AU6123500A - Microcellular foam plank - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 DIVISIONAL APPLICATION NAME OF APPLICANT: ASTRO-VALCOUR, INC.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street Melbourne, 3000.

INVENTION TITLE: "MICROCELLULAR FOAM PLANK" The following statement is a full description of this invention, including the best method of performing it known to us: P:OPER\KAd\2340422-div.do.21/0900 -la- MICROCELLULAR FOAM PLANK Background Of The Invention 1. Field Of The Invention The invention relates to non-crosslinked low or high density polyolefin foam having a fine-celled closed structure and a process of preparing the low or high density polyolefin foam.

2. Background Art 10 Non-crosslinked foams in the prior art made with the herein described extrusion accumulator process typically had cells within the 20 to 30 cells per inch range. Attempts to make the non-crosslinked thick cross-sectional foams with a higher cell count resulted in non-flat/wavy foam, voids, ripples, or the like.

Broad Description Of The Invention Advantageously, the invention alleviates the problems of the above stated prior art and provides a non-crosslinked foam product, which offers the properties of a crosslinked foam product, but with a finer cell count typically greater than 50 cells per inch and a soft, non-abrasive feel while providing capability to be recycled, which is extrinsic to a crosslinked foam product. Other advantages of the invention are set out herein or are obvious herefrom to one skilled in the art.

Generally, the present invention relates to a blended non-crosslinked polyolefin composition which is processable into a foamed product having a fine-celled structure, comprising a polyolefin, optionally a copolymer of an olefin and a different ethylenic monomer, an effective amount of a fatty acid compound permeability control agent, and an effective amount of a nucleating agent. There is also generally provided a process for preparing an expanded non-crosslinked low or high density polyolefin foam having a finecelled closed structure, comprising forming a mixture of a polyolefin, a copolymer of an olefin and a different ethylenic monomer, an effective amount of a fatty acid compound stability agent, an effective amount of a nucleating agent and an effective amount of isobutane blowing agent, dissolved in the polyolefin and copolymer, under pressure, said mixture having a temperature at which the viscosity of said mixture is sufficient to retain P:\OPER\Axd2340422-div.doc-21/09/00 bsaid blowing agent when said mixture is allowed to expand; extruding said mixture into a holding zone maintained at a temperature and pressure which does not allow the resulting mixture to foam, said holding zone having an outlet die defining an orifice opening into a zone of lower pressure at which said mixture foams, and an openable gate closing said die orifice; and periodically opening said gate and substantially concurrently applying mechanical pressure by a movable ram on said mixture to eject said mixture from said holding zone through said die orifice into said zone of lower pressure, at a rate greater than that at which substantial foaming in said die orifice occurs and less than that at which substantial irregularities in cross-sectional area or shape occurs; and permitting said ejected 10 mixture to expand unrestrained in at least one dimension to produce an elongated cellular body.

"According to one aspect of the invention, there is provided a process for preparing a non-crosslinked polyolefin foam elongated cellular body having a fine-celled closed structure, said fine-celled structure having a cell count greater than 50 cells/inch, said process comprising the steps of: *:melting a polyolefin and a copolymer of an olefin monomer and an ethylenic monomer different from the monomer of said polyolefin to form a polymeric blend, the amount of said copolymer being in the range of from 5 to 25 percent by weight of said blend; forming a mixture of said blend, an amount of fatty acid effective to provide stability, and an amount of a nucleating agent sufficient to produce a cell count greater than 50 cells/inch; dissolving an effective amount of a blowing agent in said mixture to form a blowing-agent-containing mixture; then extruding said blowing-agent-containing mixture into a holding zone; maintaining said holding zone at conditions, including temperature and pressure, at which said blowing-agent-containing mixture does not foam; transferring said blowing-agent-containing mixture into an expansion zone; and permitting said blowing-agent-containing mixture to expand in the expansion zone to produce said elongated cellular body.

