CA1062424A - Sheets and films of polyolefinic material, similar to paper, and process for producing them - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Sheets, films and other articles having a fibrous structure similar to that of cellulosic paper and consisting entirely or prevailing of polyolefin fibers are prepared by (a) forming a sheet or homogeneous panel which is substantially anhydrous and consists for at least 70% by weight of fibrils of at least one polyolefin having a molecular weight of from 30,000 to 300,000 and a Melt Index of from 1.5 to 30;
(b) sintering the polyolefin fibrils by heating the sheet or panel under pressure at a temperature equal to or higher than the softening temperature of the polyolefin and until the polymer fibrils at the surfaces only of the sheet or panel are at least partially melted; and (c) cooling the sheet or panel to room temperature.

Description

THE PRIOR ART
It has been known fox some time that it is possible to prepare fibrils and microfibers of polyolefins which are morphologically similar to cellulosic fibers and useful sub-stitutes or at least part of the cellulosic fibers nor~ally employed in the manufacture of paper and paper-lik2 article~.
In general, such fibers, which are known in the art as fibrils or fibrids, have a length comprised betw~en 1 and.
50 mm., an average diameter in the range fxom 1 to 400 microns, ;~
and a surface area ~specific surface) larger than 1 m2/g.
A process for preparing such fibers or fibrils of .
polyolefinic material and use thereof in the manufacture of semi-synthetic paper are disclosed in Italian Patent No.
947,197 of Montedison.
According to that process, a solution of the olefin polymer is extruded at a temperature above the boiling point of the solvent under normal conditions, and under autogenous or greater than autogenous pressure, into a zone of lower pressure in which it at least partially expands, and the at least partially exp~nded solution is then hit by a jet of high speed fluid ~hich is at a temperature lower than the tempera- .
ture of the solution and has an angled dixection with respect . ;
to the dixection of extrusion of the solution~ ::
Other methods for obtaining ibrils or ~ibrids of .; ;
synthetic polymers suitable for replacing the aellulosic fibers .:
in the manufacture of paper or for ma~ing paper or paper-like products, are disclosed, for instance, in United States Patents ;~ ;
Nos. 2,999,788 and 3,402,231; in British Patent No. 1,262,531;
and in German Patent Publications DT-OS No. 1,951,576.5 and DAS No. 1,290,040. .

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The sheets of semi-synthetic paper comprising such ~ .-polyolefin fibrils in addition to cellulosic fibers, and in . :~
which the latter are present prevailingly, substantially retain ;.
the characteristics o~ paper made exclusively of the CellUlOsiG ~:
fi.bexs, esp.ecially as concerns xeceptivity for writing or print~
ing thereon. . . :
However, prior to this invention, sheets made entirely .
OX prey~ilingly o~ polyolefin~c fibrils have exhi~ited few satisfactory characteristics, especially when it has been attemp-ted to make them economically by conventional paper-making pro-cesses and without special treatments and procedures. The poor characteristics are due to the poor cohesive power possessed by .:
the polyolefinic material present and which results in products of low resistance and deficient in the necessary mechanical .
properties.
THE PRESEN~ INVENTION
An object of this invention is to provide new paper .: and paper-like products consisting at least prevailingly (for over 7~ by weight~ of polyolefin fibrils which do not have the aforesaid de~ects; are similar in all respects to sheets, films ..
and other articles made entirely of cellulosic fibers and which are made by processes and devices not substantially different from those used conventionally in the papex industry~
In one particular aspeat the present in~ention provides a process ~or preparing paper-like 9heets, film~ and other arti-cles wh.ich comprises the following operations carried out in the ~.
order stated: ;. .
~a) forming a substantially anhydrous sheet or panel :
consisting of from 70% to 100% by weight of fibrils of at least one olefinic polymer having a molecular weight of from 30,000 to 300,000 and a Melt Index of from 1.5 to 30, the remainder being cellulose fibers or synthetic polymer fibers having a ~ :.
saftening temperature not lower than that of the polyolefins ..

