Method of manufacturing of a foam-formed cellulosic fibre-material, a bulk sheet and a laminated packaging material comprising the cellulosic fibre-material

Abstract

The invention relates to a method for manufacturing a foam-formed cellulosic fibre-material comprising coarse cellulosic fibres a cellulose reinforcement fraction. Furthermore, the invention relates to a foam-formed cellulosic fibre-material, a cellulose bulk sheet for a packaging material and a laminated packaging material comprising the foam-formed cellulosic fibre-material.

Claims

1. A method for manufacturing a foam-formed cellulosic fibre-material, comprising: (a) providing an aqueous foam comprising a gas dispersed as bubbles in an aqueous phase, wherein said aqueous phase comprises a surfactant; (b) adding cellulose fibres to the aqueous foam, thus forming a fibrous foam composition, wherein the cellulose fibres are added as coarse cellulosic fibres, selected from the group consisting of mechanical, chemi- mechanical, thermomechanical, chemithermomechanical pulp (CTMP) fibres and Neutral Sulfite Semi Chemical (NSSC) pulp fibres, in an amount of 85% to 97%, by weight of the total amount of cellulose fibres, wherein the coarse cellulosic fibres have a Canadian Standard Freeness value of 400-750 ml; and a cellulose reinforcement fraction in an amount of 6% to 12%, by weight of the total amount of cellulose fibres, wherein the cellulose reinforcement fraction is a heavily refined fibre component selected from the group consisting of heavily refined chemical pulp having a SR range higher than SR°80, heavily refined chemithermomechanical pulp (hrCTMP) having a CSF less than 70 mL, and a combination thereof, wherein the fibrous foam composition comprises a starch in an amount of 1 to 4% based on dry solids content of the fibrous foam composition; (c) distributing the fibrous foam composition onto a substrate or into a mould; and (d) reducing the amount of water in the distributed fibrous foam composition to obtain the foam-formed cellulosic fibre-material in its final shape, wherein the foam-formed material produced by the method has a density of 200 to 450 kg/m.sup.3 and a delamination strength of at least 100 J/m.sup.2.

2. The method according to claim 1, wherein the cellulose reinforcement fraction has been treated with a cationic dry strength agent, wherein the cationic dry strength agent is selected from the group consisting of cationic starch (CS), cationic polyacrylamide (CPAM), glyoxalated polyacrylamid (GPAM) and polyaminoamid-epichlorohydrine (PAE).

3. The method according to claim 1, wherein the cellulose reinforcement fraction has been treated with polyelectrolyte multilayering method (PEM), resulting in three polymer layers, wherein a first polymer layer on the cellulose reinforcement fraction is a cationic polymer; a second polymer layer on the cellulose reinforcement fraction is an anionic polymer; and wherein a third polymer layer on the cellulose reinforcement fraction is a cationic polymer.

4. The method according to claim 1, further comprising (e) mixing the coarse cellulosic fibres and the cellulose reinforcement fraction to form a cellulose fibre mixture; wherein the mixing is performed before the adding of the cellulose fibres to the aqueous foam.

5. The method according to claim 1, wherein the surfactant is sodium dodecyl sulphate (SDS) or sodium lauryl ether sulfate (SLES).

6. The method according to claim 1, further comprising: (f) adding a retention system to the fibrous foam composition obtained in (b), wherein the retention system comprises polyethylene oxide (PEO) and tannic acid (TA).

7. The method according to claim 1, further comprising: (g) performing hydrophobic sizing by adding alkylketene dimer (AKD), alkyl succinic anhydride (ASA) and/or rosin sizing directly before (c).

8. The method according to claim 1, further comprising: (h) performing hydrophobic sizing by applying sizing agent by spray on the distributed fibrous foam composition obtained in (c), wherein the sizing agent comprises alkylketene dimer (AKD) and/or alkyl succinic anhydride (ASA).

9. The method according to claim 1, wherein the density of the fibrous foam composition before reduction of an amount of water is about 600-750 kg/m.sup.3, and wherein the average bubble size is 100 μor below.

