TREATMENT OF CELLULOSIC MATERIALS

Description

Technical field

[0001] The present invention is within the field of paper or board or similar cellulosic materials used as wrapping and packaging materials. More specifically the invention relates to a novel process for the treatment of such a cellulosic material to impart thereto water vapour barrier characteristics to make said material useful as a wrapping and packaging material for moisture sensitive articles, e.g. copying or printing quality papers, certain foodstuffs or similar. At the same time, however, the treated material shows repulpability properties of such a nature that it can be recycled as a waste material to a paper or board production line without prior screening or sorting being necessary.

[0002] The invention also relates to the material treated by said process as well as to the coating agent utilized in said treatment process.

Background of the invention

[0003] Although the present invention is generally useful in many applications it will in the following be described with reference to the wrapping of fine quality papers.

[0004] Fine paper qualities have to be wrapped in a wrapping material having such a moisture or water vapour impermeability that the wrapped papers remain more or less at a constant relative humidity for lengthy periods of time. Today the dominating wrapping material for this purpose is a composite material where polyethylene has been extruded onto paper.

[0005] However, with the advent of regulations or laws being passed on the subject of preservation of our natural resources, highlighting especially on recycling of paper and similar materials, polyethylene-extruded paper is said to be far from an ideal material. Thus, polyethylene-extruded paper can be rendered recyclable only after difficult, time and money consuming screening processes. A direct recycling of said wrapping material is, thus, impossible as the use thereof in a paper manufacturing process will indispensably give a paper quality that is deficient or said use may even cause a production failure.

[0006] Therefore, recently new wrapping materials have been suggested, but up to now no real alternative to polyethylene-coated or -extruded paper has been found on the market, the main reasons being that new processes for obtaining water-vapour impermeable paper are complex, time consuming and/or expensive or that a proper balance between water vapour permeability characteristics and recyclability properties has not been possible to reach.

[0007] As will be described below, the present invention is based on the use of a poly(vinyl alcohol)-based material as a coating on paper inspite of the fact that poly(vinyl alcohol) is known to be a water sensitive material. In this context it should be noted that although poly(vinyl alcohol) has been suggested for use in connection with coatings of the type referred to said poly(vinyl alcohol) has been utilized merely as a primer coating or similar, the proper water vapour barrier characteristics being accomplished by means of additional coating materials deposited on top of said poly(vinyl alcohol). As prior art relating to poly(vinyl alcohol) as minor ingredients only of surface coating materials for paper materials within this technical field EP-A-393 451 and EP-A-487 497 can be referred to. Furthermore, AT-A-395 617 discloses a process for imparting vapour barrier and repulpability properties to a cellulosic material by means of poly(vinyl alcohol) with added particulate fillers and curing agents. The process includes several coating steps and the curing temperature is between 120°C and 170°C.

Description of the invention

[0008] By the present invention it has unexpectedly become possible to utilize a poly(vinyl alcohol)-based composition as a surface coating for paper and similar materials to obtain a wrapping of the type referred to above, which wrapping has a unique combination of water vapour barrier and recyclability properties. Thus, inspite of the fact that poly(vinyl alcohol) is per se a water sensitive substance, the paper treated with said poly(vinyl alcohol) coating composition has been made moisture vapour impermeable to such a degree that it matches polyethylene-coated paper as to water vapour permeability and can still be recycled to a conventional pulper of a paper production plant for direct use therein. This is indeed non-obvious as these two properties are of a contradictory nature.

[0009] More specifically, according to a first aspect of the invention there is provided a new process for the treatment of a cellulosic material, such as selected from the group consisting of paper, board, paperboard and similar materials, to impart thereto water vapour and aroma barrier characteristics while retaining the repulpability properties thereof so as to enable a direct recycling to a pulper of a paper, board or paperboard production plant or line, said process being characterized by:

A) coating said material, on one or both sides thereof, with a coating agent, preferably in the form of an aqueous slurry, comprising

a) 30-70% by weight of poly(vinyl alcohol), and

b) 70-30% by weight of a non-spherical particulate filler, preferably having an aspect ratio, i.e. a ratio of average particle diameter to thickness, of at least 2:1, and

c) 0.2 - 7% by weight of at least one cross-linking agent for said poly(vinyl alcohol) selected from the group consisting of ammonium-zirconium carbonate, borax and boric acid, said percentage being calculated as solids contents based on the combined weights of a) + b), and

B) subjecting the coated material to a drying and curing operation at a temperature of at most 105°C so as to form a cross-linked barrier layer onto said material, said barrier layer being the sole or major water vapour and aroma barrier-forming layer on the cellulosic material.

