How the Composite Packaging Material Adapts to the High Temperature Cooking Process at 121°C

【Chinese Packaging Network News】 High-temperature cooking is a highly efficient and thorough sterilization process that is widely used in the disinfection of meat, bean products, some medical products and medical injections. In recent years, this process has also gradually been used to mature chestnut and corn syrup beverages. , Sterilization of baby food, vegetable, and other foods. High-temperature cooking sterilization temperature range is generally between 121-135 °C, there are also 145 °C to meet the ultra-high temperature sterilization of flexible packaging materials. The research data show that under the condition of 145°C, as long as the treatment time is about 3 minutes, the most heat-resistant spores of Bacillus botulinum can be completely killed, and the resulting composite flexible packaging material has also been widely used. According to the sterilization and sterilization conditions of the contents of the package, this article will focus on the requirements of the 121 °C high-temperature packaging bag design and processing technology to adapt to the requirements of high-temperature cooking.

The structural design of composite flexible packaging material must meet the process requirements of high temperature sterilization, usually considering many factors, in addition to packaging materials in the production process to ensure its own function, but also to consider more content requirements, taking into account the sterilization treatment The influence of process conditions, circulation storage conditions and sales and use links on the properties of the packaging materials is discussed below.

First, the purpose of cooking sterilization and cooking bag classification

There are two main purposes of sterilization:

1. Thoroughly destroy harmful bacteria and meet sterility requirements, such as sterilization of medical supplies.

2. After thorough sterilization, the growth of the contents can be suppressed with little or no preservatives, and the shelf life of the contents can be prolonged, so that the contents can maintain the originally designed flavor at room temperature for a long time, such as various foods. High-temperature cooking products.

The heat-resistant sterilizing bags are classified according to current international standards as follows:

1, can be resistant to 121 °C cooking bag, high temperature time ranging from 30-60min.

2, can withstand 135 °C cooking bag, temperature time ranging from 15-30min.

3, can be resistant to ultra-high temperature cooking bag 145 °C, is currently the highest level of cooking bag, temperature less than 5min.

Nowadays, the domestic market generally uses high-temperature cooking bags that can withstand 121°C. In general, solid materials such as meat high-temperature cooking and packaging also meet the vacuum requirements.

Second, high temperature cooking bag on the film substrate and chemical materials requirements

The film base material for the production of high-temperature cooking bags is the basis for satisfying the cooking conditions. Usually, according to the cooking conditions of the high-temperature cooking bag and the characteristics of the contents, it is determined which base materials, specifications and combination order are selected, and which type of ink is used. Glue and so on. Commonly used film substrates include: BOPET, B0PA, HDPE, RCPP, AL, co-extruded EVOH, co-extruded PVDC, co-extruded PE, etc.; there are also new types of co-extruded films with more than five layers such as: PP/AC/EVOH/AC/PP , PP/AC/PA/EV0H/PA/AC/PP, etc.; In addition, copolymerized nylon MXD6, ceramic evaporation film such as SiOxPET12um, multi-layer co-extruded film and ceramic evaporation film are currently in high temperature due to technical process and price factors. Application on cooking bags is rare.

According to the order of the surface layer (or printing layer), barrier layer and heat seal layer, the structure of the composite packaging material can be combined, and also the single layer material can be used as both the printing layer and the barrier layer, so the packaging bag can be designed as two layers or three according to need. Layers, four or more layers, such as: BOPET//RCPP, BOPA//RCPP, BOPET//BOPA//RCPP, BOPET//A1//RCPP, BOPET//A1//BOPA//RCPP, etc. For the substrate thickness is usually selected: BOPET12um, BOPA15um, AL7um or AL9um, RCPP50um, RCPP70um, RCPP80um, RCPP100um, etc., for the barrier layer usually choose BOPA and AL, according to actual needs also have the choice of BOPA25um and AL12um, large capacity and special requirements The RCPP thickness of the high-temperature cooking bag also exceeds 100um. The liquid packaging bag overcomes the defect that RCPP is not resistant to falling. Generally, additives are added in the film to enhance its anti-drop performance.

