WO2008100501A2 - Mousse de polyoléfine souple au toucher - Google Patents

Mousse de polyoléfine souple au toucher Download PDF

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Publication number
WO2008100501A2
WO2008100501A2 PCT/US2008/001839 US2008001839W WO2008100501A2 WO 2008100501 A2 WO2008100501 A2 WO 2008100501A2 US 2008001839 W US2008001839 W US 2008001839W WO 2008100501 A2 WO2008100501 A2 WO 2008100501A2
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WO
WIPO (PCT)
Prior art keywords
foam
resin
modifier
base resin
olefin
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PCT/US2008/001839
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English (en)
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WO2008100501A3 (fr
Inventor
Suresh Subramonian
Phillip Filiccia
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Dow Global Technologies Inc.
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Publication date
Application filed by Dow Global Technologies Inc. filed Critical Dow Global Technologies Inc.
Publication of WO2008100501A2 publication Critical patent/WO2008100501A2/fr
Publication of WO2008100501A3 publication Critical patent/WO2008100501A3/fr

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0066—Use of inorganic compounding ingredients
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/20—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of indefinite length
    • B29C44/30—Expanding the moulding material between endless belts or rollers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0061—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof characterized by the use of several polymeric components
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/06—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent
    • C08J9/08—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent developing carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/06—Polyethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/08—Copolymers of ethene
    • C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing more than three carbon atoms
    • C08L23/0815—Copolymers of ethene with aliphatic 1-olefins
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/02—Foams characterised by the foaming process characterised by mechanical pre- or post-treatments
    • C08J2201/03—Extrusion of the foamable blend
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2205/00—Foams characterised by their properties
    • C08J2205/04—Foams characterised by their properties characterised by the foam pores
    • C08J2205/052—Closed cells, i.e. more than 50% of the pores are closed
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/04—Homopolymers or copolymers of ethene
    • C08J2323/06—Polyethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00—Polymer mixtures characterised by other features
    • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group

Definitions

  • the present invention relates to a polyolefin foam, preferably a continuously extruded, non-crosslinked, fine cell, soft touch polyolefin foam, a process of manufacturing the foam product, and an article comprising the foam product.
  • the foam of the present invention comprises a) a blend of a base resin such as low density polyethylene (LDPE) and a modifier resin b) a permeability modifier and c) a nucleator.
  • LDPE low density polyethylene
  • Microcellular crosslinked polyolefin foam has been the material of choice for automotive materials handling applications. However, such foams are generally not recyclable. Therefore, environmental pressures have created an unmet market need for a 100% recyclable replacement product.
  • Vinyl and nitrile rubber foams have been the materials of choice for athletic sports gear (e.g. hunting jackets, athletic pads and gym mats) and buoyancy equipment (e.g. life vests, personal flotation devices).
  • athletic sports gear e.g. hunting jackets, athletic pads and gym mats
  • buoyancy equipment e.g. life vests, personal flotation devices.
  • these materials are not recyclable and the cost of making the products by these materials is high. Therefore, market pressures have created an unmet need for a low cost replacement product.
  • such foam is a non-crosslinked, fine cell, soft touch foam made of thermoplastic polyolefin materials. Therefore, it is an object of the present invention to provide such a foam and a process for manufacture thereof.
  • An accumulating extrusion process has been used in the past to make polyolefin foam having fine-celled structure.
  • the accumulating extrusion process is discontinuous.
  • the polymer melt is extruded in a holding zone (accumulator) and periodically ejected by a movable ram out into ambient conditions where unrestrained foam expansion occurs.
  • a continuous extrusion process is employed in the present invention.
  • a continuous extrusion process is advantaged over a discontinuous process in terms of more consistent product quality (e.g. uniform fine cell foam having a flat profile) and lower processing cost.
  • the present invention has shown that a dimensionally stable and fine cell foam can be produced over a broad density range on a continuous extrusion line without folding or warping problems.
  • the present invention provides a polyolefin foam, preferably a non-crosslinked and soft touch foam, comprising: a) a resin blend of a base resin and a modifier resin, b) a permeability modifier, and c) a nucleator.
  • the base resin comprises a low density polyethylene (LDPE) and the modifier resin comprises a substantially linear polymer of ⁇ -olefin.
  • LDPE low density polyethylene
  • the foam is a continuously extruded polyolefin foam that is substantially free of corrugation.
  • the substantially linear polymer of ⁇ -olefin comprises a homopolymer of a C2-C20 ⁇ -olefin or an interpolymer with at least one C3-C20 ⁇ -olefin and/or a C4-C18 diolefin; more preferably, the substantially linear polymer of ⁇ -olefin is a low modulus polyolefin plastomer (POP).
  • POP polyolefin plastomer
  • the soft touch foam comprises fine cells in a substantially closed cell structure.
  • the present invention provides an article comprising a polyolefin foam.
  • the foam is a non-crosslinked and soft touch polyolefin foam.
  • the foam comprises: a) a resin blend of a base resin and a modifier resin, b) a permeability modifier, and c) a nucleator,
  • the base resin comprises a low density polyethylene (LDPE) and the modifier resin comprises a substantially linear polymer of ⁇ -olefin.
  • the foam is a continuously extruded polyolefin foam that is substantially free of corrugation.
  • the article may comprise additional components that, when formed together with the article, form any of the following: athletic sports gear, buoyancy equipment, packaging cushion support, or specialty packaging case inserts for decorative display.
  • the present invention provides a process of making the polyolef ⁇ n foam, wherein the process comprises: a) processing a resin blend of a base resin and a modifier resin, a permeability modifier, a nucleator, and a blowing agent in an extruder and a mixer at a temperature sufficient to melt the resin blend and to form a gel mixture, b) uniformly cooling the gel mixture in a cooler to a predetermined foaming temperature, preferably, the predetermined foaming temperature is in the range of about 95- 115°C, and c) extruding the gel mixture through a die to form extruded foam at a predetermined pressure, preferably, in the range of above a prefoaming pressure that causes poor skin quality but below a predetermined pressure that causes corrugation.
  • the process is a continuous extrusion process.
  • Figure 1 illustrates the foaming temperature window of polyethylene (PE)/polyolefin plastomer (POP) foam formulations.
  • PE polyethylene
  • POP polyolefin plastomer
  • Figure 2 illustrates the foaming pressure window of PE/POP foam formulations.
  • Figure 3 illustrates the stress-strain behavior of PE & PE/POP foams.
  • Figure 4 illustrates the Shore A hardness of PE/POP, PE and crosslinked PE foams. DETAILED DESCRIPTION OF THE PRESENT INVENTION
  • the technology detailed in the present invention involves the use of a modifier resin in the resin blend with a base resin, e.g. low density polyethylene (LDPE), to produce a polyolefin such as soft touch, fine cell size, and substantially closed cell polyolefin foam.
  • a base resin e.g. low density polyethylene (LDPE)
  • LDPE low density polyethylene
  • the soft touch foam comprising the modifier resin and the base resin has superior elongational properties, improved soft feel characteristics, and good abrasion protection, especially for Class A surfaces.
  • the technology covers the composition including resin and additive formulations and the process of foaming the soft touch foam.
  • a foam with a substantially closed cell usually contains about 80% or more closed cells or less than about 20% open cells according to ASTM D 2856-A.
  • Cell refers to cavity contained in foam. A cell is closed when the cell membrane surrounding the cavity or enclosed opening is not ruptured and has all membranes intact.
  • the soft touch foam of the present invention has a desirably lower Shore A hardness. This feature indicates that the soft touch foam has a reduced material stiffness.
  • the soft touch characteristic of the polyolefin foam is a qualitative attribute that is related to the cell size, initial compressive modulus, Shore A hardness and gloss retention during abrasion.
  • the soft touch foam of the present invention preferably has the following preferred characteristics with a density in the range of about 1.5-4 pound/cubic foot (pcf) (24-64 kg/m3), more preferably a foam with density of about 2 pcf (32 kg/m3):
  • the cell size of the foam is preferred to be less than about 0.7 mm, more preferably less than about 0.6 mm,
  • the initial compressive strength at 10% deflection is preferably less than about 5 psi (35 kPa),
  • the Shore A hardness is preferably less than about 10,
  • the fine cell structure of the foam is important for achieving the soft feel characteristic and low abrasion performance.
  • the fine cell foam preferably has a cell size less than about 0.7 mm and, preferably, less than about 0.6 mm. For a given cell size or density, the foam of the present invention shows excellent abrasion resistance for highly polished or painted Class A automotive surfaces.
  • Class A surface is used in automotive design to describe high finish surfaces of automobile parts that are visible to the customer and need to be aesthetically pleasing and free of nicks, dents, scratches and scuff marks.
  • the soft feel characteristics and low abrasion performance provide the foam with superior performance in protecting high quality automotive parts from nicks, dents, scratches and scuff marks during storage, handling and transportation from the OEMs (original equipment manufacturers) to the assembly plant.
  • the foam is competitively advantaged over the existing materials in several high value applications, such as automotive parts protection, athletic sports gear, and buoyancy equipment.
  • the polyolefin foam of the present invention comprises a) a blend of a base resin and a modifier resin b) a permeability modifier, and c) a nucleator.
  • the foam is a non-crosslinked, substantially closed cell, soft touch foam. Because the inventive foam is not crosslinked, it is fully recyclable in an extruded foam process.
  • the base resin for the present invention may be low density polyethylene resin (LDPE) with moderate shear viscosity at low shear rates and adequate shear thinning behavior at high shear rates for good processability in an extrusion process line.
  • the base resin preferably has broad molecular weight distribution (MWD) and long chain branching (LCB), which are desirable for good foamability.
