Pitch control

Accumulation of pitch or stickies in pulp or paper making is controlled by applying to the pulp or paper making equipment which is not in continuous contact with water separately a water soluble cationic polymer and a water soluble anionic polymer.

This invention relates to the control of pitch and stickies in the 
manufacture of pulp and paper. 
It is well known that "pitch" can accumulate in paper making and also in 
the manufacture of pulp, causing significant problems. "Pitch" is the term 
used to describe the sticky materials which appear in paper making; these 
originate from the wood from which the paper is made. However, nowadays 
when more recycled paper is used, "pitch" is now used as a general term 
for all material soluble in organic solvents but not soluble in water, for 
example the ink or adhesive present in recycled paper. The depositing 
material originating from recycled fibre is also called "stickies". The 
pitch or stickies can accumulate at various points in the system. It can 
block the felt and thus hinder drainage of the paper web. It can adhere to 
the wires or drying cylinders causing it to pick holes in the paper. It 
may also deposit on press rolls or other rolls and the like which come 
into direct or indirect contact with the paper sheet. 
Many materials have been used in an attempt to eliminate these problems. 
Such materials include inorganic treatments such as talc and anionic 
dispersants. However, conventional dispersants can be ineffective in a 
closed system as there can be a build-up of "pitch". In such systems the 
pitch particles have to be removed from the water system in a controlled 
way without being allowed to accumulate on the felt or rolls or, for 
example, the pipe work used in the paper making machinery. These products 
have also been found to give a limited effect and there is a need for 
further improved treatments. It is also known to spray an aqueous 
formulation of certain cationic polymers to reduce the build-up of 
deposits. However this treatment is not fully effective. 
It has now been found, according to the present invention, that the 
build-up of pitch on the papermaking machinery can be controlled by 
applying thereto both a cationic polymer and an anionic polymer. 
Accordingly, the present invention provides a method for the control of 
pitch or stickies in pulp or paper making which comprises applying to the 
pulp or papermaking equipment separately which is not in continuous 
contact with water a water-soluble cationic polymer and a water-soluble 
anionic polymer. 
By using the combination of cationic and anionic polymers it has been found 
that it is possible to obtain a coating on the pick up felt, paper forming 
wire, press roll or dandy roll, for example, which prevents pitch from 
adhering to them. In contrast a machine chest, back water tank or a pipe 
cannot be treated because these are in continuous contact with the process 
water. Although the polymers can be applied , for example, by means of a 
hopper or other applicator it is preferred that the polymers are sprayed 
onto the equipment. In a particularly preferred embodiment, the anionic 
product is applied subsequent to the application of the cationic product. 
By producing a coating on the surfaces in this way there is improved paper 
machine runnability as well as improved sheet quality resulting from 
improved performance due to reduced build-up of deposit. 
A wide variety of different water soluble cationic and anionic polymers can 
be employed. It will be appreciated that the invention resides in the 
application of the polymers rather than in their precise nature. These 
will generally have a molecular weight from 250 to 500,000. For cationic 
polymers the preferred molecular weight is 1000 to 100,000, especially 
20,000 to 50,000. The charge density (determined by e.g., streaming 
current potential titration) of suitable polymers is 0.1 to 10, especially 
2 to 8, meq/g. 
The polymers will normally be formulated as a concentrated aqueous 
solution, the concentration of each polymer being, in general, from 0.1 to 
50% by weight and preferably from 1 to 20% by weight. This concentrate 
will normally be diluted to an applied concentration from 1 to 10,000 ppm, 
especially from 1 to 5,000 ppm. The dilution should, of course, be made 
with water which is sufficiently pure that it does not reverse the charge 
of the diluted system. 
Such compositions can also contain the usual wetting agents (i.e. materials 
capable of reducing the surface tension of water) and other additives 
conventionally used for pitch control. In particular cationic or nonionic 
surfactants may be used with the cationic polymers and anionic or nonionic 
surfactants may be used with anionic polymers. 
The precise nature of the surfactants which may be used is not important 
and a considerable variety of different surfactants can be used in 
combination with the polymer component, provided that they are water 
soluble. Suitable nonionic surfactants include condensation products of 
ethylene oxide with a hydrophobic molecule such as, for example, higher 
fatty alcohols, higher fatty acids, alkylphenols, polyethylene glycol, 
esters of long chain fatty acids, polyhydric alcohols and their partial 
fatty acid esters, and long chain polyglycol partially esterfied or 
etherified. A combination of these condensation products may also be used. 