[0010] Thus, by using poly(vinyl alcohol) at a percentage of at least 30% by weight and a non-spherical filler at a percentage of at least 30% by weight as well as a cross-linking agent at a percentage of 7% by weight and by curing the coated material so as to cross-link said poly(vinyl alcohol), generally at a moderate temperature, a coated material is obtained where said coating agent is the sole or major water vapour barrier-forming agent and outstanding water vapour barrier properties are still accomplished. In addition thereto, the new barrier-provided material is directly repulpable without any other equipment than those conventional pulpers which are indigenous to the paper or board industry.

[0011] The cellulosic base material to be barrier coated in accordance with the present invention can be any type of material suitable as a wrapping or packaging material. For instance it can be any type of bleached or unbleached kraft or sulphite paper which has been refined in such a way that it achieves high tensile, tearing and bursting strengths.

[0012] As concerns the major ingredients of the coating agent, i.e. ingredients a) and b), the following details can be given.

[0013] The poly(vinyl alcohol) can generally be selected among such qualities which are suitable for coating purposes. Furthermore, it should be highly hydrolyzed and have a low to medium molecular weight. Preferably this means a degree of hydrolysis within the range of 95-100%, more preferably 97-100%, for instance 98% or around 98%, expressed as mole %. The molecular weight or mass is preferably within the range of 16 000-200 000, more preferably 16 000-75 000, most preferably 16 000-47 000, g/mole, the molecular weights being determined according to the GPC (Gel Permeation Chromatography) method.

[0014] A molecular weight of at most 47 000 is preferable for instance for the reason that it enables low viscosities of the coating agent to be attained (e.g. below 5 000 cps/Brookfield, 100 rpm), which in turn makes it possible to carry out the coating process with a great precision.

[0015] It is also possible to mix two or more poly(vinyl alcohols) together, such as one with a molecular weight close to the lower limit (e.g. 16 000-30 000) and the other with a molecular weight more close to the upper limit (e.g. 130000-200 000), for instance in a ratio of from 8:2 to 6:4, depending on the desired viscosity of the coating agent. One specific example of a preferable embodiment in this respect is one with a molecular weight of about 16 000 and a degree of hydrolysis of about 98%, and the other with a molecular weight of about 145 000 and a degree of hydrolysis of about 99%.

[0016] Although generally a homopolymer of vinyl alcohol is referred to, the invention does not exclude the possibility of copolymerizing said vinyl alcohol with a minor amount of any monomer that is copolymerizable therewith without substantially altering the favourable barrier properties aimed at.

[0017] The term "major water vapour and aroma barrier-forming agent" in connection with the coating agent means that said poly(vinyl alcohol) based coating agent represents more than 50% by weight, preferably more than 75% by weight and more preferably more than 85% by weight of the total weight of the coating materials used to cover the cellulosic material.

[0018] The particulate filler for the poly(vinyl alcohol) can be of any type or nature that is generally used in connection with poly(vinyl alcohol) or any other particulate filler normally used for pigment coating. A major feature of the filler to be used in the present invention is, however, that it is non-spherical, i.e. it has to be elongated, flat, flaky or similar, as it seems that some kind of mutual over-lapping arrangement of the filler is needed for obtaining the required moisture vapour transmission rate. In other words the aspect ratio, which is defined as the ratio of average particle diameter to thickness of the filler, should preferably be at least 2:1. The upper limit of said aspect ratio should not be critical to the invention, but generally said ratio is within the range of 2:1-300:1. According to a preferable embodiment thereof said ratio is 3:1-300:1, more preferably 5:1-300:1, and most preferably 5:1-200:1.

[0019] According to a preferable embodiment of the invention the filler is a mineral pigment, especially preferred pigments being kaolin, talcum, chalk and marble (CaCO₃), the two latter in a chemically precipitated form (such as precipitated CaCO₃).

[0020] The cross-linking agent c) includes an agent that can create covalent bonds between the linear chains of the poly(vinyl alcohol) to form a network structure as well as an agent that can create such a network by means of ionic bonds. Thus, said network formation can also be referred to as gelling or similar.

[0021] The first group of cross-linking agent creating covalent bonds is generally selected among agents which are previously known per se as cross-linking agents for poly(vinyl alcohol), especially as thermal cross-linking agents which do not react to any appreciable extent until the temperature is raised above room-temperature. This means that generally they are added together or admixed with the coating agent a) + b).

[0022] A cross-linking agent of this type for use in connection with the present invention is ammonium-zirconium carbonate.

[0023] The other type of cross-linking agent is, thus, an agent selected from the group consisting of salt or ionic bond-forming substances which immobilize or gel the poly(vinyl alcohol) coating agent.

[0024] An example of this type of cross-linking agent is borax, e.g. in the form of a diluted aqueous solution (typically a 4% solution).

[0025] Another agent of said second type is boric acid (a typical acid being a 1% aqueous solution thereof) which is added together with a) and b) but for said agent it will generally be necessary to adjust the pH of the coating agent to an alkaline or basic one, e.g. at least pH 8, before the curing step B) is performed, to initiate the curing or gelling reaction. Such a pH adjustment can e.g. be made by the addition of a base, such as Na₂HPO₄, or by using a buffer or acid-base system with a volatile acid, such as acetic acid, which is evaporated before step B) is finalized.

