Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-12
2002-11-05
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S463000
Reexamination Certificate
active
06476114
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a film comprising a layer of a thermoplastic polymer having a fluorochemical hydrophilicity-imparting compound dispersed therein. In particular, the present invention relates to a film comprising a layer of polypropylene. The present invention also relates to a method of coating such film.
BACKGROUND OF THE INVENTION
Films from extruded thermoplastic polymers, such as poly(alpha)olefins, are widely used in a variety of applications including, for example, as overhead transparencies, packaging materials and backing material for adhesive tapes. In many applications, the films need to be provided with one or more coatings. In order to provide good adhesion and coatability of such coatings, and particularly aqueous-based coatings, it is generally required to treat the film surface with a corona discharge before coating.
While this treatment is generally effective, it makes the film surface rough. Moreover, the effect of a corona discharge treatment on the film surface may degrade with time. Accordingly, corona discharge treatment is generally only useful if it can be done in line with the coating of the film. However, in a number of applications that may not be practical.
Accordingly, there is a need for a solution that can provide the thermoplastic polymer films with good coatability properties that can be maintained over a long period of time and that allow for coatings to be provided to the film with good adherence between the film and the coating. As will be set forth in detail below, the present invention solves this problem by dispersing a fluorochemical hydrophilicity imparting compound in the thermoplastic polymer layer of the film.
While the addition of certain fluorochemicals during the extrusion of thermoplastic polymers is known, the prior art does not disclose or suggest that the addition of a fluorochemical hydrophilicity imparting compound to an extruded thermoplastic polymeric film can provide good coatability properties to the film which can be maintained for a long period of time, nor does the prior art teach or disclose that good adhesion of the coating to the film can be obtained.
EP 0 516 271 discloses the use of a fluoroaliphatic group containing a compound in the extrusion of polypropylene fibers to impart durable wettability properties to the fiber's surface. Particularly exemplified compounds are those that have a perfluorinated alkyl group linked to a poly(oxyalkylene) group terminated with a hydroxyl group or a lower alkyl ether.
WO 92/18569 and WO 95/01396 describe fluorochemical additives for use in the extrusion of thermoplastic polymers to prepare films and fibers with repellency properties. It is specifically disclosed that films can be prepared with good anti-wetting properties. It is further taught that polypropylene films with the fluorochemical dispersed therein have good antistatic properties.
U.S. Pat. No. 5,043,195 further describes a multi-layer sheet material including an electrically insulating film with a conductive layer on the upper surface and an antistatic layer carried by the lower surface. The antistatic layer comprises polyethylene and a fluoroaliphaticsulfonamide polyether compound.
U.S. Pat. No. 3,787,351 discloses the addition of polyethylene oxide containing fluorochemicals to self supporting structural filled or reinforced resinous shaped articles made of, for example, polypropylene. It is stated that the fluorochemical creates better bonding between fillers and the resin such that the amount of voids in the article is minimized.
SUMMARY OF THE INVENTION
The present invention provides a method of making a coated film comprising the steps of:
(A) providing a film comprising a layer of thermoplastic polymer having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I):
R
f
—Q—Z—X—T (I)
wherein R
f
represents a partially or fully fluorinated aliphatic group having at least 3 carbon atoms, Q is a linking group or a covalent bond, Z is a poly(oxyalkylene) group, X is oxygen or NR where R is a hydrogen atom or an alkyl or aryl group, and T is a hydrogen atom or an organic group having not more than 6 carbon atoms;
(B) applying a coating comprising at least one non-volatile component on said film; and
(C) when said coating contains volatile components, drying said coating to remove said volatile components from said coating.
In another aspect, this invention provides a film comprising a layer of thermoplastic polymer having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I) that is coated on at least one surface with a composition comprising at least one non-volatile component.
One preferred embodiment of the invention is a multi-layer film comprising a first and second layer of thermoplastic polymer, said first and second layer being in contact with each other, said second layer forming an outermost layer of said film and having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I), and said first layer being substantially free of the fluorochemical hydrophilicity-imparting compound.
It has been found that the film of the invention can be readily coated without the need for prior treatments such as corona discharge. The film can be readily coated with an aqueous coating and good adhesion of the coating to the film can be obtained. Even films with smooth surfaces can be readily coatable. Finally, it was found that films can be obtained that are bright and highly transparent.
DETAILED DESCRIPTION OF THE INVENTION
It will be understood that in connection with the invention the term “dispersed therein” denotes merely the presence of the fluorochemical hydrophilicity-imparting compound in the thermoplastic polymer without limitation as to where the fluorochemical hydrophilicity-imparting compound is located in the layer. Thus, the fluorochemical hydrophilicity-imparting compound may be uniformly dispersed in the bulk of the polymer or a major portion of the fluorochemical hydrophilicity-imparting compound may have migrated to the surface of the thermoplastic polymer layer.
The films of the invention can consist of a single layer of thermoplastic polymer or the films can consist of multiple layers of thermoplastic polymer. In case the film is a single layer of thermoplastic polymer with the fluorochemical hydrophilicity imparting compound dispersed therein, both major surfaces of the film can be readily coated. When the film consists of multiple layers of thermoplastic polymer, various constructions are possible. For example, the film may consist of two layers of thermoplastic polymer and only one of them contains the fluorochemical hydrophilicity imparting compound. In such a film, the side of the multilayer film comprising the thermoplastic polymer layer with the fluorochemical hydrophilicity imparting compound will be readily coatable. Another embodiment of the film consists of three thermoplastic polymer layers whereby a core layer of thermoplastic polymer without the fluorochemical hydrophilicity imparting compound is provided on each side of a layer of thermoplastic polymer with fluorochemical hydrophilicity imparting compound. Such film is readily coatable on both sides.
Films with multiple layers of thermoplastic polymer are especially preferred in this invention because the above described properties of the film can be obtained without substantially impairing the mechanical properties of the film. Moreover, the properties can be obtained with less fluorochemical hydrophilicity imparting compound than would be needed in case of a film that consists of a single layer. Typically, a multilayer film will have one or two outer layers of thermoplastic polymer with a fluorochemical hydrophilicity imparting compound dispersed therein. The thickness of these outer layers may vary broadly, but it is typically no more than about 30 &mgr;m, preferably between about 0.5 &mgr;m and 30 &mgr;m, and more preferably between about 1 &mgr;m and 15 &mgr;m.
Goeman Bart
Spielmann Rolf D.
3M Innovative Properties Company
Michl Paul R.
Voortmans Gilbert
Weiss Lucy C
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