Paper making and fiber liberation – Processes and products – Conditioning – preparing or repairing of apparatus
Reexamination Certificate
1999-10-15
2001-10-16
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
Conditioning, preparing or repairing of apparatus
C162S168200, C162S168300, C162S165000, C162S166000, C162S183000, C162S164300, C162SDIG004, C162S168100
Reexamination Certificate
active
06303002
ABSTRACT:
The invention relates to a process for the production of paper, board and cardboard from paper stocks which contain tacky impurities by the addition of surfactants and cationic polymers having a charge density of at least 1.5 meq/g (measured at pH 7) and drainage of the paper stocks with fixation of the tacky impurities in the paper produced.
The process described above is disclosed in TAPPI Proceedings, Recycling Symposium 1994, 67-77. According to this publication, the polymers must have a charge density of at least 1.5 meq and a low molar mass of about 10,000.
U.S. Pat. No. 5 292 403 discloses a process for inhibiting the deposition of organic impurities in papermaking, a mixture of a charged polymer and an oppositely charged surfactant being added to the paper stock and the latter being drained.
WO-A-96/34913 discloses a process for inhibiting the deposition of pitch, cationically modified guar derivatives and a nonionic polymer being used.
DE-A-195 152 273 discloses a process for controlling the settling of tacky impurities from paper stock suspensions. The settling of the stickies is controlled by adding to the paper stock suspension an effective amount of an alkoxylation product which is obtainable by reacting alkylene oxides with OH-containing C
10
-C
22
-carboxylic acids or derivatives thereof.
EP-A-0 649 941 likewise discloses a process for controlling the settling of tacky impurities from paper stock suspensions. In order to inhibit the deposition of pitch, polymers which contain N-vinylformamide units, alkyl-substituted N-vinylcarboxamide units or the vinylamine units formed therefrom by hydrolysis are used.
Owing to the reuse of fibers from waste paper for the production of paper, board and cardboard, tacky impurities, i.e. stickies and white pitch (binders originating from paper coats) enter the water circulation of paper machines and thus cause production problems. The tacky impurities are preferentially deposited in wires, felts, rolls and other moving parts of the paper machine. These impurities furthermore impair the efficiency of the retention aids usually used in papermaking. As shown by the abovementioned prior art, the tacky impurities can, for example, be fixed in the paper produced. If the procedure is carried out in the absence of fixing agents as process assistance, various problems may occur. For example, defects form in the paper web, generally in the form of thin parts or even holes, which can cause tears in the paper machine as well as in the printing press.
Sources of interfering substances for stickies in addition to resins and lignin components, which are dissolved out of the wood in fiber production by boiling and mechanical treatment, are mainly dispersions of natural colloidal systems, such as starch, casein and dextrin, and hotmelt adhesives. Specifically, these are resins, lignin residues, adhesives from the gluing of book spines, adhesives from pressure-sensitive adhesive labels and envelopes and white pitch, i.e. binders from coatings and printing inks. During working up of fibers from waste paper, the tacky impurities are in most cases removed only to an insufficient extent from the mixture. In order to reduce the tack of the undesired impurities, substances having a large surface area, eg. talc, chalk or bentonite, have long been added to the paper stock. This is intended to reduce the tack of the tacky impurities substantially, cf. TAPPI Press-1990, Vol. 2, pages 508 and 512. However, the disadvantage of the tacky impurities treated in this manner is their sensitivity to shearing and the limited retention of these particles in papermaking. Occasionally used dispersants, such as ligninsulfonates, naphthalenesulfonates, nonylphenols or alkoxylated fatty alcohols, prevent an agglomeration of stickies to form particles having a size troublesome for the papermaking process, but severe frothing of the paper stocks occasionally occurs when these process assistants are used.
It is an object of the present invention to provide an improved process for the production of paper, board and cardboard, starting from paper stocks which contain interfering substances dissolved in water and water-insoluble tacky impurities.
We have found that this object is achieved, according to the invention, by a process for the production of paper, board and cardboard from paper stocks which contain tacky impurities by the addition of nonionic surfactants and cationic polymers having a charge density of at least 1.5 meq/g (measured at pH 7) to paper stocks and drainage of the paper stocks with fixation of the tacky impurities in the paper produced, if
polymers containing vinylamine units
water-soluble, crosslinked polyamidoamines
water-soluble, ethyleneimine-grafted, crosslinked polyamidoamines
uncrosslinked polyamidoamines
crosslinked polyethyleneimines
polydiallyldimethylammononium halides and/or
cationic polyacrylamides
dicyandiamide/formaldehyde condensates are used as cationic polymers and
if the molar mass M
w
of the cationic polymers is from 50,000 to 1 million.
The present invention furthermore relates to the use of from 0.005 to 0.5% by weight of nonionic surfactants and from 0.01 to 1.0% by weight of cationic polymers from the group consisting of
polymers containing vinylamine units
water-soluble, crosslinked polyamidoamines
water-soluble, ethyleneimine-grafted, crosslinked polyamidoamines
uncrosslinked polyamidoamines
crosslinked polyethyleneimines
polydiallyldimethylammononium halides and/or
cationic polyacrylamides
dicyandiamide/formaldehyde condensates having a molar mass M
w
of the cationic polymers of from 50,000 to 1 million
and a charge density of at least 1.5 meq/g (measured at pH 7), the data in % by weight in each case being based on dry paper stock, in the production of paper, board and cardboard as an additive in the paper stock for the fixation of interfering substances which are dissolved in water, and of water-insoluble tacky impurities, in the paper produced.
Suitable fibers for the production of the pulps are all qualities conventionally used for this purpose, for example mechanical pulp, bleached and unbleached chemical pulp and paper stocks from all annual plants. Mechanical pulp includes, for example groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semichemical pulp, high-yield chemical pulp and refiner mechanical pulp (RMP). Examples of suitable chemical pulps are sulfate, sulfite and soda pulps. The unbleached chemical pulps, which are also referred to as unbleached craft carrier pulp, are preferably used. Suitable annual plants for the production of paper stocks are, for example, rice, wheat, sugarcane and kenaf. Waste paper alone or as a mixture with other fibers is also used for the production of the pulps. Waste paper includes coated waste which, owing to the content of binders for coatings and printing inks, gives rise to white pitch. The adhesives originating from pressure-sensitive adhesive labels and envelopes and adhesives from the gluing of book spines as well as hotmelts give rise to the formation of stickies.
The stated fibers can be used alone or as a mixture with one another. The pulps of the type described above contain varying amounts of water-soluble and water-insoluble interfering substances. The interfering substances can be quantitatively determined, for example, with the aid of the COD or with the aid of cationic demand. Cationic demand is understood as meaning that amount of a cationic polymer which is necessary to bring a defined amount of white water to the isoelectric point. Since the cationic demand depends to a very great extent on the composition of the respective cationic polymer used for the determination, a condensate obtained according to Example 3 of DE-C-2 434 816 is used for standardization, said condensate being obtainable by grafting of a polyamidoamine of adipic acid and diethylenetriamine with ethyleneimine and subsequently crosslinking with a polyethylene glycol dichlorohydrin ether. The pulps containing interfering substances have, for example
Linhart Friedrich
Meixner Hubert
Melzer Jaroslav
BASF - Aktiengesellschaft
Fortuna Jose
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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