The chemical materials used in high-temperature cooking package mainly refer to ink, glue and solvent. Ordinary ink does not have high temperature resistance, it will leave the layer after cooking, some colors will change, high temperature cooking ink should be a two-component reactive polyurethane as the linking material of the ink, it has good printing and fastness, cross-linking curing reaction After it can withstand high temperature cooking, it can form a very strong bond with the glue. At the same time, for a large area of ​​spot colors and white patterns, but also choose the matching ink curing agent. When choosing inks, special attention should be paid to distinguishing common inks, boiled inks that are resistant to temperatures below 100°C, and high-temperature cooking inks that are resistant to temperatures above 121°C to avoid misuse. The glue should be selected for high-temperature cooking grades, and it is generally considered that it satisfies the cooking requirements above 121°C at least. After compounding, it must have good adhesive fastness, high temperature resistance, medium resistance, and heat resistance. The most commonly used is a two-component polyurethane. glue. The choice of solvent and ink, glue can be a good match, can meet the process requirements, but can not affect the ink, glue, high temperature cooking performance.

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Third, the high temperature cooking bag requirements of the production process

In order to control the quality of high-temperature cooking products, in addition to the production requirements of ordinary products, special requirements have to be made for individual places. For the sake of clarity and simplicity, only a few precautions for each process are listed here.

1, printing process

The actual production of the printing process should pay attention to the problem:

(1) The most commonly used printing substrates for high-temperature cooking bags are BOPET12um and BOPA15um. The grade of the substrate used must be high and the quality must be guaranteed, including a corona value of 52 dyne or more, and uniform corona; uniform thickness. No lotus leaf, no foreign body pollution. High-temperature cooking BOPA15um (including composite) is different from ordinary bags, the best choice for simultaneous stretching, in order to ensure the same direction in all directions, fixed longitudinal stretch ratio and special mechanical properties.

(2) Select ink according to the ink manufacturer's technical data, use at least “R” grade ink, and the different manufacturers of high-temperature cooking ink cannot be mixed. The proportion of mixed solvent used with the ink must be appropriate, and the purity of the active ingredient should reach 99%. the above. To meet hygiene requirements, be aware that solvents and inks do not contain benzene, toluene, xylene, ketones, or other high-boiling solvents. According to the characteristics of the printing materials and composite film structure to select the appropriate ink, such as the use of BOPA for the printing layer, the individual colors of the ink in the cooking state of the pigment may be in the BOPA penetration, also for only the printing layer and the heat seal layer In a structured cooking bag, the ink also has the potential to permeate on the RCPP, thereby posing a risk of contamination of the contents.

(3) Spot colors and white inks that need to be used in large areas should be added with 1%-3% of ink curing agents. The amount of added ink must be determined according to the technical data provided by the ink manufacturers, but not too much or too little. The remaining ink recovered in the ink tray, no matter how long it has been stored, can no longer be used for high-temperature cooking products.

(4) To minimize the amount of solvent residues in the printing material, and the ink adhesion is good, we must select the standard production process parameters, such as oven temperature, air volume and machine speed, etc. For large-area inks with ink curing agents, The oven temperature is 10-15°C higher than other inks.

(5) The printed BOPA film must be tightly wrapped with an AL foil composite film to prevent moisture shrinkage and performance changes.

(6) The printing material added with the ink curing agent should preferably be rewound once more, and the storage time should not exceed three days, that is, at least the printing layer is compounded within three days.

2, the complex process

At present, the high-temperature cooking bag mainly uses the dry complex process. How this process is controlled is the key to the success or failure of the high-temperature cooking bag. The following issues must be paid attention to during production:

(1) The use of high-temperature cooking glue must be according to the manufacturer's instructions, such as the ratio, aging temperature and time, etc., the purity of the ethyl acetate solvent used for dilution should be more than 99%.

