above-mentioned bands were 16 mm in width and 0.6 uct
orresponds to said resin with a moisture con
mrn in thiclmess. tent of 0.05% or more and which has been dried in the TABLE 1*
Band Nozwmmww Mm wk (i) _ (ii) (iii) (iv)
Intrinsic viscosity (IV) of 0.97 0.97 0.82 0.82
Stretching method Two-step One-step Two-step One-step
Draft (times) lst-step 4.8 lst-step 4.8
2nd-step —- 2nd-step
5.0 5.0 Stretching temperature lst-step, hot Hot water lst-step, hot llot water
water 90° C. 98’ C. water - 80" C. 98" C.
2nd~step, — 2nd-step, hot —
dry 300° C. water - Ell" C.
Temperature of heat treatment Dry 200° C. Dry 250° C. -- Dry 250° C.
Speed reduction 0—5% 0~5% - 0%
Strength Kg 0 488 402 408 394-
Kg/mmz 50.8 41.8 42.5 41.0
Elongation % 11.9 10.9 12.7 10.5
Sealing strength Kg o 449 A 352 X 315 x 3'14
Shrinkage,‘ % 0 0.30 A 0.80 2: 4>.7O A 0.85
Weather resistant % (strength 0 98 0 95 A 85 A 84
retained after 2 years of outdoor exposure) Longitudinal cracking“
As will be seen from Table 1, the polyethylene terephthalate (PET) band according to this invention is superior in tensile strength, sealing strength and weathering quality and does not undergo longitudinal crackmg.
Because a PET resin with a high intrinsic viscosity is employed, the band according to this invention is highly heat-scalable and has an increased strength without a tendency toward longitudinal cracking. As the PET resin is stretched at a temperature over 150° C., the axial orientation and crystallization of the resin progresses to yield a greater strength. In the two-stage stretching process of this invention, crystallization at right angles with the fiber axis (first stage) and crystallization along the fiber axis take place in substantially distinct steps, and since a step for removing the residual strain (heat treatment after stretching) is provided, the band has an increased strength without a tendency toward longitudinal cracking and a reduced tendency toward shrinking at elevated temperatures. As regards the weather resistance of the band, is strength is not significantly affected by two years of outdoor exposure, thus demonstrating the advantage of the band according to this invention over conventional plastic bands.
It is very important to take note in the practice of this invention that if the PET resin obtained by polycondensation of terephthalate resin obtained by polycondensation of terephthalic acid and ethylene glycol contains water in hot fused condition, the PET is hydrolyzed and its viscosity lowered, with the result that the quality of products is adversely effected. Therefore, usually the PET resin is dried in a drying hopper equipped with a dehurnidifying device at about 150° C. for more than about 4 hours so as to reduce the moisture content of the resin up to 0.20%.
Table 2 shows the physical properties of the bands produced by the method of this invention (see Table 3) under various states of dryness of the raw material (PET resin). ll-‘roduct @ corresponds to the raw material (PET resin) dried in a dehurnidifying hopper at 150° C. for ll hours as in the example of this invention. Prod
same dehumidifying hopper at l50° C. for 30 minutes. Product @ corresponds to said raw material with a moisture content of 0.005% or less which has been dried in vacuo at 150° C. for 6 hours and vacuum-extruded.
There is a large difference in intrinsic viscosity of products (bands) according to the degree of dryness of material resin. Even with a raw material with an IV value of 0.90 or less, the decrease of intrinsic viscosity can be minimized by improving the dryness of the PET resin. Thus, in physical properties, the product is comparable with one produced from a raw material with an intrinsic viscosity of 0.95 or more. It is thus clear that the quality of products depend not only on the intrinsic viscosity of raw material but also on the intrinsic viscosity of the products themselves.
in the conventional drying method, the decrease of viscosity of 8 to 10% is inevitable in the extrusion process. However, the viscosity reduction can be held within 5% by such procedures as vacuum dryingvacuum extrusion, prolongation of drying time, a minimization of resin stagnation in the extrusion cylinder and die, etc.
These are why, in the practice of this invention, it is essential to use a polyethylene terephthalate resin material with an IV value of 0.90 to 1.20 and to ensure that the IV value of the formed product be not less than 0.80.
The packing band of this invention is especially suited for the packing of heavy products. Particularly in an automatic paclcing line, the desirable heat-sealing quality of the paclting band of this invention helps to increase the work efficiency to a considerable measure. Moreover, the band can be left standing outdoors for long periods of time. Thus, the packing band of this invention is commercially very useful. The production method according to this invention ensures production of the band with efficiency and high productivity.
The intrinsic viscosity (IV) of polyethylene terephthalate (PET) used in the above-reported runs or examples was determined by the following method, which is also the rnethod used to determine IV recited in the claims presented infra: