Process for producing injection stretch blow molded polyolefin containers

Abstract

Injection stretch blow molding process for preparing polyolefin containers, comprising the following steps: 1) preparing a preform by injection molding a polyolefin composition comprising a polymer (A) selected from ethylene polymers, propylene polymers and mixtures thereof, and a heat absorber (B); 2) supplying heat to reheat the preform prepared in step 1) and stretch blow molding said preform; wherein the heat absorber (B) is selected from phosphates, condensed phosphates, phosphites, and mixed hydroxide/phosphate oxanion compounds of Copper (Cu), Calcium (Ca), Tin (Sn) and/or Iron (Fe).

Claims

1. An injection stretch blow molding process for preparing polyethylene containers comprising: 1) preparing a preform by injection molding a polyethylene composition comprising (A) ethylene polymers and a heat absorber (B) comprising 250-1000 ppm Cu.sub.2(OH)PO.sub.4; 2) heating the preform of step 1) to a temperature of 120-135 C. on the inner and outer surfaces of the preform; and 3) stretch blow molding the preform of step 2.

2. The injection stretch blow molding process of claim 1, wherein the preforms prepared in the injection molding step 1) are left to cool to a preform temperature of 25 C. before subjecting them to the stretch blow molding step 3).

3. The injection stretch blow molding process of claim 1, wherein the stretch ratio in step 3) is 2-4.

4. The injection stretch blow molding process of claim 1, wherein the preforms are reheated by means of an infrared source.

5. The injection stretch blow molding process of claim 1, wherein the polymer (A) is an ethylene homopolymer or copolymer comprising a density equal to or greater than 0.945 g/cm.sup.3.

6. The injection stretch blow molding process of claim 1, wherein the heat absorber (B) comprises 250-600 ppm Cu.sub.2(OH)PO.sub.4.

7. The injection stretch blow molding process of claim 1, wherein the heat absorber (B) comprises 400-1000 ppm Cu.sub.2(OH)PO.sub.4.

8. The injection stretch blow molding process of claim 1, wherein the preform in step 1) is injection molded at a temperature of 210-260 C. and a pressure of 25-80 bar.

9. The injection stretch blow molding process of claim 1, wherein the polyolefin container comprises a bottle.

10. The injection stretch blow molding process of claim 1, wherein the polyolefin container exhibits a 50% reduction in haze value versus a polyolefin container lacking the heat absorber.

Description

EXAMPLES 1 AND 2 AND COMPARISON EXAMPLES 1 AND 2

(1) Two types of 1000 ml bottles are prepared, using a laboratory-scale, two-step injection stretch blow molding equipment.

(2) Type 1 is prepared by using an ethylene polymer having density (ISO 1183) of 0.954 g/cm.sup.3, Melt Flow Rate E of 1.45 g/10 min. and F/E ratio of 87.5, sold by Lyondellbasell with trademark Hostalen ACP 6541 A UV.

(3) Type 2 is prepared by using a propylene polymer composition containing 50 wt % of a propylene random copolymer a.sup.I) having an ethylene content of 1 wt %, and 50 wt % of a propylene random copolymer a.sup.II) having an ethylene content of 2.3 wt %. The total composition has Melt Flow Rate of 12 g/10 min. (ASTM D 1238, 230 C., 2.16 kg). Such composition was prepared by first prepolymerizing with propylene a high-yield, high-stereospecificity Ziegler Natta catalyst supported on magnesium dichloride. The pre-polymerized catalyst and propylene were then continuously fed into a first loop reactor. The homopolymer formed in the first loop reactor and ethylene were fed to a second loop reactor. The temperature of both loop reactors was 72 C. The polymer was discharged from the second reactor, separated from the unreacted monomers and dried.

(4) Before preparing the performs, the polymers used in Examples 1 and 2 are melt-mixed, in a conventional extrusion apparatus, with 500 ppm by weight (referred to the total weight) of Cu.sub.2(OH)PO.sub.4 (Budit LM16). In the polymers used in Comparison Examples 1 and 2 no heat absorbent is added.

(5) The process conditions are reported in Table 1, and the characteristics of the so obtained bottles are reported in Table 2. Between process step 1) and process step 2), the preforms are left to cool to 25 C. (preform temperature).

(6) The reheating in process step 2) is carried out by passing the preforms in front of IR lamps.

