Aqueous pressure sensitive adhesive formulations

Details Aqueous pressure sensitive adhesive formulations Aqueous pressure sensitive adhesive formulations

1998-11-12

2003-02-18

Mulcahy, Peter D. (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...

C524S167000, C524S522000, C524S523000, C524S528000

Reexamination Certificate

active

06521696

ABSTRACT:

FIELD OF THE INVENTION
The subject invention pertains to pressure sensitive adhesive formulations. In particular, the subject invention pertains to water-borne pressure sensitive adhesive formulations comprising at least one homogeneous olefin polymer or at least one substantially random interpolymer of ethylene and a monovinylidene aromatic or hindered aliphatic monomer.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives (PSA's) are materials which are aggressively and permanently tacky at room temperature at the time of application, and which firmly adhere to a variety of dissimilar surfaces with the application of light pressure, such as pressing with a finger. Despite their aggressive tackiness, PSA's may be removed from smooth surfaces without leaving significant residue. PSA's are widely used in everyday applications, such as masking tape, clear office tape, labels, decals, bandages, decorative and protective sheets (such as shelf and drawer liners), floor tiles, sanitary napkin/incontinence device placement strips, sun control films, and the joining of gaskets to automobile windows.
Historically, pressure sensitive adhesives were based on natural rubber and wood rosins, which were carried by a solvent. Articles bearing such adhesives were manufactured by applying a solution of the adhesive on a suitable backing, and removing the solvent by a devolatizing process. However, in response to cost increases in solvents and regulatory restrictions regarding emissions, water-based adhesives and solid-form hot melt adhesives have been developed.
Water-based adhesives have met with some degree of success in the industry. Exemplary water-based adhesive systems are based on styrene-butadiene, natural rubber, and acrylic latexes. However, improved water-based adhesive systems are sought.
In particular, the industry would find advantage in water-based pressure sensitive adhesive systems which are characterized as having good peel strengths, and which are not susceptible to degradation upon exposure to the elements. Industry would further find advantage in water-based adhesives which provide enhanced adhesion to non-polar substrates.
U.S. Pat. No. 3,734,686 discloses a mechanically stable aqueous emulsion of polyethylene particles having an average molecular weight ranging from about 7,000 to 40,000.
U.S. Pat. No. 3,418,26 teaches that aqueous film-forming ethylene polymer latexes containing ethylene polymer particles of submicron size can be prepared by dispersing in water an ethylene polymer and a water-soluble block copolymer of ethylene oxide and propylene oxide. No examples of stable dispersions of ethylene polymers having a molecular weight above 27,000 are reported.
U.S. Pat. No. 5,574,091 discloses latexes that are film forming at room temperature, and which are prepared from copolymers of ethylene and C
3
-C
20
&agr;-olefins higher in molecular weight.
U.S. Pat. No. 5,530,054 claims a hot melt adhesive composition consisting essentially of: (a) 30 to 70 weight percent of a copolymer of ethylene and about 6 to about 30 weight percent of a C
4
to C
20
&agr;-olefin produced in the presence of a catalyst composition comprising a metallocene and an alumoxane and having an M
w
of from about 20,000 to about 100,000; and (b) a hydrocarbon tackifier which is selected from a recited list. Exemplified are compositions consisting of 45 weight percent of ethylene/butene-1copolymer having a specific gravity of either 0.898 g/cm
3
or 0.901 g/cm
3
.
U.S. Pat. No. 5,548,014 claims a hot melt adhesive composition comprising a blend of ethylene/&agr;-olefin copolymers wherein the first copolymer has a M
w
from about 20,000 to about 39,000 and the second copolymer has a M
w
from about 40,000 to about 100,000. Each of the hot melt adhesives exemplified comprises a blend of copolymers, contains 45 weight percent copolymer, with at least one of the copolymers having a polydispersity greater than 2.5. Furthermore, the lowest density copolymer exemplified has a specific gravity of 0.894 g/cm
3
SUMMARY OF THE INVENTION
The subject invention provides a pressure sensitive adhesive comprising an aqueous dispersion of:
a. at least one polymer selected from the group consisting of:
i. homogeneous ethylene/&agr;-olefin interpolymers characterized as having a molecular weight distribution (M
w
/M
n
) of less than 3.5; and
ii. substantially random interpolymers of ethylene and at least one vinylidene aromatic or hindered aliphatic comonomer;
b. at least one surfactant.
DETAILED DESCRIPTION OF THE INVENTION
The pressure sensitive adhesives of the invention comprise at least one homogeneous ethylene/&agr;-olefin interpolymer which is an interpolymer of ethylene and at least one C
3
-C
20
&agr;-olefin and/or at least one substantially random interpolymer of ethylene, a monovinylidene aromatic monomer, and an optional C
3
-C
20
&agr;-olefin. The term “interpolymer” is used herein to indicate a copolymer, or a terpolymer, or a higher order polymer. That is, at least one other comonomer is polymerized with ethylene to make the interpolymer.
The term “hydrocarbyl” means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic, or cycloaliphatic substituted aromatic groups. The aliphatic or cycloaliphatic groups are preferably saturated. Likewise, the term “hydrocarbyloxy” means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
The term “monomer residue” or “polymer units derived from such monomer” means that portion of the polymerizable monomer molecule which resides in the polymer chain as a result of being polymerized with another polymerizable molecule to make the polymer chain.
The term “substantially random” in the substantially random interpolymer comprising an &agr;-olefin and a vinylidene aromatic monomer or hindered aliphatic vinylidene monomer as used herein means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in POLYMER SEQUENCE DETERMINATION, Carbon-13 NMR Method, Academic Press New York, 1977, pages 71-78. Preferably, the substantially random interpolymer comprising an &agr;-olefin and a vinylidene aromatic monomer does not contain more than 15 percent of the total amount of vinylidene aromatic monomer in blocks of vinylidene aromatic monomer of more than 3 units. More preferably, the interpolymer was not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the 13C-NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
Density is measured in accordance with ASTM D-792, after annealing for 24 hours.
Melt index (I
2
) is measured in accordance with ASTM D-1238, Condition 190° C./2.16 kg

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