NO843919L - PROCEDURE FOR MANUFACTURING TREMASS - Google Patents

Description

The present invention relates to paper and paper products, and in particular improved methods for the production of wood pulp for use in paper production while obtaining an improved wood pulp, and the ultimately obtained paper product. More specifically, the present invention relates to the use of a special s-triazine additive, such as melamine, in the production of wood pulp for use in the manufacture of paper products, wood pulp containing the additive and an improved paper produced from the wood pulp containing the s-triazine.

Paper production, including the methods for producing paper pulp, is a well-known technique. Thus there are well-known methods for producing wood pulp from firewood using thermomechanical, chemical or semi-chemical treatments. These treatments are extensively described in the literature, e.g. in Pulp and Paper, Chemistry and Chemical Technology, by James P. Casey; third edition, 1980-1983, published in four volumes by John Wiley&Sons, Inc., New York. The usual method involves that logs obtained from trees are first cut into small pieces and then into chips in the first stage of the pulping process. The chips are then boiled by a semi-mechanical or chemical operation to separate the lignin that holds the wood fibers together,

from the cellulose or hemicellulose. The lignin is scrapped, and the cellulose material is further processed for use in papermaking.

In the thermomechanical process (TMP), cooking is carried out by preheating the wood chips, preferably under pressure, to soften the lignin present in the wood to enable separation of the fiber components. The lignin is then partially separated from the cellulose products by bleaching operations. In a chemical process, the wood chips are boiled, normally in a closed digestion tank, in the presence of a suitable chemical reagent. In the sulfite process, this chemical reagent is a bisulfite salt. In the sulphate or kraft process, the chemical reagent is sodium hydroxide or sodium sulphide. In the soda process, sodium hydroxide is used as the chemical reagent. All the chemical processes are similar in the sense that the chemical reagent is used to dissolve the lignin that holds the cellulose or hemicellulose fibers together. The masses obtained through chemical processes are known as chemical masses.

After the initial digestion step, regardless of whether it is a thermomechanical, a semi-chemical or a chemical process, the masses are typically exposed to a series of subsequent treatments. In one such treatment, the wood pulp is bleached with a bleaching agent, such as chlorine or an oxygen-containing material, such as hydrogen peroxide, gaseous oxygen or ozone, to bleach the wood pulp, followed by various washing steps. In another finishing operation of the pulp, this is mechanically treated or ground to fibrillate and fiberize the wood fibers so that the fibers can be bound in a subsequent papermaking process. The purpose of such post-processing of the pulp is to provide wood pulps that are suitable for <p>subsequent paper production while obtaining a final paper with the desired properties for a given application, such as the correct colour, lightness, printing ink absorption capacity, pigment absorption capacity and various other properties, such as wet and dry strength, grease resistance and/or electrical properties depending on the end use.

In the various after-treatments of the pulp, it has been recognized that additives can be added to improve the treatment. At the refining stage, for example, it is known to use dye additives, such as Congo red, to speed up the grinding process and to reduce the process's energy requirements. Although Congo red used as a dye is advantageous, the use of the dye will cause a red coloring of the wood pulp, and unless the color is removed, the color will be transferred to the paper product made from the pulp.

Although wood pulps are known to exhibit excellent properties, there is therefore a recognized need for improvements in the production of wood pulps for use in papermaking, both from an economic point of view and from the point of view that paper products with the desired properties for a special application.

Able to include and general description of the invention

It is therefore a main purpose of the invention to provide an improved additive for use in paper production, and in particular for use in the production of wood pulp, including recycled pulp, which is later used for paper production.

It is a further object of the invention to provide an additive for use in paper production, and in particular in the production of wood pulp, which is relatively reasonable and which will provide improved economy for wood pulp production processes.

It is a further object of the invention to provide an additive for use in paper production, and in particular in the production of wood pulp for subsequent use in paper, as the additive when retained in the pulp will give an improved wood pulp.

