WO2024126892A1

WO2024126892A1 - A surface size composition

Info

Publication number: WO2024126892A1
Application number: PCT/FI2023/050674
Authority: WO
Inventors: Asko Karppi; Matti Hietaniemi; Markus Korhonen; Mikko Virtanen; Jan‐Luiken HEMMES
Original assignee: Kemira Oyj
Priority date: 2022-12-12
Filing date: 2023-12-11
Publication date: 2024-06-20

Abstract

There is provided a surface size composition comprising interpenetrating polymer network of anionic polyacrylamide and starch, and zirconium carbonate. The surface size composition may further comprise an additional polymer such as starch and a hydrophobation agent. Additionally, there is provide use of the surface size composition for surface sizing paper or board.

Description

A SURFACE SIZE COMPOSITION

TECHNICAL FIELD

The present disclosure generally relates to a surface size composition. The disclosure relates particularly, though not exclusively, to a surface size composition comprising interpenetrating polymer network of anionic polyacrylamide and starch, and zirconium carbonate.

BACKGROUND

This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

Cost efficiency is one important aspect when lower grades of paper or board are produced. Typical measures for obtaining cost efficiency are, for example, reduction of the basis weight of produced paper or board, increase of the filler content in the stock, as well as use of cheap fibre raw materials. However, many of these measures may have a negative impact on the properties of the obtained paper or board product, especially on the strength properties of the paper or board product.

Compression strength and burst strength are important strength properties for paper and board, especially for board grades, which are used for packaging. Compression strength is often measured and given as Short-span Compression Test (SCT) strength, which may be used to predict the compression resistance of the final product, e.g. cardboard box. Burst strength indicates paper's or board's resistance to rupturing, and it is defined as the hydrostatic pressure needed to burst a sample when the pressure is applied uniformly across the side of the sample. Both the compression strength and burst strength are negatively affected when the amount of inorganic mineral fillers and/or recycled fibres in the stock is increased.

Various properties of paper or board can be improved by surface sizing. For example, surface sizing can be used to increase hydrophobicity of the paper/board surface or to improve the strength properties of paper/board. In conventional surface sizing the sizing solution is applied on the surface of the formed, at least partially dried fibre web. Typically surface size solutions comprise mainly starch, but they may also comprise synthetic polymers. The amount of synthetic polymer in the surface size solution has been limited by the increase of viscosity of the size solution. If the viscosity of the surface size solution becomes too high, it cannot be applied on the surface of the paper or board with present size applicators. Synthetic polymers are often also expensive, which make their use in low grade paper/board products uneconomical.

Consequently, there is a constant need and search for compositions, which are suitable for use in surface sizing and which can be used to increase the strength properties of the paper or board. Especially, there is a continuing need for novel cost-effective surface size alternatives for improving the strength properties of paper or board.

SUMMARY

The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and/or methods in the description and/or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention.

In a first aspect the present invention provides a surface size composition comprising interpenetrating polymer (IPN) network of anionic polyacrylamide (APAM) and starch, and zirconium carbonate.

In a second aspect the present invention provides use of the surface size composition according to the present invention for surface sizing of paper or board.

In a third aspect the present invention provides a method for producing paper or board, the method comprising: (a) treating a paper stock with a paper auxiliary, a filler, or both to obtain a treated paper stock; (b) draining the treated paper stock with sheet formation to obtain a paper web; and (c) applying on the paper web the surface sizing composition according to the present invention to obtain treated paper web; and (d) drying the treated paper web.

In a fourth aspect the present invention provides paper or board comprising the surface size composition according to the present invention or produced with the method according to the present invention. It has been surprisingly found that performance of interpenetrating polymer network (IPN) of anionic polyacrylamide (APAM) and starch can be improved by zirconium complexation which takes place inside board after sizing process.

It was also found that if pH of a surface size composition comprising IPN of APAM and starch is set slightly at acidic level, then complexation of APAM and zirconium does not significantly happen in the surface size composition. When pH of a board, such as RFC, is neutral it is enough to increase pH level to level in which complexation between carboxylates and zirconium occur. Crosslinking reaction of carboxylates and zirconium then happens after sizing process, and not earlier. Slightly acidic pH level of the surface size composition prevents viscosity increase due to zirconium complexation. It is important to prevent too early complexation as viscosity increase impacts negatively on penetration of the surface size composition, runnability and pick-up.

