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
2000-06-14
2002-08-13
Szekely, Peter (Department: 1713)
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...
C524S271000, C524S474000, C524S484000, C524S485000, C524S486000, C525S095000, C525S099000, C525S314000, C428S3550BL, C156S327000, C156S334000
Reexamination Certificate
active
06433069
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a removable grade hot melt pressure sensitive adhesive based on a block copolymer having a high level of A-B diblock. The adhesive is characterized as being low in viscosity and exhibits minimal staining of substrates. The adhesive is useful where minimal staining of paper is desired especially in the bookbinding and labeling industries where the aesthetics of printed material is important.
BACKGROUND OF THE INVENTION
Hot melt pressure sensitive adhesives are usually based on a block copolymer such as styrene-ethylene/butylene-styrene, styrene-ethylene/propylene-styrene, styrene-isoprene-styrene and styrene-butadiene-styrene in combination with a tackifying resin and a plasticizing oil. Hot melt pressure sensitive adhesives can be divided into four general categories including permanent, semi-permanent, removable and freezer categories, each category having different adhesive characteristics. Permanent adhesives are designed to permanently adhere one substrate to another and provide either substrate failing or substrate distorting bonds. Semi-permanent adhesives are designed to be repositionable for a short period of time after application of one substrate to another. Freezer grade adhesives are designed to have good adhesion to substrates at temperatures of about −30° C.
Removable hot melt pressure sensitive adhesives are designed to allow separation of substrates at any time after application of one substrate to another without substrate failure or adhesive transfer. These adhesives are generally characterized as having low 180° peel values and high initial tack. These properties are typically achieved through the use of high levels of block copolymers, low levels of tackifying resin and high levels of a plasticizing oil. The block copolymer provides increased flexibility and a smooth, low peel value. The tackifying resin provides high tack, high adhesion and reduces viscosity. The plasticizing oil reduces peel values, viscosity and glass transition temperatures, increases flexibility and decreases the storage modulus.
To assure that the adhesive does not adhere too aggressively to the substrate and therefore assure its removability, it is necessary to utilize low levels of tackifying resin. This means that either the level of block copolymer or the level of oil must be increased. Increasing the concentration of block copolymer results in an increase in viscosity, whereas increasing the concentration of oil results in a product which stains the substrate.
The function of an oil is primarily to reduce the viscosity of the final product, plasticize the block copolymer, therefore increasing tackiness, and also to reduce the adhesive cost. However, the existence of high amounts of oil may result in an adhesive composition which allows some oil to migrate resulting in staining of substrates. The pressure sensitive properties of the adhesive also may deteriorate.
Oil may be replaced with either liquid resins or liquid elastomers but these components also increase viscosities and peel values resulting in products which are not removable. This quality is undesirable for many labeling applications and for skin attachment adhesives. Liquid resins and liquid elastomers are often not as economically attractive as oils as well.
The block copolymers provide a medium for dissolution or suspension of the tackifying resin and the plasticizing oil. A hot melt pressure sensitive adhesive utilizing the proper amount of a plasticizer should retain a solid physical nature upon aging while having significant flexibility. However, the block copolymers will reach a point at which they can retain no more oil, the oil will then separate from the adhesive and bleed into the substrate causing staining of the substrate. Increasing the levels of block copolymer or increasing the molecular weight of the block copolymer typically allows for the utilization of higher levels of oil which is necessary when compounding a removable hot melt pressure sensitive adhesive.
There remains a need in the industry for a removable hot melt pressure sensitive adhesive that is low in viscosity and which does not stain the substrates to which it is applied. The current inventors have discovered a removable hot melt pressure sensitive adhesive composition which allows for very low viscosities and does not stain a substrate upon aging, even at high temperatures.
SUMMARY OF THE INVENTION
The present invention relates to a removable hot melt pressure sensitive adhesive comprising from about 5% to about 30% by weight of the adhesive of a block copolymer having styrene endblocks and ethylene/butylene or ethylene/propylene midblocks and having a diblock content of greater than about 35% and a melt index of greater than about 20 grams/10 minutes; from about 10% to about 50% by weight of the adhesive of at least one block copolymer having styrene endblocks and having a coupling efficiency from about 65% to about 100%; from about 20% to about 60% by weight of the adhesive of a tackifying resin and from about 10% to about 40% by weight of the adhesive of a liquid plasticizing oil.
These adhesives are characterized as having minimal staining of substrates, even at temperatures of about 60° C. They are further characterized by 180° peel values to stainless steel of less than about 2.0 pounds per linear inch (about 360 grams/cm) and preferably less than about 1.5 pounds per linear inch (about 270 grams/cm) and viscosities of preferably less than about 3500 cPs at about 175° C. and more preferably less than about 2500 cPs at 175° C.
The present invention further relates to a nonstaining hot melt adhesive comprising from about 10% to about 60% by weight of the adhesive of at least one block copolymer having styrene endblocks and isoprene midblocks, a styrene content of less than about 20 wt-% and a diblock content of greater than about 40 wt-%, from about 20% to about 70% by weight of the adhesive of at least one tackifying resin and from about 5% to about 40% by weight of the adhesive of at least one plasticizing oil. The resultant hot melt adhesive composition exhibits superior antibleeding properties.
Preferably the block copolymer has a styrene content of less than about 16% and a diblock content of greater than about 40% and preferably greater than about 50% by weight of the block copolymer.
The present invention further relates to a hot melt adhesive having superior stain resistance comprising from about 10% to about 60% by weight of at least one block copolymer having styrene endblocks and midblocks selected from the group consisting of isoprene, ethylene/butylene and ethylene/propylene, from about 20% to about 70% by weight of the adhesive of at least one tackifying resin and from about 5% to about 40% by weight of the adhesive of at least one plasticizing oil. The hot melt adhesive exhibits superior anti-bleeding properties.
Preferably the block copolymer is linear and has a styrene content of greater than about 20 wt-% of the block copolymer and preferably greater than about 25% by weight of the block copolymer.
DETAILED DESCRIPTIONS
The present invention may utilize substantially saturated block copolymers including those having styrene endblocks and ethylene/butylene or ethylene/propylene midblocks and having a coupling efficiency of less than about 65% (or an A-B diblock content of greater than about 35%), a coupling efficiency of preferably less than about 50% and more preferably less than about 35%. The coupling efficiency refers to the ratio of A-B diblock to A-B-A triblock. A block copolymer having a coupling efficiency of less than about 65% will have a diblock content of greater than about 35% by weight of the block copolymer and an A-B-A triblock content of less than about 65% by weight of the block copolymer. The block copolymers useful herein preferably have a melt index of greater than about 20 grams/10 minutes, more preferably greater than about 30 g/10 min, even more preferably greater than about 50 g/10 min. and most preferably greater than about 60 g/10 min.
Asai Daisuke
Kodama Yoshihiro
Lindquist Jeffrey S.
Oeltjen Susan T.
Allison A. Johnson, P.A.
H. B. Fuller Licensing & Financing Inc.
Szekely Peter
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