Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-03-03
2002-07-23
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S448000, C428S450000, C428S451000, C556S413000, C106S287110, C427S387000
Reexamination Certificate
active
06423416
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coating compositions having barrier properties which are useful in packaging applications. The coating compositions of this invention are formed by the reaction of bis-aminosilanes with phenolic compounds, and are particularly useful to reduce the diffusion of gases through organic polymer based packaging materials.
BACKGROUND OF THE INVENTION
Organic polymers, such as polypropylene and polyethylene terephthalate, have gained wide acceptance in the packaging industry because of their inherent advantages over conventional materials such as glass. However, a need exists to improve the barrier properties of organic polymer films for various packaging applications. More particularly, improvements are sought to prevent the loss of gaseous, oil, and flavor components of compositions packaged with organic polymer film substrates.
Coating compositions containing silane compounds are known to improve the gas, oil, and flavor barrier performance of organic polymer film substrates, for example as described in PCT/BE98/00006, the corresponding US equivalent of which is U.S. Ser. No. 09/341253. Moreover, the adhesion of the coating to the film surface, as well as the improved barrier characteristics provided by the silane coating, are greatly enhanced by exposing the coated film to electron beam radiation.
Useful barrier compositions are described in U.S. Pat. No. 5,215,822, which teaches a methanol solution of a vinyl benzyl amine silane, itaconic acid, and water; coating this solution on a corona treated low density polyethylene film, drying, and then subjecting the coated film to electron beam radiation to graft the coating to the film surface and further improve the barrier properties of the silane coating. However, while this coating gives excellent gas barrier properties at low to moderate relative humidity values, the gas permeability increases drastically at very high relative humidity values.
U.S. Pat. No. 5,434,007 teaches a silane resin coated on a plastic film, where the silane resin is composed of a monofunctional acrylate and an amino functional silane.
U.S. Pat. Nos. 5,260,350 and 5,374,483 relate to a silicone coating composition which, when cured on a solid substrate either by ultraviolet or electron beam radiation, provides a transparent abrasion resistant coating firmly adhered thereon. The silicone coating is prepared by reacting at least one multifunctional acrylate monomer with an amino-organofunctionalsilane, mixing the modified silane with at least one acrylic monomer and thereafter adding colloidal silica.
JP (Kokai) publication 7-18221 published on Jan. 20, 1995 teaches a surface treatment composition for gas barrier comprising an amino functional silane and a compound having an aromatic ring or hydrogenated ring.
These coatings represent a significant advance in the art. However, it has been observed that while the barrier properties of the prior art coatings are excellent in environments at relative humidities of 80% or less, their performance suffers significantly at relative humidities of 90% or more.
The present inventor has surprisingly discovered that the reaction products of an amino functional silane and a phenolic compound give excellent gas barrier properties at low to moderate relative humidity values, as well as excellent gas barrier properties at very high relative humidity values of 90% or more.
Coating compositions for improving barrier properties of organic polymer films based primarily on the reaction product of amino functional silanes and phenolic compounds heretofore are not known. Amino functional silanes are commonly used as surface treatments of silicate based materials (such as glass or silica) to enhance the adhesion of a wide variety of organic polymers. Examples of the type of organic polymers reacted with amino functional silane treated silicate materials includes phenol-formaldehyde polymers. Furthermore, the addition of phenolic compounds to phenol-formaldehyde-resin coating compositions are known. In particular, U.S. Pat. No. 4,062,690 teaches a coating composition for glass fibers based on phenol-formaldehyde-resins containing at least one monocyclic or polycyclic aromatic compound having at least three hydroxyl groups on the aromatic ring. While the '690 patent further teaches the treatment of the glass fibers with an amino functional silane, it does not specifically describe or suggest the reaction product of a amino functional silane with a non-resin phenolic compound is useful to improve the barrier properties of organic polymer films. Rather, the '690 teaches the necessity of mixing a phenolic compound in a phenol-formaldehyde-resin to obtain a coating composition.
Silamines have been reacted with phenols to create curing agents for epoxide resins, as taught in U.S. Pat. No. 4,393,180. However, these silamines differ from the amino functional silanes of the present invention in that they do not contain an alkoxy group and have not been suggested for improving the barrier properties of organic polymer films.
SUMMARY OF THE INVENTION
The present invention is directed to a composition, useful for improving the barrier properties of organic polymer films, prepared by reacting;
(A) a bis-aminosilane and
(B) a phenolic compound
to form a reaction product, wherein the bis-aminosilane has at least one molecule of the formula;
R
1
b
X
3-b
Si—Z—SiX
3-b
R
1
b
wherein Z is R
2
NH(R
2
NH)
p
R
2
, each R
1
is a hydrocarbon group, each X is an alkoxy group with 1 to 4 carbon atoms, an oxime group or an acyloxy group, each R
2
is a divalent hydrocarbon group having 1 to 12 carbon atoms; b is from 0 to 3 and p is 0 or 1.
The composition can be applied to a variety of substrates used in packaging applications. The composition can be cured by further heating in the presence of moisture.
The present invention also teaches a method for preparing substrates with improved barrier properties by coating a variety of substrates used in packaging applications with the inventive compositions.
The substrates prepared by the method of the present invention show improved resistance of the substrate to transmission of gases and aromas there through. For example, a 30 micrometers uncoated biaxially oriented, corona treated polypropylene film is generally found to have a permeability to oxygen of 1200 cc/m
2
/day as measured according to ASTM D3985-81 at 90% relative humidity. With the preferred embodiments of the present invention, the oxygen transmission rate of the same film is reduced to less than 1 cc/m
2
/day as measured at 90% relative humidity. As used herein, the terminology “improved barrier” refers to a coating which can reduce oxygen transmission rate of the aforementioned un-coated polypropylene film from 1200 cc/m
2
/day to less than 100 cc/m
2
/day as measured at ASTM D3985-81 measured at 90% relative humidity.
DETAILED DESCRIPTION OF THE INVENTION
The bis-aminosilane useful as component A) in the composition of the present invention are described by the formula:
R
1
b
X
3-b
Si—Z—SiX
3-b
R
1
b
wherein Z is R
2
NH(R
2
NH)
p
R
2
. In this formula each R
1
is preferably a monovalent hydrocarbon group having 1 to 10 carbons, for example a saturated or unsaturated aliphatic or aromatic group, for example alkyl, alkenyl, or phenyl groups; Each X is an alkoxy group with 1 to 4 carbon atoms, an oxime group or an acyloxy group. X is preferably an alkoxy group, with methoxy and ethoxy as the preferred alkoxy groups. R
2
is a divalent hydrocarbon group having 1 to 12 carbon atoms, preferably each R
2
has from 2 to 3 carbons. Each b is from 0 to 3, but is preferably 0, and p is 0 or 1. The best results are obtained by use of compounds in which each X is a methoxy group, each R
2
is a propylene group, b is 0, and p is 0, i.e. when the compound is bis-(&ggr;-trimethoxysilylpropyl)amine, such as Silquest A1170 supplied by Witco/OSi, (Greenwich, Conn.). In another embodiment, the bis-aminosilane can be bis-[(3-trimethoxysilyl)propyl]-ethylenediamine, such as bis-TMSEDA from Geles
Dawson Robert
Dow Corning Corporation
Robertson Jeffrey B.
Zombeck Alan
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