High-kappa thicknessed chemi-thermo mechanical pulp and process for making same

Abstract

The application discloses a kind of high thickness of high bulk pulp and its preparation process, belong to papermaking technical field.The technical scheme is as follows: including the following steps, raw material preparation and pre-soaking treatment, reaction bin reaction, high consistency refining treatment, bleaching, latent elimination, low consistency refining, screening and washing, 1) raw material preparation and pre-soaking treatment: the raw material wood chip is broken, then pre-soaking is carried out, control pre-soaking temperature 80~90 ℃, pH value 9.8~10.2, liquid level ≥50%, ADI back pressure ≥4bar, NaOH dosage is 1.5%~2.0% of dry wood chip weight;2) high consistency refining treatment: the wood chip after pre-soaking is sent into high consistency refiner for refining, refining consistency 35~45%;3) bleaching: pulp after refining is sequentially subjected to one-stage bleaching and two-stage bleaching.The application process has high stability, and can realize the synchronous and stable improvement of bulk and freeness.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, specifically relating to a high bulk mechanical pulp and its preparation process. Background Technology

[0002] Chemimechanical pulp (CMP) is a high-yield pulping product. Among them, bleached chemithermomechanical pulp (BCTMP) has become one of the core raw materials in the paperboard production industry due to its significant technological advantages. Compared with traditional chemical pulp, BCTMP has a yield of up to about 90%, far exceeding the approximately 50% yield of chemical pulp, which greatly improves the utilization rate of fiber raw materials and effectively reduces raw material consumption costs. At the same time, its production cost is lower than that of chemical pulp, and the pulp bulk is excellent, enabling paperboard to have better stiffness and cushioning performance at the same basis weight. This aligns with the current trend of lightweight and high-strength paperboard production, and therefore it is widely used.

[0003] In the preparation of chemimechanical pulp and the production of paperboard, bulk is a key indicator for measuring the quality of chemimechanical pulp and even the performance of the finished paper, directly determining the market competitiveness of the final product. Specifically, the amount of bulk not only directly affects the stiffness of the paper—higher bulk allows the paperboard to have better rigidity without increasing the basis weight, avoiding deformation and damage during transportation and use; it also significantly affects the printability of the paper. Appropriate bulk allows ink to penetrate evenly, reducing lint and dust, and improving the clarity and layering of printed patterns. In addition, the stability of bulk is closely related to the uniformity of the finished product's basis weight. If the bulk fluctuates too much, the basis weight deviation of the paperboard will exceed the standard range, affecting the product qualification rate and increasing production losses.

[0004] However, in actual production, the control of bulk thickness mainly relies on the adjustment of process parameters in the prepreg stage. However, existing technologies often struggle to stably and synergistically optimize multiple indicators such as bulk thickness, freeness, and brightness by adjusting a single or a few parameters simultaneously. Common challenges include: increasing bulk thickness may lead to fluctuations in freeness or a decrease in brightness; improper combinations of process parameters can easily cause fiber over-reaction or degradation, affecting pulp strength and yield.

[0005] Therefore, there is an urgent need for a systematic, stable, and collaboratively optimizable process to improve the bulk thickness of chemical mechanical pulp. Summary of the Invention This invention provides a high bulk mechanical pulp and its preparation process, which has high process stability and can achieve a simultaneous and significant increase in bulk and freeness.

[0006] The technical solution of this invention is as follows: The first aspect discloses a process for preparing high bulk mechanical pulp, including the following steps: raw material preparation and pre-impregnation treatment, reaction chamber reaction, high-consistency pulping treatment, bleaching, anti-latency treatment, low-consistency pulping, screening and washing.

[0007] 1) Raw material preparation and pre-impregnation treatment: The raw wood chips are crushed and then pre-impregnated. The pre-impregnation temperature is controlled at 80~90℃, the pH value at 9.8~10.2, the liquid level at ≥50%, the back pressure of the pre-impregnation spiral ADI at ≥4 bar, and the amount of NaOH used is 1.5%~2.0% of the oven-dry weight of the wood chips. The synergistic effect of high temperature and alkali can ensure that the wood chips are fully and uniformly chemically pretreated, and the fibers are moderately softened, preserving the potential for bulk in subsequent pulping. High temperature can significantly increase the temperature of the wood chips, effectively softening lignin and hemicellulose, and greatly reducing the binding force between fibers, laying the foundation for the complete separation (rather than cutting) of fibers in the subsequent process. This temperature is the key range for the glass transition of lignin, which can maximize the softening effect without causing a large amount of degradation. Moderate alkalinity can effectively neutralize the acidic substances in the wood chips, promote the dissolution of some hemicellulose and resin, and further weaken the connection between fibers. At the same time, it avoids excessive swelling of cellulose and serious damage to the strength of the fibers caused by excessive alkalinity, protecting the inherent stiffness and length of the fibers.

