The hottest talk about dry composite process

Talk about the dry compounding process

the so-called dry compounding is the process of coating the adhesive on one layer of film, drying it in the oven, and then hot pressing it with another layer of film to form a composite film. It is suitable for all kinds of substrate films. With high freedom of substrate selection, it can produce composite films with various properties, such as heat-resistant, oil-resistant, high barrier, chemical resistant films, etc. In addition, the dry compounding process is also applicable to the compounding of products with multiple varieties and small quantities, and the replacement of substrate adhesive is convenient, so it is widely used in small and medium-sized color printing plants. Next, the author will talk about the dry compound production process based on the production experience in recent years and relevant data, and I hope relevant experts in the industry will give me a correct answer

1 preparation before compounding

1) slitting

slitting the wide film roll into narrow rolls of the required specifications. A spokesman should be placed during slitting. During an interview, he confirmed that the "chance" material has been put into production with appropriate margin. Generally, the first base material is about 10mm wider than the finished product, the second base material is about 10mm wider than the first base material, and the third base material is about 10mm wider than the second base material, so as to avoid compounding, The adhesive sticks to the roller. Both ends of the slitted narrow film coil shall be flat and the coiling tension shall be appropriate

2) printing

gravure printing is generally carried out before compounding. In addition to ensuring the printing quality, it is also required that the film does not wrinkle, the winding is neat, and the tension is appropriate

3) select the appropriate adhesive according to the packaging requirements, the characteristics of raw materials and the performance of contents

2 production operation

1) preparation of adhesive

in order to obtain the best comprehensive performance and bonding performance of composite products, for two-component adhesive, the proportion of main agent and solidifying agent must be in accordance with the product instructions provided by the manufacturer. During the mixing operation, first weigh an appropriate amount of the main agent, curing agent and ethyl ester as required, then pour the main agent into the container, dilute it with ethyl ester to an appropriate level, and estimate the solid content of the adhesive of the product according to previous experience. Generally, the solid content of the adhesive used is 15% - 30%. When adding ethyl ester, stir it in the same direction with a wooden stick until it is uniform. Finally, add curing agent, and then stir it with a wooden stick until it is uniform

note that in dry compounding, the control of adhesive coating amount is very important, which affects the quality of composites to a great extent. The amount of glue is too small, the adhesive cannot form a continuous film, and spots appear, which affects the appearance quality of the composite, and the adhesion is poor, reducing the cooking resistance and heat sealing strength of the composite; Too much glue will not only waste adhesive, but also make the film wrinkle and harden, tunnel phenomenon and poor opening. At the same time, too much glue will make the solvent difficult to volatilize, and too much residual solvent in the adhesive layer will produce peculiar smell. The amount of adhesive shall be determined according to the variety of substrate, the purpose of composite materials and printing conditions. Generally, for substrates without printing or with small printing area, the gluing amount is 1.5~2.5g/㎡, for substrates such as paper or substrates with large printing area, the gluing amount is 2.5~3.5g/㎡, for substrates with cooking resistance, the coating amount is 2.5~4g/㎡, and for substrates for aluminum foil cooking, the coating amount is more than 4G/㎡

2) specific operations

① first install the paper drum on the winding shaft, then install the first base material film roll, penetrate the film according to the direction specified by the equipment, and install the second base material film roll, and then lift a group of rollers of the upper rubber roll so that the base material does not contact the upper rubber roll

② add adhesive into the adhesive tray, turn on the drying channel heater, start the auxiliary drive motor, adjust the pressure between the upper rubber roller and the corrugated roller, so that a thin and uniform adhesive is coated on the rubber roller. When the temperature of the drying channel meets the requirements, turn on the cooling water, start the blower and exhaust fan, turn off the auxiliary motor, put down the roller above the upper rubber roller, press the first base material against the rubber roller, turn on the host, and stick the second base material on the first base material for compounding. The blowing industry, mainly plastic film blowing machines, accounts for a large proportion in the market

③ adjust the film tension and composite pressure. Tension control is one of the most important conditions in the composite process. If the tension is not properly controlled, the film will curl or wrinkle, resulting in a series of problems such as difficult bag making, reduced peel strength, bag deformation and so on. The tension setting is determined by the type, width and thickness of the substrate, the temperature and humidity of the oven and other conditions. The composite pressure should increase the temperature and pressure of the composite roll as much as possible without damaging the film, which will help to improve the fluidity of the adhesive, promote the adhesive to quickly wet the second substrate and enter the micropores on the surface of the substrate, so as to improve the composite strength. Generally, the composite temperature is 70~90 ℃

