WO1996007677A1

WO1996007677A1 - Water dispersible ethylene ionomers

Info

Publication number: WO1996007677A1
Application number: PCT/US1995/011396
Authority: WO
Inventors: Ta Yen Ching; Ruth A. Broussard; James Wang
Original assignee: Chevron Chemical Company
Priority date: 1994-09-09
Filing date: 1995-09-08
Publication date: 1996-03-14
Also published as: AU3716595A

Abstract

A water dispersible ethylene polymer contains (a) structural units produced from at least one alpha-olefin, and (b) at least one solubility enhancing functionality selected from among salts of an alpha,beta-ethylenically-unsaturated carboxylic acid and esters of polyalkylene glycol monoethers, which functionalities are present in an amount effective to render the polymer at least substantially dispersible in water. Preferably, the polymer also contains structural units produced from esters of alpha,beta-ethylenically-unsaturated carboxylic acids. These polymers can find particular utility as components within adhesives, e.g., hot melt adhesives, and as packaging materials. Moreover, due to their water dispersibility, they are considered recyclable and/or repulpable and thus, they can be effectively employed within the paper and pulp industry. In another aspect, a process for the production of these water dispersible polymers is provided.

Description

WATER DISPERSIBLE ETHYLENE IONOMERS

Background of the Invention

The present invention relates to ethylene polymers and/or ionomers which are capable of being dispersed in water, methods of making such polymers, and their use in compositions such as adhesives and packaging materials which can be employed, e.g., in the pulp and paper industry.

Ethylene ionomers, i.e., ionomers derived from ethylene polymers and copolymers include, e.g., alkali metal salts of copolymers of ethylene and acrylic and/or methacrylic acid, are recognized in the art. See, for example, U.S. Patent 3,970,626, which patent is incorporated herein by reference in its entirety for all purposes. In producing the ionomers discussed within this patent, alkali metal salt structural units are introduced into the ethylene polymers by saponifying copolymers with ethylene and an alkyl ( eth)acrylate in the presence of an aqueous solution of alkali metal hydroxide.

Moreover, the art has recognized a variety of techniques for producing such ionomers. For example, as illustrated by the above patent, the batch hydrolysis of ethylene-alkyl acrylate copolymers, e.g., ethylene- methyl acrylate copolymers, such as EMAC* (E1VIAC* is a registered trademark and a product of the Chevron Chemical Company) and the like, can be employed in the production of such ionomers.

Furthermore, the art has also recognized the use of reactive extrusion in the production of such ionomers. See, for example, copending U.S. application Serial No. 727,773 which is incorporated herein by reference. However, despite the effectiveness of these processes, and in particularly reactive extrusion in producing ionomers, these ionomers have not found particular utility in certain areas in as far as the ionomers are largely insoluble in water. For example, one area in which these ionomers have not been employed is the area of hot melt adhesives.

Hot melt (or thermoplastic) adhesives are well recognized within the art and are finding increased usage in a variety of industrial applications. These adhesives, or hot melts, are solid or semi-solid combinations of film forming resins, tackifying resins, rubbery polymers, plasticizers, waxes and similar materials which are added to the adhesive composition in order to impart various properties thereto. One particular advantage of adhesives derived from hot melts are their very rapid setup or bonding time, i.e., strong bonds are formed when the adhesive cools below its melt point and crystallizes. Depending on their composition, hot melt adhesives can have good tack, high bond strength, good flexibility, low temperature properties, good environmental resistance, and the like.

The typical class of hot melt adhesive compositions utilize polyolefin polymers as the base are carrier materials therein. This polyolefin base is typically blended with other polymers and copolymers, resin tackifiers as well as other modifiers and additives. Despite their use, typical polyolefin based hot melts suffer from a variety of problems, e.g. , they are not typically water-dispersible, thus when employed in a paper application recycling options are limited. Due to increasing environmental pressures in the pulp and paper industry, repulpable (or recyclable) hot melts are becoming an area of recent interest. For example, an ethyl-vinyl acetate copolymer which is produced by blending conventional EVA with 30 weight percent of a specially grafted EVA, i.e., obtained by grafting a polar monomer onto EVA has been disclosed as being "repulpable".

Furthermore, the art has also recognized the ability to improve the water dispersibility of hot melt adhesives by providing a combination of PVP and polyethylene oxide water soluble polymers therein.

However, despite these attempts, the need still exists for a repulpable hot melt adhesives having superior adhesion and mechanical properties associated therewith. Summarv of the Invention

Among other aspects, the present invention is based on the surprising discovery that ethylene polymers containing effective amounts of certain functionalities selected from among salts of an alpha,beta-ethylenically- unsaturated carboxylic acid and esters of polyalkylene glycol monoethers are water dispersible, and thus, can be effectively employed in adhesive compositions and in packaging products.

In one preferred aspect, ethylene polymers of the present invention can be employed in compositions that are "repulpable" and can therefore be advantageously employed in the paper and pulp industry.

In particular, the present invention relates to a water-dispersible ethylene polymer containing:

(a) structural units produced from at least one alpha-olefin, and

(b) at least one solubility enhancing functionality selected from among salts of an alpha,beta-ethylenically-unsaturated carboxylic acid and esters of polyalkylene glycol monoethers, which functionalities are present in an amount effective to render the polymer at least substantially dispersible in water and in particular hot water.

Preferably, the ethylene polymer further includes: (c) structural units produced from esters of alpha, beta-ethylenically- unsaturated carboxylic acids. Moreover, it is also preferred that the polymer contains at least about 10 wt % of esters (c) and at least about 10 wt % of the functionalities (b).

In yet another aspect, the present invention relates to a process for making such polymers which comprises:

(a) providing a ethylene polymer containing structural units produced from at least one alpha-olefin, and structural units produced from esters of alpha, beta-ethylenically-unsaturated carboxylic acids

(b) converting an effective amount of ester structural units into at least one solubility enhancing functionality selected from among salts of an alpha,beta-ethylenically-unsaturated carboxylic acid and esters of polyalkylene glycol monoethers, so as to render the polymer at least substantially dispersible in water.

In a preferred embodiment of this aspect of the invention, the process comprises the reactive extrusion of the ethylene polymer of (a) with a inorganic metal base and/or ammonium solution, and in particular the sequential, multiple-port introduction of the inorganic metal base and/or ammonium solution into the extrusion process.

Detailed Description of the Preferred Embodiments As discussed above, the present invention relates to a water soluble ethylene polymer or ionomer which contains solubility enhancing functionalities. In addition, the present invention relates to a process for making such ethylene polymers and ionomers.

As discussed previously, the present invention seeks to provide a composition that can be effectively employed in polymer-containing repulping environments. To this end, although there is no one specific art recognized definition of "repulping", i.e., there are over 220 repulping mills in the U.S. which employ a variety of different processes and equipment, the resins of the present invention can be termed "repulpable" at least in as far as they can be dispersed in the repulping processing water.

Furthermore, in order to simplify terminology in this specification, the term "copolymer" can include 2 or more monomer constituents as well as substituted derivatives thereof.

The ethylene polymers can be employed as a starting material in the process of the present invention include both structural units produced from (i) alpha-olefins and (ii) esters of alpha, beta-ethylenically-unsaturated carboxylic acids. Suitable examples of preferred copolymers include ethylene-alkyl (meth)acrylate copolymers of ethylene and acrylic or methacrylic esters of α,/3,ethylenically-unsaturated carboxylic acids. Monomer (i) comprises alpha-olefins having from 2 to 8 carbon atoms. Preferably, monomer (ii) comprises alpha-olefins having from 2 to 3 carbon atoms, and more preferably, monomer (i) consists essentially of ethylene.

Monomer (ii) comprises esters of alpha, beta-ethylenically-unsaturated carboxylic acids having from 1 to 18 carbon atoms on esters. Preferably, monomer (ii) has from 1 to 12 carbon atoms on ester chains, and more preferably has from 1 to 4 carbon atoms. Examples of monomer (ii) include methyl acrylate, butyl acrylate, and butyl methacrylate. Methyl acrylate is the preferred monomer (ii).

