Recycled paper and printing quality

The U.S. federal government has a defined meaning for recycled paper. In 1995, they set the standard to 25% recycled fiber, which was raised to 30% in 1999. A research unit in the United States has found that the paper strength will continue to decrease when circulating fibers in the paper increase, but when the recycled fiber content exceeds 40%, the paper strength will increase. The concept of the average person thinks that the fiber structure will be damaged during the cycle, and the loss of water-soluble hemicellulose and the original strength agent will weaken the overall paper strength. Some people later refuted this statement and found that even if the paper undergoes six cycles, the change in fiber length is very small. This shows that there are other factors that cause this phenomenon.
Stone and Scallan's research report clearly pointed out that in the drying process, the surface area of ​​pulp shrinks, reducing the part of the binding capacity, which often occurs in chemical pulp. Conversely, during the cycle, the lignin in the mechanical pulp is gelatinized, the binding capacity and elasticity are enhanced, and the overall paper strength is increased.
Nowadays, many recycle paper manufacturers are constantly improving their production processes in order to bring the characteristics of recycled paper and log fibers closer together. For example, additives are added to the chemical pulp or chemical treatment steps increase paper strength. However, since the ink and the contaminants in the paper are not completely removed, the brightness decreases as the amount of recycled fibers increases. In view of this, manufacturers will add some filler pigments or use different bleaching steps to increase brightness. The characteristics of recycled fiber are by no means good, it can increase the opacity of paper, reduce the reflection, and improve the quality of printed products.
From the physical properties of paper, surface strength, water resistance, and smoothness are all important factors. In addition, optical properties, opacity, brightness, and the color of the paper itself are items to pay attention to. Note that the recycled fiber in the paper will change the brightness of the paper, and then reduce the color gamut that can be expressed, but it will not affect the clarity of the print.
The use of recycled paper has become more and more common, and manufacturers have continued to conduct research in the areas of color gamut, texture clarity, quality, etc., in order to achieve better paper properties.