WO2000020205A1

WO2000020205A1 - Elastic laminates and method for making the same

Info

Publication number: WO2000020205A1
Application number: PCT/US1998/021011
Authority: WO
Inventors: Kazuyuki Ohnishi; Yoko Mizutani; Ebrahim Rezai
Original assignee: The Procter & Gamble Company
Priority date: 1998-10-02
Filing date: 1998-10-02
Publication date: 2000-04-13
Also published as: CA2345926A1; AU1068099A

Abstract

In one aspect, the present invention is directed to an elastic laminate which is elastically extensible in at least one direction. The elastic laminate (70) includes an elastomeric material (124) having a first surface (150) and a second surface (152) opposing the first surface. The elastomeric material includes a polystyrene thermoplastic elastomer. The elastic laminate further includes a first nonwoven layer (122) including component fibers which include a polyester. The elastomeric material (124) is bonded to the first nonwoven layer (122) through a continuous heat/pressure bond which is formed by application of a bonding temperature which is lower than the melting point of the polyester. In another aspect, the present invention is also directed to a method for forming an elastic laminate. The method comprises the steps of: a) providing an elastomeric material made from a polystyrene thermoplastic elastomer, the elastomeric material having a first surface and a second surface opposing the first surface; b) providing a first nonwoven layer having a first surface and a second surface opposing the first surface, the first nonwoven layer including component fibers which are made from a polyester; c) placing the first surface of the elastomeric material against the first surface of the first nonwoven layer; and d) forming a continuous heat/pressure bond between the elastomeric material and the first nonwoven layer, by an application of a bonding temperature which is lower than the melting point of the polyester.

Description

ELASTIC LAMINATES AND METHOD FOR MAKING THE SAME

FIELD

The present invention relates to elastic laminates. More specifically, the present invention relates to elastic laminates which include an elastomeric material including a polystyrene thermoplastic elastomer and a nonwoven layer including a polyester. The present invention also relates to methods for making such elastic laminates.

BACKGROUND Elastic laminates have previously been used in a variety of disposable products, including sweat bands, bandages, body wraps, and disposable garments including disposable diapers and incontinence devices. Herein, "elastic laminate" refers to an elastically stretchable two or more layered, at least partially, materials including at least one elastically stretchable single layer material. It is generally expected that these products provide good fit to the body and/or skin of the user by using suitable elastic members during the entire use period of products. Those elastic laminates typically include, at least, a fibrous material layer

(e.g., a nonwoven layer) and an elastomeric material joined to the fibrous material layer. These materials are joined together typically through an adhesive (or glue) bond or a heat/pressure bond formed therebetween.

The adhesive bond is often used for forming elastic laminates. However, it tends to cause several problems in its manufacturing process(es) and its usage by consumers. For example, a manufacturing process which includes an adhesive application tends to become more complicated than that which does not need it (e.g., a heat/pressure bond process). In addition, the adhesive application tends to cause a contamination problem in manufacturing equipments or production lines because the use of adhesive. Further, an elastic laminate which uses an adhesive tends to cause an odor problem to consumers of disposable products, since some adhesive materials have a strong and/or uncomfortable smell.

The heat/pressure bond is preferably used for forming elastic laminates. For example, Japanese Laid-Open (Kokai) Patent Publication No. H 10-165437 published on June 23, 1998 discloses a disposable diaper which includes a three- layered structure of nonwoven/elastomer film/nonwoven which are bonded together through a number of non-continuous bonding points. However, this structure tends not to provide an enough bonding strength or toughness in the layered structure against a stress which is generated in the use of the diaper (or which may be applied in the manufacturing process), thereby causing a separation of the layered materials. It is believed that this problem is caused because the layered structure does not have enough peer strength required by the disposable products.

Based on the foregoing, there is a need for an elastic laminate that provides an enough bonding strength or toughness between a elastomeric material and a fibrous material layer (or a nonwoven layer) against a stress which is generated in the use of disposable products diaper (or which may be applied in the manufacturing process).

SUMMARY In one aspect, the present invention is directed to an elastic laminate which is elastically extensible in at least one direction. The elastic laminate includes an elastomeric material having a first surface and a second surface opposing the first surface. The elastomeric material includes a polystyrene thermoplastic elastomer. The elastic laminate further includes a first nonwoven layer including component fibers which include a polyester. The elastomeric material is bonded to the first nonwoven layer through a continuous heat/pressure bond which is formed by application of a bonding temperature which is lower than the melting point of the polyester.

