Further discussion on paper plastic composite process

In depth discussion on paper plastic composite process the lamination process has been adopted by many packaging and printing enterprises because of its low investment and quick effect. However, lamination is a post press process. If there is a problem, it will cause irreparable losses. There have also been examples of losses of hundreds of thousands of yuan and millions of Yuan caused by lamination. Therefore, how to improve the quality of lamination has become the focus of technical personnel The author once went deep into the machine and worked with the technicians of the adhesive manufacturer to find out some methods to improve the quality of film covering, and discussed with the majority of colleagues here.

Bonding principle

Bonding principle lamination is to bond polypropylene and other films to the surface of printed matter through adhesive. The bonding process is a complex physical and chemical process. The generation of bonding force depends not only on the surface structure and properties of the adhesive and the adherend, but also on the operating conditions of the bonding process. Theoretically, when the two solid surfaces are close to each other to a distance of 0.4nm, due to the existence of intermolecular forces, bonding can be achieved even without adhesives. But this is impossible to achieve manually For! To achieve real contact between the surfaces of the adhered objects, adhesives must be used as adhesives

It must have several characteristics, fluidity, be able to wet the surface of the adherend and have cohesion.

The main factors affecting the bonding strength include the following aspects

(1) Properties of adhesives. Choose adhesives with high cohesion.

(2) Solvent effect, high polarity adhesives should choose high polarity solvents

(3) The influence of the surface properties of the adherend.

The ideal condition for bonding is that the surface tension of the adhesive is equal to that of the adherend The surface treatment of the adherend is conducive to improving the bonding effect, such as corona treatment

Types of film adhesive

There are three types of film covering adhesives: chemical reaction type, heat sensitive type and solvent type. Heat sensitive adhesives are mainly used for pre coating, while chemical reaction type is very inconvenient to use It is no longer commonly used in paper plastic composite, but the most commonly used is solvent based adhesive

Solvent based adhesives have stable properties, wide application range and easy operation. As the laminating adhesive plays a decisive role in the laminating process, we must choose the special laminating adhesive produced by regular manufacturers If possible, it is best to ask the manufacturer to provide the following data

(1) Performance of adhesive: storage period, solid content, pH value, viscosity, molecular weight, etc,

(2) Bonding strength of adhesive •

Weatherability, heat resistance, chemical resistance, etc. of adhesives

Selection of film for film covering

BOPP film is generally used for film covering, and the following two aspects should be paid attention to when choosing BOPP film.

(surface tension of bonding surface of dbopp film. The surface tension of untreated BOPP film is small, and the adhesive is not easy to wet its surface, which will directly affect the bonding effect

(2) The surface roughness of BOPP film has a great influence on the adhesion. The function of adhesive is to fill the gap of the contact surface of the adherend, and make it bond with the help of inlay 'and adhesion The surface is too flat, and the adhesive cannot enter the BOPP surface, so the bonding effect is poor; The surface is too rough There are obvious irregularities The adhesive cannot enter some places, and the bonding effect is also not ideal. Therefore In order to improve the bonding strength, we must pay attention to the treatment of the bonded surface, corona treat the bonded surface of BOPP, increase its surface tension and improve the surface roughness.

Surface properties of printed matter

1. Flatness of substrate surface

There are more and more kinds of modern packaging and printing materials There are offset paper, coated paper and whiteboard White cardboard, composite aluminum foil, etc

The jujube surface of offset paper and paperboard is too rough when laminating

The adhesive is not easy to fill the gap on its surface, the film covering effect is poor, and the bonding force is small. In work 'often: because such products are low-grade products and are ignored, after; Often cause quality problems. For this kind of substrate with rough surface, you can increase the amount of film covering adhesive, increase the pressure, and make the adhesive fill the surface gap of the substrate, so as to improve the film covering quality.

art paper. White cardboard is an ideal substrate for film coating, with flat surface and many fine pores on the surface Using less adhesive can achieve a good film covering effect.

