CA2159937A1 - Process for elastication of articles, such as hygienic articles, and article thereof - Google Patents

Abstract

The invention relates to providing elastication in defined areas of an article by applying a thermoplastic elastomeric composition under elastic tension to the article and deactivating or partially deactivating elastic tension in the composition outside the said defined areas. Elastic tension may be deactivated by (i) heating to a temperature of at least 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 equal to at least the value of G' at that temperature.
The article may be an absorbent article, such as a disposable diaper and elastic tension may be retained in the crotch area and deactivated outside the crotch area.
Alternatively the thermoplastic elastomeric composition may be applied to the article as a thread or strip and subjected to complete or partial deactivation of elastic tension at a series of points along the length of the thread or strip in order to improve adhesion to the article.

Description

21~993~1 PROCESS FOR ELASTICATION OF ARTICLES, SUCH AS
HYGIENIC ARTICLES, AND ARTICLE THEREOF
This invention relates to the elastication of articles and structures and more particularly the use of a single elastic material to produce some regions which are under elastic tension together with other regions not under elastic tension or to produce regions under differing levels of elastic tension.
Typical articles and structures which need to be provided with elastication include absorbent articles such as disposable diapers where elastic strips are used to provide leg and waist elastication. Typically, the elastic strip consists of a vulcanisable rubber elastic which is fixed to the body of the diaper by layers of adhesive. It is usually the case in the manufacture of elasticated articles that continuous production technology makes it almost essential to apply the elastic continuously (since application of discontinuous strips would require special machinery and would be very costly), but elastication is required only over part of the article. For example in the manufacture of disposable diapers, leg elastication is only required in 21.5993' the central part (crotch area) of the diaper and it is important that the end parts are not elasticated.
One way of providing elastication only to certain parts of articles and structures whilst still applying the elastic strip continuously has been to bond the elastic strip to the article with adhesive only in those parts where elastication is required. If the elastic strip is not attached to the article or structure in a particular region then it cannot provide elastication to the article or structure in that region. However this type of structure has considerable disadvantages particularly in the case of absorbent articles.
Generally absorbent articles comprise an absorbent top sheet intended to be in contact with the user and a backsheet with an absorbent material disposed between the top sheet and the backsheet and retained in place by virtue of the, fact that the top sheet and the backsheet are bonded around the edges of the article. The elastic strip is generally also disposed between the top sheet and the backsheet towards the side edge of the article.
The fact that the elastic strip needs to remain unbonded to the rest of the article at the ends of the article means that an "open tunnel" is created around the elastic - ~1~993~

strip though which absorbent from the interior of the absorbent article can escape unless the tunnel is closed by means of an additional process step after the shrinking of the elastic.
An object of the present invention is to achieve elastication in defined regions only of an article in a way which avoids the disadvantages referred to above whilst at the same time being convenient and of general applicability.
According to one aspect, the present invention provides a method of providing elastication in defined areas of an article which comprises applying a thermoplastic elastomeric composition under elastic tension to the article and deactivating elastic tension in the composition outside the said defined areas.
According to another aspect, the present invention provides an elasticated article in which elastication is provided by a thermoplastic elastomeric composition applied under elastic tension characterised in that 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 as single - 2I5~~3~
_ _ 4 polymers or blends and compositions containing thermoplastic elastomers provided that the overall composition retains the properties of a thermoplastic elastomer. As a class, thermoplastic elastomers are known and are described in more details below and they are characterised by the fact that at room temperature they behave as a cured rubber showing high elasticity but, in contrast to cured rubbers, they can be melted and reprocessed in the same way as normal thermoplastics.
Thermoplastic elastomeric compositions can thus be used to provide elastication to an article in a similar way to cured rubbers by applying the composition to the article under elastic tension. The present invention makes use of the fact that, under certain conditions defined by the rheological parameters of the thermoplastic elastomeric composition, the elastic tension can be wholly or partially inactivated thereby eliminating or modifying the elastic properties of the material.
The conditions under which elastic tension can be deactivated may be determined in any particular case by reference to the classical method of Dynamic Mechanical Analysis for viscoelastic materials under sinusoidal 21~99~~

stress and account needs to be taken of the values of the two rheological parameters:
- elastic or storage modulus G' - viscous or loss modulus G"
in the range of temperatures where melting of the material occurs. G' is higher than G" when the material is solid but in the range where the material melts an inversion of values takes place so that G' becomes lower than G" at the temperature at which the material melts.
Indeed, the inversion temperature between G' and G" can be taken as the true rheological solidification (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 may be in the range 90°C up to 250°C or higher. However, in the application of the composition in the manufacture of disposable sanitary products, compositions with inversion temperatures in the lower part of the range will usually be employed to avoid damage to some of the raw materials such as polyethylene fibres and cellulose fibres. The relative values of G' and G" means that, if heated to a temperature equal to or ~1~99~'~

higher than the inversion point, any internal tension in the material will spontaneously relax. Thus when G" > G' the material behaves like a liquid and any molecules which were previously stretched imparting elastic tension to the material thereby flow destroying any stress.
Accordingly, one method of deactivating elastic tension according to the invention is simply to heat the thermoplastic elastomeric composition to a temperature equal to or above the inversion temperature.
However, it is also possible to relax internal stresses to obtain areas where the elastic tension is deactivated by heating to a temperature below the inversion temperature provided that an appropriate pressure is applied at the same time. The inversion temperature may be regarded as the temperature at which relaxation of internal stresses takes place spontaneously without application of pressure. The same result can be achieved by a combination of heat and pressure provided that the pressure which is applied is at least equal to the value of G' at the temperature which is applied.
Thus, by way of example, if the elastic modulus of a thermoplastic elastomeric composition is 0.02 MPa at 90°C, then internal stresses could be relaxed and elastic tension deactivated at 90°C by applying a pressure of at least 0.02 MPa.
It is also possible by applying an elevated temperature below the inversion temperature or a combination of heat and pressure which falls short of that required to relax completely internal stresses, to achieve a partial relaxation thereby achieving a partial deactivation of elastic tension. The extent of the deactivation can be varied as desired in any particular case by use of an appropriate temperature or by an appropriate combination of temperature and pressure.
The present invention can be applied generally to thermoplastic elastomeric compositions but it cannot be applied to elastomers which are not thermoplastic, e.g.
conventional vulcanised rubber elastics, since these decompose chemically before reaching conditions which would bring about relaxation of internal stresses.
Thermoplastic elastomers may also be adhesive or may be formulated into compositions in such a way that the composition is adhesive, in which case the thermoplastic elastomeric composition may be applied directly to the article without a separate adhesive. The thermoplastic elastomeric composition may be a hot melt adhesive, i.e.

~~.~993'~
it is adhesive when applied to the article in a molten state and this does not preclude the possibility that the thermoplastic elastomeric composition may show adhesive properties at room temperature, e.g. pressure sensitive adhesive properties. As explained in more detail below, heat and/or pressure, which has the effect of complete or partial deactivation of elastic tension, may be applied to zones or points of the thermoplastic elastomeric composition to promote or improve adhesion. If the thermoplastic elastomeric composition is not adhesive, then a separate adhesive will be required and suitable adhesives are already well known for use with vulcanised rubber elastics or thermoplastic elastics.
As already indicated, individual thermoplastic elastomeric polymers are a very interesting chemical and technological class which are distinguished by their characteristic behaviour. At room temperature they behave as cured rubbers showing high elasticity but in contrast to cured rubbers they can be melted and reprocessed in the same way as normal thermoplastics.
This behaviour results from a particular chemical structure. Most thermoplastic elastomers are block copolymers, i.e. their molecules are formed by blocks of _ 2159~y7 _ _ 9 different natures linked together. Different blocks can alternate along the chain as relatively short blocks (multiblock structure of the form A-B-A-B-A etc); or the molecules can have a three block structure of the form A-B-A where A are terminal blocks and B is a central block of a different nature (linear three block copolymers); or the molecules can have a "radial" or "star" structure represented as (AB)x where all midblocks B are chemically linked together at a central point and terminal blocks A are radially disposed each at the end of block B. Structures formed by only two blocks (diblocks) of the form AB are ineffective as thermoplastic elastomers in terms of their elastic behaviour.
The chemical nature of the different blocks can be varied and the resulting copolymers can be classified for example as polyurethanes, polyesters, polyethers, polyether- ester amides, etc. However, a common characteristic is the following: different blocks are physically incompatible so that they are mutually insoluble. The material can thus be considered an heterogeneous system in which different blocks, even if chemically linked in the same molecule, exist as separate 2~~~~3~

entities. Blocks A of different molecules tend to associate together in microscopic regions or "domains"
with the same happening for blocks B. The material so formed has an heterogeneous structure of domains A and B, each well separated, with the one present at the lower level being dispersed microscopically in the other one which constitutes a continuous phase. This continuous phase is generally formed by "soft" or rubbery blocks B
which give to the material its elastic properties, while the dispersed phase A is formed by "hard" non-elastomeric blocks. Below the glass transition temperature or softening point of the hard blocks each molecule of the copolymer has its A blocks fixed in at least two points, i.e. they are "confined" in the hard domains.
Accordingly, the rubbery part of the molecule can undergo stretching but without flowing relative to other molecules and when the external stretching force is relaxed it returns to its initial position for reasons of entropy.
Thus in thermoplastic elastomers, the hard blocks work as a physical vulcanization and the advantages of this processing are clear. The chemical linkages that form the vulcanized structure of a standard rubber cannot 21~993'~
-- n be removed by heating and at sufficiently high temperature the rubber simply begins to decompose. On the other hand, in thermoplastic elastomers heat can effectively melt the hard domains; the material can thus be melted and processed, but hard domains giving back the pseudo-vulcanization, are formed again simply by cooling the material. It is apparent from the above explanation that diblocks, which contain only one hard and one soft block, cannot contribute to elastic properties.
Diblocks can improve processibility but their content in the material must be confined within certain limits so that they do not reduce elasticity to an unacceptable extent. In addition, the total amount of hard blocks is important; too low a content will give poor elastic properties (similar to an insufficiently cured rubber), whereas too high a content will make the material behave as a very hard, super- cured rubber, again with very poor elasticity.
Amongst thermoplastic elastomeric block copolymers, the so called Styrenic Block Copolymers (SBC) are well known and widely used in many applications on account of their very good properties. Styrene block copolymers as a class are described for example in Thermoplastic 2~~9~37 Elastomers: A Comprehensive Review, Legge, Holder &
Schroeder (Eds), Hauser Publishers (1987), Chapters 3, 4 and 12(1). They can have the structures already mentioned above 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 "hard" block of a vinyl-arene polymerized monomer, generally styrene or alpha-methyl-styrene; and B
represents a "soft midblock" generally formed by a rubbery monomer such as poly(butadiene), (isoprene), (ethylene- butylene) or (ethylene-propylene) rubbers.
The content of diblock molecules A-B in such products can be as high as 80~ by weight and in special commercial products can even form the totality of the polymer. These products are used for particular applications because, for the reasons discussed above they have no or very poor elastic properties. Diblocks can help processing and improve adhesive properties but in order to retain good elastic characteristics their content in the thermoplastic elastomeric block copolymer should be kept lower than 40~ by weight.

