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Application of Suspension-polymerized Latexes in Surface Sizing and Pigment Coating of Paper

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dc.contributor.advisor이학래-
dc.contributor.author아라즈라자비-
dc.date.accessioned2019-05-07T05:51:05Z-
dc.date.available2019-05-07T05:51:05Z-
dc.date.issued2019-02-
dc.identifier.other000000154930-
dc.identifier.urihttps://hdl.handle.net/10371/152172-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 농업생명과학대학 산림과학부(환경재료과학전공), 2019. 2. 이학래.-
dc.description.abstract최근 펄프가격 상승에 따른 원가상승을 극복하기 위해 펄프 섬유를 충전물로 대체하는 하이로딩 기술의 중요성 및 고도공량의 도공지 생산에 대한 관심이 고조되고 있다. 고도공지 생산 기술의 발달과 더불어 발생되는 핵심적인 문제점의 하나로 도공지의 접힘터짐 (fold crack) 문제가 대두되고 있다. 이를 완화하기 위한 방안으로 본 논문에서는 서스펜션 중합을 통하여 제조된 나노 입경의 라텍스를 표면사이즈액의 첨가제 및 도공액의 보조 바인더로 사용하였으며, 나노 라텍스 첨가에 따른 표면사이즈액 및 도공액의 특성, 종이의 강도적, 표면화학적 특성에 대한 연구를 수행하였다.

표면사이징용 첨가제로 활용할 경우, 일반적인 유화중합법이 아닌 서스펜션 중합방식으로 라텍스를 제조하기 때문에 라텍스 입자를 전분 등의 친수성 고분자로 안정화시킬 수 있었으며, 이는 라텍스입자의 pH 변화에 대한 안정성을 부여함이 구명되었다. 또한 유화중합에 사용되는 계면활성제를 배제함으로써 공정의 거품 발생 억제 및 우수한 파포 특성을 부여 할 수 있었으며, 표면사이징용 전분과의 상용성을 자연스럽게 증대시키고, 전분필름의 신장율을 증가시킴으로 표면사이징된 종이의 접힘터짐 현상 개선이 가능한 것으로 나타났다.

도공액의 보조바인더로 서스펜션 중합 라텍스를 사용할 경우, 친수성 보호콜로이드의 영향으로 도공액의 점도가 상승하며 보수성이 향상되는 결과를 나타내어 도공 작업성 및 도공지의 품질 향상에 기여할 것으로 판단되었다. 하지만 서스펜션 중합 라텍스의 투입량이 5 pph이상으로 과다할 경우 보수성 및 점도가 지나치게 증가하여 적정 투입량을 대체하는 것이 필요하다는 것이 밝혀졌다.

또한 도공지의 제반물성의 경우 서스펜션 중합 라텍스의 투입에 따른 인장강도 개선은 미미하였으나, 도공지의 신장율이 뚜렷이 증가하였으며, 이로 인해 접힘터짐 현상이 개선됨을 밝혔다. 서스펜션 중합된 라텍스가 투입된 도공층의 경우 안료와 바인더 간에 상호 작용이 증가하여 도공층의 공극이 증가하는 경향이 나타났으며, 5 pph 이하의 투입조건에서는 모틀 및 잉크 흡수 성능이 개선되는 결과를 나타냈다.

본 논문에서는 서스펜션 중합 라텍스를 표면 사이징 및 도공에 적용함으로써 최근 펄프원료 절감 및 이를 통한 원가절감을 위한 하이로딩 기술로 유발되는 접힘터짐 문제를 완화시키기 위한 방안을 모색하였으며, 보조바인더의 사용에 따른 도공지의 강도적, 표면화학적 특성 등 다양한 측면에서 효과를 검증함으로써 개발된 라텍스가 도공지의 품질 향상에 큰 효과를 나타냄을 증명하였기에 농학박사학위 논문으로서 충분한 가치가 있다고 판단된다.		-
dc.description.abstractFold cracking of coated paper is one of the most frequent and troublesome problems affecting the use of coated paper and boards. Paper industry is facing more fold cracking problem because substantial amount of filler is being used in papermaking and heavier coatings are applied to substitute the use of expensive fibers with pigment coating.

Fold cracking of coated paper is highly dependent on the properties of coating layer. The coating composition including pigments and binders affects the properties of coating layer. A latex with a good extensional property could improve the flexibility of coating layer and result in a less crack area after folding of coated paper. To minimize fold cracking of coated paper and board, a method to improve the extensional property and tensile strength of the base sheet and coating layer is necessary. Improving the fold crack resistance by optimization of surface sizing or paper coating by use of additives seems a practical method. Hence application of additives which provide both strain and strength might be a useful method to minimize the fold crack.

