In order to obtain the maximum performance from your equipment, it is important to have an understanding of the relationship of the printer with the supplies. A label printer / applicator is basically a labeling robot that must print, strip, and apply a label without operator intervention. A 1% error rate is unacceptable on a system with a production throughput of 40 labels / minute - this would result in almost 200 rejects per day. As such, it is imperative that the equipment be properly maintained and the supplies be properly matched in order for the equipment to run at optimum efficiency.
The labels used in most label printers consist of a label sandwich with five parts:
> liner or carrier sheet
> liner release coating
> adhesive
> label material
> label topcoat
The ribbons consist of three parts:
> silicone
> carrier sheet
> wax, wax/resin or resin ink
Following is a list of some of the most common supply problems we save encountered in our twenty plus years of building and servicing label printer / applicators. When differences exist between thermal and thermal transfer a (TT) designates a thermal transfer issue, a (TH) designates a direct thermal issue.
1) Mismatch Of Supplies
Symptom: (TT): Poor print quality, ink smearing, poor ink adhesion to label creating voids.
Common causes: Wax based ribbons used on synthetic label stocks, resin based ribbons used on paper label stock, using labels not designed for thermal transfer printer,
Symptoms: (TH):(1) Poor print quality. (2) Premature Printhead Failure
Common causes: (1) Printhead heat setting is either too low or too high for the label. (2) Thermal label coating is too abrasive. Improper / inadequate printhead cleaning cycle (TT & TH).
2) Die Strikes
Symptom: The labels are difficult to peel or not consistently peeling from the backing.
Common causes: Label converter using incorrect tools for label material construction. The result can either be a die strike that is too deep or not deep enough. A deep die strike breaks through the liner surface thereby exposing the paper interior to the adhesive. The adhesive then grips the liner making stripping difficult. To test for this, use a black felt tipped marker to outline the die cutting area, if a solid black line appears along the die cut, the die strikes are too deep. A shallow die strike does not properly cut through the adhesive leaving adhesive 'legs' that hold on to the label stock.
3) Incorrect Release Specification
Symptoms: (1) Labels lift up or drop off as the label web is pulled through the machine. (2) Labels difficult or impossible to peel.
Common causes: (1) During the label construction, the adhesive coater can adjust the amount of release agent on the liner that will effect the amount of tension required to release a label from the liner. If the labels are lifting as they travel through the equipment, one cause can be that the release was set too low during label construction. (2) In the case where the labels are difficult to peel, the release was set too high.
4) Core Diameter
Symptom: This problem is most common is those applications where a label five inches or longer is being used. Those labels near the end of the label roll have a permanent curl that will make it difficult for the vacuum system to hold the label in place on the applicator pad.
Common cause: The label roll ID is too small, normally a 3" core is being used. We recommend that any label five inches or longer use a 5" ID label core.
5) Label Winding
Symptom: (1) Label sticking as the labels are unwound from the roll. Adhesive buildup on equipment rollers. (2) The label rolls are difficult to pick up and mount because the center core falls out or telescopes.
Common causes: (1) In the first case, the sticking during unwind is the result of the adhesive oozing from under the label as the result of the labels wound too tight. (2) Labels wound too loose causes the second symptom of the cores falling out. Specifying and monitoring the correct wind is more an art than a science and relies on the experience and expertise of the label supplier.
6) Label Length Varies
Symptom: In those applications where the label must fit within a tight space, the label will randomly be to large or too small - on the same roll.
The label printer will periodically and randomly lock up and give a label length error.
Common cause: The improper web tension was used by the label convertor during the die cutting operation.
7) Label Liner Stiffness
Symptoms: (1) The label is difficult to peel. (2) The liner breaks.
Common causes: (1) The liner is too thick for the label printer/applicator peel bar thereby providing insufficient release tension for the label. (2) Conversely, the liner is too thin and will break away from the label web tension as it is pulled through the machine. This condition can be aggravated when there are die strikes on the liner.
8) Label Stiffness
Symptom: As the label is peeled from the backing, the label wrinkles or falls off the applicator pad.
Common cause: As the label is stripped from the backing, a minimum label stiffness is needed to move the label out under the applicator pad. Labels lacking sufficient stiffness tend to curl and fall off the pad.