EP2785530A2

EP2785530A2 - Methods of improving sheet gloss

Info

Publication number: EP2785530A2
Application number: EP11879159.9A
Authority: EP
Inventors: Christopher Arend Toles
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2011-11-29
Filing date: 2011-11-29
Publication date: 2014-10-08
Anticipated expiration: 2031-11-29
Also published as: WO2013105912A2; EP2785530A4; EP2785530B1; WO2013105912A3

Abstract

Methods of improving sheet gloss are disclosed herein. A composition is established directly on a base to form a recording medium, where the composition includes modified calcium carbonate and precipitated calcium carbonate. The recording medium is exposed to a calendering process at a pressure ranging from about 1200 pressure per linear inch (PLI) to about 1500 PLI and at a temperature ranging from about 85C to about 95C. The calendering process is performed for a number of passes ranging from 2 to 5.

Description

METHODS OF IMPROVING SHEET GLOSS

BACKGROUND

The present disclosure relates generally to methods of improving sheet gloss.

Recent trends in digital printing technology include utilizing inkjet inks in high-speed digital commercial or industrial printers. Inkjet inks are often aqueous based inks, which contain a minor amount of colorant and a large amount of water and co-solvent(s). As such, in high-speed digital inkjet printing, it is desirable to utilize a medium having suitable absorption properties. The medium used in inkjet printing determines, at least in part, the quality of the image printed thereon. When the absorption properties of the medium are poor, the quality of the resulting image is often poor as well. In many instances, an ink-receiving layer is included which improves the ink receptive properties of the medium.

BRIEF DESCRIPTION OF THE DRAWING

Features and advantages of examples of the present disclosure will become apparent by reference to the following detailed description and drawing.

Fig. 1 is a flow diagram illustrating an example of a method for improving sheet gloss.

DETAILED DESCRIPTION

Examples of the recording medium disclosed herein include one layer that functions as both an ink-receiving layer and a coating layer. The single ink- receiving and coating layer imparts a high ink adsorption rate (i.e., fast absorption of the liquid component in the ink, e.g. water) and exhibits improvements in image qualities after printing, including reduced graininess, improved image gloss, low ink bleed, low mottle, high gamut, and high black optical density. Examples of the recording medium disclosed herein are also subjected to a calendering process that utilizes specific pressure and temperature conditions, which are relatively high compared to standard calendering conditions. The level of calendering disclosed herein unexpectedly results in the recording medium having desirable print quality (e.g., low ink bleed, etc.) as well as desirably high (>40) sheet gloss levels. The single ink-receiving and coating layer disclosed herein achieved desirable gloss without a second layer (i.e., without an additional ink-receiving layer), and also provides desirable absorption after the calendering process is performed, which is in contrast to other recording sheets that suffer from poor absorption as a result of over calendering.

The recording medium includes a base. The base is a supporting substrate upon which the single ink-receiving and coating layer is formed. The base may be in the form of a sheet or a continuous web suitable for use in an inkjet printer. In one example, the base is a base paper manufactured from cellulose fibers. More specifically, the base paper may be produced from chemical pulp, mechanical pulp, thermal mechanical pulp and/or the combination of chemical and mechanical pulp. The base paper may also include additives, such as internal sizing agents and/or fillers. When utilized, the internal sizing agents are added to the pulp before it is converted into a paper web or substrate. Any suitable internal sizing agent may be selected, such as alkyl succinic anhydride, diketene, and rosin. Any suitable filler may also be selected, such as calcium carbonate, talc, clay, kaolin, titanium dioxide and combinations thereof. Examples of substrates other than base paper include cloth, nonwoven fabric, felt, and synthetic (non-cellulosic) papers. The base may be an uncoated raw base or a pre-coated base. The pre-coated base includes a pre-coating that is established on the raw base. The pre-coating may include any of a variety of inorganic pigment coatings applied in-line or offline using a size press, a gateroll press or any variety of blade coater. As an example, a pre- coat may be from about 5 gsm to about 10 gsm of calcium carbonate with a binder, such as polyvinyl alcohol or latex.

