CA1145107A - Procedure for forming refiner pulps - Google Patents
Procedure for forming refiner pulpsInfo
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- CA1145107A CA1145107A CA000356028A CA356028A CA1145107A CA 1145107 A CA1145107 A CA 1145107A CA 000356028 A CA000356028 A CA 000356028A CA 356028 A CA356028 A CA 356028A CA 1145107 A CA1145107 A CA 1145107A
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- pulp
- treatment
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- weight
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C3/00—Pulping cellulose-containing materials
- D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
- D21C3/06—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites sulfites
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Abstract
ABSTRACT OF THE DISCLOSURE
Refiner mechanical pulp, in the form of RMP or TMP, of improved properties suitable for substitution for chemical pulp, especially in newsprint furnish, is obtained in a sub-stantially pollutant-free process by subjecting the pulp, between the stages of refining, to chemical treatment using sodium sulphite solution to result in increased wet stretch and stress-strain properties while retaining high drainage and avoiding substantial yield loss. Strength properties of dried paper are enhanced and energy requirements to obtain improved pulp quality in the second stage of refining are less.
Refiner mechanical pulp, in the form of RMP or TMP, of improved properties suitable for substitution for chemical pulp, especially in newsprint furnish, is obtained in a sub-stantially pollutant-free process by subjecting the pulp, between the stages of refining, to chemical treatment using sodium sulphite solution to result in increased wet stretch and stress-strain properties while retaining high drainage and avoiding substantial yield loss. Strength properties of dried paper are enhanced and energy requirements to obtain improved pulp quality in the second stage of refining are less.
Description
11~51(~7 IMPROVED PROCEDURE FOR FORMING REFINER PULPS
The present invention is directed to the formation of impxoved mechanical wood pulps useful for substitution for chemical pulps.
The term "mechanical pulp" as used herein has its normal meaning in the art and refers to the product of disruption of a woody substance by mechanical action to yield a product consisting mainly of liberated and separated single woody fibres and their fragments and which is suitable for use in the manufacture of paper.
The term "fibre" as used herein also has its normal meaning in the art and refers to individual plant cells which make up *he woody material and which, in softwoods, are known botanically as parenchyma cells and tracheids. These fibres inherently have diameters generally below 0.05 mm and in the case of wood species commonly used in pulp formation ~nd paper making, such as, spruce, balsam, pine, aspen and poplar, considerably below ~05 mm.
"Refiner pulps" are a class of mechanical pulps formed by passing particulated cellulosic fibrous material, usually - wood chips through a small gap betwean two ribbed parallel , plates rotating with respect to each other (known as a disc refiner). The procedure may be effected at atmosph?sric pressure, the product being known as "refinèr mechanical pulp"
2S (RMP), or under pressure, typically about 1 to 2 atmospheres greater than atmospheric pressure, and at elevated temperature, such as, about 120C, the product being known as "thermo-mechanical pUlp~? ~TMP). The refining process usually is effe?~-ted in two stages. In the first stage, the fibres are separated and liberated and in the second stage, additional refining energy is supplied to increase the fibre flexibility and conformability, fibrillation and bonding. Usually about . .
.
. .
,~ :
.
-11~51~7 half the overall refining energy of about 100 to about 120horsepower-days per ton is applied to the f~IEr~ration stage.
Because mechanical wood pulps can be made in yields over 95% with minimal pollution problems, there is strong 5 incentive to increase their usage in paper manufacture.
In general, however, it is not possible to transport a sheet, formed entirely of mechanical pulp, at high speed through the forming, pressing, drying and reeling sections of the paper making machine, without an unacceptable number of 10 breaks. Chemical pulp is usually added to the furnish to improve its machine runnability. Traditionally newsprint is manufactured from a furnish consisting of about three parts groundwood or other mechanical pulp and one part chemical pulp.
"Runability" refers to that combination of properties which allows the wet web to be transported at high speed through the forming, pressing and drying sections of the r paper making machine and allows the dry sheet to be reeled and printed with not more than an acceptable number of breaks.
20 In effect, runability is a measure of the efficiency with which the paper passes through the paper machine and printing press.
The chemical pulp component is usually manufactured by the kraft or sulphite process in yields ranging from about 45 to 65%. Chemical pulps are expensive, make heavy demands 25 on the mills wood resources, and entail formidable pollution problems. As already noted, mechanical wood pulps are obtained in yields in excess of 95% with minimal pollution problems.
Despite all the disadvantages associated with the use 30 o~ chemical pulps, they are generally employed in making news-print because runability is the key ~o paper making machine and press-room efficiency, which in turn i9 the key to profit-ability.
In accordance with this invention, there is provided 35 a process for the formation of an improved refiner pulp which is suitable for use as a replacement for chemical pulps in many applications, including newsprint furnish.
, ~1~5107 The process of this invention results in an increase in the elongation to rupture (hereinater known as "wet stretchi'~ and an improvement in the stress-strain properties of the wet web formed from the pulp, while simultaneously maintaining rapid drainage. We have discovered a hitherto unknown phenomenon that high wet stretch and ~igh wet stress-strain characteristics, in combination with rapid drainage, are the fundamental pulp properties which impro~e the runability of a newsprint ~urnish.
The fibre-to-fibre bonding within a dry paper sheet formed from the pulp produced by the process of the invention is impro~ed, thereby resulting in the desirable properties of increased tensile and burst strengths and increased shaet density.
One important feature of this invention is that there is formed a refiner ~ulp which ca~ be used as a substitute, in whole or in part, for chemical pulp in many of its applications and which results from a procedure which does not produce more than insignificant quantities of pollu-20 ting effluents, in complete contrast to chemical pulping pro- !
cedures,where large quantities of polluting effluents must be handled. The overall energy requirements of the refining operation to provide a predetermined level of pulp quality also are decreased, as compared with the conventional refiner pulp-formation operation.
The process of the invention comprises three steps, namely (a) subjecting particulated cellulosic fibrous mater-ial to mechanical action in a disc refiner to form a pulp consisting mainly of single fibres and fragments thereof, 30 (b) chemical reaation of the pulp with a soluble salt of sulfurous acid under certain precise elevated temperature and pressure conditions as detailed below, and (c) subjecting the chemically-treated pulp to mechanical action to refine the same and improve the pulp quality.
The cellulosic fibrous material species and refining conditions required to manufacture a usable mechanical pulp are well known to the art. For example, it is well known that most hardwoods cannot be refined to yield ~echanical .
- - -.
, 11~5107 pulps with adequate strengths. Application of the invention is restricted to refiner pulps which are generated from soft-woods, or other cellulosic fibrous material species which are recognized in the industry as being suitable for the prepara-tion of refiner pulps. The invention is described furtherwith particular reference to wood species.
The three individual steps comprising the proces of the invention are discussed separately below:
STEP (a) Fibre Separation A wood fibre consists essentially of a cell wall, whose outer surface is made up of cellulose-rich fibrillar layers known as the Sl and S2 layers. In wood, the space between the fibres, known as the middle lamellae, is filled with a lignin-rich material.
lS The process of the invention requires that, in the initial liberation of the ibre from the wood in a disc refiner, the fracture occurs mainly in the Sl and S2 layers, thus exposing the cellulose-rich fibrillar material which is the source of the fibrillation characteristic of a good mech-20 anical pulp. Since this fibre morphology is established at - the moment of fibre liberation, it is necessary that the pro-cess of fibre liberation proceed largely to completion.
Therefore, the product of the initial mechanical fibre separa-tion step of the proce~s of the invention must consist mainly 25 of single wood fibres, which inherently have average diameters less than 0.05 mm. More than the minimum energy to accomplish this separation may be applied, but is unnecessary.
It is well known that, in thermomechanical pulping, if the refining temperatuxe exceeds the thermal softening 30 point of lignin, fibre separation occurs in the middle lamellae to yield a smooth fibre with a lignin-rich surface.
This fibre i8 difficult or impossible to fibrillate by further refining and is generally unsuitable for use as a mechanical pulp. Hence the initial fibre separation step 35 in this invention is effected at a temperature below the thermal softening point of lignin. The latter temperature is .. . .
