Modified gypsum, preparation method thereof and application of modified gypsum in corrugated base paper production

Abstract

The invention relates to the technical field of papermaking, in particular to modified gypsum, a preparation method of the modified gypsum and application of the modified gypsum in corrugated base paper production. According to the invention, the stabilizer is added to modify the gypsum, so that the obtained modified gypsum not only has the advantage of crystal morphology, but also has obviously reduced solubility in water, and can be stable for a long time. When the modified gypsum is used for preparing corrugated base paper, the papermaking cost can be remarkably reduced under the condition that the mechanical property of paper is met.

Description

Technical Field

[0001] The present invention relates to the technical field of papermaking, and in particular to modified gypsum, a preparation method thereof and application thereof in the production of corrugated paper. Background Art

[0002] Corrugated paper products are widely used in the packaging industry, primarily produced from deinked waste pulp. However, after repeated recycling, waste pulp fibers become short and fragmented, weakening their bonding strength, leading to a significant decrease in the strength of the finished paper. Current corrugated base production typically rarely adds traditional fillers such as calcium carbonate to avoid further weakening the fiber network. This has become a key bottleneck hindering production cost reductions – the inability to reduce raw material consumption by replacing fibers with fillers, coupled with the dual challenges of insufficient waste pulp performance.

[0003] There are some research results in the prior art that use modified calcium sulfate whiskers as papermaking fillers (such as CN102852031A, CN107083724A, CN108103839A, etc.), but there are two major natural obstacles in the preparation of corrugated paper: (1) cost barrier: the artificial synthesis process of whiskers is complex and the cost is high, which cannot reduce the production cost of corrugated paper; (2) performance mismatch: the core requirement of corrugated paper is the balance between ring crush strength (compressive performance) and cost, while the "high strength reinforcement property" of whiskers is an excess of performance. Its fibrous structure is easy to agglomerate in the waste paper pulp short fiber system, which leads to flocculation problems in the papermaking process. The actual reinforcement effect is not proportional to the cost investment.

[0004] Gypsum, primarily composed of calcium sulfate dihydrate, is not typically used as a filler in papermaking due to its water solubility (solubility at 0°C is 0.23g / 100mLH2O). However, gypsum naturally possesses a crystalline morphology of flakes or short fibers. This structural characteristic, intermediate between particles and fibers, demonstrates unique potential for improving the ring crush index (a core indicator of compressive strength) and tightness of corrugated paper by filling interfiber gaps and optimizing the arrangement of fiber contact points.

[0005] If the water solubility of calcium sulfate dihydrate can be modified in a targeted manner, gypsum will be able to achieve "low-cost structural reinforcement" in corrugated paper due to its special crystal morphology: it will not only avoid the high cost and excess performance of whiskers, but also break through the strength loss bottleneck of traditional fillers, providing a new path of "cost reduction and efficiency improvement" for waste pulp-based corrugated paper. Summary of the Invention

[0006] The first object of the present invention is to provide a method for preparing modified gypsum, which comprises: at room temperature, using stabilizer A and stabilizer B in water to modify gypsum to obtain modified gypsum; wherein the stabilizer A reacts with the gypsum to form Ca x R y, wherein the valence of R is -m, and the relationship between x and y satisfies x=(m*y) / 2; the Ca x R y The Ksp in water at room temperature is less than CaSO4; the stabilizer B is selected from water-soluble calcium compounds.

[0007] The second object of the present invention is to provide a modified gypsum, which is prepared by the preparation method of the modified gypsum.

[0008] The third object of the present invention is to provide the use of the modified gypsum as a filler in the production of corrugated paper.

[0009] The present invention also provides a method for producing corrugated paper, which comprises: using the modified gypsum to replace part of the paper pulp, and adding it in the pulping stage or the pre-papermaking preparation stage.

[0010] The present invention also provides a corrugated base paper produced by the corrugated base paper production method.

[0011] The present invention modifies gypsum by adding a stabilizer. The resulting modified gypsum not only has advantageous crystal morphology, but also significantly reduces its solubility in water and is stable over a long period of time. When used to produce corrugated paper, this modified gypsum can significantly reduce papermaking costs while still maintaining the mechanical properties of the paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 Schematic diagram of the mechanism of action of calcium sulfate dissolution inhibition in the present invention. DETAILED DESCRIPTION

[0014] The following describes specific embodiments of the present invention in detail. It should be understood that the specific embodiments described herein are intended only to illustrate and explain the present invention and are not intended to limit the present invention. Those skilled in the art may make various modifications and variations to the present invention without departing from the scope or spirit of the present invention. For example, features illustrated or described as part of one embodiment may be used in another embodiment to produce further embodiments.

