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
1997-09-04
2002-02-05
Teskin, Fred (Department: 1713)
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...
C524S274000, C524S296000, C524S553000, C524S577000, C156S334000, C526S347000
Reexamination Certificate
active
06344515
ABSTRACT:
The subject invention pertains to olefin-based compositions. In particular, the subject invention pertains to compositions comprising at least one substantially random interpolymer of at least one &agr;-olefin and a vinylidene aromatic monomer or a hindered aliphatic vinylidene monomer, preferably at least one substantially random interpolymer of ethylene, optionally at least one &agr;-olefin and a vinylidene aromatic monomer, in conjunction with at least one tackifier, and optionally at least one extending or modifying composition or processing aid.
Substantially random interpolymers of at least one &agr;-olefin and a vinylidene aromatic monomer or a hindered aliphatic vinylidene monomer, including materials such as &agr;-olefin/vinyl aromatic monomer interpolymers, are known in the art and offer a range of material structures and properties which makes them useful for varied applications, such as compatibilizers for blends of polyethylene and polystyrene as described in U.S. Pat. No. 5,460,818.
One particular aspect described by D'Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 [1995]) is that such interpolymers can show good elastic properties and energy dissipation characteristics. In another aspect, selected interpolymers can find utility in adhesive systems, as illustrated in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd.
Although of utility in their own right, the industry seeks to improve the applicability of these substantially random interpolymers. For example, it may be desirable in certain instances to manipulate the glass transition temperature of the substantially random interpolymer, and thus allow materials based on substantially random interpolymers to find application, for example, in molded articles and as sealants and adhesives.
The glass transition temperature of a polymer is one of the major physical parameters that determines its mechanical properties. Below the glass transition temperature, polymers are commonly stiff load bearing rigid plastics. Above the glass transition temperature, materials exhibit more rubbery behavior. When the glass transition temperature is in the range of room temperature, the properties observed for the polymer may change depending on the ambient conditions. It is therefore advantageous to be able to control the glass transition temperature of a polymer to achieve the desired property profile.
For instance, in the case of substantially random interpolymers which have a glass transition temperature of about −25 to about 25° C., it would be desirable in certain instances to raise the glass transition temperature. For instance, substantially random interpolymers having a glass transition temperature at about ambient temperature are susceptible to detrimental blocking. Further, when the glass transition temperature is about ambient temperature, the product properties will vary, depending on the actual temperature, which leads to an undesired product variance. Further, when the glass transition temperature is at ambient temperature, optimized utility in certain applications, such as in pressure sensitive adhesives, is desired.
One way to control the glass transition temperature of a copolymer is to change the type of comonomer and the amount of it present in the copolymer. For instance, this approach is employed for controlling the glass transition temperature of acrylic copolymers.
An alternative to varying comonomer content is to add to a base material another material having a different glass transition temperature. However, it is known that the addition of a low molecular weight brittle diluent, while it may increase the glass transition temperature, will typically lead to a degradation in mechanical properties, such as tensile strength. It was expected that the addition of the class of materials commonly described as tackifiers to substantially random interpolymers, particularly those interpolymers which are elastomeric, would dilute the polymer network and lead to tensile properties, that is, tensile strength at break and elongation at break, which are less than the substantially random interpolymer alone.
There is a need to provide compositions comprising substantially random interpolymers of at least one &agr;-olefin and at least one vinylidene aromatic or hindered aliphatic monomer which have an increased glass transition temperature over unmodified substantially random interpolymers, particularly which have a glass transition temperature greater than room temperature. There is a need for such a composition which is attained without a corresponding loss in tensile properties. There is a need to provide improved hot melt adhesive formulations comprising substantially random interpolymers of at least one &agr;-olefin and at least one vinylidene aromatic or hindered aliphatic monomer which accords superior performance characteristics to the unmodified polymers, which will further expand the utility of this interesting class of materials.
Hot melt adhesives generally comprise three components: a polymer, a tackifier, and a wax. Each component may comprise a blend of two or more components, that is, the polymer component may comprise a blend of two different polymers. The polymer provides cohesive strength to the adhesive bond. The tackifier provides tack to the adhesive which serves to secure the items to be bonded while the adhesive sets, and reduces the viscosity of the system making the adhesive easier to apply to the substrate. The tackifier may be further used to control the glass transition temperature of the formulation. The wax shortens the open/close times and reduces the viscosity of the system. Hot melt adhesives may further typically comprise oil as a filler and/or to reduce the viscosity of the system.
Hot melt adhesives based on previously used polymers include ethylene vinyl acetate copolymers (EVA), a tactic polypropylene (APP), amorphous polyolefins, low density polyethylene (LDPE), and homogeneous linear ethylene/&agr;-olefin copolymers. Prior art hot melt adhesives typically employed large levels of tackifier to reduce the viscosity of the system to levels which enabled its facile application to the substrate, for instance, to viscosities less than about 5000 centipoise.
Pressure sensitive adhesives are materials which are aggressively and permanently tacky at room temperature at the time of application, and which firmly adhere to a variety of dissimilar surfaces with the application of light pressure, such as pressing with a finger. Despite their aggressive tackiness, pressure sensitive adhesives may be removed from smooth surfaces without leaving significant residue. Pressure sensitive adhesives are widely used in everyday applications, such as masking tape, clear office tape, labels, decals, bandages, decorative and protective sheets (such as shelf and drawer liners), floor tiles, sanitary napkin/incontinence device placement strips, sun control films, and the joining of gaskets to automobile windows.
Historically, pressure sensitive adhesives were based on natural rubber and wood rosins, which were carried by a solvent. Articles bearing such adhesives were manufactured by applying a solution of the adhesive on a suitable backing, and removing the solvent by a devolatilizing process. However, in response to cost increases in solvents and regulatory restrictions regarding emissions, water-based adhesives and solid-form hot melt adhesives (HMA's) have been developed.
Historically, adhesives have been based on one of four types of polymers: elastomers (such as natural rubber, styrene-isoprene-styrene block copolymers, styrene-butadiene-styrene block copolymers, and styrene-butadiene random copolymers); acrylics (such as interpolymers of butyl acrylate, 2-ethyl hexyl acrylate, and methyl methacrylate); hydrocarbons (such as a tactic polypropylene, amorphous polypropylene, poly-1-butene, and low density polyethylene); and ethylene vinyl acetate. More recently, hot melt adhesives based on homogeneous linear and substantially li
Guest Martin
Parikh Deepak R.
Speth David R.
Teskin Fred
The Dow Chemical Company
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