Method of forming thin, embossed, textured barrier films

Details Method of forming thin, embossed, textured barrier films Method of forming thin, embossed, textured barrier films

1998-12-04

2001-07-24

Silbaugh, Jan H. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Reshaping running or indefinite-length work

C264S293000, C425S505000, C425S365000, C425S385000, C156S199000, C156S209000

Reexamination Certificate

active

06264872

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to barrier films. More particularly the present invention relates to embossed barrier films and methods of making the same.
BACKGROUND OF THE INVENTION
Films have been utilized in a variety of articles as a means of providing a barrier to the passage of physical matter. As an example films have been utilized as a barrier layer in rain wear, diapers and incontinence garments, feminine hygiene products, protective apparel and other articles. Barrier films are typically employed within such articles to prevent the passage of physical matter such as, for example, water, bodily exudates, blood, toxic materials, pathogens, etc. Due to the nature of such articles the usefulness and reliability of the same is related to the articles ability to provide the desired barrier properties. Thus, it follows that loss of the barrier properties through film defects, e.g. pin holes or tears, often destroys the usefulness of the entire article. Providing reliable barrier properties is of even greater importance in infection control products and protective apparel since these articles seek to prevent potentially dangerous matter such as blood borne pathogens or toxic agents from coming in to direct physical contact with the wearer.
However, in addition to providing the desired barrier function, since these articles are often worn or handled it is also desirable that the article have a pleasing touch or “hand.” Desirably the film has a drape and feel similar to that of cloth or other apparel fabrics. Providing a film capable of exhibiting excellent barrier properties while likewise having good drape and hand has proven difficult. Thus, there exists a need for economically produced films having improved visual and/or tactile properties which also exhibit and retain excellent barrier properties.
In the past film and/or film laminates have been processed with heated patterned rolls in order to create embossed patterns therein. As an example, U.S. Pat. No. 3,857,144 to Bustin recognizes the difficulty in embossing thin films to create a “hole-free” film and teaches use of matching patterned rolls driven at the same circumferential speed to emboss polyethylene films having a thickness less than 0.025 mm. Alternatively, heated patterned rolls have been extensively used to aperture films or other materials. For example, U.S. Pat. No. 4,280,978 to Dannheim et al. teaches embossing and aperturing a film using a series of patterned rolls. Additionally, U.S. Pat. No. 5,620,779 to Levy et al. teaches the use of one or more heated patterned calendar rolls to create fused bonded areas which rupture, i.e. form apertures, upon stretching of the fabric. As a further example, U.S. Pat. No. 5,370,764 to Alikhan teaches pattern bonding a film
onwoven laminate using two patterned bonding rolls rotating at different circumferential speeds in order to enhance formation of apertures within the film. However, despite the foregoing, it has been found that use of counter-rotating bonding rolls rotating at different circumferential speeds can be utilized to achieve a film having an improved texture or hand without forming apertures or overly weakened areas of the film, that is to say without destroying the barrier properties of the film.
SUMMARY OF THE INVENTION
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by the process of the present invention of forming an embossed, textured barrier film comprising (a) providing a thermoplastic polymer film having a hydrohead of at least 30 mbar; (b) causing the thermoplastic film to travel through the nip of a counter-rotating bonding roll assembly formed by first and second rolls rotating at different circumferential speeds wherein the resulting film has a pattern imparted therein, a textured surface and a hydrohead of at least 30 mbar. Desirably the first and second rolls have a speed differential between about 5% and about 200%. In a further aspect, the film can be heated either prior to entering the nip or while within the nip. As an example, one or both of the nip rolls can be heated. In still a further aspect of the invention, the first or patterned roll rotates at a greater circumferential speed than the second roll. Alternatively, the second roll is a smooth roll which rotates at a greater circumferential speed than that of the first roll. In this regard, running the patterned roll faster creates a film having an embossed film with a ridge and valley type structure whereas running the smooth roll faster creates an embossed film having a creped or undulated type structure. Selection of the film temperature, speed differential and nip pressure can be made to create a more highly embossed and/or textured film.
Definitions
As used herein the term “comprising” is inclusive or open ended and does not exclude additional unrecited elements, compositional components, or method steps.
As used herein the term “nonwoven” fabric or web means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted or woven fabric. Nonwoven fabrics or webs have been formed by many processes such as for example, meltblowing processes, spunbonding processes, hydroentangling, air-laid and bonded carded web processes.
As used herein the term “spunbond fibers” refers to small diameter fibers of molecularly oriented polymeric material. Spunbond fibers may be formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,502,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,542,615 to Dobo et al, U.S. Pat. No. 5,382,400 to Pike et al.
As used herein the term “meltblown fibers” means fibers of polymeric material which are generally formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter. Thereafter, the meltblown fibers can be carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,549,241 to Butin et al. Meltblown fibers are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.
As used herein “multilayer nonwoven laminate” means a laminate of two or more nonwoven layers such as, for example, wherein some of the layers are spunbond and some meltblown such as a spunbond/meltblown/spunbond (SMS) laminate. Examples of multilayer nonwoven laminates are disclosed in U.S. Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 5,178,931 to Perkins et al. and U.S. Pat. No. 5,188,885 to Timmons et al. Such a laminate may be made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer and then bonding the laminate such as by point bonding as described below. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step.
As used herein, the term “machine direction” or MD means the length of a fabric in the direction in which it is produced. The term “cross machine direction” or CD means the width of fabric, i.e. a direction generally perpendicular to the MD.
As used herein the term “polymer” generally includes but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limit

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