JP2021161544A - Method for producing unbleached recycled kraft paper - Google Patents

Abstract

To provide a method for producing unbleached recycled kraft paper that can produce unbleached recycled kraft paper having the color tone and texture of unbleached kraft paper, while reusing heavy duty packaging bags.SOLUTION: A method for producing unbleached recycled kraft paper of the present invention comprises: a waste paper pulp manufacturing process for producing waste paper pulp; and a raw material pulp manufacturing process for producing raw material pulp containing the waste paper pulp and unbleached kraft pulp or raw material pulp containing the waste paper pulp, wherein the waste paper pulp includes waste paper pulp of heavy duty packaging bags, and the pulp of heavy duty packaging bags is made from a heavy duty packaging bag having an inner bag made of a resin film and an outer bag containing the inner bag and mainly composed of unbleached kraft pulp; the waste paper pulp production process includes a step for producing the waste paper pulp of heavy duty packaging bags; and the step for producing the waste paper pulp of heavy duty packaging bags includes a first crushing step to crush the heavy duty packaging bag, and a second crushing step to crush the crushed material having the paper component as the main component among the crushed material crushed in the first crushing step.SELECTED DRAWING: None

Description

The present invention relates to a method for producing unbleached recycled kraft paper.

Kraft paper uses kraft pulp obtained by kraft-melting wood and has excellent strength such as tensile strength. Therefore, it is used for filling and transporting agricultural products, chemicals, flour, cement, etc. Widely used as a packaging bag. It is also used in envelopes because of its excellent strength.

In recent years, from the viewpoint of protection of wood resources and economic efficiency, it has been oriented to use used paper as a pulp raw material, but the same applies to kraft paper. It has been proposed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2000-336590

On the other hand, as used paper pulp used as a raw material for recycled paper, corrugated cardboard used paper is widely known as tea-based used paper pulp. However, unlike the used paper pulp of magazines and newspapers, the used paper pulp of corrugated cardboard has a problem that the color is not stable because there are many sticky foreign substances that cause deterioration of the quality of recycled paper. From the viewpoint of the quality of used paper pulp that can be secured, recycled kraft paper is bleached kraft paper with high whiteness or light brown semi-bleached kraft paper that is a mixture of unbleached kraft pulp and used paper pulp with high whiteness. Is in circulation. However, there is an increasing demand for unbleached recycled kraft paper as a wrapping paper with a lower environmental load.

Further, in recent years, from the viewpoint of improving the strength of the kraft packaging bag, a heavy bag in which a resin film is inner-layered on a kraft paper bag has been used. However, when reusing the heavy bag, the resin film in the inner layer of the heavy bag causes various quality deterioration factors in the papermaking process, so that it is necessary to separate the resin film. On the other hand, the manual separation of the kraft paper and the resin film of the heavy bag may increase the labor cost and reduce the cost-effectiveness of collecting the packaging bag.

The present invention has been made based on the above circumstances, and is capable of reusing heavy bags and producing unbleached recycled kraft paper having the color and texture of unbleached kraft paper. It is an object of the present invention to provide a method for producing paper.

The invention made to solve the above problems is a method for producing unbleached recycled kraft paper, which comprises a waste paper pulp manufacturing process for producing waste paper pulp and a raw material pulp containing the waste paper pulp and unbleached kraft pulp. The raw material pulp manufacturing process for producing the raw material pulp containing the used paper pulp is provided, the used paper pulp contains heavy bag waste paper pulp, and the heavy bag used paper pulp contains an inner bag made of a resin film and the inner bag. The heavy bag used as a raw material and having an outer bag containing unbleached kraft pulp as a main component, and the used paper pulp manufacturing process has a heavy bag used paper pulp manufacturing process for producing the heavy bag used paper pulp, and the heavy bag The used paper pulp manufacturing process includes a first crushing step of crushing the heavy bag and a second crushing step of crushing a crushed product containing a paper component as a main component among the crushed products crushed in the first crushing step. It is a manufacturing method of unbleached recycled kraft paper having.

According to the method for producing unbleached recycled kraft paper of the present invention, the heavy bag can be reused and unbleached recycled kraft paper having the color and texture of unbleached kraft paper can be produced.

It is a figure which shows a part of the flow of the manufacturing method of the unbleached recycled kraft paper which concerns on one Embodiment of this invention.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

The method for producing unbleached recycled kraft paper according to one aspect of the present invention is a method for producing unbleached recycled kraft paper, which comprises a waste paper pulp manufacturing process for producing used paper pulp and the above-mentioned used paper pulp and unbleached kraft pulp. The raw material pulp containing the raw material pulp or the raw material pulp manufacturing process for producing the raw material pulp containing the used paper pulp is provided, the used paper pulp contains heavy bag waste paper pulp, and the heavy bag used paper pulp is an inner bag made of a resin film. The waste paper pulp manufacturing process includes a heavy bag waste paper pulp manufacturing process that includes the inner bag and has an outer bag containing unbleached kraft pulp as a main component. Then, the heavy bag waste paper pulp manufacturing process crushes the first crushing step of crushing the heavy bag and the crushed material containing the paper component as the main component among the crushed products crushed in the first crushing step. It has a second crushing step.

Heavy bags are discharged in large quantities at each business establishment (factory, fishery cooperative, etc.) and are not sold to the general market, so they are not overprinted and there is almost no contamination of used paper other than heavy bags. , There is little mixing of ash. In addition, the amount of tapes mixed in is very small. The method for producing the unbleached recycled kraft paper includes a waste paper pulp manufacturing process for producing waste paper pulp and a raw material pulp for producing the waste paper pulp and the raw material pulp containing the unbleached kraft pulp or the raw material pulp containing the waste paper pulp. The waste paper pulp contains a heavy bag waste paper pulp made from a heavy bag having an inner bag made of a resin film and an outer bag containing the inner bag and containing unbleached kraft pulp as a main component. As a result, it is possible to produce unbleached recycled kraft paper that is uniform, has few foreign substances, and has an unprecedented appearance (texture close to that of unbleached kraft paper).
Further, the waste paper pulp manufacturing process includes a heavy bag waste paper pulp manufacturing process for producing the heavy bag waste paper pulp, and the heavy bag waste paper pulp manufacturing process includes a first crushing step for crushing the heavy bag and the first crushing step. By having a second crushing step of crushing a crushed product having a paper component as a main component among the crushed products crushed in the crushing process, an inner bag made of a resin film and unbleached kraft pulp as a main component are used. Since the heavy bag having the outer bag can be efficiently crushed, the production efficiency of the heavy bag waste paper pulp can be improved. Therefore, according to the method for producing unbleached recycled kraft paper, the heavy bag can be reused and unbleached recycled kraft paper having the color and texture of unbleached kraft paper can be produced.

It is preferable that the method for producing unbleached recycled kraft paper further includes, after the second crushing step, an identification step of identifying a crushed product containing the paper component as a main component using a hyperspectral camera. When the method for producing unbleached recycled kraft paper further includes the identification step after the second crushing step, it is possible to accurately distinguish between kraft paper and contraindicated products other than kraft paper from the heavy bag waste paper pulp raw material.

It is preferable that the method for producing unbleached recycled kraft paper further includes a sorting step of separating the crushed material crushed in the second crushing step by size before the identification step. The method for producing unbleached recycled kraft paper further includes the above-mentioned sorting step before the above-mentioned identification step, so that a high-quality recycled paper raw material can be provided by the identification step of the next step.

The waste paper pulp further contains corrugated cardboard waste paper pulp, the waste paper pulp manufacturing process further includes a corrugated cardboard waste paper pulp manufacturing process for producing the corrugated cardboard waste paper pulp, and conforms to JIS-P8148 (2001) in the unbleached recycled kraft paper. It is preferable that the whiteness measured in the above method is less than 30% and the ash content in the paper in the 525 ° C. combustion method is 1.0% or more and 12.5% or less. As the used paper pulp, a corrugated paper waste paper pulp may be used in addition to the heavy bag waste paper pulp, and the waste paper pulp production process may include a cardboard waste paper pulp production process for producing the above-mentioned corrugated paper waste paper pulp. In addition to corrugated cardboard waste paper, cheap waste paper and waste paper with a high ash content are mixed in the middle layer of corrugated cardboard, so it has a higher ash content and a higher degree of whiteness than unbleached kraft waste paper pulp. Therefore, although the addition of corrugated cardboard waste paper pulp affects the quality deterioration of unbleached recycled kraft paper, it is possible to mix it arbitrarily according to the required quality of unbleached recycled kraft paper because of its cost merit and high collection stability of used paper. The most economical. Further, when the whiteness of the unbleached recycled kraft paper and the ash content in the paper are within the above ranges, the appearance and texture of the unbleached kraft paper can be further enhanced.

[Details of Embodiments of the present invention]
Hereinafter, a method for producing unbleached recycled kraft paper according to an embodiment of the present invention will be described in detail.

<Manufacturing method of unbleached recycled kraft paper>
The method for producing unbleached recycled kraft paper is a method for producing unbleached recycled kraft paper. The method for producing unbleached recycled kraft paper includes a waste paper pulp production process for producing waste paper pulp and a raw material pulp production process for producing raw material pulp. Further, it is preferable that the method for producing the unbleached recycled kraft paper usually further includes a papermaking step, a drying step, a winding step, and the like for making the raw material pulp.

