Patent Application
20140305606
During paper making, sizing compositions are often added to desirably affect the properties of the paper. For example, the sizing composition may improve surface absorbency for the ink or toner to be printed on the paper, may improve water repellency, and may reduce surface stickiness. Some sizing compositions include calcium chloride, which is particularly suitable for papers used in inkjet printing. In particular, soluble calcium ions dissolve into the ink upon contact, and facilitate rapid flocculation of the ink pigment, which in turn alleviates bleed between colors, and intensifies the optical density of black and the saturation of colors.
Features and advantages of examples of the present disclosure will become apparent by reference to the following detailed description and drawings.
While calcium chloride improves the characteristics of paper for inkjet printing, occasionally it has been found to contribute to the corrosion of parts used in the manufacturing of the paper. The contribution of calcium chloride to corrosion often occurs when the level of the chloride ions is not well controlled. The present inventors have unexpectedly found that not all calcium salts are equivalent in terms of improving paper characteristics while also reducing part corrosion. In fact, the present inventors have found that calcium propionate (also known as calcium propanoate), used alone or in combination with certain amounts of calcium chloride, provides the beneficial effect of soluble calcium ions while also being less corrosive (when compared, for example, to other calcium salts).
It has been suggested that any water soluble salt of calcium can be used in a paper sizing composition to enhance print results and reduce corrosion on the parts of a papermaking machine. Based upon this, it would be expected that calcium salts, such as calcium acetate, calcium ethylenediaminetetraacetic acid (EDTA), calcium lactate (which is slowly soluble), calcium nitrate, calcium tartrate (which is slightly soluble), and calcium stearate (which is slightly soluble), may be used in the paper sizing composition to enhance print results and reduce corrosion. The test results of the Example(s) disclosed herein illustrate that this is not the case. In fact, the results show that some water soluble salts, including calcium acetate and calcium nitrate, do not reduce corrosion of stainless steel or carbon steel as much as calcium propionate, and that calcium lactate does not reduce corrosion of carbon steel as much as calcium propionate. Other salts (e.g., calcium tartrate and calcium stearate) are believed to be unsuitable for the sizing composition at least in part because their solubility in aqueous solutions is low. Low solubility may prohibit the use of loadings that are high enough to improve print quality or may lead to other issues, such as precipitate formation.
Further, without being bound to any theory, it is believed that the blends of calcium chloride and calcium propionate create a synergistic result (at least on carbon steel) that minimizes the corrosive effects of the calcium chloride. For example, chloride used alone may cause corrosion in a size press by weakening the iron oxide passivation film at point defects, which in turn forms pitting corrosion. Pits usually have a low pH in them, and the propionate may have a buffering effect that leads to a reduction in the corrosion rate. As illustrated in the Example(s) disclosed herein, sizing compositions including from 25:75 to 75:25 of calcium propionate to calcium chloride significantly reduce corrosion on carbon steel when compared to solutions with higher amounts of calcium chloride.
Some examples of the sizing composition disclosed herein include a single calcium salt, namely calcium propionate, without any other salts. Other examples of the sizing composition disclosed herein include two calcium salts, namely calcium propionate and calcium chloride, without any other salts. Whether calcium propionate is used alone or in combination with calcium chloride, the total amount of salt ranges from about 3 kg/ton of paper to about 15 kg/ton of paper. In some examples, the total amount of salt ranges from about 5 kg/ton of paper to about 9 kg/ton of paper. The ratio of calcium propionate to calcium chloride ranges anywhere from 100:0 (i.e., no calcium chloride) to 50:50.
The composition may also include one or more additives selected from the group consisting of starch, an optical brightener, a biocide, a defoamer, a surface size agent, a wet strength additive, and a pigment filler. It is to be understood that one of these additives may be used, or any combination of the additives may be used.