2~ ~~93 SBC's are widely used as substitutes for vulcanized rubbers, their hardness, modulus and general mechanical and elastic properties being strongly related to the content of hard blocks, formed especially by polystyrene.
They have also found use as base polymers for hot melt adhesives because of their generally good mechanical characteristics, easy tackification of their rubbery midblocks and good thermal stability which make them superior to traditional bases for hot melts such as ethylene-vinylacetate copolymers. However the main object of standard compositions has been to optimize adhesive properties with retention of at least some of the elastic properties, typical of the base polymer, not being taken into account.
Thermoplastic elastomeric block copolymers known as SBC's, thus typically have the following characteristics:
- They are formed by two kinds of monomers each polymerized in blocks of the same monomer units, the blocks being distinct even if chemically linked inside the copolymer molecule. Moreover the two kinds of blocks must be mutually incompatible.
- The structure according to which the two kinds of present blocks are linked in the molecule can be:

2.~5993~

- alternating multiblock as .... A-B-A-B-A-B....
- triblock linear as A-B-A
- radial or star structure 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 hard blocks because at room temperature these polymeric species are hard, glassy and fragile materials being under their glass transition temperature (Tg).
Typically useful constituents for hard blocks have Tg well above room temperature and preferably higher than 90°C.
- "B" represents blocks of a rubbery polymer having a Tg < 0°C and preferably < -40°C.
Typically these "soft" blocks are formed by rubbers such as polybutadiene and polyisoprene.
In the common technological lexicon the resulting thermoplastic elastomeric block copolymers are often referred to by the abbreviations SBS and SIS
respectively.
As already discussed in terms of the mechanism of the generation of elastic properties in these type of polymers, and particularly the function of hard blocks in 2~~~93~
IS
giving a physical vulcanization to the polymer, useful SBC's contain at least two hard blocks "A" per molecule and at least one soft block "B". Molecules formed by one block of A and one block of B (the so called diblocks) should, for use in the present invention, be kept lower than 40$ by weight in the base polymer.
All thermoplastic elastomers can be processed in the molten state using various technologies and in various apparatus, in all cases showing in the solid state properties similar to those of a cured rubber.
Potentially all thermoplastic elastomers can be made adhesive. Some adhere well enough in the molten conditions to different substrates. However it is clearly highly desirable to obtain thermoplastic elastomeric compositions which are capable of adhering at room temperature or at only moderately elevated temperature to various substrates.
Thus, whilst pure thermoplastic elastomers have some adhesivity at high temperature, this adhesivity can be conveniently enhanced both in terms of the strength of the bonds formed with different substrates and in terms of the range of temperatures at which strong bonds are formed.

This enhancement is generally obtained by the use of at least one suitable tackifying resin. More particularly, much better adhesive properties and even self adhering properties at room temperature (pressure sensitive behaviour) can be obtained by blending thermoplastic elastomers with the materials known as tackifying resins which, as a class, are well known in the literature.
When thermoplastic elastomers are assembled at room temperature (e. g. because it is desired to pre-stretch them in the solid state and bond under tension) it is necessary that they exhibit the typical behaviour of true pressure sensitive adhesives and this generally requires a blend of a thermoplastic block elastomer and tackifying resin. It should be noted that in order to enhance the adhesive properties of the thermoplastic elastomer (both at high temperature and at room temperature), only the soft (rubbery) blocks of its molecule should be modified by the tackifying resin. Thus, only interactions between the soft (rubbery) blocks and a resin, substantially compatible with them, causes the generation of tack;
while the eventual modification of hard blocks with a ~'.~~~~3~

resin never leads to the development of adhesive behaviour.
Not only do the hard blocks not exhibit any adhesive activation but their eventual modification by a tackifying resin could "soften" their mechanical strength. This risks impairing their ability to function as "centers of physical vulcanization" for the elastomer, consequently destroying elastic behaviour.
So, for the various thermoplastic block elastomers, depending on the chemical nature of their soft and hard blocks, suitable tackifying resins can be identified which must be compatible (i.e. soluble and capable of creating the appropriate physical modification of the system) only with the soft or rubbery blocks, whilst compatibility with the hard blocks is as low as possible or even zero, in order to retain as much as possible of primary elastic properties of the polymer. However, the amount of tackifying resin must be controlled since the addition of quantities of tackifying resin(s), which are too large, even if the tackifying resin is compatible only with the midblocks (soft blocks) and fully incompatible with the hard blocks, could still impair the elastic properties of the resulting formulation. In any _ 2~.~993'~
case, the addition of the resin constitutes a dilution of the concentration of the hard block domains, weakening their ability to function as centers of "physical crosslinking" for the elastomer. Thus both the content of hard domains in the base thermoplastic block elastomer and the content of the elastomer in the final formulation must be such to ensure a sufficient final concentration of hard domains in the formulation to retain appropriate levels of "physical vulcanization" and thus of elastic properties.
Therefore, on the one hand, it is important to control the final concentration of hard blocks in the composition. On the other hand, the addition of resins) which are compatible only with the hard blocks and their domains, is completely ineffective in the development and/or improvement of adhesive properties. Resins compatible with the hard blocks will, by swelling the hard domains, stiffen the composition, increase modulus and (compared to similar levels of tackifying resins compatible with the midblock) will tend to increase viscosity. In a system already containing a tackifying resin compatible with the soft domains, the addition of resins compatible with the hard domains will also decrease the adhesivity. Accordingly, in general terms, only limited quantities of resins compatible with the "hard blocks" can be used without too great an impairment of the overall properties of the adhesive elastic hot melt.
Generally they will only be used in special cases, for example, if an additional increase in modulus is required for some applications; or (using high softening point hard block compatible resins) if a higher setting temperature or a better temperature resistance is desired.
In accordance with one embodiment, the present invention provides a method of providing elastication in defined areas of an article which comprises: (a) applying a thermoplastic elastomeric composition under elastic tension to the article; and (b) deactivating or partially deactivating elastic tension in the composition outside the defined areas.
In accordance with a further embodiment, an elasticated article is provided in which elastication is provided by a thermoplastic elastomeric composition applied to the article under elastic tension characterised in that the elastic tension has been completely or partially deactivated in defined areas of the article.
According to a preferred embodiment the thermoplastic elastomeric composition used to provide elastication is an elastomeric hot melt adhesive composition comprising at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer(s) being a styrene/butadiene/styrene (SBS) block copolymer or a blend of styrene/butadiene/styrene with styrene/isoprene/styrene (SIS) block copolymer on which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer the composition being characterised in that:

_ ~1~9937 a) it is capable of bonding, when applied from the molten state, to plastic and/or cellulosic materials with a 90° peel force of not lower than 0.5 N/cm (as herein defined);
b) it has a tensile strength retention after 50 cycles (as herein defined) of at least 40~; and c) it has a viscosity of 120,000 cps or less at 180°C and an applied shear of 80 sec-1.
Compositions as defined above form the subject of our co-pending patent application [-] (internal reference DR 2 ) .
Feature a) referred to above relates to the adhesive properties of the composition and the composition should have the properties of a hot melt adhesive in that it is capable of bonding appropriate substrates, typically plastic and/or cellulosic materials, when applied from the molten state. In particular, "capable of bonding"
means that the composition is capable of showing adhesion on plastic and/or cellulosic materials sufficient especially for application in the construction of hygienic absorbent articles. When applied from the molten state between two substrates of plastics and/or cellulosic materials the composition gives a bond _ 21~993~

strength, measured as 90° peel of not lower than 0.5 N/cin. The composition at a weight of 5 g/m2 is applied in the molten state between the substrates and 48 hours after bond formation the 90° peel strength is measured at 23°C and at a separating speed of 300 mm/min.
Many compositions as disclosed herein also bond appropriate substrates at room temperature and may show the properties of a pressure sensitive adhesive.
Feature b) referred to above relates to the elastic properties of the composition. The test which is used is described in more detail below and involves measuring the extent to which elastic properties are retained over 50 cycles of stretching and relaxation. The range over which the composition is stretched is related to the modulus of the composition and the likely degree of stretching of the composition in use. The figure of 40~
for tensile strength retention indicates that the elastic properties of the composition are comparable with those of natural rubber and are preferably superior thereto.
Preferably the tensile strength retention is at least 50~, more preferably at least 60$.
Feature c) above relates to the processability of the composition and a viscosity of 120,000 cps or less at - 215993~l 180°C (applied shear 80 sec-1) indicates that the composition can be applied using conventional apparatus for use with hot melt adhesives. Preferably the viscosity is 60,000 cps or less, more preferably 30,000 cps or less. It is also highly desirable that the composition according to the invention show substantially Newtonian rheological behaviour, in particular viscosity does not vary significantly with applied shear. Many compositions as disclosed herein show Newtonian behaviour at intended processing temperatures, e.g. around 180°C.
Elastomeric hot melt adhesive compositions as defined above can be formulated with any desired modulus depending on the precise nature of the desired end use.
However the modulus has effects on the main properties of the composition and it is convenient to divide the compositions into low modulus and high modulus compositions.
Low modulus compositions are defined as compositions having a modulus of 0.5 MPa or less at 500 elongation (six times the initial length of sample) measured at 23°C
under an elongation rate of 500 mm/minute. Generally low modulus compositions have a modulus in the range 0.05 to 0.5 MPa, preferably 0.05 to 0.3 MPa. Low modulus __ ~~5993~r _ 23 compositions generally show good adhesive properties at rooiri temperature and may also be pressure sensitive adhesives. These compositions are usually stretched immediately after they are formed, for example after extrusion from the melt as a strip or thread. Stretching may take place immediately before or during application to an article so that the compositions are effectively applied in the stretched state. Low modulus compositions are typically used under an elongation of 400$ to 1000$.
Since low modulus compositions will usually be stretched immediately after extrusion it is desirable that they should have a relatively high setting point so that they solidify quickly on extrusion. Preferably the setting point (measured by the Dynamic Mechanical Analysis method described in more detail below) is at least 80°C, more preferably at least 100°C.
High modulus compositions are defined as compositions having a modulus of greater than 0.5 MPa at 500 elongation (six times the initial length of sample) measured at 23°C under an elongation rate of 500 mm/minute. Preferably the high modulus compositions have a modulus of from 1 MPa to 10 MPa. Since pressure sensitive adhesive character is generally inversely _ _ 24 proportional to modulus, compositions with high modulus are-often applied from the molten state although some may retain sufficient pressure sensitive adhesive character to be applied at room temperature. Application from the melt implies that the composition is applied without stretching with stretching generally taking place in use and this applies particularly to compositions with a modulus of 1 MPa or higher. For this reason high solidification temperature is less critical for high modulus compositions but for convenience these are also preferably formulated to have a setting point of at least 80°C, more preferably at least 100°C. High modulus compositions are generally used at a lower degree of stretching. They are capable of giving sufficient elastic force at low deformation (typically no higher than 50~). However, in cases where the compositions retain sufficient pressure sensitive adhesive character so that they can be applied at room temperature in a stretched state, they can be used at an elongation of up to 400$.
The elastomeric hot melt adhesive compositions referred to above provide elastication to products in which they are applied, for example absorbent products, _ 21~993~
without the use of any glue, these being for example structures where elastication has been obtained conventionally by elastic formed of vulcanized rubbers bonded to the structure by means of a glue. Thus, one material (the adhesive elastic hot melt) can substitute for the use of two materials (the rubber and the glue to fix it) with a substantial saving in costs. Normally rubber elastics are covered with talc to prevent sticking of the elastics in the packaging. Talc can give rise to problems at the stage of adhesion with glues.
Moreover the elastomeric hot melt adhesive composition can be directly extruded in varied geometrical forms directly during the construction of products which are to be elasticated. It can be extruded as strands or yarns, as bands, as films, etc. Structures such as bands or films can be also foamed before the extrusion, obtaining elasticated structure which are particularly soft. Elastication can be also applied according to non-linear (curved) geometries which makes the anatomical fitting, of the product comprising the elastication, to the wearer's body particularly good.
This is very difficult to obtain with standard rubber yarns of ribbons. Under different geometrical forms the _ 2I~993~