[0008] 2) High-consistency pulping treatment: The pre-impregnated wood chips are fed into a high-consistency pulper for pulping. The pulping concentration is 35~45%. The gap between the cone and the flat sections of the pulper is controlled at 0.25~1.25mm. If the pulp concentration is too low (e.g., <35%) during the pulping process, the pulping action is mainly characterized by shearing and cutting between fibers, resulting in a large number of fine fibers and a sharp decrease in freeness. If the concentration is too high (e.g., >45%), although the friction between fibers is large, the flowability is poor, energy consumption is high, and it is easy to cause excessive fiber crushing and fibrillation, which also leads to a loss of bulk and freeness. Pulping at a concentration of 40% ensures that there is a sufficient fiber pad between the pulping discs, so that the pulping force is mainly transmitted through friction, compression, and kneading between fibers, prioritizing the dissociation and loosening of fiber bundles rather than the cutting and fibrillation of individual fibers. This perfectly matches the "easily separable but inherently strong" fiber state created by the prepreg stage, effectively balancing fiber separation and the preservation of its inherent structure, which is the key to achieving high bulk.

[0009] High-temperature alkali pre-impregnation and medium-concentration refining work together to ensure that the refining path is dominated by physical decomposition of fibers. This increases bulk while maximizing the preservation of fiber length and coarseness, which is the fundamental reason why the freeness is kept at a high level (630-640 mL CSF).

[0010] 3) Bleaching: After grinding, the pulp is subjected to first-stage bleaching and second-stage bleaching in sequence; during the first-stage bleaching, the concentration of bleaching agent is controlled at 18~20%, the temperature is 90~100℃, and the time is 80~85min. In the first stage of bleaching, the dosage of hydrogen peroxide is 20-40 kg / bdt (kg / dt), the dosage of alkali is 10-20 kg / bdt, the dosage of stabilizer is 1-4 kg / bdt, and the dosage of chelating agent is 0.5-3.5 kg / bdt. In the second stage of bleaching, the dosage of hydrogen peroxide is 45-65 kg / bdt, the dosage of alkali is 15-25 kg / bdt, the dosage of stabilizer is 1.5-4.5 kg / bdt, and the dosage of chelating agent is 0.5-3.5 kg / bdt. The temperature is controlled at 90~100℃ and the bleaching time is 90~100min during the two-stage bleaching process; the pulp concentration is maintained at 25~28%; this can effectively improve the pulp whiteness without affecting the already obtained bulk.

[0011] Preferably, the wood chips are a mixture of 80% poplar and 20% eucalyptus.

[0012] Preferably, in step 3), the bleaching agent is H2O2, the chelating agent is diethyltriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA), the stabilizer is one or more of sodium silicate, magnesium sulfate, and sodium tripolyphosphate, and the alkali is NaOH.

[0013] Preferably, the screening process is divided into a first-stage screening, a second-stage screening, and a slurry screening. The first-stage slurry discharge rate is 17-22%, the flow rate is ≤10000L / min, and the concentration is ≥2%. The second-stage slurry discharge rate is 30-40%, the flow rate is ≤8000L / min, and the concentration is ≥2%. The slurry from the first-stage and second-stage screenings is then ground. The slurry concentration entering the grinding mill is ≥5.5%, the good slurry flow rate is ≤7000L / min, the reflux pipe valve opening is ≥35%, and the mill power is ≥1500kW. After grinding, the slurry screen is an external flow pressure screen with a screen gap of 0.15mm. The good slurry passing through the slurry screen, as well as the good slurry from the first-stage and second-stage screenings, enters the subsequent washing process. The slurry from the slurry screen is circulated and ground.

