Process for the production of coverings exhibiting a cracked appearance and the product obtained therefrom

A process for the production of synthetic coverings for floors, walls, etc. which exhibit a cracked effect is presented. The process includes the step of depositing on a compatible substrate, a plastisol coating composition containing a gel previously prepared from a mixture of two materials, the mixture being comprised of (1) a solid sorbent agent and (2) a solvent which causes swelling by absorption of the solvent in and on the sorbent agent; or alternately, by an aqueous dispersion of a (1) dry mixture of PVC and of (2) a plasticizer containing at least one resin forming a gel in water. Subsequent to depositing this plastisol coating on the substrate, a thermal treatment for the formation of a film or for drying is carried out at a sufficient temperature whereby an irreversible process of preliminary gelling of the coating and shrinkage of the gel by desorption of the solvent from the sorbent agent or by evaporation of the water, respectively, simultaneously occurs. Thereafter, conventional finishing operations may be carried out on the synthetic coverings.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the production of synthetic surface 
coverings. More particularly, this invention relates to a method of making 
synthetic coverings for floors, walls, etc. which exhibit a cracked 
appearance. This invention also relates to the products obtained in 
accordance with this novel process. 
Increasingly, in the production of synthetic decorative coverings intended 
for floors, walls, and the like, attempts have been made to manufacture 
the coverings using conventional and naturally occurring materials such as 
ceramics and the like. A particularly decorative effect obtained when 
using ceramic materials resides in the naturally occuring cracks. However, 
such a cracked appearance is difficult to obtain with synthetic materials 
deposited in the form of a coating, for example, on a conventional 
substrate. Moreover, the attempted reproduction of cracks by printing 
leads to the problem of precluding an authentic reproduction of the 
"natural" cracked effect, and the motifs obtained are necessarily 
repetitive, i.e., without a random nature. Also, printing does not permit 
depth (relief) to be imparted to the synthetic covering material. 
French Specification No. A2,126,658 discloses a known process for applying 
a covering material in the form of an emulsion in order to produce crazed 
(cracked) configurations. In this case, a lower synthetic covering 
material containing a mineral material having a high swelling property is 
deposited on a substrate. This lower covering material is dried, and a 
hardened covering material containing a silicon dioxide base is then 
applied thereon. In the process described in the French specification, the 
lower covering material absorbs the water contained in the hardened 
covering material and simultaneously causes both the contraction of the 
hardened material and the formation of crazed configurations. A 
disadvantage of this French process resides in the fact that there are two 
different layers of composition to be applied, which necesitates 
intermediate drying. This process is therefore time consuming and 
burdensome. 
French Patent document No. A2,247,494 relates to a cracked film of a PVC 
polymer including at least one plasticizer homogenously distributed 
therein. French Pat. No. A2,247,494 also discloses a synthetic covering 
comprised of a conventional substrate covered with the PVC, a polymeric 
film, as well as a process for the preparation of the latter. This process 
relies on a two-phase system consisting of (1) polymer-plasticizer and (2) 
water. However, this process does not permit adequate control of the 
formation of the cracks or of the size of the cracks. Moreover, this 
process requires large quantities of water. 
U.S. Pat. No. 2,612,456 similarly relates to a process for the production 
of a decorative and protective covering which exhibits a cracked 
appearance. This process utilizes an organosol including particles of an 
organic copolymer of vinyl chloride and vinyl acetate, said particles 
being dispersed in a volatile organic liquid. The organic liquid must have 
a swelling effect on particles of polymer. As in the above-discussed 
process, this process is also difficult to control making it quite 
difficult to obtain a dense network of cracks. Moreover, this process 
like-wise requires large quantities of solvent. 
Accordingly, an object of the present invention is to provide a process for 
the production of synthetic coverings (i.e. for floors or walls), which 
exhibit a cracked appearance and which requires only a single layer of 
synthetic material to obtain the cracked effect. 
Another object of the present invention is to provide a process for the 
production of synthetic coverings having a cracked appearance in which the 
required quantities of solvent or of water are substantially reduced as 
compared with the prior art. 
Another object of the present invention is to provide a process for the 
production of synthetic coverings including cracks with depth, that is, 
relief being provided substantially throughout the mass of at least one 
layer of the covering. 
