Surface sizing is divided into two types: internal sizing and external sizing. In-machine sizing is carried out on the paper machine and is widely used. Off-machine sizing is to put the finished roll paper on a special sizing device outside the paper machine. It is mostly used for wet-impregnated or wet-pressed special paper, and it is generally used less.

Surface sizing methods are mainly as follows.

Pool type surface sizing

The traditional tank-type surface sizing is still commonly used at low speeds, and it is suitable for fourdrinier paper machines with a speed of less than 500m/min. It is divided into two types: roll type and trough type. The roller type is divided into horizontal type, vertical type and inclined type. The amount of sizing in this sizing method is largely controlled by the solid content of the sizing solution and the depth of immersion of the paper in the sizing.

Advantages of this method: less maintenance required for the sizing unit, stable paper quality and good runnability at low machine speeds. Disadvantages: When the vehicle speed exceeds 800m/min, a large number of paper breaks and glue splashes will occur.

Pool-type surface sizing mainly includes the following methods:

Horizontal roller surface sizing

The sizing device is composed of a pair of sizing rollers arranged horizontally, one of which is a driving roller and the other is a driven roller. This kind of surface sizing method paper sheet bears less tension and rarely breaks.

Vertical roller surface sizing

The sizing device is composed of a pair of upper and lower rollers, the upper roller is a driving roller made of hard materials, and the lower roller is a driven roller, mostly rubber rollers. Vertical roller surface sizing is prone to breakage, the top of the paper is in contact with the glue before the bottom of the paper, and the amount of sizing on both sides is uneven.

Inclined roller surface sizing

Its two sizing rollers are installed with a large inclination, and the angle between the center line of the two sizing rollers and the horizontal plane is about 60°. The paper threading operation is more convenient, and it is mostly used for surface sizing of cultural paper.

Trough surface sizing

This method is to put the glue in the sizing tank, and introduce the paper into the sizing tank to immerse in the glue to achieve the purpose of sizing. It can be used for sizing inside and outside the machine.

Surface sizing of calender

It is only suitable for thick paper and cardboard, without auxiliary drying equipment. It is required that the paper and cardboard immersed in the calender should not have too much moisture. The drying after sizing mainly depends on the heat generated by the friction of the calender roller. In the case of thick paper, there are also methods of adding spray and air bubbles. The method of spraying is added between the lip plate of the headbox of the paper machine and the water line on the net or not far after the wet end is pressed. When the paper passes through the drying process, it is formed between the fiber and the filler. Adhesive film. This method is also used in multilayer corrugated paper machines.

Membrane surface sizing

Membrane sizing, also known as membrane transfer sizing, is mainly suitable for producing high-quality paper and running on high-speed paper machines. Currently, Lee & Man and Nine Dragons are using this method. It uses different forms of metering devices to first apply the glue on a transfer roller, and then the transfer roller transfers the glue on the roller surface to the feeding roller that is in contact with the paper, and the glue forms a uniform distribution on the surface of the feeding roller. A layer of film, and then transfer this layer of film to the surface of the paper by the feeding roller. Its characteristic is that the amount of glue applied to the bottom layer of the surface can be measured and controlled separately. At present, the applicator metering membrane press is a relatively common surface sizing technology.