Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D123/00—Coating compositions based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Coating compositions based on derivatives of such polymers
  • C09D123/02—Coating compositions based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
  • C09D123/04—Homopolymers or copolymers of ethene
  • C09D123/06—Polyethene

Definitions

• This invention relates to two-component polyethylene blends that are useful for extrusion 5 coating on various substrates.
• neck-in connotes the narrowing down of the extruded film Q immediately upon leaving the extruder head, presumably due to internal forces in the film, and which causes a thickening of the film edges so that trimming thereof is required.
• Poor neck-in properties or stability of a polymer or blend may ⁇ 5 result in as much as 15% waste or more in certain coating operations.
• the maximum width and uniformity of the coating depend on good neck-in stability characteristics.
• neck-in stability connotes the change 20 in neck-in per unit change in temperature of the film.
• a poor neck-in stability means a large change of neck-in per small change in temperature. Such temperature variations result, for example, from the on and off cycling of the extruder and die heaters.
• 5 Good neck-in stability is particularly desirable from the standpoint of maintaining a uniform coating thickness over a wide range of extrusion temperatures, as well as maintaining a constant coating width.
• the pinhole problem is manifested in poor barrier properties, and the resistance of a polyethylene coating to pinholing appears to be directly related to its thermal stability as reflected, for example, in neck-in thermal stability.
• the resultant limited 5 coating speeds are undesirable, of course, from the standpoint of poor economics of production resulting
• Patent 798,908 The blends disclosed in that patent have a high melt index and a high swell ratio.
• the melt index is at least 8 dg./min and the swell ratio is at least 1.50.
• the polyethylene blends of this invention have a lower melt index and a lower swell ratio than the prior art blends. These blends provide extrusion
• blends can be coated by extrusion at commercially acceptable speeds.
• polyethylene blends of this invention provide coatings that have better
• the blends are prepared by mixing a low density polyethylene having a density above .91 to .93 with a high density polyethylene having a density of .96 to .98 to provide blends having a melt index of .1 to
• From 10% to 90% by weight of a high density polyethylene is mixed with from 90% to 10% by weight of a low density polyethylene.
• the preferred blends contain from 20% to 70%, most preferably, 30% to 65%, by weight, of
• the melt indices range from .1 dg/min. to 7 dg/min. These blends also have a DSC melting point greater than a homopolymer of ethylene having the density of the blend. 5
• the blends may contain such additives as ultraviolet degradation inhibitors, stabilizers, pigments, inert fillers and the like which are commonly employed in resinous systems for a variety of purposes.
• the blends may be prepared in various 10 ways such as dry-blending and then passing through a compounding extruder, milling roll, or Banbury mixer. Any method whereby melts of the components can be mixed will also produce the desired blend.
• the low density polyethylene has a density of 15 0.912 g/cc to 0.
• the preferred low density polyethylene has a density of 0.915 g/cc to 0.920 g/cc and a melt index of 2.9 dg/min to 16 dg/min.
• Several such low density polyethylenes which have 20 been most preferred are as follows: 0.919 g/cc, 3.g dg/min; 0.917 g/cc, 3.5 dg/min; 0.919 g/cc, 15 dg/min.
• the high density polyethylene has a density of 0.96 g/cc to 0.98 g/cc, a melt index of 5 dg/min to 18 dg/min.
• One such high density polyethylene which has been most preferred has a density of 0.970 g/cc, and a melt index of 9.0 dg/min. 30
• density is determined in conformance with ASTM Designation D1505-57D. Density specimens are first annealed to give maximum density by conditioning under a 63.5 cm or higher mercury vacuum for 1 hour at 150-155°C. 35 followed by cooling under this vacuum at no greater than 20°C. per hour to a final temperature of less than 50°C. Melt index is determined in conformance with ASTM Designation D1238-62T.
• a polyethylene blend having a density of 0.935 g/cc, a melt index of 3.1 dg/min, and a swell ratio of 1.44 was prepared by blending 70 weight percent of a low density polyethylene with 30 weight percent of a high density polyethylene.
• Those of the high density component are as follows: density ⁇ 0.971; MI s 15.0 dg/min.
• the blend was fed to a 8.89 cm Egan extruder having a barrel length to diameter ratio of 24:1.
• the four zones of the extruder were maintained, from back to front, at 204°C, 260°C, 316°C, and 338°C.