. . .
il~5107 s variable with the wood species, duration of heating and re-fining conditions, but is generally below about 150C.
Attempts have been made to decrease the energy required for fibre separation and improve pulp quality by a chemical softening of the wood prior to refining. Such a process, 5 using sulphite as the treating chemical, is disclosed in U.S.
Patent No. 4,116,758. The products of the latter process are smooth walled fibres showing little tendency to fibrillation, similar to those described abo~e resulting from refining above the lignin softening temperature, and are unsuitable for use 10 as a mechanical pulp in this invention.
It is within the scope of this invention, however, to add the chemicals required in the subsequent treatment step to the wood chips prior to their entering the disc refiner, pro, vided that the temperature and time of contact is such that 15 no substantial reaction occurs and no significant chemical softening of the chips results. The disc refiner acts as an e~ficient mixer of the pulp and chemicals at the high con-sistency normally encountered.
It is also withi~ the scope of the invention to 20 subject the wood chips, prior to refining, to steam under pressure at a temperature below the thermal softening tempera--ture of the lignin, typically below about 140C in accordance with conventional industrial practice in TMæ manufacture.
A product of step (a), suitable for further treatment 25 in accordance with this invention, is obtainable simply by following the first stage refining procedures well known to the art, for the production of a good mechanical pulp. This is usually accomplished by presteaming wood chips, usually at a temperature of about 120~ to about 135C and 1 to 2 30 atmospheres pressure for 2 to 10 minutes, then passing the presteamed wood chips, which have not been softened by chemical action, through a disc refiner at a temperature below the thermal softening temperature of the lignin, and applying sufficient refining energy to yield a mechanical wood pulp 35 consisting mostly of single fibres and their fragments, such fibres and fragments being predominantly below 0.05 mm'in average diameter. This operation is generally effected at a :
' 11~5i~7 consistency of about 10 to about 40% by weight, usually about 25 to 30% by weight.
STEP (b) Chemical Reaction After the required physical form of the wood fibre is obtained in step (a), the chemical nature of the fibre is modified by reaction with an aqueous solution of a soluble : salt o~ sulphurous acid, usually sodium sulphite. The reac-tion is effected at temperatures above about 110C under a superatmospheric pressure for a time sufficient to yield a chemically-treated mechanical wood pulp capable of forming a paper web having improved wet stretch and stress-strain properties and exhibiting rapid drainage, but for a time in-sufficient to cause s~stantial dissolution of lignin with consequent loss of yield and generation of polluting ef~luents. The exact nature of the chemical reactions in-volved in the chemical treatment effected in this invention are not fully understood, but are thought to involve sulphon-ation.
During the reaction, the pH of the solution drops and alkali is consumed. It is essential to the process of the present invention that sufficient alkali be present in the chemical charge to prevent a pH drop below 3 during treatment, otherwise there is a risk of damaging the fibres through hydrolytic action with consequent loss of strength. The exact amount of alkali required varies according to the acetyl content of the wood supply and cannot ~e specified exactly, but is readily established by experimentationO
The alkali re~uirement may ~e met entirely with sodium sulphite. However, since only half of the sodium of sodium sulphite is available for neutralization, it is usually more economical to meet part of the alkali require-ments by additions of sodium hydroxide or sodium carbonate.
The pH of the mixture, however, is preferably kept below about 12 because hemicelluloses are dissolved from wood fibre by higher pH's r with consequent loss in yield.
.
In a preferred embodiment of the invention, the amount of sodium sulphite used in the chemical treatment is in the range of about 4% to about 15~ by weight based on the mechanical wood pulp resulting from step (a), although 5 lower concentrations down to about 1% by weight may be used with reduced beneficial effect, with the provision that the residual sulphite content of the mixture, as measured iodi-metrically, does not fall substantially to zero before termination of the reaction. Below 1% by weight of sodium 10 sulphite,improvements are too small to justify the expense of treatment. Similarly improvements are observed with chemical charges up to about 25% by weight of the pulp, but the additional cost is not justified by the small additional improvement. Generally, therefore, a chemical charge of 15 between about 1~ and about 25% by weight, preferably between about 4~ and about 15% by weight, of the mechanical pulp, is used. The chemical charge preferably has a pH between about T and about 12, and contains sodium sulphite and sufficient alkali to maintain a pH greater than 3 throughout the 20 reaction.
The reactions of sulphite with wood are known to consist of a large number of different reactions, whose rates are dependent on reaction conditions, particularly pH and temperature. The present state of our knowledge of 25 this complex subject has been summarized by G. Gellerstedt in Svensk Papperstidning nr. 16, 1976, p. 537 to 543.
It has been established that the reactions necessary for the application of the process of the invention and the results attained thereby are those that proceed at pH I 8 30 greater than 3 and pre~erably over 7, and at temperatures over about 110C, and preferably over about 130C. Other reactions of woody substances with sulphite which proceed at lower pH's and at temperatures below lQ0C are known, such as those described by H.~. Kvisgaard in Norsk 35 Skogindustri 1~, no. 4, 1965, p,155-163. Such reactions, however, are not ef~ective to produce an improvement in wet and dry properties, in fibre flexihility and consolidàtion and in power requirements, such as is contemplated in this invention.
11451~)7 We have found that the maximum improvement, namely, maximum increase in wet stretch, maximum improvement in stress-strain, maximum increase in strength characteristics, and maximum decrease in refiner power requirements for the 5 second stage (step ~c) discussed below~, is obtained from the process of the invention when the mechanical pulp ~rom step (a) with adaed chemical is heate~ at about 160C for 30 minutes. As with any other chemical reaction, the temper-ature can be lowered if the reaction time is increased.
10 Below about 120C, reaction time becomes impractically long, and below liOC, the required reactions effectively cease.
Similarly, the reaction temperature can be increased if the reaction time is shortened. The practical upper limit of temperature appears to be about 200C with reaction times 15 of 1 to 2 minutes. We prefer not to operate under these extreme conditions because the precise control of conditions and reaction times needed to achieve an optimum product are difficult to secure.
It is also possible to operate at shorter or longer than the optimum reaction times to produce a less than optimum but still useful result. If the reaction time is shorter than optimum, the improvements in wet stretch, stress-strain and strength properties and energy requirements are less than may be otherwise obtained by operating under optimum conditions. If the reaction time is too long, substantial dissolution o~ the lignin from the pulp, in the treating chemical occurs, with consequent loss of yield and formation of polluting effluent. While the process is still operable to produce property improvements under these condi-tiong gome of the advantages of wood economy and low~ollution are lost and generally are avoided.
The chemical treatment is operable over a time-temperature range from about lLoC for about 12 hours to about 200C for about 1 minute. It is understood that an increase in temperature must be accompanied by a concomit-tant decrease in reaction time. For example, the process is not operable at a temperature of 200C for 12 hours.
To derive maximum benefits from the chemical treatment step, ll~SlV7 it is preferred to operate in the more limited range of about 130C for about 2 hours to about 180C for about 15 minutes.
Because of uncertainties in specifying the exact upper limits of the chemical treatment step in terms of 5 time and temperature, it is considered more useful and precise to specify the upper limit in terms of the effect of the chemical treatment on pulp yield therefrom. Reaction conditions which decrease the yield, based on mechanical wood pulp, below about 85% are outside the scope of our process, lO since wood losses and the pollution capability of the spent aqueous phase become significant and intolerable beyond this limit. It is preferred to select maximum reaction conditions such that the yield of treated pulp is greater than about 90%.
The exact conditions required vary with wood species, chemical lS charge and consistency, but will fall within the limits of time and temperature as defined above, and are easily estab-lished by experimentation.
