一、Fundamental principle of top sizing machine:
　　Purposes of top sizing machine are to prevent infiltration, and to promote physical property of paper like surface strength and inner cementing property. It’s one of paper property promoting method. Example: top sizing of offset printing is to promote surface strength, to control infiltration of water and printing ink, and to prevent powder losing; purpose of packaging paper sizing is to prevent infiltration of oil, fat and solvent, to promote tension to prevent damage.
　　The most common top sizing agent is starch which exists in carbohydrate of plants like grain, tapioca and potato. It is polymer belonging to dextroglucose unit. The polymer exists in two forms: linear organization formed by about 500 glucose units and branch organization formed by thousands of glucose units. Linear catenulate polymer is called straight-chain which is 27% in starch. Branch polymer is called branched chain which is 73% of the starch. Starch is supplied in the form of white granular powder. It is water-immiscible because of polymer structure and hydrogen bond among the closing chains. But when hydrated suspension is heated, gelating solution and starch paste is formed because water enters micro crystallite. Steaming makes solution rare, and viscosity is reduced. Hot solution becomes thick when it cools off. This is called “re-congeal”. Because of poor rheological property and hard treatment, modification treatment or using of modified starch is necessary. The starch is available for top sizing which has been streamed continuously or discontinuously.
　　The work of top sizing is done by top sizing machine which is also called size press. In the size press, sizing solution irrigates the press area entrance. Paper absorbs some sizing solution, and the extra parts are wiped off in the press area. The escaping sizing solution enters the funnel and then loops into the press area.
　　There’re two fundamental principles of combination of sizing solution and paper: 1. adsorbing capacity has relations to quantity, tension, smoothness, structure of fibrous tiny pipes, hole size, sizing level of pulp and water ratio; 2. it has relations to liquid film thickness, state of division of paper and roll surface, solid ratio, temperature, viscosity, speed, sizing materials tank depth, pressure and width of press area. In common condition, low viscosity, high temperature, low speed, low sizing level are helpful for promoting paper adsorbing capacity; surface roughness, high speed, low pressure and high viscosity are good for thickening liquid film.
　　In size press, sizing solution enters the press area between a pair of press rollers which rotate in opposite directions, and a sizing material tank is formed. Sizing materials can absorb power from the moving paper and rotating press rollers. In this way sizing solution enters the press area, and its quantity is limited by the press roller’s pressure. The extra sizing solution flows back. The counter-moving of sizing solution makes perturbation of the tank. It will run over the press area when the perturbation is too big. All of this make the paper adsorb evenly.
　　The size press equipment should be promoted to reduce the perturbation of the sizing material tank. Lengthen press roller diameter and reduce the accelerating force to sizing solution from press rollers is helpful for reduce the perturbation. In this way, it makes paper adsorb evenly. Working speed of paper making machine should fit the press roller diameter.
　　The other problem is liquid film division. Though most of liquid film is adsorbed by the paper after going through the press area, there is also some extra liquid film on the paper surface which is between the paper and roller surface. The liquid film is divided into two layers. Some of them are taken away by the paper while the others still stay on the roller surface. There are thick sizing materials staying on the rollers. It’s a very obvious problem when working speed and sizing solution viscosity is high.
　　To reduce affect of liquid film, sizing solution set and size press set should be promoted. Through adjustment of chemical process, sizing solution is made which has high solid ratio, and good rheological property; to reduce extra sizing solution by increase press roller’s pressure. As the result, affect of liquid film division is reduced, water brought to the drying part by paper is reduced, and steam cost is reduced in the drying part.
　　The water which enters size press paper also has affect on adsorb quantity of sizing solution. It adsorbs faster because of high water ratio of paper, so control of the water entering size press is very important. If paper is too dry, speed is limited, and costs too much. If it is not dry enough, even distribution of water can not be ensured.
　　Matching of the two press rollers is one of the most important thing. If it is not accurate enough, corrugation and damage may occur, and paper is easy to be broke. Along with the increasing of speed, accurate matching of rollers is more important.
二、starch preparation：
　　Native starch is a kind of insoluble white powder which becomes suspension in water and then becomes gelatineous dispersoid by steaming. It’s called starch paste. Continuous method and discontinuous method can be used to steam suspension. Viscosity of solid must be controlled by measuring water and starch. Wetting and stirring is essential for steaming to get even dispersoid. The starch suspension should better be filtered before steaming.
　　Discontinuous steaming system’s main set is steaming vat which consists of an open vat and stirring sets. At the same time of stirring, reaction temperature is achieved, and then heat preservation is practiced by oxygen treatment; it goes through stream again. When temperature reaches the turning point, viscosity of suspension increases. If continue to steam, viscosity will reduce again. Final temperature of starch suspension should be lower than boiling point. If suspension is boiling, foam can be produced, and once it spill out, it’s harmful to people.
　　Steaming and oxidizing of starch is also called hot chemical transformation which is composite of depolymerization and high temperature disgregation. The purpose of adding oxidizer is to reduce starch viscosity by the combining effect of oxidation and disaggregation. Coagulation of linear chain is easy to occur because all the steamed starch is acidic. Hydrate of sodium should be added immediately and PH value should be adjusted between 8 and 8.5 to reduce coagulation of linear chain.
　　Accurate measurement is an important part in sizing solution. The basic condition of steady viscosity and rheological property is steady temperature. Adjustment and controlling of starch steaming temperature is the core of sizing solution preparing.
3. Practice of top sizing machine technology in corrugated paper making.
　　Major technical target of corrugated paper: transverse ring crush index, longitudinal breaking length, tension and hydroscopic property. transverse ring crush index is one of the most important index of examining of producer and customers.
　　Analysis of corrugated paper making process: Through contrastive analysis of producing process, material proportion, machine structure and product physical index, we make the following conclusion: beside strength and combination state of fiber, paper’s water content also affects transverse ring crush index; it’s up to the standard when it is just produced, but its index reduces after some time.

