CA2159939C - Adhesive composition and process therefor - Google Patents
Adhesive composition and process therefor Download PDFInfo
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Abstract
The invention relates to an elastomeric hot melt adhesive in the form of a stable foam which can be used to elasticate structures such as absorbent articles which can be applied without the use of any glue. A
hot melt adhesive composition is used as the basis for the foam, which composition comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer(s) being a styrene/butadiene/styrene (SBS) copolymer or a blend of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, and wherein the hot melt adhesive composition is further characterized 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); 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.
hot melt adhesive composition is used as the basis for the foam, which composition comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer(s) being a styrene/butadiene/styrene (SBS) copolymer or a blend of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount equal to or less than 50% by weight of the total block copolymer, and wherein the hot melt adhesive composition is further characterized 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); 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.
Description
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ADHESIVE COMPOSITION AND PROCESS THERE~'~OR
The present invention relates to an adhesive composition in the form of a foam. More particularly the invention relates to a hot melt adhesive which, on the one hand has elastic properties and is in the form of a foam in the solid state while, on the other hand, has very low and in many cases negligible elasticity in the molten state as shown by essentially Newtonian behaviour at the processing (application) temperature.
In the manufacture of many different types of article it is necessary to bond an elastic material to a non-elastic substrate. One example is in the manufacture of disposable diapers where elastic strips are used to provide leg and waist elastication. Typically, the elastic strips consist of stretchable rubber which is fixed to the body of the diaper by layers of adhesive, for example hot melt adhesive, affixed to both surfaces.
This arrangement involves a number of difficulties.
For example, the elastic strip is often covered with an anti- blocking agent such as talc during manufacture to prevent the strip bonding to itself. However, this anti-blocking agent can, in turn, render bonding of the elastic strip to the body of the article much more difficult. Furthermore, since the hot melt adhesives which are used do not themselves have real elastic properties, application of adhesive tends to "kill" the stretch of that portion of the elastic to which it is applied. Finally, the use of the two materials, rubber and adhesive, is costly.
A composition having adhesive properties on application from the molten state and preferably also pressure sensitive adhesive properties, and elasticity comparable to that, of rubber, whilst also possessing suitable rheological properties for melt processing, is highly desirable since it would be capable of replacing the rubber and the adhesive used at present and would represent a considerable advance in the manufacture of articles such as diapers. Such a composition would also find numerous other applications in many diverse fields.
Further advantages would follow if the composition could be presented for use as a foam.
Many types of composition are in use commercially as hot melt adhesives and a much wider range of compositions have been suggested for use in this field. A hot melt adhesive can be defined as a composition which shows adhesive properties when applied to a substrate in the molten state. This does not preclude the composition also showing adhesive properties at room temperature, e.g. pressure sensitive adhesive properties. In general, hot melt adhesives are formulated for properties such as adhesion to a variety of surfaces, heat stability and processing properties rather than for elasticity and any attempt to increase elasticity has a detrimental effect on adhesion and other desirable properties of the composition. As yet, none of the commercial hot melt .._ 219939 adhesive compositions combine good adhesion with elastic properties comparable to those of rubber. In addition whilst there have been proposals to foam certain hot melt adhesives, no foamed hot melt adhesive has come into general use.
Natural rubber is generally too viscous to be used as a basis for hot melt adhesives and cured rubber cannot be melted. Many hot melt adhesives are based on thermoplastic block elastomers since these can be melted.
Many such elastomers with a variety of properties are available commercially. For use as an adhesive, thermoplastic block elastomers generally have to be blended with tackifying agents to improve adhesion.
Other additives such as plasticisers may also be necessary depending on the application.
Certain prior art proposals have attempted to provide hot melt adhesives which also have elastic properties. For example US-A-4 418 123 attempts to provide a self-adhering elastic having a combination of elastic and adhesive properties. The composition is defined in very broad terms as a combination of a block copolymer comprising at least one substantially amorphous rubbery polymeric mid block and at least two glassy poly(vinylarene) end blocks, together with a midblock associating resin and an endblock associating resin. All of the specific examples (with the exception of a comparative example with unsatisfactory properties) are based on styrene-isoprene-styrene block copolymers.
Despite the claims made for them, as far as the present applicants are aware, none of the compositions exemplified in US-A-4 418 123 show true elastic properties comparable to those of rubber combined with good adhesion and processability (see Comparative Example A below) .
Similarly EP-A-0 424 295 (HB Fuller France SARL) relates to a thermoplastic elastic intended particularly for elastication of diapers which comprises:
a) at least one synthetic rubber which is of the block copolymer type comprising at least one rubber middle block and at least two glassy end blocks;
b) 20 to 150 by weight based on the block copolymer of at least one "tackifying" resin which associates with the middle block of the copolymer;
c) 10 to 50$ by weight based on the block copolymer of at least one "tackifying" resin which associates with the terminal blocks of the copolymer; and - d) 5 to 35~ based on the weight of the composition of a mineral oil.
It is suggested that these compositions can be foamed. The compositions exemplified in EP-A-0 424 295 are generally based on SIS and an example of a composition based on SBS shows unsatisfactory properties.
There are no examples of the production of foams.
It has now been found that, by careful selection of the components, hot melt adhesives can be produced having the desirable combination of properties referred to above, i.e. good adhesion from the melt (and in many embodiments also at room temperature), elastic properties comparable to those of rubber;
and good processibility from the melt and it has also been found that these hot melt adhesives can be foamed to provide stable foams.
Various aspects of the invention are as follows:
An elastomeric hot melt adhesive in the form of a stable foam comprising a hot melt adhesive composition which comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of l0 styrene/butadiene/styrene (SBS) copolymers and blend of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount not more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterized in that:
15 a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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%;
2 0 and c) it has a viscosity of not more than 120,000 cps at 180°C and an applied shear of 80 sec-1.
A process for the production of an adhesive which comprises (i) providing a hot melt adhesive composition which comprises 2 5 at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of styrene/butadiene/styrene (SBS) copolymers and blends of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount not 3 0 more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterised in that:
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof with a 90° peel force of not lower than 0.5 3 5 N/Cm;
~,.
5a 2 1 5 9 9 3 9 b) it has a tensile strength retention after 50 cycles of at least 40%;
and c) it has a viscosity of not more than 120,000 cps at 180°C and an applied shear of 80 sec-1;
(ii) foaming the said hot melt adhesive composition;
(iii) extruding the foam produced; and (iv) cooling the foam.
Feature a) referred to above relates to the adhesive properties of the composition and in all cases the composition should have the properties of a hot melt A' ~~59939 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 strength, measured as 90° peel of not lower than 0.5 N/cm. 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.
As described in more detail below, many compositions which may be foamed according to the invention also bond appropriate substrates at room temperature and may show tl~e 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 2.59939 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 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 which may be foamed according to the invention show substantially Newtonian rheological behaviour, in particular viscosity does not vary significantly with applied shear. As discussed in more detail below, many compositions which may be foamed according to the invention show Newtonian behaviour at intended processing temperatures, e.g. around 180°C.
Compositions which may be foamed according to the invention can be formulated with any desired modulus depending on the desired end use. In this connection, reference can be made to the intrinsic modulus which is the modulus of the composition prior to foaming and the apparent modulus which is the modulus of the foamed composition. Apparent modulus is a function of the intrinsic modulus and percent foaming (i.e. foam density). Apparent modulus of a foamed composition is, of course, always lower than intrinsic modulus.
__ Intrinsic modulus has effects on the main properties of the composition and it is convenient to divide the compositions of the invention into low intrinsic modulus and high intrinsic modulus compositions. As used herein the terms "low modulus composition" and "high modulus composition" refer to intrinsic modulus.
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 compositions generally show good adhesive properties at room 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 and foaming using a blowing agent. 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 and foaming 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 2~~9939 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 proportional to modulus, compositions with high modulus are often applied immediately after foaming with the material still in a molten or semisolid state although some may retain sufficient pressure sensitive adhesive character to be applied at room temperature. Application in a molten or semisolid state 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 beyond the need to foam a stable foam 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 ~I~9939 so that they can be applied at room temperature in a stretched state, they can be used at an elongation of up to 400. For practical reasons, the lower limit of apparent modulus is about 0.05 MPa although given that the apparent modulus is a function of intrinsic modulus and foam density, this lower limit applies to both high and low intrinsic modulus compositions.
