GB/T 6595-2025Plastics — Test method for fish eye count of polypropylene resin (English PDF)

3.1 Fish eye

4.1.1 Projector

The magnification of the projector shall not be less than 8 times; the size of the observation board shall not be less than 200 mm x 200 mm.

4.1.2 Projection area

The projection area is a screen or other suitable flat object with a flat surface, uniform color and no pollution. The projection area is perpendicular to the horizontal plane.

4.1.3 Standard orifice plate

The material of the standard orifice plate is organic glass or other transparent materials, with a specification of 230 mm x 230 mm x 3 mm, and 3 standard holes with apertures of phi0.8 mm, phi0.4 mm, phi0.2 mm, respectively. It has smooth edges; the aperture distance is about 12 mm. The holes are roughly located in the center of the plate.

4.2 Specimen preparation

4.2.1 Prepare polypropylene film by tape casting method according to the requirements

of Appendix A.

4.2.2 Start cutting the specimen at 1 m from the end point of the film roll of the film specimen; cut 3 specimens in total. The interval between each specimen is 5 m; the specimen shall be flat and wrinkle-free.

4.2.3 Each specimen consists of 4 layers of film with a size of not less than 250 mm x 250 mm and a thickness of 0.030 mm ± 0.005 mm. The 4 layers of film are fixed at one corner.

4.2.4 The test size of each film layer is 190 mm x 200 mm; the total test area of 4 layers of film is 1520 cm2.

4.2.5 The test part is more than 30 mm away from the edge of the film. When the film width is not enough, the test size in the length direction of the film can be increased to ensure that the total test area is 1520 cm2.

4.3 Preparation

4.3.1 Prepare the projection area.

4.3.2 Draw a rectangle of 190 mm x 200 mm or equal area on the observation board of the projector. When the observation board is not long enough, draw the rectangle on the stacked film during the test, or use other effective methods to ensure the film test area and area.

4.3.3 Adjust the projector to the appropriate magnification; the projection light shall be

perpendicular to the projection area.

- Scanning frequency. Adjustable;

- Camera depth of field. Not less than 2 mm.

The distance between the camera and the film shall ensure that the camera is accurately focused; the geometric center of the camera lens, film width and light source are aligned;

the length direction of the camera sensor is perpendicular to the film processing direction.

The image acquisition system receives the digital image data transmitted by the camera and collects and stores the data.

5.1.4 Image processing system

The computer receives the image data and performs image analysis, size measurement, result calculation.

The image processing system can identify images that are not fish eyes.

Check whether the measured fish eye size is accurate according to Appendix B.

5.2 Test steps

5.2.1 Setting the matrix gray level

Set the matrix gray level according to the instrument manufacturer's recommendations, combined with the actual test conditions and test results.

Note. The matrix gray level is usually 170 (8-bit camera).

5.2.2 Setting the detection limit

Draw a curve of the relationship between different detection limits and the number of fish eyes. The value corresponding to the inflection point of the curve is the detection limit of the film. Other effective methods can also be used to determine this value, or it can be set according to the recommendations of the instrument manufacturer.

Note. The detection limit is usually 85 (8-bit camera).

5.2.3 Preparation of film

Prepare the film according to Appendix A.

5.2.4 Film detection

After the material is fully replaced and the film meets the requirements of 5.2.3, start image acquisition and analysis.

The distance between the edge of the detection area and the edge of the film is not less than 30 mm.

The size of the fish eye is expressed as the equivalent circle diameter. The recommended sizes are phi0.8 mm, phi0.4 mm, phi0.2 mm (consistent with method A). Other sizes can also be used.

The film detection unit is 1 m2; the total area of continuous detection is not less than 5 m2.After the detection, the system stops collecting data and outputs the results; saves the image data of the fish eye.

5.3 Calculation and representation of results

The number of fish eyes of each size is expressed as the average value of 5 consecutive tests, rounded to one decimal place according to GB/T8170, in the unit of pieces/m2.