Reduction of stickers contamination in papermaking process using recycled paper

In a papermaking operation which utilizes secondary fiber furnish containing hot melt or pressure sensitive adhesive contaminants, a method of inhibiting stickies comprising adding to the pulp slurry at least one surfactant selected from the group consisting of fatty alkanolamides and ethoxylated compounds in addition to a hydrocarbon solvent.

FIELD OF THE INVENTION 
The present invention relates to the use of secondary fiber in the 
papermaking industry. It is directed toward the reduction of stickies 
contamination resulting from the use of recycled paper. 
BACKGROUND 
The papermaking industry utilizes various amounts of recycled fiber or 
papers as a source of paper fiber furnish in the production of finished 
paper products. These recycled papers are often contaminated with pressure 
sensitive or hot melt adhesive tapes, seam bindings, labels, decals, 
stamps and stickers (e.g., bumper). These adhesives are referred to as 
stickies in the papermaking art. 
Stickies are a diverse mixture of synthetic polymeric organic materials 
which are generally found in the application of recycled fiber papermaking 
processes. Stickies are relatively larger particles with a size in the 
range of several microns to several hundred microns. Pitch is a natural 
resinous substance which consists of resin/fatty acids and exists in the 
virgin fibers. White pitch occurs in paper mill recycling systems using 
broke with a latex coating binder. The size of pitch or white pitch is 
very small, and usually appears as colloidal particles. 
During the pulping process, stickies are liberated from recycled fibers due 
to mechanical and thermal energy. For recycled fiber furnishes which 
contain a large quantity of plastic tapes, such as old corrugated 
containers, a significant amount of stickies are released during pulping. 
These stickies will not disperse well in the water and will either 
ultimately end up as "dirt spots" on the paper sheets or stick onto the 
wires, felts or other equipment requiring shutting down the manufacturing 
equipment in order to remove the stickies by solvent washing techniques. 
According to the criteria developed by M. Doshi of Doshi & Associates, 
stickies can be classified on the basis of size: 
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Large, retained on 35 mesh screen, 
&gt;0.42 mm 
Medium, retained on 200 mesh screen, 
0.074-0.42 mm 
Small, passed through 200 mesh screen, 
&lt;0.074 mm 
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Large stickies are relatively easily removed by cleaning and screening and 
therefore do not pose significant problems. Stickies with small size are 
generally less of a problem as long as they remain stable in the stock. 
Medium stickies are more likely to be a problem because they cannot 
efficiently be removed from the stock by a mechanical cleaning system. 
These stickies have a tendency to agglomerate and cause wire deposition or 
are a detriment to product quality. 
Several non-chemical approaches which have been used in the paper industry 
to combat stickies include furnish selection, screening and cleaning, and 
thermal/mechanical dispersion units. Each of these approaches has 
limitations. Furnish selection may reduce but not completely eliminate the 
stickie contaminants in the system. It also increases the production cost 
significantly. Stickies cannot be completely removed with mechanical 
cleaning equipment since minimum slot size is limited to 0.15 mm for 
manufacturing reasons. Thermal/mechanical dispersion units can enhance 
breakup of stickies, but cannot prevent the agglomeration downstream, 
where problems usually occur. In addition, this approach requires capital 
investment and energy expenditure. 
Chemical treatment can considerably reduce or alleviate stickies problems 
at a lower cost although its application technology may prove slightly 
complicated. Current chemical treatment techniques for stickies 
removal/control include detackification (passivation), dispersion, wire 
treatment (electrochemical control), maximization of solids retention, and 
chemical enhanced stickies removal during mechanical cleaning. 
DESCRIPTION OF RELATED ART 
Conventional treatment programs directed toward a reduction in stickies 
related contamination in papermaking operations deal with either 
detackifying or tying up the suspended stickies particles. U.S. Pat. No. 
4,886,575 is an example of one such program. It discloses adding a polymer 
of polyvinyl alcohol to the pulp slurry to either reduce the adhesion of 
stickies particles onto the paper making equipment or prevent them from 
adhering to the finished paper product. 
In a related patent, U.S. Pat. No. 4,923,566, a similar process is taught. 
Here, urea is added to the pulp slurry for the purpose of pacifying the 
suspended stickies particles. 
GENERAL DESCRIPTION OF THE INVENTION 
It is often desirable to leave adhesive material with the plastic 
backing/facestock where it can be removed from the system instead of 
remaining with the paper fibers. In order to make adhesive material remain 
with the plastic backing/facestock, the adhesive-fiber bonding must be 
significantly reduced. This can be achieved with the addition of chemical 
agents. The reduction of adhesive-fiber bonding strength allows the 
adhesive material to be easily released from the fiber when applying the 
mechanical/thermal energy. A lower level of adhesive loss from the plastic 
backing/-facestock indicates that less adhesive would be present in the 
the fiber slurry as the adhesive would be removed with the plastic 
backing/facestock via cleaners. This results in a significant reduction of 
fiber/adhesive agglomeration due to the lower levels of stickies 
contamination. Improved cleaning efficiency results in increasing fiber 
yield. Meanwhile, pulping difficulties are also reduced. 
Since mechanical cleaning systems are not 100% effective, those stickies 
which are liberated from the fiber and plastic backing/facestock cannot be 
removed completely. They behave like free hydrophobic particles in the 
fiber slurry. Due to characteristics such as tackiness, deformability, 
hydrophobicity, etc., these stickies particles have a tendency to 
agglomerate and deposit on wires or felts and detrimentally affect product 
quality. Therefore, it is important to prevent them from agglomerating or 
to further break them down into smaller particles downstream. This can be 
done by adding a proper type of surface-active agent.

