Process for producing hygienically treated pulp

Abstract

A process for producing sanitized pulp is provided. Also provided is the use of sanitized pulp in the manufacture of paper, cardboard, molded fiber articles, or other fiber-based articles, including sanitized pulp.

Description

Technical Field

[0001] The present invention generally relates to a process for producing hygienically treated pulp and further to hygienically treated pulp.

Background Art

[0002] In this section, useful background information is exemplified without admitting that any of the techniques described herein represents the state of the art.

[0003] Currently, hygienic paperboard grades for food packaging (folding carton board, FBB, and liquid packaging board, LPB) are often manufactured from virgin fibers. Examples of such packaging include food service items, beverage packages, beverage service items, product packages, product service items, and packaging items such as ovenable trays, microwaveable trays, clam shell boxes, other food boxes, soup cups, trays for raw meat and poultry, plates, and cup lids.

[0004] Debates about sustainability have increased interest among consumers and packaging manufacturers in the use of recycled fibers.

[0005] Recycled fiber materials typically contain large amounts of bacterial spores in addition to bacteria. Fiber materials collected from consumers and industrial sources for recycling often contain contaminants such as residues of food or oil that provide a good growth medium for bacteria. Even relatively clean-looking recycled fiber materials such as office paper scraps collected usually contain large amounts of spores because spore counts are not actively monitored in the production of non-hygienic / non-food packaging paper or paperboard grades. Furthermore, the collected fiber materials are often packed and stored under dirty, moist, and / or warm conditions, increasing the risk of spreading bacterial growth. As a result, fiber suspensions produced from recycled fiber materials usually contain large amounts of bacterial contaminants in the form of bacteria and bacterial spores.

[0006] When paper or cardboard products are intended for packaging food or beverages, the permissible amount of bacterial spores in the final paper and cardboard products is strictly limited to avoid the possibility of contamination of the packaged material. These limitations mean that recycled fiber materials are not actually used in hygienic paper and cardboard products intended for food and beverage packaging.

[0007] International Publication No. 2022 / 112663 relates to a method for producing paper, cardboard, tissue, etc. In this method, bacterial spores are reduced to less than 1000 CFU / ml in an aqueous fiber suspension containing regenerated cellulose fibers having an initial spore count of 10000 CFU / ml or more by adjusting the pH to an acidic value, adjusting the oxidation-reduction potential (ORP) of the fiber suspension to 200 mV or more with a first oxidizing agent, and then introducing a certain amount of performic acid into the fiber suspension as a second oxidizing agent. The treated fiber suspension is further treated with chemicals such as (one or more) retainers, (one or more) internal sizing agents, wet strength improvers and / or dry strength improvers, which are commonly used in the production of paper, cardboard, tissue, etc.

[0008] To manufacture hygienically treated pulp products, there is a need for an effective method to reduce the amount of bacterial spores in aqueous fiber suspensions containing cellulose fibers, such as regenerated cellulose fibers, through a simpler process. [Overview of the Initiative]

[0009] The following is a simplified overview of the features disclosed herein to provide a basic understanding of some exemplary embodiments of the present invention. This overview is not a comprehensive overview of the present invention. It is not intended to identify the main / important elements of the present invention or to limit its scope. Its sole purpose is to present some of the concepts disclosed herein in a simplified form as a prelude to a more detailed explanation.

[0010] According to the method of the present invention, hygienically treated recycled pulp can be manufactured in a single production line. Subsequently, in a separate production line for manufacturing, for example, hygienically treated cardboard packaging, functional chemicals such as strength-enhancing chemicals and hydrophobic chemicals can be added to the hygienically treated pulp to obtain the desired functional properties of the final cardboard packaging. Pulp made from virgin fibers can be used together with the hygienically treated recycled pulp in any appropriate ratio.

[0011] In a first aspect, the present invention provides a process for producing hygienically treated pulp, the process being: The process of providing cellulose fibers, A step of forming a fiber suspension having an initial spore quantity of >1000 CFU / ml containing cellulose fibers during the pulping stage, The process involves removing impurities from the fiber suspension during the screening stage to produce a purified fiber suspension, A process in which the purified fiber suspension is subjected to a concentration step, followed by, (i) Adjust the pH of the fiber suspension to a pH value of <6.5, (ii) Using the first oxidizing agent, adjust the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value of >200mV. (iii) A step of introducing a certain amount of performic acid into the fiber suspension as a second oxidizing agent in order to reduce the amount of spores in the fiber suspension, A process of forming a web of fiber suspension on a wire, The process includes pressing and drying a web to obtain dry pulp, wherein the dry pulp has a bacterial spore content of <1000 CFU / g of dry pulp, preferably <50 CFU / g of dry pulp, In this process, functional chemicals such as strength-enhancing chemicals and hydrophobic chemicals are not used substantially, and preferably, functional chemicals such as strength-enhancing chemicals and hydrophobic chemicals are not used.

