CA2083406C - Press felt conditioner for neutral and alkaline papermaking systems - Google Patents

Abstract

A process for the felts of a papermaking operation in order to inhibit the deposition of particulate matter in the felt comprising applying to the felt a fatty acid imidazoline compound.

Description

0-%30 PRESS FELT CONDITIONER FOR NEUTRAL
AND ALKALINE PAPERMAKING SYSTEMS
FIELD OF THE INdENTION
The present invention relates to inhibiting the deposition of particulate materials in the press felts of a papermaking operation. Specifically, this invention pertains to the use of a press felt conditioner directed at controlling the deposition of polymerically flocculated particulate materials in neutral to alkaline papermaking systems.
I0 BACKGROUND OF THE INIfENTION
In a paper manufacturing process, ionically charged, rela-tively high molecular weight, water soluble polymers are often emplq~ed to enhance retention of cellulosic fibers, fines, and .inorganic fillers. The addition of these polymers produces a cleaner process stream by reducing the solids level in the process filtrate. The high molecular weight, ionically charged polymers control solids by adsorbing onto solid particulate surfaces in the papermaking furnish slurry and invoking charge newt ralixation (coagulation) and/or bridging (flocculation) mechanisms which cause the solid particles to flocculate. The flocculate can be retained by the formed mat of cellulosic fibers more easily than smaller individual particles. However, these flocculated particulate materials can be transferred from the surface of the sheet to the papermachine press felts. In the flocculated state, the particles cannot pass through the fine, porous structure of the press felts) and become entrapped therein. If not controlled by adequate felt IO conditioning practices, these agglomerated particulate substances can severely impair the ability of the press felts to absorb water thereby requiring reduced production rates and shortening the useful.life of the felts. In addition, it has been found that common polymeric retention aids can render normally effective prior 15 art felt conditioners useless or marginally effective.
Typical polymers employed as retention aids are generally relatively high in molecular weight; far example, copolymers made from monomers such as; acrylic acid, acrylamide, dimethyl/diallyl ammonium chloride, dimethylamine, epichlorohydrin, and ethylene 20 diamine. Typically, polymeric retention aids have average molecular weights greater than 1,000,000 and can range up to around ZO,OQA,000 for anionically charged polymers and up to 15,000,000 forrcationically charged polymers. These ionically charged poly-mers adsorb onto the various solid particulate surfaces within the 25, papermaking furnish causing flocculation.

'~~ a~~~
In neutral and alkaline papermaking (pH approximately s.0 -8.5), the utilization of polymeric retention aids is particularly critical for efficient operation. Without them, such common system additives as cellulosic reactive sizes, Alkenyl Succinic Anhydride (ASA) and Alkene Ketene Dimer (AKD), can cycle up on the process system and hydrolyze causing numerous operational problems, particu-larly in the press section. Subsequently, most of the particulates that are transferred from the sheet to the press felts in the neu-tral and alkaline papermaking system are generally in a flocculated IO state and are therefore too large to easily pass through a press felt. Subsequently, these contaminants are either embedded into the felt structure or transferred back to the sheet and cause spots, holes, etc., ar deposit in the dryer section and cause problems there. Because of their size', they are relatively unresponsive to prior art felt conditioning treatments.
In addition to the aforementioned contaminants, most press felts associated with coated alkaline fine paper experience exces-sive filling due to white pitch deposition. This arises from natural wood resins such as fatty esters, fatty acids,, resin acids ZO and othertypical papermaking furnish components .such as sizing agents, alumina and fiber fines. The paper coating binders such as polyvinyl acetate or styrene butadiene latices and inorganic coating pigments such as clay, calcium carbonate and titanium dioxide also contribute to,the felt filling. If not effectively controlled by adequate chemical and mechanical press felt conditioning practices, this high level of contaminating material plugging or filling the _g_ ~~".~a~~~~i paper machine press felt severely impairs their water absorbancy capability, which in turn, reduces paper machine production rates, produces paper quality defects and/or requires the premature removal and replacement of the expensive felts.
.Chemical analyses of used press felts associated with coated neutral and alkaline papermaking also reveal a number of ,, polymerically flocculated components. Significant quantities of inorganic fillers such as calcium carbonate, clay and titanium dioxide are typically found in addition to normally smaller amounts of sizing agents and wood pitch components.
While various anionic or nonionic surfactant-type felt conditioners commonly employed in the art demonstrate substantial efficacy for conditioning press felts subject to wood pitch and/or paper sizing agent-related contamination, they have proven to possess limited efficacy against white pitch contamination at commercially viable treatment dosage levels.
DESCRIPTION OF THE RELATED ART
Processes to inhibit contamination deposition in pape,r-maE~ng felts are known in the art. U.S. Pat. No. 4,715,931, Shellhamer et al., discloses a process for inhibiting aluminum hydroxide deposition in papermaking systems which comprises adding to the felts a hydroxylated carboxylic acid. The use of -~-~~~ i~~r~~
the carboxylic acid in combination with surfactants, such as octyi phenol ethoxylates, nonyl phenol ethoxylates and others listed therein inhibit aluminum hydroxide deposition and associated organic contaminants.
In addition to the control of inorganic contaminants, pitch formation is of concern in papermaking systems. Filler materials can become trapped within the organic matrix formed by pitch coalescence compounding deposition problems. Methods of controlling the pitch deposition formation are known in the art.
U.S. Pat. No. 4,184,912, Payton, discloses a method of preventing pitcy formation by dispersing and emulsifying pitch particles in the pulp furnish to an exceptionally fine state and uniformally distributing the particles throughout the finished paper. The pitch deposition is controlled by the addition of a three com-ponent formulation comprising a nonionic surfactant plus an anionic surfactant and a low molecular weight anionic polymer.
The three component mixture is added to the papermaking pulp system at a point.prior to where pitch deposits normally form.
In U.S. Pat. No. 3,992,249, Farley, a process for inhibiting pitch deposition is disclosed wherein the pulp is washed with an aqueous solution of anionic polymer having between 25 to 85 mole percent.
hydrophobic-oleophilic linkages and 15 to TO mole percent hydro-philic acid linkages to complex with the pitch. The pitch-polymer complex is washed away with water.

