Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
  • B32B27/322—Layered products comprising a layer of synthetic resin comprising polyolefins comprising halogenated polyolefins, e.g. PTFE
• • 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
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2314/00—Polymer mixtures characterised by way of preparation
  • C08L2314/02—Ziegler natta catalyst

Definitions

• the invention is directed to a food packaging material having a multi layered structure comprising a low density polyethylene containing inside layer.
• a food packaging material is an aseptic liquid food package.
• Such a package may provide a shelf life-time up to one year and a typical laminate structure of the package comprises layers of for instance low density polyethylene (LDPE) -paperboard-LDPE-aluminium foil-adhesive-LDPE.
• LDPE low density polyethylene
• the upper outside layer of LDPE is used to protect the paperboard from direct contact with water and to avoid moisture from penetrating into the paperboard.
• the paperboard layer mainly contributes to grip stiffness of the package.
• the outside layer may also function as the decor layer.
• a second intermediate LDPE layer is used as laminate layer to laminate the paperboard and aluminium foil (Al-foil) together.
• Al-foil prevents oxygen and light from reaching the packed food product.
• the last layer of the LDPE is laminated to the Al-foil by an adhesive layer, which increases the adhesion to a desired level.
• This inner LDPE layer is the layer that is actually in contact with the food.
• the coating weight of the outside LDPE layer may range between
• the coating weight of the intermediate LDPE layer between the paperboard and the foil may range between 15 and 20 g/m 2
• the coating weight of the inside LDPE layer ranges between 30 and 50 g/m 2
• the average coating weight of the inside LDPE layer is about 40 g/m 2 .
• the invention is directed to a food packaging material having a laminated structure comprising a low density polyethylene containing inside layer wherein the inside layer contains a blend of low-density polyethylene and Ziegler-Natta catalysed linear low-density polyethylene.
• the use of the blend comprising LDPE and Ziegler-Natta catalysed linear low-density polyethylene (ZNLLDPE) results in a reduction of the inside layer thickness as compared with an inside layer made from LDPE.
• the coating weight of the inside LDPE layer comprising the blend according to the invention ranges between 15 and 30 g/m 2 .
• the average coating weight of the inside layer comprising the blend according to the invention is about 20 g/m 2 .
• the down gauging from about 40 g/m 2 to about 20 g/ m 2 is a considerable improvement with respect to material efficiency.
• the present invention results in the required rheological properties to ascertain good web width variation, neck in (shrinkage in width of the LDPE comprising web) and draw down (the maximum line speed at which the LDPE comprising web breaks).
• the present invention has also advantages in comparison with a co extruded layer consisting of two separate layers of LDPE and LLDPE.
• the blend according to the invention comprises
• a low density polyethylene having a density between 910 kg/m 3 and 935 kg/m 3 (according to ISO 1183) and a melt index (MFR) between 1 dg/minute and 20 dg/minute (according to ASTM D 1133) and
• the blend comprises
• a low density polyethylene having a density between 910 kg/m 3 and 935 kg/m 3 (according to ISO 1183) and a melt index (MFR) between 1 dg/minute and 20 dg/minute (according to ASTM
• the blend comprises
• a low density polyethylene having a density between 910 kg/m 3 and 935 kg/m 3 (according to ISO 1183) and a melt index (MFR) between 1 dg/minute and 20 dg/minute (according to ASTM D 1133) and
• the MFR ratio of the low density polyethylene and the Ziegler-Natta catalysed copolymer ranges between 1 :3 and 3:1.
• the density of the low density polyethylene ranges between 915 kg/m 3 and 925 kg/m 3 .
• other layers of the packaging may comprise the blend comprising LDPE and Ziegler-Natta catalysed LLDPE.
• the inner LDPE layer may also be composed of for example a layer of LDPE and a layer of the blend comprising of LDPE and Ziegler-Natta catalysed LLDPE.
• the blend according to the invention may also comprise for example other polymers to improve specific characteristics of the end product. These polymers may be present in an amount of for example between 0.1 and 15 % by weight.
• the packaging material obtained with the blend according to the present invention is preferably obtained with extrusion coating.
• Liquid packaging is the largest market segment for extrusion coating in Europe.
• Today LDPE produced by using high-pressure autoclave technology is the commercially applied polyethylene for use in extrusion coating applications.
• LDPE obtained with an autoclave process is suitable to be applied in extrusion coating for reasons of processing (for example web stability, draw-down and neck-in) in relation to the molecular composition (broad molecular weight distribution, long chain branching) of the polymer.
• polymers and substrates are combined to form products with specific synergetic characteristics.
• the increasing processing and product requirements and quality demands may result in several different problems that can occur in the extrusion coating process.
• LDPE low density polyethylene
• LLDPE linear low density polyethylene
• the catalysts can be divided in three different subclasses including Ziegler Natta catalysts, Phillips catalysts and single site catalysts.
• the latter class is a family of different classes of compounds, metallocene catalysts being one of them.
• a Ziegler-Natta catalysed polymer is obtained via the interaction of an organometallic compound or hydride of a Group l-lll metal with a derivative of a Group IV-VIII transition metal.
• An example of a (modified) Ziegler-Natta catalyst is a catalyst based on titanium tetra chloride and the organometallic compound triethylaluminium.