[0026] A combination of the two types of cross-linking agents is of course also possible.

[0027] As has been described above the mutual composition of the coating agent concerning poly(vinyl alcohol) to filler is essential to the invention, which means that said ingredients a) and b) are present in a weight ratio of from 3:7 to 7:3. A more preferred composition as to said two ingredients is when a) is present at 40-60, especially 42-58, % by weight and b) is present at 60-40, especially 58-42, % by weight, calculated as defined above, i.e. as solids contents based on the combined weights of a) + b).

[0028] The cross-linking agent c) is, as was mentioned above, present in an amount of 0,2 to 7% by weight, also based on the solids contents and calculated on the combined weights of a) + b). On the same basis the percentage of c) is preferably 0,5-6% by weight and most preferably 1-5% by weight.

[0029] Thus, by using the cross-linking agent at the above-defined percentages a proper curing or cross-linking degree can be obtained, which satisfies the water vapour barrier characteristics as well as the repulpability characteristics referred to above.

[0030] Step B) of the process according to the present invention is preferably of a short duration, depending on the temperature, and often the duration or contact time is not more than 10 secs, very often at most 5 secs, preferably at most 2 secs and most preferably at most 1 sec.

[0031] The above-mentioned duration or contact times are related to a drying or curing temperature that is rather moderate, preferably at most 120°C, more preferably at most 105°C. By temperature is hereby meant the temperature which the coated material reaches during said drying and curing step. Preferably said temperature is within the range of about 70-120°C, more preferably 70-105°C, such as 75-100°C.

[0032] The coating agent to be used in step A) is generally prepared in the form of an aqueous slurry in a conventional manner, e.g. by first dissolving the poly(vinyl alcohol) in water to a 20-50% solution and then adding the filler and the cross-linking agent to the formation of a slurry having a solids content of 20-50% by weight.

[0033] Since, as was mentioned above, the poly(vinyl alcohol)-based coating used in the process claimed is the major or only water vapour and aroma barrier, the coating operation per se can be performed in a simple way and with a non-complex equipment. However, if said coating operation will not be sufficient for certain intended purposes, it may well be repeated one or more additional times with the same or similar coating agent. Within the scope of the invention it is also possible to coat one or both sides of the substrate material.

[0034] At all events, the coating or combined coatings of step A) are preferably performed to a dry surface weight of 2-30 g/m², especially 3-15 g/m², per side of said coating agent.

[0035] Generally this means that a coated end product is manufactured, which has a water vapour transmission rate of at most 25 g/m² and 24 h, according to the test method referred to below. Preferably a product is manufactured having a water vapour transmission rate of at most 20, more preferably at most 15, especially 7-15, g/m² and 24 h, according to the same test method.

[0036] The test method used for determining the water vapour transmission rate is TAPPI Standard T 448 m-49, "Water Vapour Permeability of Paper and Paper Board".

[0037] The process according to the present invention is preferably performed as a continuous operation where a running web of said material is surface coated in step A), and then immediately dried and cured in step B). This operation can be performed in a step separate from the manufacture of the paper web or in direct connection therewith.

[0038] According to a second aspect of the invention a novel coated material obtainable by the above-defined process is provided.

[0039] More specifically the coated material according to the present invention comprises a cellulosic based substrate, such as selected from the group consisting of paper, board, paperboard and similar materials, said material having water vapour and aroma barrier characteristics as well as repulpability properties, which coated material is characterized in that the coating layer(s) thereof has (have) been obtained essentially from a coating agent comprising:

a) poly(vinyl alcohol)

b) a non-spherical particulate filler, preferably having an aspect ratio, i.e. a ratio of average particle diameter to thickness, of at least 2:1, and

c) a cross-linking agent for said poly(vinyl alcohol) selected from the group consisting of ammonium-zirconium carbonate, borax and boric acid,

a) and b) being present in a weight percentage of 30-70% and 70-30%, respectively, and c) being present in a weight percentage of 0,2 to 7%, all percentages being calculated as solids contents based on the combined weights of a) + b), said coating agent forming a cross-linked layer having water vapour and aroma barrier characteristics as well as repulpability properties.

[0040] As concerns preferable embodiments of said coated material according to the invention reference is made to the preferable embodiments of the process according to the invention, which are also applicable to said novel coated material.

[0041] A third aspect of the invention relates to the coating agent per se, i.e. a coating agent for a cellulosic based material, such as selected from the group consisting of paper, board, paperboard and similar materials to impart thereto water vapour and aroma barrier characteristics while retaining the repulpability properties thereof, the characterizing features of said coating agent being the same as have been defined above in connection with the process aspect of the invention.