The chemical reaction which is effected in step (b) on the mechanical wood pulp resulting from step (a) is quite 20 distinct from the methods used in the pulping of woody sub-stances with sulphite or bisulphite to form chemical pulp. In sulphite pulping, heat and chemical are supplied to the woody material in chip form ti-e., fibre bundles) by circulating hot cooking liquor through a bed of the woody ~,aterial. With the 2S mechanical pulp produced in step (a~ of the process of the invention, the resistance to 10w of liquor is so great that circulation of liquor therethrough is impractical. In con-sequence, all of the chemical required to effect the reaction of step (b) must be incorporated in the pulp when it entexs 30 the reactor. It is advantageous to incorporate the chemical in solution in a volume of water which can be totally absorbed by the pulp. In practice this means that the consistency after chemical addition normally should be above about 15%
by weight. Consistencies below about 50% by weight are pre-35 ferred because it is easier to secure uniform mixing ofchemical and pulp below that level. The consistency range of about 15% to about 50~ by wei~ht, therefore, is preferred for reasons of convenience, but the operability of the process is not limited by consistency.
. ... .. . ., ~ . . .. . . . . . . . .
:, 51S~7 The chemical treatment step in the process of the invention i5 also distinguished from chemical pulping process-es in that the process of the invention cannot be oonducted prac~ically in a ba1:ch process,such as is used in chemical pulping. ~his is because the thermal insulating properties of the mechanical pu:Lp are so high that a large pulp mass cannot be heated `~ to reaction temperature by conduction in a reasonable length of time. The chemica1 treatment may be carried out batch-wise using dielectric or microwave heating techniques but such methods are expensive. It is preferred to carry out the chemical reaction step in an apparatus wherein pulp is continuously raised to reaction temperature and introduced into one end of a reaction vessel of such size as to provide the desired reaction duration, while treated pulp is lS removed simultaneously from the other end.
Step (c) Refining In the third, and final, step of the process of the invention, the product of step (c~ is subjected to further refining action in a disc refiner, following the usual practice of the industry for second stage refining of a mechanical wood pulp. The results of this second refinir.g action differ from those obtained with an ordinary mechanical wood pulp because the application of steps La~
and ~b~ in accordance with this invention places the pulp in the required physical and chemical configuration to utilize further refining energy efficiently and economically.
It is well known that the quality of a mechanical wood pulp can be improved by increased refining, but at a cost of -~~~~ ~~~ ` slower drainage and increased enërgy demand~ The product of step ~b) may be refined to equivalent quality with significantly less energy, while achieving a faster drainage, as compared to mechanical pulp from step (a) which has not been subjected to step (b~. These results are illustrated graphically in Figure 1, in which a measure of pulp quality is plotted against refining power for two cases. The measure of pulp quality employed was the tensile strength of the wet web, measured at 5~ wet stretch to eliminate the effects o pulp latency. Similar plots are obtained using such other measures of pulp quality as breaking length or burst factor.
~145107 Point A in Figure 1 defines the state of the pulp at the completion of step (a) of the process of the invention.
Point B represents the same pulp after completion of step (b~. The line B-C gives the properties of the pulps derived 5 from step (b~ by the application of varying amounts of refining energy in accordance with step (cJ of the process of the invention. The line A-D represents the properties ~f pUlpe obt~ined by directly refining the product of step (a~, without the application of step (b). The dramatic 10 effect of the chemical treatment of step (bl in improving the drainage of refined pulp, as measured by Canadian Standard Freeness (C.S.F.), in increasing the pulp strength, . .
and in decreasing the energy requirements in the appli-cation of the refining o step ~c) is clearly e~ident from 15 the graphical representation of Figure 1.
The consistencies employed in the application of step (c) may be varied over the range normally employed in the second stage refining of a mechanical wood pulp, but the properties of the product depend to some extent on the refin-20 ing consistency chosen. Higher consistencies over about 20by weight yield products with higher wet stretch while lower consistencies tend to produce pulps with higher strength.
By adjustments in refinin~ consistency, the desired balance between wet stretch and strength for a particular application 25 can be achieved. For most applications, it is preferred to carry out the refining step (c) at consistencies between about 1% and about 35% by welght.
The amount o~ energy applied in step Cc~ may be varied according to the desired properties of the product and 30 the intended end use. The degree o~ refining to which the pulp is subjected is usually controlled by the freeness of the finished pulp. For most applications, this freeness should fall within the range of about 50 to about 700 C.S.F. For example, boxboard stock is typically of higher 3~ freeness than magazine grade paper stock. For newsprint application, it is preferred to refine to a freeness in the range about 100 to about 400 C.S.F. in step ~c2.
. ~
The invention is illustrated by the following Examples:
Exam_le 1 Spruce chips were pre-steamed for 25 minutes at 35 psig and fed to a 1000 HP Sprout-Waldron 36 ICP refiner under the following conditions:
Throughput: - 25.0 tons per day Discharge consistency: 25 - 30%
Specific energy: 45 horsepower-days per ton The pulp from the pressurized refiner, consisting mainly of single fibers, and substantially free of particles greater than 0.05 mm in diameter, was divided in three portions.
One portion was mixed with 10% by weight of sodium sulphite at pH 9 and heated at 18% consistency at 90C for 1 hour.
15 Another portion was mixed with 10% sodium sulphite at pH 7 and heated at 18% consistency and 160C under a pressure of 75 psig for 1 hour. A third portion was untreated. Each portion was then refined further in a 12 inch Sprout-Waldron open ischarge refiner at 18% consistency and a specific 20 energy input at 63 horsepower-days per ton. All three pulps thus received a total of 113 horsepower-days per ton of refining energy.
The usual practice in mechanical pulping is to remove latency prior to screening, cleaning and final use. This pro-25 cedure was explained by L. R. Beath, M. T. Neill and F. A.Masse in an arti~le entitled "Latency in Mechanical Pulps", Pulp and Paper Magazine of Cànada 67 (10)T423(1966). To correspond to this common industrial practice, latency was removed from our pulps by treatment at 90C for 15 minutes, 30 prior to testing. The properties of these pulps are compared ln the following Table I:
, ' .' ~
11~5107 TABLE I
T~eatment None 90C 160C
Yield, % 100 98 93 Freeness 194 197 80 Drainage, sec. 0.83 0.93 2.16 .
Wet tensile, N/m 62 63 75 Wet s`tretch, % 3.3 3.7 5.3 Wet caliper, mm 0.344 0.353 0.302 Bulk 2.68 2.57 2.12 Burst 16 17 23 Breaking Length 3100 3300 5100 Using the same total refining power, the untreated sample and the sample treated at 90C refined to essentially the same ~reeness with insignificant differences in wet and dry properties. By contrast, the sample treated at 160C
' refined to lower freeness with the same power, yielding over 60% increases in wet stretch and breaking length, as well as significant increases in wet tensile strength and burst. The drainage rate is much faster than an untreated TMP
of similar quality.
The wet caliper and bulk are measures of the fiber's ability to consolidate in the paper sheet. The low values obtained with the pulp treated at 160C arè indicative of a flexible fiber which consolidates well to form a dense, coherent sheet.
Example 2 A TMP prepared in a pressurized refiner as described in Example 1 was mixed with 10% sodium sulphite at pH 9.0 and heated at 18% consistency at 160C and 75 psig for 1 hour.
Samples of the treated and untreated TMP were then refined to comparable freeness levels, and the pulp properties measured after latency removal at 90C for 15 minutes. Power consumptions and the corresponding pulp properties are out-lined in the followlng Table II:
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. -, ' ~ .
TABLE II
Untreated Treated Untreated Treated Power, HPD/T 126 101 101 82 Freeness 107 118 305 331 Drainage, sec. 1.27 1.63 0.66 0.83 -Wet tensile, N~m 58 77 59 76 Wet stretch, % 4.0 5.1 3.3 4.3 Wet caliper, mm 0.322 0.290 0.385 0.326 Bulk 2.47 1.92 3.14 2.08 Burst 14 28 14 32 Breaking Length 3200 5600 2800 5800 Yield, % 100 94 100 96 These data show, that by treatment according to the ' process of the invention, power requirements to reach a desired freeness and drainage target can be reduced over 20%.
In addition these power savings are accompanied by substantial improvements in wet web properties, in dry strengths, and in fiber consolidation.
Example 3 Southern pine pulp from the pressurized first stage refiner of a commercial newsprint mill was treated at 145C
for 1 hour with 10~ by weight of sodium sulphite at pH 9.
