Commercially available packages of inkjet papers are sold under various product descriptions such as glossy paper, photo-quality paper, photo paper, coated paper, matte paper, plain paper, non-coated paper, etc. This is because the manufacturers all use different product category descriptions. Below is a brief explanation of inkjet papers. Inkjet papers can be classified as shown in the figure below. There are also some products that are not paper. Material for inkjet printing as a whole, including non-paper media such as cloth and film, are referred to as "inkjet media."

Classification is made depending on the existence of an ink receptor layer to absorb ink from an inkjet printer. Papers with no ink receptor layer are called "plain paper" or "non-coated paper," and those with an ink receptor layer are called "coated paper." Coated papers are greatly superior in image quality and color because their ink receptor layer is developed taking into consideration color development and fixing of ink. Coated papers are classified into several types such as glossy, non-glossy, etc., depending on the different kinds of surface. All plain papers have non-glossy surfaces, and are inexpensive. Plain paper is suitable for the printing of color data that mainly consists of text. Printing on media other than paper -- such as film, cloth, and metal foil -- becomes possible by forming an ink receptor layer on the material's surface.

>Click here for details of the "Principles of ink absorption"

The ink receptor layer formed on coated papers uses various materials. The ink receptor layers of photo-quality papers/photo papers can be roughly classified into two groups: the "polymer type" and the "particle type." Both types have their advantages and disadvantages in respect to production method, cost, quality, and performance, and it is difficult to say which is better. However, the market seems to be polarizing into the two camps of the "cost-oriented polymer type" and the "quality performance-oriented particle type." The picture below is a cross sectional view of representative polymer-type and particle-type media.

This type of ink receptor layer consists of water-soluble macromolecules. A water-soluble macromolecule means a compound that has a giant molecule soluble in water. Water-soluble macromolecules often used for the ink receptor layer include cellulose, gelatin, polyvinyl alcohol, etc.

This type of ink receptor layer consists of small particles, barely visible or invisible. They are also called colloidal particles. Particles used for the ink receptor layer are mainly inorganic compounds such as silica and alumina particles.

The principles of ink absorption of the "polymer-type" and the "particle-type" can be explained with familiar examples. The absorption principle of the polymer-type can be compared to the "principle of the paper diaper," and the particle-type can be compared to the "principle of the drying agent of silica gel." In the "principle of the paper diaper," moisture is absorbed by the swell of the filler. In the "principle of the drying agent of silica gel," moisture is absorbed into fine spaces of the filler.

1) The left figure shows the state in which an ink droplet is about to touch the surface of the particle-type and the polymer-type layers. There is no difference between them in this state.

2) The figure in the middle shows the very moment that an ink droplet reached the surface of the paper. The two types of papers are completely different in their principles of ink absorption. Ink is infiltrated into spaces among particles on the particle-type layer, while ink is absorbed by swelling polymers on the polymer-type layer.

3) The right figure shows the surface condition after printing. The surface of the particle-type is dry because ink has infiltrated the spaces between particles. The surface of the polymer-type, however, is wet because ink is absorbed in the structure of swelled polymers. Ink absorbed in polymers hardly ever dries completely.

Commercially available inkjet papers are not classified into the polymer-type and particle-type by their ink receptor layer. It is difficult to distinguish them by appearance. If the package of the product says "particle technology," "micro-technology," "no drying time," or "quick drying," it may be a package of inkjet papers with a particle-type ink receptor layer. When you touch the surface of inkjet papers with a polymer-type ink receptor layer you may feel some stickiness.