Note: Descriptions are shown in the official language in which they were submitted.
~o~Z619
This invention is concerned with improvements in
the manufacture of sheet materials having a relief effect.
In particular the present invention is concerned with
the production of sheet materials by the differential
expansion of areas of a thermoplastic sheet. The sheet
materials so formed possess utility as, for example,
wall-coverings, floor covexings, decorative laminates
and decalcomania.
The production of sheet materials having a relief
effect by differential expansion of a thermoplastic sheet
offers the important advantage that, in the manufacturing
process, the use of embossing rolls may be eliminated.
Thus, while the effect of an embossing roll is to physically
alter the surface character of the sheet material, a similar
lS appearance m~y be obtained by chemical means if selected
areas of the sheet material are expanded to a different
degree.
Expansion of a thermoplastic sheet may be effected
by incorporating a blowing agent in the sheet and heating
the sheet to a temperature at which decomposition of the
blowing agent occurs. The blowing agent is conveniently
dispersed in the thermoplastic material prior to formation
of the sheet thereby ensuring thorough distribution of
the blowing agent in the sheet. Differential expansion of
the thermoplastic sheet may be achieved with the aid of a
- 2 - ~
1~)42619
~ "kicker". Kickers are well known in the art and their
- effect is to lower the decomposition temperature of
certain blowing agents. If a kicker is in association
with the blowing agent in certain areas only of the sheet,
depression of the decomposition temperature of the
blowing agent is obtained in only those areas. Hence a
greater degree of expansion of those areas of the sheet
containing kicker will be obtained than those areas not
containing kicker w~en the sheet is heated to a given
temperature for a suitable time.
Differential expansion of an expandable thermoplastic
sheet material containing a blowing agent may be obtained
by applying a kicker to certain areas only of the surface
of the sheet before heating the sheet to achieve expansion.
Application of a kicker to the surface of the sheet possesses
attractive advantages since the sheet containing the
blowing agent may be formed in one operation and the need
to incorporate a kicker into selected parts of the sheet-forming
mix is eliminated. Furthermore the use of complicated
printing techniques involving the application of chosen
inks to those areas of the sheet containing kicker
is obviated because, if desired, the kicker may be applied
together with an ink. Indeed the difficulty of registering
kicker and ink when they are applied separately to the sheet
is such as to direct one, in most circumstances, to apply
them together
- 1~4Z619
- In our experience however when the kicker is
applied together with an ink to the surface of an
expandable thermoplastic sheet the adhesion of the
ink to the thermoplastic sheet is inadequate during
subsequent treatment of the sheet. In particular, when
multi-colour printing is employed ink from one printing
station has a tendency to pick-off at a subsequent
printing station or onto a path roller. Moreover the
a &esion of the ink to the thermoplastic sheet has to
be sufficient to withstand handling between printing
and expansion which may or may not be in-line.
If the adhesion of the ink is inadequate prior to
; expansion of the thermoplastic sheet removal of ink
may occur during processing of the sheet material thus
resulting in an inferior product.
We have now found that the ink adhesion obtained
in the prQduction of a differentially expanded thermo-
plastic sheet may be significantly improved by applying
an organic solvent possessing an affinity for the
thermoplastic material to the surface of the sheet before
applying the kicker. The organic solvent is preferably
applied in combination with a resinous binder as a
lacquer in which case it will form at least part
of the solvent phase. The advantage of applying a
-- 4
~0426~9
lacquer is that, with one coating, the thermoplastic
sheet may be treated with the organic solvent and
with one or more additional agents present in the
lacquer such as, for example, a silica or silicate
matting agent, a pigment or a metallic powder.
According to one feature of the present invention
therefore there is provided a process for the preparation
of a differentially expanded sheet material which comprises
applying an organic solvent to the surface of an expandable
thermoplastic sheet containing a blowing agent and allowing
the treated sheet to at least partially dry, applying
a composition comprising an ink and a kicker for the
blowing agent to selected areas of the treated surface
and heating the sheet to a temperature at which the
blowing agent in contact with kicker decomposes and
retaining the sheet at this temperature for a suitable
time so that those areas of the sheet in contact with
the kicker are expanded to a greater extent than those
areas not in contact with the kicker.
