Aqueous dispersions comprising polyurethane and ethylenic copolymers for heat sealable coatings

Abstract

A film forming aqueous dispersion having utility as heat seal coatings for blister packaging applications comprises a blend of 10-90% by weight of one or more polyurethane dispersions; 90-10% by weight one or more compatible ethylenic copolymer dispersions/emulsions; an anti-blocking additive at 0.1-12 weight % of the total solids; and optional additives including wetting, defoaming, thickener, antifungal additives. The heat seal coating compositions provide enhanced and balanced properties such as a reduction of organic solvents, a tack free coating surface off the press, good press runnability, easy clean-up, antiblocking from ambient temperature to 50 C., heat-activation with no pot life at elevated temperatures, and, heat sealability to various plastic substrates including Virgin Poly(ethylene terephthalate) (PET), recycle PET (RPET), Amorphous PET (APET), PET-Glycol modified (PETG), PETG/APET/PETG (GAG) and Polyvinyl chloride (PVC).

Claims

1. A film forming aqueous dispersion coating composition having utility as a heat seal coating for blister packaging applications comprising: A) 10% to 90% by weight of one or more polyurethane dispersions having a melting point when dried in the range of 30 C. to 120 C.; B) 90% to 10% by weight of one or more compatible ethylenic copolymer dispersions; C) an anti-blocking additive at 0.1-12 weight % of total solids; and D) optionally one or more wetting, defoaming, thickener, or antifungal additives; the heat seal coating when dried having a shear storage modulus G at a heat seal activation temperature range of 170 F.-240 F. in the range of 3.510.sup.4 to 6.010.sup.5 Pascals; the ethylenic copolymer dispersion having a glass transition temperature Tg in the range of 30 C. to 130 C.

2. The film forming aqueous dispersion coating composition of claim 1 wherein a solid resin weight ratio between A and B is in a range of 15/85 to 85/15.

3. The film forming aqueous dispersion coating composition of claim 1, wherein the ethylenic copolymer dispersion comprises a styrene monomer content of less than 80% by weight.

4. The film forming aqueous dispersion coating composition of claim 1, wherein the anti-blocking additive is selected from waxes or inorganic particles.

5. The film forming aqueous dispersion coating composition of claim 4 wherein the wax is in a micronized form or is an aqueous paste and has a melting point higher than 60 C. and is present in a range of 0.1 to 12 weight % of total solids.

6. The film forming aqueous dispersion coating composition of claim 1, wherein the one or more polyurethane dispersions has a melting point or softening point in the range of 25 C. to 110 C.

7. The film forming aqueous dispersion coating composition of claim 6, wherein the one or more polyurethane dispersions has a melting point of 15 C. to 100 C.

8. The film forming aqueous dispersion coating composition of claim 1, wherein the ethylenic copolymer dispersion has a glass transition temperature, Tg, in the range of 20 C. to 120 C.

9. The film forming aqueous dispersion coating composition of claim 1, wherein the ethylenic copolymer dispersion has a glass transition temperature, Tg, in the range of 10 C. to 110 C.

10. The film forming aqueous dispersion coating composition of claim 3, wherein the styrene monomer content in the copolymer is less than 50% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The annexed FIGURE is a plot of shear storage modulus for five different dispersions over a temperature range of 0 to 150 C.

DETAILED DESCRIPTION OF THE INVENTION

(2) The unique advantages of polyurethane dispersions in relation to coatings are their ability to form a coherent film, generally having good adhesion to plastic substrate, and the ease of property (such as tensile, elongation, and morphology) design by controlling the soft and hard segments in the polymer chains. The preparation of polyurethane dispersions is mentioned in the prior art and is known by those skilled in the art of polyurethane formulation through the utilization of various isocyanates and polyols and chain extenders to disperse the polymer in aqueous media. High abrasion resistance, superior toughness, elastic properties and high extensibility at low temperature are typical benefits for many surface coating and adhesive applications including heat seal coatings. However, the very same toughness and chemical resistance make such dispersions difficult to clean up and easily clog up anilox cells, thus resulting in poor press runnability. In heat seal blister coating applications, the medium heat activation temperature range of 170 F. to 240 F. (76 C. to 116 C.) also causes these polyurethanes to exhibit tackier surfaces even after proper drying, creates blocking issues right off the press (stacking on top of one another) as well as during storage and transportation. The higher raw material cost as compared to ethylenic copolymer dispersions and emulsions such as acrylic copolymer systems also restricts its broader use in many industrial applications.

