JP2008144346A - Coated paper for printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide coated paper for printing which has high opacity and improved strike through by using a recycled pigment recovered from papermaking sludge or the like. <P>SOLUTION: The coated paper for printing is provided with a coating layer consisting essentially of a pigment and an adhesive on at least one surface of base paper. The recycled pigment produced by carrying out a carbonizing treatment 52 of papermaking sludge which is a mixture of an organic material with white inorganic particles and then conducting a whitening treatment 53 of the carbonized material obtained by the carbonizing treatment is used as the pigment. The recycled pigment is preferably subjected to a pulverizing treatment so as to have a median diameter of 0.1-5 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a coated paper for printing containing a recycled pigment made from waste as a coating layer, and more specifically, a pigment having high whiteness regenerated from a mixture containing organic matter such as paper sludge and white inorganic particles. The present invention relates to a coated paper for printing having high opacity and excellent print back-through.

White inorganic particles are used in pesticide spreaders, extenders, printing ink modifiers, rubber reinforcements, plastics (molded articles, films, fibers, etc.) fillers, modifiers, and in the paper industry. It is used as an additive filler or coating pigment. Here, a usage form in the paper industry where the amount of kaolins, calcium carbonate, etc. used as white inorganic particles is the largest will be described as a representative example.

In general, in order to improve optical properties such as whiteness and opacity of paper, smoothness, etc., paper is made by adding white inorganic particles as a filler for internal addition to a paper stock mainly composed of pulp. . In addition, for the purpose of improving printability, a pigment coating layer mainly composed of white inorganic particles and an adhesive is provided on paper (base paper).

Examples of white inorganic particles for papermaking used for such internal addition or coating include kaolin, calcined kaolin, calcium carbonate, zinc oxide, aluminum hydroxide, zinc sulfide, titanium dioxide, calcium sulfate, calcium sulfite, and sulfuric acid. Mainly composed of inorganic pigments (fillers) such as barium, satin white, talc, and silica, one or more organic pigments called plastic pigments are appropriately mixed and used as necessary.

On the other hand, when pulp is recycled from waste paper, waste paper is processed by combining steps such as disaggregation, beating, soaking, washing, flotation treatment, and bleaching according to the desired pulp quality and used paper raw material quality. In each process, it is diluted or dewatered to an optimum concentration, but the squeezed water dehydrated in each process is called white water, and it contains fine fibers derived from waste paper, printing ink adhering to them, and the above white color. Inorganic particles are included.

Also in the papermaking process, fine fibers such as pulp in the stock, organic substances mainly composed of adhesives such as starch and synthetic adhesive, and some inorganic substances mainly composed of the above-mentioned white inorganic particles are used as papermaking wires. Passing through and flowing into the white water. However, when white water containing a mixture of these organic substances and white inorganic particles is reused as it is as dilution water for pulp, the volume and paper strength of the produced paper may be inferior. Therefore, white water is separated into solid and clarified water by a solid content separation device using precipitation or flotation, etc., and clarified water is used as dilution water for pulp, and the solid content is dehydrated with a centrifuge or dehydrator. After being disposed of. Furthermore, when white water generated in the process of regenerating pulp from waste paper or the paper making process is discharged as waste water, biological treatment such as activated sludge treatment is generally performed. Such surplus sludge generated by the final biological treatment of solids and wastewater separated and recovered by the wastewater treatment of white water and factory wastewater is generally referred to as papermaking sludge (hereinafter simply referred to as sludge).

In recent years, as the waste paper utilization rate increases, sludge derived from the waste paper deinking process has increased. Among them, used newspapers and high-quality used papers have a relatively small amount of sludge generated because there are few inorganic substances (inorganic fillers) contained in the used papers, and thus the utilization rate of such used papers is high. On the other hand, leaflets and magazine waste papers with pigments have a lot of inorganic substances contained in waste paper, resulting in a large amount of sludge generation. This is because the utilization rate of magazine waste paper is lower than newspaper waste paper and high-quality waste paper. It is a cause. In the future, in order to further promote the use of waste paper, it will be necessary to improve the utilization rate of magazine waste paper. However, if the utilization rate increases, a new problem arises that the amount of sludge generated increases.

Therefore, sludge separated and recovered from wastewater has been conventionally disposed of in landfills after dehydration in order to cope with the large amount of sludge generated, but recently incinerators such as fluidized bed furnaces and stoker furnaces. Thus, the organic matter in the sludge is burned to recover the energy, and at the same time, the volume of the sludge is reduced.

Combustion of sludge in an incinerator can effectively extract and collect organic materials such as fibers that have not been used in the past as energy, but since sludge contains a lot of inorganic materials, a large amount after incineration. There is a problem that a residue (ash) remains. Currently, some of the incineration ash is mixed with cement and used as soil conditioners, but most of it is landfilled as industrial waste. For this reason, if not only the organic matter recovered as energy by incineration but also the inorganic matter remaining as incineration ash can be reused as white inorganic particles for papermaking (internal filler, coating pigment), it will be required for landfill disposal This not only reduces the environmental burden, but also leads to an increase in the utilization rate of used magazine paper, which currently has a low utilization rate.

However, incineration ash has a low whiteness depending on the state of combustion, or the sintering of inorganic substances (incineration ash) progresses and the particle size is uneven, and the particles become large and can be used as fillers and pigments for papermaking. There is also a difficulty that can not be. Under these circumstances, Patent Document 1 and Patent Document 2 propose to improve the whiteness by further supplying ash left after burning organic matter in the presence of oxygen to sludge. ing.
Japanese Patent Laid-Open No. 10-029818 Japanese Patent Laid-Open No. 10-505055

Reduction of industrial waste is urgent due to the need for environmental conservation, and waste recycling is also required from the viewpoint of effective use of resources. Accordingly, the present inventors collect incineration residue (incineration ash) obtained by burning sludge, which is a mixture of organic matter and inorganic matter discharged from the paper manufacturing process, at a high temperature from the incinerator, and use it as a pigment for printing coated paper Tried to reuse.

However, the method described in the above publication recovers the incineration residue (ash) burned by the first stage heat treatment and improves the whiteness in the second stage firing furnace, and the first stage burns. Since the whiteness of the ash obtained is uneven due to the treatment method, it has been found that it is difficult to perform uniform firing in the second stage firing. As a result, it has been found that there is a drawback that the whiteness of the coated paper is lowered.

Furthermore, it was found that the incinerated ash obtained was changed into a form different from the filler and pigment contained in normal paper both chemically and physically. As a result, it has been found that the roll surface and the cutter blade are severely worn during the production and processing of the coated paper and have a problem to be solved in producing the coated paper.

An object of the present invention is to collect inorganic substances, which have been disposed of in the past because of adverse effects during the production of coated paper, from sludge as regenerated pigments that can reduce the adverse effects on the production of coated paper, and to apply coated paper for printing. The purpose is to propose a method for effectively using the pigment as a working pigment. More specifically, the object of the present invention is to provide a coated paper for printing having high opacity and excellent print back-through by treating the surface of the base paper with a coating solution containing such a regenerated pigment.

The printing coated paper of the present invention is a printing coated paper in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one side of a base paper. As the pigment, a mixture of an organic substance and white inorganic particles is used. It is characterized by containing a regenerated pigment produced by carbonizing and then whitening the carbide obtained by carbonization.

Such a regenerated pigment carbonizes a mixture of organic matter and white inorganic particles under a low oxygen condition in which the presence of an oxygen-containing gas is limited at a temperature of 1000 ° C. or lower, and then the carbonized product obtained by the carbonization treatment has a temperature of 450 ° C. A pigment produced by a whitening treatment step of decarbonizing in the presence of an oxygen-containing gas controlled to oxidize in a range of ˜1000 ° C. is preferable because the pigment has a balance between whiteness and opacity. Further, when the regenerated pigment is used after being pulverized so that the median diameter becomes 0.1 to 5 μm, the wear of the roll surface, the cutter blade, etc. in the manufacturing process and the processing process of the coated paper for printing is further improved. Therefore, it is preferable. Furthermore, when the absolute value of the difference between the whiteness of the base paper (in accordance with ISO 2470) and the whiteness of all the pigments constituting the coating layer containing the regenerated pigment is within 10 points, the printing coating without unevenness in whiteness is assumed. It is preferable because a working paper is obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, the reproduction | regeneration method from the sludge of the pigment suitable for using for the coated paper for printing of this invention is demonstrated.
(material)
This will be described using the flow shown in FIG. In the present invention, papermaking sludge 51 is used as a raw material for the regenerated pigment. Papermaking sludge is a mixture of organic matter and white inorganic particles contained in squeezed water called dehydrated white water in the used paper pulp manufacturing process and papermaking process. More specifically, contaminants removed in the waste paper processing process, those generated during the deinking process and cleaning process, those generated during the cleaning process in the pulping process, and organic substances that flowed into the white water through the wire during papermaking And a mixture containing white inorganic particles can be used. In this embodiment, the sludge is recovered from the white water in the disaggregation process, which is a pre-stage of the deinking process in the used paper recycling process, thereby reducing the load of the deinking process, the bleaching process, and the cleaning process in the used paper recycling process. In addition to reducing the treatment cost, the load of wastewater treatment can be reduced, which is preferable.