The essential components of the composition which may be foamed according to the invention are a thermoplastic elastomer and a tackifying resin and these will now be discussed in general terms.
Thermoplastic elastomers are a very interesting chemical and technological class of polymers 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 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 _ n "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 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 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 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 _ 14 content in the thermoplastic elastomeric block copolymer should be kept lower than 40$ by weight.
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, 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:
- 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.
2~ 59939 - "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 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 H (the so called diblocks) should, for use in the present invention, be kept lower than 40$ by weight in the base polymer.
It is widely recognised in the literature that differences exist between SIS and SBS copolymers which are relevant to the formulation of hot melt adhesives.
SBS copolymers generally cost less than comparable SIS
copolymers and SBS copolymers can be synthesized to exhibit better elasticity than comparable SIS copolymers.
However it has not hitherto been possible to take advantage of these potentially advantageous properties of SBS copolymers as a result of the fact that SBS
copolymers have not generally shown adequate adhesive properties and SIS copolymers are much easier to tackify.
For this reason hot melt adhesives have generally been formulated using SIS copolymers as the predominant SBC.
Both US-A-4418123 and EP-A-0424295, which are discussed above, clearly prefer SIS as the SHC on which the compositions are based and neither document discloses a composition based on SBS which has satisfactory properties.
It has been found according to the present invention that compositions in which SBS copolymers are the main polymers) can be produced with satisfactory adhesive properties. At the same time these compositions retain the advantages of SBS copolymers with respect to elasticity which have been mentioned above. Thus, compared to compositions based on other SBC's, compositions can be formulated according to the present invention with better elastic properties, quicker elastic return, more flat stress/strain diagrams even at elongations > 1000 ~ and give compositions of better processability (more Newtonian rheological behaviour).
-- m However, it should be noted that direct comparison between SIS and SBS based compositions is very difficult since the compositions need to be formulated in different ways. Accordingly, it would not generally be possible to substitute an SBS copolymer for an SIS copolymer in a hot melt composition and obtain satisfactory properties and other adjustments need to be made to the formulation depending on the nature of the SBC in order to obtain optimum results. The way in which compositions according to the invention should be formulated to obtain the desired properties is discussed in more detail hereinafter.
Thus the compositions foamed according to this invention are based on SBS copolymers or a blend of SBS/SIS in which SIS is present at levels equal or less than 50~ by weight of the total block copolymer.
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 elastomers which are capable of adhering at room temperature or at only moderately elevated temperature to various substrates.
1g 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 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 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 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.
~1 ~993g The compositions which are foamed according to the invention can be used to elasticate structures in which they are applied without the use of any glue, for example structures where elastication is obtained conventionally by elastic formed of vulcanized rubbers. One material (the foamed 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 thermoplastic, adhesive elastic hot melt can be directly extruded in varied geometrical forms directly during the construction of product which are to be elasticated. It can be extruded as strips and as films, etc. Structures such as strips 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 foamed 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 foaming 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 and immediately after foaming, pressure sensitive behaviour is less important because although foamed the material is still in a liquid or semisolid state and bonding is made when the material is still above room temperature.
All these features are particularly suitable for the elastication of hygienic, absorbent articles, although the potentialities of the foamed materials according to the invention are clearly not limited to these applications. 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 2j59939 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 the foamed elastic adhesive hot melts over rubber elastics is worthy of note. As will be shown in more detail below, 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 modulus and in the tensile strength that is perceived by the wearer. This is especially true for low modulus compositions.
Compositions foamed 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.
24 ' 2 1 5 9 9 3 9 In summary the use of thermoplastic block elastomers, in different physical forms and with different application processes, for the elastication of structures and particularly of hygienic articles, is very advantageous.
The foamed formulations of 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 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 2 0 distinct pressure sensitive character, can be applied even at room temperature, both in the unstretched or preferably in the stretched state for the elasHcation, _ 25 in different geometrical forms in various items and particularly in absorbent, 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 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, the basic compositions which are foamed 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 is concerned with foams made from a family of compositions, based on at least one thermoplastic elastic block copolymer in which SBS
21 ~993t9 copolymers) are 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 room temperature of the aforementioned copolymer. 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 of strips or continuous films. 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.
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 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.
2j 59939 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.
2~~9939 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 actuated 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 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 foamed according to the present invention is capable of giving materials which, whilst retaining very 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 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 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 2~5993g 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 CS resins - synthetic C5/C9 resins - rosins and rosin esters 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 50~
of the total amount of resin, are characterised by having a softening point between 85 and 150°C and more _ 32 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 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 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 " .
G' is higher than G " when the material is solid.
When the material is fluid G " becomes higher than G'.
Naturally, G' is higher at low temperature and the reverse at high temperatures. 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 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, it being understood that, as already indicated, these terms refer to intrinsic modulus. As already noted, apparent modulus, which depends on intrinsic modulus and degree of foaming, should for practical reasons, be higher than 0.05 MPa.
The low modulus compositions are elastic, extrudable, 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 the highest level, is a polystyrene/ polybutadiene block copolymer. In this embodiment the compositions foamed according to the invention have an intrinsic 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.
- 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 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, -- ' 2159939 have poor elastic properties. However, adding them in quantities up to 15% 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 EUROPRENE
SOLT"' 1205 and by Fina under the trade name FINAPRENET"' 1205. This product is described as an SBR in which styrene is partially distributed in blocks. Of the total styrene content of 25% by weight, from 15 to 18% 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.
2 0 In general, the composition may contain up to 40% by weight of plasticiser(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, 2 5 - up to 20% by weight, and preferably up to 15% by weight, of a liquid hydrocarbon resin, rosin ester or A
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 10% by weight in order not to interfere with the styreruc 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 example PARAPOLT"~ (Exxon), or LIRTM
(from KURARAY).
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 plasticizer content in a low modulus formulation is not less than 10% by weight and not higher than 40% by weight.
In low modulus compositions, the use of aromatic resins, which have no effect on adhesive properties, which interfere with the hard 2 0 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 2 5 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 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. In the unfoamed state, the compositions are characterized by very high .
elongation at break (over 1100 and often over 19000 and very good adhesive, often pressure sensitive adhesive properties. Elongation at break in the foamed state depends on degree of foaming as well as the nature of the foaming, i.e., the size of individual voids as well as total void volume.
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 490 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 according to the invention generally have 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 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 an intrinsic 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 25 % by weight.
ADHESIVE COMPOSITION AND PROCESS THERE~'~OR
The present invention relates to an adhesive composition in the form of a foam. More particularly the invention relates to a hot melt adhesive which, on the one hand has elastic properties and is in the form of a foam in the solid state while, on the other hand, has very low and in many cases negligible elasticity in the molten state as shown by essentially Newtonian behaviour at the processing (application) temperature.
In the manufacture of many different types of article it is necessary to bond an elastic material to a non-elastic substrate. One example is in the manufacture of disposable diapers where elastic strips are used to provide leg and waist elastication. Typically, the elastic strips consist of stretchable rubber which is fixed to the body of the diaper by layers of adhesive, for example hot melt adhesive, affixed to both surfaces.
This arrangement involves a number of difficulties.
For example, the elastic strip is often covered with an anti- blocking agent such as talc during manufacture to prevent the strip bonding to itself. However, this anti-blocking agent can, in turn, render bonding of the elastic strip to the body of the article much more difficult. Furthermore, since the hot melt adhesives which are used do not themselves have real elastic properties, application of adhesive tends to "kill" the stretch of that portion of the elastic to which it is applied. Finally, the use of the two materials, rubber and adhesive, is costly.
A composition having adhesive properties on application from the molten state and preferably also pressure sensitive adhesive properties, and elasticity comparable to that, of rubber, whilst also possessing suitable rheological properties for melt processing, is highly desirable since it would be capable of replacing the rubber and the adhesive used at present and would represent a considerable advance in the manufacture of articles such as diapers. Such a composition would also find numerous other applications in many diverse fields.
