How To Seal PET Bottles?

I. The Importance Of PET Bottle Sealing

1. Affect Product Shelf Life

In daily life, PET bottles can be seen everywhere and are widely used to hold various beverages, medicines, and other products. For these products, good sealing performance plays a crucial role. The external environment contains air, moisture, and various microorganisms, and the good sealing of PET bottles can act as a strong defense line, blocking these factors that may affect product quality.

Taking beverages as an example, such as fruit juice drinks, carbonated drinks, etc., if the sealing is not good, the outside air will slowly seep into the bottle, and the oxygen in it will undergo oxidation reactions with the ingredients in the beverage, resulting in the loss of nutrients, color changes, and even spoilage of the beverage. For drugs, many drugs have strict requirements for storage environment. Once poorly sealed, the active ingredients of the drug may decompose or become ineffective when exposed to moisture, and microorganisms may also take the opportunity to invade, contaminating the drug and preventing it from functioning properly, which may even pose a threat to the health of the user.

It is precisely because of its good sealing performance that PET bottles can effectively prevent the product from coming into contact with these adverse factors, avoiding adverse phenomena such as deterioration and decay, thereby significantly extending the shelf life of the product, allowing the product to maintain its intended use effect within the specified time, and providing strong protection for consumer safety.

2. Ensure Product Taste And Quality

We all know that the taste and quality of a product are one of the key factors that attract consumers, and the sealing performance of PET bottles has a direct impact on this. Take beverages as an example. If there is a problem with the seal, such as air or liquid leakage, the originally stable environment inside the bottle will be broken. For example, carbonated beverages, once leaked, the carbon dioxide inside will escape, causing the beverage to lose its original refreshing taste and unique bubbly sensation, becoming plain and unremarkable. If the sealing of fruit juice drinks is not good, the loss of moisture or the entry of external impurities will change the proportion and state of its internal components, and the originally rich and pure fruit juice flavor will be greatly reduced.

For some products that require high stability of ingredients, such as functional drinks, health drinks, and certain special formula drugs, the quality of sealing is crucial to maintaining consistency in their quality. Good sealing can ensure that the content and proportion of various components inside the product are maintained in the optimal state after production packaging is completed until consumer use, ensuring that the efficacy and taste of the product are not affected, and allowing consumers to obtain the expected experience every time they use it. So, the sealing performance of PET bottles is of great importance in maintaining the taste and quality of products.

II.Factors Affecting PET Bottle Sealing

1. Design Factors Of Bottle Mouth And Cap

The design factors of the bottle mouth and cap play a fundamental and crucial role in PET bottle sealing. The shape, size, and thread specifications of the bottle mouth are closely related to whether the bottle cap matches.

Firstly, let’s take a look at the shape of the bottle mouth. Common shapes include circular, square, etc. Different shapes are suitable for different types of products. For example, a circular bottle mouth, due to its uniform circumference, is subjected to relatively balanced force when sealing with a screw cap, and is widely used in the packaging of various beverages, seasonings, and other products. Square bottle mouths may appear more frequently on some creative packaging or products that facilitate pouring specific contents.

In terms of size, there is no room for any carelessness. The diameter of the bottle mouth needs to be precisely designed to fit the inner diameter of the bottle cap. If the diameter of the bottle mouth is too large, the bottle cap will become loose and prone to shaking, which will provide opportunities for external air, moisture, etc., making it difficult to ensure a good sealing effect. On the contrary, if the diameter of the bottle mouth is too small, the bottle cap may not be able to be smoothly fitted, let alone sealed.

The design of threads is the key to sealing. The pitch, depth, and other parameters of the thread all affect the sealing performance. For example, if the pitch is designed too large, the distance for the bottle cap to rise or fall will be too long for each rotation when tightening the bottle cap, which may cause the bottle cap not to fit tightly with the bottle mouth, leading to gaps and sealing failure. If the pitch is too small, more rotations are required when screwing the cap, which is inconvenient to operate and may also affect the sealing effect due to friction between the threads. Threads with insufficient depth also cannot provide sufficient fixing and sealing force for bottle caps, and are prone to loosening, air leakage, and other situations.

