Polysaccharide resins for flexographic and digital inks - InkRes® 33

Blog Archive | 8 minutes  | Author: Danielle Williams , MChem.

Plant-based polysaccharide binders for eco-friendly formulations

Polysaccharides can be utilised in a wide range of applications; from creating stable water-in-oil emulsions in solvent-based alkyd paints (LPR76® & LPR® 221), to improving workability in ready-mix jointing compounds (LTB™29). 

For the water-based ink formulator, Lorama’s InkRes® 33 offers a number of benefits when used as a replacement for conventional water-based acrylics.  When incorporated into an ink formulation it not only increases the print quality, colour and gloss - but also improves the re-wettability of the ink, ensuring that it does not dry on the press.  Based on Lorama Polysaccharide Resin Technology (LPRT) and produced from plant-based starches, InkRes® 33 also increases the green content of a formulation, helping formulators work towards eco-friendly and renewable inks.

 

In this technical article:

 

 

Flexographic ink formulations

In flexographic formulations, InkRes® 33 benefits include:

  • Improved re-wettability and longer open time in the anilox.
  • Improved colour strength.
  • Improved gloss.
  • No adverse effect on adhesion.

Furthermore, it can also be used to reduce the use of expensive viscosity modifiers; offering a cost-saving on total formulation. 

 

Flexographic ink for printing on white corrugated board

In the flexographic ink formulation for corrugated board (Table 1), InkRes® 33 was used as a complete replacement for the solution acrylic binder.

 

Product

Benchmark Ink (%)

Lorama Ink (%)

Pigment Dispersion

40

40

Styrene Acrylic Emulsion

34

34

Solution Acrylic

15

0

InkRes® 33

0

10

PE Wax Emulsion

3

3

Glycol Ether DPM

1.5

1.5

Surfactant

2

2

Defoamer

0.5

0.5

Water

4

9

TOTAL

100

100

Table 1. Flexographic ink formulation for corrugated board.

 

Both colour strength (Table 2) and gloss (Table 3) were improved in the InkRes® 33 modified formulation when compared to the benchmark. This is also achieved without adverse effect on adhesion (ASTM F2252), as Lorama LPRTs have a secondary wetting ability and can help stabilise pigments in the formulation.

 

Product

Benchmark Ink

Lorama Ink

Yellow Ink

Good transfer and colour strength (0.99)

Good transfer and colour strength (1.05)

Black Ink

Good transfer and colour strength (1.45)

Good transfer and colour strength (1.40)

Cyan Ink

Good transfer and colour strength (1.20)

Good transfer and colour strength (1.25)

Green Ink

Good transfer and colour strength (1.25)

Good transfer and colour strength (1.30)

Table 2. Printability and density results with corrugated board. Tested using a 200 line screen anilox (200 lpi). Colour density measured by X-Rite Densitometer.

 

Product

Benchmark Ink - Gloss

Lorama Ink - Gloss

Yellow Ink

85

95

Black Ink

78

85

Cyan Ink

80

90

Green Ink

85

90

Table 3. Gloss values obtained with flexographic ink formulations for corrugated board. Measured with a BYK gloss meter at 60°.

 

Rewettability (Table 4) was also improved in all CMYK colours. This was measured by placing ink on a flexo roller, leaving it exposed for one minute, and then observing the subsequent print quality.

 

Product

Benchmark Ink - Gloss

Lorama Ink - Gloss

Yellow Ink

85

95

Black Ink

78

85

Cyan Ink

80

90

Green Ink

85

90

Table 4. Flexographic ink re-wettability results with corrugated formula.

 

 The gloss and colour saturation of these inks, on corrugated board substrates, can be seen in Figure 1 below.

 

Figure 1. Colour saturation and gloss of the flexographic ink formulations for corrugated board.

 

Flexographic ink for printing onto film

In more demanding formulations the binder can be partially replaced with InkRes® 33 to maintain adhesion onto difficult substrates.  In the formulation shown in Table 5, 5% of a self-crosslinking acrylic was replaced 1:1 with InkRes® 33 (more was not possible due to increased viscosity).

 

Product

Benchmark Ink (%)

Lorama Ink (%)

Pigment Dispersion

40

40

Self-Crosslinking Acrylic Emulsion

49

44

InkRes® 33

0

5

PE Wax Emulsion

3

3

Glycol Ether DPM

1.5

1.5

Surfactant

2

2

Defoamer

0.5

0.5

Water

4

4

TOTAL

100

100

Table 5. Flexographic ink formulation for film printing.

 

In this instance, colour strength (Table 6) improved in all CMYK colours and gloss (Table 7) was either maintained or increased at 60°.