Yet another object of the present invention is to provide a synthetic 
covering for floors, walls and the like which exhibit a cracked appearance 
having a random nature. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a process for the production of 
synthetic coverings for floors, walls, etc. which exhibit a cracked 
appearance comprises the steps of depositing on a compatable substrate a 
coating composition of a plastisol containing a gel previously prepared 
from a mixture of two materials, the mixture being comprised of a solid 
sorbent agent; and by a solvent which causes the swelling by absorption of 
the solvent in and on the sorbent agent; or alternatively by a dispersion 
in water of a dry mixture of PVC and plasticizer containing at least one 
resin forming a gel in the water. A thermal treatment is then preformed 
for the formation of a film or for drying at a sufficient temperature so 
that there takes place concomitantly an irreversible process of 
preliminary gelling of the coating and the shrinkage of the gel by 
desorption of the solvent from the sorbent agent or by evaporation of the 
water, respectively. Therafter, conventional and known finishing 
operations may be carried out. 
The process of the present invention permits the achievement of the above 
enumerated objects of the invention, and in particular, permits the 
production of a covering exhibiting a cracked effect, in which the cracks 
extend in a random manner, with depth, within the mass of the synthetic 
covering.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An important feature of the present invention is the selection of the 
sorbent agent/solvent mixture which is utilized under the particular 
conditions of the process of the invention. Preferably, the solvent should 
not interfere with the plasticizing effect of the other additives of the 
synthetic material used for the production of the covering. Use preferably 
is made of a solvent which does not participate in the plasticizing 
process, although the use of a solvent which does participate in 
plasticizing may also be contemplated. In accordance with a particularly 
preferred embodiment of the present invention, the absorbent agent is a 
silica or a silicate, preferably having a specific surface according to 
BET in the range of between 250 and 700 m.sup.2 /g, preferably on the 
order of 300 to 400 m.sup.2 /g. The coating composition advantageously 
includes about 0.5% by weight of sorbent agent. 
Preferably, use is made of a solvent having a vapor pressure which is very 
high at the temperature of formation of the synthetic film, so that the 
sorbent agent is withdrawn by desorption of the solvent as soon as the 
film forms during the thermal treatment (with a view to "tearing" it by 
forming cracks). It should be understood that the temperature at which the 
solvent has a high vapor pressure, or the boiling point of the solvent, 
must be close to the temperature of formation of the film, since, if this 
temperature is too high, there will be no formation of cracks, by reasons 
of both (1) fusion and (2) of the surface tension of the snythetic 
coating. On the other hand, if this temperature is too low, there will be 
evaporation prior to formation of the film. It is important to ensure that 
the force of the retraction is greater than the force of cohesion of the 
film. Accordingly, the solvent should be one in which the hydrocarbon 
fractions, and in particular white spirits, are at a level on the order of 
about 15 to about 35% by weight of the plastisol coating. 
The following products may also be suitable as solvents (It will be 
appreciated that the following list is by way of example only, and is not 
limiting in any manner): 
(1) solvents of the SHELLSOL.RTM. TD or AB type; 
(2) hydrocarbon fractions other than white spirit, having suitable 
evaporation/retention properties; 
(3) solvents of the POLYSOLVAN.RTM. type, i.e. N-butyl esters of glycol; 
and 
(4) solvents of the DOWANOL DPN.RTM. type, i.e. the methyl ether of 
dipropylene glycol. 
Previously, the temperature of formation of the plastisol coating film is 
selected from between about 110 and about 160.degree. C. It is possible to 
subsequently subject the coating to, for example, a temperature on the 
order of 200.degree. C. for 1 minute to 2 minutes 30 seconds, if it is 
desired to modify the initial opening of the cracks without any effect on 
the number of cracks. 
In the alternative enbodiment of the present invention wherein the 
substrate is applied with a coating of a dispersion in water of a dry 
mixture of PVC and plasticizer, it will be appreciated that the resin 
forming a gel in the presence of water may be selected from a wide range 
of products which are commercially available. For reasons of compatibility 
with the medium employed and the substrate on which it is coated, 
preference is given to mixtures based on cellulose resins having a 
thickening action. 
The addition of a solvating agent such as ethyl glycol to the water is 
particularly useful in order to bring about swelling of the resin forming 
a gel. 
The additives which are required for the stabilization of the aqueous 
dispersion are well known in the art, and a large quantity of commercial 
products are available. 
