Stringent Quality Control for Food Containers - Yangrui Printing & Packaging

Plastic food containers not only protect food from contamination, their quality is also closely related to human safety. For example, they should be safe to use, such as heating in a microwave or storing in a freezer, and not release any harmful substances.

So we use a series of tests to evaluate the characteristics of these containers, such as strength and safety. This is to ensure that they can effectively perform their intended functions.

Raw Material Testing

Before the production of plastic food containers, raw material inspection is mainly carried out. The following are the specific contents and inspection methods:

Plastic Particle Appearance

This is to avoid defects such as black spots and streaks on the finished container. We place the plastic particles on a white background board. Under normal lighting conditions (light intensity is about 500 - 1000 lux), unqualified materials are screened out through manual observation.

Particle Size Distribution

Our operator uses the sieving method or laser particle size analyzer to determine the particle size distribution. Because the particle size and distribution state of plastic particles will affect the subsequent fluidity and lead to uneven wall thickness of the container.

Melt Flow Index(MFI)

Melt Flow Index Detection (MFI) Under specified temperature and load conditions, we extrude the plastic particles through a standard capillary, and measure the mass (in grams) of the extruded plastic per unit time. This mass is the melt flow index. A suitable index means that the plastic smoothly fills the mold during the molding process.

Additive Detection

Chemical analysis methods such as Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) are used to identify the types of additives. These include plasticizers and antioxidants. We need to strictly control the content of additives and ensure that they are within a safe range.

Production Equipment Inspection

Before production, our engineers will inspect all of the sheet, drawing, forming and baling machines, to prevent temporary failures.
Cause they may affect production efficiency and product quality.

Inspection During Production

Temperature Monitoring

Plastic molding processes such as injection molding and blow molding have specific temperature requirements to uniformly melt and form plastics. Thermocouples or infrared temperature sensors are installed in the barrel and mold parts of injection molding machines and blow molding machines. They measure the temperature in real - time and feed the data back to the control system. When the temperature deviates, the system will send an alarm.

Pressure Testing

The injection system and mold cavity are equipped with pressure sensors. They detect the pressure received of the plastic particles. Taking injection molding as an example, the injection pressure is between 50 - 150MPa, and the holding pressure is between 30 - 80MPa. By monitoring the pressure curve, the operator judge if the plastic can completely fill the mold cavity to form a complete container.

Finished Product Inspection

Appearance inspection

Through outlook inspection and machine vision inspection, we eliminate products with surface defects. Quality inspectors conduct an appearance inspection of the containers under appropriate lighting conditions (generally 800 - 1200lux). For bubble defects, our equipment can identify them by detecting abnormal changes in the gray value in the image.

Dimensional inspection

During the production process, due to mold wear, the final dimensions of the container are prone to deviation. At this time, we use a laser displacement sensor or an optical image measuring instrument. They can measure the height, diameter, and wall thickness of the container, compare the data with the preset standards, and send a reminder when the error is too large.

Strength test

This includes compressive strength test and drop test, toughness test and sealing test. We use different equipment and experimental methods to record various values of the container and determine whether its strength meets the standard. For example, the pressure value when it starts to deform and finally breaks, the integrity after falling, and the state after impact.

Safety analysis

Through component analysis, migration testing, microbial testing, mold and yeast testing, etc., we test the characteristics of plastic food containers in different chemical environments. And based on the obtained values, we judge whether it releases harmful substances into food to ensure food safety.

Warehouse Quality Inspection

When qualified plastic food containers are ready for storage, we also have them sampling inspected and quantity verified. So that we keep track of inventory management and conduct financial accounting at any time.