ITRM980281A1 - BOW FIBER FROM MIXTURES OF POLYPROPYLENE RESINS WITH POLYETHYLENE FOR THE PRODUCTION OF THERMO-SEALED FABRIC-NON-FABRIC - Google Patents

Description

DESCRIPTION

accompanying a patent application for an invention entitled: "Staple fiber from mixtures of polypropylene resins with polyethylene for the production of heat-sealed non-woven fabric"

The present invention relates to a staple fiber from mixtures of polypropylene resins with polyethylene for the production of heat-sealed non-woven fabric. More specifically, the invention relates to polypropylene fibers obtained in staple, of the type suitable for the production of non-woven according to technologies based on "thermal-bonding" (formation of the fabric by heat-sealing the fibers), in which the composition of the polymeric mixture is such as to confer improved characteristics of mechanical isotropy and softness to the resulting non-woven The invention also relates to the non-woven material obtained starting from the staple and laminated composite materials comprising a layer of such non-woven coupled to a polyolefin film.

As is known, polypropylene fibers are widely used not only for textile applications (for example in yarns for carpets, for furnishing fabrics and for industrial uses) and for the production of ropes, but also and above all for the production of non-woven fabrics. - fabrics, for numerous applications in various sectors such as, for example, the medical sector, that of domestic hygiene, geotextile, that of clothing and, above all, the hygienic-sanitary sector. In this last field, particularly important is the production of lightweight non-woven fabric for diapers for children and for incontinents, as well as for feminine sanitary napkins, in particular for the realization of the upper layer of the same, destined to enter directly. contact with the skin. This layer, sometimes referred to with the corresponding English term "top-sheet" (while the relative non-woven material is commonly referred to in the sector with the generic name of "coverstock") is characterized by the particular requirements of softness, and by the ability to perform the function of rapid transfer of moisture to the absorbent inner layer, leaving a feeling of "dry" in contact with the skin. These requirements are added to the normal toughness specifications (breaking strength), which in any case a non-woven it must present in order to be worked and used without problems.

Another specific application for lightweight polypropylene non-woven fabric in the production of diapers and sanitary napkins is in the production of the relative waterproof outer coating ("back sheet"), which in the past was simply made up of polyethylene film. . In order to give a textile, and therefore more pleasant, appearance to the worn diaper, it is currently used to couple the polyethylene film (or polyolefin in general) with a layer of non-woven polypropylene fabric, intended to be exposed from the outside in the finished diaper. In general, the coupling to produce the laminated composite material can be achieved through the use of adhesives, glues or "hot melts", or by heat-sealing in the calender fabric with the fabric and film separately produced, or even by coextruding the polyolefin resin directly on the non-woven fabric. -tissue.

Normally polyolefin fibers, of which polypropylene (PP) is by far the most widely used starting material, are produced by melt spinning exploiting the thermoplastic characteristics of the material, while very little widespread and limited to particular cases is the solution spinning technique. One such particular case is that of ultra-high molecular weight polyethylene, UHMWPE (Ultra High Molecular Weight Polyethylene), which is used for the production of high performance technical fibers, i.e. with high tenacity and modulus of elasticity, for highly resistant ropes and fabrics. or as a reinforcing fiber for other materials. This polymer is not spun by melt, but by "gel spinning" from a solution of a suitable solvent. After cooling and partial or total removal of the solvent, in order to obtain the desired levels of mechanical performance, the fibers are stretched at high stretch ratios (equal to 10-100 - the stretch ratio being defined as the ratio between the speed of the downstream roller and that of the upstream roller in the stretching operation of the fiber by traction).

Returning to the much more usual case of spindle spinning, polyolefin fibers (intended both for yarns and for the production of non-woven fabric) can be obtained according to numerous different technologies, two of which, in particular, are suitable for the production of fiber in jib: the one known as “long spinning” and the one known as “short spinning”.

In both processes the molten polymer, suitably with additives, is fed from an extruder to a series of dies by means of as many volumetric pumps, and the bundles of filaments emerging from the dies are cooled with jets of cold air, solidifying. The two processes differ in that in long spinning (referred to by some as "conventional spinning") the number of holes present in each spinneret is relatively low (normally 500-3000), the spinning speed is high (of the order of 500-2500 m / min), and the distance between the spinneret and the collection system, necessary for cooling the fibers that run at high speed, is wide (3-9 m - hence the definition of long spinning), while short spinning is characterized by dies with a high number of holes (normally 15,000-60,000), a low spinning speed (<100 m / min) and a short distance between the spinneret and the collection system (1-2 m, hence the definition of short spinning).

