Blow molding is one of the main plastic container manufacturing methods in cosmetic packaging, with diverse molding processes including injection blow molding, injection stretch blow molding, and extrusion blow molding. Commonly used blow molding materials include HDPE, LLDPE, LDPE, PP, EVA, PETG, PETP, etc. Blow-molded products are widely used in skin care and personal care products.
As a professional cosmetic packaging solution provider with years of experience, Auber Packaging has rich expertise in blow molding technology, continuously optimizing processes to help customers solve quality problems and improve product competitiveness. In this article, we will analyze several common quality defects of blow-molded products, providing valuable references for procurement friends in the premium packaging community, along with Auber Packaging’s professional insights and solutions.
I. Insufficient Bottom Molding (Concave Foot)
Symptoms: The contour of the petal-shaped bottom is not ideal, especially the depression at the bottom corner. Although insufficient bottom molding has little impact on filling, it affects the stability of the bottle.
Influencing Factors
- Insufficient high-pressure air supply.
- Insufficient temperature in the area where the bottom corner is located.
- Too short high-pressure blowing time (too long pre-blowing time).
- Too late pre-blowing air intake.
- Clogged exhaust holes in the bottom mold.
Solutions
- Check if the high-pressure air intake reaches above 28BAR. Auber Packaging equips its production lines with high-precision pressure detection equipment to ensure stable air pressure supply during the blow molding process, effectively avoiding defects caused by insufficient pressure.
- Check if the high-pressure filter on the side of the mold is unobstructed. Auber Packaging’s professional mold maintenance team conducts regular inspections and cleaning of molds and filters to ensure the smooth operation of the production process.
- Check the working status of various valves to ensure accurate positioning of stretching during pre-blowing and high-pressure molding.
- Check the pre-blowing and high-pressure control components to ensure correct set values and internal smoothness.
- Ensure that pre-blowing air intake is not too late and the time is not too long; otherwise, the high-pressure blowing time will be too short, and the effective cooling time of the bottle in the mold will be insufficient. Auber Packaging optimizes the pre-blowing and high-pressure time parameters according to different bottle types and materials to achieve the best molding effect.
- Ensure that the exhaust holes in the mold are unobstructed.
- Increase the heating percentage of the area where the bottom corner is located or add the number of lamp tubes to increase the temperature of the area.
- According to the actual situation of the bottle (weight and thickness of the bottle in different zones), reduce the temperature of the thinner zone to distribute the material at the bottom corner to these zones. Auber Packaging’s customized molding solutions can adjust the material distribution according to customer needs, effectively solving the problem of insufficient bottom molding.
II. Bottle Mouth Expansion (Thread Expansion)
Symptoms: The thread area expands, starting from the bottle mouth and spreading to the air-proof groove, which is more serious in hot weather. Due to high temperature, it occurs during blow molding, and a burst sound of high-pressure air leakage can be heard.
Influencing Factors
- Too high temperature of the furnace cooling water.
- Insufficient flow rate of the furnace cooling water.
- Incorrect position of the furnace cooling plate.
- Poor ventilation of the furnace.
- Incorrect height adjustment of the furnace lamp holder.
- Too high temperature in Zone 1.
Solutions
- Check the temperature and flow rate of the furnace cooling water. Auber Packaging adopts intelligent temperature control systems in its production workshops to accurately control the temperature and flow rate of cooling water, ensuring the stability of the bottle mouth molding.
- Adjust the position of the cooling plate to protect the thread area of the bottle mouth (keep the cooling plate 1.5mm away from the preform front and back, and 2mm higher than the preform support ring plane). Auber Packaging’s mold design team optimizes the structure of the cooling plate according to the characteristics of different bottle mouths, improving the cooling effect.
- Increase the blowing and exhaust volume of the furnace to reduce the ambient temperature, or open the heating furnace door to enhance air convection for good heat dissipation of the heating furnace.
- Reduce the heating percentage of Zone 1 or decrease the number of lamp tubes.
- If the cooling plate design is unreasonable, Auber Packaging’s R&D team can provide customized mold improvement solutions to solve the root cause of bottle mouth expansion.
III. Neck Bending (Crooked Neck)
Symptoms: Usually, the neck is inclined and bent to one side. The convex ring under the bottle mouth thread is deformed and not perpendicular to the center of the bottle body. Such bottles seriously affect filling and capping.
