Communication from the PLACE div. of TAPPI

Providing practical information to the converting and packaging industries…

EXECUTIVE SUMMARY
Seal Integrity In Medical Device Packages
by Anton Stauffer, PTI Packaging Technologies

Application: Non-conduct airborne ultrasound can perform a variety of non-destructive and non-invasive inspections in the packaging industry.

Package and seal integrity are issues that packaging companies of all industries are trying to overcome. Most options for leak testing and seal integrity testing are destructive methods that are costly and time consuming. Recently, non-destructive leak testing has become available. It is finding use to validate and inspect a large variety of packages for leaks to insure maximum shelf-life and a leak-free high quality package. These non-destructive testers can inspect filled and sealed bottles, blisters, vials and ampoules, IV bags, cups with heat sealed lids, pouches, and brick packs. These non-destructive systems pull a vacuum and monitor and measure absolute vacuum and the change in vacuum.

Conventional wisdom holds that ultrasonic inspection is only possible with a liquid or dry coupling. Non-contact ultrasound such as through air coupling therefore seems impossible due to the differences in acoustic impedance between air and test media. After many years of struggle, this barrier has been broken through novel transducers designed to allow extremely high transmission of ultrasonic energy through air and other gaseous media. It is now possible to propagate ultrasound in non-contact mode through a wide variety of materials. This non-contact airborne ultrasound technique has recently been integrated for a variety of non-destructive and non-invasive inspection approaches in the packaging industry.

Using non-contact airborne ultrasound requires placing the seal or package material in a direct line between the transducer and the receiver. It makes a linear scan along a heat seal using a special focused transducer. The result of the scan is evaluated as Pass, Warn, or Fail based on a proprietary algorithm that calculates and monitors average signal strength, minimum and maximum signals, and variation of signal.



EXECUTIVE SUMMARY
The Effect Of Multilayer Rheology On Coextrusion Die Design
by Joseph Dooley, The Dow Chemical Co.

Application: Proper techniques are available for using rheology data to design coextrusion dies based on experimental rheology data for monolayer and multilayer structures.
Production of many different types of monolayer and coextruded polymeric films and sheets currently uses different styles of dies. One common style is the coat-hanger die. This type of die has wide acceptance in industry because of its relatively simple geometry and its ability to produce uniform thickness products. Analyzing the flow of polymer melts can be difficult.

Many polymers are extruded through various styles of dies to produce monolayer and multilayer products. Coextrusion is a common method used for producing multilayer structures. Coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. This technique allows the processor to combine the desirable properties of multiple polymers into one structure with enhanced performance characteristics. The coextrusion process has had wide use to produce multilayer sheet, blown film, cast film, tubing, wire coating, and profiles.

This paper discusses the proper techniques for using rheology data to design dies for coextruded structures. Experimental data will be shown on the viscosity of single polymer and coextruded encapsulated melts measured using a unique rheometer for coextruded structures.

One difficulty in designing a die for uniformly distributing a coextruded structure is determining the rheology of the coextruded structure. The purpose of this work was to experimentally measure the rheology of monolayer and coextruded encapsulated structures and to show how that information can be used in die design.

A unique apparatus can measure the rheology of coextruded structures. This apparatus has use to measure the rheology of monolithic and coextruded encapsulated structures. The results of these experiments show that the rheology of the coextruded structures used in these experiments was controlled by the material used as the 10% skin layer in the structure. These findings are significant since they allow a die designer to use the rheology of the skin layer to approximate the rheology of the coextruded structure when designing a coextrusion die.



EXECUTIVE SUMMARY
Die Lip Sensitivity In Cast Film Dies
by Gary Oliver, Cloeren Inc.

Application: Testing looks at the issue of die lip sensitivity with different polymers extruded at different lip openings.
Die designs for production of cast polymer films typically include a flex lip for varying the geometry of the lip opening. The cast film process requires die lip gaps ranging from 0.4 mm to 0.8 mm. Flex lip gap and the adjustment of said gap becomes increasingly difficult to control as it is reduced. The paper examines the issue of die lip sensitivity with different polymers extruded at different lip openings.