P:\OPER\Axl2340422-div.doc-2109/00 Ic- According to another aspect of the invention, there is provided a non-crosslinked fine-celled foam product comprising: a polymeric structure being substantially composed of fine cells and having the cell count being greater than 50 cells/inch, said polymeric structure being a blend of a polyolefin and a copolymer of an olefin monomer and an ethylenic monomer different from the monomer of said polyolefin, the amount of said copolymer being in the range of from 5 to 25 percent by weight of said blend.

The invention involves a blended non-crosslinked polyolefin composition which is 10 processable into a foamed product, preferably foamed plank, comprising a polyolefin, optionally a copolymer of an olefin and a different ethylenic monomer, an effective amount of a fatty acid compound permeability agent, and an effective amount of a nucleating agent. The non-crosslinked foamed product of the invention offers the properties of a crosslinked foam product and has a finer cell count typically greater than cells per inch and a soft, nonabrasive feel. The non-crosslinked foamed product has the capability of being recycled, which is extrinsic to a crosslinked foamed product. To improve the softness of the foam product, the optional o*oo *go copolymer is a copolymer of an olefin and an ester monomer. To improve the strength and/or stiffness of the foam product, an ionomer resin can be included in the blend. Isobutane blowing agent is also usually present in an amount of from 5 to 30 parts, best from 10 to 20 parts, per 100 parts of the polymer blend composition during the operation/process of preparing the foam.

Preferably the polyolefin is polyethylene. Preferably the copolymer is ethylene vinyl acetate copolymer or ethylene methyl acrylate copolymer.

Preferably the fatty acid compound stability agent is glycerol monostearate.

Preferably the nucleating agent is crystalline silica, or sodium bicarbonate-citric acid, or talc.

In the most preferred blended polymer composition the polyolefin is low density polyethylene, the copolymer is ethylene methyl acrylate copolymer, the fatty acid compound permeability control agent is glycerol 15 monostearate and the nucleating agent is crystalline silica.

The invention also involves a process for preparing an expanded noncrosslinked low or high density polyolefin foam, which offers the properties of a crosslinked foam product, with a finer cell count typically greater than cells per inch and a soft, non-abrasive feel while also providing capability to be recycled, whereas crosslinked foam does not. The process includes forming a mixture of a polyolefin, optionally a copolymer of an olefin and a different ethylenic monomer, an effective amount of a fatty acid compound permeability agent, an effective amount of a nucleating agent and an effective amount of isobutane blowing agent, dissolved in the polyolefin and copolymer, under pressure. The mixture has a temperature at which the viscosity of the mixture is sufficient to retain the blowing agent when the mixture is allowed to expand. The mixture is extruded into a holding zone maintained at a temperature and pressure which does not allow the resulting mixture to foam. The extrusion is done without an extrusion die. The holding zone has an outlet die defining an orifice opening into a zone of lower pressure at which the mixture foams. An openable gate closes the die orifice and periodically the gate is opened and substantially concurrently therewith mechanical pressure is applied by a movable ram of the mixture to eject the mixture from the holding zone through the die orifice into the zone of lower pressure, at a rate greater than that at which substantial foaming in the die orifice occurs and less than that at which substantial irregularities in crosssectional area or shape occurs. The ejected mixture is permitted to expand unrestrained in at least one dimension to produce an elongated cellular body.

In the invention process, using the accumulator process described in U.S. Patent No. 4,323,528, flat fine-celled closed plank structures can be produced.

The invention further involves an expanded non-crosslinked low or high density polyolefin foam having a fine-celled closed structure, which is prepared by the invention process.

The invention foam is a plank foam with dimensions of typically 108 inches by 24 inches by 2 inches (or 3 inches). The invention foam will replace bun stock crosslinked foam. Manufacturers of such crosslinked foam include Sentinel, Voltek, and Monarch Rubber Company. The invention foam is a fine-cell (microcellular), soft material. The invention foam is preferably made with low density polyethylene, ethylene vinyl acetate or ethylene methyl acrylate, isobutane blowing agent, a fatty acid (glycerol monostearate) to prevent collapse of the foam, and a nucleating agent, for example, crystalline silica or sodium bicarbonate-citric acid or talc. The invention non-crosslinked foam compares favorably to many of the physical characteristics of a crosslinked foam. However, unlike crosslinked foam, the invention foam is recyclable.

Detailed Description Of The Invention The invention involves non-crosslinked polyolefin foam which offers the properties of a crosslinked product with fine-celled (microcellular) structure with cell counts typically greater than 50 cells per inch and a soft, nonabrasive feel while also providing capability to be recycled (whereas crosslinked foam does not).

The foamed product is prepared from a blend of a polyolefin and a copolymer of an olefin and a different (nonionic) ethylenic monomer.

Preferably the polyolefin is a low density ethylene homopolymer. Preferably the copolymer is an ethylene vinyl acetate copolymer or an ethylene methyl acrylate copolymer. The copolymers are usually soft or have low stiffness.

Examples of the thermoplastic polyolefins are polyethylenes and polypropylenes. The polyethylenes can be HDPE, MDPE, LDPE and LLDPE.

Examples of the ethylene copolymers are ethylene vinyl acetate copolymers, ethylene-1-butene copolymers, ethylene methyl acrylate copolymers, ethylene-acrylic acid copolymers, and the like.

The amount of the polyolefin in the polymer blend typically is 5 to percent, preferably about 85 percent based on the total weight of the polymer 0 blend composition (excluding the blowing agent).

0 o 0 The amount of the copolymer of an olefin and a different ethylenic "°oi monomer in the polymer blend typically is 5 to 25 percent, preferably about 12 0 percent, based on the total weight of the polymer blend composition o 00 15 (excluding the blowing agent). In the copolymer, the different ethylenic monomer is preferably used in the amount of about 5 to 20 percent, based on the total weight of the copolymer.

To improve softness, copolymers containing esters, such as, ethylene methyl acrylate (EMA) or ethylene vinyl acetate (EVA), can be added to the mixture with a total ester monomer content of the final product (or the polymer blended composition, excluding the blowing agent) in the range of up to 0 percent, preferably about 2.4 percent, to allow best control of the process.

The melt indices for some of the preferred components of the invention blends are: Material Melt Index (gms/10 min.) EMA EVA (UE 630) 1.8 PE 1.8-2.2 A fatty acid compound permeability control agent is added to the polymer blend composition to enhance dimensional stability in the foam product. Preferred fatty acid permeability control agents include amides and esters of C 12 24 fatty acids. Such permeability control agents are taught in Other nucleating agents, such as, clay, mica, titanium oxide, zinc oxide, calcium silicate, and metallic salts of fatty acids such as barium stearate, zinc stearate and aluminum stearate, can be used. Nucleating agents are usually finely divided and may be pelletized, encapsulated, and the like.

The polymer blend composition can also contain up to 10 percent, preferably about 3 percent, based upon the total weight of the polymer blend composition (excluding the blowing agent), of an ionomeric resin. The ionomeric resin is a cation initiated crosslinked polymer of ethylene and a vinyl acid, preferably a zinc or sodium ion initiated crosslinked polymer of ethylene and methacrylic acid. An ionomer is a thermoplastic polymer that is ionically crosslinked to form bonds between the acid groups within a chain and neighboring chains. The ionomers improve the strength and/or the stiffness of the microcellular foam planks. In general, ionomers are transparent, resistant to abrasion and solvents, have excellent electrical properties, and have outstanding puncture and low temperature impact resistance. lonomeric resins are recyclable. (Note that the ionomeric resin is not a crosslinking agent regarding the foam of the invention.) The preferred blowing agent used is isobutane. One or more conventional or useful blowing agents can be used. Such other suitable volatile blowing agents include halocarbons such as fluorocarbons and chlorofluorocarbons; hydrohalocarbons such as hydrofluorocarbons and hydrochlorofluorocarbons, such as, dichlorotetrafluoroethane, dichlorodifluoroethane, dichloromonofluoromethane and trichloromonofluoromethane; alkylhalides, such as methyl chloride and ethyl chloride; hydrocarbons such as alkanes or alkenes; carbon dioxide, nitrogen, argon, water; and the like. Examples of useful alkanes'having from 2 to 9 carbon atoms are ethane, propane, butane, pentane, isopentane, hexane, isohexane, heptane, and the like.