(3) The term ethylenic copolymers dispersions or emulsions encompasses copolymers derived from the emulsion polymerization of monomers and includes ethylenic monomers, vinyl monomers, esters of acrylic acids and methacrylic acid, and ,-ethylenically unsaturated carboxylic acids etc., as mentioned in the prior art and as known by those skilled in the art of ethylenic copolymers formulation. These copolymer dispersions provide very good press runnability due to their semi-dry film formation and can be easily re-dispersed by its own dispersion, without clogging, and provide a tack free surface by the proper selection of blends of soft and hard copolymers as described in the prior art. However, these copolymers suffer from poor adhesion to the very plastics used in blister packaging, especially RPET, APET, virgin PET, PETG, and GAG.

(4) The present invention discloses a waterborne dispersion composition having significant utility as a heat seal coating for blister packaging applications comprising A) 10% to 90% by weight of one or more polyurethane dispersions, B) 90% to 10% by weight of one or more compatible ethylenic copolymer dispersion/emulsions, C) an anti-blocking additive at 0.1 to 12 weight % of the total solid, and optional additives, including wetting, defoaming, thickening, and antifungal additives; and that the shear storage modulus, G, of the dried film at heat seal activation temperature range (from 170 F. to 240 F.) is tailored to be in the range of 3.510.sup.4 to 6.010.sup.5 Pascals. The weight ratio between A and B, based on the solid resins, is in the range of 15/85 to 85/15. The heat seal coating compositions of the invention provide enhanced and balanced properties such as a reduction of organic solvents, a tack free coating surface off the press, good press runnability, easy clean-up, anti-blocking from ambient temperature to 50 C., heat-activation with no pot life at elevated temperature, and heat sealability to various plastic substrates including virgin poly(ethylene terephthalate) (PET), recycled PET (RPET), amorphous PET (APET), PET-glycol modified (PETG), PETG/APET/PETG (GAG) and polyvinyl chloride (PVC).

(5) It has been found that there is a synergistic effect by blending a polyurethane dispersion and a compatible ethylenic copolymer dispersion/emulsion for a heat seal coating. The term compatible means that there is no significant viscosity build up or coagulation, crosslinking or significant loss of film transparency immediately, or after normal storage conditions. With compatible blends, both the adhesion to blister plastics derived from the polyurethane dispersion component and the press runnability and easy to clean features from the copolymers are maintained as compared to the individual polymers when evaluated for a blister heat seal application. The film formation for the blend is also improved, even when a high Tg copolymer is used, since the polyurethane also impart its film forming capability. The inclusion of anti-blocking additives to the blend composition is crucial to allow the use of a softer copolymer dispersion and/or a softer polyurethane dispersion; to extend the applicable range of Tg for the copolymers as well as the applicable melting point or softening point range for the polyurethane dispersion; and to maintain a high level of block resistance as required by blister applications. Optional additives can be used, such as wetting agents, defoaming thickeners, and antifungal additives, as known by those skilled in the art of aqueous dispersion formulation.

(6) During the heat seal step (activation temperature of the coating film from 170 F. to 240 F.), the heat seal coating film has to be soft enough to gain the mobility to flow into the mating substrate to create maximum contact and also has to be strong enough during the cooling immediate after releasing from the seal jars to hold the 2 substrates together through the process. Storage modulus such as shear storage modulus (G) is an useful measurable indication of such physical properties described above. It is, therefore, crucial to define the shear storage modulus values of the heat seal coating film in the heat seal activing temperature range to achieve desired heat seal performance. It is our finding that it is important to tailor the shear storage modulus of the dried film of the composition to be in the range of 3.510.sup.4 to 6.010.sup.5 pascals in heat seal activation temperature range from 170 F. to 240 F. for the heat seal application. This shear storage modulus is also an inherent properties of the individual polyurethane dispersion (component A) and compatible ethylenic copolymer dispersion/emulsion (component B); and therefore, it can be expected that by determining or knowing the G values of the dried film of the individual dispersion or emulsion at heat seal activation temperature range (from 170 F. to 240 F.), one can estimate/calculate the G values of the mixtures in the same temperature range based on their weight ratio. Conversely, one can also expect to estimate the needed weight ratios among these polyurethane and compatible ethylenic copolymer dispersion/emulsion to achieve the target G values at heat seal activation temperature range (from 170 F. to 240 F.) to be in the range of 3.510.sup.4 to 6.010.sup.5 Pascals. This also means that the G values at heat seal activation temperature range (from 170 F. to 240 F.) for individual dispersion/emulsion can fall outside of the range of 3.510.sup.4 to 6.010.sup.5 Pascals since one can use the blend ratio to bring the resulting G value of the blend into the targeted range.