  • the base resins of the present invention preferably have density in the range of about 0.915-0.930 g/cc, melting point in the range of about 106-120 0 C, and crystallinity in the range of about 40-60%.
  • a preferred range for the melt index (ASTM D- 1238) of the base resin is about 0.5-5 dg/min.
  • the melt strength and drawability of the base resin are measured by the RheotensTM melt tension apparatus and should be at least about 10 cN and 100 mm/s, respectively.
  • the base resin makes up about 95-50% of the resin blend based on total weight of the base resin and modifier resin.
  • the modifier resin is important in the present invention. It ensures good foamability and processability of the formulation on the continuous extrusion process line to produce good quality foam with the desired properties.
  • the modifier resin may comprise substantially linear polymer of ⁇ -olefin polymers, for example, the substantially linear olefin polymers described in U. S. Patent Nos. 5,272,236 and 5,278,272, both incorporated herein by reference.
  • the substantially linear olefin polymers used in the present invention may be homopolymers of a C2-C20 ⁇ olefin, or preferably, interpolymers of ethylene with at least one C3-C20 ⁇ -olefin and/or a C4-C18 diolefin. These polymers contain a small amount of long-chain branching, about 0.01 to 3, preferably about 0.01-1, and more preferably about 0.3-1 long chain branch per 1000 carbon atoms. These polymers typically exhibit only a single melting peak by Differential Scanning Calorimetry (DSC).
  • DSC Differential Scanning Calorimetry
  • ⁇ -olefin is used herein to indicate a polymer containing essentially no polymerized monovinylidene aromatic monomers and no sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.
  • Particularly suitable ⁇ -olefins have from about 2 to about 20 carbon atoms, preferably from about 2 to about 8 carbon atoms.
  • Examples of the ⁇ -olef ⁇ ns may be ethylene, propylene, 1-butene, 4-methyl-l-pentene, 1- hexene, 1-octene and the like.
  • the preferred ⁇ -olef ⁇ n polymers are homopolymers of ethylene and interpolymers of ethylene with a C 3 -C 8 ⁇ -olefin.
  • interpolymer is used herein to indicate a polymer with at least two different monomers polymerized to make the interpolymer. This includes copolymers terpolymers, etc.
  • Particularly suitable substantially linear olefin polymers for the present invention preferably have a melt index (ASTM D 1238, Condition 190°C/2.16 kg) of from about 0.1 to about 100 dg/min, preferably from about 0.5 to about 5 dg/min, and a density of from about 0.850 to 0.970 g/cc, preferably about 0.850 to 0.950 g/cc, and more preferably about 0.850 to 0.920 g/cc.
  • Examples of the substantially linear olefin polymers include polyolefin plastomers (POP) marketed by The Dow Chemical Company under the tradename AffinityTM or polyethylene elastomers (POE) under the tradename EngageTM.
  • the differentiation of the POP and POE is based oh density and crystallinity and comonomer content ( ⁇ 20 wt % octene for AffinityTM polyethylene plastomers and >20 wt % octene for EngageTM polyethylene elastomers).
  • Suitable modifier resins used in the present invention may preferably be low modulus polyolefin plastomers (POP), such as ethylene-octene copolymers made by Dow constrained geometry catalyst technology (CGCT). These modifier resins have narrow molecular weight distribution (MWD), short chain branching (SCB) and controlled long chain branching (LCB). The modifier resins have lower melt strength, higher drawability and limited strain hardening compared to the base resins.
  • POP low modulus polyolefin plastomers
  • CGCT Dow constrained geometry catalyst technology
  • MWD molecular weight distribution
  • SCB short chain branching
  • LCB controlled long chain branching
  • the modifier resins have lower melt strength, higher drawability and limited strain hardening compared to the base resins.
  • low modulus is used to describe resins with low crystallinity, preferably less than about 40%, and low density, preferably less than about 0.915 g/cc.
  • a low modulus polyolefin plastomer with low crystallinity and low density has good flexibility and low stiffness.
  • the preferred POP resins have density in the range of about 0.860-0.910 g/cc, preferably about 0.885-0.905 g/cc, crystallinity in the range of about 25-35%, and contain about 10-20 weight % of octene comonomer. Resins from other suppliers that have the desired morphology and shear/extensional rheology may also be used. These resins bridge the gap between elastomers and plastic with rubber like properties and plastic processability.
  • One of the preferred POP resins may be AffinityTM, which is commercially available from The Dow Chemical Company.
  • the low modulus modifier resin makes up about 5-50% of the resin blend of the base resin and modifier resin. If the amount of the modifier resin is less than about 5-50%, the modulus reduction of the foam will be minimal. If the amount of the modifier resin is more than about 5-50%, the foamability of the foam will be affected.
  • the modifier resin of the present invention has narrow molecular weight distribution, short chain branching and controlled long chain branching. However, the use of this resin alone for foaming is not practical because of its poor melt strength, high drawability and limited strain hardening compared to the base resin.
