Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2001-01-22
2003-10-28
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S354000, C428S906000, C428S910000
Reexamination Certificate
active
06638637
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to films useful as tape backings, and more particularly to multilayer laminate biaxially-oriented backings comprising a propylene-containing primary layer and at least one polyolefin-containing secondary layer and further including a surface finishing layer, such as a surface matte layer.
BACKGROUND OF THE INVENTION
Commercially available pressure sensitive adhesive tapes are usually provided in a roll form and can be provided on a tape dispenser (see e.g. U.S. Pat. Nos. 4,451,533 and 4,908,278). Typically, commercially available dispensers have either a metal or plastic serrated cutting blade. In the case where no dispenser is provided, it is desirable that the tape can be torn by hand.
“Severability” of adhesive tape is defined as the ability to cut or sever a length of tape by pulling the tape over the teeth on the serrated cutting edge of a tape dispenser with a desired amount of energy or work. Severability is also referred to as “dispensability.” It is desired that the severed tape does not chip, sliver, fracture or break in an unpredictable manner (see U.S. Pat. Nos. 4,451,533 and 4,908,278). Such severability is desirable to produce a cleanly serrated cut edge on the severed tape strip.
Adhesive tapes are produced from many different films. Films that tend to be too tough and stretch significantly before breaking while under load, render such films extremely difficult to sever, particularly on a plastic bladed dispenser. Tape dispensers with plastic cutting blades are commonly used for hand-held units such as a Catalog No. 104 3M Magic™ tape dispenser, available from Minnesota Mining and Manufacturing Company, St. Paul, Minn. However, dispensers with plastic cutting blades are typically not sharp and durable enough to sever oriented polypropylene tapes. For this reason, typical dispensers for biaxially oriented polypropylene tape usually are equipped with sharp metal blades. Such metal blade dispensers are more costly and difficult to manufacture than dispensers with plastic blades.
Biaxially oriented isotactic polypropylene films are well known for their toughness, low cost, good color, moisture and slivering resistance, and clarity and have long been used as adhesive tape backings (see U.S. Pat. Nos. 3,241,662 and 3,324,218). Although, as stated above such films are more difficult to dispense, particularly using a plastic dispenser. In addition, such films are considered very difficult to tear by hand and are typically slit with roughened or flattened rotary blades in order to provide sufficient edge defects to allow some degree of finger tearability. This process results in non-uniform, unsightly edges and much reduced tape strength.
There have been several attempts to improve polyolefin films to produce severable and finger tearable adhesive tape backing films.
For example, JP 53034834 describes a mixture of polypropylene with low molecular weight polyolefins in order to produce a more brittle, finger tearable film backing. U.S. Pat. No. 3,887,745 describes a 2-layer polypropylene tape in which a thick secondary layer is uniaxially oriented in the transverse (or perpendicular) direction to facilitate straight line tearing in the tape crosswise direction. Similarly, U.S. Pat. No. 3,952,073 and U.S. Pat. No. 4,045,515 describe tape backings comprising blends of isotactic polypropylene with random propylene-ethylene copolymers, which are sequentially oriented to give a film having greater orientation in the transverse than in the machine direction in order to produce film having good finger tearability across the film.
U.S. Pat. No. 4,410,582 describes a sequentially biaxially oriented multilayer film consisting of a low molecular weight polyolefin primary layer having a melting point lower than higher crystallinity secondary layers in order to produce a finger tearable film backing. U.S. Pat. No. 4,137,362 describes adhesive tape backings produced by the sequential biaxial orientation of single layer blends of isotactic polypropylene with other polyolefins. U.S. Pat. No. 4,393,115 and U.S. Pat. No. 4,414,261 and JP Application 11-1998835 describe sequentially biaxially oriented multilayer films which include polypropylene-ethylene block copolymer or hydrocarbon resins in blends or layers, which are intended to promote finger tearability by increasing the film's brittle behavior.
Similarly, U.S. Pat. No. 4,447,485 and U.S. Pat. No. 4,513,028 describe stretched film having a base sheet comprising polypropylene blended with polymethylpentene, the latter present to produce a more brittle construction. JP Application 6-305014 describes a single composition, single sheet film comprising a polypropylene-ethylene copolymer which develops a secondary/primary structure due to thermal processing conditions using a sequential biaxial orientation process.
Pressure sensitive adhesive tapes with a matte surface opposite the adhesive coated surface are commonly sold for use in offices, retail shops and schools. These tapes are typically used in conjunction with paper, for mending tears, posting memos, and attaching documents together, and as such, it is preferred that the pressure sensitive tape remain invisible in its final use, yet allow for any printing underneath to be viewed and photocopied clearly and cleanly. Additionally, it is preferred that the matte surfaces of these tapes can be written on with a variety of writing instruments, such as ball-point pens, pencils and permanent markers. Cellulose acetate film with an embossed matte finish has been predominantly used as the substrate for matte adhesive tape due to its excellent optical properties and write-on characteristics.
Biaxially oriented polypropylene (BOPP) films are widely used as film substrates for adhesive tapes due to their excellent strength, moisture resistance and low cost. Generally, BOPP films cannot be imparted with a matte and/or writable surface simply by embossing the surface of the film. Typically, such methods involve the provision of an additional layer atop the base polypropylene layer of the BOPP film, wherein some of the desired properties of a matte or writable surface are provided by the additional layer.
Such known additional layers have frequently been produced by combining two or more polymers in the form of a blend. At least one of the polymers in such a blend is usually a polyolefin, as this provides adhesion to the polypropylene main layer in the BOPP film. Polyolefin-based components in such blends have included polypropylene, co- or terpolymers based on propylene, polyethylenes such as high density polyethylene (HDPE), polypropylene/polyethylene block copolymers, ethylene based co- or terpolymers modified with polar groups, polymers containing butene-1 monomer, and methylepentene polymer. Non-polyolefin components in such blends have included thermoplastics such as polystyrene, polyamides, polyalkyl metbacrylates, and polyesters. Additionally, some of the known additional layer compositions have included inorganic fillers, such as silica, calcium carbonate, or clay. Examples of such known additional layers can be found in U.S. Pat. Nos. 5,501,905, 5,474,820, 5,425,990, 5,366,796, 5,364,704, 4,960,637, 4,513,028, 4,447,485. EP 03382431, and JP 76032668B.
The problem remains, however, that none of the known methods satisfactorily provides a matte surface that combines all of the desirable attributes of a matte appearance, is writable with pencil, ball-point pen, and permanent ink markers, does not “ghost” on photocopying, and is easy to produce. In particular, there is a need for a matte layer composition that provides all the aforementioned properties but does not require slow cooling of the extruded film sheet to optimize the matte appearance, and does not limit the temperature range useful for stretching the film.
However, none of the alternatives set forth above provides an adhesive tape backing combining all the desirable attributes of strength, easy dispensability, easy finger tear, good clarity, good mechanical stre
Bartusiak Joseph T.
Denker Martin E.
Hager Patrick J.
Hamer Kevin M.
Kozulla Randall E.
3M Innovative Properties Company
Jonas George W.
Tarazano D. Lawrence
Trussell James J.
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