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fibrils;
(b) sintering the olefinic polymer fibrils by heating the sheet or panel under pressure at a temperature equal to or higher than the softening temperature oE the olefinic polymer and until the polymer .;
fibrils at the surfaces only of the sheet or panel are at least partially melted; and ~
(c) coo].ing the sheet or panel. ;
In another particular aspect the present invention provides paper-like sheets, films and other paper-like articles consisting of from 70% .
to 100% by weight of fibrils of at least one olefinic polymer having a ~.
molecular weight of from 30,000 to 300,000 and a Melt Index of from 1.5 ~:
to 30 and the remainder being cellulose fibers or synthetlc polymer fibers having a softening temperature not lower than that of the poly- ~ ~ -;~.
olefin fibrils, in which said fibrils are thermally bonded to each other or to other fibers present by sintering the olefinic polymer fibrils by heating the sheets or films under pressure at a temperature equal to or higher than the softening temperature of the olefinic polymer until ,.: :, .
the polymer fibrils at the surfaces only of the sheets or films are at i Ieast partially melted and then cooling the sheets or films.

The polyolefin fibrils can be obtained by any suitable method, .. . : .
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including the prior art methods referred to hereinabove and may consist ;..: ;
of crystalline polyolefins such as high or low density polyethylene, polypropylene made up completely or prevailingl.y oE isotactic macro- ~ . ;
.. ,; . .
molecules, polybutene-l, poly (~-methyl-pentene-l), ethylene/propylene copolymers of the block or statistical type, and mixtures thereoE.
Preferably, the olefin polymer fibrils used in practicing this . i :

invention have a length of from 1 to 10 mm, and a diameter of from 2 to i :
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50 microns, even more preferably of from 20 to 4a microns. `~ .
For preparing the sheet or panel to be conveyed to the sintering :
operation, there may be used exclusively polyolefin fibrils or mixt~ires . ,:

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comprising at least 70~ by weight of such fibrils with the remainder made up of a different matexial of fibrous ~tructure, such as, for instance, cellulosic fibers, fibers of synthetic polymers other than olefin polymers and having a softening temperature not lower than that of the given olefin polymer and having fiber dimensions at least close to those of the polyole-finic fibrils~ Also, the remaining material different fxom the polyolefinic material can be in the form of a powder which serves as an inert filler or pigment such as, for instance, kaolin, ln talcum powder, calcium carbonate, etc.
For preparing the sheet or panel according to operation ~ :
(a) of the present process, the polyolefin fibrils, possibly together with not more than 30~ by weight of the total of one or more of the other materials aforementioned, are disper~ed in ~; :
~ater and the mixture is homogeniæed until a clot-free aqueous pulp having a solids content of about 1-20 qm/lt i5 obtained~ $~ : .
insure a good dispersion and avoid floating and/or agglomeration ,.... . .
of the fibers, it is convenient to effect the dispersion in water in the pres~nce of a wetting and/or dispersing agent. Known `
;. , .
wetting and dispersing agents, such as, for instance, polyvinyl :~
alcohol, ethoxylated amines, alkyl phosphates, fatty acid soaps, : :
, etc., are usefulO
It is particularly useul, or obtaining a speedy, and satisfactory, dispersion of the polyolefin fibers in the wat~r, to give those fibers or fibrils a superficial pre-treatment with an aqueous solution of a polyvinyl alcohol-aliphatic aldehyde condensate and then coat the fibers or fibrils with hydrophilic materials according to the pending Canadian application of Luciano Baldi et al Serial No 217,709 filed January 10, 1975. -'~;

