Barrier coatings having bis-silanes

Details Barrier coatings having bis-silanes Barrier coatings having bis-silanes

2000-03-03

2002-07-09

Cameron, Erma (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S387000, C427S388400, C427S388500, C427S391000, C427S392000, C427S393500

Reexamination Certificate

active

06416817

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the preparation of barrier coatings on films and particularly to oxygen, carbon dioxide, flavor and aroma barrier coatings on films for use in packaging.
BACKGROUND OF THE INVENTION
The pharmaceutical and food industries have, over recent years, increasingly provided products in a prepackaged form. Fruit and vegetables for example, apples and tomatoes, meat and cheese are often prepackaged in a tray and the tray and the fruit are covered with a transparent film.
One of the most important requirements for films used for packaging applications is that they should protect products from aromas or odors in the vicinity in which the products are stored, i.e. they should act as barriers to such aromas or odors. Similarly the films are utilized as barriers to prevent strong smelling products contained in packages from tainting the surrounding area with their aroma during storage.
Oxygen barrier coatings are utilized to prevent the ingress of oxygen into products with a view to extending the shelf life of products and carbon dioxide barrier coatings are typically utilized to prevent the release of carbon dioxide from rigid plastic bottles holding carbonated drinks.
U.S. Pat. No. 5,215,822, describes a process of controlling the impermeability of a film to gases by mixing a vinyl benzylamine silane with an ethylenically unsaturated carboxylic acid e.g. itaconic acid, in a solvent, solubilising, hydrolyzing and equilibrating the resultant solution and coating this solution on a corona treated low density polyethylene film and drying the resulting film. The coated film is then subjected to an electron beam radiation to graft the coating to the film surface and further improve the barrier properties of the silane coating. The vinyl benzyl amine silane was also co-polymerised with 3-(2-aminoethyl)-aminopropyl trimethoxy silane or gamma aminopropyltriethoxysilane prior to mixing with the acid. The resultant mixture was then used to coat the relevant substrate. While these coatings gave excellent gas barrier properties at low to moderate relative humidity values, the gas permeability was less satisfactory at very high relative humidity values. In addition, the use of electron beam radiation may lead to cross-linking or chain scission in underlying plastics substrates, with concomitant loss of tensile properties. The use of electron beam radiation and several other complicated and/or expensive procedures with respect to coatings of this type containing mono-silyl constituents can make the use of such compounds for the manufacture of coated films for use in the packaging industry unattractive.
U.S. Pat. No. 4,689,085/U.S. Pat. No. Re. 34675 describes the preparation of disilylated hydrocarbons of the general structure (RO)
3
SiR′Si(OR)
3
where OR is a hydrolysable group and R′ is a divalent organic radical. They further teach the combination of a silane coupling agent for example, 3-methacryloxypropyltrimethoxysilane with a disilyl cross-linking compound of the general formula structure (RO)
3
SiR′Si(OR)
3
where OR is a hydrolysable group and R′ is a divalent organic radical for example, an alkylene group or a selection of branched, unsaturated or aryl substituted groups as an improved coupling agent and primer mixture demonstrating that the combination of the components provided improved results compared with either component when used alone.
These compositions are said to be useful as primer coatings between non-particulate surfaces and polymer coatings as pretreatments for particulate fillers before compounding, and as additives to filled polymer systems during compounding as well as for treating glass cloth.
Various proposals to employ organosilicon compounds in the treatment of plastics films to achieve gas barrier properties have been made. However, bis-silanes have not previously been utilized to control the gas barrier properties of a substrate. Furthermore, it is to be noted that none of the prior art discussed above suggests the use of such compounds for coating materials to be cured on plastic, cellulosic, glass or metal substrates to achieve gas barrier properties.
It is one of the various objects of the present invention to provide a process for treating a surface of a substrate to provide improved barrier properties.
The present inventors have now surprisingly found that substrates having coatings of selected moisture cured disilylated secondary amines demonstrate excellent gas barrier properties at low to high relative humidity values. Furthermore, these properties may be achieved without the need for exposure of the coating to electron beam or other forms of ionizing radiation.
SUMMARY OF THE INVENTION
The present invention provides, in accordance with one of its aspects, a process for treating a surface of a substrate with a compound of the general formula
R
a
X
3-a
Si—Z—SiX
3-a
R
a
wherein Z is R′NH(R′NH)
p
R′, each R is selected from the group consisting of a hydrogen atom and a hydrocarbon group, each X is selected from the group consisting of an alkoxy group with 1 to 4 carbon atoms, a halogen atom, an oxime group or an acyloxy group, each R′ is a divalent hydrocarbon group having 1 to 12 carbon atoms; a is from 0 to 3 and p is 0 or 1; which process comprises applying the compound on to the substrate to form a layer and exposing the layer to moisture.
DETAILED DESCRIPTION OF THE INVENTION
In a process according to the present invention there is used a compound of the general formula
R
a
X
3-a
Si—Z—SiX
3-a
R
a
wherein Z is R′NH(R′NH)
p
R′.
In this formula each R is preferably a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, for example a saturated or unsaturated aliphatic or aromatic group, for example alkyl alkenyl or phenyl groups; preferred groups are methyl and ethyl, the most preferred of which are methyl groups. Each X is an alkoxy group with 1 to 4 carbon atoms, a halogen atom, an oxime group or an acyloxy group, of these methoxy and ethoxy groups are preferred, the most preferred being methoxy groups. R′ may be a divalent hydrocarbon group having 1 to 12 carbon atoms, preferably each R′ has from 2 to 3 carbon atoms. Each a is from 0 to 3 but is most 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′ is a propylene group, a is 0, and p is 0, i.e. when the compound is bis-(gamma-trimethoxysilylpropyl)amine.
These materials, referred to as disilylated secondary amines may be prepared by processes known in the art for example, as disclosed in U.S. Pat. Nos. 2,832,754, 2,920,095, and 5,101,055.
In a process according to the invention the surface of a substrate is treated with a compound as aforesaid with or without the addition of:
i) a solvent selected from the group consisting of an alcohol, an ether, an ester, a hydrocarbon, and water in the presence of a polybasic acid;
ii) an organic acid having two or more acid substituents wherein the organic acid is a polybasic carboxylic acid selected from the group consisting of itaconic acid, citric acid, succinic acid, butane tetracarboxylic acid, ethylene diamine tetracetic acid, ascorbic acid, tetrahydrofuran tetracarboxylic acid, cyclopentane tetracarboxylic acid, and benzene tetracarboxylic acid;
iii) a polymer or co-polymer of an unsaturated carboxylic acid selected from the group consisting of itaconic, citraconic, mesaconic, maleic, fumaric, acrylic, methacrylic, sorbic, cinnamic acid, wherein the co-polymer is a co-polymer with any appropriate unsaturated monomer selected from the group consisting of one or more other unsaturated carboxylic acids, ethylene, propylene, styrene, butadiene, acrylamide and acrylonitrile;
iv) a condensation catalyst;
v) a filler selected from the group consisting of silicone resin, silica, magnesium oxide, clay, diatomaceous earth, calcium carbonate, finely ground quartz and nanoparticles.
While the process of the present application may proceed using a solventless

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