Stock material or miscellaneous articles – Layer or component removable to expose adhesive
Reexamination Certificate
2002-06-25
2004-06-29
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Layer or component removable to expose adhesive
C428S040200, C428S041300, C428S041500, C428S041900, C428S042100, C428S212000, C428S220000
Reexamination Certificate
active
06756098
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pressure sensitive adhesive compositions. In particular, the invention discloses fiber reinforced pressure sensitive adhesives and methods for their preparation and use.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives are generally characterized by their properties. Pressure sensitive adhesives are well known to one of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence to a substrate with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Many pressure sensitive adhesives must satisfy these properties under an array of different stress rate conditions. Additives may be included in the pressure sensitive adhesive to optimize the characteristics of the pressure sensitive adhesive.
In particular systems, the additive improves the cohesive strength of the pressure sensitive adhesives, yet the tack is reduced. For example, a non-tacky additive may be mixed with a pressure sensitive adhesive, reducing the tack of the mixture (as compared to the tack of the pressure sensitive adhesive without the additive). In a specific example, thermoplastic polymers have been added to styrene block copolymer adhesives to reduce the tack of the resulting pressure sensitive adhesives. However, to avoid loss of tack when enhancing the pressure sensitive adhesive's cohesive strength, care must be taken in choosing an additive.
U.S. Pat. No. 6,063,838 discloses a pressure sensitive adhesive comprising a blend of at least two components, wherein the first component is at least one pressure sensitive adhesive and the second component is at least one thermoplastic material, wherein the components form a blended composition having more than one domain and, wherein one domain is substantially continuous (generally, the pressure sensitive adhesive) and the other domain is substantially fibrillous to schistose (generally, the thermoplastic material). The blended pressure sensitive adhesives of the U.S. Pat. No. 6,063,838 patent provide adhesives having one or more of the following properties including: (1) a peel adhesion greater than and shear strength similar to that of the pressure sensitive adhesive component if used alone, (2) a shear strength greater than and peel adhesion similar to that of the pressure sensitive adhesive component if used alone, (3) an anisotropic peel adhesion, (4) an anisotropic shear strength, (5) a tensile stress in the down-web direction that is at least two times greater than the tensile stress in the cross-web direction for all elongations up to the break elongation, and (6) a resistance to impact shear that is at least two times greater than that of the pressure sensitive adhesive component if used alone.
What is desired is an adhesive composition that has improved cohesive strength without losing the tackiness indicative of a pressure sensitive adhesive. In conjunction, it is desirable to create an adhesive composition that is removable from a substrate with ease without losing the tackiness indicative of a pressure sensitive adhesive. Additionally, a stretch removable adhesive composition is desirable.
SUMMARY OF THE INVENTION
This invention is directed to a fiber reinforced adhesive composition comprising a pressure sensitive adhesive matrix and a fibrous reinforcing material within the pressure sensitive adhesive matrix. The fiber reinforced adhesive composition of the invention allows for an improved cohesive strength over the pressure sensitive adhesive alone, yet the tack of the pressure sensitive adhesive remains substantially unreduced.
The adhesive composition has a yield strength and a tensile strength. In one embodiment, the tensile strength is about 0.7 MPa or greater. In another embodiment, the tensile strength is at least about 150% of the yield strength when tested according to ASTM D 882-97 at a crosshead speed of 12 inches/minute (30 centimeters/minute). In one embodiment, the adhesive composition exhibits at least 50% elongation when measured according to ASTM D 882-97 at a crosshead speed of 12 inches/minute (30 centimeters/minute). In certain embodiments, the fibrous reinforcing material comprises substantially continuous fibers within the pressure sensitive adhesive matrix. Additionally, in preferred embodiments, the fiber reinforced adhesive composition will display stretch removable characteristics and easy removal from a substrate.
In addition, the invention is directed to a method for making a fiber reinforced adhesive. The method comprises forming a mixture comprising a pressure sensitive adhesive with a reinforcing material capable of forming fibers when subjected to an elongating shear force, and subjecting the mixture to the elongating shear force.
In this application, the following terms are defined as follows, unless otherwise stated:
“Stretch removable” means that a pressure sensitive adhesive, when pulled and elongated (preferably from a substrate surface at a rate of 30 centimeters/minute and at an angle of no greater than 45°), detaches from a substrate surface without significant damage to the substrate surface (e.g. tearing), and without leaving a significant residue, preferably that which is visible to the unaided human eye on the substrate.
“Substantially continuous” means that for an at least 0.5 centimeter length sample of the adhesive composition taken in the machine direction, at least 50% of the fibers present in the sample are continuous (i.e. unbroken).
“Tensile strength” is the maximum tensile strength at break when tested according to ASTM D 882-97 at a crosshead speed of 12 inches/minute (30 centimeters/minute).
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a fiber reinforced adhesive composition comprising a pressure sensitive adhesive matrix and a reinforcing material within the pressure sensitive adhesive matrix. In one embodiment, the fiber reinforced adhesive composition of the present invention has improved cohesive strength, as represented by a higher tensile strength of the fiber reinforced adhesive composition as compared to the pressure sensitive adhesive without the reinforcing material. Additionally, in a preferred embodiment, the adhesive composition is stretch removable. The adhesive composition of the invention has these properties while maintaining substantially unreduced tack properties in many embodiments.
In another embodiment, the adhesive composition has a lower flow, or lower creep, under certain conditions than an adhesive without the reinforcement material. Creep or flow during storing or transport can be very detrimental to adhesive systems. This is particularly true when adhesive systems are delivered in roll, tape or sheet form. The adhesive within a roll of tape or a stack of sheets is subject to pressure from the weight of the layers above it and can flow or creep. This flow or creep can result in adhesive oozing out of the side of the roll or stack making the edge tacky and picking up dirt or other debris or causing adjacent rolls or stacks to stick together. If the liner or low adhesion backsize (LAB) of the roll of tape or stack of sheets has microstructuring, adhesive flow or creep into the microstructuring can result in a build-up in adhesion forces, even to the point that the tape, roll or stack cannot be unwound. The flow of the adhesive under normal conditions typically leads to edge residue, black rings (on skin) and adherand surface feature encapsulation (for example hair on skin). Reinforcement of the adhesive decreases or prevents this flow or creep.
In the present invention, the adhesive composition has a yield strength. In certain embodiments, the yield strength is no less than about 0.1 MPa when measured according to ASTM D 882-97 at a crosshead speed of 12 inches/minute (30 centimeters/minute). In specific embodiments, the yield strength is no less than about 0.2 MPa when measured according to ASTM D 882-97 at a
Everaerts Albert I.
Zhou Zhiming
Ahmad Nasser
Blank Colene H.
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