Further advantages would follow if the composition could be presented for use as a foam.
Many types of composition are in use commercially as hot melt adhesives and a much wider range of compositions have been suggested for use in this field. A hot melt adhesive can be defined as a composition which shows adhesive properties when applied to a substrate in the molten state. This does not preclude the composition also showing adhesive properties at room temperature, e.g. pressure sensitive adhesive properties. In general, hot melt adhesives are formulated for properties such as adhesion to a variety of surfaces, heat stability and processing properties rather than for elasticity and any attempt to increase elasticity has a detrimental effect on adhesion and other desirable properties of the composition. As yet, none of the commercial hot melt .._ 219939 adhesive compositions combine good adhesion with elastic properties comparable to those of rubber. In addition whilst there have been proposals to foam certain hot melt adhesives, no foamed hot melt adhesive has come into general use.
Natural rubber is generally too viscous to be used as a basis for hot melt adhesives and cured rubber cannot be melted. Many hot melt adhesives are based on thermoplastic block elastomers since these can be melted.
Many such elastomers with a variety of properties are available commercially. For use as an adhesive, thermoplastic block elastomers generally have to be blended with tackifying agents to improve adhesion.
Other additives such as plasticisers may also be necessary depending on the application.
Certain prior art proposals have attempted to provide hot melt adhesives which also have elastic properties. For example US-A-4 418 123 attempts to provide a self-adhering elastic having a combination of elastic and adhesive properties. The composition is defined in very broad terms as a combination of a block copolymer comprising at least one substantially amorphous rubbery polymeric mid block and at least two glassy poly(vinylarene) end blocks, together with a midblock associating resin and an endblock associating resin. All of the specific examples (with the exception of a comparative example with unsatisfactory properties) are based on styrene-isoprene-styrene block copolymers.
Despite the claims made for them, as far as the present applicants are aware, none of the compositions exemplified in US-A-4 418 123 show true elastic properties comparable to those of rubber combined with good adhesion and processability (see Comparative Example A below) .
Similarly EP-A-0 424 295 (HB Fuller France SARL) relates to a thermoplastic elastic intended particularly for elastication of diapers which comprises:
a) at least one synthetic rubber which is of the block copolymer type comprising at least one rubber middle block and at least two glassy end blocks;
b) 20 to 150 by weight based on the block copolymer of at least one "tackifying" resin which associates with the middle block of the copolymer;
c) 10 to 50$ by weight based on the block copolymer of at least one "tackifying" resin which associates with the terminal blocks of the copolymer; and - d) 5 to 35~ based on the weight of the composition of a mineral oil.
It is suggested that these compositions can be foamed. The compositions exemplified in EP-A-0 424 295 are generally based on SIS and an example of a composition based on SBS shows unsatisfactory properties.
There are no examples of the production of foams.
It has now been found that, by careful selection of the components, hot melt adhesives can be produced having the desirable combination of properties referred to above, i.e. good adhesion from the melt (and in many embodiments also at room temperature), elastic properties comparable to those of rubber;
and good processibility from the melt and it has also been found that these hot melt adhesives can be foamed to provide stable foams.
Various aspects of the invention are as follows:
An elastomeric hot melt adhesive in the form of a stable foam comprising a hot melt adhesive composition which comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of l0 styrene/butadiene/styrene (SBS) copolymers and blend of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount not more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterized in that:
15 a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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%;
2 0 and c) it has a viscosity of not more than 120,000 cps at 180°C and an applied shear of 80 sec-1.
A process for the production of an adhesive which comprises (i) providing a hot melt adhesive composition which comprises 2 5 at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of styrene/butadiene/styrene (SBS) copolymers and blends of styrene/butadiene/styrene (SBS) copolymer with styrene/ isoprene/ styrene (SIS) in which SIS is present in an amount not 3 0 more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterised in that:
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof with a 90° peel force of not lower than 0.5 3 5 N/Cm;
~,.
5a 2 1 5 9 9 3 9 b) it has a tensile strength retention after 50 cycles of at least 40%;
and c) it has a viscosity of not more than 120,000 cps at 180°C and an applied shear of 80 sec-1;
(ii) foaming the said hot melt adhesive composition;
(iii) extruding the foam produced; and (iv) cooling the foam.
Feature a) referred to above relates to the adhesive properties of the composition and in all cases the composition should have the properties of a hot melt A' ~~59939 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 strength, measured as 90° peel of not lower than 0.5 N/cm. 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.
As described in more detail below, many compositions which may be foamed according to the invention also bond appropriate substrates at room temperature and may show tl~e 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 2.59939 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 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 which may be foamed according to the invention show substantially Newtonian rheological behaviour, in particular viscosity does not vary significantly with applied shear. As discussed in more detail below, many compositions which may be foamed according to the invention show Newtonian behaviour at intended processing temperatures, e.g. around 180°C.
Compositions which may be foamed according to the invention can be formulated with any desired modulus depending on the desired end use. In this connection, reference can be made to the intrinsic modulus which is the modulus of the composition prior to foaming and the apparent modulus which is the modulus of the foamed composition. Apparent modulus is a function of the intrinsic modulus and percent foaming (i.e. foam density). Apparent modulus of a foamed composition is, of course, always lower than intrinsic modulus.
__ Intrinsic modulus has effects on the main properties of the composition and it is convenient to divide the compositions of the invention into low intrinsic modulus and high intrinsic modulus compositions. As used herein the terms "low modulus composition" and "high modulus composition" refer to intrinsic modulus.
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 compositions generally show good adhesive properties at room 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 and foaming using a blowing agent. 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 and foaming 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 2~~9939 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 proportional to modulus, compositions with high modulus are often applied immediately after foaming with the material still in a molten or semisolid state although some may retain sufficient pressure sensitive adhesive character to be applied at room temperature. Application in a molten or semisolid state 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 beyond the need to foam a stable foam 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 ~I~9939 so that they can be applied at room temperature in a stretched state, they can be used at an elongation of up to 400. For practical reasons, the lower limit of apparent modulus is about 0.05 MPa although given that the apparent modulus is a function of intrinsic modulus and foam density, this lower limit applies to both high and low intrinsic modulus compositions.
The essential components of the composition which may be foamed according to the invention are a thermoplastic elastomer and a tackifying resin and these will now be discussed in general terms.
Thermoplastic elastomers are a very interesting chemical and technological class of polymers 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 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 _ n "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 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 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 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 _ 14 content in the thermoplastic elastomeric block copolymer should be kept lower than 40$ by weight.
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, 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:
- 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.
2~ 59939 - "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 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 H (the so called diblocks) should, for use in the present invention, be kept lower than 40$ by weight in the base polymer.
It is widely recognised in the literature that differences exist between SIS and SBS copolymers which are relevant to the formulation of hot melt adhesives.
SBS copolymers generally cost less than comparable SIS
copolymers and SBS copolymers can be synthesized to exhibit better elasticity than comparable SIS copolymers.
However it has not hitherto been possible to take advantage of these potentially advantageous properties of SBS copolymers as a result of the fact that SBS
copolymers have not generally shown adequate adhesive properties and SIS copolymers are much easier to tackify.
For this reason hot melt adhesives have generally been formulated using SIS copolymers as the predominant SBC.
Both US-A-4418123 and EP-A-0424295, which are discussed above, clearly prefer SIS as the SHC on which the compositions are based and neither document discloses a composition based on SBS which has satisfactory properties.
It has been found according to the present invention that compositions in which SBS copolymers are the main polymers) can be produced with satisfactory adhesive properties. At the same time these compositions retain the advantages of SBS copolymers with respect to elasticity which have been mentioned above. Thus, compared to compositions based on other SBC's, compositions can be formulated according to the present invention with better elastic properties, quicker elastic return, more flat stress/strain diagrams even at elongations > 1000 ~ and give compositions of better processability (more Newtonian rheological behaviour).
-- m However, it should be noted that direct comparison between SIS and SBS based compositions is very difficult since the compositions need to be formulated in different ways. Accordingly, it would not generally be possible to substitute an SBS copolymer for an SIS copolymer in a hot melt composition and obtain satisfactory properties and other adjustments need to be made to the formulation depending on the nature of the SBC in order to obtain optimum results. The way in which compositions according to the invention should be formulated to obtain the desired properties is discussed in more detail hereinafter.
