WO1995034716A1

WO1995034716A1 - Method for producing cellulose pulp and use of a compound in the method

Info

Publication number: WO1995034716A1
Application number: PCT/SE1995/000708
Authority: WO
Inventors: Svante WÅHLÉN; Ingmar Thebrin; Lisbeth Ankarbratt; Kerstin Malmborg
Original assignee: Eka Chemicals Ab
Priority date: 1994-06-15
Filing date: 1995-06-13
Publication date: 1995-12-21
Also published as: CA2191226A1; SE9402098D0; SE9402098L; FI965007A; SE510828C2; EP0765418A1; FI965007A0

Abstract

Cellulose pulp, which has a low tendency to give rise to static electricity when subjected to dry defibration and has retained its good wettability, is produced by adding an ammonium compound, which contains one quaternary nitrogen and one or two substituents, which contains a higher hydrocarbon group having 6-15 carbon atoms, and has an HLB value of 9-14 according to Davies, the quaternary nitrogen having been assigned the value +9.4, to wet or dry cellulose pulp in an amount of 0.1-5 kg/tonne of absolutely dry cellulose pulp.

Description

METHOD FOR PRODUCING CELLULOSE PULP AND USE OF A COMPOUND IN THE METHOD

The present invention relates to a method for pro¬ ducing cellulose pulp having good wettability as well as a low tendency to give rise to static electricity when sub¬ jected to dry defibration. This is achieved by the addition of a quaternary ammonium compound having an HLB value of 9- 14, preferably 9-12, as antistatic agent.

Dry defibration of cellulose pulp, resulting in a cotton-like material usually referred to as fluff, is a method used for making, among other things, various absorb¬ ing sanitary articles, such as napkins for babies or people suffering from incontinence, sanitary towels, medical towels and wound compresses. In addition, similar methods are em¬ ployed for making various sorts of dry-laid paper. The defibration is carried out with the aid of hammer mills, shredders, or the like. Usually, the cellulose pulp is con¬ tinuously fed in the form of a ribbon from a roll and to the defibrator. After the defibration, the cellulose pulp is blown, in the form of more or less laid-bare fibres borne by the air current, through a piping system to a forming de¬ vice, where the fibres are dewatered through a moving screen cloth to form a coherent fibre mat.

For reasons not fully understood, static electricity is generated in the defibration. The fibres thus laid bare may become highly charged, and charges of several dozen kilovolt have frequently been measured. Usually, the charges are positive relative to earth, but negative charges have also been measured in exceptional cases. Such electric charges often cause severe process disturbances. Thus, the fibres tend to spread in an uncontrolled fashion, which may create serious dusting problems, both in the machine itself and on the premises. Furthermore, it is quite common that the fibres get stuck in pipe bends in the defibrator, re¬ sulting in the formation of lumps of fibres, which then may come unstuck and thus produce an uneven fibre mat on the forming device. Moreover, there is a risk of dust explo¬ sions.

In order to reduce the inconvenience of static elec¬ tricity, one has recourse to various measures. Thus, one may increase the air humidity on the premises, spray the pulp with water, and add neutral salts to the pulp even in the pulp mill. In practice, these measures, which aim at in¬ creasing the electrical conductivity, have however proved to be insufficient in the dry defibration of cellulose pulp. It is further known to add cationic compounds, such as tertiary and quaternary ammonium compounds containing long-chain alkyl groups, to the cellulose pulp before or during the wet forming thereof to sheets, thereby facilitating the dry defibration of the pulp sheets (see, for instance, US Patent 3,554,862). However, this method is disadvantageous in that it impairs the wetting rate of the dry-defibrated pulp, which of course is undesirable in the case of absorbing products of the type at issue. Furthermore, it is known to use compounds of this type as antistatic agents in other contexts.