In another aspect, the present invention is also directed to a method for forming an elastic laminate. The method comprises the steps of: a) providing an elastomeric material made from a polystyrene thermoplastic elastomer, the elastomeric material having a first surface and a second surface opposing the first surface; b) providing a first nonwoven layer having a first surface and a second surface opposing the first surface, the first nonwoven layer including component fibers which are made from a polyester; c) placing the first surface of the elastomeric material against the first surface of the first nonwoven layer; and d) forming a continuous heat/pressure bond between the elastomeric material and the first nonwoven layer, by an application of a bonding temperature which is lower than the melting point of the polyester. These and other features, aspects, and advantages of the present invention will become evident to those skilled in the art from reading of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the invention will be better understood from the following description of preferred embodiments which is taken in conjunction with the accompanying drawings and which like designations are used to designate substantially identical elements, and in which: Fig. 1 is a fragmentary enlarged perspective view of an elastic laminate of one preferred embodiment of the present invention, prior to being formed into the elastic laminate;

Fig. 2 is a enlarged perspective view of an elastic laminate of yet another embodiment of the present invention, wherein a portion of the nonwoven layer has been removed to show the bonded structure; Fig. 3 is a fragmentary enlarged perspective view of an alternative embodiment of the elastomeric material; and

Fig. 4 is a schematic representation of a lamination device for forming the elastic laminate shown in Fig. 2.

DETAILED DESCRIPTION All cited references are incorporated herein by reference in their entireties. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention. Herein, "comprise", "include" and "have" mean that other element(s) and step(s) which do not affect the end result can be added. These terms encompass the terms "consisting of and "consisting essentially of. Herein, "gf stands for gram force.

Herein, "joined" or "joining" encompasses configurations whereby an element is directly secured to another by affixing the element directly to the other element, and configurations whereby the element is indirectly secured to the other element by affixing the element to intermediate member(s) which in turn are affixed to the other element.

Herein, "layer" does not necessarily limit the element to a single stratum of material in that a layer may actually comprise laminates or combinations of sheets or webs of materials.

Herein, "nonwoven" may include any material which has been formed without the use of textile weaving processes which produce a structure of individual fibers which are interwoven in an identifiable manner. Methods of making suitable nonwovens includes a spunbonded nonwoven process, a meltblown nonwoven process, a carded nonwoven process, or the like.

A. Laminate Structure

The present invention relates to an elastic laminate that provides an enough bonding strength or toughness between a elastomeric material and a nonwoven layer (or a fibrous material layer) against a stress which is generated in the use of disposable products diaper (or which may be applied in the manufacturing process). This and other advantages of the invention are described in more detail herein. Fig. 1 is a fragmentary enlarged perspective view of an elastic laminate 70 of one preferred embodiment, prior to being formed into the elastic laminate. (One preferred embodiment of the elastic laminate 70 after the formation is shown in Fig. 2.) Referring to Fig. 1 , the elastic laminate 70 of the present invention includes an elastomeric layer 124 having a first surface 150 and a second surface 152 opposing the first surface 150; and a first nonwoven layer 122 which is joined to the first surface 150 of the elastomeric layer 124. In a preferred embodiment, the first surface 150 and second surface 152 of the elastomeric layer 124 are substantially parallel with the plane of the first nonwoven layer 122. The first nonwoven layer 122 has an inner surface (or a first surface) 142 and an outer surface (or a second surface) 144. The inner surface 142 of the first nonwoven layer 122 is the surface that is positioned facing the elastomeric layer 124.

In a preferred embodiment, the elastic laminate 70 further comprises a second nonwoven layer 126 joined to the second surface 152 of the elastic material 70. The second nonwoven layer 126 also has an inner surface 146 and an outer surface 148. The inner surface 146 of the second nonwoven layer 126 is the surface that is positioned facing the elastomeric layer 124. The second surface 152 of the elastomeric layer 124 is substantially parallel with the plane of the second nonwoven layer 126. In a preferred embodiment, the nonwoven layer 126 is formed by an identical nonwoven material with that is employed in the first nonwoven layer 122. Alternatively, the nonwoven layer 126 may be formed by a different material from that is employed in the first nonwoven layer 122.

