Patent Application
20120128927
1. Field of the Invention
The present invention relates to an air permeable elastic laminate, and a method for fabricating an elastic laminate having air permeability.
2. The Prior Arts
In the disposable product market sectors, the needs for better-fitting and more comfortable disposable hygiene products, such as disposable diapers, and infant learning pants, have increased. As such, a laminate having high elasticity, high elastic recovery rate and high air permeability can satisfy these needs. Generally, the elastic laminate is also expected to be elastically stretchable in dual directions. Disposable personal care products and health care products usually have enough air permeability and strength to be used for general purposes. The air permeability refers to the rate of passage of air or water vapor through fabric. The strength is relative to the tensile strength. In theory, the above-mentioned properties of the polymer films of the laminate can be individually enhanced, but it is hard to maintain the strength of the laminate and increase the air permeability of the polymer films at the same time. For example, when one polymer film has a better air permeability compared to other polymer films, the tensile property of the one polymer film can be expected to be weak. On the other hand, when a polymer film has a better tensile property, the air permeability thereof becomes lower. As a result, there is always a need for fabricating personal care products or health care products using the elastic laminates having good air permeability and strength.
In the past, a method for endowing the nonwoven fabric laminate with high tensile property would often damage the structure of the laminate, and thereby the strength of the laminate is lowered, especially the tensile strength. Moreover, the laminates fabricated by conventional methods do not have sufficient elastic recovery rate, and thereby they can not be effectively used in the desired application.
Before combining an elastic film or a nonwoven fabric to form a laminate, hole-punching to the elastic film or the nonwoven fabric is a commonly used technique for providing air permeability to the laminate. However, the through holes may cause the whole strength of the laminate to decrease so that the laminate cannot meet the use demand.
Moreover, in the conventional hole-punching method, after the hole punching process is carried out, the residual materials may be left at edges of the holes of the elastic film or the nonwoven fabric, and thereby the additional cleaning or trimming process is required after the hole-punching process. Furthermore, the numbers of punched holes can not be precisely controlled, and also the processing efficiency for punching holes is low.
Furthermore, the hole-punching process can be carried out after combining an elastic film or a nonwoven fabric to form a laminate in order to endow the laminate with air permeability. However, the tear points may appear on the laminate after hole-punching process, which results in poor tensile strength.
Accordingly, there is a need for developing a laminate having high elasticity and a method for fabricating the laminate having high elasticity and elastic recovery rate in order to meet the needs of disposable product market. Moreover, the tear points existing in the laminate fabricated by the conventional method have to be reduced. Furthermore, the complicated processes for fabricating the laminate should be simplified while the desired properties (high air permeability and high tensile strength) are kept.
Accordingly, the present invention provides an elastic laminate including at least two different elasticity coefficients of materials. When fabricated, the elastic laminates of the present invention are strong enough, and have sufficient tensile strength and air permeability to meet different application needs.
One feature of the air-permeable elastic laminate of the present invention comprises at least one elastic nonwoven fabric and an elastic film including elastic polymer combined together. The elastic nonwoven fabric can use the elastic nonwoven fabric disclosed in U.S. Pat. No. 6,746,978. According to the present invention, the laminate can have single-direction elasticity (e.g. horizontal direction), or bi-direction elasticity (e.g. horizontal and vertical directions) due to the properties of the elastic nonwoven fabric. The laminates, which are just stacked together, can have good elasticity and good elastic recovery properties without further processing treatments. Comparing with a quasi elastic laminate fabricated by the conventional methods using the non-elastic material which was stretched out or hole-punched, the elastic laminate of the present invention has better elastic performance and the fabricating method thereof can be simplified.
Another feature of the present invention is that the elastic laminate can be formed with a plurality of layers of elastic nonwoven fabrics, and the elastic laminate of the present invention can have single-direction or bi-direction elasticity according to the properties of the elastic nonwoven fabrics.
One solution provided by the present invention is to apply a local hot pressing to the laminate just formed so as to form a plurality of hardened parts on the laminate. Then, a stretch stress is applied to the elastic laminate, such that the hardened parts formed on the elastic laminate are broken due to the brittleness of the press-hardened parts generated by locally hot-melting and cooling. The elastic laminate is elastically recovered after the stretch stress is released. The air permeability is generated by breaking the hardened parts, and because the unbroken parts of the laminate still have good elasticity, the high tensile strength of the laminate is kept.