However, it has now been found that cellulose pulp, which has a low tendency to give rise to static electricity in dry defibration and has retained a good wettability or even obtained a slightly improved wettability, can be pro¬ duced by adding, to cellulose pulp in wet or dry state and per tonne of absolutely dry cellulose pulp, 0.1-5 kg of an ammonium compound containing one quaternary nitrogen and one or two substituents, which contain a higher hydrocarbon group with 6-15 carbon atoms, and having an HLB value of 9- 14 according to Davies, the quaternary nitrogen having been assigned the value 4-9.4. Preferably, the ammonium compound has an HLB value of 9-12 and most preferably 10-12. The higher hydrocarbon group can be aromatic as well as ali¬ phatic. Examples of such higher hydrocarbon groups are alkyl groups, such as hexyl, n-octyl, isooctyl, n-decyl and dode- cyl, and alkyl phenyl groups, such as butyl phenyl, octyl phenyl and nonyl phenyl. The remaining nitrogen substituents are lower alkyl groups having 5 carbon atoms at the most, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, iso- butyl and tertiary butyl, and organic oxygen-containing groups containing a hydroxyl, ether or ester group and one or more lower hydrocarbon group having 1-5 carbon atoms, and/or suitable oxygen-containing groups are hydroxyalkyl groups, such as hydroxyethyl, hydroxypropyl and alkoxilated hydroxyalkyl groups, and ether- and ester-containing groups, such as a alkyl(oxyalkylene)₀_₅glycidyl groups and carboxylic acid esters having hydroxyalkyl substituents, in which the hydrocarbon residues contain 1-5 carbon atoms. Preferred quaternary ammonium compounds are those which have an HLB value of 10-12 and contain one substituent containing the higher hydrocarbon group and the remaining three substitu¬ ents are the lower hydrocarbon groups and/or the organic oxygen-containing groups.

Examples of suitable compounds to be used in the method according to the invention are compounds having the general formula

R₂ - N⁺ - R₄ X^" (I) R₃ wherein one or two, preferably one of the groups R_1# R₂, R₃ and R₄ consist of a hydrocarbon group having 6-15 carbon atoms, preferably 8-12 carbon atoms, a group R₅(A)_nCH₂CH(OH)CH₂(A)_n(B)_r, wherein R₅ is a higher hydrocarbon group having 6-15 carbon atoms, preferably 8-12 carbon atoms, A is an oxyalkylene group having 2 or 3 carbon atoms, B is an oxyalkylene group having 1-5 carbon atoms, n is a number in the range of 0-5, preferably 0-3, and r is 0 or 1, and/or a group R₇(A)_nB, wherein R₇ is a higher acyl group having 6-15 carbon atoms, preferably 8-12 carbon atoms, and A, B and n have the significations indicated above, and the remaining groups R_lr R₂, R₃ and R₄ consist of a lower hydro¬ carbon group having 1-5 carbon atoms, a group having the formula H(A)_nB, wherein A, B, and n have the significations indicated above, a group R₈(A)_nCH₂CH(OH)CH₂(B) _r , wherein R₈ is a lower hydrocarbon group having 1-5 carbon atoms, or hydro¬ gen and/or a group R₉(A)_nB, wherein R₉ is a lower acyl group having 1-5 carbon atoms, and A, B and n have the significa¬ tions indicated above. Preferably, one or two of the groups R_{l t} R₂, R₃ and R₄ consist of a higher hydrocarbon group and/or the group R₅(A)_nCH₂CH(OH)CH₂(B)_r, wherein R₅, A, B and n have the significations indicated above, and the remaining groups R_lf R₂, R₃ and R₄ are lower alkyl groups having 1-5 carbon atoms, the group R₈(A)_nCH₂CH(OH)CH₂-(B)_r and/ or the group H(A)_nB, wherein A, B and n have the significations in¬ dicated above. Preferably, n and r are 0.

Examples of specific compounds encompassed by this formula are hexyl-, octyl- and decylglycidyltrimethyl ammonium chloride; octyl- and nonylphenyloxyethylene glyci- dyltri ethyl ammonium chloride, heptyl-, octyl-, decyl-, cocoalkyltrimethyl ammonium chloride, decyl-, dodecyldi- (hydrooxyethyl)methyl ammonium chloride, octanoyl-, de- canoyl- and dodecanoyloxyethyltrimethyl ammonium chloride; octanoyl-, decanoyl- and dodecanoyloxyethyldi(hydroxy- ethyl)methyl ammonium chloride; octanoyl- and decanoyloxy- propyldi(oxypropyl)methyl ammonium chloride or the corre¬ sponding methyl sulphate compounds. Advantageously, the quaternisation reaction may be carried out with ethylene oxide or propylene oxide in the presence of an organic or inorganic acid. If so, the quaternary compounds will contain a hydroxyethyl group or a hydroxypropyl group instead of the methyl group, as well as an anion based on the acid em¬ ployed.