In particular, in the used paper recycling process, a large amount of white inorganic particles derived from the used paper raw material flows out into the white water. The white water can be efficiently recovered by aggregating the white water. For example, it can be obtained from a normal waste paper pulp manufacturing process, and if it is a disaggregation treatment, water can be used from either a conventionally known low-concentration pulper or high-concentration pulper. Also for the deinking treatment of waste paper, any conventionally known method can be used, and water extraction from a washing machine in each step can also be used. Further, in the case of white water obtained from used paper raw materials with low whiteness, it is preferable to remove ink particles from white water by white water flotation treatment.

In the present invention, sludge generated from sewage, factory waste water, or the like can also be used as a raw material for the regenerated pigment. Since sewage and factory wastewater contain solids, they are discharged after being settled and separated by a clarifier or a coagulation sedimentation tank. At this time, the solid content contained in the wastewater as waste is recovered as sludge.

Apart from sludge, RPF (Refused Paper & Plastic Fuel) mainly composed of low-grade waste paper that is difficult to reuse as papermaking material and its accompanying plastic can also be used as a raw material. In the present invention relating to use for coated paper for printing, sludge derived from a papermaking material is a preferred raw material, so an example using a papermaking sludge derived from a papermaking material will be described below. In this embodiment, by treating the sludge with heat, a regenerated pigment suitable for producing coated paper can be separated and recovered from the organic matter.

In addition, it is preferable that iron content (Fe) in sludge is 5.0 weight% or less by solid content ratio, Preferably it is 3.0 mass% or less. The sludge containing a large amount of iron has a problem that the whiteness does not become sufficiently high. As a method for reducing the amount of iron, for example, it is preferable to use a coagulant that does not contain iron in the coagulant used for solids separation in the paper mill wastewater treatment step. Furthermore, it is possible to install a magnet or the like in the classifier to remove iron pieces such as wires and nails mixed in the sludge, or to devise not to mix them. In addition to this, it is preferable to remove foreign substances and coarse sintered ingots as necessary. These foreign matter removal treatments are preferably installed so that they can be efficiently removed according to the form of sludge and removal object between the treatment steps such as carbonization, whitening by decarbonization, and pulverization. More preferably, it is removed in the process.

It is also possible to granulate the sludge before heat treatment. By this granulation treatment, fine particles are integrated, scattering of fine particles can be prevented, and the yield after heat treatment can be improved. Further, the variation in size is reduced, the heat treatment efficiency is increased, the organic matter is efficiently thermally decomposed, and the equipment can be downsized. Although the water-containing sludge can be granulated by a rolling granulation method, a stirring granulation method, or the like, a method of compression-molding the dried sludge is preferable because heat energy can be saved by heat treatment.

As a dry granulation method, it is preferable to use a compression molding machine such as a briquette machine or a roller compactor. These compression molding machines can perform compression molding by forcibly pushing sludge between two pressurized rolls with a screw and rotating the rolls.

(Carbonization process)
In the present invention, when the regenerated pigment is produced from sludge, the sludge undergoes carbonization treatment step 52, whereby dry distillation gas is generated by thermal decomposition, and is bulky and has a high specific surface area, which is suitable as a pigment for coating. It has been found that the pigment can be recovered. More specifically, the specific surface area by the BET method of the carbide obtained after carbonizing the sludge is 15 m ² / g or more, preferably 20 m ² / g or more, and then the ratio by the BET method after whitening treatment and slurrying / pulverization By treating the surface area to be 15 to 30 m ² / g, a regenerated pigment having a preferable opacity for the coated paper for printing can be produced. When the BET specific surface area of the regenerated pigment is less than 15 m ² / g, the pigment is inferior in opacity, whereas when it exceeds 30 m ² / g, the printing surface strength is maintained. For this reason, the amount of adhesive used increases, which is not economically preferable.

As a result, the coated paper obtained by the present invention is a highly opaque printing paper having a bulky coating layer and a high scattering surface area. By passing through the carbonization process described below, the specific surface area of the carbide can be 15 m ² / g or more, preferably 20 m ² / g or more.

In the carbonization process, sludge is dried and carbonized by thermal decomposition. By collecting the white inorganic particles contained in the sludge through the carbonization treatment step and the whitening treatment step, the whiteness is high and thermal transformation of the inorganic particles can be reduced as compared with the incineration treatment of the prior art. As a result, it is possible to recover a regenerated pigment that is preferable for paper production in which wear of the roll surface and cutter blade during production of coated paper and processing is suppressed.

Since the solid content concentration in the sludge varies depending on the capacity of the dehydrator, it is usually 5 to 60% by weight. Therefore, it is preferable to dry the hydrous sludge in the first half of the carbonization process. Pyrolysis can be efficiently performed by drying the sludge. Although it is possible to carry out carbonization without separating sludge drying and pyrolysis, it is more preferable to provide separate temperature zones. That is, in the carbonization treatment of sludge, the drying and pyrolysis temperatures of the organic matter are different, so that the sludge can be efficiently carbonized by providing two or more heating zones.

In the first half of the carbonization step, the moisture in the sludge is evaporated when the atmospheric temperature of the apparatus is 400 ° C. or lower, and the thermal decomposition in the second half is performed in the range of 400 ° C. to 1000 ° C., preferably 450 ° C. to 700 ° C. The specific surface area can be 15 m ² / g or more, preferably 20 m ² / g or more, and it is preferable because a regenerated pigment suitable for producing coated paper is easily obtained.

Incidentally, if the furnace temperature is less than 400 ° C. in the latter half of the thermal decomposition after evaporation of water, the carbonization time becomes longer, and at a high temperature exceeding 1000 ° C., the melting and sintering of the white inorganic particles proceeds, and fine pulverization after incineration It becomes difficult not only to make it difficult, but also to collect a bulky regenerated pigment. The carbonization time should be considered from the form, amount, moisture, organic matter amount, economic effect, and environment of the sludge, but is generally preferably about 30 minutes to 2 hours.

In the carbonization step, when oxygen is present, organic substances are combusted along with combustion of volatile components contained in the sludge. As a result, the combustion temperature of the waste rises to a temperature higher than the atmospheric temperature in the furnace due to the combustion of the organic matter, and the undesired thermal denaturation of the pigment contained in the sludge occurs, making it difficult to recover the bulky regenerated pigment. turn into. Therefore, in the carbonization treatment step, it is preferable to prevent an increase in temperature above the furnace atmosphere temperature due to sludge ignition by limiting the inflow of the oxygen-containing gas (air). When introducing the sludge, it is preferable that the introduction port has a minimum size so that oxygen is not accompanied by the sludge as much as possible. Although oxygen-containing gas (air) accompanying the sludge may be present in the furnace, it is preferably replaced quickly with water vapor or volatile components (carbon monoxide, hydrogen gas) generated from the sludge. It is more preferable that the oxygen concentration in the furnace is 1 vol% or less, and that the oxygen is in a poor oxygen state in which oxygen does not substantially exist in the furnace.

As a method for heating the sludge, electric heating is possible, but heating with a combustion gas of kerosene or heavy oil is economically preferable. Sludge can be heated directly with combustion gas, but oxygen (air) contained in the hot air comes into contact with the sludge, and the sludge ignites and burns, so the sludge and hot air are in direct contact. It is preferable to provide a partition so that there is no. Therefore, it is preferable to use a sealed chamber in which the inflow of air is restricted as equipment for carbonizing sludge. That is, it is more preferable that the carbonization apparatus is a double-structured indirect heating furnace composed of a closed-type sludge carbonization chamber and a heating chamber for heating the carbonization chamber.

As a heating method in carbonization, sludge can be heated and dried by blowing combustion gas into the heating chamber. As the combustion gas, the combustion gas discharged from the existing incineration facilities can be used. Examples of the incineration facility include a grate method (stoker furnace), a spray floating method, a material agitation method, a hot air combustion method, and the like. Of course, it is possible to directly heat the sludge heating chamber by providing a burner in the indirect heating chamber, and it is also possible to generate combustion gas by installing a burner outside the indirect heating furnace. .

After drying the sludge, the organic matter in the sludge is thermally decomposed by heating the dried sludge. At this time, a flammable gas such as carbon monoxide, methane, or ethane is generated, whereby a bulky regenerated pigment can be recovered. Moreover, since oxygen is not substantially contained in the furnace, combustion of organic substances can be suppressed. A combustible gas can be sucked into a hot air generator and used as a heat source for drying and carbonizing sludge.