[Waste paper pulp manufacturing process]
In the used paper pulp manufacturing process, used paper pulp is manufactured. The used paper pulp contains a heavy bag waste paper pulp, and the used paper pulp manufacturing process includes a heavy bag used paper pulp manufacturing process for producing the heavy bag used paper pulp. As will be described later, it is preferable that the used paper pulp manufacturing process further includes a corrugated cardboard used paper pulp manufacturing process for producing the above corrugated cardboard used paper pulp.

(Heavy bag used paper pulp manufacturing process)
The heavy bag is a bag in which a resin film is superposed on one or a plurality of sheets of kraft paper. The heavy bag is widely used for storing heavy objects such as cement and rice, and a large amount of it is discharged at each business establishment (factory, fishery cooperative, etc.), so that stable quality recycled paper can be obtained. Further, in the heavy bag, a resin film such as polyethylene is laminated in order to impart moisture resistance according to the contents. A heavy bag provided with a resin film is less likely to tear and has excellent waterproof properties as compared with a packaging bag made only of kraft paper. Conventionally, heavy bags have not been reused as used paper because it is difficult to remove the resin film attached to the inside, but they have been incinerated and have not been effectively used by recycling. On the other hand, since the heavy bag is not sold in the general market, the deinking process is not required because it is not excessively printed, and the purpose is to obtain unbleached (brown) pulp. Is also unnecessary. Furthermore, since there is almost no contamination of used paper other than heavy bags and less contamination of ash, almost the same strength and color as virgin pulp can be obtained. In addition, since the amount of tapes mixed in is very small, the amount of adhesive foreign matter is also small. Therefore, since the used paper pulp contains heavy bag waste paper pulp, it is possible to produce unbleached recycled kraft paper that is uniform, has few foreign substances, and has an unprecedented appearance (texture close to that of unbleached kraft paper).

In the heavy bag recycled paper pulp manufacturing process, a first crushing step of crushing the heavy bag and a second crushing treatment of a crushed product containing a paper component as a main component among the crushed products crushed in the first crushing step are performed. It has a crushing process. Further, it is preferable that the heavy bag waste paper pulp manufacturing step further includes an identification step of identifying the crushed material containing the paper component as a main component by using a hyperspectral camera after the second crushing step. Further, it is preferable that the heavy bag recycled paper pulp manufacturing step further includes a sorting step of separating the crushed material crushed in the second crushing step according to the size before the identification step.

Next, each step in the heavy-bag used paper pulp manufacturing process will be described with reference to FIG. FIG. 1 is a diagram showing a part of the flow of the heavy bag waste paper pulp manufacturing process.

<First crushing process>
In the first crushing step, the heavy bag is crushed. In the first crushing step, for example, a known uniaxial crushing device can be preferably used as the crushing device. The uniaxial crushing device performs shear crushing by meshing the rotary blade attached to the rotor surface and the fixed blade of the main body. As shown in FIG. 1, the pulp raw material 1 is charged into the uniaxial crusher 10. The first crushed material 11 crushed by the uniaxial crushing device 10 is sent to the conveyor 6, and after the foreign matter is removed, it is put into the biaxial crushing device 20 used in the next step.

<Second crushing process>
In the second crushing step, among the crushed products crushed in the first crushing step, the crushed material containing the paper component as a main component is crushed. In the second crushing step, for example, a known biaxial crushing device can be preferably used as the crushing device. The biaxial crushing device is not particularly limited, but a plurality of crushing blades projecting outward in the radial direction are spaced apart from each other in the axial direction on at least two substantially parallel support shafts rotating around the axial core. As a result of being provided and repeatedly breaking or tearing, the first crushed material 11 is subdivided by the first crushing step. The second crushed material crushed by the twin-screw crushing device 20 and further subdivided is supplied to the charging feeder 30 which is a sorting means by the transport conveyor 9.