adhesive elastic hot melts can be applied both in an already stretched or an unstretched state. In the first case the extruded melt is cooled immediately after the extrusion die and stretched at the desired elongation.
In this case it is advisable that it possesses the following properties:
- a relatively high setting point so that it solidifies immediately after the extrusion and can be elastically stretched. An elastic stretching can be given only to a solid material, because any force applied to a molten or semisolid material will cause only a plastic lengthening along the direction of force without any elastic tension.
- good pressure sensitive properties of adhesion because the adhesive elastic hot melt will contact the substrates) when already cold, e.g. at room temperature.
When the material is applied without any prior elastic stretching and directly contacted to the substrates) to which it has to adhere at the outlet of the extrusion die, pressure sensitive behaviour is less important because bonding is made when the material is still above room temperature. In this case besides the geometrical forms mentioned above, the material can be 21~~~37 applied to the substrates) e.g. by spraying or fiberization or by similar processes obtaining a network of interconnected short fibers or a network of fibers having indefinite length which can have both a random or a geometrically regular network structure (e. g. each fiber can form a spiral).
All these features are particularly suitable for the elastication of absorbent articles, in particular hygienic absorbent articles such as diapers and catamenials. The use of materials applied in an already stretched form can substitute for all of the presently used rubber elastics in baby and adult diapers, in catamenials etc., when it is desired to have parts of the product already under elastic tension offering, as a result of their extreme versatility, the possibility of new elasticated structure of practically infinite variety. In this case, another advantage of elastic, adhesive hot melts over rubber elastics is worthy of note. The preferred elastic hot melt compositions have a stress/strain diagram that is much flatter than a rubber elastic, i.e. even if already under tension a further stretching (e.g. due to the movements of the wearer of the absorbent article) causes a very low increase in 2I~993~

modulus and in the tensile strength that is perceived by the wearer. This is especially true for low modulus compositions.
Compositions used to provide elastication in absorbent articles according to the invention that are more conveniently applied in the unstretched state are typically used to give elastic return to structures/products only when the whole final structure/product is subject to some deformation during use. Normally in this case the typical deformations that are given in use to an absorbent article are very limited, e.g. of the order of 5-50$. Accordingly, it is necessary that the adhesive, elastic hot melt contained in these structures is able to respond with a sufficient elastic return force to external stresses even at these low elongations. For these applications, it will be generally more convenient to use formulations at higher modulus.
The formulations based on SBC's which are used to provide elastication according to the present invention show optimum properties, typical of hot melts, ranging from compositions that can more conveniently be strongly bonded to substrates at high temperature from the melt to _ 2~5~93~

about 50°C, to compositions that retain a permanent strong adhesivity on most substrates even at room temperature being true pressure sensitive adhesives.
Moreover the compositions are characterized by retention of distinct elastic properties from the base thermoplastic block copolymer, showing all of the typical behaviours that define an elastomeric material in the technological sense.
Thus when stretched in the solid state and when the stress is relaxed they will return quickly to their initial length with only minor permanent (plastic) deformation. The formulations preferably having a distinct pressure sensitive character, can be applied even at room temperature, both in the unstretched or preferably in the stretched state for the elastication, in different geometrical forms, in absorbent products, in particular hygienic products such as baby and adult diapers or adult incontinence products different from diapers, or feminine catamenials. Compositions having lower pressure sensitive character will be more conveniently be applied at temperature over 50°C, in the stretched or preferably in the unstretched state for the elastication of the same structures and products. In 2$593 particular when applied in the unstretched state they will work at limited extension, e.g. up to 50$ (i.e.
final stretched dimension = 1.5 times initial dimension).
In order to show even at these low extensions a distinct elastic return force, these formulations will generally have a higher modulus than the previous ones, the two kinds of materials being, in fact, the extremes of one field of formulations all of which are both excellent hot melt adhesives and retain excellent elastic properties, the passage from one to another being gradual.
As already indicated, compositions used according to the invention can be divided into "low modulus" and "high modulus" formulations, this distinction being based on their modulus value and on their behaviour as pressure sensitive adhesives.
Thus the present invention makes use of a family of compositions based on at least one thermoplastic elastic block copolymer in which SBS copolymers) are preferably the main copolymers) and at least one tackifying resin essentially compatible with the soft (rubbery) blocks of the aforementioned copolymer, the tackifying resin being used mainly to improve adhesivity, both at high and at ~1~993~

room temperature of the aforementioned copolymer which compositions provide elastication to the absorbent articles. The compositions are extrudable and in the solid state retain a distinct elastic behaviour typical of elastomers from which they are derived. As typical examples and without any limitation, these compositions can be extruded and applied in the form threads, yarns, bands, continuous films, networks of fibers both continuous or having a finite length and in which fibers have both a random orientation or a geometrically regular conformation etc. As examples of applications in the field of absorbent articles, they can be used for the leg elastication of diapers, as elastic waistband in the same, for the elastication of catamenials and of adult incontinent products other than diapers, for the internal elastication of the structures of all the aforementioned products, for reinforcement under mechanical stress of their absorbent cores and for giving them stretchability and resiliency etc.
A lower modulus generally means that adhesive materials have a more aggressive adhesivity, so that the low modulus formulation generally have higher tack typical of pressure sensitive adhesives. They are able _ 2159~3~

to form very strong bonds with many substrates on simple contact even at room temperature or in any case lower than 50°C.
Ratios between hard and soft blocks in the base thermoplastic elastomeric copolymer are very important in determining the elastic behaviour and the mechanical and adhesive properties.
Generally the higher the content of hard blocks (that conventionally will be referred to as "styrene content") the higher the modulus, the more evident are elastic properties, the quicker is elastic return after relaxation of stretching but the lower is adhesivity and especially pressure sensitive behaviour. All this is true provided that the level of hard blocks does not become so high that it forms the continuous phase and the material becomes a hard and no longer elastic material.
Useful SBC's can contain from 10 to 50$ of styrene by weight. However, when modified with the tackifying resin, the behaviour of the resulting composition will be clearly governed, in terms of all of the aforementioned properties, by the resulting content of styrene or of hard blocks in the compositions so that it is determined both by the level of styrene in the base copolymers) and by the content of copolymers) in the final composition.
Too low a level of final block styrene will give poor elastic properties. Too high a level will increase the modulus and decrease the adhesivity to an unacceptable extent. Increasing final styrene level in the composition by increasing the content of copolymers) will increase excessively the viscosity and decrease processability. So both the level of copolymers) in the composition and their content of styrene should be chosen to optimize the final styrene content and thus all the above mentioned properties. Optimum ranges will be indicated below.
If desired the rubbery part of the SBC can itself be cured (in a similar manner to the curing of natural or synthetic rubbers) by using suitable chemical or physical means, in particular curing systems known for synthetic rubber which are not activated by heat. This will have the effect of increasing the modulus of the overall composition.
The tackifying resin is added mainly to improve adhesive properties of the base copolymers) even to the extent of arriving at the typical behaviour of a pressure sensitive adhesive. Moreover it improves the 21~99~'~

processability of the thermoplastic elastomer both by giving to that composition lower absolute values of viscosity (as compared to the pure block copolymer) and a rheological behaviour that, at the indicated levels of resin, is practically Newtonian, i.e. the viscosity is dependent only on temperature and does not change with applied stress, a property which is very advantageous for easy processing. It is known that SBC's which have many very interesting characteristics, may be difficult to process as a result of non-Newtonian behaviour in the molten state as pure materials. This means that not only do they show very high viscosity but also, under the influence only of temperature, they do not appear to melt even at very high temperatures near 200°C. They can even begin to thermally decompose before showing a distinct fluid state. In order to make them flow and so to be able to process them, it is necessary to apply temperature and high mechanical stress. In any case processing of pure SBC's is difficult, viscosities are high and highly dependent on the combination of temperature and applied stress.
The basic composition of SBC and tackifying resin is capable of giving materials which, whilst retaining very ~1~9937 good elastic and adhesive properties, are also easily processable because of both relatively low viscosities and of practically Newtonian (or acceptable Newtonian-like) rheological behaviour. This latter property was measured as variation at constant temperature (180°C) of the viscosity under two levels of applied shear rate, 20 and 80 sec-1. The ratio of these two viscosities is hereinafter called the "Newtonian Index" (N. I . ) .
An ideal Newtonian fluid should have N.I. - 1 while a pure SBC could have, in the same conditions an N.I.
even > 6; i.e. the viscosity variation, only due to the variation of applied shear rate from 20 to 80 sec-1 is more than 6 times which can cause severe problems for regular and easy processing. For easy processability it is necessary that the compositions have only limited variation of viscosity at constant temperature with variation of applied shear rate.
More particularly, it is preferred that compositions show a Newtonian or almost Newtonian rheological behaviour based on the molten material at 180°C, by comparing the viscosities under a shear rate of 20 and 80 sec-1. Preferred compositions do not show a variation in 2~5993~

