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Block bottom bags are used to transport and store a wide variety of dry flowable bulk materials.

There are two basic types: Open Mouth Block Bottom Bags and Valve Block Bottom Bags. An open mouth bag is a tube of laminated PP woven fabric with the bottom end sealed. The bag is filled through the open mouth and then closed by stitching or tape.
Valve bags are packed on equipment that deposits material into the bag via a horizontal filling spout. After filling, forces generated by the product inside the bag allow the valve to open to self-seal.

PP woven block bottom bags are made up of 2-3 layers (plies) of fabric and film. Or can be combined with kraft paper.

AD*STAR® block bottom woven bags are made by extruding polypropylene resin into sheets, cutting the sheets into tapes, and weaving the tapes into the tubular fabric. The tubular fabric is then laminated, cut, and converted into a finished bag. The following information demonstrates the basic steps in manufacturing a poly woven block bottom bag.

Starlinger Company supplies integrated bag converting machinery to produce the woven valve bag from start to finish. Production steps include:

Tape Extrusion: High-strength tapes are produced by stretching after the resin extruding process.

Weaving: Tapes are weaved into tear-proof flat fabric in circular looms.

Coating: A thin layer of PP film is laminated to the woven fabric. Or additional BOPP film applied which can offer more eye-catching print and marketing effect.

Printing: Both flexo print and gravure print up to 8 colors, can be printed on the bag fabric.

Slitting: Top, bottom, and valve patches are pre-cut for the converting line.

Converting: Using Starlinger machines, sacks are assembled by forming the block bottom and applying patches and the valve using hot air sealing technology. No glue is used to seal the bag.

Baling: Bags are palletized and baled. Normally 5,000 bags can be baled in a single pallet.

AD*STAR® Bag Specifications and Sizes

Specifications

Type: Block Bottom Valve
Material: Coated PP Woven fabric
Construction: Single Ply: Woven Poly
Two-Ply: Woven Poly BOPP

Two-Ply: Woven Poly Kraft Paper

Tape Width: 2.5mm – 5mm
Fabric Weight 50 – 80 gsm
Coating Weight: 17 – 25 gsm
Valve Material: Woven PP, PE Film, Non-Woven Spunbond
Perforation: Adjustable Levels of Perforation
Valve Type: Standard Internal, Tuck-in, and Ultrasonic Seal
Bag Size Min. & Max.

Width: 11.81 – 23.625 Inches
Length: 17.72 – 35.83 Inches
Bottom Width: 3.15 – 7.00 Inches