• a metering type screw having six compression flights, and 12 metering flights were used.
• Prior to entering the die the melt passed through a 9 x 9 strand per square cm. mesh screen.
• the die was an Egan die, center-fed with 1.27 cm long lands, with an opening of 40.64 cm x .05 cm.
• the temperature of the die was held at 316°C.
• the extrusion rate was held constant at 59 kg per hour.
• the resulting film extrudate was passed through a 11.4 cm air gap into the nip formed by a rubber-covered pressure roll and a chill roll.
• 18.14 kg basis weight Kraft paper was fed into the nip with the pressure roll in contact with the Kraft paper.
• the nip pressure applied was 445 N per linear 25.4 mm.
• the chill roll was a 60.96 cm diameter mirror finish chrome-plated steel roll, water cooled to maintain a temperature of 15.50°C. on the roll.
• the coated paper was taken off the chill roll at a point 180° from the nip formed by the pressure roll and chill roll.
• the chill roll was operated at linear speeds of greater than 396.24 meter per minute.
• This coating composition coated the paper substrate at a commercially acceptable rate with a ' neck-in per edge of 2.67 cm which is also commercially acceptable.
• a polyethylene blend having a density of 0.947 Q g/cc, a melt index of 6.4 dg/min, and a swell ratio of 1.38 was prepared by blending 70 weight percent of a low density polyethylene with 30 weight percent of a high density polyethylene.
• the blend was fed to a 1.38 cm Egan extruder having a barrel length to diameter ratio of 24:1.
• the four zones of the extruder were maintained, from back to front, at 204°C, 260°C, 304°C, and 332°C.
• a metering type screw having six compression flights, and 12 metering 5 flights were used.
• Prior to entering the die the melt passed 9 x 9 strand per square cm mesh screen.
• the die was an Egan die, center-fed with 1.27 cm long lands, with an opening of 40.6 cm x .05 cm.
• the temperature of the die was held at 316°C.
• the extrusion rate was held constant at 59 kg per hour.
• the resulting film extrudate was passed through a 11.4 cm air gap into the nip formed by a rubber-covered pressure roll and a chill roll. At the same time, 18.14 kg basis weight Kraft paper was fed into the nip with the pressure roll in contact with the Kraft paper. The nip pressure applied was
• the chill roll was a 60.96 cm diameter mirror finish chrome-plated steel roll, water cooled to maintain a temperature of 15.5°C. on the roll.
• the coated paper was taken off the chill roll at a point 180° from the nip formed by the pressure roll and chill roll.
• the chill roll was operated at linear speeds of about 335.3 meters per minute.
• This extrusion coating composition had a melt index which provided acceptable commercial coating speeds with good neck-in per edge of about 2.67 cm.
• a polyethylene blend having a density of 0.947 g/cc, a melt index of 13 dg/min, and a swell ratio of 1.30 was prepared and coated according to the above procedure. The composition coated at linear coating speed of only about 259 meters per minute and had an excessive neck-in per edge of about 7.6 cm which is not satisfactory for commercial operation.
• a polyethylene blend having a density of 0.932 g/cc, a melt index of 8.1 dg/min, and a swell ratio of 1.2 was prepared and coated according to the above procedure.
• a polyethylene blend having a density of 0.950 g/cc, a melt index of 5 dg/min, and a swell ratio of 1.64 was prepared and coated according to the above procedure.
• a polyethylene blend having a density of 0.954 g/cc, a melt index of 7.9 dg/min, and a swell ratio of 1.72 was prepared and coated according to the above procedure.
• the composition provided satisfactory coatings at speeds of only 13.41 meters per minute to have neck-in or edge weave of about 1.52 cm per edge.
• the coating composition of this invention provides good coating to substrates such as Kraft paper, milk carton stock, photographic papers, cellulosic sheets, primed metal foils such as aluminum and the like.
• substrates such as Kraft paper, milk carton stock, photographic papers, cellulosic sheets, primed metal foils such as aluminum and the like.
• the coated substrates find utility in food packaging, medicine packing or other well known uses.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Wood Science & Technology (AREA)
• Organic Chemistry (AREA)
• Laminated Bodies (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)

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• 1982
  • 1982-07-09 EP EP19820902499 patent/EP0084049A4/fr not_active Withdrawn
  • 1982-07-09 JP JP57502485A patent/JPS58501181A/ja active Pending
  • 1982-07-09 WO PCT/US1982/000916 patent/WO1983000490A1/fr not_active Application Discontinuation
  • 1982-07-28 ZA ZA825431A patent/ZA825431B/xx unknown

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Non-Patent Citations (1)

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