Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-03-21
2002-09-17
Barr, Michael (Department: 1762)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S500000, C428S516000, C428S910000
Reexamination Certificate
active
06451446
ABSTRACT:
This invention relates to a transparent or translucent multilayer film having at least one low gloss layer which may be readily bonded to paper. The film has particular utility for windows in envelopes.
It is known to use polymeric films for windows in paper envelopes. Such window envelopes save the resources necessary to separately address an envelope on its surface, or to apply an address label to the envelope. A letter, invoice, or other contents may be shaped to size, as by folding, as necessary, to place the address of the intended recipient appearing on the contents in a position to be visible through the window comprising the polymeric film.
Films having applicability as envelope windows are known. DE-A- 4312388.0 discloses a transparent stretched polypropylene film having a reflection-reduced surface, which is bondable. The film comprises polypropylene of at least two layers. Reduced reflection is obtained by incorporation of a substantially propylene/ethylene copolymer incorporating linear low density polyethylene and maleic anhydride. The disclosed films are stretched on two axes.
DE-A-4312388.0 reports that polystyrene film and PVC film have been used as window envelopes. Biaxially oriented polypropylene films have been used, but such films are there reported to be not readily bondable to paper by fast running envelope manufacturing equipment.
Polystyrene surfaces however are known to the manufacturers of envelopes. Adhesion products for bonding the window film to envelopes are known, and effective. Polypropylene however offers a cost advantage over polystyrene.
It is known to prepare films having layers of polypropylene and polyethylene from GB-A- 2281282, and GB-A- 2111908.
JP-A-51-28879 promotes a biaxially stretched film of propylene and laminate of styrene butadiene thermoplastic elastomer. This film is claimed to exhibit good heat-sealing characteristics.
JP-A-55-57428 discloses a film of polystyrene laminated on polypropylene which is subsequently biaxially oriented (stretched). Its use as tape suitable for wrapping of heavy objects is proposed.
JP-A-55-148155 discloses three-layer films comprising:
1) a layer of styrene and block polystyrene-butadiene in combination with a solvent for the styrene-butadiene block copolymer,
2) a flexible layer which may be polypropylene and ethylene-vinyl acetate co-polymer, and
3) a drawn layer which may be polypropylene.
The film is proposed as easy-open storage bags for food, which remains pliable at freezing temperatures, yet may withstand boiling water.
JP-A-55-163164 also discloses a food container formed from a film of biaxially stretched polystyrene onto which a polypropylene layer is cast or laminated.
JP-A-80-23746 discloses a food packaging film of polystyrene, having a polypropylene layer of 1/10 to 1/100 the thickness of the polystyrene layer. The layer film is stretched.
JP-A-56-27326 discloses a laminated sheet of polystyrene/butadiene/styrene and polypropylene which is biaxially stretched. The film is proposed for adhesives tapes.
JP-A-89-174324 discloses a biaxially stretched polypropylene film having reduced gloss and luster, as a wrapping material. The polypropylene is coated with an emulsion containing styrene, after corona discharge treatment.
JP-A-63-110150 teaches lamination of polystyrene film and a polyolefin film for use as bags.
NL-A-69-13608 discloses stencil film of oriented polypropylene film optionally laminated with polystyrene.
U.S. Pat. No. 4,608,284 teaches a laminate of an oriented polystyrene film, which may have been printed on the laminated surface, and a polypropylene film which has not been oriented. An adhesive joins the films at their interface surfaces. The films find use as heat-shrinkable printed labels.
U.S. Pat. No. 5,468,563 discloses films asserted to have utility as window film prepared from polypropylene. A reflection reduced layer is suggested of rubber modified ethylene and maleic anhydride, co- and terpolymer of propylene/ethylene/butylene having propylene as the principal component, or copolymers of propylene/polyethylene block copolymers. The core layer is comprised of isotactic polypropylene, a random propylene co-polymer. A second outer layer is constituted from the materials of the core layer having anti-block agents added. The layers may be co-extruded, then stretched
EP-A-01 22495 discloses films of biaxially oriented polypropylene, laminated to an olefin polymeric film having at least three peaks between 120° C. and 65° C. when analyzed by DSC (differential scanning calorimetry) . The multiple peaks are said to produce low gloss and a high haze. End use as a decorative wrapping paper having a metallized surface thereon for example by lamination is suggested.
JP-A-51-19079 discloses a multi-layer composite film in which one layer is formed from a polyolefin (such as polypropylene) and one layer is a thermoplastic layer obtained by adding 5-30 parts by weight of a styrene-butadiene copolymer to a polystyrene resin. The multi-layer film is manufactured by co-extrusion and thermal fusion of the layers. No orientation of the films is carried out.
U.S. Pat. No. 4,464,439 discloses a co-extruded laminate formed from at least one sheet of crystalline polypropylene and at least one sheet of polymeric material consisting of a mixture of high-impact polystyrene, crystalline polypropylene and styrene/dienic monomer block copolymer. No orientation of the films is carried out.
GB-A-1 357950 discloses a thermoplastic laminate having at least two layers, one of which is a ternary blend of a homopolymer or copolymer of a vinyl aromatic monomer; a homopolymer or copolymer of an olefin monomer; and a block copolymer having a polyvinyl/aromatic block and a polyolefin block. No orientation of the films is carried out.
Films for envelope windows require several properties. As noted in U.S. Pat. No. 5,468,563, several important properties include: bondability of the window film to the paper of the envelope using bonding agents conventional in the industry and transparency in order that the address is readable through the envelope by postal sorting machines. While transparency is important a window that is transparent and also glossy reflects light. The reflected light may impair the efficiency of the postal sorting machines and indirectly the arrival date of the envelope and contents to the addressee.
According to the invention there is provided an oriented polymeric film comprising a co-extrudate of a first layer having at least 96 weight percent of a polypropylene and of an external layer having (by weight)
a) from 70 to 97% of polystyrene, rubber modified polystyrene or a blend thereof, and
b) from 3 to 30% of a polypropylene/polystyrene compatibilizer selected from the group of ethylene vinyl acetate copolymer and block or random copolymers of a vinyl aromatic compound and an olefin, wherein the film has a minimum stretch ratio of 3 in the machine direction, and 4 in the transverse direction.
Multi-layered polymeric films may be formed by co-extruding the film layers. However, when a film is formed from a co-extrudate of two layers in accordance with the invention, it is found that the co-extrudate layers are separable simply by pulling them apart by hand, for example by using office adhesive tape adhered to each side of the film.
It has now been discovered that, if the co-extiudate layers are oriented in both the machine direction and the transverse direction after the film has been co-extruded, then this results in a film in which the co-extrudate layers are extremely difficult to separate.
Another advantage of the oriented films is that they have a higher modulus (higher rigidity) than non oriented films. Rigidity (high modulus) is a property required for window envelope film for two reasons: for the envelope converter to allow an optimum window patch unit feeding on the envelope machine, and for the final envelope to minimize wrinkling/buckling of the window panel.
The “first layer” comprising polypropylene is from time to time referred to herein as a “core layer”, since for re
Barr Michael
Dow Global Technologies Inc.
Tsoy Elena
LandOfFree
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