WO2016175594A1 - Method for manufacturing multilayer paper of unbleached pulp utilizing two-step continuous synthesis reaction method of precipitated calcium carbonate - Google Patents

Abstract

The present invention relates to a two-step continuous synthesis reaction of precipitated calcium carbonate (PCC) of synthesizing white precipitated calcium carbonate (PCC) in unbleached pulp, which has the effect of replacing conventional bleaching processes to thereby reduce toxic substances by a bleaching agent, reduce costs for the bleaching process, reduce environmental pollutants generated due to the bleaching agent, and enhance the whiteness of the unbleached pulp. In addition, the present invention relates to a method for manufacturing multilayer paper by utilizing unbleached pulp comprising precipitated calcium carbonate (PCC) through a two-step continuous synthesis reaction of the precipitated calcium carbonate (PCC).

Description

Method for manufacturing multi-layer paper of unbleached pulp using precipitated calcium carbonate two-stage continuous synthesis method

The present invention is a precipitated calcium carbonate made by a two-stage continuous synthesis method and a two-stage continuous synthesis reaction method for synthesizing precipitated calcium carbonate (PCC) in unbleached pulp to reduce the amount of bleach used and improve the whiteness of paper. It relates to a multi-layer paper production method utilizing unbleached pulp containing (PCC).

In the use of paper, the bleaching process is carried out to remove the brown lignin impurities to improve the quality. Chemical pulp is carried out through several stages of bleaching process and uses various chemicals and depending on the degree of bleaching of the pulp, it can be bleached kraft pulp (BKP-Bleached Kraft Pulp), unbleached kraft pulp (UKP-Unbleached Kraft Pulp), It is divided into semi-bleached kraft pulp (SKP-Semi-bleached Kraft Pulp).

      Chemicals commonly used for bleaching pulp include chlorine dioxide, hydrogen peroxide, ozone, and chlorine. When bleaching with chlorine dioxide, it has a strong oxidation and bleaching effect. As bleaching proceeds, the cellulose constituting the fiber decomposes, decreasing the molecular weight of the fiber, and even small amounts of chlorine dioxide remaining in the pulp can cause respiratory disorders such as dermatitis or pneumonia and bronchitis. Bleaching pulp with hydrogen peroxide also stimulates the respiratory tract. And cause skin diseases.

      In order to solve this problem, Korean Patent Laid-Open Publication No. 10-2005-0106526 discloses a cellulosic material as a bleaching material which is a mixture of a guanidine-based additive substituted with a bleach selected from peroxide, oxygen, ozone or a mixture thereof to enhance the effect of the bleaching agent. Suggesting a way to bleach. However, when bleaching using this method, a strong bleaching effect can be obtained, but there is a problem in processing cost, and it is difficult to use in the existing bleaching process, and thus has problems such as reinstallation of equipment.

      In addition, bleaching with these chemicals not only poses a danger to the human body due to chemicals remaining in the pulp, but also causes serious environmental pollutants such as chemicals such as dioxins, which are expensive. have.

      In order to solve this problem, Korean Laid-open Patent No. 10-2014-0045687 proposes a method of preparing wood powder with calcium carbonate and a method of manufacturing paper by mixing wood powder with calcium carbonate with natural pulp. However, this method uses wood powder, a granular wood powder made by pulverizing wood to nano-level, and generates the cost and energy required for the process of attaching calcium carbonate to wood powder and extracts from wood powder. If the calcium carbonate does not adhere to the wood powder with a certain level of adhesion, the retention of calcium carbonate is reduced and the whiteness is uneven, so the unattached calcium carbonate should be washed with water. Have

      Therefore, the present invention synthesizes white precipitated calcium carbonate (PCC) directly in unbleached pulp to precipitate two stages of precipitated calcium carbonate (PCC) which can increase the whiteness of unbleached pulp and white precipitated calcium carbonate (PCC). It provides a method for producing a multi-layer paper utilizing the unbleached pulp containing.

