Application and Quality Control of Adhesives on Composite Films (1)

Product quality is the root of the survival of a company. Any company that develops rapidly will not regard product quality as its life. For color printing and packaging companies, the quality of laminating products relates to the survival and development of enterprises, which is worthy of continuous research and improvement by various enterprises. Here we talk about our understanding of pre-control and post-analysis of composite quality.
First, the various factors affecting the composite quality 1, the impact of ink on the composite quality ink is composed of pigments, binders, solvents and additives.
(1) Pigments: The hiding power is not strong and the leveling performance is poor. The printed film has spots on the light. After lamination (especially duplicative aluminum film), there are obvious spots. This phenomenon is mostly caused by the hiding power of pigments.
(2) Binder: Because the binder is used to connect the film and ink. The bad adhesive force of the connecting material will make the adhesion between the ink and the outer film unsound. After the compounding, the ink will be completely transferred to the inner film. This phenomenon may also be due to poor corona treatment of the outer film. caused.
(3) Solvent: The ideal solvent should have good fast-drying properties. If the residual solvent is too much, it will cause odor and surface quality problems of the composite film.
(4) Auxiliaries: Some auxiliaries also affect the compounding; for example, the detackifier is mainly composed of heavy oil and white kerosene; it prevents post-adhesion after printing; it can quickly penetrate the surface of the ink. Due to the anti-sticking properties of the anti-sticking agent, the adhesion to the laminating adhesive is a contradiction. So the amount of anti-sticking agent is very important. For this issue, we believe that it should be explained in detail. After compounding, there is a good adhesion of ink in places where there is no ink, but not in places where there is no ink; after curing, there is no problem in bonding where there is ink, and there is almost no adhesion in places without ink. There are two reasons for this. The first one is because there are too many anti-sticking agents. After the printing, it penetrates into the surface of the ink. After the composite roller press, due to the good permeability of the ink, it quickly penetrates into the surrounding adhesive film. With time, the anti-adhesive agent It is distributed in a place where there is little glue on the periphery of the ink, so that the adhesiveness of the place where there is no ink drops. The second reason is because of the film additives. Film additives include plasticizers, lubricants, and antioxidants. Excessive amounts of these additives can also affect the composite adhesion. Some film-mulching plants see this kind of situation, generally considered to be the cause of glue, encountered similar situations, should be carefully observed, careful analysis of the reasons, to find the crux of the problem lies.
2, the impact of film on the quality of the composite film in the entire composite process, regardless of the printing or laminating film is a must consider carefully.
(1) Types of films; Films used for printing and compounding include polyethylene film (PE), polypropylene film (PP), polyester film (PET) nylon film (PA), and aluminized films. 1 Polyethylene is obtained by cracking petroleum to produce ethylene and ethylene. Due to differences in manufacturing methods and control methods, low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), and cross-linked polyethylene (CLPE) can be obtained. In general, as the density increases, the mechanical properties and barrier properties increase, and the heat resistance is also good. 2 Polyethylene is made of propylene polymer and is classified into cast polypropylene (CPP) and stretched propylene (OPP). Polypropylene is higher in heat resistance and transparency than polyethylene, and inferior in low temperature resistance than polyethylene. (3) Nylon film is a film (OPA) or cast film (CPA) made of nylon-6 resin after being bi-directionally pulled, and its barrier property is very good, and it is transparent and beautiful.
(2) Corona treatment and its effect on the composite quality 1 As the polyethylene polypropylene film is uniformly non-polar film, it is difficult to bond, and it needs to undergo halo treatment (also called telephone processing) to make the film achieve the required surface tension for compounding. The untreated film is generally 36 dyne/cm2. After the corona treatment, the general plastic film needs to reach 40 dyne/cm2, and the aluminized film should be 42 dyne/cm2. 2 The corona-treated film has a certain period of validity. As the storage time increases, the surface tension of the film decreases. Although some films have not passed their expiration date, their surface tension has not been reduced by the Dyne pen. However, in the printing and compounding process, the temperature, tension, and solvent act together to make the active film that has been stored for a long period of time easily fail. Quality issues. 3 Corona treated films are not always uniform. Uneven and uniform surface tension also affects printing and compounding.
(3) Additives: In the plastic processing, some additives are added. This assistant agent plays a very good role in the processing of the film, but it also has a certain influence on the compounding.
3. Effect of laminating adhesive on composite quality In dry composite processing, adhesive is one of the key factors affecting product quality.
(1) Types of Adhesives There are many kinds of adhesives, and they can be divided into one-component adhesives and two-component adhesives. One-component glue refers to a single component. It does not need to be mixed with other components to exhibit viscous glue. It is mostly rubber type, with non-dryness and hot melt, and it does not generate new substances in the compounding process. Adhesives and hot melt adhesives have a low adhesive strength and good initial tack. At the same time, the roller pressure is also required and the temperature is high. The two-component adhesive refers to a glue that exhibits a viscous property after being mixed with a main component and a curing agent, and is currently a polyurethane type. Polyurethane refers to a polymer having a hydroxyl group in its molecular structure and is obtained by reacting a polyhydric hydroxy compound with a polyisocyanate. In combination with isocyanate active hydrogen, it has high adhesion strength. At present, most of the A components in China are polyols, and B components are polyisocyanates.
