Adhesive composition containing a block copolymer composition and polyphenylene oxide resin and products thereof

A pressure sensitive adhesive composition comprising (a) a block copolymer composition comprising (i) a first component having a configuration of A-B, and (ii) a second component having a configuration of A-B-(B-A).sub.n where n ranges from 1 to 20, wherein A is an alkenyl aromatic or arene hydrocarbon polymer and B is polybutadiene, and wherein the first component is present in an amount ranging from about 40 weight % to about 95 weight % based on a total weight of the block copolymer composition; (b) a polyphenylene oxide resin; and (c) a tackifier resin compatible with B.

FIELD OF THE INVENTION
 This invention relates to a pressure sensitive adhesive composition
 comprising a block copolymer composition with a particular diblock content
 in combination with a polyphenylene oxide resin, and a tackifier. The
 adhesive composition achieves a peel adhesion at room temperature along
 with a static shear performance at elevated temperatures that are
 particularly suited for applications involving low surface energy
 substrates and can be formulated as a tape or an attachment system for use
 in products such as mechanical fasteners.
 BACKGROUND OF THE INVENTION
 There exists a need in industry to improve the adhesion and elevated
 temperature performance of products (e.g., specialty tapes, hook and loop
 mechanical fasteners, and self-mating mechanical fasteners) to low surface
 energy (LSE) substrates. "Low surface energy substrate" refers to
 materials that generally have a surface energy of less than about 45
 mJ/m.sup.2, typically less than 40 mJ/m.sup.2, or more typically less than
 35 mJ/m.sup.2. Examples of LSE substrates include some powder coatings and
 polyolefin polymers such as polypropylene (PP), low density polyethylene
 (LDPE), high density polyethylene (HDPE), and ultrahigh molecular weight
 polyethylene (UHMWPE). The relative low cost, improved properties, and
 increased usage of these polyolefin polymers has increased this need. The
 general rule for adhesives is that there is a tradeoff between peel
 adhesion and static shear performance. It is especially difficult to
 achieve the combination of high peel adhesion at room temperature and high
 static shear performance at elevated temperature. Designing a pressure
 sensitive adhesive (PSA) to have adhesion to LSE substrates has always
 been a challenge. Significant development efforts have concentrated on
 this problem. The challenge has been to develop products and/or systems
 which have high, consistent, and immediate adhesion to LSE substrates and
 have high temperature (.gtoreq.70.degree. C. (158.degree. F.)) static
 shear performance.
 Acrylic adhesives can be formulated to have high temperature static shear
 performance, but generally have poor peel adhesion to LSE substrates.
 Tackified acrylic adhesives, in particular non-polar acrylates, such as
 those described in U.S. Pat. No. 5,638,798 (Bennett et al.), have good
 adhesion to some LSE substrates. However, these adhesives do not typically
 exhibit desired elevated temperature static shear performance, have
 difficulty adhering to HDPE, and have a noticeable acrylate odor.
 Block copolymer adhesives can be designed to have good adhesion to LSE
 substrates and have low odor, such as those described in U.S. Pat. No.
 5,453,319 (Gobran), but generally block copolymer adhesives have poor
 elevated temperature static shear performance. The general rule for
 adhesives stated above also applies to block copolymer adhesives, i.e.,
 the higher the peel adhesion at room temperature, the lower the static
 shear performance at elevated temperatures.
 U.S. Pat. No. 5,028,646 (Miller et al.) describes block copolymer pressure
 sensitive adhesive containing tackifier resins and preferably 2-20% by
 weight of an aromatic, essentially hydrocarbon, end block reinforcing
 resin, which generally has a glass transition temperature (Tg) higher than
 the service temperature of the adhesive, for refastenable diaper tape
 applications.
 The addition of PPO to block copolymer adhesives to improve the temperature
 performance is known. For example, U.S. Pat. Nos. 4,104,323 (Hansen) and
 4,141,876 (Hansen) disclose the addition of polyphenylene ether (also
 known as polyphenylene oxide ("PPO")) resin, having a viscosity average
 molecular weight (M.sub.vis) of between about 6,000 and 25,000 Daltons
 (Da) and a glass transition temperature of between 170.degree. C. and
 200.degree. C., to a block copolymer PSA to provide hot melt adhesive
 compositions and adhesive tapes having improved service temperature
 performance. However, these patents do not mention adhesion to low surface
 energy substrates.
