MANUFACTURING A PAPERY ARTICLE

Abstract

The present invention relates to a process for manufacturing papery articles, such as paper, card and board, comprising the pH adjustment of an aqueous composition comprising at least one fiber stock by addition of methanesulfonic acid (MSA).

Description

The present invention relates to a process for manufacturing papery articles, such as paper, card and board, comprising the addition of methanesulfonic acid (MSA) to an aqueous composition comprising at least one fiber stock to set the pH.

The present invention further relates to the use of methanesulfonic acid in the manufacture of a papery article, more particularly for setting the pH of an aqueous composition comprising at least one fiber stock in the paper/board machine approach flow.

Paper and papery article for the purposes of the present invention refer to sheetlike articles manufactured from fibers, more particularly from chemically or mechanically uncovered vegetable fibers, which are formed by dewatering a fiber stock suspension using at least one wire screen usually under addition of fillers and further additives.

The manufacture of papery articles on state of the art paper/board machines generally comprises the dewatering of a fiber stock suspension, for example a chemical pulp, mechanical pulp and/or waste paper suspension, on at least one moving wire screen to form a paper web. The term paper or board machine typically subsumes the following assemblies: approach flow system, head box, wire section, press section, dry end, size press (surface sizing), film press, smoothing cylinder, smoothing system, online calender, online coating assembly and windup. Often, the manufacture of papery articles comprises downstream steps of surface treatment (e.g., calendering, coating) and comprises finishing (e.g., roll cutting, format cutting, packing). A general description of the process steps and equipment parts involved in the manufacture of papery articles is described for example in “Papiermacher Taschenbuch, 8^th edition, Dr. Curt Haefner-Verlag GmbH, Heidelberg”.

The approach flow system is where the fiber stock suspension is made machine-ready for the subsequent sheet forming in the wire section. It is where, for example, the final/compensatory beating of the fiber stock is carried out, the stock amounts and stock densities are regulated, and also the regulation of the flow rates is carried out. Within the approach flow system, it is also possible for the metered addition of fillers, process chemicals and/or performance chemicals to take place. The approach flow system is generally held to include all equipment parts and pipework between the mixing and machine chest and the head box of the paper/board machine. The approach flow system of the paper/board machine is generally also where the pH of the fiber stock suspension is set.

In the head box, the fiber suspension having a stock density of generally less than 1.4% is applied to at least one moving endless wire screen (machine wire). In the subsequent wire section as it is known, the fiber stock suspension is drained to a stock density of about 12 to 24% (augmented by application of vacuum or pressure for example) and the fibers become interfelted together to form a still wet fibrous web (sheet formation). This fibrous web is removed from the wire using a pickup felt (felt band) for example, and passes into the subsequent wet presses where the stock density is further increased to about 50%.

Thereafter, the fibrous web is generally dried in the dryer section using drying cylinders. For certain end uses, the paper can then be subjected to further processing steps (e.g., smoothing, coating, calendering).

The fiber stock suspensions used for paper or board manufacture, in addition to fibers, usually comprise fillers, more particularly inorganic fillers such as calcium carbonate, kaolin, titanium dioxide, barium sulfate and multiple process and/or performance chemicals, for example sizing agents to increase the hydrophilicity and printability of the paper, and also, for example, retention aids, drainage aids, dyes, optical brighteners, wet strength agents, dry strength enhancers, defoamers, biocide.

Possible fiber stocks for the manufacture of papery articles are generally primary fiber stocks and also secondary fiber stocks. Primary fiber stocks used are more particularly wood-free fiber stocks, more particularly chemical pulps such as sulfate pulp (SA) (also known as kraft pulp), sulfate semi-pulp, sulfite pulp (SI) of hard- and/or softwoods. However, wood-containing fiber stocks, more particularly mechanical pulps such as groundwood (HS) (also known as stone groundwood SGW), pressurized groundwood (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical thermal mechanical pulp (CTMP) and thermomechanical pulp with caustic-peroxide pretreatment (BCTMP) may also be used. Secondary fiber stocks include various waste paper varieties recycled into paper/board and card production, and also deinked pulp (DIP). DIP is produced by a waste paper recovery process in which a large proportion of the printing ink is removed from the fiber stock suspension. In the deinking process, the slurried, defibered waste paper is commonly admixed with caustic, water glass, complexing agent, surfactant and hydrogen peroxide. The printing inks detach from the fiber surface and are removed from the fiber stock suspension by flotation. Chemical pulp, such as goundwood, pressurized groundwood, TMP, RMP, but also chemical pulp are typically bleached in the course of production and/or before use. A distinction is generally made between oxidative and reductive bleaching stages, although these bleaching stages are often combined into bleaching sequences. Bleaching frequently comprises a treatment with hydrogen peroxide under alkaline conditions. When the bleaching process concludes with an alkaline stage, it is generally necessary for the fiber stock suspension to be acidified. In order to establish the pH necessary for paper production, it is therefore generally necessary to add an acid to regulate the pH.