[0015] Unless otherwise indicated, all terms (including technical and scientific terms) used to disclose the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. By way of further guidance, the following definitions are provided to better understand the teachings of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0016] The terms "and / or", "or / and", and "and / or" used in this document include any one of two or more related listed items, and also include any and all combinations of the related listed items, including any combination of any two related listed items, any more related listed items, or all related listed items.

[0017] As used herein, the terms "comprising," "including," and "comprising" are synonymous and are inclusive or open-ended and do not exclude additional, unrecited members, elements, or method steps.

[0018] The recitation of numerical ranges herein by endpoints includes all numbers and fractions subsumed within the range, as well as the recited endpoints.

[0019] Concentration values used in this invention include fluctuations within a certain range. For example, fluctuations within a certain precision range are permitted. For example, for a 3% value, a fluctuation within ±0.1% is permitted. For larger values or values that do not require overly precise control, greater fluctuations are also permitted. For example, for a 30% value, fluctuations within ±1%, ±2%, ±5%, etc. are permitted.

[0020] In the present invention, descriptions such as "plurality" and "multiple" refer to quantities greater than or equal to 2 unless otherwise specified.

[0021] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0022] In the present invention, “preferred”, “better”, “more preferred” and “suitable” are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute limitations on the scope of protection of the present invention.

[0023] In the present invention, the terms "optionally," "optional," "optionally," "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If multiple "optional" or "optional" terms appear in a technical solution, unless otherwise specified and there are no contradictions or constraints, each "optional" or "optional" term is independent of the others.

[0024] For the purposes of this disclosure, the term "gypsum" refers to both the hydrated form of calcium sulfate (CaSO4) and its anhydrous form. Based on its source, gypsum can be divided into natural gypsum (primarily calcium sulfate dihydrate, extracted through mining) and industrial by-product gypsum (a solid waste generated during industrial production, typically primarily calcium sulfate dihydrate, with small amounts of anhydrous calcium sulfate and impurities such as silica and calcium carbonate, and valuable for large-scale resource utilization).

[0025] As used herein, the term "industrial by-product gypsum" refers to gypsum waste generated during industrial production processes. Specifically, this includes, but is not limited to, desulfurized gypsum (a by-product of flue gas desulfurization in coal-fired power plants), phosphogypsum (a by-product of phosphate fertilizer production), lactic acid gypsum (a by-product of lactic acid fermentation), citric acid gypsum (a by-product of citric acid production), and fluorinated gypsum (a by-product of hydrofluoric acid production).

[0026] The first object of the present invention is to provide a method for preparing modified gypsum, which comprises: at room temperature, using stabilizer A and stabilizer B in water to modify gypsum to obtain modified gypsum; wherein the stabilizer A reacts with the gypsum to form Ca x R y , wherein the valence of R is -m, and the relationship between x and y satisfies x=(m*y) / 2; the Ca x R y The Ksp in water at room temperature is less than CaSO4; the stabilizer B is selected from water-soluble calcium compounds.

[0027] In the present invention, on the one hand, some components of stabilizer A and stabilizer B will form precipitates with smaller solubility products on the surface of gypsum (such as Figure 1 As shown), it prevents the dissolution of calcium sulfate in water; on the other hand, part of the stabilizer B can release an appropriate amount of Ca 2+ , through the "common ion effect" to reduce calcium sulfate and coating layer Ca x R y The dissolution of modified gypsum makes it more stable during storage and use in water.

[0028] In some embodiments, the stabilizer A is selected from one or more of Na2SiO4, K2SiO3, Na2CO3, K2CO3, Na3PO4, K3PO4, (Na3PO4)n, (K3PO4)n, (H3PO4)n, NaAlO2, KAlO2, sodium stearate, and potassium stearate; where n is the degree of polymerization. All of the above stabilizers A can achieve excellent modification effects in the present invention.

[0029] In some embodiments, n is 2 to 10. As an example, n can be 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0030] In some embodiments, the amount of the stabilizer A relative to gypsum (anhydrous) is 0.2 to 2 wt %.

[0031] As an example, in some embodiments, the amount of stabilizer A relative to gypsum can be 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt% or 2 wt%.

[0032] In some embodiments, the stabilizer B is selected from one or both of Ca(OH)2 and CaCO3. In some preferred embodiments, the stabilizer B is a mixture of Ca(OH)2 and CaCO3. In some more preferred embodiments, the mass ratio of Ca(OH)2 to CaCO3 is (1-9):1. The stabilizer B described above has a good stabilizing effect on the modified gypsum in the present invention.