The resulting pulp was then refined at power inputs of 19 and 38 horsepower-days per ton in a 12 inch Sprout-Waldron refiner.
The untreated pulp was refined in a like manner. The properties of these products after delatency treatment at 90C fcr 15 minutes, are listed in the following Table III:
.' ~
TABLE III
Untreated Treated Refining Power, HPD/T 38 19 38 Freeness, C.S.F. 194 243 146 Drainage, sec. 0.64 0.65 0.82 Wet tensile, N/m 36 42 46 Wet stretch, % 4.4 5.4 5.9 Ca~iper, mm 0.402 0.375 0.348 Bulk 3.65 2.74 2.56 Burst 9 19 20 Breaking length 2100 3400 3800 Tear 67 92 89 These data illustrate the application of the process of the invention to a difficult species; southern pine has a ' 15 stiffer, thicker fiber than spruce and in general yields a lower quality TMP. However by application of the process of the invention, a product of equal or better quality to that conventionally obtained can be made, with the following added advantages.
1) Less power is needed to reach equal freeness.
The present invention is directed to the formation of impxoved mechanical wood pulps useful for substitution for chemical pulps.
The term "mechanical pulp" as used herein has its normal meaning in the art and refers to the product of disruption of a woody substance by mechanical action to yield a product consisting mainly of liberated and separated single woody fibres and their fragments and which is suitable for use in the manufacture of paper.
The term "fibre" as used herein also has its normal meaning in the art and refers to individual plant cells which make up *he woody material and which, in softwoods, are known botanically as parenchyma cells and tracheids. These fibres inherently have diameters generally below 0.05 mm and in the case of wood species commonly used in pulp formation ~nd paper making, such as, spruce, balsam, pine, aspen and poplar, considerably below ~05 mm.
"Refiner pulps" are a class of mechanical pulps formed by passing particulated cellulosic fibrous material, usually - wood chips through a small gap betwean two ribbed parallel , plates rotating with respect to each other (known as a disc refiner). The procedure may be effected at atmosph?sric pressure, the product being known as "refinèr mechanical pulp"
2S (RMP), or under pressure, typically about 1 to 2 atmospheres greater than atmospheric pressure, and at elevated temperature, such as, about 120C, the product being known as "thermo-mechanical pUlp~? ~TMP). The refining process usually is effe?~-ted in two stages. In the first stage, the fibres are separated and liberated and in the second stage, additional refining energy is supplied to increase the fibre flexibility and conformability, fibrillation and bonding. Usually about . .
.
. .
,~ :
.
-11~51~7 half the overall refining energy of about 100 to about 120horsepower-days per ton is applied to the f~IEr~ration stage.
Because mechanical wood pulps can be made in yields over 95% with minimal pollution problems, there is strong 5 incentive to increase their usage in paper manufacture.
In general, however, it is not possible to transport a sheet, formed entirely of mechanical pulp, at high speed through the forming, pressing, drying and reeling sections of the paper making machine, without an unacceptable number of 10 breaks. Chemical pulp is usually added to the furnish to improve its machine runnability. Traditionally newsprint is manufactured from a furnish consisting of about three parts groundwood or other mechanical pulp and one part chemical pulp.
"Runability" refers to that combination of properties which allows the wet web to be transported at high speed through the forming, pressing and drying sections of the r paper making machine and allows the dry sheet to be reeled and printed with not more than an acceptable number of breaks.
20 In effect, runability is a measure of the efficiency with which the paper passes through the paper machine and printing press.
The chemical pulp component is usually manufactured by the kraft or sulphite process in yields ranging from about 45 to 65%. Chemical pulps are expensive, make heavy demands 25 on the mills wood resources, and entail formidable pollution problems. As already noted, mechanical wood pulps are obtained in yields in excess of 95% with minimal pollution problems.
Despite all the disadvantages associated with the use 30 o~ chemical pulps, they are generally employed in making news-print because runability is the key ~o paper making machine and press-room efficiency, which in turn i9 the key to profit-ability.
In accordance with this invention, there is provided 35 a process for the formation of an improved refiner pulp which is suitable for use as a replacement for chemical pulps in many applications, including newsprint furnish.
, ~1~5107 The process of this invention results in an increase in the elongation to rupture (hereinater known as "wet stretchi'~ and an improvement in the stress-strain properties of the wet web formed from the pulp, while simultaneously maintaining rapid drainage. We have discovered a hitherto unknown phenomenon that high wet stretch and ~igh wet stress-strain characteristics, in combination with rapid drainage, are the fundamental pulp properties which impro~e the runability of a newsprint ~urnish.
The fibre-to-fibre bonding within a dry paper sheet formed from the pulp produced by the process of the invention is impro~ed, thereby resulting in the desirable properties of increased tensile and burst strengths and increased shaet density.
One important feature of this invention is that there is formed a refiner ~ulp which ca~ be used as a substitute, in whole or in part, for chemical pulp in many of its applications and which results from a procedure which does not produce more than insignificant quantities of pollu-20 ting effluents, in complete contrast to chemical pulping pro- !
cedures,where large quantities of polluting effluents must be handled. The overall energy requirements of the refining operation to provide a predetermined level of pulp quality also are decreased, as compared with the conventional refiner pulp-formation operation.
The process of the invention comprises three steps, namely (a) subjecting particulated cellulosic fibrous mater-ial to mechanical action in a disc refiner to form a pulp consisting mainly of single fibres and fragments thereof, 30 (b) chemical reaation of the pulp with a soluble salt of sulfurous acid under certain precise elevated temperature and pressure conditions as detailed below, and (c) subjecting the chemically-treated pulp to mechanical action to refine the same and improve the pulp quality.
The cellulosic fibrous material species and refining conditions required to manufacture a usable mechanical pulp are well known to the art. For example, it is well known that most hardwoods cannot be refined to yield ~echanical .
- - -.
, 11~5107 pulps with adequate strengths. Application of the invention is restricted to refiner pulps which are generated from soft-woods, or other cellulosic fibrous material species which are recognized in the industry as being suitable for the prepara-tion of refiner pulps. The invention is described furtherwith particular reference to wood species.
The three individual steps comprising the proces of the invention are discussed separately below:
STEP (a) Fibre Separation A wood fibre consists essentially of a cell wall, whose outer surface is made up of cellulose-rich fibrillar layers known as the Sl and S2 layers. In wood, the space between the fibres, known as the middle lamellae, is filled with a lignin-rich material.
lS The process of the invention requires that, in the initial liberation of the ibre from the wood in a disc refiner, the fracture occurs mainly in the Sl and S2 layers, thus exposing the cellulose-rich fibrillar material which is the source of the fibrillation characteristic of a good mech-20 anical pulp. Since this fibre morphology is established at - the moment of fibre liberation, it is necessary that the pro-cess of fibre liberation proceed largely to completion.
Therefore, the product of the initial mechanical fibre separa-tion step of the proce~s of the invention must consist mainly 25 of single wood fibres, which inherently have average diameters less than 0.05 mm. More than the minimum energy to accomplish this separation may be applied, but is unnecessary.
It is well known that, in thermomechanical pulping, if the refining temperatuxe exceeds the thermal softening 30 point of lignin, fibre separation occurs in the middle lamellae to yield a smooth fibre with a lignin-rich surface.
This fibre i8 difficult or impossible to fibrillate by further refining and is generally unsuitable for use as a mechanical pulp. Hence the initial fibre separation step 35 in this invention is effected at a temperature below the thermal softening point of lignin. The latter temperature is .. . .
. . .
il~5107 s variable with the wood species, duration of heating and re-fining conditions, but is generally below about 150C.
Attempts have been made to decrease the energy required for fibre separation and improve pulp quality by a chemical softening of the wood prior to refining. Such a process, 5 using sulphite as the treating chemical, is disclosed in U.S.
Patent No. 4,116,758. The products of the latter process are smooth walled fibres showing little tendency to fibrillation, similar to those described abo~e resulting from refining above the lignin softening temperature, and are unsuitable for use 10 as a mechanical pulp in this invention.