[0012] In a second aspect, the present invention provides hygienically treated pulp produced by the process of the present invention.

[0013] A third aspect of the present invention provides the use of sanitized pulp produced by the process of the present invention or sanitized pulp of the present invention for manufacturing paper, cardboard, molded fiber-based articles, or other fiber-based articles.

[0014] In a fourth aspect, the present invention provides paper, cardboard, molded fiber-based articles, or other fiber-based articles containing sanitized pulp produced by the process of the present invention or sanitized pulp of the present invention.

[0015] Surprisingly, it has been found that hygienically treated pulp, such as recycled pulp, can be produced even under acidic and highly conductive process conditions using the process of the present invention. This process does not require the use of typical functional chemicals, such as strength-enhancing chemicals and hydrophobic chemicals, which are typically used to obtain the desired functionality of commercially available packaging paperboard, thus enabling the production of hygienically treated pulp, such as recycled pulp, even under acidic and highly conductive process conditions.

[0016] An advantage of the present invention is that process pH can be adjusted using a less expensive strong acid, which is expected to be consumed in smaller quantities compared to organic acids, instead of a weak organic acid such as citric acid, which is expensive and requires high doses.

[0017] Furthermore, the centralized production of hygienically treated pulps, such as hygienically treated recycled pulp, allows for better control of impurities. During the pulping and washing stages, impurities such as plastics, polystyrene foam, tape, glass, sand, metals, and other insoluble impurities are removed. These soiled process stages are carried out in the first part of the first production line and do not interfere with hygienic operating practices in the second production line that produces the final packaging paper or cardboard. In addition, undesirable chemical traces may be present in the recycled fiber raw materials, which can dissolve in the processing water. These can be removed in this first production line, for example, at some concentration stage before the final dried, hygienically treated pulp is formed and sent to the second production line.

[0018] The purpose or objective of the process of the present invention is not directed toward the functional properties of the final fiber-based product, such as the final cardboard or paper product. Surprisingly, it has enabled the production of sanitized pulp, such as recycled sanitized pulp, through a simpler process with less chemical consumption. The process of the present invention is also more economical because it does not require the use of functional chemicals.

[0019] A further advantage of the method of the present invention is that a typical production line originally designed to produce linerboards such as recycled linerboards can be utilized in the method of the present invention by using the pulping, screening, and concentration steps of the production line, followed by sanitizing steps (i), (ii), and (iii).

[0020] Sanitized pulp, such as recycled pulp produced by the method of the present invention, can be used as sanitized pulp in the manufacture of fiber-based articles.

[0021] The attached claims define the scope of protection. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 shows a flowchart of one exemplary production line designed to produce a recycled liner board. [Figure 2] Figure 2 shows a flowchart of one exemplary production line designed to produce pulp that has been sanitized by the process according to the present invention. **DETAILED DESCRIPTION OF THE INVENTION**

[0023] In a first aspect, the present invention provides a process for producing sanitized pulp, the process comprising: providing cellulose fibers; forming a fiber suspension having an initial spore count of >1000 CFU / ml, the fiber suspension comprising cellulose fibers, in a pulping stage; removing impurities from the fiber suspension in a screening stage to produce a purified fiber suspension; subjecting the purified fiber suspension to a concentration stage, followed by (i) adjusting the pH of the fiber suspension to a pH value of <6.5, (ii) adjusting the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value of >200 mV using a first oxidizing agent, (iii) introducing a certain amount of peroxyformic acid as a second oxidizing agent into the fiber suspension to reduce the amount of spores in the fiber suspension; forming a web of the fiber suspension on a wire; pressing and drying the web to obtain a dried pulp, the dried pulp having a bacterial spore count of <1000 CFU / g, preferably <50 CFU / g, of the dried pulp; wherein in the process, functional chemicals such as strength enhancing chemicals and hydrophobizing chemicals are not substantially used, preferably no functional chemicals such as strength enhancing chemicals and hydrophobizing chemicals are used.

[0024] Functional chemicals, i.e., strength-enhancing chemicals (strength enhancers) and hydrophobic chemicals (hydrophobic agents), which are agents used to impart functional properties or to modify the functional properties of a product (paper or cardboard), are substantially not used, and preferably not used in the process.

[0025] In one embodiment, during the concentration step, the concentration of the fiber suspension is adjusted to 1-30%, preferably 4-20%, more preferably 4-12%, and even more preferably 4-10%.

