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
2000-02-02
2003-10-07
Szekely, Peter (Department: 1714)
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...
C524S575000, C525S314000, C525S098000
Reexamination Certificate
active
06630531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an adhesive made from a polymodal asymmetric elastomeric block copolymer, more particularly, to such an adhesive for forming high strength bonds to low surface energy surfaces and, even more particularly, to articles made with such adhesives, including adhesive tapes.
BACKGROUND OF THE INVENTION
Block copolymers are known in the art for a variety of applications including for use in removable tape applications wherein the tape is typically removed when it is no longer needed. See, for example, U.S. Pat. Nos. 5,393,787 and 5,296,547, both of which are assigned to the present assignee. Such block copolymers can be formulated into a pressure sensitive adhesive, which may be used to make a variety of different types of tapes including removeable tapes. Specific examples of the various tapes which may be made include masking tapes, packaging tapes, medical tapes and autoclave indicator tapes. Additionally, the pressure sensitive adhesive may be used to make protective sheeting, labels, and facestock.
Articles incorporating a polymer foam core are known. The foam includes a polymer matrix and is characterized by a density that is lower than the density of the polymer matrix itself. Density reduction is achieved in a number of ways, including through creation of gas-filled voids in the matrix (e.g., by means of a blowing agent) or inclusion of polymeric microspheres (e.g., expandable microspheres) or non-polymeric microspheres (e.g., glass microspheres).
SUMMARY OF THE INVENTION
The adhesives of the present invention are particularly useful for forming strong bonds to low surface energy substrates. As used herein, low surface energy substrates are those having a surface energy of less than about 45 dynes per centimeter, more typically less than about 40 dynes per centimeter, and most typically less than about 35 dynes per centimeter.
In one aspect of the invention, a pressure sensitive adhesive is provided that comprises 100 parts by weight of a polymodal asymmetric elastomeric block copolymer and at least one tackifier or tackifying resin in an amount sufficient to raise the calculated Fox T
g
of the rubber phase of the adhesive to greater than 245° K. The amount of tackifier used depends on the resulting T
g
, of the adhesive's rubber phase, that is obtained by the addition of the tackifier. So, more tackifier can be added to obtain the T
g
desired. The adhesive composition may also include 0 to about 50 parts by weight of a crosslinking agent and 0 to about 300 parts by weight of a plasticizer. In general, the difference between a tackifier and a plasticizer is that the addition of a tackifier increases the T
g
of the adhesive's rubber phase while the addition of the plasticizer decreases the T
g
of the adhesive's rubber phase. The polymodal asymmetric elastomeric block copolymer has the formula Q
n
Y and comprises from about 4 to about 40 percent by weight of a polymerized monovinyl aromatic compound and from about 96 to about 60 percent by weight of polymerized conjugated diene. Q represents an individual arm of the block copolymer and has the formula S-B; n represents the number of arms Q in the block copolymer and is a whole number of at least 3; and Y is the residue of a multifunctional coupling agent. S is a nonelastomeric polymer segment endblock of a polymerized monovinyl aromatic homopolymer, there being at least two different molecular weight endblocks in the copolymer, a higher molecular weight endblock and a lower molecular weight endblock. The number average molecular weight of the higher molecular weight endblock (Mn)
H
is in the range of from about 5,000 to about 50,000. The number average molecular weight of the lower molecular weight endblock (Mn)
L
is in the range of from about 1,000 to about 10,000. The ratio (Mn)
H
/(Mn)
L
is at least 1.25. B is an elastomeric polymer segment midblock which connects each arm to the residue of a multifunctional coupling agent (Y) and comprises a polymerized conjugated diene or combination of conjugated dienes.
The adhesive has a rubber phase exhibiting a calculated Fox T
g
of greater than 245° K, and the adhesive forms a high strength bond to low surface energy surfaces. As used herein, low surface energy surfaces or substrates exhibit a surface energy of less than 45 dyne/cm, more typically less than 40 dyne/cm, or more typically less than 35 dyne/cm. Preferably, the rubber phase of the adhesive has a calculated Fox T
g
of at least 250° K and, more preferably, 255° K. In addition, the rubber phase of the adhesive preferably has a calculated Fox T
g
with an upper limit of less than 300° K and, more preferably, an upper limit of 285° K. In general, the ability of the present inventive adhesive to bond to low surface energy surfaces increases as the T
g
of the rubber phase increases. The T
g
of the rubber phase is dependent on the weight fraction (i.e., concentration) and the T
g
of each of the various components of the adhesive, as well as the weight fraction and T
g
of the rubber portion of the copolymer.
The present inventive adhesive can exhibit a 180° peel strength on a low surface energy substrate (e.g., high density polyethylene, or HDPE) of at least about 20 Newtons per decimeter (N/dm), preferably, at least about 60 N/dm, more preferably at least about 80 N/dm, and most preferably at least about 100 N/dm, for example, when the adhesive has a thickness of about 5 mil (125 &mgr;m) and is, for example, in the form of a film (e.g., a transfer tape).
The present adhesive can be used in combination with a backing (e.g., a foam core, a vinyl strip or sheet, etc.) having first and second major surfaces, with the adhesive coated on at least a portion of at least one of the major surfaces. The backing can include a release surface (e.g., for a tape roll). The backing can also be a foam tape core made of the same or a different polymodal asymmetric elastomeric block copolymer, and the adhesive can be in the form of at least one co-extruded layer on the foam tape core. The backing can also be an acrylic foam tape core and the adhesive in the form of at least one co-extruded layer on the foam tape core. The backing can be in the form of a foam, with at least one of its major surfaces being substantially smooth, having an Ra value less than about 75 micrometers, as measured by laser triangulation profilometry, and comprising a plurality of microspheres, at least one and preferably a plurality of which are expandable polymeric microspheres. Typically, this foam is substantially free of broken polymeric microspheres. The present adhesive can also be used in combination with at least one other polymer composition in the form of a plurality of discrete structures bonded to or embedded in the foam.
The present adhesive can exhibit a 90° peel strength on a low surface energy substrate (e.g., HDPE) of at least about 50 N/dm, preferably, at least about 75 N/dm, more preferably at least about 100 N/dm and most preferably at least about 150 N/dm, for example, when the adhesive has a thickness of about 3 mil (75 &mgr;m) to about 5 mil (125 &mgr;m) and is, for example, in the form of an adhesive skin laminated onto, or co-extruded with, an adhesive or non-adhesive foam tape core having a thickness of about 1 mm. In general, the thicker the adhesive, with or without a foam core, the higher the bond strength exhibited by the adhesive, up to a limit, such as the cohesive strength of the foam.
Preferably, the tackifier used in the present adhesive is a low acidic or neutral tackifier. As used herein, a low acidic or neutral tackifier is one with an acid number of about 1 mg KOH/g or less, as tested according to Exxon Chemical Co. analytical method specification AMS 360.25. In addition, the tackifier preferably has a T
g
, as measured by differential scanning calorimeter (DSC), in the range of from about −50° C. to about 200° C. and, more preferably, from about −30° C. to about 150° C. The T
g
of the adhesive's rubber phase is dependent, in significa
Gehlsen Mark D.
Khandpur Ashish K.
Ma Jingjing
Momchilovich Bradley S.
Stradinger John J.
3M Innovative Properties Company
Lown Jean A.
Szekely Peter
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