Influencing Factors
- Caused by mechanical reasons.
- Too high temperature of the mold body.
- Insufficient flow rate of the mold body.
- Inconsistent temperature on both sides of the mold body.
- Too thick material accumulation at the bottle neck.
Solutions
- The convex ring is clamped too tightly in the concave part of the mold top plate. The size of the preform must be fixed when it is still hot, and it needs a gap of 0.25mm. Auber Packaging’s production technicians strictly adjust the mold clamping gap to avoid deformation caused by excessive clamping.
- Check the flow rate of the mold body (insufficient flow rate leads to high temperature) and temperature (cooling water temperature or mold temperature machine temperature). Inconsistent flow rate on both sides of the mold body leads to inconsistent temperature on both sides. Inconsistent or too high temperature will cause crooked neck due to inconsistent shrinkage when the bottle is shaped after leaving the mold. Auber Packaging uses advanced mold temperature control equipment to ensure uniform temperature distribution of the mold body.
- The blowing nozzle is misaligned with the mold. Auber Packaging’s professional maintenance team regularly calibrates the alignment of the blowing nozzle and the mold to ensure accurate positioning.
- If the material accumulation at the bottle neck is too thick, increase the temperature of the corresponding area (increase the heating percentage of the area or add the number of lamp tubes). Auber Packaging’s process optimization team can adjust the heating parameters according to the actual material accumulation of the bottle neck to solve the problem of neck bending.
IV. Bottom Line Blueing (Hot Bottle)
Symptoms: Pearlescent stripes appear along the bottom cutting line, and the area with pearlescent stripes of this bottle is thinner than that of a good bottle.
Influencing Factors
- Too high pre-blowing pressure.
- Too slow stretching.
- Too early pre-blowing air intake.
Solutions
- The bottle is inflated too quickly during pre-blowing (this is often a problem with the pre-blowing solenoid valve, where high-pressure air leaks in during pre-blowing). Auber Packaging uses high-quality solenoid valves and conducts regular inspections and replacements to avoid air leakage.
- Reduce the pre-blowing air pressure. Auber Packaging’s intelligent pressure control system can accurately adjust the pre-blowing pressure according to different bottle types, avoiding defects caused by excessive pressure.
- Insufficient control pressure of the stretching cylinder, dirty solenoid valve, worn control valve seal or broken coil reel causing air leakage.
- Resistance in the mechanical movement of stretching (worn or too dirty stretching cylinder seals, misaligned stretching guide rail installation or worn linear bearings). Auber Packaging’s maintenance team regularly maintains the stretching mechanism to ensure smooth operation.
- Blocked exhaust of the stretching cylinder (clogged exhaust muffler or unsmooth air circuit).
- Adjust the pre-blowing air intake angle. Auber Packaging’s process engineers optimize the pre-blowing parameters according to the bottle structure to achieve the best stretching effect.
V. Bottom Damage
Symptoms: There is often a small fine crack at the place where the material accumulates too thick at the bottom, and it always passes through or is adjacent to the gate.
Influencing Factors
- Mechanical reasons.
- Insufficient temperature at the bottom of the preform (especially for bottle shapes with flat mold bottoms).
Solutions
- Check the gap between the stretching rod and the mold bottom (the gap is 2/3 of the thickness of the used preform bottom). Auber Packaging’s technicians strictly adjust the gap according to the preform specifications to avoid bottom damage caused by improper gap.
- Check the stretching buffer.
- Increase the heating percentage of the area where the bottom is located and add the number of lamp tubes in the area (if the temperature at the bottom of the preform is too low, when stretching, the stretching rod pushes it toward the bottom, and cracks form at the bottom. However, the bottom temperature cannot be too high; otherwise, the bottom will be convex). Auber Packaging’s temperature control system can accurately control the temperature of each area of the preform, ensuring the quality of the bottle bottom.
VI. Damage to Bottle Mouth Thread
Symptoms: The bottle mouth thread is damaged or the exhaust groove in the thread area is unnecessarily stretched.
Influencing Factors
- Caused by mechanical reasons (the preform is sent into the mold cavity by the transfer arm manipulator. When the manipulator clamps, the two sides of the preform thread area are stressed. When the manipulator takes the preform from the preform feeding guide rail, it will scratch the bottle mouth thread if the manipulator position is inaccurate. The bottle taking manipulator can also scratch the preform).
