Method of making non-woven composite transfer layer

Details Method of making non-woven composite transfer layer Method of making non-woven composite transfer layer

1999-12-07

2002-12-10

Maki, Steven D. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S181000, C156S183000

Reexamination Certificate

active

06491777

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to methods for making non-woven fabrics, and the fabrics produced thereby. More particularly, the present invention relates to methods of making composite non-woven webs useful as fluid transfer layers in absorbent articles, as well as the nonwoven webs produced thereby.
BACKGROUND OF THE INVENTION
Non-woven fabrics, because of their structure and low cost of production, have proven particularly useful as absorbent articles. By way of example, many diapers, adult incontinence products, and sanitary napkins are comprised of non-woven fabrics.
Within non-woven absorbent articles, it is known to provide an outer top sheet, an intermediate fluid transfer layer, and an absorbent inner core. The purpose of the fluid transfer layer, otherwise known as a surge layer, is to accommodate a surge of fluid and allow the absorbent core more time to absorb the surge. This prevents liquid overflow or other leaking from the product. An additional purpose of the surge layer is to isolate the top sheet from the absorbent core to minimize re-wetting of the top sheet from the absorbent core side (prevent “rewet”).
Many proposals have been made for fluid surge layers. Generally, the use of bulky, high void volume fabrics that are resistant to wet compression has been proposed. The high bulk enhances the resistance to rewet, while the resistance to wet compression improving performance and allowing the layer to retain its properties after an initial wetting.
The non-woven surge layer fabrics proposed to date are disadvantageous in that they offer limited performance, and require relatively expensive and difficult manufacturing processes. There is therefore an unresolved need for an improved surge layer fabric as well as a method for making the same.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a method for making a non-woven composite fabric useful as a fluid transfer layer.
It is a further object of the invention to provide a composite non-woven fabric useful as a fluid transfer layer.
It is a further object of the invention to provide a method for making an absorbent article having a composite non-woven fabric surge layer, as well as the article thereby made.
SUMMARY OF THE INVENTION
The present invention generally comprises a method for making a non-woven fluid transfer fabric, as well as the fabric produced thereby. The present invention further comprises an absorbent article having a composite non-woven fabric surge layer, as well as a method for making the article.
The method of the present invention generally comprises the steps of depositing a first spunbond web layer on a support, depositing a second spunbond web layer on the first web, with one of the web layers having a melting point higher than that of the other. The two layers are then thermally bonded to one another. During bonding, the difference in melting points causes a different amount of shrinkage to occur in the layers. This results in a “micro-bulking” of the bonded layers, as the lower melting point layer gathers a bit on the higher melting point layer due to a greater degree of shrinkage in the lower melting point layer. It is noted that as used herein the term “micro-bulked” is intended to refer to a condition whereby a slightly textured, bulked, crimped, or corrugated profile is present but is not apparent to the naked eye.
Thermal bonding of the two layers is followed by a mechanical bulking of the two layers to “macro-bulk” the composite fabric. It is noted that as used herein the term “macro-bulked” is intended to refer to a condition whereby a corrugated, crimped, or creped profile is apparent to the naked eye. Mechanical bulking can be achieved by a number of methods as are generally known in the art. A preferred method of bulking is a process known generally as the MICREX process. In this process, the composite web is passed between a roller and a blade, and combed into a creping chamber. Mechanical bulking occurs in the creping chamber as corrugation of the web occurs. The MICREX process is described in detail in U.S. Pat. No. 4,921,64; herein incorporated by reference.
Preferably, the first web layer is the lower melting point layer, with the second layer having a higher melting point. Preferably, the first web layer comprises spunbond poly(ethylene terephalate) (“PET”) fibers having a denier 4-10, and has a basis weight of between about 10-30 gm/m
2
. Most preferably, the first layer is comprised of PET fibers of about 6 denier, and has a basis weight between about 10-20 gm/m
2
.
A preferred second layer is comprised of spunbond PET of 10-15 denier, and has a basis weight of between about 10-45 gm/m
2
. Most preferably the second layer is comprised of fibers of about 12-15 denier, and has a basis weight between about 15-30 gm/m
2
.
The resulting fabric of the invention is of high bulk, and has substantial resistance to compression deformation and pore structure collapse. The method of the invention is more economical than prior art methods that may require bi-component or carded webs.
The fabric of the invention generally comprises the fabric produced by the method of the invention. It comprises a composite non-woven web having a first spunbond layer, a second spunbond layer thermally bonded to the first layer, with the two layers having different melting points. The difference in melting points causes differential shrinkage of the layers through thermal bonding, with the fabric having a resultant micro-bulked profile. Preferably, the fabric also has a macro-bulked profile attained through mechanical corrugation.
Preferably, the first layer comprises spunbond PET fibers having a denier 4-10, and has a basis weight of between about 10-30 gm/m
2
. Most preferably, the first layer is comprised of PET fibers of about 6, and has a basis weight between about 10-20 gm/m
2
. The preferred second layer is comprised of spunbond PET of 10-15 denier, and has a basis weight of between about 10-45 gm/m
2
. Most preferably the second layer is comprised of fibers of about 12-15 denier, and has a basis weight between about 15-30 gm/m
2
.
An additional embodiment of the invention comprise an absorbent article having the composite fluid transfer fabric of the invention overlying an absorbent core. The absorbent article generally comprises a cover sheet, a surge layer comprising the composite fluid transfer fabric layer of the invention as described above, and an absorbent core. The preferred absorbent core comprises super absorbent polymer (“SAP”).
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description that follows may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the several embodiments of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.


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