Humidity Tips

By Goitseone Lekoko, MD

A practical press-floor note on humidity control for plates, substrates and ink behaviour on South African packaging floors.

Pressroom trouble often starts with small omissions: no record of the humidity, no note on the ink room temperature, or a plate sleeve packed away while still damp. Humidity Tips covers the checks that help South African flexo teams keep ink and print behaviour steady through the shift.

Humidity shifts show up first in small signs: a plate sleeve that still feels cool after wash-up, film that clings at unwind, or ink viscosity drifting as the room warms.

Humidity checks before first pull

• Room humidity logged at start-up
• Plate sleeves checked dry before storage
• Substrate roll acclimatised before mounting
• Ink room temperature noted on job sheet

Use this note alongside the plate, ink and substrate pages that apply to the job. Humidity control is not one setting on its own, because tape, sleeves, film and drying all react differently once the air changes. The value of the note is in linking those pressroom observations to the materials actually on the machine.

Shift changes that move moisture

Humidity Tips deals with how moisture levels affect plates, substrates and ink behaviour on packaging floors in South Africa. When the room swings too dry or too damp, dot hold, drying and web handling can all shift enough to spoil a steady run.

Morning conditions in Johannesburg can be very different from the late afternoon, while Durban plants may hold higher moisture for most of the day. That matters when thin film starts handling differently, solvent balance moves, or drying looks fine at start-up and then falls away mid-run. In packaging work, these changes need to be tracked, not guessed.

Start by recording the first humidity reading before wash-up water, open doors or production heat alter the room. Then check whether rolls brought in from stores have had enough time to settle to the press area. A simple entry for time, percentage humidity and room temperature often explains later trouble with register, laydown or blocking.

South African moisture patterns to watch

Highveld winter air can leave substrates and plate storage areas much drier than coastal plants, while summer storms can swing conditions within a single shift. Those changes affect static, web handling and the way inks appear to dry or hold out on packaging stock. It helps to separate seasonal conditions from machine faults by keeping the humidity record with the production paperwork.

Near the coast, moisture can creep into board and film packs if they are opened too early or left exposed near dispatch areas. Inland sites may deal more often with dry air, dust and static on unwind and rewind. Load-shedding or generator changeovers can also alter ventilation and room conditions enough to change how the press behaves.

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