Gel Analysis

HPL/CSE/TECH/SE/4.4.4/01/03/OHPV confidential

Gel Analysis of Polyolefin Film

A. GEL COUNT OF LLDPE & PP FILM

1. Scope:

This test method covers the determination of the number of gels present in LLDPE & PP films

when observing the images formed on a screen when light is projected through the film.

2. Summary:

The test methods encompass magnification of the film specimen by 7:1 (Method followed at

ARDC) or 10:1 (Method followed at QA), thus making the images of the gels projected on a clean

screen easy to see. Standard Sizing Template (suitably magnified) for determination of the size of

gels and is employed. The defects so counted are classified according to their sizes and are

reported as number of defects per square metre.

Gels are believed to be composed of oxidized or high molecular weight materials, which is not

readily blended into the polymer matrix. Surface defects arising out of poor blendability of

additives may also contribute to gel like appearance.

3. Safety:

Standard laboratory safety procedures are to be followed. The bright light of the overhead

projector should not be directly looked at.

4. Interference:

Use of non-standard test equipment will limit the reproducibility between laboratories.

Contamination in the sample.

Inadequate purging of the extruder during processing of the film

Cross-contamination of the extruder during processing of the film

Contamination, scratches and marks in the film caused by poor handling

Contamination in the inspection apparatus from inadequate cleaning (dirty lens etc.)

Improper focus of the inspection apparatus

Excess magnification of the film specimen

Non-representative sampling (Incorrect sampling point, incorrect time of sampling)

5. Apparatus:

Standard overhead projector: 2000 lumen capability

Standard film mover

Film Properties 21


Standard wall chart viewing and sizing surface, approx. 1 gm x 2.0m., in size of

heavyweight paper with matte finish with low gloss printing ink has sizing reference

lines and circles for 0.1mm, 0.2mm, 0.5mm, 0.7mm. and 1.5mm sized for 10 times / 7

times magnification / projection of film.

Standard sizing Template Clear polyester OHP film template with sizing reference

lines (parallel line separated by distances equal to 7 times or 10 times 0.1mm,

0.2mm, 0.7mm & 1.5mm) for use with the standard wall chart.

Coin – with about 25mm (1 inch) diameter. Alternatively clear polyester OHP film with

a 1cm long line drawn on it using a marker can be used.

Vernier Calipers for accurate measurement of calibration coin accurate to 0.1mm.

Meter Ruler

Measuring tape

Clean soft cleaning cloths

Hand Tools

6. Test Method:

Setting Up the Apparatus – Method Followed at QA

Set up the overhead projector and mount it on a table facing a clean white screen

Measure the diameter of the calibration coin precisely to the nearest 0.1mm with the

vernier caliper

Multiply this dia. By 10

Turn on the projector bulb

Place the coin on the projector to project an image on the wall chart

Focus the projector so that the shadow of the coin edges appears as a sharp circle on the

wall chart

Measure the diameter of the circle accurately with a metal ruler or measuring tape. This

value should be within ±1% of the calculated in the step above

Move the table projector and film mover backwards away from or forward towards the wall

chart until a 10x magnification of the coin is obtained

Setting Up the Apparatus – Method Followed at ARDC


Turn on the projector bulb.

Place the clear polyester OHP film with a 1cm long line drawn on it on the projector to

project an image on the wall chart

Focus the projector so that a sharp shadow of the line appears on the screen

Measure the length of the image accurately with a metal ruler or measuring tape

Adjust the position of the projector till a 7X magnification of the 1cm long line is obtained.

Test Specimens - LLDPE:

Film Properties 22


A total film test area of 1520 sq.cm (240 sq. in) is employed for the testing, the area being divided

into six specimens of 40 sq.in (8” X 5”) each. The LLDPE film samples shall be prepared by blown

film extrusion and shall be of thickness 25±5 microns.

Test Specimens – PP:

A total film test area of 1520 sq.cm (240 sq. in) is employed for the testing, the area being divided

into six specimens of 40 sq.in (8” X 5”) each. The PP film samples shall be prepared by cast film

process (R103, F103) or tubular quench process (F110) and shall be of thickness 20±5 microns.

Procedure:

Mark out an area of 8”X5” on each film specimen using a marker.

Place the film on the projector and view its image on the screen.

Circle the gels on the film using a fine tip marker.

Ascertain the size of the gels by placing the standard sizing template on each surface

defect image projected on the screen. The size of the gel is taken as that closely

matching a given reference line on the template.

Record the number of gels, classified according to their size for each test specimen.

Depending on specifications requirements, defects sizes may be 0.2mm – 0.49mm,

0.5mm – 0.69mm, 0.7mm – 1.5mm and >1.5mm.

7.Reporting:

The report should consist the following details:

Complete identification of the material tested, formulation, lot number & date of manufacture.

Date of testing.

Date of film production & processing conditions.

Thickness of the film.

Number of film defects in each size category.

LLDPE: Number of defects per square meter in size categories – 0.2 – 0.5mm, 0.5 – 0.7mm &

0.7 – 1.5mm.