The invention foam structure is formed by the extrusion accumulator process disclosed in U.S. Patent No. 4,323,528, which is incorporated herein by reference. The process for producing large size, low or high density, elongated thermoplastic cellular bodies includes the forming of a mixture of a thermoplastic polymer-copolymer blend composition and the isobutane blowing agent dissolved therein under pressure and at a temperature at which the viscosity of the mixture is sufficient to retain the isobutane blowing agent when the mixture is allowed to expand. The mixture is extruded into a holding zone under conditions that prevent the mixture from foaming. The holding zone has an outlet die orifice opening into a zone of lower pressure and temperature at which the mixture foams. The outlet die orifice must be designed to allow the expansion of the fine celled foam to the appropriate stated width dimensions. An openable gate closes the die orifice.

Periodically the gate is opened and substantially concurrently mechanical o °o'o pressure is applied by a movable ram on the mixture, preferably while 0 0 0 scraping the sides of the holding zone with the ram, to eject the mixture from oo 0 the holding zone through the die orifice at a rate in excess of that at which 0 *0 0oo 15 substantial foaming in the die orifice occurs and less than that at which substantial irregularities in the cross-sectional area or shape of the cellular body occurs, preferably 9,000 Ib/hour to 11,000 Ib/hour, most preferably the foam ejection rate of 10,500 Ib/hour. The ejected mixture is permitted to o000 0e 0 0 expand unrestrained in at least one dimension to produce the elongated 0 0 thermoplastic cellular body. The apparatus for producing elongated 0 thermoplastic cellular bodies includes an extruder for feeding a mixture of the 0 *0 0 o0 0 thermoplastic polymer blend and the plasticizing isobutane blowing agent at a temperature suitable for producing a cellular body when the mixture is subjected to lower pressure, and an expandable holding chamber receiving the mixture from the extruder and maintaining the mixture in a molten state at a pressure above the foaming pressure thereof. There is ram means for ejecting the mixture out of the holding chamber, a die having an orifice, preferably in line with the ram means, through which the mixture is ejected from the holding chamber by operation of the ram means, and gate means contacting the exterior surface of the die for closing and sealing the die orifice while the holding chamber is being filled.

foam planks having a density of about 4 pcf or greater can be produced by the invention process and from the invention polymer blend compositions.

To accelerate the release of the isobutane blowing agent from the ejected thermoplastic foam, the ejected thermoplastic foam can be subjected to heat below any level having adverse effect on the thermoplastic foam or can be perforated so as to create a series of narrow channels in and/or through the thermoplastic foam.

The invention thermoplastic foams are recyclable in that the basic chemical nature of thermoplastic usually does not change significantly as a result of the extrusion process. Thermoplastic materials can generally be reground and recycled into a usable form. Thermosets undergo a crosslinking reaction when the temperature is raised above a certain point.

The crosslinking forms a three dimensional network which remains intact when the temperature is reduced. This causes an irreversible change in the material and, therefore, can not be recycled like thermoplastic materials.

