WO2022269127A1

WO2022269127A1 - Retention agent system and papermaking composition, and method of producing paper

Info

Publication number: WO2022269127A1
Application number: PCT/FI2022/050409
Authority: WO
Inventors: Jonni Ahlgren; Jaakko Hiltunen
Original assignee: Kemira Oyj
Priority date: 2021-06-22
Filing date: 2022-06-13
Publication date: 2022-12-29

Abstract

The present invention relates to a retention agent system and a papermaking composition, and a method of producing paper. The retention agent system may be used as a retention agent in papermaking and board making. The retention agent system comprises a component (A) and a component (B). Component (A) is a water soluble, cationic starch having a degree of substitution (DS) of at least 0.15. Component (B) is a cationic polyacrylamide (CPAM), having a SV viscosity of at least 4 mPas. The weight ratio of A:B is in the range of 80:20-20:80.

Description

RETENTION AGENT SYSTEM AND PAPERMAKING COMPOSITION, AND METHOD OF PRODUCING PAPER

FIELD OF THE INVENTION

The present invention relates to a retention agent system for making of paper, board or the like.

The present invention also relates to a use of a retention agent system for making of paper, board or the like.

The present invention further relates to a papermaking composition comprising a retention agent system.

Further, the present invention also relates to a method for producing paper, board or the like.

BACKGROUND OF THE INVENTION

In paper and board making solid particles of the fibre stock, such as in organic mineral filler particles, fibre fines, added process chemicals, etc. are cap tured in the formed fibre web. This process is called retention. For economical and qualitative points of view, good and uniform retention of the various fibre stock components in the formed web is advantageous, as it reduces loss of additives and improves the quality of the formed paper. The retention has become more and more important when the use of recycled fibres have been increasing in the paper and board making.

Various retention agents are available, and they can be added to the fi bre stock in order to improve the retention of additives, fibre fines, disturbing sub stances, etc. to the cellulosic fibres and to the formed web. Retention agents are usually synthetic or semi-synthetic polymeric compounds. Use of synthetic poly mers increases the costs, which is not preferred when cheaper grades of paper and board are produced. Consequently, there is a need for new effective retention sys tems, which would be more sustainable, economically competitive and produce good quality end product.

Typical main retention aid is synthetic cationic polyacrylamide. In the retention agent systems, the cationic polyacrylamide has an average molecular weight of 5000 -20000 Da. The magnitude of molecular size may also be stated as standard viscosity. Retention grade polyacrylamides have typically standard vis cosity (SV), also called UL viscosity, >2 mPas, and charge density is 0.2 - 2.5 meq/g. Cationic starches are also well-known agents in papermaking. They are mainly used in the wet end of the paper machine, where they are added to the fibre stock before the paper machine headbox. The main aim for wet end starch use is to improve dry strength, and as wet end starches have low cationic charge, they may have positive impact on retention, but they are not efficient enough as reten tion agent.

Commercial cationic wet end starches for dry strength are normally in powder form and their degree of substitution (DS) is clearly < 0.1, i.e. they are low cationic starches.

Low cationic starch is not soluble in water without cooking. Cooking means that temperature of water, in which the starch particles form a dispersion, is raised above gelatinization temperature of starch. Gelatinization temperature is starch type specific, and varies typically between 60-85 °C. For most of the starches cooking at 90-100 °C is enough.

Industrial cooking is often made using jet cooking. In jet cooking starch mixture is introduced into a jet cooker with steam. The cooking temperature in the cooker varies between 120 — 160 °C, depending on the starch type.

BRIEF DESCRIPTION OF THE INVENTION

A typical method for producing paper, board or the like, comprises at least following steps:

- obtaining a fibre stock comprising lignocellulosic fibres and adding a retention agent system comprising a cationic synthetic polymer to the fibre stock,

- forming a fibrous web from the fibre stock and drying the web.

Now it has been surprisingly found out that adding a specific high cati onic starch improves the retention when it is used together with a high enough molecular weight cationic synthetic polymer as a component of a retention agent system. Use of a specific high cationic starch makes it possible to reduce the amount of the cationic synthetic polymer, while still providing as good, or even better, re tention results. Furthermore, it was unexpectedly observed that the specific com bination of the components of the retention agent system may also provide im provement in the drainage of the fibre stock.

It has been observed that the selected average molecular weight and/or charge density of starch provide good interaction not only with the fibre stock com ponents, but also with cationic polymer, polyacrylamide, which forms the other component of the retention system. The good interaction makes it possible to re duce the amount of cationic synthetic polymer, if so desired.

Performance of cationic starch (alone) in retention is not as good as per formance of CPAM (cationic polyacrylamide). High molecular weight (MW) starch helps in performance, but different MWs are needed in different applications.

Demands for more sustainable products are increasing. High cationic starches, which can be dissolved in water without cooking, and give reasonable re tention efficiency, give possibility to reduce fossil carbon content in retention agent systems. When part of cationic polyacrylamide is replaced by high cationic starch in a retention agent system, retention efficiency of the retention agent system de creases. But the decrease in the retention efficiency can be avoided, if the high cat ionic starch is used together with a cationic polyacrylamide having higher molecu lar weight than the standard cationic polyacrylamide.

Cationic starches, which have degree of substitution (DS) of at least 0.15 are considered high cationic starches and they are relatively soluble in water with out cooking agent.

Because cationic starch can be dissolved without cooking a blend of cat ionic starch and CPAM can be used (CPAM cannot be cooked).

In this description water soluble starch refers to starches which dis solve in room temperature in water at least partly, increasing viscosity signifi cantly, though turbidity may remain higher than when cooking is made.

High cationic starches give better retention efficiency than low cationic starches, but still their retention efficiency is clearly lower than retention efficiency of cationic polyacrylamides.

It was found out that lack of performance of starch can be partly com pensated if the starch is used as a blend with very high MW CPAM, which has a standard viscosity SV>4.

Standard viscosity (SV) is measured at 0.1 weight-% polymer content in an aqueous 1 M NaCl solution using Brookfield LV viscometer equipped with UL adapter, at 25 °C, using UL Adapter Spindle and rotational speed 60 rpm.

Cationic acrylamide polymer comprises a copolymer of (methacryla mide and at least one cationic monomer. The copolymer of (meth) acrylamide, pref erably acrylamide, and at least one cationic monomer, may be obtained by copoly merisation of (meth) acrylamide and 5 - 50 mol%, preferably 6-40 mol%, more preferably 8 - 25 mol%, of cationic monomer(s). The at least one cationic monomer in the synthetic cationic copolymer of (meth) acrylamide may be selected from a group of 2-(dimethylamino)ethyl acrylate (ADAM), [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-C1), 2-(dimethylamino)ethyl acrylate benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2 -dimethylaminoethyl methacrylate (MADAM), [2-(methacrylo- yloxy) ethyl] trimethylammonium chloride (MADAM-C1), 2-dimethylaminoethyl methacrylate dimethylsulphate, [3 -(acryloylamino) propyl] trimethylammonium chloride (APTAC), [3 -(methacryloylamino) propyl] trimethylammonium chloride (MAPTAC), diallyldimethylammonium chloride (DAD MAC), or any of their combi nations.

The cationic polyacrylamide is in a form of particles, like beads or dry powder. The cationic polymer may be obtained by solution polymerisation, sus pension polymerisation, or gel polymerisation.

An object of the present invention is thus to provide a retention agent system and a papermaking composition comprising said retention agent system so as to overcome the problems in prior art.

A further object of the present invention is to provide a use of said re tention agent system in papermaking and board making.

A still further object of the present invention is to provide a method for producing paper, board or the like.

The objects of the invention are achieved by a retention agent system, use of the retention agent system, a papermaking composition, a method for pro ducing paper, board or the like, which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

In particular, the retention agent system for making of paper, board or the like, according to the invention comprises a component (A) and a component (B), wherein component (A) is a water soluble, high cationic starch having a degree of substitu tion (DS) of at least 0.15, and component (B) is a very high molecular weight cationic polyacrylamide (CPAM), having a SV viscosity of at least 4 mPas, preferably in the range of 4.0-7.0 mPas, the weight ratio of A:B being in the range of 80:20-20:80.

In a particularly preferred embodiment, the retention agent system has a viscosity, in a solution concentration of 0.5%, in the range of 10 - 1000 mPas, more preferably 50 - 500 mPas, measured at 25 °C with Brookfield LV- viscometer, in small sample adapter, spindle SC4-18.

In a preferred embodiment of the retention agent system of the inven tion the cationic starch (A) is made from a starch selected from a group comprising potato starch, waxy potato starch, rice starch, corn starch, waxy corn starch, wheat starch, barley starch, sweet potato starch, tapioca starch, pea starch and any of their mixtures.

In another preferred embodiment of the invention the cationic starch in the retention agent system has a degree of substitution, DS, in the range from 0.15 to 1.0, preferably from 0.15 to 0.7, more preferably from 0.15 to 0.5, more prefera bly from 0.15 to 0.3, most preferably 0.15-0.22.

In yet another preferred embodiment of the invention the cationic starch is non-degraded and/or free of cross-linkages.