It is a further object of the invention to provide an improved additive for use in the manufacture of wood pulp for use in paper manufacture and which, when retained in the wood pulp, provides improved properties, such as increased strength, ink absorbency, brightness, reduced accumulation of static charge, and pigment compatibility and

- retention in paper produced from the wood pulp.

The above-mentioned purposes are achieved according to the invention by

at a suitable step in the pulping process to add an s-triazine additive such as melamine. It was initially discovered that melamine when added to wood pulp before the wood pulp was subjected to common bleaching methods, such as chlorine or oxygen bleaching, not only acted as a viscosity protectant or stabilizer during the bleaching process, but also caused the bleached wood pulp to acquire improved colour, lightness and strength. It was later found that the presence of melamine in the refining step of the pulping process reduced the time and energy required for the milling process and produced a wood pulp with improved fiber properties, including flexibility, whereby improved bonding of the fibers was achieved when the pulp

was used in paper.

It has now been shown that the wood pulp will retain the s-triazine additive after the wood pulp production process and that the retained s-triazine-cellulose-lignin material gives a paper with superior properties regardless of whether the pulp has been produced by a thermomechanical, chemical or semi-chemical process. The paper produced from the wood pulp and containing the s-triazine agent, provides a paper with excellent pigment compatibility and retention, improved printing ink absorption capacity, greatly increased mechanical strength including bursting, tensile and tearing strength, and improved electrical conductivity. By using the s-triazine agent, it is also possible to achieve rapid and complete printing ink removal from the paper during a paper recycling process. It has thus been shown that the s-triazine works in such a way that it improves the transfer of wood to wood pulp suitable for papermaking and that when it is retained in the wood pulp at the time of paper production, the s-triazine agent gives a finished paper with improved properties. The provision of the present invention therefore not only eliminates the need to remove the pulping additive before the pulp is converted to paper, but also provides an improved paper product. "Paper" as used here shall mean a sheet, a blanket or a mat of single fibers of cellulose which is written from wood. The fibers can be woven or non-woven and are normally non-woven. "Pulp" as used here shall mean a mass of cellulose fibers in bulk form from which paper or other pulp products can be produced. "Wood pulp digestion" as used here shall denote the process by means of which wood chips are converted into a slurry of cellulose fibers in an aqueous medium.

The additives which can be used according to the invention are selected s-triazine compounds which contain at least two Nf^ groups and have the formula in which X is an NH,, or OH group, or a salt thereof. The preferred compound is melamine wherein X is an NH^ group, or a salt thereof, such as melamine sulfamate, melamine sulfite, melamine chloride, melamine sulfate, melamine phosphate, melamine hypochlorite, melamine chlorate, melamine chlorite, melamine perchlorate, melamine nitrate, melamine peracetate or melamine hydrogen sulfite. It has also been shown that melamine produced by means of the method described in US patent application 568408 filed on January 5, 1984, can be effectively used. The product obtained by the process described in the above US patent application will contain up to 4% of substituents that are not melamine, including melam,<C>6<H>9<N>11'<m>elem'C6H6N10'anunel:i-n' C-jN,_OHj., ammelide, C3N4°2H4'or urea. The product according to the above US patent application is usually designated by "Melamine II". The salts of "Melamine II" as indicated above in the definition of the salts of melamine have also been found to be effective additives. Another selected s-triazine additive which may be used in accordance with the present invention includes ammelin of the formula

which.is basic.

The selected s-triazine additives can be used to improve the slurry of wood which, when subjected to a digestion process to remove lignin or other resinous material, will yield a cellulose or hemicellulose product in a fibrous state. The most common and preferred materials are hardwood and softwood species, such as the various types of pine, spruce, fir, poplar, oak, maple, mahogany, ash and similar woods. The additive can also be effectively used when paper and pulp are recycled to produce a new paper or pulp material. "Firewood" as used here shall mean a mixture of lignin and cellulose fibers which are obtained from trees or similar plants that are commonly found in forests. The term "s-triazine additive" as used here shall indicate the s-triazine in the form in which it is added during the wood treatment. The term "s-triazine material" as used here shall indicate

a material of the s-triazine additive after reaction with the cellulose and lignin.