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~ 3~C36Z4;24 The aqueou pulp obtained is formed into a sheet or homogeneous panel on a conventional paper-making machine having a flat or curved table and is dried before being subjected to sintering operation (b) which can be accomplished by passing the dried sheet or panel through two or more pairs of calender rolls maintained at a temperature equal to or higher than the softening temperature of the polyolefin ~ibrils. Each sacceedin~
pair o~ rolls is positioned at a distance from the preceding pair such that the anhydrous sheet or panel is subjected to a control- -.
led pressure at each stage of the sintering/calendering operatio~ ~ :
The sintering temperature can be varied according to the weight of the sheet, the speed at which it is passed through the calender rolls, the pressure exerted on it by the rolls, and, ;: ;
finally, depending on the kind of end product de~ired, whether ? ~
opaque, semi-opaque, transparent or translucid. .
Exemplary sintering temperatures and pressures are, ..
respectively, from 90C to 160C and from 100 to 50Q kg/sq~ cm~
.. . .
when the polyolefin ibrils are fibrils of high-density poly-ethylene; respectively, from 80C to 130C and from 50 to 30Q .: :.
kgtsq. cm. when the polyolefin fibrils are ~ibrils o~ low-densîty ~ .
polyethylene; and, respectively, from 110C to 190C and from 100 to 500 kg/sq. cm. when the fibrils are polypropylene fibrils Sheets which look exac~ly like conventional parchment . .
paper can be obtained by controlling the weight of the ~heet or panel formed in operation ~a) so that it is rom 40 to 100 ~:
g/sq.mt. To obtain ~uch sheets, particularly when the produ~tion speed is high, it ~an be convenient, and is within the scope o~ : .
this invention, to subject the anhydrous sheet or panel pro- .
ceeding from operation (a) to an intermediate or preliminary pre-sintering at a moderate pressure and mild temperature not exceeding 100C

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:In operation ( c ), after the thermal sintering, the sheet or panel is cooled to below the softelling temperature of the polyolefin fibrils and, in practice, to room temperature. The cooling can be accomplished by subject-ing the sheet or par~el to a stream of cold airJ or by pacsing it over water-cooled cylinders. After the cooling, the sheet or panel is ready for use wi1;hout further treatment.
The sheets or films obtained by the proce~s of this invention have . an internal fibrous structure, ea~ily noticeable by tearing the sheet or film, and look like paper made entirely of cellulosic fibers, whether known as " paraffin ", " oil ", or " parchment paper ".
The products of this invention can be used as ~ubstitutes for those various types of paper made entirely of cellulosic fibers and are especially useful as wrapping and packing materials.
The pleat-recovery, and twist and crumpling-recovery values of the sheets or films obtained by the present process are low, in general comparable to those of cellulose-based papers. They are, therefore, particularly adapted to use as wrappings, for example, for loose foodstuffs , and various objects of small size, where a stabilized wrapping involving wrapping around and/or crumpling of the wrapper is required. For such uses, products obtained by the present process with the use of polyolefin fibrils having a minimum length of 1 mm. and a mean length of from 3 to 5 ' mm., and having a Melt Index of l. S to lO, have proved to be particularly useful.
In the following examples, ~hich are given to illustrate the invention in greater detail but ~re not inte~de~ to be limiting, the stability of the ,. .' .~ -7 -' . . ~ , ,,,~--- ~06Z~Z4 proaucts obtained to mechanical deformation was determined by measuring:
~1) the pleat-recovery angle, which was measured by folding the sample sheet on ~;
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itself, maintaining the sheet in the folded condition or 5 minutes under a weight of 0.5 kg., therea~ter removing the weight and, after a further 5 minutes, measuring `
the angle formed by the pleat (pleat-recove~ ;
angle~
(2~ Twist recovery angle.
This was determined by twisting a sample o~
the sheet under examination, 5 cm. long and . . .
1.0 cm. wide, along its greatest axis for an angle of 180, maintaining the sample in that condition ~or 5 minutes, releasing the sample and, after a further 5 minute period, measur-ing the residual angle.
The olefin polymer ibrils used in the examples wexe obtained according to the technology illustrated in Italian Patent No. 947,919. As illustrative o~ such technology, the polyethylene fibrils used in Example 1 were obtained as follaws:
A 50 1. autoclave provided with a heating chamber and stirrer was fed with 3 kg~ of high-density polyethyle~e having M W o 73,000; a Melt Index (~.I.) of 1.9, and a softening point of 110 C., together with 35 1. o~ n-hexane. The mixture was heated until the polyethylene was dissolved in the n-hexane, under the following aonditions: ;
temperature - 180C
Total pressure - 14.5 kg/sq. cm.
~including nitrogen ~ :~
pressure) . .
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'~ The solution was ejected, under tho~e temperature ~-and pressure conditions, into the atmosphere, through a -`
circular nozzle of 2 mm. diameter and so as to collide, at a distance of about one mm. from the outlet of the nozzle, with a jet of dry, saturated steam cominq from a nozzle of 4 mm.
diameter arranged at an angle of about 85 to the direction of ;~
ejection of the polymer solution and at an impact speed of the steam of about 470 m/sec. ~ -. ~.
A fibrous product was obtained and, under the optic `~
microscope, was found to be composed of individual fibrils having a mean length of 3.8 mm. and a minimum length of 1.~ mm;
an average diameter of 36 microns, and surface area (specific surface~ of 5 m~/g.