  • the low crystallinity POP resin exhibits low storage modulus compared to the base resin.
  • the use of the modifier resin in blends with the base resin such as LDPE results in improved softness and flexibility.
  • the base resin LDPE and the modifier resin POP blends exhibit a surprisingly synergistic response during extensional flow (e.g. foaming) with the blend having a higher melt strength than either of the individual resin components.
  • the LDPE and the POP have crystallization temperatures that are well separated but the blend surprisingly exhibits a single Differential Scanning Calorimetry (DSC) crystallization temperature.
  • DSC Differential Scanning Calorimetry
  • the foaming temperature of the LDPE/POP blend is close to that of the base resin LDPE, minimizing the risk of freeze-off of the base resin in the die or cooler during the foaming process.
  • the melt index of the modifier resin is chosen to be close to that of the base resin to minimize viscosity mismatch concerns.
  • the modified resin such as POP resin shows unexpected benefit for the soft touch performance.
  • the POP resin can be foamed in a continuous extrusion process as the minor component in blends with a base resin such as LDPE as a major component without any additional processing issues, despite POP resin's lower crystallization temperature compared to the base resin.
  • the POP resin as a component of the resin blend can also provide soft, substantially closed cell foams despite its low melt strength and limited strain hardening compared to the branched LDPE resin.
  • a permeability modifier In addition to the blend of base resin and modifier resin, a permeability modifier, a nucleator and a blowing agent may be employed to the polymer blend formulation of the present invention.
  • the permeability modifier is added to the polymer blend formulation to enhance dimensional stability of the foam product.
  • the preferred permeability modifier may be glycerol monostearate, which is commercially available under the trademark AtmerTM (available from Ciba).
  • Other permeability modifiers may include stearamide, stearyl stearamide, glycerol di- and tri-stearate, glycerol mono and di-oleate, etc.
  • the permeability modifier is employed in an amount of about 0.1-2.5, preferably about 0.1-1.5 parts per 100 parts polymer resin blend. Outside this range, the dimensional stability of the foam product will be affected. An understabilized foam will be formed when the amount of the permeability modifier is lower than the range, and an overstabilized foam will be formed when the amount of the modifier is higher than the range.
  • understabilized is used herein to indicate a foam that suffers irreversible contraction during the aging process.
  • overstabilized is used herein to indicate a foam that suffers irreversible expansion during the aging process. Both situations are undesirable as they result in foam with distorted cross-section and shape.
  • a nucleator preferably a decomposable nucleator, is added to the foam formulation to regulate cell size within the foam.
  • the preferred nucleator used in the present invention may be a mixture of citric acid/sodium bicarbonate, which is commercially available under the trademark HydrocerolTM (available from Clariant).
  • Other nucleators include talc, silica, or metal stearate such as calcium barium, zinc, and aluminum stearate, etc. may also be used.
  • the nucleator is employed in an amount of about 0.1-4, preferably about 0.1-3 parts per 100 parts polymer resin blend. At levels lower than this range, minimal nucleation occurs. At levels higher than this range, no significant further effect on nucleation occurs as the additive primarily acts as a filler.
  • Blowing agents suitable for making the soft touch foams disclosed herein may be inorganic blowing agents, organic blowing agents, chemical blowing agents or a combination thereof. Examples of useful blowing agents are disclosed in US 6,720,363 B2, incorporated herein by reference.
  • the blowing agent used in the present invention is preferred to be a hydrocarbon blowing agent. More preferably, the blowing agent is isobutane.
  • the amount of the blowing agents used is dependent on the desired density of the foam and, in light of the disclosure herein, it is within the skill in the art to adjust this amount in order to achieve the desired density.
  • the blend of the base resin and the modifier resin of the present invention with a sufficient amount of the permeability modifier, the nucleator and the blowing agent, produces good quality, non-crosslinked fine cell, substantially closed cell, soft touch foam over a moderate foaming temperature range on a continuous extrusion process line.
  • the soft touch polyolefin foam is prepared by heating the polymer blend, additives including the modifier and the nucleator, and the blowing agent in an extruder and a mixer at a temperature adequate to melt blend the feed, decomposing the nucleator and resulting in dispersed gas and solids.
  • the gel mixture is then uniformly cooled to the desired foaming temperature in coolers.
  • the foaming temperature may be in the range of about 95-115 0 C, more preferably in the range of about 100-11O 0 C.
  • the gel mixture can then be extruded or conveyed through a die of desired shape at a predetermined pressure above the prefoaming pressure which causes poor skin quality, but well below the pressure that causes corrugation.
  • the prefoaming pressure may be about 400 psi (2758 kPa) and the pressure that causes corrugation may be about 900 psi (6205 kPa).
  • the predetermined pressure is preferred to be in the range of about 400 psi (2758 kPa) to 900 psi (6205 kPa), more preferably in the range of about 450 psi (3103 kPa) to 850 psi (5861 kPa).
