Hot melt adhesive with improved adhesion and cohesive properties

Abstract

To provide adhesive hot-melt formulations comprising hot-melt adhesives that have both of very high adhesiveness and very high cohesion.SOLUTION: Novel adhesive hot-melt formulations comprise, as their main component, an isotactic metallocene butene-1 polymer composition, which has a low viscosity and has a bimodal composition, directly obtained during polymerization, in two consecutive and separate reaction steps. Moreover, the adhesive hot-melt formulations comprise less than 5 mass% of at least one viscosity modifier that is not solid at room temperature.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention discloses novel adhesive hot melt formulations comprising, as their main polymer component, at least one isotactic metallocene butene-1 polymer composition having low viscosity (and therefore relatively low average molecular weight) and substantially bimodal composition, obtained directly during polymerization in two separate, consecutive reaction steps, wherein the first polymer (polymer A) of the compositionally bimodal polymer composition is an isotactic butene-1 homopolymer or an isotactic butene-1 copolymer with another olefin, while the second polymer (polymer B) is an isotactic copolymer of butene-1 with another olefin having a chemical composition qualitatively and / or quantitatively distinct from A), and the hot melt further comprises less than 5% by mass of at least one viscosity modifier that is non-solid at room temperature. [Background technology]

[0002] Compared to similar metallocenebutene-1 composition-based adhesive hot-melt formulations already disclosed in some prior art (see below), the adhesive hot-melt formulations of the present invention exhibit a novel, unexpected, and enhanced combination between extremely high adhesion and cohesiveness, while still exhibiting low viscosity in the melt and excellent processability, which allows them to be used even in particularly critical and demanding applications where similar polymer-based formulations already disclosed in some prior art are completely unusable. The aforementioned particularly important features, such as the unusually high adhesion and cohesiveness required for adhesives, can be found particularly in cases where strong bonding is required between two substrates, which are two porous, fibrous, or perforated plastic films having holes in two-dimensional or three-dimensional morphology (i.e., forming what is technically defined as a “laminate structure” or “laminate”), or where it is required to bond one of the porous, fibrous, or perforated films to a non-porous plastic film, for example, in certain bonding portions / structures of hygienic absorbent articles (such as infant and adult incontinence diapers).

[0003] To ensure that hygienic absorbent articles have the overall high flexibility required by the end user, the base material (both perforated and non-perforated) must always be easily foldable and therefore very thin, generally 50 g / m², as indicated by their very low basis weight. 2 Less than 25g / m², often 25g / m² 2 Less than 15g / m², rarely 15g / m² 2 It is less than [amount missing]. Furthermore, in order to maintain very high "softness and pliability" in the laminate structure formed by bonding the substrates together, it is necessary to apply a very small amount of adhesive between the two substrates, for example, 15 g / m². 2 Preferably 10 g / m 2 The following is often 5g / m 2 The following applies:

[0004] Thus, a contradiction can arise between the properties of the materials used and the performance required for their use. For example, a particular adhesive structure (laminate) formed using a small or very small amount of adhesive to bond two very thin and flexible substrates, such as a plastic film bonded to a nonwoven fabric, can have a contradiction between the fact that it needs to withstand very high mechanical stress during use and the fact that it is bonded to a very small area. This situation typically occurs, for example, in laminates made by bonding a polyethylene film to a nonwoven fabric, which form the outer impermeable backsheet of an infant diaper or an adult incontinence diaper.

[0005] To any person with at least average skill in the manufacture of hygienic absorbent articles and the use of hot-melt adhesives in such manufacture, it is very clear, for example, that the laminates are subjected to unusually high limit stresses during use, and that the bonded laminate structure must withstand this without delamination or opening. Furthermore, due to the high softness and flexibility of these laminate structures, it is clear that the stresses that the laminate structures must withstand during use are not only quantitatively very high, but also applied to the bonding of the adhesive of the laminate according to an angle that changes continuously over time (e.g., following the movement of the user). Theoretically, this angle can vary between zero and 180° and can change with both time and the position of the laminate structure.

[0006] From the perspective of "adhesive properties," as expressed according to the characteristics commonly used in the science and technology of adhesives, this means that the above laminate structure, when in use, is subjected to peel stress that requires not only very high strength in quantity but also very high peel strength and very high shear strength. The above two parameters represent the high "adhesion" and high "cohesion" of the adhesive that bonds the two forming substrates within the laminate, respectively.

[0007] In addition to the laminate used as the impermeable backsheet on the outside of absorbent diapers, other laminate structures within hygienic absorbent articles where the adhesive is subjected to particularly strong critical stress during use in terms of both adhesion (peel strength) and cohesiveness (shear strength) include, for example, the laminate around the user's waist, known as the "landing zone," to which the adhesive or "Velcro-type" tape used to close the diaper is secured.

[0008] The adhesive formulations according to the present invention exhibit novel and remarkable properties, combining extremely high adhesion and cohesiveness, which enable their use to produce extremely strong adhesive laminate structures capable of withstanding critical stresses, for example, in the highly demanding applications reported above, where other hot-melt adhesive formulations, even when formulated with the same base polymer, fail completely according to different criteria taught by the prior art.

[0009] The novel adhesive formulations according to the present invention contain a very small amount of viscosity modifier, less than 5% by mass, which is non-solid at 23°C, compared to those taught and known in the prior art and in practice. Using such a small amount of substance, intended to reduce viscosity in the molten state, the formulations according to the present invention exhibit remarkably low melt viscosity, which is fully comparable to similar formulations with much higher plasticizer content described in some of the prior art, while also maintaining optimal processability in all techniques used for processing hot melt adhesives.

[0010] Compared to conventional technologies, the dramatic reduction in non-solid viscosity modifiers not only improves their adhesion and cohesiveness in entirely unexpected ways, making them suitable for particularly important applications, but also generates novel secondary beneficial effects. For example, this type of positive effect is the separation and release of the viscosity modifier from the core of the adhesive over time, i.e., its substantial disappearance, and the substantial reduction or complete elimination of any possible malodors that may occur, which originate from the most volatile portion of the viscosity modifier having a low molecular weight.

[0011] As a final observation, it is noteworthy that even when the adhesive hot-melt formulations according to the present invention contain amounts of several basic components (such as not solid viscosity modifiers) that are quite different from those taught by some prior art, they maintain and even improve their initial adhesiveness, cohesiveness (mechanical) and rheological properties over time, due to crystallization at room temperature that is very slow, delayed, and usually completed in several days.

[0012] In further embodiments of the present invention, the hot-melt adhesive formulations disclosed herein contain a very small amount of a non-solid viscosity modifier and a very small amount of a special type of polyethylene wax having very unique chemical properties and molecular structure, less than 5% by mass. Unlike similar waxes having different compositions and molecular structures, these unique waxes can be tuned and controlled in a very good and precise manner to avoid the extremely negative phenomenon known in adhesive technology as "bleed-through" (see later for details).

[0013] definition The expression “contains” is used herein as an unrestricted term and indicates the presence of what follows a term in the text, but does not exclude the presence of other components or features, such as elements, steps, components, etc., disclosed in the Works or herein.

[0014] The term "copolymer" is used herein to mean a polymer with a chemical composition containing at least two monomers or three or more monomers. Thus, unless otherwise specified, the term "copolymer" means not only a polymer with a chemical composition containing two different monomers, but also a polymer with a chemical composition containing three, four, or five or more different monomers.

[0015] In this specification, the term “non-solid” means that certain compounds, materials, components, or mixtures thereof, even if they have a sufficiently distinct volume, do not possess their own fixed shape, but are in a physical state that takes the shape of the container that houses them. Even if they are viscous enough to be temporarily molded into any three-dimensional shape, after being left at rest, without external stress, and away from their own weight, they spontaneously flow and deform permanently, losing their initial shape fairly rapidly (usually over a period that can vary from a few seconds to about a day), and taking the shape of the container that houses them (if these containers are not yet filled to the brim) or the solid surface on which they are placed. Thus, this definition includes not only all materials that can be defined as “liquid” (both high-viscosity and low-viscosity) according to the general meaning of this adjective, but also all materials that are defined in common language, for example, as “creamy,” “paste-like,” “jelly-like,” “flowy,” “greasy,” “semi-solid,” etc. In the present invention, a further way to define in rheological terms what it means when a particular compound, material, component, or mixture thereof is referred to as "non-solid" at room temperature, i.e., conventionally 23°C, is to identify that the above-mentioned "non-solid" substance can be defined as a "rheological liquid," i.e., having a viscosity coefficient G greater than the elastic modulus G' at a specified temperature of 23°C, as defined in rheology; an equivalent definition is that their tangent delta is greater than 1.

[0016] The equivalent expressions "rheology set point" or "rheology set temperature" or "cross-over temperature of elastic modulus" or "crossover point" and its symbol Tx mean the temperature at which two coefficients cross (thus the value of tangent delta is 1) in the rheology diagram where the elastic modulus G', viscous modulus G'', and their ratio tangent delta are measured as functions of temperature, in the temperature region above room temperature. The said rheology diagram mimics very well the phenomena occurring between the adhesive and the substrate in the actual process of applying a hot melt adhesive from the molten state during natural slow cooling and curing / solidification to the formation of the final adhesive bond when the temperature is lowered at a sufficiently slow cooling rate (e.g., 2 °C / min as done herein). In particular, the "rheology set point" Tx specifies the temperature at which the hot melt adhesive begins to form the final adhesive bond in the solid state when applied in a molten state onto the substrate.

[0017] The expression "cross elastic modulus" and its symbol Gc mean the absolute value in Pa or MPa that the elastic modulus and viscous modulus have at the "rheology set point" Tx in the above-mentioned rheology diagram.

[0018] "Room temperature" means a temperature equal to 23 °C unless specifically defined otherwise. "Indoor conditions" mean environmental conditions at 23 °C and 50% relative humidity where the temperature and relative humidity are controlled.

[0019] "Hygienic absorbent articles" refer to devices and / or methods related to disposable absorbent and non-absorbent articles including adult incontinence diapers and underwear, baby diapers and bibs, training pants, baby and infant care wipes, feminine sanitary napkins, interlabial pads, pantiliners, pessaries, menstrual pads, tampons and tampon applicators, wound dressings, absorbent care mats, detergent wipes, etc.

[0020] The "perforated film" typically refers to a film made of a plastic material such as polyethylene, with multiple holes, capable of having both two-dimensional and three-dimensional structures, and with typical hole sizes in the range of several hundred μm to 1 mm. This is often used as an element of absorbent hygiene products.

[0021] The "fibrous substrate" refers to a product having an essentially planar structure formed by natural or synthetic fibers or mixtures thereof in both woven and non-woven forms, which are equally used as components of absorbent hygiene products.

[0022] The "polydispersity index" or "molecular weight distribution index" or "PDI" refers to a measure of the molecular weight distribution in a specific polymer. This is defined as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn: PDI = Mw / Mn. The larger the value of PDI, the broader the molecular weight distribution curve, and vice versa. Mw, Mn and thus their ratio Mw / MN = PDI can be measured, for example, by gel permeation chromatography (GPC).

[0023] The "open time" of an adhesive, especially in the case of hot-melt adhesives, refers to the time interval after the application of the melt to the first substrate, during which the adhesive can form a sufficiently strong adhesive bond with the second substrate in contact with the first substrate under moderate pressure for the intended use. It is clear that if the open time is too short, it may be difficult to manage the application of the adhesive and the formation of a sufficiently strong bond. The open time of hot-melt adhesives can be measured according to the test method of ASTM D 4497-94 under the following conditions for the hot-melt adhesives disclosed herein. - Coating temperature of the adhesive film: 170 °C - Thickness of the adhesive film: 1 mm

[0024] The "ring and ball softening point" refers to the softening temperature of a material measured according to the method of ASTM D 36-95.

[0025] For waxes, the "softening point" (also called the "dropping point") is measured according to the method of ASTMD 3954-94.

[0026] The "needle-penetrating strength" of an adhesive is a measure of its softness. It is generally expressed as one-tenth of a millimeter, dmm, and is measured in this specification at 55°C according to the method of ASTM D 1321-04.

[0027] The kinematic viscosity of a molten or liquid material at a specific temperature is expressed in mPa·s and measured according to the method of ASTMD 3236-88.

[0028] Total adhesive strength, or "peel strength," is defined as the average strength per unit width required to separate two substrates bonded together by the adhesive under test and formed at a controlled, constant speed, at a controlled, constant peel angle. In this specification, it is measured by separating two substrates at a 180° peel angle by applying a separation rate of 150 mm / min (meaning the test dynamometer actually moves at a speed of 300 mm / min) according to the method of ASTMD 1876-01. The two substrates used herein are 22 g / m². 2 A microporous polyethylene film having a basis weight is applied thereto by direct application of a molten adhesive by spraying or slot die extrusion, and then 12 g / m² 2 A spunbond polypropylene nonwoven fabric having a basis weight is immediately bonded. Peel strength is measured by recording the average strength required to separate the two bonded substrates with a width of 50 mm.

[0029] The "tensile properties" or "tensile mechanical properties" of all materials such as the hot melt formulations disclosed in this specification, the so-called "stress-strain curve" and the corresponding "peak stress" or "tensile strength", "breaking stress" and "elongation at break", etc. are measured at 23°C and 50% relative humidity according to the following method. For each adhesive to be tested, five rectangular samples are prepared by casting the molten adhesive into a silicone mold at 170°. The length of each rectangular sample is 25 mm, the width is 6 mm, and the thickness is 2 mm. After coagulation, the samples are removed from the mold and aged at 23° and 50% relative humidity for 5 days. To evaluate the stress-strain curve, each sample is clamped at its narrowest end to the shaft of a rheometer Area G2 available from Texas Instruments equipped for tensile testing with a so-called "twisted rectangle" geometry. The free length of the sample is 10 mm. The movable upper shaft with a maximum travel of 60 mm (thus corresponding to a maximum readable strain of 600%) is started at an elongation rate equal to 6 mm / min.