[0026] In one embodiment, impurities are removed in the pulping section, in the concentration stage, in the pressing section, and / or from the process water by a membrane washing system.

[0027] In one embodiment, a certain amount of process chemicals, i.e., process-assisting agents, such as defoamers and retainers, are added to the process, preferably in a mixing chest, machine chest, or short loop in a headbox where a moist fiber web is formed, and excess water is removed in a wire section and collected in a wire silo for recirculation. The amount of process chemicals can be selected to obtain a predetermined and / or desired effect.

[0028] In one embodiment, a certain amount of biocide is added to the process, preferably to the shower water of the process. The amount of biocide can be selected to obtain a predetermined and / or desired effect.

[0029] In one embodiment, pH and ORP are monitored and measured in steps (i) and (ii), preferably online in steps (i) and (ii).

[0030] In one embodiment, steps (i), (ii), and (iii) are performed in the concentration stage.

[0031] In one embodiment, steps (i), (ii), and (iii) are performed before or after the heat disperser. In one embodiment, steps (i) and (ii) are performed before the heat disperser, and step (iii) is performed after the heat disperser.

[0032] In one embodiment, the dryness of the dry pulp is at least 85%, preferably at least 87%, more preferably 87% to 97%, and most preferably 87% to 93%.

[0033] In relation to the present invention, the term “oxidation-reduction potential” is abbreviated as ORP and refers to the oxidation or reduction potential of an aqueous fiber suspension. The ORP value for an aqueous fiber suspension can be determined by using a chemically inert electrode immersed in the suspension and measuring its potential relative to a reference electrode. Several commercially available sensors for ORP value measurement are available.

[0034] In relation to the present invention, the term “bacterial spore” is understood as a dormant, non-reproductive structure formed by a bacterium. A bacterial spore contains the DNA of the bacterium and a portion of its cytoplasm enclosed in a protective sheath. Under favorable conditions, bacterial spores can germinate into a metabolically active state, i.e., a plant state. According to one embodiment of the present invention, the method of the present invention is used, for example, to reduce the amount of bacterial spores of the genera Bacillus, Brevibacillus, and / or Paenibacillus. These genera are known to grow under process conditions such as paper, cardboard, and tissue machines. These bacterial genera can produce heat-resistant spores that can withstand the heat of dryer sections used in processes for producing cellulose fiber webs such as paper, cardboard, and tissue.

[0035] The fiber suspension comprises a liquid phase, which is usually water, and a solid phase, which contains at least cellulose fibers and optional inorganic particles suspended in the liquid phase. The initial aqueous fiber suspension subjected to bacterial spore reduction treatment in steps (i), (ii), and (iii) of the process of the present invention contains cellulose fibers, such as regenerated cellulose fibers, and its initial bacterial spore count is at least 1000 CFU / ml, typically at least 5000 CFU / ml, and more typically at least 10000 CFU / ml. The fiber suspension comprises an aqueous liquid phase and a solid phase containing regenerated fibers. The cellulose fibers in the fiber suspension may be bleached fibers, unbleached fibers, or a mixture of bleached and unbleached fibers, such as regenerated fibers. The cellulose fibers in the fiber suspension are non-synthetic natural fibers originally obtained by mechanical pulping, chemical pulping, or any combination of mechanical and chemical pulping. The cellulose fibers may be wood fibers and / or non-wood fibers, preferably wood fibers such as hardwood, softwood, or a combination thereof. Recycled fibers can be obtained from any available recycled industrial and / or consumer textile material. Recycled fibers can be obtained, for example, from old corrugated cardboard containers (OCC), office waste, mixed office waste, sorted office waste, or any mixture thereof. Recycled fibers can be obtained, for example, from recycled pre-consumer textile material and / or recycled post-consumer textile material. Recycled fibers may also be secondary fibers from the manufacturing processes of paper, cardboard, tissue, etc., such as waste paper.

[0036] In one embodiment, the cellulose fibers include regenerated cellulose fibers. In one embodiment, the cellulose fibers consist of regenerated cellulose fibers.

[0037] In one embodiment, the cellulose fibers include natural cellulose fibers or lignocellulose fibers derived from molded pulp products.

[0038] In one embodiment, the cellulose fibers include regenerated cellulose fibers, natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or mixtures thereof.

[0039] Molded pulp products consist mainly of cellulose, lignin, and hemicellulose. Natural fibers can come from a variety of resources, such as wood, recycled fibers, agricultural biomass waste, and mixtures thereof, produced through chemical and mechanical pulping processes, including canola straw, wheat straw, rice straw, hemp fiber, bagasse and bamboo fiber, sugar beet, and mixtures thereof.

