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.

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For unsaturated polyester resins combined with thermoplastic resins, microstructure and volume changes were observed both before and after curing. The shrinkage-reduction (so-called low profile mechanism) of unsaturated polyester resins was studied in relation to miscible single-phase and immiscible two-phase systems.
In the case of a two-phase system, shrinkage-reduction is due to formation of voids in the dispersed phase. These voids are generated by both the volume expansion of the dispersed phase and the difference in thermal contraction between the matrix phase and the dispersed phase. On the other hand, shrinkage-reduction of a single-phase system is due to the generation of continuous voids among granulated cross-linked polymers. The granulation is caused by incompatibility between the cross-linked polymer and shrinkage-reducing additives. The size of granulated resins is one of the important factors for shrinkage-reduction. A single-phase system has optimum curing temperature for low profile, and does not always require high reactivity for unsaturated polyester resins. It is suggested that the shrinkage-reducing effect depends on both the glass transition temperature and the difference in solubility parameter between unsaturated polyester resins and shrinkage-reducing additives for various thermoplastics. Therefore, the shrinkage ratio can be approximately estimated by using the expansion coefficient of shrinkage-reducing additives and a parameter determining the ratio of the two phases.

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A simple method that has been adopted in recent years for increasing the strength and modulus of injection-molded plastic products is to mix in short glass fibers when the products are molded. Because the mechanical properties and dimensional accuracy of fiber-reinforced products strongly depend on the fiber orientation and fiber content, it has become increasingly important to clarify experimentally the fiber orientation distribution in molded products. The fiber orientation can sometimes cause molding defects, typified by warpage, because it induces anisotropic mechanical properties or anisotropic shrinkage rates in molded products. There can also be times when the injection gates can not be ideally positioned due to the cooling pipe arrangement for the mold or in the case of products with corners, such as box-shaped items or ones with reinforcement ribs. In such cases, the local fiber orientation can produce a nonuniform fiber orientation distribution in various parts of injection-molded products or along their thickness, which is thought to be conducive to warping.
In this research, a ribbed flat plate was used to make clear how the presence or absence of fibers and the injection gate positions affected warpage behavior (direction and amount), and the mechanism of warping was examined on the basis of observation results. Warpage predictions were also made using an evaluation method that was independently devised from the observation results.
These efforts made the following points clear. The amount of warpage increased depending on the fiber strength and, when a side gate was used, the peak deformation shifted toward that gate. The increase in warpage due to the fiber strength is attributed to a difference in shrinkage rates stemming from differences in the fiber orientation between the plate and rib portions of the molded specimen. The shift in peak deformation toward the side gate is ascribed to the influence of the gate position on the state of the fiber orientation. In addition, it was found that the evaluation method proposed here was capable of accurately assessing the contribution of fibers to inhibiting shrinkage in the direction of warping, and the results obtained with this method explained well the Warpage mechanism originating in the fiber orientation.

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