(7) It is also reasonable to expect that hybrid dispersion blends of the polyurethane and ethylenic copolymers will have the same synergistic outcome. A hybrid blend can be achieved by one of the two ways: 1) By polymerization of one polymer in present of the other polymer to form a interpenetrating network through single or multi-stage polymerization, or 2) by including a type of monomer/pre-polymer carrying a functional group that can react into the other polymer chains, such as a hydroxyl-carrying copolymer grafted on the polyurethane chain.

(8) The heat activation temperature range for blister applications is from 170 F. to 240 F. (76 C. to 116 C.) and the block resistance temperature is 120 F. (50 C.). The selection guideline for both the copolymers and the polyurethanes is to correlate their Tg, softening point or melting point to the upper limit of this heat seal temperature range. With the use of anti-blocking additives of appropriate melting point, the low limit of the Tg, softening point or melting point of the copolymer or the polyurethane dispersion can then be extended to well below 50 C. where the blocking resistance test is conducted.

(9) Suitable polyurethane dispersions should have their melting point or softening point in the range of 30 C. to 120 C., preferably in the range of 25 C. to 110 C., and more preferably in the range 15 C. to 100 C. and to have inherent adhesion to various plastics. The polyurethane dispersions include, but are not limited to the products from Royal DSM N.V. (Neorez R-551, R-563, R-600, R-1400, R-9249, R-9330, and R-9621); from Bayer Material Science A.G. (Dispercoll U 42, U 53, U 53, U 56, U 4101, U 8755, U XP2643, U XP2682, and U XP2824); From Alberdingk Boley Inc. (U 216, U 3251, U 3700, U 400N, U 4040, U 4101, and U800); Bond Polymers International LLC (Bondthane UD-104, UD-302, UD-303, UD-312, UD-375, UD-410; other non-self crosslinkable UD products are suitable but contain co-solvent and are not preferred); from Union Specialties Inc. (Unithane IC-407SF, IC-551NF, IC-555NF, IC-652NF, IC-653NF, IC-807NFJC-850NF, IC-950NF, IC-951NF, IC953CD, 9717, 9787, XL-2945, and XL-2899); from Essential Polymers (R4300, R4310, R4370, R4388, R4400, R4560, ALU081, R4100, R4188, R4196, R4242, R4584, and R9010); and from C. L. Hauthaway & Sons Corp. (Hauthane L-2875, L-2877, L-2882, L-2892, L-2896, L-2942, L-2969, L-3101, HD-2001, HD-3011, HD-4664, HD-4669, and HD-4675). The major blister plastic adhesion property is expected to, but not limited to, come mainly from the polyurethane dispersion.

(10) A suitable ethylenic copolymer dispersion is selected to have its glass transition temperature, Tg, in the range of 30 C. to 130 C., preferably in the range of 20 C. to 120 C. and more preferably in the range of 10 C. to 110 C. The styrene monomer content in the copolymers should be less than 80% by weight, and preferably less than 50%. The ethylenic copolymer dispersion can be selected from the materials from BASF Corporation (Joncryl 1674, 8211, 9010, 9012, 9022, 9030, 1665, and 750); from Alberdingk Boley (AC 548, AC 2310, and Ac 2389); and from copolymer dispersions as mentioned in the prior art.

(11) Exemplary anti-blocking additives are selected from waxes or inorganic particles. Suitable waxes (in either micronized form or aqueous paste) have a melting point higher than 60 C. so as not to create blocking issue in the 50 C. blocking test, more preferably above 80 C., and most preferably above 100 C. In particular, polyethylene, and oxidized polyethylene waxes provide anti-block and slip properties without interfering with the heat seal performance. The anti-blocking additive is used in the range of 0.1 to 12 weight % of the total solids, in particularly 0.5% to 8% and more particularly 1% to 5%. Appropriate anti-blocking additives include, but are not limited, to waxes from BYK Additives & Instruments (Aquacer 1547, 8026, 8032, 8052, 8059, 8592, Aquamatt 208, 263, Ceraflour 929, 950); from The Lubrizoil Corporation (Liquitron 442, 4405GA, CEX4640, Pinnacle 1610, 1993); and from Micropowders Inc. (Aquapoly 215, 225, AquaTex 270, 325, Aquamatte 31). Suitable inorganic includes but not limited to materials like silica (Syloid ED3, Ludox AM, AD30 (from W. R. Grace and Company); and Aerodisp 750 (from Evonik Industries AG).

