U.S. patent number 3,860,472 [Application Number 05/159,637] was granted by the patent office on 1975-01-14 for method for manufacturing a synthetic leather base.
This patent grant is currently assigned to Cursel. Invention is credited to Marc Derville.
United States Patent |
3,860,472 |
Derville |
January 14, 1975 |
METHOD FOR MANUFACTURING A SYNTHETIC LEATHER BASE
Abstract
A needled sheet of synthetic or artificial fibers is bonded by a
polymerizable binder. The method comprises four successive
continuous phases, to produce a thick, dense needled sheet. A first
phase consists of preparing two non-woven primary sheets from
fibers of fine denier, at least to a major extent unshrinkable,
having a high level of curl and a good curl permanence. A second
phase consists of needling separately the two primary sheets. A
third phase consists of superposing the two thus needled primary
sheets and a fourth phase consists of subjecting the sheet thus
formed to intense needling. This sheet once bound is then subjected
to splitting operations dividing it into layers of the desired
thickness, which layers can then be buffed individually.
Inventors: |
Derville; Marc (Bondues,
FR) |
Assignee: |
Cursel (Ranbaix,
FR)
|
Family
ID: |
26215839 |
Appl.
No.: |
05/159,637 |
Filed: |
July 6, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Jul 7, 1970 [FR] |
|
|
70.25220 |
Jun 24, 1971 [FR] |
|
|
71.23135 |
|
Current U.S.
Class: |
156/148; 28/111;
28/112; 28/115; 156/254; 428/904; 442/402 |
Current CPC
Class: |
D04H
1/48 (20130101); D04H 1/488 (20130101); D04H
1/498 (20130101); B32B 5/06 (20130101); D06N
3/0013 (20130101); B32B 5/26 (20130101); D06N
3/0031 (20130101); Y10T 156/1059 (20150115); Y10T
442/682 (20150401); Y10S 428/904 (20130101) |
Current International
Class: |
D04H
1/48 (20060101); B32b 005/06 (); D04h 018/00 ();
B29j 001/04 () |
Field of
Search: |
;28/72.2R,4R
;161/80,81,154,155,156,DIG.2 ;156/148,247,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,029,651 |
|
May 1966 |
|
GB |
|
6,600,684 |
|
Aug 1966 |
|
NL |
|
Other References
Nutter, W., "An Outline of Nonwoven Textiles, Part 2," Textile
Month, June 1970, pg. 71 & 74-76..
|
Primary Examiner: Van Balen; William J.
Assistant Examiner: Lipsey; Charles E.
Attorney, Agent or Firm: Waters, Roditi, Schwartz &
Nissen
Claims
I claim:
1. Method of manufacturing a synthetic leather base exhibiting a
homogeneous cross-section, comprising preparing a thick,
homogeneous sheet of high density from synthetic fibers, said
fibers having a denier less than 3, a curl frequency over 6, a curl
ratio over 10 and a curl permanence over 50 percent, said method
being a continuous method and including four successive phases, the
first phase consisting of preparing two continuous non-woven
primary sheets from said fibers, the second phase consisting of
needling the two primary sheets separately from one side only with
needles striking in the same direction, the third phase consisting
of turning over one of said primary sheets and superposing the two
thus needled primary sheets such that the surfaces which have been
initially contacted with the needles are on the outside of the
sheet formed by their superposition, and the fourth phase
consisting of subjecting the sheet thus formed to intense needling
from both sides, applying a curable binder through the resulting
sheet, curing said binder so as to bind together the fibers to form
a bound sheet and subjecting the bound sheet to splitting
operations dividing it into layers of the desired thickness.
2. Method according to claim 1, wherein the needling of the
superposed primary sheets is effected in several successive
needlers each equipped with a needle board working from above to
below and with a needle board working from below to above.
3. Method according to claim 1, wherein the fibers are oiled before
forming the primary sheets, with 0.5 to 2 per cent (with respect to
the weight of the fibers) by suitable oiling agent to avoid the
formation of static electricity on forming the sheet and to ensure
sufficient lubrication for the needling.
4. Method according to claim 1, wherein said binding is effected by
coagulation in situ of a synthetic latex.
5. Method according to claim 1, wherein the thickness of each
primary sheet is of the order of 150 mm before preneedling, of 20
to 25 mm after pre-needling and of 7 mm after the last needling,
and wherein the sheet emerging from the last needler has a
thickness of the order of 6 mm, weighs 1,250 to 1,400 g/m.sup.2 and
has a perforation density comprised between 600 and
1,000/cm.sup.2.
6. Method according to claim 1, wherein needles are used having a
triangulated portion possessing two "regular" barbs per edge.
7. Method according to claim 1, wherein the needles used for the
needling operations have gauges of the order of 42 to 46.
8. Method according to claim 1, including buffing the resulting
layers individually.
9. Method according to claim 1 wherein the needling phase of each
primary sheet comprises effecting pre-needling with continuous
advance of the sheet in a pre-needler, then needling in a needler
with discontinuous advance of the sheet.
Description
The invention relates to methods for the manufacture of a synthetic
leather base, which consists in preparing a thick and dense needled
batt or sheet from synthetic or artificial fibers and in binding
this sheet by a polymerisable binder and in then dividing it into
several layers which can if necessary be buffed.
It is known that such a synthetic leather base can especially
receive a finish or a coating to constitute a shoe upper or similar
product. A similar synthetic leather base, produced with a mixture
of suitable fibers, can result in a range of new articles usable
for the inner lining of shoes.
In the methods and installations known hitherto, the preparation of
the thick and dense needled sheet was done by discontinuous
operations by superposing primary batts of limited lengths which
have to be passed successively into the same needlers.
It is an object of the invention to provide a method for
manufacturing a synthetic leather base which overcome the drawbacks
mentioned above whilst being simple and economical.
Moreover, in the previously known methods, the fibers composing the
needled sheet were generally constituted, to a relatively large
extent, of polyester fibres shrinkable or retractable by heat so as
to enable a shrinkage operation to be effected between the
preparation of the needled sheet and the bonding. These methods
lead to articles which had generally a good "hand" but of which the
physical characteristics were inferior to those of natural leather.
There was noted, especially, a mediocre breaking strength, too
great a deformability as well as a low resistance to bursting and
to repeated flexing. In addition, the desirable homogeneity was not
realized, the properties of the product in the "machine" direction
and in the "cross" direction showing often considerable
differences.
It is a further object of the invention, in certain cases, to
overcome the latter disadvantage.
The method according to the invention is characterized by the fact
that it is continuous and comprises four successive phases, to
produce a thick needled sheet of high density, namely a first phase
consisting of preparing two non-wowen primary sheets from fibers of
fine denier, at least a major proportion of which are substantially
non-shrinkable and have a high curl or crimp ratio and a good curl
permanence, a second phase consisting of needling the two primary
sheets separately, a third phase consisting of superposing the two
thus needled primary sheets, and a fourth phase consisting of
subjecting the sheet thus formed to intense needling, after which a
curable binder is applied to this sheet the binder is cured and the
bonded sheet is subjected to splitting operations dividing it into
layers of the desired thickness, which layers can then be
individually buffed.
The needling phase of each primary sheet preferably comprises
continuously passing each sheet through a pre-needler then
discontinuously passing each sheet through a needler.
Preferably, the operation of binding is effected by coagulation of
a synthetic latex in situ.
The method according to the invention lends itself particularly
well to continuous manufacturing in large quantities, under
particularly economical and uniform conditions.
In addition, the very extensive needling effected according to the
invention orients vertically (that is to say in the direction of
the thickness) a large number of fibres and there is thus obtained
an article having a good "hand" and a good "fold." In the usual
methods, on the contrary, needling is of low density, the
retraction completing the arrangement of certain number of fibers
in the vertical direction; too considerable a needling would give,
in fact, after shrinkage, an article having a consistency similar
to that of cardboard, which would be a defect for a synthetic
leather base.
The production of a thick and dense needled sheet, rendered
possible by needling in two successive principal phases and
followed by splitting after bonding, has the advantage of giving a
finished product of better quality since, with a large thickness,
there is obtained a better entanglement of the fibers and a closer
texture than when the manufacture is effected so as to provide
directly a single finished layer or so as to needle together more
than two primary sheets. The needling effected according to the
invention is also more economical for the same density of needling
since several layers are perforated at the same time.
As a specified below, the product obtained has properties similar
to those of a split hide (or flesh-side hide) of natural
leather.
It has a good "hand" and a good "drape" or "fold."
The values of tensile strength and bursting strength are high; the
characteristics of deformation observed by a dynamometer and by a
tensometer are advantageous since, approaching those of natural
leather, they enable the avoidance of using an intercalary fabric
between the non-woven base and the finish, in the production of the
synthetic leather, especially for shoe uppers. This therefore
avoids "blocking" the finished article and leaves it a certain
"give" which is indispensable if the shoe is to be comfortable.
