JPH06264394A - Preparation of pulp slurry and method for papermaking - Google Patents

Abstract

PURPOSE:To fix an internally added chemical to pulp fiber without using aluminum sulfate in good yield by dehydrating and thickening a pulp slurry and mixing internally added chemicals in a specific state with the pulp. CONSTITUTION:A pulp slurry is dehydrated and thickened to 5-15wt.% pulp concentration and internally added chemicals such as a filler, a sizing agent, a paper strengthening agent and a yield improving agent are then uniformly mixed with the thickened pulp slurry by applying a strong shearing force to the pulp. The obtained mixture is then diluted with white water, etc., to afford a papermaking pulp slurry, which is subsequently fed to a wire part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a pulp slurry for papermaking, which is capable of efficiently adding chemicals to pulp, and a papermaking method using this pulp.

[0002]

2. Description of the Related Art Generally, pulp is bleached during papermaking.
After undergoing steps such as beating, mixing, and dilution, the pulp is finally prepared into a suspension having a pulp concentration of about 1% by weight, and then sent to a wire part for dehydration. When the pulp suspension is dewatered on the wire, the water filtered down the wire is commonly referred to as white water. This white water is circulated through a papermaking system and a raw material system and is reused as a recovered raw material or as diluted water, but in the white water, fine fibers and fillers that could not be captured by a wire, eluate from pulp, and bleaching process It contains the residual substances of the chemicals used at the time.

Incidentally, before the pulp suspension is sent to the wire part, internal additives such as fillers, sizing agents, and paper strengthening agents are added. These internal additives are usually mixed chest, In a preparation step immediately before a paper machine such as a machine chest, it is added to a pulp suspension having a concentration of 1 to 3% by weight. However, as described above, the white water used for diluting water contains inorganic anions such as sulfuric acid, sulfurous acid, chlorine, silicic acid, and phosphoric acid, and fatty acids, resin acids, and other dissolved substances from pulp. And, since many of these dissolved substances are negatively charged, while pulp is also negatively charged in water, a chemical added as an internal additive chemical is inhibited from fixing to pulp fiber and manifestation of effect. Will end up.

Therefore, in order to suppress the influence of the negatively charged dissolved substances as much as possible, a sulfuric acid band has been added in advance to neutralize the electric repulsive force of the pulp suspension prior to the addition of chemicals. , Sizing agents, paper strength agents, retention aids and other chemicals are added.

[0005]

In recent years, from the standpoint of resource conservation, the blending ratio of used paper has increased, while the degree of whiteness of newspaper has also increased. Therefore, it is necessary to strengthen the bleaching of the mechanical pulp to raise the whiteness of the pulp, but when the bleaching is strengthened, the dissolved components generated from the mechanical pulp tend to increase. That is, the zeta potential of the pulp suspension becomes negatively high because the amount eluted from the mechanical pulp and the residue of the added chemicals from the bleaching step increase. For this reason, the required amount of the sulfuric acid band for neutralizing the system increases, but addition of a large amount of the sulfuric acid band does not result in papermaking.
Not only does H decrease and the storage stability of the paper deteriorates, but an excessive sulfate band, on the contrary, inhibits the fixing of the chemical.

That is, the increase and accumulation of the dissolved solid content in white water due to the increase of the blending amount of mechanical pulp and the enhancement of bleaching cannot be completely eliminated by only adding the sulfuric acid band. An increase in dissolved substances in white water leads to a decrease in the yield of the added chemicals on the pulp fiber, and the added chemicals that have not settled on the pulp circulate in the white water, react with hydrolysis and other dissolved substances, and Make the atmosphere worse. As a result, it causes operational troubles such as stains on the paper machine, and makes it more difficult to control the paper quality by adding chemicals.

Therefore, the present invention provides a method for preparing a pulp slurry for papermaking, which is capable of efficiently fixing a chemical agent to pulp fiber without being affected by a dissolved substance in white water, instead of adding a sulfuric acid band. The purpose is to provide. A further object of the present invention is to provide a method for making paper using a novel papermaking pulp slurry.

[0008]

A method for preparing a pulp slurry for papermaking according to the present invention comprises dehydrating and reducing water content from a pulp slurry prepared by suspending and dispersing pulp in water to reduce the pulp concentration to 5
~ 15% by weight, a step of applying a strong shearing force to the pulp to fluidize it, and a filler, a sizing agent, and a paper strengthening agent before the fluidization of the pulp after the dehydration, during the fluidization or after the fluidization. From the step of adding internal additives such as agents and retention aids, the step of uniformly mixing the pulp and the internal additives in the fluidized state, and the step of diluting by adding water to supply to the wire part It is characterized by Further, the papermaking method according to the present invention is characterized in that a papermaking pulp slurry having a pulp concentration of 0.5 to 1.5% by weight obtained as described above is used to carry out papermaking by a conventional method.

