Matsui Under Base Blocker 301-LG Black — When Standard Blocking Is Not Enough

Blocker 301 Gray handles the vast majority of polyester dye migration. It is the everyday workhorse blocker for standard polyester jobs.

But some garments bleed harder than standard.

Deep red polyester jerseys. Royal blue performance polos. Sublimated all-over-print garments where the sublimation dyes are concentrated and aggressive. Dark camo patterns on polyester where multiple saturated dyes sit in close proximity and migrate simultaneously. These are the garments that can push through a standard gray blocker and still discolor your ink.

Under Base Blocker 301-LG Black is the heavy-duty answer.

It is the same carbon-based dye barrier chemistry as Blocker Gray — but in a pure, concentrated black formulation that provides the maximum blocking density the Matsui acrylic system offers. Where Blocker Gray is a premixed 90/10 blend, Black LG is the full-strength concentrate. More carbon. More density. More dye-stopping power per square inch of deposit.

The deep black color is a functional characteristic, not just a cosmetic choice. The denser the carbon loading in the blocker, the more effective the dye barrier. Black LG is as dense as the Matsui acrylic blocker platform goes.

The tradeoff is visual: a pure black underbase can shift lighter top colors slightly darker if your white layer does not provide complete coverage over the black. Under Blocker Gray, a thinner white layer might be sufficient. Under Blocker Black LG, your white needs enough opacity to fully hide the black. For designs with white or light-colored top layers, use a heavier white deposit or double-stroke your white over Black LG.

For dark top colors — dark reds, navies, blacks, and dark greens — the black underbase is invisible. The colors are unaffected. And the blocking is at maximum density.

Works Under Plastisol Inks Too

Everything that applies to Blocker Gray applies to Blocker Black LG — but with maximum blocking power.

Traditional plastisol dye blockers are thick, stiff, and heavy. Matsui Blocker Black LG is water-based — it cures to a thinner, softer, more flexible barrier than traditional plastisol blockers. Print Matsui Blocker Black LG first, flash at 320°F, then print your plastisol colors on top. The water-based blocker foundation makes the entire print stack softer.

For plastisol shops that regularly print on aggressive bleed-prone polyester — deep red jerseys, royal blue polos, and sublimated athletic wear — switching the blocker layer from plastisol to Matsui Blocker Black LG delivers two upgrades at the same time: maximum dye blocking and softer hand feel.

The workflow for plastisol shops: Print Matsui Under Base Blocker 301-LG Black → flash at 320°F → print plastisol white → flash → print plastisol colors on top as normal.

When You Need Black LG Instead of Gray

Not every polyester job needs the heavy-duty blocker. Here is how to decide.

Use Blocker 301 Gray when:

• Standard polyester garments in light to medium colors
• White, light gray, light blue, and pastel performance garments
• Standard poly/cotton blends such as 50/50 and 60/40
• Standard Dri-Fit in lighter shades
• Top colors are light or medium and you want a neutral gray underbase that does not darken them
• The vast majority of your daily polyester work

Use Blocker 301-LG Black when:

• Deep red, royal blue, black, dark forest green, and dark burgundy polyester garments are involved
• Sublimated garments such as all-over-print jerseys and sublimated polos are involved
• Dark camo patterns on polyester are being printed
• A garment has already bled through Blocker Gray in testing
• Top colors are dark, making the black underbase effectively invisible
• You need the absolute highest blocking density the acrylic system offers

The escalation path: Start with Blocker Gray. If a specific garment bleeds through Gray in your 48-hour test, move up to Black LG. Stock both.

Under Base Blocker 301-LG Black vs. Under Base Blocker 301 Gray

Both blockers stop dye migration. The difference is blocking density, top-color effect, and when each one should be used.

The bottom line: Stock both. Blocker Gray is the daily driver for standard polyester work. Blocker Black LG is the escalation product for the garments that Gray cannot hold. You can also use Black LG to mix your own Gray: 90% Black LG + 10% Matsui Stretch White.

The Dye Migration Problem — Why Blockers Exist and When You Need One

What is dye sublimation migration?

Polyester and many synthetic fabrics are dyed using sublimation dyes — dyes that bond to the fabric by converting from a solid to a gas under heat. This is how the color gets into the polyester fibers. The problem is that this process reverses when you apply heat during screen printing. When your dryer or flash unit heats the garment to cure your ink, the sublimation dyes in the polyester re-gasify and migrate upward through your ink layer, discoloring your print. Red garments turn white ink pink. Blue garments turn white ink purple. Black garments turn white ink gray-green.

This can happen immediately on press or over the 24–72 hours after printing, as residual heat energy continues driving dye migration. A print that looks perfect on the press can show bleed the next morning. Always test 48 hours out.