The single ink-receiving and coating layer is established directly on the base (i.e., on the raw base or on the pre-coating of the base). It is to be understood that this single layer is one layer that contains the coating composition disclosed herein. The single layer may have any desirable thickness, and in some instances may include multiple sub-layers to achieve the desirable thickness. However, the single layer acts as both the ink-receiving layer and the coating layer, and thus the recording medium does not include any other layers on the single layer. As such, the single ink-receiving and coating layer is the outermost layer of the recording medium.

The single ink-receiving medium and coating layer is made up of an aqueous pigmented dispersion composition that includes both modified calcium carbonate (MCC) and precipitated calcium carbonate (PCC).

The modified calcium carbonate used herein refers to pre-existing calcium carbonate (ground or precipitated) which has been post-treated with phosphoric acid and CO₂ gas as well as a variety of other additives (such as soluble silicates) for the purpose of altering both the structure and the chemical composition of the original particle. The post-treatment of the calcium carbonate results in a pigment particle made up of a shell of various calcium compounds surrounding a core of the original carbonate molecule. Suitable MCC material may take the form of a slurry dispersion of structured calcium minerals, which include primarily calcium

carbonate (CaCOs), calcium phosphate and/or calcium silicate (Ca₂SiO₄). Calcium phosphate includes compounds containing calcium ions together with phosphate ions, and may include octacalcium phosphate (Ca8H₂(PO₄)6-5H₂O) or other forms of calcium phosphate. An example of octacalcium phosphate is OMYAJET® 5010 available from Omya Inc. The amount of modified calcium carbonate pigment included in the composition ranges from about 15 dry parts to about 25 dry parts of the total dry parts of the composition. Precipitated calcium carbonate pigments may be obtained by calcining crude calcium oxide. Water is added to obtain calcium hydroxide, and then carbon dioxide is passed through the solution to precipitate the desired calcium carbonate. Precipitated calcium carbonate is commercially available, for example, under the tradename OPACARB® A40 (Minerals Technologies Inc.). In an example, the amount of precipitated calcium carbonate used in the composition ranges from about 75 dry parts to about 85 dry parts.

The total amount of inorganic pigments present in the coating composition ranges from about 60 wt.% to about 90 wt.%. "Wt.%" as used herein refers to dry weight percentage based on the total dry weight of the coating composition.

In an example, the composition excludes clay. The composition disclosed herein develops desirable gloss (due, at least in part, to the calendering process) and maintains sufficient coating openness for adequate absorption without the use of clay. However, in another example, clay, such as calcined clay, kaolin clay, or other phyllosilicates, may be included. Clay(s), in some instances, may be added to further increase the gloss and/or increase the absorption rate. As an example, calcined clay may be desirable to further enhance the absorption rate of the single ink-receiving and coating layer. In an example in which calcined clay(s) is/are added, for example, to provide additional porosity, the calcined clay(s) may be added in an amount ranging from about 0.5 dry parts to about 10 dry parts (based on the total parts of inorganic particles). In another example in which uncalcined clay(s) is/are added, for example, to boost gloss, the uncalcined clay(s) may be added in an amount ranging from about 0.5 dry parts to about 5 dry parts (based on total parts of inorganic particles).

The coating composition disclosed herein may also include a polymeric co- pigment. Examples of suitable polymeric co-pigments include plastic pigments (e.g., polystyrene, polymethacrylates, polyacrylates, copolymers thereof, and/or combinations thereof). Suitable solid spherical plastic pigments are commercially available from The Dow Chemical Company, e.g., DPP 756A and HS 3020. The amount of polymeric co-pigment in the coating composition may be in the range of 1 dry part to 10 dry parts based on 100 parts of inorganic pigments. In an example, the amount of polymeric co-pigment or plastic pigments ranges from about 3 dry parts to about 7 dry parts per 100 parts of inorganic pigments.