Depending on the pH of the fiber stock suspension used for paper formation, a general distinction is made between the conventional acidic process (pH in the range from 4.5 to 6.8) comprising generally the addition of acidic aluminum salts and the neutral process in the pH range from 6.8 to 10.8. In the ideal case of a neutral process, the pH is adjusted to a value between 7.0 to 7.5. In recent decades, the neutral process has become more and more established, particularly because it enables calcium carbonate (CaCO₃) to be used as a filler, for example in the form of ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC).

Fiber stock suspension pH is of decisive importance for paper production and has a direct influence on paper/board machine runnability. A high pH leads to increased swelling of the fibers and impedes fiber stock suspension drainage. Accurate and reliable pH setting further contributes to preserving the whiteness of the papery articles and to preventing yellowing by alkalis. The choice of suitable acids for setting the pH as part of the manufacture of papery articles is very limited. Owing to the requirements of availability, price and stability, a person skilled in the art chooses from a very limited number of acids suitable for paper production. The use of phosphoric acid, or of a combination of phosphoric acid and phosphonates, or the use of carbon dioxide for pH setting is described in the prior art. It is further known to use sulfuric acid and/or bisulfite to set the pH in paper production. It has also been written that the pH of a fiber stock suspension can be adjusted by adding an electrolyte, such as aluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC) and aluminum hydroxide chloride.

The WO 98/56988 document describes a process for stabilizing the pH of a pulp suspension for paper production using a combination of an alkali metal hydroxide and carbon dioxide.

The US 2010/0175839 document describes a multi-stage process for adjusting the pH of a cellulosic pulp suspension wherein the pulp is treated at least twice with carbon dioxide and at least once with a strong acid, e.g., sulfuric acid, sulfurous acid or bisulfite, and wherein a step for carbonate removal is included.

The WO 2009/003770 document discloses a process for making paper wherein a fiber stock suspension comprising a mechanical pulp is subjected to an acid-base treatment to avoid reducing the brightness. In the process, the fiber stock suspension is treated initially with a strong acid, more particularly sulfuric acid, sulfurous acid, hydrochloric acid and bisulfite, and then with a weak base (e.g., an alkali metal bicarbonate or alkali metal carbonate).

The prior art use of phosphoric acid and phosphonates results in increased formation and deposition of calcium phosphates in various parts of the paper machine. The paper/board machine thus has to be increasingly idled to allow for cleaning.

Many state of the art paper machines operate at very high speeds of up to 1800 meters per minute and outputs of up to 1000 t of paper per 24 h to increase the production of paper/card. Paper/board machine idling and the increased production of broke are therefore the decisive factors for the efficiency and economics of the production process.

Furthermore, phosphorus compounds pollute the wastewater cleaning facilities of paper mills which, unlike communal water treatment facilities, generally have no phosphorus-eliminating stage.

One particular problem with using carbon dioxide for pH regulation of fiber stock suspensions is the outgassing of carbon dioxide in the wire water circuit and also the attendant fluctuations in the pH. In addition, metering the gaseous additive carbon dioxide requires costlier metering devices.

It is an object of the present invention to provide a pH-regulating additive, more particularly an acid, for fiber stock suspensions in paper production, and/or an improved process for paper production. The process should firstly meet all wastewater-relevant and environmental requirements as well as provide for an efficient, simple and inexpensive operation. Simple metering, minimal introduction of additional salt content into the wire water/wastewater of the paper machine and also good drainage behavior of the fiber stock suspension should be ensured for instance.

We have found that, surprisingly, adding methanesulfonic acid (MSA) is a particularly effective way to adjust the pH of fiber stock suspensions in papermaking. Methanesulfonic acid has a pK_a value of about −0.6 and so is a strong or very strong acid. Methanesulfonic acid is generally non-oxidizing and is marked by heat and hydrolysis resistance in particular. Methanesulfonates are used in washing and cleaning compositions for example. Methanesulfonic acid is further used in acidic electroplating solutions for metal coatings.

