Backaround of the Invention Poly(vinyl alcohol) is a water-soluble synthetic polymer made by alcoholysis of polyvinyl acetate. Among other things, it is known for utility as a laminating adhesive. When used in packaging films, poly(vinyl alcohol) has been described as providing a film which is impervious to oils, fats and waxes and to be an excellent oxygen barrier. For this reason, poly(vinyl alcohol) is often used as barrier coatings on thermoplastic films.

Summarv of the Invention The invention relates to a primer coating for plastic films which comprises a blend of poly(vinyl alcohol), glyoxal and an adhesion promoter andlor an epoxy resin. The primer coating demonstrates water resistance.

Detailed Description of the Invention The primer coating of this invention comprises a blend of poly(vinyl alcohol), glyoxal and an adhesion promoter andlor an epoxy resin.

Aqueous poly(vinyl chloride) composition containing no additional additives applied over a film primed with a blend of poly(vinyl alcohol) and an adhesion promoter, specifically poly(ethylene imine) and about 15 parts per hundred of an epoxy resin demonstrates water resistance. In contrast, when the same primed and coated films containing about 30 parts per hundred epoxy resin were tested for water resistance the poly(vinyl alcohol) layer was easily wiped off with warm water.

It was surprising to discover that coating a film pnmed with the primer of this invention with a solution of poly(vinyl alcohol), typically a 1 to 6% solution, resulted in crosslinking of the poly(vinyl alcohol) of the top coating by the

glyoxal. For the cross linking, the amount of the epoxy component should be less than about 30 parts per hundred, usually about 15 parts per hundred.

The term "epoxy" means a blend containing polyethyleneimine, at a pH of 6.8, hardener, commercially available under the trade designation NSK7000, epoxy, commercially available under the trade designation Daubond DCg92X 6311, water and a wetting agent, typically cellusolve.

The poly(vinyl alcohol) is commercially available under the designation Elvanol.

The invention has been found to provide adhesion for photographic emulsions. Aldehyde-based cross-linkers such as glyoxai, melamine formaldehyde, glutaraldehyde, and the like, reduce the silver halide in the photographic emulsion. By using a multi-functional aldehyde such as gloxal, melamine formaldehyde, glutaraldehyde and the like with an adhesion promoter, the poly(vinyl alcohol) top coat reacts with excess aldehydes remaining in the primer layer. This functions to scavenge unreacted aldehydes from the primer layer and provide a functional barrier between the primer and the photographic emuision.

The invention might find utility in an acid-catalyzed melamine formaldehyde resin to cross link the poly(vinyl alcohol) where control of the pH, pot life of the blend and degree of curing are of concern. The invention is beneficial in glyoxal-based cross linking systems, providing complete cure off- line and stable pot life, without the tendency to yellow when printed with inks that contain amines Examples Oriented polypropylene film samples were primed and coated with the coatings described in the Table.

