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
2001-02-23
2002-08-27
Sanders, Kriellion A. (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...
C524S428000, C524S451000
Reexamination Certificate
active
06441080
ABSTRACT:
BACKGROUND OF INVENTION
(a) Field of the Invention
This invention relates to a composition for providing a repulpable chlorine free moisture vapor barrier coating for packaging material, especially flexible packaging material. This invention also relates to a method of coating a flexible packaging material with such composition and to repulpable packaging materials provided with such coating.
(b) Description of Prior Art
Polyethylene films and wax coatings, which are generally laminated or coated on paper and paperboard are widely used in packaging applications to protect products from moisture. However, it is well known that packaging containing polyethylene films and wax coatings are considered to be non repulpable mainly because they introduce quality problems in the fiber recovery process.
Polyethylene films and wax coatings are considered by waste dealers to be contaminant and if inadvertently used by a recovery mill, they will introduce quality problems into the fiber recovery process either by upsetting the process (plugging the screens) or contaminating the finished product.
Polyvinylidene chloride copolymer (PVdC) is another type of moisture barrier coating which provides outstanding moisture barrier and which is widely used in packaging applications. However, because of its Theological properties, PVdC does not easily form a continuous film onto the cellulose-based substrates used for packaging. Thus, to achieve the required water vapor barrier performances, the application of a heavy weight coat is necessary. However, heavy weight coat PVdC that contains chlorinated hydrocarbons has a negative impact on the environment.
There has been considerable concern about the environmental impact of chlorinated hydrocarbons. Market forces have been pressing for decreased use of chlorine and chlorine containing compound packaging. This has required a search for, alternate water vapor barrier coatings, or to decrease the amount of PVdC used in packaging.
U.S. Pat. No. 5,929,155 to Bérubé disclosed a modified PVdC composition, which permits a lighter coat weight than a regular PVdC with excellent water vapor barrier properties. In addition, packaging materials provided with such coatings are repulpable.
U.S. Pat. No. 5,562,980 to Koutitonsky discloses a multi-layer paper composition which is easily repulpable and which contains a layer of PVdC.
EP 0 718 437 A1 to Wittosh et al. discloses a repulpable paper stock provided with a base coat which contains PVdC as the main water vapor barrier ingredient.
From the prior art mentioned above, it seems that these coatings, even though they require lesser amounts of PVdC, still needs PVdC to give the necessary water vapor barrier requirement for packaging applications.
Some acrylic copolymers are also suggested in the prior art, however they have limited water vapor barrier and do not meet the necessary requirement for packaging applications. There has been a call for chlorine free paper products by environmental groups, by consumer groups, producers, retailers and government agencies. Thus, it would be desirable to have an alternative for conventional polyethylene films, wax coatings, PVdC and coatings containing PVdC that has comparable water vapor barrier properties but also has the added benefit or repulpability,
A chlorine free, wax free repulpable water vapor barrier coating should have the following essential properties:
excellent water vapor barrier property at 100% RH and 37.8° C. (tropical conditions);
good rheological properties to achieve a continuous film on paper and paperboard to provide the necessary water vapor barrier when applied at low weight;
good water resistance;
good flexibility at room temperature;
no blocking;
be repulpable as defined in U.S. Pat. No. 5,929,155;
be based on non polluting technology which is essentially a chlorine free, wax free, formaldehyde free water based dispersion mixture
On the other hand, it is known that water vapor transmission rate takes place through a mechanism that is different than for liquid water, a water vapor barrier coating depends on a continuous film and its degree of crystallization that restricts the passage of water vapor.
The use of free chlorine compositions in providing a repulpable moisture vapor barrier is described in U.S. Pat. No. 5,897,411 which discloses a resin latex which may be carboxylated styrene butadiene and a hydrophobic component which may be mica, talc, silica, clay or kaolin. This composition does not provide a satisfactory coating on packaging material.
On the other hand, U.S. Pat. No. 6,103,809 discloses a thermoplastic composition which may be used as repulpable/recyclable adhesives and which comprises a crystalline water sensitive thermoplastic polymer blended with an amorphous water sensitive thermoplastic polymer. Tackifyier resins such as glycerol ester of hydrogenated rosin may also be included in the composition. This composition cannot be used to provide a moisture vapor barrier coating for paperboard or the like.
U.S. Pat. No. 4,284,542 discloses a hot melt adhesive composition, which includes an alkali metal ionomer of a random copolymer of ethylene methyl acrylate, a carboxylated termonomer, as well as a tackifier and a plasticizer.
U.S. Pat. No. 4,650,822 discloses an adhesive composition, which includes an elastomeric, polymeric resin, a tackifier and a terpene ether.
SUMMARY OF INVENTION
It is an object of the present invention to provide a repulpable, chlorine free, wax free, water vapor barrier coating for flexible packaging that is capable of commercial applications.
It is another object of the present invention to provide a repulpable coating for flexible packaging material, which is based on the combination of a tackifier and a polymer.
These and other objects of the invention may be achieved by providing a composition for providing a chlorine free vapor barrier coating for flexible packaging material, which comprises a tackifier resin, a hydrophobic chlorine free polymer having a Tg between about −40° C. and 45° C. and a minimum film forming temperature (MFFT) which is substantially the same or above the Tg of the polymer and which is capable of bonding crystallized tackifier resin to a substrate, and water in an amount sufficient to provide aqueous dispersions of the tackifier resin and the chlorine free polymer.
According to a preferred embodiment, the coating composition according to the invention may comprise a filler, which has a plate like structure, such as mica or talc, and enough water to disperse the filler in the aqueous phase. In this case, the hydrophobic chlorine free polymer must also be capable of bonding the filler.
The invention also relates to a method, which comprises coating the composition according to the invention on a flexible packaging material, and to a flexible packaging material as obtained by the method according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Tackifier, which are either natural or synthetic resinous materials, are mainly used in the formulation of pressure sensitive adhesives to impart tack. In a lesser degree, they are also used in the formulation of other types of adhesives to impart tack as well.
According to the present invention, tackifiers are used for their tendency to crystallize. Tackifiers by themselves are unsuitable for use in water vapor barrier packaging coatings because the resulting film is either hard or brittle or soft and tacky and does not provide the necessary water vapor barrier requirement for packaging applications.
One important polymer property, which has a significant impact on the barrier performance of the coating, is the glass transition temperature (Tg) or the softness of the polymer, The Tg of the polymer defies the extent of compaction of the coating during drying. The lower the Tg of the polymer (or the softness of the polymer), the better the degree of compaction of the coating. As a result, the final coating structure will be more “close”. This has a significant impact on the moisture barrier performance as will be observed hereinbelow
Crowell & Moring LLP
Le Groupe Recherche I.D. Inc.
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