④ adjust the drying temperature and wind speed. Drying is an important factor in dry compounding. Drying directly affects the peel strength and transparency of the composite film, and is conducive to increasing the initial adhesion. The temperature of the first, second and third sections of the drying channel is generally 50~60 ℃, 60~70 ℃, 70~80 ℃, and the temperature must be raised. This processing technology enhances the performance level of 3D printing parts. The temperature of the first stage should not be too high, and the solvent should gradually overflow, otherwise the surface of the adhesive will harden, and the inner solvent will remain in the adhesive, which will greatly affect the strength and transparency of the composite film. For the composite film used for composite cooking, the upper limit of the three-stage temperature can be adopted, and the drying path must have sufficient length, usually not less than 8~9m, so as to facilitate the complete drying of the adhesive, otherwise the speed can only be reduced

another key control point of drying is the wind speed, which directly affects the residual amount of solvent. The minimum wind speed is set at 25m/s, and it is best to reach 35m/s at the air outlet nozzle. In this way, an air shovel can be formed, and the heat can reach the depth of the adhesive film, which is conducive to the complete drying of the adhesive. In addition, the balance of inlet and outlet air is also very important, otherwise it is easy to cause membrane jitter and wrinkles, and the pre ventilation must be turned on during production

the drying system must ensure the complete drying of the adhesive, especially when producing pet/pet aluminum or pet/al structures. In this structure, pet, pet aluminum and pet/al are very barrier materials. For example, the adhesive cannot be completely dried, and the residual solvent sandwiched between the two films cannot be released quickly, which will inevitably form bubbles between the two films

⑤ take a newly produced composite film about 1 meter long and full width, place it in an oven at 80 ℃ for 30min, check its appearance and peeling after taking it out, find problems in time, and take corresponding measures

⑥ when stopping the machine, turn off the power supply of the main machine, electric heater, blower and exhaust fan, stop the cooling water, and wipe the corrugated roller and rubber roller with ethyl ester. Don't stop the roll when the production stops. Add a certain amount of ethyl ester to the adhesive according to the downtime in the middle of production, so as to avoid roller blockage. When cleaning the embossing roller at the end of production, because it is to clean the whole gluing system, a principle that should be grasped is to clean the gluing roller on it from top to bottom, and then clean the embossing roller. When cleaning the wrinkle roll, use a fine copper brush dipped in ethyl ester to wash repeatedly, and finally wipe it with a clean dry cloth

during the use of the wrinkle roll, some adhesive will not be cleaned out at the corners of the eyes, and this part of adhesive will solidify at the corners of the holes. With the passage of time, it will become more and more, which will seriously affect the stability of the coating amount. These cured adhesives cannot be cleaned with ethyl ester and must be cleaned with a special roller cleaner

3 curing control

curing is also called curing. 2. Touch key operation mode is to put the composite film into the curing room, so that the main agent of polyurethane adhesive and curing agent have a cross-linking reaction, and interact with the surface of the composite substrate. The main purpose of curing is to make the main agent and curing agent fully react in a certain period of time to achieve the best composite strength; The second is to remove residual solvents with low boiling points, such as ethyl ester. Curing control is mainly the control of time and temperature. Different adhesive varieties have different curing temperature and time. The curing temperature is too low (below 20 ℃), and the reaction of the adhesive is very slow; If the curing temperature is too high, the additives of the substrate film will precipitate, which will affect the performance of the composite film and increase the odor; The curing time is too long, which affects the performance of the composite membrane and increases the odor

note that the curing temperature of pet, Al, CPP and other films can be increased due to their good heat resistance and high shrinkage temperature, while the curing temperature of LDPE, BOPP, EVA and other films cannot be too high. For products with high gluing amount, the curing time should be extended. For products delivered in the form of film roll, the curing time can be appropriately reduced. When the film thickness and film roll diameter are large, the curing time can be appropriately extended. In order to reduce the amount of residual solvent, the curing time can be extended. Therefore, the curing time should be appropriately adjusted according to the purpose of the product. When the curing temperature is 45~55 ℃, the curing time of ordinary transparent bags is 24h, that of aluminum foil bags is 48h, and that of cooking bags is 72h

in a word, the dry-type composite process is a complex process that looks easy but is difficult to do. The personnel engaged in the composite production process should produce in strict accordance with the internal control standard of product quality, do not cut corners, carefully analyze various quality problems in the process during production, and summarize practical experience. When more experience is accumulated, the composite will become easier, so as to produce high-quality composite films

source: PRINT world author: Shi Peiqin