The surface of the popular gold (silver) cardboard

It is aluminum foil, and the surface flatness reaches the mirror effect. Although the surface is pre coated with a connecting layer to meet the printing requirements, the surface is still very flat and the surface gap is small 'the adhesive has little' inlaying 'force on the surface of gold (silver) paperboard. Therefore The adhesion of film to gold (silver) paperboard is relatively small, especially after the gold (silver) paperboard is coated with film, the quality problem of separation of film and gold (silver) paperboard often occurs. 'due to the high cost of gold (silver) paperboard packaging, the occurrence of quality problems will cause heavy losses. We have summarized the experience of gold (silver) paperboard coating in practice Due to the small 'inlaying' force of the adhesive on the surface of the gold (silver) paperboard, it mainly depends on the adhesive force to bond. Therefore, when the gold (silver) paperboard is coated, the amount of adhesive should be sufficient, the speed should be slow, the pressure should be large, and the temperature should be high, so as to facilitate the complete volatilization of the solvent.

2. Properties of the ink layer surface of the substrate

If it is a product printed by multi-color machine Coating often encounter powder spraying problems If too much powder is sprayed during printing, a layer of powder will be formed on the surface of the printed matter. The adhesive is not adhered to the paper or ink layer during film covering Instead, it adheres to the powder layer, which is prone to quality problems. Therefore, the amount of powder sprayed during printing should be strictly controlled for the coated products. For the coated printed matter, the powder layer can be removed with tools such as chicken feather broom, cotton yarn, powder remover, and then coated

The ink layer of offset printing, embossing and other printing products is dried by oxidation conjunctiva, and the film covering time should be well controlled If the ink layer is not dry The ink layer will dissolve the adhesive; Swelling, causing blistering and poor adhesion of the film! Series of problems' if the ink layer dries excessively and the surface J of the ink layer crystallizes, there will also be quality problems such as poor adhesion For urgent items with less ink layer and need to be coated, it is best to dry the paper through the oven Make the solvent in the ink layer volatilize as soon as possible, and accelerate the oxidation of the ink layer at the same time. For the crystallized printed matter, the crystallized layer can be destroyed by physical methods Then cover the film.

3. Printing ink

The binder in the ink contains not only resin, but also solvent. Whether the solvent volatilizes completely or not directly affects the adhesion of the film covering adhesive to the ink layer, especially some high boiling point solvents are not easy to volatilize. Therefore, after printing, the print must be dried thoroughly before laminating

In the printing process, some high boiling solvents, such as kerosene, are sometimes artificially added to achieve the purpose of ink debonding Xylene, etc., which will directly affect the film quality Cause major quality accidents. We have encountered this kind of thing. Because we found it early, we avoided the occurrence of major accidents.

In the printing process, because you want to improve the printability of the ink, you will add some ink additives to the ink, such as viride oil and anti sticking agent Debonding agents, etc. these additives contain solvents, waxes or coarse particles, which will affect the bonding performance of adhesives For example Ink additives are unevenly stirred in the ink, and white spots will appear on the printed matter after lamination, or even blister piece by piece, so it is best to use less ink additives

Film covering operation

The film covering operation is divided into three parts, namely, gluing, drying and thermal compounding.

1. The glue must be applied evenly

When gluing, the viscosity of the adhesive shall be moderate to facilitate the leveling of the glue. In addition, the adhesive is required to be free of impurities. Left when gluing The adhesive dosage on the right side should be the same, so that the effect of the whole layout looks the same after the printing is covered with film.

The most important point of gluing is to control the amount of glue. Generally speaking, a large amount of sizing can fill the concave and convex parts of the printing surface. The product has high gloss, but the amount of sizing is too large. The sizing solution is not easy to dry

The residual solvent in the adhesive may eventually become the culprit of the film quality accident

2. Dry the film completely

The solvent in the glue should be volatilized. Ideally, the solvent should be 100% volatilized. However, due to electric heating, speed exhaust and the appearance of conjunctiva on the surface of the adhesive when it is heated, there are more or less solvents left in it. As the drying temperature of electric heating cannot be too high, we have to control the speed. Now there is a laminating machine that uses microwave for drying. Microwave makes molecules vibrate and heat up, and its drying effect is excellent. If the film coated with hot melt adhesive is used, the drying process can be avoided, and the hidden danger of quality accidents caused by residual solvent in the adhesive can be avoided.