(12) Optional additives including wetting, defoaming, thickener, antifungal additives are commonly used to improve runnability and stability of the coating composition and are known by those skilled in the art of aqueous dispersion formulation.

(13) The aqueous heat seal coating composition of the invention can be applied through a flexographic (flexo) coater from a flexo press or from a lithographic (offset) press at the end of the press, through a roller coater or through a gravure coater onto the printed blister boards. The aqueous heat seal coating can either be applied either in-line or off-line with the printing steps and drying with the dryer designed for the press. The heat seal coating is applied on the clay coated side of the blister board to prevent excessive dive-in and at appropriate coat weight, 0.25 to 0.8 lb/MSF (pounds per thousand square feet) or 1.22 to 3.91 gm/m.sup.2 (gsm), enough to bond the blister plastics.

(14) The viscosity of the heat seal coating composition of this invention is in the range of 80 to 600 centipoises (cps) measured with a Brookfield Viscometer model LV using an appropriate spindle for the device (#2 or #3 spindle depending on the viscosity) and at appropriate spindle speed (10 to 100 rpm) at 25 C., preferably in the range of 150 to 600 cps and more preferably in the range of 200 to 400 cps as known by people skill in the art of formulating aqueous coating for the application methods mentioned above. The percent solid of the coating composition of this invention is in the range of 20% to 60%, particularly in the range of 25% to 50%, more particularly in the range of 35% to 45%.

(15) The heat seal process for the coating composition in this invention is performed using heating jaws to reach the heat activation temperature is in the range of 170 F. to 240 F. (76 C. to 116 C.) at the coating interface by properly adjusting the temperature setting, pressure, and dwell time of the jaws. The heat is transmitted from the non-coated side of the backing (blister board), through the backing, to the coating/blister plastic interface.

EXAMPLES

(16) The following parameters are applicable to the examples presented herein:

(17) ViscosityViscosity was measured with a Brookfield Viscometer model LV with an appropriate spindle and rpm at 25 C. or a specified temperature per manufacturer instructions.

(18) Percentage solid: EPA method 24 and theoretical calculations based on the solid of each raw material is used to determine the solid percentage of the water based coating composition.

(19) Heat Sealing: A Lab heat sealing unit from Packaging Industries, Inc., Model 12A9 was used to perform sealing of the blister card to blister plastics; heat is transmitted through the card to the coating-plastic interface. The setting conditions were 345 F. (174 C.), 80 psi, for 2 seconds to achieve the coating activation temperature of 200 F. (93 C.) which was determined by an 8-temperature indicator label (170 F. to 240 F.) from the Paper Thermometer Company. If adjustment is required, the temperature setting was changed while keeping the pressure and dwell time the same.

(20) Drying: After the coating was applied to the C1S blister board, a blister Blue M oven was used to dry the coating at 100 C. for 10 seconds.

(21) Block Resistance: The blocking test is performed for a face to back (coated side to uncoated side) orientation under 1 pound per square inch (psi) at 50 C. for 24 hours. The block resistance is rated from 1 to 5: 5: Excellent: Falls apart easily; 4: Good: Slight cling, No picking, very light or no force separating; 3: OK: No picking, slight force separating; 2: Some paper picking; and 1: Bad: Fiber tearing.

(22) Shear storage modulus curve determination: TA instrument RDA model ARES G2 was used in generating the shear storage modulus cure. 8 mm or 25 mm parallel plate geometry was used to conduct the temperature sweep run on RDA instrument from 0 C. to 150 C. at 5 C./minutes ramp rate, at angular frequency of 10 rads/sec., and under auto-tension and auto-strain mode. A sample film was prepared by casting about 4 to 5 grams of a wet sample on a releasable silicone rubber cup with diameter of 5 cm. The filled cup is then put in 50 C. oven for 24 hours followed by applying vacuum at 50 C. for another 24 hours to remove residual water in the film. The achieved dried film is about 0.8 to 1.5 mm thick. Once the shear modulus curve is generated, the modulus at 170 F. (77 C.) and at 240 F. (116 C.) are recorded for comparison.