[0033] As an example, in some embodiments, the mass ratio of Ca(OH)2 to CaCO3 in the stabilizer B can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1.

[0034] In some embodiments, the pH value of the aqueous solution used for the modification treatment is adjusted to 8±0.5 by adding the stabilizer B. In specific implementation, those skilled in the art can determine the specific amount of stabilizer B based on this description.

[0035] As an example, in some embodiments, by adding the stabilizer B, the pH value of the aqueous solution used for the modification treatment is 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, or 8.5.

[0036] In some preferred embodiments, the amount of the stabilizer B relative to gypsum (anhydrous) is 0.1 to 5 wt %.

[0037] As an example, in some embodiments, the amount of the stabilizer B relative to the gypsum can be 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0038] In some embodiments, the gypsum is industrial by-product gypsum. The modification method of the present invention has a good modification effect on industrial by-product gypsum. By using industrial by-product gypsum as a modification raw material, it will further facilitate the reuse of industrial solid waste resources and further reduce paper production costs.

[0039] In some embodiments, the gypsum is an industrial by-product gypsum containing 70 wt% or more (e.g., 70 wt%, 80 wt%, 90 wt%, 95 wt%, 98 wt%, etc.) of calcium sulfate dihydrate (CaSO4·2H2O) and / or anhydrous calcium sulfate (CaSO4).

[0040] In some specific embodiments, the main chemical component of the industrial by-product gypsum is calcium sulfate dihydrate, with a content of not less than 70 wt % (e.g., 70 wt %, 80 wt %, 90 wt %, 95 wt %, 98 wt %, etc.). Optionally, the industrial by-product gypsum may contain a small amount (e.g., 5-15 wt %) of anhydrous calcium sulfate and a small amount of impurities.

[0041] In some specific embodiments, the industrial by-product gypsum is dihydrate industrial by-product gypsum.

[0042] In some embodiments, the sanitary index of the industrial by-product gypsum meets the requirements for corrugated paper. If the requirements are not met, the industrial by-product gypsum can be pre-treated by conventional means such as purification and water washing to meet the requirements.

[0043] In some embodiments, the solid content of the gypsum in the aqueous solution used for the modification treatment is 5 to 30 wt %.

[0044] As an example, in some specific embodiments, the solid content of the gypsum in the aqueous solution used for the modification treatment may be 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, or 30 wt %.

[0045] In some embodiments, the preparation method of the modified gypsum specifically includes: dispersing gypsum in water at room temperature, adding the stabilizer A, and modifying the gypsum under stirring conditions for 10 to 30 minutes (such as 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes); and then adding the stabilizer B and modifying the gypsum under stirring conditions for 10 to 30 minutes (such as 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes).

[0046] In some embodiments, the method for preparing modified gypsum further comprises: filtering the reaction solution after the modification treatment is completed to obtain modified gypsum.

[0047] A second object of the present invention is to provide a modified gypsum produced by the aforementioned method for preparing the modified gypsum. While retaining the advantages of gypsum crystal morphology, the modified gypsum of the present invention significantly reduces its solubility and exhibits long-term stability, thereby facilitating its use as a filler in corrugated paper production. Furthermore, the method is simple and easy to operate, making it readily applicable in practical production.

[0048] The third object of the present invention is to provide the use of the modified gypsum as a filler in the production of corrugated paper.

[0049] In some embodiments, the corrugated base paper is suitable for use as a raw material in preparing the following corrugated paper products: corrugated core paper, corrugated board, dry-pressed paper tray, wet-pressed paper tray, and corrugated board composited with kraft paper surface and / or kraft lining paper.

[0050] The present invention also provides a method for producing corrugated paper, comprising: using the modified gypsum to replace part of the paper pulp, and adding it during the pulping stage or the pre-papermaking preparation stage. This method can reduce the papermaking cost while ensuring the quality of the corrugated paper.

[0051] In some embodiments, the modified gypsum is first dispersed in water to form a 5-30 wt% gypsum slurry, and the gypsum slurry is mixed with paper pulp in a beating tank or a pre-cutting tank under stirring conditions.

[0052] As an example, in some embodiments, the modified gypsum is dispersed in water to form a gypsum slurry with the following concentrations: 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%.

[0053] In some embodiments, when added in the beating stage (such as in the beating tank), the amount of the modified gypsum is controlled to be 3 to 30 wt % of the dry pulp mass.