One desirable attribute of cast film versus alternative methods of fabrication is film flatness. While internal flow geometry of cast film dies can theoretically be designed to give uniform flow across the width of a die, the related design calculations and their precision depend on the accuracy of not only the flow models themselves but also the data input into flow models and the consistency of the physical properties of the polymer or composite being processed. Because isothermal conditions rarely exist in application and polymer temperature and viscosity uniformity are rare, cast film dies incorporate a flexible lip to enable adjustment of the exit geometry for final flow balancing.

Various geometries and cross sections are incorporated to increase or decrease die lip flexibility of cast film dies. The flexibility of the lip beam and the spacing and coupling of lip adjustment bolts are important features to insure die gap precision and adjustability. Die bolt coupling or the impact a single bolt has on adjacent areas of a flex lip varies from 37 mm to 150 mm depending on lip beam design. Lip adjustment bolt spacing has long been an area of interest. One company established a standard 50 mm die bolt spacing on automatic dies. Another organization established a standard of 28.6 mm. My company established a standard of 25 mm. While this subject is important in overall flatness of cast film, the issue of die bolt spacing and coupling will not be subjects of this paper. In addition to geometrical details, the variables in mass flow calculations include pressure drop and the viscosity of the polymer flowing through a slot.

Given the sensitivity of the pressure drop across the lips of a cast film die with reduced lip gap, minimal lip movement is necessary to balance flow in a cast film die. The finest adjustment possible or an adjustment with less range of motion will provide the maximum resolution and the most desirable adjustment method for the ultimate film flatness.



EXECUTIVE SUMMARY
Waterborne Adhesives For Bottle Labeling
by Robert S. Forsyth, Retired

The vast majority of glass bottle labeling in the United States and globally uses "wet glues" such as starch, dextrin, casein, non-caseins, and other types of water borne adhesives. Despite some in-roads made by hot melts and pressure sensitive adhesives, the "wet glues" still dominate in many industries. For many years, packaging and adhesive magazines have mentioned the growth of certain segments of the labeling adhesive market such as the labeling of polyester and other plastic containers, use of hot melts for shrink and sleeve plastic labels, and the growth of labeling with pressure sensitive adhesives. Rarely do these magazines mention the long term and wide spread use of water borne labeling adhesives. They still dominate the labeling market and remain the most inexpensive way to decorate a container.

This paper considers the labeling of glass and plastic containers and not the labeling of metal containers that generally uses a hot pick up adhesive and a starch based lap paste. Labeling of glass and plastic containers can use cold glues, hot melts, pressure sensitive labels, heat seal labels, in-mold labeling, and other types of decorating such as screen printing. Cold glues are the dominant form of adhesive used. In Europe pressure sensitive labeling accounts for 43.6 % of the market while glue applied labeling accounts for 41.5 %. The growth rate for the latter is approximately 2–3%. Glue applied labels remain the dominant choice for prime labeling because of their large share of the beer and beverage markets. One analysis estimates that packaging is about 47% of the United States adhesive market. This market is 58.1% water borne and 20.9 % hot melt.

One can safely say that water borne "cold glue" labeling adhesives still have a major share of the labeling market despite inroads made into the market by hot melts and pressure sensitive adhesives. Generally, the latter products have a higher market share in the labeling of plastic containers such as polyester or when a special decorating effect is desirable. An example of the latter is clear no-label look decorating. On production lines at high, low, or intermediate speeds where paper labels are employed, water borne adhesives still dominate. Food and beverage labeling still largely uses water borne adhesives. Products employed in the United States are starch based (jelly gums), casein, non-caseins, dextrines, and synthetic based polymer adhesives. In general, the first three types have the widest use. Adhesive manufacturers continue to upgrade these products with new developments and technology, and they provide technical service support to help an end user adopt these new products. One should consult their adhesive supplier to obtain the latest products and also to request technical service support including trouble shooting literature from both the machine and adhesive suppliers.



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