Classifications

• • 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
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • 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
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/18—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets by squeezing between surfaces, e.g. rollers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
• • 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

Definitions

• This invention relates to films of linear low density polyethylene (LLDPE) .
• LLDPE has a molecular structure which is characterized by the substantial absence of long chain branching.
• conventional low density polyethylene (LDPE) has substantial long chain branching.
• LLDPE also has a significantly higher melting point (typically 120-135°C) than LDPE (typically 105-115°).
• LDPE is sometimes referred to as high pressure polyethylene because it is produced at high pressures.
• LLDPE is produced commercially at low pressures in a gas phase process. However, LLDPE may also be produced in a liquid phase solution process.
• Various alpha-olefins are typically copolymerized with ethylene in producing LLDPE.
• the alpha-olefins which have 3 to 15, preferably 4 to 8, carbon atoms, are present in the polymer in an amount of up to about ten weight percent.
• the comonomer influences the density of the polymer, which is less than 0.94 grams per cubic centimeter, and preferably is from about 0.915 to 0.935 g/cc.
• This invention provides films of LLDPE having substantially improved impact strength compared to conventional films of LLDPE.
• the films of the invention also have good tear strength in both the transverse and machine directions.
• the films of this invention are prepared by compression rolling films of LLDPE.
• compression rolling refers to the process of passing a plastic film through the nip of a pair of rolls at a temperature below the softening point of the film at a pressure which is sufficient to reduce the thickness of the film at least five percent, preferably at least fifty percent.
• the length of the film is increased by an amount corresponding to the reduction in thickness. For example, a film whose thickness has been reduced fifty percent by compression rolling has a length which is about twice as great as its original length. Compression rolling is described in U.S. Patents 3,504,075 and 4,085,187, which are incorporated herein by reference.
• This invention is based on the discovery that compression rolling of films of LLDPE substantially improves the impact strength of the films and ensures that they have good tear strength in both the machine and transverse directions. This result is surprising and unexpected in view of the effect of compression rolling on the impact strength and tear strength of films of other polyolefins.
• the rolled films of LLDPE of this invention have notched Elmendorf tear strengths (ASTM D-1922) of at least 300 (in preferred embodiments at least 350) grams per mil in both the machine and transverse directions, which cannot be said for other rolled polyolefin films.
• the films of this invention also have a falling dart impact strength (ASTM D-1709) of at least 500 grams per mil when the dart is dropped from a height of 8.75 inches, and at least 160, preferably at least 180, grams per mil when the dart is dropped from a height of 26 inches.
• ASTM D-1709 falling dart impact strength
• the impact strength of conventional LLDPE film is much lower.
• the compression rolling is preferably carried out with semiboundary lubrication, as taught in U.S.P. 4,085,187, with the preferred lubricant being water.
• the film is preferably rolled at a temperature of about 15 to 80 °C, more preferably 20 to 55°C.
• the thickness of the film is preferably reduced between about 50 and 90 percent.
• the final thickness of the films of this invention is preferably between about 0.5 and 6 mils, more preferably between one and three mils.
• the films of this invention have other excellent properties compared to conventional films, including stiffness, tensile strength, and water vapor transmission rate.
• LLDPE low density polyethylene
• PP polypropylene
• copolymers of ethylene or propylene with minor amounts of other ethylenically unsaturated monomers are also useful.
• the proportion of LLDPE blended or coextruded with other polymers is preferably at least 25, more preferably at least 50, percent by weight.
• Examples 1-4 and F, H and J cast films consisting of a single polymer, identified in the following Table, were compression rolled at ambient temperature. The ratio of the thickness of the film before rolling to the thickness after rolling is shown in parentheses in the Table. The properties of the compression-rolled films are compared to representative cast and blown unrolled films (Examples A, B, C, D, E, G and I) in the Table.
• the rolled films are compared in the Table with unrolled films of comparable thickness, rather than with the films before rolling, because the thickness of the films before rolling is so much greater that a comparison with them would not be as meaningful as a comparison with films of comparable thickness.
• rolling might reduce the tear strength of LLDPE in the transverse direction, that is not believed to be the case.
• the very high tear strength in the transvere direction of the film of Example C is believed to be due to orientation of the film that inherently or inadvertently occurred when the film was extruded. However, such orientation also apparently caused a sharp reduction in the tear strength of the film in the machine direction, which does not occur with compression rolling of LLDPE film.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)

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• 1984
  • 1984-01-03 EP EP19840900656 patent/EP0131617A1/de not_active Withdrawn
  • 1984-01-03 WO PCT/US1984/000003 patent/WO1984002707A1/en unknown

Non-Patent Citations (1)

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