Stable blend of ketene dimer size and colloidal silica

Abstract: A composition containing a ketene dimer size for sizing paper that is a stable aquasol of positively charged colloidal silica, positively charged colloidal alumina, or positively charged colloidal zirconia, and also contains the ketene dimer, and a method for sizing a paper product of sheeted cellulosic fibers comprising treating the fibers with the said composition, are disclosed.

Description: This invention relates to sizing paper with ketene dimer sizes under alkaline papermaking conditions. Use of ketene dimers as sizing agents in papermaking, usually at alkaline pH levels, is well known. Ketene dimer sizes function by forming covalent bonds with cellulose to give proper orientation and anchoring of the hydrophobic chains. Ketene dimers and their hydrolysis products (stearones) are waxy solids that can reduce the coefficient of friction (COF) of the paper surface, and thus contribute to slipperiness, particularly when added internally at high levels (greater than 0.15 weight%), or when used as a surface size. Reduced COF contributes to problems in paper handling and converting, including telescoping of paper rolls, as well as sliding of stacked, flattened cardboard boxes. A low COF can also cause potential conversion problems with fine paper grades, such as bond and reprographic paper grades. To help control the COF of alkyl ketene dimer-sized paper, a solution of colloidal silica has been conventionally applied directly to the surface of paper sheets and boxes at the end of the manufacturing process. This requires an extra step in the papermaking process, reducing productivity and increasing costs. U.S.-A-2,865,743 to C. A. Weisgerber discloses a process for internal sizing of paper by dispersing a ketene dimer on a carrier comprising finely-divided amorphous silica to form a free-flowing powder in which the particles of silica have a high level of oil absorption and contain a deposit or coating of the ketene dimer. The patent claims that the powder is readily dispersible without the need for a dispersing agent. GB-A-804,504 to C. A. Weisgerber discloses a process of sizing paper which comprises the addition of activated clay and a sizing material which reacts chemically with the hydroxyl groups of cellulose such as ketene dimers, anhydrides, or organic isocyanates. EP-A-0 261 820 describes a filler composition suitable for use in the manufacture of paper that may include colloidal silica. EP-A-0 445 953 discloses a cationic polymer-modified filler material such as modified calcium carbonate and its use to improve paper processing with reduced sizing agent level. According to the invention, a composition containing a ketene dimer for sizing paper, is characterized in that it is a stable aquasol of a positively charged colloidal silica, positively charged colloidal alumina, or positively charged colloidal zirconia, and also contains the ketene dimer. Also according to the invention, a method for sizing a paper product of sheeted cellulosic fibers comprising treating the fibers with an ketene dimer size, is characterized in that the fibers are treated with a stable aquasol containing the ketene dimer size and positively charged colloidal silica, positively charged colloidal alumina, or positively charged colloidal zirconia. The composition can be conventionally incorporated internally by adding it to the paper-making furnish or applied as a surface size to achieve the desired level of sizing while increasing the COF. Also according to the invention, a paper product comprises sheeted cellulosic fibers treated with the composition or the process according to the invention. Stable cationic aquasols of colloidal silica, alumina, and zirconia are well known for instance from U.S.-A-3,007,878, US-A-3,620,978, US-A-3,719,607, 3 745 126 and US-A-3,956,171. Typically, such sols contain colloidal, dense, finely divided particles, e.g., silica, having a surface area of about 20-600 square meters per gram, about 5-150 µm in diameter. They are generally stabilized with a small amount of an alkali, such as sodium hydroxide. Typical known aquasols are those containing positively charged particles having a dense silica core coated with a hydroxyl or other oxygen compound of a polyvalent metal such as aluminum, along with an anionic counter ion such as a nitrate ion. Preferred cationic silica dispersions are available from Nalco Chemical under the name NALCO-1SJ612, or from E. I. du Pont de Nemours & Co. under the name LUDOX CL. Examples of stable aquasols of colloidal zirconia suitable for use in the composition and method according to the invention include zirconia-nitrate stabilized available under the name NYACOL Zr-50-20 or Zr-100-20 from Nyacol Products Inc., Ashland, MA, and a suitable example of stable aquasols of colloidal alumina is a colloidal alumina dispersion available under the name NYACOL Al-20 from Nyacol Products Inc. Ketene dimer sizes useful in accordance with the present invention are well known cellulose-reactive sizing materials. They include cationic, anionic, and non-ionic materials such as alkyl (including C 11-22 ) and cycloalkyl ketene dimers, aryl and aralkyl ketene dimers, and mixtures thereof. The present invention also contemplates the use of known stabilizers, such as cationic starch and cationic polymers, and other adjuvants in conjunction with the ketene dimer size. Typical ketene dimer sizes as well as stabilizers and other adjuvants are disclosed in many U.S. Patents, including US-A-4,240,935, US-A-4,522,686, US-A-4,861,376, US-A-4,919,724, and US-A-4,927,496. The amount of the ketene dimer applied to paper in accordance with the present invention will vary conventionally depending on the type of paper or pulp to be sized, ketene dimer size used, and amount of sizing desired. Preferably, the amount of ketene dimer applied either internally or as a surface size is about 0.01 to about 1.0% by weight% based on the dry weight of fiber, more preferably about 0.05 to about 0.2% by weight. The stability criteria for the sol containing the ketene dimer size is that the viscosity value of the material is preferably less than 100 cps after storage for four weeks at 32°C. The amount of silica used varies depending on the amount of ketene dimer employed. Preferably, up to 33 parts by weight of particulate silica per 100 parts by weight ketene dimer is used. Optionally, alum is included in the aquasol, preferably at higher levels of silica, in order to aid in stabilization. Preferably, the amount of alum varies from 0.1 to 2.5% by weight of the composition. As an alternative to alum, polyaluminum chloride can be used in similar amounts. Dispersions of negatively charged colloidal silica, such as available from Du Pont Company under the designations LUDOX HS-30 and HS-40, can also be mixed with the aquasol, with enough cationic material to convert the overall blend of the colloidal ingredients to a positive charge. In the following examples, all parts and percentages are by weight unless indicated otherwise. EXAMPLES 1-3 Materials are prepared as follows. A stirred mixture in 92.17 parts water of 1.5 parts cationic starch having an ash content of 3-6%, maximum moisture of 12%, pH 3.5-5.5, 10% maximum common starch, 2.5% amylose maximum, maximum 5% eosin stain, 1.5% minimum protein, 0.24% minimum nitrogen, and viscosity (cold funnel ratio 1-2.5, 190/75 °C.) of 45-60 (available under the name AMAIZO 2187 from American Maize-Products Company, Hammond, IN) and 0.25 parts sodium lignin sulfonate dispersant (available from Ligno Tech, Greenwich, CT under the name LIGNISOL XD) is heated at about 95°C for about 30 minutes at neutral pH. Water lost through evaporation is replaced, cooling the solution to about 65°C. To the mixture is added 6 parts of a mixed hexadecyl-hexadecanyl-ketene dimer size, prepared from a mixture of 45% stearic acid and 55% palmitic acid by forming the acid chlorides thereon and then reacting the acid chlorides with a tertiary amine and 0.06 parts of a biocide (Biocide N521 available from Stauffer Chemical) and the mixture is blended until homogeneous. The resulting pre-mix is homogenized (about 211 kg/cm 2 at 65°C with the collected homogenizate cooled to about 21°C in a cold water bath). Alum (0.02 parts) is then added. The size is available from Hercules Incorporated under the name Aquapel® 360XC (U.S. Patent 4,927,496). To the foregoing mixture, which is kept under stirring in a container at room temperature (about 25°C), a cationic silica sol dispersion is slowly added. The cationic silica sols and their amounts are recorded in the following Table 1. Brookfield Viscosity (cps) Ex. silica sol % amount As made 4 weeks 1 sol #1 9.0 5 6 2 sol #1 36 83 55 3 sol #2 9.0 10 12