  • the mixer may be any of a variety of mixers, not limited to a second extruder, a static mixer, an interface surface generator, any of several varieties of rotary mixers including a rotating shaft in tube mixer, counter-rotating shafts in an elongated housing, a spline mixer, a cavity transfer mixer, and so on.
  • the devices used for cooling the gel mixture may be any of a variety of coolers, including a second extruder, shell and tube cooler, tubular or plate type heat exchangers and the like.
  • the mixing and cooling operation can be combined in one step as with a second extruder, a cooled cavity transfer mixer and a cooled static mixer device.
  • a corrugated foam is a foam with surfaces (faces) that are not smooth and flat but are warped and folded into peaks and valleys. Corrugation, or folding of the foam, is usually caused by the rapid volumetric expansion rate of the small cells close to the die and the ease of expansion of the foam board in the extrusion and vertical directions relative to the difficulty in expansion in the horizontal (transverse) direction, i.e., due to the mismatch between the increase in the cross-sectional width of the board (occurs fast) relative to the horizontal spreading of the board (occurs slowly).
  • the process of this invention also includes an additional step to form the extruded foam using forming equipment such as rollers or belts close to the die.
  • the maximum processing temperature for making the foam should be about 180- 200 0 C to obtain optimum gas yield and best nucleation efficiency from the dual mode nucleator.
  • the die pressure is selected to be above the prefoaming pressure that causes poor skin quality, (typically about 400 psi (2758 kPa) for 10% blowing agent in the formulation) and well below the pressure that causes corrugation (typically about 900 psi (6205 kPa) for 10% blowing agent in the formulation.
  • the conventional accumulating extrusion process used to make the fine cell foam is discontinuous.
  • the polymer melt is extruded in a holding zone (accumulator) and periodically ejected by a movable ram out into ambient conditions where unrestrained foam expansion occurs.
  • the continuous extrusion process used in the present invention is capable of producing uniform fine cell foam having a flat profile that is substantially free of corrugation or without corrugation (wavy surface).
  • Foam with small cell size is important for achieving the soft feel characteristic and low abrasion performance.
  • An elevated level of the permeability modifier e.g. glycerol monostearate (GMS)
  • GMS glycerol monostearate
  • the permeability modification mechanism is believed to be due to migration of the permeability modifier to the polymer-air interface during foaming, due to its limited compatibility with the polymer, to form an ordered barrier structure.
  • the ordered barrier structure reduces the diffusion of large molecular sized blowing agents, such as isobutane, out of the foam relative to the ingress of air and thereby minimizes excessive dimensional change of the foam board during the aging step.
  • Nucleation to achieve a foam with fine cell structure is provided by two routes: a) primary nucleation by a nucleator such as a mixture of citric acid and sodium bicarbonate that is effective at low-to-moderate loading but incrementally less effective at higher loading, b) Secondary nucleation by manipulating process conditions and die design (pressure drop and pressure drop rate at the die) so that the die pressure is above the prefoaming limit but sufficiently below the level that causes board corrugation. Operating below the prefoaming pressure results in foam with poor skin quality. Further improvement in foam board flatness may be achieved by the use of forming devices close to the die that alter the blow-up, redirecting expansion from the width of the board to the thickness.
  • a nucleator such as a mixture of citric acid and sodium bicarbonate that is effective at low-to-moderate loading but incrementally less effective at higher loading
  • Secondary nucleation by manipulating process conditions and die design (pressure drop and pressure drop rate at the die) so that the die pressure is above the prefoaming limit
  • the polyolefin foam of the present invention may be competitively advantaged over the conventional materials in several valuable applications.
  • the foam is very useful in automotive material handling, specialty packaging applications and as a key component in athletic sports gear and buoyancy devices. Possible applications may be for athletic sports gear such as hunting jackets, athletic pads and gym mats, buoyancy equipment such as life vests, personal flotation devices or protective cushion packaging of automotive parts with Class A surfaces. Further, the foam may also be used in specialty packaging applications, such as decorative displays and high end case inserts, where soft feel and high aesthetics are required.
  • LDPE low density polyethylene
  • POP polyolefin plastomer
  • GMS glycerol monostearate
  • the additives including the permeability modifier and the nucleator are present as parts per hundred parts (pph) of total polymer resins.
  • the blowing agent is present as parts per hundred parts solids feed (including resins and additives).
  • PE620i melt index: 1.8 dg/min, density: 0.924 g/cc,
  • DSC heat of crystallization 82 J/g, storage modulus, G': 8.9, melt strength: 14 cN, drawability: 200 mm/s.
  • melt index 0.88 dg/min, density: 0.923 g/cc, melt strength: 15 cN, drawability: 180 mm/s.
  • PL- 1880 melt index: 1.0 dg/min, density: 0.902 g/cc,
  • DSC heat of crystallization 53 J/g
  • storage modulus G' 2.4
  • melt strength 5 cN
  • drawability 275 mm/s.
  • the melt index is determined using ASTM D 1238.
