Prevention of Foaming and Defilming of Paper-plastic Composite Packaging

Prevention of Foaming and Defilming of Paper-plastic Composite Packaging Cao Hua

First, the production process

1. Avoid the defects of the adhesive coating process. That is, there are conflicting problems in the adhesive coating process itself such as adhesives and thinners, coating methods and coating uniformity, adhesive amount and adhesive force, drying degree and after-effect. In paper-plastic composites, adhesives are used to create two-way forces on films and paper prints. Effective adhesives must be dried and cured to produce sufficient two-way adhesive strength. That is, the adhesive in the adhesive coating process can be used in the paper-plastic composite production after being diluted and synthesized and diluted. Because of the existence of the diluent, the adhesive cannot form a true dry cure, which is an inherent one. Sexual defects are also the key to easy foaming and release of paper plastic composite products.

The adhesive bond depends on its composition. Adhesives in the main body material synthetic resin, auxiliary material curing agent, plasticizers, etc., need to rely on solvent dissolved before they can participate in the polymerization reaction. Solvent In addition to synthetic adhesives, the main role of the adhesive coating process lies in reducing the viscosity and surface tension of the adhesive, increasing the wettability of the plastic film, and improving the rheology of the adhesive itself. After the solvent has changed these properties of the adhesive, the adhesive is easy to apply on the plastic film. The content of solvent in all types of adhesives is above 65%. That is, only 1/3 of the binding material is used for adhesives. When paper-plastic composites are used, it is necessary to add 1 more. /4 ~ 1/2 times the solvent dilution, in order to facilitate the coating operation in the actual production. Otherwise, the adhesive does not form a uniform continuous coating on the low surface energy plastic film.

High-dose solvents, which reduce the viscosity and surface tension of the adhesive to facilitate uniform coating on the plastic film, also swell the plastic film and decompose the oil and color in the ink layer, resulting in the adhesive Plastic film, paper and ink prints have a serious reduction in affinity.

Although all types of glue-type laminating machines are designed with hot air drying devices, they are dissolved with various types of resins and chemical raw materials to form solvents in the binder mixture, relative density, boiling point, and specific evaporation rate. The flash point and Other properties have undergone major changes and are much more volatile than pure solvents. The pure solvent (toluene) and the binder synthesized and diluted with toluene were uniformly coated on the 20 μm corona-treated biaxially stretched BOPP film surface. After the same hot air bake, the residual toluene solvent was measured. The amount is 21PPm, and the toluene residual solvent mixed in the adhesive is 322PPm, which is a difference of 15.33 times. This set of data shows that the volatilization rate of the solvent mixed in the adhesive is only 1/15 of the pure solvent. Through the long heating tunnel of the laminator, the feel of the adhesive coating on the film surface was not sticky. This is just the surface condition of the adhesive coating. Generally, the adhesive layer is more than 5 μm, and the solvent in the adhesive coating of 2 to 3 μm under the surface layer is difficult to be used in such a short time (through heating the drying tunnel), so high temperature (40°C to 70°C) °C), the strong airflow (0.4m3/s) is exhausted and the total solvent is included. The surface of the adhesive coating is formed as a "dry-up" and the inside of the outer layer does not dry out.

The solvent of the binder encapsulated in the "dry" skin must gradually evaporate. In the process of gradual volatilization of the solvent, on the one hand, the attached material, the plastic film, does not swell, while the surface of the already dried adhesive layer is infiltrated and softened. As a result of the gradual volatilization, the adhesion and anchoring property to the printing layer of the ink and the paper are reduced, and the formation of a tackiness and blistering is caused, and the film is severely removed.

The use of the adhesive coating process in the production of paper and plastic composite manufacturers, but also pay attention to the direction of the coating roller and the film running in the opposite direction of the coating tend to occur due to the host speed (thrust film operation) and the roller speed does not match (usually the ratio of the two is between 1:1 and 1:2), it will cause the regular coating overlap (coating roller speed is faster than the host rotation speed) or coating dilution (coating roller speed is slower than the host rotation speed), The seemingly uniform motion of the film is due to changes in the rhythm and the contact surface of the rags on the squeegee that changes in rotation speed. The thickness of the adhesive coating is irregular, the degree of drying is uneven, and the adhesion strength appears on the same plane. error.