The present application is directed to a process for manufacturing a papery article, such as paper, card and board, comprising the steps of:

• • a) providing an aqueous composition comprising at least one fiber stock;
  • b) adding methanesulfonic acid to the aqueous composition comprising at least one fiber stock to adjust the pH;
  • c) draining the aqueous composition comprising at least one fiber stock.

The use of methanesulfonic acid is associated with the following advantages in particular:

• • Methanesulfonic acid is readily biodegradable and is halogen-free and thus reduces the burden on the wastewater treatment of the production process. Moreover, no or distinctly less phosphorus/phosphate ends up in the wastewater of the paper/board machine.
  • There is less, if any, formation of deposits of calcium phosphate, for example, in the parts of the paper/board machine.
  • Owing to the high acid constant of methanesulfonic acid, comparatively low quantities need to be added. The salt burden of process waters in papermaking can accordingly be reduced.
  • Economic viability/efficiency of the manufacturing process is improved.
  • Methanesulfonic acid is colorless, odorless and available in high purity, hence there is no alien impact on the manufacturing system (process water, wastewater, circuit water, papery articles). Therefore, methanesulfonic acid is particularly suitable for use in the manufacture of papery articles (packaging materials for example) which are used in the food sector.
  • Methanesulfonic acid has high thermal stability, a low vapor pressure, hydrolysis resistance and unlimited miscibility with water, hence handling and metering are simple.
  • Methanesulfonic acid is halogen-free and has minimal corrosivity compared with sulfuric acid for example.

The use of methanesulfonic acid is thus able to provide a distinct improvement in the economics of manufacturing papery articles.

Paper and papery article for the purposes of the present invention refer to sheetlike articles manufactured from fibers, more particularly from chemically or mechanically uncovered vegetable fibers, which are formed by dewatering a fiber stock suspension using at least one wire screen usually under addition of fillers and further additives. Additives are generally distinguished into process chemicals (e.g., biocides, deaerators, retention aids) and performance chemicals (e.g., dyes, optical brighteners, wet strength agents). Paper and papery articles for the purposes of the present invention are more particularly graphic papers, office communications papers, packaging papers, hygiene papers and specialty papers. Graphic papers for the purposes of the invention are all papers used for printing in flexographic printing, letterpress, offset printing or gravure printing for example, e.g., news print. Office communication papers are writing, printing and copying papers, for example photoprint and digital printing papers. Packaging papers are papers, card and board for packaging purposes, for example corrugated fiberboard. Hygiene papers for the purposes of the invention are papers of high specific volume and high absorbency, which are typically used in the sanitary or kitchen sector or in the industrial sector. The term specialty papers identifies papers and paperboards for specific technical uses, for example decor papers and filter papers.

Papery articles can be classified, according to their mass per unit area, as paper, card or board. According to German standard specification DIN 6730, a mass per unit area of not more than 225 g/m² is indicative of paper and above 225 g/m² of board. Papery articles having a mass per unit area in the range from 7 to 150 g/m² are often also referred to as paper, in the range from 150 to 600 g/m² as cardboard and from 600 g/m² as paperboard. Cardboard and paperboard typically consist of multiple layers.

The present invention more particularly provides a process as described above, wherein the step of draining the aqueous composition (step c) results in the formation of a fibrous web which is pressed and/or dried in one or more further process steps.

The aqueous composition more particularly is a suspension (slurry) of a fiber stock in water. The aqueous composition may comprise further dissolved, colloidally dissolved or solid constituents. The constituents in question are more particularly known to a person skilled in the art and used/generated in the course of manufacturing papery articles.

The fiber stock can be more particularly selected from:

• • chemical pulp (ZS), such as sulfate pulp (SA) (also called kraft pulp), sulfate semichemical pulp, sulfite pulp (SI);
  • mechanical pulp, such as groundwood (HS) (also called stone groundwood SGW), pressurized groundwood (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP), thermomechanical pulp with caustic/peroxide pretreatment (BCTMP);
  • secondary fiber stock, such as waste paper (AP) and deinked pulp (DIP).

Fiber stocks used can be more particularly the above-described bleached and/or unbleached pulps and/or fiber stocks from hard- or softwoods. Preference is given to using beech sulfite pulp and/or long fiber sulfate pulp.

More particularly, the aqueous composition comprises at least one fiber stock selected from the group consisting of sulfate pulp (SA), sulfate semi-pulp, sulfite pulp (SI), groundwood (HS), pressurized groundwood (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP), thermomechanical pulp with caustic/peroxide pretreatment (BCTMP), waste paper (AP) and deinked waste pulp (DIP).