viscosity > 50$ i.e. a ratio between viscosities (N. I.) not higher than 1.5.
It has been found that the most preferred compositions based on SBS's have an almost ideally Newtonian behaviour, with an N.I. not higher than 1.05.
In order to retain sufficiently the elastic properties of the base polymer it is necessary that the tackifying resin is compatible mainly with and preferably essentially only with, the soft, rubbery blocks of the block copolymer and does not interfere to a significant extent with hard blocks. This is governed both by the chemical nature of the resin and by its molecular weight.
The compatibility of the resin with the rubbery blocks and its incompatibility with the hard blocks can be measured, for example, by determining the variation of Tg of soft and hard blocks deriving from the addition of resin. In particular, incompatibility with the hard blocks is considered satisfactory if their Tg (originally at 100°C if they are formed from polystyrene) is not changed more than 15°C by the addition of 100 parts of resin to 100 parts of copolymer. Measurements of the two Tg's requires appropriate equipment. Accordingly both the experience of formulators and the technical 21~~~37 _ 37 literature of resin suppliers can be taken into account to determine which tackifying resins are chemically compatible with the soft blocks and incompatible with the hard blocks of SBC's. As used herein, the term "compatible essentially only with the soft blocks" means that a tackifying resin is compatible with the soft blocks of the copolymer and is incompatible with the hard blocks to the extent that Tg of the hard blocks is not significantly changed and more preferably decreased by no more than 15°C on admixture of 100 parts of tackifying resin to 100 parts of copolymer. Preferably the Tg of hard blocks is not decreased at all.
More specifically a suitable main tackifying resin will be chosen from the following chemical groups which have high compatibility with soft blocks of SBC's and low or no compatibility with their hard blocks - hydrocarbon resins - aliphatic resins - polyterpene resins - terpene phenolics - synthetic C5 resins - synthetic C5/C9 resins - rosins and rosin esters 2I~993'~

as well as their totally or partially hydrogenated derivatives. They can be used as the pure resin or also in blends.
When more than one resin is used, the main tackifying resin system, defined as the essential resin/blend of resins present at least at a level of 500 of the total amount of resin, are characterised by having a softening point between 85 and 150°C and more preferably between 100 and 140°C (all softening points being measured by the well known Ring & Ball (R & B) method) .
Tackifying resins having softening point < 85°C are considered to have a prevailing plasticizing effect which may in any case be important for the development of good adhesive and elastic properties but is to be distinguished from the tackifying effect. This is due to the fact that in the processing of the present elastic hot melt compositions quick setting of the material after extrusion is desirable, especially for compositions which are to be stretched before application on the substrate, which is clearly possible only with solid materials. For this reason it is desirable that the setting point of 21~~9~'~

these compositions is not less than 80°C and more preferably greater than or equal to 100°C.
Setting point is most accurately determined by using the technique referred to above known 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 storage modulus G' - the viscous or loss modulus G"
- the angle ° (delta) and its tangent, being the phase shift between G' and G".
As already indicated, the crossing temperature between G' and G" is taken as the true rheological solidification (or melting) point of the material.
For use according to the present invention, it is preferable that the crossover temperature for the composition is greater than or equal to 80°C and more preferably greater than or equal to 100°C.
The position of the crossover point is dependent on many physical parameters of the hot melt. However, it has been found that the main influence is the softening 2.~5993"l point of the main tackifying resin and a secondary influence is the content and molecular weight of the copolymer. So the tackifying resin should preferably have a softening point from 85 to 150°C and more preferably from 100 to 140°C provided that in any case the overall composition has a true rheological solidification temperature at least of 80°C and more preferably at least of 100°C.
Besides the thermoplastic elastomeric block copolymer and the main tackifying resin, compositions can contain additional components which improve specific properties. A more detailed description of the compositions and of their principal properties is given below.
For practical reasons of clarity of description, further description will relate specifically to "low modulus" and "high modulus" compositions.
The low modulus compositions are elastic, e~ttrudable, adhesive compositions based on at least one thermoplastic elastomeric block copolymer, suitably modified by the proper addition of at least one tackifying resin essentially compatible with its soft blocks. The polymer, or at least the polymer present at 21~993~

the highest level, is a polystyrene/ polybutadiene block copolymer. In this embodiment the compositions have a modulus of 0.5 MPa or less, essentially from 0.05 MPa to 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 sample) under an elongation rate of 500 mm/minute. Moreover the compositions have viscosities at 180°C and with an applied shear rate of 80 sec-1 of 120000 centipoise (cps) or less and preferably 60000 cps or less and more preferably 30000 cps or less.
The low modulus compositions will typically contain from 10 to 80~ by weight, and more preferably from 15 to 50$ by weight, of SBC or of a blend of SBCs having the following characteristics:
- a molecular structure that can be multiblock, linear or radial (star) provided that it contains per molecule, at least two hard-blocks formed by a vinyl-arene polymer and preferably polystyrene or poly-alpha-methyl-styrene, and at least one soft or rubbery block, the soft block of the SBC, or of the SBC present at the highest level, being polybutadiene. The diblock content in the SBC(s) should be kept lower than 40$ by weight.

_ 21~993~

- the aromatic content (conventionally referred to hereinafter as "block styrene content") of the SBC(s) can vary from 10 to 50$ by weight and preferably from 20 to 50$ by weight.
However in order to retain significant elastic properties, both the SBC(s) level in the final composition and the styrene content thereof should be chosen so to have a final block styrene content in the composition from 3 to 17$ by weight and preferably from 6 to 15$ by weight.
The composition also contains tackifying resin or a blend of the same essentially compatible with the soft blocks of SBC.
The preferred resins belong to the chemical groups known as:
hydrocarbon resins - aliphatic resins - polyterpene resins terpene phenolic resins - synthetic C5 resins - synthetic C5/C9 resins - rosin and rosin esters 21~9~3~

as well as their totally or partially hydrogenated derivatives thereof.
The tackifying resin/blend of resin has/have a R&B
softening point from 85 to 150°C and preferably from 100 to 140°C. The level of such resin/blend of resin in the composition can be from 20 to 90$ by weight. However, in a preferred embodiment the content of resin/blend of resin described above is from 30 to 55~ by weight the remainder being formed by the additional components described below which enhance elastic and/or adhesive properties.
In any case both the level and the softening points of the tackifying resin/blend of resins as well as those of additional components described below will be chosen so that the final composition has a true rheological setting temperature (measured as crossing temperature of G' and G") not below 80°C and preferably not below 100°C.
It has also been found that adhesive and/or elastic and/or mechanical properties of the binary blends SBC/tackifying resin can be improved by using additional components.
Adhesive properties can be enhanced by adding limited quantities of high molecular weight rubbers such as polyisoprene, polybutadiene, polyisobutylene, natural rubber, butyl rubber, styrene/butadiene rubber (SBR) or styrene/isoprene rubber (SIR) and blends thereof. These polymers have high viscosities and, in the uncured state, have poor elastic properties. However, adding them in quantities up to 15o by weight of the formulation and using polymers with Mooney viscosities ML (1+4) at 100°C from 30 to 70, the resulting compositions show improved pressure sensitive adhesive properties whilst still retaining final viscosities within a useful range and without any detrimental effect on final elastic properties. A
particularly suitable SBR is the product sold by Enichem under the trade name EUROPRENETM SOL 1205 and by Fina under the trade name FINAPRENETM 1205. This product is described as an SBR in which styrene is partially distributed in blocks. Of the total styrene content of 25s by weight, from 15 to 18o has a block structure and the remainder is randomly co-polymerised with the butadiene.
Plasticization of the composition can have very good effects not only on the adhesive properties and on the viscosity but can also even improve elastic behaviour by reducing the internal (molecular) frictions that dissipate elastic energy during stretching and subsequent relaxation. In general, the composition may contain up to 40% by weight of plasticizer(s).
In a preferred embodiment, the compositions contain at least one of the following plasticizers:
- up to 40% by weight of a tackifying resin with a softening point from 50 to 85°C, - up to 20% by weight, and preferably up to 15% by weight, of a liquid hydrocarbon resin, rosin ester or polyterpene resin with a softening point not higher than 30°C, - from 3 to 30% by weight and preferably from 5 to 15% by weight of a paraffinic or naphthenic mineral oil having an aromatic content of less than l0% by weight in order not to interfere with the styrenic domains, - up to 15% by weight of a liquid polyisoprene or depolymerized natural rubber or polyisobutylene, polybutene or polypropylene oils and the liquid copolymers thereof, for examp 1 a PAPAPOLT"" ( Exxon ) , or L I RT"" ( f rom KURAPAY ) .
The amount of plasticizer should be such that the setting temperature is not lowered beyond the limit referred to above. In a preferred embodiment the total 2I59~~~

plasticizes content in a low modulus formulation is not less than 10~ by weight and not higher than 40o by weight.
In low modulus compositions, the use of aromatic resins, which have no effect on adhesive properties, which interfere with the hard blocks of SBC's and which stiffen the composition and tend to increase viscosity, is generally not desirable and the preferred level of aromatic resins is zero. However, limited quantities 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 low total styrene content (say up to 6$) or which include significant amounts of SIS, for example 30~ by weight or more of SIS based on the total SBC(s). In fact SIS copolymers, especially the ones which have a styrene content < 30~ by weight when diluted into the composition by resin and other additives, can show an inadequate (too low) modulus and poor characteristics of elastic return as a result both of the intrinsic lower modulus of SIS and the low concentration of styrene, acting as a physical vulcanizing agent. In this case the aromatic resin can both increase modulus to 21~993~
_ _ 47 a useful level and increase the density of hard domains, that are swollen by the resin. Useful aromatic resins have a softening point from 115 to 160°C and are chemically identified as derivatives of styrene, alpha-methyl-styrene, vinyl-toluene, coumarone- indene and copolymers thereof; alkyl-aryl resins etc.
Apart from the components discussed above the compositions can contain the usual additives such as antioxidants, U.V. inhibitors, pigments and colouring materials, mineral fillers etc. Generally in a total amount up to 20~ by weight.
Without limitation as to their most suitable processing and use, the low modulus formulations are typically used in the stretched state at typical extension levels of 400-1000$. They are characterized by very high elongation at break (over 1100$ and often over 14000 and very good adhesive, often pressure sensitive adhesive properties.
In order to simulate the application of the composition into an absorbent article, pressure sensitive adhesive properties were measured as loop tack (or "Quick Stick Tack") and 90° peel according to the standard methods FINAT Test MEthod No 9 for the loop tack and FINAT test Method No 2 for the 90° peel, modified as defined herein.
- For both tests the compositions were applied on a polyester film at a weight of 80 g/m2.
- Adhesive properties, both as loop tack and 90° peel, were measured on a polyethylene film fixed on the standard test plate.
- Loop tack values were expressed as peak values, ignoring the initial peak.
- The 90° peel was evaluated after compression by a 400 g roll passed back and forth, i.e. two passes, one in each direction, and measurements were made 20 minutes after contact of adhesive and polyethylene.
The compositions used according to the invention generally have a loop tack > 5 N/cm and 90° peel > 7 N/cm (separating speed = 300 mm/min). Materials which can usefully be bonded and assembled at room temperature into a hygienic product are considered to be those which show on polyethylene loop tack > 2.5 N/cm and 90° peel strength > 3 N/cm.