In addition, the flatness of the bottle mouth cannot be ignored. In the production process, if the end face of the bottle mouth is not flat enough, even a small deviation, when the bottle cap is tightened, gaps will form locally, resulting in poor sealing. For example, on some high-speed production lines, minor defects in molds or processing techniques may cause flatness issues at the bottle mouth, which in turn can affect the sealing quality of the entire batch of PET bottles. Therefore, in the design stage of PET bottles, it is necessary to rigorously consider and optimize the various design parameters of the bottle mouth and cap to ensure that they can be perfectly matched, laying a solid foundation for good sealing effect.

2. Considerations For The Selection Of Sealing Materials

Sealing material is one of the key elements to ensure the sealing performance of PET bottles. Commonly used sealing materials include rubber, silicone, etc. They each have different characteristics, and these characteristics play an important role in the sealing process.

Rubber material is a widely used sealing material, which has certain elasticity and plasticity. Its elasticity allows it to deform according to the shape and pressure changes between the bottle mouth and the bottle cap when the bottle cap is tightened, thus better filling those tiny gaps. For example, some PET bottle packaging that uses extrusion sealing principle, rubber sealing material can play a good role. For example, rubber gaskets are installed inside the caps of some beverage bottles. When the caps are tightened, the rubber gaskets are squeezed and deformed, tightly adhering to the surface of the bottle mouth, preventing the entry and exit of air and liquid. Moreover, rubber materials have relatively low costs and a wide range of sources, and are given priority consideration in many product packaging with strict cost control measures.

Silicone materials are highly favored for their excellent elasticity, high temperature resistance, and chemical stability. Its elasticity is superior to rubber, and it can maintain good rebound performance under long-term use and different environmental conditions. Even after opening and closing the bottle cap multiple times, it can still maintain its sealing effect. In terms of high temperature resistance, for some products that require high temperature filling or high temperature disinfection treatment, such as canned hot drinks, drugs that require sterilization treatment, etc., silicone sealing materials can stably function without aging, deformation, or other factors that affect the sealing due to high temperature. Meanwhile, silicone has good chemical stability and is not prone to chemical reactions with the contents of the bottle, ensuring the quality and safety of the product.

In addition, the temperature resistance of sealing materials is a key indicator that must be considered when selecting. Different products may face various temperature environments during production, transportation, and storage. For example, in the high-temperature transportation environment of summer, if the temperature resistance of the sealing material is poor, it may become soft and melt, leading to seal failure. In the cold winter, if the low-temperature resistance is poor, it may become brittle and crack, which can also damage the sealing structure. For PET bottles that require cold chain transportation of drugs or food packaging, it is necessary to choose sealing materials with good low-temperature resistance to ensure stable sealing performance even in low-temperature environments.

Therefore, in practical applications, the most suitable sealing material should be selected based on various factors such as the characteristics of the product contained in the PET bottle, the usage environment, and the cost, in order to ensure that the bottle mouth and cap can maintain a tight fit for a long time and achieve good sealing effect.

3. Key Controlling Points Of Production Process

The influence of production process on the sealing performance of PET bottles runs through the entire manufacturing process, and multiple key control points are directly related to the sealing reliability of the final product.

The first issue is the machining accuracy of the bottle mouth and cap. In the production process, it is necessary to accurately process the dimensions of the bottle mouth and cap to ensure the best fit between the two. If the machining accuracy of the diameter, thread, and other dimensions of the bottle mouth is not sufficient and deviates from the design standards, the bottle cap cannot fit tightly with the bottle mouth when tightened, which can easily lead to local gaps or overall poor sealing. Similarly, if the dimensional accuracy of the bottle cap does not meet the standard, it will also affect the sealing effect.

For example, if the inner diameter of the bottle cap is too large, even if tightened, it is difficult to apply enough uniform pressure to the bottle mouth to ensure sealing. If the inner diameter is too small, it may not be possible to tighten the bottle cap properly. This requires production enterprises to adopt high-precision processing equipment and advanced mold technology, strictly control processing errors, and ensure that every bottle mouth and cap produced can meet the dimensional accuracy requirements of the design.

