Common quality problems of packaging bags and answers to popular production problems

1. Composite packaging Bag What are the appearance quality requirements for aluminum-plated film?

The aluminum layer is uniform and bright, without watermarks or haze; the number of pinholes does not exceed 5 / m2 ; The winding is flat, the tension is appropriate, and there is no serious stretching or bulging phenomenon.

The appearance inspection of aluminum-plated film mainly includes the following aspects:

Pinhole (spatter) If the temperature control of the evaporation boat is poor or the position of the wire feeding point is not good during aluminum plating, the aluminum liquid will spatter. If the spattered aluminum liquid reaches the film, it will form small pinholes on the film. Too many pinholes on the aluminum-plated film will reduce the barrier performance of the film. Generally, the number of pinholes in the aluminum-plated film is allowed to be 2～ 3 个 /m ².

Aluminum-free lines (track lines) When producing aluminum-plated film with a winding-type vacuum aluminum plating machine, if the base film has wrinkles in the vapor deposition area, the film folded inside will not have an aluminum layer attached, thus forming a linear area with a shallower aluminum layer on the aluminum-plated film, which is called an aluminum-free line. Aluminum-free lines mainly occur on base films with softer properties such as CPP, PE etc.

Scratches on the aluminum-plated surface This phenomenon is mainly caused by damage to the aluminum plating layer by foreign objects on the guide roller during the operation of the aluminum-plated film.

2. Reasons for uneven thickness of LDPE blown film?

The uniformity of the die gap directly affects the uniformity of the film thickness. If the die gap is uneven, some parts have a larger gap and some parts have a smaller gap, resulting in uneven extrusion, so the thickness of the formed film is also inconsistent, some parts are thin, and some parts are thick.

Uneven temperature distribution at the die, with high and low temperatures, resulting in uneven thickness of the blown film.

Uneven air volume around the cooling air ring, resulting in uneven cooling effect, which causes uneven thickness of the film.

Inappropriate blow-up ratio and draw ratio make it difficult to control the bubble thickness.

The draw speed is not constant and keeps changing, which will naturally affect the thickness of the film.

3. Reasons for poor heat sealing of LDPE blown film?

Cause of failure:

The dew point is too low, the polymer molecules are oriented, so that the performance of the film is close to the oriented film, resulting in a decrease in heat sealing performance.

Inappropriate blow-up ratio and draw ratio (too large ) ，The film is stretched and oriented, thus affecting the heat sealing performance.

Solution:

Adjust the air volume in the air ring to make the dew point higher, and blow and draw as much as possible below the melting point of the plastic to reduce molecular stretching and orientation caused by blowing and drawing.

The blow-up ratio and draw ratio should be slightly smaller. If the blow-up ratio is too large and the draw speed is too fast, the film will be excessively stretched in both the transverse and longitudinal directions, which will make the film performance tend to be biaxially stretched, and the heat sealing performance of the film will deteriorate.

4. Reasons for rough and uneven surface of LDPE blown film?

Cause of failure:

The extrusion temperature is too low, and the resin is not well plasticized.

The extrusion speed is too fast.

Solution:

Adjust the extrusion temperature setting and appropriately increase the extrusion temperature to ensure good resin plasticization.

Reduce the extrusion speed appropriately.

5. Reasons and solutions for brown stripes on the surface of aluminum-plated film?

Reasons and solutions:

Low vacuum Clean the aluminum feeding, vapor deposition device, cooling system, unwinding, winding device and guide rollers in the vacuum chamber; check the vacuum system; reduce the ambient humidity.

Film releases gas Pre-dry the film; extend the vacuum time.

Excessive aluminum spraying Increase the vehicle speed; reduce the evaporation boat current; reduce the aluminum feeding speed.

Impurities in the evaporation boat Clean the evaporation boat and heat shield.

Aging of the evaporation boat Replace the evaporation boat.

6. Reasons and solutions for holes on the surface of aluminum-plated film?

Reasons and solutions:

Too much aluminum in the evaporation boat Reduce the aluminum feeding speed; increase the evaporation boat current.

Short circuit between evaporation boats in the vacuum chamber Eliminate the short circuit.

Impurities splashing in the vacuum chamber Clean the vacuum chamber wall, aluminum feeding and vapor deposition device, cooling drum, unwinding, winding device and various guide rollers.

7. Reasons and solutions for stretching phenomenon on the surface of aluminum-plated film?

Reasons and solutions:

Too much base material tension Adjust the unwinding and winding tension control system and reduce the tension appropriately.

Cooling system malfunction Check the cooling system and troubleshoot.

Evaporation boat temperature is too high. Reduce heating current for the evaporation boat and increase vehicle speed.

8. What should be noted regarding metallized film during storage, transportation, and use?

The aluminum layer on the surface of metallized film is very susceptible to moisture or water oxidation. Therefore, during the rewinding process, control the ambient relative humidity to prevent water vapor from being trapped inside the film.

It should be tightly packaged and stored in a clean, cool, and dry environment. During transportation, protect it from rain and sun exposure. When printing and dry laminating, control the environmental humidity, especially in humid and rainy southern regions. Opened film rolls should be used up at once to prevent moisture absorption, oxidation, and deterioration.

9. What should be noted when designing small text?

Generally, when electro-engraving plate-making technology cannot achieve clear effects for small text below 4Pt, the design should be changed to be at 4Pt or above, to prevent positive text from becoming thick and negative text from becoming thin or blurring during printing.

For independent fine lines, the width should not be too thin; generally, it should be greater than 0.2mm. If laser engraving is used, it can produce 2Pt clear small characters, which can be used for special anti-counterfeiting marks and other products.

For some jobs, the printing roller has large areas of solid color with small reversed-out text. In this case, communication with the client is needed to explain that the solid depth of gravure electro-engraving and the small reversed-out text cannot both be perfect. If the solid density is ensured, the reversed-out small text will certainly not be smooth and will not appear clear enough.

Conversely, if the small text is clear, it is often impossible to ensure sufficient solid depth.

The overprint accuracy of gravure printing can only reach 0.2mm, so strokes smaller than 0.4mm text and graphics ( especially text ) cannot be printed using multi-color superposition; only single ink printing can be used, otherwise ghosting is very likely to occur.

For fine text and patterns with hollow printing, single-color hollowing is recommended, and multi-color superimposed hollowing printing is not advisable. It is also not suitable to directly hollow print using the background color of a photo. For fine text and patterns, it is also not suitable to use text/pattern hollow overprint text/pattern.

10. What should be noted when designing gold and silver colors?

Generally, gold and silver inks are primarily applied to solid areas or color blocks. For very fine negative text, positive text, and gradient transitions, it is best not to design them in gold or silver.

When printing gold and silver inks on paper, a base color ink is usually laid down first. For example, when printing silver ink, a thin layer of white ink is laid down first, and then the silver ink is printed. This not only improves the glossiness of the silver ink layer but also enhances the adhesion of the silver ink to the paper.

If the substrate material is aluminum foil or vacuum metallized paper, printing transparent yellow on it can achieve a golden effect.

In the inner printing process of plastic film lamination, printing transparent yellow on OPP plastic film and then laminating with aluminum foil or metallized film can also achieve a golden effect for the printed ink layer, which saves expensive metallic inks while achieving the desired effect.

In the plate-making design process, the color sequence arrangement for gold and silver inks should be considered to ensure metallic luster.

If it is a surface printed product, after printing gold and silver inks, UV varnishing or water-based varnishing, or laminating the printed product, should also be considered to prevent the gold ink from oxidizing, discoloring, or peeling off.