Thus the compositions foamed according to this invention are based on SBS copolymers or a blend of SBS/SIS in which SIS is present at levels equal or less than 50~ by weight of the total block copolymer.
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 elastomers which are capable of adhering at room temperature or at only moderately elevated temperature to various substrates.
1g 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 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 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 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.
~1 ~993g The compositions which are foamed according to the invention can be used to elasticate structures in which they are applied without the use of any glue, for example structures where elastication is obtained conventionally by elastic formed of vulcanized rubbers. One material (the foamed 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 thermoplastic, adhesive elastic hot melt can be directly extruded in varied geometrical forms directly during the construction of product which are to be elasticated. It can be extruded as strips and as films, etc. Structures such as strips 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 foamed 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 foaming 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 and immediately after foaming, pressure sensitive behaviour is less important because although foamed the material is still in a liquid or semisolid state and bonding is made when the material is still above room temperature.
All these features are particularly suitable for the elastication of hygienic, absorbent articles, although the potentialities of the foamed materials according to the invention are clearly not limited to these applications. 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 2j59939 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 the foamed elastic adhesive hot melts over rubber elastics is worthy of note. As will be shown in more detail below, 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 modulus and in the tensile strength that is perceived by the wearer. This is especially true for low modulus compositions.
Compositions foamed 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.
24 ' 2 1 5 9 9 3 9 In summary the use of thermoplastic block elastomers, in different physical forms and with different application processes, for the elastication of structures and particularly of hygienic articles, is very advantageous.
The foamed formulations of 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 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 2 0 distinct pressure sensitive character, can be applied even at room temperature, both in the unstretched or preferably in the stretched state for the elasHcation, _ 25 in different geometrical forms in various items and particularly in absorbent, 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 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, the basic compositions which are foamed 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 is concerned with foams made from a family of compositions, based on at least one thermoplastic elastic block copolymer in which SBS
21 ~993t9 copolymers) are 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 room temperature of the aforementioned copolymer. 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 of strips or continuous films. 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.
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 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.
2j 59939 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.
2~~9939 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 actuated 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 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 foamed according to the present invention is capable of giving materials which, whilst retaining very 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 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 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 2~5993g 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 CS resins - synthetic C5/C9 resins - rosins and rosin esters 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 50~
of the total amount of resin, are characterised by having a softening point between 85 and 150°C and more _ 32 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 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 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 " .
G' is higher than G " when the material is solid.
When the material is fluid G " becomes higher than G'.
Naturally, G' is higher at low temperature and the reverse at high temperatures. 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 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, it being understood that, as already indicated, these terms refer to intrinsic modulus. As already noted, apparent modulus, which depends on intrinsic modulus and degree of foaming, should for practical reasons, be higher than 0.05 MPa.
The low modulus compositions are elastic, extrudable, 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 the highest level, is a polystyrene/ polybutadiene block copolymer. In this embodiment the compositions foamed according to the invention have an intrinsic 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.
- 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 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, -- ' 2159939 have poor elastic properties. However, adding them in quantities up to 15% 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 EUROPRENE
SOLT"' 1205 and by Fina under the trade name FINAPRENET"' 1205. This product is described as an SBR in which styrene is partially distributed in blocks. Of the total styrene content of 25% by weight, from 15 to 18% 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.
2 0 In general, the composition may contain up to 40% by weight of plasticiser(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, 2 5 - up to 20% by weight, and preferably up to 15% by weight, of a liquid hydrocarbon resin, rosin ester or A
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 10% by weight in order not to interfere with the styreruc 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 example PARAPOLT"~ (Exxon), or LIRTM
(from KURARAY).
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 plasticizer content in a low modulus formulation is not less than 10% by weight and not higher than 40% by weight.
In low modulus compositions, the use of aromatic resins, which have no effect on adhesive properties, which interfere with the hard 2 0 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 2 5 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 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. In the unfoamed state, the compositions are characterized by very high .
elongation at break (over 1100 and often over 19000 and very good adhesive, often pressure sensitive adhesive properties. Elongation at break in the foamed state depends on degree of foaming as well as the nature of the foaming, i.e., the size of individual voids as well as total void volume.
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 490 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 according to the invention generally have 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 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 an intrinsic 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 25 % 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 VECTORT"'.
5) The preferred SBC(s) contain from 20 to 50% by weight of styrene 2 0 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.
6) The tackifying resin/blend of tackifying resins has/have the same 2 5 chemical and physical characteristics as already discussed above.
However, the preferred content is from 20 to 40% by weight.
A
2~ X9939 7) The content of high molecular weight rubbers such as polyisoprene, polybutadiene, polyisobutylene, natural rubber, butyl rubber, SIR and SBR should not exceed 10~
by weight and preferably is less than 5$ by weight based on the total composition.
However, the preferred content is from 20 to 40% by weight.
A
2~ X9939 7) The content of high molecular weight rubbers such as polyisoprene, polybutadiene, polyisobutylene, natural rubber, butyl 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 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 intrinsic 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 foamed according to the invention still retain distinct and useful pressure sensitive behaviour (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.
Adhesive properties are measured under the same conditions as for low modulus compositions.
The unexpectedly good level of elasticity of the foams 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.
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 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.
As will be shown in the following examples, compositions, both low and high modulus, which can be foamed to produce foams according to the invention show good elastic behaviour, at the same level or better than the natural rubber vulcanized elastic.
More specifically high modulus compositions retained up to 67.5 of their initial tensile force and low modulus compositions up to 59.8.
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 present invention also provides a process for the production of foams. For the production of foams, the compositions described above can extruded in various desired forms, for example in the form of a strip, and foamed at the moment of extrusion by use of conventional foaming technology to provide an adhesive foam. The foamable composition is generally extruded at a temperature at which it is molten, for example at from 130 to 230°C, and foaming can be effected by physical or chemical means. Foaming by physical means involves use of an inert gas or an inert liquid. For example an inert gas such as nitrogen or carbon dioxide can be blown under pressure into the molten composition. Alternatively, an inert volatile liquid, such as methylene chloride, can be included in the composition which then evaporates at the extrusion temperature and acts in the same way as the inert gas. Foaming by chemical means involves use of a chemical blowing agent such as diazocarbonamide which decomposes at the extrusion temperature to release 2~~9939 _ 47 sufficient amounts of gas to foam the extruded composition. Preferably the foaming is achieved using an inert gas.
Immediately following blowing and extrusion the composition is cooled, generally by natural cooling to room temperature, to stabilise the foam. At the same time the blowing action helps cooling and stabilises the walls of the cells of the foam and helps in setting up the foam. The apparent modulus of the foamed composition can be adjusted to a required value by varying the density of the foamed mass, for example by varying the quantity of blowing agent or the pressure where the foaming agent is a gas blown directly into the molten composition.
If required, the composition can be foamed and extruded on-line in the production of an article into which the foamed composition is to be incorporated to yield a foamed elastic, for example in the form of a strip, which is sufficiently adhesive to bond to the body of an article, for example the body of a diaper. Strips of the elastic/adhesive material foamed according to the invention produced in this way can be used in those applications where two materials (an elastic foam, for example a polyurethane foam, and an adhesive) have been used previously with consequent savings in cost, increased assembling efficiency and better performance of elasticated portions of the article. In addition, for use, for example, in the waistband of a diaper a foamed elastic adhesive has the advantage that for a given contact area and a defined elastic force, the weight of the foamed elastic adhesive is lower than the weight of a non-foamed composition performing the same function with consequent cost saving. The foamed structure is also thicker but at the same time softer.
The invention is 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 all suitable for foaming according to the invention by the method described in Example 1 or by other methods described herein. 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 0.5 N/cm measured as 90° peel.
An SBC polymeric system based on SBS
(styrene-butadiene- styrene block copolymers) was formulated as follows:
CARIFLEXT"' TR-4113 S 36% by weight 2 5 EUROPRENE SOL 1205 8%
DERCOLYTET"" A 115 45.8%
FORALT"' 85-E 6%
A
HERCOLYNT"" D-E 4%
IRGANOXT"" 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 plasticizes, and containing less than 5% of aromatics.
