Modifying LDPE for Improved Adhesion to Aluminum Foil. Hariharan.K Technical Specialist, Packaging & Industrial Polymers, E I DuPont India Pvt. Ltd.

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1 Modifying LDPE for Improved Adhesion to Aluminum Foil Hariharan.K Technical Specialist, Packaging & Industrial Polymers, E I DuPont India Pvt. Ltd.

2 Outline Why modify LDPE? Modification Technology Factors that Influence Adhesion Benefits Example Conclusions

3 Extrusion Coating/Lamination to Al Foil LDPE is predominately used Low cost Good processing Typical structures: Paper / LDPE / Al / LDPE OPET/primer / LDPE / Al / LDPE Typical applications: Packaging of dry powders and mixes

4 Why Modify LDPE? Moderate Adhesion Inconsistent Adhesion Oxidation required High temperature processing smoke odor/taste Line speed limitations

5 Ways to Enhance Adhesion to Al Ozone treatment- promotes oxidation but has similar drawbacks to LDPE Acid copolymers Ethylene (meth)acrylic acid Acid groups bond to basic Al surface Provides durable bonds But too expensive for some applications Primers

6 Goal of this work Develop a modifier for LDPE to enhance its adhesion to foil extrusion coating/lamination process pellet blend moderate cost (between LDPE and acid copolymers)

7 Resin Designations Resin LDPE ACR1 ACR2 AE Characteristics 7 MI, g/cc Acid copolymer with 14 MI, 12% acid Acid copolymer with 11 MI, 4% acid Adhesion modifier - "adhesion enhancer"

8 Approach: Add Acid Functionality Peel Strength, g/25mm Peel Strength to Foil 50-μm Al / 35-μm resin 320 C, 63 ms TIAG Simply blending standard grades of ACR s does not improve adhesion 50 0 LDPE 80% LDPE, 20% ACR1

9 Discovery: Need Compatible Modifer Poor Compatibility LDPE Poor compatibility gives large domains - ACR may not be accessible to surface for adhesion Large domains increase haze ACR 700 Compatibility Study Good Compatibility Peel Strength to Foil, g/25mm Film Haze, %

10 Modification Provides Mid-Level Performance 1400 Extrusion Coating Results 50-μm Al / (8-μm blend - 38-μm LDPE) 320 C, 244 m/min line speed, 127 mm air gap Peel Strength to Foil, g/25mm % LDPE 20% AE/80% LDPE 100% ACR2 Layer Next to Foil * Results will vary with processing conditions.

11 Factors That Affect Adhesion Statistically Designed Experiment Structure: 50μm Al / coating Four Variables % AE blended with LDPE (0 to 20%) Temperature ( C) Thickness (20-45 μm) TIAG ( ms) TIAG = air gap / line speed Kept air gap at 152 mm and varied line speed from 91 to 152 m/min

12 Results of DOE Analysis 700 Peel Strength, g/25mm TIAG, msec = 80.0 Thickness, um = Peel Strength, g/25mm Temperature, C = Thickness, um = ECHIP 100 ECHIP %AE Low Temperature, C = Middle Temperature, C = High Temperature, C = %AE Low TIAG, msec = 60.0 Middle TIAG, msec = 80.0 High TIAG, msec = 100.0

13 Results of DOE Analysis 700 Peel Strength, g/25mm Temperature, C = TIAG, msec = ECHIP %AE Low Thickness, um = 20.0 Middle Thickness, um = 32.5 High Thickness, um = 45.0

14 Advantages of LDPE Modification Retains processing characteristics of LDPE Reliability - higher and more consistent adhesion than LDPE Productivity - higher line speeds without sacrificing adhesion Lower temperatures for same adhesion Improved organoleptics less smoke less gel lower energy costs These depend on the structure and processing conditions

15 Lower Temperature (DOE Model Results) 20% AE, 80% LDPE 293 ºC 450 g/25mm Peel Strength,g/25mm TIAG, msec = 80.0 Thickness, μm = 38 %AE ECHIP % LDPE 325 ºC 450 g/25mm Temperature, C

16 Improved Productivity (DOE Model Results) %AE Peel Strength,g/25mm Temperature, C = 315 Thickness, μm = 38 20% AE, 80% LDPE 150 m/min 580 g/25mm 100% LDPE 90 m/min 450 g/25mm 5 0 ECHIP % LDPE 150 m/min 380 g/25mm Line Speed, m/min

17 Improved Reliability Converter Trial Foil lamination Used Six Sigma Methodology Project Y: Peel strength to Al Unit: Peel strength, 3 measurements per production lot Defect: Peel strength below 250 g/25mm

18 Xbar Control Charts Subgroup UCL=218.8 Mean=165.6 LCL= % LDPE 325 C 85 m/min UCL=383.3 Mean=308.1 LCL= % AE, 80% LDPE 325 C 85 m/min Subgroup UCL=448.3 Mean=384.1 LCL= % AE, 80% LDPE 330 C 85 m/min Subgroup

19 Box Plots Peel Strength, g/25mm %AE, 325C 20%AE, 330C Resin, Temperature LDPE, 325C

20 Summary Statistics Temperature Peel Strength, g/25mm Resin deg C Mean Stdev Yield* DPMO LDPE % % AE, 80% LDPE % % AE, 80% LDPE % 4400 * Specification of 250 g/25mm or higher Statistically significant increase in peel strength by using modifier and by raising temperature Improved process by 4 sigma levels: improved yield from 4% to greater than 99%.

21 Conclusions Appropriate modifier can significantly improve the adhesion of LDPE to Al DOE techniques help map out the key factors that influence performance % Modifier Temperature Thickness TIAG Benefits include higher productivity, lower temperature and improved reliability Statistical analysis and modeling were found to be useful in demonstrating the benefits