The uniformity of coating of sealing materials on bottle caps is also an important factor affecting sealing. In the production of bottle caps that use coating sealing materials, such as applying a layer of sealant or sealing grease on the inner surface of the cap, if the coating is uneven, with some areas thick and some areas thin, then after tightening the cap, the thinner area of the sealing material may not be able to effectively fill the gap between the bottle mouth and the cap, resulting in local sealing problems. This not only affects the sealing performance of the product, but may also lead to leakage, deterioration, and other issues during storage and transportation. Therefore, in the coating process, precise equipment control and reasonable operating procedures are necessary to ensure that the sealing material can be evenly covered on the corresponding position of the bottle cap.

The degree of thread engagement also needs to be strictly controlled during production. The processing of threads should follow standard requirements to ensure accurate parameters such as pitch and tooth shape, so that the bottle cap can perfectly mesh with the threads of the bottle mouth when tightened. If there are deviations during thread processing, such as inconsistent pitch or mismatched tooth profile, the bottle cap may feel stuck or unable to be tightened properly during the tightening process, which greatly reduces the reliability of the seal. External air, moisture, etc. can easily enter the bottle through the gaps between the threads, damaging the storage environment of the product.

In short, every step of the production process is related to the sealing performance of PET bottles. Only by strictly controlling each key point can we produce PET bottle products with excellent sealing performance and meet the market’s requirements for product packaging sealing.

III. Preparations Before Sealing PET Bottles

1. Selection And Inspection Of PET Bottles

Careful selection and inspection of the PET bottle itself is a crucial step before performing the PET bottle sealing operation. Firstly, it is crucial to carefully inspect the appearance of the PET bottle and observe whether the bottle mouth is smooth. This is extremely important. Because even if the bottle mouth is only slightly uneven, gaps may form locally after tightening the bottle cap, leading to poor sealing. For example, on some high-speed production lines, due to minor defects in molds or processing techniques, the bottle mouth is prone to flatness issues, which can affect the sealing quality of the entire batch of PET bottles.

At the same time, pay attention to whether there are cracks on the bottle mouth and body. Even small cracks can cause leakage of substances inside the bottle during storage or transportation, damaging the sealing effect. In addition, the uniformity of the material of the bottle body cannot be ignored. Uneven material may indicate unstable quality of the bottle during the production process. Even if the subsequent sealing operation is correct, there may still be leakage and other poor sealing phenomena.

We can inspect the bottles one by one through visual observation and simple touch, remove those with obvious quality problems, and ensure that the PET bottles left for sealing packaging have good basic conditions, laying the foundation for achieving reliable sealing effect.

2. Preparation Of Sealing Materials

The selection and preparation of sealing materials play a decisive role in the sealing effect of PET bottles. Due to differences in their own characteristics and usage environment, different products are suitable for different sealing materials.

For example, for food products, due to direct contact with the human body, it is more inclined to choose silicone materials that meet food safety standards as sealing materials. Silicone has many advantages such as excellent elasticity, high temperature resistance, and chemical stability. Its excellent elasticity enables it to maintain good rebound performance and continuous sealing effect during multiple opening and closing of bottle caps and long-term use. For some foods that require high-temperature filling or high-temperature disinfection treatment, such as canned hot drinks, silicone sealing materials can stably function without aging, deformation, or other factors that affect the sealing due to high temperature. And it is not prone to chemical reactions with the food contents inside the bottle, which can fully ensure the quality and safety of the product for consumption.

For some ordinary daily necessities, rubber material is also a commonly used choice. Rubber has certain elasticity and plasticity, relatively low cost, and wide sources. When the bottle cap is tightened, it can produce corresponding deformation according to the shape and pressure changes between the bottle mouth and the bottle cap, thus better filling those small gaps and achieving the purpose of sealing.

Regardless of which sealing material is chosen, it is important to ensure its quality is qualified, carefully inspect for any damage, and ensure that its surface is free from contamination. Only when the sealing material itself is in good condition can it function properly in the subsequent sealing process, ensuring good sealing performance of PET bottles.

