JPS6247999B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the production of mechanical pulp with improved properties. Traditionally, newsprint is made of about 3 parts groundwood pulp and 1 part groundwood pulp.
It is manufactured from a furnish consisting of 100% chemical pulp. 100% groundwood pulp is produced by pressing logs against a rotating grinding stone.
It is a component of paper furnish that is obtained at a yield close to that of Apart from economic considerations, groundwood pulp imparts several desirable properties to the sheet. In particular, the high light scattering coefficient of groundwood pulp provides opacity to the paper and allows the use of very thin sheets. The high oil absorption properties of groundwood pulp improve ink absorption during printing. Pollution problems associated with the production of groundwood pulp are minimal. Chemical pulp components are usually produced by either a kraft or sulfite process.
A yield of 45-65% by weight is obtained. Chemical pulp is expensive, requires a large amount of wood resources for the crusher, and creates serious pollution problems. The current trend in newsprint manufacturing is therefore towards a reduction in the use of chemical pulp. Chemical pulps are used to impart properties to the furnish that improve its runability. Runability is the combination of the properties that allow a wet paper web to move at high speed through the forming, compacting and drying sections of a paper machine, and the properties that allow a dry paper to be wound and printed an acceptable number of times without breaking. Regarding. Runability is critical to the efficiency of paper machines and printing rooms, and this efficiency is critical to profitability. Despite the above-mentioned disadvantages, chemical pulps still remain a practically essential component of newsprint stocks due to runability. Surprisingly, the mechanism by which chemical pulp improves runability is still not fully understood. There is growing evidence that the critical properties for efficient operation of high speed paper machines are high wet web elongation and drainage rates. Wet and dry elongation prevents stress concentration around paper flaws where paper breaks would normally occur. A high drainage rate reduces moisture content, resulting in a paper web that is less weak.
These effects have recently been discussed in DMHarvey, A.J.
"Pulp and Paper Canada" by Barnet and LMLyne (7)
Papers and DF in T154-6 (July 1977)
Rutland, AY Jones, PMShallhorn, J. Ticky
and A. Karnis in Pulp and Paper Canada 78(4) T99-105 (April 1977). In conventional mechanical wood pulp, wet elongation is obtained at the expense of drainage. That is, highly refined pulps have high wet elongation and low drainage rates, while the opposite is true for lightly refined pulps. Mechanical wood pulp can be produced in two open refiners and in pressurized equipment at higher temperatures. The resulting pulps are called refined mechanical pulp (RMP) and thermomechanical pulp (TMP), which are of higher quality than groundwood pulp and are obtained with a yield of more than 95%, and
Pollution problems are minimal. These, however, are not substitutes for chemical pulp and are generally not accepted as the sole furnish for newsprint machines. Attempts have been made to further improve mechanical pulp by chemical pretreatment of wood chips prior to refining. A number of such processes are currently under development and are referred to as chemical mechanical processes (CMP) and thermochemical mechanical processes (TCMP). Generally, these processes increase energy requirements during manufacturing. Although useful properties are developed at some cost, substantial improvements in properties of fundamental importance to runability, namely drainage and wet elongation, are generally not observed. Surprisingly, it has been found that both the drainage and wet elongation of mechanical wood pulps can be improved by controlled chemical treatment after production of these pulps. According to the present invention, the pulp is heated to about 3
A method for processing mechanical wood pulp is provided, which comprises heat treating with a treatment solution containing sodium sulfite containing sufficient alkali to maintain the above pH.
Although the heat treatment is sufficient to cause a reaction with the pulp and increase the wet elongation of the pulp, it substantially dissolves the lignin from the pulp and reduces the pulp yield to less than about 90% by weight. carried out at high temperatures for an insufficient period of time. Due to the improvements in both drainage and wet elongation achieved by the present invention, newsprint has been treated with this treatment in order to reduce the proportion of chemical pulp or to achieve high runability without the use of chemical pulp. It becomes possible to use pulp. The method of the present invention can be applied to any type of mechanical pulp mentioned above, i.e. groundwood pulp, RMP, TMP,
CMP and TCMP can also be implemented.