Another solution provided by the present invention is to place an elastic laminate on a surface of a jig having a plurality of concave holes. Audio wave energy is utilized to pass through the elastic laminate, such that the material's molecular structures of the elastic laminate at the locations corresponding to the concave holes on the surface of the jig are changed with the change of electronic energy levels, so that the hardened parts of the laminate are formed on the locations where the concave holes are disposed. Then the elastic laminate is applied with a stretch stress for breaking the hardened parts. The elastic laminate is elastically recovered after the stretch stress is released.
The combination of the elastic nonwoven fabric and the elastic film containing elastic polymer for forming the elastic laminate of the present invention can be achieved by attaching them via ultrasonic wave, hot pressing, electrically discharging, electronic beam, or static electricity.
The shape of the hardened parts formed on the elastic laminate can be in the points, lines, or any other geometric shapes, or the combination thereof.
The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which:
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
As shown in
The elastic nonwoven fabric 1A is made of short chemical fibers or/and long chemical fibers. The elastic nonwoven fabric naturally has properties of extensibility and high elastic recovery property. The fibers of nonwoven fabric can be single polymer, bicomponent, or blended fibers.
The elastic film 1B can be made of several types of elastic polymers. But the fluids such as air or liquid cannot permeate into the material used. In this embodiment, an elastic polyurethane film having a thickness of 0.02 to 0.03 mm is used. In another embodiment, the elastic film 1B can be composed of a plurality of film. Other elastic materials can also be used for fabricating the elastic film, e.g. a single-layer elastic member or a foamed plastic layer, but the films have to be made of materials capable of preventing air or liquid from permeating.
The elastic film 1B can also be composed of the films of high elastic compounds, such as a block copolymer, which is composed of long sequences (“blocks”) of the same monomer unit (A), covalently bound to sequences of unlike type monomer unit (B). The blocks can be connected in a variety of ways; schematics of AB diblock and ABA triblock structures. Generally, these compounds exhibit excellent elastic recovery property. When being extruded as a single layer, the extension can exceed 100% while the elasticity and the elastic recovery property are still kept. In a specific embodiment, the elastic material includes high-performance elastic materials, e.g. styrene/isoprene/styrene, styrene/isoprene/butadiene or styrene/ethylene-butene/styrene (SIS, SIB or SEBS) or the elastic resin (Kraton™ manufactured by Kraton chemical Co.), which are all elastic block copolymers. The special configuration of the block copolymer provides the functionality to the main body.
Other useful elastic composition used for the elastic film 1B includes ethylene copolymer, e.g. ethylene vinyl acetate, ethylene/propene copolymer or ethylene/propene/diene terpolymer. The present invention can use a mixture of the above-mentioned copolymers or a mixture of the above-mentioned copolymers mixing with other modified elastic or non-elastic materials for fabricating the elastic film of the present invention.
In the present invention, a plurality of the brittle hardened parts 11 with relatively weak strength on the elastic laminate as compared with the unhardened parts on the elastic laminate can be formed by an ultrasonic equipment which can be used for economical and massive manufacturing process. As shown in
The preset invention can also utilize a hot pressing technique to perform a partial hot pressing treatment to the elastic laminate 1 so as to form a plurality of hardened parts on the elastic laminate 1. As shown in
After the elastic laminate 1 with a plurality of hardened parts 11 is formed, two opposite ends of the elastic laminate 1 are applied with stretch forces in opposite directions through a stretching equipment so as to generate a proper stretch stress. Because the elastic laminate 1 has elasticity, stretching deformations are generated on the elastic laminate 1 when subjected to the stretch stress, and the hardened parts 11 are damaged or broken due to fragileness and having different elasticity coefficients (referring to
For providing the air permeability to the elastic laminate 1, the area of the hardened parts 11 preferably occupies 5% to 35% of the total surface area of the elastic laminate 1.
When the water vapor permeation rate of the air permeable elastic laminate fabricated by the method of the present invention is measured, the laminate exhibits commercially acceptable air permeability. In the present invention, the parameters, which include the change of the weight of the elastic nonwoven fabric, the selection of polymers of the elastic film, the thickness of the elastic film, and the size, quantity and distribution of the hardened parts, can be adjusted according to the desired applications.
Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.
