Classifications

• • 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
  • 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
  • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
  • B29C43/22—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of indefinite length
• • 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
  • B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
  • B29C55/06—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed
• • 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
  • B29K2077/00—Use of PA, i.e. polyamides, e.g. polyesteramides or derivatives thereof, as moulding material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2007/00—Flat articles, e.g. films or sheets

Definitions

• This invention relates to oriented polyamide strapping and, more particularly, to a process for reducing internal strain in such strapping.
• Camber is defined as the maximum deviation from a straight line (while not under tension) of an 8-foot length of strapping when placed on a fiat surface so that both ends of the strapping touch said line. A maximum of 4 inches of cam-her is permissible when such strapping is to be used in automatic packaging machines.
• Cupping is used with reference to strapping at least several inches wide. Cupping results when the center of the strapping is longer than the edges and is manifested by an arc-shaped cross section in strapping which has been cut transversely to its length.
• cupped strapping is slit in half, lengthwise, the two separated halves curve outwards, thus exhibiting a phenomenon analogous to camber.
• Cupping may be measured quantitatively by slitting such wide strapping lengthwise and measuring the camber thereof. For example, strapping of 3-inch width is slit lengthwise into 3 traps each 1 inch wide, on which camber may be measured as above. A maximum of 4 inches of camber is desired here also.
• the strapping to be treated according to the present invention are derived by orientation of polyamide billets.
• the billets can be made by extrusion (i.e., by pressuring molten molding composition from an orifice to form a solid billet at least one-eighth inch wide and 40 mils thick), or by the modified extrusion or molding process and apparatus disclosed in U.S. application Ser. No. 552,191, filed May 23, 1966, by R. T. Fields et al. Orientation of such billet is carried out by passing the billet between at least one part of the orienting rollers as disclosed in British Patent 1,017,175, i.e., the length of the billet is extended at least 4 times while the width of the resultant oriented shape is maintained within 0.7-
• the oriented strapping is then subjected to tension of at least 1000 p.s.i. (stress) at temperatures at least 50 C. below the melting point (as described in ASTM test D2117-64) of the polyamide resin employed.
• the preferred polyamides of this invention are polyhexamethylene adipamide, polycaprolactam, and a copolymer of -85% (by weight) of hexamethylene adipamide units and 15-25% of caprolactam units.
• plasticizers for the polyamide resin (based on the total weight of polyamide and plasticizer).
• suitable plasticizers include those conventionally used to plasticize polyamides, such as N-ethyl toluene sulfonamide, 2-ethyl-hexanediol-l,3, and tetramethylene sulfone.
• the process variables in this stretch-straightening process are selected interdependently.
• the preferred degree of tension varies inversely with temperature.
• the method employed'to heat the oriented shape according to this invention may be varied.
• the strapping may be heated by passage through 1) a hot oil bath, (2) heated pull rolls, (3) radiant heaters, or (4) a combination of these methods.
• the strapping to be stretch-straightened can be heated to the desired temperature before the application of tension as described in British Patent 1,017,175.
• the temperature of the stretch-straightening process generally is at least 50 C. below the melting point of the polyamide (whether or not plasticizer has been added), as measured by ASTM method D2117-64, which measures the disappearance of birefringence in seniicrystalline polymers.
• the present process improvement can be applied to the strapping as an in-line treatment just after manufacture of the strapping.
• strapping which has been stored can be treated according to this invention just prior to use to remove any camber or cupping which develops in storage.
• Stretch-straightening is especially important with a multi-end strapping line where the individual ends must be straight, parallel, and in place. It is also important in making wide oriented strapping such as belting reinforcing tapes for power transmission belts (as disclosed in U.S. Patent 2,999,764).
• EXAMPLE 1 Strapping 0.022 inch by 0.505 inch was made as follows. Billet was extruded and molded according to U.S. application Ser. No. 552,191, filed May 23, 1966, from polyhexamethylene adipamide of relative viscosity 50 (as determined by ASTM method D789). The billet was then oriented in two rolling stages as described in British Patent 1,017,175, to produce strapping.
• Each of the strands was found to have camber .in.
• camber varied up to about 4 inches, as did camber in strapping which had been stretch-straightened under conditions identical to those of the example except that the tension was only 3,600
• Example 2 This example is identical to Example 1, except that the tension to which each strand of strapping was subjected was 14,400 psi. (stress). Camber was found to be in the range'O to /2 inch.
• EXAMPLE 3 Strapping 0.015 inch by 3.0 inches was made as follows. Billet was extruded and molded according to U.S. application Ser. No. 552,191, filed May 23, 1966, from a copolymer of 80% (by weight) hexamethylene adipamide units and 20% caprolactam units (relative viscosity of the copolymer being 50, according to ASTM method D789). The'billet was then oriented in two rolling stages as in British Patent 1,017,175, to produce the strapping.
• Cupping is related to camber in that, when the 3-inch strapping is slit into three l-inch wide straps, none of the 1-inch wide straps exhibit camber greater than 4" inches.
• a process for forming highly oriented strapping comprising the steps of (1) extruding a composition comprising an intimate mixture of 80-100% by weight of a polyamide resin selected from the class consisting of polyhexamethylene adipamide, polycaprolactam, and a copolymer of 75-85% by weight of hexamethylene Hadipamide units and 15-25% of caprolactam units and 0-20% by weight complementally of a plasticizer for said composition to form a solid billet at least one-eighth inch wide and 40 mils thick, and (2) passing said billet between at least one pair of rollers to extend the length of said billet at least 4 times while maintaining the width of the resultant oriented strapping within 0.7-1.5 times the width of the billet by taking up the extended billet under tension, the additional step of stretch-straightening the resultant oriented strapping by subjecting it to tension at an elevated temperature at least C. below the melting point, according to ASTM method D2117-64, of said polyamide, whereby, according to said stretch-straight
• polyamide resin is a copolymer of -85% by weight of hexamethylene adipamide units with 15-25% by weight complementally of caprolactam units, and wherein in said stretch-straightening step the tension is 3,00012,000 p.s.i. (stress) and the temperature is ISO- C.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
• Polyamides (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24599966

Family Applications (1)

Country Status (5)

Cited By (2)

Citations (5)

• 1967
  • 1967-06-23 US US648235A patent/US3504077A/en not_active Expired - Lifetime
• 1968
  • 1968-06-19 FR FR1570936D patent/FR1570936A/fr not_active Expired
  • 1968-06-20 GB GB29563/68A patent/GB1176617A/en not_active Expired
  • 1968-06-21 BE BE716961D patent/BE716961A/xx unknown
  • 1968-06-21 DE DE19681778927 patent/DE1778927A1/de active Pending

Patent Citations (5)

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