In a preferred embodiment, the fiber stock used is at least one secondary fiber stock, more particularly waste paper and/or deinked pulp (DIP).

More preferably, the aqueous composition comprises at least one fiber stock which has been alkali-oxidatively bleached.

Preferably, the aqueous composition comprising at least one fiber stock has a stock density in the range from 0.01 to 5%, preferably in the range from 0.1 to 5% and more preferably in the range from 0.2 to 1.4%.

The stock density of an aqueous composition comprising at least one fiber stock (fiber stock suspension) is the percentage of the dry mass of the filterable solids in the composition relative to the mass of the entire composition. Commonly, the dry mass is reported as absolute dry mass or as dry mass on drying under standard conditions (oven dry, otro). The determination of the stock density of fiber stock suspensions is described in DIN 54359 (EN ISO 4119) for example.

By further constituents, the aqueous composition may comprise at least one customary additive (process and performance chemicals) known to a person skilled in the art. The additive may be selected from:

• • process chemicals, such as
    • electrolyte, for example aluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC), aluminum hydroxide chloride, inorganic precipitants
    • organic precipitant
    • biocide (e.g., slime control agent)
    • deaerator
    • defoamer
    • dispersant
    • adsorbent (e.g., talc)
    • fixative (e.g., short-chain cationic polymers)
    • retention aid (e.g., long-chain anionic and cationic polymers, also partially crosslinked)
    • drainage accelerant
  • and performance chemicals, such as
    • dye
    • optical brightener
    • internal sizing agent (resin size, AKD, ASA, polymer size)
    • surface sizing agent
    • wet strength agent
    • dry strength enhancer
    • internal wet web strength polymer (IWWS)

More particularly, the aqueous composition additionally comprises at least one further additive selected from the group consisting of aluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC), aluminum hydroxide chloride, organic precipitant, biocide, deaerator, defoamer, dispersant, adsorbent, fixative, retention aid, drainage accelerant, dye, optical brightener, internal sizing agent, wet strength agent, dry strength enhancer and internal wet web strength polymer (IWWS).

Preferably, the aqueous composition additionally comprises at least one inorganic filler selected from the group consisting of ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, titanium dioxide and barium sulfate, preferably selected from the group consisting of ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC).

Adjusting the pH of an aqueous composition comprising at least one fiber stock is more particularly effected by adding methanesulfonic acid until the desired pH value or the desired pH range is reached. A person skilled in the art is familiar with common methods of pH control. The amount of methanesulfonic acid added depends on the type of the aqueous composition comprising at least one fiber stock and its original pH and also the desired pH target value.

Adjusting the pH of the aqueous composition comprising at least one fiber stock can be effected by adding a mixture of acids comprising methanesulfonic acid. It is further conceivable to use a mixture of methanesulfonic acid and carbon dioxide, or a mixture of acids comprising methanesulfonic acid and carbon dioxide. More particularly, methanesulfonic acid is added as sole acid to adjust and/or stabilize the pH. It is further conceivable to adjust/regulate the pH of the aqueous composition by additionally adding a base known to a person skilled in the art.

The present invention provides more particularly a process for manufacturing a papery article as described above, wherein the pH of the aqueous composition comprising at least one fiber stock is adjusted to a value in the range from 4 to 11, more particularly in the range from 4.5 to 6.8 and more particularly in the range from 6.8 to 10.8.

When the process of the present invention relates to a process for manufacturing a papery article using the acidic method, it is particularly a pH in the range from 4.5 to 6.8 which is set by adding methanesulfonic acid. When the process of the present invention relates to a process for manufacturing a papery article using the so-called neutral method (usually with use of calcium carbonate as filler), the pH of the aqueous composition comprising at least one fiber stock is preferably adjusted to a range from 6.8 to 10.8 and more particularly from 7.0 to 7.5.

The process described in the present application for manufacturing a papery article may comprise further common process steps of paper/board production, for example steps in stock preparation comprising dispersing, sorting, beating of the fiber stock, steps downstream of drying, such as calendering, coating, cutting, and also steps concerning finishing.

The addition of methanesulfonic acid to the aqueous composition comprising at least one fiber stock can take place at one or more different process sections of the manufacturing process of the papery article. More particularly, the addition of methanesulfonic acid to the aqueous composition comprising at least one fiber stock takes place in a paper machine approach flow.