- Poor alignment between the blowing nozzle and the mold (the blowing nozzle determines the preform position by the force of the spring, which is not enough to correct the alignment gap between the two. At the start of blowing, there is a considerable impact force, which will cause thread damage).
- Too high temperature in the bottle mouth thread area (when the temperature in the thread area is too high, the exhaust groove in the thread area is deformed by the stretching force. This situation is generally caused by the deformation and upward warping of the support ring).
Solutions
- Ensure accurate adjustment of the transfer arm manipulator (synchronization adjustment between the manipulator and the main turntable, synchronization adjustment between the manipulator and the bottle, gap adjustment between the manipulator and the upper plane of the mold [1mm for preform feeding, 0.7mm for bottle taking]). Auber Packaging equips its production lines with high-precision manipulators and conducts regular calibration to avoid thread damage caused by manipulator misalignment.
- Align the blowing nozzle and the mold with special tools. Auber Packaging’s professional maintenance team uses professional tools to ensure accurate alignment, reducing thread damage.
- Adjust the distance of the cooling plate to better protect the thread, or strengthen ventilation, reduce the percentage of Zone 1, reduce the number of lamp tubes in Zone 1, and raise the furnace frame. (Some solutions refer to the section on Thread Expansion). Auber Packaging’s comprehensive process optimization can effectively solve various thread-related defects.
VII. Excessive Liquid Level Drop After Filling
Symptoms: Once the PET container is filled, the change of the container itself should be as small as possible. This change is due to excessive creep.
Influencing Factors
The container should be blow-molded at as low a temperature as possible. At too high a temperature, there is no pearlescent phenomenon on the container at all, but maximum biaxial stretching is required, so the container lacks sufficient creep resistance after filling. Bottles made at high temperatures are prone to burst after expansion. Auber Packaging strictly controls the blow molding temperature to ensure that the containers have excellent creep resistance.
Solutions
Some visible pearlescent phenomena usually appear at the end of blow molding. Therefore, the heating temperature should be correctly set when starting the equipment to avoid starting at too high or too low temperature. Auber Packaging’s intelligent control system can automatically adjust the heating temperature according to the material and bottle type, ensuring the stability of product quality.
VIII. Bursting
Symptoms: The bottle bursts at or near the bottom, and some bursts are in the transition area where the bottom is thinned.
Influencing Factors
There are several possibilities as follows:
- The material fails to reach its natural stretching limit during blow molding, which will cause radial changes (creep) of the container after filling, leading to bottom cracking.
- The wrinkles generated at the bottom burst during or after filling.
- The bottle bottom is too thin or too thick.
- Low IV value causes the bottle to expand after filling, leading to bursting.
- The transition area of the bottom is damaged by external force after molding.
- The alkali concentration of the chain lubricant is too high.
Solutions
The solutions to the above factors are shown in the previous section “Bottom Damage”. For factor 2, refer to the following section “Bottom Wrinkles”. Observe more during blow molding; if it is a fixed preform number, it is related to the factors. Auber Packaging’s quality inspection team conducts strict inspections on each batch of products, timely find it and solves potential bursting problems, ensuring product safety.
IX. Flat Mold Clamping Line (Flat Bottle)
Symptoms: The mold clamping line of the bottle in the vertical direction is flat, and there is a tendency to separate the mold under the blow molding pressure.
Influencing Factors
- Since the bottle is blown up in all directions, the applied air pressure will escape through the ventilation holes (exhaust holes) of the mold. If the excess air cannot be discharged in time, the air will separate the mold clamping. If not timely, the thin layer of material on the mold wall will enter the exhaust holes at the mold clamping place, causing blockage.
- The mold compensation air pipe is blocked or leaking, or the mold shell rubber ring is worn and leaking, resulting in too small compensation pressure.
- Too large mold gap.
- Wear of the mold clamping positioning short pin and bushing.
Solutions
- Slow down the high-pressure air supply and adjust the high-pressure blowing delay time, that is, reduce the high-pressure blowing time, but this will reduce the effective cooling time of the mold. Auber Packaging optimizes the air supply speed and blowing time to balance molding quality and production efficiency.
- Drill a few more ventilation holes along the mold clamping line (aperture: 0.5-0.7mm). Auber Packaging’s mold design team optimizes the number and position of ventilation holes according to the bottle structure to ensure smooth air exhaust.