Prepared in the present invention is the final papermaking pulp slurry for feeding to the wire part. The pulp used here is, for example, groundwood pulp (GP), refiner ground pulp (RG).
P), thermomechanical pulp (TMP), sulfate pulp (KP), semi-chemical pulp (SCP) and the like can be mentioned, but there is no problem even if they are produced by a manufacturing method other than the above. Similarly, there is no restriction on the type of pulp material, and recycled pulp may be used.

The pulp slurry prepared by suspending and dispersing the above pulp in water is dehydrated to a pulp concentration of 5 to 15% by weight,
Preferably, the internally added chemicals are added and mixed in the medium concentration range of 8 to 12% by weight. Conventionally, it has been common knowledge that the pulp concentration when an internal additive is added and mixed in the papermaking step is 1 to 3% by weight. This is because when the pulp concentration exceeds 3% by weight, the free water outside the pulp is extremely small even if the pulp is sufficiently moist, and even if a chemical is added, uniform mixing and fixing can be achieved. Because I can't hope. When the pulp slurry and the filler slurry are compared at the same concentration of 10% by weight, the filler slurry is in a state where the filler is present in the water, whereas the pulp slurry has most of the water retained in the pulp, and the free water is extremely high. There are few and it cannot be said that it is a slurry state. Reflecting such a water content of the pulp, while the pulp slurry having a pulp concentration of 1 to 3% by weight, which is a conventional pulp concentration when a chemical is added, is in a water suspension dispersion state, the concentration of the present invention is 5 to 15%. When it is more than 8% by weight, it cannot be called a slurry.

Regarding the relationship between pulp and water, DWReev
e: Tappi, 69 (6), 84 (1986) reported as follows.
The amount of water that the pulp fiber can hold is, for example, in the case of unbeaten unbleached softwood kraft pulp, the water content per ton of dry pulp is 1 to 2 m ³ inside the fiber wall and 1 inside the rumen.
It is about 10 m ³ . These waters are not easily replaced with so-called free water outside the fibers and do not contribute to the dissolution or dispersion of the added chemicals. According to the calculation based on this report, the amount of water retained by the fibers in the 3% by weight pulp suspension is very small compared to the total amount of water. In the case of liquid, 22-100 of the total amount of water
% Are retained inside the fiber walls and the lumen.

Therefore, it is common knowledge that when the concentration is 5 to 15% by weight, particularly 8% by weight or more, the amount of free water is too small to uniformly disperse and mix the additive chemicals. Contrary to this common sense, the fact that the present invention enables uniform mixing at a pulp concentration of 5 to 15% by weight is based on fluidizing pulp. In other words, when the pulp in the medium-concentration region with a pulp concentration of 8% by weight is agitated as it is, it never fluidizes and is not in a state where chemicals can be added, but by applying a strong shearing force to the pulp to agitate it. For the first time, it will fluidize and behave like water. Fluidization can be explained from the relationship between shear force and shear stress. Under weak shear, the shear stress of pulp increases significantly with increasing pulp concentration. Therefore, when the shearing force is increased, the turbulent flow of the pulp suspension proceeds, and the shearing stress does not depend on the pulp concentration. The state at this time is fluidization, and the relationship between the shearing force and the shearing stress has a linear relationship similar to that of water which is a Newtonian fluid. In this case, as a means for stirring while applying a strong shearing force, for example, a hermetic mixer having an inhibiting plate at several places on the inner wall surface of a cylindrical container and a stirring blade rotating at high speed in the center of the container -, And a medium-concentration high-share mixer known to be used in a multi-stage bleaching process of chemical pulp can be diverted.

In the present invention, the internal chemicals to be added include fillers such as talc, clay, white carbon and calcium carbonate, rosin emulsions, sizing agents such as alkyl ketene dimer, paper strengths such as high molecular weight polyacrylamide and starch. Examples thereof include enhancer, anionic or cationic polymer polyacrylamide, retention aid such as polyethyleneimine, and sulfuric acid band. It is important that these chemicals are added in a high concentration range of pulp concentration of 5 to 15% by weight. Regarding the specific timing of addition, the chemical may be added first and the pulp may be subsequently treated with a strong shearing force, or may be added during the shearing treatment. One chemical may be added twice or more, or a plurality of chemicals may be added at different timings. In any case, the pulp is fluidized by the strong shearing force, and chemicals such as sizing agents and paper strengthening agents are evenly mixed with the pulp and efficiently adhere to the pulp fiber, resulting in high yield and excellent chemical effect. Show.