The loss of strength in a humid environment and in the presence of
solvents employed in manufacturing shoes remains within reasonable
limits.
The product, highly needled, has excellent delaminating
resistance.
It has good resistance to abrasion and to repeated flexing.
Finally, the absorbing power is, as for all synthetic materials,
less than that of natural leather, but moisture is eliminated much
more rapidly.
It must also be mentioned that the product obtained is perfectly
adapted to the new techniques used for the manufacture of shoes,
which techniques consist in placing on a mold a plastisol, a
preparation of suitable resins or a thermoplastic film, in then
placing thereon a synthetic leather base and in finally subjecting
the assembly to the action of pressure and heat treatment, by high
frequency, ultrasonics or the like, to ensure gelling and
shaping.
All in all, the product lends itself fully to the manufacture of
quality synthetic leather for shoe uppers.
It is even possible to obtain by this method suitable products for
lining the inside of the shoe, and more especially the rear part
called "anti-slipper."
For such use a portion of the mixture of fibers is constituted of
synthetic fibers having a relatively low melting point, comprised
between 60.degree. and 120.degree.C, and undergoing a certain
shrinkage with heat. These fibers will give the finished article
advantageous properties of thermoweldability and of
deformability.
A thick and dense needled sheet is made, as indicated previously,
with however a lower number of perforations than for the product
intended for the upper of a shoe, so as to preserve good
deformability.
A shrinkage of the sheet by 10 to 25 percent is obtained on thermal
treatment effected at the moment of bonding. It contributes to
bestowing on the product a good "hand" comparable to that of
natural leather.
The bonding is effected preferably by coagulation in situ of a
synthetic latex. It is advisable to watch that a good attachment of
the binder to the fibers is obtained in order for the abrasion
resistance to be adequate. If necessary, the latter can be
improved, after splitting, by a suitable surface treatment, based
on polyurethane for example.
After needling, bonding, splitting and if necessary surface
treatment, the product obtained has excellent characteristics for
use as a shoe lining, and more particularly as an anti-slip
material. It has good properties for the shoe manufacture: "handle"
similar to that of natural leather breaking and tear strength,
deformation and thermoformability, thermoweldability and more
generally ease of employment. In the same way, for the user, it
offers qualities of appearance and comfort due to good absorbing
power and solidity.
For the application of the method concerned, an installation is
provided comprising successively four continuously operating means,
namely a first means in two parts to manufacture separately two
non-woven primary batts or sheets from fibers of fine denier, a
second means in two parts to needle separately the two primary
sheets thus formed, a third means to superpose the two primary
sheets thus needled and a fourth means to subject the resulting
assembly to intense needling, and, following these means, a means
for bonding fibers and splitting device to divide the bonded sheet
into layers of the desired thickness and, if necessary, a buffing
means.
The invention will, in any case, be well understood with the aid of
the supplementary description which follows as well as of the
accompanying drawings, which supplement and drawings relate to
preferred embodiments of the invention, given purely by way of
illustrative but non-limiting example.
In the drawings:
FIG. 1 illustrates diagrammatically the successive operations of
the method according to the invention.
FIGS. 2 and 3 show, respectively in elevation and in cross-section
along the lines III--III of FIG. 2, a needle used in one of the
abovesaid operations.
FIG. 4 shows, on a larger scale, a detail of the needle of FIGS. 2
and 3; and
FIG. 5, lastly, illustrates a needling operation.
According to the invention and more particularly according to that
of its methods of application, as well as according to those of its
methods of production of its various parts, to which it would seem
that preference should be accorded, in order to prepare a synthetic
leather base for shoe uppers, procedure is as follows or in
analogous manner.
After opening the fibers in a conventional apparatus 1 (FIG. 1),
the fibers are made to pass into two carding machines or groups of
carding machines 2a, 2b and the continuous webs issuing from these
carding machines are superposed by means of two horizontal or
vertical fleecers 3a, 3b (especially of the "camel-back" type)
which form continuous primary sheets. The carding machines can be
two, four or six in number, according to their type and the
production desired and their linings must, in any case, be adapted
for working with fine deniers. There may also, instead of the
assembly 2a, 2b, 3a, 3b, be used the usual pneumatic equipments
enabling the production of non-woven continuous sheets of
considerable thickness.