That is, zirconium reaction/bonding can be reduced in size press slurry by selecting pH to slightly acid, which allows reaction/bonding after the surface size composition is applied on the board.

Additionally, without bounding to any theory it is believed that the IPN of APAM and starch has less viscosity impact on surface size composition compared to surface size composition comprising APAM and starch as a mixture.

It has been additionally surprisingly found that addition of zirconium carbonate together with anionic polyacrylamide-starch interpenetrating polymer network (i.e., interpenetrating network of polyacrylamide and starch) clearly improves strength properties (SCT strength and burst strength) of liner compared to liner not containing said components. Additionally internal bond is improved. It was also found that the SCT strength is also improved at high humidity conditions, which is important for packages of frozen food, vegetables and fruits.

Additionally, it was found that the surface size composition of the present invention allows use of higher temperatures in paper or board manufacturing process compared to processes not using the surface size composition of the present invention

In addition, if sizing agents are also used, their efficiency is also improved significantly by the zirconium carbonate. The strength increase could be used to reduce starch consumption at size press which would give many benefits, such as less starch is needed, energy consumption is reduced and reduction of COD in wastewater. DETAILED DESCRIPTION

In a first aspect the present invention provides a surface size composition comprising interpenetrating polymer network (IPN) of anionic polyacrylamide (APAM) and starch, and zirconium carbonate.

An interpenetrating polymer network (IPN) is a polymer comprising two or more networks which are at least partially interlaced on a molecular scale. A mixture of two or more preformed polymer networks is not an IPN.

The interpenetrating polymer network of anionic polyacrylamide (APAM) and starch can be produced by polymerising acrylamide in presence of starch.

In one embodiment anionic amount in the APAM is from 3 mol-% to 30 mol-%, preferably 5 mol-% to 30 mol-%. The APAM can be linear or cross-linked.

In one embodiment the starch of the IPN is viscosity reduced starch.

By “viscosity reduced starch” is meant starch which structure, i.e. carbon chain, has been shortened so that the viscosity of the viscosity reduced starch is smaller than viscosity of native starch. The viscosity of the starch can be reduced by thermally or enzymatically or chemically converting starch.

Preferably the starch of the IPN is cationic starch, anionic starch, amphoteric starch or a mixture thereof.

In one embodiment the starch of the IPN has degree of cationic substitution (DS) 0.01 -0.1 and/or anionic substitution (DS) 0.005-0.05.

In one embodiment amount of the APAM of the IPN is from 50 wt-% to 95 wt-%, preferably from 70 wt-% to 90 wt-% based on total dry weight of the IPN material.

In one embodiment amount of the starch of the IPN is from 5 wt-% to 50 wt-%, preferably from 10 wt-% to 30 wt-%, based on total dry weight of the IPN material.

In one embodiment the zirconium carbonate comprises ammonium zirconium carbonate, potassium zirconium carbonate or a mixture thereof. In one embodiment the surface size composition further comprises an additional polymer comprising carbohydrate polymer, such as carboxymethylcellulose (CMC), guar gum, starch, preferably the additional polymer is a viscosity reduced starch, more preferably thermally or enzymatically converted starch, even more preferably enzymatically converted starch, further even more preferably converted with alpha amylase, further even more preferably converted with thermosensitive alpha amylase.

In one embodiment the surface size composition further comprises a hydrophobation agent, preferably acrylate esters, more preferably styrene acrylate, such as alkylketene dimer (AKD).

In one embodiment the hydrophobation agent is an acrylate based hydrophobation agent stabilized with anionic polymer, cationic polymer or amphoteric polymer.

In one embodiment pH of the surface size composition is slightly acidic, preferably the pH is 3.0-6.5, more preferably 3.5-6.0, even more preferably 5.0-6.0.

In one embodiment viscosity of the surface size composition is 100%-250% of the original viscosity of enzymatically degraded starch compared at sizing conditions of temperature and concentration.