[0030] Therefore, these test conditions correspond to a strain rate of the sample equal to 0.01 s -1 i.e., a frequency of 0.01 Hz, which is a typical frequency at which the phenomenon of slow peeling in a loaded state occurs, as is well known to all those with an average proficiency in the rheology of adhesives. The tensile test stops when the sample breaks or when the rheometer reaches the maximum readable strain (600%). The rheometer measures the maximum "peak stress" or "maximum tensile strength", the maximum strain for each stress-strain curve, and also calculates the area under the curve itself, i.e., the area expressed in J / m 3 equal to the toughness of the material.

[0031] Finally, (as will be shown in detail later), a specific isotactic metallocenebutene-1 polymer composition having a substantially bimodal composition obtained directly during polymerization in two consecutive separate reaction steps is included in the hot-melt adhesive formulation according to the present invention, and such hot-melt adhesive formulations, as well as the hot-melt adhesive formulations themselves, substantially change their adhesive, mechanical, and rheological properties over time due to the slow crystallization of the isotactic metallocenebutene-1 polymer composition at room temperature (between about 1 and about 7 days, typically completed in about 5 days). Therefore, it is necessary to distinguish between the "time zero properties" or "initial properties" of the adhesive, mechanical, and rheological properties (i.e., before the start of the crystallization of the butene-1 polymer composition) and the same properties measured after aging, for example, 5 days at room temperature, i.e., after the completion of the crystallization.

[0032] In particular, all properties defined below as “5-day” aging for all materials and laminate adhesive structures disclosed herein mean that the measurements were taken at 23°C and 50% relative humidity for samples aged for 5 days in a room where the environment was maintained at 23°C and 50% relative humidity. The 5 days are calculated from the moment the adhesive is set from its molten state, and therefore the moment of manufacture of the laminate adhesive structure under test.

[0033] On the other hand, all properties of the material and laminate adhesive structure defined below as "time zero" or "initial" mean those measured at 23°C and 50% relative humidity, but within 3 hours (180 minutes) from the moment the adhesive is set from its molten state, and therefore from the moment of manufacture of the laminate adhesive structure under test. In fact, the slow (slow) spontaneous crystallization of the specific metallocenebutene-1 polymer compositions used herein at room temperature does not substantially begin / not significantly occur within a few hours (specifically up to 3 or 4 hours) from the moment of solidification of the polymer composition and the hot-melt adhesive constituting them from their molten state (and therefore does not produce any detectable variation in properties using any measurement method).

[0034] Other less common parameters are measured according to specific methods and will be defined later, along with a detailed explanation of how they are measured.

[0035] prior art Isotactic homopolymers and copolymers of polybutene-1 (with other olefins, e.g., ethylene) were initially manufactured on an industrial scale and have long been sold since 1977 by major global manufacturers such as Hals, Mobil, Witco, and especially Shell, but their production has now been taken over by Lyondellbasell. All "old generation" production of polybutene-1 was carried out using Ziegler-Natta type catalysts, which produce polymers with high or very high molecular weights, and therefore high or very high melt viscosities.

[0036] Recently, several polymer manufacturers have abandoned the classic Ziegler-Natta catalyst system and are using new metallocene-type catalysts, which allows for the synthesis of a new generation of polybutene-1 with novel and highly improved properties, such as significantly lower and much more controlled average molecular weight (and thus much lower melt viscosity), a much smaller polydispersity index (and a very narrow distribution of molecular weight), and all of these properties also result in other improved properties of these polymers, such as much better processability and good mechanical properties even at relatively low melt viscosity.

[0037] For example, two patent applications by Basel Polyolefins Italy (Patent Document 1 and Patent Document 2) disclose the synthesis of an isotactic metallocene butene-1 polymer composition having a high melt flow rate (and therefore low molecular weight and melt viscosity), being bimodal, and obtained directly in two consecutive separate reaction steps during polymerization, where the first polymer (polymer A) is an isotactic butene-1 homopolymer or an isotactic butene-1 copolymer with another olefin, and the second polymer (polymer B) is an isotactic copolymer of butene-1 and another olefin, with a chemical composition clearly different from polymer A.

[0038] The unusual bimodal nature of these butene-1 polymer compositions, obtained directly in two separate steps of polymerization, gives these materials very unique and interesting properties, particularly with regard to their use as components of hot-melt adhesives.

[0039] The patent application (Patent Document 3) discloses a hot-melt adhesive formulation comprising, as its main polymer component, at least one low-viscosity isotactic metallocenebutene-1 polymer composition having a bimodal composition and corresponding precisely to the butane-1 polymer composition disclosed and claimed by Basel Polyolefins Italy in the two patent applications mentioned above.

[0040] With respect to such formulations, Patent Document 3 above shows novel and superior properties regarding good adhesion, good cohesiveness and optimal processability for both spraying and fiberization, as well as coating by slot die coating, and in particular, all of these properties are completely different from and substantially improved compared to all similar hot melt adhesive formulations based on “older generation” polybutene-1 from Ziegler-Natta type catalysts described in all prior art.

[0041] The aforementioned prior art relating to adhesive formulations based on polybutene-1 from Ziegler-Natta type catalysts is discussed in detail in the above-mentioned Patent Document 3. [Prior art documents] [Patent Documents]

[0042] [Patent Document 1] European Patent No. 3266824 [Patent Document 2] European Patent No. 3266825 [Patent Document 3] International Publication No. 2018 / 007451 [Overview of the project] [Problems that the invention aims to solve]

[0043] Regarding the hot-melt adhesive formulations claimed by Patent Document 3, the inventors of Patent Document 3 specify that they contain, in addition to the above-mentioned butene-1 polymer composition, at least one non-solid viscosity modifier at room temperature in an amount of 5% to 40% by mass, preferably 8% to 30% by mass, and more preferably 10% to 20% by mass, or a mixture thereof. That is, all hot-melt adhesive formulations disclosed in Patent Document 3 are considered to be highly plasticized by the use of a large amount of at least one viscosity modifier. In fact, all examples of the invention disclosed in Patent Document 3 contain 13% by mass of a viscosity modifier that is liquid at room temperature and in its particular case is paraffinic mineral oil. Furthermore, the hot-melt adhesive formulations described in Patent Document 3 may contain a small amount of wax of 5% by mass or less, which is said to be used essentially to change the “open time” of the adhesive. However, regarding the aforementioned general additional wax, the inventors do not specify either their chemical properties or molecular structure, or state that they prefer polypropylene wax.

[0044] The problem that the present invention aims to solve is to formulate a hot-melt adhesive that has unexpectedly good properties, namely very high adhesion and very high cohesiveness, which allows them to be used in very important and demanding applications, such as certain laminate structures in hygienic absorbent articles, applications already disclosed in the prior art, where similar polymer-based formulations are unsuitable. [Means for solving the problem]

[0045] These novel and unexpectedly enhanced properties maintain the most useful qualities of previous formulations, such as extremely low melt viscosity (despite very low viscosity modifier content), optimal processability in both spray / fiberization and slot die extrusion / coating, and further improve the adhesion, cohesiveness, and rheological properties of the adhesive and the relative bonded laminate structure over time due to slow crystallization occurring at room temperature.

[0046] Compared to similar formulations disclosed previously, the significantly improved additional qualities include a much more precise and effective control of a highly negative phenomenon called "bleed-through" (see below), a significantly improved or eliminated potential for unpleasant odors from the adhesive (a secondary but still important characteristic), and the virtually complete elimination of migration / bleed of low molecular weight compounds (essentially found in most viscosity modifiers), the possibility of migration that could significantly worsen the adhesive properties of the formulation over time.

[0047] The aforementioned problems are solved by adhesive compositions having the properties of claims 1 and 29-33, adhesive structures having the properties of claim 49, articles having the properties of claims 51-53, and articles having the properties of claims 55-57. Other dependent claims disclose preferred embodiments. [Modes for carrying out the invention]

[0048] [Detailed description of preferred embodiments and main properties of the adhesive according to the present invention] Isotactic metallocenebuten-1 polymer composition having low viscosity and bimodal composition As described above, the adhesive hot-melt formulations according to the present invention have substantially bimodal compositions, comprising at least one isotactic metallocenebutene-1 polymer composition of low viscosity (and therefore relatively low average molecular weight) as their main components, obtained directly during polymerization in two consecutive separate reaction steps, wherein the first polymer (polymer A) of the compositionally bimodal polymer composition is an isotactic butene-1 homopolymer or an isotactic butene-1 copolymer with another olefin, and the second polymer (polymer B) is an isotactic copolymer of butene-1 and another olefin, and its chemical composition is qualitatively and / or quantitatively distinct from that of A).

[0049] The novel metallocenebutene-1 polymer compositions, along with their chemical and physicochemical properties and methods for their synthesis, are described in detail in the above-mentioned Patent Documents 1 and 2, and such embodiments are incorporated herein by reference. These aforementioned metallocenebutene-1 polymer compositions (and adhesive formulations containing them at a related level) exhibit highly peculiar behavior, substantially altering their adhesive, mechanical, and rheological properties over time due to the slow spontaneous crystallization of the polybutene-1 chains under room temperature conditions. In particular, these slow spontaneous crystallization phenomena, which are completed on average in 5 days, are the reason why adhesive formulations according to the present invention have an elastic modulus G' at 5 days that is significantly larger than the elastic constant measured at time zero, and a tangent delta at 5 days that is significantly smaller than the tangent delta measured at time zero.

[0050] The crystallization phenomenon described above, and the slow time-dependent changes in the adhesive, mechanical, and rheological properties of the metallocenebutene-1 polymer compositions having a bimodal composition, and adhesive formulations containing them, have already been described in Patent Document 3, and are incorporated herein by reference only in such respects.

[0051] Each of the metallocenebutene-1 polymer compositions can be briefly described as a butene-1 polymer composition having a melt flow rate (MFR) of 200 to 6000 g / 10 min, preferably 400 to 5000 g / 10 min, measured according to ISO 1333 under a load of 2.16 kg at 190°C, and having a bimodal type composition comprising the following: A) A butene-1 homopolymer or a copolymer of butene-1 and one or more comonomers selected from ethylene and higher alpha-olefins having 3 or 4 or more carbon atoms, having a copolymerized comonomer content (CA) of 5 mol% or less, preferably 4 mol% or less. B) A copolymer of butene-1 and one or more comonomers selected from a copolymer of ethyleneethylene and one or more comonomers selected from higher alpha-olefins having 3 or 4 or more carbon atoms, having a copolymerized comonomer content (CB) of 6 mol% to 25 mol%, preferably 8 mol% to 20 mol%.

[0052] The polymer composition has a total copolymer comonomer content of 3 mol% to 18 mol%, preferably 5% to 15 mol%, which is referred to as the total mass of A) and B).

[0053] In the first embodiment of the present invention, the polymer composition contains a xylene-soluble portion at 0°C of 65% by mass or more, preferably 70% by mass or more, and the xylene-soluble portion is determined based on the total mass of A) and B).

[0054] In a second embodiment of the present invention, the polymer composition has a xylene-soluble portion content of 60% by mass or less, preferably 55% by mass or less, at 0°C, and the xylene-soluble portion is determined based on the total mass of A) and B).

[0055] Components A) and B) are preferably obtained directly in polymerization consisting of two consecutive separate reaction steps, and therefore, the polymer compositions described herein can be obtained directly in polymerization without requiring the use of other substances that can generate peroxides or free radicals to cleave the polymer chains into lower molecular weight molecules, even if they have a sufficiently high global value of MFR (low viscosity).

[0056] In a first embodiment of the present invention, a specific amount of the butene-1 polymer composition provided herein that is soluble in xylene at 0°C is expressed as the mass content of the portion measured by extraction with xylene relative to the total mass of A) and B), and is in the range of 65% to 95% by mass, preferably in the range of 70% to 90% by mass.

[0057] In a second embodiment of the present invention, with respect to the butene-1 polymer composition provided herein, a specific amount of portion soluble in xylene at 0°C is expressed as the mass content of the portion measured by extraction with xylene relative to the total mass of A) and B), and is in the range of 35% to 60% by mass, preferably in the range of 40% to 55% by mass.

[0058] If A) is a copolymer, the specific lower limit of the comonomer content is 1 mol%.

[0059] Preferably, if both A) and B) are copolymers, the difference in the percentage values ​​of the copolymerized comonomer content of B) and A) satisfies the following relationship. (CB)-(CA)≧5 or (CB)-(CA)≧6 (1)

[0060] The relative amounts of components A) and B) can be easily determined depending on the desired total content of the copolymerized comonomers, the comonomer content of the single component, and the content of the portion soluble in xylene at 0°C.

[0061] The preferred amounts in the above-described first embodiment of the present invention are 10% to 40% by mass, preferably 15% to 35% by mass of A), and 60% to 90% by mass, preferably 65% ​​to 85% by mass of B), based on the total mass of A) and B).

[0062] The preferred amounts in the above-described second embodiment of the present invention are 35% to 65% by mass, preferably 40% to 60% by mass of A) and 35% to 65% by mass, preferably 40% to 60% by mass of B), based on the total mass of A) and B).

[0063] In components A) and B), specific examples of higher alpha-olefins having 3 or more carbon atoms that can exist as comonomers in addition to or instead of ethylene are alpha-olefins of the formula CH2=CHR, where R is methyl or an alkyl radical containing 3 to 8 or 3 to 6 carbon atoms, such as propylene, hexene-1, or octene-1. However, particularly for component B), ethylene is the preferred comonomer.