'~;~~ ~~~~~~a U.S. Pat. No. 3,873,417, Otrhalek et al., discloses a pitch and pigment dispersant which comprises a neutralized solution of polymer prepared by free radical polymerization of an'alpha, beta unsaturated acid with an alkyl ester and an allyl alcohol.
Another pitch control process is disclosed in U.S. Patent No. 3,398,047, Michalski. The patentee teaches that the use of an organic polydentate ligand such as aminopolycarboxylic acids, and an organic sulfonate offer an efficient pitch deposition inhibitor.
Of further interest is U.S. Patent No. 3,582,461, Lipowski et al., which discloses a pitch control process utilizing a dicyandiamide-formaldehyde condensate compound.
U.S. Patent No. 3,642,572, Endres et al., discloses that polyamidoamines are useful not only as flocculants, but also as retention aids and dewatering agents in papermaking processes.
Additional polyamines are disclosed by Ziemann et al., in U.S.
Patent No. 3,893,885 as being useful as retention aids and dewatering agents.
Some treatment programs are directed specifically at the reduction of contaminants within the felt or other sheet farming surfaces. EP 0359590, Aston et al., addresses the control of deposits on and within papermill felts by employing the use of a cationic polymer in conjunction with nonionic or cationic surface tants. The base products used to create the cationic polymers preferably contain amine groups. U.S. Patent No. 4,895,622, ~~C'~~~'~~~
Barnett et al., discloses a felt conditioner comprising a relatively low molecular weight anionic organic polymer and a hydrophilic anionic or nonionic surfactant. The polymers preferably contain acrylic acid or methacrylic acid moieties.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed toward inhibiting the deposition of polymerically flocculated particulate material in a felt in the press section of a papermaking system. Several functionally similar members of fatty acid imidazolines are surprisingly effective when employed as felt conditioning agents for inhibiting contamination of press felts subjected to the aforementioned flocculated particulate .
substances. An effective inhibiting amount of these felt conditioning agents may be metered into one or more fresh water showers directed onto a press felt on its runs between the press nip and the vacuum or uhle box utilized for dewatering the treated felts.
Also surprisingly, other types of fatty acid imida-zolines did not produce positive results when employed as felt conditioners.
Examples of highly effective fatty acid imidazolines that can be utilized in accordance with this invention are represented by the general structure:
~ H2 ~---C CH2 where R is an alkyl hydrophobe, radical with a preferred carbon chain length of C12 or greater, more preferably C18.
Fatty acid imidazolines, according to this invention, will provide for an effective continuous press felt conditioning treat-ment when the press felts are subjected to significant quantities of the aforementioned polymerically flocculated particulate substances originating from coated neutral and alkaline pH papermaking furnishes, with or without sizing agent being present. The choice of the fatty acid imidazoline appears to be critical and the imida-zoline embodied in this invention may fall within a hydrophobe carbon chain length of C12 or greater with the preferred hydrophobe chain length of C18.
Furthermore, it is also believed that the embodied invention can also be effectively used to prevent these same types of contami-nant~.=from building up on paper machine press section press rolls whet fed continuously through an aqueous shower directed upon the press rolls. .In either case, the required amount or concentration of fatty acid imidazoline will depend on, among other things, the volume of shower water employed, the production rate, and the concentration of poiymerically flocculated contaminants. Generally the total concentration of fatty acid imidazoline added to the aqueous showering medium is from 10 to 1500 parts per million parts of the aqueous medium. Preferably, they are added at concentrations from 100 parts to 300 parts per million parts o~f aqueous. showering medium..
.. In order to more clearly illustrate the present invention the following data were generated. The following examples are included as illustrations of the present invention and should not be construed as limiting the scope thereof.
EXAMPLES
The examples contained herein will demonstrate the unexpected superior responses produced by the present invention.
The results were obtained utilizing a continuous press felt conditioning test apparatus and a~simulated caated alkaline fine paper contaminant system. The testing incorporates a clean (unused) press felt sample of known initial weight and air permeability placed on a heavy-mesh support screen through which the treated or untr~ted contaminant solution is pressed. The simulated coated alts-line fine papermaking contaminant test slurry consisted of the following: ~ .

_1o-Ingredient Concentration (PPm) Ground Calcium Carbonate 375.00 Clay , 125.00 Fatty ester/fatty acid pitch mixture 50.00 *Coating solids (cured, redispersed 1596 slurry) 300.00 Alkaline Size (ASA/starch, 1:3 ratio, 1096 slurry) 48.75 Cationic Retentian Aid (High Molecular freight, Cationic Polyacrylamide) 2.00 * Pre-cured casting formulation contains:
5~ PVAc latex, 5% S8R latex, 32~ Clay, 8~ Ti02 and 50~ water Table 1 contains data generated in this slurry syst em showing the performance characteristics of several commercially available surfactants and polymers as defined below, employed in the art for continuous or intermittent conditioning of paper machine press felts in comparison to the fatty acid imidazolines according to the invention. Table 2 s~immarizes data generated to evaluate the effectiveness of the present invention in the same slurry sy stem excluding the alkaline size.
As can be seen from Tables 1 and 2, the results show that in two critical test parameters, namely percent weight gain and percent permeability loss, the values for the fatty acid imidazolines with a hydrd~hobe carbon chain length of C12 to C18 were significantly lower than the control or any other surfactant or polymer commonly employed in the continuous or intermittent conditioning of paper machine felts.

