Connection between Hot Tack Force and Form-Fill-Seal Performance of Packaging Films

Abstract

Recently, most packaging with plastic film for liquids such as soap, sauce and ketchup is performed on vertical automatic form-fill-seal packaging systems. The major technical issue for form-fill-seal packaging has been the packaging speed, which is restricted by leakage at the horizontal seals due to insufficient heat sealing. It has been known that the packaging speed depends on the type of packaging film and the hot tack force of the packaging film has been regarded as a main controlling factor of the leakage. However, a quantitative correlation between the hot tack force of the packaging film and the leakage at the horizontal seals has not been determined yet, and the means to improve the packaging speed are unknown.By means of hot tack force measurements and actual form-fill-seal packaging tests for several packaging films, we studied the quantitative correlations between the hot tack force and the leakage at the horizontal seals. We also developed a method to predict and compare the form-fill-seal packaging performance (proper range of heat seal temperature and heat seal time: packaging speed) for various packaging films by utilizing the quantitative correlation obtained in the above study. As samples for the study, we used laminate films of bi-axially oriented nylon (15μm)/polyethylene type sealants (50μm). The sealant resins used were metallocene plastomer, low density polyethylene, ethylene copolymers of EVA and EMAA and ethylene ionomers.The following results were obtained:1. It was confirmed that the leakage at the horizontal seals arises in the range of heat seal conditions (heat seal temperature and heat seal time: packaging speed) where the hot tack force of the seal is less than the stress to peel the horizontal seal part. A quantitative correlation between the hot tack force of the packaging film and the leakage at form-fill-seal packaging was determined.2. The agreement in the predictions for the proper range of packaging conditions (heat seal temperature and heat seal time: packaging speed) based on hot tack force measurements as a function of heat seal time and with those obtained by actual form-fill-seal packaging tests was confirmed. A method to predict and compare the packaging performance (proper range of heat seal conditions) for various packaging films was developed.3. It was reconfirmed that the hot tack property of various packaging films depends on the type of sealant resin, which results in a difference in form-fill-seal packaging performance among various films that differ in sealant resin type.• m-plastomer: hot tack force develops with very short heat seal time, which results in good performance under high speed packaging.• ionomer: has very large hot tack force both at very short heat seal time and under a wide range of heat seal temperatures, resulting in superior performance.• LDPE & EVA: small hot tack and slow hot tack force development speed, resulting in inferior packaging performance.