polishing process

Paper bag polishing process

We often see some items with varnish technology in our daily life.

The main thing we share today is to varnish the paper bags.

What is the varnish process on paper bags?

Varnish is a kind of paper bag surface decoration processing technology, it is coated with a layer of colorless transparent material on the surface of the paper bag, after leveling, drying and Calendering, a thin and uniform transparent bright protective layer is formed on the surface of the paper bag, in order to increase the ink wear resistance of the printing paper bag, play a protective role, and prevent the paper bag from being contaminated. At the same time, the oiling technology of the hand-held paper bag can improve the gloss and color purity of the surface of the hand-held paper bag, and improve the visual effect of the whole paper bag.

The process of applying varnish on a paper bag is to use a UV printer to varnish on a local or small surface of the printed paper. If you apply varnish on a large area of the paper surface, it will affect the working efficiency and life of the UV printer.

The polishing process of the handbag can not only improve the color absorption capacity of the paper bag surface, but also accelerate the drying speed of the ink. For the printing products treated with varnish coating, the paint can protect the ink on the surface of the paper and reduce the shedding of printing products due to friction in daily use.

What are the main uses of the glazing process?

The printed matter is covered with a bright film after being glazed. Its scope of application is as follows:

1.Book binding, such as covers, covers, inserts and calendars, calendars, advertisements, promotional samples, etc., after glazing can make the paper surface glossy and colorful.

2. Packaging and decoration paper products, such as paper bags, envelopes, trademarks, etc., play a role in beautifying and protecting the goods after polishing.

3. Cultural items, such as playing cards.

After the postcard and gold printing pattern are polished, it can play the role of anti-mechanical friction and chemical corrosion.

4.Daily necessities, food, etc. Such as cigarettes, food, detergents and other trademarks can play a moistureproof, mildew-proof role.

5. Pressing copper foil on the hard cover can make the appearance beautiful, its brightness is very high, very much like gold. If the copper foil and the substrate are not firmly bonded, good adhesion can be obtained after glazing.

What are the characteristics of water-based varnish?

1. Good glossiness, the highest glossiness can reach more than 75 degrees, colorless, strong sense of transparency.

2. High wear resistance, good chemical resistance.

3. Good weather resistance, high and low temperature resistance, strong aging resistance, there is no difference among the four seasons.

4. Fast drying speed, no peculiar smell and high gloss.

5. Green and environmentally friendly.

What are the types of varnish on paper bags?

The oiling process of handheld paper bags includes glossy varnish, matte (matte) gloss oil and pearlescent oil (enamel).

1.Glossy varnish.

Glossy glazing, strong reflective ability, is a very common type of varnish. Designers often use this varnish to improve the performance of the picture.

2.Matt varnish.

Matt glazing is a non-glossy glazing method, which is especially suitable for text pages, so that it can reduce the effect of light reflection and make it easy for readers to read.

3.Pearlescent varnish.

This is a special paint varnish, which can show psychedelic color effect under the emission of light.

Why varnish on the surface of paper bags?

The process of polishing oil on hand-held paper bags can improve the color brilliance of paper bags and speed up the drying speed of ink at the same time. The paper bag is treated with varnish coating, and the printing ink of the paper bag is protected by paint, which can reduce the ink shedding due to friction in the daily use of hand-held paper bags.

The process of glazing is to prevent ink between paper bags and paper bags, because a large area of printing content accumulates a lot of ink, and the ink will not dry in a short period of time, it is easy to scrape the ink on other paper bags. This is a common decolorization, but it can be effectively prevented by polishing.

The purpose of polishing the paper bag is to beautify the paper bag, protect the printing pattern on the paper bag, strengthen the publicity effect of the paper bag, and improve the practical value of the paper bag.

After polishing the paper bag, the surface of the paper bag appears smoother, so that the gloss reflected on the surface of the paper bag is uniform and bright, and the ink printed on the paper bag is brighter.

Glazing is a coating process on the surface of a paper bag. The paper is glazed after printing, and then the surface is covered with subfilm or bright film.

There are two main ways of glazing: printing and coating processing and special glazing coating machine processing.

1. Printing coating processing, is the use of printing press equipment for glazing coating, in fact, varnish as a special ink for printing. Specifically, in the process of printing, varnish is transferred to the printing plate through the ink transmission system, covering the ink that has not yet been dried, varnish and ink will be absorbed by the paper fiber.

2. Special glazing coating machine coating processing, when the printing ink is dry, the use of coating machine equipment for oiling operation, reducing the paper’s absorption of varnish coating, maintaining the gloss of varnish. The ink absorption capacity of the paper is an important factor to ensure the gloss effect, so it is necessary to give priority to the coated paper.