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2 kg of polyethylene fibrilæ, obtained as described above, were refined for 5 minute6, without reducing their length, in a Sprout-Waldron type di3c beater, and were then coated with 0. 5% b. w. of a dispersant consiæting of a polyvinyl alcohol jbutyric aldehyde condensate ~ containing 4. 2 aldehyde re~idues ~100 vinyl-monomeric units ), by immersion in an aqueous solution of 9û C of said condensate and by successive centrifuging and drying.
The fibrils, thus made hydrodispersible, were dispersed in water in such a way a~ to obtain a pulp having a concentration in fiber~ of 5 g/
liter.
Using said pulp and a continuous paper machine having a flat table 30 cm. wide, a fibrll sheet was obtained which, on emerging from the drying section, had a thickness of 120 microns, a specific weight of 80 gtsq. mt. and a content in water of 0. 2% by weight.
This sheet was then passed at a speed of 14 mt/min. between a pair of calender rollers maintained at a temperature of 115 C and exerting a pre~sure of 270 kg/sq. cm. Thereby was obtained asheet which, after . cooling down, appeared to be transparent and had an aspect altogether similar to that ~f convention~âl paper of the " parchment " type, and which turned out to be easily tearable by hand and revealing at the tearing a fibrous interior ~tructure.
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Its main characteristice were the following:
.. thickness ,, - 80 microns ~ii weight 70 g/sq. mt.
C. T. S. ( cross tensile strength ) 1. 6 kg.
L. T, S. ( longitudinal tensile strength ) 2. 3 kg.
transverYal elongation at break 1. 3 %
longitudinàl elongation at break 3. 7 %
L.T, B. ~ length tran~ver~al break ~ 1390 mt.
L. L, B. ( length longitudinal break ) 2044 mt.
bursting pressure 0. 91 kg/sq. cm.
tearing resistance 69 grams rigidity 4, a g. cm.
angle of pleat-recovery angle of twist-recovery 40 A sheet of cellulo~ic paper of the " parchment " type, having the same thickne~s, had a pleat-recovery angle of 39 and a twist-recovery angle of 40, .~'''' , ' ` ~ ' ' `
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~,;" . , :~06Z4Z4 ;~ EXAMPLE a 2 kilos of fibrils of high density polyethylene having a molecular weight ( m. w. ~ = 58, 000, softening point = 110 C and M. W. = 5. 2, a minimum length of 1. 2 mm, a mean length of 3 mm, a mean diameter of 32 microns, and surface area of 6 m /g and incorporating 30% by weight of kaolin powder, superficially treated as in Example 1 with an aqueous solution of a similar dispersant, were dispersed in water in such a way as to form a pulp having a fiber concentration of 5 g/lt.
With the pulp thus obtained, using the same paper rnachine as in Example 1, there was prepared a panel which, after drying, had a thick-ness of 70 microns, a weight of 55 g/9q, mt. and a content in water below ,~ 0.1% by weight.
Said panel wns then passed, at a speed of 10 mt/min. between twocalendering rolls maintained at 126 C and exerting a pressure of 250 kg/sq. cm. After one single pass there was obtained a sheet which, after cooling down, was altogether similar to a semi-mat cellulosic paper sheet, easily tearable and showing the following character;stics: .
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~06Z4Z4 , ~thicknes~ 60 microns ,)~,; weight ; ~ 50 g/sq. mt.
C.T. S. 1.04 kg ~ -L. T. S. 1. 68 kg transversal elongation at break 1, 4 %
longitudinal elongation at break .3, 2 ~0 ; length transver~al break 1297 mt.
length longitudinal break 2101 mt.
angle of pleat-recovery 56 angle of twlst-recovery 35 A conventional cellulosic paper sheet of the semi-mat type, of the same thickness,: shows a pieat-recovery angle of 42 and a twi~t-recovery .
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106Z4~4 ~ EXAMPLE 3 0. 8 kg of polyethylene fibrils with a m. w. = 50, 000, a M. I. of 9, .~ . and softening point of 110C, having a mean length of 4, 2 mm, a minimum length of 1. 5 mm, a mean diameter of 25 microns and surfase area of 5 m /g were dispersed in 160 lt. of water containing 0. 5% by weight of a dispersant consisting of polyvinyl alcohol.
With the pulp thus obtained and using the same equipment as in Example 1, a fiber sheet was prepared which, on emerging from the drying ~:
section, had a thickneæs of 70 microns, a weight of S0 glsq. mt. and a content in water of 0.1% by weight.
By one pas~ of this sheet, at a rate of 5 mt/min., between two calender rolls maintained at 119 C and exerting a pressure of 270 kg/sq. cm, there was obtained a mat sheet, ea~ily tearable by hand, and characterized as follows:
~ thickness 5 3 microne weight 45 g /sq. mt.
C.T.S. 1,12 kg L.T. S. 1. 51 kg transversal elongation at break 1. 6 ,'%
! ; longitudinal elon~ation at break 3. 4 %
length transversal bréak 1560 mt.
length longitudinal break 2100 mt.
burstin'g pressure , 0. 40 kg/sq. cm.
tearing resistance 36 gram~
i rigidiv 1 g. cm.