The physical and chemical properties of latexes depend upon various factors including polymerization methods, and monomers and stabilizer used in the polymerization. In this research, sterically stabilized suspension-polymerized acrylate (SP) latexes were used as additives for surface sizing and pigment coating of paper. A protective shell containing oxidized starch and polyvinyl alcohol (PVA) provided the steric hindrance to the SP latexes.

The property of the suspension-polymerized latex was examined and compared with that of conventional emulsion-polymerized ones. As an approach to decrease the fold cracking of coated paper, SP latexes were tested as a surface sizing additive. By preparation of starch films, it was possible to compare the film properties without variability caused by the base sheet. The strength and stretch properties of starch films without and with SP latex were measured. The effect of using SP latexes as a surface sizing additive on the mechanical properties of the paper was examined.

SP latexes with different acrylic acid content were used as cobinders for paper coating. The physical properties of these latexes including viscosity, particles size and zeta potential as a function of pH were compared. The viscoelastic properties of the coating color containing SP latex as a cobinder were evaluated. Moreover effect of partial substitution of the styrene butadiene (S/B) latex with SP latex on porosity, surface and optical properties of dried coating composite was investigated.

The coating layers containing SP latex as a cobinder were prepared and the tensile strength and strain property of the coating layers were evaluated. Finally the effect of SP latex on fold cracking of low- and high- basis weight coated paper in machine direction (MD) and cross machine direction (CD) was investigated.

The SP latex showed less tendency to generate foam than conventional styrene-butadiene and styrene-acrylate latexes, and they were highly compatible with the conventional surface sizing solution as the strength and stretch of the starch films increased. The SP latex resulted in a greater tensile strength and extensional properties of sized paper than the emulsion-polymerized latexes, which suggested their potential applicability for reducing the fold cracking of coated paper.

Acrylic acid monomer was found to be an important factor affecting viscosity, particle size and zeta potential of SP latexes. As a result of partial substitution of S/B latex with SP latexes in coating color, the viscoelastic properties of coating color was influenced by interaction between coating components. Because of this interaction, a weakly flocculated structure was built up in coating color which affected the formation of coating layer and thereby a more porous coating layer with higher opacity and brightness was formed.

Use of SP latex in coating layer, improved the strength and strain of the coating layer which was attributed to the protective shell and monomer composition of the SP latex. The extensional properties of the coated papers were improved when SP latex was used in coating formulation. Higher tensile strength and extensional properties of coating layer and coated paper, resulted in less crack area after folding. A base paper with higher basis weight gave a larger crack area as did the CD fold. Presence of SP latex in pre- and top-coating reduced the fold crack area, however it was found more effective in top-coating layer. Starch amount and total binder content of pre-coating layer contributed to appearance of larger fold crack area.





Keywords: Suspension-polymerized (SP) latex, surface sizing, paper coating, coating layer, extensional properties, fold cracking, folding direction		-
dc.description.tableofcontentsTable of Contents





Chapter 1

Introduction 1



1. Introduction 2

2. Objectives 6

3. Literature reviews 8

3.1 Suspension-polymerized latexes 8

3.2 Surface sizing 10

3.3 Rheological properties of coating color and its effect on structure formation of coating layer 12

3.4 Fold cracking 14

3.4.1 Effect of base paper on fold cracking 15

3.4.2 Effect of coating color components on fold cracking 16

3.4.2.1 Effect of coating pigments on fold cracking 17

3.4.2.2 Effect of coating binder on fold cracking 18

3.4.3 Strengths and characteristics of the coating layer and its effect on fold cracking 20



Chapter 2

Sterically stabilized latex as an additive for surface sizing of paper with oxidized starch 23