Preferred cationic surfactants suitable for use in this invention include 
water soluble surfactants having molecular weights from 200 to 800 and 
having the general formula: 
##STR1## 
wherein each R is independently hydrogen, a polyethylene oxide group, a 
polypropylene oxide group, an alkyl group having 1 to 22 carbon atoms, an 
aryl group, or an aralkyl group, at least one of said R groups being an 
alkyl group having at least about 8 carbon atoms and preferably an n-alkyl 
group having 12 to 16 carbon atoms; and wherein X.sup.- is an anion, 
typically a halide ion (e.g. chloride), or 1/n of an n-valent anion. 
Mixtures of these compounds can also be used as the surfactant of this 
invention. 
Preferably two of the R groups of the cationic surfactants of the formula 
are methyl or ethyl, and most preferably methyl; and preferably one R 
group is an aralkyl group 
##STR2## 
and is most preferably benzyl. Particularly useful surfactants thus 
include alkyl dimethyl benzyl ammonium chlorides having alkyl groups with 
12 to 16 carbon atoms. One commercially available product of this type 
includes a mixture of alkyl dimethyl benzyl ammonium chlorides wherein 
about 50% of the surfactant has a C.sub.14 H.sub.29 n-alkyl group, about 
40% of the surfactant has a C.sub.12 H.sub.25 n-alkyl group, and about 10% 
of the surfactant has a C.sub.16 H.sub.33 n-alkyl group. This product is 
known for its microbicidal effectiveness. 
Other surfactants which can be used include the group of pseudo-cationic 
materials having a molecular weight of 1,000 to 26,000 and having the 
general formula NR.sub.1 R.sub.2 R.sub.3, wherein R.sub.1 and R.sub.2 are 
polyethers such as polyethylene oxide, polypropylene oxide or a combined 
chain of ethylene oxide and propylene oxide, and wherein R.sub.3 is a 
polyether, alkyl group, or hydrogen. Examples of this type of surfactant 
are diclosed in U.S. Pat. No. 2,979,528. 
The anionic polymers employed will, in general, be sulphonates or 
carboxylates although it is possible to use polymers derived from natural 
products such as anionic saccharides, anionic starch and water soluble 
cellulose derivatives. 
Thus suitable anionic polymers include lignin sulphonates, polynaphthalene 
sulphonates, tannins and sulphonated tannins and melamine formaldehyde 
condensates which are optionally sulphonated. Other anionic polymers which 
may be employed include homo and copolymers of various carboxylic acids 
including acrylic acid, methacrylic acid and maleic acid and their 
derivatives. These include polymaleic acid and polyacrylates and 
polymethacrylates as well as copolymers of acrylamide and acrylic or 
methacrylic acid, including those which are obtained by the hydrolysis of 
polyacrylamide. Other polymers include copolymers acrylamide and AMPS 
(2-acylamido-2-methylpropane sulphonic acid) as well as copolymers of 
styrene or styrene sulphonic acid with maleic acid, acrylic acid or 
methacrylic acid. 
It will, of course, be appreciated that the anionic polymers can be used 
either in the free acid form or in the form of water soluble salts 
thereof. 
A considerable variety of different cationic polymers can be used. These 
include for instance, polyethyleneimines, especially low molecular weight 
polyethyleneimines, for example of molecular weight up to 5,000 and 
especially up to 2,000, including tetraethylene pentamine and triethylene 
tetramine, as well as various other polymeric materials containing amino 
groups such as those described in U.S. Pat. Nos. 3,250,664, 3,642,572, 
3,893,885 and 4,250,299 but it is as generally preferred to use protonated 
or quaternary ammonium polymers. These quaternary ammonium polymers are 
preferably derived from ethylenically unsaturated monomers containing a 
quaternary ammonium group or are obtained by reaction between an 
epihalohydrin and one or more amines such as those obtained by reaction 
between a polyalkylene polyamine and ephichlorohydrin, or by reaction 
between epichlorohydrin dimethylamine and either ethylene diamine or 
polyalkylene polyamine. Other cationic polymers which can be used include 
dicyandiamide-formaldehyde condensates. Polymers of this type are 
disclosed in U.S. Pat. No. 3,582,461. Either formic acid or ammonium 
salts, and most preferably both formic acid and ammonium chloride, may 
also be included as polymerization reactants. One 
dicyandiamide-formaldehyde type polymer is commercially available as 
Tinofix QF from Ciba Geigy Chemical Ltd. of Ontario, Canada and contains 
as its active ingredient about 50 weight percent of polymer believed to 
have a molecular weight between about 20,000 and 50,000. 