Improvements in drainage and wet elongation properties are also achieved with each of these types of mechanical pulps. The term "mechanical wood pulp" is used herein to mean wood pulp that has been converted into a fibrous form by mechanical action and is suitable for being formed into sheets of paper. Therefore, wood pulp with a non-fibrillated, smooth surface, rigid and unsuitable for the production of paper sheets, such as those obtained by heating wood to a temperature above the softening point of lignin and subjecting it to mechanical action, is be excluded. Mechanical pulp is often produced by two-step refining. In the production of thermomechanical pulp, for example, a pressure refining step is usually followed by an atmospheric refining step. The chemical treatment of this invention can be applied to the pulp during the above-mentioned refining to achieve advantageous effects. The invention can also be applied to the respective parts separated from the mechanical pulp. For example, mechanical pulp is commonly separated into "accept" and "reject" portions by screens or hydrocyclone separators. The present invention can be applied to either or both of these separated parts. In particular, the invention provides mechanical pulp with acidic sodium sulfite or sodium sulfite, with or without additional alkali such as sodium hydroxide or soda carbonate, at elevated temperatures sufficient to cause a reaction with the pulp. However, it consists of a treatment for a time not long enough to cause substantial dissolution of lignin from the pulp. It was found that as the reaction progressed, the PH of the treatment liquor decreased, probably as a result of hydrolysis of the acetyl groups on the pulp. When the pH drops below 3, there is a risk of damaging the fibers through hydrolytic action which leads to a decrease in the strength of the fibers. Wood fibers that have been subjected to mechanical processes such as refining are particularly susceptible to acid degradation. Therefore, it is essential to the present invention that sufficient alkali be present in the chemical charge to prevent the PH from dropping below 3 during processing. The exact amount of alkali required will depend on the acetyl content of the feed wood and cannot be precisely specified, but is readily determined by experimentation. The alkali requirement can be fully met with sodium sulfite. However, since only half of the sodium in sodium sulfite is utilized for neutralization, it is usually more economical to meet a portion of the alkaline demand by addition of sodium hydroxide or soda carbonate. However, the PH of the mixture is preferably kept below about 12. This is because hemicellulose is dissolved from the wood fibers due to the high pH, resulting in a decrease in yield. In a preferred embodiment of this invention, the amount of sodium sulfite used is 4-10% by weight based on the dry fiber content of the mechanical pulp. However, lower amounts, up to about 1% by weight, can be used with diminishing beneficial effects. Below 1% by weight of sodium sulfite, the improvements obtained are too small to justify the processing costs. Similarly, about 25 of the pulp
Improvements are also observed with chemical loading up to % by weight, but the additional expense is not justified by small additional improvements. Therefore, generally between about 1% and about 25%, preferably between about 4% and about 10%, of the chemical is charged by weight of the mechanical pulp. The chemical charge preferably has a pH between about 9 and about 12 and contains sufficient alkali to maintain the pH above 3 during the reaction with the sodium sulfite. The concentration of the pulp, expressed in parts by weight per 100 parts by weight of water, is between 5% and 50%, preferably about
Preferably it is carried out at a concentration of 25%. Lower concentrations increase equipment size and energy costs, and dilution of the reactants reduces reaction rates and requires longer reaction times. Pulp with a consistency higher than 50% is not easily obtained by mechanical compaction of aqueous pulp. Reaction times and temperatures can vary over a wide range. The reaction must not proceed to such an extent that the lignin is substantially dissolved, as the reaction must increase drainage and wet elongation, and dissolution of lignin will reduce pulp yield and also cause pollution problems. This is an essential requirement. In practice,
Application of our invention is 90% on starting mechanical pulp basis
Limited to processes that result in pulp yields exceeding . The minimum reaction time to obtain an improvement in wet elongation of more than about 10% with the present invention is about 30% at 100°C.
minutes; at higher temperatures, shorter reaction times are used. The effects of time and temperature are
Pulp and Paper Magazine Canada (Pulp and Paper Mag.Can.
), 58(3), 228 (1957). An "H-factor" can be used to simultaneously vary time and temperature to produce a given degree of heat treatment. In the practice of this invention, the pulp is therefore subjected to a minimum degree of heat treatment equal to 30 minutes at 100°C and a pulp yield of 90°C.
exposed to a maximum degree of heat treatment equal to or greater than %. The invention is further illustrated by the following examples. In each of the Examples, the pulp yield as defined above exceeded 90%. In addition, in the following examples, the pulp was drained using a 4-diameter wire mesh with a 58 x 64 mesh inside.
A pulp suspension was added to an inch-sized cylinder, and the time required for the water level to drop by 8 inches when the lower pot was opened to drain the water was measured and used as the value.
In addition, the wet elongation was defined as the point at which the maximum load was applied when the handmade paper was clamped and stretched without drying. For details of these measurement methods, please refer to the above-mentioned "Pulp and Paper Canada" (7) T154-6. Example 1 This example illustrates the application of the present invention to various mechanical pulps. The mechanical pulp was immersed in a sodium sulfite solution at pH 9.0 and pressed to a pulp consistency of 25%. The amount of chemicals remaining with the pulp was 4% by weight based on dry fiber content. The pulp is
Handsheets were produced by heating in an autoclave at 140° C. for 30 minutes and the paper properties were measured. The results obtained are shown in Table 1. Note that the pH of the treatment solution after the heat treatment was all over 3.0.