- EUROPRENE SOL 1205 is a 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 polymerised 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 as partially (typically from 15 to 18%) distributed in blocks with the 2 0 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.
- DERCOLYTE A 115 (the main tackifying resin)is available from 2 5 DRT. It is a polyterpene resin derived from alpha- pinene having a softening point of 115°C.
2~ ~993g - 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 - intrinsic modulus at 500$ elongation - 0.182 MPa (low modulus) - elongation at break > 1400$ (1400$ was the maximum elongation achievable on the machine used for this determination) - rheological setting temperature (crossover point of G' and G'~') - 125°C
- 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 21 ~~~3~
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 composition is foamed to varying foam densities using a commercially available foaming apparatus intended for hot melt compositions (FOAMMELT apparatus produced by Nordson, Germany). Foaming was carried out using nitrogen under pressure as the blowing agent at a temperature of 180°C and gas pressure was adjusted to give foams of varying densities. The flow rate of the elastomeric hot melt was about 1-2 grams per minute and the foam produced was about 1 cm thick depending on the foam density.
The following properties have measured on the foamed composition:
_ Density Apparent Modulus 0.94 g/cm2 0.182 MPa 0.83 g/cm2 0.162 MPa 0.79 g/cm2 0.136 MPa 0.69 g/cm2 0.113 MPa 0.52 g/cm2 0.058 MPa 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:
- total styrene content = 11.5$ by weight of which 10.9$ is in blocks - viscosity at 180°C at 80 sec-1 = 28180 cps - intrinsic modulus at 500$ elongation = 0.188 MPa (low modulus) - elongation at break > 1400$
- rheological setting temperature = 120°C
- 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 1, the main variation being the fact that about 50$ 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 ....
' 215 9939 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 % .
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%
ZONATACT"" 115 LTTE 45.8 2 0 FORAL 85-E 6.3 HERCOLYN D-E 4.0%
SHELLFLEXT"" 4510 FC 11.0%
IRGANOX 1010 0.2%
where:
2 5 - 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.
A
21~993~
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.
- intrinsic modulus at 500 elongation = 0.223 MPa (low modulus) - elongation at break > 1300$
- rheological setting temperature = 107°C
90° peel on PE = 14 N/cm - tensile strength retention after 50 cycles between 800 and 920 = 50~
- elastic energy retention after 3 hysteresis cycles between zero and 800$ = 44.9 - Newtonian index (N. I.) - 1.04.
The composition showed properties typical of a very good and easily processable elastic, extrudable adhesive material.
5 The following high modulus composition was made with the formulation:
VECTOR 4461-D 44.8% by weight ZONAREZT"" 7115 LTTE 37%
ZONAREZT"' ALPHA 25 3%
IRGANOX 1010 0.2%
15 where:
- VECTOR 4461-D is a linear SBS copolymer having 43% by weight of styrene and non diblock content available from DEXCO Co.
- ZONAREZ 7115 LTTE is a polyterpene tackifying resin, having a softening point of 115°C, derived from limonene, available from 2 0 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, paraffiruc mineral oil available from 2 5 EXXON, which is said to contain non aromatics.
The following properties were measured:
- total block styrene content =19.3% by weight - viscosity at 180°C at 80 sec-1=16810 cps.
A
- intrinsic modulus at 500% elongation =1.07 MPa (high modulus) - elongation at break = 987%
- rheological setting temperature = 111°C
- 90° peel on PE = 6.5 N/cm - tensile strength retention after 50 cycles between 300 and 345% _ 67.5 - elastic energy retention after 3 hysteresis cycles between zero and 300% = 63.3%
- Newtonian Index (N.L) = 1.05.
The composition was a good elastic material useful especially at low elongations. It showed acceptable semi-pressure sensitive characteristics so that it can be bonded to materials also at room temperature in the stretched state.
~~r a ~~rnr ~ ~
The formulation was:
VECTOR 4461-D 54.8% by weight ECR 368 35%
PRIMOLT"' 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 = 39000 cps.
- intrinsic modulus at 500 elongation = 1.61 MPa (high modulus) - elongation at break = 947 - rheological setting temperature = 114°C
- 90° peel on PE = 2.6 N/cm - tensile strength retention after 50 cycles between 300 and 345 = 62.3 - 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 return 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.
COMPARATIVE EXAMPLE A
The formulation was:
KRATONT"" D1107 40.2% by weight WINGTACKT"' 95 32.9%
IC-145 26.5 WESTONT"~ 618 0.2%
IRGANOX 1010 0.2%
where:
- KRATON D1107 is a linear SIS block copolymer available from SHELL containing 14% by weight of styrene.
- WINGTACK 95 is a synthetic polyterpene resin, having a softening point of 95°C available from Goodyear Co.
- IC-145 is a coumarone-indene aromatic resin, having a softening point of 145°C and available from the German Company VFT.
2 0 - WESTON 618 is a phosphite based antioxidant available from Borg Warner Co.
- IRGANOX 1010 is as described in Example 1.
This formulation was made in accordance with the teaching of US
A-4 418123 (Example IV). According to the US patent the composition is 2 5 said to have completely satisfactory elastic, adhesive and processing properties. The formulation of Comparative Example A has the following differences from Example IV of US-A-4 418123:
59 2 1 5 9 9 3 g 1) The coumarone-indene resin CUMART"' LX-509 is not widely available in Europe and the equivalent resin IC-145 was used. The resins are chemically similar but IC-145 has a softening point of 145°C as compared to the figure of 155°C reported for CUMAR LX-509 in the US
patent;
2) For practical reasons, the pigment (1.5 % titanium dioxide) was omitted. The pigment was presumably present in the original formulation to mask the light brown colour and would be expected to have a negligible effect on adhesive and elastic properties.
The main properties can be summarised as follows:
- total block styrene content = 5.6% by weight - viscosity at 180°C at 80 sec-1 =192000 cps - intrinsic modulus at 500% elongation = 0.365 MPa (low modulus) - elongation at break > 1400% (1400% was the maximum elongation achievable on the machine used for this determination) - rheological setting temperature (crossover point of G' and G") _ 2 0 145°C
- 90° peel on PE = 15.7 N/cm - tensile strength retention after 50 cycles between 800 and 920% _ 34.3 - elastic energy retention after 3 hysteresis cycles between zero and 800% = 19.8%
- Newtonian Index (N.L) = 2.03.
A
_ 60 It was found that the above formulation had good adhesive, pressure sensitive characteristics as indicated by the US patent in that as measured on PE under the above described conditions, the 90° peel was 15.7 N/cm.
However it was also found that both elastic and processing properties for an extrudable material were unsatisfactory. In particular:
- The processability, especially the application under thin strips, was very difficult owing to the extremely high viscosity and the highly non Newtonian rheological behaviour.
- The modulus at 500$ elongation was found to be 0.365 MPa and the elongation at break to be > 1400$. However elastic properties were unsatisfactory. In particular under the cyclic deformation test between 800 and 920 the formulation was found to lose 65.7 of its initial tensile strength after 50 cycles and to lose 80.28 of its elastic energy after 3 hysteresis cycles between 0 and 800 making it unsuitable for the elastication of products such as hygienic absorbent articles that are stressed in use many times by subsequent stretchings due to movements of wearer. It is worthy of note that 45~ of the loss of tensile strength occurred between the first and the second cycle, confirming an easy and unrecoverable plastic deformation.
COMPARATIVE EXAMPLE H
The formulation was:
TUFPRENET"~ A 30.0% by weight ESCOREZT"" CR 368 55.0%
CATENEXT"' P941 10.0%
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 40% 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 paraffiruc 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 2 0 and styrene available from Hercules and having a softening point of 100°C.
This formulation was made in accordance with the teaching of EP-A-0424295 (Example V). The formulation of comparative example B has 2 5 the following difference from Example V of EP-A-0424295:
0.2 parts per 100 parts by weight of the antioxidant IRGANOX
1010 was added to the composition as set out in Example V of EP-A-0424295. As would be apparent to any person skilled in the art, attempting to compound and process the composition exactly as disclosed in EP-A-0424295, i.e. without an antioxidant would undoubtedly have led to thermal degradation of the system. In order to follow the teaching of EP-A-0424295 as closely as possible the antioxidant used in the comparative example A of that document was used.