(Whitening process)
Next, whitening is performed by decarbonization of the carbide in a whitening treatment step 53. In the whitening treatment step by decarbonization, carbon derived from an organic substance contained in the carbide is oxidized and decarbonized to be whitened, and the regenerated pigment is recovered. This process is also called a baking process.

Finally, the carbide is decarbonized, and the whiteness of the regenerated pigment (in accordance with ISO 2470) is 60% to 90%, preferably 70 to 85%, thereby producing a regenerated pigment suitable for coated paper for printing. be able to. Depending on the type of white inorganic particles contained in the sludge, the whiteness can be reduced to 90% if the white inorganic particles are subjected to whitening treatment at a low temperature (700 ° C. or lower) for a long time so that the white inorganic particles do not undergo thermal denaturation. Although it is possible to increase it, it is preferable to keep it to 85% in consideration of the scale of the apparatus, fuel cost, and the like. In the present invention, when baking is performed so that the absolute value of the difference between the whiteness of the base paper to be used (based on ISO 2470) and the whiteness of all pigments constituting the coating layer containing the regenerated pigment is within 10 points, This is preferable because a coated paper for printing with little unevenness in whiteness can be obtained.

On the other hand, the higher the whiteness of the pigment particles constituting the coating layer, the lower the opacity of the coated paper, and the lower the whiteness, the higher the opacity of the coated paper. This is because it is influenced by the absorption coefficient of the pigment. In the method combining the carbonization treatment step and the whitening treatment step, in addition to obtaining a pigment having a large specific surface area by carbonization, the whiteness degree suitable for the pigment for coating is controlled by controlling the decarbonization rate in the whitening treatment step. There is an advantage that a regenerated pigment having opacity can be produced. That is, the regenerated pigment with high opacity, which is removed so that the black carbide having a high absorption coefficient partially remains, can be recovered in the whitening treatment step. At this time, the whiteness level is preferably 78 to 83%.

By adjusting the atmospheric temperature and the treatment time of the whitening treatment furnace, it is possible to adjust the residual carbon ratio derived from any organic matter. If the whitening treatment temperature is 600 ° C. or lower, the burning rate of carbon and oxygen becomes low, so that the whiteness is lowered but the residual carbon ratio can be increased. Conversely, by setting the treatment temperature to 650 ° C. or higher, preferably 700 ° C. or higher, it is possible to obtain a high whiteness regenerated pigment with a very low residual carbon ratio. Thus, by controlling the temperature of the whitening treatment, the regenerated pigment obtained in the present invention can arbitrarily control the whiteness and the residual carbon ratio in accordance with the quality of the paper.

In the preceding carbonization step, the combustible gas having a large calorific value has already volatilized. Therefore, in the whitening treatment step, combustion above the furnace temperature due to combustion of volatile matter can be suppressed. As a result, undesired thermal denaturation of the white inorganic particles contained in the sludge due to the combustion of organic matter can be prevented. For this reason, in the whitening process after a carbonization process, it becomes possible to fully supply oxygen (air) required in order for a carbide to oxidize. This state is called an oxygen-rich state. Eventually, by combining the preceding carbonization step and the whitening treatment step, the white inorganic particles contained in the sludge can be recovered as a regenerated pigment under suitable conditions.

In the whitening treatment step of decarbonizing from the carbide, the whiteness of the regenerated pigment can be efficiently improved by heating so that the temperature of the whitening chamber is in the range of 450 ° C to 1000 ° C. Incidentally, when the whitening treatment temperature is less than 450 ° C., the treatment time becomes long, and when the temperature exceeds 1000 ° C., the inorganic particles are melted and sintered, and it is difficult to finely pulverize the obtained regenerated pigment. In addition, a colored substance is generated, which is not preferable. The treatment time should be considered not only from the form, amount, moisture, and carbon content of the carbide, but also from the economic effect and the environment, but is preferably about 30 minutes to 2 hours.

In the whitening treatment step, rapid heating of the carbide is not preferable because melting and sintering of the inorganic particles proceeds and carbon molecules are taken into the white inorganic particles, making whitening difficult. Although it is possible to keep the inside of the furnace in a single temperature zone, it is more preferable to perform a whitening treatment in two or more temperature zones in order to prevent rapid heating of the carbide. In the whitening treatment, it is more preferable to go through two or more heating zones such as 450 ° C. to 600 ° C. and 600 ° C. to 1000 ° C., for example. It is preferable to perform decarbonization in the former stage so that the temperature of the object to be processed does not rise above the atmospheric temperature in the latter stage in the heat treatment of two or more stages. At this time, it is more preferable to manage the temperature of the workpiece itself. However, since it is difficult to measure the local temperature change of the workpiece, a temperature sensor is installed in the whitening chamber, and oxygen-containing gas (air) is supplied so that the ambient temperature of the whitening chamber is 800 ° C or lower. However, it is preferable to manage the temperature so that the temperature of the carbide itself does not rapidly increase due to the self-combustion of the carbide.

When the whitening treatment is performed in a temperature range where calcium carbonate is not decomposed, sludge-derived calcium carbonate is mixed in the regenerated pigment after decarbonization. Therefore, the residual carbon ratio in the regenerated pigment may be a high value even after the whitening treatment. The residual carbon ratio derived from organic matter was calculated by calculating the residual ratio of calcium carbonate from the calcium carbonate content estimated from the amount of calcium contained in the raw material sludge and the calcium carbonate decomposition rate estimated by X-ray diffraction after whitening treatment, and then elemental analysis Can be estimated by subtracting the carbon content derived from residual calcium carbonate from the total carbon content obtained by the above. It is preferable to make the residual carbon ratio derived from the organic matter as low as possible, and by setting it to 1% by weight or less, a regenerated pigment suitable for a coating pigment can be recovered. In addition, in order to make the residual carbon ratio derived from an organic substance 1% by weight or less, for example, it can be achieved by performing a whitening treatment at a processing temperature of 450 ° C. or higher, preferably 600 ° C. or higher until whiteness becomes 70% or higher.

Through the carbonization and whitening treatment, the calcium carbonate contained in the raw material sludge is thermally decomposed into calcium oxide. The decomposition rate of calcium carbonate can be estimated by measuring the peak intensity ratio between the two and the calorific value of the decontamination reaction after whitening using an X-ray diffraction analyzer. In the case of sludge having a high content of calcium carbonate, if the decomposition of calcium carbonate proceeds beyond 50%, the viscosity increases when the regenerated pigment is slurried, making transfer and coating operations difficult. Although it is possible to neutralize the slurry containing calcium hydroxide by adding carbon dioxide or sulfuric acid, the viscosity can be lowered. However, the less decomposition of calcium carbonate saves the neutralization reaction tank, acid, time, etc. Connection is preferable. For this reason, the decomposition rate of calcium carbonate is preferably 50% or less, and more preferably 30% or less. Specifically, the decomposition rate of calcium carbonate can be reduced to 50% or less, more preferably 30% or less by setting the baking conditions not exceeding 800 ° C. in the whitening apparatus.

As a heating method of the carbide, it is also possible to directly heat the carbide with the combustion gas, but the unburned carbon contained in the hot air comes into contact with the whitened white inorganic particles, and the whiteness is lowered. It is more preferable to provide a partition so that hot air does not come into direct contact. That is, in the whitening treatment step by decarbonization, it is more preferable to use a double-structured indirect heating furnace including a whitening chamber and a heating chamber by decarbonization of a sealed carbide as in the carbonization step.

Although heating of the heating chamber is possible, heating with a combustion gas of kerosene or heavy oil is economically preferable. Hot air obtained by collecting and burning the volatile gas derived from the sludge can also be used. In addition, it is possible to use combustion gas discharged from existing incinerators such as incinerators. Examples of the incineration facility include a grate method (stoker furnace), a spray floating method, a material agitation method, a hot air combustion method, and the like.

In addition to this, rotary kilns installed as part of wastewater treatment equipment at each paper mill and existing incinerators (cyclone furnaces and fluidized bed incinerators) can be used. It is preferable to use a rotary kiln capable of

In addition, between the carbonization treatment and the whitening treatment, after the temperature of the object to be treated is once cooled to 400 ° C. or less, the subsequent treatment is performed to completely remove the combustible gas derived from the organic matter thermally decomposed by the carbonization treatment. Can be removed. Furthermore, during this time, the carbide is brought into contact with water and / or water vapor and cooled, thereby increasing the specific surface area of the carbide and recovering a regenerated pigment that is bulky and has a high specific surface area. Moreover, by doing so, the reaction efficiency with oxygen in the whitening treatment step is improved, and whitening by decarbonization can be performed efficiently.

