METHOD FOR THE PRODUCTION OF AN ELASTIC LAMINATE AND LAMINATED ELASTIC PRODUCT

Abstract

A method for the production of an elastic laminate, with the following steps in a production line: coextrudeing a first web of elastic film with at least three layers, with at least two different polymer materials, to feed contemporaneously said coextruded first elastic film web and two second nonwoven webs to a thermal, binding calender, wherein the first elastic film web is arranged between said two second nonwoven webs when entering the calender; wherein said first elastic film web, during the movement from the coextrusion step to the thermal binding step, passes from a melted state, to a solidified and cold state when entering the calender, to join, through spot welding in said calender, said second nonwoven webs with respective opposite outer layers of said first elastic film web, thus producing an intermediate web, to stretch mechanically said intermediate web according to a direction transverse to the same web.

Claims

1. An elastic laminate comprising: a polymer intermediate elastic film formed by three coextruded layers, wherein outer layers of said three coextruded layers are made of the same polymer material, and an inner layer of said three coextruded layers is made of a different polymer material from polymer material of said outer layers; two nonwoven fabrics joined, through spot or areas welding, to two opposite faces of said polymer intermediate elastic film, wherein at least one of: a ratio between MD elongation at break at 10 N, and laminate thickness after stretching of said polymer intermediate elastic film is lower than one of 8 and 7.5; a ratio in (N/50 mm)/(mm), between CD tensile strength and laminate thickness after stretching is lower than one of 79 and 78; a ratio in g/m.sup.2/mm between laminate weight and thickness after stretching is lower than one of 105 and 100.

2. An elastic laminate according to claim 1, wherein one or more layers of said polymer intermediate elastic film are made of one or more of: elastomers comprising at least one of poly (ethylene-butene), poly (ethylene-hexene), poly (ethylene-octene), poly (ethylene-propylene), poly (styrene-butadiene-styrene), poly (styrene-isoprene-styrene), poly (styrene-ethylene-butylene-styrene), poly (ester-ether), poly (ether-amide), poly (ethylene-vinyl acetate), poly (ethylene-methyl acrylate), poly (ethylene-acrylic acid), poly (ethylene butyl acrylate), polyurethane, poly (ethylene-propylene-diene) and ethylene-propylene rubber; polymers made using polyolefins from single-site catalysts; polyolefin elastomers; and a combination of elastomers, polymers made using polyolefins from single-site catalysts and/or polyolefin elastomers.

3. An elastic laminate according to claim 1, wherein at least part of said materials forming said outer layers of said coextruded elastic film are thermally compatible with at least part of materials of said nonwoven webs with which said outer layers are in contact.

4. An elastic laminate according to claim 1, wherein at least one of said second nonwoven webs is extendible.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In the drawings:

[0052] FIG. 1 is a scheme of a plant for implementing the method according to the invention;

[0053] FIG. 2 is a schematic cross section of a laminated product according to the invention;

[0054] FIG. 3 is a table showing the thermal compatibility of materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] With reference to the previously mentioned figures, number 10 indicates, as a whole, a plant for implementing a production method allowing to produce an elastic laminate especially, but without limitation, suitable for hygienic and sanitary products etc., having high elasticity, high tensile strength and increased softness with respect to known products.

[0056] This plant comprises an extruder 11 suitable to coextrude a multi-layer elastic film made of polymer material F.

[0057] In this example, the extruder 11 allows the coextrusion of a three-layer film, with the outer layers F1 having the same thickness and being made for example with polyolefin elastomers, for instance Dow®Infuse™, ExxonMobile® Vistamaxx®, and the like, together with polyolefin polymers like poly (ethylenebutene), poly (ethylene-hexene), poly (ethylene-octene), poly (ethylenepropylene) and or polyolefin thermoplastic polymers thereof. The inner layer F2 is made, for example, of one or more of the following materials: block copolymers containing SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-30 styrene, SEBS (styrene-ethylene-butylene-styrene) and polyolefin elastomers like Dow®Infuse™, ExxonMobile® Vistamaxx®, and the like.

[0058] In this example, the inner layer is a combination of SEBS (styrene-ethylene-butylene-styrene) and the outer layers are based on one or more polyethylene polymers.

[0059] The film is substantially impermeable and not transpiring. The extruder may have a roller, not shown in the figures, for depositing the film as it exited the extruder mouth.