Which garments always need a blocker?

• 100% polyester — all colors, especially dark and bright shades
• Performance fabrics and Dri-Fit garments
• Sublimated garments
• Camo patterns on polyester

Which garments should be tested first?

• 50/50 cotton/poly blends
• Dark tri-blends
• Recycled polyester

Which garments typically do not need a blocker?

• 100% cotton
• Ring-spun cotton
• Low-poly blends under 25% polyester

The golden rule: if you are unsure, test. Print a sample, cure it, and check it at 48 hours. Dye migration can take up to 72 hours to fully appear.

The Blocker Print Sequence

For water-based top colors

• Print Under Base Blocker 301-LG Black → flash at 320°F (160°C)
• Print Matsui white such as 301W-B, Stretch White, or EasyPrint White → flash. Use a heavier deposit or double-stroke to fully cover the black.
• Print Matsui color layers using bases plus Neo Pigments
• Cure at 320°F (160°C)

For plastisol top colors

• Print Under Base Blocker 301-LG Black → flash at 320°F (160°C)
• Print plastisol white → flash with a heavier deposit to cover black
• Print plastisol color layers on top
• Cure at your standard plastisol cure temperature

For dark top colors where the black underbase is invisible

• Print Under Base Blocker 301-LG Black → flash
• Print dark color layers directly on top without a white layer when the top color is dark enough that the black underbase will not show through
• Cure

Additive Compatibility

For the color layers printed on top of the blocker, use the full Matsui additive lineup as normal — including Quick Additive in your base and pigment mixes. Browse the complete Matsui additive collection here.

Why Screen Printers Choose Under Base Blocker 301-LG Black

I print on deep red polyester jerseys and my Blocker Gray cannot hold the dye back.

This is the core Black LG use case. Deep red is one of the most aggressive dye migration colors in polyester. When Blocker Gray is not enough, Black LG provides the maximum carbon density to stop even the most aggressive red sublimation dyes. Print Black LG first, flash, then white and colors on top.

I print on sublimated all-over-print garments and the sublimation dyes destroy my screen print.

Sublimated garments contain the most concentrated sublimation dyes. Black LG is the go-to blocker for sublimated substrates because it provides the highest blocking density. Always test, since some sublimation dye systems are more aggressive than others.

I print dark colors on dark polyester and do not need a white layer.

When your top colors are dark, such as navy, black, dark red, or dark green, the black underbase is invisible. You can print Black LG, flash, then print the dark color directly on top without a white layer in between. That gives you maximum blocking, no visual impact, and fewer print stations used.

I use plastisol inks and need the strongest possible blocker that is still softer than plastisol blockers.

Print Matsui Blocker Black LG, flash at 320°F, then print plastisol colors on top. You get maximum dye blocking with a softer, more flexible foundation than a plastisol blocker can provide.

I want to stock one blocker and mix my own Gray when needed.

Blocker Black LG is the building block. Stock Black LG and Matsui Stretch White. For standard jobs, blend 90% Black LG + 10% Stretch White to create Gray. For aggressive bleeders, use Black LG full-strength. One product gives you two blocker options.

My blocker keeps drying in the screen during production.

Add Retarder MG at 1–5% to extend open time. Browse all Matsui additives here.

I need the heaviest possible blocker deposit for maximum dye stopping power.

Use lower mesh counts such as 110–120 with a thicker stencil. Matsui recommends up to 120 mesh for Black LG specifically to achieve the heaviest deposit and best fabric coverage. A thicker stencil means more blocker on the garment and a stronger dye barrier.

Matsui Under Base Blocker 301-LG Black Key Features

• Maximum dye blocking density — pure black, concentrated carbon-based formulation provides the highest blocking density in the Matsui acrylic system
• Works under both water-based and plastisol inks — use it under Matsui water-based colors or under plastisol for softer prints than traditional plastisol blockers
• Softer than plastisol blockers — water-based acrylic formula cures to a thinner, more flexible barrier with noticeably improved hand feel
• Low tack formula — smooth, clean prints with minimal fabric lift during production
• Building block for Gray Blocker — blend 90% Black LG + 10% Matsui Stretch White to create Blocker 301 Gray
• Invisible under dark top colors — maximum blocking with zero visual impact when printing dark colors on dark polyester
• High mesh capability — prints through 110–305/inch, with thicker stencil at 110–120 mesh recommended for maximum deposit and blocking performance
• Compatible with all Matsui acrylic bases and whites — works under every acrylic Matsui ink and all Neo Pigment colors
• PVC-free and eco-compliant — OEKO-TEX® Standard 100, CPSIA, and HR4040 compliant
• Zero viscosity modifications required — prints from the container