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Surface roughness of zipper poly bag fastener rails

Micron-area shape measurement using a laser microscope

Zipper poly bag
Zipper poly bag


Poly bags are widely used in our daily lives. Poly bags with zippers are very convenient because they are easy to seal and also economical because they can be resealed as many times as needed. The material the bags are made of differs widely depending on what is going to be stored inside the bag, but polyethylene and polypropylene are typical bag materials. One of the important functions needed for zipper bags is a sealing ability that prevents the contents from leaking out or becoming exposed to air. Confirming the surface property of the top of the fastener rail (the area that makes contact with its counterpart when the bag is closed) is essential for helping to ensure excellent sealing performance.

The Olympus solution

Olympus' LEXT 3D laser scanning microscope is designed to make 3D shape measurements with high resolution and high precision. These features enable users to create accurate profile measurements of the roughness of a surface as well as the depth (or height) of surface irregularities. The LEXT microscope provides the same roughness (two-dimensional) parameters as contact-type microscopes do, generating measurement results that are compatible with those from contact microscopes. The LEXT microscope also provides three-dimensional roughness parameters that comply with ISO25178, enabling you to obtain more information than line roughness through surface-area evaluation using 3D images as well as numerical data. Although it would be difficult for conventional contact-type microscopes to take measurements by placing the stylus on the top of the thin rail, the LEXT microscope enables non-contact measurement at low to high magnifications without losing sight of the small area being measured.

Images of a poly bag rail at different magnifications

Plastic bag with zipper_ob20×z1
Objective lens 20X
Zoom 1x

Plastic bag with zipper_ob50×z1
 Objective lens 50X
Zoom 1x

Plastic bag with zipper_ob100×z3
Objective lens 100X
Zoom 1x

Plastic bag with zipper_ob100×z3
 Objective lens 100X
Zoom 1x


Plastic bag with zipper_ob100×z3_3Dprofile

Plastic bag with zipper_ob100×z3_profile

Before curved surface correction

Plastic bag with zipper_ob100×z3_3Dprofile_change_scale

Plastic bag with zipper_ob100×z3_profile_change_scale

After curved surface correction 

Olympus IMS

Products used for this application


With the Olympus LEXT OLS5000 laser scanning confocal microscope, noncontact, nondestructive 3D observations and measurements are easy to produce. Simply by pushing the Start button, users can measure fine shapes at the submicron level. Ease of use is combined with leading-edge features to deliver an acquisition speed four times faster than our previous model. For customers with larger samples, LEXT long working distance objectives and an extended frame option allow the system to accommodate samples as large as 210 mm.
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