 WO 90/14396 (Audett) describes pressure sensitive and hot melt adhesive
 compositions having improved shear adhesion failure temperatures (SAFT)
 comprising a block copolymer having at least two monoalkenyl arene polymer
 endblocks (A) and at least one elastomeric conjugated-diene mid-block (B),
 said blocks (A) comprising 8-55% by weight of the block copolymer, about
 50-200 phr mid-block tackifying resin, and 5-50 phr low molecular weight
 PPO polymer. The molecular weight (M.sub.vis) of the PPO polymer is from
 about 1,000 to about 5,000 Da and the Tg is from about 100.degree. C. to
 165.degree. C., preferably between 140 and 163.degree. C. This application
 also generically describes a tape construction utilizing the adhesive
 composition. Utility of the adhesive for bonding LSE substrates is not
 specifically mentioned, but T-peel adhesion at room temperature of
 polyethylene (PE) to itself with the adhesive is reported as 0.0175 kN/m
 (0.1 lb/inch).
 WO 90/14397 (Audett) describes improved shear adhesion failure temperatures
 (SAFT) adhesive compositions containing low molecular weight PPO similar
 to that of
 WO 90/14396. This application also generically describes tape constructions
 utilizing these adhesive compositions and substrates coated with these
 adhesive compositions. T-peel adhesion of 0.0175 kN/m (0.1 lb/in) for PE
 to PE is exemplified for one adhesive formulation.
 WO 97/11997 (Chu) describes use of a polyphenylene oxide delivery system
 for increasing an upper service temperature of an A-B-A block copolymer
 adhesive composition. The delivery system comprises a preblend of about 5
 to 45 parts by weight of a PPO resin having a Tg with the range of from
 about 150 to about 210.degree. C. and from about 1 to 450 parts by weight
 of a B-block (i.e., mid block) compatible resin. This application also
 describes an adhesive formulation produced with the PPO/resin delivery
 system. The amount of PPO resin incorporated into the block copolymer
 adhesive ranges from about 6 to 30% by weight of the total elastomer
 weight in the formulation. This application also generically describes a
 tape construction utilizing this adhesive composition. Adhesion to LSE
 substrates is not mentioned.
 U.S. Pat. No. 5,412,032 (Hansen) describes linear styrene-isoprene-styrene
 block copolymers with an overall molecular weight of above 280,000 up to
 520,000 with lower coupling efficiencies to produce adhesive compositions
 which adhere strongly to difficult to adhere substances such as skin or
 polyolefins, for example, polyethylene.
 It is also known that the use of block copolymers having an increasing
 diblock content in PSA formulations can improve tack and peel adhesion but
 generally at the expense of shear performance.
 There still exists a need for improved adhesive compositions that bond to
 LSE substrates having high room temperature peel adhesion and high
 temperature static shear performance.
 SUMMARY OF THE INVENTION
 The pressure sensitive adhesive composition of the present invention,
 comprising a block copolymer composition with a diblock content ranging
 from about 40 weight % to about 95 weight %, based on the total weight of
 the block copolymer composition, in conjunction with PPO, gives rise to an
 unexpected combination of peel adhesion performance to LSE substrates and
 static shear performance at elevated temperatures.
 In one embodiment, the present invention relates to a pressure sensitive
 adhesive composition comprising (a) a block copolymer composition
 comprising (i) a first component having a configuration of A-B, and (ii) a
 second component having a configuration of A-B-(B-A).sub.n where n ranges
 from 1 to 20, wherein A is an alkenyl aromatic or arene hydrocarbon
 polymer and B is polybutadiene, and wherein the first component is present
 in an amount ranging from about 40 weight % to about 95 weight % based on
 a total weight of the block copolymer composition; (b) a polyphenylene
 oxide resin; and (c) a tackifier resin compatible with B.