In the long spinning process, after the application of an antistatic and lubricating agent to the bundle of cooled fibers collected by each spinneret (known as "finishing"), the fibers are usually deposited in containers to be fed to the subsequent treatments in a separate process step. This is due to the difference between the production speed of the fiber and that at which subsequent operations can be carried out.

In the second processing phase of the long spinning process, the fibers are stretched using roller systems that rotate at different speeds and, after stretching, are subjected to "crimping", making them pass under pressure through a slit to give them a wavy deformation, after of which are cut into lengths of a few centimeters to give the bow. Crimping is necessary to have a certain cohesion between the staple fibers in subsequent processing.

In the case of short spinning, the same drawing, erecting and cutting operations are carried out directly on the spinning line, in a continuous process. This is made possible by the low speed that characterizes the production of the fiber in short spinning, which allows to balance the speeds of the different operations, and obviously involves a reduction in both plant and labor costs, which are reflected in a lower cost of the staple obtained from short spinning compared to long spinning.

In the most common technology for the production of non-woven fabric from polypropylene staple fiber, the non-woven web is obtained by carding, by passing the flakes in a machine called "carding" or "carding machine" which, through a series of toothed rollers, "combs" the staple, orienting the fibers mainly in the machine direction (or M.D., machine direction) and forming the so-called "card web." This is then heat-bonded, usually by passing through a calender heated, in which due to the effect of heat and pressure the fibers melt superficially and weld together. To avoid excessive rigidity and a "papery" appearance of the non-woven fabric obtained, heat sealing is obtained only on a portion of the surface of the web , using an “embossed” calender cylinder, in which the raised areas cover approximately 20-30% of the surface of the cylinder.

The greater cost-effectiveness of production of the staple by short spinning, noted above, is balanced in the finished non-woven by lower mechanical performance, especially as regards toughness.

This parameter assumes, for non-woven fabrics obtained from staple according to the two technologies reported above, considerably different values depending on the direction in which it is measured, due to the fact that in the carding phase the staple tends to orient itself in the machine direction. Therefore, the toughness of the non-woven is high in the latter direction and modest in the direction transverse to that of the machine (C.D., crossmachine direction). To take this difference into account, the characterization of the mechanical strength of non-woven fabrics is more correctly indicated by giving not only the toughness in M.D., but also that in C.D .. An overall parameter normally used is the so-called "heat-sealability index" ( T.B.I., thermal bonding index), which is given by the geometric mean of the toughness values in M.D. and in C.D. (square root of the product of these values). Evaluated in terms of this parameter, a heat-sealed non-woven fabric with a grammage of 20 g / m <2> obtained from long spinning staple can have a T.B.I. of the order of 20-30 N / 5 cm, while one obtained from short spinning staple can have a T.B.I. ≡ 15-20 N / 5 cm.

Other spindle spinning technologies, other than long spinning and short spinning, can lead to the production of nonwovens directly from spinning and without going through the staple, in an integrated process. The most widespread of these processes is known as "spunbonded" technology (or "spun laid" - respectively "spun and welded" or "spun and laid"), while another more recent method is that known as the "melt blown" process. (or "melt blowing" - literally, "melted and blown"). In the "spunbonded" technology the continuous fiber emerging from the spinneret is extracted at very high speeds (for example in the order of 35004000 m / min) with the help of an aerodynamic system and is directly deposited on a conveyor belt, with a random distribution of the filaments, to give the non-woven web. The latter is generally consolidated by heat sealing by passing through a calender and oven. Given the non-oriented distribution of the fibers, the material thus obtained is characterized by a greater mechanical isotropy, and in this case there is no marked difference between toughness in M.D. and toughness in C.D. found in non-woven fabrics obtained from staple. Conversely, "spunbonded" non-woven materials have other defects, including the uneven appearance due to an uneven coverage and the considerably less soft and more papery hand, more like that of a film.

In the production technology of "melt blown" non-woven fabrics, similar to the previous one, two converging jets of compressed hot air are directed onto the fiber at the outlet of the spinneret, causing it to thin and break. The fibrils obtained are aspirated and deposited on an underlying porous conveyor belt, to form the web of non-woven fabric. The materials obtained with this technology are mainly used in the production of bandages and filter materials for medical use and clothing, in particular articles of sports and work clothing, and alone are not suitable for application as coating layers (upper and outer ) in diapers and sanitary napkins.

In order to improve the performance of the resulting non-woven fabrics, or to obtain particular properties useful for specific applications, we normally intervene on the characteristics and composition of the starting polymeric material for spinning, in order to obtain composition fibers or modified constitution compared to simple homopolymer polypropylene.