10. The method according to claim 1, wherein the cellulose reinforcement fraction has been treated with polyelectrolyte multilayering method (PEM), resulting in three polymer layers, wherein a first polymer layer on the cellulose reinforcement fraction is a cationic polymer comprising cationic starch (CS); a second polymer layer on the cellulose reinforcement fraction is an anionic polymer comprising carboxy methyl cellulose (CMC), anionic starch (AS) or anionic polyacrylamide (APAM); and wherein a third polymer layer on the cellulose reinforcement fraction is a cationic polymer comprising cationic starch (CS).

11. The method according to claim 1, wherein the coarse cellulosic fibres are CTMP fibres, wherein the cellulose reinforcement fraction is highly refined hardwood fibres.

12. The method according to claim 1, wherein the cellulose reinforcement fraction is heavily refined chemithermomechanical pulp (hrCTMP) having a CSF less than 70 mL.

13. The method according to claim 1, wherein the cellulose reinforcement fraction is a heavily refined fibre component having an average fibre diameter of about 20 to 30 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

(2) FIG. 1 shows the effect of retained cationic starch content (as weight/weight %) on delamination resistance. The diamonds represent a foam density <500 kg/m.sup.3 and low amount (300 g/t of dry solids content both CPAM and microparticle) of retention agent (ra), × denote a foam density of 700 kg/m.sup.3 and low amount (300 g/t of dry solids content both CPAM and microparticle) of retention agent, the triangles represent a foam density of 700 kg/m.sup.3 and high amount (550 g/t of dry solids content both CPAM and microparticle) of retention agent and the squares represents a foam density of 700 kg/m.sup.3 and wherein no starch was used at all. The target starch content, where 1% corresponds to a dose of 10 kg/t, 2% corresponds to a dose of 20 kg/t, and so forth is shown for each data point.

(3) FIG. 2 shows the delamination resistance for different materials produced according to the present invention, compared to a reference sample not comprising the cellulose reinforcement fraction. The data is collected from five separate pilot-machine trials. Hr stands for highly refined fibres (the same as hrHW—hardwood fibres) in Table 1 and RA stands for retention agent. The black bars represent experiments where the foam density was 700 kg/m.sup.3 and the white bars represent experiments where the foam density was between 500 kg/m.sup.3.

(4) FIG. 3 shows how the delamination resistance depends on the hrHW content. The diamonds represent a foam density <500 kg/m.sup.3 and low amount (300 g/t of dry solids content both CPAM and microparticle) of retention agent (ra), × denotes a foam density of 700 kg/m.sup.3 and low amount (300 g/t of dry solids content both CPAM and microparticle) of retention agent, the triangles represent a foam density of 700 kg/m.sup.3 and high amount (550 g/t of dry solids content both CPAM and microparticle) of retention agent, the squares represent a foam density of 700 kg/m.sup.3 and wherein no starch was used at all and o denotes a foam density of 700 kg/m.sup.3 and high amount (550 g/t of dry solids content both CPAM and microparticle) of retention agent. The target starch content, where 1% corresponds to a dose of 10 kg/t, 2% corresponds to a dose of 20 kg/t, and so forth is shown for each data point.

(5) FIG. 4 shows how the z-residual strain depends on the sheet density. The filled diamonds represent a foam density <500 kg/m.sup.3 and 10% (weight/weight) hrHW, the triangles denote a foam density of 700 kg/m.sup.3 and 12% hrHW and the diamonds represent a foam density of <500 kg/m.sup.3 and 12% MFC (microfibrillated cellulose). MFC has an average fibre length of 100 nm to 0.1 mm and fibre diameter of 3 to 50 nm.

(6) FIG. 5 shows the mini-Cobb 30-values for materials produced according to the present invention using different sizing agents. Sufficient sizing has been achieved when the mini-Cobb 30-value is less than 50 g/m.sup.2 (the dotted line in the diagram). A is anionic while B and C are cationic products. Other details of the formulations are not known.

(7) FIG. 6 shows a flowchart of a method according to the present invention.

(8) FIGS. 7a and 7b are cross-sectional views of laminated packaging materials according to the present invention.

(9) FIG. 8 shows the turbidity of DDJ filtrates of pulp suspensions wherein different retention systems were used at different concentrations of SDS. Filled diamonds represent pulp suspensions to which no retention system was added; filled squares represent pulp suspensions to which CPAM was added before the microparticles were added; filled triangles represent pulp suspensions to which PEO was added before TA was added; and × denote pulp suspensions to which TA was added before PEO was added. The dose of each retention aid component, i.e. CPAM, microparticles, PEO and TA was 0.3 kg/t of dry pulp.

(10) FIG. 9 shows the turbidity of DDJ filtrates of pulp suspensions with different retention systems at high shear forces.

DEFINITIONS

(11) Fibre coarseness is defined as weight per fibre length and is normally expressed in units of mg/m or g/m. Coarseness depends on fibre diameter, cell wall thickness, cell wall density and fibre cross section. The coarseness value has a great influence on the paper structure. A high coarseness value indicates a thick fibre wall, giving stiff fibres unable to collapse. Thin walled fibres with low coarseness value give flexible fibres and a denser sheet. The coarser the fibres, the stronger and stiffer they will be. Coarser fibres make bulky paper. This is important for packaging paper and less important for printing paper. Coarse fibre will, however, cause an uneven paper surface.

(12) A “foam-formed cellulosic fibre-material”, “foamed cellulose material”, “foamed cellulose” or a “foam-formed material of cellulose fibres” is a material that provides volume or thickness to an article from the material, without necessarily adding a lot of weight, i.e. by having a higher bulk property than conventional fibrous papers or paperboards.

(13) “Bulk property” is the inverse of the material's density. In other words, foamed cellulose is a fibrous material, with tunable density, that can be manufactured by a foam forming process.

(14) “Delamination” is when a material separates into different layers. Delamination is a mode of failure for fibrous materials like paperboard where fibre layers and fibres separate leading to significant loss of mechanical properties.

(15) The “delamination strength” can be characterised by the internal bond strength of the material and can be determined by for example the Huygen Internal Bonding Energy testing device which follows TAPPI T569 and provides a value of J/m.sup.2. Paper materials are subjected to out-of-plane loading in many converting operations, such as in printing, creasing, lamination, splicing and folding, which may result in delamination. The “internal bond strength”, measured by a Scott Bond type test, may correlate with the “delamination resistance” of the paper material in such converting operations.

(16) “Internal bond strength” (J/m.sup.2) is defined as the energy per unit in-plane area required to delaminate a paper material in the through-thickness direction, i.e. z-direction, in a Scott Bond type test.

(17) “Compression strength” of board is the maximum compressive force per unit width that a test piece can withstand until the onset of failure. It is expressed in kilonewtons per metre (kN/m). Measurement standard ISO 9895:2008.

(18) “Canadian Standard Freeness” (“CSF” or “freeness”) of pulp is designed to give a measure of the rate at which a dilute suspension of pulp (3 g of pulp in 1 L of water) may be drained (standard ISO 5267-2:2001).

(19) “Compression strength ratio” MD/CD is determined as the ratio of machine directional (MD) compression strength to cross directional (CD) compression strength, which are both measured according to standard ISO 9895:2008

(20) “Z-strength” is thickness directional tensile strength, measurement standard ISO 15754.

(21) “Edge wicking index” (EWI) is defined as the amount of test solution absorbed by the edges of a test piece under the specific testing conditions. The result is given in kg/m.sup.2.

(22) The Schopper-Riegler test (see ISO 5267) is designed to provide a measure of the rate at which a dilute suspension of pulp may be dewatered. It has been shown that the drainability is related to the surface conditions and swelling of the fibres, and constitutes a useful index of the amount of mechanical treatment to which the pulp has been subjected.

(23) “Grammage” is expressed as weight per unit in-plane area of paper materials and is measured in g/m.sup.2.

(24) The “ply grammage” of a layer in a laminated packaging material is the weight per unit area in g/m.sup.2 of that layer.

(25) “Thickness” is the distance between two flat surfaces, which are placed on each side of a paper material and subjected to a pressure of 100 kPa. It is expressed in micrometers (μm).

(26) A “bulk layer” or a “core layer” is a layer that contributes largely to the mechanical rigidity and strength properties and dimensional stability properties, of a laminated material. This is normally the thickest layer of a laminated (sandwich) material, without necessarily being the strongest or densest material. In a stiff sandwich material, there is often a “bulky” distancing or spacer layer in the center, between two flange layers, i.e. facing layers, which contribute to the total stiffness of the construction by their Young's modulus and/or higher tensile stiffness properties. The grammage of the bulk layer is assessed in accordance with ISO 536. The bulk layer thickness can be assessed by microscopy or by a ply grammage method, as discussed herein below. The grammage of a bulk layer in a laminated packaging material is calculated as the difference between the total grammage and the ply grammages of the polymer and aluminium foil layers.

