REUSE: cups and other container types, made of plastics: searching for non-conformities after cleaning
Some examples of reuse cups after cleaning
Reuse cups for HORECA experienced a tremendous increase in demand in recent years. Mainly driven by legislation, single-use cups are being banned step by step.
Sorting, Cleaning and redistributing of cups are becoming a fast-growing business. The inspection for non-conformities after cleaning however is still mainly delegated to visual inspection, executed mainly by the operator at the back-end.
Possible non-conformities of reuse cups after cleaning:
- Lip stick at the upper rim
- burn marks from cigarettes
- mold stains, inside and outside
- Deformation due to squeezing
The miho toolbox for inspection of reuse cups:
finish, inner surface, base
outer surface, code reading
finish, base, inner and outer surface
Reuse cups may appear from transparent to fully opaque, with serigraphy or 2D-codes on it. Thus, the matching inspection device needs to be identified as a result of a close cooperation between the customer and the supplier.
REUSE: information on labels and adhesives and their removal without residue during the washing process of reusable glass containers
Carried-over label residues and carried-over adhesive accumulate and disturb the flow of bottles.
The conveyor belts in the Empty Bottle Inspector become dirty. Bottles get stuck during discharge and fall over.
To ensure that all kinds of stickers or labels and also the adhesive can be completely removed from reusable glass containers in a washing machine, the following should be observed:
The most important prerequisite first: Both stickers/labels and the adhesive or wet glue must be caustic-soluble! Only then, the glass containers can be cleaned without residue during the washing process.
2. Label or sticker: the influence of Printing ink, protective coating and hot foil stamping
Components such as hot foil stamping, varnish or printing ink seal the surface of the label and make it difficult for the caustic to penetrate the paper fibers in order to detach the adhesive. Applied primers (especially with digital printing systems such as Indigo) also seal the surface of the material additionally. The higher the proportion of such components on the label, the more difficult it will be to remove them later. In the case of #adhesive labels or #self-adhesive labels that are to be removed later by a caustic solution, full-surface coating and film lamination must therefore be avoided. Furthermore, it is advisable to rasterize areas and not to make formats of hot foil stamping too large.
The most suitable labels for reuse are still the traditional #wetglue labels.
3. Washing machine
The residue-free removal of labels, including self-adhesive labels, is ensured by a warm caustic bath. Temperature, caustic content and dwell time in the caustic bath depend on the recommendations of the adhesive manufacturer. For #self-adhesive labels, it is usually 1-1.5% caustic at a temperature of 60-80°C and ten to fifteen minutes exposure time, depending on the manufacturer. In the case of unprinted #wet-glue labels, detachment of the label may be possible after just one minute. The properties of the label paper as well as the above-mentioned treatments of the surface can influence and possibly extend the detachment time.
4. Return logistics / handling of the empties
Proper storage is a prerequisite for the removal of labels from used glass. Optimal storage of the empties is dry and protected from the weather. The adhesives in #adhesive labels and #self-adhesive labels react very quickly, especially to the effects of the weather. In addition, rain can cause the adhesive to dissolve and, when it subsequently dries, to adhere permanently. In general, the longer the empties are stored, the more difficult it is for the adhesive labels to come off later. If stored properly, the adhesive can be expected to adhere optimally for up to 12 months after labeling.
Due to the various influencing factors and material properties, no guarantee can be given as to removability.
For #wet glue labels, the storage instructions described above apply accordingly. The washability of the labels is of course significantly longer, since no adhesive is applied. With proper storage, paper labels have a storage time of many years.
5.Storage of labels / stickers
The storage of the labels before they are applied to the container also has an influence on their subsequent removability. The following applies here
– optimal storage of labels/stickers (20-23°C, 50-55% relative humidity)
– Storage in the dark (even neon tubes radiate in the UV range)
– Storage time of the labels as short as possible
6. Adhesive PP-labels (no-label-look)
Wash-off needs be considered case-by-case. However, adhesive PP-labels should be avoided from the ecological point of view since the recycling of washed-off labels is well established for paper and requires pure materials.
REUSE: bad label, bad glue: how to avoid that residual label and glue does not contaminate the inspection?
Apo 0,75 L after washing – bad glue:
the glue for labelling is not suitable for reuse
since it cannot removed with standard washing procedures.
Residual glue will contaminate all subsequent railing and devices.
Apo 0,75 L after washing – bad label:
the plastics foil as label was manually removed after washing so the glue appears.
Residual glue will contaminate all subsequent railing and devices.
The fundamental change from single use to reuse affects many process steps, also the labelling. Formerly, in the reuse regime, a later remove of the label and glue was not to be taken into account. In a reuse circle, an inappropriate label or glue results in residual parts of it after the washing! In consequence, railing, inspection devices, robots e.g., for palletization will be contaminated.
That means such bottles should be rejected right after washing!
Our evaluation based on a series of washed bottles with residual glue and label was conducted with the miho Multicon 3 infeed control as part of the empty bottle inspection miho David 2. Bottles were checked under dry and wet conditions.
As a result, a bottle with label, glue, or other type of stains covering about 2/3 of the circumference can be securely detected and thus rejected before entering the empty bottle inspector.
REUSE: Sorting of “identical” bottles only by variation of the height of the dome
Bordeaux 0,75 L of glass manufacture A – lower dome
Bordeaux 0,75 L of glass manufacture B – higher dome
Taking the Bordeaux 0,75 L bottle as an example, different bottle manufactures use slightly varying designs. This way, the nominal filling volume of 750 mL leads to filling levels of different heights! In the REUSE world, a mixture of “identical” bottles causes problems when refilling.
Our evaluation took the different heights of the dome as possible pattern for discrimination into consideration. The empty bottle inspector miho David 2 with its modular design and high level of flexibility allows to securely discriminate such bottles while inspecting the side wall.
Innovation: thermally tempered lightweight glass for returnable bottles – no restrictions to worry about during empty bottle inspection
Vetropack, as a manufacturer of glass packaging, has introduced the world’s first returnable bottle made of thermally tempered lightweight glass at Drinktec 2022. The advantages are low weight and less wear and tear, resulting in more turnarounds. Fortunately, empty bottle inspection shows no limitations in inspection accuracy, for example due to polarization effects, which was to be feared due to the special material structure.
REUSE: Sorting of “identical” bottles only by 2-mm-variation of the finish width
The bottle discrimination by the finish diameter runs securely with the miho Multicon 4. Key prerequisite is to remove the longcap and cleaning the bottle in advance. A measurement with partly attached caps or other closures will not be accurate. However, the sorting of bottles with caps and other closures runs securely. There is no impact by the type of the color: Blue, brown, green.
NO impact of the color depth on the detection accuracy of our Empty Bottle Sight
For the range of bottle colors tested, color depth has no impact on detection accuracy. All tested bottle samples are inspected by our David 2 Empty Bottle Inspector with the same accuracy. Even bottle No. 4, the darkest bottle, provides optimal defect detection.
We can conclude that neither the color nor the color depth impact the defect detection capacity.