The antistatic compound may be added to the cellulose pulp suspended in water before this is formed to wet sheets, or be sprayed on the pulp sheets before or after drying. In a preferred mode of implementation of the method, the anti¬ static agent is added by spraying or some other conventional means immediately before or during the dry defibration of the pulp. Such an addition is highly advantageous, enabling the amount added to be varied according to the degree of seriousness of the inconvenience in each separate defibra- tor. Regardless of when and where the antistatic agent is added, a preferred amount is 0.5-1.5 kg per tonne of abso¬ lutely dry pulp. Usually, the antistatic agent added is dis¬ solved in water. Optionally, pH-adjusting agents may be added.

The present invention will now be further elucidated with the aid of the following Examples.

Example 1

In a laboratory, dry test sheets of bleached sulphate pulp of softwood were produced in customary fashion. The sheets were sprayed with aqueous solutions of quaternary ammonium compounds, as accounted for in Table 1, and were weighed to verify that the amount sprayed on the sheets corresponded to one kilo of active substance per tonne of pulp. A corresponding blank was sprayed with clean water. After the final drying, the sheets were examined with re¬ spect to their strength properties (burst factor according to SCA -P 24:68). Then, the sheets were dry-defibrated to fluff, and their tendency to give rise to static electricity was measured. Finally, the wetting rate of the fluff was determined according to SCAN-C-33:80. In order to determine the tendency of the pulp to give rise to static electricity in dry defibration, use was made of measuring equipment com¬ prising a pin defibrator of laboratory scale and an electri¬ cally insulated screen cloth of bronze for collecting the laid-bare fibres to form a fluff pad. By an electric cable, the bronze wire was connected to the measuring head of a meter for static electricity. The meter was connected to a printer to enable continuous recordation of the procedure of the defibration of test-sheet strips. The HLB values of the ammonium compounds had been determined according to Davies. However, the quaternary nitrogen was, for want of the true value, in all cases assigned the value +9.4, which otherwise belongs to tertiary nitrogen. Since a quaternary nitrogen, but no tertiary nitrogen, is present in all cases, the relative order of the compounds is not affected by this. The results are indicated in Table 1 below.

Table l

Ammonium chloride compound Static Wet¬ HLB Burst poten¬ ting (Davies) factor tial time % of kVolt s blank

Blank 10 3.6 100

1 Hexylglycidyltrimethyl -2 3.4 12.00 100

2 Octyltrimethyl -1 3.3 11.17 100

3 Decyltrimethyl -1 3.3 10.22 95

4 Cocodi(hydroxyethyl) methyl -3 3.6 10.10 95

5 CocoaIkyltrimethyl -1 3.8 9.27 75

A Tri(hydroxyethy1)methy1 6 3.6 18.77 100

B Tetradecyltrimethyl -1 4.2 8.32 90

C Dioctyldimethyl -3 4.3 7.85 100

D Cetyltrimethyl -3 4.7 7.37 90

E Dodecyldimethylbenzyl -2 4.4 6.42 85

F Cocoalkyldimethylbenzyl -1 4.6 6.42 100

G Didecyldimethyl -5 5.9 5.95 70

H Tetradecyldimethyl -2 4.8 5.47 70

I Octadecyldimethylbenzyl -3 5.3 3.57 70

J Tallow alkylbenzyl -6 5.6 3.57 80

K Dioctadecyldimethyl -6 53.0 -0.95 45

It is evident from the Table that all the ammonium compounds tested have the capacity to reduce the static potential, which amounted to +10 kVolt in the blank. In some cases, one even obtained an undesirable, negative static potential. However, it also appears that the compounds have different effects on the wetting rate of the fluff. Thus, products having a lower HLB value have a clearly hydrophobic effect, which prolongs the wetting time. Products having an HLB value exceeding about 9 do not seem to have any adverse effect at all on the wettability, but rather have a slight favourable effect. Should the HLB value be too high, the favourable effect on the static electricity tends, however, to be impaired.

Example 2

In another series of tests, the quaternary ammonium compounds were added to the suspended cellulose pulp before this was formed to laboratory sheets. Also here, the amount added was one kilo of active substance per tonne of pulp. After the final drying, the sheets were examined as in Example 1. The results are indicated in Table 2 below.

