Semi-crystalline ethylene vinyl acetate emulsion polymers for heat seal applications

• US 20040175589A1
• Filed: 03/04/2003
• Published: 09/09/2004
• Est. Priority Date: 03/04/2003
• Status: Active Grant

• Current Assignee: Wacker Chemical Corporation
• Original Assignee: Air Products Polymers LP
• Inventors: Daniels, Christian Leonard, Rabasco, John Joseph, Bott, Richard Henry, Vratsanos, Menas Spyros, Horwat, David William
• Granted Patent: US 7,189,461 B2
• Time in Patent Office: Days
• US Class Current: 428/511
• CPC Class Codes: C08F 2/24 with the aid of emulsifying agents
• CPC Class Codes: C08F 210/02 Ethene
• CPC Class Codes: C08F 218/08 Vinyl acetate
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 2500/20 Activation energy or enthalpy
• CPC Class Codes: C08L 1/02 Cellulose; Modified cellulose
• CPC Class Codes: C08L 2666/26 Natural polymers, natural resins or derivatives thereof according to C08L1/00 - C08L5/00, C08L89/00, C08L93/00, C08L97/00 or C08L99/00
• CPC Class Codes: C09D 123/0853 Vinylacetate
• CPC Class Codes: Y10T 428/31855 Of addition polymer from unsaturated monomers
• CPC Class Codes: Y10T 428/31895 Paper or wood

Abstract

This invention is directed to aqueous-based ethylene-vinyl acetate (EVA) polymer emulsions suited for use in heat seal applications. The EVA polymers of this invention are produced by a relatively low-pressure process, i.e., less than 2000 psig, preferably from about 1000 to about 2000 psig. The aqueous-based EVA based polymer emulsions contain crystalline segments resulting from ethylene linkages and are prepared by emulsion polymerizing ethylene and vinyl acetate, preferably with a carboxylic monomer, in the presence of a stabilizing system containing surfactant or a cellulosic protective colloid in combination with surfactant.

Claims

1. An aqueous-based ethylene-vinyl acetate polymer emulsion suited for use in heat seal applications said ethylene-vinyl acetate polymer comprised of crystalline ethylene segments prepared by emulsion polymerizing ethylene and vinyl acetate in the presence of a stabilizing system consisting essentially of a surfactant or a cellulosic protective colloid in combination with a surfactant, said ethylene-vinyl acetate polymer having:

(a) a crystalline melting point ranging from 35 to 110°

C. measured at a heat rate of 20°

C. per minute; and

,

(b) a tensile storage modulus of at least 1×

10⁵ dynes/cm² at a temperature of 115°

C. and measured at 6.28 rad/sec.

2. The polymer emulsion of claim 1 wherein the polymer is comprised of from 15 to 90% by weight of polymerized units of vinyl acetate and from about 10 to 85% by weight of polymerized units of ethylene based upon the total weight of the polymer.

3. The polymer emulsion of claim 1 wherein the polymer is comprised of from 25 to 80% by weight of polymerized units of vinyl acetate and from about 20 to 75% by weight of polymerized units of ethylene based upon the total weight of the polymer.

4. The polymer emulsion of claim 1 wherein the polymer is comprised of from 35 to 75% by weight of polymerized units of vinyl acetate and from about 25 to 65% by weight of polymerized units of ethylene based upon the total weight of the polymer.

5. The polymer emulsion of claim 1 wherein the polymer is comprised of from 30 to 50% by weight of polymerized units of vinyl acetate and from about 50 to 70% by weight of polymerized units of ethylene based upon the total weight of the polymer

6. The polymer emulsion of claim 2 wherein polymerized carboxylic acid units are present in said polymer in an amount from about 0.2 to about 10% by weight of said polymer.

7. The polymer emulsion of claim 6 wherein said polymer has a tensile storage modulus of at least 2×

10⁵ dynes/cm² at 115°

C. and measured at 6.28 rad/sec.

8. The polymer emulsion of claim 7 wherein the polymer is comprised of polymerized units of ethylene, vinyl acetate, and acrylic acid.

9. The polymer emulsion of claim 7 wherein the crystalline heat of fusion of said polymer is from about 5 to 100 joules per gram as measured at a heat rate of 20°

C. per minute.

10. The polymer emulsion of claim 7 wherein the glass transition temperature is from +25°

C. to about −

35°

C. as measured at a heat rate of 20°

C. per minute.

11. The polymer emulsion of claim 8 wherein crystalline thermal melting point ranges from 50 to 90°

C. as measured at a heat rate of 20°

C. per minute.

12. The polymer emulsion of claim 8 wherein a portion of the emulsion polymerization is carried out at a pressure of from 1000 to 2000 psig (6,996 to 13,891 kPa).

13. The polymer emulsion of claim 12 wherein the stabilizing system consists essentially of hydroxyethyl cellulose in combination with a surfactant.

14. The polymer emulsion of claim 13 wherein the vinyl acetate is present in an amount from 15 to 90% by weight, the ethylene is present in an amount from 10 to 85% by weight, and the acrylic acid is present in an amount from 0.5 to 5% by weight of the polymer.

15. The polymer emulsion of claim 14 wherein the crystalline heat of fusion ranges from preferably 15 to 70 joules per gram as measured at a heat rate of 20°

C. per minute.

16. A process for making an aqueous-based semi-crystalline ethylene vinyl acetate polymer emulsion which comprises reacting vinyl acetate and ethylene with optionally one or more other ethylenically unsaturated monomer, under emulsion polymerization conditions in the presence of a stabilizing system consisting essentially of a surfactant or a cellulosic protective colloid in combination with a surfactant, said ethylene-vinyl acetate polymer having:

(a) a crystalline melting point ranging from 35 to 110°

C. measured at a heat rate of 20°

C. per minute; and

,

(b) a tensile storage modulus of at least 1×

10⁵ dynes/cm² at a temperature of 115°

C. and measured at 6.28 rad/sec.

17. The process of claim 16 wherein the addition of monomers, except ethylene, to the emulsion polymerization are completed within the first 75% of the total reaction time.

18. The process of claim 16 wherein a portion of the process is carried out at pressures of from 1000 to 2000 psig (6,996 to 13,891 kPa).

19. A process for forming a paper stock for heat seal application which comprises:

coating a paper substrate with a polymer emulsion comprising emulsion polymerized units of vinyl acetate and ethylene with one or more other ethylenically unsaturated monomer, wherein said polymer emulsion is stabilized with a stabilizing system consisting essentially of a surfactant or a cellulosic protective colloid in combination with a surfactant, said polymer containing crystalline ethylene segments and having (a) a crystalline melting point ranging from 35 to 110°

C. as measured at a heat rate of 20°

C. per minute; and

, (b) a tensile storage modulus of at least 1×

10⁵ dynes/cm² at a temperature of 115°

C. and measured at 6.28 rad/sec; and

then,

drying the coating, said dried coating being non-blocking at ambient temperature.

20. A multi-layer heat sealable material comprising

(a) at least one substrate;

and

(b) at least one coating of a polymer emulsion comprising emulsion polymerized units of vinyl acetate and ethylene with one or more other ethylenically unsaturated monomer, wherein said polymer emulsion is stabilized with a stabilizing system consisting essentially of surfactant or a cellulosic protective colloid in combination with surfactant, said polymer containing crystalline ethylene segments and having (a) a crystalline melting point ranging from 35 to 110°

C. measured at a heat rate of 20°

C. per minute; and

, (b) a tensile storage modulus of at least 1×

10⁵ dynes/cm² at a temperature of 115°

C. and measured at 6.28 rad/sec.