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: 16:~;Z~24 a~gle of pleat-recovery 29 angle of twist-recovery 30 f . , A sheet of conventional mat cellulosic paper of the same thickness sho d a 1 at-roFovery ~ngle oi ZO and a twi~t-recovery nngle of as .

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5 kg. of high density polyethylene fibrils, showing a m. w. = 65, 000, a melt index of 3. 5, softening point = 125 C with a mean length and diameter of respectively 3. 5 mm. and 30 microns, a minimum length of l. 5 mm, and surface area of 6 m /g w~re treated with a polyvinyl alcohol/butyric 0 aldehyde condensate in order to facilitate their dispersion in water and finalb were dispersed in water to obtain a pulp having a concentration of ~i 5 grams of fibrils per liter of water.
¦l ~ Using this pulp, by rnean~ of a continuous flat table paper machine with a 30 cm, wide table, there wa~ prepared a panel which, at the outlet ~,~ 15 of the drying section showed a thiokness of 80 microns, a weight of 50 g jsq. mt. and a water content of 0. 2%. By means of just one single pass of this panel between two calender rolls maintained at the temperature of ' 129 C and exerting a pres~ure of 270 C, at the rate of 20 mt/min., there was obtained a sheet similar to " parchment " type paper, easib tearable 20 a~d having the following characteristics:
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., 1062424 thickne~ 65 microns ,,~, ,!~ i' ' weight 48 g /9q. mt.
, C.T.S. 1,06 kg. -;, L.T.S. 1.57 kg.
tran~versal elongation at break l. 7 %
longitudinal elongation at break 4, 3 %
. length transver~al break 1380 mt.
length longitudinal break 2050 mt .
bursting pressure 0, 53 kg/sq. cm.
tearing resistance 40 grams rigidity 1.1 g. cm.
angle of pleat-recovery 45 angle of twist-recovery 40 A conventional paper eheet of the " parchment " type, of the same thicknes~, 6how~ a pleat-recovery angle of ~30 and a twist-recovery angle of~5.'`