The amount of additive to be used together with the food wood or wood pulp will vary depending on the stage of the addition and the effect of the additive. If the selected s-triazine additive is to be added during the wood slurrying process, the amount used should preferably be 0.05-20 parts for every 100 parts of wood. The addition of the selected s-triazine additive to a sulphide or sulphite process will preferably be within the range of 0.5-10 parts per 100 pieces of wood. The addition of the selected s-triazine additive to a thermomechanical or chemical-mechanical wood slurry process should preferably be within the range of 0.05-5 parts per 100 pieces of wood. Normally, some of the s-triazine additive will be lost under wood treatment conditions, and this may be desirable

to add additional additive by a recycling process under constant conditions. The composition of the s-triazine additive -cellulose-lignin will exert beneficial effects on further pulping in accordance with the pulping conditions and the obtained material retained in the pulp. If the s-triazine additive is to be added during the bleaching process, the amount used should be 0.05-3 parts per 100 parts wood pulp. Normally, part of the additive will be lost during the bleaching and during subsequent washing steps, and it may therefore be desirable to add further additive after the bleaching process has ended, in order to thereby achieve an effective amount of the additive in a subsequent treatment step, e.g. in the refining step of a thermomechanical process

or in the grinding step of a chemical or thermomechanical process. It has also been shown that if the amount of the selected s-triazine agent is kept at more than 0.05 part per 100 parts in the wood pulp, paper produced from the pulp will exhibit increased strength properties, printing ink and pigment retention, dirt and grease resistance and electrical properties. It is particularly desirable, if the paper is to be effective for repro<graphy (which assumes that the paper is capable of receiving electrical deposits of printing ink), that the amount of additive is present at the upper end of the above range. Based on the above guidelines as well as the currently preferred embodiments as described in more detail below, the person skilled in the art will be able to select an effective amount of the s-triazine additive to achieve the desired goals.

It is currently not certain how or how the s-triazine additive provides its beneficial effect at the various stages of the pulping process. However, it is believed that during the slurry process and the grinding process the s-triazine additive reacts with the wood's cell structure and causes the fiber bundles to separate into cellulose fibers and lignin-containing components are provided by a mass containing the s-triazine material. It is believed that during the bleaching or recycling process where the fibers have already been isolated, the s-triazine additive will react with the lignin or lignin-coated cellulose by hydrogen bonding or covalent bonding to the individual fibers.

In any case, the melamine or melamine derivative does not need to be removed from the treated cellulose fibers and thus provides an improved physical property effect that cannot be achieved with an additive that is only mechanically mixed with cellulose fibers.

Currently preferred embodiments and

detailed description of the invention

After the invention has now been generally described, the following examples of the currently preferred embodiments of the invention are presented. Examples 1-3 describe the addition of the selected s-triazine additive during the bleaching step of pulp production. Examples 4 and 5 describe addition of the s-triazine additive during the refining step of a thermomechanical pulping process. Example 6 describes the addition of the s-triazine additive in a milling step after the pulp slurry. Example 7 describes the addition of the s-triazine in a recycling process. Example 8 describes a trial carried out in a paper-making mill on a technical scale. In the examples below, the various tests are carried out in accordance with standard TAPPI (Technical Association of the Pulp and Paper Industry, Atlanta, Georgia) methods, with the test methods carried out being designated as follows:

Test methods and TAPPI standards

Example 1

Melamine as viscosity stabilizer

in the bleaching step of pulp production

Unbleached kraft process pulp with a kappa number of 38.7 was treated with sulfamic acid, urea or melamine in various percentage amounts relative to the pulp, in accordance with the following bleaching method. The individual capital letters, C, E, D, are used to describe particular bleaching steps, as described in Pulp and Paper, Chemistry and Chemical Technology, by James P. Casey, third edition,

Vol. 1, 1980, p. 669, John Wiley & Sons, Inc., New York. The removal of lignin during the bleaching step is expressed as a reduction in the kappa number.