1. Introduction 24

2. Experimental 26

2.1 Materials 26

2.2 Viscosity measurement 26

2.3 Particle size measurement 26

2.4 Transmission electron microscopy (TEM) 27

2.5 Fourier transform infrared spectroscopy (FTIR) 27

2.6 Surface tension of latexes 27

2.7 Foaming tendency of latexes 27

2.8 Zeta potential of the latexes as a function of pH 28

2.9 Effect of pH on the stability of latexes 28

2.10 Effect of salt concentration on the stability of latexes 28

2.11 Effect of polyelectrolytes on the stability of latexes 29

2.12 Preparation of sizing solution 29

2.13 Starch film preparation 29

2.14 Tensile property of starch film 30

2.15 Surface sizing 31

2.16 Mechanical properties of surface sized papers 31

2.17 Mill trial 31

3. Results and discussion 33

3.1 Characteristics of the sterically stabilized latex 33

3.2 Surface tension and foaming tendency of latexes 36

3.3 Chemical stability of latexes 38

3.4 Tensile properties of starch films 47

3.5 Properties of surface sized papers 49

3.6 Mill trial and fold crack 54

4. Summary 59









Chapter 3

Suspension-polymerized latex as a cobinder for pigment coating- Influence on rheology of coating color and structure formation of coating layer 61



1. Introduction 62

2. Experimental 64

2.1 Materials 64

2.2 Transmission electron microscopy (TEM) 64

2.3 Fourier transform infrared spectroscopy (FTIR) 65

2.4 Preparation of latex dispersion at different pH 65

2.5 Preparation of coating color 65

2.6 Viscosity and viscoelastic measurement 67

2.7 Particle size and zeta potential evaluation 67

2.8 Sedimentation of coating color 68

2.9 Dewatering capacity analysis 68

2.10 Porosity of the coating layer 68

2.11 Surface properties of coating layer 69

2.11 Optical properties of coating layer 69

3. Results and discussion 70

3.1 Characteristics of the latexes 70

3.2 Viscosity and particle size distribution of SP latexes as a function of pH 73

3.3 Particle size distribution of SP latexes as a function of pH 75

3.4 Rheological properties of SP latex as a function of pH 80

3.5 Effect of SP latexes as a cobinder on rheological properties of coating color 86

3.6 Zeta potential of coating color 90

3.7 Sedimentation of coating color 92

3.8 Viscosity and water retention property of coating color 93

3.9 Effect of SP cobinder dosage on rheology of coating color 95

3.10 Effect of cobinder dosage on sedimentation of coating color 101

3.11 Pore structure of coating color 102

3.12 Surface characteristics of coating layer 105

3.13 Brightness and opacity of coating layer 107

4. Summary 109



Chapter 4

Effect of suspension-polymerized cobinder on properties of coated papers 111



1. Introduction 112

2. Experimental 114

2.1 Materials 114

2.2 Transmission electron microscopy (TEM) 115

2.3 Fourier transform infrared spectroscopy (FTIR) 115

2.4 Pore size distribution of coated paper 115

2.5 Surface properties of coated paper 116

2.6 Optical properties of coated paper 116

2.7 Ink absorption ratio of coated paper 116

2.8 Properties of latex films 117

2.8.1 Gel content of the latexes 117

2.8.2 Moisture content of the latexes 118

2.8.3 Latex film preparation for tensile measurement 118

2.8.4 Tensile properties of latex films 121

2.9 Tensile properties of coating layers 121

2.9.1 Coating color preparation 121

2.9.2 Preparation of coating layer 122

2.9.3 Effect of SP latex on tensile strength of coating layers 123

2.9.4 Effect of acrylate monomers, starch and PVA on tensile strength of coating layers 124

2.10 Paper coating 125

2.10.1 Single coating 125

2.10.2 Double coating 126

2.10.3 Coating on two sides of paper 128

2.11 Mechanical properties of coated paper 129

2.12 Crack area evaluation 130

2.13 Cross section images using FE-SEM 132

2.14 Dry pick strength 133

3. Results and discussions 135

3.1 Characteristics of the latexes 135

3.2 Pore size distribution of coated paper 137

3.3 Surface properties of coated paper 138

3.4 Optical properties of coated paper 140

3.5 Ink absorption ratio of coated paper 142

3.6 Tensile properties of latex film 142

3.7 Tensile properties of coating layer 145

3.8 Tensile properties of coated papers 150

3.8.1 Tensile properties of single coated paper 151

3.8.2 Tensile properties of double coated paper 154

3.9 Fold crack evaluation 156

3.9.1 Fold crack evaluation of single coated paper 157

3.9.2 Fold crack evaluation of double coated paper 161

3.9.3 Fold crack evaluation of two sides coated paper 165

3.10 Dry pick strength 166

4. Summary 169



Chapter 5

Overall conclusions and remarks 171



References 177



List of Tables



Table 2-1. Properties of the latexes 33

Table 2-2. Foam stability of latexes 38

Table 2-3. Properties of base paper and surface sized papers with O.S. (oxidized starch) and 5 pph of the S/B and SP latex for the CD 53