In the case where the carbonization treatment and the whitening treatment are performed continuously, a screw and a stirring blade are installed in each heat treatment chamber, and sludge and carbide can be forcibly transferred. By adjusting the shape and size of the screw and the stirring blade, stirring is promoted and the heat treatment efficiency can be improved. Conversely, sludge and carbide can be transferred by rotating the polygonal carbonization chamber.

An example of a heat treatment apparatus that can be used when producing the regenerated pigment used in the present invention will be described in detail with reference to FIG. FIG. 2 is a schematic system diagram of an example of a heat treatment apparatus for performing a carbonization step and a whitening treatment step by decarbonization. The carbonization step is performed by the first indirect heating furnace 1 and the second indirect heating furnace 6. The whitening process by decarbonization is performed in the third indirect heating furnace 10. The first indirect heating furnace 1 is a drying zone of the carbonization process, and the sludge is input from the sludge input port 2 of the first indirect heating furnace and dried in the sludge drying chamber 3. A hot air inlet 4a for heating the sludge drying chamber and a hot air, water vapor, and dry distillation gas outlet 5a are provided. Although not shown, a minute opening is provided in the latter half of the sludge drying chamber 3 in the vicinity of the discharge port 5a in order to discharge water vapor generated from the sludge to the discharge port.

The 2nd indirect heating furnace 6 is a thermal decomposition zone of a carbonization process. The sludge pyrolysis of the second indirect heating furnace, one of the carbonization chamber 7 is provided with a hot air intake 4b for heating the heating chamber for carbonizing the dried sludge, and the other is provided with hot air, water vapor, and dry distillation gas discharge port 5b. . Although not shown, in the vicinity of the discharge port 5b, a minute opening is provided in the latter half portion of the sludge pyrolysis and carbonization chamber 7 in order to discharge dry distillation gas and the like generated from the sludge to the discharge port. . When the carbonization is completed, the carbide is discharged from the carbide discharge port 8.

The carbide discharged from the carbide discharge port 8 is transferred to the third indirect heating furnace 10 via the carbonized carbon distribution route 9, and is whitened by decarbonization. Carbide is introduced from the carbide inlet 11 of the third heating furnace, the air intake 12 for oxidizing the carbide, the whitening chamber 13 by decarbonization of the carbide, and the hot air intake 4c for heating the whitening chamber by decarbonization. Further, a hot air and water vapor outlet 5c is provided. The regenerated pigment that has been whitened by decarbonization is discharged from the regenerated pigment recovery port 14.

In FIG. 2, the carbonization step will be described. The carbonization apparatus is provided with a two-stage indirect heating zone. This is because the drying and thermal decomposition temperatures of sludge in the carbonization process are different. Sludge is dried in the first indirect heating furnace 1. Moisture in the sludge can be evaporated when the atmospheric temperature of the sludge drying chamber 3 is 400 ° C. or lower.

By blowing air from the hot air intake 4a, the sludge can be indirectly heated and dried. Water vapor and hot air generated from the sludge are discharged from the discharge port 5a. The hot air intakes 4a, 4b, 4c and the discharge ports 5a, 5b, 5c are respectively connected to a hot air generator not shown, and the hot air supplied from the hot air generator has a temperature, supply amount, and discharge amount. Can be adjusted. In addition, it is possible to use combustion gas discharged from existing incinerators such as incinerators.

After the sludge is dried, the dried sludge is pyrolyzed and carbonized by the second indirect heating furnace 6. In the dry sludge carbonization chamber 7, organic matter in the dry sludge is thermally decomposed. At this time, combustible gases such as carbon monoxide, methane, and ethane are generated. However, since oxygen is not substantially contained in the furnace, combustion of organic substances can be suppressed. The combustible gas sucked from the fine opening provided in the latter half of the carbonization chamber is discharged together with hot air from the hot air, water vapor, and dry distillation gas outlet 5b. These gases are also burned by a hot air generator not shown, and can be used as a heat source for drying and carbonizing sludge.

By promoting the temperature of the carbonization chamber 7 to 400 ° C. to 1000 ° C., preferably 450 ° C. to 700 ° C., the thermal decomposition of the organic matter is promoted at a temperature that does not cause undesired thermal denaturation of the white inorganic particles in the sludge. Can do. These temperatures can be adjusted by the temperature, supply amount and discharge amount of hot air generated by the hot air generator.

In the case of continuously whitening by carbonization and decarbonization, sludge can be forcibly transferred by installing a screw or a stirring blade in the heat treatment chamber. The sludge inlet is the minimum necessary so that air does not accompany the carbonization chamber. By compulsorily pushing with a screw, the amount of entrained air can be limited. Moreover, since stirring of sludge is accelerated | stimulated with a screw, thermal efficiency can be improved.

The carbonization time can be adjusted by measuring the amount of combustible gas generated by thermal decomposition using a gas detector. At this time, the residence time of the sludge can be adjusted by adjusting the rotational speed of the screw. FIG. 2 shows an example in which the carbonization process is performed in two stages, but it is also possible to perform the process in one stage. By using a biaxial screw, the carbide can be carbonized while being crushed. As a result, it is preferable that carbon derived from organic matter is fixed carbonized, and carbon derived from calcium carbonate is retained as calcium carbonate and carbonized.

The whitening process by decarbonization will be described with reference to FIG. Carbide transferred through the carbonized physical distribution route 9 is input from an input port 11 provided in the third indirect heating furnace 10. At this time, air required for the oxidation of the carbide can be taken in from the air intake 12. A flow controller can be installed at the intake to control the oxidation of carbides. Heating of the whitening chamber 13 by decarbonization can be performed by combustion gas discharged from existing incineration equipment such as an incinerator. In addition, it is preferable to adjust the supply amount of oxygen-containing gas (air) or hot air (combustion gas) so that the carbide self-combusts in a preferable temperature range. In particular, when the sludge as a raw material is unknown or the fluctuation is large, it is preferable to observe the temperature change of the carbide in more detail by installing many more sensitive temperature sensors in the whitening device.

By heating so that the whitening chamber 13 by decarbonization is in a range of 450 ° C. to 1000 ° C., the whiteness can be improved efficiently. At this time, it is preferable to adjust the temperature of the hot air, the supply amount and the discharge amount, and the air flow rate so that the carbide is not rapidly heated. Thereby, it is preferable to provide two or more heating zones of 450 ° C. to 600 ° C. and 600 ° C. to 1000 ° C. The regenerated pigment that has been whitened by decarbonization is discharged from the regenerated pigment recovery port 14.

FIG. 3 is an example in which an internal rotary kiln is installed in place of the third indirect heating furnace used in the whitening treatment step by decarbonization in FIG. 2, and a reservoir 16 is installed in place of the carbonized carbon distribution route 9. This will be described in detail with reference to FIG. Since the carbonization step is the same as the example shown in FIG.

This is an example of whitening treatment by decarbonization in the internal combustion type rotary kiln 15. Carbide is once stored in the carbide storage device 16 and is introduced from the carbide inlet 17 of the internal combustion type rotary kiln. A whitening treatment chamber 18 by decarbonization, a burner 19, and a regenerated pigment recovery port 20 are provided.

The carbide obtained by the carbonization process is stored in the storage 16 without being directly sent to the whitening process by decarbonization. Here, it is preferable to cool the carbide once and volatilize the combustible gas completely. Further, water can be sprayed to increase the specific surface area of the carbide. By spraying water pressurized with a pump using a spray nozzle, it is possible to uniformly spray the water. If a two-fluid nozzle that injects water and pressurized air at the same time is used, the size of water particles can be adjusted to 100 μm or less, and a more uniform spraying process is possible.

Next, a process using a rotary kiln for the whitening treatment process by decarbonization will be described. The carbide introduced from the carbide outlet 17 of the internal combustion rotary kiln 15 is directly heated by a burner 19 installed in the vicinity of the regenerated pigment recovery port 20. By heating so that the temperature in the furnace is in the range of 450 ° C. to 1000 ° C., the whiteness can be improved efficiently. At this time, it is preferable to adjust the furnace temperature by adjusting the fuel supplied to the burner 19 so that the carbide is not heated rapidly. By adjusting the rotation speed and inclination angle of the rotary kiln 15, the whitening time by decarbonization can be easily adjusted. The treatment time can be adjusted according to the whiteness of the desired regenerated pigment. In addition, although illustration was abbreviate | omitted, it is preferable to process the combustion gas discharged | emitted from the internal combustion type rotary kiln 15 using an exhaust gas processing apparatus.

Although the carbide storage device 16 is used in FIG. 3, it is also possible to directly connect the indirect heating furnace in the carbonization treatment process and the rotary kiln in the whitening treatment process by decarbonization by the carbonized physical distribution route 9. In FIG. 2, it is also possible to use a carbide reservoir 16 instead of the carbonized physical distribution route 9.