[0060] Downstream of the extruder 11, a cooling station R of the known type is provided, formed, for example, by two cooled rollers, between which the film from the extruder is fed.

[0061] The plant also comprises two areas 12 and 13, occupied by accumulations, for instance reels, of nonwoven webs T1 and T2, that in this example have equal dimensions and composition. In this example, the nonwoven webs have bicomponent fibers of the coaxial type. For example, the inner part of the inner coaxial fibers is made of polyethylene, whilst the outer part is made of polypropylene. These nonwovens are preferably spun bound.

[0062] The plant 10 furthermore comprises a calender 14 for joining, through spot welding, the web of film F produced by the extruder 11 with two nonwoven webs T1 and T2 coming from the reels 12 and 13. It should be noted that at least part of the materials forming the outer layers of the elastic film are thermally compatible with at least part of the materials forming the fibers of the nonwoven web they respectively face.

[0063] At least one nonwoven web (and preferably both the webs) has a thickness, before entering the calender, comprised between 0.1 mm and 0.6 mm, and more preferably between 0.15 mm and 0.5 mm. In this example, the thickness is equal to 0.199 mm. Each nonwoven web has a weight, before entering the calender, comprised between 10 g/m.sup.2 and 40 g/m.sup.2, and in this example the weight is approximately 20.37 g/m.sup.2.

[0064] The elastic film F has a thickness, before entering the calender 14, comprised for example between 0.04 mm and 0.14 mm, and in this example it is approximately 0.05 mm. The thickness of the inner layer F2 of the film F is comprised between 0.017 mm and 0.075 mm, and in this example it is approximately 0.045 mm. The ratio between the sum of the thicknesses of the two outer layers and the thickness of the inner layer of the coextruded elastic film entering the calender is comprised between 113 and 1/25 and more preferably between 117 and 1/21. In this example the ratio is 1/9.

[0065] The laminate is produced in line. Practically, the production line implemented with the plant 10 has three branches L1, L2, L3, that are respectively for the film web and the two nonwoven webs and join in the calender 14, and a fourth branch L4, exiting from the calender, where the webs F, T1 and T2 are joined together.

[0066] According to preferred embodiments, at least part of the materials forming the outer layers of the elastic film are thermally compatible with at least part of the materials forming the fibers of the nonwoven web they respectively face.

[0067] Thermal compatibility means the ability of two materials to remain joined together after heat-welding, or to remain joined together when they are thermally fused above each other and then cooled.

[0068] Along the line branch L4, downstream of the calender 14, a cooling station 15 is provided for the semi-finished laminated product P1 (formed by the three webs T1, F and T2 joined together through spot welding in the calender), for example of the type with known cooling rollers.

[0069] A cross stretching station 16 is provided downstream of the cooling station 15 for stretching the semi-finished laminated product P1 in CD. This cross stretching station 16 is, for example, of the type called “Ring Rolls.” The web exiting from the cross stretching station 16 substantially matches with the elastic laminated product P according to the invention. The elastic laminate may be cut into portions of the desired length, that are wound in reels and stored.

[0070] The elastic laminate therefore comprises the polymer intermediate elastic film F formed by the three coextruded layers F1, F2, wherein the outer layers F1 are made of the same polymer material and the inner layer F2 is made of a different polymer material, and by the two nonwovens T1 and T2 joined to the outer faces of the coextruded elastic film F through welding spots or areas Z.

[0071] The weight of the laminated product P at the end of processing is comprised between 60 and 140 g/m.sup.2, and in this example it is approximately 80.2 g/m.sup.2.

[0072] The thickness of the laminated product P at the end of processing is comprised between 0.5 and 0.15 mm, and in this example it is approximately 0.81 mm.

[0073] The ratio between MD elongation at break at 10 N, and laminate thickness after the stretching step is lower than 8, and preferably lower than 7.5. In this example, it is approximately equal to 6.70.

[0074] The ratio in (N/50 mm)/(mm) between CD tensile strength and thickness of the laminate P after the stretching step is lower than 79, and preferably lower than 78. In this example, it is approximately equal to 77.0. The ratio (in g/m.sup.2/mm) between weight and thickness of the laminate P after the stretching step is lower than 105, and more preferably lower than 100. In this example, it is approximately equal to 99. The welding spot or welding area density is comprised between 15 and 60 spots/cm.sup.2.

[0075] The elastic film F is coextruded by means of the extruder 11. At the end of the coextrusion step, the elastic film has a temperature comprised between 220° C. and 270° C. In this example, it is approximately equal to 250° C.

[0076] The film F is fed from the extruder 11 to the calender 14. The temperature of the coextruded elastic film entering the calender after having passed through the cooling station R is comprised between 10° C. and 40° C., more preferably between 15° C. and 35° C., and in this example it is approximately 20° C.

[0077] It has been found that, adequately, a given ratio between film temperature immediately after extrusion and before the calender allows to obtain high performances in terms of elasticity and strength. The coextruded elastic film F has conveniently a temperature, when entering the calender, equal to, or lower than, 1/7 of the temperature the elastic film has at the end of the coextrusion step; conveniently, this temperature is preferably lower than 1/10.

[0078] In order to contribute to the cooling, the first web of coextruded elastic film F may adequately travel, from the extrusion step to the entrance into the calender, an air path whose length is comprised between 5 m and 20 m, and more preferably comprised between 8 m and 13 m; in this example, it is approximately 11 m at average ambient temperature (i.e. the temperature of the place where the production line is arranged).

[0079] Also the nonwoven webs T1 and 2 are fed to the calender 11 together with the film F. The calender 11 has a flat roller 14A and a roller 14B provided with appendices or protuberances, whose vertexes form the welding spots or areas Z. The temperature of the rollers 14A and 14B of the calender is comprised between 120° C. and 160° C., and in this example it is approximately 140° C. 10 Preferably, the lamination pressure between the calender rollers is comprised between 70 kg/m.sup.2 and 160 kg/m.sup.2.

[0080] The pressure and the temperature of the calender allows the formation of spots or areas Z where the portions of webs T1 and T1, whose dimensions are similar to those of the protuberances of the roller 14B, are fused with at least 15 corresponding portions of the outer layers F1 of the coextruded elastic film F.

[0081] In this example, after having exited the calender, the semi-finished laminated web P1 passes through the cooling station. The web P1 is cooled up to a temperature comprised between 15° C. and 40° C., in this example up to approximately 35° C.

[0082] After having passed through the cooling station 15, the semi-finished laminated web P1 passes through the mechanical stretching station 16, where it is stretched in CD. The stretching values are comprised between 150% and 250%, in this example approximately 200%.

[0083] Once the laminated web P has been stretched, it can be cut into portions of the desired length, that can be wound and stored. In order to make the laminated product P functionally transpiring or permeable, it is possible to perform a punching step, preferably between the exit of the calender 11 and the entrance of the stretching station 16, and more preferably after the cooling station, if any. The punching may be, for example, a needle punching. In other examples, the punching may be performed after the stretching step. The webs T1, T2, P1, and P move substantially continuously during the production step.

[0084] It has been found that an important aspect of the present invention is the fact of extruding the elastic film directly in the laminate production line, laminating the extruded film together with the nonwovens. Namely, a comparison has been made (see the following table) between a laminated product directly coextruded in the line, as described above (case A, with the values mentioned above), and a laminated product made by using an elastic film produced in advance, for example one month before, fed for instance from a reel, together with the nonwovens in the calender (case B).

TABLE-US-00001 Case A-Laminate Case B-Laminate with film with previously coextruded in line produced film MD elongation at break at 10N (%) CD tensile strength 63.00 60.41 (  shape) Grammage (g/m.sup.2) 80.2 79.6 Thickness (mm) 0.81 0.76 mm Softness (qualitative greater test)  measurements according to EDANA WSP 110.4 indicates data missing or illegible when filed

[0085]

[0086] Practically, it has been found that producing the coextruded elastic film in line allows a decrease of approximately 13% in the elongation at break at 10 N (value of significance for the machinability of the material on the production lines for hygienic sanitary products), an increase of about 4% in CD tensile strength (value of significance during the assembly of diapers; they break less easy), an increase of about 7% in the thickness, and a qualitatively greater softness. It is understood that what illustrated above purely represents possible non-limiting embodiments of the invention, which may vary in forms and arrangements without departing from the scope of the concept on which the invention is based. Any reference numbers in the appended claims are provided for the sole purpose of facilitating the reading thereof in the light of the description before and the accompanying drawings and do not in any way limit the scope of protection of the present invention.