However, the antioxidant was added at the usual level of 0.2~ (this being the level also used in the preceding examples according to the invention) rather than the unusually (and also unnecessary) high level used in Comparative Example A of EP-A-0424295.
The main properties can be summarised as follows:
- total block styrene = 12~ by weight - viscosity at 180°C at 80 sec-1 = 5620 cps - intrinsic modulus at 500 elongation = 0.204 MPa (low modulus) elongation at break > 1300 - rheological setting temperature (crossover point of G' and G" ) - 106°C
- 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 2~ 5993 _ _ 63 It was found that processability, as shown by viscosity and NI was acceptable although NI was high for an SBS based composition. However, the formulation had poor pressure sensitive characteristics and the value of 0.8 N/cm for 90° peel shows 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. Elastic properties were unsatisfactory as indicated by the loss of about 80$ of the tensile strength of the composition after 50 cycles of subsequent stretching and of 75$ of its elastic energy after 3 hysteresis cycles.
The unsatisfactory properties of the composition may be related to the diblock content of TUFPRENE A. This is not stated by the manufacturer and direct measurement is difficult. However the value provided by the manufacturer for Tensile Set at break measured according to ASTM method D412 is 47$. This compares to much lower values of around 10$ or lower quoted for SBS copolymers with a diblock content < 20$ by weight. On the other hand SHELL technical literature gives the following figures for Tensile Set at break for copolymers with a high diblock content - KRATON D-1112 (SIS containing 40$ by weight diblock) - 20$
- KRATON D-1118X (SBS containing 80$ by weight diblock) -40$.
From this, it can be inferred that TUFPRENE A probably has a diblock content well in excess of 40$.
It should be noted that the above results seem to be inconsistent with the results reported in EP-A-0424295 in at least some respects. Thus the 90° peel of 0.8 N/cm reported above compares to 3.7 N/cm for 180° peel derivable from EP- A-0424295. This may be explained at least in part by both the different peel angle, and the compression used in the test (400 g as compared to 2 kg) since the composition is stiff and bonding is very much influenced by compression. It should also be noted that the weight of adhesive per square meter is not specified in EP-A-0424295 and this is extremely important in determining bond strength. The tests used according to the present invention provide a realistic measure of the suitability of the compositions for use in the proposed applications. The poor properties of the composition of EP-A-0424295 may also be related to the combination of a hard SBS (40~ styrene) with an aromatic resin at low plasticiser levels (10~).
This example relates to the stress/strain diagrams of the compositions of Examples 1 to 5 and Comparative Examples A and B. The elastic hot melt compositions according to the invention should desirably have a stress/strain 21 ~993~
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:
EXAMPLE NO. MEAN INCREASE IN MODULUS PER
100$
STRETCHING
1 0.044 MPa/100$ stretching 0.045 MPa/100$ stretching 0.063 MPa/100$ stretching Comparative Example A 0.099 MPa/100$ stretching Comparative Example B 0.079 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 ~1 X9939 _ 66 in modulus per 100 increase in elongation between zero and 300$ final elongation:
EXAMPLE N0. MEAN INCREASE IN MODULUS PER
100$
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 220$) showed, between zero and 220, an average increase in modulus of 0.89 MPa per 100 elongation.
It is possible to compare the behaviour of a natural rubber elastic and of a low modulus composition according to the invention.
In the case of rubber elastic, even limited m9vements of the wearer that cause for instance a further stretching of the elasticated parts as low as say 10~
elongation, will cause a mean increase in modulus of about 0.09 MPa. By using a low modulus composition the increase in modulus will be about 20 times lower and even with the strongest high modulus compositions several times lower so that the movements of the wearer of an absorbent article elasticated by the compositions disclosed in the present invention are much more free.
Accordingly, in these applications low modulus and low variation of modulus with strain are a clear advantage.
However, as in the previous case, these materials can be present at levels up to 20~ by weight with acceptable properties in the composition provided that the non-adhesive/non elastomeric part of the composition does not exceed 50~ by weight of the total composition.
This non-adhesive/non-elastomeric part is formed by the sum of the total styrene content in the composition plus the content of aromatic resin/resins.
Other requirements and other possible further components and additives remain the same. In particular it is still required that the true rheological setting temperature (measured as the crossing point between G' and G ") is not lower that 80°C and preferably not lower that 100°C.
Again with no limitations on their processing and use, these high intrinsic modulus compositions are often applied in the unstretched state, especially the ones having moduli > 1 MPa. This preferred use is due to the fact that they are capable of giving sufficient elastic return forces even at low deformations (typically not higher than 50$) 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 foamed according to the invention still retain distinct and useful pressure sensitive behaviour (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.
Adhesive properties are measured under the same conditions as for low modulus compositions.
The unexpectedly good level of elasticity of the foams 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.
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 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.
As will be shown in the following examples, compositions, both low and high modulus, which can be foamed to produce foams according to the invention show good elastic behaviour, at the same level or better than the natural rubber vulcanized elastic.
More specifically high modulus compositions retained up to 67.5 of their initial tensile force and low modulus compositions up to 59.8.
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 present invention also provides a process for the production of foams. For the production of foams, the compositions described above can extruded in various desired forms, for example in the form of a strip, and foamed at the moment of extrusion by use of conventional foaming technology to provide an adhesive foam. The foamable composition is generally extruded at a temperature at which it is molten, for example at from 130 to 230°C, and foaming can be effected by physical or chemical means. Foaming by physical means involves use of an inert gas or an inert liquid. For example an inert gas such as nitrogen or carbon dioxide can be blown under pressure into the molten composition. Alternatively, an inert volatile liquid, such as methylene chloride, can be included in the composition which then evaporates at the extrusion temperature and acts in the same way as the inert gas. Foaming by chemical means involves use of a chemical blowing agent such as diazocarbonamide which decomposes at the extrusion temperature to release 2~~9939 _ 47 sufficient amounts of gas to foam the extruded composition. Preferably the foaming is achieved using an inert gas.
Immediately following blowing and extrusion the composition is cooled, generally by natural cooling to room temperature, to stabilise the foam. At the same time the blowing action helps cooling and stabilises the walls of the cells of the foam and helps in setting up the foam. The apparent modulus of the foamed composition can be adjusted to a required value by varying the density of the foamed mass, for example by varying the quantity of blowing agent or the pressure where the foaming agent is a gas blown directly into the molten composition.
If required, the composition can be foamed and extruded on-line in the production of an article into which the foamed composition is to be incorporated to yield a foamed elastic, for example in the form of a strip, which is sufficiently adhesive to bond to the body of an article, for example the body of a diaper. Strips of the elastic/adhesive material foamed according to the invention produced in this way can be used in those applications where two materials (an elastic foam, for example a polyurethane foam, and an adhesive) have been used previously with consequent savings in cost, increased assembling efficiency and better performance of elasticated portions of the article. In addition, for use, for example, in the waistband of a diaper a foamed elastic adhesive has the advantage that for a given contact area and a defined elastic force, the weight of the foamed elastic adhesive is lower than the weight of a non-foamed composition performing the same function with consequent cost saving. The foamed structure is also thicker but at the same time softer.
The invention is 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 all suitable for foaming according to the invention by the method described in Example 1 or by other methods described herein. 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 0.5 N/cm measured as 90° peel.
An SBC polymeric system based on SBS
(styrene-butadiene- styrene block copolymers) was formulated as follows:
CARIFLEXT"' TR-4113 S 36% by weight 2 5 EUROPRENE SOL 1205 8%
DERCOLYTET"" A 115 45.8%
FORALT"' 85-E 6%
A
HERCOLYNT"" D-E 4%
IRGANOXT"" 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 plasticizes, and containing less than 5% of aromatics.
- EUROPRENE SOL 1205 is a 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 polymerised 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 as partially (typically from 15 to 18%) distributed in blocks with the 2 0 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.
- DERCOLYTE A 115 (the main tackifying resin)is available from 2 5 DRT. It is a polyterpene resin derived from alpha- pinene having a softening point of 115°C.