By way of summary, the product is a polyolefin foam with a density in the range of about 1.2 and about 9.0 pcf. The polyolefin foam planks can be low density, density of about 1.2 to about 2.6 pcf, or high density, e.g., "density of about 4.0 to 9.0 pcf. The polyolefin is usually low density polyethylene. The foam is made in plank form, with nominal dimensions of 24 inches x 108 inches x 2 to 3 1/2 inches. The foam has a fine-celled structure containing 50 to 120 cells per inch (cpi). Using the accumulator process as described in U.S. Patent No. 4,323,528, the invention process is able to produce a flat foamed plank structure. The foam is a non-crosslinked thermoplastic material and is recyclable, unlike crosslinked foam. Like crosslinked foam, the invention foam is smooth to the touch and passes the surface abrasion resistance as required of the packaging of Class A surfaces.

This invention foam is physically comparable with a crosslinked foam product with recyclability as an added bonus. The invention foam can be white or colored and can also contain additives, such as, UV stabilizers, antistats, pigments, antioxidants, etc. To improve softness, ethylene copolymers containing esters such as ethylene vinyl acetate (EVA) or ethylene methyl 9 9@ 9 .9 9 9*9* 9* 99*9 9 99 *9 acrylate (EMA) can be added to the LDPE. The total ester monomer content of the final product (excluding the blowing agent) is in the range of 0.1 to (or 20) percent. To improve stiffness of the ester modified foam, an ionomeric resin can be added in the range of up to 5 percent 0.01 to 5 (or percent]. The invention foam is preferably made with a crystalline silica nucleating agent or a sodium bicarbonate nucleating agent or a talc nucleating agent, and isobutane as the sole blowing agent. Glycerol monostearate (most preferred) or a similar fatty acid compound can be used as the permeability control agent.

A comparison of prior art crosslinked foam materials with invention non- crosslinked foam materials follows:

MATERIALS

PROPERTIES Sentinel Sentinel Inven. Inven. Inven.

MC1900e MC1900 PE/EMA PE/EVA PE/EVA/ xipeleva xipe 2 wk test 2 wk test lonomer literature literature 4 wk test Density 2 2 2 2 2 CPI 169 169 70-80 70-80 70-80 Comp. Strength 25% 4.5 8.5 7.6 6 8.2 Comp. Sets 20 15 12.5 19 15.6 Tensile Strength (psi) 50 40 44 Tear Resistance (pli) 8 7 Water Absorption (ps) 0.05 max 0.05 max <0.05 Therm. Stab. shrink CMD MD Thickness Die Cut, CMD <2% MD <2% Thickness P:\OPER\Axd\2340422.iv.doc-21/09100 lOa- Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (21)

11- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A process for preparing a non-crosslinked polyolefin foam elongated cellular body having a fine-celled closed structure, said fine-celled structure having a cell count greater than 50 cells/inch, said process comprising the steps of: melting a polyolefin and a copolymer of an olefin monomer and an ethylenic monomer different from the monomer of said polyolefin to form a polymeric blend, the amount of said copolymer being in the range of from 5 to 25 percent by weight of said blend; forming a mixture of said blend, an amount of fatty acid effective to provide 10 stability, and an amount of a nucleating agent sufficient to produce a cell count greater than 50 cells/inch; dissolving an effective amount of a blowing agent in said mixture to form a blowing-agent-containing mixture; then extruding said blowing-agent-containing mixture into a holding zone; maintaining said holding zone at conditions, including temperature and pressure, at which said blowing-agent-containing mixture does not foam; transferring said blowing-agent-containing mixture into an expansion zone; and permitting said blowing-agent-containing mixture to expand in the expansion zone to produce said elongated cellular body. 2. The process of claim 1, wherein said polyolefin is selected from the group consisting of polyethylene and polypropylene. 3. The process of claim 2, wherein said polyethylene is selected from the group consisting of HDPE, MDPE, LDPE and LLDPE. 4. The process of claim 1, wherein said copolymer is selected from the group consisting of ethylene vinyl acetate and ethylene methyl acrylate. The process of claim 1, wherein said fatty acid is selected from the group consisting of amides and esters of C12-24 fatty acids. 6. The process of claim 5, wherein said fatty acid is selected from the group consisting of steryl stearamide, glycerol monostearate, glycerol monobehenate, and sorbitol monostearate. 7. The process of claim 6, wherein said fatty acid is glycerol monostearate. P:%OPERAxd\2340422div.doc-21/90 -12- S8. The process of claim 1, wherein said nucleating agent is selected from the group consisting of crystalline silica, sodium bicarbonate and citric acid, talc, clay, mica, titanium oxide, zinc oxide, calcium silicate, barium stearate, zinc stearate and aluminum stearate. 9. The process of claim 8, wherein said nucleating agent is selected from the group consisting of crystalline silica, sodium bicarbonate and talc. The process of claim 9, wherein said nucleating agent is crystalline silica, said crystalline silica being used in the amount of 10 to 25 percent by weight of the total weight of said mixture. 10 11. The process of claim 10, wherein said crystalline silica is used in an amount of 13 to 17 percent by weight of the total weight of said mixture.