[0064] While current butene-1 polymer compositions certainly possess measurable crystallinity after aging for 5 days, they can also possess measurable crystallinity even at time zero, with a period during which spontaneous crystallization at room temperature occurs and completes, guaranteeing a change in both the crystalline form and the total amount of crystallinity. In fact, as detailed in the previously mentioned literature, this butene-1 polymer composition can form a relatively limited amount of a crystalline form called "form II" with a thermodynamically unstable tetragonal structure even at time zero during solidification from the molten state. While slowly and spontaneously crystallizing over time, the initial crystals of the unstable form change to a thermodynamically stable hexagonal form called "form I" in about 5 days, while simultaneously, the new crystals of form I also undergo a significant improvement in overall crystallinity.

[0065] The crystallinity of all materials disclosed herein is identified and measured in a DSC (Differential Scanning Calorimetry) diagram through the presence of crystalline portions, such as the melting (or crystallization) of the temperature peak of polybutene-1.

[0066] DSC measurements during both the crystallization cycle (i.e., temperature decrease) or the melting cycle (temperature increase) are performed according to the method of ASTMD 3417-99, and the above cycles are performed between +180°C and -70°C (or vice versa) to obtain complete information on all phenomena occurring in the material, such as the glass transition temperature Tg.

[0067] The enthalpy of crystallization or melting is expressed in J / g and is given by the area of ​​the peak (obtained by integration) or the sum of the areas of multiple peaks that may appear during a DSC cycle.

[0068] DSC analysis of butene-1 polymer compositions, and all single pure components of adhesive formulations in general, is performed at a temperature change rate of 10°C / min, as recommended in ASTMD 3417-99.

[0069] In contrast, the DSC measurement of the hot melt adhesive formulation of the present invention follows the same method, but is performed using a temperature lamp equal to 1°C / min. This modification of the method was introduced because, particularly in the crystallization cycle, a cooling rate equal to 1°C / min very well mimics the actual phenomena that occur during the application of the molten adhesive to the substrate and its slow spontaneous cooling, curing, and possible crystallization.

[0070] In particular, even at time zero, the metallocenebutene-1 polymer composition of the present invention having a bimodal composition may exhibit a certain level of crystallinity, measured by the presence of one or more melting peaks, in a DSC thermal cycle performed for curing from a molten state from -70°C to +180°C (by definition of time zero) within a maximum of 180 minutes. If the melting peaks are present at time zero, they are generally located at temperatures below 110°C, mainly between approximately 75°C and approximately 110°C. These are due to the melting of form II (TmII) of polybutene-1, and the area under the above peaks is adopted as a measure of the relative overall enthalpy of melting (delta H TmII). If multiple melting peaks are present, the peak corresponding to the highest temperature is considered to be TmII. More specifically, the metallocenebutene-1 polymer composition having a bimodal composition used in the adhesive formulation of the present invention has a total enthalpy of melting delta H TmII of 20 J / g or less, preferably 1 J / g to 20 J / g, when measured at a temperature rise rate of 10°C / min. Furthermore, in a DSC heating cycle performed after aging the material at room temperature for 5 days, the metallocenebutene-1 polymer composition shows one or more melting peaks, which are generally located at temperatures below 110°C, particularly between 30°C and 110°C. The one or more peaks after 5 days are due to the melting of crystalline form I (TmI) of polybutene-1, and the area under the one or more peaks is used as a measure of the relative total enthalpy of melting (delta H TmI). If multiple melting peaks are present, the peak corresponding to the highest temperature is taken as TmI.

[0071] More specifically, the metallocenebutene-1 polymer composition used in the adhesive formulation of the present invention has a total melting enthalpy delta H TmI of 50 J / g or less, preferably 3 J / g to 50 J / g or 5 J / g to 50 J / g, when measured at a temperature rise rate of 10°C / min.

[0072] Regardless of theory, the stable hexagonal crystal form (Form I) of polybutene-1 measured after 5 days is preferable to optimize the final adhesive and mechanical properties of the hot melt adhesive. Therefore, the TmI measured as described above is preferably quite high, and in particular, TmI is preferably 60°C or higher, and more preferably 80°C or higher.

[0073] The preferred and above-specified values ​​of the total MFR of the metallocenebuten-1 polymer composition having a bimodal composition contained in the adhesive formulation of the present invention can be obtained by combining components A) and B) in appropriate ratios, and theoretically any individual MFR value is possible. However, in practice, the preferred metallocenebuten-1 polymer composition having a bimodal composition in the present invention has sufficiently high individual MFRs of the two components A) and B), particularly in the range of 200 to 6,000 g / 10 min, preferably 400 to 5,000 g / 10 min.

[0074] In accordance with conventional technical practices in the field of hot-melt adhesives, the viscosity of both the final adhesive and its components in the molten state is often measured by the so-called "Brookfield viscosity" according to the method of ASTMD 3236-73.

[0075] In this embodiment, the metallocenebutene-1 polymer composition having a bimodal composition contained in the adhesive of the present invention has a Brookfield viscosity of 1,000 to 50,000 mPa·s, more preferably 2,000 to 50,000 mPa·s, as measured at 190°C.

[0076] Furthermore, the isotactic metallocenebuten-1 polymer composition contained in the adhesive formulation of the present invention exhibits at least one of the following further characteristics: - The overall polydispersity index PDI = Mw / Mn = Mw / Mn, where Mw is the mass-average molecular weight and Mn is the number-average molecular weight, which is 4 or less, preferably less than 3, more preferably less than 2.5, and in any case the lower limit is 1.5. - The polydispersity index of a single component A or B is preferably 2.5 or less. -Mw is set to 5,000 or more, preferably between 10,000 and 100,000. The intrinsic viscosity of tetrahydronaphthalene (THN), measured at -135°C, is 0.6 dl / g or less, preferably 0.1 to 0.6 dl / g, and more preferably 0.2 to 0.6 dl / g. -150.91 MHz, isotactic pentad (mmmmm) measured by 13C-NMR, greater than 90%, preferably greater than 93%, more preferably greater than 95%. A 4,1 insertion undetectable by 13C-NMR operating at -150.91MHz. - A yellowness index measured according to ASTM D 1925, less than or equal to zero, preferably between 0 and -10, more preferably between -1 and -9, and even more preferably between -1 and -5. A D Shore hardness value of -50 or less, preferably 45 or less, particularly within the range of 15 to 50, and preferably between 15 and 45. -Fracture stress of 1 MPa to 25 MPa, preferably 1 MPa to 20 MPa, in accordance with ISO 527. -Fracture elongation consisting of 100% to 1,500%, preferably 450% to 1,000%, in accordance with ISO 527. -Glass transition temperature measured by DSC, consisting of -35°C to -10°C. - 0.875 g / cm³ at room temperature 3 Preferably, the above is 0.875 g / cm³. 3 ~0.92g / cm 3 , more preferably 0.88 g / cm³ 3 ~0.91g / cm 3 The density of.

[0077] Isotactic metallocenebuten-1 polymer compositions having bimodal compositions corresponding to the above are manufactured and sold by Lyondelbasell, which has the trademark KOATTRO® PB M, such as Koattro PB M 0600M, Koattro PB M 1500M, and Koattro PB M 2500.

[0078] The hot-melt adhesive formulation of the present invention comprises at least 10% to 99.5% by mass, preferably 25% to 90% by mass, and more preferably 30% to 70% by mass of at least one isotactic metallocenebutene-1 polymer composition, and as described above, has low viscosity and substantially a bimodal composition.

[0079] Non-solid viscosity modifier at room temperature The hot melt adhesive formulation according to the present invention also comprises, in addition to the above-described butene-1 polymer composition, a very small amount (see below) of at least one viscosity modifier or mixture of viscosity modifiers that are "non-solid" at room temperature in the previously defined sense. However, unlike those previously disclosed and claimed in, for example, Patent Document 3 already mentioned, and contrary to those disclosed in all prior art, the hot melt adhesive formulation disclosed and claimed herein contains a very small amount, i.e., less than 5% by mass of a non-solid viscosity modifier at room temperature.

[0080] As is well known to anyone with average skill in formulating hot melt adhesives, the majority of these adhesive formulations typically contain large amounts of one or more viscosity modifiers that are very low molecular weight and liquid at room temperature.

[0081] The purpose of adding such additives is to significantly alter the melt viscosity of the final formulation, in most cases to a value far lower than the melt viscosity of the only molten polymer present in the formulation. This significant reduction in viscosity makes the hot melt adhesive easier to process, allowing application at relatively low temperatures (e.g., generally below 180°C, often much lower), resulting in not only energy savings but also the ability to apply the adhesive to very thin, heat-sensitive substrates, such as plastic films and nonwovens, which are primarily used in hygienic absorbent articles, and which would be damaged or unacceptably deformed upon contact with the hot melt adhesive at temperatures above 180°C.

[0082] The same person who is reasonably skilled in the technique of compounding hot melt adhesives is also familiar with the positive and negative effects of affecting the general properties of the adhesive by changing the viscosity modifier content, sometimes referred to as "plasticizer" or "fluidizer" in this technique, in one direction or the other.

[0083] Before delving into this discussion, it is important to remember that, according to the fundamental principles of adhesive science, achieving the "optimal" performance of any adhesive is closely related to a precise and correct balance between its adhesive properties and cohesive properties.

[0084] In all cases, the “total adhesive strength” of an adhesive—that is, the strength required to break a particular bond between the adhesive and the substrate—is the sum of two distinct families of contributions that can be defined as “pure adhesion” and “pure cohesiveness.” The first is generated by chemical and physicochemical interactions (van der Waals forces, molecular dipole forces, hydrogen bonds, etc.) established between the molecules of the adhesive and the molecules of the substrate at a distance comparable in magnitude to the molecular size; therefore, these forces depend strongly on the chemical properties of the materials and the “ease” with which the adhesive can come into close contact with the substrate (or, in technical terms, how it “wets” the substrate). Furthermore, their contributions are directly proportional to the “wetted” area of ​​the substrate, i.e., the actual contact area between the adhesive and the substrate, due to their “softness” and “tackiness,” which are not only rigorously demonstrated by the science of adhesives but are also intuitive. The “wetting” of a wider area of ​​the substrate by the adhesive, and thus the potential to create a strong “pure adhesion” interaction, is facilitated.

[0085] The second family of contributors to overall adhesive strength, namely cohesive force, is, conversely, proportional to the adhesive's cohesive force, or "inherent mechanical resistance," in other words, the strength required to "physically break" the adhesive film present within a particular bond structure. A typical adhesive bond will break if the applied strength exceeds the sum of the "pure adhesive" strength and "pure cohesive" strength of the adhesive used. When the former strength is dominant, certain adhesives are said to fail "primarily due to poor adhesion," while in the latter case, they are said to fail "primarily due to poor cohesiveness."

[0086] Adhesives that are too hard have optimal cohesive force, but conversely, hard adhesives are not "soft and tacky" enough to sufficiently wet the substrate, so the contribution of "pure adhesion" is very low. On the other hand, adhesives that are too soft and tacky have high adhesion, but break easily due to poor cohesiveness. In both cases, the observed total adhesive strength is unacceptably low. Therefore, it is clear that optimizing and maximizing the total adhesive strength of a general adhesive necessarily requires optimizing, maximizing, and balancing both the adhesiveness and cohesiveness of the adhesive.

[0087] Returning to the consequences of increasing or decreasing the viscosity modifier content in hot melt adhesives, it is well known that by reducing the level of such additives (often fluids with low or very low molecular weights), an increase in the mechanical properties of the adhesive formulation can be observed. This mechanical strengthening of the adhesive is represented by a significant increase in its parameter, the elastic modulus G' (both in the solid and molten states). This is also reflected in a significant increase in the tensile coefficient, i.e., the difficulty of "mechanically breaking" the adhesive, in other words, a significant increase in the cohesive force of the adhesive can be observed. While this may seem like a positive effect, it is not actually so. As is well known to anyone with an average level of rheology, increasing the elastic modulus G' also means making the adhesive "harder," and therefore reducing its tackiness, thus impairing its pure adhesive properties. Thus, the effect of significantly reducing the level of viscosity modifiers present in hot melt adhesives means that the tackiness and adhesion of the formulation will be much lower, in addition to the obvious fact that it will significantly increase the melt viscosity, significantly worsen the processability, and force users to apply them at higher temperatures with excessively high limits.

[0088] As is known to anyone with an average level of expertise in the formulation of hot melt adhesives, the levels of viscosity modifiers added to the majority of such formulations are generally quite high for all these reasons. And, in accordance with these standards, the inventors of the aforementioned Patent Document 3, using the same isotactic metallocenebutene-1 polymer composition as the polymer base, which is also used in the present invention, advocate a viscosity modifier content ranging from a minimum of 5% by mass to a maximum of 40% by mass. In fact, the present invention prefers much higher levels of these additives, consisting of 8% to 30% by mass, and even 10% to 20% by mass. In fact, all the examples shown in Patent Document 3 actually include 13% of viscosity modifiers with a low molecular weight.

[0089] Therefore, in contrast to those taught by prior art, particularly by Patent Document 3 as mentioned above, the present invention, surprisingly, utilizes the above-mentioned novel isotactic metallocenebuten-1 polymer composition, which has low viscosity and a substantially bimodal composition, a narrow bimodal distribution of both chemical composition and molecular weight, and not only is the usual large addition of viscosity modifiers unnecessary to improve the adhesion and processability of the formulations of the present invention, but can even adversely affect the optimal balance of adhesion and cohesiveness values ​​of the adhesive formulations of the present invention and their increase to significantly higher values ​​(compared to those obtained with known large amounts of these additives).

[0090] Therefore, the hot melt adhesive formulations according to the present invention contain substantially less of a non-solid viscosity modifier or mixture of viscosity modifiers at room temperature compared to all prior art dealing with polybutene-1 based hot melt adhesives, particularly those taught by Patent Document 3 already mentioned. More specifically, the hot melt adhesive formulations according to the present invention contain less than 5% by mass of a non-solid viscosity modifier or mixture of viscosity modifiers at room temperature, preferably 4.5% by mass or less of the non-solid viscosity modifier or mixture of viscosity modifiers at room temperature.