Examples 1 to 4 and Comparative Examples 1 and 2

(23) TABLE-US-00001 TABLE 1 Heat Seal Coating Compositions of Examples 1 to 4 and Comparative Examples 1-2 Comparative Comparative Ingredient Class Example 1 Example 1 Example 2 Example 3 Example 2 Example 4 Joncryl 750 Ethylenic 85.90 76.00 38.00 11.00 N/A 10.00 (BASF) Copolymer dispersion H2O Distill water 10.00 N/A N/A N/A N/A N/A Foam-A-Tac Defoamer 0.30 0.30 0.30 0.30 0.30 0.30 617 (ESP Specialty Products, Inc) R4242 Polyurethane N/A 20.10 58.20 84.20 95.00 82.00 (Essential dispersion Polymer) ACRYSOL RM- Rheology 0.30 0.10 N/A 1.00 1.20 1.20 8W (Dow modifier Chemical Company) CEX4640 Oxidized 2.00 2.00 2.00 2.00 2.00 5.00 (Lubrizoil) Polyethylene wax Sodium Wetting 1.50 1.50 1.50 1.50 1.50 1.50 Dioctyl additive Sulfosuccinate (DOSS) 70% in Propylene Glycol (Midwest Graphic Sales, Inc.) Total 100.00 100.00 100.00 100.00 100.00 100.00 % Solid 45.1 46.7 40.3 35.5 33.6 35.5 % PU Solid per Solid Resins 0.0% 14.9% 50.3% 83.5% 100.0% 84.5% % Wax Solid of Total Solid 1.78% 1.71% 1.99% 2.26% 2.38% 6.64% Viscosity, cps 242 272 333 195 208 278

(24) The components of the example compositions in accordance with the present invention were prepared by adding the acrylic copolymer dispersion(s) and defoamer in a high density polyethylene plastic container of proper size and adding the remaining ingredients one at a time while mixing with a saw-tooth mixing blade at a medium speed 700 rpm. The whole composition was then mixed for 30-60 minutes to reach a stable viscosity. When a rheology modifier was used, the recommended mixing time was 60 minutes. The viscosity was measured with a Brookfield Viscometer model LV with a #2 spindle at 60 rpm and 25 C. The listed percentage solid, % polyurethane (PU) solids per solid resins (polyurethane resin plus acrylic copolymer resin solids), and percent solid wax per total solids were calculated from the solids of each ingredient and all percentages used are by weight percentage.

(25) Each coating composition was then applied with a #4 wire wound rod onto the coated side of a 20 caliper 1 side coated Candesce blister board from Clearwater Paper Corporation and dried in a 120 C. oven for 10 seconds.

(26) Heat seal performance for the compositions from Table 1 were based on sealing to various blister plastics provided by converters at 345 F., 80 psi for 2 seconds using a lab heat sealer as described above to reach an interface temperature of 200 F. (93 C.). The plastics dimension was 2.5 inches by 0.5 inch and each sealed strip was then cut into 6 small strip for a hand peel test and the peel results rated by the failure mode. The most idea failure mode was a 100% fiber tearing (FT) of the blister board and in general a FT mode over 85% may be acceptable, depending on the converter's specification. Other undesirable failure modes includes pop (the blister plastic pops off the heat seal coating indicating bad plastic adhesion), clay split (the clay coating is pulled off from the blister board without causing fiber tear; indicating poor penetration and bond strength), and ink split (inks has poor cohesive strength; not applicable in this case since no ink in used). The results of the heat seal tests for heat seal coating compositions from Table 1 are listed in Table 2 below, expressed by consideration of the area % of each failure mode.

(27) An Ease of clean evaluation was performed by applying the coating composition using a wire wound rod #10 on a clean glass plate, letting it blow dry to dried for about 20 second to have a semi-dried film, and then rubbing the film with a 50/50 blend of isopropyl alcohol and water. The evaluation is rated as follows: 1. Easy to re-disperse without any visible, insoluble film/particles; 2. Medium easy with no or few difficult to view insoluble film/particles; 3. Hard to re-disperse with visible and insoluble film/particles which would cause clogging of anilox cells and be difficult to cleanup on a press). The results are also listed in Table 2.

(28) Table 2 also includes one comparative example 3 of an all polyurethane dispersion and one comparative example 4 of an all acrylic copolymer dispersion.