Although the amount of the ester present in the polymer is not critical to the present invention, the minimal amount is that needed to provide, upon conversion, the effective amount of solubility enhancing functionalities. In general, a high percentage of conversion on a high ester would give higher water dispersibility.

From a practical standpoint, these copolymers contain from about 10 to 40 wt percent of esters of alpha, beta-ethylenically-unsaturated carboxylic acids with from 10 to 23 or 24 wt percent being currently more preferred when the resulting products are to be employed in food environments.

Suitable ethylene polymers can also contain structural units grafted thereto, e.g., vinyl monomer derived units, for example structural units produced from alpha,beta-ethylenically unsaturated monomers which impart desirable polymer properties.

Specific examples of additional structural units include maleic anhydride, acrylic acid, methacrylic acid, acrylonitrile, styrene, vinyl acetate, and vinyl silane, depending upon the desired application for the final product. For example, styrene-containing polymers can have enhanced rigidity while vinyl acetate can provide for reduced costs.

Additionally, these copolymers can contain stabilizers, such as UV stabilizers, antioxidants, dispersants, emulsifiers, pigments and the like.

Furthermore, as long as both the copolymer starting material and the resulting product are capable of being effectively processed, the melt index is not critical to the present invention. Suitable starting material copolymers typically have a melt index of about 0.5 to about 1200 g/10 min, with greater than about 100 g/10 min being preferred.

Examples of the suitable copolymers include ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-methyl acrylate copolymer, ethylene- propylene-methyl methacrylate copolymer, ethylene-methyl acrylate-acrylic acid copolymer, ethylene-methyl methacrylate-methacrylic acid copolymer, maleic anhydride-grafted-ethylene-methyl acrylate copolymer, ethylene- methyl acrylate-maleic anhydride copolymer, acrylic acid-grafted-ethylene- methyl acrylate copolymer, and ethylene-methyl acrylate-butyl acrylate copolymer. Preferably, the copolymers are ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, maleic anhydride-grafted-ethylene-methyl acrylate copolymer, and ethylene-methyl acrylate-butyl acrylate copolymer. Most preferred is ethylene-methyl acrylate copolymer.

Techniques for making such polymers are well recognized in the art, however, for sake of completeness, attention is directed to the following. One process for making these copolymers comprises polymerizing ethylene, an alkyl acrylate and/or an alkyl methacrylate, and the optional comonomer in autoclaves using free-radical initiation catalysts. This process is described in U.S. Patent No. 3,350,372, which is incorporated herein by reference in its entirety. Another process for producing copolymers useful in making the ionomer compositions of this invention comprises free-radical polymerization of ethylene and an alkyl acrylate and/or an alkyl methacrylate as described above, followed by reactive extrusion with a compound such as acrylic acid or maleic anhydride.

The process of the present invention involves converting an effective amount of the ester structural units into solubility enhancing structural units with this amount being effective to provide a water dispersible ethylene polymer. In particular, it is preferred that about at least 10 weight percent of the copolymer are such functionalities. Alternatively, the conversion can be expressed in terms of the degree of hydrolysis. It has been found that ionomers having a higher degree of hydrolysis will be more water dispersible. In this regard, while ionomers produced from EMAC* having 28 % methyl acrylate will show an appreciable repulpability at a level of hydrolysis of not less than 35%, a level of hydrolysis of not less than 70% is preferred.

In the process of the present invention, the method of conversion of the ethylene polymer depends upon the functionality. Moreover, such techniques are generally recognized in the art. For example, where the salt is the desired solubility enhancing functionality, the process is performed in the presence of an alkaline metal-containing solution and/or ammonium solution. The particular solution is not critical to the present invention as long as it provides the necessary salts.

The alkaline metal-containing solutions comprises a suitable metal ion in a solvent, where the solvent can comprise any solvent which does not prevent the conversion reaction from occurring. Such solvents can be organic or inorganic, with common solvents including water, alcohols, and the like, or water is preferred.

The metal which can be employed in the solution can be selected from among the Group IA, Group HA, and transition metals. Specific examples of suitable metals include, lithium, sodium and potassium.