The pulp having a pulp concentration of 5 to 15% by weight mixed with the additive chemicals in the fluidized state as described above is subsequently diluted with white water or the like to give a pulp concentration of 0.5 to 1.
A pulp pulp for papermaking of about 5% by weight is prepared.

Further, the papermaking method according to the present invention uses the pulp slurry for papermaking obtained as described above to make a paper by a conventional method. The paper is made into paper by being squeezed by the press part and dehydrated by the dryer part.

[0016]

As described above, the present invention has a pulp concentration of 5 to 15
Although the internal chemicals are mixed at a high concentration, which exceeds the conventional wisdom of weight%, chemical mixing at such a high concentration is
It cannot be discussed in the same dimension as the usual addition and mixing at a concentration of 1 to 3% by weight. In other words, the fibers in the pulp suspension and the degree of contact between the fibers and the chemicals are influenced by the thickness of the layer of free water that enables suspension. In the low concentration range of 1 to 3% by weight, there is a thick layer of free water, and the thinner the layer of free water, the greater the chances of fibers coming into contact with each other and the degree of contact between fibers and chemicals. Therefore, it is considered that the efficiency of adhesion of chemicals to pulp fiber is improved accordingly. However, for example, in the medium concentration range of 8% by weight or more, since the layer of free water originally does not exist or is extremely thin, there is no relationship between the amount of free water and the fibers and the degree of contact between the fibers and chemicals. can not see. Thus, the behavior of pulp fibers in the low-concentration region and the behavior of pulp fibers in the medium-concentration region are completely different, and in all concentration regions, the degree of contact between fibers or between fibers and chemicals does not increase with increasing concentration.

In the present invention, it is considered that by mixing the chemicals at a high pulp concentration, the chemicals are efficiently adhered to the pulp fibers and a high yield and an excellent addition effect are obtained, for the following reason. To be done. First, when a high-concentration pulp fluidizes, it behaves similarly to water, so even if it does not have a layer of free water, it easily blends evenly with the chemicals present around the fluidized pulp fiber. Can be mixed. Secondly, the mixing of chemicals at high pulp concentrations is done in the absence or only a small amount of white water containing many dissolved substances that also impede chemical addition, which are also negatively charged. It will be. For this reason,
The adverse effects of dissolved substances in white water can be suppressed, chemicals can be efficiently fixed to pulp, and the yield is dramatically improved.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples.

[Example 1] Unmelted softwood bleached sulphate pulp (LBKP) which has been thoroughly washed with fresh water as pulp, TMP with the highest dissolved solid content such as eluate from pulp and residual bleaching chemicals as diluted water I prepared bleached white water. First, using a centrifuge, LBKP was once dehydrated to a pulp concentration of 25% by weight, and then diluted with bleached white water to obtain a pulp concentration of 1% by weight (comparative example), 3% by weight (comparative example), 10% by weight ( Three types of pulp slurry samples (invention examples) were prepared. Apart from
200mm inner diameter as a device that gives strong shearing force to pulp
On the inner wall of the 2.5 L capacity cylindrical closed container, four vertical ribs with a height of 20 mm and an isosceles triangular cross section are attached at equal intervals, and a height of 10 mm and a width of 15 are provided around a 100 mm diameter rotor.
Rotation speed 0 to 34 with 3 mm vertical ribs attached at even intervals
A mixer of 00 rpm was prepared.

Pulp was put in this mixer, and the number of rotations of the rotor for every pulp concentration sufficient for the fluidization of the pulp by 60 seconds after the start of operation, which was confirmed in a preliminary experiment, 9
00 rpm (concentration 1% by weight) 1200 rpm (concentration 3
Wt%), 1850 rpm (concentration 10 wt%),
The rotor speed was set and operation was started. Start operation 6
After 0 seconds, chemicals were injected into the fluidized pulp from the wall surface of the mixer with an injection needle, and the operation was continued. Operation start 135
After a few seconds, it slowed down and stopped naturally. The chemicals were added in the order of a sulfuric acid band, a sizing agent (rosin emulsion), and a size fixing agent (cationic acrylamide: molecular weight 200,000).
In addition, the test was performed four times for each pulp concentration while changing the addition rate of the sulfuric acid band.