The approach flow system for the purposes of the present invention is generally held to include all equipment parts and pipework between the mixing and machine chest and the head box of the paper/board machine. The approach flow system is where the fiber stock suspension is made machine-ready for the subsequent sheet forming in the wire section. It is where, for example, the final/compensatory beating of the fiber stock is carried out, the stock amounts and stock densities are regulated, and also the regulation of the flow rates is carried out. The approach flow system of the paper/board machine is where more particularly the aqueous composition comprising at least one fiber stock (fiber stock suspension) is uniformly diluted from about 3 to 5% stock density (thick stock) to about 0.2 to 1.4% stock density. In addition, the fiber stock suspension can be cleaned of fiber bundles, sand, plastics, etc. This is done more particularly in the so-called stock fine screening via centrifugal, pressure and/or vibration screeners for example. The approach flow system is also where fillers, process chemicals and/or performance chemicals can be added. The approach flow system of the paper/board machine is generally also where the pH of the fiber stock suspension is set.

It is particularly preferable for the addition of methanesulfonic acid for adjusting the pH to take place before, after and/or during the stock fine screening of the aqueous composition comprising at least one fiber stock. Stock fine screening is more particularly effected using common screening assemblies, for example centrifugal, pressure and/or vibration screeners. It is preferable to add methanesulfonic acid before the last screening assembly before the head box.

The process of the present invention can generally be used for manufacturing any papery articles known to a person skilled in the art. The process of the present invention relates more particularly to the manufacture of a papery article selected from graphic paper, office communication paper, packaging paper, card, board, hygiene paper and specialty paper, preferably a process for manufacturing a graphic paper or an office communication paper. In a preferred embodiment, the invention provides a process for manufacturing a papery article wherein the papery article is a packaging material for the food sector.

The present application is further directed to the use of methanesulfonic acid in the manufacture of a papery article.

More particularly, the use which the present invention provides for methanesulfonic acid in the manufacture of a papery article comprises adjusting the pH of an aqueous composition comprising at least one fiber stock.

More particularly, the present invention provides for the use of methanesulfonic acid in the manufacture of papery articles on industrially common paper and/or board machines. Preferably, the use of methanesulfonic acid comprises adjusting the pH of an aqueous composition comprising at least one fiber stock in a paper and/or board machine approach flow. The methanesulfonic acid may be more preferably used before the head box.

More particularly, the present invention provides for the use of methanesulfonic acid in the manufacture of a papery article selected from graphic paper, office communication paper, packaging paper, board, card, hygiene paper and specialty paper, more particularly a packaging material for the food sector.

Claims

1-12. (canceled)

13. A process for manufacturing a papery article comprising the steps of:

a) providing an aqueous composition comprising at least one fiber stock;

b) adding methanesulfonic acid to the aqueous composition comprising at least one fiber stock to adjust the pH; and

c) draining the aqueous composition comprising at least one fiber stock.

14. The process according to claim 13, wherein the step of draining the aqueous composition (step c) results in the formation of a fibrous web which is pressed and/or dried in one or more further process steps.

15. The process according to claim 13, wherein the fiber stock used is at least one fiber stock selected from the group consisting of sulfate pulp (SA), sulfate semi-pulp, sulfite pulp (SI), groundwood (HS), pressurized groundwood (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP), thermomechanical pulp with caustic/peroxide pretreatment (BCTMP), waste paper (AP) and deinked waste pulp (DIP).

16. The process according to claim 13, wherein the aqueous composition comprises at least one fiber stock which has been alkali-oxidatively bleached.

17. The process according to claim 13, wherein at least one secondary fiber stock is used.

18. The process according to claim 13, wherein the aqueous composition comprising at least one fiber stock has a stock density in the range from 0.01 to 5%.

19. The process according to claim 13, wherein the aqueous composition additionally comprises at least one further additive selected from the group consisting of aluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC), aluminum hydroxide chloride, organic precipitant, biocide, deaerator, defoamer, dispersant, adsorbent, fixative, retention aid, drainage accelerant, dye, optical brightener, internal sizing agent, wet strength agent, dry strength enhancer and internal wet web strength polymer (IWWS).

20. The process according to claim 13, wherein the aqueous composition additionally comprises at least one inorganic filler selected from the group consisting of ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, titanium dioxide and barium sulfate.

21. The process according to claim 13, wherein the pH of the aqueous composition comprising at least one fiber stock is adjusted to a value in the range from 4 to 11.

22. The process according to claim 13, wherein the step of adding methanesulfonic acid to the aqueous composition comprising at least one fiber stock takes place in a paper machine approach flow.

23. The process according to claim 13, wherein the papery article is selected from graphic paper, office communication paper, packaging paper, board, card, hygiene paper and specialty paper.

24. The process according to claim 13, wherein the papery article is a packaging material for the food sector.