An object of the present invention is to synthesize white true rigid calcium carbonate (PCC) through two-step continuous synthesis reaction in unbleached pulp fibers to improve the whiteness of unbleached pulp and to improve the utilization range of unbleached pulp.

In the present invention, precipitated calcium carbonate (PCC) two-stage continuous synthesis reaction and precipitated calcium carbonate (PCC) have the effect of reducing the toxic substances by bleach, reducing the cost of bleaching process, and reducing the environmental pollution produced by bleaching. It provides a multi-layer paper manufacturing method using a non-bleached pulp comprising a paper.

In order to achieve the above object, the present invention is (a) pulp preparation step, (b) pulp slurry and slaked mixing step (CaO + H₂O → Ca (OH) ₂, hydration step, step 1), and (c) pulp Spraying carbon dioxide (CO₂) on the mixed slurry of slaked lime, (d) precipitated calcium carbonate (PCC) synthesis step (CaO + CO₂ → CaCO₃, PCC synthesis step, step 2) by carbonation reaction, (e) step (d) After the reaction of the reaction is completed, the slurry recovery step, and (f) using the slurry of step (e) to prepare a multi-layer paper of the upper layer is bleached paper, the middle layer is unbleached paper, the lower layer is bleached paper, and (g) do.

The present invention can replace the existing bleaching process by a two-step continuous synthesis reaction for synthesizing white precipitated calcium carbonate (PCC) in unbleached pulp, thereby increasing the application range of unbleached pulp with improved whiteness, and precipitated calcium carbonate ( The use of unbleached pulp containing PCC) has the effect of reducing the toxic substances caused by bleach, reducing the cost of bleaching process, and reducing the environmental pollution produced by bleaching.

 Figure 1. Two-step continuous synthesis reaction method

 2. Schematic diagram of a two stage continuous synthesis reactor

 Figure 3. Multi-layer paper structure using unbleached pulp containing precipitated calcium carbonate (PCC)

 4. Unbleached pulp whiteness measurement graph according to the amount of precipitated calcium carbonate (PCC) synthesis

 5. Multi-layer paper whiteness measurement graph according to the amount of precipitated calcium carbonate (PCC) synthesis

 Figure 6. Thermal shear measurement graph according to the amount of precipitated calcium carbonate (PCC) synthesis

 Figure 7. Elongation rate measurement graph according to the amount of precipitated calcium carbonate (PCC) synthesis

In order to achieve the above object, the present invention is a two-step continuous synthesis reaction for synthesizing white precipitated calcium carbonate (PCC) in unbleached pulp, and two-step continuous synthesis reaction of precipitated calcium carbonate (PCC), which can replace the conventional bleaching process. Provided is a method for preparing a multilayer paper of unbleached pulp using an in-situ process.

That is, (a) the pulp preparation step,

(b) mixing the pulp slurry and slaked lime,

     (CaO + H₂O → Ca (OH) ₂, hydration stage, stage 1)

(c) spraying carbon dioxide (CO) on the pulp and slaked mixed slurry,

(d) synthesizing precipitated calcium carbonate (PCC) by carbonation,

            (CaO + CO₂ → CaCO₃, PCC synthesis stage, 2 stage)

(e) recovering the slurry after the reaction of step (d) is completed;

(f) using the slurry of step (e) to prepare a multi-layered paper of which the upper layer is bleached paper, the middle layer is unbleached paper, and the lower layer is bleached paper.

(g) analyzing the prepared multilayer paper.

The amount of precipitated calcium carbonate (PCC) synthesized by the present invention is synthesized 0.5 to 3 times the weight of the unbleached pulp dry weight.

The mixed lime (CaO) may be added as calcium hydroxide (Ca (OH) ₂) in a hydrated state by calcining limestone (CaCO₃) and reacting with water. The step (e) is maintained at 25 ~ 35 ℃, to help the reaction by rotating the stirrer of the carbonation reactor to 600rpm, to check the end point of the reaction by installing a pH meter inside the vessel of the reactor pH is less than 7 If so, terminate the reaction and recover the unbleached pulp slurry.