  • the melt strength and drawability are determined by RheotensTM melt indexer, the density is determined by ASTM D 792, crystallization temperature and heat of crystallization are determined by Differential Scanning Calorimetry (DSC) (ASTM D 3417/3418).
  • a pilot extrusion process line used for making the foam includes the following equipment:
  • resin and additive feeders and a single screw extruder used to melt, mix and forward the resin and additives
  • a mixer used to disperse the blowing agent into the melt, with an optional gear pump to provide consistent feed rate and dampen pressure fluctuations
  • Coolers are used to uniformly cool the polymer resins, additives and blowing agent mixture to the foaming temperature
  • a die with an adjustable slit is used to shape the extrudate as it emerges from the pressurized line to ambient conditions, facilitating the expansion of the foam to the desired profile and stabilization of the foam structure by external air cooling with fans or blowers.
  • the resins and solid additives are added from gravimetric or volumetric feeders to the feed throat of the extruder in starve feed mode.
  • the blowing agent and liquid additives are fed to the mixer via positive displacement pumps.
  • the line is run at about 40 lb/hr (residence time of about 15 min) using a Vi" or 1" wide adjustable die and is controlled with a process control system. After a formulation change is made, the line is allowed to stabilize for at least three residence times before a representative sample is taken.
  • feed zone set at about 120 0 C
  • the mixer is set at about 180 0 C.
  • the maximum gel temperature in the extrusion line, at the extruder outlet (about 200 0 C), is higher than the metering zone set-point (about 180 0 C) due to shear heating.
  • the maximum pressure is at the mixer outlet (about 3200 psi or 22060 kPa) after blowing agent addition.
  • the heat transfer fluid temperature set-points for the coolers are adjusted so that the temperature of the gel entering the die is between about 95°C and 115°C.
  • the temperature set point of the cooler and die body are adjusted to make good quality foam.
  • the die pressure is maintained above the prefoaming limit that causes poor skin quality (about 400 psi, 2758 kPa) and below the pressure that causes corrugation (about 900 psi, 6205 kPa) by adjusting the die opening.
  • the foaming temperature window is the temperature range of the polymer resins/additive/blowing agent mixture at the die that results in stable foam with the lowest density and open cell content less than about 20%. Above the temperature range specified, the foam has generally poor stability, high open cell content (> about 25%) and collapses. Below the temperature range, the polymer crystallizes out of the melt and freezes in the die and cooler, resulting in poor heat transfer.
  • the foaming temperature window of a formulation in the foam extrusion process is experimentally determined by changing the cooler and die body temperatures in step-wise fashion while monitoring the die pressure, the density, open cell content and foam quality.
  • foam samples designated 60/40 PE/POP in Figure 1 are made with the following formulation:
  • resin blend 60/40 polyethylene (PE) XSS 84812.06/polyolefin plastomer (POP) PL- 1880;
  • nucleator 1.5 pph CF-20
  • blowing agent 10 pph iC4.
  • the results in Figure 1 indicate a foaming temperature range of 102-105°C and a foaming temperature window, ⁇ Tf 0am i ng> of 3°C for producing dimensionally stable foam with open cell content below 20%.
  • the foaming temperature window obtained experimentally on a pilot scale line is moderately broad and is believed to be adequate for scaling purposes to make good quality foam on a large scale production line.
  • the die pressure for the foam formulations is ranged between about 420 and 462 psi (2896-3185 kPa).
  • the density of all the foams is ranged between about 1.9-2.1 pcf (30-34 kg/m 3 ). All the foam products exhibit good skin quality with no corrugation or folding.
  • the results show that for the 60/40 PE/POP formulation, the continuous extrusion process of the invention can be used to make good quality, corrugation free, substantially closed cell foam with a foaming temperature preferably in the range of 102-105°C and a moderately broad foaming temperature window of 3°C.
  • resin blend 50/50 polyethylene (PE) XSS 84812.06/polyolefin plastomer (POP) PL- 1880;
  • nucleator 1.5 pph CF-20
  • blowing agent 10 pph iC4.
  • the results in Figure 1 indicate a foaming temperature range of 100-102 0 C and a foaming temperature window, ⁇ T f0am i ng , of 2°C for producing dimensionally stable foam with open cell content below 20%.
  • the foaming temperature window obtained experimentally on a pilot scale line is moderately broad and is believed to be adequate for scaling purposes to make good quality foam on a large scale production line.
  • the die pressure for the foam formulations is ranged between 444 and 455 psi (3061-3137 kPa).
  • the density of all the foams is ranged between 1.9-2.0 pcf (30-32 kg/m3). All the foams exhibited good skin quality with no corrugation or folding.
  • the continuous extrusion process of the invention can be used to make good quality, corrugation free, substantially closed cell foam with a foaming temperature preferably in the range of 100-102°C and a moderately broad foaming temperature window of 2°C.
  • the continuous extrusion process of the invention can be used to make good quality, corrugation free, substantially closed cell foam with a foaming temperature in the range of 95 to 115°C and, more preferably, in the range of 100-110 0 C.