(29) TABLE-US-00002 TABLE 2 Heat Seal, Ease of Clean & Block Evaluation Results for Table 1 Compositions Block Blister Plastic Type Ease of Resistance Examples RPET APET PETG GAG PVC Clean Rating Comparative 60-40% FT; 40-60% 79% FT; 92% FT; 80% FT; 100% FT Easy re- 2, some Example 1 Pop 5% Pop; 8% Pop 20% Pop disperse picking, (Acrylic 16% Clay strong force Copolymer Split Dispersion) Example 1 95% FT; 5% Pop 100% FT 95% FT; 84% FT; 100% FT Easy re- 2-3, slight 5% Clay 16% Clay disperse picking, Split Split medium force Example 2 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 3, No re-disperse picking, slt force Example 3 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 3, No re-disperse picking, slt force Comparative 100% FT 100% FT 100% FT 100% FT 100% FT Hard to re- 3, No Example 2 disperse, picking, slt (Polyurethane insoluble force Dispersion) (Without wax: 2, some picking) Example 4 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 5, Fall apart re-disperse Comparative 100% FT 100% FT 100% FT 100% FT 100% FT Very Hard to 1, fiber Example 3 re-disperse, tearing (Polyurethane insoluble Dispersion) Comparative 70-60% FT; 30-40% 80% FT; 80% FT; 90% FT; 100% FT Easy re- 2-3, some Example 4 Pop; slt 20% Pop 20% Pop 10% Pop disperse picking, (Acrylic Corner lift medium Copolymer) force FT: Fiber tear; Slt slight

(30) All the heat seal coating compositions from Table 1 and Table 2 have good heat seal to PVC blister plastic, however, PVC plastics are being gradually faced out of the marketplace globally due to their environmental impact in depleting the earth's ozone layer. The heat seal performance over other blister plastics, on the other hand, is drastically different. Acrylic copolymer dispersion coating compositions, Comparative examples 1 and 4, show poor heat seal adhesion over RPET, APET and either PETG or GAG. Their block resistance rating is marginal, even though they can be further improved by a proper anti-block resistant additive. Both examples, as expected, have good re-solubility and thus are expected to have good press runnability and easy cleanup properties.

(31) Polyurethane dispersion coating compositions, Comparative Examples 2 and 3, exhibit excellent heat seal adhesion to all the plastics tested as might be expected and they are more difficult to clean up due to their excellent film property and therefore will cause clogging of anilox cells which makes it difficult to maintain a consistent coat weight in longer press runs. Comparative Example 3 has a poor block resistant rating of 1, which causes undesirable fiber tearing and problems in press runs and handling afterwards. Comparative Example 2 has good block resistance with an anti-blocking additive as specified in this disclosure, while having marginal block resistance if an anti-blocking additive is not used.

(32) Polyurethane dispersions and acrylic copolymer dispersions normally do not have good compatibility for various reasons, such as but not limited to, their respective chemical structures, functional group interactions, the amine extenders used, and their morphology. The most frequent results of the incompatibility are gel structure formation and hazy film formation. Example 1, 2, 3 utilize compatible polyurethane dispersions and acrylic copolymer dispersions, with solid PU % at 15%, 50% and 84% per solid resin along with an oxidized polyethylene anti-blocking additive at 1.7 to 2.4% as specified. The resulting synergistic effect for heat seal blister plastic adhesion as compared to pure acrylic copolymers, ease of clean up as compared to pure polyurethane dispersions, and anti-block resistance are achieved as demonstrated in Table 2. Even when the specified anti-blocking additive is doubled, as in Example 4, the heat seal properties to all the blister plastics tested remained at 100% fiber tearing bond performance, while block resistance reached the highest 5 rating (fall apart between sheets). Better economic value by incorporating an acrylic copolymer dispersion is also realized.

(33) To further demonstrate the synergistic performance of the heat seal coating compositions from this invention, Examples 5 to 9 below utilize harder or softer compatible polyurethane dispersions and acrylic copolymer dispersions than those from Examples 1 to 4. Heat seal blister plastic adhesion, ease of cleaning, (better runnability), anti-block resistance, as well as better economics are achieved as demonstrated in Table 4. The heat seal performance for virgin PET is the same or better than for the prior examples.