In addition to the internal combustion rotary kiln used in FIG. 3, existing incinerators (cyclone furnaces and fluidized bed incinerators) installed as part of the wastewater treatment apparatus at each paper mill can be used. An indirectly heated rotary kiln can also be used, and the hot air can use combustion gas discharged from existing incinerators such as an incinerator. In particular, although not shown, it is preferable that the whitening apparatus by carbonization and decarbonization uses a heat insulating material to cover the periphery and keep the apparatus warm. In addition, the material of the apparatus can be selected from ceramics and alloys in consideration of processing temperature and economy.

(Slurry / Crushing process)
Next, the slurrying / pulverizing process 54 in FIG. 1 will be described. In the present invention, the regenerated pigment recovered from the papermaking sludge can be used as it is, but it is difficult to avoid mixing of coarse particles, and there is a risk of causing coating defects such as streaks. It is preferable to use after wet pulverization. In the present invention, although the optimum particle size varies depending on the target coated paper, it is preferable to perform a pulverization treatment so that the median size is in the range of 0.1 to 5 μm.

As a pulverization method, pulverization using only a dry pulverizer or pulverization using only a wet pulverizer is possible, but it is preferable to appropriately combine a dry pulverizer and a wet pulverizer. It is also possible to provide a plurality of stages of each crusher or only one of them. It is more preferable in terms of pulverization efficiency to make the particles smaller by dry pulverization before wet pulverization. At this time, if the particle size of the dry pulverized powder exceeds 35 μm, the dispersion of the powder in the disperser becomes poor, the pulverization efficiency in the pulverizer deteriorates, and the disperser and the pulverizer wear. The whiteness of the regenerated pigment decreases. Further, it is not economically preferable to pulverize the powder to less than 2 μm by dry pulverization because of poor pulverization efficiency.

In this way, a dry pulverizer and a wet pulverizer are combined, and the median diameter of the granules is pulverized to 2 μm to 35 μm, preferably 2 μm to 10 μm by dry pulverization to obtain an aqueous slurry having a predetermined solid content concentration, for example, 50% or more. By wet pulverization, fine particles can be efficiently pulverized while preventing a decrease in whiteness due to wear of the disperser or wet pulverizer. If the pulverization treatment is insufficient, the roll surface may be worn during the production or processing of the coated paper, or the blade of the cutter may be remarkably worn, causing serious problems.

Hereinafter, the dry pulverizer will be described in more detail. Examples of the pulverizer that pulverizes several millimeters to several tens of micrometers include a roll crusher, a roll mill, a stamp mill, an edge runner, a cutter mill, a rod mill, and the like. In addition, as a dry fine pulverizer that is several μm or less suitable for a coating pigment, a roller mill, a jet mill, a dry ball mill, an impact pulverizer, or the like is used. In these dry pulverizers, consideration is given to wear, such as using wear-resistant steel.

Next, examples of the wet pulverizer include pulverizers such as a sand mill, a wet ball mill, a vibration mill, a stirring tank mill, a flow tube mill, and a coball mill. In order to prevent contamination of the regenerated pigment due to abrasion of the pulverizer (whiteness reduction), it is desirable to coat the pulverization zone of the pulverizer with an abrasion-resistant material such as rubber or abrasion-resistant plastic. The pulverization zone refers to the inner surface of the pulverization chamber, the outer surface of the stirring member, and the like, and is a zone where the powder in the slurry comes into contact during pulverization. When members such as a partition plate are provided in the pulverization chamber, these are also part of the pulverization zone. In wet pulverizers that use grinding media such as balls and beads, it is desirable to use abrasion-resistant grinding media such as wear-resistant ceramic balls and zirconium beads.

Examples of wear-resistant plastics include urethane resins and nylon resins, and it is desirable to coat them with a thickness of about 1 mm to 10 mm, but they can be appropriately selected depending on the frequency of use and pulverization conditions. In addition, before and after the wet pulverization, the hardly pulverized sintered product can be removed through a screening device such as an open-type vibrating screen, a multi-tube vibrating pressure filter, or a mechanical pressure filter. In the above-described disperser, it is desirable to coat the dispersion zone with rubber, wear-resistant plastic or the like, similarly to the wet pulverizer.

In wet pulverization, a dispersant is added to form a slurry in order to uniformly disperse the powder. By adding a dispersant, an increase in viscosity can be prevented even when the concentration of the slurry is increased, and an increase in viscosity due to wet pulverization can be prevented, and the pulverization efficiency and handling properties can be improved. Since the sulfonic acid group-containing polyacrylate has an advantage of superior salt resistance and heat resistance compared to other dispersants, the sulfonic acid group-containing polyacrylate has a molecular weight of about 1000 to 10,000 containing a sulfonic acid group as a dispersant. The acid group-containing polyacrylate may be added in an amount of 0.05 to 3% by weight based on the pigment. Incidentally, even if the addition amount exceeds 3%, the effect of improving the dispersibility reaches its peak, and if it is 0.05% or less, the dispersibility is poor and the wet pulverization cannot be performed efficiently.

When the regenerated pigment is made into a suspension in an aqueous medium or pulverized, the pH of the suspension can be adjusted to 8 to 13 using carbon dioxide.

(Paint preparation process)
Next, the coating liquid preparation step 55 in FIG. 1 will be described. In the present invention, the ratio of the regenerated pigment to the pigment constituting the pigment coating layer is a single layer, a multilayer, or where the regenerated pigment is used in the multilayer coating layer, Furthermore, it can be appropriately adjusted according to the target quality of the target coated paper for printing, and is not particularly limited. However, in order to obtain a coated paper for printing with high opacity which is an object of the present invention, 10% by weight or more, preferably 20% by weight or more of the total pigment constituting the coating layer becomes a regenerated pigment. It is desirable to blend in. Further, the upper limit of the ratio of use of the regenerated pigment can be, for example, 100% by weight when blended in the undercoat coating layer, while the regenerated pigment is applied to the outermost layer of the single layer coating layer or the multilayer coating layer. When blended, it is preferable to blend so that about 50% by weight of the total pigment constituting the coating layer becomes a regenerated pigment in consideration of the opacity and whiteness of the coated paper. .

Examples of pigments that can be used in combination with regenerated pigments include kaolin, clay, calcium carbonate, aluminum hydroxide, zinc oxide, barium sulfate, calcium sulfate, silica, activated clay, talc, and satin used in the production of ordinary printing paper. Examples thereof include inorganic pigments such as white and lake, and organic pigments such as plastic pigments. At this time, by blending so that the absolute value of the difference between the whiteness of the base paper and the whiteness of all the pigments constituting the coating layer containing the regenerated pigment is within 10 points, the whiteness unevenness is high opacity. Coated paper can be obtained.

Newsprint paper is also included in the coated paper for printing in the present invention. The whiteness of newsprint is generally about 50%, but the opacity of newsprint reduced in weight is required to be 90% or more. Therefore, as a countermeasure against the opacity of such newspaper paper, a processing layer (coating layer) mainly composed of a regenerated pigment and an adhesive can be provided on the newspaper base paper. In newsprint paper, opacity is the most important paper quality, so the difference between the whiteness of the base paper and the whiteness of all the pigments constituting the coating layer may not fall within the range of ± 10 points.

In the coated paper for printing of the present invention, the adhesive used together with the pigment is not particularly limited. For example, proteins such as casein, soy protein, and synthetic protein: styrene / butadiene copolymer, etc. Conjugated diene polymer latex, acrylic polymer latex such as acrylic acid ester and / or methacrylic acid ester polymer / or copolymerization, vinyl polymer latex such as ethylene / vinyl acetate copolymer, or various kinds of these Alkali-soluble or alkali-insoluble polymer latex modified with a functional group-containing monomer such as carboxyl group: Synthetic resin adhesive such as polyvinyl alcohol, olefin / maleic anhydride resin, melamine resin: positive starch , Oxidized starch, enzyme modified starch, thermochemically modified starch, etherified starch, esterified starch , Starches such as cold water soluble starch: carboxymethyl cellulose, cellulose derivatives such as hydroxyethyl cellulose, adhesives for ordinary coated paper may be appropriately selected and used.

The blending ratio of the adhesive is 5 to 25 parts by weight, more preferably about 10 to 20 parts by weight with respect to 100 parts by weight of the pigment as compared with the solid form. In the pigment coating composition, a dispersant, a thickener, a water retention agent, a flow modifier, a defoaming agent, a release agent, a water-resistant lubricant, a bluing agent, an antiseptic, a lubricant, Various auxiliaries such as dyes and pH adjusting agents can be appropriately blended.

