CN-117042955-B - Multilayer film with foamed polyolefin-based adhesive composition

CN117042955BCN 117042955 BCN117042955 BCN 117042955BCN-117042955-B

Abstract

The present invention provides multilayer films having enhanced toughness and optical properties. The multilayer film includes a substrate layer, an outer layer, and an adhesive layer between the substrate layer and the outer layer. The multilayer film may also include additional layers. Methods of making such multilayer films are also provided. The multilayer film according to the invention is particularly useful for packaging applications where resistance to cracking and high transparency are desired.

Inventors

M.C. Henry
ZHANG GANG
W - R - Leopold Bern

Assignees

伊奎斯塔化学有限公司

Dates

Publication Date: 20260512
Application Date: 20220310
Priority Date: 20210312

Claims (19)

1.A film, comprising: a. A base layer; b. a first outer layer, and C. A first tie layer disposed between the first outer layer and the base layer, the first tie layer comprising a first foamed polyolefin-based adhesive composition, and the first foamed polyolefin-based adhesive composition comprising a polyolefin and a functionalized olefin-based polymer, wherein the first foamed polyolefin-based adhesive composition comprises a reaction product of: a. feeding the polyolefin-based adhesive composition and gas into an extruder; b. mixing the polyolefin-based adhesive composition and the gas in the extruder under pressure and temperature conditions sufficient to form a mixture of molten polyolefin-based adhesive composition and dissolved gas; c. Discharging the mixture from a die attached to the extruder to reduce the pressure of the mixture by an amount sufficient to produce a matrix of molten polyolefin-based adhesive composition comprising a dispersed phase of air cells, and D. The temperature of the matrix of the molten polyolefin-based adhesive composition comprising the dispersed phase of air cells is reduced at a rate to induce collapse of at least a portion of the air cells prior to curing of the polyolefin-based adhesive composition.
2. The film of claim 1, wherein the gas is produced in the extruder by thermal decomposition of a chemical blowing agent.
3. The film of claim 2, wherein the chemical blowing agent comprises an azo blowing agent, a nitroso blowing agent, an azide blowing agent, a bicarbonate blowing agent, or a combination thereof.
4. The film of claim 1, wherein the gas is added to the extruder from an external source.
5. The membrane of claim 1, wherein the gas is nitrogen, carbon dioxide, or a mixture thereof.
6. The film of claim 1, wherein the polyolefin-based adhesive composition comprises the reaction product of a mixture of: a. the polyolefin, and B. The functionalized olefin-based polymer; Wherein the mixture is heated and melt blended at a temperature sufficient to melt at least a portion of the polyolefin and at least a portion of the functionalized olefin-based polymer.
7. The film of claim 6, wherein the functionalized olefin-based polymer comprises the reaction product of a mixture of: a. Olefin-based polymer, and B. a functional monomer; wherein the functional monomer is grafted to the olefin-based polymer by reactive extrusion or solution processes.
8. The film of claim 7, wherein the olefin-based polymer comprises a vinyl polymer, a propylene-based polymer, or a combination thereof.
9. The film of claim 7, wherein the functional monomer comprises a carboxylic acid, a carboxylic acid derivative, an anhydride derivative, and combinations thereof.
10. The film of claim 6, wherein the polyolefin comprises a vinyl polymer, a propylene-based polymer, or a combination thereof.
11. The film of claim 1, wherein the first outer layer comprises a polyethylene homopolymer, a copolymer or unit derived from ethylene and a unit derived from one or more ethylenically unsaturated C 3 -C 8 non-polar comonomers, a polypropylene homopolymer, a copolymer or unit derived from propylene and a unit derived from one or more of ethylene and ethylenically unsaturated C 4 -C 10 non-polar comonomers, or a combination thereof.
12. The film of claim 1, wherein the base layer comprises an ethylene vinyl alcohol copolymer, a polyamide, or a combination thereof.
13. The film of claim 1, further comprising: a. A second outer layer, and B. A second tie layer disposed between the second outer layer and the base layer, the second tie layer comprising a second foamed polyolefin-based adhesive composition.
14. The film of claim 13, wherein the first foamed polyolefin-based adhesive composition comprises the reaction product of: a. feeding the polyolefin-based adhesive composition and gas into an extruder; b. mixing the polyolefin-based adhesive composition and the gas in the extruder under pressure and temperature conditions sufficient to form a mixture of molten polyolefin-based adhesive composition and dissolved gas; c. Discharging the mixture and dissolved gas from a die attached to the extruder to reduce the pressure of the mixture by an amount sufficient to produce a matrix of molten polyolefin-based adhesive composition comprising an air chamber, and D. The temperature of the matrix of molten polyolefin-based adhesive composition comprising air cells is reduced at a controlled rate to induce collapse of at least a portion of the air cells prior to curing of the polyolefin-based adhesive composition.
15. A method of forming a multilayer film, comprising: a. Adding the polyolefin-based adhesive composition and the gas to an extruder and mixing under pressure and temperature conditions sufficient to produce a mixture of molten polyolefin-based adhesive composition and dissolved gas, wherein the polyolefin-based adhesive composition comprises a polyolefin and a functionalized olefin-based polymer; b. Heating a portion of each: i) A first polymer, and Ii) a second polymer which is a polymer, C. And (3) coextrusion: i) A first layer comprising the first polymer, Ii) a second layer comprising said second polymer, and Iii) A tie layer disposed between the first layer and the second layer, the tie layer comprising a matrix of a molten polyolefin-based adhesive composition having a dispersed phase of air cells formed as the tie layer exits the extruder, To form a multilayer melt, and D. The temperature of the multilayer melt is reduced at a controlled rate to induce collapse of at least a portion of the air cells prior to curing of the polyolefin-based adhesive composition.
16. The method of claim 15, wherein the first polymer is a polar polymer and the second polymer is a non-polar polymer.
17. The method of claim 15, wherein the gas is added to the extruder by thermal decomposition of a chemical blowing agent or from an external source.
18. A method of forming a multilayer film, comprising: a. Providing an extrusion apparatus having at least one extruder with a die through which polymer in the extruder is discharged during extrusion, wherein components of the apparatus are arranged such that during extrusion of a matrix of molten polyolefin-based adhesive comprising a dispersed phase of air cells, cooling of the molten polyolefin-based adhesive after discharge from the die is limited to a rate sufficient to cause at least a portion of the air cells to collapse before the polyolefin-based adhesive crystallizes, wherein the polyolefin-based adhesive composition comprises polyolefin and functionalized olefin-based polymer; b. Adding the polyolefin-based adhesive composition and the gas to an extruder and mixing under pressure and temperature conditions sufficient to produce a mixture of molten polyolefin-based adhesive composition and dissolved gas; c. discharging the mixture from a die attached to the extruder to reduce the pressure of the mixture by an amount sufficient to produce a layer comprising a matrix of a molten polyolefin-based adhesive composition comprising a dispersed phase of air cells; d. forming a multilayer structure comprising: i) A first layer; ii) a second layer, and Iii) The layer comprising a matrix of a molten polyolefin-based adhesive composition comprising a dispersed phase of air cells disposed between and co-extensive with the first and second layers, and E. The temperature of the matrix of molten polyolefin-based adhesive composition comprising air cells is reduced at a controlled rate to induce collapse of at least a portion of the air cells prior to curing of the polyolefin-based adhesive composition.
19. The method of claim 18, wherein the composition of the first and second layers are each independently selected from a polymer, paper, or metal foil.