(34) TABLE-US-00003 TABLE 3 Heat Seal Coating Compositions of Examples 5 to 9 Ingredient Class Example 5 Example 6 Example 7 Example 8 Example 9 Joncryl 750 Ethylenic 28.00 37.50 (BASF) Copolymer dispersion Joncryl HSL9012 Ethylenic 60.00 35.00 10.00 (BASF) Copolymer dispersion AC 548 Ethylenic 35.40 (Alberdingk Copolymer Boley) dispersion Foam-A-Tac 617 Defoamer 0.30 0.30 0.30 0.30 0.30 (ESP Specialty Products, Inc) R4242 (Essential Polyurethane 57.70 48.20 Polymer) dispersion ALU081(Essential Polyurethane 33.20 57.00 10.00 Polymer) dispersion Dispercoll U Polyurethane 57.20 4101 (Bayers dispersion Material Science) ACRYSOL RM- Rheology N/A 1.00 0.80 0.50 0.50 8W (Dow modifier Chemical Company) CEX4640 Oxidized 5.00 5.00 5.00 2.00 2.00 (Lubrizoil) Polyethylene wax Sodium Dioctyl Wetting 1.50 1.50 1.50 1.50 1.50 Sulfosuccinate additive (DOSS) 70% in Propylene Glycol (Midwest Graphic Sales, Inc.) Total 100.00 100.00 100.00 100.00 100.00 % Solid 37.6 39.9 39.9 39.1 40.1 % PU Solid per Solid Resin 31.9% 62.6% 51.5% 51.5% 50.6% % Wax of Total Solid 5.31% 5.01% 5.02% 2.05% 2.00% Viscosity, cps 750 261 345 200 225

(35) TABLE-US-00004 TABLE 4 Heat Seal, Ease of Cleaning, and Block Evaluation Results for Table 3[AL1] Compositions Block Blister Plastic Type Ease of Resistance Examples RPET APET PETG GAG PVC Clean Rating Example 5 100% FT 100% FT 100% FT 100% FT 100% FT Easy re- 2-3, slight disperse picking, medium force Example 6 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 3, No re-disperse picking, slt force Example 7 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 3, No picking re-disperse Example 8 100% FT 100% FT 95% FT; 100% FT 100% FT Medium easy 3, No picking 5% Clay Split re-disperse Example 9 100% FT 100% FT 100% FT 100% FT 100% FT Medium easy 3, No picking re-disperse

(36) The annexed FIGURE shows the shear storage modulus curves generated from the RDA instrument under the conditions specified for five of the dispersions, including two ethylenic copolymer emulsions/dispersions and three polyurethane dispersions. The two solid lines outline the activation heat seal temperature at 170 F. (77 C.) and at 240 F. (116 C.) and the two dotted lines outline the targeted shear modulus range for the heat seal coating composition, i.e. 3.5104 to 6.0105 Pascals. Table 5 records the corresponding G values at 170 F. (77 C.) and at 240 F. (116 C.) for each dispersion. One can see that only IC556NF and HSL9012 have G values within 3.5104 to 6.0105 Pascals at a temperature range from 77 C. to 116 C., while R4242 well above the range, Joncryl 750 is slightly below the range and U-54 is well under the range at the same temperature range.

(37) TABLE-US-00005 TABLE 5 Shear Storage Moduli for individual dispersion/ emulsion at 170 F. and 240 F. Shear Storage modulus G (pascals) G at 170 F. G at 240 F. Ingredient Chemistry (77 C.) (116 C.) Joncryl HSL9012 Ethylenic Copolymer 3.2 10.sup.5 7.2 10.sup.4 Dispersion Joncryl 750 Ethylenic Copolymer 1.2 10.sup.5 2.1 10.sup.4 Dispersion IC556NF Polyurethane Dispersion 6.4 10.sup.5 1.9 10.sup.5 R4242 Polyurethane Dispersion 3.4 10.sup.6 4.5 10.sup.5 U54 Polyurethane Dispersion 6.7 10.sup.4 Too flowable and can not be measured

(38) Despite that only two individual dispersions with G values fall within a 3.510.sup.4 to 6.010.sup.5 Pascals range at a heat seal activation temperature range of 170 F. (77 C.) to 240 F. (116 C.), the examples below not only demonstrate how we can utilize the blend ratio to tailor to this target shear modulus range but also show the correlation of the target range of shear storage modulus to the quality of seal.

(39) Table 6 shows the shear storage moduli of the heat seal coating compositions as outlined in Table 1 (their seal performance in Table 2) and Example 10.