In the coated paper for printing of the present invention, particularly when the regenerated pigment is used in the coating layer that is the outermost layer, the fluorescent dye may be added in an amount of 0.3 to 3.0% by weight based on the regenerated pigment. preferable.

Such a fluorescent dye absorbs light in the vicinity of 340 to 380 nm and emits fluorescence in the visible part near 430 to 440 nm to increase the whiteness of the coated paper. Specifically, the following compound systems can be exemplified. These may be used alone or in combination of two or more. 4,4′-bis (4,6-disubstituted-1,3,5-triazinyl-2-amino) stilbene-disulfonic acid, α, β-bis (benzoxazolyl) ethylene, alkoxynaphthalic acid An organic compound having a structure such as an -N-substituted imide, benzoxazole, coumarin, or thiophene can be given.

In the present invention, as described above, it is also possible to form two or more pigment coating layers on one side of a base paper, and it is possible to impart functions such as smoothness, gloss and print ink acceptability to the coating layer. Therefore, it is preferable to form two or more (usually two) coating layers. It is also possible to form coating layers on both sides of the base paper. At this time, the regenerated pigment may be added to any layer. In the present invention, it is essential that the whiteness of the regenerated pigment to be used does not fall below 60%. However, if the whiteness is lower than this, this can be achieved by adding a fluorescent dye. This is because it is difficult to obtain the coated paper for printing. The fluorescent dye can be divided and added to each paint of the multilayer coating.

The solid content concentration of the paint for forming the pigment coating layer is generally about 40 to 75% by weight, but is preferably in the range of 45 to 70% by weight in consideration of operability.

Paints prepared under the above conditions are, for example, blade coaters, air knife coaters, roll coaters, reverse roll coaters, bar coater curtain coaters, dice rod coaters, gravure coaters, champlex coaters, gate roll coaters, size presses, etc. Coating is performed by an on-machine or an off-coater provided with a coating apparatus. When finishing a coated paper with high glossiness, it is preferable to employ a blade coater, a rod blade coater or the like.

The coating amount of the paint on the base paper can be appropriately adjusted in the range of about ² to 50 g / m ² per side in terms of dry weight. In addition, this coating amount is a total coating amount including multilayer coating. The pigment coating layer is dried and then finished through a finishing device such as a super calender or a gloss calender.

In the present invention, waste paper pulp can be used as the pulp raw material constituting the base paper, and examples of the raw material waste paper include newspaper waste paper, printing waste paper, magazine waste paper, and OA waste paper. In addition, virgin pulp can also be used, and there is no restriction on hardwood and softwood, and pulp obtained from both raw materials can be arbitrarily blended. In addition, in this pulp manufacturing method, kraft pulp (KP) and sulfite pulp (SP), which are chemical pulping methods that are delignified by cooking liquor, and ground wood pulp (GP) that is mechanically ground. Refiner pulp, groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemiground pulp (CGP), semi-chemical pulp (SCP), or any other mechanical pulping method may be used. In addition, when compounding waste paper pulp, it can be an arbitrary blending ratio, but the absolute value of the difference between the whiteness of the base paper and the whiteness of all the pigments constituting the coating layer containing the regenerated pigment, In order to obtain a coated paper having no whiteness unevenness, it is desirable to blend it so that it is within 10 points.

Since the coated paper for printing of the present invention has a coated layer containing a regenerated pigment obtained by a specific method, it has a feature that it has a high scattering surface area and a high opacity. At this time, as described below, by mixing old paper pulp with high whiteness obtained by adding a bleaching step in addition to the normal deinking step, high opacity and High whiteness coated paper for printing can be obtained. Of course, even in this case, the whiteness of the pigment and the base paper should be adjusted so that the difference between the whiteness of the base paper and the whiteness of all the pigments constituting the coating layer containing the regenerated pigment is within a range of ± 10 points. Thus, a coated paper with little unevenness in whiteness can be obtained. In the following, a method for producing waste paper pulp (deinked pulp) suitable for use in the present invention will be described. However, such waste paper pulp can be blended in the base paper at a high rate of 50% by weight or more. It is also preferable from the viewpoint of environmental conservation and effective use of resources.

In general, as a method of producing deinked pulp from waste paper, (printing) waste paper disaggregation process, alkali soaking (alkali soaking) process, flotation process, washing process are appropriately combined to treat pulp and ink. Yes. In the present invention, a combination of such a deinking step and a peroxide bleaching step, particularly a hydrogen peroxide bleaching step, is suitable for application of a coating solution containing a specific regenerated pigment. Black pulp can be produced.

In such a peroxide bleaching step, it is more preferable to use a surfactant or an alkaline chemical in combination because the pulp fibers can be swollen and the ink can be more easily separated. At this time, the peroxide also has an effect of preventing yellowing of the pulp due to alkali. More preferably, following the peroxide bleaching step, the ink particles are adhered to and floated on the bubbles by a flotation step to separate the ink particles from the pulp.

By adding the peroxide bleaching step as described above, a deinked pulp having a whiteness of 70% or more, preferably 80% or more, suitable for the base paper of the present invention can be easily obtained. The peroxide addition rate in the peroxide bleaching step is 0.5 to 5% by weight, preferably 1 to 3% by weight, based on pulp. When the addition ratio is less than 0.5% by weight, not only the whiteness improvement effect is low, but there is a possibility of causing alkali yellowing due to the alkali used together. On the other hand, adding over 5% by weight is not economical because the whiteness reaches equilibrium and reaches a peak. In addition, it is preferable to perform a plurality of stages of peroxide bleaching treatment rather than adding a large amount of peroxide at a time because the whiteness can be improved efficiently.

As the peroxide used for peroxide bleaching, sodium peroxide, calcium peroxide, hydrogen peroxide, peracetic acid and the like can be used. Of these, hydrogen peroxide, in particular, dissociates into peroxide ions, which are nucleophilic attack reagents under alkaline deinking conditions, oxidatively decomposes the colored structure without damaging the fibers in the pulp, and lightens the pulp. This is more preferable.

When a plurality of peroxide bleaches are provided, it is preferable to appropriately combine the flotation step and the washing step. Further, when reduction bleaching is combined with peroxide bleaching, a deinked pulp having a whiteness of 80% or more suitable for the base paper of the present invention can be obtained more efficiently.

The addition rate of the alkaline chemical in the peroxide bleaching step is generally 0.5 to 10% by weight with respect to the pulp. When the addition ratio is less than 0.5% by weight, the whiteness improvement effect is low. On the other hand, if the addition rate is too high, alkali yellowing occurs. Further, as the alkaline chemical, caustic soda, sodium silicate, or the like is appropriately used, but two or more types of alkaline chemicals can be added in combination. As the deinking agent in the peroxide bleaching step, a nonionic hydrophilic surfactant, a cationic surfactant and an anionic surfactant which are usually used for alkali soaking can be appropriately selected and used.

In order to improve the additive effect of the additive chemical (liquid) in peroxide bleaching, the pulp concentration is desirably 5 to 35% by weight, preferably 10 to 20% by weight. When the pulp concentration is less than 5% by weight, the reaction efficiency between the pulp fiber and the peroxide is deteriorated, and when the pulp concentration exceeds 25% by weight, uniform reaction becomes difficult.

The temperature in peroxide bleaching is generally in the range of 30 to 120 ° C, preferably in the range of 50 to 80 ° C. When the temperature is lower than 30 ° C., the bleaching reaction rate is low, and a sufficient dust (ink particle) reduction effect cannot be obtained. On the other hand, when the temperature exceeds 120 ° C., the decomposition reaction of the peroxide increases, so the amount of effective peroxide to the pulp decreases, and the radicals generated attack the pulp. Is not suitable because it happens.

Moreover, the residence time of the pulp in peroxide bleaching is in the range of 5 to 120 minutes, preferably in the range of 10 to 90 minutes. If the time is less than 5 minutes, the increase in whiteness is small. On the other hand, even if it exceeds 120 minutes, the whiteness reaches equilibrium and reaches a peak, which is not economical, and the remaining amount of peroxide is reduced. Yellowing of the pulp also occurs.

As fillers for base paper used in the present invention, heavy calcium carbonate, light calcium carbonate, talc, clay, kaolin, titanium dioxide, synthetic silica, aluminum hydroxide and other inorganic fillers used in normal paper production, polystyrene resin In addition, synthetic polymer fine particles such as urea formaldehyde resin can be appropriately selected and used, but the regenerated pigment used for the coating layer of the present invention can also be used. Of course, two or more of these may be used in combination. The amount of filler added is preferably about 1 to 30% by weight with respect to the solid content of the total stock. In addition, a paper strength enhancer, a sizing agent, a dye, a fluorescent dye, an antifoaming agent, a pitch control agent, a slime control agent, and the like can be appropriately added to the stock containing pulp and filler as necessary. .