Preferably, not only sufractants will be added to the preparation for 
stabilization purposes; but also antifoam agents will be added to 
facilitate the preparation of the dispersion and to produce a regular 
coating. 
The preparation of the dispersion, advantageously includes the presence of 
fillers (which may or may not be pigmenting). These fillers particularly 
effect the size of the cracks or crazed formations which are observed. 
Advantageously, the temperature of the thermal drying treatment is selected 
to be from about 180 to about 210.degree. C. Subsequently, the coating may 
be subjected (by example only) to a temperature on the order of 
200.degree. C. for 1 minute to 2 minutes 30 seconds, if it is desired to 
modify the initial opening of the cracks without having any effect on the 
number therof. 
As already discussed, in accordance with the present invention, a coating 
composition of plastisol containing the sorbent agent/solvent mixture; or 
the aqueous dispersion of a dry mixture of PVC and of a plasticizer 
containing a resin forming a gel in water is applied to a substrate. In 
one embodiment of the present invention, the substrate may consist of a 
conventional substrate material which may already include one or more 
deposits of synthetic material. It will be appreciated that the deposits 
may be provided with an imprint. 
In an effort to obtain particular decorative effects, in accordance with 
the present invention, the coating composition of plastisol of PVC 
containing the sorbent agent/solvent pair or the aqueous dispersion of PVC 
and a resin may be applied to form a gel locally, such that only a part of 
the decorative motif will exhibit a "cracked" appearance. This 
discontinuous application may be undertaken by well known techniques, for 
example, by a serigrpahic technique. In this way, it becomes possible to 
imitate particular floor or wall coverings, comprising tiles exhibiting a 
cracked effect and comprising joints having the appearance of cement 
joints which are not cracked. 
In a preferred embodiment of the present invention, after the cracks have 
been formed, a plastisol coating may be scraped, for example, onto the 
covering obtained, in such a manner as to fill in the cracks with a 
suitable material. In one particularly preferred embodiment, it is 
possible to scrape either a plastisol containing up to 30% carbon black 
onto the product obtained or an aqueous emulsion of plasticized PVC and 
conductive carbon black, in such a manner as to fill in the cracks with a 
material which conducts electric current. Such a covering is particularly 
suitable for avoiding the accumulation of static electricity for coverings 
intended for operating theatres, computer rooms, etc. The use of a 
composition containing carbon black leads to a value on the order of 
10.sup.8 ohm.cm for the transverse electrical resistance of the covering 
obtained (which is normally 10.sup.14 ohm.cm). 
It is similarly advantageous, depending upon the effects sought, to provide 
an imprint or any other traditional operation on the cracked product. 
Also, a conventional foamable paste which, in the course of the thermal 
treatment, undergoes swelling so as to create an emergent veining at the 
surface, having the appearance of a roughcast wall may be coated into the 
cracks. 
Finally, a coating of a conventional wear surface layer may be deposited on 
the synthetic covering which further improves the life of the covering 
obtained in accordance with the various above mentioned embodiments of the 
present invention. 
The form, the depth and the opening of the cracks may be controlled by the 
temperature of the thermal treatment, by the selection of the sorbent 
agent/solvent pair and/or of the resin forming a gel in water, and by the 
quantity of solvent used. However, it should be noted that the depth and 
the opening of the cracks may be modified subsequently to a large extent 
by the thermal treatment, unless prior coating of the surface has taken 
place. 
The several conventional operations which may be carried out on the cracked 
product obtained in accordance with the present invention do not need to 
be described in great detail in the present specification. Such known and 
conventional steps include, by way of example, the deposit of additional 
coatings, which may or may not be pigmented, imprints, deposits of a wear 
layer, convention thermal treatments and the final firing. 
The present invention will now be described in greater detail with 
reference to the examples in which follow and in which all the proportions 
are expressed by weight, except where otherwise indicated: 
EXAMPLE 1 
A gel is prepared in advance, having the following composition: 
100 parts of butyl-glycol acetate 
10 parts of pyrogenic silica (300 m.sup.2 /g)- Aerosil.RTM. 300 
A plastisol composition referred to as "compact" is also prepared, 
containing: 
650 parts of PVC in emulsion (for example: K value 72) 
100 parts of PVC in suspension (for example: K value 66) 
540 parts of phthalate plasticizer 
500 parts of carbonate-containing fillers (calcium carbonate) 
25 parts of titanium oxide 
2 parts of tin-based stabilizer. 