[0014] Secondly, the process for preparing the chemimechanical pulp described above is disclosed.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves a simultaneous and significant increase in both bulk and freeness: through specific optimization of the combination of pre-impregnation temperature, pH, and pulping concentration (pre-impregnation temperature 80~90℃, pH=9.8~10.2, pulping concentration 35~45%), the bulk of the chemimechanical pulp is stably increased to 3.18cm. 3 / g, and successfully maintained the freeness at a high level of over 630mL CSF, providing a basis for excellent freeness and bulk in the paper.

[0016] 2. The process of this invention not only increases the bulk but also successfully solves the problem of possible decrease in whiteness. By optimizing the two-stage bleaching conditions, the whiteness can be simultaneously achieved (≥76.0% ISO) while maintaining the stability of freeness (630-650 mC SF).

[0017] 3. The process of this invention has high stability and good reproducibility, and is suitable for large-scale industrial production. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.

[0019] Example 1 The preparation process of the high bulk mechanical pulp includes the following steps: raw material preparation and pre-impregnation treatment, reaction chamber reaction, high-consistency pulping treatment, bleaching, anti-latency treatment, low-consistency pulping, screening and washing, specifically: 1) Raw material preparation and pre-impregnation treatment: The raw material is a mixture of 80% poplar and 20% eucalyptus wood chips, which are then crushed and pre-impregnated. The pre-impregnation temperature is controlled at 88℃, the pH value is 10.0, the liquid level is 50%, the back pressure of the pre-impregnation spiral ADI is 4 bar, and the amount of NaOH used is 1.8% of the weight of the oven-dry wood chips. 2) High-consistency pulping treatment: The pre-impregnated wood chips are fed into a high-consistency pulper for pulping. The pulping concentration is 40%. The gap between the cone and the flat zone of the pulper is controlled at 0.75 mm and 0.95 mm, respectively. 3) Bleaching: After grinding, the pulp is subjected to first-stage bleaching and second-stage bleaching in sequence; during the first-stage bleaching, the bleaching agent concentration is controlled at 18%, the temperature is 100℃, and the time is 80min. In the first stage of bleaching, the dosage of hydrogen peroxide is 30 kg / bdt, the dosage of alkali NaOH is 15 kg / bdt, the dosage of stabilizer is 2.5 kg / bdt, and the dosage of chelating agent diethyltriaminepentaacetic acid (DTPA) is 2 kg / bdt. In the second stage of bleaching, the dosage of hydrogen peroxide is 55 kg / bdt, the dosage of alkali NaOH is 20 kg / bdt, the dosage of stabilizer magnesium sulfate is 3 kg / bdt, and the dosage of chelating agent diethyltriaminepentaacetic acid (DTPA) is 2 kg / bdt. The temperature was controlled at 90℃ and the bleaching time was 95 minutes during the two-stage bleaching process; the pulp concentration was maintained at 28%. The screening process consists of primary screening, secondary screening, and slurry screening. Primary screening has a slag discharge rate of 20%, a flow rate of 10,000 L / min, and a concentration of 2%. Secondary screening has a slag discharge rate of 35%, a flow rate of 8,000 L / min, and a concentration of 2%. The slurry from primary and secondary screening is then milled. The milling process uses a slurry concentration of 5.5%, a good slurry flow rate of 7,000 L / min, a return pipe valve opening of 35%, and a mill power of 1500 kW. After milling, the slurry is screened using an external flow pressure screen with a screen gap of 0.15 mm. The good slurry passing through the slurry screen, along with the good slurry from primary and secondary screening, enters the subsequent washing process. The slurry from the slurry screen is then recycled to the slurry mill.

