ITTO940798A1 - PROCEDUREI FOR ELASTICIZING ITEMS, SUCH AS FOR EXAMPLE SANITARY AND SANITARY ITEMS, AND RELATED ITEM - Google Patents

Abstract

The invention relates to providing elasticization in defined areas of an article by applying a thermoplastic elastomeric composition under elastic tension to the article and partially deactivating or deactivating the elastic tension in the composition outside said defined areas. The elastic tension can be deactivated by (i) heating to a temperature corresponding at least to the inversion temperature between G 'and G "; or (ii) heating to a temperature below the inversion temperature between G' and G" with application of a pressure at least equal to the value of G 'at that temperature.The article can be an absorbent article such as a diaper - disposable panty and the elastic tension can be maintained in the fork surface and deactivated outside the fork surface. the thermoplastic elastomeric composition can be applied to the article as a yarn or strip and subjected to complete or partial deactivation of the elastic tension in a series of points along the length of the yarn or strip to improve adhesion to the article. (Figure 3) .

Description

DESCRIPTION of the industrial invention entitled: "Process for elasticizing articles, such as for example sanitary articles, and related article",

DESCRIPTION

The present invention relates to the elasticization of articles and structures and more particularly to the use of a single elastic material to produce some zones which are under elastic tension together with other zones not under elastic tension, or to produce zones under different values of elastic tension.

Typical articles and structures that need to be elasticized include absorbent articles such as disposable panty diapers in which elastic strips are employed to provide elasticization around the legs and waist. Typically, the elastic strip consists of a vulcanizable rubber band which is attached to the diaper body by layers of adhesive. In the production of elasticized articles it is normal that the continuous technological evolution makes the continuous application of the elastic almost essential (since the application of discontinuous strips would require a special machinery and would be very expensive), but the elasticization is required only on part of the 'item. For example, in the manufacture of disposable panty nappies, the elasticization around the legs is required only in the central part (crotch part) of the panty nappy and it is important that the ends are not elasticized.

One way of providing elasticization only in certain parts of articles and structures while applying the elastic strip continuously, has been to fix the elastic strip to the article with adhesive only in those parts where elasticization is necessary. If the elastic strip is not attached to the article or structure in a particular zone, it cannot provide elasticization of the article or structure in that zone. However, this type of structure has considerable disadvantages, particularly in the case of absorbent articles. Generally, the absorbent articles comprise an absorbent topsheet intended to be in contact with the user and a backsheet with an absorbent material disposed between the topsheet and the backsheet and held in its position by the fact that the topsheet and the backsheet are fixed between each other. them around the edges of the article. The elastic strip is also generally disposed between the topsheet and the backsheet in the direction of the lateral edge of the article. The fact that the elastic strip must remain unfastened to the rest of the article at the ends of the article itself, means that an "open tunnel" is created around the elastic strip, through which the absorbent from the inside of the absorbent article can come out, unless the tunnel is closed by means of a further processing after the withdrawal of the elastic.

An object of the present invention is to provide elasticization only in defined areas of the article in a way that avoids the drawbacks indicated above while at the same time being convenient and of general applicability.

According to one aspect, the present invention provides a process for achieving elasticization in defined zones of an article, which comprises applying a thermoplastic elastomeric composition under elastic tensioning to the article and deactivating the elastic tension in the composition on the outside of said defined zones.

According to another aspect, the present invention provides an elasticized article in which the elasticization is ensured by a thermoplastic elastomeric composition applied under elastic tension, characterized in that the elastic tension of the thermoplastic composition has been completely or partially deactivated in defined areas.

As used herein, the term "thermoplastic elastomeric composition" includes thermoplastic elastomers such as single polymers or blends and compositions containing thermoplastic elastomers, provided the final composition possesses the properties of a thermoplastic elastomer. As a category, thermoplastic elastomers are known and are described in more detail below and are characterized by the fact that, at room temperature, they behave like a vulcanized rubber which has high elasticity but, unlike vulcanized rubbers, they can be melted and reworked in the the same way as normal thermoplastic products. The thermoplastic elastomeric compositions can thus be used to provide elasticization of an article in a manner similar to polymerized rubbers, by applying the composition to the article under elastic tension. The present invention exploits the fact that, under certain conditions defined by the rheological parameters of the thermoplastic elastomeric composition, the elastic tension can be completely or partially deactivated, thus eliminating or modifying the elastic properties of the material.

The conditions in which the elastic tension can be deactivated can be determined in each particular case by referring to the classic method of Dynamic-Mechanical Analysis for viscoelastic materials under sinusoidal stress, and it is necessary to take into account the values of two rheological parameters:

- elastic or conservation modulus G1

- viscous or dissipation modulus G "

in the temperature range in which the melting of the material occurs. G 'is higher than G "when the material is solid, but in the field in which the material melts, an inversion of the values occurs, so that G" becomes lower than G "at the temperature at which the material melts. In fact, the inversion temperature between G 'and G ”can be taken as the real real rheological solidification point (or melting point) of the material.

The inversion temperature for thermoplastic elastomeric compositions can be varied depending on the intended application of the composition. For example, the inversion temperature can be between 90 ° C and up to 250 ° C or higher. However, in the application of the composition in the production of disposable sanitary products, compositions with inversion temperatures in the lower part of the range are used, to avoid damage to some of the raw materials, such as polyethylene fibers and cellulose fibers. The relative values of G and G "indicate that, if heated to a temperature equal to or above the inversion point, any internal tension of the material will cancel out spontaneously. Thus, when G"> G ', the material behaves as a liquid and any molecule that was previously stretched by imparting elastic tension to the material, can thus flow, eliminating any tension. Consequently, a method of deactivating the elastic tension according to the invention simply consists in heating the thermoplastic elastomeric composition to a temperature equal to or higher than the inversion temperature.

However, it is also possible to loosen the internal tensions to obtain zones where the elastic tension is deactivated by heating to a temperature below the inversion temperature, as long as appropriate pressure is applied at the same time. The inversion temperature can be considered as the temperature at which the release of internal tensions occurs spontaneously without the application of pressure. The same result can be obtained by means of a combination of heat and pressure, provided that the pressure that is applied is at least equal to the value of G 'at the working temperature. So, by way of example, if the elastic modulus of a thermoplastic elastomeric composition is 0.02 MPa at 90 ° C, the internal tensions can be released and the elastic tension deactivated at 90 ° C, by applying a pressure of at least 0, 02 MPa.

It is also possible, by applying a high temperature lower than the inversion temperature, or a combination of heat and pressure that falls close to that necessary to completely loosen the internal tensions, to obtain a partial release, so as to obtain a partial deactivation of the elastic tension. The extent of deactivation can be varied as desired in each particular case, by the use of an appropriate temperature or by an appropriate combination of temperature and pressure.

The present invention can generally be applied to thermoplastic elastomeric compositions, but it cannot be applied to elastomers that are non-thermoplastic, i.e. normal vulcanized elastic rubber, since these chemically decompose before reaching the conditions that could lead to the loosening of internal tensions. . The thermoplastic elastomers can also be adhesives or they can be formulated in composition so that the composition is adhesive, in which case the thermoplastic elastomeric composition can be applied directly to the article, without a separate adhesive. The thermoplastic elastomeric composition may be a hot melt adhesive, i.e. it is adhesive when applied to the article in the molten state and this does not preclude the possibility that the thermoplastic elastomeric composition may exhibit adhesive properties at room temperature, e.g. adhesive properties at pressure. As explained in more detail below, heat and / or pressure, which has the effect of complete or partial deactivation of the elastic tension, can be applied to areas or points of the thermoplastic elastomeric composition to promote or improve the adhesion. If the thermoplastic elastomeric composition is non-adhesive, a separate adhesive will be required, and suitable adhesives are already well known for use with vulcanized rubber bands or thermoplastic bands.

As already indicated, the single thermoplastic elastomeric polymers constitute a very important chemical and technological category which is distinguished by their characteristic behavior. At room temperature they behave like vulcanized rubbers, presenting a high elasticity but, unlike vulcanized rubbers, they can be melted and reworked in the same way as normal thermoplastic materials.

This behavior is a consequence of a particular chemical structure. Most thermoplastic elastomers consist of block copolymers, that is, their molecules are formed from blocks of different nature connected to each other. Different blocks can alternate in the chain, such as relatively short blocks (multi-block structure of the type A-B-A-B-A, echo.); or the molecules can have a triblock structure of the A-B-A type, in which A are terminal blocks and B is a central block of a different nature (linear triblock copolymers); or the molecules can have a "radial" or "star" structure represented as (AB) X, in which all the intermediate blocks B are chemically connected to each other at a central point, and the terminal blocks A are each arranged radially at the end of a block B. The structure formed by only two blocks (diblocks) of the AB type, are ineffective as thermoplastic elastomers from the point of view of their elastic behavior.

The chemical nature of the various blocks can be different and the resulting copolymers can be classified for example as polyurethanes, polyesters, polyethers, polyether-ester amides, etc. However, a common feature is the following: different blocks are physically incompatible as they are mutually insoluble. The material can thus be considered as a heterogeneous system in which different blocks, even if chemically connected to the same molecule, exist as separate entities. The A blocks of different molecules tend to associate with each other in microscopic areas or "domains" and the same happened for the B blocks. The material thus formed has a heterogeneous structure of domains A and B, each well separated, with the one present in lower quantity dispersed microscopically in the other, which constitutes a continuous phase. This continuous phase is generally formed by "soft" or rubbery blocks B, which give the material its elastic properties, while the dispersed phase A consists of "rigid" non-elastomeric blocks. Below the glass transition temperature or softening point of the rigid blocks, each molecule of the copolymer has its A blocks fixed in at least two points, ie these are "confined" to the rigid domains. Consequently, the rubbery part of the molecule can undergo stretching without however sliding with respect to the other molecules, and when the external traction force is loosened it returns to its initial position due to the entropic effect.

Thus in thermoplastic elastomers, the rigid blocks operate as a physical vulcanization, and the advantages of this process are clear. The chemical bonds that form the vulcanized structure of a standard rubber cannot be destroyed by heating and, at a sufficiently high temperature, the rubber simply begins to decompose.

On the other hand, in thermoplastic elastomers heat can actually melt the rigid domains; the material can thus be melted and processed, but the rigid domains that give rise to the pseudo-vulcanization are reformed again by simple cooling of the material. From the above explanation, it is evident that diblocks, which contain only one hard and one soft block, cannot contribute to the elastic properties.

Diblocks can improve workability, but their content in the material must be limited to certain values, in order not to reduce the elasticity in an unacceptable way. Also, the total amount of hard blocks is important; too low a content will impart modest elastic properties (similar to those of insufficiently cured rubber), while too high a content will cause the material to behave like a very hard and super vulcanized rubber, again with very modest elasticity.

Among the block thermoplastic elastomeric copolymers, the so-called styrenic block copolymers (SBCs) are well known and are widely used in many applications, due to their excellent properties. The class of styrene block copolymers is described, e.g., in Thermoplastic Elastomers: A Comprehensive Review, Legge, Holder & Schroeder (Ed.), Hauser Publishers (1987), Chapters 3, 4 and 12 (1). They may have the structures already mentioned, such as:

- multiblock A-B-A-B-A-B- ... etc.

- linear triblock A-B-A

- radial or star polymers (AB) X where x> 2.

A represents a "rigid" block of a polymerized vinylarene monomer, generally styrene or alpha-methyl-styrene; and B represents a "soft intermediate block" generally formed from a rubbery monomer, such as poly (butadiene), poly (isoprene), poly (ethylene-butylene) or poly (ethylene-propylene).