2~ ~993g - 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 - intrinsic modulus at 500$ elongation - 0.182 MPa (low modulus) - elongation at break > 1400$ (1400$ was the maximum elongation achievable on the machine used for this determination) - rheological setting temperature (crossover point of G' and G'~') - 125°C
- 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 21 ~~~3~
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 composition is foamed to varying foam densities using a commercially available foaming apparatus intended for hot melt compositions (FOAMMELT apparatus produced by Nordson, Germany). Foaming was carried out using nitrogen under pressure as the blowing agent at a temperature of 180°C and gas pressure was adjusted to give foams of varying densities. The flow rate of the elastomeric hot melt was about 1-2 grams per minute and the foam produced was about 1 cm thick depending on the foam density.
The following properties have measured on the foamed composition:
_ Density Apparent Modulus 0.94 g/cm2 0.182 MPa 0.83 g/cm2 0.162 MPa 0.79 g/cm2 0.136 MPa 0.69 g/cm2 0.113 MPa 0.52 g/cm2 0.058 MPa 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:
- total styrene content = 11.5$ by weight of which 10.9$ is in blocks - viscosity at 180°C at 80 sec-1 = 28180 cps - intrinsic modulus at 500$ elongation = 0.188 MPa (low modulus) - elongation at break > 1400$
- rheological setting temperature = 120°C
- 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 1, the main variation being the fact that about 50$ 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 ....
' 215 9939 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 % .
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%
ZONATACT"" 115 LTTE 45.8 2 0 FORAL 85-E 6.3 HERCOLYN D-E 4.0%
SHELLFLEXT"" 4510 FC 11.0%
IRGANOX 1010 0.2%
where:
2 5 - 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.
A
21~993~
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.
- intrinsic modulus at 500 elongation = 0.223 MPa (low modulus) - elongation at break > 1300$
- rheological setting temperature = 107°C
90° peel on PE = 14 N/cm - tensile strength retention after 50 cycles between 800 and 920 = 50~
- elastic energy retention after 3 hysteresis cycles between zero and 800$ = 44.9 - Newtonian index (N. I.) - 1.04.
The composition showed properties typical of a very good and easily processable elastic, extrudable adhesive material.
5 The following high modulus composition was made with the formulation:
VECTOR 4461-D 44.8% by weight ZONAREZT"" 7115 LTTE 37%
ZONAREZT"' ALPHA 25 3%
IRGANOX 1010 0.2%
15 where:
- VECTOR 4461-D is a linear SBS copolymer having 43% by weight of styrene and non diblock content available from DEXCO Co.
- ZONAREZ 7115 LTTE is a polyterpene tackifying resin, having a softening point of 115°C, derived from limonene, available from 2 0 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, paraffiruc mineral oil available from 2 5 EXXON, which is said to contain non aromatics.
The following properties were measured:
- total block styrene content =19.3% by weight - viscosity at 180°C at 80 sec-1=16810 cps.
A
- intrinsic modulus at 500% elongation =1.07 MPa (high modulus) - elongation at break = 987%
- rheological setting temperature = 111°C
- 90° peel on PE = 6.5 N/cm - tensile strength retention after 50 cycles between 300 and 345% _ 67.5 - elastic energy retention after 3 hysteresis cycles between zero and 300% = 63.3%
- Newtonian Index (N.L) = 1.05.
The composition was a good elastic material useful especially at low elongations. It showed acceptable semi-pressure sensitive characteristics so that it can be bonded to materials also at room temperature in the stretched state.
~~r a ~~rnr ~ ~
The formulation was:
VECTOR 4461-D 54.8% by weight ECR 368 35%
PRIMOLT"' 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 = 39000 cps.
- intrinsic modulus at 500 elongation = 1.61 MPa (high modulus) - elongation at break = 947 - rheological setting temperature = 114°C
- 90° peel on PE = 2.6 N/cm - tensile strength retention after 50 cycles between 300 and 345 = 62.3 - 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 return 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.
COMPARATIVE EXAMPLE A
The formulation was:
KRATONT"" D1107 40.2% by weight WINGTACKT"' 95 32.9%
IC-145 26.5 WESTONT"~ 618 0.2%
IRGANOX 1010 0.2%
where:
- KRATON D1107 is a linear SIS block copolymer available from SHELL containing 14% by weight of styrene.
- WINGTACK 95 is a synthetic polyterpene resin, having a softening point of 95°C available from Goodyear Co.
- IC-145 is a coumarone-indene aromatic resin, having a softening point of 145°C and available from the German Company VFT.
2 0 - WESTON 618 is a phosphite based antioxidant available from Borg Warner Co.
- IRGANOX 1010 is as described in Example 1.
This formulation was made in accordance with the teaching of US
A-4 418123 (Example IV). According to the US patent the composition is 2 5 said to have completely satisfactory elastic, adhesive and processing properties. The formulation of Comparative Example A has the following differences from Example IV of US-A-4 418123:
59 2 1 5 9 9 3 g 1) The coumarone-indene resin CUMART"' LX-509 is not widely available in Europe and the equivalent resin IC-145 was used. The resins are chemically similar but IC-145 has a softening point of 145°C as compared to the figure of 155°C reported for CUMAR LX-509 in the US
patent;
2) For practical reasons, the pigment (1.5 % titanium dioxide) was omitted. The pigment was presumably present in the original formulation to mask the light brown colour and would be expected to have a negligible effect on adhesive and elastic properties.
The main properties can be summarised as follows:
- total block styrene content = 5.6% by weight - viscosity at 180°C at 80 sec-1 =192000 cps - intrinsic modulus at 500% elongation = 0.365 MPa (low modulus) - elongation at break > 1400% (1400% was the maximum elongation achievable on the machine used for this determination) - rheological setting temperature (crossover point of G' and G") _ 2 0 145°C
- 90° peel on PE = 15.7 N/cm - tensile strength retention after 50 cycles between 800 and 920% _ 34.3 - elastic energy retention after 3 hysteresis cycles between zero and 800% = 19.8%
- Newtonian Index (N.L) = 2.03.
A
_ 60 It was found that the above formulation had good adhesive, pressure sensitive characteristics as indicated by the US patent in that as measured on PE under the above described conditions, the 90° peel was 15.7 N/cm.
However it was also found that both elastic and processing properties for an extrudable material were unsatisfactory. In particular:
- The processability, especially the application under thin strips, was very difficult owing to the extremely high viscosity and the highly non Newtonian rheological behaviour.
- The modulus at 500$ elongation was found to be 0.365 MPa and the elongation at break to be > 1400$. However elastic properties were unsatisfactory. In particular under the cyclic deformation test between 800 and 920 the formulation was found to lose 65.7 of its initial tensile strength after 50 cycles and to lose 80.28 of its elastic energy after 3 hysteresis cycles between 0 and 800 making it unsuitable for the elastication of products such as hygienic absorbent articles that are stressed in use many times by subsequent stretchings due to movements of wearer. It is worthy of note that 45~ of the loss of tensile strength occurred between the first and the second cycle, confirming an easy and unrecoverable plastic deformation.
COMPARATIVE EXAMPLE H
The formulation was:
TUFPRENET"~ A 30.0% by weight ESCOREZT"" CR 368 55.0%
CATENEXT"' P941 10.0%
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 40% 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 paraffiruc 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 2 0 and styrene available from Hercules and having a softening point of 100°C.
This formulation was made in accordance with the teaching of EP-A-0424295 (Example V). The formulation of comparative example B has 2 5 the following difference from Example V of EP-A-0424295:
0.2 parts per 100 parts by weight of the antioxidant IRGANOX
1010 was added to the composition as set out in Example V of EP-A-0424295. As would be apparent to any person skilled in the art, attempting to compound and process the composition exactly as disclosed in EP-A-0424295, i.e. without an antioxidant would undoubtedly have led to thermal degradation of the system. In order to follow the teaching of EP-A-0424295 as closely as possible the antioxidant used in the comparative example A of that document was used.
However, the antioxidant was added at the usual level of 0.2~ (this being the level also used in the preceding examples according to the invention) rather than the unusually (and also unnecessary) high level used in Comparative Example A of EP-A-0424295.