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pressure OI 270 kg/~q, cm. There was thu~ obtained a sheet with an aspect similar to that of cox~ventio~al " oilpaper " and having the following characteristics:
thickness 58 microns weight 45 g /9q, mt .
lO C. T. S. 1, 21 kg.
. L.T.S. 1,6 kg.
transversal elongation at break l. 8 %
longitudinal elongation at break 5, 2 % .
length transversal break 1680 mt.
length longitudinal break '2250 mt.
bursting pressure 1 0. 68 kg/~q. cm. ~ , tearing resistance 40 grams ~!' , rigidity , 1. 2 g. cm.
: angle of pleat-recovery 32 .
20 angle of twi~t-recove~ry 42 .~ A ~heet o~ conventional paper of the " oiled " type and of the same ~1 ~ . thickne~e ehowed a ple.at-recovery angle of 3û and a twist-recovery angle of 35. ~:

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A fibrous panel similar to that prepared in Example 4 and consisting of low density polyethylene fibrils having a m. w. = 59, 000, a M. I. ~ 5, softening point = 100 C and with a minimum length of 1. 5 mm, a mean length of 4. 8 mm., a mean diameter of 25 microns and surface area of 5 m /g was passed between two calender rolls maintained at a temperature of 100 C and exerting a pressure of 270 kg/sq. cm, at a rate of 5 mt/rnin.
The sheet thus obtained of translucid a~pect, showed the following charac-teri6tics: ~
t~ickness~ 63 microns weight 50 g /8q. mt.
C.T.S. 0.61 kg.
L. T. S. 1 . 01 kg.
transversal elongation at break 1. 8 %
longitudinal elongation at break 1. 4 %
~ 15 L. T. B. , 764 mt.
,~ L.L.B. 1260 mt. . ,' , bur8ting pressure 0. 81 kg/sq~ cm.
tearing resistance . 37 grams rigidity . 0. 8 g. cm.
pleat recovery angle 45 twi~e-F-cw-rY angle 4i ., . ' ' ,'" .
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5 kg. of polypropylene fibrils having a m,w. -150,000, softening point = 135C, a M.I. equal to 2, a mean diameter of 30 microns, a mean length of 2.5 mm, a minim~m length of 1 mm, and sur~ace area of 7 m2~g were coated with 0.6~ by we~ght of a dispersant consisting o~ a polyvinyl alcohol/butyric aldehyde condensate (4.5 aldehyde residues/100 units of vinyl monomer) by immersion in an aqueous solution of the dispersant at 90C and then centrifuged and dried.
10- The thus treated fibrils were then dispersed in water to obtain an aqueous pulp having a fibril concentration of .~