[0091] Such very small amounts of viscosity modifiers are unexpectedly associated with the unexpected increase in adhesion and cohesiveness of the formulations disclosed herein, and with an optimal balance, so that they can meet and withstand critical and demanding applications, particularly those that would fail in adhesives formulated according to the prior art with much higher levels of viscosity modifiers.

[0092] Even more surprisingly, the adhesives disclosed in this invention have been found to maintain low melt viscosity and excellent processability even in processes with high or very high applied "shear rates," such as spraying, fiberization, and slot die coating, and even in industrial lines operating at high speeds of 250 m / min or more, despite having a very low viscosity modifier content.

[0093] Furthermore, the unusually low level of viscosity modifiers in this adhesive formulation allows for the achievement of highly beneficial additional properties compared to standard hot-melt adhesives with much higher molecular weights and higher content of these additives. In particular, Viscosity modifiers almost always contain very low molecular weight components, which are volatile enough to be noticeable even at room temperature. This often imparts a distinctive and unpleasant odor to these materials, which must be avoided at all costs, especially in hygienic absorbent articles. -The above-mentioned portions with very low molecular weight may slowly migrate to the outside of the adhesive itself over time, potentially causing a bleeding phenomenon. If this occurs, the very bad consequences are not only unacceptable fluctuations and degradation of the adhesive's properties over time, but also the possibility of serious problems such as skin irritation, sensitization / allergic reactions, and even toxic reactions if these bleeding substances come into contact with the user's skin.

[0094] Therefore, reducing the amount of viscosity modifier added to the adhesive formulation as much as possible is a very positive and desirable fact, especially when high adhesion and cohesiveness and low viscosity are maintained. More specifically, the adhesive formulation according to the present invention has a Brookfield viscosity measured at a temperature of 170°C of 30,000 mPa·s or less, preferably 15,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 5,000 mPa·s or less.

[0095] In one embodiment of the present invention, the hot melt adhesive formulations disclosed herein have a sufficiently low viscosity even at temperatures significantly lower than 170°C, and as a result, they can be optimally processed and applied to a substrate at temperatures of 145°C or lower, preferably 140°C or lower, and more preferably 135°C or lower, by both spraying and slot die coating techniques.

[0096] This particular group of formulations according to the present invention can be processed and applied even at unusually low temperatures and exhibits a Brookfield viscosity measured at 130°C of 15,000 mPa·s or less, preferably 12,000 mPa·s or less, and more preferably 10,000 mPa·s or less.

[0097] Viscosity modifiers that are non-solid at room temperature and are present in the adhesive formulation of the present invention at a level of less than 5% by mass include, for example, paraffinic mineral oils; naphthenic mineral oils; paraffinic and naphthenic hydrocarbons and mixtures thereof that are non-solid at room temperature; polyolefins and their copolymers, such as non-solid oligomers at room temperature derived from ethylene, propylene, butene, isobutylene, and their copolymers; plasticizers that are non-solid at room temperature formed by esters such as phthalates, benzoates, and sebacates; vegetable oils; natural and synthetic fats; and mixtures thereof. Both paraffinic and naphthenic mineral oils and fats, as well as mixtures thereof, are particularly preferred. Equally preferred are non-solid oligomers of polyolefins synthesized via metallocene catalysts, which, like metallocenes, have a particularly low polydispersity index Mw / Mn of 2 or less, preferably 1.8 or less, and more preferably 1.5 or less. Polyolefin oil (PAO), marketed by ExxonMobil under the trademarks SPECTRASYN® and ELEVAST®, and propylene-ethylene, a non-solid oligomer copolymer at room temperature, are marketed by Clariant under trademarks such as LICOCENE® PPA330.

[0098] The optimal adhesion and cohesiveness of the requested formulations, as well as their characteristic stress-strain curves. As already stated, despite their low melt viscosity, the adhesive formulations according to the present invention exhibit a very good balance between high adhesion and high cohesiveness, thereby successfully passing particularly important tests that simultaneously challenge both the adhesion and cohesiveness of the adhesive, such as other similar formulations formulated according to the teachings of the prior art failing.

[0099] A test method that simultaneously challenges both the adhesion and cohesiveness of an adhesive, especially under harsh conditions, is the so-called "hang test" or "hang time test" (see below for a detailed explanation). It very well simulates extremely harsh conditions of very high stress, such as that applied according to an angle that changes over time, when the laminate is used in particularly demanding applications, such as the external impermeable backsheet of a baby or adult incontinence diaper. The adhesive functions within a laminate adhesive structure formed, for example, from a plastic film and a nonwoven fabric.

[0100] Furthermore, in addition to the aforementioned hang test, it was found that the unexpectedly excellent improved properties of the current adhesive formulations can also be detected as both extremely high adhesion and cohesiveness, as well as by the completely unique shape indicated by the stress-strain curve that breaks in the tensile test using the method described above.

[0101] In fact, by testing samples of various formulations in parallel using both hang tests and tensile tests, it has been observed that the two types of tests correlate very well in some way, and therefore, by using specific values ​​of several parameters in the stress-strain curve of the adhesive under test, it is also possible to predict the possible resistance of the laminate structure in use (a situation that is well simulated, measured, and predicted by hang tests).

[0102] More specifically, adhesives that are "too soft" will therefore (as already seen) break in both actual use and hang tests, mainly due to their insufficient cohesiveness (failure of the adhesive's cohesiveness), exhibiting a stress-strain curve with a very low peak / maximum tensile strength and a very low elongation. In fact, the peak of the curve is proportional to the elastic modulus G' of the material, and if the material is very "soft", the parameter G' will be low as well as the elongation at fracture, because the material with low cohesiveness will physically burst even under very limited stress. Thus, if the cohesiveness of the adhesive is insufficient, the region below the stress-strain curve will be small. This is perfectly logical, as mechanical science teaches that the region below the stress-strain curve is the so-called "toughness" of the material, representing the amount of energy per unit volume that the material can absorb by plastic deformation / stretching before fracture. Thus, low cohesiveness corresponds to low toughness and a small region below the stress-strain curve. The said region (and the toughness of the material) is J / m 3 or MJ / m 3 It has physical dimensions represented by [the specified dimensions].

[0103] Conversely, adhesives that break because they are "too hard" and therefore fail due to insufficient adhesion (poor adhesion) exhibit stress-strain curves with excessively high peaks, as is evident from the fact that their high hardness is represented by their high elastic constant G' value (and thus peak stress). The region below the curve, and therefore the toughness of the material, can be relatively large, but this is not beneficial to the strength and integrity of the adhesive, as the adhesive film can easily burst with low elongation even under very limited deformation (and thus as a result of small "movements" of the laminate structure in use) due to its excessive hardness and brittleness.

[0104] Therefore, in order for an adhesive to have particularly high overall adhesive strength, formed by a balanced combination of high adhesion and high cohesiveness, and consequently pass the hang test, the stress-strain curve of the adhesive during the test must simultaneously exhibit the following three characteristics. a) A large region below the curve, and therefore large toughness / cohesive force (i.e., the toughness of the adhesive is greater than a certain minimum value). However, the following is also necessary: b) The peak of the maximum stress on the curve (or "maximum tensile strength") and the value of the elastic modulus G' of the adhesive (which are mutually proportional) fall between the minimum and maximum values ​​(i.e., the adhesive is soft and tacky enough, but not "too soft" or too hard and unbreakable). c) The elongation at the breaking point of the adhesive exceeds a certain minimum value (i.e., the adhesive is not too hard and does not break easily).

[0105] Clearly, all properties of this formulation change significantly over time after application from the molten state due to the unique spontaneous, slow crystallization of the butene-1 composition, which occurs at room temperature and is completed in approximately 5 days. Therefore, all of the above mechanical and rheological parameters, measured both in the adhesive itself (rheological parameters and stress-strain curves) and in the laminate structure containing the adhesive (hang time tests, etc.), were measured after aging for 5 days at 23°C and 50% relative humidity, perfectly mimicking the properties that users of sanitary absorbent articles containing the adhesive would actually use and test.

[0106] To also highlight the substantial increase observed during aging in the rheological, cohesive, and adhesive properties of the specific adhesive formulations of the present invention, for comparison, the same test can be performed at time zero, i.e., from the moment the adhesive hardens / solidifies from a molten state as previously defined, and within 180 minutes of the time the laminate structure is manufactured.

[0107] Returning to the unique shape of the stress-strain curves shown by the hot-melt adhesive formulations of the present invention, it was discovered that these adhesives have stress-strain curves that satisfy the following conditions after aging at a temperature of 23°C and 5 days at room temperature: -0.2 MJ / m 3 Preferably 0.4 MJ / m 3 Area under the above stress-strain (toughness) curve. -200% or more, preferably 250% or more elongation at break. The maximum stress (i.e., the peak of the stress-strain curve or ultimate tensile strength) is comprised of -0.15 MPa to 1.5 MPa, preferably 0.20 MPa to 1.2 MPa, and more preferably 0.25 MPa to 1.0 MPa. Alternatively, as an alternative to the condition immediately above: Elastic modulus G' measured at -23°C and 1Hz, consisting of a range of 3.0MPa to 25.0MPa, preferably 5.0MPa to 20.0MPa.

[0108] The excellent combination of adhesive strength and cohesive strength of these hot-melt formulations can be appropriately measured directly, even under particularly harsh conditions, by an experimental method called the “hang test” or “hang time test,” which will be described later, even in adhesive structures containing at least one fibrous or perforated substrate, as already mentioned.

[0109] Other components of the hot melt adhesive according to the present invention Wax with a unique chemical composition and structure In embodiments of the present invention, the hot melt adhesive formulations disclosed herein also include waxes or wax mixtures formed by less than 5% by mass of wax or wax mixture, preferably polyethylene wax, and more preferably waxes or wax mixtures characterized by a highly linear / unbranched structure and an unusually small polydispersity index (details below).

[0110] This embodiment stems from the fact that within all hygienic absorbent articles, there exists a laminated adhesive structure in which at least one (and possibly both) substrates have holes, cavities, or is a fibrous substrate, such as a plastic film, or a nonwoven fabric bonded to two bonded nonwoven fabrics or a nonwoven fabric bonded to a cellulose / cotton fabric.

[0111] As always, in these cases, it is essential to ensure very high adhesive and cohesive strength (e.g., by passing a hang time test). However, it is also essential to avoid an even more negative potential phenomenon known in bonding technology as "bleed-through" (see below for details).

[0112] Patent Document 3, mentioned earlier, has already asserted that the adhesive disclosed therein may contain a small amount of wax, less than 5% by mass. The stated purpose for adding these small amounts of wax is to adjust the release time of the adhesive.

[0113] However, when Patent Document 3 asserts the existence of small amounts of general waxes, it does not specify the waxes in terms of both their chemical composition and chemical structure, nor does it require any specific properties. The present inventors limit them, and as will be described later, among all waxes, polypropylene wax is particularly preferred, and polypropylene wax modified with maleic anhydride and having a softening point of 120°C or higher is even better.

[0114] There are at least three reasons why modified polypropylene wax with a considerably high softening point is preferable. - Waxes with a fairly high softening point (and therefore a very high hardening point) are most effective in shortening the adhesive release time when the adhesive release time is considered to be too long. - Waxes modified with maleic anhydride, in particular, are well known in hot-melt adhesive technology as additives that can promote wetting of the substrate and therefore generally promote high adhesion. -It is reasonable to assume that this particular preference for polypropylene wax in Patent Document 3 stems from the fact that polybutene-1 and polypropylene are highly compatible and perfectly miscible (see, for example, the article "Polymer-polymer interaction parameters in polybutene-1 / polypropylene mixtures," Journal of Polymer Research, Vol. 3, No. 4, 235-238, October 1996, which is incorporated herein by reference). Therefore, it is reasonable to assume that the intent of Patent Document 3 was to maximize the compatibility and complete miscibility of these additives to adhesive formulations by preferentially using polypropylene wax that is highly compatible with polybutene-1-based adhesives.

[0115] Contrary to the criteria used in Patent Document 3 when selecting the optimal wax to add to these adhesive formulations, the inventors of the present invention have surprisingly discovered that the addition of polyethylene wax (in any case always in small amounts, less than 5% by mass), especially when they have specific characteristic properties of their molecular structure, also unexpectedly imparts to the hot-melt adhesive formulations of the present invention the ability to control and avoid the "bleed-through" phenomenon, while simultaneously maintaining an excellent and surprisingly improved balance between high adhesion and high cohesiveness, as demonstrated by passing hang-time tests, even in all applications where this phenomenon is particularly important.

[0116] Switching between polypropylene wax (recommended in Patent Document 3) and polyethylene wax (recommended in the present invention) is not a straightforward or intuitive switch, especially considering the significant differences in compatibility / miscibility exhibited by the common base polymer, polybutene-1, since one uses polypropylene wax and the other uses polyethylene wax.

[0117] Indeed, as mentioned above, polybutene-1 and polypropylene are fully compatible and miscible, but the behavior of polybutene-1 and polyethylene systems is diametrically opposed. In fact, these two modern polymers are very miscible and, when mixed in a molten state, rapidly separate and crystallize into two completely separate phases (see, for example, the article "Crystallization Behavior of Polyethylene and i-Polybutene-1 Mixtures," "Polymer," Vol. 27, No. 3, 337-343, March 1986, which is incorporated herein by reference).

[0118] Therefore, the fact that significant, even very positive, effects can be observed in current hot-melt adhesives based on polybutene-1 by adding highly incompatible waxes such as polyethylene wax is a completely unexpected and surprising discovery. In fact, since the above wax is correctly recognized as completely incompatible and miscible with the base polymer, it has never been used as an additive to polybutene-1 based adhesives in both the prior art of all relevant patents we are aware of and current industrial practice.

