Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Of varying cross-sectional area or with intermittent...
Reexamination Certificate
2000-04-04
2001-03-20
Loney, Donald (Department: 1772)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Of varying cross-sectional area or with intermittent...
C264S175000, C264S284000, C156S209000, C156S244150
Reexamination Certificate
active
06203741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The inventions disclosed herein relate to apparatus and methods for forming thermoplastic liners and thermoplastic liners formed thereby, more particularly, apparatus and methods for forming micro spike thermoplastic liners and micro spike thermoplastic liners formed thereby.
2. Description of the Prior Art
Thermoplastic liners have been used extensively in the prior art to seal tunnels, excavation sites, landfills, and the like. Typically, to cover the desired area with the thermoplastic liner, continuous lengths of the liner are placed in either partial overlapping or abutting contact and caused to be connected in some leak-proof method, such as welding. It can be readily appreciated that some concerns arise with the use of thermoplastic liners. First, since thermoplastic liners must be used at various grades, the liners must be provided with at least one surface which can frictionally engage the graded surface and maintain the liner in a desired location. Second, due to the tremendous area often required to be covered by a thermoplastic liner, the costs of manufacturing such liners needs to be minimized.
Several approaches have been taken in the prior art to produce an acceptable thermoplastic liner. For example, a repeated embossed pattern is provided on one surface of the thermoplastic liner, such as shown in U.S. Pat. No. 4,612,152 to Kawabata, et al. Prior art embossing techniques, however, suffer from several drawbacks. First, the underlying base substrate of the thermoplastic liner must be substantially deformed to achieve a desired embossed pattern, which may result in damage to the base substrate. Second, typically, the repetition of an embossed pattern creates regular, continuous grooves in the thermoplastic liner between the embossed projections. Over time, the continuous grooves may cause the underlying engaged material, such as soil, to furrow therein, with further furrowing allowing movement of the liner relative to the underlying material and eroding the gripping force thereof. Third, although the process of embossing thermoplastic seeks to define sharp edges in the embossed substrate, the edges are often formed rounded with a small radius. This effect, of course, reduces the grip of the film on underlying material.
To overcome the shortcomings of the prior art, it is an object of this invention to provide a roughened thermoplastic liner formed with a plurality of even-spaced projections, which are each irregularly formed.
It is also an object of the subject invention to provide a calendering roll for forming a roughened thermoplastic liner having a plurality of evenly-spaced projections, which are each irregularly formed.
It is yet another object of the subject invention to provide a method for forming a thermoplastic liner having a roughened surface with a plurality of evenly-spaced projections, with each projection being irregularly formed.
It is still a further object of the subject invention to provide a method for forming a calendering roll which is for forming a thermoplastic liner having a roughened surface with a plurality of evenly-spaced projections, with each projection being irregularly formed.
SUMMARY OF THE INVENTION
The above-stated objects are met by a thermoplastic liner of indeterminate dimensions, which has two opposing surfaces, with at least one of the surfaces being roughened and having a plurality of projections extending therefrom. The liner of the subject invention is formed by a calendering process.
The thermoplastic liner is formed with a base layer having two opposed outer surfaces. The outer surfaces are substantially parallel and are coextensive with the overall length and width dimensions of the liner. At least one of the outer surfaces is roughened with a repeated irregular pattern. The projections are each irregularly shaped and extend from the roughened surface. Preferably, the projections are evenly-spaced both laterally and longitudinally on the roughened surface, but, alternatively, the projections can be offset in lateral and/or longitudinal directions or be randomly located. Each projection is irregularly formed, due to the process of forming the subject liner described below. The combination of the projections and the roughened surface allows the liner of the subject invention to frictionally engage a desired location. The roughened surface and irregular shapes of the projections prevent the underlying engaged material from furrowing, thereby ensuring good frictional engagement between the liner and the underlying material. The term “irregular”, or any derivative thereof as used herein, is intended to describe a shape which is not an evenly-formed geometric shape such as a circle, oval, rectangle, parallelepiped, etc.
The liner of the subject invention is formed by a calendering process which utilizes a new and improved calendering roll. The calendering roll of the subject invention is generally cylindrically-shaped with an outer surface which is roughened. Blind apertures extend into the roll from the outer surface. Each blind aperture is formed with an irregularly shaped opening, which is coextensive with the outer surface of the roll, and a constant circular cross-section portion extending therefrom into the roll of the subject invention.
The calendering roll of the subject invention is formed by drilling a plurality of blind apertures into a generally cylindrically-shaped roll. The apertures are each drilled to define a constant cross-section. Preferably, the drilled apertures are evenly spaced circumferentially and axially about the body of the roll. Subsequently, the outer surface of the roll is made roughened with an irregular pattern by any method known by those skilled in the art. For example, knurling can be used. The outer surface must also be roughened about the openings of each of the apertures such that the openings each become irregularly formed.
The above-described calendering roll is used in a method for forming the above-described thermoplastic liner. To form the thermoplastic liner, molten thermoplastic is continuously extruded through a slot die to form a thermoplastic sheet having opposed substantially smooth outer surfaces. The above-described calendering roll is provided in a parallel spaced relationship from a second roll to define a nip therebetween. The extruded thermoplastic sheet is fed into the nip with the thermoplastic being urged, under pressure generated in the nip, into various apertures of the calendering roll and into pressing engagement with the roughened outer surface of the calendering roll, as the sheet passes through the nip. The sheet is then disengaged from the roll with the pattern of the roughened surface formed on the calendering roll being impressed thereon. Also, the projections are each damaged and elongated upon removal from the respective apertures, due to the irregularly shaped openings through which the respective projections must pass, and the irregular forming of the projections is achieved.
The calendering roll can be heated or chilled. Heating or cooling the thermoplastic liner during the calendering process affects the elongation and extent of damage of the respective projections, accordingly. It should be noted that heating or cooling the calendering roll is not required. Preferably, the temperature of the calendering roll should be maintained such that, prior to removal of the projections from the apertures of the calendering roll, the outer surface of the respective projections hardens, and the cores of the respective projections are in a molten state. As such, upon removal of the projections from the respective apertures, the irregularly shaped openings cause the hardened outer surfaces of the projections to be damaged by the irregular edges of the apertures and, simultaneously, cause the molten cores to be elongated. Heating or cooling the calendering roll will cause the projections to harden to varying degrees, resulting in varying degrees of damage to the projections and varying degrees of elongation.
AGRU Kunststofftechnik GmbH
Casella Anthony J.
Hespos Gerald E.
Loney Donald
Porco Michael J.
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