Typical cationic polymers which can be used in the present invention and 
which are derived from an ethylenically unsaturated monomer include homo- 
and co-polymers of vinyl compounds such as vinyl pyridine and vinyl 
imidazole which may be quaternised with, say, a C.sub.1 to C.sub.18 alkyl 
halide, a benzyl halide, especially a chloride, or dimethyl or diethyl 
sulphate, or vinyl benzyl chloride which may be quaternised with, say, a 
tertiary amine of formula NR.sub.1 R.sub.2 R.sub.3 in which R.sub.1 
R.sub.2 and R.sub.3 are independently lower alkyl, typically of 1 to 4 
carbon atoms, such that one of R.sub.1 R.sub.2 and R.sub.3 can be C.sub.1 
to C.sub.18 alkyl; allyl compounds such as diallyldimethyl ammonium 
chloride; or acrylic derivatives such as a dialkyl 
aminomethyl(meth)acrylamide which may be quaternised with, say, a C.sub.1 
to C.sub.18 alkyl halide, a benzyl halide or dimethyl or diethyl sulphate, 
a methacrylamido propyl tri(C.sub.1 to C.sub.4 alkyl, especially methyl) 
ammonium salt, or a(meth)acryloyloxyethyl tri(C.sub.1 to C.sub.4 alkyl, 
especially methyl) ammonium salt, said salt being a halide, especially a 
chloride, methosulphate, ethosulphate or 1/.sub.n of an n-valent anion. 
These monomers may be copolymerised with a(meth)acrylic derivative such as 
acrylamide, an acrylate or methacrylate C.sub.1 -C.sub.18 alkyl ester or 
acrylonitrile. Typical such polymers contain 10-100 mol % of recurring 
units of the formula: 
##STR3## 
and 0-90 mol % of recurring units of the formula: 
##STR4## 
in which R.sub.1 represents hydrogen or a lower alkyl radical, typically 
of 1-4 carbon atoms, R.sub.2 represents a long chain alkyl group, 
typically of 8 to 18 carbon atoms, R.sub.3, R.sub.4 and R.sub.5 
independently represent hydrogen or a lower alkyl group while X represents 
an anion, typically a halide ion, a sulfate ion, an ethosulfate ion or 
.sup.1 /n of a n valent anion. 
Other quaternary ammonium polymers derived from an unsaturated monomer 
include the homo-polymer of diallyldimethylammonium chloride which 
possesses recurring units of the formula: 
##STR5## 
as well as copolymers thereof with an acrylic acid derivative such as 
acrylamide. 
Other polymers which can be used and which are derived from unsaturated 
monomers include those having the formula: 
##STR6## 
where Z and Z' which may be the same or different is --CH.sub.2 
CH.dbd.CHCH.sub.2 -- or --CH.sub.2 --CHOHCH.sub.2 --, Y and Y', which may 
be the same or different, are either X or --NH'R", X is a halogen of 
atomic weight greater than 30, n is an integer of from 2 to20, and R' and 
R" (I) may be the same or different alkyl groups of from 1 to 18 carbon 
atoms optionally substituted by 1 to 2 hydroxyl groups; or (II) when taken 
together with N represent a saturated or unsaturated ring of from 5 to 7 
atoms; or (III) when taken together with N and an oxygen atom represent 
the N-morpholino group, which are described in U.S. Pat. No. 4,397,743. A 
particularly preferred such polymer is poly(dimethylbutenyl) ammonium 
chloride bis-(triethanol ammonium chloride). 