  • the lower limit of the operating pressure range is the pressure at which prefoaming occurs, which is the minimum die pressure to maintain the blowing agent solubilized in the melt. At pressures below the prefoaming pressure, premature release of the blowing agent occurs with degassing at the die, evidenced by a crackling sound, and results in a poor quality foam with very rough skin due to the rupture of surface cells.
  • the upper limit of the operating pressure range is the pressure at which corrugation occurs. Corrugation or folding is caused by the uneven directional expansion of the gas for a given die take-up configuration resulting in a wavy or warped profile rather than the desired smooth flat surface. Corrugation occurs due to the ease of expansion in the vertical and extrusion directions accompanied by the difficulty in expansion in the horizontal direction, especially in the presence of higher levels of blowing agent necessary to attain lower density.
  • resin blend 60/40 polyethylene (PE) XSS 84812.06/polyolefin plastomer (POP) PL- 1880;
  • nucleator 1.5 pph CF-20
  • blowing agent 10 pph iC4.
  • the exit temperature from the cooler and die temperature are maintained at 107 0 C and the die pressure is varied between 400 and 900 psi (2758 - 6205 kPa) by changing the die opening of the adjustable slit die in a step-wise fashion and noting the quality of the foam skin and board profile.
  • the die opening is reduced for a given throughput rate, the cross-sectional area of the die decreases resulting in a decrease in foam thickness and an increase in the linear speed of foam exiting the die.
  • the prefoaming pressure for the formulation of the invention is about 400 psi (2758 kPa). At pressures below this pressure, the quality of the skin deteriorates significantly due to rupture of the surface cells and a crackling sound is audible due to the degassing of the blowing agent at the die.
  • the corrugation pressure for the formulation of the invention is about 900 psi (6205 kPa). At pressures above this pressure, the quality of the board deteriorates significantly due to the die induced nucleation and the faster expansion rate in the extrusion and vertical directions relative to the horizontal (or cross) direction resulting in a corrugated profile with peaks and valleys rather than a flat board.
  • the use of a modifier resin in blends with low density polyethylene is important to achieve a reduction in modulus resulting in softer foam.
  • the stress (force per unit area) and strain (ratio of change in length per original length) are recorded as the foam is compressed by a universal testing machine (e.g. InstronTM).
  • the modulus is the ratio of stress to strain over the linear (elastic) range and is obtained from the initial slope of the stress vs. strain curve. As the modulus decreases, the compressive strength (stress) of the foam for a given deflection (strain) decreases.
  • PE/POP The samples in Figure 3 denoted as PE/POP are prepared using the following formulations at a foaming temperature of 102°C and a die pressure of 438 - 463 psi (3020 - 3192 kPa):
  • resin blend polyethylene (PE) XSS 84812.06/polyolefin plastomer (POP) PL- 1880, with blend ratios varying from 80/20 to 60/40;
  • nucleator 4.0 pph CF-20
  • blowing agent 10 pph iC4.
  • the sample in Figure 3 denoted as PE is prepared using the following formulation at a foaming temperature of 105 0 C and a die pressure of 409 psi (2820 kPa):
  • nucleator 4.0 pph CF-20
  • blowing agent 10 pph iC4.
  • incorporación of the POP resin in the PE foam formulation produces a foam with superior abrasion performance.
  • the abrasion performance of the foam on a high gloss substrate is determined with a modified ASTM D 5264 procedure using a Sutherland 2000 abrasion tester.
  • a 4" x 2" x 2.125" foam sample is skived to remove the skin and inserted into the sample holder of the rubbing arm with the desired static load.
  • the test surface is a high gloss painted automotive metal plaque. Prior to the test, the gloss of the test surface is measured at three points with a gloss meter at 20° and 60° angles and the average initial gloss before testing is calculated.
  • the rubbing arm is lowered to contact the metal plaque and the skived foam is rubbed against the high gloss painted metal plaque under a given load and predetermined speed for a fixed number of cycles.
  • the gloss of the test surface is remeasured at the same three points at 20° and 60° angles and the average final gloss after testing is calculated.
  • the abraded plaque is also visually rated on a qualitative scale of 0-5 for the level of scratches, marks or haze.
  • Table I The results of abrasion testing of several foam samples of the invention and comparative foam samples are presented in Table I below. The quantitative results of the change in gloss of the surface of the substrate after abrasion with the foam measured with a gloss meter and the qualitative results by visual observation are provided.
  • the sample labeled Ex. 1 in Table I is prepared using the following formulation at a foaming temperature of 104°C and a die pressure of 441 psi (3040 kPa) to make a corrugation-free foam with good skin:
  • nucleator 2.0 pph CF-20
  • blowing agent 10 pph iC4.
  • the sample labeled Ex. 2 in Table I is prepared using the following formulation at a foaming temperature of 102°C and a die pressure of 451 psi (3110 kPa) to make a corrugation-free foam with good skin:
  • blowing agent 10 pph iC4.
