Surface finishing

On book cover or other printed matter, coating, laminating, foiling, die cutting, creasing or other processing are called surface finishing.

Surface finishing processing not only improves the artistic effect of printing, but also protects the printed matter.



First, glazing

A layer of colorless and transparent paint is applied (or sprayed, printed) on the surface of the printed matter to protect it from dryness and increase the gloss of the print. This process is called coating. The surface of prints such as book covers, illustrations, wall calendars, and logos must be polished.

(I) Coatings

There are many kinds of glazing coatings, such as oxidative polymerization glazing coatings, solvent evaporating glazing coatings, heat-curing glazing coatings and photo-curable glazing coatings.

1. The composition of the coating

Although there are many types of glazing coatings, the basic composition is basically the same, composed of the main agent, additives and solvents.

The main agent is a film-forming substance of a glazing coating, usually a natural resin or a synthetic resin.

Additives are substances that improve the physicochemical properties and processing characteristics of glazing coatings. Commonly used are to increase the film of the cohesive strength of the curing agent; reduce the surface tension of the coating surfactant; easy to apply antifoaming agent; to improve the elasticity of the film plasticizers.

The solvent is a substance that disperses and dissolves the main agent and auxiliary agent. The commonly used solvents are: toluene, xylene, ethanol, isopropanol, methanol, ethyl acetate, methyl acetate, butyl acetate and the like.

2. Quality requirements for glazing coatings

The glazing coating has a certain level of adhesion to the surface of the printed product, and has a good leveling property. After the film is formed, the film surface is smooth.

The coating film formed by glazing coating shall have certain toughness and wear resistance, transparency and color change, wide adaptability after printing, good solvent resistance and heat resistance.

The glazing coating should be odorless, odorless, non-hazardous to the human body, free from environmental pollution, cheap and safe to use.

(b) Glazing process

The glazing of prints generally includes coating and calendering of glazing coatings.

1. Coating coating

The methods used are: spray painting, printing and coating, and coating the coating machine, and other three major methods.

Spray coating, all manual operation, although the slow speed, poor coating quality, but flexibility, suitable for rough surface or uneven printed matter (corrugated paper) or packaging containers and other special-shaped prints.

Printing and coating, usually coated with a printing press, the coating coating is stored in the ink fountain of the printing press, and a solid printing plate is used to print the coating one or more times in accordance with the requirements of the coating. Printing coating coating, do not need to purchase new equipment, a dual-purpose machine, suitable for medium and small printing factory coating coating process.

Special coating machine coating is currently the most common method. The coating machine is composed of print transmission mechanism, drying mechanism, mechanical transmission and electrical control. Applicable to various types of coating coating process, can accurately control the amount of coating, coating quality is stable, suitable for a variety of grades of glazing coating processing.

2. Quality requirements for gloss coating

In order to obtain the desired glazing effect, the glazing coating should meet the following requirements:

(1) Uniform coating layer, no blisters, no bubbles and no leakage coating;

(2) Appropriate amount of coating, coating can be completed at a certain temperature, coating speed drying conjunctiva;

(3) The coating is not affected by the performance of printing ink, printing graphics and printing density, good leveling property, and has a certain adhesion to the surface of printed matter;

(4) The coating can adhere to the surface of the calender belt during calendering and can be easily peeled off after cooling. Bump

3. Calendering

The use of a calender press to change the surface condition of the dried glazing coating allows it to form an ideal mirror surface. This process is called calendering. Many fine prints require calendering after coating.

The calender is usually a continuous roll type and consists of conveying machinery, mechanical transmission, and electrical control. The printed matter enters the calender belt between the heating roller and the pressure roller from the paper feeding table. Under the effect of temperature and pressure, the coating adheres to the surface of the calender belt and is calendered. After the calendered coating layer cools gradually, a bright surface layer is formed. The calender belt is made of special stainless steel that is not treated. The electro-hydraulic pressure regulating system is used to adjust the pressure of the pressure roller to meet the calendering requirements of various printed matters.



Second, film

The process of overlaying a plastic film such as polypropylene on the surface of a print and using an adhesive to heat and press it together is called lamination.

The coating process is divided into two types: pre-coated and coated. In the precoating process, the adhesive is pre-coated on a plastic film, dried, rolled, and sold as a product. In the film processing department, hot stamping can be performed on a film-covering equipment without an adhesive coating device to complete a film coating. The process simplifies the operation of the film coating process, has no environmental pollution, and has a high coating quality, and thus has a broad application prospect. The pre-coating process is still at an exploratory stage in China.

That is, the process flow of coating film is:
Film preparation → unwinding → adhesive coating → drying → compounding → rewinding

(A) Film preparation

Preparations for laminating production include: inspection of pending prints, selection of plastic films, and preparation of adhesives.

1. Inspection of pending prints

At present, most of the printed matter is printed with a multi-color high-speed printing press. In order to prevent back-scratching of the printed product, the method of dusting is often used to isolate the printed sheet. If a large amount of silt particles remain on the surface of the printed matter, the adhesive cannot contact and adhere to the ink layer of the printed matter, which seriously affects the lamination quality. Therefore, measures should be taken to eliminate dusting materials. A positive approach is to minimize dusting or dusting during printing.

Check the print flatness. Prints with poor flatness are used directly for lamination. When hot-pressed, the edges of the product will wrinkle and cause serious waste.