DETAILED DESCRIPTION OF THE INVENTION 
It has been discovered that the addition of specific blends of surfactants 
and solvents to the pulper in a papermaking operation utilizing secondary 
fiber inhibits stickies contamination by significantly reducing the amount 
of stickies liberated from the furnish into the aqueous pulp slurry and 
preventing the re-agglomeration of those particles remaining in the 
aqueous slurry. The present invention comprises blending at least one 
surfactant with a hydrocarbon solvent. 
The surfactant is selected from the group consisting of fatty alkonolamides 
and ethoxylated compounds. Representative fatty alkanolamides include 
oleic diethanolamide (Varamide A7, Sherex), Coco-N,N-bis(hydroxyethyl) 
amide (Varamide A10, Sherex) and coconut diethanolamide (Alkamide CDO, 
Rhone-Poulenc). Representative ethoxylated compounds include ethoxylated 
alkylphenols, such as alkylphenol ethoxylate (Surfonic N-95, Texaco), 
coconut amine ethoxylate (Varonic K-205, Sherex), tallow amine ethoxylate 
(Varonic T-205, Sherex) and fatty alcohol ethoxylate (Alfonic 1412-60, 
Vista). 
The hydrocarbon solvent required by the present invention is selected from 
the group consisting of terpenes and aliphatic hydrocarbons. Exemplary 
terpenes include orange terpene (#1100 Orange Terpene, Intercit, Inc.) and 
d-limonene (citrus d-Limonene, Golden Gem Growers, Inc.). A characteristic 
aliphatic hydrocarbon may be acquired from Ashland Chemicals as 140 
Solvent. 
For the best results, the stickies inhibitor of the present invention is 
added to the repulping or papermaking system at a location that will allow 
intimate contact between the treatment and the contaminated paper stock 
for a period of time sufficient to permit the inhibitor to perform its 
function. The amount of stickies inhibitor added to the pulp slurry should 
be sufficient sufficient to allow for subsequent dilution so that a 
concentration of about 1-200 ppm is maintained in the repulper or on the 
paper machine at the point where stickies deposit control is desired. 
The amount of individual chemical components of the stickies inhibitor may 
vary depending upon the amount and chemical makeup of the stickies 
present. Generally, the stickies inhibitor will contain from about 5-95% 
by weight of the surfactant and from about 5-95% solvent. Preferably, 
1/2surfactant content will be in the range of about 50-90% by weight, and 
solvent content will be about 10-50% by weight. 
EXPERIMENTAL 
In order to determine the efficacy of the stickies inhibitor according to 
the present invention, a test using adhesive tape was devised. 
The following results demonstrate the effectiveness of the 
surfactant/solvent composition on the reduction of adhesive material 
liberated from tape backing as well as on the dispersion of stickies in 
the pulp. An adhesive tape was placed on the surface of a paper and 
pressed at 20 psi to insure even adhesion. The paper furnish was treated 
with various products under the following pulping condition: 4% 
consistency, 140.degree. F., pH 7.0, 60 minutes pulping time, and 500 rpm 
pulper speed. After repulping, all of the plastic backing was collected, 
rinsed with D.I. water, and dried in an oven at 120.degree. F. for 24 
hours. The percent loss of adhesive from the plastic backing was 
determined and the results are shown in FIG. 1. The results showed that 
furnish treated with formulations A, B, and C (Table 1) always provided 
lower levels (&lt;2%) of adhesive released from the plastic backing compared 
to that of untreated (10.67%). Under the tested conditions, one percent of 
adhesive loss was equivalent to 3.75 lbs. stickies per ton of paper. A 
lower level of adhesive loss from the plastic backing indicated that less 
adhesive would be present in the fiber slurry as the adhesive would be 
removed with the plastic backing via cleaners. 
TABLE 1 
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List of Formulations 
Formulation Composition (By Weight) 
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A Alkamide CDO 70% 
Surfonic N-95 
10% 
Orange Terpenes 
20% 
B Alkamide CDO 70 
Surfonic N-95 
10% 
140 Solvent 20% 
C Varamide A7 35% 
Varamide A10 35% 
Orange Terpenes 
30% 
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The effect of these formulations on the relative reduction of stickies was 
studied using the laboratory pulper dispersion test. Ethylene 
copolymerized with Vinyl Acetate (EVA) was chosen in this work to 
represent hot melts. A sample of EVA stickies (retained on 50 mesh) 
equivalent to 10 lb/T was added directly to the laboratory pulper. The 
selected chemical treatment was added, and the slurry was repulped at 5% 
consistency for one hour at 1000 rpm and 150.degree. F. The results are 
shown in FIG. 2. It is clear that all formulations were effective for the 
reduction of EVA stickies via dispersion. 
While this invention has been described with respect to particular 
embodiments thereof, it is apparent that numerous other forms and 
modifications of this invention will be obvious to those skilled in the 
art. The appended claims and this invention generally should be construed 
to cover all such obvious forms and modifications which are within the 
true spirit and scope of the present invention.