Wallpaper

Wallpaper comprises a coating layer (2) containing latex binder and pigment on top of a base paper (1). The coating layer (2) contains a surface coating (PP) containing pigment and latex binder and its amount is at least 20 g/m.sup.2 as dry matter. The total amount of the coating layer (2) is at least 30 g/m.sup.2 as dry matter. The surface coating (PP) contains at least 30-70 parts of the latex binder per 100 parts of a water-insoluble pigment, whereof the amount of a water-insoluble inorganic mineral pigment is at least 40 wt-%. The wallpaper has essentially the same external properties as an ordinary PVC coated wallpaper and improved printing and embossing properties.

BACKGROUND OF THE INVENTION 
The invention relates to a wallpaper comprising a coating layer containing 
latex binder and pigment on top of a base paper, said coating layer 
containing a surface coating containing pigment and latex binder, the 
amount of the surface coating being at least 20 g/m.sup.2 as dry matter 
and the total amount of the coating layer being at least 30 g/m.sup.2 as 
dry matter. 
Polyvinyl chloride (PVC) is now used commonly as the coating of wallpapers. 
Said material has been used a coating mainly because of its protecting 
effect, such as good resistance to moisture, fat and mechanical stress. 
However, the use of PVC in coatings involves some drawbacks. One of these 
drawbacks is the waste problem, which on one hand is due to the recycling 
problems of the used wallpaper and on the other hand to the wastes of the 
PVC coating process itself. Another problem is the devices and chemicals 
required by the process itself. In the coating the polyvinyl chloride is 
applied as a so-called plastisol on top of a web to be coated. This kind 
of plastisol is composed of a plasticizing medium that is usually an ester 
formed by an aromatic acid and an aliphatic long-chain alcohol, e.g. 
dioctyl phthalate, and of fine PVC particles suspended therein. In the 
process a uniform solid coating is created by heating the flowing 
plastisol applied on top of the web approximately above 150.degree. C. For 
creating a decorative surface relief this kind of coating can be embossed 
by means of heat (so-called hot-embossing). 
The aforementioned coating process requires special equipment and the use 
of organic aromatic chemicals causes problems of handling and waste 
disposal. One drawback associated with the finished product is that the 
PVC coating generates toxic substances when burning, for example 
hydrochloric acid, which decreases the fire safety of the wallpaper. 
German Patent No. 2.501.684 shows a wallpaper coating where the coating 
contains a water-based styrene-butadiene latex as a binder as well as a 
pigment that can be insoluble starch or a mixture of calcium carbonate and 
calcium silicate. The amount of this type of coating on a base cardboard 
is usually 8-15 g/m.sup.2. This publication mentions the drawbacks of a 
coating containing solely an inorganic pigment being that it is too glossy 
and rough after calendering and its gravure printing properties are 
insufficient, and further, that the wet attrition resistance is 
essentially lowered after it has been embossed. 
British Application Publication No. 2201613 shows a wallpaper coating 
containing water-based acrylic or vinyl acetate based binder together with 
alumina hydrate serving as a fire retardant and optionally also with an 
inorganic coating pigment. In a typical coating composition shown by the 
examples there is 100 parts alumina hydrate per 100 parts binder. The 
possibility to use mineral fillers is mentioned only in the description. 
German Auslegeschrift No. 1771129 shows a wallpaper coating containing 
water-based binder and water-glass and barium sulphate as inorganic 
components. The large amount of water-glass causes undesirable colour. The 
large amount of water-soluble water-glass does not render the wallpaper 
suitable to be printed with water-based printing inks. 
SUMMARY OF THE INVENTION 
The object of the invention is to carry a coated wallpaper into effect that 
can replace the PVC coated wallpapers and that at the same time has good 
matt surface, good printing ink absorption especially for water-based 
printing inks, good wet attrition resistance, smoothness and printability 
in gravure printing, and that can be well embossed cold. For achieving 
this object the wallpaper according to the invention is mainly 
characterized in that the coating layer contains a surface coating 
containing at least 30-70 parts of the latex binder per 100 parts of a 
water-insoluble pigment, whereof the amount of a water-insoluble inorganic 
mineral pigment is at least 40 wt-%. It has now been surprisingly 
discovered that by choosing a suitable ratio of latex binder and pigments, 
combined with a relatively high weight of coating per surface unit, it is 
possible to accomplish a wallpaper that externally does not differ from a 
wallpaper with a PVC coating, but is more safe to environment as regards 
the manufacture, the wastes produced by the manufacture, and the discharge 
after the use, being also more fire-safe. 