Table 2-4. Properties of the surface sized paper with SP latex additive 54

Table 2-5. Properties of the base paper surface sized with and without SP-M latex 55

Table 2-6. Percentage of fold crack areas and reduction percentage in the MD and CD 57



Table 3-1. Formulation of coating color for evaluation of the effect of acrylic acid monomer content of SP cobinder on the rheological properties of coating color 66

Table 3-2. Formulation of coating color for evaluation of the effect of S/B latex and SP cobinder substitution rate on coating layer preparation 67

Table 3-3. Properties of the SP latexes 70

Table 3-4. Effect of SP co-binder on viscosity and dewatering of coating color 95

Table 3-5. Effect of SP co-binder dosage on viscosity and dewatering of coating color 101

Table 3-6. Pore characteristics of coating layer 103

Table 4-1. Formulation of latex dispersions for film preparation 120

Table 4-2. Formulations of coating color 122

Table 4-3. Formulations of coating color for evaluation of the effect acrylate monomers of latex, starch, and PVA on tensile strength of coating layer 125

Table 4-4. Formulations of coating color 126

Table 4-5. Formulations of pre-coating color 127

Table 4-6. Formulations of top-coating color 127

Table 4-7. Combinations of pre and top-coating colors for double coating 128

Table 4-8. Formulations of coating color 129

Table 4-9. Combinations of coating on top and bottom sides of the paper 129

Table 4-10. Formulation of coating colors 134

Table 4-11. Properties of the latexes 135

Table 4-12. Tensile properties of coated papers for the cross machine direction (CD) 154

















 

List of Figures



Fig. 1-1. Schematic representation of a suspension-polymerized latex particle 9

Fig. 1-2. Cross-sectional images of the cracked coated paper 19

Fig. 2-1. Starch samples for the tensile strength measurement 30

Fig. 2-2. TEM micrograph of the SP latexes 34

Fig. 2-3. Particle size distribution curves of S/B, S/A, and SP latexes 35

Fig. 2-4. FT-IR spectra of the latex films 36

Fig. 2-5. Surface tension of latexes as a function of latex concentration 37

Fig. 2-6. Zeta potential of latexes as a function of pH 40

Fig. 2-7. Viscosity of latexes as a function of pH 41

Fig. 2-8. Viscosity of S/B and SP latexes at different pH levels as a function of shear rate 42

Fig. 2-9. Effect of the cationic PAM on the viscosity and particle size of S/B and SP latexes 44

Fig. 2-10. Zeta potential of the latexes as a function of the salt concentration 45

Fig. 2-11. Particle size distribution (PSD) curves for the S/B latex at four different salt concentrations 46

Fig. 2-12. Particle size distribution (PSD) curves for the SP latex at four different salt concentrations 46

Fig. 2-13. Tensile stress, elongation at break, and MOE of the starch films prepared with 5 pph of S/B and SP latex		-
dc.description.tableofcontentsO.S. (oxidized starch) 48

Fig. 2-14. Tensile stress, elongation at break, and MOE of the base paper and sized papers with O.S. (oxidized starch) and 5 pph of the S/B and SP latex for the machine direction (MD) 51

Fig. 2-15. Microscopic images obtained from the cross-section of papers sized with only oxidized starch and oxidized starch containing SP-M latex 56

Fig. 2-16. SEM images of the fold cracked papers: folded coated papers that were surface sized with starch only		-
dc.description.tableofcontentsfolded coated papers that were on the trial base stock surface sized with starch and 2.9 pph of SP-M latex 58

Fig. 3-1. Particle shape of S/B, SP-1, SP-2, and SP -3 latexes 72

Fig. 3-2. FT-IR spectra of the latex films 73

Fig. 3-3. Viscosity of the SP latexes depending on pH 74

Fig. 3-4. Average particle size of the SP latexes depending on pH 76

Fig. 3-5. Particle size distribution of SP-1, SP-2, and SP-3 latexes depending on pH 78

Fig. 3-6. Particle shape of SP-3 at pH of 5 and 9 79

Fig. 3-7. Viscosity of SP latexes at different pH as a function of shear rate 81

Fig. 3-8. Zeta potential of SP latexes as a function of pH 82

Fig. 3-9. Amplitude sweep of SP-3 latex for a range of stress at a constant angular frequency as a function of pH 84

Fig. 3-10. Frequency sweep of SP-3 latex for a range of stress at a constant angular frequency as a function of pH 85

Fig. 3-11. Amplitude sweep of coating colors for a range of stress at a constant angular frequency 87