Preferably, the solution comprises an aqueous solution of a Group IA, metal hydroxide and/or oxide or a Group IIA hydroxide. Specific examples of preferred solutions include LiOH, NaOH and KOH, of these, sodium and potassium hydroxide being preferred. Further, these agents may be used individually or in combination thereof.

The reaction occurs under conditions which are also well recognized in the art. For example, reaction typically occurs at a temperature of 150- 250 C and a pressure of about atmospheric to 200 psi. Moreover, in conversion to the ionomer, the melt index typically drops. Because a melt index of not less than about 0.5 MI is desired is extrusion operations, the use of starting material having a MI of not less than 400 g/lOmin is preferred. Alternatively, rheology modification additives, e.g., low molecular weight ethylene-acrylic acid copolymers, which do not adversely effect repulpability can be introduced into the ionomers. With respect to the functionalities based on polyalkylene glycol monoethers, the reaction is an exchange reaction which is also recognized in the art and thus need not be described in detail here.

In one preferred embodiment, the invention relates to the reactive extrusion of the ethylene polymers so as to provide the desired conversion. A reactive extruder which is useful in producing compositions of this invention comprises an extruder having a copolymer feed section, one or more reaction sections, a subsequent devolatilization section, and an extrusion section. Typically, these sections are separately jacketed to allow for heating or cooling within each section. These sections can also be vented with one or more vent ports per section to allow the escape of volatile components, such as the solvent from the metal solution and byproducts of the saponification reaction, such as alcohols. Generally, the reactive extruder will also have optional means for introducing reactants into any reaction sections as well as means for mixing components in the reaction section(s) and means for conveying the components through the extruder.

Typically, the means for mixing and conveying components to be reacted are screws.

Reactive extruders can have a single screw or multiple screws. Each screw typically has a central shaft with a key-way or spline upon which mixing elements are secured. The reactive extruder may have either co- rotating or counter-rotating screws.

Typically, copolymer to be reacted is fed to the screw through a loss- in-weight feeder, and the solid copolymer is melted in a feed section of the reactive extruder. In some embodiments, all reactants (i.e., copolymer and metal-containing solution) can be fed to the reactive extruder through a feed section. In a preferred embodiment, copolymer is introduced into the reactive extruder in a feed section, and the metal ion-containing solution is fed to one or more reaction sections. A devolatilization section is a convenient means for removing any solvent and byproducts of the saponification reaction from the saponified composition. Equivalent or additional means for removing volatile components can be used, however, such as drying the ionomer composition under reduced pressure in a falling- film evaporator.

One reactive extruder which was particularly effective in producing compositions of this invention is a Werner and Pfleiderer co-rotating and intermeshing twin-screw extruder. The reactive extruder has a feed section, a reaction section, a devolatilization section, and a pressurization or pumping section which pushed the product through an extrusion die. The devolatilization section had a first portion which was vented to a condenser maintained at atmospheric pressure, and a second portion of the devolatilization section was vented with sufficient vacuum and capacity to remove essentially all of the volatile components from compositions prior to conveying and extruding them.

Typically, copolymer pellets are introduced into a feed section of a reactive extruder, where the pellets are heated and worked by the screw to form molten or fluid copolymer. The screw elements also convey the molten copolymer from this feed section to a first reaction section, where the molten copolymer and metal-containing solution are mixed.

Furthermore, known techniques in the field of reactive extrusion can also be utilized in the present invention, for example, the multiport and/or sequential injection of an organic metal base and/or ammonium solutions can be employed. Similarly, known techniques for the treatment of the melt strands, e.g., non-aqueous cooling of the melt strands, can also be effectively employed in the process of the present invention.

By the process of the present invention, a water dispersible ethylene ionomer is produced. In particular, this ionomer includes an effective amount of solubility enhancing functionalities as well as any remaining amount of unreacted esters, e.g., alkyl (meth)acrylates.

In one particular preferred embodiment, the ionomer includes 10-20 weight percent of the acrylic acid salt and 10-30 weight percent of the ester which ethylene ionomer is nearly 100% soluble in water. In light of its solubility in at least hot water, the ethylene ionomers according to the present invention can be effectively employed in a variety of environments including but not limited to repulpable hot melt compositions and compositions for producing packaging products.

