Package making – Methods – With contents treating
Reexamination Certificate
1999-12-21
2002-08-13
Rada, Rinaldi I. (Department: 3721)
Package making
Methods
With contents treating
C053S453000, C053S450000, C053S140000
Reexamination Certificate
active
06430898
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improvement in the method of packaging thermoplastic compositions, particularly hot melt adhesive compositions. The method comprises substantially surrounding a portion of adhesive composition with a plastic packaging film having a relatively low complex viscosity at low temperatures. The packaging material is meltable together with the adhesive composition, blendable into the molten adhesive composition, and does not adversely affect the adhesive properties to the extent that it is unnecessary to remove the packaging material from the hot melt adhesive composition prior to usage. The invention is particularly useful for certain low viscosity pressure sensitive adhesive compositions, that are typically applied by melting the packaged adhesive composition in a melt tank. More particularly, the invention is useful for hot melt adhesives that are applied by application means that are very sensitive to inhomogeneity of the combination of molten hot melt adhesive and molten packaging material such as spraying, screen printing, bead applicators and gravure coating hot melt application techniques.
BACKGROUND OF THE INVENTION
Hot melt adhesives (HMA's) are solid at room temperature and are generally applied to a substrate while in a molten state. Hot melt adhesives are typically characterized as hot melt pressure sensitive adhesives (HMPSA's,) which are tacky to the touch even after the adhesive has solidified and non-tacky hot melt adhesives which will be denoted as simply “HMA's”. HMA's have been packaged in a variety of forms ranging from small pellets that can be vacuum fed into a melting device, to drum sized quantities. The packaging of HMA's has typically been unproblematic, since after the adhesive is solidified, it will maintain its shape and not adhere to the container, other pieces of hot melt, the operator's hands, machinery, etc. until remelted.
HMPSA's on the other hand, present a variety of challenges. Historically, these adhesives were, and continue to be, provided in the form of blocks. Due to the tacky nature of these materials, there are problems associated with handling and packaging them. The solid HMPSA blocks not only stick to each other and adhere to the operator's hands and mechanical handling devices, but they also pick up dirt and other contaminants. Additionally, certain high tack formulations result in blocks that will deform or cold flow unless supported during shipment. The needs and advantages for providing tackless or nonblocking hot melt pressure sensitive adhesive forms and packages are apparent and various ways of accomplishing this have been developed.
Several references relate to the use of certain low viscosity materials, particularly waxes, for use as a non-tacky coating. The coating may be coextruded onto a strand of HMPSA and squeeze-cut to form pillows, applied to a mold that is subsequently filled with hot melt adhesive, or provided in the form of an aqueous dispersion which upon evaporation of the water leaves a nontacky powder coating or residue on the adhesive surface.
Specifically, EP 0 557 573 A2 relates to a packaging composition for cold-flowing adhesive compositions wherein the composition contains an intimate blend of styrene-isoprene-styrene block copolymer; an aromatic hydrocarbon resin, a suitable mineral oil, a wax, and an antioxidant/stabilizer.
Other references employ plastic packaging materials that substantially surround the adhesive composition. For example, Rouyer et al., U.S. Pat. No. RE 36,177 reissued April 6, 1999 teaches a method of packaging an adhesive composition in a plastics packaging material. The claims of Rouyer are directed to selecting a plastic packaging material having a softening point below about 120° C., and having physical characteristics which are compatible with and do not substantially adversely affect the adhesive characteristics of a molten mixture of said adhesive and said material and whereby the mixture is substantially compatible with the operation of hot melt application equipment. Subsequent patents employing plastic packaging materials in the adhesive field include U.S. Pat. No. 5,715,654; U.S. Pat. No. 5,669,207; U.S. Pat. No. 5,401,455; U.S. Pat. No. 5,373,682.
SUMMARY OF THE INVENTION
The present inventors have discovered that an easily measured property, namely complex viscosity, directly relates to physical film compatibility and have further identified a class of polyolefin materials that exhibit such properties. It is important to note that this discovery assumes that the film material is first chemically compatible with the thermoplastic composition to be packaged, consistent with the teachings of Rouyer et al.
The invention is particularly useful for low viscosity thermoplastic compositions having a Brookfield viscosity of less than about 10,000 cPs at 350° F., such as pressure sensitive hot melt adhesive compositions which are typically applied by melting the packaged adhesive composition in a melt tank wherein the melt tank lacks an active mixing means. The invention is also useful for hot melt adhesives that are applied by application means that are very sensitive to inhomogeneity of the combination of molten hot melt adhesive and molten packaging material such as spraying, screen printing, bead applicators and gravure coating hot melt application techniques.
Accordingly, one aspect of the present invention is an improved method of packaging a thermoplastic composition in a film material wherein the film material is selected such that it is similar to the complex viscosity of thermoplastic composition being packaged, yet high enough in complex viscosity such that the film exhibits sufficient mechanical strength to serve its intended packaging function. Preferably the difference in complex viscosity between the thermoplastic composition and the film at the application temperature is less than about 15000 poise and more preferably less than about 10,000 poise at the application temperature of the adhesive. Most preferably the film exhibits a relatively flat complex viscosity curve as a function of temperature, similar to the curve of the corresponding adhesive that is being packaged. Thus, the film is generally not comprised of a wax-like material having a molecular weight (Mw) of less than about 40,000 or other materials that generally rise steeply in viscosity at lower temperatures, ranging from about 70° C. to about 100° C. Hence, the complex viscosity of the film is typically less than 100,000 Pa*s at 90° C. and most preferably less than 100,000 Pa*s at 70° C. to 80° C.
In another embodiment, the present invention relates to a packaged thermoplastic composition comprising a hot melt adhesive composition, surrounded by a plastic packaging film material wherein the complex viscosity of the film material is less than 100,000 Pa*s. at about 90° C. and preferably less than 100,000 Pa*s at 70-80° C.
In another embodiment, the present invention relates to a thermoplastic composition surrounded by a plastic packaging film wherein the film material has a melt index greater than 20 g/10 min. and preferably greater than about 30 g/10 min. at 190° C.
In another embodiment, the present invention relates to a thermoplastic composition surrounded by a plastic packaging film wherein the film material comprises certain homogeneous ethylene/&agr;-olefin interpolymers. The applicants have found that the complex viscosity of low density homogeneous ethylene/&agr;-olefin interpolymer based films is substantially lower than a higher density film having the same melt index. Accordingly, low density homogeneous ethylene/&agr;-olefin interpolymers film materials are particularly preferred.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is useful for packaging a variety of thermoplastic compositions, particularly hot melt adhesives, wherein the packaging material need not be removed from the thermoplastic composition prior to use. These types of methods and corresponding packaged articles ma
Baumung Joachim
Chanak Michelle M.
McKay Kevin W.
Remmers Peter
Wittkopf Thomas
H.B. Fuller Licensing & Financing Inc.
Johnson Allison A.
Rada Rinaldi I.
Su Bin
Tawfik Sameh
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