The main properties can be summarised as follows:
- total block styrene = 12~ by weight - viscosity at 180°C at 80 sec-1 = 5620 cps - intrinsic modulus at 500 elongation = 0.204 MPa (low modulus) elongation at break > 1300 - rheological setting temperature (crossover point of G' and G" ) - 106°C
- 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 2~ 5993 _ _ 63 It was found that processability, as shown by viscosity and NI was acceptable although NI was high for an SBS based composition. However, the formulation had poor pressure sensitive characteristics and the value of 0.8 N/cm for 90° peel shows 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. Elastic properties were unsatisfactory as indicated by the loss of about 80$ of the tensile strength of the composition after 50 cycles of subsequent stretching and of 75$ of its elastic energy after 3 hysteresis cycles.
The unsatisfactory properties of the composition may be related to the diblock content of TUFPRENE A. This is not stated by the manufacturer and direct measurement is difficult. However the value provided by the manufacturer for Tensile Set at break measured according to ASTM method D412 is 47$. This compares to much lower values of around 10$ or lower quoted for SBS copolymers with a diblock content < 20$ by weight. On the other hand SHELL technical literature gives the following figures for Tensile Set at break for copolymers with a high diblock content - KRATON D-1112 (SIS containing 40$ by weight diblock) - 20$
- KRATON D-1118X (SBS containing 80$ by weight diblock) -40$.
From this, it can be inferred that TUFPRENE A probably has a diblock content well in excess of 40$.
It should be noted that the above results seem to be inconsistent with the results reported in EP-A-0424295 in at least some respects. Thus the 90° peel of 0.8 N/cm reported above compares to 3.7 N/cm for 180° peel derivable from EP- A-0424295. This may be explained at least in part by both the different peel angle, and the compression used in the test (400 g as compared to 2 kg) since the composition is stiff and bonding is very much influenced by compression. It should also be noted that the weight of adhesive per square meter is not specified in EP-A-0424295 and this is extremely important in determining bond strength. The tests used according to the present invention provide a realistic measure of the suitability of the compositions for use in the proposed applications. The poor properties of the composition of EP-A-0424295 may also be related to the combination of a hard SBS (40~ styrene) with an aromatic resin at low plasticiser levels (10~).
This example relates to the stress/strain diagrams of the compositions of Examples 1 to 5 and Comparative Examples A and B. The elastic hot melt compositions according to the invention should desirably have a stress/strain 21 ~993~
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:
EXAMPLE NO. MEAN INCREASE IN MODULUS PER
100$
STRETCHING
1 0.044 MPa/100$ stretching 0.045 MPa/100$ stretching 0.063 MPa/100$ stretching Comparative Example A 0.099 MPa/100$ stretching Comparative Example B 0.079 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 ~1 X9939 _ 66 in modulus per 100 increase in elongation between zero and 300$ final elongation:
EXAMPLE N0. MEAN INCREASE IN MODULUS PER
100$
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 220$) showed, between 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 according to the invention.
In the case of rubber elastic, even limited m9vements of the wearer that cause for instance a further stretching of the elasticated parts as low as say 10~
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.
Claims (10)
1. An elastomeric hot melt adhesive in the form of a stable foam comprising a hot melt adhesive composition which comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of styrene/butadiene/styrene (SBS) copolymers and blend of styrene/butadiene/styrene (SBS) copolymer with styrene/isoprene/styrene (SIS) in which SIS is present in an amount not more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterized in that:
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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 not more than 120,000 cps at 180°C and an applied shear of 80 sec-1.
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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 not more than 120,000 cps at 180°C and an applied shear of 80 sec-1.
2. An elastomeric hot melt adhesive according to claim 1 comprising:
1) 10 to 80% by weight of styrenic block copolymer(s) 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 (diblock);
2) 20 to 90% of at least one tackifying resin compatible essentially only with the rubbery mid blocks;
1) 10 to 80% by weight of styrenic block copolymer(s) 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 (diblock);
2) 20 to 90% of at least one tackifying resin compatible essentially only with the rubbery mid blocks;
3) 0 to 40% of plasticizer(s);
4) 0 to 20% of an aromatic resin.
3. A process for the production of an adhesive which comprises (i) providing a hot melt adhesive composition which comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of styrene/ butadiene/ styrene (SBS) copolymers and blends of styrene/butadiene/styrene (SBS) copolymer with styrene/isoprene/styrene (SIS) in which SIS is present in an amount not more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterised in that:
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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 not more than 120,000 cps at 180°C and an applied shear of 80 sec-1;
(ii) foaming the said hot melt adhesive composition;
(iii) extruding the foam produced; and (iv) cooling the foam.
4. A process according to claim 3, wherein the composition is extruded at a temperature from 130 to 230°C.
3. A process for the production of an adhesive which comprises (i) providing a hot melt adhesive composition which comprises at least one thermoplastic elastomer and at least one tackifying resin, the thermoplastic elastomer being selected from the group consisting of styrene/ butadiene/ styrene (SBS) copolymers and blends of styrene/butadiene/styrene (SBS) copolymer with styrene/isoprene/styrene (SIS) in which SIS is present in an amount not more than 50% by weight of the total block copolymer, and wherein the said hot melt adhesive composition is further characterised in that:
a) it is capable of bonding, when applied from the molten state, to materials selected from the group consisting of plastic and cellulosic materials and mixtures thereof 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 not more than 120,000 cps at 180°C and an applied shear of 80 sec-1;
(ii) foaming the said hot melt adhesive composition;
(iii) extruding the foam produced; and (iv) cooling the foam.
4. A process according to claim 3, wherein the composition is extruded at a temperature from 130 to 230°C.
5. A process according to claim 3, wherein the foaming is by chemical or physical means.
6. A process according to claim 5, wherein the said physical means is selected from the group consisting of an inert gas and an inert volatile liquid.
7. A process according to claim 6, wherein the said liquid is methylene chloride and the said gas is selected from the group consisting of nitrogen and carbon dioxide.
8. A process according to claim 5, wherein the said chemical means comprises a chemical blowing agent.
9. A process according to claim 8, wherein the said blowing agent is diazocarbonamide.
10. A process according to claim 3, wherein the foam is subjected to natural cooling to room temperature.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT94TO000793A IT1268621B1 (en) | 1994-10-07 | 1994-10-07 | Adhesive composition and corresponding process of preparation |
| ITTO94A000793 | 1994-10-07 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2159939A1 CA2159939A1 (en) | 1996-04-08 |
| CA2159939C true CA2159939C (en) | 2001-05-01 |
Family
ID=11412812
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2159939 Expired - Lifetime CA2159939C (en) | 1994-10-07 | 1995-10-05 | Adhesive composition and process therefor |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2159939C (en) |
| IT (1) | IT1268621B1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103146216A (en) * | 2013-03-26 | 2013-06-12 | 厦门市豪尔新材料有限公司 | High-energy rubber product as well as preparation method and application thereof |
| US20210290818A1 (en) * | 2016-03-24 | 2021-09-23 | Locate Therapeutics Limited | Scaffolding material, methods and uses |
-
1994
- 1994-10-07 IT IT94TO000793A patent/IT1268621B1/en active IP Right Grant
-
1995
- 1995-10-05 CA CA 2159939 patent/CA2159939C/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103146216A (en) * | 2013-03-26 | 2013-06-12 | 厦门市豪尔新材料有限公司 | High-energy rubber product as well as preparation method and application thereof |
| CN103146216B (en) * | 2013-03-26 | 2015-06-17 | 厦门市豪尔新材料有限公司 | High-energy rubber product as well as preparation method and application thereof |
| US20210290818A1 (en) * | 2016-03-24 | 2021-09-23 | Locate Therapeutics Limited | Scaffolding material, methods and uses |
Also Published As
| Publication number | Publication date |
|---|---|
| ITTO940793A1 (en) | 1996-04-07 |
| IT1268621B1 (en) | 1997-03-06 |
| CA2159939A1 (en) | 1996-04-08 |
| ITTO940793A0 (en) | 1994-10-07 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKEX | Expiry |
Effective date: 20151005 |