In particular, the production of so-called "bicomponent" fibers is known, consisting of two different polymers (for example, polypropylene and polyethylene) which are extruded simultaneously in the spinning phase, but without having been previously mixed together, so as to give origin in composite fibers with two clearly distinct areas. Depending on the geometric configuration of the spinning head, for example, bicomponent fibers of the "sheath-core" type can be obtained (ie with a core of one of the two polymers and an external cortex of the other, normally with a crown-shaped section circular) or fibers of the "side-by-side" type (with one side all of one polymer and the other all of the other polymer, and a section normally made up of two complementary semicircles). These fibers are produced with a spinning line comprising at least two extruders (one for each polymeric material) and spinnerets with a complex structure in which the two materials are kept separate up to the output head, from where they emerge with the desired geometric arrangement.

An example of a two-component sheath-core fiber, described in JP-A-21 39469 (Unitika), consists of a polypropylene core and an outer bark of linear low density polyethylene (LLDPE, obtained by copolymerization of ethylene with a reduced amount of an a-olefin with 3-12 carbon atoms, preferably 1-octene, which introduces short branches into the resulting linear polymer, which lower its density). According to the document, the resulting non-woven fabric, obtained with the melt-blown technique described above, has good softness and toughness characteristics, and could be used as a lining in articles such as diapers. It is evident from the foregoing, however, how the two-component fibers involve excessive production costs (equal to about double that of a normal heat-sealable polypropylene fiber) in order to be used as a basic constituent of the top-sheef of diapers and the like. In fact, in the field of non-woven fabrics, the two-component PP / PE fibers of the sheath-core type with the PE exterior are normally used in a mixture with other fibers and in a reduced percentage, with the function of binder, in order to exploit the lower melting point of the latter compared to polypropylene.

In addition to the "two-component" fibers, another possible modification on the constitution of the base material consists in the production of fibers known as "biconstituted". The latter are produced by a “blend” of two polymers which are mixed together in a phase prior to spinning, or directly in the extruder of the spinning line. In this case, the fiber structure is not made up of two separate areas of one and the other polymer, but of a random dispersion of small areas of a polymer in a matrix made up of the other. The size and dispersion of these areas depend on the relative concentration and compatibility of the two polymers. It is evident that special spinning lines or special dies are not required to produce biconstituted fibers, but the same equipment normally used for single-product fibers can be used.

Document EP-A-0663695 (Moplefan) describes the production of a type of such biconstituted fibers in which a quota not exceeding 20% of a second modifying polymeric material, with the function of increasing the softness properties of the resulting non-woven fabric. The modifying component consists of a heterophasic polymer (where "heterophasic" means a particular type of copolymer in which one polymeric phase is intimately dispersed in the other, normally obtained with two or three successive polymerization stages, of which the first gives takes place in a porous and flaky matrix of a first polymer within which a second polymer is grown, in the second stage) comprising a portion of random ethylene-propylene copolymer with low ethylene content and a portion of rubbery copolymer based on propylene , preferably an ethylene-propylene or ethylene-propylene-diene rubber. The polymeric composition is used for the production of biconstituted fibers with the preferred technology of long spinning, and from the staple thus obtained are made light heat-sealed non-fabrics suitable for the production of the top-sheet and the back-sheet (after coupling with a film polyolefin) of diapers and sanitary napkins. Compared to nonwovens made of propylene polymer only obtained with the same technology, these materials have a much softer hand and only slightly reduced mechanical resistance.

In addition to being slightly lower, the toughness values of the heat-sealed nonwoven resulting from the staple according to the aforementioned document are also significantly different from each other in M.D. and in C.D., and the document does not take into consideration the problem of obtaining acceptable levels of resistance even in the direction transverse to that of processing. In reality, this problem is of fundamental importance, because a non-woven fabric is subject, in the subsequent processing steps that lead to the finished product (for example, the packaged diaper) to stresses in all directions, and not only in that of the car. Particularly in the field of incontinent diapers, moreover, the products are subjected to considerable efforts even in use, for example when they are applied to patients who are unable to move.

The need to have a better mechanical isotropy in the nonwoven obtained from polypropylene yarn has been further accentuated with the development of new high-speed industrial cards (200-300 m / min, susceptible to further increase), with which the staple tends to orient yourself more in the direction of machining. To try to mitigate the aforementioned problem, there is a tendency to produce polypropylene fiber with a lower draw ratio, which makes it less orientable in the card, which however entails other drawbacks. Firstly, a reduction in the stretch ratio while maintaining the final count (i.e. the fineness of the filaments, which for a light non-woven fabric for "coverstock" must be around 2, 2-2, 3 dtex) requires the production of a fiber, upstream of the drawing operation, with a lower count, and can only be obtained by reducing productivity, or by increasing the spinning speed. Secondly, a lower drawing ratio can cause problems of insufficient permanence and fixability of the cretto, with negative consequences on the processability of the fiber itself.

Another application aspect for which it is highly desirable that the polypropylene staple non-woven has an acceptable mechanical isotropy is linked to the production of materials coupled with polyolefin film for the realization of the back-sheet of diapers. that the composite layer must be "breathable", and the polyolefin film is normally made such by incorporating a mineral filler in its extrusion (usually calcium carbonate at a concentration of 20-40% by weight) and subsequently subjecting it to a ironing operation to obtain microporosities. In the case of production of coupled by welding of a non-woven and of a film produced separately, this operation of stretching the film can be carried out in advance, but in the much more convenient case of production of the 'coupled by direct coextrusion of the polyolefin resin on the non-woven, the stretching must be carried out on the final laminate. to that this product has a remarkable toughness in M.D. and it would not give, in this direction, the desired elongation, the stretching to make the product breathable should be applied in the direction transversal to that of processing, in which however the non-woven is very little resistant.

The present invention therefore proposes the purpose of providing a formulation of biconstituted fiber suitable for the production of polypropylene staple, that is, it can be spun with the "long spin" and "short spin" technologies, for the production of heat-sealed non-woven fabrics that have , in addition to the softness necessary for use in the sanitary sector, also an improved mechanical isotropy, with toughness values in M.D. and in C.D. more balanced, even with the same thermal reliability index (T.B.I.).

In this regard, none of the solutions of the prior art in which biconstituted polypropylene / polyethylene fibers, i.e. with the same two basic materials as those proposed here, are proposed for various purposes and with various application methods, is aimed at the problem of anisotropy. mechanics of “thermal bonded” non-woven fabrics from carded staple.

In particular, the document EP-A-0260974 (Dow Chemical) concerns PP / PE biconstituted fibers with improved toughness and softness characteristics containing, together with polypropylene, an amount between 20 and 45% by weight of linear polyethylene a low density (LLDPE). The fibers, which are produced by short spinning (as can be deduced from the number of holes, 20,500, indicated for the spinneret of the examples), are also proposed for the production of light non-woven fabrics, but only the increase of these is experimentally detected toughness in M.D., while toughness in C.D. is not mentioned. PE contents below 20% are excluded from any consideration, on the grounds that they do not result in improvements in toughness. It should also be noted that a PP / PE blend with polyethylene concentrations of 20% or more does not lend itself, except under particular conditions, to the long spinning technique (at high spinning speed) because the high polyethylene content causes, to such speeds, a frequent breakage of the filaments.

Document WO-A-90 10672 (Dow Chemical) describes heat-sealed non-woven fabric articles obtained from fibers of a type similar to those of the previous document, in which the PP / PE ratio is between 0.6 and 1.5 (≡ 40-62% of PE). Also in this case, the mechanical tests on the non-woven fabric, carried out only in the processing direction, show an increase in toughness in M.D ..

A biconstituted fiber substantially similar to those of the two previous documents, but particularly designed for production with high-speed spinning techniques (not only long spinning, but also "spunbonded" spinning) is described in document US-A-4874666 (Kubo et al., Unitika). In this case, the polymer blend contains polyethylene as the dominant phase (50-99% LLDPE and 1-50% PP), and is proposed for the same typical uses as the two-component fiber of PP with an exterior in PE previously mentioned, that is with the functions of "binding" fiber. In order to solve the problems connected with the difficulties of fast spinning of fibers with a high PE content, the document imposes precise limitations on the viscosity characteristics of the two constituent polymers, setting a maximum limit of 20 g / 10 min. for the "melt index" (or melt flow index, or meli flow rate, fluidity index) of polypropylene and minimum and maximum limits of 25 and 100 g / 10 min. respectively for the melt index of polyethylene (LLDPE). description, furthermore, a mixture that contains more crystalline polypropylene than LLDPE is difficult to spin at high speed. Also in this case, the tensile strength of nonwovens produced starting from the proposed fibers is evaluated only in M.D ..

Document WO-A-9606210 (Kimberly-Clark) describes a bicomponent fiber based on polypropylene (50-95% by weight) in which the second material is an ethylene-propylene (random block) copolymer, which has the purpose of improve the softness of the resulting non-woven. However, the yarn does not concern the staple fiber field, but is intended for the production of "spunbonded" non-woven fabric, possibly laminated with an intermediate "melt-blown" non-woven layer and with another "spunbonded" layer ( SMS laminates) The addition of the ethylene-propylene copolymer has the purpose of obtaining a greater softness than that obtainable in a “spunbonded” non-woven polypropylene only.

Finally, document JP-A-4214405 (Mitsui) concerns the use, for the production of high mechanical performance fibers, of a polypropylene / UHMWPE blend with 85-99.5% polypropylene and 0.5 -15% polyethylene. Not only polyethylene, but also PP has a very high molecular weight (an intrinsic viscosity of at least 5 dl / g being specified, which corresponds to an average molecular weight of about 1,300,000 g / mol, while the PP that is used for spinning from melt has an intrinsic viscosity of about 1.5 dl / g and an average molecular weight of 250,000 g / mole or less), and the production of fiber is carried out not by melt spinning but by "gel spinning", as previously mentioned , using decalin as a solvent. The fiber obtained is subjected to stretching ratios in the range 10-100 and the resulting product can be used to produce plates, sheets, films, tapes and even non-woven fabrics. Given the stiffness and high mechanical stability performance of the material, the latter are used not in the sanitary field, but for industrial uses, as reinforcement and support structures for composite materials.

In the context of the present invention it has been found that by adding an extremely small quantity of polyethylene to a polypropylene resin of the type normally used for the production of polypropylene nonwoven from staple, and by spinning the resulting mixture, a much less orientable staple is obtained. in card, which gives rise, in the finished nonwoven, to a mechanical behavior much more balanced between resistance in M.D. and resistance in C.D. than that obtainable, under the same conditions, with a staple fiber of polypropylene only. In practice, the non-woven fabric made by thermal bonding with the PP / PE biconstituted fiber according to the invention has resistance values in M.D. minor and resistance values in C.D. higher than those obtainable with an analogous nonwoven but without the polyethylene component, while the geometric mean of these values (i.e. the T.B.!.) remains unchanged or even increases. The respective percentages of elongation at break in the two directions undergo similar modifications, which is extremely advantageous, as will be more evident in the following, for the production of coupled non-woven materials / polyolefin film.

Therefore, the specific object of the present invention is a staple fiber for the production of heat-sealed non-woven fabric obtained from a polymeric blend essentially consisting of:

A) 85-99.9% by weight of polypropylene homopolymer or polypropylene copolymer, random or heterophasic, or mixtures thereof;

B) 0.1-15% by weight of polyethylene.

The polypropylene which constitutes the main component of the fiber is preferably isotactic or predominantly isotactic PP, with an isotacticity index (fraction by weight insoluble in n-heptane at boiling) greater than 85%, but the invention could also be applied, to for example, syndiotactic polypropylene based polymeric blends.

In both cases, component A) of the mixture can be either polypropylene homopolymer or a random copolymer of propylene with ethylene and / or other α-olefins, in which the overall content of comonomers varies from 0.01 to 25% by weight, or , according to other embodiments of the invention, it can have the formulation with modifying heterophasic polymeric component which is the subject of the European patent referred to above as document EP-A-0663965. In this case, component A) has the following composition:

• from 80 to 99.9% by weight of polypropylene homopolymer or random copolymer of propylene with ethylene and / or other α-olefins, in which the overall content of comonomers varies from 0.01 to 25% by weight; And

• from 0.1 to 20% by weight of a heterophasic polymer consisting of: a) 10-60% by weight of polypropylene homopolymer or copolymer with isotacticity index higher than 80%;

b) 3-25% by weight of an ethylene-propylene copolymer insoluble in xylene at 23 ° C;

c) 15-87% by weight of a rubbery copolymer ethylene-propylene, or ethylene-prolipene-diene, soluble in xylene at 23 ° C.

The polyethylene component B) is preferably present in the mixture in quantities ranging from 0.5 to 5% by weight, and can be chosen from high density polyethylene (HDPE), low density polyethylene (LDPE), linear low polyethylene density (LLDPE) and their mixtures, with a preference for HDPE.

The melt index of component A), when this consists of PP homopolymer or random copolymer, is preferably between 1.5 and 60 g / 10 min. (measured according to ASTM D-1238, as grams of polymer extruded in 10 min. through a standard orifice under a load of 2.16 kg at 230 ° C), which corresponds to an intrinsic viscosity of 2.5-0, 9 dl / g. When component A) is constituted by the heterophasic mixture according to the aforementioned prior art, the global melt index of the modifying heterophasic component is preferably between 5 and 25 g / 10 min. The fluidity values of the polyethylene component B) are not relevant. , given the reduced concentration of this component in the polymeric blend.

As usual, the polymeric products for the production of the fiber according to the invention can comprise one or more stabilizing additives, such as antioxidants and light stabilizers, in particular organic phosphites or phosphonites or disulfides, phenolic antioxidants, light stabilizers based on spherically hindered amines or HALS (hindered amine light stabilizers), in concentrations from 0.01 to 1% by weight. Other additives, such as one or more organic or inorganic pigments and / or opacifiers, can optionally be introduced in the spinning step.

As noted in relation to the general production technology of biconstituted fibers, the mixing between the two constituent polymers can be carried out in a special device or can be obtained by putting the two polymers in contact in the extruder immediately upstream of the spinning. Advantageously, the polyethylene is added directly into the extruder of the spinning line using traditional dosing systems, such as a continuous gravimetric dosing device.

The invention also relates to non-woven fabrics obtained by thermal bonding from the staple fiber described above, in particular of the light type, suitable for use in disposable sanitary products such as diapers for children and incontinents, and feminine sanitary napkins. A further object of the invention is the use of a polymeric composition as defined above for the production of staple fiber, preferably using the "long spinning" technology (long spinning), for the production of heat-sealed non-woven fabric.

As already noted, the non-woven fabric according to the invention can be advantageously used to make a coupled fabric-non-woven material / polyolefin film, in particular in which said polyolefin film is a polyethylene film. In this application, the better toughness and greater elongation of the non-woven fabric in the direction transversal to that of processing allow, in the production of the laminate by coextrusion of the film directly on the non-woven, to have a better stretchable laminate, and to be able to also decrease the thickness of the film and / or non-woven fabric. Furthermore, the presence of polyethylene dispersed in the fiber improves adhesion with the polyolefin film, without having to resort to the use of adhesives and "hot melts", or to the addition of two-component fiber with a "sheath-core" structure to the polypropylene staple. with external PE, which binds badly with the staple during calendering and which lowers the overall toughness (both in CD and MD) of the non-woven fabric.

It is important to note that the non-woven fabrics produced with the staple according to the invention also have a higher softness than completely similar products without the addition of polyethylene.

The advantageous features of the products of the invention will be more evident with reference to the embodiments shown in the following examples, which should not be understood as having any limiting function of the scope of the invention.

EXAMPLE 1

A pilot line of long spinning and finishing of polypropylene was used to produce staple fiber from the following blend:

• 97% by weight of homopolymer polypropylene with isotacticity index of 96.5% and melt index 12 dg / min.

• 3% by weight of high density polyethylene (HDPE) at melt index 2 dg / min.

The spinning and finishing conditions were as follows: 2400 hole die

extruder temperature 267 ° C

spinning head temperature 272 ° C

harvesting speed 700 m / min

spinning count 4.1 dtex

stretching ratio 2.4

final title 2, 2-2, 3 dtex

ensimage 0.4-0.55%

cut 40 mm

The carding-calendering conditions for the formation of the nonwoven were the following:

carding-calendering speed 40 m / min calender cylinders pressure 50 kg / linear cm calender cylinders temperature 145/150 ° C

weight of the non-woven product 20 g / m <2> For the non-woven fabric obtained, the toughness and elongation characteristics, measured according to the UNI 8639 standard, both in M.D. that in CD, as well as softness, evaluated as the average of the judgments of a panel of "tasters" who had a scale of reference values from 1 (rigid) to 5 (very soft). The results obtained were as follows: MD toughness 54.0 N / 5 cm

CD toughness 13.8 N / 5 cm

T.B.I. 27.3 N / 5 cm

MD elongation 48%

CD elongation 106%

softness 4.0

Comparison example 1a

Under the same conditions of spinning and finishing of the fibers and of carding-calendering for the production of the non-woven of Example 1, the following was used:

• 100% homopolymer polypropylene with isotactic index 96.5% and melt index 12 dg / min.

The characteristics of the non-woven fabric, measured with the same methods as above, were:

toughness MD 66 N / 5 cm

toughness CD 9.2 N / 5 cm

T.B.I. 24.6 N / 5 cm

MD elongation 51%

CD elongation 73%

softness 2.0

It is evident from the data reported that a minimum addition of polyethylene (3% by weight) has led to a significant improvement in mechanical isotropy, without in any way penalizing the heat-sealability index, indeed improving it. Equally remarkable is the improvement in the performance of the product in terms of softness.

EXAMPLE 2

In the same conditions of spinning and finishing of the fibers and of carding-calendering for the production of the non-woven of Example 1, the following mixture was used:

• 80% by weight of homopolymer polypropylene with isotacticity index 96.5% and melt index 12 dg / min.

• 10% by weight of crystalline copolymer of propylene with ethylene (3.5% by weight) at melt index 6 dg / min.

• 10% by weight of LLDPE at melt index 9.

The characteristics of the non-woven fabric, detected with the same methods of example 1, were:

toughness MD 50 N / 5 cm

toughness CD 12.2 N / 5 cm

T.B.I. 24.7 N / 5 cm

MD elongation 42%

CD elongation 98%

softness 4.5

Comparison example 2a

In the same conditions of spinning and finishing, and carding-calendering of example 1, the following mixture was used:

• 90% by weight of homopolymer polypropylene with isotacticity index 96.5% and melt index 12 dg / min.

