Uni-ball ZENTO Refill black (0.38 mm)

The uni-ball ZENTO Mine UBR-Z-38 is the replacement refill system for all ZENTO rollerball pens from Mitsubishi Uni – from Basic to Signature. At its core is the specially developed ZENTO ink: a water-based pigment ink with POA surfactant (Polyoxyalkylene), which acts as a molecular buffer layer between the ball and paper. The result is an evenly flowing, smooth line – at a line width of 0.38 mm, which remains precise enough for narrow-lined planners and bullet journals.

Special Features

• POA surfactant as friction buffer: The polyoxyalkylene in the ink works directly on the ball bearing surface. Compared to conventional water-based Uni rollerballs, writing resistance drops by approximately 40% – the line flows smoothly without the scratching that often occurs with fine 0.38 mm tips.
• Water-based pigment ink – document-proof: The pigment particles settle on the paper surface and do not penetrate deep into the fiber. The ink is water and light-resistant – writing remains permanently high-contrast and archive-safe.
• Quick-drying with low smudging tendency: The water-based ink dries quickly, which is particularly relevant for rapid note-taking and left-handed users.
• Attraction Particles – sharp line without feathering: Special particles in the ink composition hold pigment particles together. This limits line feathering and show-through on the back of the paper – even on lighter paper such as Tomoe River 52g or 68g.
• Precise fit: The refill is exclusively designed for ZENTO pens from Mitsubishi Uni – for consistently uniform ink flow and secure hold in the mechanism.
• Scope of delivery: 1 refill in black, 0.38 mm.

Application & Tips

• Daily note-taking and journaling: 0.38 mm hits the sweet spot between precision and writing flow – fine enough for narrow lines in A5 planners, fluid enough for multiple pages at a stretch.
• On smooth, ink-proof paper: On calendered or ink-proof paper, the pigment particles particularly shine: the line remains sharp and uniform without seeping into the fiber.
• Tomoe River Paper: Tomoe River 52g and 68g are well-suited – the low show-through tendency of ZENTO ink keeps the back side clean, and the smooth surface allows the ball to glide particularly smoothly.
• Document storage and archiving: Water and light-resistant pigment ink is the right choice when notes need to remain permanently readable – in notebooks, planners, on labels or in file storage.
• Refill replacement: When inserting the refill, ensure that the click mechanism is completely relaxed before introducing the refill – this protects the tip mechanism.

For Rollerball Enthusiasts

The POA surfactant (Polyoxyalkylene) in ZENTO ink differs conceptually from classic gel pen inks: instead of lowering overall viscosity – which often leads to more show-through and uncontrolled ink flow – the surfactant acts specifically as a separation layer on the ball bearing surface. Writing resistance drops without increasing the amount of ink per stroke. For those who work with fine pigment inks and have struggled with the dry-scratchy characteristics of some 0.38 mm tips, the ZENTO refill offers a technically independent solution for everyday EDC.

Technical Specifications