 

Product

Benchmark Ink

Lorama Ink

Yellow ink

Good transfer and colour strength (0.98)

Good transfer and colour strength (0.99)

Black ink

Good transfer and colour strength (1.40)

Good transfer and colour strength (1.45)

Cyan ink

Good transfer and colour strength (1.19)

Good transfer and colour strength (1.20)

Green ink

Good transfer and colour strength (1.20)

Good transfer and colour strength (1.25)

Table 6. Printability and density results with film ink formulation. Tested using a 200 line screen anilox (200 lpi). Colour density measured by X-Rite Densitometer.

 

Product

Benchmark Ink - Gloss

Lorama Ink - Gloss

Yellow ink

90

90

Black ink

89

90

Cyan ink

95

95

Green ink

95

98

Table 7. Gloss values obtained with flexographic ink formulations for film. Measured with a BYK gloss meter at 60°.

 

Re-wettability: the benchmark ink formula dried in faster, producing an inferior print quality vs. the InkRes® 33 modified formula. This was measured in the same way as done previously – by placing ink on the anilox roller, leaving it exposed for 1 minute, and then observing the print quality after proofing.

 

Digital ink formulations

InkRes® 33 shows particular benefit in digital ink formulations where it helps prevent ink from drying, reducing the risk or having to replace costly print heads.  When partially replacing N-methyl pyrrolidone, no changes to viscosity were observed and neither printability nor adhesion were affected on paper, glossy photo paper or coated polypropylene.  Digital ink formulations were made as outlined in Table 8 (benchmark ink contained 6.55% N-methyl pyrrolidone). Print quality is again improved in digital inks with visually higher colour densities - even after leaving the print heads uncapped for 5 days (Table 9).

 

Components

Loading in Black (%)

Loading in Cyan (%)

Loading in Magenta (%)

Loading in Yellow (%)

DI water

19.08

39.47

15.85

16.59

N-methyl pyrrolidone

3.55

3.55

3.55

3.55

InkRes® 33

3.50

3.50

3.30

3.50

Resin dispersion

11.00

11.00

13.00

11.00

Defoamer

0.50

0.50

0.50

0.50

Surfactant

0.50

0.50

0.50

0.50

Glycerol

20.00

20.00

20.00

20.00

Amine (pH to 8)

0.60

0.60

0.60

0.60

Pigment dispersion

36.67

18.53

38.10

39.16

Target pigment % (benchmark)

4.50

2.25

4.50

4.50

Anti-microbial

0.10

0.10

0.10

0.10

TOTAL

100.00

100.00

100.00

100.00

Table 8. Inkjet formulation utilising InkRes® 33 to partially replace N-methyl pyrrolidone.

 

Colour Space

OEM Yellow

Lorama Yellow

OEM Black

Lorama Black

OEM Cyan

Lorama Cyan

OEM Magenta

Lorama Magenta

*L

84.50

85.70

21.50

22.36

56.98

63.20

51.60

51.50

*a

0.36

3.30

-4.34

-4.15

-34.40

-34.65

60.55

63.50

*b

92.10

85.90

-2.25

-2.10

-40.55

41.82

1.90

3.07

*h (hue angle)

93.30

92.10

217.50

210.75

230.75

229.30

3.19

2.69

Initial density (coated stock)

0.98

0.99

1.30

1.38

1.10

1.20

1.25

1.28

Initial density (uncoated stock)

1.08

1.15

1.40

1.40

1.15

1.15

1.30

1.30

Restart density (print head uncapped for 5 days)

0.97

0.96

1.15

1.13

1.10

1.10

1.20

1.20

Table 9. Optical colour density and L*a*b values of the benchmark and InkRes® 33 containing inkjet formulations. Tested using X-Rite colour spectrophotometer & X-Rite densitometer.

 

Printability and adhesion on Inkjet paper, glossy photo paper and coated polypropylene were good – with no notable changes when compared against the benchmark. Neither rub resistance nor wet bleed transfer were detrimentally affected as a result of including the InkRes® 33.

 

Summary

InkRes® 33 has been developed using Lorama Polysaccharide Resin Technology (LPRT) and is an invaluable tool for the ink formulator. It allows them to replace conventional – hazardous - humectants with a renewable, eco-friendly solution.  Furthermore, the inclusion of InkRes® 33 into flexographic and digital ink formulations leads to an improvement of gloss level, an increase in colour strength and – perhaps most importantly - eliminates premature drying on the press (or in the print heads). All of these benefits without negatively impacting on adhesion or rub resistance.

Lawrence Industries are the UK supply partner to Lorama and will be happy to assist you further. Please get in touch with one of our technical sales team today on 01827 314151, or submit a sample request for InkRes® 33 through our sampling page.

Author: Danielle Williams , MChem.

Danielle studied chemistry at the University of York, where she earnt her MChem with a focus on Green Chemistry.  As a senior member of the sales team, she is an expert in the field of Coatings and Inks.