Then, the two continuous primary sheets are subjected separately to
a needling operation. This needling operation comprises,
preferably, a continuous preneedling of each primary sheet on
needlers 4a and 4b respectively and a discontinuous needling in a
needler 5a or 5b, that is to say in which the sheet is stopped
before each needling, which does not prevent the overall operation
from being considered as continuous. For each primary sheet, the
pre-needler 4a or 4b and the needler 5a or 5b are each equipped
with needles striking in the same direction, in general from above
to below.
Then, by means of an apparatus 6, the two continuous primary sheets
thus needled are superposed, this apparatus 6 comprising a turning
mechanism which acts on one of the primary sheets so that the
surfaces of these sheets, which have been first in contact with the
needles of the pre-needlers 4a, 4b and the needlers 5a, 5b, occur
outside the sheet formed by their superposition, which ensures a
better adhesion of the primary sheets.
The resulting continuous sheet is then subjected to intense
needling in several successive needlers, such as 7,8, 9 and 10,
each equipped with needles working from above to below and with
needles working from below to above.
If necessary after reception in a reeling device 11, the sheet
passes into a tank of binder 12, then into an oven 13 where the
coagulation of the binder is effected. The latter is, preferably, a
synthetic latex enabling, in the oven 13, a coagulation in situ to
produce a homogeneous article by avoiding migration of the binder
towards the outside of the sheet. The sheet containing the
coagulated binder is then wrung by mechanical means 14, then dried
and vulcanised in a heating dryer 15. Then, the sheet obtained is
divided in the direction of the thickness into several layers each
having the desired thickness for the synthetic leather base, in a
splitting machine 16 identical with those used in the leather
industry, and finally the split pieces are treated on each surface
in a buffing device 17 to give them a completely regular thickness
and a good touch. There are thus obtained synthetic leather bases
which can receive, in the usual manner, a finish or a coating to
constitute a shoe upper or similar product.
There will now be given more specific information as regards the
initial materials and the various phases of the method.
1. General indications 1.1 -- Fibers
Curled or artificial synthetic fibers, alone or in mixture with
other fibers.
Denier less than 3 (namely 3.3 decitex) preferably 1.5.
Length 40 to 60 mm.
Curl measured according to BISFA method:
Frequency greater than 6, preferably of the order of 10;
Curl ratio greater than 10, preferably at least equal to 14;
Curl permanence greater than 50 percent -- preferably 70 percent
and more.
The BISFA method is an international method employed for synthetic
and artificial fibers, principally in Europe: the frequency
expresses the number of half-waves counted on the curled fiber,
related to 1 cm of the uncurled fiber; the curl ratio is the
difference between the uncurled length and the curled length,
expressed in percentage of the uncurled length; the permanence is
expressed as a function of the loss of curl ratio, or as a function
of the residual curl after a given placing under tension and
rest.
For products intended to produce a thermoweldable lining, it is
necessary to replace 30 to 70 percent of the fibers described above
by fibers with low melting point having the following
characteristics:
Denier equal or less than 3,
Length 40 to 60 mm,
Softening point 60.degree. to 120.degree. C.
There can be used, for example, fibers of polyvinyl chloride,
copolymers of vinyl chloride and vinyl acetate or copolymers of
ethylene and vinyl acetate.
1.2 Oiling
The fibers are oiled with a suitable oiling preparation to avoid
the formation of static electricity during the fabrication of the
sheet and to ensure sufficient lubrication for needling.
1.3. Needling
1.3.1. Pre-needling
The pre-needler 4a or 4b comprises a small number of rows of
needles which strike from above to below. Their arrangement is such
that, over a centimeter of width of board, there are two to five
needles, and preferably three.
The striking speed is 600 punches/min.
The advance of the batt or sheet is continuous.
Thickness of batt before pre-needling: 150 mm.
Thickness of batt after pre-needling: 20 to 25 mm.
1.3.2. --First needling
The first needler 5a or 5b comprises at the minimum 20 rows of
needles which strike from above to below. Their arrangement is such
that, over 1 cm of width of the needle board, there is a minimum of
30 needles and preferably 45.
The striking speed is of the order of 300 punches/min. and can be
higher according to the production effected.
The feed of the batt is discontinuous.
Thickness of the batt before needling: 20 to 25 mm.
Thickness of the batt after needling: 7 mm.
The weight of the batt after needling can reach 700 g/m.sup.2 and
the number of perforations per cm.sup.2 is from 50 to 150, and
preferably 100.
