Packaging bag quality is unstable, what to do if I can't find a good supplier?

Recently, some manufacturers have left messages saying that they often receive customer complaints about product quality issues. However, when looking for reasons from raw materials and product technology, many times it is the packaging that is the problem. Although it has been found that the packaging is the problem, there are no other cooperating suppliers, and it is unclear what exactly caused the poor packaging quality, so they dare not purchase rashly. What should they do?

Shunxingyuan Packaging, a professional flexible packaging manufacturer, believes that no matter what the packaging problem is, strengthening packaging quality control is an effective method to prevent quality accidents.

To stay ahead of quality problems and ensure product packaging quality, it is necessary to eliminate product packaging accidents from the source. Shunxingyuan Packaging will explain how we control packaging quality from the source, from raw materials, printing, lamination, slitting, and bag making, so you will understand what to do.

I. Raw Material Quality Control Points

1. Film Appearance

First, check the flatness and thickness of the film and whether there are any sawtooth shapes at both ends. The thickness of the film is generally considered qualified within ±5um. If the thickness difference is large, it will cause fluctuations in the printing pattern registration and the uniformity of the composite bonding. Visually inspecting the sawtooth shape at both ends of the film will cause film breakage during printing and lamination, resulting in a large number of rejects. Common methods for detecting film thickness are thickness gauges and visual inspection.

The static and dynamic friction coefficients of the original film should be tested using a film friction coefficient instrument.

2. Film Corona Value

The quality of the corona value directly affects the adhesion of the ink and the peel strength after lamination. (Corona pen, self-prepared corona solution can be used)

The following table shows the corona values that various film substrates need to achieve:

Self-prepared corona solution formula:

3. Selection and Application of Film Materials

When making retort pouches with PA film, A-grade products should be selected. In the production of PA film, there are step-by-step stretching and simultaneous stretching methods. The step-by-step stretching method is to stretch the longitudinal or transverse direction first, and then stretch the other direction, while the simultaneous stretching method stretches the transverse and longitudinal directions simultaneously, so its shrinkage rate is basically the same when encountering temperature. During the retort process, the different shrinkage ratios of PA often cause the retort pouch to curl, resulting in a warped corner phenomenon.

AL film: Density is 2.67g/cm3, excellent barrier properties, poor tensile strength, and easy to break. AL has the characteristic that one side has an extremely high corona value, while the other side only has about 38 dynes.

The most important factor determining the quality of AL is that the oil used for cooling during aluminum foil production must be cleaned, otherwise it will have a great impact on the composite strength. A cotton swab can be dipped in distilled water or tap water and wiped on the aluminum foil surface at a 45° angle. If the water can spread evenly, it proves that the oil is well treated. Conversely, if the water is in a water droplet shape on the aluminum foil, it can be determined that there is oil on the aluminum foil, which is a defective product.

Aluminum foil not cleaned

Aluminum-plated film: The density is basically the same as the aluminum-plated base material, without much change. Mainly check: the adhesion strength of the aluminum plating, pinholes, and the uniformity of the aluminum layer.

4. Other Raw Material Quality Control Methods

Film Additives:

Place the film in a curing room at 50～60℃ for about 8～20h, and test the friction coefficient of the film. If the friction coefficient increases significantly compared to before curing, it indicates that the additive content is high. This method can only detect the presence or absence of additives, not the amount of additives. (Film friction coefficient instrument can be used here)

Solvent Purity Test:

Purity and water content of solvents such as ethyl acetate, toluene, n-propyl acetate, isopropyl alcohol, and butyl acetate (using gas chromatography).

Simple Viscosity Test of Ink and Glue:

Dilute to a certain ratio, fill a No. 3 Zahn cup with ink or glue, and judge the viscosity by the time it takes to flow out. The longer the flow time, the greater the viscosity, and vice versa (the flow hole of the No. 3 cup must be cleaned).