12. The process of claim 1, wherein said cell count is from 50 to 120 cells/inch.

13. The process of claim 1, wherein said cell count is greater than 70 cells/inch.

14. The process of claim 1, wherein said ethylenic monomer is used in the amount of from 5 to 20 percent by weight of said copolymer.

15. The process of claim 1, wherein said elongated cellular body is a foam plank.

16. The process of claim 15, wherein said foam plank has a density of about 1.2 to about 2.6 pounds per cubic foot.

17. The process of claim 15, wherein said foam plank has a density of about to about 9.0 pounds per cubic foot.

18. The process of claim 1, wherein said blowing agent is selected from the group consisting of halocarbons, hydrohalocarbons, alkylhalides, hydrocarbons, carbon dioxide, nitrogen, argon, and water.

19. The process of claim 18, wherein said blowing agent is a hydrocarbon, said hydrocarbon being selected from the group of alkanes and alkenes, said group of alkanes being selected from the group consisting of ethane, propane, butane, isobutane, pentane, isopentane, hexane, isohexane, and heptane. The process of claim 19, wherein said blowing agent is isobutane.

21. The process of claim 1, wherein said mixture further includes an ionomer to improve the strength of said elongated cellular body. P:\OPER\Axd\2340422-div.doc-21/0900 -13-

22. The process of claim 1, wherein said polyolefin is low density polyethylene, said copolymer is selected from the group consisting of ethylene vinyl acetate and ethylene-methyl acrylate, said fatty acid is glycerol monostearate and said nucleating agent is selected from the group consisting of crystalline silica, sodium bicarbonate and citric acid, and talc.

23. A process according to claim 1 and substantially as hereinbefore described with reference to the Examples.

24. A product formed by a process of any one of the preceding claims.

25. A non-crosslinked fine-celled foam product comprising: 10 a polymeric structure being substantially composed of fine cells and having the cell count being greater than 50 cells/inch, said polymeric structure being a blend of a polyolefin and a copolymer of an olefin monomer and an ethylenic monomer different from the monomer of said polyolefin, the amount of said copolymer being in the range of from 5 to percent by weight of said blend.

26. The product of claim 25, wherein said product is an elongated cellular body.

27. The product of claim 25, wherein said product is a foam plank.

28. The product of claim 27, wherein said foam plank has a density of from about 1.2 to about 2.6 pounds per cubic foot.

29. The product of claim 27, wherein said foam plank has a density of from about 4.0 to about 9.0 pounds per cubic foot. The product of claim 25, wherein the cell count is from 50 to 120 cells/inch.

31. The product of claim 25, wherein the cell count is greater than 70 cells/inch.

32. The product of claim 25, wherein said foam product is recyclable.

33. A product substantially as hereinbefore described with reference to the Examples. DATED this 21st day of SEPTEMBER, 2000 ASTRO-VALCOUR, INC. by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s)