And in one embodiment of the present invention, the upper layer of the step (f) is bleached paper, the middle layer is unbleached paper, the lower layer is bleached paper, the upper layer is bleached paper, the lower layer can be produced as unbleached paper.

On the other hand, the present invention provides a paper prepared by using the unbleached pulp synthesized precipitated calcium carbonate (PCC) in the unbleached pulp by the method described above.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein and the experimental methods described below are well known and commonly used in the art.

 The present invention is a precipitated calcium carbonate two-stage continuous synthesis method that can replace the existing bleaching process by a two-stage continuous synthesis reaction to synthesize white precipitated calcium carbonate (PCC) in unbleached pulp as described below. It is a method of manufacturing multi-layer paper of unbleached pulp using situ process.

 (a) the pulp preparation step,

 (b) mixing the pulp slurry and slaked lime,

     (CaO + H₂O → Ca (OH) ₂, hydration stage, stage 1)

 (c) spraying carbon dioxide (CO₂) on the pulp and slaked mixed slurry,

 (d) synthesizing precipitated calcium carbonate (PCC) by carbonation,

     (CaO + CO₂ → CaCO₃, PCC synthesis stage, 2 stage)

 (e) recovering the slurry after the reaction of step (d) is completed;

 (f) using the slurry of step (e) to prepare a multi-layered paper, wherein the upper layer is bleached paper, the middle layer is unbleached paper, and the lower layer is bleached paper;

 (g) analysis step

      The present invention provides a two-step continuous synthesis method for synthesizing white precipitated calcium carbonate (PCC) in unbleached pulp and a method of utilizing unbleached pulp with increased whiteness, including precipitated calcium carbonate (PCC) in order to reduce the use of bleach. to provide.

      Precipitated Calcium Carbonate (PCC) A two-step continuous synthesis reaction is performed to prepare a multilayer paper using unbleached pulp with increased whiteness, including white precipitated calcium carbonate (PCC). It is possible to produce paper with the effect of reducing the toxic substances caused by bleach, reducing the cost of bleaching process, and reducing the environmental pollutants produced by the bleaching agent by replacing the stepwise continuous reaction method.

      Precipitated calcium carbonate (PCC) two-stage continuous synthesis reaction of the present invention synthesizes white precipitated calcium carbonate (PCC) directly in unbleached pulp, thereby increasing the whiteness, and there is no additional process, so it is time and economically efficient and whiteness. It can improve the utilization of unbleached pulp by providing high and eco-friendly unbleached pulp.

     Precipitated calcium carbonate (PCC) two-step continuous synthesis reaction of the present invention will be described in more detail with reference to FIG.

In the present invention, the pulp preparation step is first performed. That is, the present invention is a method of increasing the whiteness of the unbleached pulp without the bleaching process, to prepare the unbleached pulp as the object of the invention. However, it does not exclude the use of anti-bleaching pulp in terms of reducing existing bleaching process steps.

     When the pulp is ready, the pulp slurry and slaked lime are mixed. This process is the first step of the two-stage continuous synthesis reaction. The unbleached pulp slurry prepared above is mixed with calcined lime (CaO) calcined limestone (CaCO₃), a raw material of precipitated calcium carbonate (PCC). In addition, it is preferable not to mix calcined lime (CaO) but to hydrate it first to make it into a calcium hydroxide (Ca (OH) ₂) state, and then mix it with an unbleached pulp slurry. In addition, calcium hydroxide (Ca (OH) ₂), in which hydrated lime (CaO) is hydrated, may be mixed with an unbleached pulp slurry after sieving. Limestone (CaCO₃), a raw material of precipitated calcium carbonate (PCC), is calcined with CaO when decarbonate occurs during firing. Withholding of precipitated calcium carbonate (PCC) in unbleached pulp that can occur in the process of limestone (CaCO₃) is calcined to become calcareous (CaO) and calcareous is hydrated to become calcium hydroxide (Ca (OH) ₂). A sieving step is used to remove any obstructing debris.