[0020] Example 2 The preparation process of the high bulk mechanical pulp includes the following steps: raw material preparation and pre-impregnation treatment, reaction chamber reaction, high-consistency pulping treatment, bleaching, anti-latency treatment, low-consistency pulping, screening and washing, specifically: 1) Raw material preparation and pre-impregnation treatment: The raw material is a mixture of 80% poplar and 20% eucalyptus wood chips, which are then crushed and pre-impregnated. The pre-impregnation temperature is controlled at 90℃, pH value at 10.2, liquid level at 52%, and the back pressure of the pre-impregnation spiral ADI is 5 bar. The amount of NaOH used is 2.0% of the weight of the oven-dry wood chips. 2) High-consistency pulping treatment: The pre-impregnated wood chips are fed into a high-consistency pulper for pulping. The pulping concentration is 41%. The gap in the conical zone of the pulper is controlled at 0.80 mm, and the gap in the flat zone is controlled at 1.0 mm. 3) Bleaching: After grinding, the pulp is subjected to first-stage bleaching and second-stage bleaching in sequence; during the first-stage bleaching, the bleaching agent concentration is controlled at 18%, the temperature is 95℃, and the time is 85min. In the first stage of bleaching, the dosage of hydrogen peroxide is 35 kg / bdt, the dosage of alkali is 18 kg / bdt, the dosage of stabilizer is 3.0 kg / bdt, and the dosage of chelating agent is 2.5 kg / bdt. In the second stage of bleaching, the dosage of hydrogen peroxide is 60 kg / bdt, the dosage of alkali is 23 kg / bdt, the dosage of stabilizer is 3.5 kg / bdt, and the dosage of chelating agent is 2.5 kg / bdt. The temperature was controlled at 90℃ and the bleaching time was 100 minutes during the two-stage bleaching process; the slurry concentration was maintained at 26%. In step 3), the bleaching agent is H2O2, the chelating agent is diethyltriaminepentaacetic acid (DTPA), and the stabilizer is sodium silicate.

[0021] The screening process consists of primary screening, secondary screening, and slurry screening. Primary screening has a slag discharge rate of 20%, a flow rate of 10,000 L / min, and a concentration of 2%. Secondary screening has a slag discharge rate of 35%, a flow rate of 8,000 L / min, and a concentration of 2%. The slurry from primary and secondary screening is then milled. The milling process uses a slurry concentration of 5.5%, a good slurry flow rate of 7,000 L / min, a return pipe valve opening of 35%, and a mill power of 1500 kW. After milling, the slurry is screened using an external flow pressure screen with a screen gap of 0.15 mm. The good slurry passing through the slurry screen, along with the good slurry from primary and secondary screening, enters the subsequent washing process. The slurry from the slurry screen is then recycled to the slurry mill.

[0022] Comparative Example 1 Unlike Example 1, in step 1) of this comparative example, pH=9, but the rest of the preparation methods and steps are the same as in Example 1.

[0023] Comparative Example 2 Unlike Example 1, in step 1) of this comparative example, pH=11, while the rest of the preparation methods and steps are the same as in Example 1.

[0024] Comparative Example 3 Unlike Example 1, the pre-soaking temperature in step 1) of this comparative example is 79°C, while the rest of the preparation methods and steps are the same as in Example 1.

[0025] Comparative Example 4 Unlike Example 1, the pulp concentration in step 2) of this comparative example is 34%, while the rest of the preparation methods and steps are the same as in Example 1.

[0026] Comparative Example 5 Unlike Example 1, the pulp concentration in step 2) of this comparative example is 46%, while the rest of the preparation methods and steps are the same as in Example 1.

[0027] The slurries from the examples and comparative examples were prepared to a concentration of 150 g / m³. 2 Kraft paper was tested, and its performance was evaluated. The test results are shown in Table 1.

[0028] Table 1

[0029] Compared with Example 1, Comparative Example 1 has a lower pH and insufficient alkalinity. The acidic substances in the wood chips are not fully neutralized, and the fibers are not sufficiently softened. As a result, the fibers are mainly cut rather than dissociated during pulping, and the bulk is reduced. At the same time, the decrease in alkalinity affects the activation of the bleaching agent, and the decomposition of H2O2 is insufficient, resulting in low bleaching efficiency. The severe fiber cutting produces a large number of fine fibers, which leads to a decrease in water filtration performance.

[0030] Compared with Example 1, Comparative Example 2 has a higher pH, which leads to excessive swelling, softening and even degradation of the fibers. The fiber structure is damaged and the stiffness decreases. Although this is beneficial to the bleaching reaction, the fiber strength decreases and the bulk does not improve. After the excessive softening of the fibers, the pulping resistance decreases, but the fiber structure is loose and the bulk is not ideal.