The content of diblock molecules A-B in such materials can even reach <'> 80% by weight, and in special commercial products it can also constitute the whole of the polymer. The latter materials are used for particular applications since, for the reasons described above, they do not have elastic properties or have very modest them. The diblocks can facilitate workability and improve adhesion properties, but to maintain good elasticity characteristics their content in the thermoplastic elastomeric block copolymer must be less than 40% by weight.

SBCs are widely used as substitutes for vulcanized rubbers, since their hardness, modulus and general mechanical and elastic properties are strongly linked to the content of rigid blocks, especially formed of polystyrene. They have also found use as base polymers for hot melt adhesives, due to their generally good mechanical characteristics, the ease of developing adhesive properties in their rubbery intermediate blocks and their good thermal stability, which makes them superior to traditional bases for hot melts, such as ethylene-vinyl acetate copolymers. However, the main purpose of the standard compositions is to optimize the adhesive properties, without worrying about maintaining at least part of the elastic properties typical of the base polymer.

Block elastomeric thermoplastic copolymers known as SBCs therefore typically have the following characteristics:

- They are formed by two types of monomers each polymerized in blocks of the same monomer units, the blocks being distinct even if chemically connected within the copolymer molecule.

Furthermore, the two types of blocks must be mutually incompatible.

- The structure according to which the two types of blocks present are connected in the molecule, can be:

- alternating multi-block, such as ... A-B-A-B-A-B

- linear triblock like A-B-A

- radial or star structure, such as (A-B) x where x> 2.

- "A" represents blocks of a polymer derived from a vinyl-arene monomer, typically styrene or alpha-methyl-styrene. They are called rigid blocks because at room temperature these types of polymer are rigid, glassy and brittle, being below their glass transition temperature (Tg).

Typically, constituents useful for rigid blocks have Tg well above ambient temperature, and preferably above 90 ° C.

- "B" represents blocks of a rubbery polymer having a Tg <0 ° C, and preferably <-40 ° C.

Typically these "soft" blocks are formed from rubbers such as polybutadiene, polyisoprene.

In the common technological lexicon, the block thermoplastic elastomeric copolymers thus formed are often indicated respectively with the abbreviations SBS, SIS.

As already mentioned with reference to the mechanism of the generation of elastic properties in these types of polymer, and particularly to the function of the rigid blocks in imparting a physical vulcanization to the polymer, useful SBCs contain at least two rigid blocks "A" for molecule, and at least one soft block "B". Molecules formed by a block A and a block B (the so-called diblocks) should, to be used in the present invention, be present in the base polymer in an amount of less than 40% by weight.

All thermoplastic elastomers can be processed in the molten state with various technologies and in various apparatuses, showing in any case in the solid state properties similar to a vulcanized rubber. Potentially, all thermoplastic elastomers can be made adhesive. Some adhere quite well in the molten state to different substrates. However, it is clearly very desirable to obtain thermoplastic elastomeric compositions capable of adhering at room or only moderately elevated temperatures to various substrates.

Hence, while pure thermoplastic elastomers have a certain adhesiveness at high temperatures, this adhesiveness can be conveniently improved both in terms of the strength of the bonds formed with different substrates and in terms of the temperature range within which strong bonds are formed.

This improvement is generally achieved with the use of at least one suitable tackifier resin. More particularly, much better adhesive properties and also adhesive properties at room temperature (pressure adhesive behavior) can be obtained by mixing thermoplastic elastomers with materials known as tackifier-like resins which, as a category, are well known in the literature.

When thermoplastic elastomers are used at room temperature (e.g. because you want to pretension them in the solid state and fix them under tension) they need to exhibit the typical behavior of true pressure adhesives, and this generally requires a blend of a block elastomer thermoplastic and a tackifier-type resin. It should be noted that to improve the adhesive properties of the thermoplastic elastomer (both at high temperature and at room temperature), only the soft (rubbery) blocks of its molecule need to be modified by the tackifier resin. Therefore, only the interactions between the soft (rubbery) blocks and a resin, which is substantially compatible with them, generates adhesiveness; while any modification of the rigid blocks with a resin never leads to the development of an adhesive behavior.

Not only do the rigid blocks have no adhesive activation, but their eventual modification with a tackifier resin can "soften" their mechanical strength. This risks worsening their ability to act as "physical vulcanization centers" for the elastomer, thereby destroying the elastic behavior.

Therefore, for the various thermoplastic block elastomers, depending on the chemical nature of their soft and rigid blocks, suitable tackifier resins can be identified, which are compatible (i.e. soluble and able to create the appropriate physical modifications of the system) only with rubbery or soft blocks, while compatibility with rigid blocks must be as low as possible or even zero, to keep the primary elastic properties of the polymer to the maximum. However, the amount of tackifier type resin must be controlled, as the addition of too large amounts of tackifier type resin (or resins), even if the tackifier type resin is only compatible with intermediate blocks (soft blocks) and completely incompatible with rigid blocks, it can still worsen the elastic properties of the obtained formulation. In any case, the addition of the resin constitutes a dilution of the concentration of the rigid block domains, weakening their ability to function as "physical crosslinking" centers for the elastomer. Thus, both the content of the rigid domains in the base block thermoplastic elastomer and the content of the elastomer in the final formulation must be such as to ensure a final concentration of rigid domains in the formulation sufficient to maintain an appropriate "physical vulcanization" value. "and therefore of elastic properties.

On the one hand, it is therefore important to control the final concentration of the rigid blocks in the composition. On the other hand, the addition of a resin (or resins) compatible only with the rigid blocks and their domains, is completely ineffective for the development and / or improvement of the adhesive properties. The resins compatible with the rigid blocks, by swelling of the rigid domains, will stiffen the composition, increasing the modulus and (compared to similar contents of tackifier-type resins compatible with the intermediate block) will tend to increase viscosity. In a system already containing a tackifier-type resin compatible with soft domains, adding resins compatible with hard domains will also decrease adhesiveness. Consequently, in general, only limited quantities of resins compatible with the "rigid blocks" can be used, without too great a deterioration of the general properties of the elastic hot melt adhesive. Generally they will only be used in special cases, eg if a further increase of the module is required for some applications; or (using resins compatible with high softening point rigid blocks) if a higher solidification temperature or better temperature resistance is desired.

According to a preferred embodiment, the thermoplastic elastomeric composition used to provide elasticization is an elastomeric hot melt adhesive composition comprising at least one thermoplastic elastomer and at least one tackifier resin, the thermoplastic elastomer (or elastomers) being a styrene block copolymer / butadiene / styrene (SBS) or a mixture of styrene / butadiene / styrene copolymer, with styrene / isoprene / styrene copolymer (SIS), in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, the composition being characterized in that:

a) is able to bind, when applied in the molten state, to plastic materials and / or cellulosic materials with a peel force under a 90 ° angle of not less than 0.5 N / cm (as defined in this office);

b) has a retention value of tensile strength after 50 cycles (as defined here) of at least 40%; And

c) has a viscosity of 120,000 cps or less at 180 ° C under a shear stress of 80 sec.

The compositions as defined above form the subject of our application filed on the same date entitled "Adhesive composition".

Characteristic a) previously indicated refers to the adhesive properties of the composition and the composition must have the properties of a hot melt adhesive which is capable of binding to appropriate substrates, typically plastic and / or cellulosic materials, when applied in the molten state. . In particular, "capable of binding" indicates that the composition is capable of exhibiting sufficient adhesion on plastics and / or cellulosic materials especially for application to the construction of absorbent sanitary articles. When applied in the molten state between two substrates of plastic and / or cellulosic materials, the composition produces a bond strength, measured as a 90 ° peel, of not less than 0.5 N / cm. The composition, in grammage of 5 g / m ^, is applied melted between the substrates, and 48 hours after the formation of the bond the resistance to peel under an angle of 90 ° is measured at 23 ° C, with a separation speed of 300 mm / min.

Many compositions of the type described herein bind to suitable substrates even at room temperature and may exhibit the properties of a pressure adhesive.

The previously indicated characteristic b) refers to the elastic properties of the composition. The test used is described in more detail below, and involves measuring the level of retention of the elastic properties after 50 elongation and release cycles. The percentage of elongation to which the composition is subjected is correlated to the modulus of the composition itself and is similar to the degree of elongation to which the composition is subjected upon use. The retention value of the tensile strength of 40% indicates that the elastic properties of the composition are comparable with those of natural rubber and are preferably superior to these. Preferably the retention of the tensile strength is at least 50%, more preferably at least 60%.

The aforementioned characteristic c) refers to the workability of the composition, and a viscosity of 120,000 cps or less at 180 ° C (shear stress 80 sec ~ 1) indicates that the composition can be applied using conventional equipment for use. of hot melt adhesives. Preferably, the viscosity is 60,000 cps or less, more preferably 30,000 cps or less. It is also highly desirable that the composition according to the invention have a substantially Newtonian rheological behavior, in particular the viscosity must not vary significantly as the shear stress varies. Many compositions described herein exhibit Newtonian behavior at the expected processing temperatures, e.g. around 180 ° C.

The elastomeric hot melt adhesive compositions, as defined above, can be formulated with any desired modulus, depending on the precise nature of the intended end use. However, the modulus has influence on the main properties of the composition, and it is convenient to divide the compositions into low modulus compositions and high modulus compositions.

Low modulus compositions are defined compositions having a modulus of 0.5 MPa or less with an elongation of 500% (six times the initial sample length) measured at 23 ° C and with an elongation rate of 500 mm / minute. Generally, the low modulus compositions have a modulus of between 0.05 and 0.5 MPa, preferably between 0.05 and 0.3 MPa. The low modulus compositions generally exhibit good adhesive properties at room temperature and can also be pressure adhesives. These compositions are normally stretched immediately after their formation, e.g. after extrusion from the melt, such as strip or wire. Ironing can occur immediately before or during application to an article, so that the compositions are effectively applied in the stretched state. Low modulus compositions are typically employed with an elongation of 400% to 1,000%.

Since low modulus compositions will normally be stretched immediately after extrusion, it is desirable that they have a relatively high solidification point, so that they solidify quickly upon extrusion. Preferably the solidification point (measured with the Dynamic-Mechanical Analysis method described in more detail below) is at least 80 ° C, more preferably at least 100 ° C.

High modulus compositions are defined as compositions having a modulus greater than 0.5 MPa at an elongation of 500% (six times the initial sample length) measured at 23 ° C with an elongation rate of 500 mm / minute. Preferably, the high modulus compositions have a modulus comprised between 1 MPa and 10 MPa. Since the pressure adhesive character is generally inversely proportional to the modulus, high modulus compositions are often applied in the molten state, although some may maintain a pressure adhesive character sufficient to be applied at room temperature. Molten application implies that the composition is applied without prior elongation, with elongation generally occurring during use, and this is particularly true for compositions with a modulus of 1 MPa or more. For this reason, a high solidification temperature is less critical for high modulus compositions, but for convenience these are also preferably formulated to have a solidification point of at least 80 ° C, more preferably at least 100 ° C. High modulus compositions are generally used with a lower elongation value. They are able to give a sufficient elastic force with low deformation (typically not more than 50%). However, in cases where the compositions maintain an adhesive character under sufficient pressure to be applied at room temperature in the stretched state, they can be used with an elongation of up to 400%.

The elastomeric hot melt adhesive compositions previously indicated, allow the elasticization of products in which they are applied, for example absorbent products, without the use of any glue, these being for example structures in which the elasticization is conventionally obtained with a elastic in vulcanized rubber fixed to the structure by means of a glue. Therefore a single material (the hot melt elastic adhesive) can replace the use of two materials (the rubber elastic and the glue to fix it) with a substantial cost saving. Normally rubber bands are covered with talc to prevent the bands from sticking to themselves in the package. Talc can cause problems when bonding with the glue.