The delignification/bleaching steps were carried out as follows: Protectants were added in the indicated percentages, based on pulp, and the chlorination with chlorine water (step C) was carried out with 9.66% chlorine, based on pulp, at room temperature for 1 hour at a pulp consistency of 3%.

Alkaline extraction with sodium hydroxide (step E) was performed with 4% NaOH, calculated by mass, at 70°C for 1 hour at a pulp consistency of 12%. Chlorine dioxide bleaching with C102

(D) was performed with 1.5% C102, calculated by mass, at 70°C

for 2.5 hours and at a pulp consistency of 12%.

In Table I, the pulp properties after steps C and D and after steps C, E and D are indicated when the various protective agents were added to the power process pulp. About. 0.25% melamine, calculated on pulp, is as effective after steps C and E as 0.50% sulfamic acid. With continued bleaching in the chlorine dioxide step (step D), the data in the table indicate that in the two experiments where the viscosity was measured (28.6 and 29.2), the viscosity is significantly higher than the base case of 17.1 when no melamine was used.

Example 2

Melamine as viscosity stabilizer used

at different temperatures in the chlorination step

Unbleached kraft pulp with a kappa number of 38.7 was bleached in C-E-D sequences with and without the use of melamine and sulfamic acid in the chlorination step at different temperatures. Table II contains a summary of the comparative mass properties after steps C-E, and Table III contains a summary of the comparative properties after steps C-E-D. It appears from these figures that melamine in reduced concentration (0.25%) is as effective as sulfamic acid (0.5%) even at higher chlorination temperatures. Conclusions: At all temperatures, the kappa number achieved was lowest with melamine. Viscosity values obtained with melamine are comparable to those obtained using a higher percentage of sulfamic acid.

Conclusions: At each temperature level, the effect of melamine on viscosity is comparable to the effect of sulfamic acid, but at a lower additive concentration (0.25% melamine compared to 0.5% sulfamic acid).

Example 3

Melamine as a viscosity stabilizer in the hypochlorite bleaching step in pulp production

Unbleached kraft pulp with a kappa number of 38.7 was bleached in a C-E-H sequence using sulfamic acid (0.5%) or melamine (0.25%) in the hypochlorite stage (stage H) in two separate trials. A third experiment was carried out as a blind experiment without any additive. The comparative results given in Table IV show the effect of melamine as a viscosity stabilizer in the hypochlorite stage of the bleaching.

Conclusions: The results suggest comparable viscosities for melamine compared to those obtained with sulfamine at higher additive concentrations.

Example 4 describes the use of melamine in the first pressurized refining step and in the second refining step at atmospheric pressure in a thermomechanical pulp production process.

Example 4

A pilot plant experiment was conducted using loblolly pine that had first been debarked, chipped and silted. The material had a specific gravity of 0.461 g/cm 3 and a moisture content of 41.1%. The particle filter analysis appears in Table V.

The chips were pre-based in the digester for 3 minutes at 207 kPa (gauge) steam and refined in a primary refiner at 207 kPa (gauge). The primary refinery used was a "Pressurized DoubleTÆsk Refiner" of the type C-E Bauer model 418 and equipped with 31104/7 R0869 MC plates. In the blind experiment, no chemicals were added, but in the experiment according to the invention, melamine was added in the form of a solution in an amount of 1.4 parts by weight of melamine per 10 0 parts by weight dry wood on site for the primary refiner's plug stripper.

The mass from the primary stage was divided into different batches and refined in a second-stage refiner at atmospheric pressure and with varying specific energy inputs. The second stage ref iner was a C-E Bauer Model 401 Atmospheric Double DisJc Ref iner fitted with 3610X plates.

Samples were taken from the obtained pulps in accordance with standard TAPPI methods and they were examined to determine Canadian Standard Freeness, Somerville chips, Bauer-McNett classifications, physical properties and optical properties in accordance with the above TAPPI methods . The data obtained appears in Table VI.