Description

Multilayer film with foamed polyolefin-based adhesive composition Technical Field The present application is filed according to the patent cooperation treaty, claiming priority from U.S. provisional application No. 63/160,461 filed on 3/12 of 2021, the contents of which are incorporated herein by reference in their entirety. The present invention relates to a multilayer film structure comprising a foamed adhesive composition as a tie layer between two other layers. Multilayer films comprising foamed adhesive tie layers exhibit improved toughness and optical properties compared to multilayer film structures having conventional tie layers. The invention also relates to a method of making a multilayer film structure having a tie layer comprising a foamed adhesive composition. Background Tie-layer adhesives are used to bond polyolefins to various substrates in multilayer coextruded structures, particularly for blown and cast films, extrusion coating, blow molding, sheet extrusion, wire and cable, pipe and other industrial applications. In particular, the adhesives are useful for bonding plastics, wood, glass, paper, composites, metal substrates and incompatible polymers. Tie-layer adhesives can be used in lamination, coextrusion, extrusion coating, and other processes. The tie-layer adhesive is typically made of and/or includes a polyolefin base resin and a grafted polyolefin, which may or may not be the major components. Grafted polyolefins are prepared by reacting a polyolefin with an unsaturated monomer at a higher temperature, with or without a free radical initiator. Commercially available tie-layer adhesives include Plexar TM resins, a product available from LyondellBasell, which includes anhydride modified polyolefins. Multilayer films and sheets are widely used in food packaging applications and in the packaging of bulk materials. The number and arrangement of resin layers and the type of resin used will vary depending on the intended application. Polyethylene resins are often included as one of the layers for food contact and sealing properties. Ethylene vinyl alcohol (EVOH) copolymers and polyamides (nylon) are widely used as oxygen barrier layers. It is desirable to improve the toughness and clarity of multilayer film structures with improved tie layers without increasing the thickness or using more expensive polymers for the existing performance layers of the structure. However, adhering different resin layers in multilayer films and sheets is always challenging. There is a need for improved tie-layer adhesive compositions suitable for preparing multilayer structures having good adhesion, high clarity and improved toughness. Valuable processes would avoid expensive additives and property balances. Desirably, the improved tie-layer adhesives can be prepared using economical starting materials, conventional equipment, and familiar techniques. U.S. patent publication 2017/0335149 discloses polyolefin-based adhesive compositions formed by melt blending an olefin-based polymer with a functionalized polyolefin and the use of the adhesive compositions as tie layers in multilayer structures. U.S. patent 10,053,574 discloses adhesives comprising linear low density polyethylene grafted with maleic anhydride and the use of such adhesives as tie layers in multilayer structures. However, there is a continuing need for multilayer structures comprising layers of polyethylene, propylene polymers, styrene polymers and/or polar polymers (e.g., EVOH or nylon) that have a common tie layer that has the ability to adhere different layers in the structure while maintaining or improving mechanical and/or optical properties. Disclosure of Invention In general, the present invention relates to a multilayer structure comprising a substrate layer, an outer layer, and an adhesive layer disposed between the substrate layer and the outer layer. The tie layer comprises a foamed polyolefin-based adhesive composition. As defined herein, the polyolefin-based adhesive composition is foamed by applying the following steps. In some embodiments, the polyolefin-based adhesive composition and the gas soluble in the polyolefin-based adhesive composition are added to an extruder. The mixing of the polyolefin-based adhesive composition and the gas is performed in an extruder under pressure and temperature conditions sufficient to form a mixture of molten polyolefin-based adhesive composition and dissolved gas. The mixture of molten polyolefin-based adhesive composition and dissolved gas is then discharged from the extruder through a die attached to the extruder. The discharge of the material through the mold reduces the pressure of the mixture by an amount sufficient to produce a matrix of molten polyolefin-based adhesive composition comprising a dispersed phase of air cells or bubbles. The molten polyolefin-based adhesive composition containing dissolved gas is discharged simultaneously with and in the vicinity of the discharge of the molten