Figure 1: Display of adhesive scraping samples

II. The Effect of Two and Four Doctor Blades on Ink Film Thickness

Under fixed printing parameters, the ink layer thicknesses of the four squeegees exhibit a stable decreasing trend: 70A > 62A > 75A > 83A 。

62A Conventional theory generally holds that lower squeegee hardness yields thicker ink layers; this conclusion rests on the idealized assumption that the squeegee undergoes only vertical compression with no lateral spreading. In practice, however, a 62A squeegee bends significantly under pressure, readily deforming through lateral spreading. Although the larger contact area between the squeegee and the screen allows more ink to be contained within the mesh openings, lateral ink overflow and stress relief cause some ink to be squeezed and retained on the screen surface, resulting in an actual ink layer thickness transferred to the substrate that is lower than that achieved with a 70A squeegee. This hardness is suitable for thick ink coatings, anti-slip inks, and printing on curved workpieces; however, the squeegee is highly sensitive to fluctuations in printing pressure—even minor variations can lead to uneven ink thickness. Moreover, prolonged production causes rapid blade wear, increasing the likelihood of abnormal ink-layer variations and out-of-tolerance batches in the mid-to-late stages.

Figure 2

70A The 70A exhibits moderate deformation; its blade can stably compress the mesh openings, resulting in minimal ink bleed to the sides and the highest ink transfer efficiency. Among the four models tested, it delivers the greatest measured ink film thickness. Minor fluctuations in pressure and speed do not cause abrupt changes in film thickness, blade wear is gradual, and batch-to-batch thickness consistency is excellent, making it the most stable, general-purpose model for standard mass production.

Figure 3

75A It offers greater rigidity, reduced deflection under pressure, and lower ink transfer compared to 62A and 70A, resulting in a thinner overall ink layer. Its advantages include minimal thickness variation during prolonged continuous production and superior wear resistance, making it suitable for products that demand high thickness stability and uninterrupted mass production.

Figure 4

83A The blade makes nearly rigid contact with the printing surface, resulting in a narrow ink‑squeezing zone, minimal ink pickup, and the thinnest ink layer. Its advantages are exceptional wear resistance and virtually no change in ink thickness during prolonged production; its disadvantages are limited ink‑adjustment range and insufficient pressure, which can easily cause show‑through or ink starvation, making thick‑ink printing impossible.

Figure 5

The impact of hardness grades 3 and 4 of squeegees on print appearance quality

62A Low-hardness doctor blades exhibit significant deformation; when compressed, their edges tend to deflect and deform, causing ink to bleed outward from solid areas during printing. This results in noticeable fringing at the edges of solid patches and slight ink overflow, with poor edge definition. However, these blades are less likely to scratch or mark the surface of the print.

Figure 6

70A Deformation has been reduced, ink bleeding and fringing at the edges of color blocks have improved significantly, edge contours are smoother, overall visual defects are fewer, representing a relatively well-balanced overall performance.

Figure 7

75A Rigidity is further enhanced, resulting in reduced deformation of the squeegee and sharper edges on color blocks; burrs and ink bleeding are essentially eliminated. However, localized stress at the blade edge increases, and minor substrate irregularities can occasionally cause faint, fine scratches along the color block edges.

Figure 8

83A There is virtually no visible deformation, and the edges of the color blocks are exceptionally sharp and clear, with no ink bleeding or fringing. However, because the rubber blade is very hard and concentrates pressure, continuous scraping marks are more likely to appear along the edges of the color blocks, and slight impressions from the blade edge may also occur locally, negatively affecting the appearance of the finished product.

Figure 9

IV. Four Guidelines for Precise Selection of Doctor Blades

Based on ink layer requirements, appearance precision, production mode, and actual sample prints, the selection criteria are summarized as follows:

1. 62A: Suitable for thick‑paste inks, anti‑slip coatings, and printing on curved workpieces; the rubber strip is soft and provides excellent conformability to irregular substrates. Due to ink overflow and stress relief, the actual transferred ink layer is slightly lower than 70A, making it ideal for applications that require a certain ink thickness and can tolerate minor edge bleeding or fraying.

2. 70A: A universal solution for all applications, ideal for standard fiberglass board printing, packaging color blocks, and ordinary labels. It offers the highest ink transfer efficiency while balancing ink film thickness, appearance quality, and production‑line fault tolerance.

3. 75A: Suitable for applications where ink bleeding at color block edges is unacceptable, for high-volume production with long machine run times, and balances wear resistance with the visual quality of color block edges.

4. 83A: Suitable for applications where ink bleed or frayed edges at color block boundaries are unacceptable, and for high-volume production runs with extended machine uptime; balances wear resistance with the visual quality of color block edges.

V. Conclusion

This empirical test demonstrates that a softer doctor blade does not necessarily result in a thicker ink layer in actual printing. The 70A blade achieved the highest ink transfer efficiency and produced the thickest measured ink layer; the 62A blade, being relatively soft, tends to laterally overflow and relieve pressure under compression, yielding an actual ink layer slightly thinner than that of 70A, while also being prone to edge bleeding and fuzziness in solid areas. The 75A blade further improved edge appearance and abrasion resistance but resulted in a thinner ink layer; the 83A blade provided the sharpest edge definition and the thinnest ink layer, yet it has the lowest process tolerance and is more susceptible to edge‑scratching defects. Manufacturers can select the appropriate durometer based on target ink layer thickness, desired edge appearance, and production volume. All conclusions presented here are supported by physical print samples, which are readily verifiable and enable frontline technicians to reference these samples for component selection and yield optimization.