blade coating, reverse coating, etc. generally to 10 to 50 g 
(dry)/m.sup.2, preferably about 20 to 30 g (dry)/m.sup.2, followed by 
heating and drying. From the standpoint of easy dispersibility of the 
colorant when a pigment is used as the colorant, its amount which can be 
mixed, a coating precision, etc., the coating method according to gravure 
roll coating is the most suitable. 
When the colorant contained in the adhesive layer is an inorganic pigment, 
there is the same effect as when an inorganic filler is added.

EXAMPLE 1 
On a tissue paper of 30 g/m.sup.2 prepared by a paper making process with 
pulp fibers having a cationic acrylic resin adsorbed thereon, printing of 
a wood grain pattern was performed by a conventional gravure printing 
method. On the above printed surface was applied a curable urethane resin 
[UM-50: Morohoshi Ink K.K.] by means of a gravure printer in a quantity of 
5 g (solid component)/m.sup.2, which step was followed by curing thereof 
to obtain a decorative sheet comprising a printed pattern paper having a 
surface protective layer. 
Then, a solvent type urethane resin [BSS-1400: Morohoshi Ink K.K.] was 
applied on the back surface of the above decorative sheet at room 
temperature according to the reverse coating method in a quantity of 30 g 
(solid component)/m.sup.2 and subsequently heated, dried and cooled to 
obtain a decorative sheet having an adhesive layer on its back surface 
which was the desired product. 
Further, the decorative sheet thus obtained was caused by application of 
heat and pressure to adhere, by utilizing the adhesive layer at the back 
surface thereof, to a particle board under the conditions of a line 
pressure of 50 kg/cm, a hot roll temperature of 150.degree. C. and a roll 
speed of 15 m/min to obtain a decorative board comprising the above 
decorative sheet. 
The decorative sheet obtained as described above had a great adhesive 
strength between the printed pattern paper and the adhesive layer, and no 
peeling occurred between the printed pattern paper and the adhesive layer 
when the sheet was subjected to a cross cut test and a peeling test. 
The above mentioned decorative plate obtained by hot pressure bonding the 
decorative sheet to a particle board had a strong adhesive strength 
between the decorative sheet and the particle board, and there was no 
creasing or swelling whatsoever on the decorative sheet surface forming 
the surface layer of the decorative plate, thus giving a decorative plate 
of good quality. 
EXAMPLE 2 
After a decorative sheet was obtained similarly as in Example 1, a 
composition comprising mainly a solvent soluble type polyamide resin 
having the following formulation was applied on the back surface of the 
decorative sheet in a quantity of 30 g/m.sup.2 (solid component), and 
subsequently dried by heating at a temperature of 150.degree. C. for 30 
seconds, followed by cooling to obtain a decorative sheet having an 
adhesive layer on its back surface. 
Dimer acid based polyamide resin 40 parts by wt. 
N-ethylorthoparatoluenesulfonamide 3 parts by wt. 
Microsilica 1 part by wt. 
Calcium carbonate 20 parts by wt. 
Toluene/xylene/isopropanol (1/1/1) 60 parts by wt. 
The decorative sheet obtained was bonded onto a particle board similarly as 
in Example 1, whereby the tolerable range of the hot roll temperature 
during lamination was broadened as compared with the case of Example 1. 
EXAMPLE 3 
After a decorative sheet was obtained similarly as in Example 1, an 
ethylene-vinyl acetate resin [NUC copolymer J6169: Nippon Unicar K.K.] 
thermally molten at 200.degree. C. was applied by means of a slot orifice 
coater on the back surface of the above decorative sheet, followed by 
cooling to form an adhesive layer with a thickness of 10 um, thereby 
obtaining a decorative sheet having an adhesive layer of its back surface, 
which was the desired product. 
When the decorative sheet was bonded onto a particle board similarly as in 
Example 1, the same performance as in Example 1 could be obtained. 
EXAMPLE 4 
Example 3 was repeated except for the use of 15 parts by weight of Iron 
Oxide Yellow and 5 parts by weight of Carbon Black added to 80 parts by 
weight of the same ethylene-vinyl acetate resin as used in Example 3 to 
obtain a decorative sheet. 
When the decorative sheet obtained was bonded onto a ply plate, there was 
no influence from the color of the ply plate on the decorative sheet. 
Also, when a flaw was attached on the decorative sheet on the ply plate and 
a part of the decorative sheet was peeled off, the flaw was found to be 
not very conspicuous. 
EXAMPLE 5 
On a print base paper for construction material comprising a colored tissue 
paper with a basis weight of 23 g/m.sup.2, a wood grain pattern printing 
was effected by a conventional gravure printing method, and subsequently 
on the above printed surface was applied a curable urethane resin [UM-50: 
Morohoshi Ink K.K.] by means of a gravure printer at a ratio of 5 g (solid 
component)/m.sup.2, followed by curing thereof, to obtain a decorative 
sheet comprising a printed pattern having a surface protective layer. 