The starch of the IPN material and the additional starch comprises any typical botanical starch such as potato starch, rice starch, wheat starch, corn starch, waxy corn starch, barley starch, tapioca starch, sweet potato starch, preferably potato starch.

In one embodiment the surface size composition is aqueous surface size composition.

In one embodiment amount of the IPN material in the surface size composition is from 1 wt- % to 8 wt-%, preferably from 1 wt-% to 5 wt-%, based on dry weight of the surface size composition. in one embodiment amount of the zirconium carbonate in the surface size composition is from 0.01 wt-% to 1.0 wt-%, preferably from 0.01 wt-% to 0.5 wt-%, more preferably from 0.05 wt-% to 0.2 wt-%, as zirconium dioxide (ZrC>2), based on dry weight of the surface size composition. In one embodiment amount of the additional polymer in the surface size composition is from 85 wt-% to 99 wt-%, preferably from 95 wt-% to 99 wt-%, based on dry weight of the surface size composition.

In one embodiment amount of the hydrophobation agent in the surface size composition is from 0.01 wt-% to 5 wt-%, preferably from 0.01 wt-% to 2 wt-%, based on dry weight of the surface size composition.

In one embodiment temperature of the surface size composition is at least 60 °C, such as 60 °C-95 °C, preferably at least 70 °C, such as 70 °C-95 °C.

In a second aspect the present invention provides use of the surface size composition of the present invention for surface sizing paper, board or the like.

The paper or board can be any suitable paper or board known in the art.

In one embodiment the board is selected from fluting, folding boxboard (FBB), white lined chipboard (WLC), solid bleached sulphate (SBS) board, solid unbleached sulphate (SUS) board and gypsum board.

In one embodiment the paper is selected from white top liner, liner including test liner, uncoated fine paper, label paper and release paper.

In a third aspect the present invention provides a method for producing paper and board, the method comprising: (a) treating a paper stock with a paper auxiliary, a filler, or both to obtain a treated paper stock; (b) draining the treated paper stock with sheet formation to obtain a paper web; and (c) applying on the paper web the surface sizing composition of the present invention to obtain treated paper web; and (d) drying the treated paper web.

In one embodiment the IPN and the zirconium carbonate of the sizing composition are applied sequentially on the paper web. In one embodiment the IPN is applied on the paper web prior applying the zirconium carbonate on the paper web. In one embodiment the zirconium carbonate is applied on the paper web prior applying the IPN on the paper web. Preferably, in sequential application, the IPN is applied on the paper web prior applying the zirconium carbonate on the paper web.

The paper stock used in the method may comprise virgin and/or recovered fibers. Any softwood or hardwood fiber typically used in the paper industry may be employed. Examples are unbleached chemical pulp, mechanical pulp including, for example, groundwood, thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), pressure groundwood, semichemical pulp, high-yield pulp, and refiner mechanical pulp (RMP), recycled fiber (RCF), such as corrugated cardboard (OCC).

The recycled fiber may be selected from old corrugated containerboard, mixed office waste, old newsprint, old magazines, double liner kraft, and any mixtures thereof. In one embodiment the recycled fiber material may be selected from old corrugated containerboard or mixed waste or old newsprint without deinking stage. Old corrugated containerboard (OCC) denotes recycled fiber material comprising corrugated containers, which have liners of test liner, jute or kraft, and the term may cover also double sorted corrugated containerboard (DS OCC). Mixed waste (MXW) denotes recycled mixture of recycled board, such as OCC, white lined chipboard and/or folding boxboard, and recycled paper, such as old newsprint, old magazines and/or office waste papers. Mixed office waste (MOW) denotes recycled fiber material mainly containing copying papers, printer papers and offset papers. Double lined kraft denotes recycled fiber material comprising clean sorted unprinted corrugated cardboard cartons, boxes, sheet or trimmings, e.g. of kraft or jute liner. White lined chipboard (WLC) denotes multiply board comprising deinked fiber material and/or undeinked recycled fiber material originating e.g. from OCC, mixed office waste or old newspapers (ONP) in or more of the layers.

The paper stock is preferably produced using wastepaper, which is used either alone or in a mixture with other fibrous materials.

In one embodiment temperature of the surface size composition of the present invention during the applying is at least 60 °C, such as 60 °C-95 °C, preferably at least 70 °C, such as 70 °C-95 °C.

The filler can be any suitable filler used in producing paper stock, such as s an inorganic pigment or a mixture of inorganic pigments.

The paper auxiliaries are for example, sizing agents, wet strength agents, dry strength agents, cationic or anionic retention agents based on synthetic polymers, dewatering agents, optical brighteners, defoamers, biocides, and paper dyes.

The sizing agents include alkylketene dimers (AKDs), alkenylsuccinic anhydrides (ASAs), and rosin size. The wet strength agents are synthetic dry strengtheners such as polyvinylamine, or natural dry strengtheners, such as starch.

The wet strength agents include polyamidoamide-epichlorohydrin (PAE).

The dry strength agents are synthetic cationic polymers such as polyvinylamines, glyoxylated polyacrylamides or low molecular weight cationic or amphoteric polyacrylamides or natural polymers such as cationic starch.

The retention aids comprise anionic microparticles (colloidal silica, bentonite), anionic polyacrylamides, cationic polyacrylamides, cationic starch, cationic polyethyleneimine, or cationic polyvinylamine.

Drainage takes place on the wire of the paper machine, with sheet formation. The paper web obtained accordingly then passes through the press section, in which the paper web is generally dried to a solids content of <40 wt %. This is followed by further dewatering by drying.

In a fourth aspect the present invention provides a paper or board comprising the surface size composition according of the present invention or produced with the method of the present invention.

EXAMPLES

Example 1

Strength of recycled paper boards grades was improved by adding anionic IPN of APAM and oxidized starch together with zirconium carbonate to surface sizing solution. The effect of additions of were tested on SCT (short span compression strength) and burst strength (Table 1 ). Surface sizing was done with laboratory size-press (Mathis) and drum-dried. Size-press and drying parameters are listed below (Table 2). Surface sizing formulations were kept at 70 °C before use and approximately 170 g of formulation was used for surface sizing in each trial point. Size-press was washed between trial points. Five board sheets of A5 size were surface sized per trial point. After surface sizing and drying, board sheets were cured in oven (105 °C, 10 min) and after curing they were taken into climate-controlled laboratory (RH 50%, 23 °C) for conditioning. Each board sheet was weighed at controlled conditions (RH50%, 23 °C) before and after surface sizing in order to determine the surface size pick-up. Pick-up was calculated by using equation 1 :

Pick - up(%) = (1 H-sized paper/lTT-unsized paper) * 100 (1 )

In this test surface sizing starch was mixture of dextrin starches C*Film 07311 and 07312 (50%+50%). Untreated base paper for the study was obtained from European board mill producing testliner (grammage 100g/m2) from RCF (recycled cellulose fiber). Addition level of IPN was 3.5% of sizing solution and zirconium carbonate 15% of IPN (0.525% of sizing solution). In all the test points pH of the sizing solution was adjusted to pH 5. This was done in to avoid crosslinking of zirconium carbonate and carboxylic groups of IPN occurring (occurs above pH6.5) in the sizing solution (to avoid viscosity increase). IPN was added first followed by zirconium carbonate. Concentration of the sizing solution was 12% in all the test points.

Addition of IPN and zirconium carbonate increased viscosity of the sizing solution resulting lower pick-level (Table 3). However, results clearly show that IPN together with zirconium carbonate improved SCT CD and burst even though pick-up level of sizing solution was 7.5% lower compared to board sized with pure starch (only starch). This indicates that crosslinking of carboxylic groups and zirconium occurs in the base paper as the pH is increased due to calcium carbonate present in the base paper.

Table 1. Sheet testing devices and standard methods used for produced paper sheets.

Table 2. Laboratory size-press and drying parameters.