(40) TABLE-US-00006 TABLE 6 Shear Storage Moduli for Examples showed in Table 1. Target Shear Storage Modulus Range (pascals): 6.0 10.sup.5 to 3.5 10.sup.4 G at 170 F. (77 C.) G at 240 F. (116 C.) Seal Quality Comparative Example 1 Ethylenic Copolymer 1.5 10.sup.5 2.1 10.sup.4 poor seal (too soft) Dispersion Example 1 Joncryl 750/R4242 blend = 7.0 10.sup.5 1.2 10.sup.5 almost perfect seal 79.1/20.9 by wt ratio Example 2 Joncryl 750/R4242 2.3 10.sup.6 2.7 10.sup.5 perfect seal blend = 39.5/60.5 by wt ratio Example 3 Joncryl 750/R4242 3.1 10.sup.6 3.9 10.sup.5 perfect seal blend = 11.6/88.4 by wt ratio Comparative Example 3 Polyurethane Dispersion 1.7 10.sup.5 4.0 10.sup.4 perfect seal, but hard to clean Example 5 Joncryl HSL9012/ALU081 = 5.5 10.sup.5 1.3 10.sup.5 perfect seal and good 64.4/35.6 by wt ratio cleaning Example 10 Joncryl 750/U-54 = 7.2 10.sup.4 2.1 10.sup.3 too soft and less than 11.6/88.4 wt ratio 60% FT in most cases Example 10: same formula as Example 3 but substitute R4242 (high G) with U-42 (lowest G)

(41) Note that the detailed seal quality information for the examples in Table 6 can be found in Table 2. For Comparative Example 1 based on Joncryl 750 ethylenic copolymer dispersion, its G at 240 F. is lower than 3.510.sup.4 Pascals and the material is too soft during the heat seal step and could not regain the film strength fast enough after the heating jar pressure is off and thus resulted in poor quality of seal quality. Examples 1, 2, and 3 are different among them by varying the ratio between ethylenic copolymer emulsion, Joncryl 750 (lower G value at 240 F.; softer material) and the polyurethane dispersion, R4242 (higher G at 170 F.; stiffer material). Example 1 has slightly higher G at 170 F. and achieved almost perfect seal quality while Example 2 and 3 have G values within the target shear storage modulus range between 170 F. and 240 F. and showed perfect seal quality and appropriate film strength behavior. By blending these two emulsions together, we are able to not only achieve the synergistic effect as mentioned earlier but also tailor desired physical strength required to go through the heat seal cycle. Comparative Example 3 and Example 5 both have G values within the target shear storage modulus range between 170 F. and 240 F. and showed perfect seal quality except that Comparative Example 3 is use all polyurethane dispersion and thus has inherent clean-up problem. Example 5 are formulated with HSL9012 and ALU081 and such composition also exhibits good seal quality and G values within the target range between 170 F. and 240 F. Example 10 is the same as Example 3 except using softer U-54 (lower end of the G value even at 170 F. and G does not even registering at 240 F.). Example 10 has poor seal quality mainly due to poor physical strength at the heat seal process resulting from softer emulsions of Joncryl 750 and U-54.

(42) The use of anti-blocking additives in the present invention has broadened the selection of polyurethane dispersions and acrylic copolymer dispersions in heat seal coating compositions; both softer polyurethane dispersions and softer acrylic copolymer dispersions can be used while still having proper block resistance as required in blister coating applications. The incorporation of a polyurethane dispersion in the heat seal coating compositions of this invention provides a coating film toughness and adhesion to various plastics (RPET, Virgin PET, APET, PETG, GAG, and PVC), while harder acrylic copolymer dispersions and harder polyurethane dispersions can be used at the same time without scarifying the flexibility of the resulting dry coating.

(43) The examples above have demonstrated the synergistic effect and benefits in heat seal blister coating applications by a blend of A) 10% to 90% by weight of one or more polyurethane dispersions; B) 90% to 10% by weight of one or more compatible ethylenic copolymer dispersions/emulsions; C) an anti-blocking additive at 0.1 to 12 weight % of the total solids; and D) optional additives including wetting, defoaming, thickener, and antifungal additives. It is also crucial that the shear storage modulus, G, of the dried film at heat seal activation temperature range (from 170 F. to 240 F.) are tailored to be in the range of 3.510.sup.4 to 6.010.sup.5 Pascals to ensure best heat seal success. It is even more preferable to have the heat seal blister coating composition comprised of A) 20% to 80% by weight of one or more polyurethane dispersions; B) 80% to 20% by weight of one or more compatible ethylenic copolymer dispersions/emulsions and having the shear storage modulus, G, of the dried film at heat seal activation temperature range (from 170 F. to 240 F.) tailored to be in the range of 3.510.sup.4 to 6.010.sup.5 Pascals. A weight ratio between A and B based on the solid resin content is in the range of 15/85 to 85/15. As can be reasonably expected by those in the skilled in the art, a hybrid blend of the polyurethane and acrylic copolymers, with polymerizing of one resin dispersion in the presence of the other resin dispersion or grafting onto one another can achieve the same synergistic effect.

(44) Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.