Satisfactory expansion through the full depth of
the sheet is dependent upon migration of the kicker
through the depth of the sheet. Hence, the application
of a solvent and, in particular, a lacquer prior to
applying the kicker may be thought to provide an
additional physical barrier to the desired migration
104Z619
of the kicker. It is, however an additional and
unexpected advantage of the process according to
the invention that the improvement in ink adhesion
may be obtained without any significant reduction in
the quality of the relief effect.
It is believed that treatment of the surface of
the sheet with the chosen solvent causes some etching
of the surface thereby improving adhesion of the ink
to the sheet and the presence of the solvent facilitates
migration of the subsequently applied kicker into the
depth of the thermoplastic sheet. The chosen solvent
may be applied over the whole surface of the sheet or
to only those areas which are to be subsequently printed
with ink containing the kicker.
The process according to the invention is of
particular value in the production of wall coverings
since the thermoplastic sheet material may be formed
as an unsupported sheet or as a coating on paper, a
non-woven synthetic fibre web, a spunbonded web or another
suitable base. Differential expansion of the thermoplastic
material results in the formation of a sheet having a
visually attractive appearance which is well suited to
decoration of a wall or ceiling. The process according
1~4Z6~9
- to the invention is however not limited to the
production of wall coverings and the sheet materials
may also find utility as floor coverings, decorative
laminates, display stickers and decalcomania. In
the production of floor coverings the thermoplastic
sheet will ordinarily be formed on a relatively
substantial base which may be a suitable plastics
material, a felted sheet, or a woven or knitted fabric
formed, for example from natural or synthetic fibres.
The thermoplastic sheet may be formed of any
convenient expandable synthetic resinous material.
Preferred materials include polymers of vinyl chloride
or copolymers of vinyl chloride and another copolymerisable
monomer such as vinyl acetate or an acrylic or methacrylic
monomer such as an ester of acrylic or methacrylic acid
or acrylic or methacrylic acids themselves The
expandable sheet may be formed from a plastisol in which
case the thermoplastic polymer or copolymer will be mixed
with a blowing agent, a stabiliser having controlled
catalytic action with the blowing agent under the chosen
processing conditions, a plasticiser which may be any of the
the usual phthalate compounds and pigments or extenders.
The plastisol is formed into a sheet in any convenient
~4Z619
manner and may, for example, be applied to a base web
of paper or like substance as discussed above, the weight
of plastisol being for example, from 40 to 800 g/m2.
The precise choice of blowing agent will depend
upon the particular thermoplastic material employed and,
its decomposition temperature in the presence of the
kicker should be appropriate to the thermoplastic
material. Blowing agents are well known and have
been described in the literature. Suitable blowing
agents include azobis-formamide and azobis-isobutyro-
nitrile. The blowing agent may conveniently be present
in the thermoplastic sheet in amounts of up to 15%, e.g. 1
to 15/~, preferably from 3 to 9%, by weight based on the
weight of the expandable, synthetic resinous material.
An alternative technique for use in the production
of the expandable thermoplastic sheet is hot melt
coating. This technique may be applied to a wide
range of materials such as polyethylene, polyvinyl
chloride, polyester and acrylic polymers.
Application of the solvent may be made in any
convenient manner and satisfactory results are achieved
simply by wetting the thermoplastic sheet with the chosen
solvent. Since the function of the solvent appears to
be, in part at least, to etch the surface of the sheet
the solvent should be chosen according to the character
-- 8 --
- ~)4Z6~9
of the thermoplastic material. Thus, in the case of
expandable thermoplastic sheets based upon polymers of
vinyl chloride or copolymers of vinyl chloride and another
copolymerisable monomer, we prefer that the organic solvent
should be polar since such solvents usually possess a
greater affinity for the thermoplastic material than do
non-polar solvents.
Suitable solvents for application to the thermoplastic
sheet include hydroxylic compounds for example mono- and
polyhydric alcohols; aliphatic and alicyclic ethers such
as tetrahydrofuran; esters such as ethylacetate or
isopropyl acetate; glycol ethers; glycol esters such as
2-ethoxyethyl acetate; aliphatic and alicyclic ketones such
as methyl ethyl ketone, methyl isobutylketone or cyclohexanone;
halogenated hydrocarbons in particular chlorinated aliphatic
hydrocarbons; nitro compounds such as nitro propane or
nitrobenzene; and Lewis bases such as substituted amides
for example dimethylformamide and dimethylacetamide and
di(loweralkyl)sulphoxides for example dimethylsulphoxides.