The "compact" composition and the gel which have previously been prepared 
are then mixed as follows: 
70 parts of "compact" 
35 parts of gel 
10 parts of TXIB 
(texanol isobutyrate - secondary plasticizer) 
3.5 parts of barium-based and zinc-based stabilizer. 
The content of Aerosil 300.sup.R and of solvent are 2.68% and 26.31% 
respectively in the plastisol coating. The coating thus obtained is 
applied to a traditional substrate which may already have received at 
least one coating and/or one imprint. 
The product thus obtained is subjected to a thermal treatment in such a 
manner as to create the cracks. This thermal treatment preferably consists 
of a step having a duration of 2 minutes 30 seconds, at a temperature 
within the range between 110.degree. and 120.degree. C., which is obtained 
by heating, for example, by means of a pulsating air oven or by infared 
radiation or a combination of the two. 
The product obtained may then be subjected to an imprint of a decoration in 
accordance with known process. 
It is also possible to subject the product to a second thermal treatment 
which permits opening of the cracks which have already been formed. Such a 
thermal treatment consists of a step, having a duration of 1 minute to 2 
minutes 30 seconds, at a temperature on the order of 200.degree. C. 
The product is then passed under a rubber scraper, which introduces a fluid 
pigmented plastisol into the cracks which then undergoes preliminary 
jelling. 
Surprisingly it has been found that, after coating by a plastisol, the 
cracks no longer open in the course of this preliminary jelling. 
The whole assembly is then covered with a plastisol coating of PVC serving 
as a wear layer, and the product obtained is subjected to a jelling 
operation, for a period of 2 minutes 30 seconds, at a temperature of about 
190.degree. C. 
It is also possible to use a poyurethane varnish cross-linkable by any 
appropriate means, for example UV or by an electron beam. 
EXAMPLE 2 
plastisol+gel 
A gel is prepared, having the following composition: 
80 parts of white spirit 
35 parts of barium silicate such as Dutch Boy BAROSIL.RTM. (product of 
National Lead, Inc. USA). 
A "compact" composition, similar to that of Example 1 is also prepared, and 
the previously prepared gel is incorporated therein at the rate of: 
50 parts of "compact" composition, 
35 parts of gel, 
The content of BAROSIL.RTM. and of white spirit in the coating is 12.5% and 
28.7%, respectively. 
The coating obtained in this manner is deposited on a conventional 
substrate, which is then subjected to a thermal treatment in such a manner 
as to create the cracks. The thermal treatment consists of a step, having 
a duration of 2 minutes at 110.degree.-120.degree., in, for example, an 
oven. The product thus obtained is then passed below a scraper in such a 
manner as to urge a PVC paste containing 30% of carbon black into the 
cracks. A thermal treatment or final firing is then carried out. The 
resulting product is a covering referred to as "homogeneous", the 
transverse electrical surface resistance of which is reduced to a value on 
the order of 10.sup.8 ohm.cm. (while it is 10.sup.14 ohm.cm for PVC) and 
which thus permits dispersal of the local electric charges. Such a 
covering could be used in a medium exhibiting high sensitivity to local 
charges, such as computer rooms. 
EXAMPLE 3 
plastisol+gel 
A gel is prepared in advance, having the following composition: 
10 parts by weight of AEROSIL.RTM. 300. 
100 parts by weight of white spirit. 
A "compact" plastisol composition is prepared in accordance with Example 1. 
The following are then mixed: 
70 parts of "compact" 
37 parts of gel 
10 parts of TXIB. 
The procedure is then carried out as in Example 1. 
EXAMPLE 4 
The procedure is carried out as in Example 1 or 2, but a foamable paste 
having the following composition is coated into the cracks obtained; 
30 parts of PVC suspension of value K=66 
70 parts of PVC emulsion of value K=70 
32 parts of phthalate plasticizer 
20 parts of TIXB 
25 parts of fillers (calcium carbonate) 
2 parts of TiO.sub.2 
2 parts of self-dispersing swelling agent. 
EXAMPLE 5 
(comparative example) 
The graphs in FIGS. 1-6 show the results of laboratory tests in accordance 
with an annular pumping technique. FIGS. 1 to 3 show, as abscissa, the 
frequencies (in Hz) and, as ordinate, the modulus G" or dissipation 
modulus (in N/m.sup.2). FIGS. 4-6 show, as abscissa, the frequencies (in 
Hz) and, as ordinate, the modulus K or rigidity modulus (in N/m). 
