Screen printing on recycled polyester (rPET) sportswear combines the excitement of high‑performance apparel with the responsibility of sustainable production. Because rPET behaves a bit differently from virgin polyester---its fibers are slightly more porous, its surface tension can vary, and its heat tolerance is lower---the printing process needs a tailored approach. Below is a step‑by‑step workflow that balances vivid, durable graphics with the eco‑friendly nature of the fabric.
Material Selection & Inspection
| Factor | What to Look For | Why It Matters |
|---|---|---|
| Fiber Content | 100 % rPET or a blend (e.g., 80 % rPET/20 % elastane) | Pure rPET offers the cleanest recycling story; blends improve stretch but may affect ink adhesion. |
| Fabric Weight | 150‑250 gsm for typical athletic tees, 250‑350 gsm for compression wear | Heavier fabrics hold more ink and tolerate higher cure temperatures. |
| Surface Finish | Smooth, low‑pilling surface; no heavy texturing | Ink transfer is more consistent on a uniform surface. |
| Moisture Content | 4‑6 % (measure with a moisture meter) | Excess moisture can cause ink "cooking" or uneven curing. |
Inspect each batch for uneven dyeing, pilling, or fabric defects---any anomaly can become a print failure point later on.
Design Preparation
- Vectorize Artwork -- Convert logos and graphics to vector format (AI, EPS, SVG).
- Color Separation -- Use CMYK or spot colors that match the ink palette you'll be printing (e.g., polyurethane water‑based inks).
- Halftone Choice -- For gradients on sportswear, use a 45‑degree line screen with 150‑180 LPI; this balances detail and ink deposit.
- Screen‑Ready File -- Export each layer as a high‑resolution (300 dpi) bitmap or vector for the film‑positive stage.
Tip: Keep line widths ≥ 0.2 mm to avoid clogging on fine‑mesh screens.
Screen & Mesh Selection
| Parameter | Recommended Value for rPET |
|---|---|
| Mesh Count | 200‑230 threads per inch (TPI) for standard colors; 230‑260 TPI for fine details. |
| Mesh Material | Stainless steel (for durability) or polyester (lighter weight, less expensive). |
| Emulsion | Dual‑cure (UV + heat) emulsion to guarantee robust stencil on low‑absorbency fibers. |
| Stencil Thickness | 2‑3 mil for water‑based polyurethane inks; 4‑5 mil if using plastisol (rare on rPET due to heat). |
Coat the screen in a light‑ready environment, expose at the emulsion's recommended time (usually 12‑15 seconds at 365 nm), then wash out the positive. Perform a quick "flash cure" of the stencil (≈ 80 °C for 1 min) to ensure it won't lift during printing.
Pretreatment & Surface Preparation
Recycled polyester often has a slightly waxy surface that hampers ink adhesion. A light pretreatment improves wet‑out and reduces ink spread.
- Pre‑wash -- Run the fabric through a gentle, low‑temperature wash (30 °C) with a mild surfactant.
- Dry -- Use a low‑heat dryer (≤ 80 °C) to avoid shrinking.
- Surface Activator -- Apply a water‑based polymer primer (e.g., a thin layer of polyether‑based adhesion promoter) using a spray or foam applicator. Allow 5‑10 minutes of flash time.
- Dust Removal -- Use a lint‑free air blower or vacuum to clear any residue before printing.
Ink Selection
| Ink Type | Suitability for rPET | Pros | Cons |
|---|---|---|---|
| Water‑Based Polyurethane | ✅ (recommended) | Soft hand, excellent wash durability, low VOC, good elasticity. | Requires precise curing temperature (130‑150 °C). |
| Discharge Ink | ❌ (not ideal) | Can achieve vivid colors on dark fabrics. | Requires high‑temperature cure (> 180 °C) → risks melting rPET. |
| Plastisol | ⚠️ (use with caution) | Thick film, vivid colors. | Needs > 180 °C cure → may degrade recycled fibers. |
| Eco‑Solvent / Low‑VOC | ✅ (alternative) | Good adhesion on low‑energy surfaces. | Slightly stiffer hand. |
Curing Guidelines for polyurethane inks:
- Set dryer to 130‑150 °C.
- Speed: 1.0--1.5 m/min depending on ink thickness.
- Ensure the garment's internal temperature never exceeds 155 °C (use infrared thermometer checks).
Printing Process
- Setup -- Mount the screen on a platen or automatic press. Align the garment using registration marks.
- Squeegee Selection -- Use a 70‑80 durometer rubber squeegee; angle 45°--60° for optimal ink deposit.
- Flood & Print --
- Off‑Contact -- Allow a 1‑2 mm off‑contact distance to avoid smearing.
- Multiple Colors -- Use a separate screen for each color. Register each layer within ± 0.1 mm tolerance.
- Dry to Touch -- Let the print air‑dry for 30‑60 seconds before handling.
Curing & Post‑Cure Treatment
| Step | Temperature | Time | Purpose |
|---|---|---|---|
| Initial Cure | 130 °C | 45‑60 s | Polymerizes the ink, bonds it to fibers. |
| Cooling | Ambient (≤ 30 °C) | 5 min | Prevents heat set‑off, stabilizes dimensions. |
| Heat‑Set (Optional) | 150 °C | 10 s | Improves wash fastness for high‑stress areas (e.g., underarms). |
After curing, perform a quick visual inspection for tackiness or under‑cure (ink should be matte and dry to the touch).
Quality Control
- Visual Check -- Look for pinholes, smudging, or color shift.
- Tactile Test -- Ensure the print feels soft and integrated, not rigid.
- Wash Test -- Run a 5‑cycle rub test (ISO 105‑C06) with detergent at 40 °C. The print should retain ≥ 90 % color intensity.
- Stretch Test -- Pull the fabric 30 % longitudinally; the print should not crack or delaminate.
Document any deviations and adjust mesh tension, ink viscosity, or cure temperature accordingly.
Finishing & Packaging
- Trimming -- Remove excess threads with a rotary cutter; avoid cutting too close to the printed area.
- Steaming -- Light steam (≤ 80 °C) can relax fibers and reduce curl for a professional presentation.
- Tagging -- Label each garment with its recycling content (e.g., "Made from 100 % recycled polyester") and care instructions (cold wash, low‑heat tumble dry).
- Packaging -- Use biodegradable polybags or recycled cardboard boxes to keep the sustainability thread consistent from start to finish.
Continuous Improvement
- Data Logging -- Record screen tension, ink batch numbers, cure temperature, and humidity for each run.
- Feedback Loop -- Collect post‑sale feedback from athletes and coaches regarding print durability and comfort.
- R&D Trials -- Test emerging inks (e.g., bio‑based polyurethane) and low‑temperature curing technologies (infrared, UV‑LED) to further reduce energy use.
Bottom Line
Screen printing on recycled polyester sportswear demands careful attention to pretreatment, ink chemistry, and curing temperature. By following the workflow above---starting with a thorough material inspection and ending with rigorous QC---you'll achieve vibrant, flexible graphics that stand up to the rigors of athletic use while staying true to a sustainable ethos. Happy printing!