Process of forming a perforated web

Details Process of forming a perforated web Process of forming a perforated web

2003-04-23

2004-08-24

Eashoo, Mark (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

Perforation by differential fluid pressure; or smoothing,...

C264S154000, C264S284000, C264S293000

Reexamination Certificate

active

06780372

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a process of forming a soft and resilient web and a soft and resilient web formed by the process. More particularly, the present invention relates to a process utilizing a locally heating process to form a soft and resilient web exhibiting a substantially continuous pattern of debossments or apertures. The present invention also relates to a soft and resilient web exhibiting a substantially continuous pattern of debossments or apertures.
BACKGROUND
In processes disclosed in prior art for producing a web such as a formed film, a web of heat-softened film is provided on the patterned, perforated outer surface (referred to herein as a forming surface) of a structure such as an endless belt or a drum cylindrical surface. A vacuum beneath the forming surface pulls the heat-softened film into conformity with the forming surface. Alternatively, a positive pressure may be used to force the heat-softened film against the forming surface. Whether the web of film is simply embossed or is debossed and perforated will depend on the size of the holes in the forming surface, the softness and thickness of the film being formed, and the fluid pressure differential across the film.
Processes for producing webs of embossed thermoplastic film are disclosed in U.S. Pat. Nos. Re 23,910 issued to Smith & Smith on Dec. 12, 1954; U.S. Pat. No. 2,776,451 and 2,776,452 both issued to Chavannes on Jan. 8, 1957; and U.S. Pat. No. 2,905,969 issued to Gilbert & Prendergast on Sep. 29, 1959. Processes for the production of webs of debossed and perforated thermoplastic films are disclosed in U.S. Pat. No. 3,038,198 issued to Shaar on Jun. 12, 1962; U.S. Pat. No. 3,054,148 issued to Zimmerli on Sep. 18, 1962; U.S. Pat. No. 4,151,240 issued to Lucas & Van Coney on Apr. 24, 1979; U.S. Pat. No. 4,155,693 issued to Raley on May 22, 1979; U.S. Pat. No. 4,226,828 issued to Hall on Oct. 7, 1980; U.S. Pat. No. 4,259,286 issued to Lewis, Sorensen & Ballard on Mar. 31, 1981; U.S. Pat. No. 4,280,978 issued to Dannheim & McNaboe on Jul. 28, 1981; U.S. Pat. No. 4,317,792 issued to Raley & Adams on Mar. 2, 1982; U.S. Pat. No. 4,342,314 issued to Radel & Thompson on Aug. 3, 1982; and U.S. Pat. No. 4,395,215 issued to Bishop on Jul. 26, 1983. A process for the production of perforated seamless tubular film is disclosed in U.S. Pat No. 4,303,609 issued to Hureau, Hureu & Gaillard on Dec. 1, 1981.
The processes disclosed in the references cited above require that the thermoplastic film be heat-softened in order to achieve the desired embossing or debossing and perforation of the film. This can be achieved as disclosed in many of the above references by heating an existing web of film to a temperature above its melt temperature range such that it is in a molten state and will readily flow and attain a new configuration. Alternatively, the molten film may be achieved by feeding a web of film directly from a film extruder onto the forming surface. Such a process is disclosed in U.S. Pat. No. 3,685,930 issued to Davis & Elliot on Aug. 22, 1972, where a web of thermoplastic film is extruded directly onto the outer surface of an endless belt and a vacuum is pulled beneath the belt to make the molten web of film assume the configuration of the outer belt surface. Similarly, U.S. Pat. No. 3,709,647 issued to Barnhart on Jan. 9, 1973 discloses a web of molten thermoplastic film extruded directly onto the outer cylindrical surface of a vacuum forming drum.
It is known to shape molten thermoplastic sheet material by the use of a fluid pressure forcing the sheet against a mold; such processes are disclosed in U.S. Pat. No. 2,123,552 issued to Helwig on Jul. 12, 1938; and U.S. Pat. No. 3,084,389 issued to Doyle on Apr. 9, 1963.
When webs of embossed or debossed and perforated thermoplastic film are produced on a patterned surface by the above prior art processes, it is generally necessary to cool the film below its melting temperature range to set its three-dimensional structure prior to removing the web of formed film from the forming surface. This makes the web of formed film much less susceptible to distortion of its bulk conformation.
To make webs of formed film by these prior art processes, it is necessary to have the film within or above its melting temperature range in order to form the film. This limits the range of desired properties that can be engineered into the formed film since all previous thermo-mechanical history of the film is erased.
Other attempts to produce a web, such as a formed film, are to apply a liquid pressure to the web on the forming surface. The liquid pressure has sufficient force and mass flux to cause the web to be deformed toward the forming surface such that the material acquires a substantial three-dimensional conformation. The temperature of the web of material is controlled such that it remains below the transformation temperature range of the material throughout the process. Such process is disclosed in U.S. Pat. No. 4,695,422 issued to Curro et al. on Sep. 22, 1987.
In the process disclosed in the reference, the web is exposed to the liquid pressure, however, the temperature is below the transformation temperature range of the material which does not melt the material. When the material deforms by the liquid pressure, the material substantially ruptures and the some “spring-back” of the material generally occurs after it passes the zone of liquid pressure. This “spring-back” of the material causes dimensionally unstable, three-dimensional apertures on the web which results in poor resiliency of the web.
Therefore, it is an objective of the present invention to provide a process of forming a soft and resilient web utilizing a locally heating process to form a substantially continuous pattern of debossments or apertures on the web.
It is a further objective of the present invention to provide a soft and resilient web formed by the process utilizing a locally heating process to form a substantially continuous pattern of debossments or apertures on the web.
SUMMARY
The present invention provides a process of forming a soft and resilient web exhibiting a substantially continuous pattern of debossments or apertures being formed by locally heated at predetermined points along the surface of the web. The process comprises: continuously bringing the web in contact relation with a forming structure exhibiting a substantially continuous pattern of apertures corresponding to the debossments or apertures of the web, the continuous pattern of the apertures extending from the outermost to the innermost surface of the forming structure; locally heating the region of the web at the predetermined points along the surface of the web by an energy source, the energy source heating the region of the web above its melting temperature range; applying a substantially uniform fluid pressure differential to the locally heated web at least in those regions to be debossed or apertured while the web is in contact with the forming structure, whereby the web is debossed or apertured at the predetermined points and generally maintains its surface structure at least in those areas in which the web is not debossed or apertured; and removing the debossed or apertured web from the forming structure.
The present invention also provides a soft and resilient web exhibiting a substantially continuous three-dimensional pattern of macro-apertures. The web comprises a fluid impermeable plastic material. The web has a first surface, a second surface, a multiplicity of micro-apertures and a multiplicity of macro-apertures. The web has a land area on the first surface and a wall protruding beyond the second surface of the land area. The land area includes a pattern of fine-scale, volcano-like micro-apertures comprising discrete volcano-like surface aberrations and micro-openings. The aberrations protrude from the land area beyond the first surface of the land area. The micro-opening locates at the top of each aberration. The macro-apertures are defined by the wall, an opening on the first surfa

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