Claims: A composition containing a ketene dimer size for sizing paper, characterized in that it is a stable aquasol of positively charged colloidal silica, positively charged colloidal alumina, or positively charged colloidal zirconia, and also contains the ketene dimer. A composition containing a ketene dimer size for sizing paper as claimed in claim 1, further characterized in that it is a stable aquasol of dense, finely divided particles of silica, alumina, or zirconia, having a surface area of about 20-600 square meters per gram, and about 5-150 µm in diameter. A composition containing a ketene dimer size for sizing paper as claimed in claim 1, or 2, further characterized in that the finely divided particles are stabilized with an alkali. A composition containing a ketene dimer size for sizing paper as claimed in claim 1, 2 or 3, further characterized in that the finely divided particles are coated with an oxygen compound of a polyvalent metal and an anionic counter ion. A method for sizing a paper product of sheeted cellulosic fibers comprising treating the fibers with an ketene dimer size, characterized in that the fibers are treated internally or externally with a stable aquasol of positively charged colloidal silica, positively charged colloidal alumina, or positively charged colloidal zirconia, that also contains the ketene dimer. A method for sizing a paper product of sheeted cellulosic fibers as claimed in claim 5, further characterized in that the aquasol contains an oxygen compound of a polyvalent metal and an anionic counter ion. A method for sizing a paper product of sheeted cellulosic fibers as claimed in claim 6, further characterized in that the aquasol further contains alum. A paper product comprising sheeted cellulosic fibers, characterized in that the fibers are treated with the composition as claimed in any one of claims 1 to 4, or by the process as claimed in any one of claims 5 to 7.

Inventors: DASGUPTA SUNIL PRIYA, DASGUPTA, SUNIL PRIYA
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1993
Main classification: D21H17
IPC codes: D21H21, B01J13, D21H17