[0031] Compared with Example 1, Comparative Example 3 had a lower pre-impregnation temperature, which was below the lignin glass transition range. The wood chips were not sufficiently softened, and the fiber bundles were difficult to dissociate during pulping, resulting in a large number of cut fibers. The bulk was significantly reduced, the fiber surface was rough, the bleaching solution penetrated unevenly, the reaction efficiency was low, and the whiteness decreased. The number of fine fibers increased, the pulp's water filtration performance deteriorated, and the degree of freeness decreased.

[0032] Compared with Example 1, Comparative Example 4 has a lower pulp concentration, insufficient fiber pad between the grinding discs, and the grinding action is mainly shearing and cutting, resulting in poor fiber length retention, reduced bulk, severe fiber damage, more lignin exposed on the surface, increased bleaching difficulty, reduced whiteness, high content of fine fibers, poor water filtration performance, and decreased freeness.

[0033] Compared with Example 1, Comparative Example 5 has a higher pulp concentration, greater inter-fiber friction, which easily leads to fiber crushing, excessive fibrillation, damaged bulk, excessive fiber treatment, decreased water filtration performance, and reduced freeness.

[0034] Although the present invention has been described in detail by way of preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A process for preparing high-bulk mechanical pulp, comprising the following steps: raw material preparation and pre-impregnation treatment, reaction chamber reaction, high-consistency pulping treatment, bleaching, anti-latency treatment, low-consistency pulping, screening and washing, characterized in that, 1) Raw material preparation and pre-impregnation treatment: Crush the raw wood chips and then pre-impregnate them. Control the pre-impregnation temperature at 80~90℃, pH value at 9.8~10.2, liquid level at ≥50%, back pressure of the pre-impregnation spiral ADI at ≥4 bar, and the amount of NaOH used at 1.5%~2.0% of the weight of the oven-dry wood chips; 2) High-consistency pulping treatment: The pre-impregnated wood chips are fed into a high-consistency pulper for pulping. The pulping concentration is 35~45%. The gap between the cone and the flat sections of the pulper is controlled at 0.25~1.25mm. 3) Bleaching: After grinding, the pulp is subjected to first-stage bleaching and second-stage bleaching in sequence; during the first-stage bleaching, the concentration of bleaching agent is controlled at 18~20%, the temperature is 90~100℃, and the time is 80~85min. In the first stage of bleaching, the dosage of hydrogen peroxide is 20-40 kg / bdt, the dosage of alkali is 10-20 kg / bdt, the dosage of stabilizer is 1-4 kg / bdt, and the dosage of chelating agent is 0.5-3.5 kg / bdt. In the second stage of bleaching, the dosage of hydrogen peroxide is 45-65 kg / bdt, the dosage of alkali is 15-25 kg / bdt, the dosage of stabilizer is 1.5-4.5 kg / bdt, and the dosage of chelating agent is 0.5-3.5 kg / bdt. During the two-stage bleaching process, the temperature should be controlled at 90~100℃ and the bleaching time at 90~100min; the slurry concentration should be maintained at 25~28%.

2. The preparation process of high bulk thickness mechanical pulp as described in claim 1, characterized in that, The wood chips are a mixture of 80% poplar and 20% eucalyptus.

3. The preparation process of high bulk thickness mechanical pulp as described in claim 1, characterized in that, In step 3), the bleaching agent is H2O2, the chelating agent is diethyltriaminepentaacetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA), the stabilizer is one or more of sodium silicate, magnesium sulfate, and sodium tripolyphosphate, and the alkali is NaOH.

4. The preparation process of high bulk thickness mechanical pulp as described in claim 1, characterized in that, The screening process is divided into primary screening, secondary screening, and slurry screening. The primary screening has a slag discharge rate of 17-22%, a flow rate of ≤10000L / min, and a concentration of ≥2%. The secondary screening has a slag discharge rate of 30-40%, a flow rate of ≤8000L / min, and a concentration of ≥2%. The slurry from the primary and secondary screenings is then milled. The slurry concentration entering the mill is ≥5.5%, the good slurry flow rate is ≤7000L / min, the reflux pipe valve opening is ≥35%, and the mill power is ≥1500kW. After milling, the slurry is screened using an external flow pressure screen with a screen gap of 0.15mm. The good slurry passing through the slurry screen, along with the good slurry from the primary and secondary screenings, enters the subsequent washing process. The slurry from the slurry screen is then recycled to the slurry mill.

5. The chemimechanical pulp prepared by the process according to any one of claims 1-4.

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