There may be advantages associated with the
use of strongly polar solvents in certain cases and, in
such cases it may be desirable to use the chosen solvent
in conjunction with a less polar or non-polar solvent. The latter
_ 9 _
104Z619
material serves as a diluent for the polar solvent and
may conveniently be a hydrocarbon such as toluene, xylene
or methylated spirits.
In the particular case of thermoplastic sheets formed
of vinyl chloride homopolymers and copolymers we have
found aliphatic ketones such as methyl ethyl ketone
and aromatic hydrocarbons such as toluene or xylene to
be advantageous solvents to use.
The rate application of the chosen solvent to the
expandable thermoplastic sheet will depend upon the method
of application used. In general a rate of application of
from 10 to 700 g/sq.m, preferably 30 to 500 g/sq.m, will
yield satisfactory results. In the particular case of
application of the solvent by gravure printing the rate
of application may be from 25 to 300 g/sq.m, preferably
from 50 to 150 g/sq.m.
As stated above the chosen solvent may be applied
as the solvent phase of a lacquer. The use of a lacquer
is a convenient way of treating the surface of the
thermoplastic material with an additional component
such as a matting agent or pigment. The heat treatment
in the expansion step may produce a glossy surface
on the resulting sheet and it may be desirable to introduce
- 10 -
~5)4'~619
a matting agent to reduce~his effect. The lacquer
may contain, as binder, any suitable resin such as a
polymer or copolymer of ethylenically unsaturated
monomers for example vinyl and/or acrylic or methacrylic
monomers. Other suitable binders for the lacquer include
polyurethanes, polyesters and epoxy resins. The lacquer
may be applied by any of the well-known techniques such
as gravure, roller coating, screen printing or flexo-
graphic printing and since these methods may also be
used to apply the composition containing a kicker the
whole technique readily lends itself to an in-line
industrial operation.
We particularly prefer to employ gravure rollers
in the application of a lacquer to the surface of the
thermoplastic sheet. The gravure rollers will preferably
be engraved with 80 to 2001ines per linear inch.
The kicker composition may include the chosen
kicker as a solution or suspension in an ink. The
composition will thus, typically, include the kicker
in admixture with a pigment, binder and dispersed phase.
The kicker will ordinarily be a compound of zinc,cadmium
or lead and conveniently the kicker will be a salt
1~4Z619
of zinc, cadmium or lead although other compounds of
the chosen metals may be employed such as, for example,
zinc oxide. Zinc, cadmium or lead salts may be formed
of inorganic or organic acids. Inorganic acids which
may be used in salt formation include hydrochloric
and nitrlc acids whilst suitable organic acids include
carbonic, oxalic, acetic, lactic, citric, formic, sebacic,
octanoic,stearic, phthalic and benzoic acids. The ink
composition will conveniently contain up to 25% by weight
of the kicker preferably from 5 to 20% by weight. A
convenient kicker to employ is zinc octoate.
The solvent for the ink may be any of the usual
solvents for inks employed in the production of printed
wall coverings. Thus, for example, ketones such as
methyl ethyl ketone; esters such as 2-ethoxyethyl acetate;
nitro compounds such as nitropropane and hydrocarbons such
as toluene may all be used with advantage. The pigment
content of the ink will vary according to the precise
pigment chosen however effective results will generally
be achieved with ink compositions containing up to 20%
preferably 5 - 15% by weight of pigment.
1~34Z619
Formulation of the kicker composition will depend
upon the precise manner in which the ink is to be printed
onto the treated sheet material. The kicker composition
may however be applied with equal advantage in printing
using any of the conventional techniques such as those
listed above for application of the lacquer.
As mentioned above the expandable thermoplastic
sheet is preferably formed from a plastisol and in the
case of such sheet materials the degree of gelation of
the expandable sheet materials at the time of application
of the organic solvent and the kicker is important. Thus,
if the degree of gelation is too low the surface character
of the sheet will be destroyed during the application of
the solvent, especially if such application involves
passage of the sheet through the nip of printing rollers.