The retention agent system of the invention preferably has a weight ra tio of A:B in the range of 50:50-30:70.

The present invention also provides a use of a retention agent system according to the invention in papermaking and board making or the like.

In the use of the invention the retention agent is preferably used in com bination with at least one type of microparticles, or at least one type of other reten tion agents, or a combination thereof.

The present invention further provides a papermaking composition comprising a retention agent system according to the invention.

In a preferred embodiment thereof, the papermaking composition ac cording to the invention further comprises at least one type of microparticles, or at least one type of other retention agents, or a combination thereof.

The present invention further provides a method for producing paper, board or the like, comprising at least following steps:

- obtaining a fibre stock comprising lignocellulosic fibres and adding a retention agent system comprising a component (A) and a component (B) to the fibre stock, wherein component (A) is a water soluble, high cationic starch having a degree of substitution (DS) of at least 0.15, and component (B) is a very high molecular weight cationic polyacrylamide (CPAM), having a SV viscosity of at least 4 mPas, preferably in the range of 4.0-7.0 mPas, the weight ratio of A:B being in the range of 80:20-20:80,

- forming a fibrous web from the fibre stock and drying the web. In a preferred embodiment of the method of the invention component (A) and component (B) are in the form of a blend in particle or solid form, such as powder form which is dissolved, and if necessary, diluted before adding to fibre stock. In a further preferred embodiment, component (A) and component (B) are mixed as dry particles into a blend, using e.g. a mechanical mixer, or, the flows of the dry particles are combined upon packaging before said dry particles introduced into a sack or bag.

The invention is based on the finding that by combining a very high MW CPAM, and a cationic starch a retention agent system showing a retention response close to that of a standard MW CPAM is obtained, while at the same time, sustaina bility of the retention agent system is increased, because less fossil carbon needs to be used as starch is used instead of CPAM.

Further, high cationic starches, which can be dissolved in water without cooking, and give reasonable retention efficiency, give possibility to reduce fossil carbon content in retention agent systems. When part of cationic polyacrylamide is replaced by high cationic starch in a retention agent system, retention efficiency of the retention agent system decreases. But the decrease in the retention efficiency can be avoided, if the high cationic starch is used together with a cationic poly acrylamide having higher molecular weight than the standard cationic polyacryla mide.

DETAILED DESCRIPTION OF THE INVENTION

The following examples describe the invention more in detail. Each re tention performance test was performed on a 1:1 blend of pine and birch. Dosing sequence was as follows: retention polymer dosing at 10 s, microparticle dosing at 30 s. Polymer retention was estimated from floe size at 20 s and microparticle re tention from the floe size at 40 s.

Retention performance of a variety of different blends of a cationic starch and a cationic polyacrylamide (CPAM) was tested by using focused beam reflectance measurement (FBRM). The method follows floe size development and is comparable to retention. Retention performance is estimated with the floe size at certain time after polymer dosing.

EXPERIMENTAL EXAMPLES

Focused Beam Reflectance Measurement (FBRM) testing is known to correlate well with retention testing [Gerli et al., Appita Journal 54(l):36-40, Janu ary 2001]. FBRM testing was used to describe retention performance in these tests for examples.

Used FBRM apparatus is Lasentec FBRM Model D600L by Laser Sensor Technology, Redmond, WA, USA, Serial No. 1106, and its detector is D600L-HC22- K, Serial No. 961. The FBRM instrument is a flocculation analyzer using a highly focused laser beam and back-scattered geometry as a principle of operation. From the collected data the FBRM instrument yields chord length distribution, mean of the chord length values and the number of particles detected. The measurement range of the device is 1 - 1000 gm.

Mean of the chord length value is used as the relative value for retention performance.

EXAMPLE 1 Starch dissolution

1, 2 and 3 weight-% starch solutions in water were made at room tem perature and their water solution viscosity, salt solution viscosity and turbidity were measured.

Three different starches were used: Roquette’s Hl-CAT 1574A, Penford Products’ PAF#9152ER and one experimental cold soluble starch (i.e. starch solu ble without cooking).

Water solution viscosity and salt solution viscosity were measured us ing a Brookfield LV viscometer with a small sample adapter at 25 °C, using spindle SC4-18 or SC4-31 depending on viscosity level. The viscosity measurement is per formed by using maximum possible rotational speed. The starch sample was first dissolved in deionized water to the target weight-% solution. Water solution vis cosity was measured from this solution. Then sodium chloride (NaCl) in weight ra tio NaCkstarch of 5:1 was added and let to dissolve under mixing before salt solu tion viscosity was measured. E.g. when a 2 weight-% salt solution viscosity was made, it was measured at 1.8 weight-% concentration of starch in an aqueous so lution comprising 9.1 weight-% of NaCl.