[0119] In contrast, the inventors of the present invention have remarkably discovered that the addition of at least one polyethylene wax or a mixture of two or more polyethylene waxes in a total amount of less than 5% by mass, especially when they are certain, can remarkably effectively control and stop a very negative phenomenon known in adhesive technology as "bleed-through" (see below), even if the wax is chemically incompatible with the base polymer polybutene-1 due to the specific properties of its molecular structure (described below). This objective is achieved without the possibility that these polyethylene waxes (and their very low levels of addition) will interfere with the main mechanism of crystallization of the isotactic metallocene-butene-1 composition constituting the adhesive through their high degree of crystallinity.

[0120] In contrast, waxes that are highly compatible with butene-1 polymer compositions, such as the polypropylene wax preferred and claimed in Patent Document 3, are completely ineffective in controlling and stopping the "bleed-through" phenomenon in the adhesive formulations of the present invention.

[0121] In particular, among polyethylene waxes, which are generally remarkably effective in controlling and stopping bleed-through phenomena, polyethylene waxes with an average molecular weight Mn of 3,000 or less are even more effective and therefore preferred. Even more preferred are waxes having a very small polydispersity index Mw / Mn (i.e., a very narrow distribution of molecular weight), especially waxes with an Mw / Mn of 2.5 or less, preferably 2.0 or less, and even more preferably 2.5 or less.

[0122] Particularly preferred is, for example, a polyethylene wax having a perfectly linear structure and a very small polydispersity index consisting between 1.08 and 1.1, manufactured and sold by Baker Hughes (USA) under the trademark POLYWAX®. As described above, polyethylene wax or a mixture of polyethylene wax may be present in the adhesive formulation of the present invention in an amount of less than 5% by mass, preferably 3% by mass or less.

[0123] Other non-polyethylene waxes, such as polypropylene wax, may be optionally added, for example, to promote wetting of the substrate, even if they are not entirely effective in controlling and stopping "bleed-through," especially if they are modified with maleic anhydride. Their percentage levels are in no case below 3% by mass, and if polyethylene wax is also present, the overall level of all waxes present is in no case below 5% by mass.

[0124] Explanation and Measurement of the Bleed-Through Phenomenon The phenomenon known as bleed-through is defined and explained as follows: In many industrial technologies utilizing hot-melt adhesives, at least one (or more importantly, both) of the two substrates being bonded often has holes, cavities, or voids. Particularly in the field of hygienic absorbent articles, various different substrates have holes, cavities, or voids, such as nonwoven fabrics and fibrous substrates. Perforated plastic films and microporous plastic films with holes having a two-dimensional or three-dimensional structure are commonly used.

[0125] When a molten adhesive is applied to one of these fibrous or perforated substrates, the adhesive hardens and adheres to the substrate by slowly cooling and solidifying. During this slow, spontaneous cooling and hardening of the molten adhesive, the adhesive adheres not only by "wetting" the surface of the substrate (in the special sense given to the verb "wetting" in adhesive science, i.e., becoming very intimate contact), but also by partially penetrating into the interior of the holes, cavities, and voids of the substrate (for example, by partially penetrating between the fibers if the substrate is a fibrous substrate). The partial penetration of the molten or semi-molten adhesive into the holes or cavities of the fibrous or perforated substrate is a positive phenomenon in itself. In fact, thanks to this, in addition to the "pure adhesive" interaction between the surface of the adhesive and the surface of the substrate, in these cases there will also be a true "mechanical connection" between the portion of the adhesive and the holes or fibers of the substrate.

[0126] It is also worth noting that it is appropriate and beneficial in any case to enhance the adhesion of the adhesive on the fibrous or perforated substrate by promoting the partial penetration of the adhesive itself into those holes, cavities, voids, or spaces. In fact, fibrous substrates or perforated plastic films have a real area available for contact with the adhesive due to the presence of holes in their fibrous structure, which may be less than 50% of the total geometric area of ​​the substrate itself. Furthermore, since it is well known that in the adhesion of all adhesives, the contribution of "pure adhesion" to the total adhesive strength is directly proportional to the actual contact area between the adhesive and the substrate, it is clear that it would be difficult to strongly bond fibrous and perforated substrates with a significantly reduced contact area with the adhesive due to "pure adhesive interaction," and thus a robust mechanical bond is also created between the adhesive and the substrate unless partial penetration into the holes of the substrate and spaces in the substrate are desired simultaneously.

[0127] Therefore, when it is necessary to bond a structure having holes, cavities, or voids in at least one of two substrates, the most suitable hot-melt adhesive is one that can partially penetrate into the interior of such holes, cavities, voids, or spaces during application from the molten material and during their curing. However, if this penetration is not merely "partial"—that is, if the molten or semi-molten adhesive cannot cure and harden quickly due to certain thermal and rheological properties, and therefore does not "stop" penetrating into holes or rapidly penetrating between fibers—a considerable portion of this semi-molten adhesive may continue to penetrate into the interior of the fibers or perforated substrate, and may even appear in considerable quantities on the outside of the opposite side of the substrate.

[0128] This behavior, known in hot-melt bonding technology as "bleed-through," is a highly negative phenomenon that absolutely must be stopped and avoided both during the industrial production of the bonded structure and during the use of the final product containing the adhesive, as bleed-through can contaminate the production line itself with traces of adhesive. In fact, in this latest case, if bleed-through is present in any of the bonded structures within an article, it can unfortunately adhere to other parts of the same article where it should not, or the aforementioned structure may feel irritatingly sticky to the end user's skin, etc.

[0129] Clearly, the need to avoid bleed-through of hot-melt adhesive within an adhesive structure becomes even more difficult and critical when both or one of the substrates have holes, cavities, or voids, as often occurs in adhesive structures used in hygienic absorbent articles, such as two bonded nonwoven fabrics, or nonwoven fabrics bonded to cellulose / cotton fabrics.

[0130] The importance of such phenomena and the difficulty of avoiding them (in any case, ensuring optimal hang time and therefore partial penetration of adhesive into holes or between fibers) becomes even more apparent when considering that these substrates used inside hygienic absorbent articles are always very thin, mostly thinner than 25 microns, and often thinner than 15 microns. Therefore, the illustrated concept can be summarized as follows: - In bonding structures where at least one of two substrates has holes, cavities, or spaces, such as fibrous substrates or perforated plastic films, it is recommended (and often essential) to ensure that the adhesive flows during its application and curing from the molten state, allowing it to partially penetrate into the holes or between the fibers of the substrate. If this does not occur, i.e., if the adhesive hardens too quickly and does not penetrate or penetrates insufficiently, the actual contact area between the adhesive and the substrate is greatly reduced due to the presence of holes or the fibrous structure, and the adhesive strength of this type of substrate is generally unacceptably low (often more than about 50%). Conversely, if the adhesive remains semi-fluid for too long near the application and curing temperature, allowing it to continue flowing and penetrate into the interior of the fibrous or fibrous substrate, a very negative phenomenon called "bleed-through" can occur when a significant portion of the adhesive passes through the entire fibrous or fibrous substrate and reappears on the other side.

[0131] Obviously, as anyone with an average level of rheology knows well, the ability of an adhesive to stop curing around this curing point in a sufficiently fast way (but not too fast!), or conversely, to cure too slowly and continue to flow in a semi-fluid state (thus causing bleed-through), depends on the rheological setting temperature Tx and the values ​​of the main rheological parameters at that temperature. In particular, the elastic modulus G' and viscosity modulus G'' depend on the values ​​they have at that temperature (the same value in the definition of Tx), which are commonly called the cross modulus and are denoted by the symbol Gc.

[0132] It is also quite intuitive how the two parameters Tx and Gc control the ability of the semi-molten adhesive to flow for a longer or shorter time, and therefore to penetrate more or less deeply into the holes and spaces of a fibrous or perforated substrate, as this can be demonstrated in a rigorous manner. Since the rate at which a hot-melt adhesive coated in a molten state cools spontaneously can be considered substantially constant (given a particular coating process), it is obvious that the lower the rheological setting temperature Tx, for example, the longer the molten adhesive will take to flow spontaneously and penetrate into the possible holes and spaces of the substrate before it takes effect. Furthermore, as is well known to the average rheology expert, the absolute value of the cross modulus Gc (i.e., the absolute values ​​of the two rheological moduli at the hardening point Tx) is directly proportional to the viscosity of the semi-molten adhesive at that temperature, for example, and therefore, at equal Tx between two different adhesives, if Gc is too low, this can cause bleed-through anyway.

[0133] Clearly, these considerations are valid because the existence of upper limits for such parameters must also be taken into account. This is because, as is obvious, in order to maximize adhesion to fibers or perforated substrates, it is prudent anyway to support the partial penetration of the semi-molten adhesive into the holes or between the fibers. Therefore, if the set temperature Tx is too high, or if the absolute value of Gc at that temperature is too high, the semi-molten adhesive will solidify too quickly or become too viscous, even though it can partially penetrate into the holes or between the fibers, resulting in an overall adhesive strength that is too low to be completely acceptable.

[0134] In certain cases, it has been found that a structure in which at least one of the two substrates is fibrous or porous provides optimal adhesion while simultaneously avoiding bleed-through, and therefore, it is recommended that the hot-melt formulation of the present invention have a rheological setting temperature Tx between 30°C and 80°C.

[0135] Furthermore, at that temperature, it is recommended that the value of the cross modulus Gc be between 0.01 MPa and 0.25 MPa, preferably between 0.015 MPa and 0.20 MPa. Obviously, since the measurement of such parameters is performed in a rheological cycle that mimics the application of molten adhesive, its spontaneous slow cooling, and solidification accompanied by the formation of adhesive bonds, all of these parameters are measured while lowering the temperature between 170°C and -20°C at a cooling rate of 2°C / min in the rheological experiment, with a time of zero, a frequency of 1 Hz, and a cooling rate of 2°C / min.

[0136] Regarding the unexpected effectiveness of polyethylene waxes, particularly those with low molecular weight and a very narrow molecular weight distribution (very small Mw / Mn), in controlling and stopping bleed-through in current adhesive formulations based on butene-1 polymer composition, despite the substantial chemical incompatibility and miscibility between polyethylene and polybutene-1, and unrelated to theory, it is reasonable to consider, from one side, that this depends on such fundamental incompatibility between polyethylene and polybutene; on the other side, it is also reasonable to consider that this unexpected effect depends on the "partially / slightly reduced" incompatibility of these particular waxes due to their very low molecular weight and very small polydispersity index.

[0137] In other words, if it is necessary to add polyethylene with a high molecular weight or broad PDI to the adhesive formulation of the present invention based on polybutene-1, it is reasonable to assume that the polyethylene will immediately separate and completely migrate across the surface of the adhesive due to the very strong incompatibility between the two polymers, causing immediate "freezing" / solidification (due to the high crystallinity of crystalline polyethylene). This fact will immediately stop the penetration of the adhesive into the pores or between the fibers of the substrate, even partial penetration. In such a situation, there will certainly be no bleed-through. However, because there is no penetration, not even partial penetration, and no "mechanical bonding" between the adhesive and the substrate, the contact area between the adhesive and the substrate will decrease, and the observed adhesive strength will be unacceptably low.

[0138] Conversely, when polypropylene wax is added, as demonstrated in Patent Document 3, for example, it is perfectly compatible with the polybutene-1-based formulation, miscible, and no effect on bleed-through is observed. Polypropylene wax solubilizes in the molten formulation and, in most cases, continues to flow and solidifies slowly, which can cause bleed-through.

[0139] On the other hand, polyethylene waxes with sufficiently low molecular weights and very small Mw / Mn ratios (i.e., chemically incompatible) (conversely, all factors favorable to a partial "reduction of incompatibility"—see below) will exhibit intermediate and balanced behavior.

[0140] In fact, polyethylene wax is incompatible anyway, so that part will separate and bleed on the surface of the adhesive regardless, supporting a relatively rapid curing process and thus avoiding bleed-through.

[0141] However, thanks to the partial "reduction in incompatibility" due to the low molecular weight and very small polydispersity index, the aforementioned separation occurs more slowly than in the previous case with high molecular weight and high PDI polyethylene. In this way, the curing rate of the adhesive is adjusted on one side to a level fast enough to avoid bleed-through. On the other side, it is not too fast either, allowing the adhesive to partially penetrate into the holes and voids of the substrate, thus achieving high adhesive strength even with substrates that are very difficult to bond strongly.

[0142] Regarding the fact that in incompatible polymer mixtures, higher molecular weights tend to increase incompatibility, while lower molecular weights and smaller polydispersity indices tend to reduce it (without completely eliminating it, of course), we can see, for example, the statement in the book "Polymer Blends" by D. Paul and S. Newman, particularly in Chapter 2 of Volume 1, which is incorporated herein by reference.

[0143] The optimal performance of the adhesive formulation according to the present invention, which contains less than 5% by mass of one or more polyethylene waxes and has the above-described characteristic properties, even when used on perforated fibrous or porous substrates, is demonstrated by the "bleed-through test" described in detail below.

[0144] At this point, all hot-melt formulations according to the present invention are always optimized and remarkably improved in adhesion and cohesiveness, as demonstrated by the fact that they all pass rigorous hang-time tests, as will be described later, due to the combination of the above-mentioned butene-1 polymer composition and a very low level of viscosity modifier compared to conventional ones.

[0145] However, as mentioned above, some of these formulations, which do not contain polyethylene wax and have certain thermal and rheological properties, may exhibit unoptimized behavior with respect to the bleed-through phenomenon. Furthermore, these latest formulations should be considered excellent adhesives with very high and improved adhesion and cohesiveness. However, they are preferable for use in applications where the bleed-through phenomenon does not occur (e.g., joining two non-perforated substrates such as two plastic films) or in applications where the bleed-through phenomenon is not significant, such as in laminates that cannot adhere to other elements of an absorbent article at specific locations within the article, or in laminates that cannot come into contact with the user's skin during use.