[0054] As an example, when added in the beating stage (such as in the beating tank), the amount of the modified gypsum is controlled to be 3wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, or 30wt% of the dry pulp mass.

[0055] In some embodiments, when added in the pre-papermaking preparation stage (such as at the pre-papermaking tank), the amount of the modified gypsum is controlled to be 3-8 wt % of the paper mass.

[0056] As an example, in some embodiments, the amount of the modified gypsum is 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt% of the paper mass.

[0057] In some embodiments, the pulp is new pulp or waste pulp. Using the modified gypsum of the present invention (such as modified gypsum made from industrial by-product gypsum) and new pulp or waste pulp can produce corrugated paper with satisfactory performance in all aspects, and is conducive to further reducing production costs.

[0058] The present invention also provides a corrugated base paper produced by the corrugated base paper production method.

[0059] The embodiments of the present invention will be described in detail below with reference to the examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. For experimental methods in the following examples where specific conditions are not specified, reference is made to the guidance provided in the present invention, and may also be made to experimental manuals or conventional conditions in the art, other experimental methods known in the art, or conditions recommended by the manufacturer.

[0060] The industrial by-product gypsum used in the following implementation is all dihydrated industrial by-product gypsum, which has undergone two-stage reverse flotation. The sample has a drying whiteness of 50-68 at 45° C., and its sanitary index meets the requirements of corrugated paper.

[0061] In the following specific examples, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument testing accuracy or operational accuracy are allowed.

[0062] Example 1

[0063] The purified desulfurized dihydrate gypsum was dispersed in water (solid content 30 wt%), stabilizer A (Na2SiO4, 5 wt‰ relative to the dihydrate industrial by-product gypsum) was added at room temperature and stirred for 10 minutes, and stabilizer B (Ca(OH)2) solution was added until the pH = 8, the amount of stabilizer B relative to the dihydrate industrial by-product gypsum was 0.15 wt%. After stirring for 30 minutes, the modified gypsum was obtained by filtration.

[0064] Example 2

[0065] Using dihydrate phosphogypsum that has undergone flotation treatment as raw material, the flotation phosphogypsum is dispersed in water (solid content 10wt%), stabilizer A (mass ratio W(Na2CO3):W(Na3PO4)=1:1, stabilizer A relative to dihydrate industrial by-product gypsum 5wt‰) is added at room temperature and stirred for 20 minutes, stabilizer B (mass ratio W(Ca(OH)2):W(CaCO3)=4:1) solution is added until pH=8, stabilizer B relative to dihydrate industrial by-product gypsum 0.15wt% is used, stirring is continued for 20 minutes, and then filtered to obtain modified gypsum.

[0066] Example 3

[0067] Using dihydrate phosphogypsum that has been flotated as raw material, the flotation gypsum is dispersed in water (solid content 20wt%), stabilizer A ((H3PO4)3, 3wt‰ relative to dihydrate gypsum) is added at room temperature and stirred for 30 minutes, and stabilizer B (mass ratio W(Ca(OH)2):W(CaCO3)=5:1) solution is added until the pH is 8, and the amount of stabilizer B relative to dihydrate industrial by-product gypsum is 0.1wt%. After continuing stirring for 30 minutes, the modified gypsum is obtained by filtration.

[0068] Example 4

[0069] 3%, 5%, and 8% of the paper weight of modified phosphogypsum powder (prepared in Example 3) were added to the pre-cutting tank as filler, and the effect of the addition of gypsum slurry on the physical properties of the paper was measured. Specifically, the modified gypsum was first dispersed in water to form a 30wt% gypsum slurry. The gypsum slurry was then mixed with the paper pulp in the pre-cutting tank under stirring. The product weight was set at 120g / m 2 The pulp used in the test was waste paper pulp with a beating degree of 240SR. Referring to relevant national standards, the mechanical properties of corrugated base paper with different addition amounts were tested, and the results are shown in Table 1.

[0070] Table 1 Mechanical properties of corrugated paper filled with modified industrial by-product gypsum at different contents

[0071] Filling amount Ring pressure index Tightness Fracture length 3％ 7.89Nm / g <![CDATA[0.521g / cm 3 ]]> 3.65km 5％ 7.07Nm / g <![CDATA[0.501g / cm 3 ]]> 2.82km 8％ 5.45Nm / g <![CDATA[0.445g / cm 2 ]]> 2.37km

[0072] Note: (Ring crush index of blank sample is 8.63Nm / g).