The coating composition also includes a binder. The binder(s) may be hydrophilic or water-soluble binders such as polyvinyl alcohol (e.g., MOWIOL® 15- 98, Kuraray) and derivatives thereof (e.g. carboxylated polyvinyl alcohol, sulfonated polyvinyl alcohol, acetoacetylated polyvinyl alcohol, and mixtures thereof), polystyrene-butadiene, polyethylene-polyvinyacetate copolymers, starch, gelatin, casein, alginates, carboxycellulose materials, polyacrylic acid and derivatives thereof, polyvinyl pyrrolidone, casein, polyethylene glycol, polyurethanes (for example, a modified polyurethane resin dispersion), polyamide resins (for instance, an epichlorohydrin-containing polyamide), a polyvinyl pyrrolidone-vinyl acetate) copolymer, a polyvinyl acetate-ethylene) copolymer, a polyvinyl alcohol-ethylene oxide) copolymer, styrene acrylate copolymer, resin latex, styrene butadiene latex (e.g., STYRONAL® D628, BASF Corp.), or a poly(butadiene-styrene-acrylonitrile) latex (e.g., XZ96750 , Styron Corp.), or the like, or mixtures thereof. In general, the binder is present in an amount sufficient to bind the inorganic pigments. In some examples, the total amount of binder is present in an amount ranging from about 5 to about 20 parts based on 100 parts of inorganic pigments. In an example, the coating composition includes from about 3 dry parts to about 10 dry parts of a latex binder and from about 2 dry parts to about 7 dry parts of a polyvinyl alcohol binder.

The coating composition may also include other coating additives such as calcium chloride, surfactants, rheology modifiers, defoamers, optical brightening agents, sheet color adjusting agents, biocides, pH controlling agents, dyes (e.g., violet dye), and other additives for further enhancing the properties of the coating. The total amount of coating additives may be in the range of 0 to about 10 parts based on 100 parts of inorganic pigments. In an example, the coating composition includes from about 8 dry parts to about 10 dry parts of calcium chloride (CaC ), from about 0.3 dry parts to about 0.4 dry parts of a defoaming agent (e.g.,

AGITAN™ 103, Munzing), from about 0.004 dry parts to about 0.006 dry parts of a sheet color adjusting agent (e.g., CATEREN™ Violet 79732, Clariant), and from about 0.4 dry parts to about 0.6 dry parts of an optical brightening agent (e.g., TINOPAL®, BASF Corp.).

Water is added to the inorganic pigments and other components in order to form the coating composition. The amount of water added may depend, at least in part, on the desirable solids percentage for the final coating composition. In an example, enough water is added to obtain composition including from about 40% solids to about 55% solids.

Referring now to Fig. 1 , at reference numeral 100, the composition is established directly on the base to form the recording medium. The coating composition may be applied to one or both opposing sides of the base. The double-side coated recording medium has a sandwich structure, i.e., both sides of the supporting base are coated with the same coating, and both sides may be printed with images or text. The coat weight of the single ink-receiving and coating layer may be in the range of about 4 gsm (grams per square meter) to 45 gsm per side. In an example, the coat weight of the single ink-receiving and coating layer may be in the range of about 4.5 gsm to about 30 gsm per side. The coating composition of the present disclosure may be applied to the base using any one of a variety of suitable coating methods, such as blade coating, jet blade coating, air knife coating, metering rod coating, curtain coating, or another suitable technique. To obtain a low-cost coated medium for inkjet printing, it may be desirable to have relatively low manufacturing costs in addition to formulation material costs.

Therefore, it may be desirable to use a low-cost coating method, like blade coating or metering rod coating, and run the coating process at high speed. For a double- side coated recording medium, depending on the set-up of production machine in a mill, both sides of the base may be coated during a single manufacture pass, or alternatively, each side may be coated in separate passes.