3. Selection Of Sealing Tools

The selection of sealing tools is also an indispensable part of PET bottle sealing preparation work, and it will vary depending on the sealing method.

If manual capping sealing is used, suitable capping tools such as common manual capping tools need to be prepared. This type of tool should ensure that the bottle cap can be easily and effectively tightened to fit tightly with the bottle mouth. When choosing a capping tool, attention should be paid to whether its size is suitable for the PET bottle cap used. If the size is not suitable, it may not be possible to operate smoothly or tighten the cap to a sufficient degree, which will affect the sealing effect.

If machine sealing is adopted, it is particularly important to debug the sealing equipment in advance. It is necessary to carefully check whether the operation of each component of the equipment is normal, such as whether the transmission components are smooth and whether the sealing head can work accurately. At the same time, it is necessary to verify whether the parameter settings of the equipment are accurate. Parameters such as sealing pressure and time need to be accurately set according to the specific requirements of PET bottles and products to ensure that the equipment can efficiently and accurately complete the sealing operation. Only when the sealing tools are properly prepared can the subsequent sealing process proceed smoothly and achieve the desired sealing state.

IV. Common Sealing Methods For PET Bottles

1. Screw Sealing Method

The screw cap sealing method is the most common way of sealing PET bottles, which is widely used in daily life and many industrial production fields. Whether it’s the dazzling array of beverage bottles on supermarket shelves or various sauce bottles stored at home, most of them use this sealing method.

When it comes to specific operations, we can either manually use tools such as manual capping machines to tighten the threaded bottle cap onto the bottle mouth, or use professional equipment such as capping machines to complete the sealing operation. However, there are two key points to pay extra attention during the screwing process.

Firstly, the capping operation should be carried out according to the appropriate torque. The control of torque size is very important. If the torque is too large, it is likely to damage the bottle mouth or cap. For example, some thinner PET bottle mouths may break due to excessive torque, or the threads of the cap may be twisted, which will affect the subsequent normal use and sealing effect. If the torque is too small, the bottle cap and bottle mouth cannot fit tightly, the seal is not firm, and external air, moisture, and microorganisms are easy to enter the bottle, which has a negative impact on the quality of the products inside the bottle. For example, in beverage production, insufficient torque may cause carbonated beverages to leak air, causing the beverage to lose its original bubbly taste, and fruit juice beverages may also deteriorate due to poor sealing.

Secondly, when screwing the cap, it is necessary to ensure that the bottle cap is aligned with the bottle mouth, so that the threads can fully engage. This requires checking whether the threads of the bottle mouth and cap match well before operation, and ensuring that the two are aligned and tightened during the capping process to avoid thread misalignment and gaps, which can damage the sealing structure. Only by accurately controlling these key links, can good sealing effects be achieved through the screw cap sealing method, ensuring the quality and shelf life of PET bottle products.

2. Pressure Sealing Method

The pressure sealing method has important applications in PET bottle packaging that requires high sealing requirements and the bottle cap design is suitable for compression. For example, PET bottle packaging for some drugs, high-end cosmetics, and other products is used to ensure good sealing during long-term storage and under different environmental conditions.

This method mainly utilizes specialized capping equipment to achieve sealing. During operation, the device will apply a certain amount of pressure to the bottle cap, promoting a tight fit between the cap and the bottle mouth. In this process, precise control of pressure magnitude and pressure application time is the key to ensuring uniform and stable sealing effect. If the pressure is too high, it may cause deformation of the bottle mouth, especially for PET bottles with relatively soft texture. Once the bottle mouth is deformed, it not only affects the appearance, but also destroys the original good sealing structure, resulting in sealing failure.

On the contrary, if the pressure is too low, the gap between the bottle cap and the bottle mouth cannot be tightly compacted, and there will be small gaps. External air, water vapor, etc. are easy to penetrate into the bottle, causing damage to the products inside the bottle. Moreover, the pressure application time also needs to be reasonably controlled. If the time is too short, it may lead to the end of the pressure application before the bottle cap and bottle mouth are fully adhered, while if the time is too long, it may unnecessarily increase the pressure burden on the bottle mouth and other parts, which also affects the sealing effect and the overall quality of the bottle.

