Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-01-21
2002-10-01
Copenheaver, Blaine (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S413000, C428S423100, C428S447000, C428S479300, C428S480000, C428S500000, C428S515000, C428S529000
Reexamination Certificate
active
06458468
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to polyester articles coated with a bendable and stress crack resistant photocured coating. The polyesters contain dibasic acid moieties comprising at least 80 mole % terephthalic, naphthalene dicarboxylic, isophthalic and/or 1,4-cyclohexanedicarboxylic acid and glycol moieties derived from ethylene glycol and 1,4-cyclohexanedimethanol.
BACKGROUND OF THE INVENTION
Environmental stress cracking is the crazing and/or cracking that may occur when a thermoplastic under a tensile stress is exposed to aggressive chemicals. It is undesirable because it detracts from the aesthetic appearance of the plastic and, more importantly, could lead to mechanical failure of the molded article formed from the plastic. The potential for environmental stress cracking is of paramount concern when plastics are used in applications as diverse as injection-molded medical packaging and parts and blow-molded carbonated soft drink containers, where mechanical failure can have unwelcome ramifications.
Thermoplastics commonly coated for the purpose of improving stress crack resistance include polyethylene and polycarbonate. Poly(ethyelene terephthalate) (PET) and other polyesters are less commonly coated for this purpose. Heat cured siloxane systems, which are disclosed in U.S. Pat. No. 4,348,431 and commonly applied to polycarbonate plastics do not work on PET because the curing temperature is too high. This coating system is also expensive since it requires drying ovens and a curing time which may be as long as 4 hours. Polyurethane coatings, such as those disclosed in U.S. Pat. Nos. 5,300,334 and 5,681,628, also require undesirably long curing times and high temperatures for use on PET carbonated soft drink containers). The photocurable acrylate siloxane system disclosed in U.S. Pat. No. 4,197,173 and supplied by GE Plastics exhibits poor adhesion to PET copolyesters and the coating is brittle. The photocurable acrylate used by Yoshino Kogyosho for PET bottles require a primer coating in order to achieve adhesion of the acrylate to the substrate (U.S. Pat. No. 4,569,869). Acrylate coatings in general are stiff films and even if they adhere to PET, they result in the loss of impact properties and bendability.
“UV and EB Curing Formulation for Printing Ink, Coatings and Paints” edited by R. Holman, published by SITA-Technology Ltd., 203 Gardiner House, Broomhill Road, London SW18, England (1984) and “Chemistry & Technology of UV and EB Formulation for Coatings, Inks and Paints”, Volumes I-IV, edited by P. K. T. Oldring, published by SITA Technology Ltd., (1991) disclose general methods and compositions for coating plastic substrates.
U.S. Pat. Nos. 5,300,334 and 5,681,628 describe a pressurizable thermoplastic container having an exterior polyurethane layer and its method of making. The solvent -based polyurethane was cured at 60° C. for 10 minutes.
U.S. Pat. No. 4,569,869 discloses a saturated polyester bottle-shaped container with hard coating and method of fabricating the same. The hard coating is a UV-cured methyl methacrylate resin. The polyester bottle was coated with a primer layer prior to coating with the hard coat in order to promote adhesion of the hard coat to the container.
U.S. Pat. No. 4,348,431 discloses a continuous coating process for plastic films including polycarbonates, polyesters (PET and PBT), acrylic resins and others in which an aqueous dispersion of colloidal silica in an aliphatic alcohol-water solution of an organosilicon compound is applied and cured at elevated temperatures.
U.S. Pat. No. 5,086,087 describes a coating composition containing UV curable unsaturated monomers and/or oligomers, a photoinitiator and colloidal silica with an organosilane compound. The examples illustrate putting the coatings on polycarbonate samples.
U.S. Pat. No. 4,557,975 describes curing of a photocurable coating mixture containing polyfunctional acrylates, acrylonitrile, and a photoinitiator on polymeric substrates, especially the polycarbonates.
Many coatings have been disclosed as useful for coating polycarbonates. For example, U.S. Pat. No. 5,571,570 describes using a UV curable blend of three acrylic modified aliphatic polyurethanes, U.S. Pat. No. 4,197,173 describes a photocurable composition containing a polythiol, a polyene, and a silicone modified polyester copolymer, U.S. Pat. No. 4,198,465 describes a photocured coating containing the photoreaction products of certain multifunctional acrylate ester monomers or mixtures thereof and resorcinol monobenzoate, U.S. Pat. No. 4,384,026 describes photocured coatings containing the reaction of certain multifunctional acrylate ester monomers and certain acrylate modified polymers, U.S. Pat. No. 4,929,506 describes a hard, abrasion and chemical resistant coating which is the photoreaction product of an acrylated urethane oligomer, a difunctional acrylate monomer and preferably also a monofunctional olefinic monomer and U.S. Pat. No. 5,236,968 describes a UV hardenable lacquer.
Therefore, there remains a need in the art for solventless coating compositions which would adhere well to PET and other polyesters, be bendable, and provide good resistance to environmental stress cracking.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that UV-curable coatings can be applied to the surface of films, sheeting, and molded objects of certain polyesters to provide bendable, stress crack resistant coatings with good adhesion to the substrate.
More specifically the present invention relates to improving stress crack performance of a polyester article by applying an UV-curable, stress crack resistant topcoat to one or more sides. By increasing the resistance of the surface to stress cracking, the polyester can be used more safely in existing applications as well as find applications in more aggressive environments.
Polyesters
Polyesters which are suitable for use in the present invention include crystallizable polyester homopolymer or copolymer that are suitable for use in packaging, and particularly food packaging. Suitable polyesters are generally known in the art and may be formed from aromatic dicarboxylic acids, esters of dicarboxylic acids, anhydrides of dicarboxylic esters, glycols, and mixtures thereof. More preferably the polyesters are formed from repeat units comprising terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalenedicarboxylate, 2,6-naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1,4-cyclohexane-dimethanol, 1,4-butanediol, and mixtures thereof.
The dicarboxylic acid component of the polyester may optionally be modified with up to about 15 mole percent of one or more different dicarboxylic acids. Such additional dicarboxylic acids include aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms. Examples of dicarboxylic acids to be included with terephthalic acid are: phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, mixtures thereof and the like.
In addition, the glycol component may optionally be modified with up to about 15 mole percent, of one or more different diols other than ethylene glycol. Such additional diols include cycloaliphatic diols preferably having 6 to 20 carbon atoms or aliphatic diols preferably having 3 to 20 carbon atoms. Examples of such diols include: diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 3-methylpentanediol-(2,4), 2-methylpentanediol-(1,4), 2,2,4-trimethylpentane-diol-(1,3), 2-ethylhexanediol-(1,3), 2,2-diethylpropane-diol-(1,3), hexanediol-Q1,3), 1,4-di-(hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetram
Germinario Louis Thomas
Moskala Eric Jon
Salyer David Gayle
Copenheaver Blaine
Eastman Chemical Company
Graves, Jr. Bernard J.
Harding Karen A.
Paulraj Christopher
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