Furthermore, the elastomeric hot melt adhesive composition can be extruded into various geometric shapes directly during the production of the products to be elasticized. It can be extruded as strands or wires, such as strips, films, etc. Structures such as strips or films can also be expanded before extrusion obtaining particularly soft elastic structures. The elasticization can also be applied according to non-linear geometries (curves) which make the anatomical adaptation of the elasticized product to the user's body particularly good. This is very difficult to achieve with ordinary rubber threads or strips. In the different geometric shapes, the hot melt elastic adhesive can be applied both in the already stretched state and in the unstretched state.

In the first case, the molten extruded product is cooled immediately after the extrusion die and stretched to the desired elongation value. In this case it should have the following properties:

- a relatively high solidification point, so that it solidifies immediately after extrusion and can be stretched elastically. An elastic stretching can only be done on a solid material, since any force applied to a molten or semi-solid material will only cause a plastic stretching in the direction of the force without any elastic tension.

- good pressure adhesion properties, since the adhesive elastic hot melt will come into contact with the substrate (or substrates) when it is already cold, i.e. at room temperature.

When the material is applied without any previous elastic stretching and brought directly into contact with the substrate (or substrates) to which it must adhere, at the exit of the extrusion matrix, the pressure adhesive behavior is less important since the bond is achieved when the material is still above room temperature. In this case, in addition to the aforementioned geometric shapes, the material can be applied to the substrate (or substrates), for example by spraying or in the form of short fibers or similar processes, obtaining a network of short interconnected fibers or a network of fibers of indefinite length that can have both a random and a geometrically regular reticular structure {eg. each fiber can form a spiral).

All these characteristics are particularly suitable for the elasticization of absorbent articles, in particular sanitary absorbent articles such as nappies, pants and absorbent pads. The use of materials applied in pre-stretched form can completely replace the rubber elastics currently used in diapers for children and adults, in sanitary napkins, etc., when it is desired to have part of the product already in conditions of elastic tension offering, as a result of their extreme versatility, the possibility of new stretch structures of practically infinite variety. In this case, another advantage of hot melt elastic adhesive over rubber bands is noteworthy. Preferred elastic hot melt compositions have a stress / strain diagram that is much flatter than a rubber band, i.e. even if the material is already under tension, additional tension (e.g. due to user movements of the absorbent article) causes a very low increase in modulus and tensile strength which is felt by the user. This is especially true for low modulus compositions.

Compositions used to provide elasticization of absorbent articles according to the invention, which are most conveniently applied in the unstretched state, are typically used to provide springback to structures or products only when the entire structure or final product is subjected to a certain deformation. during use. Normally, in this case, the typical deformations that are imparted in the use of an absorbent article are very limited, e.g. of the order of 5-50%. It is therefore necessary that the hot melt elastic adhesive contained in these structures is able to respond with an elastic return force sufficient to external tensions even at these low elongations. For these applications, it will generally be more convenient to employ higher modulus formulations.

SBC-based formulations that are used to provide elasticization according to the present invention exhibit optimal properties, typical of hot melts, ranging from compositions that can more conveniently be strongly bonded to high temperature substrates, ranging from melting point to about 50 ° C, to compositions that maintain a strong permanent adhesiveness on most substrates even at room temperature, as they are authentic pressure adhesives. Furthermore, the compositions are characterized by the maintenance of excellent elastic properties deriving from the basic thermoplastic block copolymer, which show all the typical behaviors that define an elastomeric material in the technological sense.

Hence, when they are stretched to the solid state and when the tension is released they quickly return to their initial length with only minimal permanent (plastic) deformation. The formulations which preferably have a distinct character of pressure adhesive, can also be applied at room temperature, both in the unstretched state and preferably in the stretched state for elasticization, in different geometric shapes, in various articles, and in particular absorbent hygienic products. such as panty nappies for children and adults or products for adult incontinence other than panty nappies, or absorbents for female use. Compositions having a more modest pressure adhesive character will be more conveniently applied at temperatures higher than 50 ° C, in stretched conditions or preferably in the unstretched state for the elasticization of the same structures and products. In particular, when applied in the unstretched state, they will operate under limited deformations, e.g. up to 50% (i.e. final stretched length = 1.5 times the initial length).

To show even with these low elongations a clear springback force, these formulations will generally have a higher modulus than the previous ones, the two kinds of materials being, in effect, the extremes of a formulation field in which all are excellent. hot melt adhesives and all maintain excellent elastic properties, the transition from one to the other being gradual.

As already mentioned, the compositions used according to the invention can be divided into "low modulus" formulations and "high modulus" formulations, this distinction being based on the value of their modulus and on their behavior as pressure adhesives.

Therefore the present invention makes use of a family of compositions based on at least one thermoplastic elastic block copolymer in which the SBS copolymer or copolymers preferably constitute the main copolymer or copolymers, and at least one tackifier-type resin practically compatible with the soft (rubbery) blocks ) of the aforesaid copolymer, the tackifier-type resin being mainly used to improve the adhesiveness, both at high temperature and at room temperature, of the aforesaid copolymer, and these compositions ensure the elasticization of the absorbent articles. The compositions are extrudable and in the solid state they maintain a distinct elastic behavior typical of the elastomers from which they are derived. As typical examples and without any limitation, these compositions can be extruded and applied in the form of strands, threads, strips, continuous films, fiber grids both continuous and having a finite length and in which the fibers can have a random orientation or a conformation geometrically regular, etc. As examples of applications in the field of absorbent articles, they can be used for the elasticization around the legs of panty diapers, as an elastic at the waist of the same, for the elasticization of sanitary pads and products for adult incontinence other than diapers. panties, for the internal elasticization of the structures of all the aforementioned products, for the reinforcement under mechanical tension of their absorbent cores and for imparting their stretch and elasticity, etc.

A lower modulus generally means that adhesive materials have a more aggressive tack, so low modulus formulations generally have a higher tack typical of pressure adhesives. These have the possibility of forming very strong bonds with many substrates by simple contact even at room temperature, or in any case at temperatures below 50 ° C.

The ratios between the hard and soft blocks in the basic thermoplastic elastomeric copolymer are very important for determining the elastic behavior and the mechanical and adhesion properties.

Generally, the higher the content of rigid blocks (which is conventionally indicated as "styrene content") the higher the modulus, the more evident are the elastic properties, the faster the springback after the elongation is released but it will be lower adhesiveness and especially the pressure adhesive behavior. All this is true as long as the level of rigid blocks does not become so high as to form a continuous phase, and the material becomes a rigid and no longer elastic product.

Usable SBCs may contain from 10 to 50% styrene by weight. However, when they are modified with the tackifier type resin, the behavior of the resulting composition will be clearly regulated, in terms of all the above properties, by the resulting styrene content, that is, by that of the rigid blocks in the composition; whereby it is determined both by the content of styrene in the copolymer or in the base copolymers and by the content of copolymer or copolymers in the final composition. Too low block styrene content in the final material will impart modest elastic properties. Too high a content will increase modulus and decrease adhesiveness to an unacceptable level. By increasing the final content of styrene in the composition with increasing the content of copolymer or copolymers, the viscosity will be excessively increased and therefore processability will decrease. Thus, both the content of copolymer or copolymers in the composition and their styrene content will have to be chosen so as to optimize the final styrene content and therefore all the previously mentioned properties. Optimal limits will be indicated below.

If desired, the rubber part of the SBC can itself be vulcanized (similar to the vulcanization of natural or synthetic rubbers) using suitable chemical or physical means, in particular known vulcanization systems for synthetic rubbers which are not activated by the heat. This will have the effect of increasing the modulus of the final composition.

The tackifier resin is mainly added to improve the adhesive properties of the copolymer or base copolymers, even to the point of reaching the limit of the typical behavior of a pressure adhesive. Furthermore, it improves the workability of the thermoplastic elastomer by imparting to the composition both lower absolute values of viscosity (compared to the pure block copolymer) and a rheological behavior such that, at the indicated resin values, it is practically Newtonian, i.e. such that the viscosity depends only by the temperature and does not change with the applied stress, a property that is very advantageous to facilitate processing. It is known that SBCs, which have several very interesting characteristics, can be difficult to work with due to the non-Newtonian behavior in the melt state as pure materials. This means that not only do they have a very high viscosity, but also that under the influence of temperature alone, they appear not to melt even at very high temperatures, close to 200 ° C. They may also begin to thermally decompose before showing a distinct fluid state. To make them fluid and therefore be able to process them, it is necessary to heat them and apply high mechanical stress. In any case, the workability of pure SBCs is difficult, the viscosities are high and strongly dependent on the combination of temperature and applied stress.

The basic compositions of SBC and tackifier-type resin are able to provide materials which, while maintaining very good adhesive and elastic properties, are also easily workable both for their relatively low viscosity and for their practically Newtonian rheological behavior (or acceptable Newtonian type). The latter property was measured as a constant temperature (180 ° C) change in viscosity by applying two shear stresses, 20 and 80 sec-1. The ratio of these two viscosities is hereinafter referred to as the "Newtonian index" (N.I.).

An ideal Newtonian fluid should have N.I. = 1, while a pure SBC can have, under the same conditions, a N.I. even greater than 6; that is, the viscosity variation, due only to the variation of the applied shear stress from 20 to 80 sec <-1>, is greater than six times, which can cause serious problems for the regularity and ease of processing. In order to have an easy workability it is necessary that the compositions have only limited variations of viscosity at constant temperature with the variation of the applied shear stress.

More particularly, it is preferred that the compositions exhibit a Newtonian or near-Newtonian rheological behavior, referred to the molten material at 180 ° C, by comparing the viscosities under a shear stress of 20 and 80 seconds. The preferred compositions do not have a viscosity variation higher than 50%, i.e. a viscosity ratio (N.I.) not higher than 1.5.

It has been found that the most preferred SBS-based compositions have an almost ideal Newtonian behavior, with an N.I. not exceeding 1.05.

In order to sufficiently maintain the elastic properties of the base polymer it is necessary that the tackifier-type resin is compatible mainly with, and preferably essentially only, the soft rubber blocks of the block copolymer, and does not significantly interfere with the blocks. rigid.

This depends on both the chemical nature of the resin and its molecular weight. The compatibility of the resin with rubber blocks and its incompatibility with rigid blocks can be measured, eg, by determining the variation in Tg of the soft and hard blocks caused by the addition of resin. In particular, the incompatibility with rigid blocks is considered satisfactory if their Tg (originally at 100 ° C if formed from polystyrene) does not change more than 15 ° C by adding 100 parts of resin to 100 parts of copolymer. The measurement of the two Tgs requires appropriate equipment. Consequently, both the experience of the formulators and the technical literature of the resin suppliers can be taken into account in determining which tackifier-type resins are chemically compatible with the soft blocks and incompatible with the rigid blocks of the SBCs. As used herein, the expression "essentially compatible with soft blocks only" indicates that a tackifier-type resin is compatible with the soft blocks of the copolymer and is incompatible with hard blocks, to the extent that the Tg of the blocks stiffness does not change significantly and more preferably decreases by no more than 15 ° C by mixing 100 parts of tackifier resin with 100 parts of copolymer. Preferably the Tg of the rigid blocks does not decrease at all.

