Barrier coatings using polyacids

Details Barrier coatings using polyacids Barrier coatings using polyacids

2000-03-03

2002-09-10

Nakarani, D. S. (Department: 1773)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S496000, C427S508000, C428S341000, C428S450000, C428S451000, C428S452000

Reexamination Certificate

active

06447845

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the preparation of barrier coatings and particularly to flavor, aroma and gas 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 ethylenicallyunsaturated carboxylic acid e.g. itaconic acid, in a solvent, solubilising, hydrolyzing and equilibrating the resultant solution and applying a layer of 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 gas barrier properties of the silane coating. The vinyl benzyl amine silane was also co-polymerized with 3-(2-aminoethyl)-aminopropyltrimethoxy silane or gamma aminopropyltriethoxysilaneprior to mixing with the acid. The resultant mixture was then used to coat the relevant substrate. Whilst 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.
U.S. Pat. No.5,368,941 proposes a deformable, abrasion-resistantcoating formulated from at least one multi-functional acrylate monomer, at least one aminofunctional silane, colloidal silica and at least one acrylate-terminatedpolyalkylene oxide. The acrylate-terminated polyalkylene oxide is provided in order to prevent the coating composition from gelling during stripping and is also said to provide the coating with a degree of deformability, without sacrificing abrasion resistance.
Japanese Laid Open (Kokai) No. 09165483 proposes the preparation of a resin composition by reacting an ethylene/vinyl alcohol co-polymer with a variety of alternative compounds including one or more polybasic acid(s) to form a transparent film with good gas barrier, transparency and mechanical properties for use as a packaging material.
Japanese Application No. 91125211/Laid Open (Kokai) No.4325545 describes a composition of a polyester (A), prepared by copolycondensation of a terephthalic acid, a glycol and a polybasic carboxylic acid having at least three carboxyl groups, with a branched polyester,(B). The terephthalic acid was used in the form of a mixture with isophthalic acid and aliphatic dicarboxylic acids and the polybasic carboxylic acid with three or more carboxylic groups is used in one alternative 1,2,4-benzenetricarboxylicacid or 1,2,4,5-benzenetetracarboxylicacid. The resultant product is said to be useful as a heat sealing material for food packaging which prevents the permeation of food flavor through the packaging material.
U.S. Pat. Nos. 5,260,350 and 5,374,483 describe 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 multifunctionalacrylate monomer with an amino-organofunctionalsilane, mixing the modified silane with at least one acrylic monomer and thereafter adding colloidal silica.
Japanese Laid Open (Kokai) No. 7003206 proposes a composition for a gas barrier coating comprising a water dispersed polymer prepared by emulsion polymerization of an aminosilane of the formula R
1
N(R
2
)A
1
Si(R
3
)
W
(OR
4
)
Z
where A
1
is an alkylene group, R
1
is H, lower alkyl or A
2
—N(R
5
)—R
6
; A
2
is a direct bond or an alkylene group; R
2
, R
5
, and R
6
are H or a lower alkyl group; R
3
is a lower alkyl group, aryl or an unsaturated aliphatic moiety; R
4
is H, lower alkyl or acyl and R
1
, R
2
, R
5
and/or R
6
are H. The resultant polymer is proposed as a gas-barrier coating for a packaging material.
SUMMARY OF THE INVENTION
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 gas barrier properties.
The present inventors have surprisingly found that substrates treated with coatings essentially consisting of a polybasic carboxylic acid or a polymer and co-polymer of organic acids, demonstrate excellent gas barrier properties at low to moderate relative humidity values.
Furthermore, the inventors have surprisingly found that substrates treated with a composition of the acid with one or more of a variety of additives demonstrate excellent gas barrier properties at low to moderate relative humidity values.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is a process for treating the surface of a substrate with an organic acid having at least two carboxylic acid groups, wherein the organic acid is selected from the group consisting of a graft polymer, a polybasic carboxylic acid, a polymer of an unsaturated carboxylic acid and a co-polymer of an unsaturated carboxylic acid, which process comprises applying the acid on to the substrate to form a layer and drying the layer.
The graft polymer is a copolymer molecule comprising a main backbone chain to which side chains of carboxylic acids are attached and the backbone may be any appropriate polymer to which carboxylic acid functional compounds may be grafted. In particular, backbone polymers used in the process of the present invention may be selected from the group consisting of hydroxyethylmethacrylate and polyethylenimine to which any suitable unsaturated carboxylic acid such as itaconic acid may be grafted.
If the organic acid is a polybasic carboxylic acid, it may be selected from the group consisting of itaconic acid, citric acid, succinic acid, ethylenediamine tetracetic acid (EDTA), ascorbic acid, butane tetracarboxylic acid, tetrahydrofuran tetracarboxylic acid, cyclopentane tetracarboxylic acid, and benzene tetracarboxylic acid. Alternatively, if the organic acid is a polymer or copolymer of an unsaturated carboxylic acid, in which case it is preferably selected from the group consisting of itaconic, citraconic, mesaconic, maleic, fumaric, acrylic, methacrylic, sorbic, and cinnamic acids. Co-polymers of the unsaturated carboxylic acids described above may be used with any appropriate unsaturated monomer selected from the group consisting of any other unsaturated carboxylic acid referred to above, ethylene, propylene, styrene, butadiene, acrylamide and acrylonitrile. The polymer or co-polymer preferably has a molecular weight of from 200 to about 1,000,000.
While the organic acid may be used alone to treat the surface of a substrate, it may also include additional components such as a compound (i) of the formula R
a
X
3−a
Si(CH
2
)
n
Y, a condensation catalyst (ii) which may be used when compound (i) is added to the acid, a solvent (iii), or a filler (iv).
The organic acid may be used, for example, with a compound (i) of the formula R
a
X
3−a
Si(CH
2
)
n
Y wherein each R is selected

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