Starch may be included in an amount ranging from about 15 kg/ton of paper to about 50 kg/ton of paper. The starch may be corn starch, potato starch, tapioca starch, or the like. Modified or unmodified starch may be used. Examples of modified starches include oxidized starch, ethylated starch, cationic starch, esterified starch, enzymatically denatured starch, etc. One specific example of a starch additive is 2-hydroxyethyl starch ether, which is commercially available under the tradename PENFORD® Gum 270 (Penford Products, Co.).
Examples of optical brighteners (i.e., optical brightening agent or OBA) include triazine-stilbenes (di-, tetra- or hexa-sulfonated), coumarins, imidazolines, diazoles, triazoles, benzoxazolines, pyrazolines, and biphenyl-stilbenes. Many commercially available optical brightening agents are based on stilbene, coumarin and pyrazoline chemistries. Some examples include 4,4′-bis-(triazinylamino)-stilbene-2,2′-disulfonic acids, 4,4′-bis-(triazol-2-yl)stilbene-2,2′-disulfonic acids, 4,4′-dibenzofuranyl-biphenyls, 4,4′-(diphenyl)-stilbenes, 4,4′-distyryl-biphenyls, 4-phenyl-4′-benzoxazolyl-stilbenes, stilbenyl-naphthotriazoles, 4-styryl-stilbenes, bis-(benzoxazol-2-yl) derivatives, bis-(benzimidazol-2-yl) derivatives, naphthalimides, triazinyl-pyrenes, 2-styryl-benzoxazoles, 2-styryl-naphthoxazoles, benzimidazole-benzofurans, or benzimidazole-oxanilides. The optical brightener may be included in an amount ranging from about 1 kg/ton of paper to about 10 kg/ton of paper.
When included, the biocide may be present in an amount ranging from about 0.01 kg/ton of paper to about 0.5 kg/ton of paper. Suitable biocides for the sizing composition include, for example, PROXEL™ GXL, KORDEK™ MLX, and/or BIOBAN™ CS-1246.
The defoamer may be included in the sizing composition in an amount ranging from about 0.01 kg/ton to about 0.5 kg/ton. Suitable defoamers are based on silica, silicone oil, polyglycol, or ethylene bis-stearamide chemistries. Examples of the defoamer include FOAMASTER® 1410, 1420, 1430, all of which are available from BASF Corp., Florham Park, N.J.
As mentioned above, the sizing composition may also include the surface size agent. This additive may be included in an amount ranging from about 0.5 kg/ton of paper to about 5 kg/ton of paper. Examples of suitable sizing agents include acrylic emulsion products, polyurethanes, styrene acrylic solutions, styrene acrylate emulsions, ethylene acrylic acids, and styrene maleic anhydride.
The sizing composition may also include the wet strength additive in an amount ranging from about 0.01 kg/ton of paper to about 0.5 kg/ton of paper. Suitable examples of the wet strength additive include dialdehyde starch and polyamine-polyamide-epichlorohydrin resins (e.g., polyamido-amine-epichlorohydrin, PEA).
In an example, the sizing composition also includes pigment filler. Examples of suitable pigment fillers include calcium carbonate (e.g., precipitated calcium carbonate (PCC) or ground calcium carbonate (GCC)), barium sulfate, clay, or titanium dioxide. When included in the sizing composition, the pigment filler may be present in any amount up to about 60% of the composition by dry weight.
The balance of the composition is water. It is to be understood that the amount of water used is sufficient to render the sizing composition with a total solids content ranging from about 8% to about 15%.
It is desirable that the pH of the sizing composition range from 7 to 8. In an example, the pH ranges from 7.2 to 7.5. If the composition is too acidic, a basic pH buffer may be added (e.g., tris(hydroxymethyl)aminomethane (TRIS)); and if the composition is too basic, an acidic pH buffer may be added. The neutral to slightly basic pH is desirable for the paper making process. An acidic pH could deleteriously contribute to higher corrosion rates. It is to be understood that enough pH buffer may be added to achieve the desirable pH.