According to the data in Table VI, it turned out that refining proceeded better and faster in the presence of melamine. Lower energy was needed to achieve an equivalent fr eeness. In this experiment, the specific energy (BHPD/ADT) was 117 HP

to achieve a freeness of 200 without melamine, while it was only 103 HP when using melamine as a refining additive to the primary refiner. Fewer chips were produced. Tear, burst and tensile strength were maintained at the lower specific energy input, and this result is significant. There was no effect on the optical properties of the masses. No noticeable changes in opacity or lightness were observed.

Example 5

The thermomechanical masses prepared according to example

4 was used for this experiment to assess the effect of melamine in a post-treatment, such as bleaching.

The bulk samples - the blank (without melamine) and according to the trials (with 1.4% melamine in the primary refiner's pluggav irons) - were bleached in two independent trials with ^ 2®2

(1% by weight, calculated on the mass) in the presence of sodium silicate

(5%, calculated by mass, of a 40% silicate solution), magnesium sulfate (0.05%, calculated by mass) and sodium hydroxide (1.25%, calculated by mass). The reaction was allowed to proceed for 2 hours at 60 -2°C at a mass consistency of 10%. The initial pH of the pulp was 10.0 and at the end of 2 hours it was 9.6.

The lightness achieved for the blank was

51.5 with a spreading coefficient of 38.9 m 2/kg, while the corresponding figures for the melamine-treated pulp were respectively 55.8 and 47.9 m<2>/kg.

These figures suggest that the presence of melamine in the pulp improves the bleaching effect of a subsequent treatment.

In example 6, different paint additives are compared using the PFI mill. This is one of a number of laboratory instruments used to determine the refining properties of wood pulp. In this experiment, the number of revolutions for the measuring device is recorded, and the freeness of the mass obtained by this total number of revolutions is measured.

Example 6

Unbleached spruce kraft pulp and bleached spruce kraft pulp were refined in a laboratory apparatus for grinding pulp (PFI mill, Papirindustriens Forskningsinstitutt, Oslo, Norway, TAPPI standard 248 pm-74). The pulps were refined without additives (blind test), with 1.7 parts by weight of Congo red per 100 parts by weight pulp, with 1.5 parts by weight melamine per 100 parts by weight pulp or with 6.7 parts by weight "Procion Yellow M-RS", which is a fibre-reactive dye, per 100 parts by weight mass. The dye treatment in the case of the fiber-reactive dye was carried out at a pH of 10.5 and at a high NaCl concentration, NaCl being used in the same amount by weight of the pulp. In the PFI mill, 25 g of pulp is used for a total suspension weight of 250 g (i.e. 10% consistency).

The effect of the different additives in the PFI mill refining of unbleached spruce kraft pulp on the Canadian Standard Freeness, tensile factor, burst factor, tear factor and MIT fold number is reproduced in Table VII.

An examination of CSF-freeness for each total number of revolutions in Table VII shows that when melamine is present, a lower number of revolutions is required to

reach any desired level of freedom regardless of whether this level is e.g. 500, 400 or 300 ml.

An investigation of the strength properties reproduced in

Table VII (stretch factor, burst factor, tear factor and MIT double fold number or fold endurance) shows that at any level of refinement, the addition of melamine leads to an increased strength.

The effect of the different additives during the PFI mill refining of bleached spruce pulp in terms of Canadian Standard Freeness, stretch factor, burst factor, tear factor and MIT double fold number is reproduced in Table VIII.

An examination of CSF freeness for each total number of revolutions in Table VIII shows that when melamine is present, a lower number of revolutions is required to reach any level of freeness regardless of whether this level is e.g. 500, 400 or 300 ml. An examination of the strength properties reproduced in Table VIII shows that at any given level of refinement, the addition of melamine leads to increased strength properties.