The elastic laminate 70 of the present invention is elastically extensible in at least one direction (first direction). For example, the elastic laminate 70 shown in Fig. 1 is elastically extensible in the structural direction D. Herein, "structural direction" (e.g., D and B) is intended to mean a direction which extends substantially along and parallel to the plane of the first nonwoven layer 122. In a preferred embodiment, the elastic laminate 70 is also elastically extensible in the second direction which is perpendicular to the first direction. For example, the elastic laminate 70 shown in Fig. 1 is also elastically extensible in the structural direction B.

B. Nonwoven Layers

The first nonwoven layer 122 of the present invention may be manufactured from a wide range of component fibers which are formed from a polyester. Preferred polyester materials includes a polyethylene terephthalate, a polybutylene terephthalate and a polypropylene terephthalate, or mixtures thereof. In a preferred embodiment, the first nonwoven layer 122 additionally includes component fibers formed from the other materials (i.e., non-polyester materials) such as polyolefin and nylon. In a preferred embodiment, the individual component fibers are formed from a single type of material which is selected from the above materials (i.e., the individual fiber is not made from polyolefin and nylon). Preferably, the component fibers are formed from a polyester, more preferably a polyethylene terepthalate, or one of its relatives which has an average molecular weight from about 5,000 to about 60,000, preferably from about 10,000 to about 40,000, more preferably from about 14,000 to about 23,000. Alternatively, the component fibers may be formed from a mixture of two (or more) materials which are selected from the above materials.

In one embodiment, the component fiber has a bi-component fiber structure formed from two distinct materials of a polyester and a polyolefin. In an alternative embodiment, the component fiber has a bi-component fiber structure formed from two distinct molecular weight materials of one identical material, for example, a polyester. Preferred bi-component fiber structures may include a side-by-side bi- component fiber structure and a sheath-core bi-component fiber structure known in the art. In one embodiment, the component fiber has a bi-component fiber structure having a core of polyolefin and a sheath of a polyester.

In a preferred embodiment, the first nonwoven layer 122 has a basis weight of less than about 60 g/m , and comprises fibers having a fiber diameter of less than about 50 μm. More preferably, for products such as disposable garment and the like, the first nonwoven layer 122 has a basis weight of from about 3 g/m² to about 50 g/m², more preferably from about 10 g/m² to about 25 g/m², and a fiber diameter of from about 1 μm to about 30 μm, more preferably from about 3 μm to about 20 μm. The component fibers may be joined together by adhesives, thermal bonding, water-jetting, needling/felting, or other methods known in the art to form nonwoven fabrics. In a preferred embodiment, the first nonwoven layer 122 is formed from a nonwoven manufacturing process handling continuous component fibers or filaments known in the art. Preferred manufacturing process are described in, for example, EP 0843036A1 (Kurihara et al.) published on May 20, 1998; U.S. Patent No. 5,312,500, entitled "Non-Woven Fabric and Method and Apparatus for Making The Same", issued to Kurihara et al. on May 17, 1994; Japanese Laid-Open Patent Publication (Kokai) No. H2-269859 published on November 5, 1990; and Japanese Patent Publication (Kokoku) No. S60-25541 published on June 19, 1985.

In a preferred embodiment, the first nonwoven layer 122 is formed from component fibers which are joined together. The component fibers have a primary fiber direction. The first nonwoven layer 122 has a Fiber Orientation Ratio within about ±20 degrees from the primary fiber direction (FOR20) of at least about 65%; more oreferably at least about 75%; more preferably still at least about 85%. In a more preferred embodiment, the first nonwoven layer 122 additionally has a Fiber Orientation Ratio within about ±10 degrees from the primary fiber direction (FOR10) of at least about 45%; more preferably at least about 60%; more preferably still at least about 70%. "FOR#" (e.g., FOR10) indicates the ratio of the number of the component fibers whose directions are within about ±# degrees, (e.g., ±10 degrees) from the primary fiber direction to the total number of component fibers. Herein, "primary fiber direction" refers to an average direction of component fibers in the nonwoven layer. One preferred method for measuring the Fiber Orientation Ratio of nonwoven layers is explained in more detail below.

In a more preferred embodiment, the first nonwoven layer 122 has a Tensile Strength Ratio (TSR) of at least about 15, more preferably at least about 60. The TSR is defined by the following calculation: TSR = TS1 / TS2 (1) wherein,

TS1 (gf/inch): a tensile strength (TS) at the breaking point in the primary fiber direction; and

TS2 (gf/inch): a tensile strength (TS) at the breaking point in the perpendicular direction which is perpendicular to the primary fiber direction.

