Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Reexamination Certificate
1998-08-17
2003-11-18
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
C428S446000, C428S451000, C428S453000, C156S106000
Reexamination Certificate
active
06649235
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the production of coated polymeric articles, and particularly, articles with barrier coatings.
BACKGROUND OF THE INVENTION
Polymeric articles, including films and bottles, are widely used for packaging products, particularly foods. No unmodified polymeric article, however, has the gas and moisture barrier characteristics needed for packaging.
Thus, multilayer polymeric films have been designed with have improved gas and moisture barrier properties. For example, in U.S. Pat. No. 5,192,620 (Chu et al), a polypropylene film is coated with a blend of an ethylene-acrylic acid copolymer and polyvinyl alcohol and then metalized to produce a film with moisture barrier properties. U.S. Pat. No. 5,491,023 describes the application of a layer of polyvinylalcohol to the surface of a polyolefin substrate which has been modified by a maleic anhydride modified polypropylene.
Unfortunately, certain of the layers which have been applied to polymeric films in order to improve gas and moisture barrier properties have been faced with problems with adhering to the substrate. Various approaches have been taken to address these problems. However, to date, none of these approaches has provided a product with adequate barrier properties, which may be efficiently produced.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a process for making a coated polymeric article. The process involves co-extruding a selected polyolefin and a maleic anhydride modified polyolefin, thereby producing a polymeric substrate having a modified maleic anhydride surface. The maleic anhydride surface of the polymeric substrate is surface treated and the polysilicate barrier coating applied to the treated polymeric substrate.
In another aspect, the process of the invention further involves biaxially orienting the substrate prior to application of the barrier coating.
In another aspect, the present invention provides a coated polymeric article comprising a substrate consisting of coextruded maleic anhydride modified polypropylene and a selected polyolefin and a polysilicate coating on the surface of the coextruded substrate.
Other aspects of the present invention will be apparent from a review of the detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method of producing a polymeric article with a barrier coating. Advantageously, the method of the invention enables good adhesion of the barrier coating to the substrate without separate application of a primer layer (e.g., a solvent coating) to the substrate. Thus, the method of the invention also provides advantageous in production of the coated articles.
In one aspect, the present invention provides a method for making a coated polymeric article by co-extruding a selected polyolefin and a modified polyolefin. Suitably, the modified polyolefin is hydrophilic. Most suitably, the modified polyolefin is, prior to modification, the same as the selected unmodified polyolefin. In a preferred embodiment, the polyolefin is a polypropylene homopolymer or copolymer. However, other suitable polyolefins may be readily selected. Examples of other suitable polyolefins include, without limitation, polyethylene, polyesters, polybutene, polycarbonate, polyacrylonitrile, and olefin copolymers, including cycloolefin copolymers (COC), such as a copolymer of ethylene and norbornene [U.S. Pat. No. 5,087,677].
Preferably, the modified polyolefin is a maleic anhydride modified polypropylene. The maleic anhydride modified polypropylene can be prepared by any process, for example, the process described in U.S. Pat. No. 3,433,777, U.S. Pat. No. 4,198,327, or U.S. Pat. No. 5,153,074. One commercially available maleic anhydride modified polypropylene or propylene copolymer has the following physical characteristics: density of 0.90 (ASTM D1505), Vicat softening point of 143° C. (ASTM D1525); Shore hardness of 67° C. (ASTM 2240) and a melting point of 160° C. (ASTM D2117). Alternatively, these modified polyolefins may be produced by other means or purchased commercially (e.g., from Uniroyal (Polybond brand), Mitsui (Attmar brand), or Dow (Primacor brand)).
The polyolefin and hydrophilic modified polyolefin are co-extruded using conventional means. For example, suitable temperatures of extrusion are in the range of 180-240° C., and the resulting co-extruded substrate has a thickness in the range of 20-50 mil thick. Suitable means include the use of a selector plug or multicavity die.
The resulting polymeric substrate is provided with a layer of modified polyolefin and a layer of unmodified polyolefin. This modified polyolefin layer is pre-treated prior to application of the barrier coating. Preferably, this pretreatment involves surface treatment to permit the barrier coating to adhere. Suitable surface treatments are well known in the art and include corona treatment, flame treatment, plasma treatment, chemical treatment or corona discharge treatment. Most desirably, the surface is treated to raise the surface energy to about 45 to about 60 dynes/cm in accordance with ASTM Standard D2578-84.
Optionally, the polymeric substrate may be oriented prior to treatment and application of the barrier coating. Desirably, the substrate is biaxially oriented by sequential stretching. For example, the substrate may be stretched up to 5 times in the machine direction and up to 10 times in the transverse direction, such that a thickness in the range of about 0.5 mil to about 2 mil, and in one desirable embodiment, 0.75 mil is achieved.
Suitably, the barrier coating is an inorganic coating, and preferably, a polysilicate coating. Suitable polysilicate coatings may be readily selected from among those known in the art.
An example of one suitable coating is described in WO 97/47694 (Dec. 18, 1997), which describes a vapor barrier coating solution containing a layered inorganic mineral filler dispersed in an inorganic binder. Preferably, the filler is a layered inorganic mineral and the binder is an alkali metal polysilicate. The weight fraction of layered inorganic filler in the inorganic components of the dried coating is from 0 to 99%. Suitable inorganic minerals are selected from among phyllosilicates, illite minerals, and layered double hydroxides. Most preferably, the layered material is vermiculite. Suitable binders include metal polysilicates selected from lithium polysilicate, sodium polysilicate, potassium polysilicate and copolysilicate blends thereof.
Another suitable polysilicate coating is described in WO 97/44379 (Nov. 27, 1997), which describes lithium-potassium copolysilicates of the formula (Li
2
O)
x
(K
2
O)
1-x
(SiO
x
)
y
, in which the mole fraction of Li
2
O is x, the molar ratio of SiO
2
to M
2
O is y, and M
2
O is (Li
2
O)
x
(K
2
O)
1-x
. In this co-polysilicate, y is between 1 and 10, if x is less than about 1. Desirably, x ranges from approximately 0.5 to less than 1 and y ranges from 1 to approximately 10. Most preferably, x ranges from 0.5 to less than 1 and y is greater than 4.6 and may have a value up to about 10. These coatings typically contain up to about 25%, by weight solids. However, this percentage may be adjusted as needed.
Still another suitable inorganic coating is described in WO 97/47695 (Dec. 18, 1997). This publication describes a vapor barrier coating solution containing a metal polysilicate and transparent noncrystalline titanium dioxide (TiO
2
), which is particularly well suited for coating poly(ethylene terephthalate) polymeric articles. The metal polysilicates are defined essentially as defined as in WO 97/44379. Suitably, the nanocrystalline titanium dioxide is present in an amount up to about 25 weight percent of the total solids in the solution. Preferably, the titanium dioxide makes up about 2 to about 9 percent by weight of the total solids. Suitably, the noncrystalline titanium dioxide has an average particle size of less than about 100 nm, and preferably less than about 50 nm. Either of the two commercially availab
Hoechst Trespaphan GmbH
Hon Sow-Fun
Howson and Howson
Pyon Harold
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