[0042] Finally, according to a fourth aspect of the invention a novel use is provided, viz. the use of a coated material whenever prepared as defined in connection with the process aspect of the invention or as defined in connection with the coated material aspect of the invention, as a waste paper to be recycled directly to a pulper of a paper, board or paperboard production line.

[0043] In this context the term "directly" generally means that there is no separation or other pretreatment step needed before the coated material can be utilized in a pulper of such a line.

Figure

[0044] A schematic illustration of a suitable equipment for performing the process according to the invention, and which was in fact used in the working examples described below, is shown in the accompanying drawing.

[0045] Said figure shows a supply roll 1 for a paper substrate from which a web 2 of said paper substrate is unwound. Said runnig web 2 then passes via guide rolls 3 through a coating station 4, which is a common flexography coater with three coating rolls 5 and a backing roll 6 and over three separate heated drying cylinders 7 and via further guide rolls 3 onto a rewind roll 8. Close to the first one of the three heated cylinders 7 there is also an IR drier 9.

[0046] Thus, the coating process comprises applying the coating agent from the coating station 4 onto the running web 2 and curing the coated substrate by means of the IR drier 9 and post-drying the same by means of the drying cylinders 7, the coated and cured product then being wound onto the rewind roll 8.

EXAMPLES

[0047] The following examples serve to illustrate preferable embodiments of the invention. All examples were carried out using a coating equipment of the type illustrated in the figure.

[0048] The production speed was 75 m/min; the IR-drier increased the web-temperature from 22°C to 75°C; the web temperature after the third contact drier was 103°C; the temperature of the coating agent was 35°C; the solids content of the coating agent was 33%; and the water vapour transmission rates were determined according to TAPPI T 448-m-49 (6 hours at 23°C, 50% humidity). All percentages are % by weight.

EXAMPLE 1

[0049] The coating agent was the following mixture:

44% of poly(vinyl alcohol) (PVA) (98% degree of hydrolysis and 27 000 as molecular weight).

56% of kaolin, delaminated

4.5% of ammonium zirconium carbonate (AZC).

[0050] The coating weight was 5.0 g/m² on one side of a sulfite-based, bleached paper with a grammage of 95 g/m². The water vapour transmission rate was 8.2 g/m². 24 h.

EXAMPLE 2

[0051] Same as Example 1 except a PVA with a molecular weight of 16 000.

[0052] The coating weight was 5.2 g/m².

[0053] Water vapour transmission rate: 7.9 g/m². 24 h.

EXAMPLE 3

[0054] Coating agent:

30% of PVA (98%, 27 000 Mw)

70% of kaolin, delaminated

4.5% of AZC

   Paper: as in Example 1
   Coating weight: 5.0 g/m²
   Water vapour transmission rate: 19.7 g/m² . 24 h.

EXAMPLE 4

[0055] Paper: as in Example 1
   Coating agent:

60% of PVA (98%, 27 000 Mw)

40% of kaolin, delaminated

4.5% of AZC

   Coating weight: 5.2 g/m²
   Water vapour transmission rate: 16.5 g/m² . 24 h

EXAMPLE 5

[0056] Paper: as in Example 1
   Coating agent:

35% of PVA (98%, 27 000 Mw)

9% of PVA (99%, 145 000 Mw)

56% of kaolin, delaminated

4.5% of AZC

   Coating weight: 5.1 g/m²
   Water vapour transmission rate: 7.2 g/m² . 24 h.

[0057] Coated papers as produced in Examples 1-5 were tested for their repulpability in a laboratory desintegrator. After 30 000 revolutions hand sheets were formed and the fiber uniformity was evaluated visually. All papers proved to be fully repulpable.

Claims

1. A process for the treatment of a cellulosic material, preferably selected from the group consisting of paper, board, paperboard and similar materials, to impart thereto water vapour and aroma barrier characteristics while retaining the repulpability properties so as to enable a direct recycling thereof to a pulper of a paper, board or paperboard production line, characterized by:

A) coating said material, on one or both sides thereof, with a coating agent, preferably in the form of an aqueous slurry, comprising

a) 30-70% by weight of poly(vinyl alcohol), and

b) 70-30% by weight of a non-spherical particulate filler, preferably having an aspect ratio, i.e. a ratio of average particle diameter to thickness, of at least 2:1, and

c) 0,2- 7% by weight of at least one cross-linking agent for said poly(vinyl alcohol) selected from the group consisting of ammonium-zirconium carbonate, borax and boric acid, said percentage being calculated as solids contents based on the combined weights of a) + b), and

B) subjecting the coated material to a drying and curing operation at a temperature of at most 105°C so as to form a cross-linked barrier layer onto said material, said barrier layer being the sole or major water vapour and aroma barrier-forming layer on the cellulosic material.

2. A process according to claim 1, characterized in that a) is present at 40-60, preferably 42-58, % by weight and b) is present at 60-40, preferably 58-42, % by weight, in said coating agent.

3. A process according to any one of claims 1 and 2, characterized in that c) is used at 0.5-6% by weight, preferably 1-5% by weight.

4. A process according to any one of claims 1-3, characterized in that the aspect ratio of the filler is within the range of 2:1-300:1, preferably 3:1-300:1, and most preferably 5:1-300:1, e.g. 5:1-200:1.

5. A process according to claim 4, characterized in that the filler is a mineral pigment, preferably selected from the group consisting of kaolin, talcum, chalk and marble.

6. A process according to any one of claims 1-5, characterized in that the cross-linking agent is borax.

7. A process according to any one of claims 1-5, characterized in that the cross-linking agent is boric acid.

8. A process according to claim 7, characterized by bringing said coating agent to a basic pH of at least 8 before or in step B).

9. A process according to any one of claims 1-8, characterized in that the poly(vinyl alcohol) has a degree of hydrolysis within the range of 95-100%, preferably 97-100%, such as around 98%.

10. A process according to any one of claims 1-9, characterized in that the poly(vinyl alcohol) has a molecular weight of 16 000-200 000, preferably 16 000-75 000 and especially 16 000-47 000, g/mole.

11. A process according to any one of claims 1-10, characterized in that in step B) the coated material is subjected to the drying and curing operation for a contact time of at most 10 seconds, e.g. at most 5 seconds, preferably at most 2 seconds and most preferably at most 1 second.

12. A process according to any one of claims 1-11, characterized in that the temperature of the coated material is within the range of 70-105°C, such as 75-100°C.

13. A process according to any one of claims 1-12, characterized by preparing the aqueous slurry to be used in step A) by first dissolving the poly(vinyl alcohol) in water to a 20-50% solution and then adding the filler and the cross-linking agent to the formation of a slurry having a solids content of 20-50% by weight.

14. A process according to any one of claims 1-13, characterized in that it is performed as a continuous operation, preferably in one single operation, where a running web of said material is surface coated according to A) and then immediately dried and cured according to B).

15. A process according to any one of claims 1-14, characterized by performing the coating to a dry surface weight of 2-30 g/m², preferably 3-15 g/m², per side of said coating agent.

16. A process according to any one of claims 1-15, characterized by manufacturing a coated end product having a water vapour transmission rate of at most 25, preferably at most 20 and most preferably at most 15, g/m² and 24 h, e.g. 7-15 g/m² and 24 h, according to test method TAPPI T448-m-49.

17. A coated cellulosic material, preferably selected from the group consisting of paper, board, paperboard and similar materials, characterized in that the coating layer(s) thereof has (have) been obtained essentially from a coating agent comprising:

a) poly(vinyl alcohol)

b) a non-spherical particulate filler, preferably having an aspect ratio, i.e. a ratio of average particle diameter to thickness, cf at least 2:1, and

c) a cross-linking agent for said poly(vinyl alcohol), selected from the group consisting of ammonium-zirconium carbonate, borax and boric acid,

   a) and b) being present in a weight percentage of 30-70% and 70-30%, respectively, and c) being present in a weight percentage of 0,2-7%, all percentages being calculated as solids contents based on the combined weights of a) + b), said coating agent forming a cross-linked layer having water vapour and aroma barrier characteristics as well as repulpability properties.

18. A coated material according to claim 17, characterized in that said coating agent is as defined in any one of claims 2-7 and 9-10.

19. A coated material according to any one of claims 17 and 18, characterized in that it has a water vapour transmission rate as defined in claim 16.

20. A coating agent for a cellulosic material, pre ferably selected from the group consisting of paper, board, paperboard and similar materials, to impart thereto water vapour and aroma barrier characteristics while retaining the repulpability properties thereof, characterized in that it is as defined in any of claims 1-7 and 9-10.

21. Use of a coated material whenever prepared as defined in any one of claims 1-16 or as defined in any one of claims 17-19, as a waste paper to be recycled directly to a pulper of a paper, board or paperboard production line.

Ansprüche

1. Verfahren zur Behandlung von Zellulosematerial, vorzugsweise ausgewählt aus Papier, Pappe, Karton und ähnlichen Materialien, wodurch diesem Wasserdampf- und Aromasperreigenschaften verliehen werden. während die Wiederauflösungseigenschaften erhalten bleiben, so daß direktes Rezyklieren davon zu einem Pulper einer Papier-, Pappe- oder Kartonfertigungsstraße möglich ist, dadurch gekennzeichnet, daß:

A) das Material auf einer oder beiden Seiten davon mit einem Beschichtungsmittel, umfassend

a) 30 bis 70 Gew.% eines Poly(vinylalkohol)s und

b) 70 bis 30 Gew.% eines nicht-sphärischen teilchenförmigen Füllstoffs, vorzugsweise mit einem Seitenverhältnis, d. h. einem Verhältnis von mittlerem Teilchendurchmesser zu Dicke, von wenigstens 2:1 und

c) 0,2 bis 7 Gew.% wenigstens eines Vernetzungsmittels für Poly(vinylalkohol), ausgewählt aus Ammoniumzirkoniumcarbonat, Borax und Borsäure, wobei der Prozentsatz als Feststoffgehalt, bezogen auf die vereinigten Gewichte von a) und b) berechnet wird,

vorzugsweise in Form einer wässerigen Aufschlämmung beschichtet wird, und

B) Trocknen und Härten dcs beschichteten Materials bei einer Temperatur von höchstens 105 °C, um so eine vernetzte Sperrschicht auf dem Material zu erzeugen, wobei die Sperrschicht die einzige oder hauptsächliche Schicht auf dem Zellulosematerial ist, die eine Wasserdampf- und Aromasperre bildet.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß a) mit 40 bis 60, vorzugsweise 42 bis 58 Gew.% und b) mit 60 bis 40, vorzugsweise 58 bis 42 Gew.% im Beschichtungsmittel vorhanden ist.

3. Verfahren nach einem der Ansprüche 1 und 2, dadurch gekennzeichnet, daß c) mit 0,5 bis 6 Gew.%, vorzugsweise 1 bis 5 Gew.% eingesetzt wird.

4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das Seitenverhältnis des Füllstoffs im Bereich 2:1 bis 300: 1, vorzugsweise 3:1 bis 300:1 und am stärksten bevorzugt 5:1 bis 300:1, z. B. 5:1 bis 200:1, liegt.

5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß der Füllstoff ein Mineralpigment, vorzugsweise ausgewählt aus Kaolin, Talkum, Kreide und Marmor, ist.

6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Vernetzungsmittel Borax ist.

7. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Vernetzungsmittel Borsäure ist.

8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß das Beschichtungsmittel vor oder in Schritt B) auf einen basischen pH-Wert von wenigstens 8 gebracht wird.

9. Verfahren nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß der Poly(vinylalkohol) einen Hydrolysegrad im Bereich von 95 bis 100%, vorzugsweise 97 bis 100%, wie um 98%, aufweist.

10. Verfahren nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, daß der Poly(vinylalkohol) ein Molekulargewicht von 16000 bis 200000, vorzugsweise 16000 bis 75000 und insbesondere 16000 bis 47000 g/mol besitzt.

11. Verfahren nach einem der Ansprüche 1 bis 10, dadurch gekennzeichnet, daß in Schritt B) das beschichtete Material mit einer Kontaktzeit von höchstens 10 Sekunden, z. B. höchstens 5 Sekunden, vorzugsweise höchstens 2 Sekunden und am stärksten bevorzugt höchstens 1 Sekunde getrocknet und gehärtet wird.

12. Verfahren nach einem der Ansprüche 1 bis 11, dadurch gekennzeichnet, daß die Temperatur des beschichteten Materials im Bereich von 70 bis 105 °C, wie 75 bis 100 °C, liegt.

13. Verfahren nach einem der Ansprüche 1 bis 12, dadurch gekennzeichnet, daß die in Schritt A) einzusetzende wässerige Aufsehlämmung hergestellt wird, indem zuerst der Poly(vinylalkohol) in Wasser zu einer 20 bis 50%igen Lösung aufgelöst wird und dann der Füllstoff und das Vernetzungsmittel zur Erzeugung einer Aufschlämmung mit einem Feststoffgehalt von 20 bis 50 Gew.% zugegeben werden.

14. Verfahren nach einem der Ansprüche 1 bis 13, dadurch gckennzeichnet, daß es in kontinuierlicher Arbeitsweise, vorzugsweise in einem einzigen Arbeitsgang, durchgeführt wird, wobei eine durchlaufende Papierbahn des Materials gemäß A) oberflächenbeschichtet und unmittelbar danach gemäß B) getrocknet und gehärtet wird.

15. Verfahren nach einem der Ansprüche 1 bis 14, dadurch gekennzeichnet, daß das Beschichten bis zu einem Oberflächentrockengewicht des Beschichtungsmittels von 2 bis 30 g/m². vorzugsweise 3 bis 15 g/m² je Seite durchgeführt wird.

16. Verfahren nach einem der Ansprüche 1 bis 15, dadurch gekennzeichnet, daß ein beschichtetes Endprodukt mit einer Wasserdampfdurchlässigkeit gemäß dem Testverfahren TAPPI T448-m-49 von höchstens 25, vorzugsweise höchstens 20 und am stärksten bevorzugt höchstens 15 g/m² und 24 h, z. B. 7 bis 15 g/m² und 24 h, hergestellt wird.

17. Beschichtetes Zellulosematerial, vorzugsweise ausgewählt aus Papier, Pappe, Karton und ähnlichen Materialien, dadurch gekennzeichnet, daß dessen Beschichtung(en) im wesentlichen mit einem Beschichtungsmittel, umfassend:

a) Poly(vinylalkohol)

b) einen nicht-sphärischen teilchenförmigen Füllstoff, vorzugsweise mit einem Seitenverhältnis, d. h. einem Verhältnis von mittlerem Teilchendurchmesser zu Dicke, von wenigstens 2:1, und

c) ein Vernetzungsmittel für den Poly(vinylalkohol), ausgewählt aus Ammoniumzirkoniumcarbonat, Borax und Borsäure,

erhalten wurde(n), wobei a) und b) in einem Anteil von 30 bis 70 Gew.% bzw. 70 bis 30 Gew.% vorhanden sind, und c) in einem Anteil von 0,2 bis 7 Gew.% vorhanden ist, wobei alle prozentualen Anteile als Feststoffgehalte, bezogen auf die vereinigten Gewichte von a) + b) berechnet werden, wobei das Beschichtungsmittel eine vernetzte Schicht mit Wasserdampf- und Aromasperreigenschaften ebenso wie mit Wiederauflösungseigenschaften erzeugt.

18. Beschichtetes Material nach Anspruch 17. dadurch gekennzeichnet, daß das Beschichtungsmittel wie in einem der Ansprüche 2 bis 7 und 9 bis 10 definiert ist.

19. Beschichtetes Material nach einem der Ansprüche 17 und 18, dadurch gekennzeichnet, daß es eine Wasserdampfdurchlässigkeit, wie in Anspruch 16 definiert, aufweist.

20. Beschichtungsmittel für ein Zellulosematerial, vorzugsweise ausgewählt aus Papier, Pappe, Karton und ähnlichen Materialien, womit diesem Wasserdampf- und Aromasperreigenschaften verliehen werden, während dessen Wiederauflösungseigenschaften beibehalten werden, dadurch gekennzeichnet, daß es wie in einem der Ansprüche 1 bis 7 und 9 bis 10 definiert ist.

21. Verwendung eines beschichteten Materials, das wann auch immer, wie in einem der Ansprüche 1 bis 16 definiert oder wie in einem der Ansprüche 17 bis 19 definiert, hergestellt wurde, als Altpapier, das direkt zu einem Pulper einer Papier-, Pappe- oder Kartonfertigungsstraße rezykliert werden soll.

Revendications

1. Procédé pour le traitement d'une matière cellulosique, choisie de préférence dans le groupe constitué par du papier, du carton dur, du carton souple et des matériaux semblables, pour lui conférer des caractéristiques de barrière à la vapeur d'eau et aux arômes tout en retenant les propriétés d'aptitude à la retrituration de façon à permettre un recyclage direct de celle-ci à un triturateur d'une chaîne de fabrication de papier, de carton dur ou de carton souple, caractérisé par les étapes consistant :

A) à revêtir ladite matière, sur l'un de ses côtés ou sur les deux, avec un agent de revêtement, de préférence sous la forme d'une suspension aqueuse, comprenant

a) 30 à 70 % en poids d'un poly(alcool vinylique), et

b) 70 à 30 % en poids d'une charge particulaire non sphérique, ayant de préférence un rapport d'aspect, c'est-à-dire le rapport diamètre à épaisseur moyens d'une particule, d'au moins 2:1, et

c) 0,2 à 7 % en poids d'au moins un agent de réticulation pour ledit poly(alcool vinylique); choisi dans le groupe constitué par le carbonate d'ammonium et de zirconium, le borax et l'acide borique, ledit pourcentage étant calculé en teneur en matières solides sur la base des poids combinés de a) + b), et

B) à soumettre la matière revêtue à une opération de séchage et de durcissement, à une température d'au plus 105 °C de façon à former une couche barrière réticulée sur ladite matière, ladite couche barrière étant la couche unique ou majeure formant une barrière à la vapeur d'eau et aux arômes sur la matière cellulosique.

2. Procédé selon la revendication 1, caractérisé en ce que a) est présent à raison de 40 à 60, de préférence 42 à 58, % en poids et b) est présent à raison de 60 à 40, de préférence 58 à 42, % en poids, dans ledit agent de revêtement.

3. Procédé selon l'une quelconque des revendications 1 et 2, caractérisé en ce que c) est utilisé à raison de 0,5 à 6 % en poids, de préférence 1 à 5 % en poids.

4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que le rapport d'aspect de la charge est dans la gamme de 2:1 à 300:1, de préférence 3:1 à 300:1, et de toute préférence 5:1 à 300:1, par exemple 5:1 à 200:1.

5. Procédé selon la revendication 4, caractérisé en ce que la charge est un pigment minéral, choisi de préférence dans le groupe constitué par le kaolin, le talc, la craie et le marbre.

6. Procédé selon l'une quelconque des revendications 1 à 5, caractérisé en ce que l'agent de réticulation est le borax.

7. Procédé selon l'une quelconque des revendications 1 à 5, caractérisé en ce que l'agent de réticulation est l'acide borique.

