IE45319B1 - Method of controlling pitch in papermaking - Google Patents

Description

This invention is concerned with the control of pitch in papermaking.

Tha pitch in the fibers of wood pulps is associated with naturally occurring lignin dispersing agents. However, cooking and mechanical agitation which occur during the pulping by the sulfite process liberate the pitch but the natural dispersing agents liberated with the pitch are inadequate to keep the pitch from depositing, as a result of the mechanical work on the fibers, on the equipment employed in beating, hydrating, refining, bleaching, and even on the wire used for forming the sheet. Because of the tendency of the pitch to agglomerate within the pulp suspension or deposit on the surfaces of the wire or other equipment and then to break free in the form of particles of considerable sise, the pitch frequently causes the formation of spots or holes in the sheet formed or may adhere to the wire or press rolls or drier rolls and cause tearing to the sheet. This results In occasional tearing of the sheet during formation or in the production of sheets with numerous imperfections. Among other consequences involved are the expense of cleaning the machinery frequently, ϊ either with solvents or steam, and the loss of production ί during cleaning and during re-lacing operations caused by breakdown of the sheet.

?·' Ths most efficient prior pitch control agents are sodium ’ 25 salts, especially sodium salts of sulfonated naphthalenei .. formaldehyde condensate. The aforementioned pitch control agents are anionic which causes them to suffer from the disJ } I f a £ 319 - 3 advantage that when they are used in a system which contains cationic additives such as cationic wet strength resins, cationic sizing agents, cationic retention aids, cationic drainage aids, cationic dry strength resins, and the like, the anionic pitch control agents react and precipitate the cationic additives. Presently, when the paper system contains a cationic additive, either no pitch control agent is used, or one tries to em’lsify the pitch with surfactant, or one uses clay to detaekify pitch. Clay is cheap, but one must use large amounts of it to control pitch, often over 1% by weight based on pulp solids; furthermore, and more importantly, clay is a debonding agent and so can weaken the paper sheet, and also the pitch is non-dispersed and so can cause spots in the paper. A non-ionic pitch dispersant is disclosed in U.S. Patent No. 3,081,219 but a disadvantage of non-ionic dispersants is that they do not function to retain the pitch in the pulp.

Pitch has become more of a problem in recent years due to the growing tendency of mills to use high yield pulps Which are less pure than previously. The pulps are not cooked as long or washed as thoroughly, as in previous years, so the paper now contains increased levels of the pitch and other anionic pulpwood resins and rosin.

Another cause of increased pitch and other associated sticking problems is closed white water systems which have come into being because of ecological necessity. Another cause of increased pitch problems is the trend to cut logs into chips in the forest rather than at the mill, and so the chips are prepared while the log is still green, causing exuding. Another cause of increased pitch problems is the inclusion cf lower grade woods and fresher timber. «5319 - Λ We have now found a method of controlling pitch by which the pitch may be dispersed and deposited or retained in the pulp in finely divided form, without interfering with other additives which may be present in the pulp.

According to the invention there is provided a method of controlling pitch in paper-making which comprises incorporating in the pulp slurry from 0.01 to 0.5% by weight based on the pulp solids of a water soluble, linear cationic polymer containing units of the formula R wherein A is a (c2—C3) alkylene group, R is H or CH,; R is hydroxyethyl, hydroxypropyl, hydroxybutyl, hydrophenyl, 2 -· hydroxy - 3 - ehloropropyl, methyl, benzyl or allyl, R is a (C.—C.) alkyl group, 1 R is a (C^—cp alkyl group, and X is an anion; said polymer having a viscosity average molecular weight, M of from 35,000 to 70,000.

The pitch control additive in the invention can be introduced into the pulp at any stage of the pulping operation, including introduction prior to, or after digestion, during beating in the stock-chest, or even in the headbox of the paper making machine, but it will be understood that the polymer is added to the pulp at a stage prior to deposition of the pulp - 5 to form a sheet or web.

