Primer coated amorphous plastic films

Details Primer coated amorphous plastic films Primer coated amorphous plastic films

1999-01-11

2001-08-07

Jordan, Charles T. (Department: 3641)

Coating processes

Nonuniform coating

Applying superposed diverse coatings or coating a coated base

C427S412500, C427S416000

Statutory Invention Registration

active

H0001982

ABSTRACT:

TECHNICAL FIELD
This invention relates to plastic films used in graphic arts and, ore particularly, to such films that are amorphous and have been coated with a primer to improve adhesion of inks applied thereto and to improve slip characteristics when in contact with other films.
BACKGROUND OF THE INVENTION
In the graphic arts industry, clear plastic films or sheets made of various polymers such as polyesters, polycarbonates or polyvinyl chloride are often used as the substrate support for signs and the like. The films are typically printed on with various designs that may be utilized to provide advertising or other information. The preferred printing materials are ultraviolet curable inks or water-based inks since they are typically solvent free. Of course, solvent-based inks are still utilized. Printing techniques vary depending on the particular application and printing operation.
Adhesion problems exist with certain inks, particularly the ultraviolet curable inks, when printed on substantially amorphous polymeric substrates. Adhesion of the ink refers to the bond between the ink and the substrate. Ideally, the adhesion is such that there would be 100 percent retention of the ink to the substrate.
Blocking, a common problem in the film industry, relates to properties of the ink. Blocking occurs when a printed film that has been rolled for shipping is exposed to heat and pressure. The exposure softens the resin in the printing ink allowing the ink to adhere to the backside of the adjacent film. When the blocked films are separated, damage to either the ink film, substrate or both can occur. To solve blocking, U.S. Pat. Nos. 5,006,598 and 5,041,489 disclose ink compositions comprising linear, water dispersible copolyesters containing sulfoisophthalic acid moieties. Blocking and adhesion differ since the former deals with the cohesive properties of the ink only and the latter deals with the bonding properties between the ink and a polymeric substrate.
Another problem with substantially amorphous substrates, in particular poly(ethylene terephthalate) copolyester containing 1,4-cyclohexanedimethanol, is that the substrates when contacted with other substrates stick together, i.e. the substrates have poor slip characteristics. Often a piece of tissue-like paper is used to keep the surfaces separate.
Thus, there exists a need in the art for a primer to the surface of polymeric films to provide improved adhesion of printing inks to the polymeric films and improved slip characteristics as measured by a decrease in the static or kinetic coefficient of friction. Accordingly, it is to the provision of such that the present invention is primarily directed.
SUMMARY OF THE INVENTION
A printable plastic film comprises a substantially amorphous polymeric film substrate and at least one surface having a primer coating thereon. The primer coating is a linear water-dissipative copolyester having repeat units from a dicarboxylic acid component comprising 8 to 25 mole percent of at least one sulfomonomer containing an alkali metal sulfonate group attached to a dicarboxylic aromatic nucleus and 75 to 92 mole percent isophthalic acid and repeat units from a diol component comprising 25 to 100 mole percent diethylene glycol, 0 to 75 mole percent 1,4-cyclohexanedimethanol, and 0 to 30 mole percent ethylene glycol, based on 100 mole percent dicarboxylic acid component and 100 mole percent diol component. The substantially amorphous substrate is preferably poly(ethylene terephthalate), poly(ethylene naphthalene dicarboxylate), polycarbonate, polyvinyl chloride, or a copolyester having repeat units from a dicarboxylic acid component comprising at least 75 mole percent terephthalic acid or naphthalene dicarboxylic acid and repeat units from a diol component comprising 0.5 to 65 mole percent 1,4-cyclohexanedimethanol and 35 to 99.5 mole percent ethylene glycol, based on 100 mole percent dicarboxylic acid component and 100 mole percent diol component. The film is prepared by melt extruding a polymeric material into the substantially amorphous polymeric film, then applying the primer coating to the film as an aqueous dispersion and drying the primer coating.
DESCRIPTION OF THE INVENTION
Certain linear, water-dissipative copolyesters are excellent primer coatings for polymeric films or sheets used in graphic arts. Such copolyesters have repeat units from a dicarboxylic acid component comprising about 8 to about 25 mole percent of at least one sulfomonomer containing an alkali metal sulfonate group attached to a dicarboxylic aromatic nucleus and about 75 to about 92 mole percent isophthalic acid and repeat units from a diol component comprising about 25 to 100 mole percent diethylene glycol, 0 to about 75 mole percent 1,4-cyclohexanedimethanol, and 0 to about 30 mole percent ethylene glycol. The dicarboxylic acid and diol components are each based on 100 mole percent. These copolyesters have inherent viscosity values of about 0.2 to about 0.8 dL/g, preferably about 0.4 to about 0.6 dL/g.
Preferably the copolyester primer coating comprises 9 to 15 mole percent of the sulfomonomer containing an alkali metal sulfonate group attached to a dicarboxylic aromatic nucleus, 85 to 91 mole percent isophthalic acid, and 31 to 80 mole percent diethylene glycol. The sulfomonomer is preferably a 5-sulfo-isophthalic acid and is typically in the form of a metallic sulfonate salt. The metal ion of the sulfonate salt group may be Na
+
, Li
+
, K
+
, Mg
++
, Ca
++
, Cu
++
, Fe
++
, or Fe
+++
. It is also possible that the sulfonate salt is non-metallic and can be a nitrogen-containing base as described in U.S. Pat. No. 4,304,901, incorporated herein by reference. The most preferred repeating unit is 5-sodiosulfoisophthalic acid.
The dicarboxylic acid component of the copolyester primer coating may be modified with up to about 10 mole percent, preferably 5 mole percent, of one or more different dicarboxylic acids other than isophthalic acid. 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 to be included as the modifying acids include terephthalic acid, phthalic acid, naphthalene-2,6-dicarboxlic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Copolyesters may be prepared from one or more of the above modifying acids. It should be understood that use of the corresponding acid anhydrides, esters, and acid chlorides of these acids is included in the term “dicarboxylic acid”.
In addition, the copolyester primer coating may optionally be modified with up to 10 mole percent, preferably up to 5 mole percent, of one or more other diols. 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 modifying diols include triethylene glycol, 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-(1,3), 1,4-di-(hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4dihydroxy-1,1,3,3-tetramethyl-cyclobutane, 2,2-bis-(3-hydroxy-ethoxyphenyl)-propane, and 2,2-bis-(4-hydroxypropoxyphenyl)-propane.
The primer coating can optionally contain up to 10 weight percent of the total composition, preferably up to about 5 weight percent, of one or more additives. Such additives include waxes such as Jonwax 26, Jonwax 120 (available from S. C. Johnson and Sons, Inc. of Racine, Wis.) or Vanwax 35 (available from Vantage of Garfield, N.J.); surfactants such as Surfynol 104 or Surfynol 440 (available from Air Products and Chemicals of Allentown, Pa.), Carbowet 9

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