More specifically, a particularly suitable tackifier resin will be chosen from the following chemical groups, which have a high compatibility with the soft blocks of SBCs and little or no compatibility with their rigid blocks:

- hydrocarbon resins

- aliphatic resins

- polyiterpene resins

- phenol terpene resins

- C5 synthetic resins

- synthetic resins C5 / C9

- rosin and rosin esters

as well as their totally or partially hydrogenated derivatives. They can be used as pure resins or also in mixtures.

When more than one resin is used, the main tackifier resin system, defined as the resin / mixture of fundamental resins present at least for a content of 50% of the total quantity of resins, is characterized by having a softening point comprised between 85 and 150 ° C, more preferably between 100 and 140 ° C (all the softening points are measured with the well known procedure called "Ring and Ball" (R & B).

Tackifier-type resins that have softening points below 85 ° C are considered to have a prevalent plasticizing effect, which may in any case be important for the development of good adhesive and elastic properties, but which must be distinguished from the tackifier effect. . This is due to the fact that in the processing of the present elastic hot melt compositions, rapid solidification of the material after extrusion is desirable, especially for compositions which need to be stretched prior to application to the substrate, which is clearly only possible with solid products. . For this reason it is desirable that the solidification point of these compositions is not less than 80 ° C and more preferably is greater than or equal to 100 ° C.

The solidification point is most accurately determined using the technique previously referred to as Dynamic-Mechanical Analysis under sinusoidal stress, which is well known in the science and technology of polymers and adhesives. According to this technique, three main rheological parameters of the material are determined as a function of temperature:

- elastic or accumulation modulus G '

- viscous or dissipation modulus G "

- angle S and its tangent, since this angle δ is the phase shift between G 'and G ".

As already indicated, the crossing temperature between G 'and G ”is assumed as the real rheological solidification point (or melting point) of the material.

For use according to the present invention, it is preferable that the crossing temperature for the composition is greater than or equal to 80 ° C and more preferably greater than or equal to 100 ° C.

The location of the cross point depends on various physical parameters of the hot melt. However, the main influence has been found to be the softening point of the main tackifier resin, and a secondary influence is due to the content and molecular weight of the copolymer. Therefore, the tackifier-type resin should preferably have a softening point between 85 and 150 ° C and more preferably between 100 and 140 ° C, provided that in any case the total composition has a real rheological solidification temperature of at least 80 ° C and more preferably at least 100 ° C.

In addition to the block thermoplastic elastomeric copolymer and the main tackifier resin, the compositions may contain other components which enhance specific properties. A more detailed description of the compositions and their main properties is given below.

For practical reasons of clarity of description, the remainder of the description will refer specifically to "low modulus" compositions and "high modulus" compositions.

The low modulus compositions are extrudable elastic adhesive compositions, based on at least one thermoplastic elastomeric copolymer in blocks, suitably modified with adequate addition of at least one resin of the tackifier type essentially compatible with its soft blocks. The polymer, or at least the polymer present in greater quantity, is a polystyrene / polybutadiene block copolymer. In the present embodiment the compositions have a modulus of 0.5 MPa or less, essentially between 0.05 MPa and 0.5 MPa and preferably less than or equal to 0.3 MPa; the modulus being measured at 23 ° C at 500% elongation (six times the initial length of the sample) with an elongation rate of 500 mm / minute. Further, the compositions have viscosities at 180 ° C and under a shear stress of 80 sec -, of 120,000 centipoise (cps) or less and preferably 60,000 cps or less and more preferably 30,000 cps or less.

The low modulus compositions will typically contain between 10 and <'> 80% by weight, and more preferably between 15 and 50% by weight, of SBC or a blend of SBC having the following characteristics:

- a molecular structure which can be multi-block, linear or radial (star) provided that it contains, per molecule, at least two rigid blocks formed by a vinylarene polymer and preferably polystyrene or poly-alpha-methyl-styrene, and at least one rubbery or soft block, the soft block of the SBC, or of the SBC present in greater quantity, being polybutadiene. The diblock content in the SBC (or SBCs) must be kept below 40% by weight.

- The aromatics content (conventionally referred to below as "block styrene content") in the SBC or SBCs can vary from 10 to 50% by weight and preferably from 20 to 50% by weight.

However, in order to maintain significant elastic properties, both the SBC content (or SBCs) in the final composition and its styrene content must be chosen so as to have a final styrene block content in the composition between 3 and 17% by weight and preferably between 6 and 15% by weight.

The composition also contains a tackifier resin or a mixture thereof essentially compatible with the soft blocks of SBC.

The preferred resins belong to the chemical groups known as:

- hydrocarbon resins

- aliphatic resins

- polyiterpene resins

- phenol / terpene resins

- C5 synthetic resins

- synthetic resins C5 / C9

- rosin and rosin esters

as well as their totally or partially hydrogenated derivatives.

The resin or mixture of tackifier-type resins has or has a softening point R&B between 85 and 150 ° C and preferably between 100 and 140 ° C. The content of this resin or mixture of resins in the composition can be between 20 and 90% by weight. However, in a preferred embodiment, the content of resin or mixture of resins previously indicated is between 30 and 55% by weight, the remainder being constituted by the other components described below, which improve the elastic properties. and / or adhesive.

In any case, both the content and the softening points of the tackifier-type resin or mixture of resins, as well as those of the additional components described below, will be chosen so that the final composition has a real rheological solidification temperature ( measured as the crossing temperature between G 'and G ") not lower than 80 ° C and preferably not lower than 100 ° C.

It has also been found that the adhesive and / or elastic and / or mechanical properties of the tackifier-type binary SBC / resin mixtures can be improved by using other components.

Adhesive properties can be improved by adding limited amounts of high molecular weight rubbers, such as polyisoprene, polybutadiene, polyisobutylene, natural rubber, butyl rubber, styrene / butadiene rubber (SBR) or styrene / isoprene rubber (SIR) and their mixtures. These polymers have a high viscosity and, in the uncured state, have modest elastic properties. However, by adding them in amounts up to 15% by weight of the formulation and using polymers with Mooney ML viscosity (1 + 4) at 100 ° C, between 30 and 70, the resulting compositions show improved pressure adhesive properties, while maintaining viscosities. within a useful range and without any negative effect on the final elastic properties. A particularly suitable SBR is the product sold by Enichem under the trade name EUROPRENE SOL 1205 and by Fina under the trade name FINA-PRENE 1205. This product is described as an SBR in which styrene is partially distributed in blocks. Of the total styrene content, equal to 25% by weight, from 15 to 18% has a block structure and the rest is copolymerized in a random way with butadiene.

Plasticization of the composition can have very good effects not only on adhesive properties and viscosity but can also improve elastic behavior by reducing internal (molecular) friction which dissipates elastic energy during ironing and subsequent release. In general, the composition can contain up to 40% by weight of plasticizer (or plasticizers).

In a preferred embodiment, the compositions contain at least one of the following plasticizers:

- up to 40% by weight of a tackifier-type resin with a softening point between 50 and 85 ° C,

- up to 20% by weight, and preferably up to 15% by weight, of a liquid hydrocarbon resin, rosin ester or polytherpene resin with a softening point not exceeding 30 ° C,

- between 3 and 30% by weight, and preferably between 5 and 15% by weight, of a paraffinic or naphthenic mineral oil having an aromatics content lower than 10% by weight, in order not to interfere with the styrenic domains.

- up to 15% by weight of a liquid polyisoprene or a depolymerized natural rubber or polyisobutylene, polybutenic or polypropylene oils and the relative liquid copolymers, eg PARAPOL (Exxon), or LIR (KURARAY).

The quantity of plasticizer must be such that the solidification temperature is not lowered below the previously indicated limit. In a preferred embodiment, the total plasticizer content in a low modulus formulation is not less than 10% by weight and not more than 40% by weight.

In low modulus compositions, the use of aromatic resins, which have no effect on the adhesive properties, which interfere with the rigid blocks of SBC and which stiffen the composition tending to increase its viscosity, is generally undesirable. , and the preferred content of aromatic resins is zero. However, limited amounts of an aromatic resin or a blend of aromatic resins, for example 20% by weight or less, more preferably 10% by weight or less, can be used as a reinforcement for compositions which have a low content. total styrene (i.e. up to 6%) or comprising significant amounts of SIS, e.g. 30% by weight or more of SIS of the total SBC. Indeed SIS copolymers, especially those which have a styrene content of less than 30% by weight, when diluted in the composition by resin and other additives, may have an inadequate (too low) modulus and modest springback characteristics, as a result both of an intrinsic modulus lower than SIS, and of the low concentration of styrene, which acts as a physical curing agent. In this case the aromatic resin can both increase the modulus to a useful value and increase the density of the rigid domains, which are swollen by the resin. Useful aromatic resins have a softening point between 115 and 160 ° C and are chemically identified as derivatives of styrene, alpha-methyl-styrene, vinyl-toluene, coumaroneindene and related copolymers; alkyl-aryl resins, etc.

In addition to the components previously discussed, the compositions can contain the normal additives such as antioxidants, U.V. inhibitors, pigments and coloring materials, mineral fillers, etc., generally in a total amount up to 20% by weight.

Without limitations as regards the process and the most suitable use, the low modulus formulations are typically used in the stretched state and with typical elongation values of 400-1000%. They are characterized by very high elongation at break (over 1100% and often over 1400%) and very good adhesive properties, often with pressure adhesive properties.

To simulate the application of the composition in an absorbent article, the pressure adhesive properties are measured with stickiness values ("Loop tack" or "Quick Stick Tack") and as a peel value at 90 ° according to the standard FINAT Test methods Method N ° 9 for the loop tack and FINAT Test Method N ° 2 for the 90 ° peel, modified as described below. - For both tests the compositions are applied on a polyester film with a grammage of 80 g / m <2>.

- The adhesive properties, both as a loop tack and as a 90 ° peel, are determined on a polyethylene film fixed on the standard plate.

- Loop tack values are determined as peak values, ignoring the initial peak.

- The 90 ° peel is evaluated after a compression with a 400 g roller passed back and forth, i.e. with two passes, one in each direction, and the measurements are performed 20 minutes after the establishment of the contact between the adhesive and the polyethylene. The compositions used according to the invention generally have a loop tack greater than 5 N / cm and a 90 ° peel greater than 7 N / cm (separation speed = 300 mm / min). The materials that can be usefully adhered and applied at room temperature to form a hygienic product are considered to have a loop tack on polyethylene greater than 2.5 N / cm and a 90 ° peel greater than 3 N / cm.

The high modulus formulations are elastic, adhesive, extrudable compositions, similar to those previously described, and having the following characteristics:

1) They have a modulus higher than 0.5 MPa and more preferably not lower than 1 MPa and up to 10 MPa.

2) At 180 ° C and applying a shear stress of 80 sec-1, they have viscosities of 80,000 cps or less, preferably 50,000 cps or less and more preferably 35,000 cps or less.

3) They are based on the same types of SBC as previously indicated, but which have a final content of styrene blocks from 15 to 30% by weight and preferably between 15 and 25% by weight.

4) The SBC or the SBC mixture that is used has a diblock content not higher than 25% and preferably not higher than 10%. The most preferred polymers are those that do not contain diblocks, such as those marketed by DEXCO Co under the VECTOR brand.

The preferred SBC (or SBCs) contains between 20 and 50% by weight of styrene and the preferred content of SBC or mixture of SBC in the composition is between 35 and 75% by weight, provided that it is the content of styrene and of the SBC and its quantity present in the composition are such as to satisfy the requirements of point 3), as content of final styrene.

6) The tackifier resin or mixture of resins has / have the same chemical and physical characteristics previously indicated. However, the preferred content is between 20 and 40% by weight.