Table 2

Ammonium chloride compound Static Wet¬ HLB Burst poten¬ ting factor tial time (Davies) % of kVolt s blank

Blank 10 3.6 100

2 Octyltrimethyl 1 3.3 11.17 100

5 Cocoalkyltrimethyl 0 3.6 9.27 90

A Tri(hydroxyethyl)methyl 7 3.6 18.77 100

H Tetradecyldimethyl - 1 4.2 5.47 80

J Tallow alkylbenzyl - 6 5.2 3.57 75

K Dioctatiecyldimethyl - 4 45.0 -0.95 58

These results agree well with those obtained in Example 1.

Claims

C L I M S

1. A method for producing cellulose pulp having a low tendency to give rise to static electricity when subjected to dry defibration, while maintaining the good wettability of the pulp, characterised in that an ammonium compound con¬ taining one quaternary nitrogen and one or two substituents, which contain a higher hydrocarbon group having 6-15 carbon atoms, and having an HLB value of 9-14 according to Davies, the quaternary nitrogen having been assigned the value +9.4, is added to wet or dry cellulose pulp in an amount of 0.1-5 kg/tonne of absolutely dry cellulose pulp.

2. A method as claimed in claim 1, characterised in that the remaining nitrogen substituents are lower hydrocarbon groups having 1-5 carbon atoms, and/or organic oxygen- containing groups which contain one or more lower hydro¬ carbon groups having 1-5 carbon atoms.

3. A method as claimed in claim 1-2, characterised in that the ammonium compound has an HLB value of 9-12 and has the formula

R₂ - N⁺ - R₄ X^" (I)

wherein one or two, preferably one of the groups R_{l t} R₂, R₃ and R₄ consist of a hydrocarbon group having 6-15 carbon atoms, preferably 8-12 carbon atoms, a group R₅(A)_nCH₂CH(OH)CH₂(A)_n(B)_r, wherein R₅ is a higher hydrocarbon group having 6-15 carbon atoms, preferably 8-12 carbon atoms, A is an oxyalkylene group having 2 or 3 carbon atoms, B is an oxyalkylene group having 1-5 carbon atoms, n is a number in the range of 0-5, preferably 0-3, and r is 0 or 1, and/or a group R₇(A)_nB, wherein R₇ is a higher acyl group having 6-15 carbon atoms, preferably 8-12 carbon atoms, and A, B and n have the significations indicated above; the remaining groups R_{l f} R₂, R₃ and R₄ consist of a lower hydro¬ carbon group having 1-5 carbon atoms, a group having the formula H(A)_nB, wherein A, B, and n have the significations indicated above, a group R₈(A)_nCH₂CH(OH)CH₂(B)_r, wherein R₈ is a lower hydrocarbon group having 1-5 carbon atoms, or hydro¬ gen and/or a group R₉(A)_nB, wherein R_s is a lower acyl group having 1-5 carbon atoms, and A, B and n have the signifi¬ cations indicated above; and X is an anion.

4. A method as claimed in claim 3, characterised in that one or two of the groups R_lf R₂, R₃ and R₄ consist of a higher hydrocarbon group and/or the group R₅(A)_nCH₂CH(OH)CH₂(B)_r, wherein R₅, A, B and n have the significations indicated above, and the remaining groups R_{l f} R₂, R₃ and R₄ consist of lower alkyl groups having 1-5 carbon atoms, the group R₈(A)_nCH₂CH(0H)CH₂(B)_r and/or the group H(A)_nB, wherein A, B and n have the significations indicated above.

5. A method as claimed in claim 3 or 4, characterised in that n and r are 0.

6. A method as claimed in any one of the preceding claims 1-5, characterised in that the ammonium compound have an HLB value of 10-12 and that one of the substituents con¬ tains the higher hydrocarbon group and the remaining three substituents are the lower hydrocarbon groups and/or the organic oxygen-containing groups.

7. A method as claimed in any one of the preceding claims 1-6, characterised in that the quaternary ammonium compound is added to cellulose pulp suspended in water.

8. A method as claimed in any one of the preceding claims 1-6, characterised in that the quaternary ammonium compound is sprayed on dried cellulose pulp, either before or in connection with the dry defibration thereof.

9. The use of a quaternary ammonium compound as claimed in any one of claims 1-9 for producing defibrated cellulose pulp.

10. Dry-defibrated cellulose pulp, characterised in that it has been produced from cellulose pulp obtained according to the method claimed in claims 1-8.