Turbidities were measured using HACH, 2100 AN IS Laboratory Turbi dimeter.

The results are collected in Table 1. Table 1. Properties of starch solutions made at room temperature

As comparison the viscosities of HI-CAT 1574A solutions decreased, when the solution was cooked 30 min at 80 °C. Though, also the turbidities de- creased showing improved solubility. See Table 2 for results.

Table 2. HI-CAT 1574A solutions after cooking 30 min at 80 °C

Significant increase in solution viscosities dissolved at room tempera- ture means that at least part of starch dissolves already at room temperature. Though, decrease in turbidity after cooking means that more material is dissolving during cooking. But at the same time also solution viscosities decrease, which may have adverse effect on performance. EXAMPLE 2

The pulp used was a mixture of refined chemical pulps of pine and birch in ratio 1:1. Filler, precipitated calcium carbonate (PCC), was used in ratio dry pulp/PCC = 65/35.

Tap water was used in the furnish and the consistency was 5 g/kg. pH was adjusted to 8.

The tests were used as FBRM tests in a beaker. Amount of furnish in a test was 500 g. The furnish was continuously mixed using an overhead stirrer and a propeller impeller at 1500 rpm. The test polymer was dosed, and the mean chord length value was taken 10 s after polymer dosing. Starch used was Hi-Cat 1574A from Roquette. The other polymers used were cationic polyacrylamides (CPAM). CPAM1 was a 9 mol-% with Standard Vis cosity (SV) 4.8 mPas. SV is defined as viscosity of 0.1 % polymer solution in 1 M NaCl measured using Brookfield viscometer and UL adapter 60 rpm and at 25 °C. CPAM2 was 9 mol-% with SV 3.4 mPas. The polymers were used as 0.1 % solutions. The dissolutions were made at room temperature; no cooking for starch was done.

Retention testing results are shown in Table 3. The dosage is expressed as g or kg per dry matter of the furnish. Table 3. Comparison of retention test results with CPAM2 and with combinations of starch and different CPAMs at different dosage levels. Mean chord length values taken 10 s after polymer dosing (gm).

At lower dosages a combination of starch and a CPAM having high enough SV value performs about equally to a pure CPAM having lower SV value, and at higher dosages the performance is even better. EXAMPLE 3

The tests followed the same principles as described in Example 2, ex cept that the refined chemical pulp used was only birch pulp and in addition to starch 1574A also another starch was used, PAF#9152ER from Penford Products. No cooking of starch solutions was used either this time. Retention testing results are shown in Table 4.

Table 4. Comparison of retention test results with CPAM2 and with combinations of different starches and CPAM1 at different dosage levels. Mean chord length val- ues taken 10 s after polymer dosing fgrn).

It seems that starch 1574A performs slightly better than starch PAF#9152ER, but combinations of both starches with a CPAM having high enough SV value perform about equally or better to a CPAM having lower SV value. EXAMPLE 4

The tests followed the same principles as described in Example 2, ex cept that

The refined pine and birch chemical pulps were received from different pa per mill than in Example 2 - pH of the furnish was 8.1

Instead of CPAM2 another CPAM, CPAM3 was used; CPAM3 was a 9 mol-% with SV 3.3 mPas

Retention testing results are shown in Table 5. Table 5. Comparison of retention test results with CPAM3 and with combinations of starch and CPAM1 at different dosage levels. Mean chord length values taken 10

EXAMPLE 5

The tests were made using the same furnish as in Example 4. The poly mers were dosed in similar manner, but also a microparticle was used in the reten tion program. The microparticle used was FennoSil 5000 from Kemira. Its dosage was 2 kg/t and it was dosed 20 s after the polymer dosing. The mean chord length value was taken 10 s after microparticle dosing.

Retention testing results are shown in Table 6.

Table 6. Comparison of retention test results with CPAM3 and with combinations of starch and CPAM1 at different dosage levels when microparticle is used in the retention program. Microparticle dosing 2 kg/t. Mean chord length values taken 10 s after microparticle dosing

EXAMPLE 6

Viscosity effect of high cationic starch in a retention agent blend was tested by comparing viscosities of blends to viscosities of pure polyacrylamides. The starch used was the same as in Example 2, Hi-Cat 1574A (1574A). It was blended with the same CPAM1 polyacrylamide as in Example 2. The other poly acrylamide, CPAM2, was also the same used in Example 2.

