Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1993-12-09
2002-09-24
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S323000, C428S343000, C428S346000, C428S347000, C428S349000, C428S354000, C428S3550EN, C428S515000, C428S516000, C428S523000, C156S244110, C264S173160
Reexamination Certificate
active
06455150
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of composite polymer films of reduced surface frictional characteristics and to a method of making such films. It more particularly refers to a biaxially oriented composite film structure having improved properties, including heat sealability, good machinability and reduced coefficient of friction.
BACKGROUND OF THE INVENTION
In the packaging of certain types of foods, such as snack foods including candies, potato chips, cookies and the like, it is common practice to employ a multi-layer film. Polypropylene films are widely used in the packaging industry due to their superior physical properties, such as, transparency, stiffness, moisture barrier characteristics and others. Despite these highly desirable properties, unmodified polypropylene film has the disadvantageous property of having a high inherent coefficient of friction and film-to-film destructive blocking on storage. This high film-to-film coefficient of friction makes polypropylene films difficult to be successfully employed in automatic packaging equipment in their unmodified form.
In the past, coefficient of friction characteristics of polypropylene and other thermoplastic films have been beneficially modified by the inclusion in the polymer of fatty acid amides, such as, erucamide and oleamide. The effectiveness of this type of material depends upon its ability to migrate to the surface of the film in order to reduce the coefficient of friction. Both of the aforementioned amides are commonly used for reducing coefficient of friction. The development of the desired low coefficient of friction value is strongly dependent upon the type and amounts of amides, and time and temperature aging effects. Even the heat history of the film while in storage and shipping and during subsequent converter processes, significantly affects the coefficient of friction. In addition, the presence of these types of fatty acid amides on the film surface results in visible adverse appearance effects, manifested by an increase in haze, a decrease in gloss and the presence of streaks. These materials also adversely effect the wettability and adhesion of solvent and water-based inks, coatings and adhesives.
In the case of oriented polypropylene films which are widely used in the food packaging industry, it is common to laminate this film with itself or with other thermoplastic films or with paper films. When oleamide or erucamide are used in the polypropylene films a significant increase in coefficient of friction has been observed after lamination to such films. It is theorized that this is due either to the migration of the amide back into the polypropylene film or to the loss of the additive layer at the film surface. Therefore, these types of oriented laminated polypropylene films have limited usage for particular converting processes. Attempts to replace these amides to provide a consistent coefficient of friction have not been successful.
In U.S. Pat. No. 4,533,509, there is described a multi-layer structure comprising a comparatively thick base layer of an optically clear thermoplastic resin and a comparatively thin surface layer containing a finely divided inorganic material in a proportion sufficient to thereby impart anti-block characteristics and decrease film-to-film coefficient of friction. The resulting film has non-blocking and improved slip characteristics without the adverse appearance, wetting and adhesion effects typically experienced with amide-modified films. However, when laminated to other films, such structures exhibit significantly higher coefficient of friction values and cannot be used in conventional form, fill and seal machines.
U.S. Pat. No. 4,618,527, discloses a biaxially oriented film structure comprising (I) a comparatively thick base layer of a thermoplastic resin containing: an antistatic combination of (a) a compound of the formula RN(R
1
)
2
wherein R is a C
6
-C
24
alkyl group R
1
is H(OCH
2
CH
2
)
n
; n=1-25; and (b) a monoester of an aliphatic C
2
-C
24
fatty acid; and a slip improving proportion of (c) a C
12
-C
24
fatty amide; and (II) a comparatively thin surface layer on at least one surface of (I), the surface layer comprising a thermoplastic resin containing an anti-block and COF reducing proportion of a finely divided inorganic material. This structure can be laminated to another film such as a polymeric film or a paper film.
In U.S. Pat. No. 4,652,489, a sealable, opaque polyolefinic multilayer film composed of a polypropylene base layer, a non-sealable surface layer, and a sealable surface layer, is disclosed. The. sealable surface layer has a low minimum sealing temperature and is made from a copolymer of propylene and ethylene or butene-1 units and/or a terpolymer of ethylene, propylene and butene-1 units. The non-sealable layer is a combination of a propylene homopolymer and a slip agent. The base layer contains an additive which is incompatible with polypropylene. The process includes stretching of the film, and during the stretching step, the polymer matrix is torn open around the additive particles to form vacuoles which give the base layer a degree of opacity
U.S. Pat. No. 4,659,612 discloses an oriented, polymer film laminate possessing a low coefficient of friction, good receptivity for water-based coatings and good optical characteristics.
U.S. Pat. No. 4,692,379 discloses an oriented, heat sealable polymer film laminate possessing a low coefficient of friction, good receptivity for water-based coatings and good optical clarity and a method for manufacturing such a laminate.
U.S. Pat. No. 4,720,420 discloses a sealable, transparent polyolefinic multilayer film composed of a polypropylene base layer, a non-sealable surface layer, and a sealable surface layer. The sealable surface layer has a low minimum sealing temperature and is made from a copolymer of propylene and ethylene or butene-1 units and/or a terpolymer of ethylene, propylene and butene-1 units. The non-sealable layer is a combination of a propylene homopolymer, a slip agent, and an anti-blocking agent. The process provided includes coextruding the three layers, biaxially stretching the coextruded film, and subjecting the non-sealable layer to a corona-discharge treatment.
U.S. Pat. No. 4,734,317 relates to a polyolefin film having a base layer composed essentially of propylene polymers and having sealing layers present on both sides, composed essentially of sealable olefin polymers. Polydialkylsiloxane is incorporated in a first of the two sealing layers, and this layer is not subjected to corona treatment. The second sealing layer is subjected to corona treatment and has polydialkylsiloxane, not incorporated, but present on its outer surface, the polydialkylsiloxane having been transferred to this layer by contact with the sealing layer in which polydialkylsiloxane is incorporated. The relative polydialkylsiloxane occupancy on the second layer, which is determined by means of ESCA spectroscopy, is not more than 15. The three-layer polyolefin film is prepared by a coextrusion process. It is particularly suitable for use as a packaging film on high-speed packaging machines.
U.S. Pat. No. 4,764,425 discloses an oriented, heat-sealable polypropylene film which possesses a low coefficient of friction, excellent anti-static behavior and good optical clarity.
U.S. Pat. No. 4,961,992 relates to a polymer film laminate having improved machinability on modern high speed belt drive machines, particularly when these machines are set up to form lap seals. A method of assembling such a film is also provided. The film includes an outside web having-an upper surface layer containing a silicone oil. This laminating web can be used with virtually any co-laminate, metallized or not, which is bonded thereto with an adhesive. Upon winding the composite film laminate upon a core, silicone oil is transferred to the inside surface of the laminates thus providing an inside coefficient friction which is about equal to or less than the outside coefficient of friction. Hot slip
Ambroise Benoit
Brew Joseph E.
Keung Jay Kin
Sheppard Karen A.
The-Dzuy Francis Tran
Chen Vivian
James Rick F.
Santini Dennis P.
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