Example 7

A previously used paper is recycled. An aqueous slurry of paper pulp is made using sodium hydroxide and with "Melamine II" added in the form of an aqueous slurry to the pulp. The pulp is then milled in a batch milling operation using sodium hydroxide and the melamine additive under such conditions that the printing ink and fillers are selectively separated from the cellulose pulp fibers. The addition of the melamine additive to the alkaline pulp results in a pulp of higher quality and with less degradation of fiber strength.

Example 8

In order to demonstrate the applicability of using the s-triazine additive in a plant on a technical scale, "Melamine II" was used in a trial run in a commercial plant. During the trial run, "Melamine II" was added in an amount of 0.25 parts per 100 parts pulp material during the chlorinating bleaching step. The data obtained during the trial run are reproduced in Table IX.

From the data in Table IX, it can be determined that when the melamine additive was used, the pulp increased tensile, tear and burst strength. The most surprising thing was that both the tear and burst strength were significantly improved. This is a significant advantage as it is normally expected that an improved tear strength is only achieved as a result of a reduced burst strength or vice versa.

In the above preferred embodiments, the melamine used in the examples can be replaced with melamine and "Melamine II" salts obtaining essentially the same results. In addition, the melamine can be replaced with ammelin. The improved results obtained by treating the wood pulp with ammelin may, however, be somewhat inferior to treatment with melamine or "Melamine II". Moreover, the additive can be effectively used for other wood pulp production processes, including all types of chemical processes and thermomechanical-chemical processes.

It has been determined that paper products produced from the wood pulp containing the s-triazine additives as defined above exhibit improved color and brightness and have improved properties in terms of ink removal from paper to be recycled, printing, ink and pigment retention, wet and dry strength, dirt- and grease resistance, dyeability and electrical properties which enable the paper to be used for reprography.

Claims (11)

1. Method for treating wood and pulp of wood, characterized in that an s-triazine compound with the formula is added wherein X is -NH2 or -OH, to the wood or pulp of wood during a step for treating said pulp of wood, and that the treatment is then continued, the s-triazine being added in an amount that is effective in terms of improving the transfer to pulp of the wood or treatment of the pulp . 2. Method according to claim 1, characterized in that the s-triazine compound is used in an amount that is effective in terms of improving the transfer of the wood to pulp and in providing a wood pulp containing the aforementioned s-triazine in an amount that is effective in terms of improve the properties of a paper product made with said pulp. 3. Method according to claim 1 or 2, characterized in that the s-triazine compound is added during the bleaching step of the aforementioned pulp treatment. 4. Method according to claim 1 or 2, characterized in that the pulp treatment is a thermomechanical pulp treatment and that the s-triazine compound is added during the refining step. 5. Method according to claim 1 or 2, characterized in that the pulp treatment is a chemical process. 6. Method according to claim 1 or 2, characterized in that the pulp treatment is a semi-chemical process. 7. Lots of firewood, characterized in that it is processed to be effective in papermaking and contains an s-triazine compound of the formula wherein X is -NH2 or -OH, the s-triazine compound being present in said pulp in an amount which is effective in terms of improving the properties of the pulp. 8. Paper product, characterized in that it has been produced from a mass of wood containing an s-triazine compound with the formula where X is -NH2 or -OH., in that the s-triazine compound is present in the paper product in an amount which is effective in terms of improving the properties of the paper <p> product. 9. Material mix, characterized in that it includes the product formed by reaction or interaction between pulp or mass of wood and an s-triazine compound with the formula wherein X is ~ NH 2 or OH. 10. Material mix, characterized in that it includes a cellulose-lignin-s-triazine, the s-triazine compound having the formula wherein X is -NH2 or OH, the cellulose being present in an amount of 70-99%, the lignin in an amount of 0.1-30% and the s-triazine compound in an amount of 0.025-5%. 11. Material mixture, characterized in that it includes lignin-s-triazine or cellulose-s-triazine, the s-triazine having the formula wherein X is -NH2 or -OH, and wherein the s-triazine is present in an amount of 0.1-10% in the case of lignin or in an amount of 0.01-5% in the case of cellulose.