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Benefits of Spunbond Substrate Uniformity in Advanced Filtration Media

Cerex Advanced Fabrics, Inc.

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Introduction

Market demands for finer particle capture, increased dirt holding capacity and longer service lives in today’s smaller, high pressure filtration systems are driving advancements in filter media designs.

Advanced media designs often use multiple layer combinations of cellulose, micro-glass, synthetic fibers and/or membranes to achieve these increased performance requirements.

Many of these more advanced medias are relatively fragile and require structural support to prevent potential damage during processing and while in use.

Spunbond nonwoven fabrics can provide the needed structural support and may actually increase the performance of the filter media during real-life dynamic flow conditions.

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Spunbond Use in Advanced Filter Media

Typically, the spunbond fabrics are placed on one or both sides of the filter media to provide downstream and upstream support.

Some filter medias like synthetic melt blown, nano-fiber and cast membranes are produced directly onto the spunbond fabric and can be classified as “formational.”

Other types of media, like wet laid cellulose and micro glass are produced separately from the spunbond and then co-pleated or bonded to the spunbond in a separate process. These can be classified as “laminated.”

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Impact of Uniformity

The industry recognizes that the uniformity of the filter mediadoes matter and directly impacts the performance of the filter.

A variety of static test methods are used to quantify and verify the media consistency and performance, including among others: The Bubble Point test (ASTM 316, ARP-901A), The Multi-pass test (ISO 16889), TSI 8130 (fka the DOP test), and The Diesel/Petrol Filter Test (ISO 19438)

But this raises a question………

Does the uniformity of the spunbond substrateused in the filter media also matter?

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Does Spunbond Uniformity Matter?

With formational medias, the answer is unquestionably yes. Meltblown and nano-fiber formation are dependent on the substrate fiber

“web” uniformity.

Cast membrane performance is known to be dependent on the consistency of the substrate thickness.

With lamination medias, the answer is more difficult to quantify, especially using traditional “static” filter test methods. The spunbond substrate is to open a structure to act as a filter media, and

traditional filter tests do not typically detect a benefit from the spunbond.

But what happens during actual use conditions when pressures,flow rates and contaminant levels are fluctuating versus static?

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How to Quantify Spunbond Uniformity

Before we can evaluate the potential performance benefits of a more uniform spunbond substrate, we first must agree on methods to quantify uniformity. Visual comparisons have been traditionally used, but are not quantifiable or

reproducable.

One option is to measure the consistency of substrate physical properties

Another option is to utilize digital camera technology and measure the consistency of light transmission through the spunbond.

Basis Weight Thickness Air Permeability

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Most people agree that the visual uniformity of Cerex® brand spunbond nylon is better than polyester

Unfortunately, visual assessments don’t provide quantitative data for comparison

Visual Comparisons are Subjective

Polyester Nylon 6,6 Polyester Nylon 6,6

20 GSM 34 GSM

Sample size is 17 cm by 15 cm

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Physical Property ComparisonsSampling Methodology

• Six (6) 64-72” wide commercially available PET spunbond rolls

• Five (5) 60” wide Cerex® spunbond nylon rolls

• Basis Weights ranged between 20 and 51 gsm

• 10 Full Width MD Samples taken every 10 meters

• 5 to 7 CD Samples taken every 30 cm across the spunbond width

A total of 50 to 70 samples tested per roll for statistical validity

Basis Weight Thickness Air Perm

D3776 D1777 D737

And were tested using ASTM Standardized Methods

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1.30

1.63

1.32

1.62

1.82

1.39

2.31

2.71

2.87

1.80

2.51

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

20 25 29 34 36 46 46 51

Bas

is W

eigh

t St

and

ard

Dev

iati

on

(gs

m)

Basis Weight (gsm)

Standard Deviation of Basis Weight Measurements for Nylon and Polyester Spunbond Fabrics

Basis Wt Std dev (gsm) 4 dpf Nylon

Basis Wt Std dev (gsm) 4 dpf PET

Basis Wt Std dev (gsm) 2 dpf Polyester

Basis Weight Variability

More uniform basis weight leads to more uniform strength properties

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Thickness Variability

0.42

0.330.39 0.36

0.45

0.64

0.91

1.181.15

0.54

0.66

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

20 25 29 34 36 46 46 51

Basis Weight (gsm)

Thickness Std dev (mils) 4 dpf Nylon

Thickness Std dev (mils) 4 dpf Polyester

Thickness Std dev (mils) 2 dpf Polyester

Thic

knes

s St

and

ard

Dev

iati

on

(m

ils)