UV glazing is a kind of resin with light curing agent, which is similar to ink printing, except that UV is dried by UV curing. It is safer and more environmentally friendly than other glazing technologies, and has the advantages of fast drying speed, no limitation of paper types, low energy consumption, good energy saving, good quality, friction resistance, corrosion resistance and so on. The UV glazing layer can bring high gloss reflection effect to the design works, which is more and more favored by designers. UV partial glazing is usually used to emphasize the visual effect of a printed content on the paper bag, giving the paper bag texture change.

What are the technical requirements for varnish on paper bags?

Ideal varnish, the basic technical requirements are: colorless, tasteless, strong sense of gloss, rapid drying. Resistant to chemicals, etc.

Varnish on paper bags also requires the following properties:

1. The film has high transparency and does not change color.

After the printed paper is covered with a colorless varnish film, it will dry and will not change color or yellowing because of the sun or long-term use.

2. The film has wear resistance.

After the paper bag is polished, there are still many processes to be carried out, so the varnish must have wear resistance to reduce friction on the paper surface.

3. The film is flexible.

Only the varnish film has a better elasticity, the paper surface will not be damaged, dry crack, or fall off.

4. The environmental performance of the film is good.

After the varnish film is dried, the chemical properties will be very stable, with moisture-proof and mildew-proof properties. The performance will not be changed as a result of exposure to weak acids or bases in the environment.

5. It has adhesion to the surface of the printed matter.

The light oil film layer has adhesion, which can prevent the film layer from drying and cracking in the process of use.

6. The leveling property is good and the film surface is smooth.

The leveling of varnish is good, and the film surface is smooth after film formation, which can make the glazing material form a smooth film on the paper surface and increase the absorption, smoothness and wettability of the paper surface.

7. Wide suitability for post-press processing.

Glazing film trial wide, there will be no adhesion between the paper, dried film, can withstand all the post-processing procedures of the paper bag. For example, film coating, indentation, bronzing, or silver ironing process.

How to choose varnish?

Varnish needs to choose the type of varnish scientifically, economically and practically according to the characteristics of varnish.

1. science.

It is necessary to study whether the varnish accords with the basic properties of the paper surface gloss and use.

The varnish on the surface of the paper requires high transparency, good wear resistance and folding resistance. After the paper is varnished, the chemical stability is high, and it will not change color, yellowing, or stick because of folding.

2. Economics.

Choose the right varnish and paper match.

If it is a high-grade paper bag, it is necessary to cooperate with the high-grade varnish with higher cost and better quality. For example, with UV curing, or acrylic resin as the main agent of solvent-based varnish.

If it is medium-and low-grade, the paper bag requirements are not too high, you can choose moderate cost, the quality can meet the processing requirements of the general solvent-based varnish is appropriate.

3. Practical.

The choice of varnish should match the glazing equipment.

Solvent-based varnish, only suitable for ordinary varnish.

UV curing varnish must be used on machines equipped with UV drying devices.

Alcohol-soluble or water-soluble varnish, the glazing machine must meet the drying requirements of the varnish. It is generally required that the length of the drying channel is more than 6 meters and the temperature is above 65 ℃.

At the same time, glazing oil should be considered to save labor and materials, suitable for machine batch production, and reduce the production cost as much as possible.

Varnish, but also pay attention to safety, hygiene, and environmental protection requirements.

(1) Safety.

 choose varnish with good storage performance and not easy to burn.

(2) Health and environmental protection.

choose odorless, non-toxic, tasteless polish.

(3) Environmental protection requirements.

The operating environment of glazing oil needs good ventilation, and the varnish with fragrant smell can not be selected to prevent affecting the health of operators and causing environmental pollution.

What are the quality requirements of paper varnish?

Varnish should meet the following requirements:

1.The glazing coating is uniform, no trachoma, no air bubbles, no leakage.

2.The amount of coating is appropriate, and the layer can dry the conjunctiva at a certain temperature and coating speed.

3.The coating is not affected by the performance of printing ink, printing area, and integral density, and has good leveling and adhesion to the surface of the paper.

4. In Calendering, the coating can adhere to the surface of Calendering belt, and it can be peeled off easily after cooling.

What factors will affect the glazing effect?

The factors that affect the glazing effect are: paper performance, temperature, ink and printing paper crystallization and so on.

1. Paper performance: paper performance is mainly reflected in the smoothness of the paper.

High smoothness of the paper, the effect is particularly good after polishing, can improve the brightness of the printing color of the paper.

Low smoothness of the paper, because the varnish is absorbed by the rough surface of the paper, the varnish covering effect of the paper surface will be very poor. The solution is to apply casein base material once or twice on the surface of the printed paper before polishing.

2. Temperature: the best glazing temperature is 18 ℃-20 ℃.

Winter temperature is low, varnish is easy to solidify, after the paper surface light, the varnish film is not uniform. Therefore, the varnish should be stored in heat preservation before it can be used.

