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The Tea Trade

Roll stock tools

For tea packers who fill packs on automatic machines: what to tell a film supplier, how to give the unwind direction, and how to estimate the length and weight of a roll from your own numbers.

What to tell your film supplier

With these details a supplier can check the film against your machine before quoting. Gather them before you ask for prices.

  1. Tea and grams per pack For example chunmee, 25 g per pack.
  2. Machine make and model As written on the machine's name plate. A photo of the plate is enough.
  3. Web width (mm) The width of the film on the roll.
  4. Cut-off or repeat length (mm) The length of film for one pack. On printed film it is the repeat of the design.
  5. Core inner diameter (mm) The inside of the core, which fits on your machine's unwind shaft.
  6. Maximum roll outer diameter (mm) or roll weight (kg) The limit of your machine's unwind, as given in its manual.
  7. Unwind direction The position number, 1 to 8, from the chart below.
  8. Eye mark needed or not An eye mark is a printed registration mark: a sensor reads it so that each pack is cut in the same place.
  9. Splices allowed per roll How many joins in the film your line accepts on one roll.
  10. Seal type: back seal or three-side seal A back seal is one seam down the back of the pack; a three-side seal closes three edges.
  11. Printed or plain, and number of colours For printed film, the artwork or a photo of your current pack.
  12. Quantity Per order, in rolls, kilograms or metres.

Unwind direction

The unwind direction says how the print sits on the film as it comes off the roll. Find the drawing that matches the roll on your machine and give its number to your supplier.

The letter F stands for your printed design, the right way up as it reads on the pack.

  • Solid F: print wound out, on the outside of the roll (positions 1 to 4).
  • Dashed F: print wound in, facing the core (positions 5 to 8). It is drawn as it reads on the printed side.
  • The arrow shows the direction in which the film comes off the roll: the edge of the F that faces the arrow comes off first.

Print wound out: 1 to 4

Unwind positions 1 to 4, print wound out 1 2 3 4
  1. Print wound out, top comes off first
  2. Print wound out, bottom comes off first
  3. Print wound out, right side comes off first
  4. Print wound out, left side comes off first

Print wound in: 5 to 8

Unwind positions 5 to 8, print wound in 5 6 7 8
  1. Print wound in, top comes off first
  2. Print wound in, bottom comes off first
  3. Print wound in, right side comes off first
  4. Print wound in, left side comes off first
Numbering as commonly used in the label and packaging industry; some machine makers number differently. Check your machine's manual, or send your supplier a photo of the roll on your machine.

Roll calculators

Estimate the film length, packs per roll and roll weight from your own figures. Nothing is sent: the calculation runs in your browser.

The formulas

L = π × (D² − d²) ÷ (4 × t)

L
roll length, in m
D
roll outer diameter, in mm
d
core outer diameter, in mm
t
film thickness, in µm

With D and d in millimetres and t in micrometres, L comes out in metres.

Example: D = 300 mm, d = 90 mm, t = 60 µm → L ≈ 1,072 m

Packs per roll = roll length (m) × 1000 ÷ cut-off length (mm), rounded down.

Film weight (kg) = web width (mm) ÷ 1000 × roll length (m) × grammage (g/m²) ÷ 1000. The core is not included.