Conversely,if the degree of gelation is toogreat itwill be
- 13 -
1~42619
difficult to obtain satisfactory expansion of the sheet.
Satisfactory gelation of the sheet may be achieved
by heating it to 110-140C for a relatively short
period of time. A few minutes heating at low
temperatur~s is generally sufficient while heating
for less than a minute may be adequate at higher
temperatures.
Expansion of the printed thermoplastic sheet
may take place as àn in-line operation aft~r the printing
steps. Alternatively the printed sheets may be stacked
as sheets or wound on to a reel and expanded subsequently.
In this latter case there may be a tendency for kicker
from one sheet to migrate into adjacent stacked or
wound sheets causing undesired expansion in areas of
those adjacent sheets.
The thermoplastic sheet may be provided with a
coating which is impervious to the kicker after the
printing step in order to avoid this problem and the
impervious layer may be applied either to the back or
to the front of the sheet before it is stacked or reeled.
The layer is preferably applied as a transparent lacquer
to the top face of the printed sheet after the final
printing step. Application of the impervious layer to
the top face i8 preferred because, in addition to providing
1~4'~619
the barrier to migration of the kicker, such a
coating may serve as a wear layer to protect the
sheet in use. Moreover, application of a lacguer
in a final step after printing may provide a convenient
means of introducing a further agent to the surface of
the sheet such as, for example, a matting agent.
If desired the sheet material obtained by the
process according to the invention may be presented with
a coating of adhesive on the side for application to
the substrate. For example, in the particular case of
wall cov~ringsthe side of the sheet material to be applied
to the wall or ceiling may be provided with a coating
of a water-activatable adhesive. The adhesive coating
may be provided at any convenient point in the
manufacture of the sheet material.
In the case of water-activatable adhesives the
coating may be applied as an aqueous solutio~ dispersion
or emulsion to the surface of the sheet and dried.
Adhesive may be applied at the rate of 2 to 3U
grams/square metre of surface area and the adhesive may
be a natural or synthetic resinous material, a
vegetable gum, a soluble starch or starch ether or
other suitable material.
- 15 -
1~4Z619
It may be preferably to incorporate into the
adhesive coating other ingredients such as for example
surface active agents to improve the water-absorption
properties of the adhesive coating and fungicides to
inhibit mould growth.
The process according to the invention may be
used in the preparation of sheet materials having the
most variegated effects. Thus, for example, two or more
applications of a kicker composition may be made to
different areas of the surface of the sheet after the
treatment with a solvent. Different pigments may be
employed in the different kicker compositions which,
moreover, may contain differing concentrations of kicker.
After expansion of such a sheet a produc-t is formed in
which a variety of degrees of expansion have been
obtained giving a product having a pleasing decorative
effect.
In order that the invention may be well understood
the production of a sheet material according to one
preferred mode of operation according to the invention
will be described by way of illustration only with reference
to the accompanying drawings. In the drawings:-
Fi~ure 1 illustrates one method of producing a sheet
material according to the invention on-line.
_ 16 ~
1~4Z~
Fi~ure 2 is an enlarged partial longitudinal section
of an expandable thermoplastic sheet.
Fi~ure_3 is a section of the sheet shown in Figure 2
carrying a coating of a lacquer.
Fi~ure 4 is a section of the sheet shown in Figure 3
after application of an ink to the treated surface.
Fi~ure 5 is a section of the sheet shown in Figure 4
after expansion.
It should be understood that Figures 1-5 are
purely diagrammatic and no attempt is made therein to
show the relative thicknesses of the various layers that
compose the sheet material.
An expandable thermoplastic layer 1 is applied as
a plastisol to a sheet of suitable paper 2 and partially
gelled by the oven 12 to produce a sheet material as
shown in Figure 2, The sheet material so formed is
presented to the nip between a pair of rolls 6 as shown
in Figure 1 and receives a coating of a lacquer 3 from
a bath 7 whereafter it is partially dried by oven 11 to
produce a lacquered sheet as shown in Figure 3. The
lacquer contains a dispersion of a matting agent
in a solution of a vinyl chloride homo- or copolymer in an
organic solvent possessing an affinity for the thermo-
plastic sheet. Suitable lacquers are described more fully
- 17 -
1~42619
in Examples 1 and 2 below.