[0040] In one embodiment, the regenerated cellulose fibers are selected regenerated cellulose fibers, preferably double-selected regenerated cellulose fibers.

[0041] In one embodiment, the regenerated cellulose fibers include old corrugated cardboard containers, sorted office waste, mixed waste and cardboard, mixed office waste, mixed newspapers and magazines, used kraft paper, used corrugated kraft paper, used kraft paper bags, used beverage cartons, unprinted bleached sulfate cardboard, white mechanical pulp-based coated and uncoated paper, liquid cardboard packaging, sorted office paper, new kraft paper, new carrier kraft paper, unsold magazines and newspapers, unused corrugated kraft paper, unused corrugated cardboard material, unused kraft paper bags, recycled pre-consumer fiber material, recycled post-consumer fiber material, secondary fibers from manufacturing processes such as paper, cardboard, and tissue, waste paper, or mixtures thereof, preferably including old corrugated cardboard containers, unused corrugated cardboard material, used beverage cartons, or mixtures thereof.

[0042] In one embodiment, the amount of regenerated cellulose fibers, natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or mixtures thereof in the fiber suspension to be treated is at least 60% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, or at least 95% by weight, calculated from the total dry fiber weight of the suspension.

[0043] Aqueous fiber suspensions typically have negative initial oxidation-reduction (ORP) values ​​in the range of -500mV to -50mV, more typically in the range of -400mV to -100mV, and even more typically in the range of -300mV to -200mV.

[0044] In one embodiment, the fiber suspension may contain inorganic particles, such as particles of calcium carbonate, kaolin, talc, or gypsum. The inorganic particles typically originate from internal fillers, inorganic coatings, labels, stickers, etc., present in the fiber material collected for regeneration. The amount of inorganic particles given as the ash content of the cellulose fiber material used may range from 5 to 30% by weight, usually in the range of 5 to 25% by weight or 10 to 20% by weight. It is usually difficult and / or uneconomical to completely remove inorganic particles from cellulose fiber material such as regenerated fiber during the repulping of fiber material, which means that usually at least some inorganic particles remain in the fiber suspension along with the cellulose fiber material such as regenerated fiber material.

[0045] Fiber suspensions typically contain at least some dissolved carbonate ions.

[0046] The fiber suspension formed during the pulping stage contains hydrophobic contaminants such as plastic, tape, and / or adhesive residues. In addition to these contaminants, other impurities, large particles, etc., are removed in one or more screening stages following the pulping stage, typically removing contaminants and / or impurities with a size greater than 200 micrometers.

[0047] The fiber suspension is often subjected to fiber fractionation, and the fibers are separated into at least long fiber portions and short fiber portions according to their length.

[0048] In one embodiment, the pH of the fiber suspension is adjusted by introducing an acidifying agent into the fiber suspension.

[0049] In one embodiment, the pH of the fiber suspension is adjusted to a pH value of <6.5, preferably by introducing an acidifying agent into the fiber suspension. The pH of the fiber suspension can be adjusted within a pH range of 4 to 6.5, preferably 4.5 to 6.5, more preferably 5 to 6.5, and even more preferably 5.5 to 6.3. The acidifying agent may be any compound suitable for adjusting the pH value of the fiber suspension to a desired level, such as polyaluminum chloride or alum. The acidifying agent may be an organic acid such as citric acid or formic acid, an inorganic acid such as hydrochloric acid or sulfuric acid, or a mixture of organic and / or inorganic acids. The acidifying agent may be an acidifying gas such as carbon dioxide gas. If the acidifying agent is a liquid acid, it is added to the fiber suspension; if it is a gas, such as carbon dioxide gas, it is introduced into the fiber suspension. Preferably, the acidifying agent is introduced or added to the fiber suspension in an amount that adjusts the pH of the fiber suspension to a desired pH value without significantly increasing the conductivity of the fiber suspension. There are advantages to effective mixing when the acidifying agent is added to the fiber suspension.

[0050] The acidifying agent may be selected based on the properties of the fiber suspension being treated, particularly its buffering capacity. For example, a fiber suspension with high buffering capacity, such as one containing recycled fibers obtained from sorted office paper waste and having a high calcium carbonate particle content, may be treated with one or more acidifying agents selected from the organic acids, inorganic acids, or mixtures thereof, in order to obtain an economically appropriate consumption of the acidifying agent and to avoid large pH changes that could lead to undesirable changes in the conductivity of the fiber suspension.