Some examples of the sizing composition disclosed herein do not include any other components except for the listed salt(s), the listed additive(s), and water.
The sizing composition disclosed herein may be used to generate paper that is suitable for use in inkjet printing or laser printing. It is believed that the sizing composition contributes to enhanced printing performance with inkjet printing (e.g., black optical density and color gamut), and contributes to enhanced toner transfer with laser printing.
During the paper making process, the sizing composition may be used to reduce corrosion. An example of this method 100 is shown in
The selected sizing composition is used to generate a recording sheet (e.g., inkjet paper, laser jet paper, etc.), as shown at reference numeral 104. During the paper making process, the sizing composition is typically added at the size press, which may be, for example, a puddle or metered size press. The sizing composition will be in continuous contact with one or more parts of the size press, as shown at reference numeral 106. The sizing composition may also splash outside of the size press when the paper machine is run at high throughput rates. At least some of the parts touched by the size press solution may be formed of stainless steel or carbon steel, which are susceptible to corrosion. As will be illustrated in the Examples, the sizing composition disclosed herein exhibits particularly desirable results with respect to corrosion of the size press parts.
In addition to the sizing composition, the recording sheet/paper that is formed may include fibers (e.g., chemically or thermal mechanically pulped hardwood and/or softwood fibers) and fillers (e.g., titanium dioxide (TiO2), precipitated calcium carbonate, ground calcium carbonate, talc, clay (e.g., calcined clay, kaolin clay, or other phyllosilicates), calcium sulfate, or combinations thereof).
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 present disclosure.
Various sizing compositions were made using a calcium salt or magnesium sulfate. The calcium salt solutions and the magnesium sulfate solution were prepared at a molar concentration equivalent to 1% w/w CaCl2 solution with water. The calcium salts included calcium propionate as the sample, and calcium chloride, calcium acetate, calcium lactate, and calcium nitrate as the comparative samples. Each of the solutions included 0.1% PROXEL™ GXL and 0.1% TRIS buffer, and the pH of each solution ranged from 7.2 to 7.5.
Electrochemical corrosion rates were measured for each of the solutions. The experiments involved linear sweep potential scans across an open circuit potential (OCP, measured system potential and zero applied voltage). The voltage was scanned from −250 mV to +250 mV across this potential region and the resulting current was plotted (in a Tafel Plot). At the OCP (taken as the intersection of the anodic and cathodic legs of the plot), the current flow Icorr was used to calculate the corrosion rate. The corrosion rates are reported in milli-inches/year (mpy) in Table 1. All solutions were tested on fresh areas of polished metal test electrodes.
It is desirable that the sizing composition provide suitable corrosion rate results on both stainless steel and carbon steel. As illustrated in Table 1, calcium propionate is the only salt that provided these results. The performance of calcium chloride, magnesium sulfate, calcium lactate and calcium nitrate was poor on carbon steel, while the performance of magnesium sulfate, calcium acetate, and calcium nitrate was poor on stainless steel.
Each of the solutions was used to treat paper. The sizing solutions were applied on both sides of a base paper to form a coating layer on each side. This process was accomplished in small quantities by hand drawdown using a Meyer rod in a plate coating station. The coat weight ranged from 2 gsm to 4 gsm total for each side. The treated papers and one untreated paper had images printed thereon. The optical density and gamut were measured for each of the papers. These results are shown, respectively, in
Various sizing compositions were made using calcium propionate, and a comparative sizing composition was made using calcium chloride. The calcium propionate solutions were made with water and included, respectively, 0.5% calcium propionate (pH 7.53), 1.0% calcium propionate (pH 7.53), 1.5% calcium propionate (pH 7.68), 2.0% calcium propionate (pH 7.50), and 2.5% calcium propionate (pH 7.70). The calcium chloride solution was a 1% w/w CaCl2 solution having a pH of 7.43.