<Separation process>
It is preferable that the heavy bag waste paper pulp manufacturing step further includes a sorting step after the second crushing step and before the identification step described later. In the sorting step, the second crushed material crushed in the second crushing step is sorted by size. The sorting step is performed by, for example, the input feeder 30. The charging feeder 30 separates the second crushed material conveyed by the transfer conveyor 9. The charging feeder 30 has a large number of rotating shafts in the transport direction, and sorts the transported second crushed material into a heavy product 31, an undersized product 32, and an oversized product 33 while transporting the transported second crushed product. For example, the heavy object 31 mainly contains uncrushed kraft paper. The undersized product 32 mainly contains shredded kraft paper and resin film. The oversized product 33 mainly contains kraft paper having a relatively large area, and also includes a part of a resin film. As shown in FIG. 1, the input feeder 30 is arranged so as to be inclined so that the downstream side in the traveling direction is higher. Since the downstream side in the traveling direction is inclined so as to be high, the heavy object 31 is not transferred and falls. Further, the undersized product 32, which is a lightweight product that cannot be used for used paper pulp, falls through the gap of the input feeder 30. Then, the oversized product 33, which is a raw material for used paper pulp, is discharged from the input feeder 30.

The heavy object 31 is put into the uniaxial crushing device 10 again by using, for example, a forklift. Further, among the undersized products 32, the resin film is collected and reused as a raw material for a recycled resin product or used as a fuel, for example. Also, shredded kraft paper is collected and used as fuel. Further, the oversized product 33 is mainly made of kraft paper having a relatively large area, and includes a resin film, though not many others. The oversized product 33 is guided to the identification step of the next step. In the past, the undersized product 32 was manually removed, which was low in terms of cost effectiveness. By using the input feeder 30 in the sorting step, the heavy product 31 and the undersized product 32 are eliminated. Therefore, the undersized product 32 included in the oversized product 33 can be reduced as much as possible. Therefore, a high-quality recycled paper raw material can be provided in the identification step, which is the next step. The quality of unbleached recycled kraft paper produced can be improved. The oversized product 33 dispersed by the charging feeder 30 is charged into the identification device 40.

<Identification process>
It is preferable that the heavy bag waste paper pulp manufacturing step further includes an identification step after the second crushing step and the sorting step. In the identification step, a hyperspectral camera is used to identify the crushed material containing the above paper component as a main component. The identification device 40 preferably includes, for example, a conveyor and a material measuring means for measuring the material with a hyperspectral camera. Further, it is preferable to have an identification means for determining whether or not the cellulose component is dominant based on the absorbance spectrum photometrically measured by the material measuring means for each transported object.

By the identification by the identification means 45, it is determined that the paper is kraft paper when the cellulose component is dominant, and when the cellulose component is not dominant (for example, when the resin component is dominant). , It is judged that it is a resin film, and it can be sorted.

"Other than kraft paper" includes so-called contraindicated items such as adhesive tapes, patches, file metal fittings, metal clips, cellophane, foamed styrol, and sewing thread attached to the contents of the wrapping bag and the wrapping bag. As shown in the example of this contraindicated product, "other than kraft paper" is a contraindicated product and cannot be used as a raw material for used paper pulp, so it is necessary to exclude it from the used paper processing system.

For example, in order to separate laminated paper to which a resin film is attached, it is necessary to measure the material. Therefore, the material is measured by the hyperspectral camera 43. The hyperspectral camera 43 can divide a wide wavelength region from visible light to a short wave infrared region (SWIR) into fine wavelength regions, and can acquire light intensity (wavelength spectrum) in each wavelength region. For example, a near infrared region (near 750 to 1700 nm) can be photographed. Reference numeral 46 is a light source having a wavelength from visible light to the near infrared region. Molecules that make up a substance are in various motions, and when light is applied to the moving molecules, only light of a specific wavelength is absorbed according to the motion state. The wavelength in the infrared region to be absorbed is a value determined by the interatomic distance and vibration direction constituting the molecule, and has a characteristic wavelength distribution that accurately represents the type of molecule. By examining the reflected / absorbed wavelength distribution (absorption spectrum), it is possible to know what kind of molecule the measurement object contains. By this principle, the material can be measured.

The transported object identified by the identification device 40 operates the sorting device 50, for example, in the process of dropping from the transport conveyor. The sorting device 50 sorts the used paper 51 made of kraft paper and the collected resin film 52. The used paper 51 made of kraft paper can be used as a material for kraft paper or corrugated cardboard used paper pulp as a product, and the resin film 52 can be used as a resin raw material or fuel.

The used paper 51 made of a heavy bag becomes waste paper pulp through a waste paper pulp manufacturing process. In the used paper pulp manufacturing process, the same equipment as the corrugated cardboard used paper pulp manufacturing process can be used. In the used paper pulp manufacturing step, it is preferable to carry out a further selection step in order to remove the resin film meal that has not been completely removed in the identification step. In the selection step, for example, a slit screen (slit width 0.25 mm) is processed in two stages. It is possible to prevent the inclusion of foreign substances that could not be removed in the identification process and reduce the deterioration of paper quality.