 The present invention also relates to a pressure sensitive adhesive
 composition comprising (a) a block copolymer composition comprising (i) a
 first component having a configuration of A-B, and (ii) a second component
 having a configuration of A-B-(B-A).sub.n where n ranges from 1 to 20,
 wherein A is an alkenyl aromatic or arene hydrocarbon polymer and B is
 polyisoprene, and wherein the first component is present in an amount
 ranging from about 40 weight % to about 95 weight % based on a total
 weight of the block copolymer composition; (b) a polyphenylene oxide
 resin; and (c) a petroleum derived hydrocarbon tackifier resin compatible
 with B.
 The pressure sensitive adhesive composition of the present invention can be
 used to form a tape. In addition, an article can be produced bearing the
 composition of the present invention. The invention also relates to a
 method for bonding a substrate using a composition of the present
 invention.
 DETAILED DESCRIPTION OF THE INVENTION
 The adhesive composition of the present invention comprises the components
 of a block copolymer composition, a polyphenylene oxide resin, and a
 tackifier. These components and the composition will be described in more
 detail below.
 Block Copolymer Composition
 Suitable block copolymer compositions of the present invention comprise a
 diblock component, i.e., a component having a block A and a block B,
 having a configuration of A-B, and a component having at least two polymer
 end blocks A and at least one polymer midblock B, that has a configuration
 of A-B-(B-A).sub.n where n ranges from 1 to 20, preferably 1 to 3. Thus,
 the block copolymer composition of the present invention may include
 copolymers having a variety of geometric structures and can be linear,
 radial or branched.
 Block A is typically an alkenyl aromatic or arene hydrocarbon polymer block
 having a weight average molecular weight of between about 2,000 and about
 50,000 Da, preferably 9,000 to 35,000 Da. Block A may also contain minor
 proportions of other monomers such as conjugated dienes. Examples, for the
 purpose of the present invention, include styrene, its homologs and its
 analogs, such as alpha-methyl styrene, t-butyl styrene, 3-methylstyrene,
 4-n-propylstyrene, 4-p-propylstyrene, 1-vinylnaphthalene,
 2-vinylnaphthalene, and mixtures thereof.
 Block B is typically an elastomeric polymer block of a conjugated diene
 having a weight average molecular weight of between about 20,000 and about
 350,000 Da, preferably between 25,000 and 150,000 Da. Exemplary
 non-hydrogenated elastomeric polymer blocks include polybutadiene and
 polyisoprene, and copolymers thereof; and exemplary hydrogenated
 elastomeric polymer blocks include poly-co-ethylene butylene,
 poly-co-ethylene propylene, and copolymers thereof. Minor proportions, for
 example, less than about 10 weight % based on the total weight of block B,
 of other monomers may be included in the B blocks such as arenes or other
 conjugated dienes.
 Block copolymer compositions of the present invention have a diblock
 content ranging from about 40 weight % to about 95 weight %, preferably 45
 weight % to 95 weight %, more preferably 60 weight % to 95 weight %, most
 preferably 75 weight % to 90 weight %, based on the total weight % of the
 block copolymer composition. The desired diblock content may be obtained
 during polymerization by limiting the coupling efficiency or by combining
 one or more block copolymers with known diblock content in amount to
 achieve a block copolymer mixture with the desired diblock content as
 described in U.S. Pat. No. 5,412,032, which is incorporated herein by
 reference.
 The total weight % of block A can vary and is typically 8 to 55 weight %,
 preferably 10 to 30 weight %, based on the total weight % of the block
 copolymer composition, provided that the desired diblock content is
 present in the block copolymer composition.
 Suitable block copolymers include those in which block A and block B
 pairings are polystyrene-polybutadiene, polystyrene-polyisoprene,
 polystyrene-poly-co-ethylene butylene, polystyrene-poly-co-ethylene
 propylene, poly(alpha-methylstyrene)-polybutadiene,
 poly(alpha-methylstyrene)-polyisoprene, or mixtures thereof. Commercially
 available examples that have a diblock content either within the range of
 the present invention or that can be blended to achieve a diblock content
 within the range of the present invention include those available from
 Shell Chemical Company, Houston, Tex., under the trade designations
 "Kraton D1113", "Kraton D1118" and "Kraton D1119", those available from
 Housemex Inc., Houston, Tex., under the trade designations "Solprene
 1205", and those available from Nippon Zeon Company Ltd, Tokyo, Japan,
 under the trade designation "Quintac SL-113".