FIGS. 1 and 4 relate to a "compact" composition in accordance with Example 
1. 
FIGS. 2 and 5 relate to the following composition: 
______________________________________ 
Compact according to Example 1 
1,400 
Aerosil .RTM. 63 
White spirit 637 
TXIB 200 
______________________________________ 
FIGS. 3 and 6 relate to a composition as mentioned below, in which the gel 
has been prepared in advance. 
______________________________________ 
Compact according to Example 1 
1,400 
Gel 700 
TXIB 200 
______________________________________ 
The gel comprises 63 parts of Aerosil .RTM.300 and 637 parts of white 
spirit. 
As the modulus G" (FIGS. 1 to 3) is proportional to the viscosity, and the 
frequency is proportional to the velocity gradient, annular pumping 
permits expression of the viscosity as a function of the velocity 
gradient. 
It can be seen from the figures that the composition of FIG. 3 exhibits the 
highest level of viscosity; although for a composition having the same 
total contents but in which the silica and the white spirit have not been 
added in the form of a gel, the viscosity level is very low. 
It can be concluded from this that, in the case of FIG. 2, the white spirit 
is not preferentially adsorbed by the silica, but is equally distributed 
within the medium and thus has a vicosity-lowering effect on the 
plastisol. In the case of FIG. 3, on the other hand, the solvent has 
caused the inert filler to swell and has remained there even after mixing 
in the final medium. It was not used to reduce the general viscosity of 
the plastisol. It is only the thermal treatment which will permit 
desorption of the solvent from the silica, causing shrinkage of the 
latter. 
FIGS. 4 to 6 concerning the rigidity (modulus K) likewise confirm this 
behavior, for the same compositions. 
EXAMPLE 6 
Aqueous dispersion 
In a rapid mixer (Papenmeier type), a dry mixture of PVC having the 
following composition is prepared: 
______________________________________ 
PVC "suspension" K value 
100 
Plasticizer 35 
Sn stabilizer 2 
Epoxidized soya oil 3 
______________________________________ 
When the mixture reaches the temperature of 80.degree.-90.degree. C., it is 
transferred to the refrigeration cell. In order to obtain a mixture having 
improved flow properties, between 3 and 5 parts of PVC "emulsion" are 
added thereto in the course of cooling. 
An aqueous suspension prepared in a mixer (Moltini type) has the following 
composition: 
______________________________________ 
Water 100 
Ethyl-glycol 100 
TiO.sub.2 5 
Dolomite 150 
Dry PVC mixture 200 
Cellulose thickener (5% aq.) 
5 
Surfactant 2 
______________________________________ 
This aqueous suspension is deposited by means of a scraper on a substrate 
composed of a sheet of glass coated with PVC plastisol jelled on a drum 
and which has the following formulation: 
______________________________________ 
PVC "emulsion" 100 
Chalk 50-100 
TiO.sub.2 3-20 
Plasticizer 50-80 
Sn stabilizer 2 
Epoxidized soya oil 
3 
______________________________________ 
This coating is dried and baked in a hot-air oven between 180.degree.0 and 
210.degree. C. In the course of firing, a close and continuous network of 
crack appears. 
EXAMPLE 7 
Aqueous dispersion 
Starting from the dry PVC mixture of the same formulation as in Example 1, 
an aqueous suspension having the following formulation is prepared: 
______________________________________ 
water 80 
Cellulose thickener (5% aq.) 
20 
Dry PVC mixture 100 
Dolomite 20 
TiO.sub.2 4 
______________________________________ 
This suspension is scraped onto a subestrate identical to that in Example 
1, dried and fired in a hot-air oven under the same conditions. In the 
course of firing, a discontinuous and sparse network of fine cracks 
develops. 
Each type of product may be treated subsequently in various ways in order 
to provide finishing, for example by: 
(1) printing followed by varnishing; 
(2) coating with a colored varnish, which may or may not be translucent; or 
(3) coating with a conductive material. 
Furthermore, the various aqueous suspensions may be colored in the mass by 
addition of a suitable pigment to their formulation. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it is to be understood 
that the present invention has been described by way of illustrations and 
not limitation.