(Corrugated cardboard waste paper pulp manufacturing process)
As the used paper pulp, a corrugated paper waste paper pulp may be used in addition to the heavy bag waste paper pulp, and the waste paper pulp production process may include a cardboard waste paper pulp production process for producing the above-mentioned corrugated paper waste paper pulp. As a raw material for corrugated cardboard waste paper, inexpensive miscellaneous paper waste paper and magazine waste paper with a large amount of ash are used in addition to corrugated cardboard waste paper, but it is preferable to use only corrugated cardboard waste paper. However, corrugated cardboard is made of unbleached kraft pulp even if only corrugated cardboard is used as a raw material because inexpensive waste paper and ash-rich waste paper are mixed in the middle layer, back layer, and core. Compared to recycled paper pulp, it has more ash and higher whiteness. Therefore, as the amount of recycled corrugated paper pulp is increased, the color tone of unbleached recycled kraft paper becomes whitish, the strength decreases, and impurities (foreign substances) increase. Although the addition of corrugated recycled paper pulp affects the quality of unbleached recycled kraft paper, it is most economical to mix it arbitrarily according to the required quality of unbleached recycled kraft paper because the collection stability of used paper is high. ..

When corrugated cardboard waste paper pulp is used, it is preferable to strengthen the selection and adjust the undissociated pulp fibers with a disperser. It is also preferable to wash to remove the ash contained in the recycled paper pulp.

(Other recycled pulp)
As the used paper pulp other than the heavy bag waste paper pulp, it is preferable to use only the corrugated waste paper pulp and not to contain the used paper pulp derived from newspaper waste paper, magazine waste paper and the like. When a large amount of used newspaper pulp or used magazine pulp is contained, the ash content in the used paper pulp may increase and the strength may decrease. In addition, the color of the paper may be whitish or blackish, which may impair the unbleached texture.

[Raw material pulp manufacturing process]
In the raw material pulp manufacturing process, a raw material pulp containing the used paper pulp and unbleached kraft pulp or a raw material pulp containing the used paper pulp is produced. Specifically, in the raw material pulp manufacturing process, a raw paper pulp containing the used paper pulp and unbleached kraft pulp or the used paper pulp is mixed to produce a pulp slurry. Additives may be added to the pulp slurry, if necessary. The used paper pulp is produced by the used paper pulp manufacturing process.

<Unbleached kraft pulp>
As the unbleached kraft pulp, for example, softwood undiluted kraft pulp is preferable. Unbleached coniferous kraft pulp has a relatively high strength, and in particular, unbleached coniferous kraft pulp (NUKP) from which the ester compounds of lignin and sterol have not been removed so much becomes stronger due to the action of lignin remaining in the pulp. Due to the large size and the ester compound of sterol remaining in the pulp, the pulp fiber exhibits good slipperiness and has appropriate rigidity and breakage resistance. Therefore, by using softwood unbleached kraft pulp as the raw material pulp, good strength can be imparted to the unbleached recycled kraft paper.

Softwood unbleached kraft pulp is beaten before being blended as raw material pulp. In the beating process, foreign substances are finely decomposed and dispersed in water, and softwood unbleached kraft pulp is defibrated. In the beating step of softwood unbleached kraft pulp, it is preferable to beating with a double disc refiner (DDR). The range of the freeness of the softwood unbleached kraft pulp is preferably 400 ml or more and 600 ml or less. When the freeness of the softwood unbleached kraft pulp is within the above range, good strength can be imparted to the unbleached recycled kraft paper. In addition, when softwood kraft pulp is beaten at a high concentration, it becomes finer due to friction between fibers rather than cutting with a knife. For this reason, fibrillation is predominantly beaten over shortening of fibers, and shortening of fibers can be achieved while maintaining a wide average fiber width like bast fibers.

The lower limit of the content of the heavy-duty recycled paper pulp with respect to the total content of the raw material pulp is preferably 10% by mass, more preferably 20% by mass. The upper limit of the content of the heavy bag waste paper pulp may be 100% by mass, more preferably 70% by mass. When the content of heavy-duty recycled paper pulp with respect to the total content is within the above range, it is possible to provide unbleached recycled kraft paper that can improve the appearance and natural texture that unbleached kraft paper has. When the unbleached recycled kraft paper contains a large amount of corrugated cardboard waste paper pulp, the strength and impurities of the unbleached recycled kraft paper increase, and the ash content in the paper increases, so that the whiteness as a whole increases. Therefore, the lower limit of the content of heavy-duty recycled paper pulp is preferably 10% by mass. The heavy-duty recycled paper pulp can be obtained as unbleached recycled pulp that is uniform and has few foreign substances without going through an alkali deliquescent treatment, a deinking process, and a bleaching process as in a waste paper pulp manufacturing facility. By setting the content of heavy-duty recycled paper pulp relative to the total content of raw material pulp within the above range, it is possible to obtain unbleached recycled kraft paper having little change in color and foreign matter and excellent strength.