Tensile Strength (ST) is measured as the maximum tensile strength value recorded while the first nonwoven layer 122 is stretched at a rate of about 20 inches/min (about 50 cm/min) to its breaking point. The tensile strength of the first nonwoven layer 122 is measured before the first nonwoven layer 122 is joined to the elastomeric layer 124.

In a preferred embodiment, the first nonwoven layer 122 has a tensile strength of less than about 200 gf/inch (about 80 gf/cm) at 30% elongation to the direction which is perpendicular to the primary fiber direction; more preferably less than about 100 gf/inch (about 40 gf/cm), more preferably still less than about 50 gf/inch (about 20 gf/cm).

Preferred nonwoven fabrics which are suitably applicable to the first nonwoven layer 122 are available from Nippon Petrochemicals Co., Ltd., Tokyo, Japan, under Code Nos. MBE7711-2; MBE6515-10; and MBE7922-1 which have the following properties. Table

C. Elastomeric Material

The elastomeric layer 124 may be formed in a wide variety of sizes, forms and shapes. In a preferred embodiment, the elastomeric layer 124 is in the form of a continuous plane layer such as shown in, for example, Fig. 1. Preferred forms of a continuous plane layer include a scrim, a perforated (or apertures formed) film, an elastomeric woven or nonwoven, and the like. Preferably, the elastomeric layer 124 has a thickness of from about 0.05 mm to about 1 mm (about 0.002 inch - about 0.039 inch). The continuous plane layer may take any shape which can be suitably provided in products. Preferred shapes of a continuous plane layer include a quadrilateral including a rectangle and a square, a trapezoid, and the other polygons. In an alternative embodiment, the elastomeric layer 124 is in the form of discrete strands (or strings) which are not connected each other. Preferred elastomeric materials of the present invention include diblock and triblock copolymers based on polystyrene and unsaturated or fully hydrogenerated rubber bolcks, and their blends with other polymers such as polyolefin polymers.

Preferably, the polystyrene thermoplastic elastomer is selected from the group consisting of a styrene-butadiene-styrene thermoplastic elastomer, a styrene-isopren-styrene thermoplastic elastomer, a styrene-ethylene/butylene- styrene thermoplastic elastomer, a styrene-ethylene/propylene-styrene thermoplastic elastomer, a styrene-ethylene/propylene thermoplastic elastomer, a hydrogenated styrene butadiene rubber, and a mixture thereof. A preferred styrenic block copolymer based material contains from about 1 wt% to about 70 wt% of polystyrene, more preferably from about 10 wt% to about 50 wt% of polystyrene.

In an alternative preferred embodiment, the elastomeric material 124 is a porous, macroscopically-expanded, three-dimensional elastomeric web 172 as shown in Fig. 3. The web 172 has a continuous first surface 174 and a discontinuous second surface 176 opposing to the first surface 174. The elastomeric web 172 preferably comprises a formed film interconnecting member 186 including at least two polymeric layers 178 and 182. The first layer 178 is substantially elastic and the second layer 182 is substantially less elastic than the first layer 178. At least one of the two polymeric layers 178 and 182 is formed from a polystyrene thermoplastic elastomer. The elastomeric web 172 exhibits a multiplicity of primary apertures 184 in the first surface 174 of the web 172. The primary apertures 184 are defined in the plane of the first surface 174 by a continuous network of the interconnecting member 186. The interconnecting member 186 exhibits an upwardly concave-shaped cross-section along its length. The interconnecting member 186 also forms secondary apertures 188 in the plane of the second surface 176 of the web 172. The apertures 184 and 188 may take any shape. A preferred elastomeric web is disclosed in U.S. Patent application serial number 08/816,106, filed on March 14, 1997. A preferred porous elastomeric material for the elastomeric layer 124 is available from Tredegar Film Products under the designation X-25007.