(7) TABLE-US-00001 TABLE 1 Example No. Compar- Compar- ison 1 1 ison 2 2 Bottle Type 1 1 2 2 PROCESS STEP 1) - PREFORM CHARACTERISTICS Weight of preform (g) 36.0 36.0 34.0 34.0 Maximum thickness of 3.7 3.7 3.7 3.7 preform (mm) Height of preform (mm) 124 124 124 124 PREFORM MOLDING PARAMETERS Injection temperature ( C.) 250 240 240 240 Mold temperature ( C.) 15 15 35 35 Injection time (seconds) 2.01 3.98 4.99 5.59 Injection pressure (MPa) 74.6 57.0 32.9 29.3 PROCESS STEP 2) - STRETCH-BLOW MOLDING PARAMETERS Blow molding 121 121 133 133 temperature ( C.) Blow molding pressure (MPa) 1.1 1.1 1.2 1.2 Stretch Ratio 2.49 2.49 2.49 2.49 Preform Temperature 121 123 126 134 Inside ( C.) .sup.1 Preform Temperature 124 126 131 134 Outside ( C.) .sup.1 Infra-red Energy Reduction 9 29 During Reheating (%) .sup.2 Energy Reduction (of Total 4 12 SBM process) (%) Process Window ( C.) 1 3 2 8 Widening of Process 200 400 Window (%) Scrap Rate % .sup.3 14 1 10 2

(8) TABLE-US-00002 TABLE 2 Example No. Compar- Compar- ison 1 1 ison 2 2 BOTTLE CHARACTERISTICS Haze (%) .sup.4 62.6 73.1 2.3 7 Drop test at 22 C. .sup.5 (cm) >200 >200 190 >200 Drop test at 4 C. .sup.5 (cm) >200 >200 60 48 Topload (Filled) .sup.6 First Maximum load (N) 684.7 953.3 408.67 505.2 Strain at maximum load (mm) 4.9 9.3 3.5 3.0 Standard Deviation 12.96 4.87 52.58 9.82 Improvement In 39.0 23.6 Filled Topload (%) BOTTLE CHARACTERISTICS Average of 6 Wall Thicknesses (mm) Heel 0.373 0.393 0.475 0.387 Lower Label 0.336 0.508 0.496 Middle Label 0.451 0.429 0.621 0.447 Upper Label 0.363 0.432 0.531 Shoulder 0.595 0.407 0.396 0.452 Upper Shoulder 0.370 0.435 0.349 0.312 Standard Deviation Heel 0.062 0.007 0.055 0.021 Lower Label 0.044 0.004 0.009 Middle Label 0.02 0.009 0.046 0.008 Upper Label 0.1 0.003 0.021 Shoulder 0.10 0.004 0.032 0.029 Upper Shoulder 0.078 0.006 0.031 0.020 Average S. Dev. 0.067 0.006 0.041 0.018 Improvement in Wall 91 56 Thickness Distribution Tolerance (%) Notes to Tables. .sup.1Thermal Camera; .sup.2Infra red Lamp Setting to Reach Satifactory Process Conditions; .sup.3Precent of bottles with the evident defects; .sup.4measured according to ASTM D1003; .sup.5 and .sup.6measured according to the Voluntary Standard Test Methods For PET Bottles issued in 2004 by International Society of Beverage Technologists 8110 South Suncoats Boulevard Homossa, FL 34446-5006, USA.

EXAMPLES 3 TO 5

(9) Further trials were conducted using a commercial KHS-Corpoplast Blowmax machine with preferential heating specially designed for processing polyolefins, in order to prove that using the infra-red additive Cu.sub.2(OH)PO.sub.4 enables production of oval bottles with good wall thickness, which is difficult to achieve without the presence of the additive. The polyolefin used is an ethylene polymer having density (ISO 1183) of 0.950 g/cm.sup.3, Melt Flow Rate E of 0.95 g/10 min. and F/E ratio of 37, containing 500 ppm of Cu.sub.2(OH)PO.sub.4.

(10) The process conditions and the characteristics of the so obtained bottles are reported in Table 3.

(11) Bottle Size

(12) Example 3: bottle, oval, length 121 mm, ovality 1:1.6

(13) Example 4: bottle, oval, length 200 mm, ovality 1:1.6

(14) Example 5: round bottom bottle, round, length 243 mm, diameter 50 mm

(15) TABLE-US-00003 TABLE 3 Example No. 3 4 5 PREFORM CHARACTERISTICS Weight of preform (g) 10.1 11.1 12.5 Maximum thickness of preform (mm) 2.15 2.15 2.15 Height of preform (mm) 62.8 82.6 62.8 Maximum outside diameter of preform (mm) 23.6 23.6 23.6 Minimum inside diameter of preform (mm) 16.8 16.8 10.0 PREFORM MOLDING PARAMETERS Injection temperature ( C.) 215 215 215 Mold temperature ( C.) 7 C. 7 C. 7 C. Injection time (seconds) 4.75 4.75 4.75 Injection pressure (MPa) 1250 800 800 STRETCH-BLOW MOLDING PARAMETERS Blow molding temperature ( C.) 125 120 120 Blow molding pressure (MPa) 16 16 16 Stretch ration axial 1.9 2.4 3.8 BOTTLE CHARACTERISTICS Average of 6 Wall Thicknesses (mm) Upper part 0.29 0.30 0.28 Middle part 0.28 0.27 0.23 Lower part 0.33 0.32 0.28 Overall Average Wall Thickness (mm) 0.30 0.30 0.26 Standard Deviation Upper part 0.08 0.06 0.06 Middle part 0.07 0.07 0.03 Lower part 0.10 0.10 0.10 Average Standard Deviation 0.09 0.08 0.07
Conclusions

(16) The wall thickness distribution of the oval bottles as well as the round bottle was considered to be at an acceptable level for production. The specification <0.1, mm standard deviation is applicable. This confirms the possibility to produce oval bottles using 2-step injection stretch blow molding.