      The amount of calcium hydroxide (Ca (OH) ₂) mixed with the unbleached pulp is characterized by matching the amount of precipitated calcium carbonate (PCC) produced by carbonation of calcium hydroxide (Ca (OH) ₂) with carbon dioxide. Calcium hydroxide (Ca (OH) 2) is added so that the amount of precipitated calcium carbonate (PCC) is produced between 0.5 and 3 times the weight of the dried unbleached pulp. If the precipitated calcium carbonate (PCC) synthesized in the unbleached pulp is synthesized at less than 0.5 times the weight of the dried unbleached pulp, the amount of the white precipitated calcium carbonate (PCC) synthesized in the unbleached pulp is small, and thus cannot show sufficient whiteness. Calcium hydroxide (Ca (OH) 2) is mixed so that the amount of precipitated calcium carbonate (PCC) synthesized in the bleached pulp is at least 0.5 times the weight of the dried unbleached pulp.

      In addition, when the precipitated calcium carbonate (PCC) synthesized in the unbleached pulp is synthesized more than three times the weight of the dried unbleached pulp, the amount of precipitated calcium carbonate (PCC) in the unbleached pulp is increased, thereby inhibiting the inter-fiber bonds. Because of its difficulty in use due to low thermal extension and elongation rate, calcium hydroxide (Ca (OH) ₂) was added so that the amount of precipitated calcium carbonate (PCC) synthesized in unbleached pulp was not more than three times the weight of dried unbleached pulp. Mix it up.

In the present invention, the carbon dioxide (CO₂) spraying step (c) is characterized in that the injection of high-purity carbon dioxide (CO₂) to the slurry of unbleached pulp and calcium hydroxide (Ca (OH) ₂). Carbon dioxide (C0₂) is a high purity gas of 99v%, it is characterized in that the injection at a rate of 1L / min.

In the present invention, the precipitated calcium carbonate (PCC) synthesis step of step (d) is a two-step continuous synthesis reaction in which a carbonation reaction occurs, and calcium hydroxide (Ca (OH) ₂) and carbon dioxide (CO₂) in unbleached pulp. ) By the carbonation reaction to synthesize precipitated calcium carbonate (PCC). Carbonation is the reaction of calcium carbonate with the chemical reaction of calcium compounds and carbon dioxide. In step (d), calcium hydroxide (Ca (OH) ₂) and carbon dioxide (CO₂) are chemically reacted to synthesize white precipitated calcium carbonate (PCC).

In the present invention, the slurry recovery step of step (e) is reported that the synthesis is complete when the pH indicates a value of 7 or less, to terminate the reaction, characterized in that to recover the unbleached pulp sludge containing precipitated calcium carbonate (PCC) It is done. The time point when the carbonation reaction, in which precipitated calcium carbonate (PCC) is synthesized in unbleached pulp, is terminated, is determined when the pH is 7 or less by checking the pH using a pH meter. The pH before the reaction of an unbleached pulp slurry containing basic calcium hydroxide (Ca (OH) ₂) has a basicity greater than 7, and when the carbonation reaction occurs by spraying carbon dioxide (CO₂) on the slurry, calcium hydroxide (Ca (OH) ₂) It meets carbon dioxide (CO₂) and becomes precipitated calcium carbonate (PCC), so it gradually falls from basic to neutral. After all of the mixed calcium hydroxide (Ca (OH) ₂) reacts, the pH of the unbleached pulp slurry falls from neutral to acidic according to the injected carbon dioxide (CO₂), so that the precipitated calcium carbonate when the pH is less than 7 It appears that the synthesis of (PCC) is terminated. When the pH is less than 7 and the reaction is completed, the unbleached pulp slurry synthesized with precipitated calcium carbonate (PCC) is recovered.

In the present invention, using the slurry of step (e) of step (f), the upper layer is bleached paper, the middle layer is unbleached paper, and the lower layer is bleached paper. The unbleached precipitated calcium carbonate (PCC) is included. It is characterized by making paper using the pulp.