[0051] In preferred embodiments, the conductivity of the fiber suspension does not change significantly during the reduction of bacterial spores in the fiber suspension by the process of the present invention. This means that the fiber suspension typically has an initial conductivity value in the range of 2–10 mS / cm, preferably 2–7 mS / cm, measured before the adjustment of pH and ORP values ​​and the introduction of performic acid, and a final conductivity value in the range of 2–10 mS / cm, preferably 3–7 mS / cm, measured after the adjustment of pH and ORP values ​​and the introduction of performic acid.

[0052] In one embodiment, the fiber suspension has a final conductivity value measured after adjusting the pH and ORP values ​​to a range of 2 mS / cm to 10 mS / cm, preferably 2 mS / cm to 7 mS / cm.

[0053] The oxidation-reduction potential (ORP) of the fiber suspension is adjusted to an ORP value of >200 mV using a first oxidizing agent, which is added to or introduced into the fiber suspension. Preferably, the ORP value of the fiber suspension can be adjusted to an ORP value of >250 mV, more preferably >300 mV. It has been observed that when the ORP value of the fiber suspension is adjusted to a level of >200 mV, performic acid can effectively eliminate and destroy bacterial spores present in the fiber suspension.

[0054] In one embodiment, the ORP value of the fiber suspension can be adjusted to a range of +100mV to +500mV, preferably +200mV to +400mV, and more preferably +300mV to +400mV.

[0055] The first oxidizing agent for adjusting the ORP value is different from performic acid; that is, the first oxidizing agent is not performic acid. Preferably, the first oxidizing agent used does not contain performic acid. It is also possible to use an organic peracid other than performic acid as the first oxidizing agent for adjusting the ORP value. However, preferably, the first oxidizing agent may be hydrogen peroxide, H2O2, or a percarbonate, and preferably sodium percarbonate. Hydrogen peroxide and percarbonates are readily available on an industrial scale and can effectively adjust the ORP value of a fiber suspension to a desired level. The first oxidizing agent may be considered a sacrificial agent, thereby keeping the consumption of performic acid as low as possible. The use of the first oxidizing agent provides an effective means for adjusting the ORP value to a level where the potential of performic acid can be fully realized.

[0056] In one embodiment, the first oxidizing agent is H2O2 or a percarbonate.

[0057] The first oxidizing agent can be introduced into the fiber suspension containing cellulose fibers in an amount that provides a desired ORP value for the fiber suspension.

[0058] In one embodiment, the first oxidizing agent is a fiber suspension 1 m 3 The activator can be introduced into the fiber suspension in an amount of 300-1000 ppm, preferably 400-800 ppm, preferably 500-700 ppm, given as grams per unit of activator.

[0059] The addition of the first oxidizing agent to the fiber suspension does not produce a bleaching effect. This means that there is no significant change in the ISO whiteness of the fiber suspension after the addition of the first oxidizing agent. In general, any change in the ISO whiteness of the fiber suspension, if any, is less than 5 ISO%, preferably less than 3 ISO%, and more preferably less than 1 ISO%, as measured using the standard ISO 2470-1:2016.

[0060] In one embodiment, performic acid as a second oxidizing agent is introduced, i.e., added to the treated fiber suspension in an amount that reduces the amount of bacterial spores to <1000 CFU / ml, preferably <500 CFU / ml, more preferably <250 CFU / ml, even more preferably <150 CFU / ml, and in some cases to <100 CFU / ml. In one embodiment, performic acid may be introduced to the fiber suspension in an amount that reduces the amount of bacterial spores to <50 CFU / ml, even further to <30 CFU / ml, or <10 CFU / ml.

[0061] In one embodiment, performic acid is introduced into the fiber suspension in an amount that reduces the spore count in the pulp after the final drying and sanitizing treatment to <1000 CFU / gram, preferably <50 CFU / g.

[0062] In one embodiment, performic acid is used in a fiber suspension of 1 m 3The activator can be introduced, or added, to the fiber suspension in an amount of 50-500 ppm, preferably 100-400 ppm, preferably 200-300 ppm, given as grams per unit of activator. The amount of bacterial spores can be determined by using conventional techniques known to those skilled in the art.

[0063] Performic acid is introduced into the fiber suspension as an aqueous solution. Performic acid can be prepared by mixing an aqueous solution of hydrogen peroxide with an aqueous solution of formic acid, and optionally with a catalyst, such as sulfuric acid. Preferably, the aqueous solution of performic acid is used as an equilibrium solution containing performic acid, formic acid, water, hydrogen peroxide, and optionally a catalyst. The performic acid solution typically has a concentration of at least 10% performic acid by weight-to-volume, and typically about 13.5% or 14% by weight-to-volume.