For example, because these compositions are water dispersible, they can find utility in recyclable and/or repulpable compositions in the pulp and paper industry. In particular, one suitable use for the inventive ionomers is within compositions for use in packaging processes. Moreover, the combination of the inventive ionomers with their polymeric starting material, e.g. , the use of EMAC* ionomers with EMAC*, or with other water dispersible resins such as polyvinyl pyrolidone (PVP), polyethylene glycol (PEG), etc. has been found to be particularly advantageous in this regard. In such compositions, the ionomers is blended with its polymeric starting material in a ratio selected to provide the properties needed for its desired end use. For example, such compositions can be employed in producing free-standing transparent films, of coextruded onto the paper product so as to form paper laminates. Although the ratio of such components is dependent upon the desired balance of solubility of mechanical and processibility. Typically, it is preferred that ionomer: polymer ratio be about 1: 1 to about 10: 1 with about 2 : 1 to 5 : 1 being preferred and about 70:30 and 80:20 being even more preferred.

Packaging products made according to such a combination has a number of desirable properties including relative insolubility within cold water, the ability to be hot-sealed, acceptable mechanical strength, and dispersibility in hot water, e.g., water having a temperature of about 120- 150°C. Moreover, these blends can be produced by any method well recognized within the art, for example, dry mixing, kneading and/or extruding.

Another example of an advantageous use for these ionomers is in the area of adhesives, e.g. , hot melt adhesives. In this regard, the ethylene comonomers can be used as a replacement for conventional polyolefins, e.g., ethylene-vinyl acetate, within such adhesives. Moreover, they can be used with traditional hot melt components such as tackifiers and other traditional additives such as viscosity modification agents, e.g., viscosity thinners such as waxes. Because these components are well recognized in the art, they need not be described in detail here. Because water solubility is desired, it is preferred that these components, e.g., waxes and tackifiers, be water soluble or dispersible, however, because the ethylene polymers according to the present invention can aid in carrying non-soluble components into water emulsions, there is no requirement that such additional components be water-soluble. Thus, as can be seen, the water dispersibility associated with the present invention can provide a number of significant advantages over traditional ethylene ionomers.

The present invention will now be illustrated in great detail by the following examples, but is to be understood that these examples are only illustrative in nature and are not intended to limit the present invention in any manner.

Examples

Example 1

In a reactive extrusion process, EMA copolymer having a melt index of 199 and a methyl acrylate content of 25 wt % was converted to an EMAC* ionomer having a melt index of 0.03, a sodium acrylate content of 10 wt%, and a methyl acrylate content of 15 wt %, by coextrusion of the EMA copolymer with a 50% NaOH solution.

This ionomer is clearly water soluble as the cooling water for the melt extrusion was turned milky/soapy during the short contact. For this reason, it was collected by cooling on a conveyor belt under cool air.

A repulpability test designed for ionomer screening comprises the following:

1. A 1-2 mil film of the ionomer was produced and cut into 1/2 inch strips; 2. 1.5 g of the above strips was placed in 350 ml of water at a preselected temperature, e.g., 120° or 150°F;

3. The sample was mixed in a Waring blender at scale 6 for 10 min.;

4. . The solute was filtered through a 60 mesh screen; 5. The filtrate was dried overnight at 177 F and then weighed.

The amount of material which passes through the screen evidences the repulpability of the resin. In this example, the test showed that this polymer is nearly 100% repulpable at 150 C. A second EMA copolymer, having a melt index of 135 and 20 wt% methyl acrylate was converted into a 97% soluble ionomer having 10 wt % sodium acrylate and 10 wt % methyl acrylate, by reactive extruding.

Example 2 The pulpability test (TAIPPI, UM 666) of hot melts formulated based on 45/35/40 ratio of polymer/Neriz 1085 tackifier/CRW 150 wax were 72% and 65 % , which are significantly better than the control formulated with EMAC 2207, which was only 28%.

Because the tackifier and wax are not water dispersible, this experiment demonstrates that these polymers are not only emulsifiable, they also are capable of carrying other non-soluble components into the water emulsions.