[0146] In all other applications where at least one of the two substrates is fibrous or porous, it is more preferable to use the adhesive formulation according to the present invention, in a version that also includes at least one polyethylene wax.

[0147] Tackifier In one embodiment of the present invention, the adhesive composition of the present invention also comprises at least one tacky resin having a ring and ball softening point configured to be 5°C to 160°C.

[0148] Among all the possible families of tackifiers well known in the field of hot melt adhesives, those preferred in the formulations of the present invention belong to the family that is more compatible with polybutene-1 and basically polyolefins.

[0149] Generally, the tackifiers included in the formulations of the present invention can be selected from aliphatic hydrocarbon tackifiers and their partially or fully hydrogenated derivatives, aromatic hydrocarbon tackifiers and their partially or fully hydrogenated derivatives, aliphatic / aromatic tackifiers and their partially or fully hydrogenated derivatives, terpene tackifiers and their partially or fully hydrogenated derivatives, rosin and its esters and their partially or fully hydrogenated derivatives. Both aliphatic and aromatic, and aliphatic / aromatic, fully hydrogenated hydrocarbon tackifiers are particularly preferred because they have optimal compatibility with the isotactic metallocene polymer composition having a low viscosity and bimodal composition used in the hot-melt adhesive according to the present invention.

[0150] Furthermore, it has been discovered that the tackifying resin used in the formulation of the present invention preferably has a ring and ball softening temperature of 70°C to 135°C, preferably 80°C to 130°C, and even more preferably 85°C to 125°C.

[0151] In the present invention, particularly preferred tackifiers are highly purified tackifiers containing very small amounts of impurities and monomeric volatile components such as xylene, toluene, hexane, vinyltoluene, and indene, which generate an unpleasant odor in the final product and reduce the thermal stability of the adhesive resin. The volatile compounds are measured by headspace ionic gas chromatography by heating a 2-gram sample of the resin at 190°C for 30 minutes in a headspace equal to 20 ml. In the present invention, tackifiers containing volatile substances at a level of 5 ppm (parts per million) or less, preferably 2 ppm or less, and more preferably 1 ppm or less, are particularly preferred. An industrial example of such a tackifier with a very low content of volatile impurities is, for example, the tackifier supplied by Eastman (USA) under the trademark ULTRAPURE®.

[0152] In embodiments of the present invention in which the hot melt adhesive formulation includes at least one tackifying resin, they include at least one tackifier or a mixture of tackifiers in an amount of 0 to 75% by mass, preferably 10% to 70% by mass, and more preferably 20% to 65% by mass.

[0153] Other additional ingredients The hot-melt adhesive formulations according to the present invention preferably do not contain other polymers different from the novel metallocenebutene-1 polymer composition having a low viscosity and substantially bimodal composition, except for those disclosed below for specific polymers.

[0154] In particular, the adhesives of the present invention preferably do not contain amorphous α-polyolefins (APAOs), which are often used in the prior art of adhesives, and are blended with non-metallocene, older-generation polybutene-1. The APAOs mentioned above are sold, for example, by Rextac under the same trademark, or by Evonik under the trademark VESTOPLAST®.

[0155] Furthermore, the adhesive preferably does not contain semicrystalline polymers, particularly semicrystalline heteromorphic copolymers of propylene and ethylene, which are sold by ExxonMobil under the trademark VISTAMAXX® or by Lyondellbasell under the trademark HIFAX®.

[0156] However, if for any reason a small amount of the above polymer or other polymers different from the isotactic metallocenebutene-1 polymer composition which is the polymer base of the adhesive of the present invention is added, then in any case, the content of these polymers as a whole should be 15% by mass or less, preferably 10% by mass or less, of the total hot melt formulation, unlike metallocenepolybutene-1.

[0157] Furthermore, as described above, the hot-melt adhesive formulations according to the present invention include, as their main polymer component, at least one isotactic metallocene butene-1 polymer composition having low viscosity and substantially a bimodal composition, obtained directly during polymerization in two consecutive separate reaction steps, but may also include, as a secondary optional polymer component, an isotactic metallocene homopolymer or butene-1 copolymer having a monomodal composition and low viscosity in an amount of 15% by mass or less. The low viscosity of the above isotactic metallocene monomodal homopolymer or butene-1 copolymer is expressed by their melt flow rate measured at 190°C according to ISO 1133, consisting of 200 to 4,000 g / 10 min, preferably 400 to 3,000 g / 10 min.

[0158] The hot melt adhesive formulations according to the present invention may further contain at least one stabilizer, such as an antioxidant, a UV light stabilizer, or a mixture thereof, in an amount of 0.01% to 10% by mass. Furthermore, they may contain up to 15% by mass of any other additional components, such as mineral fillers, pigments, dyes, fragrances, surfactants, and antistatic agents.

[0159] Further properties of the adhesive formulation according to the present invention As already stated, the adhesive, mechanical, and rheological properties of the hot-melt adhesive formulations according to the present invention change due to the slow, spontaneous crystallization of the characteristic metallocenebuten-1 polymer composition having a bimodal composition, which occurs spontaneously at room temperature and is completed in about 1 to 7 days, typically about 5 days, and improves significantly over time.

[0160] Therefore, all tests and properties of the adhesive of the present invention and the adhesive structure containing the adhesive are generally performed and measured "in 5 days". That is, the purpose is to perform and measure on samples stored for 5 days in a climate chamber at 23°C and 50% relative humidity, counting the 5 days from the molten state of the hot melt adhesive and thus from the manufacture of the adhesive structure containing such adhesive. In fact, these are the conditions that will be seen by future users in actual use, for example, inside hygienic absorbent products, and will not reach the end user within a few months from the date of manufacture.

[0161] The above content clearly does not apply to properties or tests that are said to be specifically performed at "time zero" or "initial conditions," for example, to investigate the behavior of adhesive bond formation occurring at time zero, or to compare and quantify the changes in properties and behavior that occur between time zero and 5 days.

[0162] In particular, the rheological parameters and enthalpy of crystallization or melting of the adhesive formulation of the present invention can be described as follows. - The rheological parameters at time zero are measured in a rheological experiment at a frequency of 1 Hz, with a temperature decrease from 170°C to -20°C, and a cooling rate of 2°C / min. These conditions very well mimic the behavior of the adhesive when it is applied from a molten state to the substrate at time zero and then naturally cools and solidifies slowly to form an adhesive bond. - The rheological parameters after "5 days" are measured in a rheological experiment for a sample aged for 5 days at 23°C and 50% relative humidity, with a frequency of 1 Hz, a temperature increase from -20°C to 170°C, and a heating rate of 2°C / min. - The crystallization enthalpy from the molten material at time zero is measured by a DSC test in accordance with ASTMD 3417-99, in which the temperature is reduced from 180°C to -70°C at a cooling rate of 1°C / min. - The 5-day crystal melting enthalpy is measured by DSC testing in a sample aged at room temperature for 5 days, in accordance with the same ASTM D3417-99, where the temperature is increased from -70°C to 180°C at a heating rate of 1°C / min.

[0163] Furthermore, the hot-melt adhesive formulation according to the present invention is characterized by at least one of the following parameters and behaviors. The crystallization enthalpy from the molten material at time zero, measured by DSC testing in accordance with ASTM D3417-99 at a cooling rate of 1°C / min, is 20 J / g or less, preferably 15 J / g or less, and more preferably 10 J / g or less. This sufficiently low crystallization enthalpy at time zero is related to the fact that, in any case, only a small amount of polybutene-1 crystals of "Form II" that may be generated in this phase during solidification from the molten material and formation of the adhesive bond are present. Thus, the adhesive is initially mainly amorphous, and therefore sufficiently soft and tacky to wet the substrate and form a strong adhesive bond. The enthalpy of crystalline melting over 5 days, ranging from 1 J / g to 35 J / g, preferably 3 J / g to 30 J / g, as measured by DSC testing in accordance with ASTM D3417-99 using a heating lamp at 1°C / min. In a particularly preferred embodiment of the present invention, the enthalpy of crystalline melting results from the sum of at least three endothermic melting peaks, which may be completely separated and distinct or partially overlapping. This much higher enthalpy of crystalline melting over 5 days ensures that during aging at room temperature, a small number of possible initial crystals of Form II of polybutene-1 transform into stable, more thermally and mechanically resistant Form I crystals, while many new crystals of Form I are created, resulting in a significant improvement in both the final cohesiveness and adhesion of the adhesive. In preferred embodiments of the present invention, where multiple peaks of crystal melting are present, independent of any theory, the presence of multiple melting peaks may, presumably, be due to the presence of pure crystals of polybutene-1 form I, as well as smaller portions of different crystals resulting from both the presence of copolymers in the butene-1 polymer composition and the interaction between polybutene-1 and other components of the adhesive formulation of the present invention. The crystals of polybutene-1 form I have the highest melting point and are the most mechanically robust, contributing particularly to the very high cohesiveness of the adhesive, while other low-melting-point crystals in the mixed phase, precisely because of their lower melting point, contribute to optimal adhesion, promote wetting of the substrate, and exhibit strong adhesive force. "Open time," i.e., the period after the molten material is applied to the first substrate, during which the adhesive can form a sufficiently strong adhesive bond with the second substrate, which is brought into contact with the first substrate under moderate pressure, for the intended application, is at least 1 minute, preferably no more than 120 minutes. The open time at time zero is measured in accordance with ASTMD 4497-94 and therefore under the conditions already specified in detail. The ring and ball softening temperature for 5 days is 130°C or lower, preferably 120°C or lower, and more preferably 110°C or lower. This is measured in accordance with ASTMD 36-95. Needle penetration force measured at 55°C in accordance with ASTM D 1321-04, in the range of 10 dmm to 100 dmm.

[0164] Hang time test or hang test As already stated, the hot-melt adhesive formulations according to the present invention simultaneously exhibit excellent adhesion and superior cohesiveness, representing a substantial and remarkable improvement compared to the prior art. This combination of high adhesion and high cohesiveness enables their use in applications where other adhesives that appear similar actually fail, particularly in critical applications, such as adhesive laminate structures that form the impermeable outer layer of a baby's diaper.

[0165] As stated, the specific importance and difficulty of such use lies, for example, in that the laminate structure is subjected to stresses applied during use according to a recommended angle that is not only particularly high in absolute value but also changes continuously over time and can actually vary between 0 and 180 degrees.

[0166] Therefore, it is pointless to test adhesives separately for their adhesive properties and their cohesive properties, as is done in most of the prior art, and it does not even accurately mimic these particularly important usage conditions. In fact, generally, in most of the prior art, two independent tests are performed in exactly different ways: on the one hand, adhesive properties are measured via so-called "peel strength," and on the other hand, cohesive force of the adhesive is measured via so-called "shear strength," both performed while the adhesive is fixed and at a constant stress application angle over time.

[0167] More specifically, peel strength is defined as the average strength per unit width required to separate two substrates bonded by the adhesive under test at a controlled, constant rate, and is generally measured according to ASTMD 1876-01 by imposing a fixed angle equal to 90 degrees or sometimes 180 degrees to apply the peeling force. Shear strength is generally measured according to ASTMD 3654-02, a test method that measures the time required to peel a second substrate bonded to a first substrate by the adhesive under test from a rigid, vertical substrate (such as a vertical steel plate), and the stress is applied vertically (i.e., according to a fixed, constant angle equal to 0 degrees) by a weight oriented according to gravity, for example, by a weight placed on the second substrate.

[0168] Therefore, both of these tests give two distinct measurements of the adhesiveness and cohesiveness of the tested adhesive, measured according to a constant angle at a time equal to 90 degrees for adhesion and 0 degrees for cohesiveness, in order to apply peel stress.

[0169] In contrast, as is well known to anyone with average expertise in adhesive technology, especially in demanding applications, the stress induction angle changes continuously, and the behavior of an adhesive is far from being represented by a simple sum of "peel strength" and "shear strength," both measured independently in two tests according to a fixed angle over time, in terms of their bonding and cohesive elements.

[0170] Other inventors dealing with hygienic absorbent articles and the adhesive structures used therein have emphasized the inadequacy of measuring peel strength and shear strength in separate tests to measure the overall resistance of the adhesive structures under conditions close to actual applications, particularly the most important applications such as the impermeable outer layer of a baby's diaper.

[0171] To verify their resistance even in such critical applications, far more rigorous tests have been proposed that simultaneously expose the actual adhesive structures used in absorbent articles to "peel stress" and "shear stress" according to time-varying angles, as would occur in actual use.

[0172] In industrial practice and patent literature, this much more rigorous test is referred to by various names, such as "hang test," "hang time test," "peel hang time test," and "shear hang time test," and as mentioned above, it should not be compared to or confused with the conventional "pure peel" test in accordance with ASTM D 1876-01 or the conventional "pure shear" test in accordance with ASTM D 3654-02.

[0173] An example of the application of this rigorous “hang test” or “hang test time,” used to test the resistance of laminate adhesive structures used in absorbent diapers, can be found, for example, in U.S. Patent No. 9084699.

[0174] Generally, this test measures the time required to delaminate and open a specific area of ​​the adhesive structure when a fixed weight is suspended from one of two substrates and the entire structure is freely suspended under the stress of the weight. In particular, the hang time test differs from the shear test in accordance with ASTMD 3654-02 because the weight is applied to the adhesive structure in a strictly vertical direction, i.e., at an angle that is constant in time and equal to zero degrees. In contrast, in the hang time test, both substrates of the sample are freely suspended.

[0175] Therefore, the angle at which a weight suspended from one of the two substrates applies stress to the adhesive is not fixed in advance, but rather depends on the angle taken by the two specific substrates, which are freely suspended under the action of the weight and thus depend on the stiffness of each of them. Furthermore, while the angle can change over time, the two substrates gradually separate and open up under the action of the load, thus resulting in the latest effects of delamination and shear.