According to one advantageous embodiment, the amount of the latex binder is 
40-65 parts per 100 parts of the water-insoluble pigment. 
According to one advantageous embodiment the proportion of the 
water-insoluble pigment and latex binder of the dry mass of the surface 
coating is over 95 wt-%, preferably over 98 wt-%. 
According to one embodiment, the amount of the inorganic water-insoluble 
mineral pigment is over 95 wt-% of the total amount of the water-insoluble 
pigment. 
According to an alternative embodiment of the invention, the 
water-insoluble pigment contains at least 5 parts of particles of a 
thermoplastic halogen-free polymer. The thermoplastic polymer particles 
help to create a good and stable hot-embossed pattern, but their presence 
does not deteriorate other properties of the wallpaper. 
The optimum amount according to the above-mentioned embodiment is at least 
10 parts, preferably over 20 parts of the thermoplastic halogen-free 
polymer particles. For good distribution properties of the coating over 
the base paper and for good printability, the amount of the polymer 
particles should be not more than 60 parts. 
Still according to one embodiment, the coating layer can comprise a 
pre-coating layer containing latex binder and pigment and situated between 
the surface coating and the base paper. The pre-coating layer contains at 
least 8 parts, preferably 10-25 parts of the latex binder per 100 parts of 
the pigment. The pre-coating layer can consist of one single layer or of 
two pre-coating layers applied at different stages. The pre-coating layer 
helps to achieve a good smoothness before the surface coating, and its 
amount is at least 5 g/m.sup.2, preferably 10-25 g/m.sup.2. 
According to one advantageous embodiment, the inorganic pigment of the 
surface coating contains both magnesium silicate (talc) and calcium 
carbonate. Said inorganic pigments help to obtain a good matt surface, and 
further, the use of calcium carbonate can decrease the wetting agent that 
is required by the dispersibility of talc, which would otherwise render 
the coating too hydrophilic. 
The invention will be described more closely in the following with 
reference to the enclosed drawing and to some coating compositions for 
manufacturing a wallpaper according to the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description the substances are always expressed as dry 
matter unless there is another indication. Whenever reference is made to 
"parts" the amount of parts is expressed in relation to 100 parts of a 
water-insoluble pigment. 
FIG. 1 shows a coating layer 2 applied on top of a base paper 1. The 
coating layer has a surface coating PP that contains at least 30-70 parts 
latex binder per 100 parts water-insoluble pigment. The amount of the 
surface coating PP is at least 20 g/m.sup.2 as dry matter. 
The term "pigment" means in this context fine particles that are dispersed 
in the coating paste in addition to the latex binder and bound together by 
the binder in a finished coating. 
The total amount of the coating layer is at least 30 g/m.sup.2 as dry 
matter and most preferably it is within a range of 30 to 65 g/m.sup.2. In 
this case it can be formed either of one coating layer 2 applied on top of 
the base paper 1 in one step. Nevertheless, the coating can, as shown by 
FIG. 2, be composed of the above-mentioned surface coating PP and a 
pre-coating layer EP applied on top of the base paper 1 before the surface 
coating. The amount of the surface coating PP can in this case vary in the 
range of 20 to 40 g/m.sup.2 and the amount of the pre-coating layer EP is 
at least 5 g/m.sup.2, preferably 10-25 g/m.sup.2. The amount of latex 
binder in the pre-coating layer can be lower than in the surface coating 
PP and it can thus vary in the range of 10 to 25 parts per 100 parts of 
the pigment of the pre-coating layer. 
The broken lines illustrate in FIG. 2 that the pre-coating layer EP can be 
composed also of two layers applied in different steps, the layers being 
designated by EP1 and EP2. The composition of these layers is the same as 
mentioned above and their amount is such as to get the aforementioned 
total amount of the pre-coating layer EP. 
All water-based solvent-free latices can be used as the latex binder of the 
surface coating of the coating layer. Examples of these are the so-called 
homo- or copolymer latices generally used in wallpaper coatings, for 
example polyvinyl acetate homopolymer latex, polyvinyl acetate/acrylate 
copolymer latex, ethylene/vinyl acetate copolymer latex, styrene-acrylate 
copolymer latex, full acrylate latex and styrene-butadiene latex. 
Especially suitable for use in the invention are the polyvinyl 
acetate/acrylate copolymer, ethylene/vinyl acetate copolymer (PVAC and 
EVAC) and full acrylate latices, and less suitable for the purpose is the 
styrene-butadiene latex that tends to change colour in course of time. 