Therefore, when using the capping method, the operator needs to adjust the pressure parameters and pressure application time of the capping equipment in advance according to the specific materials, design characteristics and other factors of PET bottles and caps, so as to ensure that each capping operation can achieve an ideal sealing state and meet the strict requirements of the product for sealing.

3. Heat Sealing Method

For some special PET bottle packaging, heat sealing is an effective sealing method, such as PET bottles with plastic film seals, commonly used in the packaging of some food, health products and other products.

The principle of heat sealing technology is to soften the film by heating, and then make it adhere around the bottle mouth. After cooling, a sealed structure is formed. In the actual operation process, several key parameters must be strictly controlled. Firstly, there is the heating temperature. If the temperature is too high, the film is prone to overheating and deformation, which may lead to film rupture, melting, and other situations. This not only fails to achieve good sealing, but also may contaminate the products inside the bottle.

However, if the temperature is too low and the softening degree of the film is not enough, it will be difficult to tightly adhere to the bottle mouth, resulting in incomplete sealing, and external air, impurities, etc. can still enter the bottle. Secondly, there is the heating time. If the time is too long, it will cause adverse changes in the film, just like if the temperature is too high. If the time is too short, the film cannot fully soften to achieve the desired bonding effect.

Furthermore, the pressure should not be ignored. Appropriate pressure can ensure that the softened film is fully in contact and compacted with the bottle mouth. Insufficient pressure may result in a loose fit, while excessive pressure may damage the film or bottle mouth structure. For example, in some food packaging, if the heat sealing parameters are not well controlled, the food may spoil and become damp in advance, affecting its taste and quality.

Therefore, operators need to conduct multiple experiments and adjustments based on the material, thickness, and size of the bottle mouth of the film to accurately determine parameters such as heating temperature, time, and pressure, in order to use the heat sealing method to achieve reliable sealing and provide a good storage environment for the products inside PET bottles, extending the shelf life of the products.

V. Testing Methods For Sealed PET Bottles

1. Appearance Inspection Method

Visually inspecting sealed PET bottles is the most intuitive and simple preliminary testing method. Testing personnel can directly observe the sealed PET bottle with the naked eye, focusing on the joint between the bottle mouth and the bottle cap. For example, carefully check if there are any gaps here, even extremely small gaps can cause sealing problems. External air, moisture, or impurities may enter the bottle through these gaps, affecting the quality of the products inside the bottle.

At the same time, it is important to pay attention to any traces of liquid leakage, which is particularly crucial for PET bottles containing liquid products. Like beverage bottles, if they leak due to poor sealing, it not only causes product waste, but also may contaminate the surrounding environment and other items. In addition, checking for any signs of looseness in the bottle cap should not be ignored. A loose cap means that it is not tightly attached to the bottle mouth, which cannot guarantee a good sealing effect. Gently shake the bottle and feel whether the cap is stable to make a preliminary judgment.

For example, on the packaging assembly line of some food production enterprises, workers will conduct spot checks on PET bottles after they have been sealed. Through simple visual inspection, they will quickly screen out those bottles with obvious sealing problems, adjust or reseal them in a timely manner, and avoid products with quality risks from entering the market. Although this method is simple, it can quickly identify some obvious sealing issues, providing preliminary basis for further testing or product release.

2. Pressure Testing Method

The pressure testing method is a testing method that applies a certain pressure inside a sealed PET bottle to observe whether the bottle can withstand the pressure and still maintain a sealed state. It plays an important role in evaluating the sealing performance of PET bottles.

When performing specific operations, it is necessary to place the sealed PET bottle in a specific pressure testing equipment. For example, the LSSD-02 plastic bottle internal pressure tester can automatically display the pressure changes throughout the entire experimental process, and is suitable for various carbonated beverage bottles and other plastic bottles to maintain internal pressure and perform burst tests, meeting the requirements of internal pressure tests for plastic bottles of different capacities. It is a commonly used testing instrument by quality inspection agencies and beverage production enterprises.