7) The content of high molecular weight rubbers, such as polyisoprene, polybutadiene, polyisobutylene, natural rubber, butyl rubber, SIR and SBR must not exceed 10% by weight, and preferably is less than 5% by weight with respect to the total composition .

8) The total content of plasticizers, as previously indicated, must not exceed 25% by weight.

9) Aromatic resins or mixtures of aromatic resins are preferably avoided due to their negative effect on adhesive properties and on the stress / strain ratio (more inclined stress / strain diagrams; appearance of a yield point and, consequently, of a plastic deformation not recoverable). However, as in the previous case, these substances can be present in the composition in quantities up to 20% by weight with acceptable properties, provided that the non-adhesive / non-elastomeric part of the composition does not exceed 50% by weight of the total. This non-adhesive / non-elastomeric part is formed by the sum of the total content of styrene in the composition plus the content of resin or aromatic resins.

The other requirements and other possible additional components and additives remain the same. In particular, it is still necessary that the real rheological solidification temperature (measured as the crossing point between G 'and G ") is not lower than 80 ° C and preferably not lower than 100 ° C.

Still without wishing to limit the field of processing and use, these high modulus compositions are often applied in the unstretched state, especially those having a modulus greater than 1 MPa. This preferred use is due to the fact that they are able to ensure sufficient springback forces even with low deformations (typically not exceeding 50%) which are often encountered during the use of deformable hygienic articles that can be suitably made elastic and resilient in this way. This is also partly due to the fact that the assembly with the composition in the stretched state implies the need to apply the composition at a temperature close to room temperature, and therefore requires that it adheres strongly to the substrates even under these conditions (properties of pressure adhesive). The pressure adhesiveness character of the adhesives tends to be inversely proportional to their elastic modulus.

However, some of the high modulus compositions according to the invention still maintain an evident and useful pressure adhesive behavior (loop tack on PE> 2.5 N / cm; 90 ° peel on PE> 3 N / cm) and they can also be applied at room temperature and in the stretched state with typical elongation up to 400%, since the elongation at break of these compositions typically exceeds 900%.

The adhesive properties are measured under the same conditions adopted for the low modulus compositions.

The unexpectedly good level of elasticity of the compositions according to the invention can be measured as retention of the tensile strength after cyclic deformation. This is a test that simulates conditions of use of a hygienic article, in which the movements of the user can cause further and subsequent elongation of the elasticized parts which, for optimal behavior, must recover their initial length with only a minor loss. of tensile strength. All the compositions are tested starting from a pre-stretched state and are brought to a further elongation of about 15% of the initial stretched length, to simulate the user's movements. The compositions are cyclically stretched and released 50 times from the initial stretch to the further stretched stretch.

The percentage retention of the tensile strength at an elongation equal to the initial one, after 50 ironing cycles at a speed of 500 mm / minute, compared with the initial tensile strength, is taken as a measure of the elasticity of the material. Tests are carried out at room temperature on 2.54 cm wide tapes.

The low modulus compositions are stretched to an initial elongation typical for intended applications of 800%, and then further cyclically stretched and released 50 times between 800 and 920% (i.e. between 9 and 10.2 times the initial length of the sample).

The high modulus compositions are tested in the same way but with an initial elongation typical of the expected applications of 300%, and with 50 cycles of further elongation and release between 300 and 345%.

The expression retention of tensile strength after 50 cycles "as used herein refers to the test described above. A vulcanized natural rubber elastic manufactured by the company JPS Elastomerics, which is used for elasticization around the legs of panty diapers, and applied with an initial stretching of 220%, it is taken as a reference and is cyclically deformed 50 times between 220 and 255%. It has been found that in these conditions the elastic in vulcanized natural rubber, after 50 cycles, has an average retention of the tensile strength equal to 47% of the initial tensile strength at 220% This retention value of the tensile strength is considered indicative of good elastic behavior.

More generally it has been observed that materials which do not lose more than 60% of their initial tensile strength under these test conditions, exhibit good elastic behavior, a retention of tensile strength less than 40%, represents an unsatisfactory elasticity, indicated by a slow return to the initial length after the release of the traction, from a high permanent plastic deformation, etc.

All of the aforementioned thermoplastic elastomeric compositions can be fully or partially deactivated in the manner described by applying a suitable amount of heat and / or pressure. Depending on the use of these compositions to provide the elasticization of an article, suitable elements are provided in the processing equipment, to apply the quality of heat and / or the necessary pressure to those parts of the thermoplastic elastomeric composition which are to be deactivated. For example, in the manufacture of an absorbent article, the thermoplastic elastomeric composition may be applied to a substrate in the form of a thread or strips under elastic tension, by means of a suitable extrusion device, and then passed through closely spaced rolls adapted to apply variable levels of temperature and pressure. The elastic tension can therefore be maintained in some areas of the composition and deactivated in other areas.

The extrusion of elastomeric hot melt adhesives of the type indicated above, in the form of threads and strips is described in more detail in our application filed by us on the same date and entitled "Adhesive composition, relative process and equipment".

According to an embodiment of the invention, the application of heat and / or pressure in the manner described above can be adopted to improve the adhesion of the composition to a substrate, as already mentioned, in no way are all thermoplastic elastomeric compositions adhesive. at room temperature, and in cases where it is desired to use a composition that is not adhesive at room temperature, the adhesive properties can be improved by applying just enough heat and / or pressure so that the elastic tension can be completely or partially deactivated. However, since the deactivation / improvement of adhesive properties occurs only in limited areas of the composition, e.g. at a series of points along the strip or thread of the composition applied to the substrate, the composition will adhere to the substrate in correspondence to these areas that have been subjected to heating and / or pressure, while there will remain areas that can still ensure the necessary elasticization. The same effect can be exploited to improve the adhesion of thermoplastic elastomeric compositions which are adhesive at room temperature, e.g.

when using such compositions on difficult-to-bond substrates. This point deactivation can be provided by means of a suitable cylinder, e.g. a toothed surface cylinder.

Point deactivation as described above, to improve adhesion in areas where elastic properties are required, can be used in conjunction with complete deactivation of elastic tension in other areas where elastic properties are not required. Separate cylinders can be used for spot deactivation to improve adhesive properties and for complete deactivation: Alternatively, with a suitable cylinder design both functions (improved adhesion and complete deactivation) can be performed with the same cylinder. For example, the cylinder can be equipped with sectors which have different effects depending on whether spot deactivation is required to improve adhesion or complete deactivation to deactivate elastic tension.

As previously mentioned, the present invention also provides an elasticized article, e.g., a stretch absorbent article, in which elasticization is ensured by a thermoplastic elastomeric composition part of which has been deactivated in the manner described.

The absorbent item can be a baby panties diaper, incontinence adult panty diaper, incontinence garment, sanitary napkin, panty protector, etc. The adhesive composition can ensure the elasticization of the article in, for example, the waist belt or the leg area of a panty diaper or generally in any area where elasticization is required. Other articles which may be similarly resilient include non-absorbent articles such as masks, aprons and gloves, e.g. for surgical use, and preferably of the disposable type.

The present invention will now be illustrated with reference to a disposable hygienic article such as a panty diaper, although this cannot be considered in any way limiting the general purpose of the invention. In the attached drawings:

Figure 1 is a perspective view of a panty diaper.

Figure 2 is a partially sectioned plan view of the disposable panty diaper of Figure 1, opened in planar configuration.

Figure 3 is a schematic representation of an apparatus used to produce a disposable hygienic product, more particularly a disposable baby diaper;

Figure 4 is a cross section of a toothed surface roller used for spot deactivation.

Panty diapers having many different basic configurations are known in the art and reference may be made, for example, to U.S. Pat. Re 26152, to U.S. Pat. 3860003, to the European patent application n ° 82200801.7, to the U.S. patent. 4324245, to U.S. Pat. 4337771, to U.S. Pat. 4352355 and U.S. Patent 4253461.

The panty diaper illustrated in Figure 1 is based on the disposable panty diaper design described in U.S. Pat. 3860003. The panty diaper illustrated in Figure 1 is for illustrative purposes only and it will be understood that the present invention can be applied to any other type of panty diaper.

Figure 1 illustrates a panty diaper generally indicated at 10 which is viewed in perspective in a configuration as if worn by a child. The disposable panty diaper 10 comprises a front part 11 and a rear part 12 with a crotch part 13 interposed between the two. When used, the crotch part 13 is placed between the child's legs and the front part 11 and the rear part 12 are arranged, respectively, along the lower front and rear parts of the user's trunk. The topsheet 15 constitutes the internal surface of the disposable panty diaper 10, while the backsheet 14 constitutes its external surface. Side flaps (elements around the legs) 16 fit around the user's thighs. In use, the front lifeline 17 and the rear lifeline 18 are placed at the user's waist areas on the front and rear parts of the user's torso, respectively. The disposable panty nappy 10 is held in place around the wearer with a fastening tape 19. The outer edge of the waistline 29 is shown in Figure 1 as the top edge of the disposable panty nappy 10. Figure 2 is a plan view partially sectioned of the disposable diaper 10 open in a planar configuration. The topsheet 15 is, in this illustration, the upper surface of the panty diaper, while the backsheet 14 is its lower surface. The absorbent element 21 is interposed between the topsheet 15 and the backsheet 14.

As illustrated, the disposable panty diaper 10 is generally symmetrical about a longitudinal center line 25 and a transverse center line 26. Although this is a preferred configuration, the disposable panty diaper 10 need not be symmetrical. An asymmetrical orientation around a transverse center line 26 may also be useful, as when the crotch portion 13 is moved towards the front lifeline 17.

The disposable panty diaper 10 is equipped with elastic elements 22 arranged in the lateral margins, and are generally parallel to the longitudinal central line 25. In the illustrated embodiment, two elastic elements 22 are placed on both sides of the disposable panty diaper 10; single or multiple elastic elements can also be used.

The fastening tapes 19 are secured to the disposable panty diaper 10 at the rear waistline 18.

The front elastic element of the waist 23 and the rear elastic element of the waist 24 are located, respectively, in the front waistline 17 and in the rear waistline 18 and at the outer edge of the waistline 27. In the embodiment illustrated in the Figures 1 and 2, the disposable panty diaper 10 comprises elastic waist elements in both the front and rear waist lines. However, it is possible to have elasticization only in the anterior or posterior lifeline.

The stretch 23 and 24, as illustrated in Figures 1 and 2, extends practically across the entire side width of the disposable nappy 10. The stretch 23 and 24 can only extend across a portion of the width of the panty diaper. Preferably it extends across most of the width of the disposable diaper. The elasticization 23, 24 consists of a thermoplastic elastomeric composition, preferably a hot melt elastomeric adhesive, as described herein.

A main function of the backsheet 14 is to prevent bodily fluids from escaping from the disposable panty diaper 10 soiling the user's outer clothing and other surfaces in contact with the disposable panty diaper. As the backsheet 14, any non-irritating and flat pliable material that is impermeable to body fluids can be used. Conventional materials can be used as the backsheet, for example those described in the aforementioned patents and applications relating to panty diapers. A preferred backsheet is a polyethylene film having a thickness between about 0.012 and about 0.051 min.

The breathable backsheets (i.e. backsheets that allow the passage of vapor and air while delaying the passage of the liquid) useful in the present invention are described, for example, in patents US 3156242, US 3881489, US 3989867, US 4341216.

The size of the backsheet 14 is imposed by the precise design adopted for the panty diaper, and by the size of the child intended to wear it; it can be easily ascertained by those who know the subject.