Table 3. Effect different strength systems on board properties

Example 2

Strength of recycled paper boards grades was improved by adding anionic IPN of APAM and oxidized starch together with zirconium carbonate to surface sizing solution. The effect of additions of were tested on SCT (short span compression strength) and burst strength (Table 1 ). Surface sizing was done with laboratory size-press (Mathis) and drum-dried. Size-press and drying parameters are listed below (Table 4). Surface sizing formulations were kept at 75 °C before use and approximately 170 g of formulation was used for surface sizing in each trial point. Size-press was washed between trial points. 5 board sheets of A5 size were surface sized per trial point. After surface sizing and drying board sheets were cured in oven (105 °C, 10 min) and after curing they were taken into climate-controlled laboratory (RH 50%, 23 °C) for conditioning. Each board sheet was weighed at controlled conditions (RH50%, 23 °C) before and after surface sizing in order to determine the surface size pick-up (Equation 1 ).

In this test untreated base paper for the study was obtained from another European board mill producing testliner (grammage 80g/m2) from RCF (recycled cellulose fiber). Surface sizing starch was enzymatically degraded starch obtained from the same mill as the base paper. Addition level of IPN was 3.5% of sizing solution and zirconium carbonate 15% of IPN (0.525% of sizing solution). In all the test points pH of the sizing solution was adjusted to pH 5. This was done to avoid crosslinking of zirconium carbonate and carboxylic groups of IPN to occur (occurs above pH6.5) in the sizing solution (to avoid viscosity increase). Concentration of the sizing solution was 9% in all the test points.

Results clearly show (Table 5) that IPN together with zirconium carbonate improve SCT CD and burst significantly compared to board sized with pure starch sizing solution (only starch). Similarly as in Example 1 , this indicates that crosslinking of carboxylic groups and zirconium occurs in the base paper as the pH is increased due to calcium carbonate present in the base paper.

Table 4. Laboratory size-press and drying parameters.

Table 5. Effect different strength systems on board properties

Example 3

Surface sizing was done with laboratory size-press (Mathis) and drum-dried. Size-press and drying parameters are listed below (Table 6). Surface sizing formulations were kept at 70 °C before use and approximately 170 g of formulation was used for surface sizing in each trial point. Size-press was washed between trial points. 5 board sheets of A5 size were surface sized per trial point. After surface sizing and drying board sheets were cured in oven (105 °C, 10 min) and after curing they were taken into climate-controlled laboratory (RH 50%, 23 °C) for conditioning. Each board sheet was weighed at controlled conditions (RH50%, 23 °C) before and after surface sizing in order to determine the surface size pickup (equation 1 ).

In this example it is demonstrated the effect of crosslinking of zirconium carbonate and carboxylic groups of IPN on the viscosity of the sizing solution and thus pick-up level and strength. Surface sizing starch was mixture of dextrin starches C*Film 07311 and 07312 (50%+50%). Untreated base paper for the study was obtained from European board mill producing testliner (grammage 100g/m2) from RCF (recycled cellulose fiber) (same as in example 1 ). Addition level of IPN was 3.5% of sizing solution and zirconium carbonate 15% and 30% of IPN (0.525% and 1 .05% of sizing solution). In in this test series pH of the sizing solution was adjusted to pH 6.8 in all the test points to promote crosslinking. IPN was added first followed by zirconium carbonate. Concentration of the sizing solution was 12% in all the test points. The effect of additions of were tested on SCT (short span compression strength) and burst strength.

Since the pH of sizing solution was adjusted above 6.5 (6.8), addition of IPN and zirconium carbonate increased viscosity of the sizing solution drastically resulting significantly lower pick-level (Table 7). This resulted poor strength properties compared to pure starch. This indicates that if IPN is used together with zirconium carbonate crosslinking should happen in the base paper instead of in the sizing solution.

Table 6. Laboratory size-press and drying parameters.

Table 7. Effect different strength systems on board properties

Various embodiments have been presented. It should be appreciated that in this document, words comprise, include, and contain are each used as open-ended expressions with no intended exclusivity. The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

1. A surface size composition comprising interpenetrating polymer (IPN) network of anionic polyacrylamide (APAM) and starch, and zirconium carbonate.