In the carbonated beverage industry (such as cola), the pressure filling mode is usually tested by simulating the actual filling process of a PET bottle filling production line. In this mode, the PET bottle is quickly pressurized to the pressure value preset by the operator for 13 seconds, and then pressurized at the rate of 10 pounds per square inch (0.69 Kg/cm2) per second until the container breaks or reaches the preset maximum pressure and capacity value. This pressure filling test mode complies with the mandatory standard measurement method for “PET” bottles recommended by the PET branch of the Beverage Technology Society (ISBT).

For different products, the required pressure and holding time parameters vary, and must be strictly set according to specific product requirements. For example, for carbonated beverage bottles, due to the presence of carbon dioxide gas inside, there is already a certain pressure inside the bottle. When testing their sealing performance, it is necessary to apply appropriate air pressure according to the corresponding standards to see if there will be any leakage or other issues under this pressure, in order to determine whether the sealing performance meets the standards and ensure that the product will not experience adverse phenomena such as leakage or deterioration due to sealing problems during transportation, storage, and sales.

3. Vacuum Testing Method

The vacuum testing method mainly involves placing PET bottles in a vacuum environment and observing whether there are any air intake, air leakage, or other conditions to determine the sealing effect of PET bottles. It is particularly suitable for PET bottle sealing testing of products that are sensitive to oxygen and require high sealing environments.

In practical operation, the commonly used sealing tester operates by vacuuming the vacuum chamber of the equipment, causing a pressure difference between the inside and outside of the sample (i.e. PET bottle) immersed in the vacuum chamber water, and checking whether there is any air leakage in the sample. Alternatively, the sealing performance of the sample can be determined by observing the shape recovery of the sample after expansion and release of the vacuum.

After placing the PET bottle in a vacuum environment, if the seal is not good, external air will enter the bottle, and continuous bubbles can be observed emerging from the bottle mouth in water. PET bottles for products that require strict storage environments, such as pharmaceuticals and high-end skincare products, may oxidize and become ineffective once air enters. The composition of skincare products may also change, affecting their quality and effectiveness.

For example, in pharmaceutical companies, for drugs packaged in PET bottles, after completing the sealed packaging, a certain number of samples will be taken for vacuum testing to strictly control the sealing quality. Only products with sealing performance standards can enter the market circulation process, ensuring the stability of drug quality and allowing consumers to use them safely.

VI. Precautions For Sealing PET Bottles

1. Targeted Sealing Requirements For Different Products

Different types of products have their own targeted requirements for the sealing of PET bottles, which mainly depend on the characteristics of the product itself and factors such as usage scenarios.

For food and beverage products, food safety and preservation requirements are key considerations when sealing. For example, common fruit juice drinks are rich in various nutrients such as vitamins, sugars, etc. If the sealing is not strict enough, once a large amount of external air infiltrates, the oxygen in the juice will cause oxidation reactions of the nutrients in the juice, making the color darker, the flavor worse, and even breeding bacteria that cause spoilage and can no longer be consumed normally.

Carbonated beverages are even more so. Good sealing can lock in the carbon dioxide gas inside, maintaining the refreshing taste and sufficient bubbles of the beverage. If the sealing is poor, carbon dioxide will escape and the beverage will become bland and tasteless. Moreover, food and beverage products directly enter the human body, and the introduction of impurities, microorganisms, etc. due to poor sealing may also threaten consumers’ health. Therefore, strict control should be exercised in the sealing process to ensure a tight seal and prevent external factors from affecting product quality.

The sealing requirements for pharmaceutical products are even more stringent. The stability of the ingredients of a drug plays a crucial role in its efficacy, and many drugs need to be stored under specific environmental conditions. Sealing is an important defense line to ensure the stability of this environment. For example, for some drugs that require moisture prevention, the seal must be able to effectively block external water vapor, preventing the effective ingredients from decomposing or becoming ineffective after the drug becomes damp. Some drugs that are sensitive to oxygen need to be sealed to isolate the air as much as possible to avoid oxidation and loss of efficacy.