The blends tested were 1574A+CPAM1 in ratio 50/50 and in ratio

30/70. The samples were dissolved in deionized water in concentrations 0.4-

0.7 %.

Viscosities were measured using Brookfield LV viscometer, equipped with Small Sample Adapter, at 25 °C, using spindle SC4-18 and always the highest rotation speed allowed (max 60 rpm). The results are shown in Table7.

Table 7. Viscosity comparison of a polyacrylamide and high cationic starch + very high MW polyacrylamide blends.

The viscosity comparison tells that viscosity of a high cationic starch and very high MW polyacrylamide is at about the same level or even lower.

When comparing the retention results presented in Tables 3-6 it may be seen that the performance of the blend of CPAM and starch is at best when the major component in blend is very high MW CPAM and if no microparticle is used in the retention system. Further, no big difference is seen between different starches. The starch needs to be soluble without cooking, thus its DS needs to be at least 0.15.

A solution of a blend of starch and very high MW CPAM has a viscosity equal or lower than viscosity of a solution of standard MW CPAM. Lower viscosity is a ben efit because higher polymer concentration can be used at the same viscosity. It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The inven tion and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A retention agent system for making of paper, board or the like, com prising a component (A) and a component (B), wherein component (A) is a water soluble, cationic starch having a degree of sub stitution (DS) of at least 0.15, and component (B) is cationic polyacrylamide (CPAM), having a SV viscosity of at least 4 mPas, preferably in the range of 4.0-7.0 mPas, standard viscosity (SV) being measured at 0.1 weight-% polymer content in an aqueous 1 M NaCl solution using Brookfield LV viscometer equipped with UL adapter, at 25 °C, using UL Adapter Spindle and rotational speed 60 rpm, the weight ratio of A:B being in the range of 80:20-20:80.

2. A retention agent system according to claim 1, character ize d in that components (A) and (B) are in the form of a blend.

3. A retention agent system according to claim 1 or 2, character ize d in that the CPAM (B) has a charge in the range of 5-50 mol%.

4. A retention agent system according to any one of claims 1-3, char acterized in that the blend is in powder form.

5. A retention agent system according to claim 1 or 2, character ize d in that the retention agent system as dissolved , in solution concentration 0,5 % has a viscosity in the range of 10 - 1000 mPas, more preferably 50 - 500 mPas, measured at 25 °C with Brookfield LV- viscometer, in small sample adapter, spin dle SC4-18.

6. A retention agent system according to any one of the preceding claims, characterized in that the cationic starch (A) is made from starch selected from a group comprising potato starch, waxy potato starch, rice starch, corn starch, waxy corn starch, wheat starch, barley starch, sweet potato starch, tap ioca starch, pea starch and any of their mixtures.

7. A retention agent system according to any one of the preceding claims, characterized in that the cationic starch has a degree of substitu tion, DS, in the range from 0.15 to 1.0, preferably from 0.15 to 0.7, more preferably from 0.15 to 0.5, more preferably from 0.15 to 0.3., most preferably 0.15-0.22.

8. A retention agent system according to any one of the preceding claims, characterized in that the cationic starch is non-degraded and/or free of cross-linkages.

9. A retention agent system according to any one of the preceding claims, characterized in that the weight ratio of A:B is in the range of 50:50-30:70.

10. Use of a retention agent system according to any one of the preced ing claims as a retention agent in papermaking and board making.

11. Use according to claim 10, wherein the retention agent system is used in combination with at least one type of microparticles, or at least one type of other retention agents, or a combination thereof.

12. A papermaking composition comprising a retention agent system according to any one of claims 1-9.

13. A papermaking composition according to claim 12, further compris ing at least one type of microparticles, or at least one type of other retention agents, or a combination thereof.

14. A method for producing paper, board or the like, comprising at least following steps:

- obtaining a fibre stock comprising lignocellulosic fibres and adding a retention agent system comprising a component (A) and a component (B) to the fibre stock, wherein component (A) is a water soluble, cationic starch having a degree of sub stitution (DS) of at least 0.15, and component (B) is cationic polyacrylamide (CPAM), having a SV viscosity of at least 4 mPas, preferably in the range of 4.0-7.0 mPas, standard viscosity (SV) being measured at 0.1 weight-% polymer content in an aqueous 1 M NaCl solution using Brookfield LV viscometer equipped with UL adapter, at 25 °C, using UL Adapter Spindle and rotational speed 60 rpm, the weight ratio of A:B being in the range of 80:20-20:80,

- forming a fibrous web from the fibre stock and drying the web.

15. A method according to claim 14, wherein component (A) and com ponent (B) are blended prior to being added to the fibre stock.