3. Pay attention to the temperature, pressure and speed of hot pressing for thermal lamination

Hot pressing is to heat the adhesive on the film to make it semi molten, so that the adhesive can smoothly penetrate into the gap on the surface of the substrate, so as to improve the adhesion. The two hot sealing rollers, heating rollers and pressure rollers must be flat, and the sundries on them should be removed frequently to maintain a clean state.

The two rollers must be replaced when they are used to a certain extent Especially rubber products, which are under high temperature for a long time It is easy to age under high pressure After pressure radiation aging, due to poor pressing, there will be transverse small white spots when laminating.

Pressure is also a factor that makes the adhesive on the film embedded on the surface of the substrate The speed is used to adjust the heating and pressurization time, and at the same time, the speed will also affect the drying of the adhesive on the film. Therefore, in order to improve the quality of film covering, the speed must be limited. For the film covering of paper products that can absorb solvent, the speed should be controlled within 13m/min, while for the film covering of gold (silver) cardboard that does not absorb solvent The speed shall be controlled at 11m/min

Paper plastic composite seems simple, but it covers a wide range of areas. Every variable factor will lead to significant losses. Only by constantly summarizing in practice can we nip in the bud To produce high-quality products

A successful attempt of die cutting without connecting points on die cutting machine

Xinjiang kuidian golden leaf printing Co., Ltd. Li Xinjian, Yan Weihua

In the process of die-cutting cigarette label products, the cigarette case is connected by multiple unbroken connecting points, so that the cigarette case is not completely separated from the cigarette case. Even when the die-cutting machine is running, there will be no loose version Falling, uneven paper receipt and other very important functions.

However, cigarette factories with high quality requirements are not allowed to have connecting points on cigarette labels, which requires quality inspectors to thoroughly polish the connecting points on cigarette labels.

There are generally 8~12 connecting points on each flip and cigarette label of the box cut by the die-cutting machine. Grinding these connecting points takes at least 2 hours of time for each quality inspector every day Some printing houses use self-made opening and connecting knife to open irregular dots, which makes grinding more difficult

Grinding and connecting points not only consumes physical strength, but also wastes time, which seriously affects the work efficiency. In addition, a large amount of paper dust will be generated when sanding the connecting points It is harmful to the health of quality inspectors. Paper dust will also be adsorbed on the product surface due to electrostatic effect, which will seriously affect the product quality.

In view of these situations, we broke the Convention and made bold innovations in the dot bonding process. Taking the production of cigarette label products of our factory (flip with 12, strip box with 2, Tangshan Yutian without waste cleaning my1020 die-cutting machine, tym1020 die ironing machine, speed 4500 sheets / hour) as an example, the die-cutting plate does not open the connection point, and the die-cutting machine realizes no connection point die-cutting, which operates normally, does not affect the machine speed, and does not produce loose plates Falling, uneven paper receiving, etc. In fact, the machine speed can be increased. Our factory did not drive to a higher speed due to machine reasons.

The innovation of this process solves the following problems:

(1) The process of grinding and connecting points by quality inspectors is omitted, the labor intensity is reduced, and 2 hours of time is saved for each quality inspector every day, which effectively improves the work efficiency of quality inspectors

(2) It solves the problem that the paper dust produced by sanding and connecting points damages the health of quality inspectors and affects the sanitation of the surrounding environment, and saves gloves, sandpaper and other materials

(3) It solves the problem that the paper dust produced by sanding and connecting points affects the product quality due to electrostatic adsorption on the surface of cigarette labels

(4) The problem that the cigarette label may be damaged when the quality inspector grinds the connecting point is solved.

(5) It solves the damage of the die-cutting knife caused by the self-made opening and connecting knife. The punching is deformed. The connecting point is on the cigarette label There are problems such as concave notch (normally convex) on.

(6) Manually tearing off the edge of waste paper becomes time-saving and labor-saving, which solves the problem that cigarette labels are often damaged when tearing off the edge of waste paper due to dot connection.