 Particularly suitable block copolymer compositions include:
 (a) a blend of about 5 to 50 parts of a linear styrene butadiene (SB) block
 copolymer with a styrene content ranging from about 20 to 35% and a
 diblock content ranging from 0 to 20% with 50 to 95 parts of a linear
 styrene butadiene (SB) block copolymer with a styrene content ranging from
 about 20 to 35% and a diblock content ranging from 80 to 100%,
 (b) a blend of about 34 to 75 parts of a linear styrene butadiene (SB)
 block copolymer with a styrene content ranging from about 20 to 35% and a
 diblock content ranging from 60 to 85% with 25 to 66 parts of a linear
 styrene butadiene (SB) block copolymer with a styrene content ranging from
 about 20 to 35% and a diblock content ranging from 80 to 100%, and
 (c) a blend of about 50 to 75 parts of a linear styrene butadiene (SB)
 block copolymer with a styrene content ranging from about 20 to 35% and a
 diblock content ranging from 60 to 90% with 25 to 50 parts of a linear
 styrene butadiene (SB) block copolymer with a styrene content ranging from
 about 20 to 35% and a diblock content ranging from 80 to 100%.
 The block copolymers of the present invention can be prepared by any known
 suitable methods. Exemplary methods of preparation are disclosed in, for
 example, U.S. Pat. Nos. 5,453,319. Notably, the structure of the block
 copolymer is determined by the methods of polymerization.
 The block copolymer composition of the present invention is typically
 present in the pressure sensitive adhesive composition in an amount
 ranging from about 25 to about 65 weight %, preferably 35 to 50 weight %,
 based on the total weight of the adhesive composition.
 Polyphenylene Oxide Resin
 A polyphenylene oxide resin useful in the present invention are those with
 the following repeating unit:
 ##STR1##
 wherein the oxygen ether atom of one unit is connected to the benzene
 nucleus of the next adjoining unit, n designates repeating units and each
 X is independently a monovalent substituent selected from the group
 consisting of hydrogen, halogen, hydrocarbon radicals, halohydrogen
 radicals having at least two carbon atoms between the halogen atom and the
 phenyl nucleus, hydrocarbonoxy radicals, and halohydrocarbonoxy radicals
 having at least two carbon atoms between the halogen atoms and phenyl
 nucleus. Preferred polyphenylene oxide resins are those where X is methyl.
 Useful polyphenylene oxide resins have a glass transition temperatures (Tg)
 and a molecular weight selected to be compatible with the block copolymer
 composition used, as described in Himes et al. "Achieving High Service
 Temperatures With Thermoplastic Elastomers" 1996 Hot Melt Symposium, pages
 71-98, which is herein incorporated by reference. Typically the
 polyphenylene oxide resins have a Tg of between about 110 to 210.degree.
 C., preferably 140 to 170.degree. C., more preferably 140 to 165.degree.
 C., as determined by differential scanning calorimetry and a weight
 average molecular weight (Mw) ranging from about 1,000 to about 25,000 Da,
 preferably 2,000 to 10,000 Da, more preferably 4,000 to 8,000 Da.
 Polyphenylene oxide resin can be prepared as described in U.S. Pat. Nos.
 3,306,874 (Hay); 3,306,875 (Hay); 3,257,357 (Stamatoff); and 3,257,358
 (Stamatoff).
 A polyphenylene oxide resin is typically present in the adhesive
 composition of the present invention in an amount ranging from about 10 to
 about 200 parts, based on 100 parts by weight of block A in the block
 copolymer composition.
 Tackifier Resin
 A tackifier resin is added as a component to the adhesive composition of
 the present invention and shall mean a material which is miscible with
 block B and has a number average molecular weight (Mn) of 10,000 Da or
 less and a glass transition temperature (Tg) of -30.degree. C. or more as
 measured by differential scanning calorimetry.