     Multi-layer paper is a paper composed of several layers, the present invention provides a method of manufacturing a multi-layer paper using a non-bleached pulp, the upper and lower layers are fixed with bleached kraft pulp and the precipitated calcium carbonate (PCC) is synthesized in the middle layer. .

     In addition, in the present invention, the multi-layered paper may be manufactured into a multi-layered paper having a two-layer structure by fixing the upper layer with bleached kraft pulp and using the lower layer with unbleached pulp.

     Various modifications are possible, such as multilayer paper with more layers or multilayer paper with less layers, monolayer paper, and the like, without departing from the scope of the present invention.

     In the present invention, the analyzing step (g) is characterized in that the optical and physical characteristics of the unbleached pulp or manufactured paper containing precipitated calcium carbonate (PCC) are analyzed.

     Figure 2 shows a schematic diagram of a two-stage continuous synthesis reactor applied to the present invention. The unbleached pulp slurry and calcium hydroxide (Ca (OH) 2) are mixed into the reactor, and carbon dioxide (CO2) is injected to synthesize precipitated calcium carbonate (PCC) in the unbleached pulp by carbonation reaction. At this time, the reaction vessel is characterized in that it is maintained at 25 ~ 35 ℃. If the temperature is out of the 25 ~ 35 ℃ range of carbonation reaction is sharply reduced precipitated calcium carbonate (PCC) synthesis is not made smoothly to maintain the temperature of 25 ~ 35 ℃. Preferably it is maintained at 30 ℃.

     In addition, the stirrer installed in the reactor vessel is characterized in that when the carbonation reaction proceeds, by rotating to 600rpm to help the synthesis of precipitated calcium carbonate (PCC). In order to confirm the end of the reaction, a pH meter is installed inside the vessel, characterized in that for checking the pH when the carbonation reaction proceeds.

      3 is a multilayer paper structure using unbleached pulp containing precipitated calcium carbonate (PCC) in a two-step continuous synthesis reaction of precipitated calcium carbonate (PCC). Unlike bleached paper and multiple materials produced by using a single material, unbleached pulp in which bleached kraft pulp is fixed on the upper and lower layers and precipitated calcium carbonate (PCC) is synthesized in the pulp on the middle layer. It is a multilayer paper having a three-layer structure using.

Example

Hereinafter, the present invention will be described in more detail with reference to specific examples. The following examples are intended to illustrate the present invention more specifically, but the present invention is not limited by the following examples.

     Bleached Kraft Pulp (BKP) bleached Kraft Pulp (BKP) was used as a material for applying the embodiment of the present invention from Korea, and unbleached Kraft Pulp (UKP) was used in Chungnam National University. . BKP and UKP received were sealed and refrigerated to prevent decay after adjusting to a concentration of 5% after dissociation at a concentration of 1%.

      Precipitated calcium carbonate (PCC) In order to compare the bleaching effect of unbleached pulp through two-step continuous synthesis reaction, precipitated calcium carbonate (PCC) was synthesized in unbleached pulp slurry according to the conditions of Table 1, and generally precipitated calcium carbonate ( PCC) The two-stage continuous synthesis reaction is performed by calcination of limestone (CaCO₃) to react decalcified lime (CaO) with water to hydrate calcium (Ca (OH) ₂), followed by a sieving process. do. However, in the embodiment of the present invention, as shown in Table 1, CaO reagent (purity 98%, J company) was used by hydrating with calcium hydroxide (Ca (OH) ₂). Calcium hydroxide (Ca (OH) ₂) made with CaO reagent (98% purity, J company) omits calcining, decarbonization, and sieving of limestone (CaCO₃).

Precipitated calcium carbonate (PCC) synthesis conditions

Experimental conditions
water	2000 ml
Synthetic raw materials	CaO (purity 98%, J company)
CO2 (99%) Injection Rate	1 L / min
Temperature	30 ℃
Stirring speed	600 rpm

     The embodiment of the present invention proceeded through the reactor of FIG. 2 in the same order as FIG.