2. The choice of plastic film

Plastic film is the main material of the film. No matter which type and system of plastic film is used, the following basic requirements must be met:

Thickness between 0.01 ~ 0.02mm;

The surface tension should reach 4×102N/m or more;

High transparency

Has good light, mechanical and chemical resistance;

Stable geometry

Film surface is smooth, no bumps and wrinkles.

Commonly used plastic films are: polypropylene film (CPP), polyvinyl chloride film (PVC), polyethylene film (PE), polyester film (PET), polycarbonate film (PC) and so on.

3. Preparation of adhesive

Adhesives are usually formulated from several materials. It is generally divided into body materials and auxiliary materials.

The main material is the main component of the adhesive and plays an adhesive role in synthetic resins, synthetic rubbers, natural high molecular substances, and inorganic compounds.

Auxiliary materials are materials that are used in adhesives to improve the properties of a host material or to facilitate construction. Commonly used are curing agents, plasticizers, fillers and solvents (diluents). In order to meet certain special requirements, other components such as anti-aging agents, plasticizers, initiators, accelerators, emulsifiers and the like are also added.

(B) Laminating operation

Laminating machines generally use laminating machines. The laminating machine is composed of a unwinding section, a coating section, a print input station, a hot press recombination section, an auxiliary laminating section, a printed rewinding section, and a drying channel.

The specific operation of the film is as follows:

According to the print size, cut film, film;

Pass the plastic film through the conveyor rollers in the path specified by the machine;

Turn on the power to make the drying path, heating roller rise to the set temperature and turn on the air supply device;

Open the storage tank valve, and inject the adhesive into the coating tank of the laminator and reach the standard working level;

Start the operation of the machine, check the film advancement, the winding mechanism, and adjust the platen-regime baffle to meet the requirements;

The rubberizing roller and the hot-pressing roller are pressed together and input into the printed matter composite, and the quality of the product should be checked frequently during the compounding process.

(III) Quality Requirements for Laminated Products

Film-coated products should meet the following quality requirements:

The film is firmly bonded, the surface is clean, flat, unclear, and has a high degree of finish. No wrinkle, no blistering and no film marks.

After the film is divided, the size is accurate, the edge is smooth, no film, no obvious curl. Break no more than 10mm.

After the film is dried, the drying procedure is appropriate, and there is no phenomenon of sticking to the surface film or paper.

After placing the film for 6 to 20 hours, there is no change in the quality of the product. If conditions permit, an incubator test should be used.



Second, hot foil

The process of transferring foils or pigment foils to the surface of prints or other items by hot pressing is called hot foiling, commonly known as hot stamping, and its purpose is to enhance decorative effects.

(a) Anodized aluminum hot stamping process

1. Preparation before hot stamping

Including the selection and blanking of the model of anodized aluminum.

Electro-aluminum is made of polyester film as base, coated with alcohol-soluble dyeing resin, vacuum sprayed with aluminum, and then coated with an adhesive layer. Different types of electro-aluminum, its performance and suitable hot material and range are also different. If the hot stamping area is large, it should be easy to transfer the aluminum, hot stamping of general graphic prints, should use universal type of aluminum.

Before use, according to the hot stamping area, the aluminum foil is divided into the required size specifications, commonly known as cutting.

2. Preparation for hot stamping

Hot stamping generally uses a vertical flat stamping stamping machine. Its structure is similar to that of a flat-press flat letterpress printer. A hot stamping plate is a copper plate or a zinc plate of 1.5 mm or more, and the difference between the height of the picture and the space is as large as possible. The printing plate should be affixed or fixed on the bottom plate of the stamping machine. The bottom plate is heated by the heating plate and the heat is transferred to the printing plate for hot stamping.

3. Determination of hot stamping process parameters

After the plate is installed, the hot stamping can be done. The correct process parameters in the hot stamping operation are the key to obtaining the ideal hot stamping effect. Process parameters include: stamping temperature, pressure and speed.

Hot stamping temperature range is generally 70 ~ 180 °C, the temperature difference as far as possible not exceeding ± 2 °C; hot stamping pressure than the general printing pressure, about 25 ~ 35kg/cm2.

In actual operation, the hot stamping speed is generally used as a constant to adjust the temperature and pressure. Only in special circumstances can the hot stamping speed be adjusted.

(B) Hot Stamping Quality Requirements

Hot stamping product quality requirements are:

Hot stamping pressure, time, temperature and hot stamping material, cover material texture should be appropriate, writing and pattern scalding, not paste, text and patterns are not white, no color, no fall off, the surface is flat, lines and patterns are clear and clean .

Sets of covers that are hot for more than two times, with no leaks on the layout, clear layers, clear patterns, cleanliness, and good finish. Overprint error is less than 1mm.

The position of the frame and the text and pattern of the hot stamping cover page and book back are accurate, and the size meets the design requirements. The cover stamping error is less than 5mm and the skew is less than 2mm. The vertical error of the position of the spine is less than 2mm and the skew is not more than 10%.



Fourth, die-cutting, indentation

Die cutting is the process of arranging steel blades into a mold (or engraving a mold with a steel plate) and a frame, and cutting a sheet of paper and a printed matter into a certain shape on a die cutting machine. Paper that cannot be cut into arcs or other complex shapes with a normal paper cutter will need to be die cut.

Indentation is the use of steel wire, by embossing, stamping on paper or prints, or leaving grooves for bending.

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