[Table] From the results in Table 1, it can be seen that chemical treatment of each pulp improved water drainage and increased wet elongation in all cases, without adversely affecting other properties. Probably. Example 2 This example illustrates the effect of reaction temperature on pulp properties. As in Example 1, mechanical pulp impregnated with an aqueous solution of 4% by weight of sodium sulfite based on the dry fiber content at pH 9 was heat treated at various temperatures for 30 minutes. As a result, it had the properties shown in Table 2.

[Table] The results in Table 2 show that the water drainage and wet elongation properties of TMP at 140°C were more improved compared to 100°C. Example 3 This example illustrates the effect of chemical amount on pulp properties. In the same manner as in Example 1, TMP impregnated with an aqueous solution of 4% and 10% by weight of sodium sulfite on a dry fiber basis was heated at 140°C for 30 minutes at pH 9.
was heated to produce handsheets and their properties were measured. The results are shown in Table 3.

TABLE The results in Table 3 show the beneficial effects of both chemicals on the usage rates. The main effect of using a higher proportion of chemicals is a higher PH during the reaction.
retention resulting in greater improvements in rupture and tear length. Example 4 This example illustrates the effect of PH on pulp properties during the reaction. Mechanical pulp heated with 4% by weight of sodium sulfite on a dry fiber basis in the following PH range is 4th
A product was produced with the properties shown in the table.

[Table] From the results in Table 4, it is clear that when the pH drops below 3, the rupture and fracture length are significantly reduced by heating. It has also been observed that this deterioration becomes more pronounced as the reaction temperature increases and the reaction time increases. The present invention therefore provides a method for processing mechanical wood pulp that improves both the drainage and wet elongation properties of the mechanical pulp. Various modifications are possible within the scope of the invention.

Claims (1)

[Scope of Claims] 1. A method for treating mechanical wood pulp, comprising: subjecting wood to mechanical action to form a fibrous mechanical wood pulp suitable for forming into paper sheets; The wood pulp has a pulp concentration of about 5% to about 5%, expressed in parts by weight per 100 parts by weight of water.
50%, reacts with the pulp at elevated temperatures with a treatment solution containing sodium sulfite in an amount of about 1 to about 25% by weight, based on the dry fiber content of the pulp, and drains the pulp. and heat-treated for a time sufficient to increase wet elongation but insufficient to reduce the pulp yield to 90% by weight or less, and in which the processing liquid reacting with the pulp has a pH of approximately A method for processing wood pulp for a papermaking machine, characterized in that the pulp contains sufficient alkali to maintain a pH of 3 or higher. 2. The initial pH of the treatment liquid is between about 9 and about 12, the alkaline content of which is partially provided by sodium hydroxide and/or soda carbonate. Method described. 3. The method of claim 1 or 2, wherein the amount of sodium sulfite is from about 4 to about 10% by weight, based on the dry fiber content of the mechanical wood pulp. 4. A method according to claim 1, 2 or 3, characterized in that the minimum heat treatment time is equal to a heat treatment time of 30 minutes at a temperature of about 100°C.