A base paper is produced by making a paper with a known paper machine using such a stock. If necessary, a surface treatment agent such as starch can be size-pressed on the base paper. The basis weight of the base paper is not particularly limited, but normally, when a base paper having a basis weight of about 30 to 100 g / m ² is used, the desired effect of the present invention is remarkably exhibited. Of course, it is also possible to apply to cardboard such as card or paperboard exceeding this range.

In the present invention, since a regenerated pigment having a large specific surface area recovered from sludge by carbonization and subsequent whitening is used, printing paper with high opacity can be obtained and regenerated by the degree of whitening. Since the carbon residual ratio in the pigment can be adjusted, there is an advantage that the whiteness and opacity can be adjusted in accordance with the intended coated paper.

In addition, when a general pigment is substituted with the regenerated pigment used in the present invention, the weight of the coated paper can be reduced because the coated paper can be made smaller than the coated paper having a constant opacity. Furthermore, the present invention also includes a method of adding a black dye to a pigment coating layer which is a part of a lightweight coated paper having a basis weight of about 80 g / m ² or less and is employed as an opacity improving method. By replacing a part of a normal pigment such as calcium with a regenerated pigment, there is also an advantage that a coated paper for printing having a high opacity of 85% or more can be obtained without adding a black dye.

EXAMPLES The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In the following examples and comparative examples, “parts” and “%” mean “parts by weight” and “% by weight”, respectively.

Example 1
<Description of raw materials>
A suspension of mixed waste paper containing disaggregated newspaper and flyer was sent to a deinking tower and soaked at a temperature of 70 ° C. for 4 hours. The amount of the deinking agent added was 0.8% caustic soda, 2.5% sodium silicate, 1.2% hydrogen peroxide, and 0.1% surfactant as solids in terms of pulp. Next, the suspension taken out from the deinking tower was diluted with dilution water, this diluted suspension was washed with a washing machine, and dehydrated to a concentration of 25% to obtain waste paper pulp. Next, the waste paper pulp was diluted to a pulp concentration of 1%, put into a floater, and deinked.

To the pulp after deinking, 2.0% caustic soda, 5.0% sodium silicate, 0.15% surfactant, and 1.5% hydrogen peroxide were sequentially added as the solid content in terms of pulp. Hydrogen peroxide bleaching was carried out at 10% in a hydrogen peroxide bleaching tower at 60 ° C. for 120 minutes. After hydrogen peroxide bleaching, washing and dehydration were performed, and the same hydrogen peroxide bleaching was repeated. From the obtained bleached pulp, a handsheet was prepared based on ISO5269-1 (pulp test handsheet preparation method) and air-dried. The whiteness (based on ISO 2470) of the prepared handmade paper was 80%, and the opacity (based on ISO 2471) was 82%.

<Preparation of base paper blended with waste paper pulp>
Next, 60 parts of the waste paper pulp obtained above is mixed with 40 parts of hardwood bleached pulp (self-made LBKP) having a whiteness of 83% and an opacity of 78%. 12% calcium (self-made), 0.02% sizing agent (Fibrane 81 / Oji National), 0.8% cationized starch (Ace K100 / Oji Cornstarch), acrylic amide polymer (Himoloc NR12MLS / Himo) ) 0.005% was added to obtain a paper stock, and a base paper for coating having a basis weight of 48.0 g / m ² was produced using a long paper machine. The obtained base paper had a whiteness of 81% and an opacity of 80%.

<Description of carbonization equipment>
The configuration of the apparatus in the embodiment will be described with reference to FIG. 4. Reference numeral 21 denotes a raw material hopper, and 22 denotes a cutting device installed at the lower part of the raw material hopper. 23 is a device for conveying the cut out raw material to a drying device, and A is a raw material drying device. In the drying apparatus A, 24 is a furnace body, 25 is a hot air supply apparatus to the drying apparatus, and 26 is an in-furnace transport apparatus connected in two stages. A thermometer 30a measures the temperature inside the drying apparatus furnace body. B is a carbonization device installed directly below the drying device. In the carbonization apparatus B, 27 is a furnace body, 28 is an in-furnace transfer apparatus connected in three stages, and 29 is a hot air generating apparatus for the carbonization apparatus. 30b is a thermometer for measuring the temperature inside the main body of the carbonizer furnace.

<Description of the whitening device>
31 is a raw material conveyance apparatus which conveys the carbide | carbonized_material discharged | emitted from a carbonization apparatus to the baking apparatus (whitening apparatus) C. FIG. In the firing apparatus C, 32 is a furnace body, and 33 is an in-furnace transport apparatus connected in two upper and lower stages. Reference numeral 34 denotes a hot air generator for supplying hot air to the baking apparatus. 35a is a thermometer for measuring the temperature inside the firing apparatus furnace main body.

<Supply of sludge>
Waste water from waste paper pulp was supplied to a flotation machine and subjected to flotation to obtain white water. The obtained white water was sent to a screw press type dehydrator (Fugoku Seisakusho) to obtain sludge having a solid content concentration of about 50%. The sludge stored in the raw material hopper 21 is cut out from the cutting device 22 by a fixed amount. The cut out raw material is continuously charged into the drying device A by the transport device 23. In this example, cutting was performed at 100 kg / hr.

<Drying and carbonization of raw materials>
The raw material charged into the drying device is transported in the furnace body in the horizontal direction by the furnace transport device 26. In the drying apparatus A, indirect heating is performed by the hot combustion gas supplied from the hot air generator 25 into the furnace body to evaporate moisture in the raw material. During this time, the oxygen-containing gas such as air in the transfer device was replaced by the generated water vapor, resulting in an oxygen-poor condition with an oxygen concentration of less than 0.1%. The raw material after the drying treatment was continuously charged into the main body of the carbonization apparatus. In the carbonization apparatus, the dried raw material is indirectly heated by the combustion hot gas supplied from the hot air generator 29 while being horizontally moved in the transfer apparatus through the iron shell of the transfer apparatus, and the furnace atmosphere temperature is set to 600. C. During this time, oxygen-containing gas such as air is completely replaced by dry distillation gas generated in the carbonization process, and the oxygen concentration is reduced atmosphere under an oxygen-poor condition of less than 0.1%, which promotes carbonization of organic matter. . In this example, the deinked papermaking sludge was continuously processed, and the residence time in the furnace in the carbonization apparatus was 60 minutes. The ratio of the fixed carbon derived from organic matter in the generated carbide was 8% (weight ratio) on average. The discharge amount of the raw material (carbide) discharged from the carbonization apparatus was 30 kg / hr by performing drying and carbonization treatment. In addition, the specific surface area by BET adsorption method of the obtained carbide | carbonized_material was 21 m < ² > / g.

<Carbide whitening treatment>
The carbide discharged from the carbonization chamber B was continuously charged into the firing device (whitening device) C by the transport device 31. The oxygen concentration of the introduced combustion gas can be adjusted from 3% to 15% by the combustion air ratio and the addition of air by a blower fan. In this embodiment, the oxygen concentration in the furnace of the calciner C is set to 12%. . The in-furnace temperature of the baking apparatus C can be controlled. This temperature was set to 650 ° C. in this example. The object to be fired was horizontally moved and stirred in this atmospheric gas by a screw mechanism of a conveying device, and the decarbonization reaction with oxygen was slowly performed. The residence time in the furnace in the carbide firing apparatus C was 120 minutes. The discharge amount from the baking apparatus C was 25 kg / hr.

<Regenerated pigment after whitening treatment>
From the measurement result of calcium element using a fluorescent X-ray analyzer (XRF, Shimadzu Corporation), the estimated calcium carbonate content contained in the raw material sludge was 60% with respect to all white inorganic particles. Furthermore, the estimated decomposition rate of calcium carbonate by carbonization and whitening treatment was 20% from the measurement result of the X-ray diffraction analyzer (XRD, Mac Science) of the regenerated pigment after whitening treatment. Therefore, it is considered that about 50% of calcium carbonate is contained in the regenerated pigment after the whitening treatment. The remaining 50% is kaolin and calcium oxide.

<Crushing>
The regenerated pigment obtained above is added to water containing 1.0% of a dispersant (A6028, Toagosei Co., Ltd.) to prepare a slurry with a solid content concentration of regenerated pigment of 60%, and a bead mill (Ashizawa) is used. Wet crushed. The regenerated pigment after one pass of the pulverizer had a 50% particle size (median diameter) of 0.5 μm and a specific surface area (BET adsorption method) of 18 m ² / g. The particle size distribution of the regenerated pigment was measured using a Sedigraph particle size distribution measuring device (micromeritic).