The upper limit of the content of unbleached kraft pulp with respect to the total content of raw material pulp is preferably 70% by mass, more preferably 60% by mass. Even if the content of unbleached kraft pulp is increased, the color tone and strength do not change drastically and the quality does not improve. Therefore, even if the lower limit of the content of bleached kraft pulp is 0% by mass. good. On the other hand, from the viewpoint of stable supply of pulp raw material and Eco Mark standard for wrapping paper, the content range of unbleached kraft pulp may be 0% by mass or more and 70% by mass or less.

The lower limit of the content of corrugated paper pulp with respect to the total content of raw material pulp is preferably 20% by mass, more preferably 10% by mass. The upper limit of the content of the corrugated cardboard waste paper pulp is preferably 90% by mass, more preferably 80% by mass. When the content of corrugated cardboard waste paper pulp with respect to the total content is within the above range, it is possible to provide unbleached recycled kraft paper that can have a better appearance and natural texture as that of unbleached kraft paper. In addition, if the content of the corrugated cardboard waste paper pulp exceeds 90% by mass, the color of the unbleached recycled kraft paper may become whitish or blackish, which may impair the unbleached texture. There is. Further, when the content of the corrugated cardboard waste paper pulp exceeds 90% by mass, the strength and impurities of the unbleached recycled kraft paper increase, and the ash content in the unbleached recycled kraft paper increases, so that the paper becomes white as a whole. May increase.

(Additive)
As a method for producing the unbleached recycled kraft paper, a known additive for papermaking can be used.

<Paper Strengthening Agent>
As the paper strength enhancer, a polyacrylamide polymer is preferable, and cationic starch and amphoteric starch can be used as needed, and amphoteric starch is preferable from the viewpoint of strength improving effect. The range of the content of the paper strength enhancer in the solid content with respect to the pulp fiber is preferably 1 kg / pulp t or more and 5 kg / pulp t or less, and more preferably 2 kg / pulp t or more and 4 kg / pulp t or less.

<Size agent>
Examples of the internal sizing agent include an acidic rosin sizing agent. When the amount of waste corrugated paper pulp is high and the ash content in the paper increases, a neutral rosin sizing agent is preferable. The range of the content of the internal sizing agent in the solid content with respect to the pulp fiber is preferably 2.5 kg / pulp t or more and 15.0 kg / pulp t, and 5.0 kg / pulp t or more 10.0 kg / pulp. More preferably, it is t or less.

<Aluminum sulfate band>
The range of the content of the aluminum sulfate band in the pulp slurry is preferably 4.5 kg / pulp t or more and 12.5 kg / pulp t or less in terms of solid content.

<Other additives>
A known papermaking additive other than the above-mentioned paper strength enhancer, sizing agent, and aluminum sulfate band may be added to the base paper of the unbleached recycled kraft paper. The internal additive is not particularly limited, and various chemicals can be used alone or in combination. For example, papermaking additives such as a coagulant, a retention agent, a dye, a pitch control agent, a defoaming agent, an ultraviolet ray inhibitor, a fading inhibitor, and a slime control agent can be used.

[Papermaking process]
In the papermaking process, the pulp slurry is dehydrated (papermaking). The paper making method is not particularly limited, and paper making can be performed using a known paper machine. Examples of the paper machine include a paper machine such as a long net, a circular net, a hybrid former, and a gap former. Of these, a long net paper machine having a squeezing device is suitable. When making raw material pulp containing heavy-duty waste paper pulp and kraft pulp, it is preferable to make paper in an acidic region because there is virtually no ash contained in the used paper pulp. When the raw material pulp further contains corrugated cardboard waste paper pulp, when paper is made in an acidic region, the calcium component elutes due to the influence of the ash contained in the corrugated cardboard waste paper and reacts with the paper strength agent and sizing agent to reduce the effect of the chemicals. It is preferable to make paper in the neutral region because it causes deterioration of quality.

[Drying process]
Next, it is pressed with a pressure roll to remove water and dried in a dryer cylinder. A coating step may be provided between the drying steps. Quality can be improved by appropriately applying known chemicals such as oxidized starch, polyvinyl alcohol, polyacrylic amide, antislipper, and water repellent in the coating process. As the coating equipment, known coating equipment such as a size press, a rod metering size press, and a gate roll can be used. After drying, smoothing may be performed using a calender device such as a nip calender, a super calender, a machine calender, or a soft calender. By performing the smoothing treatment, the unbleached recycled kraft paper is imparted with high glossiness and can be suitably used for a packaging bag having a high-class feeling.