Contrastive analysis of typical data

model	material proportion	Press structure	definite quantity/㎡	Water content %	transverse ring crush index
					Inspecting value after production	Inspecting value after 24 hours
multi-cylinder long mesh	all native waste paper	Big roller diameter press	110	7.5	5.26	4.45
	mixture of native waste paper and American waste paper		110	8	5.94	5.12
multi-cylinder round mesh	all native waste paper	Common press	120	8	4.85	4.32
	mixture of native waste paper and American waste paper		120	9	5.72	5.10

　　Considering basic principle of top sizing machine, processing condition of sizing solution preparation is the central point. Proper temperature and liquid level automatic control system are essential factors that ensure stability of sizing solution. Fireretardant ability, high line pressure, and hard roller surface are basic demands of sizing press rollers. Advanced technologies like big roller diameter, double rollers, accurate Frequency Conversion Equipments are basic running conditions of sizing press machine.
Ability of sizing solution adsorbing should be strengthened in corrugated paper making. The sizing solution should be forced entering paper to strength its binding capacity. Reduce thickness of liquid film to reduce water that enters the drying part and to reduce cost of steam. Steady temperature, viscosity, quantity and high line pressure are required. They should match with proper rollers.
　　The top sizing technology is used in corrugated paper making. Emulsionized sizing solution which solid content is above 10% is formed through oxidation reaction, steaming, thinning, and accessory ingredient adding. The emulsionized sizing solution is supplied into top sizing machine continuously by sizing solution supplying system. The sizing solution is painted on the paper surface evenly by top sizing machine. Through the physical action like high temperature infiltration, interpenetration, high line pressure pressing, a water proof layer is formed on the paper surface. The ability of water resistance is improved; At the same time, some technical indexes are improved like transverse ring crush index and longitudinal breaking length.

Comparing of data before sizing and after sizing