It is preferred to add the pitch control additive to the aqueous slurry of the pulp early in the pulping or papermaking stage before the pitch is coagulated by the mechanical work performed on the pulp during the papermaking operations.

The proportion of pitch control agent employed is from 0.01 to 0.5% by weight, preferably 0.02 tc 0.2% by weight, and most preferably 0.02 to 0.1% by weight, based on pulp solids.

The molecular weight of the polymers of the invention has been found to be surprisingly important with regard to their function as pitch control agents. The polymer has a viscosity average molecular weight of from 35,000 to 70,000, preferably from 40,000 to 60,000.

When the polymer M is greater than 70,000 it has been found that dispersing action is reduced and agglomeration occurs. In this case the polymer acts as a flocculant and flocculates the pitch particles as coarse globs, causing weak spots in the paper. When the polymer is less than 35,000 it has been found that retention of the dispersed pitch in the pulp is too low. In this case, the polymer acts as a dispersing agent and, instead of distributing the pitch as fine particles and retaining it in the paper, the pitch is retained in the white water system, resulting in clogging of the papermaking apparatus, such as the wires and felts. When the polymer is in the range specified it is believed that dispersing of the pitch occurs first, followed by retention of the pitch in the paper. Thus surprisingly, when the is within the above range, both dispersing and retention action occurs. - 6 4S319 The method of preparation of the polymers v?ill be apparent to the skilled chemist. For example, they may be prepared by directly polymerising an aminoalkyl ester of acrylic or methacrylic acid or their salts to form a homo5 polymer or a copolymer or any two or more such monomers and then quaternising the polymer. Alternatively the polymer may be prepared by quaternising' the aminoalkyl ester monomer prior to polymerisation. In either ease the aminoalkyl ester may be copolymerised with one or more other ethylenically unsaturated monomers.

The molecular weights defined above are achieved by control of the amount of initiator used in the polymerization. A preferred initiator system is ammonium persulfate combined with sodium metabisulfite, in preferred amounts of from 1.0 to 1.8% by weight of each, based on monomer charge.

The polymers can also contain units derived from one or more other ethylenically unsaturated monomers, such as vinyl esters of (C^—aliphatic acids, such as vinyl acetate, laurate, and stearate; esters of acrylic acid or methacrylic acid with (C,—C,-) alcohols, including (c,—0,-) alkanols, lo 1 io benzyl alcohol, cyclohexyl alcohol, and isobornyl alcohol, such as methyl acrylate or methacrylate, ethyl acrylate or methacrylate, butyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, octadecyl acrylate or methacrylate; vinyl aromatic hydrocarbons (e.g. styrene, isopropenyl toluene, and various dialkyl styrenes); acrylonitrile, methacrylonitrile, ethacrylonitrile, and phenylacrylonitrile; acrylamide, methacrylamide, ethacrylamide, N-methylol acrylamide, N-monoalkyl and -dialkyl acrylamides and methacryl30 amides, e.g. N-monomethyl, -ethyl, -propyl, -butyl, and Ndimethyl, -ethyl, -propyl, -butyl, alkacrylamides, e.g., Nmonophenyl- and -diphenyl -acrylamides and methacrylamides; - 7 vinyl ethers, such as butyl vinyl ether; N-vinyl lactams such as N-vinyl pyrrolidone; and olefins, such as ethylene fluorinated vinyl compounds, such as vinylidene fluoride; β-hydroxyethyl acrylate or methacrylate or any of the hydroxyl-containing or amine-containing monomers mentioned in columns 2 and 3 of U.S. Patent No. 3,150,112; vinyl chloride and vinylidene chloride; alkyl vinyl ketones; e.g., methyl vinyl ketone, ethyl vinyl ketone, and methyl isopropenyl kercne; ifcaconie diesters, e.g,, the dimethyl, diethyl, dipropyl, dibutyl and other saturated aliphatic monohydric alcohol diesters of itaconic acid, diphenyl itaconate, dibenzyl itaconate, di - (phenylethyl) itaconate; allyl and methallyl esters of saturated aliphatic monocarboxylic acid, e.g., allyl and methallyl acetates, allyl and methallyl propionates, allyl and methallyl valerates; vinyl thiophene; 4~vinyl pyridine; and vinyl pyrrole. In the monomer system from which the polymers of the invention are polymerized, preferably from 0 to 50% by weight of the monomer system comprises one or more of the above-mentioned other ethylenically unsaturated monomers.