[0064] The performic acid is preferably able to interact with bacterial spores in the fiber suspension at the elevated temperature of the fiber suspension. In one embodiment, the temperature of the fiber suspension in steps (i), (ii), and (iii) is at least 20°C, for example 20-120°C, preferably at least 40°C, for example 40-50°C, more preferably at least 60°C, for example 60-100°C, and even more preferably at least 65°C, for example 65-100°C. The temperature of the fiber suspension in steps (i), (ii), and (iii) is preferably <100°C, more preferably <85°C, and even more preferably <75°C. In particular, when the pH of the fiber suspension is adjusted to the range of 5.5 to 6.5, it is advantageous that the temperature of the fiber suspension is in the range of 30 to 100°C, preferably 30 to 99°C, more preferably 40 to 80°C, for example 40 to 50°C, and even more preferably 50 to 80°C, when performic acid is introduced into the fiber suspension in steps (i), (ii) and (iii), and / or when performic acid is interacting with bacterial spores. It has been observed that the maximum spore-destroying effect can be achieved in this method. While we do not intend to be bound by any theory, it is assumed that the increased temperature makes the bacterial spores more sensitive and more susceptible to the destructive effect when performic acid is introduced into the fiber suspension. It is an advantage that effective spore reduction or destruction can be obtained at a fiber suspension temperature of already below 100°C. Thus, expensive and complex process equipment such as pressurized hot steam treatment tanks can be avoided.

[0065] The temperature of the fiber suspension can be increased to a desired value by heating the fiber suspension to a desired temperature in another process step. For example, the fiber suspension may be transferred after the pulper, preferably after one or more screening steps, to another tank. In the other tank, the fiber suspension may be heated to a desired temperature.

[0066] Preferably, before performic acid is introduced into the fiber suspension, the temperature of the fiber suspension is adjusted to the elevated temperature specified above.

[0067] In one embodiment, after treatment of the fiber suspension with performic acid, at least a portion of the aqueous liquid phase of the fiber suspension is separated from the solid phase of the fiber suspension containing cellulose fibers, and the separated aqueous liquid phase is returned to the process for regeneration and reuse in the formation of the initial fiber suspension. The separated aqueous phase typically contains the basic concentrations of the unused first oxidizing agent and / or second oxidizing agent. This means that the recirculation of the aqueous phase in this method has the potential to reduce the amount of the first oxidizing agent and / or second oxidizing agent required to adjust the ORP value to the desired level and destroy or reduce bacterial spores.

[0068] After performic acid has been allowed to interact with the fiber suspension and the amount of bacterial spores in the suspension has been reduced, the pH of the fiber suspension may, if necessary, be adjusted to a desired value by using a strong base, such as NaOH or sodium bisulfite, or neutralized. Neutralization is usually carried out after a suitable treatment or interaction time has elapsed following the introduction of performic acid. The treatment time required for the interaction between performic acid and bacterial spores may be, for example, 5 to 30 minutes, preferably 10 to 15 minutes.

[0069] Figure 1 shows a flowchart of an exemplary production line designed to produce linerboards such as recycled linerboards. Recycled cellulose fibers are subjected to a pulping step (1) to form a fiber suspension containing cellulose fibers, which is then transferred to a dump tank (2). Impurities are removed from the fiber suspension in a screening step (3) to produce a purified fiber suspension. The purified fiber suspension is fractionated into a suspension containing long fibers and a suspension containing short fibers (4), which are then subjected to concentration steps (5) and (15), respectively, preferably by a disc filter. During concentration, the concentration of the fiber suspension is increased, i.e., the fiber suspension is concentrated to a predetermined concentration.

[0070] From the concentration stage (5, 15), the concentrated suspension is heated (optionally) in a heat disperser (6, 16) to control sticky hydrophobic compounds, for example, from adhesives in the regenerated fiber material. The fiber suspension is sent to a storage tower (7, 17), from which it is transferred to a mixing chest (8) in the desired mixing ratio, then to a machine chest (9), and from there to a headbox (10). The headbox (10) distributes the fiber suspension onto wires to form a wet fiber web, from which excess water is removed first in the wire section (11), then in the press section (12), and finally the fiber web is dried in the drying section (13). Surface strength improving chemicals are then added to the dried web in a size press (20) to obtain a dried regenerated linerboard.

[0071] Fresh water may be introduced into the system in the wire section (11) and / or press section (12), for example, via wire, felt, and roll washing showers. The water discharged from the wire section (11) and press section (12) can be distributed for reuse at several locations in the process, including the pulper (1), either immediately after the machine chest (9) or via water reservoirs (19, 14). Waste paper may be stored in a waste paper storage tower (18), from which it can be delivered to the mixing chest (8).

