How to get the perfect label for your glass bottle

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5 checks for a perfect label on your glass bottle

Check 1: The bottle

The surface condition of the glass is the result of a complex alchemy due to the temperature of the parisons, the wear of the molds and the various surface treatments inherent to the manufacturing process. Thus the surface of the glass of the bottle is neither homogeneous nor perfectly cylindrical, sometimes altering the adhesive capacity of the label.

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The cylindricity of the bottle is very dependent on the condition of the molds which have a life to watch.

To facilitate the passage of these bottles on the conveyors of glassmakers and bottlers, give the bottles a good resistance to abrasion and scratches, surface treatments of the glass of the bottle are necessary.

Consequences

The adhesion problems of the label on the bottle may come from the nature of the materials in contact and the surface condition of the glass constituting the bottle itself. Inadequate or improperly executed bottle treatments can lead to problems with bubble bonding.
Taking into account that the bottles are produced in compliance with standards that define in particular the surface tension, also called wettability and technical commitments of producers who define the dimensional tolerances and straightness.

(Note: Surface tension is a force that is detected at any interface between two different materials, in our case: glass and glue of the label or glue and inside of the label).

Determining the surface tension/wettability

In order to determine the surface tension or wettability of a surface one can measure the angle of a liquid deposited on it with sophisticated devices typing Pocket Goniometer / PGX or even more simply by using various Test inks , whose ink contained corresponds to different wettability levels for a given time. The wettability most suitable for good bonding must be equal to or greater than 38/40 dynes. The bottles have a label able surface marked on the plane of the article, the tests must be performed on these surfaces.

Check 2: The labels

The labels itself (Dry label)

Labels

The structure of the label paper is not different from other papers for writing. These papers consist of several layers of bleached fibers and then the surface to receive the print receives a treatment, which make this surface more closed, smoother and homogeneous so that it can be printed easily.

The opposite face, that receives the glue, generally remains rougher to facilitate the attachment of various types of glue.

In order to meet a growing demand for richer, textured media, producers of specialized papers (paper manufacturers) are putting several new references on the market every year. These supports can be different weights, coated or textured, glossy or matte, various colors and various materials (paper or synthetic type PP, PE, PET ..).

Supports for adhesive labels

Diagram Selfadhesivelabel

The share of these adhesive labels (coil) represents approximately 50 to 60% of the total market, that of the dry label (leaf) the 40 to 50% remaining, but the figure of the dry label is on the decline. The choice of papers and possible finishes are indeed more important for adhesive labels, and the installation of labels with complex cuts is also facilitated

Check 3: The Glue

There are 3 main categories of adhesives: Rubber-based adhesives, acrylic-based adhesives based on "active" principles of adhesives based on polymer / resin mixtures or rubbers / resins and hot-melt adhesives (also called hot-melt adhesives)

Responding to the various constraints of production and markets, some new acrylic glues are specially designed for deposit.

Glue

Rubber glues

Rubber glues are a rubber/natural or synthetic resin mixture such as polychloroprene and have the advantage of having a strong initial Tack (or tack), most often intended for the use of bottles in a humid environment (refrigerator, bucket to ice cream, cellar ..).

The stickiness (adhesion / grip is the stickiness (stickiness) of a material), is the ability to adhere to a substrate in the context of a given application and specific withdrawal conditions.

The advantage of rubber glues is that they adapt perfectly to the irregularities of the glass, and if the label is perfectly glued on all its surface, then, it avoids many problems.

Acrylic glues

Acrylic glues, the base of which is water, are the most used. Although having a lower initial Tack, they are more resistant over time.
Water-removable permanent adhesive glues (different from just removable, vinyl-based monomers) were ideal for returnable bottles, making it easier to wash and avoiding the ugly traces of glue on the bottles, but are now almost used more.
So if you are pico-brewers or micro-brewer and you buy your glue catalog or in a store, make sure that it is adapted to the utility you want to give your bottle.

Any place of the label not being glued or poorly glued on its support (glass for bottle or stainless steel for barrel) will be sensitive to the variations of temperatures, humidity and will form bubbles and blister rather quickly.

Rubber glues can, for example, soften if subjected to very high temperatures. The paper can be distended by absorption of ambient moisture or simply by the water of the glue in the unglued parts. Thus both phenomena can create bubbling. In order to stabilize the paper moisture of reel or sheet labels, "cool and dry" storage is recommended (ideal temperature of 20-25 ° C and humidity / humidity stable of about 50%). A homogeneous distribution of the glue on the back of the label is also to be monitored (visible through the bottle if it is not filled, then the dark part that represents the glue will be spread over the entire surface of the bottle. label).

Hot melt adhesives

Hot melt adhesives are substances that must be heat-treated before being applied to the label. They solidify on cooling, thus ensuring the solid retention of the label on the glass of the bottle. They are reserved for difficult cases of gluing (nature of the label, bottles of other material than glass). They require adapted equipment and are rather reserved for high speed lines.


Check 4: Positioning the label

The mechanical action of placing the label can be a factor for blisters (bubbling) or folds (horizontal or vertical). It's necessary to be careful when sticking the label on the flat surface of the bottle. With long labels, you also have to be careful that labels don't come off in corners and angles. The technique of laying and smoothing the labels can have an influence on the final appearance.

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The bubbles which appear are due to a lack of initial adhesion between the adhesive itself and the bottle and to moisture phenomena. They have the following triggers:

  • Storage of the bottles under conditions of temperature shock due to excessive relative humidity.
  • The pressure of the label application systems, check the settings of your label maker (pressure foam, state of the brushes, bottling speed, cleanliness of the equipment, etc.).

Problems and special cases with some explanations:

In the case of traditional labeling, wrinkles at the ends of the labels may appear. They do not usually occur under normal storage conditions, but when humidity is high.
The machines places the glue by lines. Between those lines, there are areas of non-contact that will be more sensitive to moisture.
These wrinkles are mainly created by the use of pressure foams that are too soft or deformed by wear on automatic laying machines, preventing good adhesive + glass contact, especially in the last part of the label.

This is accentuated if the papers used are not treated with REH (anti-humidity). What is not the case of synthetic papers (no need to be REH).

Of course before changing label bonding solutions, check the compatibility of your labeling material, glue used and test with your printer to find the ideal combination of: + adhesives + coatings.

Be aware that a graphic designer does not necessarily has the needed skill in the process of printing and bottling. The ideal situation is to connect your graphic designer with the person responsible for printing your labels.

Check 5: Timing of labeling & the bottling process

In 90% of the cases the labeling of the bottle is done before cold bottling. This to avoid bottle condensation and bubbling/wrinkling of the labels due to that condensation.

But in some application labeling is after filling. Condensation can give a lot of quality problems on the label.

Blowing of condensation with air knives, just before labeling, gives a solution on several quality and production problems

Problems with labels on glass bottles? We are here to help!

Carlos
Carlos Rei (Wallonia - France) CarlosRei@rycobel.com +33(3)28 40 22 17

Our expert will answer all your questions by email or will call you back. Together we will find the right solution to your labeling issues!