[0073] Combined with the standard classification of corrugated paper, it can be seen from Table 1 that the product's ring crush index reaches the national standard for 2A grade at 3% dosage, the national standard for 1A grade at 5% dosage, and the national standard for first-class products at 8% dosage; the tightness can reach the national standard for qualified corrugated base paper; the breaking length can reach the national standard for qualified corrugated base paper at 3% dosage and 5% dosage.

[0074] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and modifications are possible without departing from the spirit of the present invention, and all such variations and modifications fall within the scope of the present invention.

Claims

1. A method for preparing modified gypsum, comprising: At room temperature, gypsum is modified in water using stabilizer A and stabilizer B in succession to obtain modified gypsum; Wherein, the stabilizer A reacts with gypsum to generate Ca x R y , wherein the valence of R is -m, and the relationship between x and y satisfies x=(m*y) / 2; the Ca x R y The Ksp in water at room temperature is less than that of CaSO4; The stabilizer B is selected from water-soluble calcium compounds.

2. The method for preparing modified gypsum according to claim 1, wherein The stabilizer A is selected from one or more of Na2SiO4, K2SiO3, Na2CO3, K2CO3, Na3PO4, K3PO4, (Na3PO4)n, (K3PO4)n, (H3PO4)n, NaAlO2, KAlO2, sodium stearate, and potassium stearate; wherein n is the degree of polymerization, and preferably n is 2 to 10.

3. The method for preparing modified gypsum according to claim 2, wherein: The amount of the stabilizer A used relative to gypsum is 0.2-2 wt%.

4. The method for preparing modified gypsum according to any one of claims 1 to 3, wherein: The stabilizer B is selected from one or both of Ca(OH)2 and CaCO3; preferably, the stabilizer B is a mixture of Ca(OH)2 and CaCO3; more preferably, the mass ratio of Ca(OH)2 to CaCO3 is (1-9):

1.

5. The method for preparing modified gypsum according to claim 4, wherein: By adding the stabilizer B, the pH value of the aqueous solution used for the modification treatment is adjusted to 8±0.5; preferably, the amount of the stabilizer B relative to the gypsum is 0.1-5 wt%.

6. The method for preparing modified gypsum according to any one of claims 1 to 5, wherein: The gypsum is industrial by-product gypsum containing more than 70 wt % of calcium sulfate dihydrate and / or anhydrous calcium sulfate; preferably, the sanitary indicators of the industrial by-product gypsum meet the requirements of corrugated paper.

7. The method for preparing modified gypsum according to any one of claims 1 to 6, wherein: The solid content of the gypsum in the aqueous solution used for the modification treatment is 5 to 30 wt %.

8. The method for preparing the modified gypsum according to any one of claims 1 to 7, which specifically comprises: At room temperature, gypsum is dispersed in water, stabilizer A is added, and the gypsum is modified under stirring for 10 to 30 minutes; Then, the stabilizer B is added and the gypsum is modified under stirring for 10 to 30 minutes.

9. The method for preparing the modified gypsum according to any one of claims 1 to 8, further comprising: After the modification treatment is completed, the reaction liquid is filtered to obtain modified gypsum.

10. Modified gypsum, obtained by the method for preparing the modified gypsum according to any one of claims 1 to 9.

11. Use of the modified gypsum according to claim 10 as a filler in the production of corrugated paper.

12. The use according to claim 11, wherein: The corrugated base paper is suitable for preparing the following corrugated paper products as raw materials: corrugated core paper, corrugated board, dry-pressed paper tray, wet-pressed paper tray, and corrugated board composited with kraft paper surface and / or kraft paper lining.

13. A method for producing corrugated paper, comprising: The modified gypsum according to claim 10 is used to replace part of the paper pulp and is added during the pulping stage or the papermaking preparation stage.

14. The method for producing corrugated medium according to claim 13, wherein: First, the modified gypsum is dispersed in water to form a gypsum slurry with a concentration of 5 to 30 wt%. Under stirring conditions, the gypsum slurry is mixed with paper pulp in a beating tank or a pre-sheeting tank.

15. The method for producing corrugated medium according to claim 13 or 14, wherein: When added in the pulping stage, the amount of the modified gypsum is controlled to be 3-30 wt% of the dry pulp mass; when added in the pre-copying preparation stage, the amount of the modified gypsum is controlled to be 3-8 wt% of the paper mass.

16. The method for producing corrugated medium according to any one of claims 13 to 15, wherein: The pulp is new pulp or waste pulp.

17. Corrugated paper produced by the corrugated paper production method according to any one of claims 13 to 16.

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