As to the inorganic water-insoluble mineral pigments, all pigments commonly 
used in wallpaper coatings can be employed, such as bolus alba, calcium 
carbonate, calcium sulphate, i.e. gypsum, magnesium silicates, i.e. talc, 
aluminium silicates, titanium dioxide, barium sulphate, mica, or some 
mixtures of these. A mixture of magnesium silicate and calcium carbonate 
has proved to be a good mixture of inorganic mineral-based pigments, being 
particularly well applicable in the coating paste by means of which a 
wallpaper according to the invention is manufactured. The dispersibility 
of the talc, i.e. magnesium silicate into latex dispersion can thereby be 
improved by means of the calcium carbonate and special wetting agents 
increasing the dispersibility and rendering a finished coating too 
hydrophilic can be decreased. The calcium carbonate used in this case is 
preferably of the pulverized grade and not of the precipitated grade. The 
optimum ratio of the magnesium silicate and calcium carbonate is in the 
range of 3:1 to 1:3. 
According to an alternative of the invention the water-insoluble pigment 
can contain also pigment particles of a thermoplastic halogen-free polymer 
besides the inorganic pigment particles. In order to make the wallpaper 
coating hot-embossable the proportion of these pigment particles should be 
at least 5 parts of the total 100 parts of the pigment. By the 
thermoplastic polymer particles it is possible to create a good and 
resistant hot-embossed pattern with properties no inferior to those of an 
ordinary PVC coated wallpaper. According to an advantageous embodiment, 
the proportion of the thermoplastic halogen-free polymer of the pigment 
particles is at least 10 parts, preferably over 20 parts. In order to 
still retain good distribution properties of the coating and good 
printability, the amount of the polymer is not more than 60 parts, the 
rest being inorganic pigment. 
Particles consisting of a polymer with a melting point in a range 
100.degree. to 250.degree. C. can be used as the thermoplastic 
halogen-free pigment particles. The thermoplastic particles can brought to 
a molten state by the heat of the embossing operation, the coating layer 
becomes more easily shapable and the particles create a stable surface 
pattern upon solidifying. FIG. 3 shows a wallpaper prepared in this way. 
In the practice when preparing the coating paste the particles formed of 
the thermoplastic polymer can be mixed together with other constituents to 
form the paste whereby they are evenly distributed in the paste and in the 
finished coating. They can be used either as ready-to-use water 
dispersions or in powder form. These substances include polystyrene, 
polypropylene, polyethylene and polyester. It is also possible to use some 
blends thereof. The use of synthetic and non-synthetic waxes composed of a 
thermoplastic polymer is also possible. These kinds of wax dispersions 
include generally available hot-melt-dispersions where the particles form 
the pigment component of the thermoplastic halogen-free polymer in the 
coating. The aforementioned compounds can be replaced either wholly or 
partly by other thermoplastic compounds as well. 
When the coating is prepared, the coating paste forming the surface coating 
PP can of course contain further fire retardants commonly used in 
wallpaper coatings, such as alumina hydrate, a swelling agent giving 
elasticity, hardeners as well as optical clarifiers, as well as other 
auxiliary substances, such as dispersing agents, defoaming agents, and 
viscosity adjusting agents, the total proportion of which the dry mass of 
the surface coating is usually below 5 wt-%, preferably below 2 wt-%. The 
amount of these substances is usually below 2 parts per 100 parts of the 
water-insoluble pigment. 
Any paper having suitable surface properties can be used as the base paper 
1. The grammage of the base paper can be for example 90-120 g/m.sup.2. 
When pre-coating layers are used the surface to be coated can have more 
mechanical pulp than in the case of one single coating layer. 
In the manufacture of the wallpaper according to the invention the coating 
layer can be applied by well-known coating methods, such as blade, air 
knife, rod, and roll coating methods. Further, it is possible to form the 
pre-coating layer EP as early as in the papermachine by means of one of 
the aforementioned methods and the surface coating PP can be formed by 
means of some off-machine method, for example air knife, blade, reverse 
roll, extrusion or silk screen method. 
EXAMPLES 
In the following some manufacturing formulas for the wallpaper according to 
the invention are presented. The amounts in the formulas are expressed as 
dry matter. 