It is within the scope of this invention, however, to add the chemicals required in the subsequent treatment step to the wood chips prior to their entering the disc refiner, pro, vided that the temperature and time of contact is such that 15 no substantial reaction occurs and no significant chemical softening of the chips results. The disc refiner acts as an e~ficient mixer of the pulp and chemicals at the high con-sistency normally encountered.
It is also withi~ the scope of the invention to 20 subject the wood chips, prior to refining, to steam under pressure at a temperature below the thermal softening tempera--ture of the lignin, typically below about 140C in accordance with conventional industrial practice in TMæ manufacture.
A product of step (a), suitable for further treatment 25 in accordance with this invention, is obtainable simply by following the first stage refining procedures well known to the art, for the production of a good mechanical pulp. This is usually accomplished by presteaming wood chips, usually at a temperature of about 120~ to about 135C and 1 to 2 30 atmospheres pressure for 2 to 10 minutes, then passing the presteamed wood chips, which have not been softened by chemical action, through a disc refiner at a temperature below the thermal softening temperature of the lignin, and applying sufficient refining energy to yield a mechanical wood pulp 35 consisting mostly of single fibres and their fragments, such fibres and fragments being predominantly below 0.05 mm'in average diameter. This operation is generally effected at a :
' 11~5i~7 consistency of about 10 to about 40% by weight, usually about 25 to 30% by weight.
STEP (b) Chemical Reaction After the required physical form of the wood fibre is obtained in step (a), the chemical nature of the fibre is modified by reaction with an aqueous solution of a soluble : salt o~ sulphurous acid, usually sodium sulphite. The reac-tion is effected at temperatures above about 110C under a superatmospheric pressure for a time sufficient to yield a chemically-treated mechanical wood pulp capable of forming a paper web having improved wet stretch and stress-strain properties and exhibiting rapid drainage, but for a time in-sufficient to cause s~stantial dissolution of lignin with consequent loss of yield and generation of polluting ef~luents. The exact nature of the chemical reactions in-volved in the chemical treatment effected in this invention are not fully understood, but are thought to involve sulphon-ation.
During the reaction, the pH of the solution drops and alkali is consumed. It is essential to the process of the present invention that sufficient alkali be present in the chemical charge to prevent a pH drop below 3 during treatment, otherwise there is a risk of damaging the fibres through hydrolytic action with consequent loss of strength. The exact amount of alkali required varies according to the acetyl content of the wood supply and cannot ~e specified exactly, but is readily established by experimentationO
The alkali re~uirement may ~e met entirely with sodium sulphite. However, since only half of the sodium of sodium sulphite is available for neutralization, it is usually more economical to meet part of the alkali require-ments by additions of sodium hydroxide or sodium carbonate.
The pH of the mixture, however, is preferably kept below about 12 because hemicelluloses are dissolved from wood fibre by higher pH's r with consequent loss in yield.
.
In a preferred embodiment of the invention, the amount of sodium sulphite used in the chemical treatment is in the range of about 4% to about 15~ by weight based on the mechanical wood pulp resulting from step (a), although 5 lower concentrations down to about 1% by weight may be used with reduced beneficial effect, with the provision that the residual sulphite content of the mixture, as measured iodi-metrically, does not fall substantially to zero before termination of the reaction. Below 1% by weight of sodium 10 sulphite,improvements are too small to justify the expense of treatment. Similarly improvements are observed with chemical charges up to about 25% by weight of the pulp, but the additional cost is not justified by the small additional improvement. Generally, therefore, a chemical charge of 15 between about 1~ and about 25% by weight, preferably between about 4~ and about 15% by weight, of the mechanical pulp, is used. The chemical charge preferably has a pH between about T and about 12, and contains sodium sulphite and sufficient alkali to maintain a pH greater than 3 throughout the 20 reaction.
The reactions of sulphite with wood are known to consist of a large number of different reactions, whose rates are dependent on reaction conditions, particularly pH and temperature. The present state of our knowledge of 25 this complex subject has been summarized by G. Gellerstedt in Svensk Papperstidning nr. 16, 1976, p. 537 to 543.
It has been established that the reactions necessary for the application of the process of the invention and the results attained thereby are those that proceed at pH I 8 30 greater than 3 and pre~erably over 7, and at temperatures over about 110C, and preferably over about 130C. Other reactions of woody substances with sulphite which proceed at lower pH's and at temperatures below lQ0C are known, such as those described by H.~. Kvisgaard in Norsk 35 Skogindustri 1~, no. 4, 1965, p,155-163. Such reactions, however, are not ef~ective to produce an improvement in wet and dry properties, in fibre flexihility and consolidàtion and in power requirements, such as is contemplated in this invention.
11451~)7 We have found that the maximum improvement, namely, maximum increase in wet stretch, maximum improvement in stress-strain, maximum increase in strength characteristics, and maximum decrease in refiner power requirements for the 5 second stage (step ~c) discussed below~, is obtained from the process of the invention when the mechanical pulp ~rom step (a) with adaed chemical is heate~ at about 160C for 30 minutes. As with any other chemical reaction, the temper-ature can be lowered if the reaction time is increased.
10 Below about 120C, reaction time becomes impractically long, and below liOC, the required reactions effectively cease.
Similarly, the reaction temperature can be increased if the reaction time is shortened. The practical upper limit of temperature appears to be about 200C with reaction times 15 of 1 to 2 minutes. We prefer not to operate under these extreme conditions because the precise control of conditions and reaction times needed to achieve an optimum product are difficult to secure.
It is also possible to operate at shorter or longer than the optimum reaction times to produce a less than optimum but still useful result. If the reaction time is shorter than optimum, the improvements in wet stretch, stress-strain and strength properties and energy requirements are less than may be otherwise obtained by operating under optimum conditions. If the reaction time is too long, substantial dissolution o~ the lignin from the pulp, in the treating chemical occurs, with consequent loss of yield and formation of polluting effluent. While the process is still operable to produce property improvements under these condi-tiong gome of the advantages of wood economy and low~ollution are lost and generally are avoided.
The chemical treatment is operable over a time-temperature range from about lLoC for about 12 hours to about 200C for about 1 minute. It is understood that an increase in temperature must be accompanied by a concomit-tant decrease in reaction time. For example, the process is not operable at a temperature of 200C for 12 hours.
To derive maximum benefits from the chemical treatment step, ll~SlV7 it is preferred to operate in the more limited range of about 130C for about 2 hours to about 180C for about 15 minutes.
Because of uncertainties in specifying the exact upper limits of the chemical treatment step in terms of 5 time and temperature, it is considered more useful and precise to specify the upper limit in terms of the effect of the chemical treatment on pulp yield therefrom. Reaction conditions which decrease the yield, based on mechanical wood pulp, below about 85% are outside the scope of our process, lO since wood losses and the pollution capability of the spent aqueous phase become significant and intolerable beyond this limit. It is preferred to select maximum reaction conditions such that the yield of treated pulp is greater than about 90%.
The exact conditions required vary with wood species, chemical lS charge and consistency, but will fall within the limits of time and temperature as defined above, and are easily estab-lished by experimentation.
The chemical reaction which is effected in step (b) on the mechanical wood pulp resulting from step (a) is quite 20 distinct from the methods used in the pulping of woody sub-stances with sulphite or bisulphite to form chemical pulp. In sulphite pulping, heat and chemical are supplied to the woody material in chip form ti-e., fibre bundles) by circulating hot cooking liquor through a bed of the woody ~,aterial. With the 2S mechanical pulp produced in step (a~ of the process of the invention, the resistance to 10w of liquor is so great that circulation of liquor therethrough is impractical. In con-sequence, all of the chemical required to effect the reaction of step (b) must be incorporated in the pulp when it entexs 30 the reactor. It is advantageous to incorporate the chemical in solution in a volume of water which can be totally absorbed by the pulp. In practice this means that the consistency after chemical addition normally should be above about 15%
by weight. Consistencies below about 50% by weight are pre-35 ferred because it is easier to secure uniform mixing ofchemical and pulp below that level. The consistency range of about 15% to about 50~ by wei~ht, therefore, is preferred for reasons of convenience, but the operability of the process is not limited by consistency.