• 10% by weight of crystalline copolymer of propylene with ethylene (3.5% by weight) at melt index 6 dg / min.

The characteristics of the non-woven fabrics were:

toughness MD 61 N / 5 cm

CD toughness 8.6 N / 5 cm

T.B.I. 22.9 N / 5 cm

MD elongation 48%

CD elongation 71%

softness 2.5

EXAMPLE 3

In the same conditions of spinning and finishing of the fibers and of carding-calendering for the production of the non-woven of Example 1, the following mixture was used:

• 80% by weight of homopolymer polypropylene with isotacticity index 96.5% and melt index 12 dg / min.

• 15% by weight of heterophasic copolymer consisting of:

a) 20% by weight of homopolymer polypropylene with 96.5% isotacticity index

b) 15% by weight of ethylene-propylene copolymer with 3.5% of ethylene c) 65% by weight of ethylene-propylene rubber (30% of ethylene) having a global melt index of 8 dg / min.

• 5% by weight of LDPE at melt index 20.

The characteristics of the non-woven fabric, detected with the same methods of example 1, were:

toughness MD 46 N / 5 cm

toughness CD 11, 1 N / 5 cm

T.B.I. 22.6 N / 5 cm

MD elongation 40%

CD elongation 87%

softness 5.0

Comparison example 3a

In the same conditions of spinning and finishing, and carding-calendering of example 1, the following mixture was used:

• 85% by weight of homopolymer polypropylene with isotactic index 96.5% and melt index 12 dg / min.

• 15% by weight of heterophasic copolymer consisting of:

a) 20% by weight of homopolymer polypropylene with 96.5% isotacticity index

b) 15% by weight of ethylene-propylene copolymer with 3.5% of ethylene c) 65% by weight of ethylene-propylene rubber (30% of ethylene) having a global melt index of 8 dg / min.

The characteristics of the non-woven fabric were:

toughness MD 53 N / 5 cm

CD toughness 7.4 N / 5 cm

T.B.I. 19.8 N / 5 cm

MD elongation 45%

CD elongation 61%

softness 4.0

EXAMPLE 4

A non-woven sample of example 1 was coupled with a 20 micron thick polyethylene film.

The coupling was achieved by welding together in a non-woven calender and film with a calender rollers temperature of 125 ° C and a speed of 40 m / min.

The characteristics of the coupled obtained were the following: MD 61 N / 5 cm toughness

toughness CD 16.7 N / 5 cm

MD elongation 54%

CD elongation 101%

excellent non-woven / film adhesion

Comparison example 4a

A non-woven sample of Comparative Example 1a was coupled with 20 micron thick polyethylene film under the same conditions of Example 4.

The characteristics of the coupled obtained were:

toughness MD 69 N / 5 cm

CD toughness 13.1 N / 5 cm

MD elongation 58%

CD elongation 71%

poor non-woven / film adhesion

In addition to producing a much improved adhesion between non-woven and film, the addition of only 3% of polyethylene to the polypropylene fiber allows to significantly increase the toughness and elongation in C.D. compared to an analogous non-woven fabric without the polyethylene constituent.

EXAMPLE 5

A non-woven sample of Example 1 was coupled with a 15 micron thick polyethylene film. The coupling was carried out as in the previous example.

The characteristics of the coupled obtained were the following: toughness MD 55 N / 5 cm

toughness CD 14.1 N / 5 cm

MD elongation 42%

CD elongation 98%

excellent non-woven / film adhesion

Comparison example 5a

A non-woven sample of the comparative example 1a was coupled with a 15 micron thick polyethylene film under the same conditions as example 4.

The characteristics of the coupled obtained were:

toughness MD 65 N / 5 cm

toughness CD 12.9 N / 5 cm

elongation MD 53%

CD elongation 65%

poor non-woven / film adhesion

EXAMPLE 6

A non-woven fabric produced as in example 1, but weighing 18 g / m, was coupled with a 20 micron thick polyethylene film under the same conditions as example 4.

The characteristics of the coupled obtained were the following: toughness MD 51 N / 5 cm

toughness CD 14.7 N / 5 cm

MD elongation 50%

CD elongation 95%

excellent non-woven / film adhesion

Comparison example 6a

A non-woven fabric produced as in the comparative example la, but weighing 18 g / m <2>, was coupled with the 20 micron thick polyethylene film under the same conditions as in example 4.

The characteristics of the coupled obtained were:

toughness MD 64 N / 5 cm

toughness CD 11.2 N / 5 cm

elongation MD 53%

CD elongation 66%

poor non-woven / film adhesion

The three preceding examples, together with the relative comparisons, show how the use of the PP / PE staple according to the invention allows, in the production of film / non-woven laminated material, to reduce the thickness of the film or the weight of the non-woven material. -fabric, still obtaining advantageous mechanical properties.