2. The surface size composition according to claim 1 , wherein the surface size composition further comprises an additional polymer comprising carbohydrate polymer, such as carboxymethylcellulose (CMC), guar gum or starch, preferably the additional polymer is a viscosity reduced starch, more preferably thermally or enzymatically converted starch, even more preferably enzymatically converted starch, further even more preferably converted with alpha amylase, further even more preferably converted with thermosensitive alpha amylase.

3. The surface size composition according to claim 1 or 2, wherein the surface size composition further comprises a hydrophobation agent, preferably acrylate esters, more preferably, styrene acrylate.

4. The surface size composition according to any one of claims 1-3, wherein the starch of the IPN is viscosity reduced starch, preferably cationic starch, anionic starch, amphoteric starch or a mixture thereof.

5. The surface size composition according to any one of claims 1-4, wherein the zirconium carbonate comprises ammonium zirconium carbonate, potassium zirconium carbonate or a mixture thereof.

6. The surface size composition according to any one of claims 1-5, wherein pH of the surface size composition is slightly acidic, preferably the pH is 3.0-6.5, more preferably 3.5- 6.0, even more preferably 5.0-6.0.

7. The surface size composition according to any one of claims 2-6, wherein amount of the additional polymer in the surface size composition is from 85 wt-% to 99 wt-%, preferably from 95 wt-% to 99 wt-%, based on dry weight of the surface size composition.

8. The surface size composition according to any one of claims 1-7, wherein amount of the IPN material in the surface size composition is from 1 wt-% to 8 wt-%, preferably from 1 wt-% to 5 wt-%, based on dry weight of the surface size composition.

9. The surface size composition according to any one of claims 1-8, wherein amount of the zirconium carbonate in the surface size composition is from 0.01 wt-% to 1.0 wt-%, preferably from 0.01 wt-% to 0.5 wt-%, more preferably from 0.05 wt-% to 0.2 wt-%, as zirconium dioxide (ZrC>2), based on dry weight of the surface size composition.

10. The surface size composition according to any one of claims 3-9, wherein amount of the hydrophobation agent in the surface size composition is from 0.01 wt-% to 5 wt-%, preferably from 0.01 wt-% to 2 wt-%, based on dry weight of the surface size composition.

11. The surface size composition according to any one of claims 1-10, wherein amount of the starch of the IPN is from 5 wt-% to 50 wt-%, preferably from 10 wt-% to 30 wt-%, based on total dry weight of the IPN material.

12. The surface size composition according to any one of claims 1-11 , wherein amount of the APAM of the IPN is from 50 wt-% to 95 wt-%, preferably from 70 wt-% to 90 wt-% based on total dry weight of the IPN material.

13. The surface size composition according to any one of claims 1 -12, wherein the starch of the IPN has degree of cationic substitution (DS) 0.01-0.1 and/or anionic substitution (DS) 0.005-0.05.

14. The surface size composition according to any one of claims 1-13, wherein anionic amount in the APAM is from 3 mol-% to 30 mol-%, preferably 5 mol-% to 30 mol-%.

15. The surface size composition according to any one of claims 1-14, wherein viscosity of the surface size composition is 100%-250% of the original viscosity of enzymatically degraded starch compared at sizing conditions of temperature and concentration.

16. The surface size composition according to any one of claims 1-15, wherein the surface size composition is aqueous surface size composition.

17. Use of the surface size composition according to any one of claims 1-16 for surface sizing paper, board or the like.

18. The use according to claim 17, wherein the board is selected from fluting, folding boxboard (FBB), white lined chipboard (WLC), solid bleached sulphate (SBS) board, solid unbleached sulphate (SUS) board and gypsum board; and the paper is selected from white top liner, liner including test liner, uncoated fine paper, label paper and release paper.

19. A method for producing paper and board, the method comprising: (a) treating a paper stock with a paper auxiliary, a filler, or both to obtain a treated paper stock; (b) draining the treated paper stock with sheet formation to obtain a paper web; and (c) applying on the paper web the surface sizing composition according to any one of claims 1-16 to obtain treated paper web; and (d) drying the treated paper web.

20. A paper or board comprising the surface size composition according to any one of claims 1 -16 or produced with the method of claim 19.