Electrochemical corrosion rates were measured for each of the solutions. The experiments involved linear sweep potential scans across an open circuit potential (OCP, measured system potential and zero applied voltage). The voltage was scanned from '1200 mV to +200 mV across this potential region, and the resulting current was plotted (in a Tafel Plot). At the OCP (taken as the intersection of the anodic and cathodic legs of the plot), the current flow Icorr was used to calculate the corrosion rate. The corrosion rates are reported in milli-inches/year (mpy) in Table 2. This data is also presented graphically in
The results in Table 2 and
Various sizing compositions were made using calcium propionate, and various comparative sizing compositions were made using calcium chloride. The calcium propionate solutions were made with water, and the pH was varied using TRIS and/or acetate or sodium acetate as a pH buffer. Each of the salt solutions was 1% calcium propionate and each of the comparative salt solutions was 1% calcium chloride. Some of the solutions also included PROXEL™ GXL. Table 3 lists the buffer(s) used and the pH.
Electrochemical corrosion rates were measured for each of the solutions. The experiments involved linear sweep potential scans across an open circuit potential (OCP, measured system potential and zero applied voltage). The voltage was scanned from −200 mV (in some cases up to −400 mV) to +200 mV across this potential region, and the resulting current was plotted (in a Tafel Plot). At the OCP (taken as the intersection of the anodic and cathodic legs of the plot), the current flow Icorr was used to calculate the corrosion rate. The corrosion rates are reported in milli-inches/year (mpy) in Table 3. This data is also presented graphically in
These results illustrate a general increase in corrosion rates with increasing acidity. These results also illustrate that the corrosion rates on the stainless steel are much lower than the corrosion rates on carbon steel. In
Acid enhanced corrosion occurred at pH below 6, and thus it appears that there is little difference between calcium chloride and calcium propionate. However, in viewing the higher pH data (i.e., pH≧6.5) separately, the data suggests that the corrosion rate for the chloride salt on carbon steel was higher than the corrosion rate for the propionate salt on carbon steel. Both salts exhibited suitable corrosion rates on stainless steel in this Example.
Various sizing compositions were made using different blends of calcium propionate and calcium chloride. In addition, one sizing composition was made with calcium propionate and without calcium chloride, while another sizing composition was made with calcium chloride and without calcium propionate. The solutions were prepared at a molar concentration equivalent to 1% w/w CaCl2 solution with water. The percentage of the respective salts used, and the pH of each composition is shown in Table 4.
Electrochemical corrosion rates were measured for each of the solutions. The experiments involved linear sweep potential scans across an open circuit potential (OCP, measured system potential and zero applied voltage). The voltage was scanned from −200 mV to +200 mV across this potential region and the resulting current was plotted (in a Tafel Plot). At the OCP (taken as the intersection of the anodic and cathodic legs of the plot), the current flow Icorr was used to calculate the corrosion rate. The corrosion rates are reported in milli-inches/year (mpy) in Table 4. This data is also presented graphically in
For a blend of calcium propionate with calcium chloride, it is desirable that the sizing composition provide suitable corrosion rate results on both stainless steel and carbon steel. As illustrated in Table 4, blends of 75% or less of calcium chloride and 25% or more of calcium propionate exhibited much less corrosion on carbon steel when compared to the sample including 100% calcium chloride, while the results for stainless steel corrosion were acceptable. It is to be understood that the threshold for determining a suitable corrosion rate may be higher for blends than for single salts, at least in part because of the presence of calcium chloride, which is believed to be more corrosive than some other salts.
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 3 kg/ton to about 15 kg/ton should be interpreted to include not only the explicitly recited limits of about 3 kg/ton to about 15 kg/ton, but also to include individual values, such as 4 kg/ton, 9 kg/ton, 13.5 kg/ton, etc., and sub-ranges, such as from about 5 kg/ton to about 10 kg/ton, from about 6 kg/ton to about 12 kg/ton, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/−10%) from the stated value.
In describing and claiming the examples disclosed herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.
Furthermore, reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.
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.