     The prepared calcium hydroxide (Ca (OH) ₂) was mixed with the unbleached pulp slurry and sufficiently stirred so that the unbleached pulp slurry and calcium hydroxide (Ca (OH) ₂) were uniformly mixed. High purity carbon dioxide (CO₂) is injected into the unbleached pulp slurry and calcium hydroxide (Ca (OH) ₂), which has been stirred, and precipitates due to the reaction of calcium hydroxide (Ca (OH) ₂) and carbon dioxide (CO₂) between the unbleached pulp slurry. Calcium carbonate (PCC) was allowed to synthesize. The amount of precipitated calcium carbonate (PCC) synthesized in this way was controlled by the amount of synthesis relative to the dry weight of the unbleached pulp, and proceeded by varying the amount of synthesis as shown in Table 2.

Precipitated calcium carbonate (PCC) synthesis rate

Synthetic raw materials	Unbleached pulp	CaO	Synthesis amount of PCC to unbleached pulp dry weight
CaO	562.9 g	51.4 g	3 times
	562.9 g	17.1 g	Twice
	562.9 g	8.6g	1x

     The reactor used was 4L and mixed with unbleached pulp slurry and calcium hydroxide (Ca (OH) ₂) at 600rpm using a stirrer, using 99% high-purity carbon dioxide (CO₂) and changing the pH change during the carbonation reaction. A pH meter was installed for the measurement. Completion of the reaction was concluded that the synthesis of precipitated calcium carbonate (PCC) was completed when the pH value is less than 7 and the experiment was terminated.

      The unbleached pulp slurry in which the precipitated calcium carbonate (PCC) was synthesized in the unbleached pulp slurry was prepared using a 60 g / m 2 TAPPI standard circular weeding machine and produced a basis weight of 60 g / m 2 in the same basis according to TAPPI Standard 205 om-88. According to KS MISO 187, the humidity characteristics were controlled at a temperature of 23 ± 1 ℃ and a relative humidity of 50 ± 2 for more than 24 hours, and then the optical and physical characteristics were compared.

 In the case of bleached pulp that did not undergo the two-step continuous synthesis reaction of precipitated calcium carbonate (PCC), optical and physical properties were also compared through the aforementioned papermaking process.

      In addition, a paper having a basis weight of 50 g / m 2 was prepared using Kraft pulp and used for the top layer, and a paper made of a basis weight of 60 g / m 2 bleached pulp was fixed to the bottom layer, and a precipitated calcium carbonate (PCC) was synthesized in the middle layer. It is made of multi-layered paper of three-layer structure by using the paper made of bleached pulp as the raw material. Also, the paper made of 60g / ㎡ Kraft paper is used on the top layer and the paper made of bleached pulp of 60g / ㎡ basis weight is fixed on the bottom layer. Three layers of multi-layered paper using unbleached pulp synthesized with precipitated calcium carbonate (PCC) in the middle layer, paper made of 100 g / m2 kraft on the top layer, and a basis weight of 60 g / m2 on the bottom layer. After fixing the paper produced with the bleached pulp of 3 layer structure using unbleached pulp synthesized with precipitated calcium carbonate (PCC) in the middle layer of a three-layer structure of the paper to the optical properties and physical We compared the properties.

(1) optical properties

     Whiteness (ISO 2470) was measured using Technidyne's COLOR TOUCH2 in order to measure the whiteness change of papermaking paper according to the amount of precipitated calcium carbonate (PCC) in unbleached pulp slurry.

      As a result of measuring the whiteness using COLOR TOUCH2, as shown in Table 3 and FIG. 4, it can be seen that as the amount of precipitated calcium carbonate (PCC) synthesized in the pulp slurry is increased, the whiteness is improved. When three times the precipitated calcium carbonate (PCC) was synthesized relative to the dry weight of the unbleached pulp, the whiteness of the prepared papermaking paper was increased to about 45% compared to the existing 33%.

