Package Construction

Hot Hole Punch

In order to produce a neat, strong hole in a VFF&S or HFF&S bag, it is desirable to use a heated punch. A hot punch is now available which will burn a hole in the bag while at the same time sealing the perimeter of the holes. The temperature of the punch is approximately 150°F hotter than the jaw surface. As the jaws come together for sealing, the punch burns a hole in the bag, and a tab is left on the bag similar to the tab left by a mechanical punch.

To date this punch has been installed on such vertical machines as Mira Pak, Transwrap, Triangle, Universal, Woodman, Hayssen, and Stokes, and on Doboy and FMC horizontal machines. These punches have been in operation for up to three years and are working very well.

We have been successful in punching all OPP single webs and laminations, as well as light (250) cellophane when laminated to OPP; however, we have determined that the punch will not work with foil or paper.

We are limited to machines with existing mechanical punches in order to make use of the existing jaws. If a customer wants to punch a hole on a machine not presently set up for a punch, they would need to order a new set of jaws from the machine manufacturer. The minimum seal width of a pouch with a punch should be 1″, ensuring that enough material is present above and below the hole to supply a good seal and support the bag when hung on a rack.

The conversion parts consist basically of a Superior Powerstat, a small heater and a punch of the shape and size the account is presently using. The cost of converting a vertical machine is approximately providing they have an existing punch. For the horizontal machines an extra set of slip rings is necessary. The cost on these machines is $500-$600.

Since many accounts have different styles and sizes of punches, it is necessary to survey each account to determine whether an existing type is suitable or another must be designed. There are currently two designs available – one is elliptical, 1/2″ wide, and one is the standard round, in 1/4″, 5/16″ and 3/8″ diameters. It is also possible to make the delta and sombrero type.

Film and Package Tests

Specular Gloss – ASTM-D-1223

Gloss (commonly referred to as “shine”) is measured on a glossmeter, an instrument with an incandescent light source and a photosensitive receptor that responds to visible light, by shining light onto a sample of film at a specified angle. Some of this light is reflected into the photosensitive receptor, and the fraction of the original light which is reflected is the gloss of the sample.

Gloss is an important merchandising factor, and this test makes it possible to specify and control this surface characteristic so that the desired effect will consistently be achieved.

Haze – ASTM-D-1003

The haze of transparent packaging materials is measured on a special hazemeter, which has an incandescent light source and geometrically arranged photocells that measure the transmitted and scattered light.

The sample is placed between the light source and the photocells, and the amount of light transmitted and scattered by both the sample and the instrument as well as the total incident light are measured. The hazemeter is then able to interrelate and measure these variables so that the percentage of scattered light can be calculated and read on the meter.

This test is important for applications where true color and high visibility are required.

Transmittance ASTM-D-1003

The percentage of light transmitted through translucent materials is measured using the same instrument as haze: the hazemeter’s incandescent light source and geometrically arranged photocells create a ratio between the amount of light transmitted through the sample and the amount transmitted with no sample present. Transmittance, opacity and optical density are related mathematically as:

Opacity = 1 / Transmittance

Optical Density = Common Logarithm (Opacity)

Tappi Opacity – T-425

Tappi Opacity is a reflectance type of Opacity measurement. It is a contrast ratio obtained by testing the samples reflectance when backed by a black material versus the reflectance when the film is backed by a white material. The incandescent light source and photocell detector are on the same side of the sample while the background is placed behind the sample.

Tappi Opacity = Light reflected when sample backed by black background / Light reflected when sample backed by white background

Water-Vapor Transmission ASTM-F372

The water vapor transmission rate (WVTR) through flexible barrier films is measured using an infrared diffusometer. To measure this rate, the diffusometer establishes a condition of 90% relative humidity at 100°F on one side of a film by means of a heated saturated salt solution and a condition of 0% relative humidity at 100°F on the other side using a stream of warm dry air. When the source of dry air is turned off, moisture vapor permeating the film from the moist side accumulates on the dry side. The rate at which this moisture buildup takes place is sensed by an infrared detector and recorded as WVTR.

This test is extremely important, since it gives a “baseline” value for comparing films in terms of moisture barrier. However, it is important to note that WVTR is normally measured on flat sheets and does not account for end-use package variables such as heat seals, folds, and creases.

Tear-ASTM-D-1922

A tear tester has a stationary clamp and a movable clamp on a pendulum, a means for holding this pendulum in a raised position, then quickly releasing it, and a scale that registers the arc through which the released pendulum swings.

Samples of paper or film are clamped into the tester and nicked to start the tear; then the pendulum clamp is released. This creates a larger tear in the sample, and the scale registers the arc. As the arc is proportional to the tear strength of the sample, calibration of the arc gives the tear strength, or the force necessary to continue tearing a sample after a nick has been made, which is reported in grams.

This test is very important for all films as well as for paper. High tear values (meaning a film is more difficult to tear) may be needed to help a package withstand vigorous machine operations or maintain its structural strength. However, low tear values (meaning a film is easier to tear) are necessary and useful for easy opening of some package types.

Tensile and Elongation ASTM-D-882

This testing machine has a pair of clamps to hold the ends of a sample strip in place, some means of gradually increasing the load on the strip until it breaks, and indicators that display the load and the amount of elongation.

To perform the test, measured, gauged samples are clamped into the testing machine and stretched until they break.

Tensile strength is usually reported in pounds per inch of width necessary to pull the material apart; for films, the usual units are pounds per square inch of original cross-sectional area. Tensile strength is quite literally the amount of force necessary to pull a material apart, while elongation is a measure of the amount that a material will stretch before breaking.

Tensile strength is a most important attribute for materials used in applications requiring extreme durability, such as heavy-duty bags. A high elongation value is therefore an index of “toughness,” since it indicates that a material will absorb a large amount of energy before breaking.

Gas Transmission

Film samples are centrally clamped in the 100 cm2 diffusion cell, and then both sides of the cell are initially purged with an oxygen-free carrier gas to remove residual oxygen from the system and de-sorb oxygen from the sample.

When a stable zero-oxygen reading has been established, oxygen is introduced into the upper half of the diffusion chamber, while the carrier gas continues to flow through the lower half and into the coulometric oxygen detector.

After a short interval, the first molecules of oxygen diffusing through the barrier are conveyed by the carrier gas to the detector. As displayed by the graphic recorder, the detector current rises, finally leveling off at a value representative of the equilibrium transmission rate of oxygen through the barrier. It should be noted that this equilibrium transmission rate is independent of the flow rate of the carrier gas.

Impact Strength ASTM-D-3420

The pendulum impact tester can be used to measure the impact strength of papers, boards, and films. To conduct this test, an impacting head on the end of a pendulum is swung through an arc into and through a sample of film. The tester has a means of measuring the difference between the potential energy of the pendulum at maximum height in free swing and the potential energy of the pendulum after rupture of the sample. This difference in energy, defined as impact strength, is reported in units of kilogram-centimeters and is useful in predicting the resistance of a material to breakage from dropping or other quick blows.

A test similar in scope, method, and significance is the dart drop test (ASTM-D-1709), in which a weighted dart is dropped from a standard height onto a taut sample. The significance and purpose of this test are the same as the above pendulum test, and the dart unit is the weight of the dart, in grams, that breaks the sample 50% of the time.

These tests give an index of a material’s dynamic strength and approximate what will occur when a package made from that material is dropped.