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:, 51S~7 The chemical treatment step in the process of the invention i5 also distinguished from chemical pulping process-es in that the process of the invention cannot be oonducted prac~ically in a ba1:ch process,such as is used in chemical pulping. ~his is because the thermal insulating properties of the mechanical pu:Lp are so high that a large pulp mass cannot be heated `~ to reaction temperature by conduction in a reasonable length of time. The chemica1 treatment may be carried out batch-wise using dielectric or microwave heating techniques but such methods are expensive. It is preferred to carry out the chemical reaction step in an apparatus wherein pulp is continuously raised to reaction temperature and introduced into one end of a reaction vessel of such size as to provide the desired reaction duration, while treated pulp is lS removed simultaneously from the other end.
Step (c) Refining In the third, and final, step of the process of the invention, the product of step (c~ is subjected to further refining action in a disc refiner, following the usual practice of the industry for second stage refining of a mechanical wood pulp. The results of this second refinir.g action differ from those obtained with an ordinary mechanical wood pulp because the application of steps La~
and ~b~ in accordance with this invention places the pulp in the required physical and chemical configuration to utilize further refining energy efficiently and economically.
It is well known that the quality of a mechanical wood pulp can be improved by increased refining, but at a cost of -~~~~ ~~~ ` slower drainage and increased enërgy demand~ The product of step ~b) may be refined to equivalent quality with significantly less energy, while achieving a faster drainage, as compared to mechanical pulp from step (a) which has not been subjected to step (b~. These results are illustrated graphically in Figure 1, in which a measure of pulp quality is plotted against refining power for two cases. The measure of pulp quality employed was the tensile strength of the wet web, measured at 5~ wet stretch to eliminate the effects o pulp latency. Similar plots are obtained using such other measures of pulp quality as breaking length or burst factor.
~145107 Point A in Figure 1 defines the state of the pulp at the completion of step (a) of the process of the invention.
Point B represents the same pulp after completion of step (b~. The line B-C gives the properties of the pulps derived 5 from step (b~ by the application of varying amounts of refining energy in accordance with step (cJ of the process of the invention. The line A-D represents the properties ~f pUlpe obt~ined by directly refining the product of step (a~, without the application of step (b). The dramatic 10 effect of the chemical treatment of step (bl in improving the drainage of refined pulp, as measured by Canadian Standard Freeness (C.S.F.), in increasing the pulp strength, . .
and in decreasing the energy requirements in the appli-cation of the refining o step ~c) is clearly e~ident from 15 the graphical representation of Figure 1.
The consistencies employed in the application of step (c) may be varied over the range normally employed in the second stage refining of a mechanical wood pulp, but the properties of the product depend to some extent on the refin-20 ing consistency chosen. Higher consistencies over about 20by weight yield products with higher wet stretch while lower consistencies tend to produce pulps with higher strength.
By adjustments in refinin~ consistency, the desired balance between wet stretch and strength for a particular application 25 can be achieved. For most applications, it is preferred to carry out the refining step (c) at consistencies between about 1% and about 35% by welght.
The amount o~ energy applied in step Cc~ may be varied according to the desired properties of the product and 30 the intended end use. The degree o~ refining to which the pulp is subjected is usually controlled by the freeness of the finished pulp. For most applications, this freeness should fall within the range of about 50 to about 700 C.S.F. For example, boxboard stock is typically of higher 3~ freeness than magazine grade paper stock. For newsprint application, it is preferred to refine to a freeness in the range about 100 to about 400 C.S.F. in step ~c2.
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The invention is illustrated by the following Examples:
Exam_le 1 Spruce chips were pre-steamed for 25 minutes at 35 psig and fed to a 1000 HP Sprout-Waldron 36 ICP refiner under the following conditions:
Throughput: - 25.0 tons per day Discharge consistency: 25 - 30%
Specific energy: 45 horsepower-days per ton The pulp from the pressurized refiner, consisting mainly of single fibers, and substantially free of particles greater than 0.05 mm in diameter, was divided in three portions.
One portion was mixed with 10% by weight of sodium sulphite at pH 9 and heated at 18% consistency at 90C for 1 hour.
15 Another portion was mixed with 10% sodium sulphite at pH 7 and heated at 18% consistency and 160C under a pressure of 75 psig for 1 hour. A third portion was untreated. Each portion was then refined further in a 12 inch Sprout-Waldron open ischarge refiner at 18% consistency and a specific 20 energy input at 63 horsepower-days per ton. All three pulps thus received a total of 113 horsepower-days per ton of refining energy.
The usual practice in mechanical pulping is to remove latency prior to screening, cleaning and final use. This pro-25 cedure was explained by L. R. Beath, M. T. Neill and F. A.Masse in an arti~le entitled "Latency in Mechanical Pulps", Pulp and Paper Magazine of Cànada 67 (10)T423(1966). To correspond to this common industrial practice, latency was removed from our pulps by treatment at 90C for 15 minutes, 30 prior to testing. The properties of these pulps are compared ln the following Table I:
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11~5107 TABLE I
T~eatment None 90C 160C
Yield, % 100 98 93 Freeness 194 197 80 Drainage, sec. 0.83 0.93 2.16 .
Wet tensile, N/m 62 63 75 Wet s`tretch, % 3.3 3.7 5.3 Wet caliper, mm 0.344 0.353 0.302 Bulk 2.68 2.57 2.12 Burst 16 17 23 Breaking Length 3100 3300 5100 Using the same total refining power, the untreated sample and the sample treated at 90C refined to essentially the same ~reeness with insignificant differences in wet and dry properties. By contrast, the sample treated at 160C
' refined to lower freeness with the same power, yielding over 60% increases in wet stretch and breaking length, as well as significant increases in wet tensile strength and burst. The drainage rate is much faster than an untreated TMP
of similar quality.
The wet caliper and bulk are measures of the fiber's ability to consolidate in the paper sheet. The low values obtained with the pulp treated at 160C arè indicative of a flexible fiber which consolidates well to form a dense, coherent sheet.
Example 2 A TMP prepared in a pressurized refiner as described in Example 1 was mixed with 10% sodium sulphite at pH 9.0 and heated at 18% consistency at 160C and 75 psig for 1 hour.
Samples of the treated and untreated TMP were then refined to comparable freeness levels, and the pulp properties measured after latency removal at 90C for 15 minutes. Power consumptions and the corresponding pulp properties are out-lined in the followlng Table II:
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. -, ' ~ .
TABLE II
Untreated Treated Untreated Treated Power, HPD/T 126 101 101 82 Freeness 107 118 305 331 Drainage, sec. 1.27 1.63 0.66 0.83 -Wet tensile, N~m 58 77 59 76 Wet stretch, % 4.0 5.1 3.3 4.3 Wet caliper, mm 0.322 0.290 0.385 0.326 Bulk 2.47 1.92 3.14 2.08 Burst 14 28 14 32 Breaking Length 3200 5600 2800 5800 Yield, % 100 94 100 96 These data show, that by treatment according to the ' process of the invention, power requirements to reach a desired freeness and drainage target can be reduced over 20%.
In addition these power savings are accompanied by substantial improvements in wet web properties, in dry strengths, and in fiber consolidation.
Example 3 Southern pine pulp from the pressurized first stage refiner of a commercial newsprint mill was treated at 145C
for 1 hour with 10~ by weight of sodium sulphite at pH 9.
The resulting pulp was then refined at power inputs of 19 and 38 horsepower-days per ton in a 12 inch Sprout-Waldron refiner.
The untreated pulp was refined in a like manner. The properties of these products after delatency treatment at 90C fcr 15 minutes, are listed in the following Table III:
.' ~
TABLE III
Untreated Treated Refining Power, HPD/T 38 19 38 Freeness, C.S.F. 194 243 146 Drainage, sec. 0.64 0.65 0.82 Wet tensile, N/m 36 42 46 Wet stretch, % 4.4 5.4 5.9 Ca~iper, mm 0.402 0.375 0.348 Bulk 3.65 2.74 2.56 Burst 9 19 20 Breaking length 2100 3400 3800 Tear 67 92 89 These data illustrate the application of the process of the invention to a difficult species; southern pine has a ' 15 stiffer, thicker fiber than spruce and in general yields a lower quality TMP. However by application of the process of the invention, a product of equal or better quality to that conventionally obtained can be made, with the following added advantages.