(2) Effects of other active hydrogens on the adhesive Because the isocyanate's NCO group is a cumulative double bond formed by heteroatoms, it easily reacts with groups such as -OH, -COOH, -NH2 and other active hydrogen atoms, for example, isocyanate reacts with water to form amines. And emit carbon dioxide; with hydroxyl compounds react to generate carbamate; and -NH2 groups react to generate urea; Therefore, we must pay attention to the storage and use of glue and curing agent, to avoid contact with active hydrogen curing agent.
(3) Effect of Polyurethane Adhesive on Compound Quality At present, there are many kinds of bi-component adhesives in the domestic market, and the quality is not the same. Therefore, the laminating manufacturers need to have a certain level of judgement criteria in order to control and manage their purchase and use. The quality of the glue is judged mainly from the appearance, adhesive strength, residual solvent and residual monomers of the glue. a. Appearance: Observe whether it is clear and transparent, whether the color is colorless to light yellow; b. Bake: Dry the glue in the drying oven for 2-3 hours (70-75°), measure the solid content; c. Drop: Soak with solvent The composite membrane was used as a solvent test; d. Tearing; The composite membrane was torn by hand for testing the adhesive strength; e. Smell: Is there any odorous smell in the adhesive to detect the presence of residual monomers? In general, the adhesive should be Only ethyl taste; f. Measurement: The use of a variety of instruments and chemical methods on the glue and composite membrane inspection, the corresponding indicators.
4, the impact of thinner on the composite quality Dry compound with two-component adhesive, in order to spread evenly and conducive to infiltration, plus solvent dilution. The main solvents are ethyl acetate, toluene, methyl ethyl ketone and so on. Many factors must be taken into consideration when selecting the solvent. Since toluene is toxic, it is difficult to dry, and it tends to produce residual components. Methyl ethyl ketone smells heavy and the price is high, so ethyl acetate is generally used, and its purity requirements are met. 99%, water ≤ 0.2%, because the curing agent -N = C = O system accumulate double bonds, very lively, and water react to produce amines and emit CO2. The reaction consumes the curing agent, which reduces the amount of curing agent involved in the reaction with the glue, and at the same time releases CO2, so that the glue layer contains bubbles, which is extremely unfavorable to dry compounding, and often results in surface quality problems affecting the adhesive strength. Similarly, the active hydrogen of isocyanate groups and alcohols, polyols, and other hydroxyl-containing compounds that react to form carbamates and react with organic acids (hydroxyl groups) to form acylate wrists will affect the normal use of the glue. Therefore, dilution must be performed during compounding. Agent for testing. There must be a clarification here. Some composite manufacturers believe that adding more diluent can reduce the cost, and this view is wrong. Diluent in the compounding process only plays a role in uniform coating and facilitates infiltration. The real adhesive effect is glue and curing agent. , And the diluent has evaporated, as long as a certain amount of dry glue is applied, less diluent is more economical.
5. Influence of other man-made and mechanical factors on composite quality (1) Human factors: Man-made factors refer to the composite quality problems caused by man-made reasons in the compounding process, such as errors in glue distribution and inappropriate control of pressure and temperature speed. and many more. The following are separately explained. 1 with glue: the correct operation of the glue is to first add the right amount of diluent to the main agent, and stir evenly, and then add the curing agent and stir. Instead of mixing the main agent and curing agent together, add a thinner. This is determined by the nature of the chemical reaction. The speed of the chemical reaction depends on the effective collision between the molecules. At the same temperature and pressure (such as at room temperature and pressure), the effective collision between molecules is related to its concentration. The higher the concentration, the effective collision. The greater the chance, the faster the reaction. The main agent and curing agent in the absence of diluent conditions, high concentration, fast reaction, rapid melons generate larger molecules and condense into clumps. After adding the diluent, the speed becomes slower. In this way, in the compounding process, the glue coated on the film has extremely uneven molecular weight, which easily causes surface quality problems and also affects the adhesive strength of the adhesive. 2 Inappropriate control: For different composite materials, different adhesives, the required pressure temperature and other requirements are not the same, so the pressure and temperature conditions must be changed according to the actual production. For example, the higher the solid content of the glue, the smaller the molecular weight and the relatively lower initial tack force. In order to achieve a higher initial tack, the temperature and pressure should be increased. Another example is that one-component adhesives are mostly self-adhesive. Increasing the temperature and pressure will greatly increase their adhesive strength. For some films, too high a temperature will cause it to curl, deform, and naturally not be too high.
(2) Mechanical factors: Mechanical factors refer to the composite quality problems caused by mechanical reasons in the compounding process. In general, when the compound film shows regular traces, it is mostly caused by the cause of the printing machine or the compound machine. These regular traces can be eliminated by mechanical inspection and replacement of parts. The factors that affect composite quality are mainly the above five factors. Attention must be paid to these aspects in the production process to avoid problems.