3 g/lt.
By means o~ a paper machine with a flat table 4Q cm.
wide a panel was prepared which, after drying, showed a thick-ness of 70 microns, a weight of 65 g/sq. mt. and a water content less than 0.2% by weight.
This panel was passed only once at a rate of 20 mt~min.
between two calender rolls maintained at a temperature o 175C
and exerting a pressure of 250 kg/sq. cm.
-2Q After cooling down, the sheet appeared to be similar to oiled parchment paper of semi-mat aspect and~had the f~ w-ing characteristios:
thickness 60 microns woight 60 g/s~ mt~
C.T.S. 1.~7 kg.
L.T. S . 2.74 kg.
transversal elongation at break 2.3 %
longitudinal elongation at 1 5 L.T.B. 1950 mt.
L.L.B. 2850 mt.
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~ ~06Z~;Z4 bursting pressure 2.5 kg/sq. cm.
tear resistance 75 g.
rigidity 8.5 g. cm.
pleat-recovery angle 35 twist-recovery angle 30 A cellulosic parchment paper o~ the same thickness ; showed a pleat-recovery angle of 39 and a twist-recovery an~}e O~ 4~
EXAMP~E 8 .; . . . .
An a~ueous pulp was prepared having a fibril concen~
tration of 5 g/lt by dispersing in water 5 kg. of fibrLls of a polypropylene having a molecular weight Of lOOrQOO~ a M.I. of ;~
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4.5 and a softening point of 135C, which fi~rils had a mean diameter of 35 microns, a mean length of 3 mm, a minimum length of 1.0 mm, and a surface area o 7 m7/g, and which had been subjected to a superficial pre-treatment as described in ~xample 7.
Using said pulp and equipment as in Example 7, there was obtained a panel of the polypropylene fibrils which, after `~
drying, had a thickness o~ 90 microns, a weight of 55 g/9q~ mt.
~ ~ and a ~ater content of Ool~ by weight.
i~ After a single pass o~ the panel at a rate of ; ~ , . , I S mt/min, between two calender rolls maintained at a temperature o 18SC and exerting a pressure of 250 kg/sq. cm., and cooling o the sheet obtained, it had the appearance o translucid l I parchment paper and had the following characteristics: ~
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~`~ l~Z4Z4 thickness 80 microns weight 50 g /sq. mt.
C.T.S. 1,44 kg.
L.T.S. 2.16 kg.
transversal elongation at break 2. 2 %
longitudinal elongation at break 1. 6 %
L. T. B. ( length transv, break ) 1800 mt.
L. L. B. ( length longit. break ) 2700 mt.
bursting pressure 2. 5 kg/sq. cm.
tear resistance 70 grams rigidity 7, 2 g. cm.
pleat -recovery angle 3 8 twist-recovery angle 40 Il ~ ~ .
A translucid conventional parchment paper of the same thickness showed a pleat-recovery angle of 39 and a twist-recovery angle of 40.

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing paper-like sheets, films and other articles which comprises the following operations carried out in the order stated:
(a) forming a substantially anhydrous sheet or panel consisting of from 70% to 100% by weight of fibrils of at least one olefinic polymer having a molecular weight of from 30,000 to 300,000 and a Melt Index of from 1.5 to 30, the remainder being cellulose fibers or synthetic polymer fibers having a softening temperature not lower than that of the polyolefin fibrils;
(b) sintering the olefinic polymer fibrils by heating the sheet or panel under pressure at a temperature equal to or higher than the softening temperature of the olefinic polymer until the polymer fibrils at the surfaces only of the sheet or panel are at least partially melted; and (c) cooling the sheet or panel.

2. The process of Claim 1, in which the olefinic polymer fibrils have a minimum length of 1 mm and a mean length of from 3 to 5 mm.

3. The process of Claim 1, in which the fibrils consist of olefinic polymers having a Melt Index of from 1.5 to 10, inclusive.

4. The process of Claim 1, in which the olefinic polymer is polyethylene.

5. The process of Claim 1, in which the olefinic polymer is an ethylene/propylene copolymer of the block type or the statistical type.

6. The process of Claim 1, in which the olefinic polymer is polypropylene consisting predominantly of isotactic macro-molecules.

7. Paper-like sheets, films and other paper-like articles consisting of from 70% to 100% by weight of fibrils of at least one olefinic polymer having a molecular weight of from 30,000 to 300,000 and a Melt Index of from 1.5 to 30 and the remainder being cellulose fibers or synthetic polymer fibers having a softening temperature not lower than that of the polyolefin fibrils, in which said fibrils are thermally bonded to each other or to other fibers present by sintering the olefinic polymer fibrils by heating the sheets or films under pressure at a temperature equal to or higher than the softening temperature of the olefinic polymer until the polymer fibrils at the surfaces only of the sheets or films are at least partially melted and then cooling the sheets or films.

8. Sheets, films and other such articles according to Claim 7, further characterized in that the olefinic polymer has Melt Index of from 1.5 to 10.

9. Sheets, films and other articles according to Claim 7, further characterized in that the olefinic polymer is polyethylene.

10. Sheets, films and other articles according to Claim 7, further characterized in that the olefinic polymer is polypropylene consisting predominantly of isotactic macro-molecules.

11. Sheets, films and other articles according to Claim 7, further characterized in that the olefinic polymer is an ethylene/propylene copolymer of the block type or the statistical type.