1.3.3. Needling of the assembled sheets
This operation is effected by passage of the assembled sheets,
through needlers 7 to 10 arranged successively and comprising
alternately needle boards striking from above to below and from
below to above.
Each board comprises, per centimeter of width, at the minimum 30
needles and preferably 45, distributed over a minimum of 20 rows of
needles.
The striking speed is from 250 to 600 punches/min. according to the
production realized.
The feed of the sheet is discontinuous.
Thickness of the sheet after superposition: 14 mm.
Thickness of the sheet after the first needler 7 with multiple
punches (two boards operating one from above to below and the other
from below to above): 10 mm.
Thickness of the sheet after the second needler 8: 8.5 mm.
Thickness of the sheet after the third needler 9: 7 mm.
Thickness of the sheet after the fourth needler 10 : 6 mm.
At the outlet from these machines, the needled sheet weighs 1,000
to 1,400 g/m.sup.2. The total number of perforations is between 300
and 1,000/cm.sup.2.
The density of the needled sheet, that is to say the weight in kg
per m.sup.2 for a millimeter thickness, must be between 0.150 and
0.250.
1.3.4. Choice of needles
This choice is important since it must achieve without needle
breakage the maximum efficiency and the best appearance of the
finished product.
As shown in FIG. 2, it is necessary to distinguish in a felting
needle 18:
The heel 19 which positions the needle when it is placed in the
needle board, 20 (FIG. 5);
The shank 21, which is implanted in the board, or in a plug of
plastics placed in the board, and holds the needle in position;
The intermediate narrowed portion 22, which is of smaller diameter
than that of the shank, and connects the shank and the triangulated
portion 23;
The triangulated portion 23, which comprises the barbs 24, and
constitutes the active portion of the needle.
The following type of needle appears to be the most suitable:
The length L of the needle is 3 inches, longer needles being more
fragile;
The barbs are placed on three edges (the three edges being arranged
with respect to the heel 19 according to FIG. 3);
There are two barbs per edge, placed according to the designation
"regular barbs" used by the suppliers, since closer barbs involve
too many fibers at once and cause breakages.
The Table below gives the different dimensions (in inches) with
reference to FIG. 2:
A = 1.156 E = 0.250 B = 0.156 F = 0.083 C = 0.156 G = 3 D =
0.250
The barbs are "standard" barbs which form a projection with respect
to the edge 25 (see FIG. 4).
The gauge is a number, given by the supplier, which corresponds to
a diameter of steel wire before triangulation, for example:
Gauge 42 : 0.016 inch
Gauge 46 : 0.012 inch
It is these two gauges which are preferably used, the first being
used for pre-needling and a portion of the needling, and the second
for the rest of the needling.
1.3.5. Feed per punch and depth of penetration
The needlers are adjusted with one advance per punch of 3 to 7 mm,
with a preference for 5 mm.
The passage of the sheet 26 is effected in each needler between two
plates 27, 28 in which holes enable the passage of the needles 18.
When the point of a needle, after having traversed the sheet,
arrives flush with the opposite plate, it is said that the
penetration is nil. The penetration p indicates therefore the
distance traversed by the point of the needle from this level (see
FIG. 5).
The depths of penetration are from 8 to 12 mm for the pre-needling
(machine 4a or 4b), from 7 to 11 mm for the first needling (machine
5a or 5b), 10 to 20 mm and 8 to 12 mm for finishing (machine
10).
1.4. Conditioning
For preparation of the sheet and the operation of needling, it is
necessary to work at a temperature above 20.degree. C and
preferably at 22.degree. C. The relative humidity must be at least
65 percent.
1.5. Binding
The binder is a dispersion of synthetic latex, preferably a
butadiene copolymer, containing vulcanizing agents and sensitized
to heat. Its concentration is from 6 to 30 percent. The latex is
destabilized when heated between 40 and 60.degree.C.
The product obtained after vulcanisation at 15 (FIG. 1), has the
following characteristics: Weight per m.sup.2 15 to 3 kg Thickness
4 to 7 mm Density 0.300 to 0.500 Ratio of binder 25 to 50 %.
2. There are now given more specific indications regarding one
embodiment of a synthetic leather base intended for shoe
uppers.
______________________________________ 2.1. Fibers Polyamide - 1.6
decitex (1.4 denier) - 50 mm Curl measured according to the BISFA
method: Frequency 10 to 11 Ratio 14 to 15 Curl permanence 70 to 75%
______________________________________
Proportion of grease : extraction with petroleum ether < 0.25
percent
2.2. Oiling
1 percent with respect to the weight of the fibers.
