Supercritical fluid pressure sensitive adhesive polymers and...

Details Supercritical fluid pressure sensitive adhesive polymers and... Supercritical fluid pressure sensitive adhesive polymers and...

2001-09-26

2003-07-08

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S328000, C526S942000, C526S203000, C526S318400, C526S242000

Reexamination Certificate

active

06590053

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to the preparation of pressure sensitive adhesive (“PSA”) polymers and more particularly to their preparation in supercritical fluid (“SCF”) reactive medium.
A variety of coatings have been developed as a response to customer and government demands that volatile organic compounds (“VOCs”) be reduced and/or eliminated from coatings formulations. These include, inter alia, powder coatings, water-borne coatings, high solids organic solvent coatings, and SCF coatings. The use of supercritical fluids as carriers and viscosity reducers for transporting a variety of coating materials and effectively spraying them onto a coatable surface while reducing the amount of VOCs that are required for application has been proposed in a number prior publications. A good review of these publications can be found in, for example, U.S. Pat. No. 5,212,229. Performance reports on SCF coatings can be found, for example, in Goad, et al., “Supercritical Fluid (SCF) Application of SMC Primers: Balancing Transfer Efficiency and Appearance”, SPI Compos Inst Annu Conf Expo,
Proc J Soc Plast Ind,
vol. 5, 2
nd
page, Session 21A (1997); and Nielsen, et al., “Supercritical Fluid Coating: Technical Development of a New Pollution Prevention Technology”,
Water-Borne & Higher-Solids, and Powder Coatings Symposium,
Feb. 24-26, 1993 New Orleans, La., sponsored by The University of Southern Mississippi Department of Polymer Science and Southern Society for Coatings Technology.
Use of SCF technology in the adhesives field, however, has been given little consideration by the art. The present invention, then, is addressed to implementing SCF technology for PSA adhesives.
BRIEF SUMMARY OF THE INVENTION
One aspect of the present invention relates to stabilizing or dispersing pressure sensitive adhesive (PSA) polymers, especially low T
g
, high tack, nonpolar and polar polymers useful in formulating PSAs, in a supercritical fluid (SCF), such as liquid CO
2
or supercritical CO
2
, by using an organic cosolvent such as toluene. Another aspect of the present invention reveals that PSA polymers can be polymerized in SCF fluids to make unique adhesive products. Inclusion of a fluorinated reactant in the SCF polymerization process yields a PSA with improved resistance to mineral oil.
In this application the term (co)polymer means either a polymer or copolymer, which includes a homopolymer. The term (co)polymerization means either polymerization or copolymerization, which includes homopolymerization. Further, the term (meth)acrylate means either acrylate or methacrylate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention extends the use of fluid CO
2
or supercritical CO
2
to PSA adhesive systems from its use in coatings systems as proposed in the art. The present invention is based upon several fundamental discoveries with respect to PSA systems and fluid CO
2
or supercritical CO
2
. Initially, certain classes of cosolvents are required in order to stabilize conventional PSA (co)polymers in fluid CO
2
or supercritical CO
2
. Next, it was discovered that PSA (co)polymers could be synthesized in fluid CO
2
or supercritical CO
2
as the reaction solvent, even to the exclusion of other conventional organic solvents. Further, it was discovered that improved oil and fuel resistance could be imparted to PSA polymers synthesized in fluid CO
2
or supercritical CO
2
by including a fluorinated monomer in the reaction mixture.
Referring initially to the use of certain classes of cosolvents to stabilize conventional PSA polymers in fluid CO
2
or supercritical CO
2
, different classes of cosolvents will be required to polar (e.g., acrylics) than for nonpolar (e.g., polybutene) PSAs. For ester type cosolvents for dissolving or dispersing polybutene (typical nonpolar PSA polymer) in fluid CO