______________________________________ 
Formula 1. Normal Pre-coating (for blade coating) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment Calcium carbonate 100,0 
Dispersing agent 
Salt of polyacrylic acid 
0,3 
Defoaming agent 
Vegetable oil and fatty acid 
0,1 
esters 
Viscosity adjustment 
Carboxymethylcellulose 
0,3 
Viscosity adjustment 
Acrylic ester 0,5 
Binder PVAC-acrylate 12,0 
Hardener Melamine-formaldehyde resin 
0,4 
______________________________________ 
dry matter content of the applied coating 58-67% 
viscosity 600-1500 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 5-25 g/m.sup.2 dry 
Formula 2. Normal pre-coating (for air knife coating) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 30,0 
Pigment 2 Calcium carbonate 60,0 
Pigment 3 Titanium dioxide 10,0 
Dispersing agent 
Ammonium salt of polycar- 
0,3 
boxylic acid 
Defoaming agent 
Vegetable oil and fatty acid 
0,1 
esters 
Viscosity adjustment 
Acrylic ester 0,3 
Binder EVAC-dispersion 20,0 
Hardener Ammoniumzirconiumcarbonate 
0,6 
______________________________________ 
dry matter content 55-65% 
viscosity 50-300 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 5-25 g/m.sup.2 dry 
Formula 3. New surface coating replacing the PVC 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 75,0 
Pigment 2 Calcium carbonate 25,0 
Dispersing agent 
Salt of polyacrylic acid 
0,3 
Viscosity adjustment 
Acrylic ester 0,4 
Binder 1 PVAC acrylate latex 45,0 
Binder 2 Polyvinyl alcohol 5,0 
Hardener Melamine-formaldehyde resin 
0,6 
______________________________________ 
dry matter content 55-65% 
viscosity 50-300 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 20-50 g/m.sup.2 dry 
Formula 4. New surface coating 
replacing the PVC (for air knife coating) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 67,5 
Pigment 2 Calcium carbonate 22,5 
Pigment 3 Titanium dioxide 10,0 
Dispersing agent 
Sodium salt of polycarb- 
0,35 
oxylic acid 
Defoaming agent 
Vegetable oil and fatty acid 
0,1 
esters 
Binder EVAC-latex 55,0 
______________________________________ 
dry matter content 55-65% 
viscosity 50-300 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 20-50 g/m.sup.2 dry 
Formula 5. New surface coating replacing the PVC 
(for blade, reverse roll, extrusion and silk screen methods) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 42,0 
Pigment 2 Calcium carbonate 42,0 
Pigment 3 Titanium dioxide 12,0 
Pigment 4 Sodium aluminum silicate 
4,0 
Dispersing agent 
Salt of polyacrylic acid 
0,4 
Defoaming agent 
White oil based 0,1 
Viscosity adjustment 
Acrylic polymer dispersion 
0.6 
Viscosity adjustment 
Carboxymethyl cellulose 
0,4 
Binder Acrylic latex 60,0 
______________________________________ 
dry matter content 55-65% 
viscosity 600-4000 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 30-50 g/m.sup.2 dry 
Formula 6. New hot-embossable surface 
coating replacing the PVC 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment Calcium carbonate 75,0 
Polymer Polyethylene 25,0 
Dispersing agent 
Salt of polyacrylic acid 
0,3 
Viscosity adjustment 
Acrylic ester 0,4 
Binder 1 PVAC acrylate latex 45,0 
Binder 2 Polyvinyl alcohol 5,0 
Hardener Melamine-formaldehyde resin 
0,6 
______________________________________ 
dry matter content 55-65% 
viscosity 50-300 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 20-50 g/m.sup.2 dry 
Formula 7. New hot-embossable surface coating 
replacing the PVC (for air knife coating) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 30,0 
Pigment 2 Calcium carbonate 60,0 
Polymer Polystyrene dispersion 
10,0 
(Rhodopas) 
Dispersing agent 
Sodium salt of polycar- 
0,35 
boxylic acid 
Defoaming agent 
Vegetable oil and fatty acid 
0,1 
esters 
Binder EVAC-latex 55,0 
______________________________________ 
dry matter content 55-65% 
viscosity 50-300 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 20-50 g/m.sup.2 dry 
Formula 8. New hot-embossable 
surface coating replacing the PVC 
(for blade, reverse roll, extrusion and silk screen methods) 
Purpose Chemical composition 
Parts 
______________________________________ 
Pigment 1 Magnesium silicate 40,0 
Pigment 2 Calcium carbonate 20,0 
Pigment 3 Titanium dioxide 10,0 
Polymer Hot-melt dispersion (wax) 
30,0 
Dispersing agent 
Salt of polyacrylic acid 
0,4 
Defoaming agent 
White oil based 0,1 
Viscosity adjustment 
Acrylic polymer dispersion 
0,6 
Viscosity adjustment 
Carboxymethyl cellulose 
0,4 
Binder Acrylic latex 60,0 
______________________________________ 
dry matter content 55-65% 
viscosity 600-4000 mPa .multidot. s/100 r/min/20.degree. C. 