PP: The gel count is reported as per the table below:

Gel Size category Test Method Number / 1520 cm2

(0.2 – 0.5) mmASTM D 3351

(0.5 – 1.5) mm

8. References:

MA 17108

MA 17329

ASTM D 3351

Film Properties 23


B. GEL COUNT OF HDPE (MITSUI) FILM

1. Scope:

This test method covers the determination of the number of gels present in an HDPE film when

observing the images formed on a screen when light is projected through the film.

2. Summary:

The test methods encompass magnification of the film specimen by 7:1 (Method followed at

ARDC) or 10:1 (Method followed at QA), thus making the images of the gels projected on a clean

screen easy to see. Standard Sizing Template (suitably magnified) for determination of the size of

gels and is employed. The defects so counted are classified according to their sizes.

Gels are believed to be composed of oxidized or high molecular weight materials, which is not

readily blended into the polymer matrix. Surface defects arising out of poor blendability of

additives are to be taken into consideration too.

3. Safety:

Standard laboratory safety procedures are to be followed. The bright light of the overhead

projector should not be directly looked at.

4. Interference:

Use of non-standard test equipment will limit the reproducibility between laboratories.

Contamination in the sample.

Inadequate purging of the extruder during processing of the film

Cross-contamination of the extruder during processing of the film

Contamination, scratches and marks in the film caused by poor handling

Contamination in the inspection apparatus from inadequate cleaning (dirty lens etc.)

Improper focus of the inspection apparatus

Excess magnification of the film specimen

Non-representative sampling (Incorrect sampling point, incorrect time of sampling)

5. Apparatus:

Standard overhead projector: 2000 lumen capability

Standard film mover

Standard wall chart viewing and sizing surface, approx. 1 gm x 2.0m, in size of

heavyweight paper with matte finish with low gloss printing ink has sizing reference lines

and circles for 0.1mm, 0.2mm, 0.5mm, 0.7mm and 1.5mm sized for 10 times / projection

of film.

Standard sizing Template Clear polyester OHP film template with sizing reference lines

(parallel line separated by distances equal to 7 times or 10 times 0.1mm, 0.2mm, 0.7mm

& 1.5mm) for use with the standard wall chart.

Film Properties 24


Coin – with about 25mm (1 inch) diameter. Alternatively clear polyester OHP film with a

1cm long line drawn on it using a marker can be used.

Vernier Calipers for accurate measurement of calibration coin accurate to 0.1mm.

Meter Ruler

Meter ruler or measuring tape.

Clean soft cleaning cloths

Hand Tools

6. Test Method:

Setting Up the Apparatus – Method Followed at QA


Measure the diameter of the calibration coin precisely to the nearest 0.1mm with the

vernier caliper

Multiply this dia. by 10

Turn on the projector bulb

Place the coin on the projector to project an image on the wall chart

Focus the projector so that the shadow of the coin edges appears as a sharp circle on the

wall chart

Measure the diameter of the circle accurately with a metal ruler or measuring tape. This

value should be within ±1% of the calculated in the step above

Move the table projector and film mover backwards away from or forward towards the wall

chart until a 10x magnification of the coin is obtained

Setting Up the Apparatus – Method Followed at ARDC


Turn on the projector bulb.

Place the clear polyester OHP film with a 1cm long line drawn on it on the projector to

project an image on the wall chart

Focus the projector so that a sharp shadow of the line appears on the screen

Measure the length of the image accurately with a metal ruler or measuring tape

Adjust the position of the projector till a 7X magnification of the 1cm long line is obtained.

Test Specimens

A total film test area of 1520 sq.cm (240 sq.in) is employed for the testing, the area being divided

into six specimens of 40 sq. in (8” X 5”) each. The HDPE film samples shall be prepared by blown

film extrusion and shall be of thickness 10 microns. For R5801, however, the film samples of

thickness 40 microns shall be prepared.

Procedure

Mark out an area of 8”X5” on each film specimen using a marker.

Place the film on the projector and view its image on the screen.

Film Properties 25


Circle the gels on the film using a fine tip marker.

Ascertain the size of the gels by placing the standard sizing template on each surface

defect image projected on the screen. The size of the gel is taken as that closely

matching a given reference line on the template.

Record the number of gels, classified according to their size for each test specimen.

Depending on specifications requirements, defects sizes may be classified as <=

0.2mm & >0.2mm

Weigh the test specimens.

7. Calculation

Total Weight of all the test samples in gm.=W

N1 = Total number of small (<= 0.2mm) gels

N2 = Total number of large (>0.2mm) gels

Number of small gels per unit film weight = A = N1 / W (in numbers / gm)

Number of large gels per unit film weight = A = N2 / W (in numbers / gm)

A = A + B/10

The gel rating of the film shall be as per the tables below:

a Gel Rating

a ≤ 1.5 7+

1.5 < a ≤ 3.0 7

3.0 < a ≤ 10 5+

10 < a ≤ 20 5

20 < a ≤ 30 5-

30 < a ≤ 40 3

40 < a 1

8. Reporting

Complete identification of the sample

Date of test

The respective numbers of large & small fish eyes in number / gm

Gel rating

9. References

ASTM D 3351

HZ – A – 320 – 1

Film Properties 26

Documents

Gel Analysis