Optical characteristics of the sheet

	Brightness (%)
KP	77
UKP Control	27
UKP -PCC Triple Composition	43
UKP -PCC 1 Composition	36
UKP -PCC 0.5	29

     In Table 4 and FIG. 5, the top and bottom layers were used as bleaching pulp, and the unbleached pulp paper was synthesized using precipitated calcium carbonate (PCC) in the middle layer. The whiteness change of a layered multilayer paper is shown. As the synthesis amount of precipitated calcium carbonate (PCC) increases in the unbleached pulp used in the middle layer, the increase in whiteness can be confirmed.

     In addition, the increase in the use of bleached pulp, which shows high whiteness in the composition ratio of multi-layer paper, can be observed.In this study, the white layer was increased in the middle layer between 100gsm bleached pulp and 60gsm bleached pulp. Using the pulp synthesized from the PCC of the pear showed that the level of white paper (about 77%) of the paper produced using only the conventional bleached pulp alone (approximately 72%).

      Although the whiteness of the pulp synthesized through the two-stage continuous synthesis reaction of precipitated calcium carbonate is higher than that of the bleached pulp, precipitated calcium carbonate (PCC) is formed in the primary bleaching pulp that has been subjected to the initial bleaching process among these multi-stage bleaching processes. It is judged that such whiteness difference can be overcome by In addition, in the manufacture of multi-layered paper products such as white paper, it is thought that the use of pulp synthesized by precipitated calcium carbonate (PCC) through a two-step continuous synthesis reaction can be used to replace the conventional bleached pulp.

Optical Characteristics of Multilayered Paper with 3 Layers

sign	Structure of multi-layer paper		Whiteness	Remarks
a	TOP	KP 60gsm	66.7	Top layer 60gms
	MIDDLE	UKP 60gsm-
	BOTTOM	KP 60gsm
b	TOP	KP 60gsm	71.1
	MIDDLE	UKP 60gsm -300% PCC
	BOTTOM	KP 60gsm
c	TOP	KP 60gsm	67.4
	MIDDLE	UKP 60gsm -100% PCC
	BOTTOM	KP 60gsm
d	TOP	KP 60gsm	67.1
	MIDDLE	UKP 60gsm -50% PCC
	BOTTOM	KP 60gsm
e	TOP	KP 100gsm	72.0	Top floor 100gsm
	MIDDLE	UKP 60gsm
	BOTTOM	KP 60gsm
f	TOP	KP 100gsm	75.0
	MIDDLE	UKP 60gsm -300% PCC
	BOTTOM	KP 60gsm
g	TOP	KP 100gsm	73.9
	MIDDLE	UKP 60gsm -100% PCC
	BOTTOM	KP 60gsm
h	TOP	KP 100gsm	73.4
	MIDDLE	UKP 60gsm -50% PCC
	BOTTOM	KP 60gsm
i	TOP	KP 50gsm	61.2	Top floor 50gsm
	MIDDLE	UKP 60gsm
	BOTTOM	KP 60gsm
j	TOP	KP 50gsm	64.5
	MIDDLE	UKP 60gsm -300% PCC
	BOTTOM	KP 60gsm
k	TOP	KP 50gsm	62.1
	MIDDLE	UKP 60gsm -100% PCC
	BOTTOM	KP 60gsm
l	TOP	KP 50gsm	61.3
	MIDDLE	UKP 60gsm -50% PCC
	BOTTOM	KP 60gsm

(2) strength characteristics

      Micro 350 from Testrometric was used to measure the thermal shear (ISO1924) and elongation of the paper according to the amount of precipitated calcium carbonate (PCC) in the unbleached pulp slurry.