 Tackifiers useful in the present invention include rosin and rosin
 derivatives, hydrocarbon tackifier resins, aromatic hydrocarbon resins,
 aliphatic hydrocarbon resins, terpene resins, etc. Commercially available
 examples include alpha-pinene resins, available from Hercules Inc.,
 Wilmington, Del. under the trade designation "Piccolyte A135" or
 "Piccolyte A115" or available from Arizona Chemical Division,
 International Paper, Panama City, Fla. under the trade designation
 "Zonarez A25"; beta-pinene resins, available from Hercules Inc.,
 Wilmington, Del. under the trade designation "Piccolyte S135" or
 "Piccolyte S115"; or petroleum derived hydrocarbon resin, available from
 Goodyear Tire & Rubber Co., Chemical Div, Akron Ohio under the trade
 designation "Wingtack Plus".
 Typically, the tackifier resin is present in the adhesive composition in
 amounts ranging from about 20 to about 80 weight %, preferably 40 to 60
 weight %, based on the total weight % of the adhesive composition.
 Adhesive Composition
 The adhesive composition of the present invention is a pressure sensitive
 adhesive which is defined as an adhesive composition that satisfies the
 Dahlquist criteria, i.e., a one second creep compliance greater than
 1.times.10.sup.-6 cm.sup.2 /dyne, at the intended application temperature,
 as defined in Handbook of Pressure Sensitive Adhesive Technology, p. 172,
 D. Satas (ed.), Van Nostrand, N.Y., (1989). Typically, a pressure
 sensitive adhesive is normally tacky at room temperature and adheres to a
 surface upon contact to the surface without the need for more than finger
 or hand pressure.
 The adhesive composition may also include additives such as fillers,
 stabilizers, antioxidants, and pigments for the conventional purpose of
 these additives.
 End block associating resins such as aromatic hydrocarbon resins, for
 example, "Endex 160" commercially available from Hercules Inc.,
 Wilmington, Del., may also be added. Typical amounts of end block
 associating resin range from 0 to 200 parts per 100 parts by weight of
 block A of the block copolymer composition. The amount of PPO may be
 adjusted based on the amount of end block associating resin used.
 An oil may also be added as a component of the adhesive composition of the
 present invention. This oil may serve to modify the viscosity of the
 adhesive composition and increase the tackiness of the composition.
 Typically, the oil is added in an amount ranging from about 0 to about 35
 weight %, based on the total weight of the adhesive composition. Suitable
 oils, typically referred to as paraffinic/naphthenic oils, are usually
 fractions of refined petroleum products and have less than about 30% by
 weight aromatic components as measured by clay-gel analysis. Commercially
 available oils include those from Shell Chemical Company, Houston, Tex.,
 under the trade designation "Shellflex 371N" and "Shellflex 6371".
 A particularly suitable adhesive composition of the present invention
 comprises a blend of about 5 to 50 parts by weight of a linear styrene
 butadiene (SB) block copolymer with a styrene content ranging from about
 20 to 35% and a diblock content ranging from 0 to 20% with 50 to 95 parts
 by weight of a linear styrene butadiene (SB) block copolymer with a
 styrene content ranging from about 20 to 35% and a diblock content ranging
 from 80 to 100%, and alpha-pinene tackifier resin with a softening point
 greater than 110.degree. C., a napthenic oil, and a polyphenylene oxide
 resin. In this composition, the amount of tackifier resin may range from
 75 to 150 parts by weight, the amount of oil may range from 0 to 50 parts
 by weight, and the amount of polyphenylene oxide resin may range from 2 to
 40 parts by weight.
 Another particularly suitable adhesive composition of the present invention
 comprises either a blend of about 34 to 75 parts of a linear styrene
 butadiene (SB) block copolymer with a styrene content ranging from about
 20 to 35% and a diblock content ranging from 60 to 85% with 25 to 66 parts
 of a linear styrene butadiene (SB) block copolymer with a styrene content
 ranging from about 20 to 35% and a diblock content ranging from 80 to
 100%, or a blend of about 50 to 75 parts of a linear styrene butadiene
 (SB) block copolymer with a styrene content ranging from about 20 to 35%
 and a diblock content ranging from 60 to 90% with 25 to 50 parts of a
 linear styrene butadiene (SB) block copolymer with a styrene content
 ranging from about 20 to 35% and a diblock content ranging from 80 to 100%
 and alpha-pinene tackifier resin with a softening point greater than
 110.degree. C., a napthenic oil, and a polyphenylene oxide resin. In this
 composition, the amount of tackifier resin may range from 75 to 150 parts,
 the amount of oil may range from 0 to 60 parts, and the amount of
 polyphenylene oxide resin may range from 2 to 40 parts.