Simple Solid Content Test:

Open the ink or glue bucket, take a certain amount of ink or glue and pour it into a beaker, do not cover it, put it in a 50℃ curing room, cure for 24h, and then divide the weight of the ink or glue at this time by the original weight, which is the so-called solid content, because all the solvents are basically volatilized in the curing room. (Measuring cup, beaker)

II. Quality Control Points to Note in Printing Processes

Surface Visual Inspection:

Accurate registration, no scratches, clear printing text and patterns. Neat winding, tension size, and whether there are any burst lines, etc. (Visual inspection)

Ink Dilution Viscosity Before Machine Operation:

Adjust the appropriate ink viscosity according to the machine speed, drying effect, etc. (No. 3 cup, stopwatch)

Ink adhesion can be tested using 3M tape at a 45° angle. The best adhesion is when the ink does not transfer. (3M tape)

Detection of Residual Solvent in Ink:

A gas chromatograph should be used to detect the residual amount of each solvent.

III. Quality Control Points to Note in Lamination Processes

Prediction Method of Adhesive Amount:

Adhesive amount = 1/5 × glue concentration × glue density × mesh depth.

Adhesive Amount Test:

After applying the glue, take three printed films (blank films) from the left, middle, and right before entering the laminating roller, weigh their weights, subtract the weight of the original film without glue, and finally take their average value. (Ten-thousandth analytical balance)

Check for bubbles, white spots, etc., on the surface of the laminated film by visual inspection. (Visual inspection)

Laminated film tension detection:

For the laminated film between the winding and laminating rollers, cut a cross shape with a blade and observe the curling direction of the laminated film at the cut. If it curls inwards, it indicates high inner film tension, and the inner film tension should be appropriately reduced. Conversely, the outer film tension should be reduced. Mismatched laminated film tension can also cause tunneling and wrinkling. (Visual inspection)

For detecting heating and exhaust in the laminator's drying tunnel, a thermometer can be used to check temperature errors, and an anemometer can check the incoming and outgoing airflow speeds, or a thin film can be used at both ends of the laminator's drying tunnel. Check if the film is blown inwards or outwards; if outwards, it indicates that incoming air is greater than outgoing air, and the outgoing airflow can be increased to try to achieve a vacuum state inside the drying tunnel. (Anemometer)

The peel strength and heat seal strength of the cured laminated film must be tested on a film tensile tester to obtain the corresponding peel data. (Film tensile tester)

Residual solvent in laminated film:

A gas chromatograph is used to detect the residual amount of solvent.

Friction coefficient of laminated film:

After curing, a film friction coefficient tester is required to obtain the necessary data.

Boiling and retort tests for laminated film:

After making bags from the laminated film, fill them with contents, vacuum seal them, and then perform corresponding boiling and retort tests (checking for bubbles, delamination, peel strength, etc.) to determine if they meet requirements or standards. (Vacuum machine, counter-pressure retort, film tensile tester)

IV. Quality requirements for slitting process

Ensure flat cut surfaces, moderate tension, and no bulging, etc. (Visual inspection method)

V. Quality requirements for bag-making process

Bag size, heat seal position (measuring tape), and bag flatness can be checked visually; heat seal strength is detected using a film tensile tester.

VI. Special testing procedures for special laminated bags

Boiling packaging bag:

The bag should be filled with objects or water (the amount of water or other liquids should be controlled to 1/2 or 1/3 of the bag's volume) and boiled at 100℃ for 40 minutes, with no bubbles or delamination.

After filling the retort bag with contents, vacuum seal it, and place it in a counter-pressure retort at 121℃ or 135℃ for 20-40 minutes of high-temperature sterilization, with no delamination or bubbles (counter-pressure retort).

The product quality of flexible packaging printing enterprises is influenced by many external factors, so enterprises should strengthen various tests during the production process. Testing is the most powerful guarantee of product quality and the most effective method to prevent product quality incidents.