In one preferred embodiment, the elastomeric layer 124 is in the form of a scrim 130 as shown in Fig. 1. The elastomeric scrim 130 comprises a plurality of first strands 125 which intersect or cross (with or without bonding to) a plurality of second strands 127 at nodes 128 at a predetermined angle α, thereby forming a net-like open structure having a plurality of apertures 132. Each aperture 132 is defined by at least two adjacent first strands 125 and at least two adjacent second strands 127 such that apertures 132 are substantially rectangular (preferably square) in shape. Other aperture configurations, such as parallelograms or circular arc segments, can also be provided. Such configurations could be useful for providing non-linear elastic structural directions. Preferably, the first strands 125 are substantially straight and substantially parallel to one another; and, more preferably, the second strands 127 are also substantially straight and substantially parallel to one another. More preferably, first strands 125 intersect second strands 127 at nodes 128 at a predetermined angle α of about 90 degrees. Each node 128 is an overlaid node, wherein first strands 125 and second strands 127 are preferably joined or bonded (although it is contemplated that joining or bonding may not be required) at the point of intersection with the strands still individually distinguishable at the nodes 128. However, it is believed that other node configurations such as merged or a combination of merged and overlaid would be equally suitable.

Although it is preferred that first and second strands 125 and 127 be substantially straight, parallel, and intersect at an angle α of about 90 degrees, it is noted that first and second strands 125 and 127 can intersect at other angles α, and that first strands 125 and/or second strands 127 can be aligned in circular, elliptical or otherwise nonlinear patterns relative to one another. Although for ease of manufacture it is contemplated that first strands 125 and second strands 127 have a substantially circular cross-sectional shape prior to incorporation into elastic laminate 70 (as shown in Fig. 1), the first and second strands 125 and 127 can also have other cross-sectional shapes such as elliptical, square, triangular or combinations thereof.

Preferably, the material for the first strands 125 is chosen so that the first strands 125 can maintain the second strands 127 in relative alignment prior to forming elastic laminate 70. It is also desirable that the materials for the first and second strands 125 and 127 are capable of being deformed (or initially formed) into predetermined shapes upon application of a predetermined pressure or a pressure in combination with a heat flux prior to forming elastic laminate 70. These deformed shapes (e.g., elliptical second strands, substantially flat first strands and the like) can provide an elastic laminate 70 which can be comfortably worn about the body without irritation or other discomfort.

In a preferred embodiment, the first and second strands 125 and 127 are formed from an identical elastomeric material. For example, the first and second strands 125 and 127 are formed from an identical polystyrene thermoplastic elastomer which is selected from the group consisting of a styrene-butadiene- styrene thermoplastic elastomer, a styrene-isopren-styrene thermoplastic elastomer, a styrene-ethylene/butylene-styrene thermoplastic elastomer, a styrene- ethylene/propylene-styrene thermoplastic elastomer, a styrene-ethylene/propylene thermoplastic elastomer, a hydrogenated styrene butadiene rubber or an unsaturated styrene butadiene rubber, and a mixture thereof. A preferred elastomeric scrim 124 which containes a styrene-butadiene-styrene thermoplastic elastomer is manufactured by the Conwed Plastics Company (Minneapolis, Minn., U.S.A.) under the designation XO2514. This material has about 12 elastic strands per inch (about 5 strands/cm) in the structural direction B (i.e., the first strands 125) and about 7 elastic strands per inch (about 3 strands/cm) in the structural direction D (i.e., the second strands 127) before lamination.

Alternatively, the first and second strands 125 and 127 are formed from two different material. For example, one of the first and second strands 125 and 127 is formed from one of the above described polystyrene thermoplastic elastomer, while the other of the first and second strands 125 and 127 is formed from material(s) other than the above described polystyrene thermoplastic elastomer. Such other material(s) may be either elastic or non-elastic, and selected from suitable materials known in the art.

P. Joining Nonwoven to Elastomeric Material

The first nonwoven layer 122 of the present invention is bonded to the first surface 150 of the elastomeric layer 124 by forming a heat/pressure bond between the first nonwoven layer 122 and the elastomeric layer 124. Herein, "heat/pressure bond" is either a physical or chemical bond formed by an application of appropriate heat and pressure to two different members so that the two members can have a portion which has an increased peel strength by the formation of the bond. Herein, "peel strength" refers to the amount of force required to separate the two members from each other. Higher peel strengths typically equate to less chance of de- lamination of the elastic laminates in use of products. To form such heat/pressure bond(s) between the first nonwoven layer 122 and the elastomeric layer 124, any pressure can be applied to the first nonwoven layer 122 and the elastomeric layer 124 at a certain temperature as long as it does not substantially damage the physical and/or chemical properties of the resulting elastic laminate. Fig. 2 is a partial perspective view of an elastic laminate 70 of yet another embodiment, wherein a portion of the first nonwoven layer 122 has been removed to show the heat/pressure bond structure. In Fig. 2, the elastomeric scrim 130 which is formed by the first and second strands 125 and 127 is used as an example for the elastomeric layer 124. Referring to Fig. 2, the first nonwoven layer 122 is bonded to the first surface 150 of the elastomeric layer 124 by forming a heat/pressure bond between the first nonwoven layer 122 and the elastomeric layer 124. In a preferred embodiment, the elastic laminate further includes a second nonwoven layer (not shown in Fig. 2) which is bonded to the second surface 152 of the elastomeric layer 124 by forming another heat/pressure bond therebetween.