Example 3

This example illustrates a blend of water dispersible EMA ionomers with EMA copolymers for the making of paper laminates, and free standing films and bags.

A blend of 72.7 wt % of a highly hydrolyzed EMAC* ionomer (55% hydrolyzed from a 174 melt index, 25 wt % methyl acrylate EMA copolymer to 12 wt % methyl acrylate and 13 wt % sodium carboxylate EMA ionomer) with 27.3% of EMA copolymer having a melt index of 0.4 at 190°C and 3.88 and 230°C was prepared.

The improved properties of this blend, e.g., improved tensile strength, heat seal and hot tack temperature, made it suitable for making into free standing transparent films, or co-extruded onto paper products to form paper laminates.

Claims

What is claimed is;

1. A water-dispersible ethylene polymer containing

(a) structural units produced from at least one alpha-olefin, and

(b) at least one solubility enhancing functionality selected from among salts of an alpha,beta-ethylenically-unsaturated carboxylic acid and esters of polyalkylene glycol monoethers, which functionalities are present in an amount effective to render the polymer at least substantially dispersible in hot water.

2. The ethylene polymer according to claim 1 wherein the polymer further includes:

(c) structural units produced from esters of alpha, beta-ethylenically- unsaturated carboxylic acids.

3. The ethylene polymer according to claim 2 wherein the polymer contains at least about 10 wt % of esters (c) and at least about 10 wt % of the functionalities (b).

4. The ethylene polymer according to claim 2 wherein the esters (c) are present in an amount of 10-30 wt %.

5. The ethylene polymer according to claim 2 wherein the functionalities (b) are present in an amount of 10-20 wt %.

6. The ethylene polymer accordmg to claim 2 wherein alpha- olefins of (a) are present in an amount of 60-90 wt % .

7. The ethylene polymer according to claim 2 wherein the copolymer further includes (d) structural units produced from carboxylic acids, vinyl acetates and/or acrylamides.

8. The ethylene polymer according to claim 2 wherein the structural unit (c) is methyl acrylate.

9. The ethylene polymer according to claim 8 wherein the functionality (b) is sodium acrylate.

10. The ethylene polymer according to claim 9 wherein structural unit (d) is vinyl acetate and is present in an amount up to 30 wt % .

11. An adhesive composition including an ethylene polymer according to claim 1.

12. A hot melt adhesive comprising a tackifier, a carrier and at least one additive selected to modify a property of the adhesive, wherein the carrier comprises the ethylene polymer according to claim 1.

13. A hot melt adhesive according to claim 12 wherein the at least one additive includes a viscosity modification agent.

14. The hot melt adhesive according to claim 12 wherein the tackifier and the at lease one additive are water-dispersible.

15. A hot water dispersible ethylene ionomer composition comprising an ethylene ionomer according to claim 1 and an ethylene polymer containing structural units produced from alpha-olefins and esters of alpha,beta-ethylenically-unsaturated- carboxylic acids, wherein the ratio of ionomer to polymer is selected so as to provide a composition which is dispersible in hot water.

16. The composition according to claim 15 wherein the ethylene polymer comprises an ethylene-methyl acrylate copolymer and the ionomer comprising an ethylene-methyl acrylate-sodium acrylate ionomer.

17. A paper laminate comprising a paper support having the composition according to claim 15 coated thereon.

18. A process of the production of a water dispersible ethylene polymer comprise:

19. The process according to claim 18 wherein (b) comprises the reactive extrusion of the ethylene polymer of (a) with a Group IA or Group IIA metal hydroxide and/or ammonium solution.

20. The process according to claim 19 wherein (b) comprises the sequential, multiple-port introduction of the Group IA or Group IIA metal hydroxide and/or ammonium solution into the extrusion process so as to provide salt functionalities.

21. The process according to claim 18 wherein the polymer of (a) includes at least about 20 wt % of the ester structural units.

22. The process according to claim 21 wherein (b) involves the conversion of at least about 10 wt% ester structural units.

23. The process according to claim 22 wherein the polymer of (a) has a melt index not less than 100.