Print products encompass a wide range of finished goods produced using printing technology. In everyday life, items such as newspapers, magazines, trademarks, labels, business cards, packaging boxes, gift boxes, and more, all fall under the category of print products.

The quality of printed materials depends on numerous factors, with the characteristics of the paper being one of the most important. High-performance paper can fully transfer ink, resulting in clear and vivid images on the paper, thereby achieving satisfactory reproduction. Below are several key points about printing paper.

01. The Influence of Paper Characteristics on Print Gloss

During the printing process, the ink film transfers to the paper surface, filling in the unevenness, resulting in a very smooth surface for the printed product. The glossy reflection of the ink film on the surface of the printed product determines its level of luster, and the ink film surface is closely related to the paper's characteristics.

● Film Thickness

The thickness of the ink film is a major factor affecting the luster of printed materials. After the binder in the paper has absorbed the maximum amount of ink, the remaining binder is still retained in the ink film, which can effectively enhance the luster of the printed materials. The thicker the ink film, the more remaining binder there is, which is more conducive to improving the luster of the printed materials.

The trend of gloss increasing with the thickness of ink film varies depending on the type of paper. For high-gloss coated papers, the printed product's gloss decreases as the ink film thickness increases, as the ink film masks the paper's inherent high gloss and the gloss formed by the ink film is reduced due to absorption by the paper. As the ink film thickness increases, the paper's inherent high gloss becomes harder to reflect through the ink film. When the ink film thickness reaches 1.5μm, the paper's absorption of the binder is essentially saturated. Afterward, the more binder retained with the continued increase in ink film thickness, the higher the gloss. For coated board prints, the gloss increases rapidly with the ink film thickness when it is relatively thin. However, once the ink film thickness reaches 3.8μm, the gloss no longer increases with the further increase in ink film thickness. Nevertheless, there should be a certain limit to the amount of gloss increase with the thickness of the ink film for any type of paper.

The impact of paper characteristics on the luster of printed products

Paper forms a capillary network structure due to the interlacing of fibers, which creates a large number of pores and serves as the basis for ink absorption. The balance between the absorption time of the ink binder and the binder curing time in the paper's capillary network determines the extent of binder penetration during the formation of the printed product's luster. Generally, the luster of printed materials decreases as the paper's absorption capacity increases.

The smoothness and luster of the paper affect the luster of the printed product. Higher smoothness contributes to the formation of an even, smooth ink film, thereby enhancing the luster of the printed product. Good paper luster improves the reflectivity of the ink film, especially for transparent inks. The correlation between the luster of the printed product and the luster of the paper is stronger than the correlation between the luster of the printed product and the paper's absorbency.

From the above discussion, it can be observed that there is also a correlation between the smoothness, gloss, and absorbency of paper. This can be easily explained by the papermaking process. For instance, calendering can improve the smoothness and gloss of paper, while also reducing the porosity, thereby decreasing the paper's absorbency. Additionally, the pH level of the paper surface is an indispensable factor in the formation of print gloss. A higher pH level is beneficial for ink drying, thus contributing to an increased gloss in the printed product.

02. The Impact of Paper Characteristics on the Reproduction of Print Image Tones

Accurate tone reproduction is a crucial process for achieving high-quality printed images, and most poor print jobs are caused by issues with tone reproduction.

The primary requirement for image duplication is that the duplicated image visually matches the original. However, in most cases, the density range of the original is broader than that of the printed image. Additionally, as paper quality decreases, the duplicable density range becomes smaller, and the same applies to saturation and color.

The solution is to compress the original copy's tonal range to match the reproducible density range of the paper.

Paper characteristics' impact on dot gain

● Network Expansion

The impact of dot gain on color phase changes is greater than any other variable. The amount of ink printed on paper affects dot gain, which in turn influences print contrast. Dot gain can alter image contrast and cause a loss of detail and clarity when printing black and white or color halftone images. In multicolor printing, dot gain can lead to lost contrast, darker images, dot muddiness, and abrupt color changes.

The impact of paper characteristics on the increase of网点量

The smooth surface of the ink yields excellent solid ink density on high-quality paper. When paper quality decreases, the solid ink density diminishes, resulting in some dot expansion, which affects the quality of the printed product.

Higher wire count results in smaller网点 diameter, allowing even minor indentations on the paper surface to distort or miss fine halftone dots. Thus, finer prints with higher wire counts demand a higher degree of paper smoothness. This is a principle to consider when selecting paper. However, in practice, adjusting certain ink properties or altering process parameters can also accommodate the paper's characteristics.

Paper Characteristics' Impact on Printing Offset Accuracy

For fine print products, registration accuracy is crucial, typically allowing for errors within 0.05mm. In multi-color printing, numerous factors can cause registration issues, but paper deformation due to changes in moisture content during the printing process is a significant factor.

It's widely known that changes in paper moisture content not only cause expansion or contraction of the paper but also lead to localized dimensional changes due to varying moisture levels, which can result in other forms of deformation, such as curling and creasing. This deformation significantly affects the printing process, with printworkers being particularly concerned about the impact of relative humidity on paper moisture content.

At a constant room temperature, the change rate of moisture content caused by variations in relative humidity is much higher under high humidity than under medium humidity; the same is true for low humidity. From this perspective, printing is favorable under medium humidity conditions.

The Moisture Retardation Phenomenon of Paper: When paper reaches an equilibrium moisture content under a certain relative humidity condition, if it is further absorbed (dehumidified) and then re-exposed to the original relative humidity environment, its moisture content will be increased (decreased) compared to the original.

To ensure consistent moisture content across the entire sheet of paper and to match the humidity and temperature in the printing workshop, and to reduce the paper's sensitivity to environmental humidity while enhancing its dimensional stability, it is generally necessary to undergo moisture conditioning (air-drying) before printing.

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