Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-06-17
2001-01-30
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550RA, C428S198000, C604S389000, C604S386000, C427S208200, C427S208400
Reexamination Certificate
active
06180229
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a hot melt pressure sensitive adhesive (HMPSA) compositions which is useful for coating onto heat sensitive substrates and articles constructed therefrom. In particular, the invention relates to a hot melt adhesive having certain rheological characteristics, indicative of a low softening point and a low molten viscosity in combination with high cohesive strength. These combinations of properties are particularly amenable to removable adhesive application wherein the adhesive is permanently adhered to a substrate and is subsequently “removably” adhered to a surface such as fabric or skin without adhesive transfer. Due to the low viscosity at low application temperatures, the adhesive composition is amenable to hot melt adhesive application methods wherein the coating device contacts the substrate being coated such as in the case of screen printing and engraved roll coating. The invention further relates to articles such as feminine napkins, tapes, and bandages wherein the novel HMPSA composition is coated onto a substrate.
BACKGROUND OF THE INVENTION
“Removable” or “releasable” HMPSA's are those in which the adhesive is permanently adhered to at least one substrate such as paper stock or a polyolefin film layer and then removably attached to a surface in order to secure an article for a period of time. Examples of articles utilizing removable HMPSA's include tapes, tags and labels and adhesive bandages. Feminine napkins, adult incontinent pads as well as some hospital pads and drapes also typically utilize removable HMPSA's commonly described as “garment attachment” or “positioning” adhesives. During manufacturing of such articles, the HMPSA is typically slot-coated directly onto a paper stock or polyolefin film substrate and then covered with a release liner. Alternatively, the adhesive may be transfer coated by first applying the adhesive to the release liner and subsequently contacting the adhesive to the substrate layer, sandwiching the hot melt PSA between the substrate and the release paper.
There are a multitude of patents pertaining to adhesive compositions for tapes, labels, adhesive bandages and the like. Alper et al., EP 525 251 A1, Collins et al., U.S. Pat. No. 4,136,699 and Raykovitz et al., U.S. Pat. No. 4,704,110 specifically relate to hot melt PSA positioning adhesives for feminine napkins. However, such patents are typically directed toward continuous slot-coating of the HMPSA.
EPO 794 202 A1 published Oct. 9, 1997 is directed to aliphatic petroleum-based resins, a method of controlling the softening point and molecular weight of such a resin, and HMPSAs containing such resins. The hot melt adhesive composition generally consists of S-I-S polymers containing 0 to 30 parts per weight of styrene.
In recent years, manufacturers have attempted to replace the continuous slot-coat method with various discontinuous methods, such as engraved roll coating and pattern coating methods, otherwise referred to as screen-printing. There are several advantages in utilizing these types of discontinuous coating techniques including aesthetic advantages due to the variety of designs as well as the ability to strategically place adhesive in precise locations. The primary advantage methods such as engraved roll coating and pattern coating offer is the ability to vastly reduce adhesive consumption since the surface area per mass of adhesive is greatly increased. However, this increase in surface area in combination with the adhesive being applied in small individual deposits rather than a continuous layer creates adhesive transfer concerns, particularly when the substrate coated is a polyolefin film. It is theorized that in order for the adhesive to have the proper balance of properties, the adhesion to the substrate must be greater than the cohesive strength of the hot melt PSA. Concurrently the cohesive strength of the adhesive must be greater than the adhesion to the surface to which the adhesive is removably attached. Adhesives that possess these qualities in a slot coat application typically exhibit adhesive transfer when engraved roll coated or pattern coated, particularly at high removal rates. Furthermore, since directly applying the adhesive to the substrate is preferred for these application methods to enhance adhesion, HMPSA's are needed that are low in viscosity at low application temperatures in combination with the proper balance of adhesion and cohesion. The applicants have found that certain novel hot melt pressure sensitive adhesive compositions meet these requirements.
SUMMARY OF THE INVENTION
The inventors have discovered that easily measured rheological properties of the adhesive can be used to predict the success of a removable HMPSA for discontinuously coating at low application temperatures. Although it is known from the Dahlquist criteria that PSAs exhibit a storage modulus of less than about 5×10
6
dynes/cm
2
, the present inventors have discovered hot melt adhesive compositions that additionally exhibit a cross-over temperature of less than 85° C., preferably less than about 80° C. Since the crossover temperature is indicative of the melt point, the adhesives of the present invention melt at a significantly lower temperature. Additionally, the G′ diminishes to below about 100 dynes/cm
2
at a temperature 10° C. cooler than low viscosity removable HMPSA compositions which are slot coated for use as positioning adhesive. Accordingly, the adhesive compositions of the present invention exhibit a G′ of less than 100 dynes/cm
2
at a temperature of less than 95° C. and preferably at a temperature of about 90° C. or less. At about 10 dynes/cm
2
the adhesive composition is sufficiently molten such that the storage modulus (G′) is difficult to measure. Further, the adhesive composition is also characterized as having a glass transition temperature (Tg) of about 0 or greater. Hence, the adhesive composition of the present invention have a relatively low molten viscosity at lower temperatures. Preferably, the Brookfield viscosity of the adhesive composition is less than about 5,000 at 125° C., and more preferably the viscosity is less than 5,000 cPs at 110° C. This combination of properties is particularly amenable to contact coating of heat sensitive materials such as pattern coating and engraved roller coating which entail applying the adhesive as a plurality of individual adhesive deposits. These rheological criteria are also believed to be amenable to other discontinuous coating methods, such as spiral spray and melt blown hot melt application methods.
In another embodiment, the present invention is a disposable article, such as a feminine napkin or a tape, comprising a HMPSA permanently adhered to at least one substrate wherein said adhesive has a crossover temperature of less than 85° C., preferably about 80° C. or less. The adhesive may be subsequently removably adhered to a surface such as fabric or skin. Preferably, the substrate is a polyolefin film layer.
The adhesive composition comprises at least one block copolymer having a styrene content of at least about 25% with respect to the total weight of the block copolymer, at least one aromatic tackifying resin, and at least one liquid diluent. Preferably, the adhesive comprises from about 10 wt-% to about 30 wt-% in the adhesive of a styrene-isoprene-styrene (SIS) or styrene-butadiene-styrene (SBS) block copolymer, from about 40 wt-% to about 65 wt-% of at least one aromatic-aliphatic tackifying resin; and from about 15 wt-% to about 35 wt-% of a plasticizer.
REFERENCES:
patent: 4136699 (1979-01-01), Collins et al.
patent: 4704110 (1987-11-01), Raykovitz et al.
patent: 4728572 (1988-03-01), Davis
patent: 5019071 (1991-05-01), Bany et al.
patent: 5300057 (1994-04-01), Miller et al.
patent: 5714254 (1998-02-01), Jacob
patent: 0 525 251 A1 (1993-02-01), None
patent: 0 745 368 A1 (1996-12-01), None
patent: 0 745 432 A1 (1996-12-01), None
patent: 0 745 433 A1 (1996-12-01), None
patent: 0 794 202 A1 (1997-09-01), None
Becker Hans-Ulrich
Remmers Peter
Fisher Carolyn A.
H. B. Fuller Licensing & Financing Inc.
Quan Nancy N.
Zirker Daniel
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