1) Less power is needed to reach equal freeness.
2) At equal power inputs, the treated pulp refined to lower freeness, with large improvements in both wet and dry properties. Burst and breaking length are approximately doubled.
3) At half the second stage power input and higher freeness, the treated product is still superior to the product derived from untreated TMP.
4) The process of the invention results in ma~or improvements in fiber consolidation as shown by the decrease in wet caliper and bulk.
Example 4 Spruce chips were refined in a Bauer 420 open dis-charge refiner at a rate of 65 tons per day and a specific energy of 60 hoxsepower-days per ton. One portion of this ~5 RMP was mixed with 10% sodium sulphite at pH 9 and hèated at 145C and 50 psi pressure for one hour. Both treated and ., .
11'~51()7 untreated pulps were further re~ined in a 12-inch Sprout-Waldron refiner at 20% consistency. The resulting RMP's had the properties outlined in the following Table IV, after latency removal at 90C for 15 minutes.
TABLE IV
Untreated Treated Secondary Refining Power Freeness, C.S.F. 388 122 81 156 10 Drainage, sec. 0.61 1.16 2.3 1.28 Wet Web Properties Tensile, N/m 36 56 63 68 Stretch, ~ 3.2 4.3 5.6 4.7 Caliper, mm 0.454 0.336 0.287 0.311 15 Dry_~roperties Bulk 3.98 2.70 1.98 2.22 Burst 8 16 23 25 Breaking Length 1700 3300 4900 4700 St~etch 1.2 1.8 1.7 1.9 20 Tear 61 66 52 69 This example illustrates several points. The RMP
from the primary refiner (first column) requires additional application of refining power for the development of adequate properties. The application of a further `45 horsepower-days per ton of refining power results in the greatly improved properties listed in column 2. However application of the same amount of power to an RMP which has been treated accor-ding to the present invention results in a product with lower freeness and superior wet and dry properties ~column 3).
Alternatively by application of only 3~ horsepower days per ton of additional refining power, a pulp is produced with comparable freeness and drainage characteristics but signifi-cantly improved in all Wet and dry properties, shown in column 4.
This illustrates that the process of the invention is applicable to refiner mechanical pulps as well as thermo-mechanical pulp.
`: :
1~451~)7 In summary of this disclosure, the present invention is directed to the formation of an improved mechanical pulp which can be used as a substitute for chemical pulp.
Modifications are possible within the scope of this invention.
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,, ~.
: ~ :
i "" : :
,~
:
Example 4 Spruce chips were refined in a Bauer 420 open dis-charge refiner at a rate of 65 tons per day and a specific energy of 60 hoxsepower-days per ton. One portion of this ~5 RMP was mixed with 10% sodium sulphite at pH 9 and hèated at 145C and 50 psi pressure for one hour. Both treated and ., .
11'~51()7 untreated pulps were further re~ined in a 12-inch Sprout-Waldron refiner at 20% consistency. The resulting RMP's had the properties outlined in the following Table IV, after latency removal at 90C for 15 minutes.
TABLE IV
Untreated Treated Secondary Refining Power Freeness, C.S.F. 388 122 81 156 10 Drainage, sec. 0.61 1.16 2.3 1.28 Wet Web Properties Tensile, N/m 36 56 63 68 Stretch, ~ 3.2 4.3 5.6 4.7 Caliper, mm 0.454 0.336 0.287 0.311 15 Dry_~roperties Bulk 3.98 2.70 1.98 2.22 Burst 8 16 23 25 Breaking Length 1700 3300 4900 4700 St~etch 1.2 1.8 1.7 1.9 20 Tear 61 66 52 69 This example illustrates several points. The RMP
from the primary refiner (first column) requires additional application of refining power for the development of adequate properties. The application of a further `45 horsepower-days per ton of refining power results in the greatly improved properties listed in column 2. However application of the same amount of power to an RMP which has been treated accor-ding to the present invention results in a product with lower freeness and superior wet and dry properties ~column 3).
Alternatively by application of only 3~ horsepower days per ton of additional refining power, a pulp is produced with comparable freeness and drainage characteristics but signifi-cantly improved in all Wet and dry properties, shown in column 4.
This illustrates that the process of the invention is applicable to refiner mechanical pulps as well as thermo-mechanical pulp.
`: :
1~451~)7 In summary of this disclosure, the present invention is directed to the formation of an improved mechanical pulp which can be used as a substitute for chemical pulp.
Modifications are possible within the scope of this invention.
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:
Claims (13)
1. A process for the formation of refiner pulp having improved properties, which comprises:
(a) subjecting wood chips which have not been softened by chemical action to mechanical action in a disc refiner at a temperature below the thermal softening temperature of lignin to cause the formation of a mechanical wood pulp consisting mainly of single wood fibres and fragments thereof, (b) treating said pulp at an elevated temperature above about 110°C and under a superatmospheric pressure with an aqueous solution of a soluble salt of sulfurous acid containing sufficient alkali to maintain a pH greater than about 3 during the treatment, said treatment being effected at a temperature and for a time to enable reaction with the pulp to occur and to produce a chemically-treated pulp capable of forming a paper web having increased wet stretch and improved stress-strain properties while rapid drainage is retained, said treatment being effected at a temperature and for a time insufficient to result in a treated pulp yield below about 85% by weight, and (c) subjecting said chemically-treated pulp to mechani-cal action in a disc refiner to improve the pulp quality of the same to provide a refined pulp having a Canadian Standard Freeness of about-50 to about 700.
(a) subjecting wood chips which have not been softened by chemical action to mechanical action in a disc refiner at a temperature below the thermal softening temperature of lignin to cause the formation of a mechanical wood pulp consisting mainly of single wood fibres and fragments thereof, (b) treating said pulp at an elevated temperature above about 110°C and under a superatmospheric pressure with an aqueous solution of a soluble salt of sulfurous acid containing sufficient alkali to maintain a pH greater than about 3 during the treatment, said treatment being effected at a temperature and for a time to enable reaction with the pulp to occur and to produce a chemically-treated pulp capable of forming a paper web having increased wet stretch and improved stress-strain properties while rapid drainage is retained, said treatment being effected at a temperature and for a time insufficient to result in a treated pulp yield below about 85% by weight, and (c) subjecting said chemically-treated pulp to mechani-cal action in a disc refiner to improve the pulp quality of the same to provide a refined pulp having a Canadian Standard Freeness of about-50 to about 700.
2. The process of claim 1 wherein said soluble salt of sulfurous acid is an aqueous sodium sulphite solution and said treatment is effected at a pulp consistency of about 4 to about 15% by weight and at an applied chemical charge of about 1 to about 25% by weight of sodium sulphite based on pulp.
3. The process of claim 1 or 2 wherein said treatment is effected at a temperature of about 130°C for about 2 hours to about 180°C for about 15 minutes, the temperature and time of treatment being effected to maintain the yield above about 90% by weight.
4. A process for the formation of refiner mechanical wood pulp capable of forming a wet paper sheet having in-creased wet stretch and increased stress-strain properties, and a dried paper sheet having increased strength properties, which comprises:
(a) subjecting wood chips which have not been softened by chemical action to steaming at a temperature of about 120° to about 135°C under about 1 to 2 atmospheres pressure;
(b) subjecting said steamed wood chips to mechanical action in a disc refiner under an elevated temperature below the thermal softening temperature of lignin, under a super-atmospheric pressure and at a consistency of about 10 to about 40% by weight to cause the formation of a mechanical wood pulp consisting mainly of single wood fibres and frag-ments thereof of diameter less than 0.05 mm, (c) treating said pulp with an aqueous sodium sulphite solution containing sufficient alkali to maintain the pH of the solution greater than about 3 during the treatment at a consistency of about 15 to about 50% by weight, an applied chemical charge of about 4 to about 15% by weight of sodium sulphite based on the pulp, and at a temperature of about 130°C for about 2 hours to about 180°C for about 15 minutes, the temperature and time of treatment being effected to achieve the maximum improvement in pulp properties while the pulp yield. from the chemical treatment is maintained above about 90% by weight, and (d) subjecting said chemically-treated pulp to mechani-cal action in a disc refiner at a consistency of about 1 to about 35% by weight to refine the same and provide a refiner mechanical pulp having a Canadian Standard Freeness of about 50 to about 700 C.S.F.