Then, on the back surface of the above decorative sheet was coated a resin 
liquid for formation of an adhesive layer having a composition shown below 
according to the gravure coating method to a ratio of 30 g-(dry)/m.sup.2, 
followed by drying and cooling to obtain a decorative sheet having an 
adhesive layer containing a colorant on the back surface which is the 
desired product. 
Resin liquid for formation of the adhesive layer 
______________________________________ 
Polyamide resin 100 parts by wt. 
(BSA40: Morohoshi Ink K.K.] 
Iron oxide 10 parts by wt. 
Benzidine Yellow 20 parts by wt. 
Solvent [toluene/isopropanol 
30 parts by wt. 
= 1/1] 
______________________________________ 
The above decorative sheet obtained had a large adhesive force between the 
printed pattern paper and the adhesive layer, and no peel-off between the 
printed pattern paper and the adhesive layer occurred even by both the 
cross cut test and the peeling test. 
The above decorative plate obtained by hot pressure adhesion of the above 
decorative sheet to the particle board similarly as in Example 1 had a 
strong adhesive force between the decorative sheet and the particle board, 
and yet there was no generation of creases or swelling on the decorative 
sheet surface forming the surface layer of the decorative plate, and 
further the adhesive layer between the decorative sheet and the particle 
board was colored in yellow. Accordingly, when the decorative plate was 
cut in small sections, existence of the adhesive layer was not conspicuous 
at all, and yet coloration in the adhesive layer could be visually 
recognized through the decorative sheet from the surface of the decorative 
plate, thus exhibiting excellent action with deep design characteristics. 
The decorative sheet obtained according to the method of the above 
embodiments 1 and 2 of the present invention comprising the constitutions 
as described above has the adhesive layer on the back surface which is 
formed by coating a resin liquid which is liquid at normal temperature 
according to the direct method, followed by heating and drying. Therefore, 
the adhesive layer is not required to be constituted of a resin having 
extrusion adaptability and a resin with relatively lower melting 
temperature can be selected and used to form the adhesive layer. 
Accordingly, this method is also excellent in that a decorative plate of 
good quality can be obtained under the hot pressure adhesion condition 
which is by far lower in temperature as compared with the decorative sheet 
of the prior art having an adhesive layer with a resin having extrusion 
adaptability in obtaining a decorative plate by adhering a decorative 
sheet to a base material for a decorative plate. 
Also, the decorative sheet obtained according to the production method of 
the present invention has an adhesive layer which is formed by coating a 
resin liquid which is liquid at normal temperature according to the direct 
method, followed by heating and drying as described above. Therefore, as 
compared with the sheet of the prior art provided with an adhesive layer 
formed with a resin having extrusion adaptability which is formed by 
utilizing melt extrusion molding, the adhesive can be thoroughly 
penetrated into the back surface of the decorative sheet, whereby the 
adhesive force between the decorative sheet and the adhesive layer is 
large, and a part of the adhesive layer will not be separated from the 
back surface of the decorative sheet before application of the decorative 
sheet to a base material for the decorative plate. Therefore, a decorative 
plate of high quality free from generation of swelling or wrinkles, which 
may be caused by non-adhesion between the adhesive layer and the back 
surface of the decorative sheet, can be obtained. 
Further, since the adhesive layer in the decorative sheet obtained by the 
production method of the present invention is formed by coating a resin 
liquid which is liquid at normal temperature, followed by heating and 
drying, as described above, a thinner adhesive layer can be formed as 
compared with the adhesive layer formed by utilizing melt extrusion 
molding. Therefore, according to the present invention, a decorative sheet 
having an adhesive layer with desired physical properties can be obtained. 
Also, since the decorative sheet obtained by the method of the present 
invention can be adhered to the base material for the decorative plate 
only with hot pressure, during production of the decorative plate, it is 
not required to use an adhesive coating machine as in the case of the 
decorative sheet of the prior art which is adhered by application of an 
adhesive to a base material for the decorative plate. Accordingly, the 
production steps of the decorative plate are simple according to the 
present invention, and also it is not necessary to provide a curing time 
for an adhesive as in the prior art method. Therefore, the method of the 
present invention also has such excellent effects that the production 
efficiency of the decorative plate is good, and yet a decorative plate of 
good quality without generation of wrinkles or swelling due to defective 
adhesion can be obtained. 
Further, the decorative sheet of the present invention also brings about 
the action and the effect of good appearance because the decorative plate 
obtained by adhesion of the decorative sheet to a base material for the 
decorative plate exhibits a colored film shape of the adhesive layer in 
the decorative plate. Therefore, when the decorative plate is cut in small 
sections or a flaw is formed on the decorative plate, etc. the existence 
of the adhesive layer will not be conspicuous.