[0072] In the manufacture of linerboard, functional chemicals, such as strength-enhancing chemicals (strength enhancers) and hydrophobic chemicals (hydrophobic agents), i.e., agents that provide functional properties or are used to modify the functional properties of recycled linerboard, are added to the wet end, i.e., the mixing chest (8) and machine chest (9), and to the dry end, i.e., the size press (20).

[0073] Figure 2 shows a flowchart of an exemplary production line designed to produce hygienically treated pulp using a process according to the present invention. Cellulose fibers are subjected to a pulping step (1) to form a fiber suspension containing cellulose fibers, which is then transferred to a dump tank (2). Impurities are removed from the fiber suspension in a screening step (3) to produce a purified fiber suspension. The purified fiber suspension is fractionated into a suspension containing long fibers and a suspension containing short fibers (4), which are subjected to concentration steps (5) and (15), respectively, preferably by a disc filter. In the concentration step, the concentration of the fiber suspension is adjusted to 1-30%, preferably 4-20%, more preferably 4-12%, and even more preferably 4-10%. After adjusting the concentration, the high-concentration fiber suspension is subjected to processing steps (i), (ii) and (iii).

[0074] After processing, the processed fiber suspension is optionally heated in a heating disperser (6, 16) to control sticky hydrophobic compounds resulting from adhesives in the fiber material, such as regenerated fiber material. The fiber suspension is sent to a storage tower (7, 17), from which it is transferred to a mixing chest (8) in the desired mixing ratio, then to a machine chest (9), and from there to a headbox (10). The headbox (10) distributes the fiber suspension onto wires to form a wet fiber web, from which excess water is removed first in a wire section (11), then in a press section (12), and finally the fiber web is dried in a drying section (13). After drying the web, dried and sanitized pulp is obtained. Certain amounts of process chemicals, i.e., process aids, such as defoamers, retainers, or biocides, may be added to the process in the process section starting from the storage tower (7, 17).

[0075] Fresh water may be introduced into the system in the wire section (11) and / or press section (12), for example, via wire, felt, and roll washing showers. The water discharged from the wire section (11) and press section (12) can be distributed for reuse at several locations in the process, including the pulper (1), either immediately after the machine chest (9) or via water reservoirs (19, 14). Waste paper may be stored in a waste paper storage tower (18), from which it can be delivered to the mixing chest (8).

[0076] In the process according to the present invention, substantially no functional chemicals (reinforcing agents and hydrophobic agents) are added to the wet end, i.e., the mixing chest (8) and the machine chest (9), preferably no functional chemicals are added, and substantially no strength-enhancing chemicals are added to the dried board after the drying section (13), preferably no strength-enhancing chemicals are added.

[0077] In a second aspect, the present invention provides hygienically treated pulp produced by the process of the present invention.

[0078] In one embodiment, the amount of bacterial spores in the hygienically treated pulp is <1000 CFU / g of dry pulp, preferably <50 CFU / g of dry pulp.

[0079] In one embodiment, the dryness of the dry pulp is at least 85%, preferably at least 87%, more preferably 87% to 97%, and most preferably 87% to 93%.

[0080] In one embodiment, the sanitized pulp includes sanitized regenerated cellulose fibers, sanitized natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or a mixture thereof.

[0081] In one embodiment, the hygienically treated pulp is in the form of a reel, a sheet, or a bale of sheets.

[0082] A third aspect of the present invention provides the use of sanitized pulp produced by the process of the present invention or sanitized pulp of the present invention for manufacturing paper, cardboard, molded fiber-based articles, or other fiber-based articles on a separate production line.

[0083] In one embodiment, the sanitized pulp includes sanitized regenerated cellulose fibers, sanitized natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or a mixture thereof.

[0084] Sanitized pulp can be used in the manufacture of any fiber-based article requiring hygienic fiber pulp. Sanitized pulp can be used in any appropriate ratio with virgin fiber.

[0085] In a fourth aspect, the present invention provides paper, cardboard, molded fiber-based articles, or other fiber-based articles containing sanitized pulp produced by the process of the present invention or sanitized pulp of the present invention.

[0086] In one embodiment, the sanitized pulp includes sanitized regenerated cellulose fibers, sanitized natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or a mixture thereof.

[0087] Fiber-based articles may include food packaging (foldable cardboard boxes, FBBs) and liquid packaging cardboard (LPBs). Examples of such packaging include food service supplies, beverage packaging, beverage service supplies, merchandise packaging, merchandise service supplies, and packaging supplies such as oven-safe trays, microwave-safe trays, clamshell boxes, other food boxes, soup cups, trays for raw meat and chicken, plates, and cup lids.

