Technical Indicators

Label Paper - Related Technical Requirements

Quality control – Physical properties, Printability, Converting 

Printing Process – Influences

Matt Reverse Side by Double Web Calandering

Reverse Side -
Main Properties – Treatment

Rough reverse side:

● Advantageous with respect to sheet separation and ink drying.

● Highest reliability, needs something more glue

Reverse side treatment

● Curling tendency / flatness

● Separation in printing process

● Flatness under changing climates

Labelling Process – Influences

The Labelling Process is complex and consequently influenced by many factors:

• Paper characteristics

• Embossing

• Varnishing

• Metallised Paper

• Printing

• Label design (shape and size)

• Container form / material

• Container surface / temperature

• Glues

• Storage of labels

• Preparation of labelling machine

• Filling / Labelling condition (temperature, moisture)

Wet Glue Label Papers

Most important Properties

• Wet tensile strength during labelling process

    - Glue absorption

• Wet Opacity

          - Condensation due

            to cold bottle surface        

• Alkaline resistance

• Ink retention

Influenced by paper characteristics

● Water absorption

● Dynamic Wet stretch

● Glue setting speed

● Glue absorption

Cobb value - water absorption

1) Low Cobb value: <12 g/m²

▶ No wrinkles, but possibly flagging and “falling off” labels

2) Medium Cobb value 12-17 g/m²

▶ Highest reliability in performance

3) High Cobb value >17 g/m²

▶ No flagging , but possibly wrinkles

Water absorption (reverse side)

Dynamic Wet Stretch (elongation)　

Glue setting speed

Quality Control – Special tests for Label Papers

• Alkaline penetration　

• Alkaline resistance　

• Wash off time / wet strength level  

• Ink retention

• Wet rub resistance

• Glue setting speed　

• Glue absorption　

• Wetability of reverse side　

• Ink adhesion in alkaline solution

• Rub resistance (wet and dry)

• Wet stretch

• Water absorption (Cobb value reverse side)

• Dynamic water penetration

• Opacity, dry and wet

• Tensile strength, dry and wet

• Stiffness, dry and wet

• Curling tendency / flatness

Structure of metallised paper

Influenced by metallising and printing

• Wet curl force

      depends on:　

                 Base paper　

                 Printing　

                 Varnishing　

                 Pre-lacquer　

                 Primer　

● Fibres expand primarily on the reverse side, therefore paper curls to front side.

● Tack of glue must be higher than curling force of the label.

● Fibres expand primarily on the reverse side, therefore paper curls to front side.

● Tack of glue must be higher than curling force of the label.

● Fibres expand primarily on the reverse side, therefore paper curls to front side.

● Tack of glue must be higher than curling force of the label.

Measurement of wet curl force

Diagram of wet curl forces

paper, metallizer, label = identical

Wet curl

Corect Fiber Direction

Influenced by Glue

Temperature

Type of glue - Casein / non Casein (synthetic or dextrin)

Amount of glue

Viscosity

Tack

Glue Pattern

Influence Factor Container Design

● Glass/PET

● Surface treatment – Water- repellent surfaces　

● Noncircular bottles and jars

● Used bottles (abrasion)

Influence Factor Labelling Machine

● Pressure between Glue Roller and Glue Pattern

● Pressure between Glue Pattern and Label

● Amount of Glue　

● Speed　

● Even glue distribution / Even Glue Pattern structure