At the same time, the sealing of drug packaging needs to be strictly carried out in accordance with the corresponding drug packaging specifications, from the selection of sealing materials to the control of the sealing process, all of which must comply with relevant quality standards and regulatory requirements, in order to ensure that drugs can maintain good quality before storage, transportation, and use, and ensure the safety of patients’ medication.

In short, the characteristics of different products determine that their sealing focus and requirements vary. In actual PET bottle sealing operations, these factors must be fully considered and appropriate sealing measures must be taken to meet the needs of different products.

2. The Impact Of Storage And Transportation Environment On Sealing

PET bottle products inevitably undergo various storage and transportation environments throughout their entire lifecycle, and these environmental factors have an undeniable impact on their sealing effectiveness.

In high-temperature environments, whether it is the storage warehouse of products or the carriages during transportation, if the temperature is too high, the sealing materials and the joint parts of bottle mouths and caps will face severe challenges. Due to the principle of thermal expansion and contraction, high temperatures may cause the sealing material to soften and expand, and there may also be slight changes in the size of the bottle mouth and cap, resulting in gaps in the originally tightly fitting parts and leading to seal failure.

For example, in the high temperature logistics transportation in summer, some PET bottles that have not been well insulated and protected are prone to loosening after prolonged exposure to sunlight, resulting in leakage or air leakage of the drinks. And for some products that have been filled at high temperatures, if they cannot withstand the corresponding high temperatures during subsequent storage, it will also affect the quality of the products.

When in a humid environment, water vapor becomes a key factor affecting sealing. If the seal is not tight enough, external moisture may slowly enter the bottle through the seal. For products that are sensitive to moisture, such as drugs, certain dry foods, etc., they are prone to spoilage, mold growth, and other problems when exposed to moisture. During the rainy season in the south, the air humidity is high. If the sealing of PET bottles does not consider moisture resistance, products stored in ordinary warehouses may be damaged due to moisture.

Therefore, before sealing PET bottles, it is necessary to fully consider the storage and transportation environment in which the product may be stored in the future. Based on the actual situation, appropriate sealing methods and sealing materials with good temperature and moisture resistance should be selected to ensure that PET bottles can maintain a reliable sealing state under different environmental conditions, ensuring that the quality and performance of the product are not affected.

3. Hygiene Requirements During The Sealing Process

The hygiene condition during the sealing process is crucial for the quality and safety of the products contained in PET bottles, especially for those containing food and medicine. The hygiene process must be strictly controlled.

Firstly, sealing operations must be carried out in a clean and hygienic environment. For food and beverage production enterprises, sealed workshops usually need to meet certain food hygiene standards, undergo regular disinfection and sterilization treatment, and prevent pollutants such as dust and bacteria from entering the bottles in the air. For example, in a sterile cold filling production line, after PET bottles enter the bottle sterilization machine area through the conveying air rail, disinfectant peracetic acid or a wetting agent is used to thoroughly disinfect and sterilize the inside and outside of the bottles by spraying or pouring. Subsequent processes such as bottle washing and cap sterilization are also strictly controlled to ensure that the bottles and caps are in a sterile and clean state before sealing.

The sealing material itself should also be kept clean and pollution-free, and undergo strict inspections before procurement, storage, and use. If the surface of the sealing material is contaminated with impurities, oil stains, or microorganisms, it will enter the bottle during sealing as the bottle cap is attached to the bottle mouth, becoming a hidden danger that affects product quality. For example, rubber sealing gaskets, if contaminated with dust during production or storage, may form suspended particles in the beverage after being used for sealing beverage bottles, affecting the appearance and taste of the beverage, and even causing hygiene problems.

In addition, operators should also follow hygiene standards for sealing operations. Operators need to wear clean work clothes, hats, masks and other protective equipment, maintain personal hygiene and cleanliness, and avoid contaminating products with bacteria and other contaminants carried by themselves. And during the operation, it is necessary to strictly follow the standard procedures for sealing operations to prevent the introduction of external pollutants due to non-standard actions.

Only by strictly implementing measures in all aspects such as environment, materials, and personnel, can hygiene requirements be ensured during the sealing process.