-11- ~~~ a~~°~a Examples are listed below of the conventional surfactants known in the art which were compared against the fatty acid r imidazolines of the present invention:
Alkyl or dialkyl phenol ethoxylates represented by the general structure: ' .. R p OCH2CHZ)nOH
R
where, R = H or alkyl group R' = H or alkyl group n = moles of ethylene oxide;
Sodium lignosulfonates;
Ethoxylated secondary alcohols;
Quaternary imidazolines;
Phosphate esters;
Polymethylnapthalene sulfonates;
Polyacrylic acid; and Sodium alkylnapthalene sulfonate.

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Performance of various surfactants and fatty acid imidazolines in a felt conditioning test system utilizing a simulated polymerically (retention aid) flocculated coated alkaline fine paper contaminant system (with sizing agent present).
CONDITIONING % WT. GAIN % PEPMEABILITY
AGENT OF TEST FELT LOSS
(over clean control) (over clean control) Untreated Control 24.4 83.4 Fatty Acid Imidazoline H.ydrophobe carbon chain length a) Clg 4.1 38.1 b) C16 5.7 41.4 c) C12 13.6 54.2 ~ d) C$ 26.I 81.2 Quaternized Fatty Imidazoline ~i_ydrophobe carbon chain le~th a) C18 22.2 71.2 "b) C16 19.4 73.3 -,~_ .
Phosphate ester ~ 16.1 59.9 Sodium Lignosulfonate ' 23.8 79.6 Palymethylnapthalene Sulfonate I9.2 61,8 Ethoxylated nonyl phenol 18.9 56.9 E~hoxylated octyl phenol * 19.1 70.6 Polyacrylic acid ~ 27.4 80.5 * Untreated Control Data were: 28.3% Wt. Gain and 84.4%
Permeabi 1 i~ty- Loss ~r'~~~,~~, ~-.
i:)s9 :v:'~~:) Performance of various surfactants and fatty acid imidazolines in a felt conditioning test system utilizing a simulated polymerically (retention aid) flocculated coated alkaline fine paper (no sizing agent employed) contaminant system.
CONDITIONING % WT. GAIN % PERMEABILITY
,. AGENT OF TEST FELT LOSS
(over c lean control) (over clean control) Untreated Control 27.9 80.4 Fatty Acid Imidazoline Hvdroohobe carbon chain len th a) C18 6.5 44.8 b) C16 6.2 33.9 c) C12 16.1 52.4 d) C8 30.3 84.7 Quaternized Fattv lmi~a'gline Hvdrophobe carbon chain length a) C18 21.0 68.2 .b) C16 23.1 71.0 Phosphate ester 20 . 75.0 Sodium Lignosu'lfonate 20 . 74.2 Polymethylnapthalene Sulfonate 20 . 77.1 Ethoxylated nonyl phenol 17 . 68.8 Ethoxylated octyl phenol 19 . 70.6 Polyacrylic acid 20 . 70.9 Sodium alkyl napthalene sulfonate19 . 75.6 la-It is clear that the process of the present invention provides a significant positive felt conditioning response to prevent the aforementioned polymerically flocculated particulate substances from depositing in the felts, regardless of whether a sizing agent is present or not.
While this invention has been described with respect~to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention should be construed to cover all such otivious forms and modifications which are within the true spirit and scope of the present invention.

Claims (6)

1. A process for conditioning the felts of a papermaking system in order to inhibit polymeric retention aid flocculated particulate deposition in the felts comprising applying to the felts an effective inhibiting amount of a fatty acid imidazoline having a structure:
where R is an alkyl hydrophobe radical having a carbon chain length of C12 or more.

2. The process of claim 1 wherein R is an alkyl hydrophobe radical having a carbon chain length of C18.

3. The process of claim 1 wherein the papermaking system is pH neutral or alkaline.

4. The process of claim 1 wherein the felt is conditioned by showering with an aqueous medium containing the fatty acid imidazoline.

5. The process of claim 4 wherein the fatty acid imidazoline is added in an amount of from about 10 to about 1,500 parts per million parts of the aqueous medium.

6. The process of claim 5 wherein the fatty acid imidazoline is added in an amount of from about 100 to about 300 parts per million parts of the aqueous medium.