The preferred other ethylenically unsaturated monomers are methyl methacrylate, methyl acrylate, ethyl acrylate, isobutyl acrylate, secondary butyl acrylate, butyl acrylate, hydroxyethyl methacrylate, vinyl acetate, styrene, and acrylonitrile.

The polymers are either partially or fully quaternized with a quaternizing agent. Preferably the polymers are at least 50% quaternized; more preferably at least 80% quaternized, and most preferably about 100% quaternized.

Preferred quaternization agents are alkylene oxides and active halides. Examples of alkylene oxides are ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and 43319 - 8 epichlorohydrin. Examples of active halides are methyl halides such as methyl chloride, bromide and iodide; benzyl halides such as benzyl chloride and allyl halides such as allyl chloride.

The anion in the polymers of the invention, represented in the formula as X, is preferably an anion such as acetate, formate, lactate, citrate, propionate, glycolate, sulfate, oxalate, nitrate, or halide.

The following examples illustrate the preparation of polymers suitable for use in this invention (Examples 1—4) and the preparation of comparative polymers outside the scope of the invention (Examples 5—7). Example 8 contrasts the performance of such polymers. In the Examples all parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 This example illustrates the preparation of a homopolymer of N,N - dimethyl - N - (β - hydroxyethyl) - N - (β - methaeryloxyethyl)ammonium acetate having a molecular weight (viscosity average) of 46,000 as determined by formula from an intrinsic viscosity measured as 0.101. 1925 parts glacial acetic acid, 6049 parts deionized water and 285.6 parts of 0.15% aqueous FeSO^ . H20 are charged to a pressure kettle. The kettle charge is deoxygenated with Ν2, heated to 6O°C., and the following materials are charged over a 3 hour period; 4781 parts dimethylaminoethyl methacrylate, 97.51 parts ammonium persulfate in 1162.49 parts deionized water, and 97.51 parts sodium metabisulfite in 1162.49 parts deionized water. The temperature is held at 60°C. for another 30 minutes, then lowered to 40°C. at which temperature 1406.9 parts ethylene oxide is gradually added. The resultant product is a clear aniber liquid having a Brookfield viscosity of 370—430 cps., and a 43319 - 9 pH of 6.5—7.0.

EXAMPLE 2 The procedure of Example I is repeated except replacing the 1925 parts glacial acetic acid with a respective one of the following: A. 2890 parts lactic acid 3. 2440 parts glycolic acid C. 1478 parts formic a cid D. 2361 parts propionic acid E. 1168 parts hydrochloric acid F. 2019 parts nitric acid G. 2885 parts oxalic acid H. 1571 parts sulfuric acid I. 6156 parts citric acid.

EXAMPLE 3 Following the procedure of Example 1, a copolymer of methyl acrylate with N,N - dimethyl - N - (β - hydroxypropyl)N - (β - methacryloxyethyl)ammonium acetate, quaternized with epichlorohydrin, having an M^ of 60,000, is prepared.

The weight ratio of methyl acrylate units to N,N - dimethylN - (β - hydroxypropyl) - N - (β - methacryloxyethyl)ammonium acetate units is 0.25.

EXAMPLE 4 The procedures of Example 3 is repeated except the following respective amounts of the following ethylenically unsaturated monomers are substituted for the methyl acrylate.