Another class of polymer which can be used and which is derived from 
ethylenically unsaturated monomers includes polybutadienes which have been 
reacted with a lower alkyl amine and some of the resulting dialkyl amino 
groups are quaternised. In general, therefore, the polymer will possess 
recurring units of the formula: 
##STR7## 
in the molar proportions a:b.sub.1 :b.sub.2 :c, respectively, where R 
represents a lower alkyl radical, typically a methyl or ethyl radical. It 
should be understood that the lower alkyl radicals need not all be the 
same. Typical quaternising agents include methyl chloride, dimethyl 
sulfate and diethyl sulfate. Varying ratios of a:b.sub.1 :b.sub.2 :c may 
be used with the amine amounts (b.sub.1 +b.sub.2) being generally from 
10-90% with (a+c) being from 90%-10%. These polymers can be obtained by 
reacting polybutadiene with carbon monoxide and hydrogen in the presence 
of an appropriate lower alkyl amine. 
Of the quaternary ammonium polymers which are derived from epichlorohydrin 
and various amines, particular reference should be made to the polymers 
described in British Specification Nos. 2085433 and 1486396. A typical 
amine which can be employed is N,N,N',N'-tetramethylethylenediamine as 
well as ethylenediamine used together with dimethylamine and 
triethanolamine. Particularly preferred polymers of this type for use in 
the present invention are those having the formula: 
##STR8## 
where N is from 0-500, although, of course, other amines can be employed. 
Other polymers which can be used include cationic lignin, startch and 
tannin derivatives, such as those obtained by a Mannich type reaction of 
tannin (a condensed polyphenolic body) with formaldehyde and an amine, 
formed as a salt e.g. acetate, formate, hydrochloride or quaternised, as 
well as polyamine polymers which have been crosslinked such as 
polyamideamine/polyethylene polyamine copolymers crosslinked with, say, 
epichlorohydrin. 
The preferred cationic polymers of this invention also include those made 
by reacting dimethylamine, diethylamine, or methylethylamine, preferably 
either dimethylamine or diethylamine with an epihalohydrin, preferably 
epichlorohydrin, such as those disclosed in U.S. Pat. No. 3,738,945 and 
CA-A-1,096,070. Such polymers are commercially available as Agefloc A-50, 
Agefloc A-50HV, and Agefloc B-50 from CPS Chemical Co., Inc. of New 
Jersey, U.S.A. These three products reportedly contain as their active 
ingredients about 50 weight percent of polymers having molecular weights 
of about 75,000 to 80,000 , about 200,000 to 250,000, and about 20,000 to 
30,000, respectively. Another commercially available product of this type 
is Magnifloc 573C, which is marketed by American Cyanamide Company of New 
Jersey, U.S.A and is believed to contain as its active ingredient about 50 
weight percent of a polymer having a molecular weight of about 20,000 to 
30,000. 
In addition polyquaternary polymers derived from (a) an epihalohydrin or a 
diepoxide or a precursor thereof especially epichloro- or epibromo-hydrin, 
(b) an alkylamine having an epihalohydrin functionality of 2, especially a 
dialkylamine having 1 to 3 carbon atoms such as dimethylamine and (c) 
ammonia or an amine which has an epihalohydrin functionality greater than 
2 and which does not possess any carbonyl groups, especially a primary 
amine or a primary alkylene polyamine such as diethylaminobutylamine, 
dimethylamino propylamine and ethylene diamine. Such polymers can also be 
derived from a tertiary amine or a hydroxyalkylamine. Further details 
regarding such polymers are to be found in, for example, GB-A-2085433, 
U.S. Pat. No. 3,855,299 and U.S. Pat. No. Reissue No. 28,808. 
The following Examples further illustrate the present invention. These were 
carried out on a test rig, which has the following features: 
flowbox to continuously deliver synthetic or actual backwater onto a wire 
or a felt; 
dewatering elements including hydrofoils, vacuum rolls and vacuum knives; 
and 
spray showers to continuously spray polymers onto wires or felts. 
A paper machine forming wire or wet press felt is continuously rotated over 
three stainless steel rolls of which one is a vacuum roll (in the case of 
a wire the vacuum pump is switched off). Where the wire/felt is running 
horizontally, synthetic or actual back water is laid onto the wire/felt 
via a flow box. Before the flow box a double spray bar is fitted to spray 
the wire/felt while still moving in an upward direction. The two spray 
bars can be operated separately and are used to apply the anionic and 
cationic polymers. 