 The pressure sensitive adhesive composition of the present invention may be
 hot melt compounded and coated. In this method, the components of the
 adhesive composition are melt-blended in a mixer such as a twin screw
 extruder. The polyphenylene oxide resin may be added as a premix with the
 tackifier resin or an oil or an end block associating resin, if present.
 The preblending can be carried out as described in WO 97/11997 or U.S.
 Pat. No. 4,104,323.
 Alternatively, the adhesive compositions may be prepared by dissolving the
 components of the adhesive composition in a solvent such as toluene and
 casting over a substrate such as a polyester film or release liner.
 When the adhesive composition comprises a block copolymer where block B is
 hydrogenated, the composite midblock glass transition temperature (CMTg)
 of the adhesive composition is greater than 245 Kelvin (K), as calculated
 using the Fox Equation by measuring the Tg of block B and the Tg of all
 midblock compatible components such as the midblock compatible tackifier
 resin and oil using differential scanning calorimetry.
 The Fox Equation is:
 ##EQU1##
 wherein w.sub.i is the weight fraction of component i and T.sub.gi is the
 glass transition temperature of component i and the summation is take over
 the components which are miscible with block B and the block B itself.
 The adhesive composition preferably achieves a 70.degree. C. (158.degree.
 F.) static shear performance of holding 250 grams for 10,000 minutes or
 greater, or 1,000 grams for 1,000 minutes or greater, per 6.45 square
 centimeters (one square inch) load where the adhesive composition is
 coated at a thickness of 0.1 mm and tested according to the Static Shear
 Strength test method.
 The adhesive composition of the invention can be coated onto a substrate.
 Examples of suitable substrates include release liners (e.g., silicone
 release liners) and tape backings (which may be primed or unprimed paper,
 metal, or plastic).
 Where multi-layer tape constructions are desirable, one method of
 construction is multi-layer coating using conventional techniques. For
 example, the coating may be applied concurrently (e.g., through a die
 coater). The coatings may also be applied sequentially.
 The adhesive composition of the invention can also be made as a tape
 construction which comprises a layer of adhesive composition evenly coated
 between two liners at least one of which is coated with a release
 material. A transfer tape can be made by coating the adhesive composition
 between two liners both of which are coated with a release coating.
 The adhesive compositions of the invention can also be coated onto a
 differential release liner, i.e., a release liner having a first release
 coating coated on one side of the liner and a second release coating
 coated on the opposite side of the liner.
 When a transfer tape is made, one of the liners of the transfer tape can be
 removed and the exposed adhesive surface can be laminated to another
 substrate such as a backing. The remaining release liner aids in
 transferring the adhesive to the substrate. The substrate can be of any of
 the typical substrates used for tapes such as those selected from the
 group consisting of polymeric films (e.g., polyester, polypropylene,
 polyurethane) metal foils, glass cloth, paper, cloth, nonwoven materials,
 foam sheets, and the like. Foam sheets are known in the industry and
 include open and closed cell foams made from polyethylene, polyurethane,
 acrylates, polystyrene, neoprene, silicone, and the like.
 Other tape constructions in which the pressure sensitive adhesives
 according to the invention are useful include mechanical fasteners such as
 a fastener available under the trade designation "Dual-Lock" from
 Minnesota Mining and Manufacturing Co. (3M), St. Paul, Minn., and a
 fastener available under the trade designation "Scotchmate" from Minnesota
 Mining and Manufacturing Co. (3M), St. Paul, Minn. The pressure sensitive
 adhesives are also useful in vibration damping applications. Further, the
 pressure sensitive adhesives can be used as a tape attachment system for
 gaskets or molded parts such as bumpers or cushioning products.
 The adhesive composition of the present invention may also be used in a
 method of bonding a substrate, for example, a polyolefin substrate, where
 the method comprises providing the substrate, and applying the adhesive
 composition of the present invention to the substrate using methods and
 techniques well understood by one skilled in the art. Another substrate
 can then be contacted to the adhesive composition. In the instance where
 the substrate is a polyolefin, the substrate may be unmodified. The term
 "unmodified" means that the substrate has not been subjected to any
 chemical or physical treatment.