How to know if a sticker is waterproof?

First, check the Face Stock. Naturally waterproof materials are Vinyl (PVC), PET (Polyester) and PP (Polypropylene). Wood‑pulp papers are not. Check the ink also; Pigment inks and laser toner are waterproof, but ordinary dye inks will run the moment that they come in contact with water.

In the 15 years of my service in the manufacturing floor of a coated paper and self-adhesive company, I have seen thousands of so-called waterproof labels fail- most of the time due to poor understanding of the chemistry of the layers by the users. It is not a case of a sticker being able to endure a splash of rain but rather the interaction of the Face Stock, the adhesive and the ink..

You may be sourcing labels on industrial drums or coming up with your own decals on water bottles, but you need to make the distinction between water-resistant and fully waterproof, or you will end up recalling your products at potentially costly costs or with dissatisfied customers. With this, let us find out the science behind sticker durability.

1. The Face Stock Test: Paper vs. Film (The First Line of Defense)

The easiest indication is the substrate- also referred to as Face Stock. In our factory tests 90 per cent of the confusion centres here.

The “Tear” Test

In order to receive a fast check, you should simply attempt to tear part of the sticker and then take it off of the liner.

• When it is easily torn into fibrous edges, the sticker should be of paper, supplied either with no woods, or cast-coated, or art paper. They are not waterproof, the cellulose fibers serve as a sponge and absorb the water, the fibre swells and the water breaks the fibre.
• When it is stretching or is not tearable, then it is a film material; PEt, PVC (vinyl) or PP. These are non-porous and waterproof plastics.

Engineer’s Insight:Gloss on paper is deceptive, it is frequently a coating of clay or a coating of light polymer. The integrity of the paper below is compromised when there is water being wicked at the edges.

2. The Adhesive Chemistry: What Lies Beneath?

The sticker has to be durable based on its bond. A waterproof vinyl face would fail too when the adhesive is dissolved in water and the label drifts away, which is common with the cheap generic labels.

Acrylic vs. Rubber-Based Adhesives

On its part, adhesives are divided into two broad families as far as water resistance is concerned:

• The industry standard on durability is emulsion acrylic adhesives. On curing, they create a water-resistant polymer chain. When it must be used outdoors or in marine applications we suggest a solvent-based acrylic adhesive as it has good initial tack and long-term immersion characteristics.
• Hot-melts are adhesives made of rubber which are extremely sticky initially but tend to turn milky or lose their stickiness after long exposure to water. They also breakdown during oxidation and UV light.

Warning:To use in a dishwasher: To ensure that stickers will be used in a dishwasher, it is necessary that the datasheet uses a permanent acrylic adhesive. An ordinary hot-melts made of rubber will probably fail when subjected to high temperature and humidity.

3. The Print Durability: Pigment vs. Dye Inks

I have witnessed this too many times: a customer is buying the high-quality PET film labels and printing them with a regular home-office inkjet. The outcome? The ink runs the moment it comes into contact with water. Why does this happen?

The murderer is the microscopic particles of the ink:

• Dye Ink: Most common inkjets use dye inks, which are water-soluble- consider sugar and water. None of them is waterproof unless covered by a laminate.
• Pigment Ink: The pigment inks have solid particles suspended in fluid. These particles become entrenched into the coating and the ink is very water-resistant once it is dry.
• Laser Toner:Printers like HP LaserJet or Brother use laser toner that is applied to the surface using heat and thereby is waterproof.

Pitfall Alert: Watchout: When printing glossy synthetic stocks (e.g., PP) on a laser printer, we found that in most cases, flaking of the toner occurred when the fuser temperature was not changed. The heat capturing properties of the plastic is not the same as that of paper hence bonding of the toner is hindered.

4. Comparative Analysis: Waterproof Standards

We test in the lab on common material which is as given below in a brief breakdown.

5. The “Sink or Swim” Testing Protocol

If you don’t have access to a spectrometer or a tensile tester like we do, here is a simple field test you can perform at home or in your office to verify if your sticker is waterproof.

Step 1: The Rub Test

You can also conduct a simple field test at home or in the office to determine whether the sticker is waterproof or not, even though you do not have a spectrometer or tensile tester.

Step 2: The Submersion Test

The label should then be stuck on a jar and left in water after 24 hours.

Pass: The label looks exactly the same as when it went in.

Fail: When the label is not changed then it passes. In case the edges peel off (adhesive failure) or the material appears bruised or waterlogged, it does not work.

Step 3: The Dishwasher Gauntlet

And this is the final sticker household test. Heat, caustic wash, and pressure of water will rob weak hot-melts and destroy non-laminated coatings. It can only survive with premium acrylic adhesives with a protective laminate, which is a clear PET overlay.

6. Understanding International Standards

In B2B we do not guess, we make use of standards. In seeking labels on chemical drums or marine equipment, seek the following certifications:

• BS 5609 (British Standard): This is the “Marine Immersion” standard. Section 2 measures the endurance of the datum substrate in seawater in three months; Section 3 measures the durability of the print. Sticker certified with BS 5609 can practically survive an unlimited supply of water.
• UL 969: UL 969 embraces marking and labeling of permanent nameplates to ensure that the labels are sticking during the product life.
• ASTM D3330: This is not an actual waterproof test but knowing this value allows one to estimate whether the water pressure will cause the label to be lifted.

7. The Role of Lamination

In other cases a sticker will not be waterproof, however, the entire system will be: we laminate it. Lamination is the process of placing a transparent sheet of plastic; normally polypropylene or polyester, over the print.

The laminate helps to create physical barriers. A huge laminate can cover it even though you should use paper stock (not necessary when using water). To be truly waterproof, you should combine synthetic face stock and a synthetic laminate- this is a waterproof, oilproof, and mildly solventproof sandwich structure.

Conclusion

It is not only a splash test to consider waterproofness, but a triad: Face stock (plastic vs. paper), adhesive (acrylic vs. rubber), and ink (pigment/toner vs. dye).

And as we say at the factory the label that fits in the wrong place is a simple waste of money. Be sure to check your materials or request your supplier to provide the technical specifications of face stock and adhesive.

Frequently Asked Questions (FAQ)