amount of coating 30-50 g/m.sup.2 dry 
The formulas 1 and 2 may also contain thermoplastic halogen-free pigments 
if the purpose is to make a hot-embossable coating. 
In the table below are presented all conceivable pre-coating and surface 
coating combinations when a wallpaper according to the invention is 
manufactured using some of the formulas above. 
TABLE 
______________________________________ 
Examples of coating amounts run in various manners, 
the figures denote the grammage of the coating as dry, g/m.sup.2 
Surface coatings (PP) 
air knife 
blade 
Pre-coating (EP) 
reverse roll 
blade 
silk screen 
air knife 
extrusion 
Alter- (alternative) 
(alternative) total 
native EP1 EP2 PP g/m.sup.2 
______________________________________ 
A -- -- 50 50 
B 12 -- 40 52 
C 20 -- 35 55 
D 12 10 20 42 
E 12 10 40 62 
______________________________________ 
It has been found out that the wallpaper according to the invention has 
considerably better heat resistance compared with normal wallpapers 
provided with a PVC coating, for instance the decrease in visual lightness 
has been tenths of one per cent while that of the PVC coatings has been 
several per cent. Further, the wallpaper according to the invention burns 
less easily and creates less visible smoke and noxious substances than a 
PVC coated wallpaper on burning. In addition, the wallpaper according to 
the invention can be embossed also when cold, which is not possible for 
normal PVC coated wallpapers. The wallpaper has also better printing ink 
absorption, that is, it does not show pearls in printing to the same 
extent as the PVC coated wallpapers do. The impression is also better. 
In the following, printing tests performed with the wallpaper according to 
the invention are described. 
The base paper was a 98 g/m.sup.2 two-ply paper, where the layer forming 
the coated surface was formed of chemical pulp and the other layer of 
mechanical pulp. The paper was coated with pre-coating layers EP1 (12 
g/m.sup.2) and EP2 (10 g/m.sup.2) of the coating according to the formula 
1. The coating was performed by blade coating. The surface coating with a 
grammage of 35 g/m.sup.2 was applied on top of the pre-coating layer by 
air-knife coating using the coating composition according to the formula 
4. The total amount of the coating applied over the base paper was thus 57 
g/m.sup.2. 
A test run was performed by a gravure printing machine designed for the 
printing of wallpaper. A PVC-coated wallpaper and the above-mentioned 
wallpaper was printed in the machine. All six ink units having acrylic 
inks dissolved in toluene/methylethylketone solvents were used in the 
printing machine. The speed of the printing machine was 150 m/min and the 
drying temperature was 105.degree. C. 
First a wallpaper coated with the most commonly used PVC plastisol was 
printed in the printing machine, the amount of the base paper being 90 
g/m.sup.2 and the amount of the coating being 90 g/m.sup.2. Thereafter the 
wallpaper according to the invention was printed with the same printing 
inks and in the same conditions. It was noteworthy that no excess 
adjustment was necessary for the printing machine when the PVC coated 
wallpaper was changed to the wallpaper according to the invention. 
The wallpaper according to the invention attained clearly a brighter and 
more colourful impression than the PVC coated wallpaper. Also the transfer 
of the colour from the gravure printing cup onto the surface of the 
wallpaper was clearly better in the case of the wallpaper according to the 
invention compared with the PVC coated wallpaper. 
In another test the printing was performed in a flexographic printing 
machine designed for wallpaper printing. The printed wallpapers were the 
same as in the previous test. The flexographic printing machine had six 
colour units and flexographic printing inks dissolved in alcohol/water 
were used. The speed of the printing machine was 150 m/min and the 
temperature was 110.degree. C. The wallpaper according to the invention 
had a clearly brighter impression than the PVC-coated wallpaper. 
The invention can be modified within the scope of the enclosed claims. It 
should be also noted that in the wallpaper according to the invention the 
surface coating PP may also contain any thin additional coating known in 
the art, applied after the coating operation in later processing steps of 
the wallpaper.