The heat/pressure bond is formed by softening only the material of the elastomeric layer 124 (i.e., without melting the component fibers of the first nonwoven layer 122). This heat/pressure bond is preferably formed by application of a bonding temperature which is lower than the melting point of the material of the first nonwoven layer 122. This generally results in a decrease in the viscosity of the material which may or may not involve a "melting" of the material. As a result, the component materials of the elastomeric layer 124 are softened to form the heat/pressure bond. In a more preferred embodiment wherein the elastomeric layer 124 is formed from a polystyrene thermoplastic elastomer including a polystyrene segment, a bonding temperature which is higher than the glass transition temperature of the polystyrene segment is applied for forming the heat/pressure bond.

Fig. 4 shows one preferred example of a lamination device for forming the elastic laminate 70 shown in Fig. 2. Referring to Fig. 4, the lamination device 800 includes a first pressure plate 801 having a first surface 803, and a second plate 802 having a second surface 804. The second pressure plate 802 is fixed, while the first pressure plate 801 is movable to apply a pressure P to the first nonwoven layer 122 and the elastomeric layer 124 in cooperation with the second pressure plate 802. Preferably, the first and second surfaces 803 and 804 are substantially plane and are substantially parallel each other. The first nonwoven layer 122 is juxtaposed with the elastomeric layer 124 such that the first nonwoven layer 122 is immediately adjacent the elastomeric layer 124. The juxtaposed two layers 122 and 124 are manually supplied to the lamination device 800. A preferred lamination device 800 is available from Toyo Tester Industry Co., Ltd., Osaka, Japan, under a trade name "Heat Sealer".

In the lamination process, the first surface 803 is heated to a temperature T1 , while the second surface 804 is heated to a temperature T2. Preferably, the temperature T1 is from about 80°C to about 160°C, more preferably from about 100°C to about 130°C. The temperature T2 is preferably from about 30°C to about 60°C, more preferably from about 45°C to about 55°C. The pressure P is preferably from about 6 kg/cm to about 15 kg/cm , more preferably from about 9 kg/crrr to about 11 kg/cm . The time period of the application of the pressure P is preferably from about 1 second to about 20 seconds, more preferably from about 5 seconds to about 15 seconds. Preferably, the application of pressure P can be performed two (or more) times to increase the peel strength of the resulting laminate 70. By the application of the temperatures T1 and T2 at the pressure P, the elastomeric layer 124 is bonded to the first nonwoven layer 122 through a heat/pressure bond which is formed by softening the material of the elastomeric layer 124 (e.g., the polystyrene thermoplastic elastomer). The elastic laminate 70 of the present invention can be incorporated into a variety of products wherein it is desired to provide an elastic stretchability in at least one structural direction either partially or entirely. Examples of such products include disposable products, including sweat bands, bandages, body wraps, and disposable garments including disposable diapers and incontinence products.

E. Test Methods

1. Test Method for Fiber Orientation

The following method is preferably used to determine the Fiber Orientation Ratio (FOR) of nonwoven material.

A sample nonwoven fabric (or layer) is placed on a specimen stub. The sample nonwoven fabric is fixed on the specimen stub at a flat condition so that the primary fiber direction (to be defined hereinafter) of the sample nonwoven fabric can be roughly aligned with the longitudinal direction of the photograph to be taken. A scanning electron microscope (SEM) is used to take a photograph at 50X magnification. A preferred SEM is available from Japan Electron Optics Laboratory (JEOL) Ltd., Tokyo, Japan, under Code No. JSM-5310