- Check and test the mold air supplement size and whether there is leakage, and replace the mold air supplement if necessary. Auber Packaging’s mold maintenance team conducts regular inspections and maintenance of the mold air supplement system to ensure stable pressure.
- Adjust the mold clamping gap (gap: 0.1-0.2mm). When mold clamping is easy, minimize the mold clamping gap as much as possible. Auber Packaging’s technicians strictly control the mold clamping gap to avoid flat bottle defects.
- Check the wear of the mold clamping positioning short pin and bushing.
X. Bottom Wrinkles (Commonly Known as “Crater”)
Symptoms: Wrinkles are brought to the bottle by the preform bottom; wrinkles may be inside or outside the bottle. Such bottles are prone to explosion or cracking.
Influencing Factors
- External wrinkles:
A: External wrinkles are usually formed because the pre-blowing pressure is insufficient, so during stretching, too much material is pushed to the bottom.
B: The bottom temperature is too low, so it cannot be stretched during stretching, and the material is pushed to the bottom.
- Internal wrinkles: The preform bottom is overheated or pre-blowing is too late after stretching starts.
Solutions
- Adjust the pre-blowing pressure to ensure good pressure at each blow molding station. Auber Packaging’s intelligent pressure control system can ensure uniform pre-blowing pressure at each station, avoiding wrinkles caused by uneven pressure.
- Do not make the preform bottom temperature too low.
- Do not make the preform bottom temperature too high.
- Ensure that the delay between the start of stretching and the pre-blowing air intake is not too long. Auber Packaging optimizes the pre-blowing time parameters to solve the problem of internal wrinkles.
XI. Internal Neck Wrinkles (Commonly Known as “Ring Belt”)
Symptoms: Internal wrinkles are common 5-8mm below the convex ring, showing obvious annular shape, and there are obvious creases when touching the outside by hand.
Influencing Factors
- It is related to the too easy stretching of the preform from the thinner end of the cone section. In severe cases, stretching will start from the parallel section below the convex ring. When the preform is stretched, it gradually cools down as the stretching rod moves downward, and the material here is very thin, so it cools quickly. Natural wrinkles are generated during blow molding.
Solutions
- Readjust the hot spot position to make it close to the preform main body. Auber Packaging’s process engineers can accurately adjust the hot spot position according to the preform structure to avoid excessive stretching.
- Adjust the pre-blowing air intake time to ensure it is not too late. Check if the pre-blowing solenoid valve is normal.
- Caused by blowing nozzle failure. It is necessary to check whether the blowing cylinder seal, disperser, spring, solenoid valve and the up and down operation of the fixed sleeve are smooth (these will cause the blowing nozzle to run slowly). Auber Packaging’s maintenance team regularly maintains the blowing nozzle to ensure its normal operation.
- The material in the area is very thin. Increase the material thickness of the area (reduce the temperature of the area or increase the temperature of the area where the bottle is thicker). Auber Packaging’s customized material distribution solution can effectively solve the problem of thin material and wrinkles.
XII. Neck Material Accumulation (Commonly Known as “Flower Neck”)
Symptoms: Neck material accumulation is common with wavy stripes 5-8mm below the convex ring, and the convex ring is irregular or elliptical.
Influencing Factors
When the preform is sent to the mold cavity by the transfer arm, it touches the cooled mold cavity and cools first, or the pre-blowing air intake is too early during preform stretching, so the preform is formed as the stretching rod stretches downward during stretching.
Solutions
- Reduce the pre-blowing pressure. Auber Packaging’s intelligent pressure control system can accurately adjust the pre-blowing pressure to avoid material accumulation caused by excessive pressure.
- Delay the pre-blowing air intake time.
- Insufficient temperature in Zone 1 (increase the heating percentage of Zone 1 or add the number of its lamp tubes).
- The lamp holder is too high; adjust the position of the lamp holder.
- Too high temperature in Zone 2 or too high temperature in other zones (it is necessary to adjust the temperature of each zone according to the actual zone weight and thickness of the bottle to reduce the neck material). Auber Packaging’s temperature control system can accurately adjust the temperature of each zone to achieve uniform material distribution.
XIII. Eccentricity
Symptoms: The bottom structure is not concentric with the container, and in severe cases, bottom corner whitening will form. The bottom stress of such bottles is poor, and cracks or bursts are likely to occur.