High modulus formulations are elastic, adhesive, extrudable compositions similar to those described previously and having the following characteristics:
1) They have a modulus higher than 0.5 MPa and more preferably not lower than 1 MPa up to 10 MPa.
2) At 180°C and with an applied shear rate of 80 sec-1 they have viscosities of 80000 cps or less preferably 50000 cps or less and more preferably 35000 cps or less.
3) They are based on the same types of SBC's referred to previously, but which have a final block styrene content of from 15 to 30% by weight and preferably from 15 to 25o by weight. 4) The SBC or blend of SBC's which is used has a diblock content not exceeding 25% and preferably not exceeding 10%. The most preferred polymers are those with no content of diblocks such as those marketed by DEXCO Co under the trade name VECTORTM
5) The preferred SBC(s) contain from 20 to 50o by weight of styrene and the preferred level of SBC or blend of SBC's in the composition is from 35 to 75% by weight, provided that both the styrene content of SBC's and their level in the composition are such as to match the requirement of point 3) above about final styrene content.

- 2~~993~
- So 6) The tackifying resin/blend of tackifying resins has~have the same chemical and physical characteristics as already discussed above. However, the preferred content is from 20 to 40~ by weight.
7) The content of high molecular weight rubbers such as polyisoprene, polybutadiene, polyisobutylene, butyl rubber, natural rubber, SIR and SBR should not exceed 10~
by weight and preferably is less than 5$ by weight based on the total composition.
8) The total content of plasticizers, as previously described should not exceed 25~ by weight.
9) Aromatic resins or blend of the same are still preferably avoided for their detrimental effect on adhesive and stress/strain properties (steeper stress/strain diagrams generation of a yield point and consequently of an unrecoverable plastic deformation).
However, as in the previous case, these materials can be present at levels up to 20$ by weight with acceptable properties in the composition provided that the non-adhesive/non elastomeric part of the composition does not exceed 50~ by weight of the total composition.
This non-adhesive/non-elastomeric part is formed by the 2~~99~~

sum of the total styrene content in the composition plus the content of aromatic resin/resins.
Other requirements and other possible further components and additives remain the same. In particular it is still required that the true rheological setting temperature (measured as the crossing point between G' and G") is not lower that 80°C and preferably not lower that 100°C.
Again with no limitations on their processing and use, these high modulus compositions are often applied in the unstretched state, especially the ones having moduli > 1 MPa. This preferred use is due to the fact that they are capable of giving sufficient elastic return forces even at low deformations (typically not higher than 50~) which are often met during use of stretchable hygienic articles which can conveniently be made elastic and resilient in this way. This is also due in part to the fact that assembling with the composition in the stretched state implies the need to apply the composition at about room temperature and so requires that it adhere strongly to substrates even in these conditions (pressure sensitive adhesive properties). The pressure sensitive character of adhesives tends to be inversely proportional to their elastic modulus.
However, some of the high modulus compositions according to the invention still retain distinct and useful pressure sensitive behaviour (loop tack on PE >
2.5 N/cm; 90° peel on PE > 3 N/cm) and can be applied also at room temperature and in the stretched state at typical elongations up to 400 with the elongations at break of these compositions typically over 900$.
Adhesive properties are measured under the same conditions as for low modulus compositions.
The unexpectedly good level of elasticity of the compositions according to the invention can be measured as retention of tensile strength after cyclic deformation. This is a test that simulates conditions in use on a hygienic article where the movements of the wearer can cause further and subsequent elongations of the elasticated parts which, for optimum behaviour, must regain their initial length with only minor losses of tensile strength. All the compositions are tested starting from an already stretched state and are given a further elongation of about 15$ of the initial stretched length, in order to simulate movements of the wearer.

2~ ~993'~

The compositions were cyclicly stretched and released fifty times from the initial elongation to the further stretched elongation.
The $ retention in tensile strength at the initial elongation after 50 cycles of stretching at a speed 500 mm/minute, compared to the initial tensile strength, was taken as a measure of the elasticity of the materials.
Tests were performed at room temperature on bands 2.54 cm wide.
- Low modulus compositions were stretched at an initial elongation typical of intended applications of 800 and then cyclicly further stretched and released 50 times between 800 and 920$ (ie from 9 to 10.2 times the initial length of the sample).
- High modulus compositions were tested in the same manner but at an initial elongation typical of intended applications of 300 and under 50 cycles of further elongation and relaxation between 300 and 345.
The term "tensile strength retention after 50 cycles" as used herein refers to the test described above. A natural rubber vulcanized elastic produced by the company JPS Elastomerics which is used in the leg elastication of diapers and applied at an initial _ 2.~~9~3~

stretched deformation of 220$ was taken as a reference and was cyclicly deformed 50 times between 220 and 255$
It was found that under these conditions the natural rubber vulcanized elastic, after 50 cycles, had an average retention of tensile strength equal to 47$ of the initial tensile strength at 220$. This level of retention of tensile strength was considered indicative of good elastic behaviour.
More generally it was observed that materials that do not lose more that 60$ of their initial tensile strength in these test conditions, show good elastic behaviour. Retention of tensile strength less than 40$
represents unsatisfactory elasticity as indicated by slow return to the initial length after release of stretching, high permanent plastic deformations etc.
All of the thermoplastic elastomeric compositions referred to above can be completely or partially deactivated in the manner described by the application of suitable levels of heat and/or pressure. Accordingly in the use of these compositions to provide elastication to an article, suitable elements are provided in the processing apparatus to apply the required level of heat and/or pressure to those parts of the thermoplastic ~~~~~3~
elastomeric composition which are to be deactivated. For example in the manufacture of an absorbent article the thermoplastic elastomeric composition can be applied to a substrate in the form of a thread or strip under elastic tension by means of a suitable extrusion device and then passed through a nip roll adapted to apply a varying level of temperature and pressure. The elastic tension can thereby be retained in some areas of the composition and deactivated in other areas.
The extrusion of elastomeric hot melt adhesives of the type referred to above in the form of threads and strips is described in more detail in our co-pending patent application No. [-] (internal reference DR 3.1).
According to one embodiment of the invention application of heat and/or pressure in the manner described above can be used to enhance the adhesion of the composition to a substrate. As already indicated by no means all thermoplastic elastomeric compositions are adhesive at room temperature and in cases where it is desired to use a composition which is not adhesive at room temperature then adhesive properties can be improved by application of heat and/or pressure to the extent that elastic tension may be completely or partially ._ deactivated. However, provided that the deactivation/enhancement of adhesive properties takes place only over limited areas of the composition, for example at a series of points along the length of a strip or thread of the composition as this is applied to the substrate, the composition will adhere to the substrate by means of those areas which have been subjected to heat and/or pressure, whilst remaining areas can still provide the required elastication. The same effect can be used to enhance adhesion of thermoplastic elastomeric compositions which are adhesive at room temperature, for example when using such compositions on substrates which are difficult to bond. Such point deactivation can be provided by means of a suitable roll, for example a toothed surface roll.
Point deactivation as described above to improve adhesion in areas where elastic properties are required can be used together with complete deactivation of elastic tension in other areas where elastic properties are not required. Separate rolls can be used for the point deactivation to improve adhesive properties and for the complete deactivation. Alternatively, by suitable design of a roll both functions (improved adhesion and _ ~.~~~~3~
complete deactivation) can be performed by the same roll.
For example, the roll can be provided with sectors which have different effects depending on whether point deactivation to improve adhesion or complete deactivation to deactivate elastic tension is required.
As mentioned above the present invention also provides an elasticated article, for example an elasticated absorbent article, wherein the elastication is provided by a thermoplastic elastomeric composition parts of which have been deactivated in the manner described.
The absorbent article may be a baby diaper, a diaper for incontinent adults, an incontinence garment, a sanitary napkin, a pantiliner, etc. The adhesive composition may provide elastication to the article in, for example, the waist or leg area of a diaper or generally in any area where elastication is required.
Other articles which can be provided with elastication in a similar manner include non- absorbent articles such as masks, gowns and gloves, for example for surgical use, and preferably of the disposable type.
The present invention will now be illustrated with reference to a hygienic disposable product such as a _ ~ ~1 X993 °~
5g diaper, although this should not be considered as in any way limiting on the overall scope of the invention.
In the accompanying drawings:
Figure 1 is a perspective view of a diaper.
Figure 2 is a partially cut away plan view of the disposable diaper of figure 1 opened out into planar configuration;
Figure 3 is a schematic diagram of an apparatus used to produce a hygienic disposable product more specifically a disposable baby diaper;
Figure 4 is a cross section through a toothed surface roll used for point deactivation.
Disposable diapers having many different basic designs are known to the art and reference can be made, for example, to U.5. Patent Re 26152, U.S. Patent 3860003, European Patent Application No. 82200801.7, U.S.
Patent 4324245, U.S. Patent, 4337771, U.S. Patent 4352355 and U.S. Patent 4253461.
The diaper illustrated in Figure 1 is based on the disposable diaper design disclosed in US Patent 3860003.
The diaper shown in Figure 1 is merely for illustration and it will be appreciated that the present invention can be applied to any other design of diaper.

2I5~93~

Figure 1 depicts a disposable diaper indicated generally as 10 which is shown in perspective in a configuration as if it were applied about an infant.
Disposable diaper 10 comprises a front portion 11 and a rear portion 12 with a crotch portion 13 interposed therebetween. In use, crotch portion 13 is placed between the legs of the infant and front portion 11 and rear portion 12 are placed, respectively, along the front and rear lower portions of the wearer's trunk. Topsheet 15 forms the inner surface of disposable diaper 10 while backsheet 14 forms its outer surface. Side flaps (or leg cuffs) 16 fit about the wearer's thighs. In use, front waistband 17 and rear waistband 18 are placed adjacent the wearer's waist regions on, respectively, the front and rear portions of the wearer's trunk. Disposable diaper 10 is held in position about the wearer by fastening tape 19. Outer margin of waistband 29 is shown in Figure 1 as the upper edge of disposable diaper 10.
Figure 2 is a partially cut away plan view of disposable diaper 10 opened out into a planar configuration. Topsheet 15 is, in this illustration, the upper surface of the diaper while backsheet 14 is the lower surface. Absorbent element 21 is interposed between _ 2~5993~
topsheet 15 and backsheet 14. As illustrated, disposable diaper 10 is generally symmetrical about longitudinal center line 25 and lateral center line 26. While this is a preferred configuration, it is not necessary that disposable diaper 10 be symmetrical. An asymmetric orientation about lateral center line 26, as when crotch portion 13 is transposed toward front waistband 17, is quite useful.
Disposable diaper 10 is provided with elastic members 22 in the side margins thereof running generally parallel to longitudinal center line 25. In the embodiment illustrated, two elastic members 22 are placed on either side of disposable diaper 10; single or multiple elastic members can be used.
Fastening tapes 19 are secured to disposable diaper 10 adjacent rear waistband 18.
Front waist elastic element 23 and rear waist elastic element 24 are positioned, respectively, in front waistband 17 and rear waistband 18 and adjacent outer margin of waistband 27. In the embodiment illustrated in Figures 1 and 2, disposable diaper 10 comprises elastic waist elements in both the front and the rear waistbands.