Standard Deviation of Thickness Measurements for Nylon and Polyester Spunbond Fabrics

Thinner composite structures allow:• More surface area (more pleats) or• Lower pressure drop (more space for fluid to flow)

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187

8881

42 40

255

194

159

122

99

62

0

50

100

150

200

250

300

20 25 29 34 36 46 46 51

Basis weight (gsm)

Air Perm Std dev 4 dpf Nylon

Air Perm Std dev 4 dpf Polyester

Air Perm Std dev 2 dpf Polyester

Air Permeability VariabilityStandard Deviation of Air Permeability Measurements for Nylon and Polyester Spunbonds

Air

Per

mea

bili

ty S

tan

dar

d D

evia

tio

n

(ft3

/min

/ft2

)

More consistent air permeability is a good indicator of a more consistent web formation

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Comparing Uniformity using Digital Camera Technology

On-line camera system provides grey scale output of transmitted light which shows thick and thin spots on fabrics

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2

15

43

133

193

125

36

48

35

71

107

130

91

45

35

19

61

0

50

100

150

200

145 150 155 160 165 170 175 180 185 190 195 200 205 210

Fre

qu

en

cy

Transmitted light Intensity

Histogram of transmitted light intensity for 20 gsm spunbond fabrics

Optical Representation of Fabrics

NylonStd Dev: 5.8

PolyesterStd Dev: 9.5

These outliers are “thin

spots”

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3

16

55

101

9397

91

38

107

19

4549

65

8184

70

62

27

117

2 3

0

20

40

60

80

100

120

115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190

Fre

qu

en

cy

Intensity

Histogram of transmitted light intensity for 34 gsm spunbond fabrics

Optical Representation of Fabrics

Transmitted light intensity data corroborates the physical property data

NylonStd Dev: 8.4

PolyesterStd Dev: 12.1

Note “Thin Spots”

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Case Study – Nanofiber ApplicationSame Process Conditions

TSI 8130 @32 lpm (0.3 μ particle)

% Penetration34 gsm Cerex®

46 gsm Polyester

Average 8.4% 6.3%

Std Dev 1.2% 2.4%

Max % Pen (@ 3 Std Dev)

12.0% 13.5%

Nanofiber E –Spin on substrates at the same equipment settings (Line Speed, Voltage, etc)• Cerex® basis weight was 25% less than the PET spunbond • TSI % Penetration variability range was twice as large for PET (14.4%) as the Cerex® (7.2%)

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Case Study - Hydraulic Dynamic Flow TestingCerex® Nylon Spunbond @ 20 gsm & 34 gsm

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5

Filt

rati

on

Rat

io

Time Interval

6 Micron Filtration Ratio

20 gsm Static

34 gsm Static

20 gsm Dynamic

34 gsm Dynamic

• ISO 16889 (Static) vs ISO 23369 (Dynamic)• Flat Sheet Composite Testing

• Epoxy coated wire both sides• Cerex substrate both sides• 6 micron microglass media

• Test Conditions• 200 sqcm test area

• 6 lpm - Static• 2.5 to 10 lpm – Dynamic

• Mil Std 5606 Oil with ISO Medium Test Dust• 125 Psid Terminal Pressure

• Clean Delta P Static Dynamic• 20 gsm 1.1 psi 1.7 psi• 34 gsm 1.2 psi 1.8 psi

Flat Sheet testing showed some positive directional data, but failed prior to test completion.

Next Step is to test filter cartridges to eliminate “blow by” failures.

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Conclusions

Visually the CEREX spunbond appears more uniform

Key physical properties were approximately twice as consistent

Digital Camera analysis showed spunbond nylon was 30 – 50% less variable

Electrospun nanofiber media performance showed lower penetration variability even at a 25% lower spunbond basis weight.

The CEREX® spunbond nylon had measurably greater uniformity than commercially available spunbond polyester.

Dynamic flow testing on flat sheet lamination type media showed favorable directional information, but failed prior to test completion

Additional testing using filter canisters is being conducted to determine if spunbond uniformity impacts “in-use” dynamic flow conditions.

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Excellent Uniformity

Exceptional Strength

Thermal Stability

Thinner Caliper

Chemical Affinity

The Nylon Advantage® Matters!

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Please visit us at booth C18 (Hall 11) or contact us for additional information

www.cerex.com

Thank You

The Nylon Advantage®