How to Improve Colorfastness in Vat Dyeing

Colorfastness Problems in Vat Dyeing- Reasons and Remedies

Causes of Poor Colorfastness in Vat Dyeing

Frequent addition of colors in the dye bath to match the shade. It disturbs the equlibrium between colors and chemicals.

- Improper oxidation

- Improper washing

- Some peculiar colors such as blue and brown also leads to this defect.

- Hardness in the water used

- Mixing of incompatible colors

- Usage of large quantities of reducing agent and alkali

- Improper temperature

- Improper wringing of the cloth

- Faults in the machine

- Not using essential chemicals such as dispersing agent or leveling agents.

- Dyeing in a finished cloth ( Resin or Silicon Finish)

- Improper preparation of the cloth or thread for dyeing ( Like not removing impurities or size)

How to improve colorfastness in Vat Dyeing

1. Dont frequently add colors during dyeing

2. Ensure proper reduction clearance

3. Ensure proper oxidation

4. Choose right colors and chemicals

5. Control Temperarue

6. Use soft water

7. Add Dispersing or levelling agent as per need

8. Dont redye finished cloths

9. Ensure proper washing after dyeing.

10. Treat the material with small amount of Ammonia and Sodium Hydrosulphite

11. Treat the cloth with large amount of reducing agent and alkali. This method can be resorted to if there is some bleeding in the colors.

The Measures of Fiber Length

The Measures of Fiber Length

1. Mean Length: Numerical Average length of fibres of given population of fibre.

2. Upper Quartile: Length for which 75% of all observed values are lower or 25% higher by weight or number

3. Modal Length: The most frequently occuring length of fiber.

4. Median Length: Length Below and above which 50% of fibres lie.

5. Half Fall Value: The fiber length higher than modal length having half the modal frequency by wt. (Group length longer than mode with frequency equal to 1/2 of mode.)

6. Effective Length: Upper quartile of numerical length distribution from which some of the shortest fibers, having length less than half of effective length are cutailed or eliminated.

7. short fiber %: It is the % of fibers having length less than 1/2 of the effective length value.

8. Uniformity Ratio: Ratio of 50% span length to 2.5 % span length.

9. Span Length: It is the distance that can be spanned by specified percentage of fibers in a test beard.

10. Irregularity: Percentage by weight fo fibers in a sample which are shorter than 3/4th of the mode.

11. Dispersion %: inter quartile range expressed as % of effective length.

How to Determine the Color Fastness of Textile material to Dry Cleaning

How to Determine the Color Fastness of Textile material to Dry Cleaning

Technical Specifications:

Apparatus:

1.To determine colorfastness to drycleaning a suitable mechanical device consisting of water bath containing a rotatable shaft which supports, radially, glass or stainless steel containers ( 75+-5mm diameter x 125+-10mm high) of approximately 550+-50 ml. capacity, being 45+-10mm high from the centre of the shaft should be used. The Shaft/container assembly is rotated at a speed of 40+-2 rev per minutes.The temperature of the water bath is thermostatically controlled to maintain the test solvent at 30 deg +-2 celcius.

2. Stainless stell disc of 30+-2mm x 3+-0.5mm, smooth and free from rough edges of mass 20+-2 gm.

3. Undyed cotton twill cloth of unit area 270+-70 gsm, free from finishing and cut into samples of size 12 cm x 12 cm

4. Grey scale for evaluating change in color and staining.

5. Glass tubes of diameter 25 mm

Preparation of the Specimen

For a fabric sample, take a specimen of size 10cm x 4cm from the sample representing the lot.

If the material to be tested is sewing thread, make a wick of parallel length 10 cm long and about 0.5 cm in diameter, tied near both ends.


Procedure

Prepare a bag with inside dimension of 10cm x 10 cm using the undyed cotton twill cloth by sewing together two squares of this cloth around three sides.

Place the specimen and 12 stell discs inside the bag and close the bag.

Place the bag in the container and add 200 ml of Perchloroethylene or any other suitable solvent at 30 +- 2 deg C

Fix the container in the mechanical device maintained at 30+-2 deg C and run the machine for 30 minutes.

Remove the bag from the container, withdraw the specimen and dry the specimen in air at a temperature not exceeding 60+-5 deg C.

Evaluate the change in color of the tested test specimen with grey scale, after attaining normal moisture content.

Filter the solvent remaining in the container through filter paper and compare the color of the filtered solvent with that of unused solvent in the glass tube placed in from the white card using transmitted light by means of grey scale for assessing staining.

In case of doubt in the color fastness rating as assessed by an observer, the assessment should be done by at least three observers and the overall average rating should be reported.

Report

Report the numerical rating for change in color of the test specimen and the numerical rating for staining of the solvent. Also report the solvent used for the test.

Listing Defect in Vat Dyeing

Listing Defect in Vat Dyeing and the Precautions to Prevent the Defect

Listing is the variation in color of centre of the fabric with the selvedge. Some of the reasons for this defect are:

1. Improper batching.
2. Non Uniformity in the selvedge
3. Redyeing of the fabric
4. Foam on the two sides of the jigger.
5. Slippage of the fabric from the roller during dyeing.
6. Shortcomings in the machine such as malfunctioning of guide roll, expander roller or improper squeezing.
7. Improper filteration of the colors, improper circlation of the liquor during dyeing. Difference in temperature of liquor in the centre and at the ends.
8. Mixing of colors which are not properly compatible.
9. Improper singeing

The remedies are:

1. There should not be any mechanical fault in the machine.
2. Take proper care during dyeing, like filter the color solution before using, ensure that all the controlling instrument ( temperature, time) work properly. Circulate the liquor continuously during dyeing.
3. If some shade is not coming out proper, dye with a slighly heavy shade without taking out the earlier color.
4. Join the fabrics of the same width while making a lot.