After the coating composition is deposited, the coated base is then subjected to a drying process to remove water and other volatile components from the ink-receiving and coating layer and the base. The drying means includes, but is not limited to, infrared (IR) dryers, hot surface rolls, and hot air flotation dryers.

After coating and drying, the recording medium is calendered to increase glossiness (reference numeral 102 in Fig. 1 ). Calendering may be accomplished using an on-line or an off-line calender machine, which may be a soft-nip calender or a supercalender. The rolls (e.g., a stainless steel roll positioned against a cotton-filled backing roll) in a calender machine may or may not be heated. The calendering process disclosed herein is performed at a pressure ranging from about 1200 PLI (pressure per linear inch) to about 1500 PLI (i.e., about 3000 psi (pressure per square inch) to about 3500 psi) and at a temperature ranging from about 85°C to about 95°C. The calendering process is performed for a number of passes ranging from 2 to 5 (reference numeral 104 in Fig. 1 ). This calendering process unexpectedly results in desirable sheet gloss (>40), while not sacrificing printability and print quality. In particular, it has been found that the calendering process disclosed herein does not negatively impact the printability because the process does not close up the structure of the coating.

To further illustrate the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the disclosed example(s).

EXAMPLES

Example 1

A composition was generated utilizing the components shown in Table 1 The composition had a total solids amount of 44.5 wt%. Table 1

The composition was coated on a pre-coated offset base via blade coating to form a recording medium having a single ink receiving and coating layer on the pre-coated base. The composition was coated at 7 gsm on 90 gsm of the pre- coated base.

The recording medium was calendered according the examples disclosed herein using a heated 2 roll calender from Independent Machine Co., Fairfield, NJ. In particular, the recording medium was calendered at 3000 psi (~ 1286 PLI) and at about 90°C for 2 passes.

The sheet gloss level of the calendered recording medium was measured at a 75° measurement angle using a Micro gloss 75, which is a gloss meter available from BYK-Gardner. The sheet gloss in this example was 60, which was well above a suitable sheet gloss level of 40. Example 2

A print was generated using the recording medium generated in Example 1 . Standard ink for a T300 webpress printer was utilized, and the ink was printed using a testbed printer that approximates the general webpress print conditions with drying. The print was tested for gamut, black optical density (KOD), image gloss, and black-to-yellow ink bleed. These results are shown in Table 2.

Table 2

Bleed was tested using an Image Analyzer from QEA Inc., and was also visually evaluated after printing. The bleed measurement was 4 mils, which is well below an acceptable level of less than 10 mils of color to color bleed. Color gamut and black optical density (KOD) were measured using an X-Rite 938

transmission/reflection densitometer. KOD was measured using DEN A settings. Gamut was calculated by measuring the L^*a^*b^* values using D65/2⁰ settings. The image gloss level was measured at a 75° measurement angle using the Micro gloss 75. The image gloss in this example was 61 .

These values represent acceptable levels of optical density and image gloss similar to sheet gloss (see Example 1 ). In addition, the ink bleed value as measured by the bleed of black into yellow ink was very low and indicated a very good print.

Example 3

Two compositions (A and B) were generated utilizing the components shown in Table 3. Each of the compositions had a total solids amount of 44.5 wt%. Table 3

Each of composition A and composition B was coated on a respective uncoated base via blade coating to form, respectively, recording medium A and recording medium B, each having a single ink receiving and coating layer on the uncoated base. The respective compositions were coated at 7 gsm on 56 gsm of the respective uncoated bases.

Recording medium A and recording medium B were calendered according the examples disclosed herein using a heated 2 roll calender from Independent Machine Co., Fairfield, NJ. Recording medium A was calendered at 3500 psi

(-1500 PLI) and at about 90°C for 5 passes. Recording medium B was calendered at 3500 psi (-1500 PLI) and at about 90°C for 3 passes.