While not wanting to be bound by theoretical interpretations, it is believed that the reasons for the considerable improvement of the mechanical isotropy of non-woven fabrics produced from staple due to the effect of even very small additions of polyethylene in the polypropylene resins normally used is to be attributed to a lower orientability of the staple following carding, which produces less parallelism of the fibers in the heat-sealed fabric. This lower adjustability is due, at least in part, to the lower stiffness of the fibers containing a small percentage of polyethylene compared to those based only on polypropylene resins, and to their consequent lower reactivity to deformations.

Furthermore, it is also possible that in such an effect the phenomenon of increase in the density of corrugation in the crack contributes, which has been observed as a consequence of the addition of small amounts of PE to PP. In fact, it has been found that even a very small addition of polyethylene to the polypropylene resin, all other conditions being equal, considerably increases the number of waves per unit length of the fiber that are produced due to kerning (under the same conditions operative), and therefore the extensibility of the cretto.

The present invention has been described with reference to some of its specific embodiments, but it is to be understood that variations or modifications may be made to it by those skilled in the art without thereby departing from the relative scope of protection.

Claims (20)

CLAIMS 1. Staple fiber for the production of heat-sealed non-woven fabric obtained from a polymeric blend essentially consisting of: A) 85-99.9% by weight of polypropylene homopolymer or polypropylene copolymer, random or heterophasic, or mixtures thereof B) 0.1-15% by weight of polyethylene. 2. Staple fiber according to claim 1, in which said polypropylene is isotactic or predominantly isotactic polypropylene, with an isotactic index greater than 85%. 3. Staple fiber according to claim 1, wherein said polypropylene is syndiotactic polypropylene. 4. Staple fiber according to any one of claims 1-3, wherein said component A) is homopolymer polypropylene. 5. Staple fiber according to any one of claims 1-3, wherein said component A) is a random copolymer of propylene with ethylene and / or other ac-olefins, in which the overall content of comonomers varies from 0.01 to 25% by weight. 6. Staple fiber according to any one of claims 1-3, wherein said component A) is a polymeric blend comprising: • from 80 to 99.9% by weight of polypropylene homopolymer or random copolymer of propylene with ethylene and / or other α-olefins, in which the overall content of comonomers varies from 0.01 to 25% by weight; And • from 0.1 to 20% of a heterophasic polymer consisting of: a) 10-60% by weight of polypropylene homopolymer or copolymer with an isotacticity index greater than 80%; b) 3-25% by weight of an ethylene-propylene copolymer Θ insoluble in xylene at 23 ° C; c) 15-87% by weight of a rubbery copolymer ethylene-propylene, or ethylene-prolipene-diene, soluble in xylene at 23 ° C. 7. Staple fiber according to any one of the preceding claims, wherein said polyethylene constituting component B) is present in the mixture in a quantity comprised between 0.5 and 5% by weight. 8. Staple fiber according to each of the preceding claims, in which said polyethylene constituting component B) is selected from high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their mixtures . A staple fiber according to claim 8, wherein said polyethylene is high density polyethylene (HDPE). Staple fiber according to any one of the preceding claims, wherein said polymeric blend also comprises one or more stabilizing additives, such as antioxidants and light stabilizers. Staple fiber according to claim 10, wherein said polymeric blend further comprises one or more organic or inorganic and / or opacifying pigments. 12. Non-woven fabric obtained by thermal bonding from the staple fiber according to any one of claims 1-11. 13. Non-woven fabric according to claim 12 of the light type, suitable for use in disposable sanitary products such as diapers for children and incontinent people, and sanitary napkins for women 14. Coupled composite material non-woven fabric / polyolefin film comprising a heat-sealed non-woven fabric according to claims 12 or 13. 15. A material according to claim 14 wherein said polyolefin film is a polyethylene film. 16. Use of a polymeric composition essentially consisting of: A) 85-99.9% by weight of polypropylene homopolymer or polypropylene copolymer, random or heterophasic, or mixtures thereof; B) 0.1-15% by weight of polyethylene for the production of staple fiber using the long spinning technology, for the production of heat-sealed non-woven fabric. 17. Use according to claim 16, wherein said polypropylene is isotactic or predominantly isotactic polypropylene, with an isotacticity index greater than 85%. 18. Use according to claims 16 or 17, wherein said component A) is polypropylene homopolymer. Use according to any one of claims 16-18, wherein said polyethylene constituting component B) is present in the mixture in a quantity comprised between 0.5 and 5% by weight. Use according to any one of claims 16-19, wherein said polyethylene constituting component B) is high density polyethylene (HDPE).