8. Procédé selon la revendication 7, caractérisé en ce qu'on porte ledit agent de revêtement à un pH basique d'au moins 8 avant ou pendant l'étape B).

9. Procédé selon l'une quelconque des revendications 1 à 8, caractérisé en ce que le poly(alcool vinylique) a un degré d'hydrolyse dans la gamme de 95 à 100 %, de préférence 97 à 100 %, comme d'environ 98 %.

10. Procédé selon l'une quelconque des revendications 1 à 9, caractérisé en ce que le poly(alcool vinylique) a un poids moléculaire de 16 000 à 200 000, de préférence 16 000 à 75 000 et spécialement 16 000 à 47 000 g/mole.

11. Procédé selon l'une quelconque des revendications 1 à 10, caractérisé en ce que dans l'étape B) la matière revêtue est soumise à l'opération de séchage ct de durcissement pendant un temps de contact d'au plus 10 secondes, par exemple d'au plus 5 secondes, de préférence au plus 2 secondes et de toute préférence au plus 1 seconde.

12. Procédé selon l'une quelconque des revendications 1 à 11, caractérisé en ce que la température de la matière revêtue est dans la gamme de 70 à 105 °C, comme 75 à 100 °C.

13. Procédé selon l'une quelconque des revendications 1 à 12, caractérisé par la préparation de la suspension aqueuse à utiliser dans l'étape A) en dissolvant d'abord le poly(alcool vinylique) dans de l'eau pour former une solution à 20 à 50 % puis en ajoutant la charge et l'agent de réticulation jusqu'à la formation d'une suspension ayant une teneur en matières solides de 20 à 50 % en poids.

14. Procédé selon l'une quelconque des revendications 1 à 13, caractérisé en ce qu'il est mis en oeuvre sous la forme d'une opération continue, de préférence en une opération unique, où une nappe de ladite matière défilant est revêtue en surface selon A) puis immédiatement séchée et durcie selon B).

15. Procédé selon l'une quelconque des revendications 1 à 14, caractérisé par la réalisation du revêtement à un poids de surface sec de 2 à 30 g/m², de préférence 3 à 15 g/m², par côté, dudit agent de revêtement.

16. Procédé selon l'une quelconque des revendications 1 à 15, caractérisé par la fabrication d'un produit final revêtu ayant une vitesse de transmission de vapeur d'eau d'au plus 25, de préférence d'au plus 20 et de toute préférence d'au plus 15 g/m² et 24 h, par exemplc 7 à 15 g/m²et 24 h, d'après la méthode d'essai TAPPI T448-m-49.

17. Matière cellulosique revêtue, choisie de préférence dans le groupe constitué par du papier, du carton dur, du carton souple et des matériaux semblables, caractérisée en ce que la (les) couche(s) de revêtement de celle-ci est (sont) obtenue(s) essentiellement à partir d'un agent de revêtement comprenant :

a) un poly(alcool vinylique)

b) une charge particulaire non sphérique, ayant de préférence un rapport d'aspect, c'est-à-dire le rapport diamètre à épaisseur moyens d'une particule, d'au moins 2:1, et

c) un agent de réticulation pour ledit poly(alcool vinylique), choisi dans le groupe constitué par le carbonate d'ammonium et de zirconium, le borax et l'acide borique,

   a) et b) étant présents en un pourcentage en poids de 30 à 70 % et de 70 à 30 %, respectivement, et c) étant présent en un pourcentage en poids de 0,2 à 7 %, tous les pourcentages étant calculés en teneurs en matières solides sur la base des poids combinés de a) + b), ledit agent de revêtement formant une couche réticulée ayant des caractéristiques de barrière à la vapeur d'eau et aux arômes ainsi que des propriétés d'aptitude à la retrituration.

18. Matière revêtue selon la revendication 17, caractérisée en ce que ledit agent de revêtement est tel que défini dans l'une quelconque des revendications 2 à 7 et 9-10.

19. Matière revêtue selon l'une quelconque des revendications 17 et 18, caractérisée en ce qu'elle a une vitesse de transmission de vapeur d'eau telle que définie dans la revendication 16.

20. Agent de revêtement pour une matière cellulosique, choisie de préférence dans le groupe constitué par du papier, du carton dur, du carton souple et des matériaux semblables, pour lui conférer des caractéristiques de barrière à la vapeur d'eau et aux arômes tout en retenant ses propriétés d'aptitude à la retrituration, caractérisé en ce qu'il est tel que défini dans l'une quelconque des revendications 1 à 7 et 9-10.

21. Utilisation d'une matière revêtue lorsqu'elle est préparée comme le définit l'une quelconque des revendications 1 à 16 ou comme le définit l'une quelconque des revendications 17 à 19, en tant que vieux papiers à recycler directement à un triturateur d'une chaîne de fabrication de papier, de carton dur ou de carton souple.

Drawing