Influencing Factors
This problem is related to two points. To identify which point, it is necessary to observe the position of the stretching point of the stretching rod. If the position of the stretching point is eccentric with the gate at the bottom of the preform, it indicates that the stretching rod is misaligned with the mold. If the position of the stretching point is concentric with the preform gate, it indicates that the stretching rod is correctly positioned but shifts during blow molding. Auber Packaging’s professional technicians can quickly identify the cause of eccentricity and provide targeted solutions.
Solutions
A. Mechanical Reasons
- The preform is misaligned with the mold.
- The blowing nozzle is misaligned with the mold.
- The preform is too tight with the upper part of the mold.
- The preform is too tight with the upper part of the mold.
- The stretching rod is bow-shaped.
- Abnormality of the stretching rod sliding guide rail or linear bearing.
- The buffer pad of the stretching rod is not properly adjusted, resulting in slow stretching descent or failure to fully descend to the bottom, resulting in slow stretching descent or failure to fully descend to the bottom.
B. Electrical Faults
- Too high pre-blowing pressure.
- Too early pre-blowing air intake.
- The stretching rod solenoid valve is dirty, the control valve seal is worn or the coil reel is broken.
- Blocked exhaust of the stretching cylinder (clogged muffler).
- Low control pressure of the stretching cylinder (air circuit turning loss).
Auber Packaging’s professional maintenance team has rich experience in solving mechanical and electrical faults of blow molding equipment, which can quickly troubleshoot and solve eccentricity problems, ensuring the concentricity of products.
XIV. Pearlescence – Bottom Corner Whitening
Symptoms: Pearlescent phenomenon exists in any part of the bottle, but it is most common at the bottom corner. A small amount of blueing at the bottom corner is normal, indicating that the maximum biaxial stretching is obtained during blow molding.
Influencing Factors
Pearlescence is a direct result of stretching exceeding the natural stretching limit. In fact, it is caused by the stretching and tearing of the microstructure of the material. The material in this area is obviously thinner.
Solutions
Because the material in this area is thin, it is best to increase the material in this area. If the material in this area is already sufficient, consider the following reasons:
- Ensure no eccentricity. Auber Packaging’s strict process control can effectively avoid eccentricity, reducing bottom corner whitening.
- Extend the pre-blowing time and pre-blowing air intake time. Reduce the pre-blowing pressure.
- Ensure the correct stretching gap (2/3 of the thickness of the blown preform bottom). Too large a gap will cause whitening. Auber Packaging’s technicians strictly adjust the stretching gap to avoid whitening.
- Ensure that the stretching operation is flexible and smooth (slow up and down movement of stretching will cause whitening).
- Caused by low preform temperature or low overall temperature of the preform during heating. Auber Packaging’s intelligent temperature control system ensures that the preform is heated evenly and to the appropriate temperature.
XV. Whitening (Bottle Body, Bottle Shoulder)
Symptoms: Whitening is common in blow molding, and the most common is bottom corner whitening (mentioned in the previous section). For whitening, it is first necessary to distinguish between high-temperature whitening and low-temperature whitening. Low-temperature whitening is foggy and opaque. High-temperature whitening is reflective pearlescent and transparent.
Influencing Factors and Solutions
A. Low-temperature whitening – Increase the temperature of the area or increase the overall heating percentage and preform temperature.
B. High-temperature whitening – Reduce the temperature of the area or the overall heating percentage and preform temperature.
C. There is another situation: if the bottle quality of other blow molding stations is good, but the bottles of individual blow molding stations are whitened, two aspects should be considered: 1. Low pre-blowing pressure. 2. Blowing nozzle air leakage. (The blowing nozzle is too high or the mold is uneven on both sides). In this case, whitening is generally on the bottle waist or a strip of whitening from top to bottom of the bottle body. Auber Packaging’s quality inspection team conducts full inspection of each station, timely find it and solves the problem of individual station whitening, ensuring consistent product quality.
As a leading cosmetic packaging manufacturer, Auber Packaging has advanced blow molding production lines, a professional R&D and technical team, and a strict quality control system. We are committed to providing customers with high-quality, customized blow-molded container solutions, solving various quality problems encountered in the production process for customers, and helping customers improve product competitiveness. Whether you are facing the above common quality defects or have other customized needs, Auber Packaging is your reliable partner.