Fig. 3-12. Frequency sweep of coating colors for a range of stress at a constant angular frequency 89

Fig. 3-13. Complex modulus of coating colors 90

Fig. 3-14. Effect of SP latex on zeta potential of coating color 91

Fig. 3-15. Sediment volume of coating colors 93

Fig. 3-16. Effect of SP latex on viscosity of coating color 94

Fig. 3-17. Effect of substitution rate of SP-2 latex on zeta potential of coating color 96

Fig. 3-18. Amplitude sweep of coating colors for a range of stress at a constant angular frequency 97

Fig. 3-19. Frequency sweep of coating colors for a range of stress at a constant angular frequency 98

Fig. 3-20. Complex modulus of coating colors 99

Fig. 3-21. Effect of SP latex on viscosity of coating color as a function of shear rate 100

Fig. 3-22. Effect of SP cobinder dosage on sediment volume of coating color 102

Fig. 3-23. Effect of SP cobinder on pore size distribution of coating layer 104

Fig. 3-24. Cumulative pore volume of dried coating layer 104

Fig. 3-25. Effect of SP cobinder dosage on roughness of coating layers 105

Fig. 3-26. FE-SEM images of coating layers 107

Fig. 3-27. Brightness and opacity of coating layers 107

Fig. 4-1. Preparation of latex film samples 119

Fig. 4-2. Latex films after drying 120

Fig. 4-3. Coating layer samples for tensile measurement 123

Fig. 4-4. Folding of coated papers using AA-GWR 130

Fig. 4-5. Definition of MD and CD foldings 131

Fig. 4-6. Scanning and image processing of folded area 132

Fig. 4-7. Folded paper for electron microscopy 133

Fig. 4-8. TEM micrograph of SP latex particles 136

Fig. 4-9. FT-IR spectra of the latex films 137

Fig. 4-10. Pore size distribution of coated paper 138

Fig. 4-11. Effect of SP latex on roughness and gloss of the coated paper 139

Fig. 4-12. FE-SEM micrographs of the surface of coated paper 140

Fig. 4-13. Effect of SP latex on opacity and brightness of the coated paper 141

Fig. 4-14. Ink absorption ratio of the coated paper 142

Fig. 4-15. Tensile stress, elongation at break, and MOE of the latex films prepared with different substitution rate of S/B with SP latex 145

Fig. 4-16. Tensile stress, elongation at break, and MOE of the coating layers prepared with different substitution rate of S/B with SP latex 147

Fig. 4-17. Effect of S/A latex, oxidized starch and PVA on tensile stress, elongation at break, and MOE of the coating layers 149

Fig. 4-18. Tensile stress, elongation at break, and MOE of the single coated papers for machine direction (MD) 153

Fig. 4-19. Tensile stress, elongation at break, and MOE of the double coated papers for machine direction (MD) 156

Fig. 4-20. Average crack area for MD and CD fold 158

Fig. 4-21. Cross-sectional images of the folded paper in CD. Base paper: 78 g/m2 159

Fig. 4-22. Cross-sectional images of the folded paper in MD. Base paper: 198 g/m2 160

Fig. 4-23. Cross-sectional images of the folded paper in CD. Base paper: 198 g/m2 161

Fig. 4-24. Crack area when S/B latex was replaced with SP latex in pre and to coating for MD and CD fold 163

Fig. 4-25. Crack area when starch was replaced with SP latex in pre-coating for MD and CD fold 165

Fig. 4-26. Crack area of two side coated paper for MD and CD fold 166

Fig. 4-27. Scanned and binary images of the coated paper after picking 167











List of Equations



Eq. 1-1. Strain in a bended beam 14

Eq. 1-2. Stiffness of the coated paper 20

Eq. 3-1. Washburn equation 69

Eq. 3-2. Stokes-Einstein equation 78

Eq. 4-1. Ink absorption ratio 116		-
dc.language.isoeng-
dc.publisher서울대학교 대학원-
dc.subject.ddc634.9-
dc.titleApplication of Suspension-polymerized Latexes in Surface Sizing and Pigment Coating of Paper-
dc.typeThesis-
dc.typeDissertation-
dc.contributor.AlternativeAuthorARAZ RAJABI ABHARI-
dc.description.degreeDoctor-
dc.contributor.affiliation농업생명과학대학 산림과학부(환경재료과학전공)-
dc.date.awarded2019-02-
dc.identifier.uciI804:11032-000000154930-
dc.identifier.holdings000000000026▲000000000039▲000000154930▲-
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