The topsheet 15 can be made of any flat, pliable, soft-looking, non-irritating (to the user's skin) material. It has the purpose of coming into contact with the user's skin, receiving the fluid flows, allowing the flows to pass through it quickly reaching the absorbent element, and to isolate the user's skin from the fluids found in the absorbent element. . To contribute effectively to this latter function, the topsheet is preferably hydrophobic.

The topsheet 15 may be of porous paper made from natural or synthetic fibers or their blends, a non-woven fabric made from natural or synthetic fibers or their blends, a plastic film with apertures, a porous foam, or the like. Examples of suitable topsheets are described in the aforementioned patents and in the aforementioned patent applications.

A preferred topsheet is a spunbonded non-woven polyester fabric, produced from fibers of about 2.2 - 2.5 denier, having a grammage of 17 g per m2. Another preferred topsheet has a grammage of 22 g / m2 and comprises 65% (by weight) 1.5 denier polyester staple fibers (such as Kodel Type 411 polyester fibers, manufactured by Tennessee Eastman. Corporation, Kingsport, Tennessee) 15% 1.5 denier rayon staple fibers, crimped; and 20% of binder consisting of an acrylic copolymer (such as Celanese CPE 8335 produced by Celanese Corporation of Charlotte, North Carolina). "Staple length" in this case means fibers having a length of at least 15 m.

Another preferred type of topsheet is made from polypropylene fibers which have been carded and thermally bonded in an open design. Fibers of 3.8 era and 1.5 to 3.0 denier lengths are suitable. A preferred topsheet of this type has a weight of 24 gsm.

Suitable topsheets can also be constructed from plastic films with apertures such as those described in US 4342314, US 4341217 and US 3929135.

As in the case of the backsheet 14, the size of the topsheet 15 is imposed by the precise design chosen for the panties diaper.

The absorbent element 21 can be any means which is generally compressible, which adapts to the shape, is not irritating to the user's skin and is capable of absorbing and retaining fluids.

The absorbent member 21 can be manufactured from a variety of materials commonly used in disposable absorbent articles, and which are described in the aforementioned patents. Examples of suitable absorbent materials include crepe cellulose wadding, absorbent foams, absorbent sponges, super absorbent polymers and, preferably, chopped, air-laid wood pulp fibers commonly referred to as absorbent fluff. An absorbent fluff having a density of between 0.05 and 0.175 g per cm2 is generally acceptable.

As in the case of the backsheet 14 and the topsheet 15, the size of the absorbent element 21 is imposed by the exact design chosen for the panty diaper.

Optionally, the absorbent member 21 may be wrapped on one or both planar surfaces with a liner sheet (not illustrated in the drawings) comprising any permeable material well known to those familiar with this technique, such as wet-resistant wadding. When used, the liner sheets are generally coextensive with the absorbent member 21 and of the same size as it or folded over and around its laterally extending edges. The cover sheets may optionally be attached to the absorbent core 21 by any means well known to those familiar with this technique.

The absorbent element 21 is interposed between the backsheet 14 and the topsheet 15. The design of the selected panty diaper determines whether or not the three elements are of the same size although, in general, the backsheet 14 or the topsheet 15 or both extend beyond the margins of the absorbent element 21.

Optionally, the backsheet 14 can be fixed to the absorbent element 21 by any suitable means (not shown in the drawings) well known to those familiar with this technique. Examples of suitable means are parallel strips of adhesive (such as hot melt adhesive) and double sided tape; each extends essentially the entire longitudinal length of the absorbent element 21. The backsheet 14 and the absorbent element can be bonded together using the hot melt elastomeric adhesive as described herein.

The elastic elements 22 serve to contract or collect the fins (longitudinally extending edges) of the disposable panty diaper 10 and keep them in contact with the legs of the user, thus ensuring an improved fit and reducing the loss of fluid from the panty diaper. The elastic elements are produced with a thermoplastic elastomeric composition, preferably a hot melt elastomeric adhesive, as described herein.

As can be seen in Figures 1 and 2, the elastic elements 22 extend for the entire longitudinal length of the disposable panty nappy 10, but after being applied to the panty nappy 10 in the stretched state, they are subjected to a heat and / or heat treatment. compression in defined areas, as described herein to deactivate elastic tension.

According to a configuration of the invention, the elastic elements 22 are subjected to total deactivation in the areas adjacent to the front and rear elastic elements 23 and 24, and to point deactivation along their remaining extension. As shown in Figure 2, the elastic elements 22 are subjected to total deactivation in the areas "A" and to point deactivation in the area "B". As noted previously, the dot deactivation has the effect of improving the adhesion of the elastic elements to the topsheet 15 of the diaper. The diaper can be manufactured in an apparatus described in more detail with reference to Figure 3 and deactivation can be accomplished using a roller with toothed surface described in more detail with reference to Figure 4.

The elasticization of the panty diaper can be ensured by the thermoplastic elastomeric composition as described herein, in the form of yarns, strands, tapes, strips, continuous films, fiber grids either continuous or having a finite length and in which the fibers have a random orientation or a geometrically regular orientation. The wires or strips can be linear or non-linear (curved) in shape.

Figure 3 is a schematic representation of an apparatus illustrating the apparatus and materials used to form a disposable baby diaper. A non-woven fabric used as a topsheet for the disposable baby diaper is fed from the roller 30 as material 11. The material 11 is passed in the vicinity of an apparatus for applying the hot melt adhesive by means of a first roller idler 12 provided with a non-adherent coating, for example made of silicone. As shown in Figure 3, this apparatus is particularly suitable for applying strands of elastic hot melt adhesive and comprises an applicator which extrudes strands of hot melt adhesive onto a conveyor belt 6 which moves in the direction of the arrow. For greater clarity the wires are not highlighted in figure 3.

The threads are cooled by a fan 7 positioned below the conveyor belt and are then transferred onto the material 11 which is brought into contact with the threads by means of the first idle roller 12 covered with silicone. The desired degree of elastic elongation of the threads at the moment of application to the material 11 is obtained by means of the speed difference between the conveyor belt 6 (which is also the speed of the threads before application) and the material 11 itself.

The threads can optionally be provided with a curved geometry with respect to the material 11, while they are transferred to the material 11 itself, by means of one or more combs 9 movable in a plane parallel to the plane of the material 11, the movement of the combs 9 being obtained by by means of a cam 10. Curved geometry can be useful, for example, in the case where the thread must go to form the elasticization around the legs for a diaper, but it is not essential and is not used in the diaper shown in figure 2 .

As noted previously, the apparatus for applying the hot melt adhesive shown in Figure 3 is suitable for applying threads of elastic hot melt adhesive due to the fact that it allows the elastic elongation of the threads during application to the material. 11. A non-elastic hot melt adhesive can in any case be applied in the form of threads directly to the material 11 using a conventional extrusion apparatus.

Following the application of the hot melt adhesive threads, the material passes through the silicone-coated rollers 14 which press the threads onto the surface of the material 11, then reaching the deactivation unit 15. The deactivation unit can for example consist of a roller with a toothed surface, described in greater detail below with reference to Figure 4, which acts in combination with a smooth counter-roller. The roller with toothed surface produces areas of total deactivation corresponding to "A" in Figure 2 and areas of deactivation in points corresponding to "B".

After deactivation, the material <'> with the threads adhering to it reaches the point 55 where it is combined with a layer of absorbent material coming from a feeding unit and a cutting unit 50 and with a backsheet coming from a roller 60 to form a composite material. The composite material then passes through an optional crimp unit 60 in which the various elements are pressed together in order to increase adhesion, particularly around the perimeter.

The material then passes through a final cutting unit 90 to form the finished product. It should be noted that in various stages of this process the components of the finished product receive the application of non-elastic hot melt adhesive 110 and pass through vacuum apparatuses 100.

As already noted, the deactivation unit 15 comprises a roller with a toothed surface as shown in FIG. 4 and a counter roller with a smooth surface. Figure 4 shows a cross section of the roller with a toothed surface which is provided at two portions of its surface with transverse grooves 16 extending parallel to the generatrix of the cylinder. The roller also has two smooth portions 17 of its surface. When the roller comes into contact with a substrate, for example the material 11, the point deactivation is carried out at the crests between the grooves 16, while the total deactivation is carried out at the smooth portions 17. The relative dimensions and positions of the grooved and smooth portions of the roller are made so that the total and dot deactivation areas on the finished product are achieved in the desired manner. Consequently, when, for example, the deactivation unit is used in the production line of a diaper like the one shown in Figures 1 and 2, the smooth sectors totally deactivate the areas that will constitute the ends of the diaper (the sections "A "in Figure 2), while the portions provided with grooves will perform the deactivation in points (which can be complete or partial) in the area that will become the median portion of the diaper (section" B "in Figure 2) in order to improve the adhesion to the substrate.

In the roller shown in Figure 4, each smooth portion 17 consists of a separate element 18. The distance between the outer surface of the element 18 and the axis of the cylinder can be adjusted before the apparatus is put into operation by means of thin shims 19 inserted between the separate elements 18 and the remaining part of the roller 22; this means that the roller can exert different pressures on the yarns with the portions provided with grooves (toothed) and with the smooth portions. The cylinder surface temperature can be independently adjusted in the grooved and smooth portions by means of electric heating elements 20 under the control of probes 21, the heating elements and probes being incorporated into the roll structure.

The compositions for use according to the invention are illustrated by the following examples, which are not to be considered in any way limitative of the invention. In the case of registered products, the details on their nature and composition are those provided by the manufacturer.

The compositions of all examples 1 to 5 are suitable for the elasticization of absorbent articles according to the invention, with deactivation of the elastic tension in areas where the elastic properties are not required. The compositions of all examples 1 to 5, when applied in the molten state between plastic and / or cellulosic materials, in an amount corresponding to 5 g / m ^, show a connection force well above 0.5 N / cm .

The elastic properties are also judged by the following procedure: the compositions in the form of strips with a width of 2.54 cm, are tested at 23 ° C and at an ironing speed of 1000 mm / minute, with three cycles of elastic hysteresis between zero and a typical elongation possible in use, i.e. 800% for low modulus compositions and 300% for high modulus compositions. The elastic energy of each cycle, evaluated as EUROPRENE SOL 1205 is a styrene / butadiene rubber (SBR) produced by ENICHEM. (The FINAPRENE 1205 product produced by FINA is similar and can also be used). It is described as a solution polymerized SBR having a Mooney ML viscosity (1 4) at 100 ° C, equal to 47 and a total styrene content of 25% by weight. This styrene is partially (typically between 15 and 18%) distributed in blocks, with the remainder randomly copolymerized with butadiene. Randomly copolymerized styrene gives the rubbery parts of the molecule the chemical structure of an amorphous SBR, which contributes to the development of particularly good pressure-sticking characteristics.

DERCOLYTE A 115 (the main tackifier type resin) is manufactured by DRT. It is a polyterpene resin derived from alphaapinene, having a softening point of 115 ° C.

FORAL 85-E is a tackifier-type resin consisting of a hydrogenated glyceric ester of rosin, produced by HERCULES Co. It has a softening point of 85 ° C.

HERCOLYN D-E is a liquid methyl ester of rosin manufactured by HERCULES.

IRGANOX 1010 is a phenolic antioxidant produced by CIBA-GEIGY.