<Measurement of whiteness of regenerated pigment>
After drying a part of the regenerated pigment pulverized as described above, about 10 g is sampled and pulverized until there are no coarse particles in a mortar. It was molded by pressurizing at 13 kgf / cm ² for 30 seconds. The cylinder is placed and operated on a strong gloss acrylic board. As a result of measuring the whiteness with the tablet-like powder attached to the cylinder, the whiteness of the regenerated pigment was 82%. The whiteness was measured according to ISO 2470 using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd.).

<Preparation of coating liquid for pigment coating layer>
As a pigment formulation, 3 parts of starch (Ace A / Oji Cornstarch Co., Ltd.), styrene-butadiene copolymer latex, in the slurry of 100 parts of the regenerated pigment after the pulverization treatment (in terms of solid content) obtained above. (JSR-0613 / JSR) 7 parts (in terms of solid content) were added to obtain a coating solution. The total solid content concentration of the coating liquid was 56%.

<Preparation of coated paper for printing> Preparation of base paper blended with waste paper pulp The above coating paper for pigment coating layer obtained above was coated on the base paper for coating (basis weight 48.0 g / m ² ) containing the waste paper pulp. The liquid was coated on both sides with a desktop blade coater so that the dry solid content was 10 g / m ² per side and dried to obtain a coated paper for printing.

Example 2
The double-sided coated paper obtained in Example 1 was smoothed with a super calendar to obtain a coated paper for printing.

Example 3
Both surfaces were the same as in Example 1 except that 0.5 part of fluorescent dye (Brancolower ZSKN / Bayer) was added to the pigment solid content (regenerated pigment) (converted to solid content) in the coating liquid of Example 1. A coated paper was prepared and smoothed with a super calendar to obtain a coated paper for printing.

Example 4
In the preparation of the coating liquid for the pigment coating layer of Example 1, 65 parts of the regenerated pigment was replaced with 65 parts of heavy calcium carbonate (self-made), and fluorescent dye (Brancowar ZSKN / Bayer) was added to the pigment solid content. Except that 0.15 part (0.4 part based on the regenerated pigment solid content) was added, and a double-sided coated paper was prepared in the same manner as in Example 1, and the resulting double-sided coated paper was smoothed with a super calendar. To obtain a coated paper for printing. The heavy calcium carbonate used had a whiteness of 93%, a 50% particle size (median diameter) of 0.9 μm, and a specific surface area of 10 m ² / g according to the BET method. The whiteness of all the mixed pigments was 89%.

Example 5
The double-sided coated paper obtained in Example 4 (before the supercalender treatment) is coated on both sides with a desktop blade coater so that the dry solid content is 10 g / m ² per side and dried. After being smoothed with a super calendar, a coated paper for printing was obtained. For the top coat, starch is added to a slurry in which 60 parts of heavy calcium carbonate (self-made) and 40 parts of kaolin (HT / Engelhard) used in the pigment coating layer coating liquid of Example 3 are blended in terms of solid content. (Ace A / Oji Cornstarch Co., Ltd.) was mixed with 3 parts (in terms of solid content) and 10 parts (in terms of solid content) of styrene butadiene copolymer latex (JSR-0613 / JSR). Kaolin had a whiteness of 79%, a particle size of 0.3 μm, and a BET specific surface area of 20 m ² / g.

Example 6
A table blade coater was used in the same manner as in Example 1 except that the base paper for coating used in Example 1 was changed to a low whiteness base paper (whiteness 69%, opacity 89%, basis weight 48 g / m ² ). Both sides were coated and dried to obtain a coated paper for printing. In addition, the low whiteness base paper is a 100% recycled paper pulp product and contains 50% of the high whiteness recycled paper pulp obtained in Example 1.

Example 7
In the whitening treatment of the carbide of Example 1, a regenerated pigment was obtained by carbonizing and baking in the same manner as in Example 1 except that the whitening temperature of the baking apparatus was set to 700 ° C. The estimated calcium carbonate content of the regenerated pigment after the whitening treatment was 40%. Further, the 50% particle size (median diameter) after one pass of the regenerated pigment pulverizer was 0.5 μm as in Example 1, and the specific surface area (BET adsorption method) was 18 m ² / g. The whiteness of the regenerated pigment measured after drying after pulverization was 85%. A coated paper for printing was obtained in the same manner as in Example 1 except that the regenerated pigment was used.

Comparative Example 1
In the preparation of the coating liquid for the pigment coating layer of Example 1, a coated paper for printing was prepared in exactly the same manner as in Example 1 except that the pigment formulation was 100 parts of heavy calcium carbonate (manufactured).

Comparative Example 2
In the preparation of the coating liquid for the pigment coating layer of Example 1, a coated paper for printing was prepared in exactly the same manner as in Example 1 except that the pigment content was 100 parts of kaolin (HT / Engelhard).

Comparative Example 3
The coated paper for printing obtained in Comparative Example 1 was smoothed with a super calendar to obtain a coated paper for printing.

<Measurement of whiteness of coated paper>
The whiteness, opacity and glossiness of the coated coated paper obtained in the above Examples and Comparative Examples were measured and the results are shown in Table 1. The whiteness and opacity were measured according to ISO 2470 and ISO 2471 using a spectral whiteness colorimeter (Suga Test Instruments Co., Ltd.). Moreover, the glossiness was measured according to ISO8254-1 using a glossiness meter (MURAKAMI COLOR RESEARCH LABORATORY). Further, the whiteness unevenness and the print back-through were visually evaluated, and the results are shown in Table 1. In addition, about printing back-through, 0.2 cc of printing ink (GEOS-G, Dainippon Ink & Chemicals, Inc.) was printed on one side of the printing coated paper, and the printed back side was visually evaluated.
"Evaluation criteria"
○: Good △: Slightly inferior

[The invention's effect]
As is apparent from the results in Table 1, the coated paper for printing of the present invention uses a specific regenerated pigment made of sludge as a raw material for the pigment coating layer, and thus has high opacity and print back-through. It was also an excellent coated paper.

The process figure which showed notionally the process which manufactures the coated paper for printing of this invention. The conceptual systematic diagram of an example of the heat processing apparatus which performs the whitening process process by the carbonization process and decarbonization for manufacturing the regenerated pigment used for the coated paper for printing of this invention. The conceptual systematic diagram of another example of the heat processing apparatus which performs the whitening process process by the carbonization process and decarbonization for manufacturing the regenerated pigment used for the coated paper for printing of this invention. The example of the heat processing apparatus applied to the Example of this invention is shown.

Explanation of symbols

1: First indirect heating furnace (drying zone of carbonization process)
2: Sludge inlet 3: Sludge drying chamber 4a: Hot air intake 5a: Hot air, water vapor, dry distillation gas outlet 6: Second indirect heating furnace (carbonization zone by thermal decomposition of carbonization process)
7: Sludge pyrolysis, carbonization chamber 4b: Hot air inlet 5b: Hot air, water vapor, dry distillation gas outlet 8: Carbide outlet 9: Carbonized logistics route 10: Third indirect heating furnace (whitening zone by decarbonization)
11: Carbide inlet 12: Air inlet 13: Whitening chamber by decarbonization 4c: Hot air inlet 5c: Hot air outlet 14: Regenerated pigment recovery port 15: Internal combustion type rotary kiln (whitening zone by decarbonization)
16: Carbide reservoir 17: Carbide inlet 18: Carbide oxidation chamber 19: Burner 20: Regenerated pigment recovery port

Claims (5)

In a printing coated paper in which a coating layer mainly composed of a pigment and an adhesive is provided on at least one side of a base paper, the mixture of an organic substance and white inorganic particles was carbonized as the pigment, and then obtained by carbonization. A regenerated pigment produced by whitening a carbide,
The regenerated pigment is carbonized at a temperature of 1000 ° C. or less under a poor oxygen condition in which the presence of an oxygen-containing gas is limited to a mixture of an organic substance and white inorganic particles; A pigment produced by a whitening treatment step of decarbonizing in the presence of an oxygen-containing gas controlled to oxidize in a range of ˜1000 ° C., and the carbonization step is divided into two stages, A coated paper for printing, wherein at least the second half of the treatment step is performed at 450 ° C to 1000 ° C. The coated paper for printing according to claim 1, wherein the regenerated pigment is a pigment pulverized so as to have a median diameter of 0.1 to 5 µm. 3. The printing according to claim 1, wherein the absolute value of the difference between the whiteness of the base paper (based on ISO 2470) and the whiteness of all pigments constituting the coating layer containing the regenerated pigment is within 10 points. Coated paper. The coated paper for printing according to any one of claims 1 to 3, wherein the mixture containing organic matter and white inorganic particles is at least one of wastes and waste paper mainly composed of paper sludge. The mixture of the organic matter and the white inorganic particles is sludge obtained by supplying waste paper washing wastewater to a flotation machine, flotation treatment, and dehydration treatment. Coated paper for printing.

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