• a difference between metallocene catalysts and Ziegler Natta catalysts is the distribution of active sites.
• Ziegler Natta catalysts are heterogeneous and have many active sites. Consequently polymers produced with these different catalysts will be different regarding for example the molecular weight distribution and the comonomer distribution.
• the LDPE applied in the blend may be produced by use of autoclave high pressure technology and may be produced by tubular reactor technology.
• LDPE has been produced by polymerising ethylene in a tubular reactor.
• the polymerisation may take place in the presence of a di-or higher functional (meth) acrylate co monomer such as for example 1 ,4-butane diol dimethacrylate (BDDMA), hexane diol dimethacrylate (HDDMA) 1 1 ,3- butylene glycol dimethacrylate (1 ,3-BGDMA), ethylene glycol dimethacrylate (EGDMA) , dodecanediol dimethacrylate (DDDMA), trimethylol propane trimethacrylate (TMPTMA) and/or trimethacrylate ester (TMA ester).
• a preferred comonomer is 1 ,4-butane diol dimethacrylate (BDDMA).
• the polymerisation in the tubular reactor may take place at a peak temperature between 29O 0 C and 35O 0 C wherein the di-or higher functional (meth) acrylate is present in an amount between 0.008 mol % and 0.200 mol % relative to the amount of ethylene copolymer.
• the linear low density polyethylene component of the composition is a low density polyethylene copolymer comprising ethylene and a C 3 - C 10 alpha-olefin co monomer.
• Suitable alpha-olefin co monomers include butene, hexene, 4-methyl pentene and octene.
• the alpha-olefin co monomer is present in an amount of about 5 to about 20 percent by weight of the ethylene-alpha olefin copolymer, more preferably an amount of from about 7 to about 15 percent by weight.
• Preferred co monomers are butene and hexene.
• the technologies suitable for the LLDPE manufacture include gas- phase fluidized-bed polymerization, polymerization in solution, polymerization in a polymer melt under very high ethylene pressure, and slurry polymerization.
• the LLDPE has been obtained with gas phase polymerisation.
• the blend according to the present invention comprises Ziegler-Natta catalysed LLDPE.
• a blend comprising metallocene catalysed LLDPE instead of Ziegler-Natta catalysed LLDPE is excluded. Applying these different blends will result in different products.
• the invention also relates to a process for producing a food packaging material having a multi layered structure comprising a low density polyethylene containing inside layer, said process comprising a step of extrusion coating the inside layer from a blend of low-density polyethylene and Ziegler-Natta catalysed linear low-density polyethylene.
• Preferred processes of the invention are analogous to the discussion on preferred blends as above.
• the packaging comprised as layers a LDPE outside layer, a paperboard substrate, an adhesive and an inside layer comprising LDPE and LLDPE wherein
• the paperboard substrate was Kraft paper 60 g/m 2 , width 800 mm,
• the adhesive tie layer was Escorene ®5020 (EAA) of Exxon
• the LDPE applied in the outside layer and in the inside layer was SABIC ®LDPE 1808AN00 of SABIC (density 919 kg/m 3 ; melt index 7.5 dg/minute) and
• the LLDPE applied in the inside layer was SABIC ®LLDPE 6318B of SABIC (density 921 kg/m 3 ; melt index 2,8 dg/minute ; polydispersity 5).
• Comparative Example C is directed to the inner layer of a co extruded product consisting of two layers wherein the first layer is a LDPE layer with a thickness of 10 g/m 2 and wherein the second layer is a LLDPE layer with a thickness of 10 g/m 2 .
• T melt maximum 305 0 C.
• Neck-in lower than 150 mm; this is finally determined by the die width substrate combination at the customer.
• Web width variation between 1 and 3 mm.
• Draw down as high as possible.
• Friction coefficient as low as possible; preferred to be maximum at pure LDPE level.
• Seal strength higher than 18 N/mm; minimum at pure LDPE level.
• Trouser test as high as possible.
• Puncture resistance as low as possible, however the customer has the possibility to provide solutions in case this value has not the initial desired value lower than 300 mJ/mm.
• the applied conditions of the coating equipment were as follows: - Screw diameter 11.4 mm - Die width 1100 mm
• the drawdown was determined by increasing the line speed in increments of 50m/min. during the draw down determination the extruder throughput was kept constant and fixed on kg/ m 2 at a starting velocity of 200 m/min. The samples were taken under the following conditions: -Line speed 400 m/min
• the other coating line processing variables such as for example die gap and air gap were kept constant.
• the neck-in was determined at a line speed of 200 m/min.
• Puncture resistance Indicates: packaging integrity (toughness; creating hole; elongation)
• Diameter ball 2.35 mm
• Trouser test Indicates: toughness (propagation of an existing hole/tear)
• Seal strength Indicates: seal quality during storage
• Comparative Experiment A resulted in a product having a coating weight of the inner layer of 40 g/m 2 and consequently there is no down gauging. Comparative Experiment B resulted in a product having an inner layer which is not processable.
• Comparative Experiment C resulted in a product having a neck- in of 241 mm. This value is unacceptable because the neck-in is preferably less than 150 mm. Furthermore the motor load was very high compared with the values according to Examples I-IV. A high motor load is disadvantageous because of the high energy consumption. A high motor load may also give throughput problems during the extrusion coating process.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Wrappers (AREA)
• Laminated Bodies (AREA)

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• 2007
  • 2007-09-10 EP EP07802234A patent/EP2069145A2/de not_active Withdrawn
  • 2007-09-10 WO PCT/EP2007/007855 patent/WO2008031540A2/en active Application Filing

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