_ 2I~~93'~

The elastication could however be only in the front or rear waistband.
The elastication 23 and 24 as shown in Figures 1 and 2 extends across essentially the entire lateral width of disposable diaper 10. The elastication 23, 24 may only extend across a portion of the lateral width of the diaper. Preferably they extend across a major portion of the lateral width of the disposable diaper. The elastication 23, 24 is provided by a thermoplastic elastomeric composition, preferably an elastomeric hot melt adhesive, as described herein.
One major function of backsheet 14 is to prevent body fluids from escaping from disposable diaper 10 and soiling the wearer's outer garments and other surfaces in contact with the disposable diaper. Any compliant, non-irritating planar material which is impermeable to body fluids can be used as backsheet 14. Conventional materials may be used as a back sheet, for example those as described in the aforementioned patents and application concerning diapers. A preferred backsheet is formed from polyethylene film having a thickness of from about 0.012 to about 0.051 millimetre (mm).

Breathable backsheets (i.e. backsheets that permit the passage of vapor and air while retarding the passage of liquid) useful in the present invention are described in, for example, US 3156242, US 3881489, US 3989867, US
4341216.
The size of backsheet 14 is dictated by the exact diaper design selected and the size of the infant intended to be the wearer; it can be readily ascertained by those skilled in the art.
Topsheet 15 can be any compliant, soft feeling, non-irritating (to the wearer's skin) planar material. It functions to contact the wearer's skin, to receive fluid discharges, to allow the discharges to pass readily therethrough into the absorbent element, and to isolate the wearer's skin from the fluids in the absorbent element. To aid in effective performance of the last function, the topsheet is preferably hydrophobic.
Topsheet 15 can be porous paper made from natural or synthetic fibers or mixtures thereof, non-woven fabric made from natural or synthetic fibers or mixtures thereof, apertured plastic film, porous foam, or the like. Examples of suitable topsheets are described in the aforementioned patents and patent application.

A preferred topsheet is spun bonded non-woven polyester fabric made from fibers of from 2.2 to 2.5 denier, having a basis weight of 17 grams (g) per square meter (M2). Another preferred topsheet material has a basis weight of 22 g per M2 and comprises 65~ (by weight) staple length, 1.5 denier polyester fibers (such as Kodel type 411 polyester fibers as sold by Tennessee Eastman Corporation, Kingsport, Tennessee) 15~ crimped, staple length, 1.5 denier rayon fibers and 20$ acrylic copolymer binder (such as Celanese CPE 8335 as sold by Celanese Corporation of Charlotte, North Carolina).
"Staple length" refers in this case to fibers having a length of at least 15 mm.
Still another preferred topsheet is constructed from polypropylene fibers which have been carded and thermally bonded in a spaced-apart pattern. Fibers 3.8 centimetres (cm) long and of from 1.5 to 3.0 denier are suitable. A
preferred topsheet of this type has a basis weight of 24 g per M2.
Suitable topsheets can also be constructed from apertured plastic films such as those described in U.S.
Patent 4342314, U.S. Patent 4341217 and U.S. Patent 3929135.

2I~99~~

As with the case of backsheet 14, the size of topsheet 15 is dictated by the exact diaper design selected.
Absorbent element 21 can be any means which is generally compressible, conformable, non-irritating to the wearer's skin, and which is capable of absorbing and retaining fluids.
Absorbent element 21 can be constructed from any of a variety of materials commonly used in disposable absorbent articles and which are described in the hereinbefore incorporated patents. Examples of suitable absorbent materials include creped cellulose wadding, absorbent foams, absorbent sponges, super absorbent polymers, and, preferably, comminuted and airlaid wood pulp fibers commonly referred to as absorbent fluff. An absorbent fluff having a density of from 0.05 to 0.175 g per cm3 is generally acceptable.
As in the case of backsheet 14 and topsheet 15, the size of absorbent element 21 is dictated by the exact diaper design selected.
Optionally, absorbent element 21 can have associated with either or both planar faces envelope tissues (not illustrated in the drawings) comprising any permeable 2~5993~
material well known to those skilled in the art, such as wet strength tissue paper. When used, envelope tissues are generally coextensive with absorbent element 21 and either coterminous therewith or folded up and about the laterally extending margins thereof. Envelope tissues can optionally be secured to absorbent core 21 by any means well known to those skilled in the art.
Absorbent element 21 is interposed between backsheet 14 and topsheet 15. The diaper design selected determines whether or not the three elements are coterminous although, in general, either backsheet 14 or topsheet 15 or both extend beyond the margins of absorbent element 21.
Optionally, backsheet 14 can be secured to absorbent element 21 by any convenient means (not illustrated in the drawings) well known to those skilled in the art.
Examples of suitable means are parallel beads of adhesive (such as hot melt adhesive) and double sided adhesive taped each extend essentially the entire longitudinal length of absorbent element 21. The backsheet 14 and absorbent element may be secured together using the elastomeric hot melt adhesive as disclosed herein.

_ 2I5993~

Elastic members 22 serve to contract or gather the cuffs (longitudinally extending margins) of disposable diaper 10 and maintain them in contact with the legs of the wearer thereby providing improved fit and reducing fluid leakage from the diaper. The elastic members are provided by a thermoplastic elastomeric composition, preferably an elastomeric hot melt adhesive, as described herein.
As shown in Figures 1 and 2, elastic elements 22 extend over the whole longitudinal length of disposable diaper 10, but following application to the diaper 10 in a stretched state is subjected to a heat and/or pressure treatment in defined areas as described herein to deactivate elastic tension. According to one embodiment of the invention the elastic elements 22 are subjected to total deactivation in areas adjacent to the front and rear elastication 23 and 24 and point deactivation over the remainder of their length. As shown in Figure 2, elastic elements 22 are subjected to total deactivation in areas designated "A" and point deactivation in the area designated "B". As noted previously, the effect of point deactivation is to improve adhesion of the elastic elements to the diaper top-sheet 15. The diaper can be - ~1~993~

produced in an apparatus described in more detail with reference to Figure 3 and deactivation can be effected using a toothed surface roll described in more detail with reference to Figure 4.
The elastication on the diaper may be provided by the thermoplastic elastomeric composition as disclosed herein in the form of threads, yarns, bands, strips, continuous films, networks of fibers both continuous or having a finite length and in which the fibers have both a random orientation or a geometrically regular orientation. The threads or strips may be in linear or non-linear (curved) geometry.
Figure 3 is a schematic diagram of an apparatus depicting equipment and materials used to form a disposable baby diaper. A non-woven used as top sheet for the disposable baby diaper is fed from roll 30 as raw material 11. The raw material 11 passes in proximity to a device for applying a hot melt adhesive by virtue of first idler roller 12 which is provided with a non-adherent, e.g. silicone, coating. As shown in Figure 3, this device has a form particularly adapted for the application of threads of elastomeric hot melt adhesive and comprises a hot melt applicator which extrudes _ 2~.~~93~
_ 68 threads of hot melt adhesive on to a conveyor belt 6 moving in the direction of the arrow. In the interests of clarity the threads themselves are not shown in Figure 3.
The threads are cooled by a fan 7 positioned beneath the conveyor belt and are then transferred to the raw material 11 which is brought into contact with the threads by means of silicone first idler roll 12. The desired degree of elastic stretching of the threads on application to the raw material 11 is achieved by the difference in speed between the conveyor belt 6 (which is also the speed of the threads prior to application) and the raw material 11 itself.
The threads may optionally be provided with a curved geometry relative to the raw material 11 as they are transferred to raw material 11 by means of one or more combs 9 which are moveable in a plane parallel to the plane of the raw material 11, movement of the combs 9 being achieved by a cam 10. Curved geometry may be useful, for example, in the case where the thread is to form leg elastication for a diaper but is not essential and is not used in the diaper shown in Figure 2.

_ 21~993~

As noted above, the device for applying hot melt adhesive shown in Figure 3 is adapted for the application of threads of elastomeric hot melt adhesive by virtue of the fact that it allows for elastic stretching of the threads on application to the raw material 11. However, a non- elastomeric hot melt adhesive can be applied in the form of threads direct to the raw material 11 using conventional extrusion equipment.
Following application of the threads of hot melt adhesive, the raw material passes to silicone rolls 14 which press the threads onto the surface of the raw material 11 and then to a deactivating unit 15. The deactivating unit may for example be a toothed surface roll as described in more detail below in connection with Figure 4 acting in conjunction with a smooth counter roll The toothed surface roll provides areas of total deactivation corresponding to "A" in Figure 2 and areas of point deactivation corresponding to "B".
The raw material with threads attached and following deactivation, then passes to point 55 where it is joined by core material from a core supply unit and cut unit 50 and back sheet from a roll 60 to form a composite material. The composite material then passes through an ~Z ~993'~
_ 70 optional crimp unit 70 in which the various elements are pressed in order to improve adhesion particularly around the perimeter. Thereafter the material passes through a final cut unit 90 to form the final product. It is to be noted that at various points in this process the components of the final product have non-elastomeric hot melt adhesive 110 applied thereto and pass through vacuums 100.
As already noted, the deactivation unit 15 comprises a toothed surface roll as shown in Figure 4 and a counter roll with a smooth surface. Figure 4 shows the toothed surface roll in cross section and the roll is provided over two segments of its surface with transverse grooves 16 that run parallel to the generatrix of the cylinder.
The roll also has two segments of its surface 17 which are smooth. When the roll is in contact with a substrate, for example raw material 11, point deactivation is brought about by the protruding ridges between the grooves 16 whereas total deactivation is brought about by the smooth segments 17. The relative sizes and positions of the grooved and smooth segments of the roll are provided in such a way that the required areas of total deactivation and point deactivation are _ 2.~~99~~
m obtained in the end product. Accordingly when, for example, the deactivation unit is used in the production line for the production of a diaper as shown in Figures 1 and 2, the smooth sectors totally deactivate areas which will become the ends of the diaper (sections "A" in Figure 2) whereas the grooved segments perform point deactivation (which may be complete or partial) in the areas which will become the middle portion of the diaper (section "B" in Figure 2) to enhance adhesion to the substrate.
In the roll shown in Figure 4, each smooth segment 17 is constituted by a separate insert 18. The distance between the external surface of the inserts 18 and the axis of the cylinder can be adjusted by thin spacer blocks 19 between the separate inserts 18 and the remainder of the roll 22 prior to starting operation of the apparatus which in turn means that the roll can exert different pressures on the threads with the grooved (toothed) segments on the one hand and the smooth segments on the other. The temperature of the surface of the cylinder can be adjusted independently in the grooved and in the smooth segments by means of electric heating elements 20 under the control of probes 21, heating 21~993~

