The boiled packaging bag
with BOPA//LDPE structure is widely used in the packaging of pickles and bamboo shoots. BOPA//LDPE boiled bags actually have high technical index requirements. Although a certain scale of soft bag enterprises can make boiled bags, the quality is also uneven, and some will have more batch quality. question. Here, this paper analyzes the key points in the production process of BOPA//LDPE boiled bags. 1. Material selection 1. Selection of BOPA film ① Bow phenomenon of nylon film BOPA film can be produced by tubular film stretching method or by plane biaxial stretching method. Biaxially oriented nylon films produced by different methods have different bow effects, which have a significant impact on the overprinting accuracy of the film and the flatness of the packaging bag (including the appearance of the bag surface before and after boiling). The specific method to detect the bowing effect of nylon film is to measure the thermal shrinkage of the diagonal. The test conditions for heat shrinkage in the national standard are that we can also test the wet heat shrinkage rate of the nylon film according to the actual use conditions of the boiled bag (such as 100 ℃ 30min). The better the balance of the product; the difference is less than 1.5%, and there will be no warping angle during bag making. ② There are two types of BOPA films available in the market: printing grade and composite grade. The printing grade can be used for printing and composite processes, and the composite grade is only recommended for composite processes that do not require printing. The thickness is generally 12μm. 15μm. 25μm two specifications. 15μm Composite film for flexible packaging, 25μm for cold-formed aluminum pharmaceutical packaging. Double-sided corona film must be used when it is used for interlayer lamination and for boiling and cooking purposes. ③The key quality requirements of BOPA film a. If the flatness is high, the synchronous stretching film with small bow effect should be selected. b, the surface tension of the film≥50mN/m, to ensure the adhesion fastness of the ink. The processing value is not the bigger the better. c. Choose a film with good adaptability to relative humidity to ensure overprinting accuracy. d. Select the film variety with smaller thermal shrinkage rate (wet heat shrinkage rate). 2. Selection of heat-sealing layer PE The difference between boiled bag PE and ordinary PE is: ① better heat sealing strength; ② good heat sealability of inclusions; ); ④ good thickness uniformity→Stable heat sealing quality; ⑤Good transparency, no obvious water streaks; ⑥No fish eyes, impurities, crystal points that affect the use→Appearance of bubbles, even piercing the PA film→Barrier performance decreased, or oil leakage occurred. The first three quality characteristics are mainly determined by the pellet formulation of each layer of the PE film during blow molding. 3. Selection of printing ink Nylon film printing generally uses special polyurethane ink: ① Benzene-free and ketone-free series; ② Benzene-free and ketone-free series. When choosing printing inks, pay attention to: ①The resistance selection of color models, such as F1200 red, 1500 red, F1150 red, F2610 golden red, F3700 orange, F4700 medium yellow and other color inks of a polyurethane ink are indicated in the manual Therefore, it cannot be used for BOPA/PE structure boiling film printing, some colors are not resistant to boiling, and the color material is easy to seep out when the water is boiled. ②Gold and silver ink should be used with caution. For gold and silver ink, the ink factory does not recommend using it for boiling purposes in the instructions, but some boiled packaging bags on the market use gold and silver colors. The general practice is to consult the ink factory for formula design before application, and also Be careful not to print in large color blocks. ③ The nylon film must have good ink adhesion fastness, so as to ensure the final peel strength of the ink part. 4. Selection of adhesive: Choose an adhesive that can withstand boiling, and ensure the degree of cross-linking and curing after compounding. In addition, the aged glue should be used with caution (generally should be avoided), because the effective ratio of the main agent and the curing agent group in the glue solution has been unbalanced during the placement process of the aged glue, and the glue layer is prone to dry phenomenon. 5. The quality requirements of ethyl acetate According to GB/T 3728-91 of my country's 'Industrial Ethyl acetate', the moisture content of the first-class product is less than 1000ppm, the moisture content of the first-class product is less than 2000ppm, and the moisture content of the qualified product is less than 4000ppm. The water and alcohols in ethyl acetate (not only ethanol, but also the content of methanol and isopropanol should be controlled) will react with the curing agent in the glue, and the curing agent will be consumed, resulting in the phenomenon that the glue layer does not dry out. One of the main reasons for the wrinkling of the rubber layer of the bag. 2. Gravure printing process 1. The selection of specific ink type is produced according to the ink type specified by the process. For example, some inks of other colors are not suitable for BOPA//PE printing. 2. When the old ink is reused, it is necessary to add more than 50% new ink, and the deteriorated ink shall not be used. 3. If necessary, a certain proportion of curing agent can be added to white ink. There are two purposes of adding a certain proportion of curing agent to white ink: one is to improve the heat resistance of the ink; the other is to offset the consumption of the curing agent by the resin groups in the ink , to avoid the incomplete curing of the adhesive layer in summer. Adding method: Dilute with solvent first, then add it to the ink while stirring slowly until it is evenly mixed. Wrong method: directly add the curing agent into the ink, or add it into the ink tray, which will not mix uniformly, but will not achieve the effect of adding the curing agent. In addition, pay attention to the timeliness: the timeliness is generally 12 hours, and the overnight ink curing agent has expired, or a certain amount of curing agent should be added again. 4. Moisture-proof management of nylon film Nylon absorbs moisture, and it is prone to ruffles, sloping edges, stripes, difficult coloring, and inaccurate color registration during printing. When printing, it is best to control the temperature and humidity of the production workshop. When the humidity of the production workshop exceeds 80%, the nylon film is easy to absorb moisture and rise, causing a series of printing product quality problems.
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