TABLE TBDM.3-1<BR> LAB COATER RUN<BR> BASE FILM = FPM F Q CHILL ROLL<BR> 33XW247 PRIMING 50 230 130 60° TREATMENT LEVEL 2<BR> TOPCOA 50 230 130 60°<BR> LABEL SAMPLES AS TBDM3 XX<BR> % % % % TOTAL COAT .....<BR> <P>.. 10 11 40 20 LESS SLDS .....<BR> <P>. .. LTX STD GLY- ..... HEXYL HEX Wo ..... ..... STD GLY-<BR> ROLL LATEX LOT&num SLDS LATEX TALC EPOXY OXAL WAX H2O CELL. HEX LTX TALC EPOXY OXAL WAX TOTAL<BR> % g g g g g g g g % PHR PHR PHR PHR PHR PHR<BR> PART 1 PRIMING NE E D E NOUGH TO MAKE SIX SOFT SAMPLES OF TOP-COATED FILM PLUS 25 FEET OF PRIMED FILM FOR PHOTOACTIVITY TESTS<BR> TBDM3 P1MCM1983 P 123&num 1 70 74 5 0 00 71 0 0 0 0 1184 1 0 200 3 100 0 15 0 0 115<BR> TBDM3 P2MCM1983 P 123&num 1 70 65 9 0 00 12 6 0.0 0.0 121.5 2 0 200 3 100 0 30 0 0 130<BR> TBDM3 P3ELVANOL 90/50 8 9 49 9 0 00 6.1 2.2 0.0 141.8 1 0 200 3 100 0 15 20 0 135<BR> P4ELVANOL 90/50 8 9 49 9 0 00 10.9 2 0 0 0 142.1 1 0 200 3 100 0 30 20 0 150<BR> PART 2. SEQUENTIALLY TOP COAT THE PRIMED SAMPLES WITH THE FOLLOWING TOP COATS<BR> % % % % .....<BR> <P>10 22 5 10 .....<BR> <P>LTX STD NA ..... HEXYL TOTAL COAT ..... ..... STD<BR> ROLL LATEX LOT&num SLDS LATEX TiO2 EPOXY L50 H2O CELL SLDS LTX TiO2 EPOXY NA L50 TOTAL<BR> % g g g g g g g g % PHR PHR PHR PHR PHR PHR<BR> TBDM3 8 ELVANOL 90/50 P3 8 9 16 9 0 00 0 0 0.0 0.00 133 1 0 0 150 1 100 0 0 0 0 100<BR> TBDM3 9 ELVANOL 90/50 P3 8 9 33 7 0 00 0 0 0 0 0.00 116 3 0 0 150 2 100 0 0 0 0 100<BR> TBDM3 10 ELVANOL 90/50 P3 8 9 50 6 0 00 0 0 0 0 0 00 99.4 0 0 150 3 100 0 0 0 0 100<BR> TBDM3 11 ELVANOL 90/50 P3 8 9 101 1 0 00 0 0 0.0 0 00 48.9 0 0 150 6 100 0 0 0 0 100<BR> TBDM3 12 ELVANOL 90/50 P4 8 9 67 4 0 00 0 0 0 0 0.00 132.6 0 0 200 3 100 0 0 0 0 100

The coated samples were tested for resistance to water by washing the film sample with warm tap water. If the coating weight is sufficiently high, wiping the coating with warm, wet paper towel usually removes any poly(vinyl alcohol) coating which is not cross-linked.

The presence of poly(vinyl alcohol) (PVOH) and epoxy primer was also checked with an iodine stain and eosin dye.

Coating the PVOH/glyoxal/epoxy primers with 1 to 6% solutions containing only PVOH showed surprising results. There was enough unreacted glyoxal in the primer to completely cross link the top coat. However, the levei of epoxy in the primer is important. At 15 parts per hundred, cross linking was observed. At 30 parts per hundred epoxy, essentially no cross linking was observed.

These results show that the PVOH adheres to the PVOH/glyoxal portion of the primer and not the epoxy. Moreover, the rapid loss of PVOH of the top coat adhesion with the increasing epoxy level suggests that the epoxy and or the polyethyleneimine in the blend competes for reactive sites, such as the aldehydes.

It was surprising that a 6% solution applied with a 130 Quad gravure is almost completely resistant to wiping with warm water after drying at 11 50C.

Using iodine stain wavy coating lines can be seen indicating that the coating is relatively viscous. These wavy lines are present in the coated film when staining is performed before and after coating. The coating weight is about 0.2 g/msi.

Wiping only removed about 0.04 g/msi, and the stained sample shows that the PVOH coating came off in only small sections, most likely from abrasion and not because it dissolved.

For a sample coated with 3% PVOH (with an anticipated coating weight of -0. 1 g/msi), no coating was removed after wiping with warm water: no significant weight change was observed after wiping. However, when the primer containing 30 parts per hundred epoxy, sample TBDM3-P4, was coated with the same coating, 0.083 g/msi was removed by wiping with warm water.