If the temperature of the varnish is lower than 10 ℃, even if the varnish is put in a room with an indoor temperature of 20 ℃ for one night, it still cannot be used. When the varnish temperature is lower than 10 ℃, the original varnish solution must be diluted with solvent properly.

3. Printing ink:

The ink of the paper that needs to be glazed after printing must have solvent resistance and heat resistance, otherwise the text information and pictures printed on the paper surface will change color, or produce wrinkles and other quality problems, seriously affecting the aesthetics of the paper bag.

The solution is to choose the printing ink for the paper bag:

(1) choose alcohol-resistant, ester-resistant, acid-and alkali-resistant inks.

(2) choose inks that will not change color and have good gloss.

(3) choose the ink that has good adhesion to the paper.

4. The crystallization phenomenon on the printing paper.

The crystallization of the printing paper is due to the fact that the paper has been placed for too long, the printing area of the ink on the paper surface is too large, and the dry oil is put too much, which leads to the crystallization of the ink on the paper surface. This crystallization will lead to glazing mimeograph can not go up, or produce “tattooing”, “dots” and other printing quality problems.

The solution is to add 5% lactic acid to the varnish and stir it evenly before use. This kind of varnish, which has been treated and changed its performance, is applied to the surface of the printed paper, which will destroy the crystallization film formed on the surface of the paper, and can make the varnish evenly spread to the surface of the paper to form a glossy varnish film.

What is Calendering?

Calendering is a glazing process carried out on two units: varnish and hot pressing. After printing, the paper is first coated with varnish on the ordinary polishing machine, and after drying, it is hot-pressed through the stainless steel belt of the calender, cooled and peeled off, so that the surface of the printed paper forms a specular reflection effect. so that the surface of the paper forms a high gloss.

What factors affect Calendering quality?

The main factors affecting Calendering quality are Calendering temperature, pressure and machine speed.

1. Calendering temperature.

Proper Calendering temperature can increase the molecular thermal movement ability of the coating film, accelerate the diffusion speed, and facilitate the secondary wetting, adhesion and penetration of the printing paper surface.

Appropriate temperature can improve the plasticity of the coating film, and the coating can improve the surface smoothness of the paper under pressure.

Proper temperature can improve the quality of Calendering film. The temperature is too high or too low, it is not conducive to Calendering.

When the temperature is too high, the adhesion strength of the coating layer decreases and the water content of the paper decreases, which is not conducive to polishing and peeling.

The temperature is too low, the coating layer can not be completely plasticized, can not adhere to the Calendering board and printing paper surface, the Calendering effect is poor, after Calendering is not easy to form a high smoothness film.

2. pressure.

The action of pressure causes the coating layer to be compressed and thinned to form a smooth surface layer.

However, if the pressure is too high, the extensibility, plasticity and toughness of the paper will become worse, and it will not be difficult to peel off.

3. Pressure velocity.

Pressure speed is the curing time of glazing oil in Calendering.

If the pressure speed is fast, the curing time will be short, the composition of the varnish can not fully interact with the ink layer on the paper surface, the surface smoothness of the film layer after drying is poor, and the adhesion strength of the glazing oil layer to the ink layer is poor.

How to polish the surface with oil?

Over-oil is divided into water-based varnish and oily varnish, water-based varnish is printed through a layer of water-based varnish through the roller, oily varnish in the way of ink bucket.

Polishing is after printing through a layer of water-based polishing oil on the reticulated roller, after drying, rolling with smooth stainless steel plate under the condition of high temperature, a special polishing machine is needed.

1. Effect:

The varnish makes the surface have a thin bright oil film, the glossiness is about 50-60 degrees, the polished surface is particularly smooth and bright, there is a kind of mirror feeling, and can feel a certain thickness; the glossiness can reach 80-85 degrees; polishing is brighter and smoother than varnish.

2. Cost

The cost of polishing is definitely higher than that of polishing oil, and the high temperature heating of polishing machine costs electricity, which is one more process to polish than polishing oil.

3. Purpose:

(1) The main purpose of varnish is to protect color, wear-resistant and anti-fade.

(2) Show bright, this is generally after printing no film coating, polishing, printing UV oil, and customers have certain requirements for color fastness will be over-oiled, specific is varnish, or dumb oil, can be chosen according to customer requirements; dumb oil cost is too high waste, rarely used.

Polishing is mainly used in packaging products, such as food packaging, drug packaging, biscuit color boxes and so on.

The above is the process of polishing paper bags shared by Wepaperbag. I hope it will be useful to you.

We are a Chinese paper bag processing and production of paper bags, can be customized and mass production of paper bags for you. We have rich experience in the production of paper bags, and we can also make varnish for your company’s paper bags. If necessary, you can contact us (sale01@wepaperbag.com).

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