A. 30% methyl methacrylate B. 25% acrylonitrile C. 50% ethyl acrylate D. 20% styrene E. 25% hydroxyethyl acrylate - 10 F. 20% secondary butyl acrylate G. 30% butyl acrylate EXAMPLE 5 (Comparative) The procedure of Example 1 is repeated except, by increasing the amount of ammonium persulfate and sodium metabisulfite catalyst to 2.00% each, the molecular weight of the polymer is reduced to 29,000 (intrinsic viscosity= 0.068).

EXAMPLE 6 (Comparative) The procedure of Example 1 is repeated except by decreasing·the amount of ammonium persulfate and sodium metabisulfite catalyst to 0.68% each, the polymer molecular weight is increased to 72,000 (intrinsic viscosity=0.150).

EXAMPLE 7 (Comparative) The procedure of Example 1 is repeated except by increasing the amount of ammonium persulfate and sodium metabisulfite catalyst to 2.72% each, the molecular weight is decreased to 22,000 (intrinsic viscosity=0.053).

EXAMPLE 8 This example shows the effect of the pitch control agents of the invention, and the improved performance of the pitch control agents of the invention versus certain closely related materials which are outside the invention. In this experiment bleached sulfite pulp in the dry form or state (unbeaten, 65OCSF) is treated with synthetic pitch (0.5 ml. Mobil 600 W per 45 grams pulp at 15°C.). (Mobil is a Registered Trade Mark). The oil contains fatty resin acids which simulate natural pitch. -45319 - Il TAPPI test method RC-324 is used to determine the amount of pitch deposited in the pulps.

The paper produced in the experiments is examined under ultraviolet light to determine the appearance of the pitch in the paper.

The results shown in Table I demonstrate the importance of molecular weight, of the pitch control additive polymer in order ro achieve hath pitch reduction, dispersion into very fine particles, and retention in the pulp.

TABLE 1 Additive of Example No. % Additive by Weight Based on Pulp Solids Deposited Pitch % Pitch Reduction Appearance of Treated Paper (U. V.) None - 37 mgs. - - 6 0.25% 6.8 81 Large agglomerates of Pitch in sheet 6 0.10% 9,2 75 Large agglomerates of Pitch in sheet 1 0.25% 6.3 S3 Very fine particles—Good retention 1 0.10% 7.9 79 Very fine particles—Good retention ς 0.25% 8.6 77 very fine particles—Poor retention 7 0.25% 11.3 69 Very fine particles—Poor retention

Claims (7)

1. A method of controlling pitch in papermaking which comprises incorporating in the pulp slurry from 0.01 to 0.5% by weight based on the pulp solids of a water soluble, linear cationic polymer containing units of the formula: —CH_ 0=C-0—A—©N r R“ R' 3 s „2 wherein A is a (C^—C g ) alkylene group, R is H or CH_, R is hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxy phenyl, 2 - hydroxy - 3 - chloropropyl, methyl, benzyl or allyl, R is a (.c 7 —C.) alkyl group, 3 1 R is a (c.—C,) alkyl group, and JL X is an anion; said polymer having a viscosity average molecular weight of from 35,000 to 70,000.

2. A method as claimed in Claim 1 hydroxyethyl or hydroxypropyl. wherein R 1 . is 20

3. A method as claimed in Claim 1 or 2 wherein the polymer also contains units derived from one or more other ethylenically unsaturated monomers.

4. A method as claimed in Claim 3 wherein said other ethylenically unsaturated monomer(s) comprises one or more of: vinyl esters of (C^—C lg ) aliphatic acids; esters of acrylic acid and/or methacrylic acid with (C.—C 1O ) alcohols; vinyl aromatic hydrocarbons and/or acrylonitrile. - 13

5. A method as claimed in any of Claims 1 to 4 wherein X is acetate, formate, lactate, citrate, propionate, glycolate, sulfate, oxalate, nitrate or halide.

6. A method as claimed in any preceding claim wherein 5 the polymer has a viscosity average molecular weight of from 40,000 to 60,000.

7. A method as claimed in any preceding claim wherein the amount of polymer is from 0.02 to 0.2% by weight based on pulp solids.