The following analysis is conducted on the photograph by using a digitizer. A preferred digitizer is available from Graphtec Co., Ltd., Tokyo, Japan, under Code No. KD9600. A photograph is placed on the digitizer. A square area (500 μm x 500 μm) is chosen at will in the photograph on the digitizer. The both ends of every component fiber which can be seen in the square area are manually identified by an operator and the coordinates thereof are detected and recorded by the digitizer. This work is conducted on three different square areas (each having 500 μm x 500 μm) which are chosen at will in the photograph to obtain coordinate data on the all fibers in the three different square areas. The orientation angle of each fiber is calculated based on the coordinate data. The primary fiber direction of the sample nonwoven fabric is determined by the average orientation angle, which is an average value of the ail orientation angle data obtained from the three different square areas. The Fiber Orientation Ratio within about ±10 degrees (FOR10) is determined by the following calculation:

FOR10 = NF10 / TNF x 100 (2) wherein, NF10: the number of fibers which have orientation angles within about ±10 degrees from the primary fiber direction; and TNF: the total number of fibers measured within the three different square areas.

Similarly, the Fiber Orientation Ratio within about ±20 degrees (FOR20) is determined by the following calculation:

FOR20 = NF20 / TNF x 100 (3) wherein,

NF20: the number of fibers which have orientation angles within about ±20 degrees from the primary fiber direction.

2. Test Method for Tensile Strength

The following method is preferably used to measure the tensile strength of materials.

A tensile tester is prepared. The tensile tester has an upper jaw and a lower jaw which is located below the upper jaw. The upper jaw is movable and is connected to an extension force measuring means. The lower jaw is fixed in the tester. A test specimen (i.e., a nonwoven fabric to be measured) which has about

2.5 cm (about 1 inch) in width and about 10.2 cm (about 4 inches) in length is prepared and clamped with the upper jaw and the lower jaw so that the effective specimen length (L) (i.e., gauge length) is about 5.1 cm (about 2 inch). An extension force is continuously applied to the test specimen through the upper jaw at a cross-head speed of about 50 cm (about 20 inches) per minute, until the test specimen is physically broken. The applied extension force is recorded by a recorder (e.g., a computer system). The tensile strength at the breaking point is determined at the maximum tensile strength value. A tensile tester suitable for use is available from Instron Corporation (100 Royall Street, Canton, MA02021 , U.S.A.) as Code No. Instron 5564.

It is understood that the examples and embodiments described herein are for illustrative purpose only and that various modifications or changes will be suggested to one skilled in the art without departing from the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. An elastic laminate elastically extensible in at least one direction, comprising: an elastomeric material having a first surface and a second surface opposing the first surface, the elastomeric material including a polystyrene thermoplastic elastomer; and a first nonwoven layer including component fibers which include a polyester; wherein the elastomeric material is bonded to the first nonwoven layer through a continuous heat/pressure bond which is formed by application of a bonding temperature which is lower than the melting point of the polyester.

2. The elastic laminate according to Claim 1 , wherein the polystyrene thermoplastic elastomer includes a polystyrene segment, and wherein the bonding temperature is higher than the glass transition temperature of the polystyrene segment.

3. The elastic laminate according to Claim 1 , wherein the polystyrene thermoplastic elastomer is a styrene-butadiene-styrene thermoplastic elastomer, a styrene-isopren-styrene thermoplastic elastomer, a styrene-ethylene/butylene- styrene thermoplastic elastomer, a styrene-ethylene/propylene-styrene thermoplastic elastomer, a styrene-ethylene/propylene thermoplastic elastomer, a hydrogenated styrene butadiene rubber or an unsaturated styrene butadiene rubber, or a mixtures thereof.

4. The elastic laminate according to Claim 1 , wherein the polyester is a polyethylene terephthalate, a polybutylene terephthalate, a polypropylene terephthalate or one of their relatives, or a mixtures thereof.

5. The elastic laminate according to Claim 4, wherein the polyester has an average molecular weight of from about 5,000 to about 60,000.

6. The elastic laminate according to Claim 1 , wherein the elastomeric material is in the form of a continuous plane layer or a strand.

7. The elastic laminate according to Claim 1 , wherein the elastomeric material contains from about 1 wt% to about 70 wt% of polystyrene.

8. A method for forming an elastic laminate, comprising the steps of: a) providing an elastomeric material made from a polystyrene thermoplastic elastomer, the elastomeric material having a first surface and a second surface opposing the first surface; b) providing a first nonwoven layer having a first surface and a second surface opposing the first surface, the first nonwoven layer including component fibers which are made from a polyester; c) placing the first surface of the elastomeric material against the first surface of the first nonwoven layer; and d) forming a continuous heat/pressure bond between the elastomeric material and the first nonwoven layer, by an application of a bonding temperature which is lower than the melting point of the polyester.