[0088] Various embodiments have been shown. It should be understood that, in this specification, the words comprise, include, and contain are used as open-ended expressions not intended to be exclusive.

[0089] The foregoing description provides a complete and useful description of the best mode currently intended by the inventors to carry out the invention, as non-limiting examples of specific implementations and embodiments. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the embodiments shown above and can be carried out in other embodiments using equivalent means or in various combinations of embodiments without departing from the features of the invention.

[0090] Furthermore, some of the features of the embodiments disclosed in advance may be used to their advantage without corresponding use of other features. Therefore, the foregoing description is merely illustrative of the principles of the present invention and is not intended to limit it. Accordingly, the scope of the present invention is limited only by the appended claims.

Claims

1. A process for producing hygienically treated pulp, wherein the process includes a step of providing cellulose fibers, A step of forming a fiber suspension containing the cellulose fibers and having an initial spore count of >1000 CFU / ml during the pulping stage, A step of removing impurities from the fiber suspension during the screening stage to produce a purified fiber suspension, A step of subjecting the purified fiber suspension to a concentration step, thereafter, (iv) Adjust the pH of the fiber suspension to a pH value of <6.5, (v) Using the first oxidizing agent, adjust the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value of >200 mV. (vi) A step of introducing a certain amount of performic acid as a second oxidizing agent into the fiber suspension in order to reduce the amount of spores in the fiber suspension, A step of forming a web of the fiber suspension on a wire, The process includes pressing and drying the web to obtain dried pulp, wherein the dried pulp has a bacterial spore content of <1000 CFU / g, preferably <50 CFU / g, of the dried pulp. The process described above substantially does not use functional chemicals such as strength-enhancing chemicals and hydrophobic chemicals, and preferably does not use functional chemicals such as strength-enhancing chemicals and hydrophobic chemicals.

2. The process according to claim 1, wherein the cellulose fibers include regenerated cellulose fibers, natural cellulose fibers or lignocellulose fibers derived from molded pulp products, or a mixture thereof.

3. The process according to claim 1 or 2, wherein in the concentration step, the concentration of the fiber suspension is adjusted to 1 to 30%, preferably 4 to 20%, more preferably 4 to 12%, and even more preferably 4 to 10%.

4. The process according to any one of claims 1 to 3, wherein impurities are removed in the pulping section, in the concentration stage, in the pressing section, and / or from the process water by a membrane washing system.

5. The process according to any one of claims 1 to 4, wherein a certain amount of process chemicals, such as defoaming agents and retaining agents and / or biocides, is preferably added in a mixing chest, a machine chest, or a short loop in a headbox where a moist fiber web is formed, and excess water is removed in a wire section and collected in a wire silo for recirculation.

6. The process according to any one of claims 1 to 5, wherein pH and ORP are monitored and measured in steps (i) and (ii), preferably, pH and ORP are monitored and measured online in steps (i) and (ii).

7. The process according to any one of claims 1 to 6, wherein steps (i), (ii), and (iii) are performed in a concentration step.

8. The process according to any one of claims 1 to 7, wherein the dryness of the dried pulp is at least 85%, preferably at least 87%, more preferably 87% to 97%, and most preferably 87% to 93%.

9. The process according to any one of claims 1 to 8, wherein the fiber suspension contains inorganic particles such as calcium carbonate particles, and the pH of the fiber suspension is adjusted to a range of 5 to 6.5, more preferably 5.5 to 6.5, and even more preferably 6 to 6.

5.

10. The process according to any one of claims 1 to 9, wherein the temperature of the fiber suspension in steps (i), (ii), and (iii) is at least 20°C, preferably at least 40°C such as 40-50°C, more preferably at least 60°C, and even more preferably at least 65°C.

11. The process according to any one of claims 1 to 10, wherein the fiber suspension has a final conductivity value measured after adjustment of pH and ORP value to a range of 2 mS / cm to 10 mS / cm, preferably 3 mS / cm to 7 mS / cm.

12. The process according to any one of claims 1 to 11, wherein the ORP value is adjusted to a range of +100 mV to +500 mV, preferably +200 mV to +400 mV, more preferably +300 mV to +400 mV.

13. Hygiene-treated pulp produced by the process described in any one of claims 1 to 12.

14. Use of sanitized pulp produced by a process according to any one of claims 1 to 12 or sanitized pulp according to claim 13 for manufacturing paper, cardboard, molded fiber-based articles, or other fiber-based articles.

15. Paper, cardboard, molded fiber-based articles, or other fiber-based articles comprising sanitized pulp produced by a process according to any one of claims 1 to 12 or sanitized pulp according to claim 13.

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