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...
Utility Patent
1998-06-04
2001-01-02
Acquah, Samuel A. (Department: 1711)
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...
C428S040100, C428S040200, C428S040300, C428S042100, C428S308800, C428S325000, C428S327000, C428S338000, C428S339000, C428S343000, C428S352000, C428S354000, C428S35500R, C428S406000, C428S407000, C428S441000, C428S500000, C521S139000, C521S140000, C524S502000, C524S505000
Utility Patent
active
06169138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to pressure sensitive adhesive foams and in particular to pressure sensitive adhesive foams which are easily compressed and conform to irregular surfaces. The invention further relates to a method of processing these pressure sensitive adhesive foams.
2. Technology Review
Pressure sensitive adhesives (PSA) that can be extruded are well known. Examples of pressure sensitive adhesives include rubbers mixed with the proper tackifying resins, cured acrylics, and interpenetrating polymer networks containing blocked copolymers in a polyurethane network.
These pressure sensitive adhesives (PSA) all suffer from the common limitation of being relatively hard to compress. The pressure sensitive adhesives therefore do not conform easily to irregular surfaces, a property that is vital to ensure 100% wetting and therefore good adhesion.
Generally, a limitation such as this could be overcome by making a composition cellular or foamed. Foams are pliable, conform easily to irregular surfaces and can be produced by either physical (e.g., frothing with nitrogen before the polymeric mass sets) or chemical (incorporation of a porophoric agent such as azodicarbonamide which undergoes a chemical decomposition under heat to produce gaseous bubbles) means. Pressure sensitive adhesive foams produced by either of the above techniques, however, suffer from another limitation. Because of their inherent tack, these pressure sensitive adhesive foams when compressed tend to irreversibly deform due to adherence between opposite sides of the cells in the cellular structure.
Presently, because of this limitation adhesive foams are produced by coating non-adhesive foam substrates with thin layers of pressure sensitive adhesives. These products both conform to irregular surfaces and are pressure sensitive thereby overcoming the limitations of solid pressure sensitive adhesive extrusions and pressure sensitive adhesive foams. These products are, however, relatively complicated to produce and cannot be used for extruded profiles. Furthermore, these products show relatively poor adherence to non-polar plastic surfaces.
The foams of the invention are characterized by superior adherence to non-polar plastic surfaces, compared to the acrylic adhesive coated foams of the art. Unlike the foams of the art, the foams of the invention have acceptable peel test values from difficult to adhere non-polar plastic surfaces, including decorative trim pieces made of polypropylene and used on products such as automotive bodies and other vehicle surfaces, manufactured appliances, and home and office furnishings and equipment.
The foams of this invention are inherently adhesive foam products which reversibly deform upon compression. This invention also describes a process for producing the above inherently adhesive foamed product, preferably utilizing expandable particulate materials, or, in some instances, glass spheres, to prevent interior foam collapse and adhesion.
SUMMARY OF THE INVENTION
The present invention relates to a pressure sensitive adhesive foam with a percentage of theoretical density less than 90 wherein the foam has a peel adhesion of greater than about 1 N/cm and a compression set under constant deflection of less than about 60 percent. The present invention further includes a pressure sensitive adhesive foam comprising a thermoplastic block copolymer; a tackifying resin; an isocyanate; a polymer comprising a backbone of selected from the group consisting of polybutadiene, polyester and polyether, wherein the polymer contains at least 2 active hydrogens capable of reacting with the isocyanate; and expandable particulate materials.
The present invention further includes a pressure sensitive adhesive foam comprising a thermoplastic olefinic polymer or copolymer, having a density less than 0.91 g/cm3 and a torsion modulus less than 18 MPa, and a tackifying resin; expandable particulate materials, or glass microspheres; and, optionally, plasticizing oil.
The invention finally further comprises a method of forming the above foam.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a pressure sensitive adhesive foam having a density that is less than 90% of the theoretical density, wherein the foam has a peel adhesion of greater than about 1 N/cm and a compression set under constant deflection of less than about 60 percent.
The foam has a percentage of theoretical density less than 90, preferably less than about 70 percent, more preferably less than about 50 percent, and most preferably less than about 40 percent. The material from which the foam is made has a density that is the “theoretical density”. The foam formed from this material has a reduced density and the extent of the reduction is indicated by the percentage of the theoretical density represented by the density of the blown foam material.
The foam has a peel adhesion of greater than about 1 N/cm, preferably greater than about 5, more preferably greater than about 10, and most preferably greater than about 20 N/cm. As used herein, “peel adhesion” is the adhesive strength of the foam expressed as the force needed to remove the foam from a prescribed surface as measured by ASTM D903 method.
The meaning of compression set for purposes of this specification is compression set under constant deflection which is the recovery of a foam after a constant deflection. ASTM Standard D 1667-76, paragraphs 21 to 25, which are incorporated herein by reference describes the test method for determining compression set with the following modification. As noted in the Examples 1 and 2, below, certain specimens were compressed to 50% of their original thicknesses, rather than to 25% of their original thicknesses as specified in the test method.
The foam has a compression set of less than about 60 percent, preferably less than about 40 percent, more preferably less than about 20 percent, and most preferably less than about 10 percent.
The foam is produced by first mixing a pressure sensitive adhesive composition with expandable particulate materials. The mixture may be coated onto a substrate (e.g., a release film), or extruded (e.g., with screw extruder or high pressure pump) into a sheet or film through a flat die or into other geometries, such as a round or semi-circle bead, through a rounded die or otherwise formed to a desired shape by molding or other means known in the art for shaping plastic materials. The viscosity of the mixture may be adjusted depending on whether the mixture is coated, extruded or formed into a shape. The mixture can either be heated just prior to, during or after coating, extrusion or forming to a temperature at which substantially all of the expandable particulate material expands. The foam can subsequently be cured if necessary.
When utilizing polyolefinic polymers as the elastomers in the adhesive formulation, the foam may be produced as described above, or it may be foamed by traditional chemical blowing techniques, with or without the addition of glass microspheres or the expandable particulate material, or by physical foaming techniques, with or without the addition of glass microspheres or the expandable particulate material, or by a combination of techniques and materials.
The pressure sensitive adhesives which may be used include adhesives which are compounded to be pressure sensitive by blending an elastomer with tackifying resins, plasticizers and other ingredients, and adhesives which consist of polymers that are inherently pressure sensitive and require little or no compounding. Examples of elastomers which are blended with tackifying resins include natural rubber; and block copolymer adhesives such as for example polystyrene-polybutadiene-polystyrene (SBS), polystyrene-polyisoprene-polystyrene (SIS), polystyrene-poly(ethylene/butylene)-polystyrene (S-EB-S), and polystyrene-poly(ethylene/propylene)-polystyrene (S-EP-S). Examples of inherently adhesive polymers which can be used with or without tackifiers to create foams include acrylics; butyl
Ladang Michel
Petit Dominique
Acquah Samuel A.
Porter Mary E.
Saint-Gobain Performance Plastics Corporation
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