[Winding process]
Finally, wind it on a reel to obtain unbleached recycled kraft paper.

(Basis weight of unbleached recycled kraft paper)
The lower limit of the unbleached reproduction kraft paper having a basis weight produced by the production method of the unbleached reproduction kraft paper is preferably 50 g / m ^2, and more preferably 70 g / m ^2. If the basis weight is ^{less than 50 g / m 2} , the paper quality strength as wrapping paper or handbag paper may not be satisfied. The upper limit is preferably 120 g / m ^2. If the basis weight of unbleached recycled kraft paper ^{exceeds 120 g / m 2} , it is not preferable from the viewpoint of weight reduction.

(Whiteness of unbleached recycled kraft paper)
When the used paper pulp manufacturing process further includes the corrugated cardboard used paper pulp manufacturing process, the whiteness of the unbleached recycled kraft paper produced by the method for producing the unbleached recycled kraft paper is preferably less than 30%, preferably 25% or less. Is more preferable. As described above, when unbleached recycled kraft paper contains a large amount of corrugated cardboard waste paper pulp, the color of the paper may be whitish or blackish, which may impair the unbleached texture. There is. Therefore, when the whiteness of the unbleached recycled kraft paper is within the above range, the appearance and texture of the unbleached kraft paper can be further enhanced. The whiteness of the unbleached recycled kraft paper is measured according to JIS-P8148 (2001).

(Ashes of unbleached recycled kraft paper)
When the used paper pulp manufacturing process further includes the corrugated cardboard used paper pulp manufacturing process, the lower limit of the ash content in the paper in the 525 ° C. combustion method of the unbleached recycled kraft paper produced by the method for producing the unbleached recycled kraft paper is 1. .0% is preferable, and 5.0% is more preferable. On the other hand, the upper limit of the ash content in the unbleached recycled kraft paper is preferably 12.5%, more preferably 10.0%. When the unbleached recycled kraft paper contains a large amount of corrugated cardboard waste paper pulp, the strength and impurities of the unbleached recycled kraft paper increase, and the ash content in the paper increases, so that the whiteness as a whole increases. When the range of the ash content in the paper in the 525 ° C. combustion method of the unbleached recycled kraft paper is within the above range, the appearance and texture of the unbleached kraft paper can be further enhanced.
If the whiteness or ash content of the unbleached recycled kraft paper is out of the above range and the whiteness increases in the appearance of the unbleached kraft paper, it can be adjusted with a known dye.

According to the method for producing unbleached recycled kraft paper, the heavy bag can be reused and unbleached recycled kraft paper having the color and texture of unbleached kraft paper can be produced.

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Test Example 1]
(1) A pulp slurry containing 100% by mass of heavy-bag used paper pulp produced in the above-mentioned heavy-bag used paper pulp manufacturing process was produced in the above-mentioned raw material pulp manufacturing process.
(2) The following chemicals were added to 100% by weight of the raw material pulp slurry.
Aluminum sulfate band: Solid content 5 kg / pulp t
Rosin-based sizing agent: solid content 4 kg / pulp t
(Harima Chemicals Harsize NES500P)
Dry paper strength agent: Solid content 3 kg / pulp t
(Polyacrylamide (T-DS688 manufactured by Seiko PMC))
(3) Next, the pulp slurry was made by using a Nagami paper machine in the paper making process.
(4) Next, after drying in the drying step, unbleached recycled kraft paper was obtained.

[Test Example 2 to Test Example 3 and Reference Example 1 to Reference Example 3]
Unbleached kraft paper and recycled kraft of Test Example 2 to Test Example 3 and Reference Example 1 to Reference Example 3 in the same manner as in Example 1 except that the types and contents of the raw materials are as shown in Table 1. I got the paper.
For corrugated waste paper pulp, only corrugated waste paper is used as the raw material waste paper, and raw materials that do not contain waste paper such as miscellaneous paper waste paper and magazine waste paper, which leads to an increase in foreign matter and ash content, are used, and a screen with a 0.25 mm width slit is used in two stages. A pulp slurry was used in which foreign substances in the recycled paper pulp were removed.
For magazine used paper pulp, a deinking agent was added to the used paper raw material, dissociated with a pulper, ink residue was removed with a floatator, and then bleached pulp slurry was used.

[evaluation]
(Whiteness)
Measured according to JIS-P8148 (2001).

(Ash in paper)
It was measured based on the 525 ° C. combustion method.