[0176] More specifically, in this invention, the hang time test is carried out by the following method: on the pilot line, 23 g / m² available from Polygov (Italy) 2 Polyethylene film with a basis weight of 12 g / m² available from Union Industries (Italy). 2 A laminated adhesive structure is fabricated using spunbond polypropylene nonwoven fabric having a basis weight of 1.0 g / m². The bonding is performed on a pilot line operating at 250 m / min, mimicking the operating conditions of an industrial line, at a temperature of 160°C and a basis weight of 1.0 g / m². 2 This is done by slot-die coating the adhesive under test with a given basis weight.

[0177] Because polyethylene film may deform or develop holes due to direct contact with the molten adhesive, the molten adhesive is coated onto a nonwoven fabric, and after coating, the nonwoven fabric is immediately brought into contact with the plastic film to which it is to be bonded.

[0178] Next, the laminate is aged for 5 days under indoor conditions. After this, five rectangular strips, 100mm wide and 80mm long, are cut from each laminate.

[0179] Each strip is tested at 23°C as follows: The strip is opened at one of its widest ends, separating the two substrates from each other, and opened to a length of 30 mm. If necessary, the separation of the strip can be facilitated by dissolving the adhesive present in the area to be separated with petroleum ether.

[0180] A mark with a horizontal line made of black, indelible ink is formed both at the starting point of the still-fully bonded laminated section and at a distance of 40 mm equal to this line on the inside of the still-bonded section. After this, the open end of the polyethylene film is suspended by clamps to a fixed metal support and positioned at a height from the floor or at least 500 mm below. Conversely, the other open end of the nonwoven fabric is spread out in the opposite direction from the plastic film and suspended completely free. This end is suspended by a weight by clamps, and as a result, the total load (weights and clamps) hanging from the free end of the nonwoven fabric is 150 g in total.

[0181] The sample is suspended freely, and the chronometer is started. Under the action of the weight, the opening of the laminate sample begins and continues under the latest action of peeling and shear stresses. When the opening of the sample reaches the second transverse line, which is 40 mm from the first line, the chronometer is stopped, and the time in minutes is recorded. This test is repeated for five samples of each laminate. The hang time of the adhesive during the test is calculated as the average of the five times recorded for the five samples.

[0182] Table 1 shows the results of hang time tests on adhesive formulations of examples from both the present invention and comparative examples (see below).

[0183] Tests to qualitatively measure bleed-through As mentioned above, in some applications involving at least one fibrous or perforated substrate (and more if both substrates are perforated, void, or fibrous), a phenomenon called "bleed-through" occurs, where, during application, the semi-molten adhesive penetrates the substrate excessively, and some of the adhesive can reach the surface on the opposite side of the perforated or fibrous substrate.

[0184] The behavior of the adhesive under test for bleed-through is examined here under very harsh conditions, specifically using thin and open fibrous substrates. Specifically, this phenomenon is observed with 12 g / m² adhesive available from Union Industries (Italy). 2 For a polypropylene nonwoven fabric having a basis weight of 16 g / m² 2 The adhesive structure formed by bonding polyethylene films available from Polygov (Italy) having a basis weight is examined.

[0185] Mimicking the operating conditions of an industrial line, the adhesive was applied to a pilot line at a speed of 250 m / min at a temperature of 160°C and a density of 6.0 g / m². 2 The adhesive is sprayed at a basis weight. The adhesive is sprayed onto a high-temperature resistant nonwoven fabric and immediately comes into contact with the plastic film to be bonded.

[0186] The test is stopped when the overall outer diameter of the molded laminate roll reaches approximately 200 mm. The roll is aged for 5 days at 23°C and 50% relative humidity. After such aging, the roll is manually unwound, and a qualitative ranking of possible "bleed-through" is made based on the observed resistance to unwinding and blocking, into four levels (high, medium, low, zero), and possible noise due to delamination of the stacked layers within the roll. In fact, if the tested adhesive bleeds from the fibrous substrate, it adheres to adjacent layers of laminate within the roll. This low or high tackiness, which is proportional to the amount of adhesive bleed-through, is also proportional to the observed resistance to unwinding and noise. [Examples]

[0187] Examples The present invention is better illustrated by the following embodiments, which are provided herein for illustrative purposes only and should not be considered to limit the scope of the invention or the ways in which it can be carried out. Unless otherwise specified, parts and percentages are given in mass.

[0188] However, before describing several examples from both the present invention and comparative examples, it is helpful to recall once again that the present invention has surprisingly discovered the following: - Exceptionally low levels of viscosity modifiers result in the latest optimal values ​​of high adhesion and cohesiveness. This is well represented by excellent hang time. - Nevertheless, the presence of the specific polyethylene wax disclosed herein, which is partially incompatible with the base polymer, is the only thing that can eliminate even the very negative phenomenon known as bleed-through.

[0189] Therefore, to avoid misunderstanding, it is necessary to emphasize that only formulations combining both of the above two formulation criteria are "complete" examples according to the present invention, as they simultaneously possess optimal hang time and optimal resistance to bleed-through.

[0190] Therefore, in the presence of low levels of viscosity modifiers, the examples reported below, which do not contain the aforementioned specific polyethylene wax or contain waxes having different chemical properties and structures, should be considered "according to the present invention" solely for their excellent hang time and for their combination of high adhesion and cohesiveness. These modern formulations are fully usable only in the absence of at least one fibrous or perforated substrate, as on such perforated substrates the above formulations may give a non-zero level of bleed-through.

[0191] Examples of the present invention Example 1 The following hot-melt adhesive formulations were prepared by mixing components in a molten state at 170°C.

[0192] [Table 1]

[0193] The hot-melt adhesive formulation of Example 1 contains a very small amount, precisely 3.8% by mass, of a non-solid viscosity modifier at room temperature. The formulation disclosed in this example exhibits excellent toughness, which is also demonstrated by its exceptional ability to dissipate the energy applied in stress-strain fracture tests.

[0194] In fact, the toughness after aging at 23°C, 0.01Hz for 5 days was 0.84 MJ / m 3 The elongation at the fracture point is 348%, and the maximum (peak) stress on the curve shown above is 0.41 MPa. Furthermore, the modulus of elasticity G' at 23°C and 1 Hz after 5 days of aging is 7.7 MPa.

[0195] Therefore, the hot-melt adhesive formulation of Example 1 exhibited optimal adhesion and cohesiveness simultaneously, as also demonstrated by the excellent results of the hang time test, which lasted for up to 105 minutes (Table 1).

[0196] However, because this formulation does not contain the specific polyethylene wax, it does not have the fully optimized rheological properties to completely avoid bleed-through that can occur in the presence of highly porous substrates. In fact, this formulation is within the acceptable limits in the bleed-through test described above, exhibiting non-zero levels of bleed-through between low and medium (Table 2). It also has a fairly long open time of 100 minutes.

[0197] The ability of this formulation to partially flow through porous and fibrous substrates, and to maintain its tackiness for a relatively long period, is further highlighted by its key rheological parameters at time zero. In fact, it exhibits a rheological setting temperature Tx (crossover temperature) equal to 35°C and a cross modulus of elasticity at the said temperature Gc equal to 0.015 MPa.

[0198] Furthermore, even at very low levels of viscosity modifiers, the formulation in this example exhibits a low viscosity of 2000 mPa·s at 170°C. This is comparable to the viscosity of similar formulations containing much higher levels of similar low-molecular-weight additives.

[0199] Regarding other key properties of the formulation in Example 1, the formulation has a crystallization enthalpy from the molten material at time zero that is undetectable by DSC. After 5 days of aging, the crystal melting enthalpy is equal to 7.4 J / g, showing three melting peaks with a maximum core temperature of 76.5°C, a ring and ball softening temperature of 85.7°C, and an eight-through after 5 days of aging at 55°C of 70 dmm.

[0200] Example 2 The following hot-melt adhesive formulations were prepared by mixing components in a molten state at 170°C.

[0201] [Table 2]

[0202] The hot-melt formulation of Example 2 is similar to that of Example 1, but still has the same very low level of viscosity modifier, and contains only 1.0 mass% of a unique polyethylene wax having a complete linear structure, an average molecular weight of 850, and a very small polydispersity index Mw / Mn of 1.08. The amount of the unique polyethylene wax, which is partially incompatible with the base metallocenebutene-1 polymer composition, is small and gives the formulation excellent behavior even in bleed-through tests with observed bleed-through at a completely zero level (Table 2). The above optimal behavior of bleed-through may also correlate with the dramatic reduction in release time caused by the introduction of such a small amount of this unique polyethylene wax, and the rheological parameters at time zero. In fact, the release time is very short at 3 minutes compared to the previous example. Meanwhile, Tx is equal to 37.7°C and its cross modulus Gc is 0.015 MPa.

[0203] The excellent behavior described above in the bleed-through is clearly related to the optimal combination of high adhesion and cohesiveness, and is not only very high, but also significantly improved compared to the already excellent Example 1, as indicated by the values ​​in the hang time test. In fact, the hang time of the formulation in Example 2 is 145 minutes.

[0204] Here again, this very long hang time can be correlated with excellent values ​​in the stress-strain curve. In fact, the area under the curve above (ductility) is 1.62 MJ / m². 3 It also has a fracture elongation of 511%, and the maximum load on the curve is 0.56 MPa. The optimal degree of cohesion can also be correlated with the value of the modulus G' at 23°C and 1 Hz after 5 days of aging, which is 15.1 MPa.

[0205] Regarding other important parameters characterizing the formulation of Example 2 of the present invention, the viscosity at 170°C is 1915 mPa·s, the crystallization enthalpy from the molten state at time zero is equal to 0.93 J / g, the crystallization enthalpy after 5 days of aging is 10.1 J / g, and the maximum core temperature consists of the sum of three melting peaks at 85.5°C. The ring and ball softening temperature of the above formulation is equal to 87.3°C, and the needle penetration force at 55°C is 67 dmm.

[0206] Comparative Example Comparative Example 1 The hot-melt adhesive formulation of Comparative Example 1 below was prepared by mixing its components in a molten state at 170°C. This formulation is similar to that of Example 1 above, but contains a much higher level of viscosity modifier (approximately 3.5 times greater), as taught by important parts of the prior art.

[0207] [Table 3]

[0208] Comparative Example 1, containing a high level of viscosity modifier, exhibits completely unacceptable adhesion and cohesiveness, as indicated by its extremely short hang time of only 11 minutes. This highly unsatisfactory result is also highlighted by the results of the fracture test under stress-strain. In fact, the area under the curve (toughness) is very small, at 0.09 MJ / m². 3 It is only equal to [a certain value]. Furthermore, the elongation at fracture is low, equal to 151%, and the maximum stress on the curve is only 0.12 MPa.

[0209] Because it does not contain the specific polyethylene wax disclosed in the present invention, the formulation of Comparative Example 1 also exhibits similarly poor behavior in bleed-through tests (Table 2). This unacceptable level of bleed-through may also correlate with the parameters of the rheological curve during cooling, particularly at the poor time zero, and the extremely long opening time of 240 minutes. In fact, the curve does not show a crossover temperature for the two coefficients even when cooled to -20°C. Even after 5 days of aging, the modulus of elasticity at 23°C and 1 Hz remains very low at a value of 2.7 MPa.

[0210] Regarding other key parameters of this formulation, its viscosity at 170°C is equal to 964 mPa·s, its ring and ball softening temperature is very low at 63°C, and its needle penetration force at 55°C is too high (the adhesive is too soft) at 118 dmm.

[0211] Comparative Example 2 The hot-melt adhesive formulation of Comparative Example 2 is similar to that of Comparative Example 1, as taught by the essential parts of the prior art, and maintains the same high level of viscosity modifier.

[0212] However, in order to somehow avoid the very poor levels of adhesion and cohesiveness (and therefore hang time) of Comparative Example 1, the bimodal isotactic metallocenebuten-1 polymer composition KoattoroPB M1500M used above is replaced with a similar bimodal isotactic metallocenebuten-1 polymer composition KoattoroPB M0600M, which has substantially higher molecular weight and crystallinity. However, as shown below, even such substitution fails to eliminate the same very negative behavior already demonstrated by Comparative Example 1 in the presence of the same excessive levels of viscosity modifier.

[0213] [Table 4]

[0214] In fact, in this case as well, the combined properties of adhesion and cohesiveness continue to be very poor, as highlighted by the poor hang time. Indeed, the formulation in Comparative Example 2 has a hang time of only 28 minutes. 1.09 MJ / m 3 Despite its clearly sufficient toughness and the maximum stress on the stress-strain curve of 0.97 MPa, the adhesive formulation of Comparative Example 2 fractures mainly because its elongation at fracture is very low, only 136%. Its modulus of elasticity G' at 23°C and 1 Hz is 14.1 MPa.

[0215] Furthermore, similar to the formulation of Comparative Example 1, this adhesive formulation also has very poor rheological parameters at time zero, despite the remarkably high molecular weight and high crystallinity of the base polymer, as highlighted by the melt enthalpy equal to 15.3 J / g. Nevertheless, the adhesive formulation disclosed above has a very low rheological setting temperature Tx, exactly equal to 26°C, slightly above room temperature, with a corresponding Gc value of 0.011 MPa. Moreover, this adhesive exhibits very poor behavior in bleed-through tests, with the level of bleed-through remaining unacceptably high (Table 2), which is substantially identical to that of Comparative Example 1.

[0216] The remaining main parameters characterizing the above adhesive formulation are a viscosity of 2050 mPa·s at 170°C, an open time of 120 minutes, a ring and ball softening temperature of 78°C, and a needle penetration force of 58 dmm at 55°C.

