How to solve the problem of pressure sensitive lab

2022-08-24
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How to solve the problem of pressure-sensitive label paper warping

Abstract: This paper analyzes the causes of pressure-sensitive label paper warping and puts forward improvement measures

key words: pressure sensitive label paper; Warping

pressure sensitive label, so the paper is composed of anti sticking base paper, adhesive film and face paper. The lotion pressure-sensitive latex is evenly coated on the anti adhesion base paper, enters the drying oven, the latex is evaporated by water, the particles are deformed, the polymer molecules penetrate, diffuse and form a film. After leaving the drying oven, the back of the anti adhesion base paper is coated with water by the wetting device, and then compounded with the surface paper. After the composite paper is cut into flat plates off the machine, it often warps to varying degrees, which not only has the advantages of raw materials. When the printing factory cuts it into small pieces, the warpage is more serious, which affects the product quality of pressure-sensitive label paper. How to solve the warpage of pressure-sensitive label paper

1. control the amount of water applied on the back

when the anti sticking backing paper after the latex is dry, while the latex evaporates and forms a film, the moisture of the backing paper also evaporates, and the backing paper will shrink laterally due to water loss. The anti sticking backing paper out of the oven is coated with water on the back, and the backing paper fiber absorbs water and swells. The amount of water added should ensure that the moisture of the base paper fiber after swelling is just in balance with the moisture of the ambient air

the amount of water added is less. After the combination of the base paper and the face paper, the moisture of the base paper fiber is less than that of the ambient air, and it will continue to absorb the moisture in the ambient air, so that the fiber will continue to swell, resulting in the post composite swelling (called post swelling), causing the pressure-sensitive label paper to warp towards the face paper layer (upward)

although new materials have been innovatively used in various fields, there is a lot of water to be added. After compounding, the fiber of the backing paper is too moist and swollen, so that the fiber moisture is greater than the moisture in the ambient air. The backing paper will volatilize the excess moisture to achieve the moisture balance with the ambient air, resulting in the lateral shrinkage (called post shrinkage) after compounding, which makes the pressure-sensitive label paper warp (downward) towards the backing paper layer

therefore, to prevent paper warping, controlling the amount of water applied on the back is the key factor

2. The proportion of back coating water and back coating agent should be appropriate

the main component of back coating agent is sodium dodecylbenzene sulfonate. The purpose of adding back coating agent is to make the water easy to form a film and apply it more evenly. The water applied by the coating on the back of the anti sticking backing paper is partially absorbed by the fibers, which makes the fibers swell, and the other part evaporates rapidly when encountering hot paper sheets. The addition of back coating agent prevents the evaporation of water, and the amount of water applied remains unchanged. When the proportion of back coating agent in the back coating liquid is large, the evaporation speed of water slows down, and the water that should be evaporated cannot be evaporated in time, so that the fiber continues to expand, causing the paper to rise horizontally. Strictly controlling the proportion of water and back coating agent can also effectively prevent paper warping

3. Strictly control the temperature curve of latex drying

adhesives usually use three-stage drying, and the temperature of the three-stage is generally controlled by the introduction of professional management company system: the first stage is 100 ℃, the second stage is 110 ~ 125 ℃, and the third stage is 110 ~ 120 ℃. If the temperature out of the oven is too high, after the water is applied on the back, most of the water will evaporate when it meets the hot paper, and only a small part will be used to compensate for the loss of water in the anti sticking base paper. The paper will still warp when the water amount remains unchanged

4. requirements for the operating environment

the moisture of the bottom paper after lamination should reach a balance with the moisture of the environment in the lamination Workshop, and the paper after lamination will be flat. Therefore, the compound operation is best carried out under the condition of constant temperature and humidity

5. Requirements for anti sticking backing paper

the expansion rate of anti sticking backing paper should be small. It is best to put the self-made anti sticking backing paper for a period of time after it is removed from the machine, so that the moisture of the backing paper is balanced and uniform

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