The lacquered sheet then proceeds to the nip
between a pair of conventional printing rolls 8 and ink
from bath 9 is applied to certain areas only of the
lacquered surface of the sheet. The ink contains a
pigment and a kicker appropriate to the blowing agent
present in the thermoplastic layer 1 and formulations
for such inks are described more fully in Examples 1
and 2 below. The sheet material is then of an appearance
as shown in Figure 4 and has a number of discreet areas
4 coated with kicker-containing ink.
The printed sheet shown in Figure 4 then passes
on to an oven 10 wherein the sheet:~ttains a temperature inter-
mediate between the decomposition temperature of the blowing
agent and a mixture of the blowing agent and the kicker.
Differential expansion is thereby obtained to form a
product, as shown in Figure 5, in which
those portions of the sheet that received an application
of kicker-containing ink are expanded to a greater extent
than those portions of the sheet which received no such
coating. The resulting sheet material is visually attractive
and may be used as a wall covering.
- 18 -
1~4Z6~9
In order that the invention may be further
understood the following examples are given by way of
illustration only. In the examples parts referred to
are parts by weight.
Example 1
(a) Preparation of expandable thermoplastic sheet
A mix comprising
Polyvinyl chloride lOC parts
Dicapryl phthalate (plasticizer) 65 parts
Organo-tin stabiliser 1 part
Epoxidised oil stabiliser 6 parts
Azobis-formamide 6 parts
Titanium dioxide 40 parts
White spirit S parts
,5 was applied by means of a doctor blade at a thickness
of 0.2 mm and a dried weight of 190 gmkn2 on to 90 gm/m2
Paper. The coating was gelled at a temperature of 120-130C
for 60 seconds to yield an expandable thermoplastic sheet
(b) Treatment of expandable sheet with solvent
A lacquer was prepared by dispersing the following
; formulation:
_ 19 -
16~4Z619
Vinyl chloride/vinyl
acetate copolymer 18 parts
Silica matting agent 8 parts
Methyl ethyl ketone 40 parts
Xylene 10 parts
Toluene 24 parts
The viscosity of the lacquer was adjusted by
addition of methyl ethyl ketone to 30 seconds (as
measured on Ford No. 4 cup) and the lacquer was then
applied to the surface of the gelled polyvinyl chloride
sheet prepared in (a) using a gravure roller engraved
with 140 lines per linear inch, After partial drying
the following ink composition was applied to the
treated sheet:-
Vinyl chloride polymer in
methyl ethyl ketone 24 parts
2-Ethoxyethyl acetate 2.5 parts
Toluene 13 parts
Zinc octoate 24 parts
Pigment 7 parts
If necessary the viscosity of the ink was adjusted to
30 seconds (as measured on Ford No. 4 Cup) by addition
of methyl ethyl ketone. The ink was applied in a
chosen pattern using a gravure roller engraved with
120 lines per linear inch and blown at 200OC for
one minute after an interval of 20 hours.
- 20 -
1~34Z619
The product obtained had an expansion in the inked
areas of more than 0.012 inches relative to the unprinted
areas and a satisfactory degree of mattness which combined
to give the material a visually attractive appearance.
Moreover the product showed good ink adhesion.
Example 2
A lacquer was prepared by dispersing the following
formulation:
Polyvinyl chloride 18 parts
Silica matting agent 15 parts
Titanium dioxide 36 parts
Methyl ethyl ketone 23 parts
Toluene 8 parts
The viscosity of the lacquer was adjusted by
addition of methyl ethyl ketone to 30 seconds (as
measured on Ford No. 4 Cup) and the lacquer was then
applied to the surface of a thermoplastic sheet prepared
as described in Example 1 (a). Application was effected
using a gravure roller engraved with 100 lines per linear
inch and thereafter the following ink composition was
applied to the treated sheet:-
- 21 -
1~426~9
~olyvinyl chloride 18 parts
Pigment 9 parts
2-Nitropropane 40 parts
Methyl ethyl ketone 8 parts
Toluene 24 parts
Zinc octoate 18 parts
If necessary the viscosity of the ink was adjusted
to 30 seconds (as measured on Ford No. 4 Cup) by
addition of methyl ethyl ketone. The ink was applied
in a chosen pattern using a gravure roller engraved
with 150 lines per linear inch and blown at 2000C
for one minute after an interval of 7 days.