(a) subjecting wood chips which have not been softened by chemical action to steaming at a temperature of about 120° to about 135°C under about 1 to 2 atmospheres pressure;
(b) subjecting said steamed wood chips to mechanical action in a disc refiner under an elevated temperature below the thermal softening temperature of lignin, under a super-atmospheric pressure and at a consistency of about 10 to about 40% by weight to cause the formation of a mechanical wood pulp consisting mainly of single wood fibres and frag-ments thereof of diameter less than 0.05 mm, (c) treating said pulp with an aqueous sodium sulphite solution containing sufficient alkali to maintain the pH of the solution greater than about 3 during the treatment at a consistency of about 15 to about 50% by weight, an applied chemical charge of about 4 to about 15% by weight of sodium sulphite based on the pulp, and at a temperature of about 130°C for about 2 hours to about 180°C for about 15 minutes, the temperature and time of treatment being effected to achieve the maximum improvement in pulp properties while the pulp yield. from the chemical treatment is maintained above about 90% by weight, and (d) subjecting said chemically-treated pulp to mechani-cal action in a disc refiner at a consistency of about 1 to about 35% by weight to refine the same and provide a refiner mechanical pulp having a Canadian Standard Freeness of about 50 to about 700 C.S.F.
5. The process of claim 4 wherein said aqueous sodium sulphite solution has an initial pH of about 9 to about 12.
6. The process of claim 4 wherein said aqueous sodium sulphite solution is added to said wood chips prior to passage of the latter through said disc refiner, whereby said aqueous solution is intermixed with the fibres as they are formed.
7. The process of claim 4, 5 or 6 wherein said refining step is effected to provide a refiner mechanical pulp of a Canadian Standard Freeness of about 100 to about 400 C.S.F.
8. In a process for the formation of refiner mechanical pulp by subjecting particulated cellulosic fibrous material to mechanical action in a disc refiner at a temperature below the thermal softening temperature of lignin to cause the formation of a mechanical pulp consisting mainly of single fibres and fragments thereof and subsequently subjec-ting the mechanical pulp to further mechanical action in a disc refiner to improve the pulp quality, the improvement which comprises chemically treating said mechanical pulp prior to said refining step whereby a refiner mechanical pulp is attained capable of forming a wet paper web having increased paper making machine runability and whereby less power is required in said refining step to achieve equiva-lent pulp quality, said chemical treatment comprising treating said mechanical pulp at a temperature of about 110°C
to about 200°C under a superatmospheric pressure for about 12 hours to about 1 minute with an aqueous solution of a soluble salt of sulfurous acid containing sufficient alkali to maintain a pH greater than about 3 during the treatment, said treatment temperature and time being insufficient to result in a treated pulp yield below about 85% by weight.
to about 200°C under a superatmospheric pressure for about 12 hours to about 1 minute with an aqueous solution of a soluble salt of sulfurous acid containing sufficient alkali to maintain a pH greater than about 3 during the treatment, said treatment temperature and time being insufficient to result in a treated pulp yield below about 85% by weight.
9. The process of claim 8 wherein said soluble salt of sulfurous acid is an aqueous sodium sulphite solution.
10. The process of claim 9 wherein said treatment is effected at a pulp consistency of about 4 to about 15% by weight and at an applied chemical charge of about 1 to about 25% by weight of sodium sulphite based on pulp.
11. The process of claim 10 wherein said treatment is effected at an applied chemical charge of about 4 to about 15% by weight of sodium sulphite based on pulp.
12. The process of claim 8, 9 or 10 wherein said treatment is effected at a temperature of about 130°C for about 2 hours to about 180°C for about 15 minutes, the temperature and time of treatment being effected to achieve the maximum improvement in pulp properties while the yield is maintained above about 90% by weight.
20a
20a
13. The process of claim 11 wherein said treatment is effected at a temperature of about 130°C for about 2 hours to about 180°C for about 15 minutes, the temperature and time of treatment being effected to achieve the maximum improvement in pulp properties while the yield is maintained above about 90% by weight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10466879A | 1979-12-17 | 1979-12-17 | |
| US104,668 | 1979-12-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145107A true CA1145107A (en) | 1983-04-26 |
Family
ID=22301732
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000356028A Expired CA1145107A (en) | 1979-12-17 | 1980-07-31 | Procedure for forming refiner pulps |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0030778B1 (en) |
| JP (1) | JPS5691093A (en) |
| AU (1) | AU531907B2 (en) |
| BR (1) | BR8005950A (en) |
| CA (1) | CA1145107A (en) |
| DE (1) | DE3064270D1 (en) |
| FI (1) | FI71779C (en) |
| MX (1) | MX156081A (en) |
| NZ (1) | NZ194407A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4718980A (en) * | 1985-12-30 | 1988-01-12 | Weyerhaeuser Company | Interstage treatment of mechanical pulp |
| US4789429A (en) * | 1985-11-06 | 1988-12-06 | Sunds Defibrator Aktiebolag | Method of making mechanical pulp |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4502918A (en) * | 1981-06-10 | 1985-03-05 | Macmillan Bloedel Limited | Two-stage chemical treatment of mechanical wood pulp with sodium sulfite |
| SE466060C (en) | 1990-02-13 | 1995-09-11 | Moelnlycke Ab | Absorbent chemitermomechanical mass and preparation thereof |
| US5607546A (en) * | 1990-02-13 | 1997-03-04 | Molnlycke Ab | CTMP-process |
| WO1997022749A1 (en) * | 1995-12-19 | 1997-06-26 | Kvaerner Hymac Inc. | Process for treating refiner pulp |
| CA2243228A1 (en) * | 1997-07-17 | 1999-01-17 | Donohue Inc. | Preparation of mechanical wood pulps with reduced energy |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4145246A (en) * | 1976-07-19 | 1979-03-20 | Crown Zellerbach Corporation | Process for making high-strength, high-yield sulfite-modified thermomechanical pulp and a linerboard composition produced therefrom |
-
1980
- 1980-07-16 AU AU60460/80A patent/AU531907B2/en not_active Ceased
- 1980-07-21 NZ NZ19440780A patent/NZ194407A/en unknown
- 1980-07-31 CA CA000356028A patent/CA1145107A/en not_active Expired
- 1980-08-08 EP EP19800302722 patent/EP0030778B1/en not_active Expired
- 1980-08-08 DE DE8080302722T patent/DE3064270D1/en not_active Expired
- 1980-08-11 JP JP10933480A patent/JPS5691093A/en active Pending
- 1980-08-22 FI FI802654A patent/FI71779C/en not_active IP Right Cessation
- 1980-09-17 BR BR8005950A patent/BR8005950A/en not_active IP Right Cessation
- 1980-11-26 MX MX18491280A patent/MX156081A/en unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4789429A (en) * | 1985-11-06 | 1988-12-06 | Sunds Defibrator Aktiebolag | Method of making mechanical pulp |
| US4718980A (en) * | 1985-12-30 | 1988-01-12 | Weyerhaeuser Company | Interstage treatment of mechanical pulp |
Also Published As
| Publication number | Publication date |
|---|---|
| FI71779C (en) | 1987-02-09 |
| FI71779B (en) | 1986-10-31 |
| JPS5691093A (en) | 1981-07-23 |
| MX156081A (en) | 1988-06-30 |
| NZ194407A (en) | 1983-02-15 |
| EP0030778A1 (en) | 1981-06-24 |
| EP0030778B1 (en) | 1983-07-20 |
| FI802654A (en) | 1981-06-18 |
| DE3064270D1 (en) | 1983-08-25 |
| BR8005950A (en) | 1981-06-23 |
| AU531907B2 (en) | 1983-09-08 |
| AU6046080A (en) | 1981-06-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |