OR PAPERBOARD SUITED FOR USE AS PACKAGING MATERIAL FOR BEVERAGE CONTAINERS, AND PAPER OR PAPERBOARD PRODUCED BY THIS PROCESS

Field of the Invention

The present invention concerns a process for producing paper or paperboard, in particular label paper or paperboard suited for use as packaging material for beverage containers.

Background to the Invention

Label paper and paperboard suited for use as packaging material for beverage cans or bottles need to meet specific requirements to ensure full functionality of the packaging material (secondary packaging material holding typically 2 or more beverage containers such as cans or bottles together). The same applies for beverage labels intended to be glued on for example glass bottles.

The major requirement for label paper is resistance to humidity as often condensation may arise on the outer surface of beverage containers and beverage bottles are typically stored outdoors for extended periods of time. Clearly exposure to humidity should not affect the label quality in terms of printability nor damage the integrity of the label paper. Therefore high wet tear resistance and high wet tensile strength characteristics are a major requirement of label papers.

The same applies to paperboard designed to be used as packaging material. Such paperboard should meet strict requirements of wet tensile strength and wet tear resistance as the structural integrity of the packaging is to be ensured over the lifetime of such (secondary) packaging product, otherwise, the beverage container risk falling out of the packaging upon lifting it.

In industrial paper making, the use of wet-strength additives is well known and common additives used for this purpose include epichlorohydrin, melamine and urea formaldehyde.

Other typical additives to wood pulp in the paper making process include: i) dry strength additives such as cationic starch; ii) binders to increase printability such as carboxymethyl cellulose, iii) retention aids allowing binding filler materials to the paper such as polyacrylamide. The present invention addresses the above industry demands and provides a method allowing producing label paper and packaging paperboard having increased wet tensile strength and wet tear resistance of paper whilst maintaining the paper / paperboard basis weight constant.

Summary of the Invention

The present invention concerns a method for producing label paper or paper for corrugated board or folding carton for packaging of beverage containers, comprising the steps of:

feeding wood fiber pulps into a paper-making process;

forming a web mixture comprising the wood fiber pulp, a cationic polymer, an anionic polymer and a cationic starch;

characterized in that the cationic starch is added to the wood fiber pulp only after the addition of the anionic polymer and cationic polymer.

The cationic polymer is preferably added to the wood fiber pulp prior to the addition of the anionic polymer.

According to a preferred method of the invention, the cationic polymer comprises or is polyamideamine epichlorohydrin (PAE), which is added to the wood fiber pulp ranging between 1 and 40 kg/ton of wood fiber pulp (dry weight), preferably between 1,5 and 4,5 kg/ton of wood fiber pulp (dry weight).

The anionic polymer preferably comprises carboxy methyl cellulose (CMC), which may be added to the wood fiber pulp ranging between 0,1 and 10 kg/ton of wood fiber pulp (dry weight), preferably between 0,5 and 2 kg/ton of wood fiber pulp (dry weight).

The amount of cationic starch added to the wood fiber pulp preferably ranges between 1 and 40 kg/ton of wood fiber pulp (dry weight), more preferably between 5 and 15 kg/ton of wood fiber pulp (dry weight).

The method of the present invention preferably comprises providing a reaction time in between the addition of cationic polymer and the addition of anionic polymer to the web mixture of wood fiber pulp and/or providing a reaction time in between the addition of anionic polymer and the addition of cationic starch to the web mixture of wood fiber pulp.

The present invention also concerns a fiber product, comprising:

a fiber web; and

an at least partially cured resin composition, wherein, preferably prior to curing, the resin composition comprises:

a cationic polymer, preferably polyamide-epichlorohydrin (resin);

an anionic polymer, preferably carboxymethyl cellulose (resin); and

cationic starch, wherein the cationic starch is added after the addition of the anionic polymer and the cationic polymer.

In a preferred embodiment, the PEC polymer is a PEC resin.

In a preferred embodiment, the CMC polymer is a CMC resin.

Note that the term "curing" refers to the step of mixing the chemicals (resin composition) with the fibers (fiber web).

The fiber product according to the present invention preferably has a wet tensile strength of at least 7 N-rn/g (ISO3781:2011) and/or a wet tear resistance of at least 9 mN-m ² /g, preferably at least 9,5 mN-m7g (ISO1794:2012).

Brief description of the Drawings

Figures 1 and 2 illustrate two alternative process schemes of a method according to the present invention;

Figure 3 shows a set-up of a forming section of a paper making machine that can be used in a method according to the present invention;

Figures 4 to 10 show characteristics of specific fiber products made during trials of the method of the present invention.

The following components are shown in the drawings:

1: Wire pit 2: Front chest 3: Storage chest

4 : Headbox pump 5 : Screen 6 : Headbox 7: Fibers out of process 8: Fibers back to chest 9: Driven roll

10: Steering guide, tension measurement 11: H igh Vacuum

12: Vacuum box with friction measurement 13: Transfer vacuum box

14: Vacuum box 1 15: MB unit 16: Apron board

Description of a preferred Embodiment

The present invention concerns a method for producing label paper or corrugated board or folding carton for packaging of beverage containers, comprising the steps of:

feeding wood fiber pulps into a paper-making process;

forming a web mixture comprising the wood fiber pulp, a cationic polymer, an anionic polymer and a cationic starch;

characterized in that the cationic starch is added to the wood fiber pulp only after the addition of the anionic polymer and cationic polymer.

Figures 1 and 2 show two alternative preferred process schemes of a method according to the present invention, wherein in Figure 1, the chemicals in particular a cationic polymer (such as polyamideamine epichlorohydrin (PAE)); an anionic polymer (preferably comprising carboxy methyl cellulose (CMC)); and cationic starch are dosed online to the furnish between a front chest and a headbox. In Figure 2, the chemicals are dosed into the furnish sequentially yet in batch to a storage chest for the furnish, downstream of the front chest and the further downstream headbox.

Both process schemes were used for some trials of papermaking as discussed in more detail below.

RAW MATERIALS AND APPLICATION OF CHEMICALS

In the trials a furnish was used consisting of 80% 'southern pine, Alabama river' and 20% hardwood (birch). The pulp mixture was refined in one batch to freeness 495 ml (refined 1000 kg in Valmet, Rautpohja). Clearly, this furnish is only provided as an example, as numerous variants can be used without departing from the present invention.

The applied chemicals for the trials were: • PAE: Kymene 25 X-Cel (Solenis), 1.5, 3.0 or 4.5 kg/ton

• CMC: Finnfix 5 (CP Celco), 1.0 or 2.0 kg/ton

• Cationic Starch: Raisamyl 50021 (Chemigate), 5 or 15 kg/ton

• Retention aid: cationic polyacrylamide cPAM, Fennopol 3400 (Kemira), 200 g/ton

The chemicals were alternatively dosed online before the headbox (Fig. 1) or to the batch of furnish (Fig. 2).

In the online addition of the chemicals (Fig. 1) the interaction time between chemicals with each other and pulp mixture (or furnish) was some seconds whereas in batch dosage (Fig. 2) interaction time was several of minutes. In both cases the addition order of the chemicals was the same: 1. PAE (cationic polymer), 2. CMC (anionic polymer), 3. Cationic starch, 4. C-PAM (retention aid). The addition places and interaction time of additives before forming section (headbox) are presented in schematic layout pictures of online dosage (Fig. 1) and batch dosage (Fig. 2).

FORMING SECTION SET-UP AND RUNNING PARAMETERS

The pilot machine consists of an approach system with different kind of containers, a forming section (Fig. 3) that can be run in gap, hybrid or fourdrinier mode, and of a press section (not shown). In the trial, the pilot machine was run in the hybrid-forming mode at speed of 400 m/min. The consistency of furnish in headbox was 0.6%. The forming section configuration is shown in the figure 3.

The press section (Fig. 3) consisted of a 1-nip shoe press having a 350 mm extended nip. The nip pressure was varied at three different levels: 400, 800 and 1200 kN/m. After the wet pressing, the paper web was reeled and sheet samples were collected and dried in cylinder drier for the laboratory analyses.

MEASUREMENTS FROM WIRE WATER, FURNISH IN HEADBOX, WET WEB AND DRY SHEET Process conditions and process inputs were measured and recorded on-line in Wedge data acquisition system.

In order to make easier to view the results the geometric average values were calculated from the machine direct (MD) and cross direct (CD) data.

PRODUCED CONDITIONS

Different conditions were produced and sampled in the pilot machine trial. The total 22 trial points are listed in table 1. During the trials some trial points were rejected based on too low or high basis weight (missing numbers in the table 1).

TABLE 1 (table split in 2 parts)

FURNISH ANALYSES

The pH or conductivity of the furnish were not chemically modified in the trials. The pH of the furnish (measured from the headbox furnish sample) was between 7.7 and 8.1 in all trial points. It is known that PAE (wet strength agent) works best in neutral or alkaline pH area. Correspondingly, the conductivity was ~180 pS in all trial points. The pH and conductivity values were very close to what was applied in the preliminary laboratory scale trials.

The freeness of the original refined pulp mixture was 475 ml. In the figure 4 are presented freeness values measured from the furnish samples sampled from the headbox. On the online dosage day the freeness value was found to level to around 500 ml. In the first trial points (reference points only measured) 1 and 3 was probably less fines washed to the white water when the pulp was recycled in the pilot compared to the trial points from 5 to 15. In the batch dosing day (run through trials) was new fresh pulp and waters changed after running reference point 18 thus, the furnish base in 18 and 22 should be comparable. BETA- FORMATION In the figure 5 can be seen that the method of the present invention did not significantly influence the beta-formation values. The furnish consisted 80% of very long southern pine fibers thus the increased flocculation of the furnish would have seen in big increase of beta-formation value. Because the formation remained in same level no significant changes in coatability or printability of the product are expected when the new strength aid solution would be utilized in the paper / board mills.

DEWATERING CHARACTERISTICS

In the Figure 6 and 7 are presented dryness values after forming section and pressing section. Based on the online dosing trial points the method of the present invention had only minor effect on the total vacuum level in the forming section (samples from the batch dosing trial day were not taken). Correspondingly, the after wet pressing dryness was not significantly changed by the method according to the present invention in online dosing or in batch dosing trial points.

STRUCTURAL CHARACTERISTICS

The average grammage of the trial points (Figure 8) was in online dosing points 100 ± 5 g/m2. In the batch dosing trial points (run through trials) the grammage was lower 91 ± 3 g/m2. Additionally, a very low grammage trial point 53 g/m2 was executed. The low grammage trial point offers possibility to preliminary estimate the potential to reduce grammage with the method according to the present invention.

The method according to the present invention did not significantly influence on the bulk of the sheet. Thus, no change expected in the bending resistance of the product. Further in the batch dosage trial points the air permeance was not changed by the method according to the present invention.

WET SHEET STRENGTH PROPERTIES The conventional wet and dry strength solution: PAE with starch was found to increase wet tear index up to 250% compared to reference with no strength aids. The method according to the present invention increased wet tear resistance further by 28% (Fig 9). The results indicate that online dosage with short interaction times of the chemicals could be possible. Likewise, the method according to the present invention increased wet tensile index (16%). (Fig 10)

CONCLUSIONS

A method according to the present invention was found to have no or no significant influence on dewatering in forming and pressing sections. Additionally, sheet formation was not affected by the dosing strategy of the chemicals in accordance with the present invention. The results indicates that wet and dry strength aids could be applied in online or in batch dosing system.

Overall, in the pilot trials was demonstrated that method of the present invention could bring end product quality benefits over conventional strength aid solution. Wet strength properties of the sheet increased significantly (wet tear index +28% and wet tensile index +16%). Alternatively, the grammage could be decreased by 25% (from 95 to 70 g/m ) without decrease in wet tear strength.

The above characteristics of the, make the fiber product according to the present invention suitable for use as label paper or corrugated board or folding carton for packaging of beverage containers, where wet tear strength and wet tensile strength are key features.