elements and probes each being incorporated into the structure of the roll.
Compositions for use according to the invention are illustrated by the following examples which should not be considered as in any way limiting on the invention. In the case of proprietary products, details of their nature and composition is that provided by the manufacturer.
The compositions of all of Examples 1 to 5 are suitable for the elastication of absorbent articles in accordance with the invention with deactivation of elastic tension in areas where elastic properties are not required. The compositions of all of Examples 1 to 5, when applied from the molten state between plastics and/or cellulosic materials at a weight of 5 g/m2 showed a bond strength well in excess of O.S N/cm.
Elastic properties were also judged by the following method: The compositions in the form of bands 2,54 cm wide, were tested at 23°C and at a stretching speed of 1000 mm/minute, with 3 cycles of elastic hysteresis between zero and a typical possible elongation in application i.e. 800 for low modulus and 300$ for high modulus compositions. The elastic energy of each cycle evaluated as the area of the cycle was recorded and the ratio between the elastic energy of the third and the first cycles was determined as retention of elastic energy after 3 hysteresis cycles. For good elastic behaviour it is believed that under these test conditions, a retention of elastic energy not lower than 30~ is required.
The conditions required to deactivate the elastic tension of the compositions described in the following examples can be calculated theoretically based on the elastic modulus of the composition i.e. as explained above a temperature at least equal to the inversion temperature must be applied in the absence of the application of pressure or a lower temperature can be used provided that pressure is applied at least equal to the elastic modulus at that temperature. However in practice deactivation will be in a processing apparatus, for example by use of a heated roll and in this case the conditions that need to be applied, for example, the temperature of the roll and the clearance between the rolls which determines pressure, will vary depending on other processing conditions such as the thickness of the material and the speed at which it is being passed through the apparatus. Thus, for example, based on elastic modulus, the composition of Example 4 below can be deactivated at 90°C by application of a pressure of 0.02 MPa. However in practice it would be necessary to determine empirically the conditions (roll temperature and clearance between the rolls) to be used to achiveve deactivation.

An SBC polymeric system based on SBS (styrene-butadiene- styrene block copolymers) was formulated as follows:
CARIFLEXT"' TR-4113 S 36 % by weight EUROPRENET"" SOL 12 0 5 8 %
DERCOLYTET~" A 115 4 5 . 8 %
FORALT"" 8 5-E 6 %
HERCOLYNT"" D-E 4%
I RGANOXT"" 1010 0 . 2 %
where:
- CARIFLEX TR-4113 S is an oil-extended SBS copolymer available from SHELL Co said to contain:

68.5% by weight of a linear triblock SBS having a styrene content of 35% by weight and with a diblock content < 20% by weight 31.5% by weight of a naphthenic mineral oil, acting as a plasticizer, and containing less than 5% of aromatics.
- EUROPRENE SOL 1205 is styrene/butadiene rubber (SBR) available from ENICHEM. (The product FINAPRENE 1205 available from FINA is similar and could equally be used.) It is described as a solution polymerized SBR having a Mooney viscosity ML (1 + 4) at 100°C equal to 47 and a total styrene content of 25% by weight. This styrene is partially (typically from 15 to 18%) distributed in blocks with the remainder being randomly copolymerized with butadiene. The randomly copolymerized styrene gives the rubbery part of the molecule the chemical structure of an amorphous SBR, which contributes to the development of particularly good pressure sensitive adhesivity.
- DERCOLYTETM A 115 (the main tackifying resin) is available from DRT. It is a polyterpene resin derived from alpha-pinene having a softening point of 115°C.

_ 21~99~7 - FORAL 85-E is a tackifying resin composed of a hydrogenated glycerol ester of rosin available from HERCULES Co. It has a softening point of 85°C.
- HERCOLYN D-E is a liquid methyl ester of rosin available from HERCULES.
- IRGANOX 1010 is a phenolic antioxidant available from CIBA-GEIGY.
The composition was found to have the following properties:
- total styrene content = 10.6$ by weight of which 10.1$ is in blocks - viscosity at 180°C at 80 sec-1 = 20520 cps - modulus at 500$ elongation - 0.182 MPa (low modulus) - elongation at break > 1400$ (1400$ was the maximum elongation achievable on the machine used for the determination) - rheological setting temperature (crossover point of G' and G") - 125°C
- loop tack on PE = 8.5 N/cm - 90° peel on PE = 16.3 N/cm - tensile strength retention after 50 cycles between 800 and 920$ = 59.8$

- elastic energy retention after 3 hysteresis cycles between zero and 800$ = 57.7$
- Newtonian Index (N. I.) - 1.05.
The composition showed extremely good elastic and adhesive properties and was considered completely suitable for elastication of structures, particularly hygienic absorbent articles. It was easily processable i.e. extrudable, having quick setting (stretchable on line) and having good pressure sensitive characteristics allowing the formation of strong bonds on simple contact with many substrates even at room temperature.

The formulation was:
CARIFLEX TR-41135 38.8$ by weight FINAPRENE 1205 8.9$
DERCOLYTE A115 26$
FORAL 85-E 26$
IRGANOX 1010 0.3$
The following properties were measured:

- 215993' - total styrene content = 11.5$ by weight of which 10.9 is in blocks - viscosity at 180°C at 80 sec-1 = 28180 cps - modulus at 500 elongation = 0.188 MPa (low modulus) - elongation at break > 1400 - rheological setting temperature = 120°C
- loop tack on PE = 8.6 N/cm - 90°C peel on PE = 10.4 N/cm - tensile strength retention after 50 cycles between 800 and 920 = 59.1 $
- elastic energy retention after 3 hysteresis cycles between zero and 800$ = 48.3 $
- Newtonian Index (N. I.) - 1.01.
The composition was similar to that of Example l, the main variation being the fact that about 500 of the high softening point tackifying resin was substituted by a lower softening point resin and the only plasticizer was the oil contained in CARIFLEX TR-4113 S (12.2 by weight of the composition). Nevertheless it was found that the composition still retained a very high solidification temperature, quick setting as well as optimum elastic and pressure sensitive adhesive properties and excellent processability, so that it was easily possible to extrude and immediately stretch it even to 800% in the form of very thin threads (diameter = 0.4 mm) that could be applied for the side elastication of an absorbent product.

A different system based on radial SBS was tested, more precisely a blend of one SBS with relatively low hard block content and one SBS with relatively high hard block content.
The formulation was as follows:
FINAPRENE 415 17.7% by weight FINAPRENE 401 7.0%
FINAPRENE 1205 8.0%
ZONATAC 115 LITE 45.8%

6.3%
HERCOLYN D-E 4.0%
SHELLFLEX 4510 FC 11.0%
IRGANOX 1010 0.2%
where:

215993' s0 - FINAPRENE 415 and FINAPRENE 401 are radial SBS
copolymers available from FINA. Both are supposed to contain less than 20$ diblock and to be formed by a "star" structure of four blocks of SB chemically linked in a central point through 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 terpene tackifying resin with a softening point of 115°C
available from Arizona Co. It is supposed to be based on limonene modified with styrene.
- SHELLFLEX 4510 FC is a naphthenic mineral oil, available from SHELL, which is supposed to have an aromatic content < 5$.
The following properties were measured:
- total styrene content = 10.6$ by weight of which 10.1$ is in blocks - viscosity at 180°C at 80 sec-1 = 12810 cps.
- modulus at 500$ elongation = 0.223 MPa (low modulus) - elongation at break > 1300$
- rheological setting temperature = 107°C
- loop tack on PE = 6.4 N/cm - 90° peel on PE = 14 N/cm 8l - tensile strength retention after 50 cycles between 800 and 9200 - 50%
- elastic energy retention after 3 hysteresis cycles between zero and 8000 - 44.9%
- Newtonian index (N. I.) - 1.04.
The composition showed properties typical of a very good and easily processable elastic, extrudable adhesive material.

The following high modulus composition was made with the formulation:
VECTOR 4461-D 44.8% by weight ZONAREZ 7115 LITE 37%

ZONAREZ ALPHA 25 3%

PRIMOLT"" 352 10 0 IRGANOX 1010 0.2%

where:

21~993~

- VECTOR 4461-D is a linear SBS copolymer having 430 by weight of styrene and no diblock content available from DEXCO Co.
- ZONAREZ 7115 LITE is a polyterpene tackifying resin, having a softening point of 115°C, derived from limonene, available from ARIZONA Co.
- ZONAREZ ALPHA 25 is a liquid tackifying resin (S. P.
- 25°C) derived from alpha-pinene having a very good plasticizing effect. It is available from ARIZONA Co.
- PRIMOL 352 is a plasticizing, paraffinic mineral oil available from EXXON, which is said to contain no aromatics.
The following properties were measured:
- total block styrene content = 19.3$ by weight - viscosity at 180°C at 80 sec-1 = 16810 cps.
- modulus at 500$ elongation = 1.07 MPa (high modulus) - elongation at break = 987 - rheological setting temperature = 111°C
- loop tack on PE = 4.3 N/cm - 90° peel on PE = 6.5 N/cm - tensile strength retention after 50 cycles between 300 and 345$ = 67.5 2.~~~937 _ 83 - elastic energy retention after 3 hysteresis cycles between zero and 3008 = 63.3$
- Newtonian Index (N. I.) - 1.05.
The composition was a good elastic material useful especially at low elongations. It showed acceptable semi-pressure sensitive characteristics so that is can be bonded to materials also at room temperature in the stretched state.
wasfaewa~w C
The formulation was:
VECTOR 4461-D 54.8$ by weight ECR 368 35~
PRIMOL 352 10$
IRGANOX 1010 0.2~
where:
- ECR 368 is a hydrogenated hydrocarbon tackifying resin, available from EXXON and having a softening point of 100°C.
The following properties were measured:

total block styrene content = 23.56 by weight viscosity at 180°C at 80 sec-1 = 34000 cps.
- modulus at 500$ elongation= 1.61 MPa (high modulus) - elongation at break = 947 - rheological setting temperature = 114°C
- loop tack on PE = 1.3 N/cm - 90° peel on PE = 2.6 N/cm - tensile strength retention after 50 cycles between 300 and 345$ = 62.30 - elastic energy retention after 3 hysteresis cycles between zero and 300 = 38.3 - Newtonian Index = 1.05.
The composition was made so to maximize modulus whilst still retaining acceptable elasticity and good adhesivity at temperatures higher than room conditions.
Such a material is more conveniently applied in the unstretched state and bonded directly at temperature >
50°C. It gives good elastic retention forces even at very low extensions, e.g. modulus at 20~ elongation =
0.236 MPa. However, it also works well in the stretched state, e.g. 300$ elongation, and shows adhesive properties on PE which are not negligible even at room temperature.