2
or supercritical CO
2
, the cosolvent should possess the following characteristics: molecular weight range of 116-297, density range of 0.855-0.898, and &khgr;
o
factor (oxygen heteroatoms) of 0.108-0.275. For alcohol type cosolvents, the cosolvent should possess the following characteristics: molecular weight range of 144-186, density range of 0.827-0.831, and &khgr;
o
factor (oxygen heteroatoms) of 0.086-0.111. Finally, for hydrocarbon type cosolvents, the cosolvent should possess the following characteristics: molecular weight range of 86-227, density range of 0.659-0.865, and &khgr;
o
factor (oxygen heteroatoms) of 0.
The &khgr; (chi) factor is based upon the McGinniss predictive relationship as defined in
Organic coatings in Plastic Chemistry,
Vols. 39 and 46, pp. 529-543 and 214-223, respectively (1978 and 1982, respectively). The McGinniss predictive relationship defines the &khgr; factor as a weight fraction of heteroatoms contained in the monomer or in the monomer repeat unit of an oligomer or polymer.
In adjudging suitable cosolvents, polybutene (MW range of 66,000 to 107,000) was dissolved in fluid CO
2
or supercritical CO
2
in equal weight parts with the cosolvent and the number of milliliters of CO
2
that can be added to a one gram same of the mixture and still remain a clear solution or form a stable dispersion recorded (Solubility Number). Representative such cosolvents, then, are displayed below.
Cosolvent
&khgr;
Solubility
No.
Type
MW
Density
Factor
Number
1
Trans-2-hexenyl acetate
142.20
0.898
0.225
2.24
2
Ethyl trans-3-hexenoate
142.20
0.896
0.225
2.37
3
Methyl caproate
130.19
0.885
0.246
2.86
4
Isobutyl isobutyrate
144.21
0.855
0.222
2.92
5
Butyl acetate
116.16
0.862
0.275
3
6
Butyl methacrylate
142.20
0.894
0.225
3.52
7
Hexyl acetate
144.21
0.876
0.222
4.32
8
Butyl butyrate
144.22
0.871
0.222
4.36
9
Pentyl Propionate
144.21
0.873
0.222
4.45
10
Methyl ethanoate
144.22
0.870
0.222
4.53
11
Ethyl caproate
144.21
0.873
0.222
4.66
12
Methyl dodecanoate
186.30
0.873
0.172
4.82
13
2-Ethylbutyl acetate
144.21
0.876
0.222
4.91
14
Methyl oleate
296.50
0.867
0.108
5.4
15
Dodecyl acetate
228.38
0.865
0.140
6.39
16
Methyl tridecanoate
228.38
0.864
0.140
6.42
17
Soybean oil methyl esters
250
0.875
0.128
8.48
18
Hexane
86.16
0.659
0
3.93
19
Heptane
100.21
0.684
0
4.26
20
Tetradecane
198.40
0.763
0
4.76
21
Hexadecane
226.45
0.773
0
5.07
22
Toluene
92.14
0.865
0
5.24
24
1-Hexadecene
224.42
0.783
0
6.63
25
1-Dodecanol
186.34
0.831
0.086
2.88
26
1-Nonanol
144.26
0.827
0.111
5.86
Cosolvents 1-17 are esters, cosolvents 18-24 are hydrocarbons, and cosolvents 25 and 26 are alcohols. The weight ratio of (co)polymer to solvent can vary from, say, about 0.5 to 2.
One of the major uses or PSAs is to adhere trim and decals on a variety of transportation vehicles (automobiles, buses, trains, tractors, trucks, boats, etc.). Current PSA technology typically uses acrylic based (co)polymers which have excellent adhesion to a variety of polar (painted, non-painted, and active) surfaces. The major problem with current acrylic PSAs is their poor resistance to oils, fuels, and greases commonly found around transportation applications and environments. One aspect of the present invention is the use of special fluorine containing monomers that greatly enhance the oil and fuel resistance of the acrylic PSA, while still maintaining it tack and good adhesive bonding properties.
By using liquid CO
2
or in supercritical CO
2
fluids as the polymerization vehicle or media, new (co)polymers can be made from low T
g
acrylic monomers in combination with fluorinated (meth)acrylic monomers. Representative low T
g
acrylic monomers are ethyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, and dodecyl acrylate. Representative fluorinated (meth)acrylic monomers include trifluoromethylacrylate and trifluoromethylmethacrylate. As the examples will demonstrate that tack values can be formulated to range from between about 480 to 0 by varying the amount of butyl acrylate and fluorinated octylmethacrylate. Resistance to mineral oil, however, can range on up to 30 minutes. An additional advantage of using liquid CO
2
or in super

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