      Tables 5 and 6 show changes in thermal shortening according to amounts of precipitated calcium carbonate (PCC) synthesized in unbleached pulp, and Tables 6 and 7 show elongation. Precipitated calcium carbonate (PCC) When the precipitated calcium carbonate (PCC) is synthesized in unbleached pulp through a two-step continuous synthesis reaction, the tensile strength decreases as the amount of precipitated calcium carbonate (PCC) is increased. This is because the inter-fiber bond zone is reduced by the synthesized precipitated calcium carbonate (PCC), which leads to a decrease in the bond area between the fibers, leading to a decrease in strength, and increases the amount of precipitated calcium carbonate (PCC) synthesized in the unbleached pulp. Accordingly, it can be seen that the decrease in tensile strength is large.

     The elongation rate can also be reduced as the synthesis rate of precipitated calcium carbonate (PCC) in the unbleached pulp slurry increases, which decreases the bond area between fibers due to the precipitated calcium carbonate (PCC) formed on the fiber surface, as with thermal shearing. Increasing the amount of sedimentary precipitated calcium carbonate (PCC) decreases the strength of the sheet.

Thermal Sheathing of Grassland According to PCC Synthesis (60gsm Sheet)

	Breaking length, (km)
KP	2.7
UKP Control	1.85
UKP -PCC 0.5	0.78
UKP -PCC 1 Composition	0.53
UKP -PCC Triple Composition	0.1

Growth Rate of Grassland According to PCC Synthesis (60gsm Sheet)

	Strain index (mm)
KP	1.3
UKP Control	1.0
UKP -PCC 0.5	0.7
UKP -PCC 1 Composition	0.43
UKP -PCC Triple Composition	0.15

Claims (6)

1. As a two-step continuous synthesis reaction that synthesizes white precipitated calcium carbonate (PCC) in unbleached pulp as shown below, a two-step continuous synthesis reaction method for precipitated calcium carbonate (PCC) that can replace the existing bleaching process. Multi-layer paper production method of unbleached pulp using.

    (a) the pulp preparation step,

    (b) mixing the pulp slurry and slaked lime,

        (CaO + H₂O → Ca (OH) ₂, hydration stage, stage 1)

    (c) spraying carbon dioxide (CO) on the pulp and slaked mixed slurry,

    (d) synthesizing precipitated calcium carbonate (PCC) by carbonation,

        (CaO + CO₂ → CaCO₃, PCC synthesis stage, 2 stage)

    (e) recovering the slurry after the reaction of step (d) is completed;

    (f) using the slurry of step (e) to prepare a multi-layered paper of which the upper layer is bleached paper, the middle layer is unbleached paper, and the lower layer is bleached paper.

    (g) Analytical step of the prepared multilayer paper.
2. 2. The method of claim 1, wherein the amount of precipitated calcium carbonate (PCC) to be synthesized is 0.5 to 3 times the amount of the unbleached pulp dry weight (In-situ Process). Method for manufacturing multi-layer paper of unbleached pulp using
3. The precipitated calcium carbonate of claim 1, wherein the mixed lime (CaO) is added as calcium hydroxide (Ca (OH) ₂) in a hydrated state by calcining limestone (CaCO₃) and reacting with water. A method for producing multilayer paper of unbleached pulp using an in-situ process.
4. According to claim 1, wherein the step (e) is maintained at 25 ~ 35 ℃, to help the reaction by rotating the stirrer of the carbonation reactor to 600rpm, install a pH meter inside the vessel of the reactor to confirm the end of the reaction Method of producing a multilayer paper of unbleached pulp using a precipitated calcium carbonate two-stage continuous synthesis method (In-situ Process), characterized in that when the pH is less than 7 to terminate the reaction and recover the unbleached pulp slurry.
5. 2. The precipitated calcium carbonate of claim 1, wherein the multi-layered paper having the upper layer of (f) as the bleached paper, the middle layer as the unbleached paper, and the lower layer as the bleached paper can be manufactured as the upper layer as the bleached paper and the lower layer as the unbleached paper. Method for preparing multi-layered paper of unbleached pulp using a step-in-situ process.
6. Paper produced by using unbleached pulp synthesized precipitated calcium carbonate (PCC) in unbleached pulp by the method of any one of claims 1 to 5.

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