(27) In this context, “low density” in connection with a cellulose material or bulk material for a laminated packaging material for liquid packaging, means a density which is lower than that of normal paperboard or carton for that purpose, i.e. ultimately lower than 900 kg/m.sup.3, such as lower than 700 kg/m.sup.3, such as from 100 to 600 kg/m.sup.3, such as from 100 to 500 kg/m.sup.3, such as from 200 to 500 kg/m.sup.3, such as lower than 450 kg/m.sup.3.

(28) A “thickness” referring to the packaging material, a packaging container, or layers thereof, is, unless otherwise defined, determined by microscopy, for example by a suitable microscope such as those marketed under the name Olympus, for example BX51.

(29) “Liquid or semi-liquid food” generally refers to food products having a flowing content that optionally may contain pieces of food. Dairy and milk, soy, rice, grains and seed drinks, juice, nectar, still drinks, energy drinks, sport drinks, coffee drinks, tea drinks, coconut water, wine, soups, jalapenos, tomatoes, sauce (such as pasta sauce), beans and olive oil are some non-limiting example of food products contemplated.

(30) “Aseptic” in connection with a packaging material and packaging container refers to conditions where microorganisms are eliminated, in-activated or killed or where the level of microorganisms is significantly reduced. Examples of microorganisms are bacteria, spores and yeasts. Generally, an aseptic process is used when a product is aseptically packed in a packaging container.

(31) The term “heat-sealing” refers to the process of welding one surface of a thermoplastic material to another thermoplastic surface. A heat-sealable material should, under the appropriate conditions such as when sufficient heating and pressure are applied, be able to generate a seal when pressed against and in contact with another suitable thermoplastic material. Suitable heating can be achieved by induction heating or ultrasonic heating or other conventional contact or convection heating means, e.g. hot air.

(32) Methods

(33) Grammage (in (g/m.sup.2) was determined using a version of ISO 536 having less samples and smaller samples size. Circular test pieces with an in-plane area of 100±1 cm.sup.2 were produced using a cutting device (disc cutter or punch). Five circular test pieces were each weighed on a balance reading to an accuracy of ±0.5%. The grammage of each test piece was calculated by dividing the mass of the test piece by the in-plane area.

(34) Thickness (the distance (in μm) between the two flat surfaces, which are placed on each side of the paper material and subjected to a pressure of 100 kPa) was determined using a version of ISO 534 wherein fewer samples were analysed, but several spots per sample were measured. Circular test pieces with an in-plane area of 100±1 cm.sup.2 were produced using a cutting device (disc cutter or punch). Five test pieces were produced for each sample. For each test piece, the thickness was measured as dead-weight micrometer in accordance with ISO 534 in three different spots and the test piece thickness was evaluated as the average value of these three measurements.

(35) Tensile properties were determined using a version of ISO 1924:3. Test piece of a given dimension, 15 mm wide and long enough (≥150 mm) were strained to break at a constant rate of elongation (100 mm/min) using a testing machine that automatically records both the tensile force and the elongation. Tests were done in machine direction (MD) and cross direction (CD) separately. 10 test pieces were used for each sample in accordance with ISO 1924:3.

(36) Compression strength (short-span compression test (SCT)) was determined using a version of ISO 9895 wherein 10 samples in each directions were tested. A test piece, 15 mm wide and >70 mm long was clamped between two clamps, spaced 0.70 mm apart, which were forced towards each other until a compressive failure occurred. The maximum force was measured and the compression strength was calculated. The paper or board was tested on 10 test pieces in MD and 10 test pieces in CD direction separately.

(37) Edge wicking in lactic acid 23° C., 1 h was determined as follows. Water resistant tape (e.g. Scotch EI-tape no. 5 from 3M) was applied on both sides of the sample (wrinkles were avoided). A cutting device was used to cut out 1 set of 5 test pieces, 75 mm (CD)×25 mm (MD), and the pieces were marked accordingly. The 5 pieces were weighed together, and the result was rounded down/up to the nearest mg. 1% (volume/volume) lactic acid solution was prepared and poured into a vessel (247×395 mm) to a level of 10±1 mm. The vessel was of plastic or stainless steel. The temperature in the vessel was held at 23° C.±1° C. The test pieces were removed after 1 h±2 min and placed between two blotting papers. A brass-roller (face width 200 mm and weight 10±0.5 kg) was moved once back and forth over the test pieces between the blotting papers without applying any extra pressure. The test pieces were weighed together, and the result was rounded down/up to the nearest mg. The edge wicking index was calculated as

(38) $\mathrm{EWI}=\frac{\left(\mathrm{Total}\mathrm{weight}\mathrm{after}\mathrm{test}\right)-\left(\mathrm{Total}\mathrm{weight}\mathrm{before}\mathrm{test}\right)}{\left(\mathrm{Board}\mathrm{thickness}\right)\times \left(\mathrm{Total}\mathrm{circumference}\mathrm{of}\mathrm{the}\mathrm{sample}\right)}$

(39) Delamination resistance was determined as follows. A test piece was cut out and mounted between a steel anvil and an L-shaped aluminium bracket using double-sided adhesive tape. A specific pressure was subjected to the metal plates to ensure repeatable bonding and a pendulum was released from an initial horizontal position and allowed to hit the L-shaped bracket when reaching its vertical position, causing the test piece to delaminate. The consumed energy by the delamination process was evaluated by recording the peak excess swing of the pendulum. The internal bond strength was calculated as the recorded energy divided by the in-plane area of the test piece.

(40) Residual z strain (the residual strain in z-direction (thickness direction)) after a specified load on the sample was determined with a Lloyd LR10K loading device. The sample area exposed to loading was 15.2 cm.sup.2, with a circular radius of 22 mm. The board sample was placed onto the loading table and a maximum pressure of 2 MPa (force 3041 N) was applied on the sample for a period of 1 s. The relative change was calculated with the initial thickness of the sheet (measured with a separate standard device) and the reading of displacement sensor showing the absolute thickness change, i.e. permanent thickness reduction, from the compression. The residual strain was determined as the point where there was no additional clear drop in the loading force. At least five parallel measurements were carried out in separate points. The residual strain measurement can also be made with sequential loadings, reporting the magnitude of thickness change after each loading.

(41) Mini-Cobb 30 measurement was determined as follows. A dry specimen was weighed and placed under a cylinder with an internal diameter of 3 cm. 7 ml of water was poured into the cylinder. After 30 s the water was poured out. The excess water was removed from the specimen using plotting paper and roller. The specimen was weighed while wet and the amount of water absorbed by 1 m.sup.2 of specimen material was calculated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(42) FIG. 1 shows the effect of retained cationic starch content on delamination resistance. Cationic starch (the same for all samples and dosed at the proportion showed next to the marker) was added to increase the strength and was added to all samples apart from the zero-reference (filled square). Includes also foam density (500 kg/m.sup.3 and 700 kg/m.sup.3) and retention agent dose (CPAM+microparticle, either 300 g/t+300 g/t (low ra) or 550 g/t+550 g/t (high ra)). As can be seen in FIG. 1 and Table 1, in foam forming with SDS, the retained cationic starch content is higher with increased foam density. In low foam density areas, with 40 kg/t dose (i.e. starch content target of 4%), the retained starch content was 1% whereas in the higher foam density, it was 1.7% with constant retention aid dose. In the experiments, the dose of cationic starch was 10, 20 or 40 kg/t (i.e. targeting starch contents of 1%, 2% and 4%, respectively) (dose marked next to each ticker), while the retained amount was 0.2% (weight/weight) to 1.0% for the samples produced in 500 kg/m.sup.3 foam density and 1.7% and 2.8% for samples produced in 700 kg/m.sup.3 foam density. The difference between the two latter values originates in the retention chemical dosage: 2.8% starch content is achieved with 550 g/t dose (high ra) of both CPAM and microparticle, whereas the content of 1.7% was achieved with doses of 300 g/t (low ra (retention aid dose)), respectively. These results show that a way to increase the delamination resistance with the selected strength additives may include the use of higher foam density and increased dosages of retention chemicals.

(43) TABLE-US-00001 TABLE 1 Retained starch hrHW content Sheet density Delamination z-residual strain content (%) (%) (kg/m.sup.3) resistance (J/m.sup.2) (%) EWI (kg/m2) Fd <500 kg/m.sup.3, ra low, 0.15 10 264 74 12.1 0.30 starch dose 10 kg/t Fd <500 kg/m.sup.3, ra low, 0.36 10 272 108 9.9 0.89 starch dose 20 kg/t Fd <500 kg/m.sup.3, ra low, 1.00 10 282 120 8.9 1.06 starch dose 40 kg/t Fd 700 kg/m.sup.3, ra low 1.70 12 285 171 6.9 0.66 starch dose 40 kg/t Fd 700 kg/m.sup.3, ra high 2.80 12 309 216 5.9 0.38 starch dose 40 kg/t Fd 700 kg/m.sup.3, no starch 0.00 12 289 117 n/a 0.22 Fd 700 kg/m.sup.3, ra high, n/a 12 325 198 6.2 0.40 hrHW 6% starch dose 40 kg/t Data showing the effect of foam density (Fd), cationic starch content, refined reinforcement fibre (hrHW) content and retention aid dose (ra) on sheet density, delamination resistance and z-directional residual strain. The main component of the furnish was coarse CTMP (CSF 620 to 650 ml) combined with highly refined hardwood (hrHW) to generate higher strength.

(44) FIG. 2 shows the delamination resistance for different materials produced according to the present invention, compared to a reference sample not comprising the cellulose reinforcement fraction (i.e. 100% CTMP). These experiments demonstrate that by adding a cellulose reinforcement fraction to the coarse cellulosic fibres (here CTMP), the delamination strength increases from about 75 J/m.sup.2 to about 120 J/m.sup.2. The addition of cationic starch as a dry strength agent further increases the delamination strength to 125 J/m.sup.2. By increasing the foam density (Fd) from 500 kg/m.sup.3 to 700 kg/m.sup.3, the delamination strength increased to about 160 J/m.sup.2. By increasing the amount of retention agent (both CPAM and microparticles) from 300 g/t to 550 g/t, the delamination strength increased to approximately 180 J/m.sup.2. Further improvement was generated by increasing the wet press load from 800 to 1000 kN/m, and the delamination strength reached values over 200 J/m.sup.2. Wet press load is an operation where water is removed from the fibre web by the means of mechanical compression. Water removal pressure is primarily influenced by the linear load (kN/m) that describes the applied force per pressing width (cross direction width).

(45) As can be seen in FIG. 3, higher foam density, due to improved fines retention, contributes to higher delamination strength of a sheet of the foam-formed cellulose material. Used additions of cationic starch were 1, 2 or 4% of the dry solids flow (respective to 10, 20 and 40 kg/t). It is also shown that, in comparison to lower foam density (500 kg/m.sup.3), higher foam density (700 kg/m.sup.3) generates higher delamination resistance with lower proportion of highly refined fibre component. Thus, Less hr is needed when density is higher and amount of retention aid is high, as well as retained content of starch.

(46) FIG. 4 shows that the Z-directional residual strain is lower for sheets with higher fines (i.e. hrHW) (and starch) retention. With MFC (which is an example of a material which is not according to the invention, denoted by an open diamond), the z-residual strain was significantly higher. With MFC containing sample, the fibre furnish consisted of 60% CTMP (CSF 600 ml), 20% of unrefined softwood kraft and 12% of microfibrillated cellulose (MFC).

(47) FIG. 5 shows the mini-Cobb 30-values for packaging materials produced according to the present invention using different sizing agents. Sufficient sizing has been achieved when the mini-Cobb 30-value is less than 50 g/m.sup.2 (the dotted line in the diagram). Surfactants are known to disturb AKD-sizing. Furthermore, the negative charge of SDS probably neutralizes cationically stabilized AKD. Thus, SDS interferes with adsorption of AKD particles onto fibre surfaces. Moreover, the AKD-product has to be compatible with the entire foam forming chemistry. For these reasons, the AKD-product was selected carefully by large laboratory tests. The tests were done using CTMP 600 mL as fibre furnish. The retention system (CPAM+microparticle) as well as cationic starch addition promoted sizing and together with them the Fennosize KD 364 AKD-product achieved the sufficient sizing level. Thus, a preferred AKD-product is of high cationicity. The reason for the compatibility of Fennosize KD 364 and the foam forming chemistry could be the proportionally high cationic charge in stabilization system of AKD. Sizing was defined to be successful if the mini-Cobb 30-value was 50 g/m.sup.2 or lower (dotted line in FIG. 5). Longer delay of AKD in foam was found to decrease the efficiency of sizing and thus the sizing agent was fed into the foam just before the head box in the pilot machine.

(48) FIG. 6 shows a flowchart illustrating one embodiment of the method according to the invention.

(49) 1: Air

(50) 2: Surfactant

(51) 3: Cellulose fibre (such as coarse CTMP)

(52) 4: Cellulose reinforcement fraction (such as highly refined hardwood)

(53) 5: Foam generation, In a separate unit (such as a tank)

(54) 6: Fibre furnish mixing

(55) 7: Foam circulation

(56) 8: Headbox feed flow

(57) 9: Distribution onto a forming wire (headbox)

(58) 10: Forming section

(59) 11: Wet pressing

(60) 12: Drying

(61) 13: Foam formed cellulosic fibre material

(62) 14: Cationic starch

(63) 15: CPAM

(64) 16: Microparticle

(65) 17: AKD

(66) 18: As an alternative retention system instead of using CPAM and microparticle

(67) 18a: TA

(68) 18b: PEO

(69) Foam generation: surfactant and gas (air) is mixed with water, the foam density will be dependent on the amount of surfactant and mixing energy. Stock preparation: the fibre components are prepared to required freeness (by refining) and mixed to a stock. Foam and stock mixing: Foam and fibre stock are combined (fibrous foam). Headbox feed flow: Fibrous foam is pumped towards the headbox and the needed chemicals are added into the headbox feed flow. Dewatering including drying: Foam is removed in the forming section by using suction boxes and forming wire (fibres retain on the forming wire while the foam goes through the wire and to foam circulation), by mechanical compression in wet pressing and by heating up the moist board, e.g. with drying cylinders.

(70) FIG. 7a schematically shows a cross-section of an example of a laminated packaging material. The outer, décor-covering layer (21) is a polyolefin such as a suitable PE or PP or blends or copolymers thereof. The outer layer may be used to provide cover of a printed pattern, a hole and/or weakening (not shown in the figure) which is provided in the bulk layer (22), which layer is arranged on one side of the outer layer (21). Between the outer layer (21) and the bulk layer (22) an additional layer (27) of paper or cellulose is arranged. The bulk layer (22), on the side opposite the outer layer, has a laminate layer (23) selected from suitable polyolefins such as PE or PP or blends or copolymers thereof. The laminate layer provides adhesion to the oxygen barrier (24), which is arranged on the opposite side of the laminate layer (23). The barrier layer (24) provides the desired barrier such as oxygen, light, water and vapour barrier depending on the specific need determined by the product to be packed. The barrier layer can for example be an aluminium foil or a vapour deposited film, such as a metallized or vapour deposition coated film, such as a PECVD (plasma enhanced chemical vapour deposition) coated film. On the side opposite the laminate layer an adhesive polymer (25) is arranged on the barrier layer. The adhesive (25) may for example be applied by extrusion coating. When the barrier layer is aluminium foil the adhesive could be a suitable ethylene (meth)acrylic acid copolymer (E(M)AA) adhesive marketed under the tradename Primacor® or Nucrel®. On the side opposite the barrier layer, the adhesive is provided with a heat-sealable layer (26) such as a suitable polyolefin such as PE or PP or blends or copolymers thereof. The heat-sealable layer is the layer facing the product in the finished packed packaging container.

(71) FIG. 7b schematically shows a cross-section of a second example of a laminated packaging material. The outer layer (21) (to be directed towards the outside of a package made from the material) is a polyolefin such as a suitable PE or PP or blends or copolymers thereof. The outer layer may be used to provide cover for a printed pattern, a hole and/or weakening (not shown in the figure) which is provided in one or more of the other layers of the laminate. On one side of and adjacent the outer layer, a thin paper (27) of a surface weight of about 100 g/m2 or lower is arranged. The thin paper layer (27) is laminated to a bulk layer (22), opposite the outer layer, by an intermediate thermoplastic outer binding layer (28). The binding layer (28) may be selected from suitable polyolefins such as PE or PP or blends or copolymers thereof. The binding layer (28) binds the bulk cellulose layer (22) and the thin paper layer (28) together. The bulk layer (22), is further laminated to a laminate layer (23) of thermoplastic polymer, on the side of the bulk layer opposite the side laminated to the binding layer (28). The laminate layer (23) provides adhesion to an oxygen barrier layer (24), which is arranged on the opposite side of the laminate layer (23). The barrier layer (24) provides the desired barrier such as oxygen, light, water and vapour barrier depending on the specific need determined by the product to be packed. The barrier layer can for example be an aluminium foil or a vapour deposited film, such as a metallized or vapour deposition coated film, such as a PECVD coated film. On the side opposite the laminate layer an adhesive polymer (25) is arranged on the barrier layer. The adhesive (25) may for example be applied by extrusion coating. When the barrier layer is aluminium foil the adhesive could be a suitable ethylene (meth)acrylic acid copolymer (E(M)AA) adhesive marketed under the tradename Primacor® or Nucrel®. On the side opposite the barrier layer, the adhesive is provided with a heat-sealable layer (26) such as a suitable polyolefin such as PE or PP or blends or copolymers thereof. The heat-sealable layer is the layer facing the product in the finished packed packaging container.

(72) A packaging material according to the present invention may be a laminate packaging material which comprises an outermost thermoplastic, heat sealable décor-covering layer which on one side of the layer has a bulk layer comprising the foam-formed cellulosic fibre-material of the invention, which bulk layer on the side opposite the décor-covering layer has a laminate layer, said laminate layer, on the side opposite the bulk layer has an oxygen barrier, and said oxygen barrier, on the side opposite the laminate layer has a heat-sealable layer.

(73) Furthermore, a laminated packaging material may comprise a bulk layer having a density of less than 700 kg/m.sup.3 and comprising foam-formed cellulosic fibre-material according to the present invention. The packaging material further comprises an additional layer arranged by means of a binding layer, such as for example a thermoplastic polymer binding layer, such as a polyolefin-based polymer or copolymer binding layer, wherein the binding layer is arranged between the bulk layer and the additional layer. The additional layer has a decorative printed pattern arranged on the side opposite the binding layer. The bulk layer is provided with a barrier layer on the side opposite the binding layer. A barrier layer may be provided with a heat-sealable layer on the side opposite from the bulk layer. The outermost layer covering the printed decorative pattern is a polyolefin layer, such as an outermost heat-sealable polyolefin layer to be in contact with the surroundings of a packaging container, for example low density polyethylene (LDPE) or polypropylene. The outermost thermoplastic layer provides additional protection, e.g. moisture resistance and scratch/wear resistance, and stability to the packaging container.

(74) FIG. 8 shows the effect of the SDS surfactant amount on turbidity (value is relative to the amount of solids that went through the 100 mesh wire) for different retention systems. The pulp contained 80% chemithermomechanical pulp (CTMP) and 20% heavily refined hardwood pulp (hrHW). The turbidity was measured using nephelometer and the result is expressed as nephelometric turbidity units (NTU). High turbidity means low retention. The turbidity was the highest (=lowest retention), when retention aids were not used (filled diamonds). The amount of surfactant (SDS) had no effect on turbidity in these test points. With low SDS concentration, 0.1-0.2 g/l, the CPAM+MP system (filled squares) and the PEO+TA system (filled triangles) gave the same retention. However, when the SDS content was increased, the retention decreased (reflected by increased turbidity) for the CPAM+MP system and improved (reflected by decreased turbidity) for the PEO+TA system. In the case where TA was added before PEO (×), the retention was the best and was improved further with increasing the SDS content. The results showed that the non-cationic TA+PEO system is very efficient in foam forming, especially when the SDS content is high.

(75) As can be seen in FIG. 9, the TA+PEO-system seems to work better than the CPAM+MP system when the suspension is subjected to high shear forces. The experiment was performed similarly to the one of FIG. 2, but the stirrer 1 was set close to the wire 3 and the stirrer 1 was on with 1000 rpm during the filtration of foam.

(76) From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.