The sheet gloss level of the calendered recording mediums A and B was measured at a 75° measurement angle using a Micro gloss 75, which is a gloss meter available from BYK-Gardner. The sheet gloss for both recording medium A and recording medium B was 51 , which was well above a suitable sheet gloss level of 40. It is believed that the higher latex amount in recording medium B also improved the sheet gloss, thus requiring less calendering passes.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from about 75 parts to about 85 parts should be interpreted to include not only the explicitly recited limits of about 75 parts to about 85 parts, but also to include individual values, such as 76 parts, 80 parts, 82.5 parts, etc., and sub-ranges, such as from about 77 parts to about 83 parts, from about 80 parts to about 84 parts, etc. Furthermore, when "about" is utilized to describe a value, this is meant to encompass minor variations (up to +/- 10%) from the stated value.

While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.

Claims

What is claimed is:

1 . A method of improving sheet gloss, comprising:

establishing a composition directly on a base to form a recording medium, the composition including modified calcium carbonate and precipitated calcium carbonate;

exposing the recording medium to a calendering process at a pressure ranging from about 1200 pressure per linear inch (PLI) to about 1500 PLI and at a temperature ranging from about 85°C to about 95°C; and

performing the calendering process for a number of passes ranging from 2 to 5.

2. The method as defined in claim 1 wherein the pressure is about 1286 PLI, the temperature is about 90°C, and the number of passes is 2.

3. The method as defined in claim 2 wherein the sheet gloss of the calendered recording medium is about 60 measured at 75° measurement angle.

4. The method as defined in claim 1 wherein the pressure is about 1500 PLI, the temperature is about 90°C, and the number of passes is 3 or 5.

5. The method as defined in claim 4 wherein the sheet gloss of the calendered recording medium is greater than 40 measured at 75° measurement angle. 6. The method as defined in claim 1 , further comprising forming the composition to include:

75 to 85 dry parts of the precipitated calcium carbonate;

15 to 25 dry parts of the modified calcium carbonate;

3 to 10 dry parts latex binder;

2 to 7 dry parts polyvinyl alcohol binder; 3 to 7 dry parts plastic pigments;

8 to 10 dry parts calcium chloride;

0.3 to 0.4 dry parts of a defoaming agent;

0.004 to 0.006 dry parts of a sheet color adjusting agent; and

0.4 to 0.

6 dry parts of an optical brightening agent.

7. The method as defined in claim 6 wherein the forming of the composition includes excluding clay from the composition.

8. A recording medium, comprising:

a base; and

a single ink receiving and coating layer established on the base, the single ink receiving and coating layer including modified calcium carbonate and precipitated calcium carbonate;

the single ink receiving and coating layer being in direct contact with the base and also being an outermost layer of the recording medium;

and the recording medium having been exposed to a calendering process performed at a pressure ranging from about 1200 PLI to about 1500 PLI, at a temperature ranging from about 85°C to about 95°C, and for a number of passes ranging from 2 to 5.

9. The recording medium as defined in 8 wherein the base is a raw base paper or a pre-coated base paper.

10. The recording medium as defined in claim 8 wherein the single ink receiving and coating layer includes:

75 to 85 dry parts of the precipitated calcium carbonate;

15 to 25 dry parts of the modified calcium carbonate;

3 to 10 dry parts latex binder;

2 to 7 dry parts polyvinyl alcohol binder; 3 to 7 dry parts plastic pigments;

8 to 10 dry parts calcium chloride;

0.3 to 0.4 dry parts of a defoaming agent;

0.004 to 0.006 dry parts of a sheet color adjusting agent; and

0.4 to 0.6 dry parts of an optical brightening agent.

1 1 . The recording medium as defined in claim 10 wherein the single ink receiving and coating layer excludes clay.

12. The recording medium as defined in claim 8 wherein the recording medium exhibits a sheet gloss greater than 40 after the calendering process is performed.

13. The recording medium as defined in claim 8 wherein the modified calcium carbonate has a median pore size of about 0.05 nm.