At the same time, attention should be paid to prints of different printing colors, and the requirements for adhesive concentration and coating thickness are different. The concentration and thickness must be set to ensure that all types of prints meet the adhesive dry basis requirements: see table

2. Promote the new process of precoating dry composites. The pre-coating film is a special material that is pre-coated on a plastic film such as BOPP by a specific amount of a hot-melt adhesive that does not contain any solvent. It replaces raw materials such as plastic films, adhesives, and thinners, simplifies the process of blending, coating, and drying of adhesives. There is no solvent to swell the film and the ink is decomposed. No adhesion occurs. The secondary softening of the agent produces tack-free and thin film swelling and foaming, and the design and control of hot melt adhesive material selection and quantitative coating have a very strict set of scientific analysis, calculation, monitoring and adjustment methods, basically satisfying The requirements for the degree of drying of the ink are not strict with the requirements for the bonding of various types of paper and various ink-made prints, and the various physical and chemical means for processing after coating.

Pre-film dry-type composite process, suitable for dry-type laminating machine, that is, glue-coated laminating machine, dry laminating machine, laminator and other models. The entire compounding process is completed in a few seconds without the need to clean components such as the glue application mechanism; it is compounded at any time, ready to be turned on at any time, bonding is rapid, and shutdown is stopped; no poison, no air pollution, no flammable and explosive dangerous goods cause fire Hidden danger.

Second, the choice of materials

1. The manufacturer that still adopts the glue coating technology should pay attention to the selection of plastic film, the surface tension must be greater than 38mN/m, the tensile strength should be greater than 103MPa/cm2 in both longitudinal and transverse directions, the heat shrinkage rate should be less than 4%.
At the same time, attention should be paid to the cool, ventilated, dust-free and oil-free environment of the film storage environment.
The choice of adhesive, to avoid using benzene, toluene, xylene as a solvent. Although some binders use other substances (such as ethyl acetate, water, etc.) as solvents, the binders themselves have aromatic hydrocarbon odors such as benzene, which can also cause swelling of the film and should be used with caution.

2. When using a precoating film dry compounding process, when using a precoating film, be careful not to use a precoated film with a benzene-based solvent odor. The toluene coated scented film is a separate production workshop for reprocessing the film. After softening and diluting the low-temperature hot-melt adhesive with a solvent, it is produced by a concave roller coating method using a simple machine. . Although called a pre-coated film, this type of pre-coated film still contains a certain amount of solvent in the adhesive layer, which still swells the plastic film and decomposes the ink.
The use of this kind of printed matter with a toluene-coated pre-coated film composite will cause problems such as blistering and voiding when the film is folded, etched, pasted, indented, die-cut, etc. When the temperature reaches 30°C or when the product is exposed to the sun or the dry hot wind, it will also produce blisters and release.

Third, the standard operation

Paper-plastic composite products are produced by hot pressing, and heat and pressure are important production factors. The heating roller only maintains sufficient heat (roller surface temperature is 85°C to 95°C) to ensure that the hot melt adhesive is fully melted, leveled, and hot melt adhesive and adhesive molecules are active. The pressure roller only maintains the proper pressure (8-15MPa/cm2), and the active molecules in the hot melt adhesive and adhesive can transfer, penetrate and anchor to the capillary pores of the printed paper and the resin molecules of the ink printed layer. , forming a close combination of paper and plastic one.

Sufficient heat and appropriate pressure can be achieved and protected by machines such as temperature control, pressure control, etc., but the constant temperature and pressure, although they do not change, are due to changes in the speed of the main machine of the laminating machine. It has a distinctly different effect on paper-plastic composites. When the speed of the host is slow, the paper-plastic composite stays on the active surface of the hot-pressing mechanism for a long time, and the bonding effect is good. When the host speed is high, the time for the paper-plastic composite to stay on the working surface of the hot-pressing mechanism is short. The bonding effect is weak; this decrease is noticeable as the host speed continues to increase. When the main engine speed exceeds 800 rpm, the paper-plastic composite running speed exceeds 15 m/min, and the bonding effect is poor.

Standard operation and careful maintenance, debugging laminating machine, so that the overall technical conditions remain good. During the production operation, the temperature is set to a lower limit of 85°C and an upper limit of 95°C; the pressure is set to 15 to 15 MPa/cm2; the main engine speed is controlled within 700 rpm; and the running speed of the paper-plastic composite is controlled within 12.5 m/min.

The kind of thinking that raising the temperature and increasing the pressure can increase the speed of the main engine and increase the production quantity. It deviates from the normal working conditions of the machine and deviates from the legitimate demand for temperature and pressure of the paper-plastic composite materials. This is unscientific and incorrect. of.