  • samples Ex. 1 and Ex. 2 are examples of the present invention.
  • the samples designated Comp Ex. 1 and Comp Ex. 2 are comparative samples and represent the commercially available non-crosslinked SynergyTM 1000 foam and EthafoamTM 220 foam, respectively. These commercially available foams are made with LDPE only.
  • the soft feel or soft touch attribute desired in the foam is a human tactile response that is difficult to simulate or characterize with test equipment.
  • the softness of the foam as measured by human touch, is a qualitative attribute that can be related to foam properties, such as cell size, and foam attributes and performance indicators, such as initial compressive modulus, Shore A hardness and gloss retention during abrasion.
  • the cell size is preferably less than about 0.7 mm, more preferably less than about 0.6 mm
  • the initial compressive strength at 10% deflection is preferably less than about 5 psi (35 kPa)
  • the Shore A hardness is preferably less than about 10
  • the gloss retention during abrasion is preferably greater than about 0.975, more preferably greater than about 0.985.

Abstract

La présente invention concerne une mousse de polyoléfine non réticulée extrudée en continu comprenant a) un mélange associant une résine de base, par exemple un polyéthylène de faible densité, et une résine modificatrice; b) un agent modificateur de la perméabilité et; c) un facteur de nucléation, ainsi qu'un procédé de fabrication de ladite mousse.
PCT/US2008/001839 2007-02-13 2008-02-12 Mousse de polyoléfine souple au toucher WO2008100501A2 (fr)

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Publication number Priority date Publication date Assignee Title
EP2803478A2 (fr) 2014-09-02 2014-11-19 Mondi Consumer Packaging Technologies GmbH Feuille à plusieurs couches en plastique
EP2815879A2 (fr) 2014-09-02 2014-12-24 Mondi Consumer Packaging Technologies GmbH Feuille de coextrusion en polyéthylène
US9260577B2 (en) 2009-07-14 2016-02-16 Toray Plastics (America), Inc. Crosslinked polyolefin foam sheet with exceptional softness, haptics, moldability, thermal stability and shear strength
US20180149191A1 (en) * 2015-05-30 2018-05-31 Charlotte Baur Formschaumtechnik GmbH Plastic Component with Fastening Pieces
EP3674355A1 (fr) * 2018-12-28 2020-07-01 SABIC Global Technologies B.V. Composition de mousse de polyéthylène

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US6720363B2 (en) * 2000-03-17 2004-04-13 Dow Global Technologies Inc. Preparation of a macrocellular acoustic foam
WO2005007729A1 (fr) * 2003-07-07 2005-01-27 Dow Global Technologies Inc. Feuilles minces de polyethylene expanse
WO2006102151A1 (fr) * 2005-03-17 2006-09-28 Dow Global Technologies Inc. Mousses souples en interpolymeres d'ethylene/alpha-olefines

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Publication number Priority date Publication date Assignee Title
US6720363B2 (en) * 2000-03-17 2004-04-13 Dow Global Technologies Inc. Preparation of a macrocellular acoustic foam
WO2005007729A1 (fr) * 2003-07-07 2005-01-27 Dow Global Technologies Inc. Feuilles minces de polyethylene expanse
WO2006102151A1 (fr) * 2005-03-17 2006-09-28 Dow Global Technologies Inc. Mousses souples en interpolymeres d'ethylene/alpha-olefines

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9260577B2 (en) 2009-07-14 2016-02-16 Toray Plastics (America), Inc. Crosslinked polyolefin foam sheet with exceptional softness, haptics, moldability, thermal stability and shear strength
US10301447B2 (en) 2009-07-14 2019-05-28 Toray Plastics (America), Inc. Crosslinked polyolefin foam sheet with exceptional softness, haptics, moldability, thermal stability and shear strength
EP2803478A2 (fr) 2014-09-02 2014-11-19 Mondi Consumer Packaging Technologies GmbH Feuille à plusieurs couches en plastique
EP2815879A2 (fr) 2014-09-02 2014-12-24 Mondi Consumer Packaging Technologies GmbH Feuille de coextrusion en polyéthylène
US9944045B2 (en) 2014-09-02 2018-04-17 Mondi Consumer Packaging Technologies Gmbh Coextruded polyethylene film
US20180149191A1 (en) * 2015-05-30 2018-05-31 Charlotte Baur Formschaumtechnik GmbH Plastic Component with Fastening Pieces
US11209033B2 (en) * 2015-05-30 2021-12-28 Charlotte Baur Formschaumtechnik GmbH Plastic component with fastening pieces
EP3674355A1 (fr) * 2018-12-28 2020-07-01 SABIC Global Technologies B.V. Composition de mousse de polyéthylène
WO2020136011A1 (fr) * 2018-12-28 2020-07-02 Sabic Global Technologies B.V. Composition de mousse de polyéthylène

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