Testing of neutral coating paper

Using an ELREPHO spectrophotometer (with UV filter at 457 nm), we measure the diffuse blue reflectance factor. For premium coated papers, brightness of 85–92% ISO is typical. Low brightness (< 75%) indicates poor coating whitening or contamination.

4. Opacity – AS 1301.413 / ISO 2471

We measure reflectance of the paper over a black backing and over a white backing. Opacity (%) is the ratio (R₀ / R∞). High opacity (> 90%) prevents show‑through. For thin coated papers (< 80 g/m²), opacity < 85% is often rejectable for double‑sided printing.

5. Surface Strength (IGT Pick Test) – AS 1301.432 / ISO 3783

We use an IGT printability tester to apply a controlled ink film to the paper surface at increasing printing speeds. The velocity (cm/s) at which coating picks or pulls off is recorded. For high‑quality coated papers, pick velocity should exceed 80 cm/s for standard inks. Low pick resistance (< 40 cm/s) leads to fluffing and poor printing uniformity.

6. Air Permeability (Bendtsen or Gurley) – AS 1301.411 / ISO 5636

We measure the time for 100 mL of air to pass through the paper under a defined pressure differential. For coated papers, low permeability (Gurley > 100 s/100 mL) is desired for ink holdout and blister resistance during drying. High permeability (> 50 s/10 mL) indicates porous coating.

7. Gloss (75° or 60°) – AS 1301.435 / ISO 8254

Using a glossmeter, we measure specular reflection at 75° (paper standard). For art papers, gloss > 60% is typical for high‑quality coated grades. Low gloss (< 30%) suggests a matte finish – acceptable for certain applications but must be specified.

8. Accelerated Aging – Heat and Humidity – ISO 5630‑1 / TAPPI T453

We age paper samples at 80°C and 65% RH for 72 hours. After aging, we re‑measure brightness, pH, and fold endurance. Acceptable changes: brightness loss < 5 points, pH drop < 0.5. Severe aging indicates poor neutrality or lignin residues.

9. Tensile Strength and Stretch – AS 1301.448 / ISO 1924

We cut strips (15 mm wide) and pull at 20 mm/min using a universal testing machine. Tensile strength (kN/m) and elongation (%) are recorded. For coated papers, tensile strength is primarily from the base paper; coating should not reduce strength by > 10%.

10. Coating Weight (Gravimetric) – AS 1301.427

We weigh a dry sample, then remove the coating by soaking in warm water or mild acid, and reweigh the base paper. Coating weight (g/m²) and coating solids (%) are calculated. Typical coating weight for art papers: 15–25 g/m² per side. Variation > 5% across the sheet indicates uneven coating application.

Quality Grading and Acceptance Criteria

Based on our testing of neutral coating paper, we classify papers into three grades (clients provide specific acceptance criteria):

• Grade A (Premium – Archival & High‑Print) – pH 7.0–8.0, Cobb 20–30 g/m², brightness ≥ 90%, opacity ≥ 92%, IGT pick ≥ 120 cm/s, aging brightness loss < 2 points.
• Grade B (Standard – General Printing & Packaging) – pH 6.5–7.5, Cobb 30–45 g/m², brightness 80–90%, opacity 88–92%, IGT pick 80–120 cm/s, aging loss 2–5 points.
• Grade C (Reject – Not Suitable) – pH < 6.0, Cobb > 60 g/m², brightness < 75%, opacity < 85%, IGT pick < 50 cm/s, severe yellowing after aging – immediate process improvement required.

Reporting and Deliverables

Our testing of neutral coating paper report includes: sample identification (paper grade, coating formulation, basis weight, batch number), pH value, Cobb absorption curve, brightness and opacity percentages, IGT pick velocity, air permeability, gloss, aging data (brightness, pH, folding endurance), tensile strength, coating weight uniformity, and a clear pass/fail conclusion based on client‑supplied criteria or AS standards. Raw data (test curves, spectrophotometer logs) are archived for 10 years.

In summary, rigorous testing of neutral coating paper ensures that Australian‑manufactured and imported coated papers deliver consistent printability, long‑term stability, and compliance with food safety and archival requirements. Contact our laboratory to schedule batch testing for your next coated paper procurement or quality verification.

Applications in the Australian Industry

• Food packaging (sustainable paper wraps, burger boxes, trays): Neutral coatings prevent off‑flavours and migration.
• Printing and publishing (books, magazines, annual reports): High‑brightness, high‑opacity papers for colour reproduction.
• Archival and museum storage: Acid‑free coated papers for document and photograph preservation.
• Label and release liner manufacturing: Coated papers with precise Cobb and surface strength.
• Office printing (premium inkjet/laser papers): Neutral pH prevents yellowing and paper jams.