Effects of Paper Manufacturing Factors on Inkjet Print Quality and Lightfastness

Digital Imaging has introduced Color Printers as proofing device. On demand printing and Low volume Printing is generally supported by color digital printing method. Color Inkjet Printing is one of the digital color printing processes. Here the ink is in form of a liquid. The ink and substrate interaction determines the quality of print and the durability of the image. In this paper, the PAPER properties and relationship with inkjet printability are studied. Inkjet Print Quality can be affected by modifying the paper characteristics, ink composition and the printer, and by improving the interactions between these variables. For light fastness properties, the interactions between the ink and the paper are the important factors. The experimental samples used in this study were produced on a pilot paper machine at three different levels of refining, filler, internal sizing and surface sizing. The optical, surface and absorption properties of paper were analyzed. The samples were then printed with inkjet printer. The solid ink density (SID) and colorimetric analysis on printed samples were performed. Color gamuts and ICC profiles for each of the paper sample were compared. In addition, the accuracy of printer color profile was investigated. The results of the profile accuracy measurements were expressed in terms of CIE La*b* coordinates and Root Mean Square (RMS) E. Results of accelerated light fastness tests for the selected paper samples were interpreted in terms of change of profile and color gamut. The results show that inkjet printability and image permanence are greatly influenced by paper properties. Introduction An inkjet imaging technique involves placing extremely small droplets of ink onto media to create an image [1-2]. The droplets are directed onto the surface of a moving sheet or web and controlled to form print characters and graphics. The inkjet print quality is highly dependent on the print head, media and ink properties and software [3-5]. Advancements in inkjet technology have also place new demands on the media due to faster printing rates, greater resolution through reduced drop volumes, and colorants added to the ink. To meet these requirements, papermakers are developing new paper grades. The paper media for inkjet printing can be divided into two major categories; plain and photo paper [2]. The plain paper is mainly targeted at the largest volume applications and composed of cellulosic fibers and fillers [6-8]. Sizing chemicals, such as AKD (Alkyl Ketene Dimer) and ASA (Alkenyl Succinic Anhydride) [6,7] are used to impart hydrophobicity to prevent ink spread and strikethrough. Highly sized papers provide good optical density by retaining the ink at the paper surface, but have a high tendency to set-off (transfer of the ink from the paper to sheet handling rollers). Film formers such as starches [8], alginate, CMC (CarboxyMethyl Cellulose) and synthetic polymers are used to further modify the media surface. The size press is probably the most common method for applying a surface coating “on machine”. Natural polymers such as starch absorb water into the paper. A balance is needed between internal and surface sizing to control the rate of penetration and lateral spreading of ink. Surface size can have a large influence on color-to-color bleed. High impression pressures are necessary in conventional presses to create uniform physical contact over the printing area [2]. Propelling a series of ink drops avoids such a requirement. The process is less dependent on the flatness of the substrate. Like most non-impact systems, ink jet printers were developed to provide hard copy devices and not to compete with conventional printing. Although ink jet printers have speeded up significantly since their introduction, they have not yet reached the speed of printing presses. However, the print quality achieved with high-resolution ink jet devices is approaching that of conventional printing. The key to creating quality images with ink jet is to generate a controlled stream of droplets. It requires control of droplets in their path to the printing medium or a method of turning the droplet stream on or off, as the nozzle moves along the substrate. All ink jet printers work on digital raster image input [2]. Thus, the development of ink jet systems has closely paralleled that of digital image processing. The ink drop is in one to one correspondence with a bit of data. Thus, droplet formation and control always takes place in response to high frequency digital electronic signals. The differences among ink jet printers relate mostly to method of jet formation and method of jet control. Other differences are dithering methods and the way the droplet stream reaches the media. A characteristic of all modern ink jet systems lies in their utilization of micro-manufacture of electronic, thermoelectric and electro-acoustic elements. EXPERIMENTAL DESIGN This work is divided into three phases: (1) to manufacture paper on a pilot machine with different conditions, (2) to print paper using an inkjet printer, and (3) to characterize the paper sample’s optical, print and permanence properties. Materials The different samples investigated during this study are shown in Table 1. A 60:40 hardwood to softwood ratio was used for furnish. The internal starch addition was kept constant to 15 lb/T. Three different levels of refining, filler (PCC), internal sizing (12.5% solid AKD) and surface sizing (Penford Gum 290) were used. Paper Testing Procedure All the paper samples were conditioned for 24 hrs at 50% RH and 23C before any measurements were made. The samples were then tested for physical, optical, and surface properties. The brightness, opacity, roughness, and porosity were measured as per TAPPI standards. The brightness of the samples was measured using a Technidyne Brightness meter, TAPPI procedure T 452. The surface roughness and air permeability (from PPS porosity) of the samples were measured using a Parker Print Surf (PP) tester (T 555) at 1000 kPa. Thicknesses of the samples were measured using a Micrometer (T 411). Table 1: Sample IDs of Different Substrates Refining Filler Int. Sizing Surface Sizing (PG 290) Sample ID CSF (mL) PCC