(Appearance evaluation)
The appearance was visually evaluated, and the color tone and texture of unbleached kraft paper were evaluated according to the following three criteria. If the evaluation is A or B, it is good.
A: Has the color and texture of unbleached kraft paper.
B: It has a relatively good color tone and texture of unbleached kraft paper.
C: No color and texture of unbleached kraft paper can be seen.

Table 1 shows the evaluation results of the whiteness (%) and ash content (%) of the unbleached kraft paper of Reference Example 1, Test Example 1 to Test Example 3, and the unbleached recycled kraft paper of Reference Example 2 to Reference Example 3. In addition, "-" in Table 1 indicates that the corresponding component is not included.

As shown in Table 1 above, the unbleached recycled kraft papers of Test Examples 1 to 3 in which the raw material pulp contains heavy bag waste paper pulp have a whiteness of less than 30% and an ash content in the paper in the 525 ° C. combustion method. It is 1.0% or more and 12.5% or less, and it can be seen from the visual evaluation of the appearance that it has the color tone and texture of unbleached kraft paper. In Test Example 2 containing 90% by mass of recycled corrugated paper pulp in the raw material pulp, a slightly large amount of impurities was contained and the ash content was 12.0%, so the appearance evaluation was B.
On the other hand, in Reference Examples 2 to 3 in which the raw material pulp is recycled kraft paper that does not contain heavy bag waste paper pulp, the whiteness is less than 30% and the ash content in the paper in the 525 ° C. combustion method is 1.0% or more and 12.5. The unbleached kraft paper was inferior in color and texture in the visual evaluation of appearance because it did not have any of% or less. In Reference Example 2, since 100% by mass of used corrugated paper pulp was contained in the raw material pulp, there were many impurities and the ash content was 13.5%, so that the color was light. Further, in Reference Example 3 containing 40% by mass of used magazine pulp in the raw material pulp, the color tone was light brown like semi-bleached kraft paper, although there were few impurities.
Generally, the whiteness of semi-bleached kraft paper is about 35%, and the whiteness of unbleached kraft paper as in Reference Example 1 is about 22%. Therefore, it was manufactured by the method for producing unbleached recycled kraft paper. From the result of whiteness, it can be seen that the color tone of the unbleached recycled kraft paper is similar to that of the unbleached kraft paper.

As a result of the above, it was shown that the unbleached recycled kraft paper produced by the method for producing the unbleached recycled kraft paper has the color tone and texture of the unbleached kraft paper.

The method for producing unbleached recycled kraft paper of the present invention is suitable for producing unbleached recycled kraft paper used for packaging bags and the like having the color and texture of unbleached kraft paper.

1 Pulp raw materials 6, 9 Conveyor 10 1st crushing device 11 Crushed material by 1st crushing process 20 2nd crushing device 30 Input feeder 31 Heavy material 32 Undersized product 33 Oversized product 40 Identification device 50 Sorting device 51 From kraft paper Recycled paper 52 resin film

Claims (4)

A method of producing unbleached recycled kraft paper
The waste paper pulp manufacturing process that manufactures used paper pulp,
It is provided with a raw material pulp manufacturing process for producing a raw material pulp containing the used paper pulp and unbleached kraft pulp or a raw material pulp containing the used paper pulp.
The above recycled paper pulp contains heavy bag recycled paper pulp,
The heavy bag used paper pulp is made from a heavy bag having an inner bag made of a resin film and an outer bag containing the inner bag and containing unbleached kraft pulp as a main component.
The waste paper pulp manufacturing process has a heavy bag waste paper pulp manufacturing process for producing the heavy bag waste paper pulp.
The above-mentioned heavy bag waste paper pulp manufacturing process
The first crushing step of crushing the heavy bag and
A method for producing unbleached recycled kraft paper, which comprises a second crushing step of crushing a crushed product containing a paper component as a main component among the crushed products crushed in the first crushing step. The method for producing unbleached recycled kraft paper according to claim 1, further comprising an identification step of identifying a crushed product containing the paper component as a main component using a hyperspectral camera after the second crushing step. The method for producing unbleached recycled kraft paper according to claim 2, further comprising a sorting step of sorting the crushed material crushed in the second crushing step according to size before the identification step. The above-mentioned waste paper pulp further contains corrugated waste paper pulp,
The used paper pulp manufacturing process further includes a corrugated cardboard used paper pulp manufacturing process for producing the corrugated cardboard used paper pulp.
The whiteness of the unbleached recycled kraft paper measured in accordance with JIS-P8148 (2001) is less than 30%, and the ash content in the paper in the 525 ° C. combustion method is 1.0% or more and 12.5% or less. The method for producing unbleached recycled kraft paper according to claim 1, claim 2 or claim 3.

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