Application methods of fluorescent whitening agents in the paper industry (1): Pulp whitening
Making pulp is the first step in the papermaking process. The whiteness of the bleached pulp still does not meet the requirements for use. At this time, a fluorescent whitening agent is often added to the pulp to make the originally yellowish and dark pulp white. When fluorescent whitening agents are used in beaters, factors that affect the whitening effect include water purity, pH value, aluminum sulfate, rubber, fillers, wet strength agents, residence time, temperature, feeding sequence, concentration, etc.
In order to ensure the whitening effect, auxiliary materials such as aluminum sulfate, rosin gum, and fillers that are white and have low iron content should be used. The pulp itself should also be white and thoroughly washed to remove chlorine. The cheap DSD acid bistriazine fluorescent whitening agent is commonly used for paper pulp whitening. For neutral or alkaline papermaking, disulfonic acid varieties should be selected, such as C.I. fluorescent whitening agents 28, 85, 134, etc.; acidic papermaking requires that the fluorescent whitening agent is stable to acid and aluminum sulfate, and tetrasulfonic acid varieties should be selected, such as C.I. Optical brighteners 24, 220, etc. Since the affinity of hexasulfonic acid varieties to pulp fibers is too small, such as C.I. Fluorescent Whitening Agent 264, etc. are not suitable for pulp whitening.
The method of adding the fluorescent whitening agent used for paper pulp whitening is: dissolve the required amount of fluorescent whitening agent in water. Those with poor solubility can be dissolved in hot water of 60 to 90°C, stir thoroughly until all is dissolved, or use liquid The fluorescent whitening agent is filtered to remove insoluble matter, diluted appropriately and directly added to the pulp mixing tank, and mixed evenly. Note that the fluorescent whitening agent solution should not be stored under sunlight for a long time and should be used as soon as it is prepared. Dissolution utensils should be made of plastic, wood, brown glass containers or pottery. Metal containers such as copper and iron should not be used.
The amount of fluorescent whitening agent and color correction dye should be determined according to the requirements of the finished product and the basic whiteness of the pulp. The fluorescent whitening agent is generally about 0. 05% to 0. 2% of the dry pulp weight. In order to ensure even distribution, the fluorescent whitening agent should be slowly added to the pulp during beating, and the pH value is preferably 7 to 8.
The order of adding materials can be that after the pulp is fully washed to remove chlorine, fluorescent whitening agent solution, rosin emulsion, pigment and other additives can be added in sequence. The interval between adding each additive should not be less than 10 minutes. Each additive must be fully beaten after addition. After beating for 30 to 40 minutes, add aluminum sulfate. Special attention should be paid not to add fluorescent whitening agent and aluminum sulfate to the pulp at the same time, otherwise the whitening agent will precipitate and affect the whitening effect.
Pulp whitening process flow:
Fluorescent whitening agent, rosin, pigment, aluminum sulfate and other additives ↓
Slurry tank → Pulp mixing tank → Pulp storage tank → Paper making → Drying
Application example 1:
Optical brightener VBL pulp whitening. Formula (for dry pulp weight):
Fluorescent whitening agent VBL 0. 05% ~ 0. 1%
Rosin regular amount
Talcum powder. regular amount
Aluminum sulfate 6%
Whitening process: Dissolve the required amount of fluorescent whitening agent VBL with 20 times the amount of warm water (about 55%), and then dilute it with cold water to a solution with a concentration of 0. 3 ~ 3g/L for later use.When the pH of the pulp = 7 ~ 8, add additives to the pulp mixing tank in the order of fluorescent whitening agent, rosin, talc, and aluminum sulfate. The time interval between adding various additives should not be less than 10 minutes, and be fully Beat. After the pulp is beaten to a certain degree, it is sent to the pulp storage tank, and then made into paper and dried.
Application example 2 :
Fluorescent whitening agent Tinopal ABP liquid is used to whiten pulp.Formula (for dry pulp weight):
Tinopal ABP liquid 0. 05% ~ 1. 0%
Rosin regular amount
Talcum powder (or calcium carbonate) regular amount
Aluminum sulfate. 6%
Whitening process: Add the required amount of fluorescent whitening agent Tinopal ABP liquid, rosin, talc, and aluminum sulfate to the pulp mixing tank in sequence. The time interval between additions is not less than 10 minutes, and the pulp is fully beaten to adjust the pH of the pulp = 4.5. ~9. After the pulp is beaten to the specified beating degree, it is sent to the pulp storage tank, and then paper is made and dried.
Application example 3:
Hakkol AP for pulp whitening. Formula (for dry pulp weight):
Pulp concentration 2% ~ 5%
Hakkol AP concentration 0. 1% ~ 0. 8%
Aluminum sulfate (or not added) 1% ~ 3%
Whitening process: Beating process for 10 minutes at 20 to 30 degrees Celsius.
This fluorescent whitening agent has good affinity for pulp without adding additives during pulp whitening. Generally speaking, the degree of stirring during the fluorescent whitening process does not affect the whitening effect. Due to its excellent acid resistance, acid catalysts have little effect on the whitening effect in rosin sizing.
