Leno Mesh Bag Specification Review Guide

Critical Quality Control points summary + Test Method
Tapes
Tapes color management 
     QATM - Visual Checking + Spectrometer maybe
Tapes Strength -warp/weft 
     QATM - Tensile Tester
Tapes thickness, width 
     QATM - Gauge Tester
 Tapes yield – Deniel 
     QATM - Balance Scale
UV resistance 
     QATM – refer ASTM G154 – UV Resistance Test. 3rd lab, these fabrics are designed to retain 50% of their tensile strength after 200 hours?

Mesh Fabric

Mesh opening size 
     QATM - Measure
Mesh density –Weft line/Warp pairs per 10 cm 
     QATM - Measure
Mesh yield -gsm 

     QATM - refer ISO 3801 – Fabric Weight GSM Determination

Bag
Sewing strength -bottom/side 
     QATM - Tensile tester, refer ASTM D1683 – Failure in Sewn Seams of Woven Fabrics. OR. Filled bag lift testing
Bag dimensions 
     QATM - Measure
Bag strength 
     QATM - Drop test, ISO 7965 – Filled Sack Drop Test
Specific Features
MBP wicket header
     Flatness (Visual) 
     Easy opening/no sticking (Special Tester like we see in the Sri Lanka factory)
     Wicket hold size/location (Measure)
Printed band label
Mouth draw string 



Process Overview
Polypropylene (PP) resin is blended with color masterbatch and fed into an extrusion line. The molten polymer is extruded into a thin film, stretched (oriented), cooled, slit into tapes, and wound onto bobbins for weaving.
Typical Process Flow
PP Resin + Color Masterbatch → Extrusion → Film Casting → Stretching / Orientation → Cooling → Slitting → Winding → Tape Rolls

Critical Controls

Stretch Ratio
     Typical stretch ratio: 5–7 times
     Common industry practice: approximately 6:1
     Directly affects tensile strength, elongation, denier, and dimensional stability.
Tape Package Size
     Warp tapes: typically, 1.0–1.1 kg/roll
     Large warp packages: 2.0–2.5 kg/roll
     Weft tapes: typically, 8–12 kg/roll
Tape Specifications
     Width
     - Typical range: 1.5–3.0 mm
     Thickness
- Typical range: 25–50 μm
oDenier (Tape Yield)
Definition: Denier = weight in grams of 9,000 meters of tape.
Example: 550D = 550 grams per 9,000 meters.
Typical mesh bag tapes: 500D–700D.
oProcess Impact on Denier Consistency
- Extruder output fluctuation
- Stretch ratio variation
- Melt pressure instability
- Temperature variation.
Color
oVirgin resin + color masterbatch provides best consistency.
oRecycled colored resin may lead to batch-to-batch variation. 
FYI. Knitpassion is sourcing used colored bottle caps and repettlize them to resins and blends into the extruder. This could be a major reason causing color inconsistencies.
Tensile Strength
oTypical values:
Warp tape >200 N
Weft tape >160 N
2.Mesh Fabric Weaving
Process Overview
Leno mesh fabric is produced on flat weaving looms. Two warp tapes twist around each other to lock the weft and create stable mesh openings. The 2 major weaving machines are shuttle weaving machines or water-jet weaving machines.
Critical Controls
Warp and Weft Density
oExample: 24 × 24 construction
24 warp pairs per 10 cm (48 actual warp tapes)
24 weft tapes per 10 cm
Mesh Size
oTypical 24 × 24 construction produces approximately 6 × 6 openings per square inch
Fabric GSM
oTypical mesh bag fabric:
Produce bags: 45–55 gsm
Heavy-duty bags: 55–70 gsm
Example GSM vs Denier Calculation
For a 50 gsm fabric:
- Fabric weight in 10 cm × 10 cm area = 0.5 g
- Warp tape length = 480 cm
- Weft tape length = 240 cm
- Total tape length = 720 cm = 7.2 m
- 0.5 g ÷ 7.2 m = 0.0694 g/m
- Denier = 0.0694 × 9000 = approximately 625D
Weaving Speed
oTypical: 1.5–3.0 m/min
oCommon production speed: approximately 2 m/min
 Draw String
oKey requirements:
Material
Width
Position in bag
Color
Tensile strength 
3.Bag Making
Process Flow
Fabric Roll → Unwinding → Folding → Hot Cutting → Side Sewing → Bottom Sewing → Inspection → Packing
Critical Controls
Side Sewing
oFolded seam allowance: 10–20 mm
oNo skipped stitches
oSeam strength and alignment verification
Bottom Sewing
oFold-over allowance: 10–20 mm
oUniform stitch pattern
oStrong seam strength
Production Efficiency
oTypical output: 15–25 bags/minute
Bag Dimensions
oTypical tolerance:
Width: ±1.0 to 1.5 cm
Length: ±1.0 to 1.5 cm
4.Special Features
1.Printed band labels
a.Typical Structure
BOPP Printed Film / PP-PE Extrusion Coating / Mesh Fabric
2.Ex. laminated header and bottom
a.Typical extrusion coating weight:
15–30 gsm (commonly about 20 gsm)
b.MPB Bag Options
i.Option 1:
- Header and bottom extrusion coated only
- Typical coating weight: 40–60 gsm
ii.Option 2:
- Printed BOPP band label laminated onto mesh fabric
iii.
3.Wicket holes for automatic packing
a.Wicket Hole Punching
- Offline punching
- Online punching during bag making