_ 2159937 _ _ 8s L'Yn~"~T.1' C
This example relates to the stress/strain diagrams of the compositions of Examples 1 to 5. The elastic hot melt compositions should desirably have a stress/strain diagram that is much flatter than a rubber elastic, i.e.
even if already under tension further stretching (e. g.
due to the movements of the wearer of the absorbent article) cause only a very low increase in modulus and in the tensile strength that is perceived by the wearer.
This is especially true for low modulus compositions and can be seen by measuring the average increase in modulus for a given extension. Low modulus compositions, which are typically applied in the already stretched state, were judged as the mean increase in modulus per 100 increase in elongation, by dividing by 8 the total increase in modulus between 0 and 800$ elongation (nine times the initial length).
Referring to the low modulus compositions mentioned in the above Examples the results were as follows:

~1 X993;

EXAMPLE N0. MEAN INCREASE IN MODULUS PER

STRETCHING
1 0.044 MPa/100~ stretching 2 0.045 MPa/100$ stretching 3 0.063 MPa/100~ stretching The high modulus compositions of Examples 4 and 5, which are generally used in the unstretched state or in any case at lower elongations, were judged as mean increase in modulus per 100 increase in elongation between zero and 300 final elongation:
EXAMPLE N0. MEAN INCREASE IN MODULUS PER

STRETCHING

4 0.169 MPa/100~ stretching 0.284 MPa/100~ stretching As a comparison, a natural rubber vulcanized elastic, used for the leg elastication of diapers, even if applied at much lower extension (typically 2200 showed, between g7 zero and 220%, an average increase in modulus of 0.89 MPa per 100% elongation.
It is possible to compare the behaviour of a natural rubber elastic and of a low modulus composition is described herein.
In the case of rubber elastic, even limited movements of the wearer that cause for instance a further stretching of the elasticated parts as low as say loo elongation, will cause a mean increase in modulus of about 0.09 MPa. By using a low modulus composition the increase in modulus will be about 20 times lower and even with the strongest high modulus compositions several times lower so that the movements of the wearer of an absorbent article elasticated by the compositions disclosed in the present invention are much more free. Accordingly, in these applications low modulus and low variation of modulus with strain are a clear advantage.

The formulation was:
TUFPRENETM A 30.0o by weight 8g ESCOREZT"" CR 368 55.0%
CATENEXT"~ P941 10 . 0 0 KRISTALEXT"" F100 5.0%
with the addition of 0.2 parts per 100 parts by weight of the above composition of the antioxidant IRGANOX 1010, where:
- TUFPRENE A is a linear SBS available from Asahi Chemical CO. and containing 40o by weight of styrene. Diblock content is not specified by the manufacturer.
- ESCOREZ CR 368 is a hydrogenated modified hydrocarbon resin available from Exxon having a softening point of 100°C.
- CATENEX P941 is a paraffinic mineral oil available from Shell which is supposed to have an aromatic content < 5% by weight.
- KRISTALEX F 100 is an aromatic resin based on °-methyl styrene and styrene available from Hercules and having a softening point of 100°C.
The main properties can be summarised as follows:
- total block styrene = 12% by weight - viscosity at 180°C at 80 sec-1 - 5620 cps - modulus at 5000 elongation = 0.204 MPa (low modulus) - elongation at break > 13000 _ ~1~993~
_ 89 - rheological setting temperature (crossover point of G' and G " ) - 10 6 ° C
- loop tack on PE = 0.7 N/cm - 90° peel on PE = 0.8 N/cm - tensile strength retention after 50 cycles between 800 and 920 = 21.3 - elastic energy retention after 3 hysteresis cycles between zero and 800 = 25.0 - Newtonian Index (N. I.) - 1.16 It was found that processability, as shown by viscosity and NI was acceptable although NI was high for an SBS based composition. The formulation had poor pressure sensitive characteristics and values of 0.7 N/cm for loop tack and 0.8 N/cm for 90° peel show it to be practically unusable as a low modulus elastic adhesive, intended to be applied in the stretched state, in the assembly of hygienic absorbent articles. However, when used with the point deactivation technique as described herein, adhesive properties can be improved to an acceptable level.

Claims (21)

1. A method of providing elastication in defined areas of an article which comprises: (a) applying a thermoplastic elastomeric composition under elastic tension to the said article; and (b) deactivating or partially deactivating elastic tension in the said composition outside the said defined areas.

2. A method according to claim 1, wherein the said thermoplastic elastomeric composition is an elastomeric hot melt adhesive composition.

3. A method according to claim 1 wherein the said elastic tension is deactivated or partially deactivated by means selected from:
(i) heating to a temperature of at least the inversion temperature between G' and G"; and (ii) heating to a temperature below the inversion temperature between G' and G" with application of a pressure equal to at least the value of G' at that temperature.

4. A method according to claim 1, for providing elastication to an absorbent article.

5. A method according to claim 4, for providing side elastication in a disposable diaper and in which the said elastic tension is retained in the crotch area and deactivated outside the crotch area.

6. A method according to claim 1, wherein the said thermoplastic elastomeric composition is applied to the said article in a form selected from threads and strips under elastic tension which is subsequently deactivated or partially deactivated outside the defined areas by means selected from application of heat, application of pressure and application of heat and pressure, the said pressure being applied by means of a suitable roller.

7. A method according to claim 1, wherein the said thermoplastic elastomeric composition is subjected to complete or partial deactivation outside of the said defined areas to improve adhesion to the said article.

8. A method according to claim 6, wherein the said thermoplastic elastomeric composition is applied to the said article in a form selected from threads and strips and is subject to complete or partial deactivation to improve adhesion to the said article at a series of points along the length of the threads or strips.

9. A method according to claim 8, wherein the said thermoplastic elastomeric composition is an elastomeric hot melt adhesive composition.

10. A method according to claim 9, wherein the elastomeric hot melt adhesive composition comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer(s) being selected from the group consisting of a styrene/butadiene/styrene (SBS) block copolymer and a blend of styrene/butadiene/styrene with styrene/isoprene/styrene (SIS) block copolymer on which SIS
is present in an amount equal to or less than 50% by weight of the total block copolymer the composition being characterised in that:
a) it is capable of bonding, when applied from the molten state, to plastic and/or cellulosic materials with a 90°
peel force of not lower than 0.5 N/cm.
b) it has a tensile strength retention after 50 cycles of at least 40%; and c) it has a viscosity of 120,000 cps or less at 180°C
and an applied shear of 80 sec-1.

11. A method according to claim 10, wherein the elastomeric hot melt adhesive composition comprises:

1) 10 to 80% by weight of a styrenic block copolymer comprising at least two styrenic end blocks and at least one rubbery mid block per molecule and containing less than 40%
by weight of the total block copolymer of a block copolymer containing only one styrenic block and one rubbery block per molecule;
2) 20 to 90% of a tackifying resin compatible essentially only with the rubbery mid blocks;
3) 0 to 40% of a plasticizer(s);
4) 0 to 200 of an aromatic resin;
the composition being further characterised in that:
a) it is capable of bonding, when applied from the molten state, to plastic and/or cellulosic materials with a 90°
peel force of not lower than 0.5 N/cm;
b) it has a tensile strength retention after 50 cycles of at least 40%;
c) it has a viscosity of 120,000 cps or less at 180°C and an applied shear of 80 sec-1.

12. An elasticated article in which elastication is provided by a thermoplastic elastomeric composition applied to the said article under elastic tension characterised in that the elastic tension has been completely or partially deactivated in defined areas of the said article.

13. An elasticated article according to claim 12, wherein the said thermoplastic elastomeric composition is an elastomeric hot melt adhesive composition.

14. An elasticated article according to claim 12, which is an absorbent article.

15. An elasticated article according to claim 14, which is selected from the group consisting of a baby diaper, diaper for incontinent adults, an incontinence garment, a sanitary napkin and a pantiliner.

16. An elasticated article according to claim 15, which is a disposable diaper provided with side elastication and in which elastic tension is retained in the crotch area and deactivated outside the crotch area.

17. An elasticated article according claim 12, wherein the thermoplastic elastomeric composition is subjected to complete or partial deactivation in defined areas to improve adhesion of the said composition to the said article.

18. An elasticated article according to claim 17, wherein the said thermoplastic elastomeric composition is applied to the article in a form selected from threads and strips and is subjected to complete or partial deactivation to improve adhesion of the said composition to the said article at a series of points along the length of the threads or strips.

19. An elasticated article according to claim 18, wherein the said thermoplastic elastomeric composition is an elastomeric hot melt adhesive composition.

20. An elasticated article according to claim 19, wherein the said elastomeric hot melt adhesive composition comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer(s) being selected from the group consisting of a styrene/butadiene/styrene (SBS) block copolymer and a blend of styrene/butadiene/styrene with styrene/isoprene/styrene (SIS) block copolymer on which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer the said composition being characterised in that:
a) it is capable of bonding, when applied from the molten state, to plastic and/or cellulosic materials with a 90°
peel force of not lower than 0.5 N/cm.
b) it has a tensile strength retention after 50 cycles of at least 40%; and c) it has a viscosity of 120,000 cps or less at 180°C and an applied shear of 80 sec-1

21. An elasticated article according to claim 19, wherein the elastomeric hot melt adhesive composition comprises:
1) 10 to 80% by weight of a styrenic block copolymer comprising at least two styrenic end blocks and at least one rubbery mid block per molecule and containing less than 40%
by weight of the total block copolymer of a block copolymer containing only one styrenic block and one rubbery block per molecule;
2) 20 to 90% of a tackifying resin compatible essentially only with the rubbery mid blocks;
3) 0 to 40% of a plasticizer(s);
4) 0 to 20% of an aromatic resin;
the said composition being further characterised in that:
a) it is capable of bonding when applied from the molten state, to plastic and/or cellulosic materials with a 90°
peel force of not lower than 0.5 N/cm (as herein defined);
b) it has a tensile strength retention after 50 cycles (as herein defined) of at least 40%;
c) it has a viscosity of 120,000 cps or less at 180°C and an applied shear of 80 sec-1.