Condensed oxide of ethylene and propylene --non-ionic -- strongly
antistatic.
2.3 Needling
Pre-needler 4a, 4b :
four rows of needles
3.15 needles per cm of board 20
600 punches/min.
Needles gauge 42
Penetration 10.5 mm
First needler 5a, 5b :
34 rows of needles
43 needles/cm of board
250 to 300 punches/min.
Needles gauge 42
Penetration 9 mm.
Superposition of Primary sheets or batts : two batts of 700
g/m.sup.2 having 100 perforations/cm.sup.2 are superposed
Four needlers 7 to 10 with multiple punch each comprising:
43 needles per cm of board striking from
above to below,
43 needles per cm of board striking from below
to above,
Rate : 300 punches/min.
Needles gauge 42 for the three needlers 7, 8 and 9.
Needles gauge 46 for the last needler 10.
Respective penetrations : 13, 17, 17 and 11 mm.
Needled sheet : 1,400 g/m.sup.2
800 perforations/cm.sup.2
Thickness : 6 mm
Density : 0.220.
2.5 Binding
The binder used is a butadiene Copolymer latex of which the
concentration is 20 percent of polymer.
The product obtained has the following characteristics:
Weight per m.sup.2 2.500 g Thickness 6 mm Density 0.400 to 0.420
Ratio of binder 40 to 45%.
3. A second embodiment relates to the production of a product for
shoe lining.
3.1 Fibers
Mixture of:
50 percent of fibers having the same characteristics as in 2.1, the
length of the fibers being however of the order of 40 mm;
40 percent of fibers constituted of a copolymer of vinyl chloride
(85 percent) and by vinyl acetate (15 percent);
3.3 dtex; length: 40 mm; softening point 70.degree.C;
10 percent of polyvinyl chloride fibers; 2 dtex; length : 60
mm.
3.2 Oiling
As in 2.2.
3.3. Needling
As in 2.3, the needled sheet having the following characteristics:
1,250 g/m.sup.2 ; 600 perforations/cm.sup.2 ; thickness: 6 to 7 mm;
density : 0.190 to 0.200.
3.5 Binding
The binder is a butadiene acrylonitrile copolyper latex of which
the concentration is 11 percent of the polymer. A shrinkage of 15
to 20 percent occurs in the course of thermal treatment, at the
same time as the coagulation of the latex (at 13 FIG. 1), and of
drying and vulcanisation (at 15) by reason of the presence of
polyvinyl chloride fibers.
There is obtained before splitting a sheet having the following
characteristics:
Weight per m.sup.2 2.1 to 2.3 kg Thickness 5.5 mm Density 0.420
Proportion of binder 33%
3.6 Splitting
Splitting is to 0.80 mm thickness. Buffing is not necessary.
3.7 Surface treatment
One of the surfaces is treated with a solution of polyurethane to
deposit a layer of 5 g/m.sup.2 of colorless polyurethane, to give
good resistance to abrasion. To differentiate this surface from the
reverse, the latter can be given a inscription.
The 40 percent of copolymer fibers with low softening point ensure
in the product, qualities of deformability and of self-welding by
heat.
4. This example relates to a variation of Example 3, with the same
possibility of use.
4.1 Fibers
Mixture of
50 percent of fibers having the same characteristics as in 2.1,
with a length of the order of 40 mm;
50 percent of fibers constituted of a copolymer of ethylene and
vinyl acetate; softening point: 105.degree.-110.degree..
4.2 Oiling
As in 2.2.
4.3 Needling
As in 2.3, the needled sheet having the following characteristics:
1,250 g/m.sup.2 : 400 perforations/cm.sup.2 ; thickness: 8 mm;
density: 0.150.
4.5 Binding
The binder is a butadiene acrylonitrile copolymer latex of which
the concentration is 9.50 percent of polymer. Shrinkage as in
3.5.
There is obtained before splitting, a sheet having the following
characteristics:
Weight per m.sup.2 : 2.1-2.3 kg
Thickness : 6-6.5 mm
Density : 0.350
Proportion of binder : 33%.
There may be added to the binder resorcinol and hexamethylene
tetramine to improve the attachment of the fibers and of the binder
and, for this reason, the abrasion resistance.
4.6 Splitting
As in 3.6.
4.7 Surface treatment
As in 3.7.
* * * * *