The composition results to have the following properties:

- total content of styrene = 10.6% by weight, of which 10.1% is in the blocks

- viscosity at 180 ° C at 80 sec ^ = 20520 cps

- modulus at an elongation of 500% - 0.182 MPa (low modulus)

- elongation at break greater than 1400% (1400% is the maximum elongation measurable with the equipment used for this determination) - rheological solidification temperature (crossing point of G 'and G ") = 125 ° C

- loop tack on PE = 8.5 N / cm

- 90 ° peel on PE = 16.3 N / cm

- retention of tensile strength after 50 cycles between 800 and 920% = 59.8%

- retention of elastic energy after 3 hysteresis cycles between zero and 800% = 57.7%

- Newtonian index (N.I.) = 1.05.

The composition exhibits extremely good elastic and adhesive properties and is considered completely suitable for the elasticization of structures, particularly of absorbent sanitary articles. It is easily workable, that is extrudable, solidifies quickly (it can be stretched during extrusion) and has good adhesive characteristics under pressure, which allows the formation of strong bonds by simple contact with many substrates even at room temperature.

Example 2

The formulation is:

CARIFLEX TR-4113 S 38.8% by weight

FINAPRENE 1205 8.9%

DERCOLYTE At 15 26%

FORAL 85-E 26%

IRGANOX 1010 0.3%

The following properties were measured:

- total content of styrene = 11.5% by weight, of which 10.9% is in blocks

- viscosity at 180 ° C and 80 sec-1 = 28180 cps

- modulus at an elongation of 500% = 0.188 MPa (low modulus)

- elongation at break greater than 1400%

- rheological solidification temperature = 120 ° C

- loop tack on PE = 8.6 N / cm

- peel at 90 ° C on PE = 10.4 N / cm

- retention of tensile strength after 50 skies between 800 and 920% 59.1%

- retention of elastic energy after 3 hysteresis cycles between zero and 800% = 48.3%

- Newtonian index (N.I.) = 1.01.

The composition is similar to that of Example 1, the main variant being the fact that about 50% of the high softening point tackifier resin has been replaced by a lower softening point resin and the only plasticizer is l oil contained in CARIFLEX TR-4113 S (12.2% by weight of the composition). However, it has been found that the composition still maintains a very high solidification temperature, solidifies quickly and retains excellent elastic properties of pressure adhesiveness and excellent workability, so that it can be extruded easily and immediately stretched even by 800%, in the form of threads. very thin (diameter = 0.4 mm) which can be applied for the lateral elasticization of an absorbent product.

Example 3

A different system based on radial SBS is tried, more precisely a mixture of an SBS with a relatively low hard block content and a SBS with a relatively high hard block content. The wording is as follows:

FINAPRENE 415 17.7% by weight

FINAPRENE 401 7.0%

FINAPRENE 1205 8.0%

ZONATAC 115 LITE 45.8%

FORAL 85-E 6.3%

HERCOLYN D-E 4.0%

SHELLFLEX 4510 FC 11.0%

IRGANOX 1010 0.2%

m which

- FINAPRENE 415 and FINAPRENE 401 are radial SBS copolymers produced by FINA. Both are believed to contain less than 20% diblock and are formed with a star structure of four SB blocks chemically bonded at a central point across the butadiene blocks. FINAPRENE 415 contains 40% by weight of block styrene and FINAPRENE 401 contains 22% of block styrene.

ZONATAC 115 LITE is a hydrocarbon modified tackifier-type terpene resin with a softening point of 115 ° C manufactured by Arizona Co. It is believed to be based on styrene-modified liraonene.

SHELLFLEX 4510 FC is a naphthenic mineral oil produced by SHELL which is believed to have an aromatics content of less than 5%.

The following properties were measured:

- total content of styrene = 10.6% by weight, of which 10.1% is in blocks

- viscosity at 180 ° C at 80 sec_l = 12810 cps

- modulus at 500% elongation = 0.223 MPa (low modulus)

- elongation at break> 1300%

- rheological solidification temperature - 107 ° C

- loop tack on PE = 6.4 N / cm

- 90 ° peel on PE = 14 N / cm

- retention of tensile strength after 50 cycles between 800 and 920% = 50%

- retention of elastic energy after 3 hysteresis cycles between zero and 800% = 44.9%

- Newtonian index (N.I.) = 1.04.

The composition has excellent properties typical of an extrudable, elastic and easily workable adhesive material.

Example 4

The following high modulus composition was prepared with the formulation:

VECTOR 4461-D 44.8% by weight

ZONAREZ 7115 LITE 37%

FORAL 85-E 5%

ZONAREZ ALPHA 25 3%

PRIMOL 352 10%

IRGANOX 1010 0.2%

in which:

VECTOR 4461-D is a linear SBS copolymer having 43% by weight of styrene and free of diblocks, manufactured by DEXCO Co.

ZONAREZ 7115 LITE is a polyterpene tackifier resin, having a softening point of 115 ° C, derived from limonene, produced by ARIZONA Co.

ZONAREZ ALPHA 25 is a tackifier-type liquid resin (softening point = 25 ° C) obtained from alpha-pinene having a very good plasticizing effect. It is produced by ARIZONA Co.

PRIMOL 352 is a plasticizing paraffinic mineral oil produced by EXXON which is believed to contain no aromatics.

The following properties are measured:

- total content of block styrene = 19.3% by weight

- viscosity at 180 ° C at 80 sec - · * · = 16810 cps

- modulus at 500% elongation = 1.07 MPa (high modulus)

- elongation at break = 987%

- rheological solidification temperature = 111 ° C - loop tack on PE = 4.3 N / cm

- 90 ° peel on PE = 6.5 N / cm

- retention of tensile strength after 50 cycles between 300 and 345% = 67.5%

- retention of elastic energy after 3 hysteresis cycles between zero and 300% = 63.3%

- Newtonian index (N.I.) = 1.05.

The composition is a good elastic material, especially useful with low elongations. It has acceptable characteristics of semi-adhesive under pressure so that it can be fixed on materials even at room temperature in the stretched state.

Example 5

The formulation is:

VECTOR 4461-D 54.8% by weight

ECR 368 35%

FIRST! 352 10%

IRGANOX 1010 0.2%

in which:

- ECR 368 is a hydrogenated hydrocarbon tackifier type resin, produced by EXXON and having a softening point of 100 ° C.

The following properties were measured:

- total content of block styrene = 23.56% by weight

- viscosity at 180 ° C at 80 sec-l = 34000 cps

- modulus at 500% elongation = 1.61 MPa (high modulus)

- elongation at break = 947%

- rheological solidification temperature = 114 ° C

- loop tack on PE = 1.3 N / cm

- 90 ° peel on PE = 2.6 N / cm

- retention of tensile strength after 50 cycles between 300 and 345% = 62.3%

- retention of elastic energy after 3 hysteresis cycles between zero and 300% = 38.3%

- Newtonian index (N.I.) = 1.05.

The composition was formulated to maximize modulus while maintaining acceptable elasticity and good adhesiveness at temperatures above room temperature. This material is more conveniently used in the unstretched state and fixed directly at a temperature below 50 ° C. It gives good springback forces even at very low elongations, eg the elongation modulus of 20% = 0.236 MPa. However, it works well in the stretched state, eg at an elongation of 300%, and exhibits adhesion properties on PE which are not negligible even at room temperature.

Example 6

This example refers to the stress / strain diagrams of the compositions of Examples 1 to 5. Hot melt elastic compositions should desirably have a much flatter stress / strain diagram than a rubber band, that is, if when they are already under tension they undergo a further stretching (due for example to the movements of the user of the absorbent article) this causes only a very low increase in modulus and tensile strength which is felt by the user. This is especially true for low modulus compositions and can be seen by measuring the average modulus increase for a given elongation. The low modulus compositions, which are typically used in the already stretched state, are evaluated as an average modulus increase for every 100% increase in elongation between 0 and 800% (nine times the initial length) i.e. the total increase in modulus divided by 8.

Referring to the low modulus compositions mentioned in the previous examples, the results are as follows:

EXAMPLE N ° AVERAGE INCREASE OF THE MODULE FOR A 100% ELONGATION 1 0.044 MPa / 100% elongation 2 0.045 MPa / 100% elongation 3 0.063 MPa / 100% elongation The high modulus compositions of examples 4 and 5, which are generally used at unstretched state or in any case with lower elongations, are examined as an average modulus increase for a 100% increase in elongation between zero and 300% final elongation:

EXAMPLE N ° AVERAGE INCREASE OF THE MODULE FOR A 100% ELONGATION 4 0.169 MPa / 100% elongation 5 0.284 MPa / 100% elongation As a comparison, an elastic in vulcanized natural rubber, used for the elasticization around the legs of the panty diapers, also if applied at a much lower elongation (typically 220%) it presents, between zero and 220%, an average modulus increase of 0.89 MPa per 100% elongation.

It is possible to compare the behavior of a natural rubber elastic and a low modulus composition as described below.

In the case of the rubber band, even limited movements of the user that cause, for example, a stretching of the elasticized parts with a further elongation of only 10%, will cause an average increase in the modulus of about 0.09 MPa. Using a low modulus composition the modulus increase will be about 20 times smaller, and even with stronger high modulus compositions, it will be several times smaller, so that the movements of the user of an absorbent article elasticized with the compositions described in the present invention are much freer. Consequently, low modulus and low modulus variation under voltage are a clear advantage in these applications.

Example 7

The formulation is:

TUFPRENE A 30.0% by weight

ESCOREZ CR 368 55.0%

CATENEX P941 10.0%

KRISTALEX F100 5.0%

with the addition of 0.2 parts per 100 parts by weight of the above composition, of the antioxidant IRGA-NOX 1010,

in which:

TUFPRENE A is a linear SBS manufactured by Asahi Chemical Co. and containing 40% by weight of styrene. The diblock content is not specified by the manufacturer.

ESCOREZ CR 368 is a modified hydrogenated hydrocarbon resin produced by Exxon with a softening point of 100 ° C.

CATENEX P941 is a paraffinic mineral oil manufactured by Shell which is believed to have an aromatics content of less than 5% by weight.

KRISTALEX F 100 is an aromatic resin based on a-methyl styrene and styrene produced by Hercules and having a softening point of 100 ° C.

The main properties can be summarized as follows:

- total block styrene = 12% by weight

- viscosity at 180 ° C at 80 sec "l = 5620 cps

- modulus at 500% elongation = 0.204 MPa (low modulus)

- elongation at break> 1300%

- rheological solidification temperature (crossing point of G 'and G ") = 106 ° C

- loop tack on PE = 0.7 N / cm

- 90 ° peel on PE = 0.8 N / cm

- retention of tensile strength after 50 cycles between 800 and 920% = 21.3%

- retention of elastic energy after 3 hysteresis cycles between zero and 800% = 25.0%

- Newtonian index (N.I.) = 1.16.

Processability, as seen from viscosity and the Newtonian index, has been found to be acceptable although the Newtonian index is high for an SBS-based composition. The formulation has modest pressure adhesive characteristics and values of 0.7 N / cm for the loop tack and 0.8 N / cm for the 90 ° peel confirm that it is practically not usable as an adhesive with a low modulus of elasticity, intended for be applied in the stretched state, in the manufacture of absorbent sanitary articles. However, when used with the dot deactivation technique as described above, the adhesive properties can be improved to an acceptable level.

A method of providing elasticization in defined zones of an article which comprises applying a thermoplastic elastomeric composition under elastic tension to the article and partially deactivating or deactivating elastic tension in the composition outside said defined zones.

Method according to claim 1, wherein the spring tension is deactivated by (i) heating to a temperature corresponding at least to the inversion temperature between G1 and G "; or

(ii) heating to a temperature below the inversion temperature between G 'and G "with the application of a pressure at least equal to the value of G' at that temperature.