The product obtained had an expansion in the inked
areas of greater than 0.015 inches relative to the
- 15 unprinted areas and a satisfactory degree of mattness.
The material was visually attractive and the ink adhesion
of the product was good.
- 22 -
~42619
Examples 3-16
Sheet materials were prepared in these Examples
in a manner analogous to that described in Examples 1 and
2, ExRmples 3 - 16 illustrate the application
of the invention when differing expandable thermoplastics
materials, solvents and kickers are used in the process
according to the invention,
(a) Preparation of expandable thermoplastic sheets
A and B
The following mixes were applied by means of a
doctor blade at a thickness of 0,13 mm and a dried weight
of 180 gm/m2 on to 90 gm/m2 paper,
.
Sheet A I B
Polyvinyl chloride 100 ~ -
homopolymer .
Vinyl chloride-vinyl acetate
copolymer - ! loo
Dicapryl phthalate 65 ~, 65
Organo-tin stabiliser
Epoxidised oil stabiliser 6 j 6
Azobis-formamide 6 I 6
Titanium dioxide 40 40
White spirit
The coatings were gelled at 120C for 60 seconds,
(b) Treatment of Sheets A and B with solvents
The following solvents and lacquers were prepared
for treatment of sheets A and B,
- 23 -
1~4~f~19
Solvent/Lac uer No 1 2 ~ 3 4 5 6 7 8
q . ! ---~-
Vinyl chloride-vinyl acetate
copolymer - - ~ 23 23 20 _ 17 12
Acrylic resin _ _ _ _ _ 20 _ 13
Silica matting agent _ _ _ 20 _ 20 _ 8
Coloured pigment _ _ _ ~ _ _ _ 10 6
ITitanium dioxide _ _ _ ~ _ _ _ _ 36
Methyl ethyl ketone _ 80 _ 115 100 80 85 107
Toluene _ _ _ _ 55 25 62 48
Cyclohexanone _ 20 _ 30 _ 10 _ _
Ethyl acetate _ _ 138 _ _ _ _ _
iso Propyl acetate _ _ 90 _ _ _ _ _
2-Ethoxyethyl acetate _ _ _ _ _ 8 _ 13
2-Nitro propane 25 _ _ 20 _ _ _ _
Tetrahydrofuran 75 _ _ ; _ _ _ _ .
The solvent or lacquer was applied to gelled sheets
A and B using a gravure roller engraved with 150 lines
per linear inch. After partial drying the following ink
compositions were applied to the treated sheets:-
Ink No, ' I II III IV i
Vinyl chloride-vinyl
acetate copolymer ¦ - _ 17 17
Acrylic resin ! 13 13 _
Lead octoate _ _ _ 20
Cadmium octoate _ 14 _ ~ _
Zinc octoate _ _ 17 1 _
Zinc benzoate 20 _ _ I _
Methyl ethyl ketone 46 50 ! 64 1 68
Toluene 28 23 j 31 ~ 29
2-Ethoxyethyl acetate 8 8
Pigment 13 13 i 10 1 10
- 24 -
1~42619
All inks were applied at a viscosity of 25 seconds
(as measured on Ford No. 4 Cup), viscosities being adjusted
by addition of methyl ethyl ketone if necessary. Inks
were applied using a gravure roller engraved with 150 lines
per linear inch and blown at 200C for one minute after
an interval of 24 hours.
The Examples and the properties of the resulting
expanded sheets are set out in the following Table.
Example Sheet Solvent/ Ink Contrast Ink
No No. NoaCquer No ~n Adhesion
3 A 1 I 0.35 Good
4 A 6 II 0.17 ..
A 7 III 0.40 ..
6 A 8 IV 0.30 ..
7 A 3 IV 0.31 ..
8 A 5 III 0.47 ..
9 A 4 III 0.45 ..
A 1 IV 0.35 -
11 B 8 I 0.20 -
12 B 3 II 0.06 ..
13 B 5 IV 0.18 ..
14 B 2 II 0.08 -
B 1 III 0.36 -
16 B 4 IV 0.2l -
(1) ~ontrast is a measure of the difference in the
expansion in the inked areas relative to the unprinted
areas.
The products obtained in Examples 4,6,9,11 and 16
were matt,
- 25 -
