Blended adhesives and articles incorporating the same

Details Blended adhesives and articles incorporating the same Blended adhesives and articles incorporating the same

1997-11-14

2001-03-06

Davis, Jenna (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S3550BL

Reexamination Certificate

active

06197419

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to pressure-sensitive adhesives and sheet material, including tapes and the like, coated therewith.
Three properties which are useful in characterizing the nature of pressure-sensitive adhesives are tack, peel strength, and shear strength. The first measures the ability of the adhesive to adhere quickly, the second its ability to resist removal by peeling back on itself from a surface, and the third its ability to hold in position when shearing forces are exerted. Generally speaking, the first two are directly related to each other but are inversely related to the third, cf, e.g., Sanderson U.S. Pat. No. 4,077,926, Column 1, lines 31-36. For example, although a given adhesive may exhibit high tack and high peel strength, the shear strength may be unacceptable for the intended purpose. Conversely, while an adhesive may exhibit high shear strength, the tack and peel adhesion may be unacceptable for the intended purpose. These shortcomings are often exacerbated at extremes of high and low temperature.
Modern industry presents a number of situations where pressure-sensitive adhesive products having balanced properties (i.e., excellent tack, peel strength, and shear strength) would be highly desirable. Some examples of these situations include installation of adhesive-coated substrates, e.g. tapes, at low temperatures. In these same situations, it is often necessary to have high peel strength at high temperatures.
Over the past several years rising energy costs have prompted occupants of buildings to conserve energy by means of insulation. The installation of, for example, shrinkable film or shrinkable/stretchable film over windows by means of double-stick tape (tape bearing a layer of adhesive on both major surfaces thereof) adhered to the interior window frame and to the film is known to exert a constant force at the film-adhesive interface and provide a degree of insulation. Generally, the film is located between the window pane and the interior of the building. Under normal room temperature conditions, the adhesive has physical properties which allow it to maintain a bond to the film and the interior window frame. However, window insulation may also be accomplished by adhering a film to the exterior window frame. There are many reasons for installing insulating film on the exterior part of the window. Some users may not want tape on their interior walls or interior window frames, they may want ready access to their windows, or they may have ornate window sills or frames which would hinder installation of the film on the inside. If the film is installed outdoors, the adhesive will be subjected to high temperatures during summer months and low temperatures during winter months. Of particular concern is the fact that, at elevated temperatures, the peel strength and shear strength of conventional pressure-sensitive adhesives is greatly reduced. At the same time the film is exerting shrink tensions as high as 510
pounds/in2
causing the bond to fail and the film to pull away from the exterior window frame. At reduced temperatures conventional pressure-sensitive adhesives have greatly reduced tack properties, making it difficult to create an adhesive bond with the film or window frame. The adhesive will be exposed to ultraviolet radiation, in addition to temperature fluctuations, that may also cause reduced tack properties.
Rubber based adhesives, which are normally used for installation of shrinkable film currently commercially available, exhibit poor weathering characteristics, loss of tack at low temperatures, e.g. 0° C., and loss of shear at high temperature, e.g. 60° C.
Thus, there is a need for pressure-sensitive adhesives which have balanced adhesive properties over a wide temperature range, good resistance to ultraviolet radiation, good adhesion to plastic films which for the most part have low energy surfaces and which can be prepared easily and economically on conventional equipment.
SUMMARY OF THE INVENTION
Pressure-sensitive adhesives require a delicate balance of viscous and elastic properties that result in a four-fold balance of adhesion, cohesion, stretchiness, and elasticity. This balance is further compounded when the end-use of the pressure-sensitive adhesive is considered. For example, the cohesion and elasticity are typically considerations when it is desired that the pressure-sensitive adhesive is to be useful over a wide temperature and be stable upon exposure to ultraviolet radiation (UV). Accordingly, the present invention involves adhesive articles including adhesive compositions that are useful over a wide temperature range and have improved UV resistance. Preferably, an adhesive composition is a pressure-sensitive adhesive that exhibits adhesion to low energy surfaces, such as a surface of films made from polyolefins (e.g., polyethylene).
In one aspect of the invention, an adhesive article includes a backing having a first major surface and a second major surface; an adhesive composition on at least the first major surface of the substrate, wherein the adhesive composition includes a styrene block copolymer blend containing styrene-isoprene-styrene (SIS) and styrene-(ethylene-butylene)-styrene (SEBS); and a tackifier component containing a hydrogenated hydrocarbon resin. In accordance with the invention, the adhesive exhibits ultraviolet radiation resistance and has a midpoint glass transition temperature of about −5° C. to about −30° C. at a frequency of about 1.0 Hz.
In another aspect of the invention, an adhesive article includes a backing having a first major surface and a second major surface; an adhesive composition on at least the first major surface of the substrate, wherein the adhesive composition includes a pressure-sensitive adhesive component comprising a natural rubber, a synthetic rubber, a styrene block copolymer, a polyvinyl ether, an acrylate, a poly-&agr;-olefin, a silicone, or mixtures thereof; and a tackifier component comprising a hydrogenated hydrocarbon resin, wherein the adhesive composition exhibits ultraviolet radiation resistance and has a midpoint glass transition temperature of about −5° C. to about −30° C. at a frequency of about 1.0 Hz.
In a further aspect of the invention, an adhesive article is provided having two surfaces formed from two simultaneously melt processed normally tacky pressure-sensitive adhesive compositions. Preferably, at least one of the simultaneously melt processed normally tacky pressure-sensitive adhesives includes a styrene block copolymer blend comprising styrene-isoprene-styrene and styrene-(ethylene-butylene)-styrene; and a tackifier component containing a hydrogenated hydrocarbon resin, wherein the adhesive composition exhibits ultraviolet radiation resistance and has a midpoint glass transition temperature of about −5° C. to about −30° C. at a frequency of about 1.0 Hz.
A method for making an adhesive article is also provided that involves providing at least two molten streams comprising a first and a second pressure-sensitive adhesive composition. Preferably, at least one of the pressure-sensitive adhesive compositions includes a styrene block copolymer blend including styrene-isoprene-styrene and styrene-(ethylene-butylene)-styrene; and a tackifier component containing a hydrogenated hydrocarbon resin, wherein the adhesive composition exhibits ultraviolet radiation resistance and has a midpoint glass transition temperature of about −5° C. to about −30° C. at a frequency of about 1.0 Hz. In addition, a third molten stream including a non-pressure-sensitive adhesive polymeric composition is also provided in the method.
The method further includes combining the three molten streams into a single molten extrudate having the third molten stream between the at least two molten streams of a first and a second pressure-sensitive adhesive composition and depositing the single molten extrudate onto a solid substrate so that a first surface of the first pressure-sensitive adhesive contacts a surface of the

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