Using the pulp slurries to which the chemicals have been added as described above, the basis weight is 60 g / m by the TAPPI method.
We made ² handmade papers and evaluated the following 2 items,
The results are shown in Tables 1 and 2. Sizing degree: Steckigt sizing degree according to JIS P-8122 Contact angle attenuation rate: About 3% by weight sulfuric acid band added paper,
5 μl of water was dropped, and the attenuation rate of the contact angle from immediately after dropping to 100 seconds after was calculated.

[0022]

[Table 1]

[Table 2]

From Table 1, when the sulfuric acid band addition rate is the same,
The invention examples (1-A to 1-D) are comparative examples (1-a to 1-).
The degree of size is more than twice that of h). On the other hand, no significant difference was observed between the 1 wt% pulp and the 3 wt% pulp between the comparative examples. Moreover, from Table 2, the attenuation rate of the contact angle of the paper is 3 in the invention example compared with the comparative example.
It shows twice as long-lasting potency.

Example 2 To the three types of pulp slurry samples prepared in Example 1, a pulp concentration of 6% by weight was added to obtain four types. For these four types of pulp slurry samples, except that cationic starch was used as the chemical,
A handmade paper was produced in the same manner as in Example 1.

With respect to the obtained handmade paper, in order to examine the effect of increasing the paper strength by adding starch, the following three items were evaluated, and the results are shown in Table 3. The results of measuring the amount of starch in each paper are shown in Table 4. Specific burst strength: JIS P-8112 Internal strength: JTAPPI 18 Breaking length: JIS P-8113

[0026]

[Table 3]

[Table 4]

From Table 3, in the comparative example, the pulp concentration is 1
% By weight (2-a to c) and pulp concentration 3% by weight (2
There is no significant difference in pulp strength between the cases of -d to f). Compared to these comparative examples, the concentration of the invention example was 6% by weight.
In the case of (2-A to C) and the concentration of 10% by weight (2-D to F), a remarkable paper-strengthening effect was observed. Also, Table 4
Therefore, the higher the pulp concentration, the higher the starch yield,
In particular, it can be seen that the yield of the invention example is dramatically high.

[Example 3] Similar to Example 2, four types of pulp slurry samples having a pulp concentration of 1% by weight, 3% by weight, 6% by weight, and 10% by weight were prepared, and a paper strengthening agent ( Except that (cationic polyacrylamide) was used.
A handmade paper was prepared in the same manner as in Example 2.

The obtained paper was evaluated from the three items of specific burst strength, internal strength and breaking length in order to confirm the effect of increasing the paper strength, and the results are shown in Table 5. Further, in order to examine the yield of the paper strength enhancer in each handmade paper, the nitrogen content in the paper was measured and shown in Table 6.

[0030]

[Table 5]

[Table 6]

In Table 5, about the relationship between pulp concentration and paper strength, almost the same result as the cationic starch of Example 2 was obtained. That is, when compared at the same level of addition rate of the synthetic paper strength enhancer, the effect of increasing the paper strength of the invention example was remarkable as compared with each comparative example. Further, from Table 6, it can be seen that in the invention examples, the nitrogen content in the paper is high, and the yield of the paper strengthening agent is high.

[0032]

As described in detail above, according to the pulp slurry preparation method of the present invention, a high yield of the chemicals added to the pulp and an excellent medicinal effect can be obtained. It has become possible to significantly reduce the rate of addition of chemicals compared to the past. Further, according to the papermaking method of the present invention, the papermaking cost can be significantly reduced.

Claims (2)

[Claims] 1. A pulp slurry prepared by suspending and dispersing pulp in water is dehydrated and reduced to have a pulp concentration of 5 to 15% by weight.
A step of fluidizing the pulp by applying a strong shearing force to the pulp, before the fluidization of the pulp after the dehydration, during the fluidization or after the fluidization, a filler, a sizing agent, a paper strengthening agent, and a retention rate. A step of adding an internally added chemical such as an improver, a step of uniformly mixing the pulp and the internally added chemical in a fluidized state,
And a method for preparing a pulp slurry for papermaking, which comprises a step of adding water to the wire part and diluting it. 2. A papermaking method characterized in that a pulp slurry for papermaking having a pulp concentration of 0.5 to 1.5% by weight is prepared according to the preceding paragraph, and the slurry is produced by a conventional method.