[0217] Comparative Example 3

[0218] [Table 5]

[0219] The objective of this Comparative Example 3 is to demonstrate that the use of a wax that is partially incompatible with the base butene-1 polymer composition, unlike the specific polyethylene wax disclosed herein, does not have the effect of reducing or stopping the bleed-through phenomenon. In particular, the formulation of Comparative Example 3 is a repetition of the formulation of Example 2 according to the present invention, but it replaces the unique and partially unsuitable polyethylene wax with polypropylene wax, which is highly compatible with the base polybutene-1. Therefore, the above formulation of Comparative Example 3 should be considered an "example according to the present invention" only in relation to the excellent hang time, due to its very low viscosity modifier content. However, the above formulation is also an inadequate "comparative example" in relation to the behavior in the bleed-through test, and the addition of polypropylene wax did not improve it at all; on the contrary, it did not improve at all compared to Example 1, which contains no wax according to the present invention, and was even worse.

[0220] What I argued above can also be summarized as follows: -The formulation of Comparative Example 3 exhibits an excellent hang time value equal to 86 minutes. This can be correlated with good parameters of the stress-strain curve. In fact, the area under the curve (toughness) is 0.74 MJ / m². 3The elongation at the breaking point is 265%, and the maximum stress on the curve is 0.60 MPa. Good cohesion can be expressed by the elastic modulus G' after aging for 5 days at 23°C and 1 Hz, which is 18.1 MPa. -In contrast, the same formulation exhibits an unacceptable level of bleed-through (Table 2). This correlates with the fact that the rheological diagrams at cooling and time zero do not show a crossover temperature for the two coefficients Tx, even when the material is cooled to -20°C. Furthermore, the open time for this formulation is very long, at 105 minutes.

[0221] Regarding other key parameters of the above formulation, the viscosity at 170°C is 1950 mPa·s, the ring and ball softening temperature is 86.9°C, and the needle penetration force at 55°C is 65 dmm.

[0222] [Table 6]

[0223] [Table 7]

Claims

1. A hot melt adhesive compound, said hot melt adhesive compound is a) A 10% to 99.5% by mass isotactic metallocenebuten-1 polymer composition having a melt flow rate (MFR) of 200 to 6,000 g / 10 min, measured at 190°C and under a load of 2.16 kg, wherein A) and B) below, i.e., A) an isotactic butene-1 homopolymer, or a butene-1 isotactic copolymer of ethylene and one or more comonomers selected from alpha-olefins having 3 or 4 or more carbon atoms, wherein the homopolymer or copolymer A) has a copolymerized comonomer content (CA) of 5 mol% or less, B) A butene-1 isotactic copolymer of ethylene and one or more comonomers selected from alpha-olefins having 3 or 4 to 8 carbon atoms, wherein copolymer B) has a copolymerized comonomer content (CB) of 6 mol% to 25 mol%, It consists of, The isotactic metallocenebuten-1 polymer composition has a bimodal composition having a total copolymerized comonomer content of 3 mol% to 18 mol% relative to the sum of A) and B), and a) b) 3.8% by mass or more and less than 5% by mass of a non-solid viscosity modifier at room temperature or a mixture of non-solid viscosity modifiers at room temperature, c) Less than 5% by mass of polyethylene wax, Includes, The viscosity modifiers that are non-solid at room temperature are selected from paraffinic mineral oils; naphthenic mineral oils; paraffinic and naphthenic hydrocarbons and mixtures thereof that are non-solid at room temperature; oligomers of polyolefins and their copolymers that are non-solid at room temperature; plasticizers that are non-solid at room temperature formed by esters; natural and synthetic fats; and mixtures thereof. Hot melt adhesive compound.

2. 4. A hot melt adhesive compound according to claim 1, comprising 4.5% by mass or less of a non-solid viscosity modifier at room temperature or a mixture of non-solid viscosity modifiers at room temperature.

3. The hot melt adhesive compound according to claim 1 or 2, wherein the homopolymer or copolymer A) has a copolymerized comonomer content (CA) of 4 mol% or less.

4. The hot melt adhesive formulation according to any one of claims 1 to 3, wherein the copolymer B) has a copolymerized comonomer content (CB) of 8 mol% to 20 mol%.

5. The hot melt adhesive formulation according to any one of claims 1 to 4, wherein the metallocenebuten-1 polymer composition has a total copolymerized comonomer content of 5 mol% to 15 mol% relative to the sum of A) and B).

6. The hot melt adhesive compound according to any one of claims 1 to 5, wherein the metallocenebutene-1 polymer composition contains a xylene-soluble portion at a rate of 65% by mass or more relative to the sum of A) and B) at 0°C.

7. The hot melt adhesive compound according to any one of claims 1 to 5, wherein the metallocenebutene-1 polymer composition contains a xylene-soluble portion at 0°C in an amount of 60% by mass or less relative to the sum of A) and B).

8. The hot melt adhesive compound according to claim 6, wherein the metallocenebutene-1 polymer composition comprises 10% to 40% by mass of A) and 60% to 90% by mass of B) based on the total of A) and B).

9. The hot melt adhesive compound according to claim 7, wherein the metallocenebutene-1 polymer composition comprises 35% to 65% by mass of A) and 35% to 65% by mass of B) based on the total of A) and B).

10. The metallocenebutene-1 polymer composition is a hot melt adhesive compound according to any one of claims 1 to 9, having a delta H TmII of 20 J / g or less as measured using a temperature scanning lamp at 10°C / min.

11. The metallocenebutene-1 polymer composition is a hot melt adhesive compound according to any one of claims 1 to 10, having a TmI of 60°C or higher.

12. The metallocenebutene-1 polymer composition has a viscosity in the range of 1,000 to 50,000 mPa·s as measured at 190°C, and is a hot melt adhesive compound according to any one of claims 1 to 11.

13. The metallocenebutene-1 polymer composition is a hot melt adhesive compound according to any one of claims 1 to 12, having a polydispersity index of 4 or less.

14. The metallocenebutene-1 polymer composition is a hot melt adhesive compound according to any one of claims 1 to 13, having an Mw value of 5,000 or more.

15. The metallocenebutene-1 polymer composition is a hot melt adhesive compound according to any one of claims 1 to 14, having a glass transition temperature of -10°C or lower.

16. A hot melt adhesive compound according to any one of claims 1 to 15, having a Brookfield viscosity of 30,000 mPa·s or less as measured at 170°C.

17. A hot melt adhesive compound according to any one of claims 1 to 16, having a solidification period of 1 minute to 120 minutes after cooling from 170°C to 23°C.

18. A hot melt adhesive compound according to any one of claims 1 to 17, having a crystallization enthalpy from the molten material at time zero of 20 J / g or less, as measured on a cooling lamp at 1°C / min in accordance with ASTM D3417-99.

19. A hot melt adhesive compound according to any one of claims 1 to 18, having a crystal melting enthalpy after 5 days in the range of 1 J / g to 35 J / g, as measured at a heating rate of 1°C / min according to ASTM D3417-99.

20. The hot melt adhesive formulation according to claim 19, wherein the crystalline melting enthalpy is the sum of at least two endothermic melting peaks, which may be separate or partially overlapping.

21. A hot melt adhesive compound according to any one of claims 1 to 20, having a ring and ball softening temperature of 130°C or lower after 5 days.

22. A hot melt adhesive compound according to any one of claims 1 to 21, further comprising at least one adhesive resin.

23. The hot melt adhesive formulation according to claim 22, wherein the adhesive resin is selected from aliphatic hydrocarbon adhesive resins and partially or fully hydrogenated derivatives thereof; aromatic hydrocarbon adhesive resins and partially or fully hydrogenated derivatives thereof; aliphatic / aromatic adhesive resins and partially or fully hydrogenated derivatives thereof; terpene adhesive resins and partially or fully hydrogenated derivatives thereof; rosin and esters thereof and partially or fully hydrogenated derivatives thereof; and mixtures thereof.

24. The hot melt adhesive compound according to claim 22 or 23, wherein the adhesive resin or mixture of adhesive resins has a certain content of a volatile compound that can be extracted by heating at 190°C for 30 minutes at a concentration of 5 ppm or less.

25. The hot melt adhesive compound according to any one of claims 22 to 24, wherein the adhesive resin or mixture of adhesive resins has a ring and ball softening temperature of 70°C or higher.

26. The hot melt adhesive compound according to any one of claims 22 to 25, wherein the adhesive resin or mixture of adhesive resins constitutes 0% to 75% by mass of the compound.

27. The hot melt adhesive compound according to any one of claims 1 to 26, wherein the polyethylene wax constitutes 3% by mass or less of the compound.

28. The polyethylene wax has an average molecular weight of 3,000 or less, as described in any one of claims 1 to 27, for the hot melt adhesive compound.

29. The hot melt adhesive compound according to claim 28, wherein the polyethylene wax has a polydispersity index of 2.5 or less.

30. A hot melt adhesive formulation according to any one of claims 1 to 29, comprising polypropylene wax modified with 3% by mass or less of maleic anhydride.

31. A hot melt adhesive formulation according to any one of claims 1 to 30, comprising 15% by mass or less of a polymer or a mixture of polymers different from the metallocenebutenbuten-1 polymer composition.

32. The hot melt adhesive formulation according to claim 31, wherein the polymer or mixture of polymers is an amorphous α-polyolefin, or a semicrystalline heterophase copolymer of polypropylene and ethylene, or a mixture thereof.

33. The hot melt adhesive compound according to claim 32, wherein the amorphous α-polyolefin is a copolymer, terpolymer, or tetrapolymer having propylene or butene-1 as its main monomer in mass ratio, and one or more olefins selected from ethylene and / or other C3 to C8 olefins as a second monomer.

34. A hot melt adhesive compound according to any one of claims 1 to 33, comprising a monomodal composition and a melt flow rate of 200 to 2,000 g / 10 min at 190°C, and also including 15% by mass or less of a homopolymer or copolymer of isotactic polybutene-1.

35. The hot melt adhesive formulation according to claim 34, wherein the homopolymer or copolymer of polybutene-1 having a monomodal composition is synthesized by a metallocene catalyst.

36. After 5 days of aging under indoor conditions, the reading was measured at 23°C and 0.01 Hz, at 0.2 MJ / m². ３ A hot melt adhesive compound according to any one of claims 1 to 35, having a fracture stress-strain curve having the above toughness.

37. The hot melt adhesive compound according to claim 36, having a maximum stress (peak) in the fracture stress-strain curve in the range of 0.15 MPa to 1.5 MPa at 23°C and 0.01 Hz.

38. A hot melt adhesive compound according to claim 36 or 37, having a breaking point elongation of 200% or more at 23°C and 0.01 Hz.

39. A hot melt adhesive compound according to any one of claims 1 to 34, having an elastic constant G' in the range of 3 MPa to 25 MPa measured at 23°C and 1 Hz after aging for 5 days under indoor conditions.

40. A hot melt adhesive compound according to any one of claims 1 to 39, having a rheological curing temperature Tx in the range of 30°C to 80°C, measured under cooling at a cooling rate of 2°C / min at time zero.

41. The hot melt adhesive compound according to claim 40, having a cross modulus Gc in the range of 0.01 MPa to 0.25 MPa, as measured under cooling at a cooling rate of 2°C / min at time zero.

42. A hot melt adhesive compound according to any one of claims 1 to 41, which, after aging for 5 days under indoor conditions, has a needle penetration force of 10 d mm to 100 d mm at 55°C.

43. In a hang time test performed on an adhesive structure comprising a first substrate, a second substrate, and a hot melt adhesive compound according to any one of claims 1 to 42, which had been aged for 5 days under indoor conditions, the yield was 1 g / m². ２ A hot melt adhesive compound according to any one of claims 1 to 42, having a weighing capacity of 60 minutes or more under a load of 150 g.

44. A hot melt adhesive compound according to any one of claims 1 to 43, which can be processed and applied onto a substrate by both spraying and slot die coating techniques at a processing temperature of 145°C or lower, and which has a Brookfield viscosity of 15,000 mPa·s or less as measured at 130°C.

45. Adhesive structure, The first substrate and A second substrate and A hot melt adhesive compound according to any one of claims 1 to 44, wherein the compound adheres the first substrate and the second substrate, and the compound is 0.5 g / m². ２ ~50g / m ２ A hot melt adhesive compound that, when applied by weighing, gives the adhesive structure a peel strength of more than 0.25 N per 50 mm width, measured after aging for 5 days at room temperature, or alternatively, gives the adhesive structure a hang time of 60 minutes or more. An adhesive structure equipped with [the following features].

46. The adhesive structure according to claim 45, wherein at least one substrate is a porous or fibrous substrate, or a perforated film having a two-dimensional or three-dimensional structure.

47. A hygienic absorbent article comprising a hot melt adhesive compound according to any one of claims 1 to 44.

48. A hygienic absorbent article comprising the adhesive structure described in claim 45 or 46.

49. The hygienic absorbent article according to claim 47 or 48, wherein the article is a baby diaper, training pants, adult incontinence diaper, or women's sanitary napkin.

50. Use of the hot melt adhesive formulation according to any one of claims 1 to 44, i) as a general building adhesive for an entire article, ii) for bonding elastic elements, iii) for enhancing and ensuring the integrity of the absorbent core of a hygienic absorbent article, iv) for bonding a perforated film to both a two-dimensional structure and a three-dimensional structure, or v) for bonding a nonwoven fabric to another nonwoven fabric or plastic film.

51. Articles, An article comprising a hot melt adhesive compound according to any one of claims 1 to 44, wherein the article is a hygienic surgical mattress, or a sheet or surgical laminate for medical use, or a wound dressing.

52. An article comprising a hot melt adhesive compound according to any one of claims 1 to 44, wherein the article is a mattress or a component of a mattress.

53. An article comprising a hot melt adhesive compound according to any one of claims 1 to 44, wherein the article is a package.

Images