3. A method according to claim 1 or 2, for providing elasticization of an absorbent article.

4. A method according to claim 3, for providing lateral elasticization of a disposable panty diaper in which the elastic tension is maintained in the crotch portion and deactivated on the outside of the crotch portion.

Method according to any one of claims 1 to 4, wherein the thermoplastic elastomeric composition is applied to the article in the form of a thread or strip under elastic tension, which is subsequently deactivated or partially deactivated outside defined areas, by application of heat and / or pressure by means of a suitable cylinder.

Process according to any one of claims 1 to 5, wherein the thermoplastic elastomeric composition is subjected to complete or partial deactivation outside defined areas, to improve adhesion to the article.

7. A process according to claim 6, wherein the thermoplastic elastomeric composition is applied to the article as a yarn or strip and is subjected to complete or partial deactivation to improve adhesion to the article at a series of points along the yarn or strip.

Process according to any one of claims 1 to 7, wherein the thermoplastic elastomeric composition is a hot melt elastomeric adhesive composition.

The process according to claim 8, wherein the hot melt elastomeric adhesive composition comprises at least one thermoplastic elastomer and at least one tackifier-type resin, the thermoplastic elastomer (or elastomers) being a styrene / butadiene / styrene (SBS) block copolymer or a mixture of styrene / butadiene / styrene block copolymer with styrene / isoprene / styrene (SIS) in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, the composition being characterized in that :

a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined here);

b) maintains a tensile strength, after 50 cycles (as defined herein) of at least 40%; And

c) has a viscosity of 120,000 cps or less at 180 ° C, under a shear stress of 80 sec- ^.

10. Process according to claim 9, wherein the hot melt elastomeric adhesive composition comprises:

1) 10 to 80% by weight of a styrene block copolymer comprising at least two styrenic end blocks and at least one rubbery middle block per molecule, and containing less than 40% by weight of the total block copolymer of a block copolymer containing only one styrene block and one rubber block per molecule (diblock)

2) from 20 to 90% of a tackifier-type resin compatible practically only with the rubbery median blocks;

3) from 0 to 40% of a plasticizer or plasticizers) 4) from 0 to 20% of an aromatic resin;

the composition being further characterized by the fact that;

a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined here);

b) maintains a retention of the tensile strength, after 50 cycles (as defined here), of at least 40%;

c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 80 sec1, 11. Stretch article in which elasticization is ensured by an elastomeric composition. thermoplastic applied under elastic tension, characterized in that the elastic tension has been completely or partially deactivated in defined zones.

The elastic article of claim 11 which is an absorbent article.

The elastic article of claim 12, which is a baby panty diaper, an incontinent adult panty diaper, an incontinence garment, a sanitary napkin or panty protector.

The stretch article according to claim 13, which is a disposable panty diaper provided with lateral stretch and the elastic tension is maintained in the crotch part and deactivated outside the crotch part.

Elastic article according to any one of claims 11 to 14, in which the thermoplastic elastomeric composition is subjected to complete or partial deactivation in defined zones, to improve adhesion to the article.

The elasticized article of claim 15, wherein the thermoplastic elastomeric composition is applied to the article as a yarn or strip, and is subjected to complete or partial deactivation to improve adhesion to the article at a series of points along the wire or strip.

An elasticized article according to any one of claims 11 to 16, wherein the thermoplastic elastomeric composition is a hot melt elastomeric adhesive composition.

The elastic article of claim 17, wherein the hot melt elastomeric adhesive composition comprises at least one thermoplastic elastomer and at least one tackifier-type resin, the thermoplastic elastomer (s) being a styrene / butadiene / styrene (SBS) block copolymer or a mixture of styrene / butadiene / styrene block copolymer with styrene / isoprene / styrene copolymer (SIS), in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, the composition being characterized in that:

a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials, with a 90 ° peel force of not less than 0.5 N / cm (as defined here);

b) maintains resistance retention, after 50 cycles (as defined here), of at least 40%; And

c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 80 sec-1.

The elasticized article of claim 17, wherein the hot melt elastomeric adhesive composition comprises:

1) from 10 to 80% by weight of a styrenic block copolymer comprising at least two styrenic end blocks and at least one rubbery middle block per molecule and containing less than 40% by weight of the total block copolymer of a block copolymer containing only one styrene block and one rubber block per molecule;

2) from 20 to 90% of a tackifier-type resin essentially compatible only with the rubbery median blocks;

3) 0 to 40% of a plasticizer or plasticizers;

4) from 0 to 20% of an aromatic resin;

the composition being also characterized by the fact that:

a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined herein);

b) maintains resistance retention, after 50 cycles (as defined here), of at least 40%; c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 8Dsec "1.

m the area of the cycle is recorded and then the ratio between the elastic energy of the third and the first cycle is determined, as retention of the elastic energy after three hysteresis cycles. For a good elastic behavior, it is believed that in these test conditions, an elastic energy retention of not less than 30% is necessary.

The conditions necessary to deactivate the elastic tension of the compositions described in the following examples, can be theoretically calculated based on the elastic modulus of the composition, i.e., as explained above, a temperature at least equal to the inversion temperature in the absence of pressure or a temperature must be applied. lower provided that pressure is applied in a value at least equal to the elastic modulus at that temperature. However, in practice, the deactivation will be accomplished in a production apparatus, e.g. using a heated roll, and in this case the conditions to be applied, e.g. the temperature of the roll and the gap between the rollers which determines the pressure, will vary depending on other operating conditions, such as the thickness of the material and the speed at which it is passed through the equipment. Thus, for example, based on the elastic modulus, the composition of the following Example 4 can be deactivated at 90 ° C by applying a pressure of 0.02 MPa to it. However, in practice, it will be necessary to empirically determine the conditions (temperature of the roller and space between the rollers) to be adopted to achieve deactivation.

Example 1

An SBC polymeric system based on SBS (styrenebutadiene-styrene block copolymer) is formulated as follows:

CARIFLEX TR-4113 S 36% by weight

EUROPRENE SOL 1205 8%

DERCOLYTE A 115 45.8%

FORAL 85-E 6%

HERCOLYN D-E 4%

IRGANOX 1010 0.2%

in which:

CARIFLEX TR-4113 S is an SBS copolymer diluted with oil produced by SHELL Co, which contains:

68.5% by weight of a linear triblock SBS having a styrene content of 35% by weight and with a diblock content of less than 20% by weight

31.5% by weight of a naphthenic mineral oil, which acts as a plasticizer, containing less than 5% aromatics.

Claims (19)

CLAIMS A method of providing elasticization in defined zones of an article which comprises applying a thermoplastic elastomeric composition under elastic tension to the article and partially deactivating or deactivating elastic tension in the composition outside said defined zones. Method according to claim 1, wherein the spring tension is deactivated by (i) heating to a temperature corresponding at least to the inversion temperature between G1 and G "; or (ii) heating to a temperature below the inversion temperature between G 'and G "with the application of a pressure at least equal to the value of G' at that temperature. 3. A method according to claim 1 or 2, for providing elasticization of an absorbent article. 4. A method according to claim 3, for providing lateral elasticization of a disposable panty diaper in which the elastic tension is maintained in the crotch portion and deactivated on the outside of the crotch portion. Method according to any one of claims 1 to 4, wherein the thermoplastic elastomeric composition is applied to the article in the form of a thread or strip under elastic tension, which is subsequently deactivated or partially deactivated outside defined areas, by application of heat and / or pressure by means of a suitable cylinder. Process according to any one of claims 1 to 5, wherein the thermoplastic elastomeric composition is subjected to complete or partial deactivation outside defined areas, to improve adhesion to the article. 7. A process according to claim 6, wherein the thermoplastic elastomeric composition is applied to the article as a yarn or strip and is subjected to complete or partial deactivation to improve adhesion to the article at a series of points along the yarn or strip. Process according to any one of claims 1 to 7, wherein the thermoplastic elastomeric composition is a hot melt elastomeric adhesive composition. The process according to claim 8, wherein the hot melt elastomeric adhesive composition comprises at least one thermoplastic elastomer and at least one tackifier-type resin, the thermoplastic elastomer (or elastomers) being a styrene / butadiene / styrene (SBS) block copolymer or a mixture of styrene / butadiene / styrene block copolymer with styrene / isoprene / styrene (SIS) in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, the composition being characterized in that : a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined here); b) maintains a tensile strength, after 50 cycles (as defined herein) of at least 40%; And c) has a viscosity of 120,000 cps or less at 180 ° C, under a shear stress of 80 sec- ^. 10. Process according to claim 9, wherein the hot melt elastomeric adhesive composition comprises: 1) 10 to 80% by weight of a styrene block copolymer comprising at least two styrenic end blocks and at least one rubbery middle block per molecule, and containing less than 40% by weight of the total block copolymer of a block copolymer containing only one styrene block and one rubber block per molecule (diblock) ^ 2) from 20 to 90% of a tackifier-type resin compatible practically only with the rubbery median blocks; 3) from 0 to 40% of a plasticizer or plasticizers) 4) from 0 to 20% of an aromatic resin; the composition being further characterized by the fact that; a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined here); b) maintains a retention of the tensile strength, after 50 cycles (as defined here), of at least 40%; c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 80 sec1, 11. Stretch article in which elasticization is ensured by an elastomeric composition. thermoplastic applied under elastic tension, characterized in that the elastic tension has been completely or partially deactivated in defined zones. The elastic article of claim 11 which is an absorbent article. The elastic article of claim 12, which is a baby panty diaper, an incontinent adult panty diaper, an incontinence garment, a sanitary napkin or panty protector. The stretch article according to claim 13, which is a disposable panty diaper provided with lateral stretch and the elastic tension is maintained in the crotch part and deactivated outside the crotch part. Elastic article according to any one of claims 11 to 14, in which the thermoplastic elastomeric composition is subjected to complete or partial deactivation in defined zones, to improve adhesion to the article. 16. The stretch article of claim 15, wherein the thermoplastic elastomeric composition is applied to the article as a yarn or strip, and is subjected to complete or partial deactivation to improve adhesion to the article at a series of points along the wire or strip. An elasticized article according to any one of claims 11 to 16, wherein the thermoplastic elastomeric composition is a hot melt elastomeric adhesive composition. The elastic article of claim 17, wherein the hot melt elastomeric adhesive composition comprises at least one thermoplastic elastomer and at least one tackifier-type resin, the thermoplastic elastomer (s) being a styrene / butadiene / styrene (SBS) block copolymer or a mixture of styrene / butadiene / styrene block copolymer with styrene / isoprene / styrene copolymer (SIS), in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, the composition being characterized in that: a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials, with a 90 ° peel force of not less than 0.5 N / cm (as defined here); b) maintains resistance retention, after 50 cycles (as defined here), of at least 40%; And c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 80 sec-1. The elasticized article of claim 17, wherein the hot melt elastomeric adhesive composition comprises: 1) from 10 to 80% by weight of a styrenic block copolymer comprising at least two styrenic end blocks and at least one rubbery middle block per molecule and containing less than 40% by weight of the total block copolymer of a block copolymer containing only one styrene block and one rubber block per molecule; 2) from 20 to 90% of a tackifier-type resin essentially compatible only with the rubbery median blocks; 3) 0 to 40% of a plasticizer or plasticizers; 4) from 0 to 20% of an aromatic resin; the composition being also characterized by the fact that: a) is capable of binding, when applied in the molten state, to plastic and / or cellulosic materials with a 90 ° peel force of not less than 0.5 N / cm (as defined herein); b) maintains a resistance retention, after 50 cycles (as defined here), of at least II40%; c) has a viscosity of 120,000 cps or less at 180 ° C and under an applied shear stress of 80sec "1.