Three major inkjet photo papers (1)

Inkjet printing photographic paper can be divided into three categories: cast coating, expansion, microporous technology.

Casting class

The grammage of the cast-coated photographic paper is usually in the range of 170-197 g/m2. The image quality of this type of photographic paper is poor due to its relatively low optical density and gloss, and its paper base absorbs ink directly. Therefore, after printing, photographic paper will have some degree of wrinkle, but because its print quality can be basically accepted, and the production cost is less than offset, it has the largest market demand and can be used as a substitute for high-end products.

Expanding

The grammage of swelled and microporous photographic papers is generally in the range of 260-300 g/m2. These two types of photographic papers can avoid the wrinkle-removing problem mentioned above. Unlike the cast photographic papers, these two types of photographic paper base coatings There is PE (polyethylene), or RC (ResinCoated) coating, which makes the ink not penetrate into the paper base and thus avoids wrinkle formation. Because the paper base with PE/RC coating is exactly the same as the paper base of traditional silver salt paper, the thickness, hardness, and flatness of the paper are no different from traditional silver salt paper. Since the paper base with the PE/RC coating does not absorb ink, the image quality formed by its decomposition mainly depends on the characteristics of the image receiving layer of the medium. Generally, the characteristics of the image receiving layer of various print media have large individual differences. The image-receiving layer is mainly formed of a soluble polymer for the expanding medium. When ink falls on the surface of the photo paper, Polymer will expand to absorb ink. This is an inconsistent process, which makes it difficult to ensure that the media has good ink absorption and water resistance at the same time, because the faster drying Polymer coating means that it has strong water solubility, so despite the fact that the expanding medium has better optical density However, its disadvantage is that the drying speed after printing is slow, and the glossiness of the medium after printing is lost, curling occurs, and the film is not waterproof.

Microporous technology:

The image receiving layer of microporous media absorbs ink without expansion. Microporous coating structures resemble bees' honeycombs. Since the coating can absorb ink without expanding, it can ensure efficient ink absorption and good water resistance at the same time. Therefore, this type of medium avoids all the disadvantages of the expansion medium and has excellent ink absorption. In fact, the superficial ink-absorbing rate is so fast that it effectively avoids the intermixing of various colors in the ink and the formation of ink droplets. The following main focuses introduce the characteristics of microporous media:

1. On a paper base with a PE (polyethylene)/RC coating, an image receiving layer of up to three layers was coated using the same simultaneous multi-layer coating technique as traditional silver salt paper and film. The total thickness of the three layers is 40 microns and their micropore density amounts to 25 ml/m.

2. The main purpose of these coatings is to use their micropores for ink absorption. Of course, the coating has other effects. In order to achieve the best effect of the photographic paper, the coating should not only have excellent ink absorption, but also should have ink-fixing properties, and at the same time, it should exhibit the lustre, solidity, and waterproof properties of the photographic paper. In order to achieve the above purpose, the coating generally employs a coating containing ICOS (inorganic core/organic shell) molecules, wherein the ICOS molecules are longitudinally aligned using a polyvinyl alcohol binder and a boric acid hardener.

The purpose of the ICOS molecule is that it can effectively control the charge in the coating to achieve charge balance, thereby controlling the absorption, adherence, and evenness of the ink droplets of the image forming layer.

Another role of ICOS is also in its ability to give printed photographic paper high gloss. Usually the ICOS molecule has a diameter of 0.05 μm, so that the luminosity of the photographic paper surface can be high without the need of a calender. Currently, microporous glossy photo paper with RC coating will take over the historical responsibility of replacing traditional silver salt printing in the next few years. Until now, this is almost the only problem in the inkjet field. The problem is that domestic manufacturers cannot produce. In the international market, only about five world-class papermaking groups have such standards, which has caused high prices and seriously affected the promotion of inkjet printing.