EXAMPLES 6 TO 8 AND COMPARISON EXAMPLE 3

(17) In a second further trial, materials were processed on the same 1-liter bottle with a 2-step laboratory scale stretch blow molding machine used for previous trials. Three materials containing different levels of the Cu.sub.2(OH)PO.sub.4 were tested, to confirm the effect of the additive and determine the optimum percentage inclusion. A comparison was made with material containing no additive. Three sample materials based upon the same ethylene polymer as in Examples 2 to 5 were used containing three different levels of Cu.sub.2(OH)PO.sub.4 i.e. 300 ppm, 500 ppm and 700 pmm. As a comparison a material with zero Cu.sub.2(OH)PO.sub.4 is included for reference.

(18) The process conditions are reported in Table 4, and the characteristics of the so obtained bottles are reported in Table 5.

(19) TABLE-US-00004 TABLE 4 Example No. Compar- 6 7 8 ison 3 ppm Cu.sub.2(OH)PO.sub.4 300 500 700 0 PREFORM CHARACTERISTICS Weight of preform (g) 35.9 35.9 35.9 35.9 Maximum thickness of preform 3.7 3.7 3.7 3.7 (mm) Height of preform (mm) 124 124 124 124 Maximum outside diameter of 43 43 43 43 preform (mm) Minimum inside diameter of 36.06 36.06 36.06 36.06 preform (mm) - wall thickness 3.47 mm PREFORM MOLDING PARAMETERS Injection temperature ( C.) 230 230 230 250 Mold temperature ( C.) 15 15 15 15 Injection time (seconds) 3.99 3.97 3.97 2.01 Injection pressure (MPa) 927 934 945 74.6 STRETCH-BLOW MOLDING PARAMETERS Blow molding 119.8 120 120 121 temperature ( C.) Blow molding pressure (MPa) 6 6 6 1.1 Stretch ratio 251 mm long 2.49 2.49 2.49 2.49 Preform Temperature 124 124 124 123 Inside ( C.).sup.1 Preform temperature 127 127 127 126 outside ( C.).sup.1 Infra-red energy reduction 13.3 16.5 19.18 during reheating (%).sup.2 Energy reduction (of total 5.5 6.8 7.9 SBM process) (%).sup.2 Scrap rate (%).sup.3 0 0 0 14

(20) TABLE-US-00005 TABLE 5 Example No. Compar- 6 7 8 ison 3 BOTTLE CHARACTERISTICS ppm Cu.sub.2(OH)PO.sub.4 300 500 700 0 Haze (%).sup.1 42.5 42.5 42.5 62.6 Drop test at 22 C..sup.5 (cm) >300 >300 >300 >300 Drop test at 4 C..sup.5 (cm) >300 >300 >300 >300 Topload (Filled).sup.6 First Maximum load (N) 910 951 943 807 Strain at maximum load (mm) 8.2 8.4 8.5 8.5 Standard Deviation 0.42 0.45 0.47 0.37 Improvement In 13 18 17 Filled Topload (%) BOTTLE CHARACTERISTICS Average of 6 Wall Thicknesses (mm) Heel 0.471 0.417 0.442 0.373 Lower Label 0.443 0.407 0.407 0.336 Middle Label 0.365 0.335 0.344 0.451 Upper Label 0.341 0.325 0.324 0.363 Shoulder 0.293 0.286 0.281 0.595 Upper Shoulder 0.471 0.417 0.442 0.370 Standard Deviation Heel 0.108 0.097 0.094 0.062 Lower Label 0.082 0.073 0.075 0.044 Middle Label 0.043 0.043 0.035 0.020 Upper Label 0.033 0.035 0.029 0.100 Shoulder 0.028 0.027 0.024 0.100 Upper Shoulder 0.021 0.017 0.019 0.078 Average Standard Deviation 0.048 0.049 0.046 0.067 Section Weights (3 sections) Max-Min weight Spread (g) 0.33 0.27 0.46 0.74 Mean Section Weight (g) 11.98 11.97 11.98 12.02 Standard Deviation of 0.13 0.07 0.16 0.27 Section Weight (g) Notes to Tables. .sup.1Thermal Camera; .sup.2Infra red Lamp Setting to Reach Satifactory Process Conditions; .sup.3Precent of bottles with the evident defects; .sup.4measured according to ASTM D1003; .sup.5 and .sup.6measured according to the Voluntary Standard Test Methods For PET Bottles issued in 2004 by International Society of Beverage Technologists.