The two pitch types used in the experiments had the following 
characteristics: 
Pitch type I: mixture of tall oil fatty acids, having an anionic charge 
Pitch type II: glycerol esters, virtually nonionic in nature

EXAMPLE 1 
Rig runs were carried out using new wet press felts which were not 
pretreated by the manufacturer. All three felts were off-cuts of one 
standard paper machine felt and had therefore the same weave pattern. The 
manufacturer was Scapa-Porritt Ltd. of Cartmell Road, Blackburn, England, 
BB2 2SZ. 
The synthetic back water used had the following composition: 
______________________________________ 
Widnes tap water 99.800% 
Pitch type I 0.075% 
Pitch type II 0.025% 
Calcium chloride dihydrate 
0.100% 
______________________________________ 
Each run was carried out at a back water temperature of 50.degree. C. over 
a period of 6 hours. The felts were examined visually after the run and a 
qualitative assessment made. 
Three separate rig runs were performed: 
Blank run without any polymer (Run 1) 
Run using one spray bar for the application of a blend of cationic polymer 
(Superfloc C573 from American Cyanamid, an ethylenediamine, dimethylamine, 
epichlorhydrin condensate; MW approximately 20,000-30,000) and cationic 
surfactant (a C.sub.12,.sub.14,.sub.16 alkyldimethylbenzylammonium 
chloride blend) in a ratio of 1:1 (Run 2) 
Run using two spray bars, one for the same cationic blend as above and the 
other for an anionic polymer (sodium lignosulphonate) (Run 3) 
The results were as follows: 
RUN 1 
Heavy pitch deposits all over the felt. Large pitch agglomerates clogging 
the felt (microscopic evaluation). Pitch agglomerates unevenly distributed 
over and throughout the entire felt. First signs of pitch deposition 
already observed after 10 to 15 minutes running time of the felt. Pitch 
deposits were also noted in the flow box and on the stainless steel rolls. 
RUN 2 
Less pitch deposits. Pitch agglomerates were smaller and mainly on the 
surface of the felt, also unevenly distributed. First signs of pitch 
deposition were observed after approximately 2 hours running time of the 
felt. Still pitch deposits in the flow box but less deposits on the 
stainless steel rolls. 
RUN 3 
No pitch deposits on the felt at all. Even after 6 hours running time the 
felt was perfectly clean. There were still deposits in the flow box but 
hardly any pitch deposits on the stainless steel rolls. 
N.B. The deposits in the flow box were not prevented because the pitch did 
not get in contact with the polymers prior to the felt since none of the 
synthetic back water which left the flow box was recirculated. 
EXAMPLE 2 
Rig runs were carried out on off-cuts of one standard forming wire 
manufactured by Unaform Ltd. of Stubbins Vale Mill, Ramsbottom, Bury, 
Lancashire, England, BLO ONT. They had therefore the same weave pattern. 
The synthetic back water had the same composition as in Example 1. 
The following rig runs were made: 
Blank run not using any polymer (Run 1) 
Run using one spray bar for the application of a cationic polymer 
(Darasperse 7951 from Grace Dearborn Ltd, a dicyandiamide/formaldehyde 
condensate; MW approximately 5,000) (Run 2) 
Run using two spray bars, one for the application of the above cationic 
polymer and the other for an anionic polymer (sodium lignosulphonate), 
respectively (Run 3) 
Each run was carried out at a back water temperature of 50.degree. C. over 
a period of 6 hours. The wires were examined visually after the run and a 
qualitative assessment made. 
The results were as follows: 
RUN 1 
Heavy pitch deposits all over the wire. Large pitch agglomerates clogging 
the wire. Pitch agglomerates unevenly distributed over the entire wire. 
First signs of pitch deposition already observed after 10 to 15 minutes 
running time of the wire. Pitch deposits were also noted in the flow box 
and on the stainless steel rolls. 
RUN 2 
Less pitch deposits. Pitch agglomerates were smaller and also unevenly 
distributed over the wire. First signs of pitch deposition were observed 
after approximately 3 hours running time of the wire. Still pitch deposits 
in the flow box but less deposits on the stainless steel rolls. 
RUN 3 
No pitch deposits on the wire at all. Even after 6 hours running time the 
wire was perfectly clean. There were still deposits in the flow box but 
hardly any pitch deposits on the stainless steel rolls. 
N.B. The deposits in the flow box were not prevented because the pitch did 
not get in contact with the polymers prior to the wire since none of the 
synthetic back water which left the flow box was recirculated.