(2) The thickness of each layer of material should be uniform and the thickness deviation should not exceed 7%. For products using AL foil, besides its mechanical performance parameters are satisfied, the surface of AL foil should be dry, and the cleanliness must reach Grade A standard, ie Distilled water should be infiltrated in all inspections, and the smaller the number of pinholes, the better. The storage time before use should not exceed three months. To enhance the composite fastness, the composite BOPA in the middle is a double-sided corona with a corona value no lower than 50 dyne.

(3) The glue coating should be uniform. According to the characteristics of different manufacturers and different types of glue, the dry basis weight should generally be 3.5-4.8g/m2. When the minimum coating amount is achieved, the left, middle, and right positions are The coating deviation should not exceed 0.3 g/m2 as a benchmark. The curing agent should be added as required. If the dry room environment humidity exceeds 80%, the amount of curing agent should be increased appropriately, generally 5%-10% on the original basis. If the product printing pattern has more yellow In areas with light colors such as white and white, the amount of coating applied during production is 0.3 g/m2 or more in comparison with the dark color pattern design to prevent visible spots after cooking.

(4) Determine the appropriate machine processing parameters, especially the three sections of the oven temperature is 5-10 °C higher than the production of ordinary products, the composite heating roller temperature is 70-80 °C, the composite pressure is increased by 0.1-0.2 MPa, according to the machine performance speed is controlled below 120m/min. The initial tension and taper of the winding are selected according to the type of material and the specifications, and the winding tension is moderate, and the winding film is not based on wrinkling.

(5) The aging must be done according to the manufacturer's use requirements according to the different types of glue, temperature and time can not deviate from too much, the temperature deviation should be less than 5 °C, time deviation can not exceed 4 hours, aging time is not enough and long Not desirable.

(6) The matured material must be cooled at room temperature for more than 12 hours before it can be cut into bags.

(7) The use of compound high-temperature cooking glue must be well matched with the ink and film. If it is not properly combined, there will be a phenomenon of separation after high-temperature cooking. Therefore, the sample test must be done before mass production.

(8) According to the characteristics of the glue, each composite layer can be aged for 12-24 hours. After the last layer is completed, the curing time required by the glue is used to complete the final curing. It is also possible to complete the multi-layer compounding at a later time into the curing chamber and complete the final curing according to the aging time required by the glue. The advantage of stratified maturation is that the quality is stable and the impact of compound wrinkling is reduced; the benefits of one-time completion are high production efficiency and ease of management, but there are wrinkle quality problems.

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3, bag making process

In general, bag making is the final process of high-temperature cooking bag, and it must be strictly controlled and checked, otherwise it will be at a loss. The following issues to note when making bags are:

(1) Prior to batch bag making, a sample test shall be performed to determine the processing parameters, including the temperature, pressure and machine speed of the heat sealing knife in each section, and these parameters can ensure that the heat seal strength before and after cooking can reach the standard. The content of the contents was loaded in a high-temperature cooking tester to make a medium-resistant test to determine the conformity of the material structure.

(2) It is ensured that the roll film before bag making has been sufficiently cooled, and the composite strength between the layers and solvent residue of the roll film have all reached the standard after testing, and the confirmation of the first inspection item is made.

(3) The width of the heat-sealing edge when making the bag is not less than 5mm. In addition, in order to ensure that the heat sealing area is flat and beautiful, the cooling mold must be kept at a sufficiently low temperature, generally below 25°C.

(4) The evaluation of the adaptability of the roll film in the bag making process should be sufficient to ensure smooth film removal, good heat sealing, and stable bag quality during each production. In particular, when RCPP is used as a heat-sealing layer, the opening properties of the bag are likely to be poor, and the opening of the bag is prevented from being caused by the poor opening.

(5) Due to the particularity of high-temperature cooking materials and processes, the sampling ratio of high-temperature cooking products in the bag making process should be appropriately increased so that the quality abnormalities in the process can be detected early. It is advisable to use a production shift once for the cooking test. The method must be correct to simulate the customer's use conditions, that is, to include the content of the same nature and capacity, according to the customer's sterilization conditions (mainly cooking temperature, time, pressure, such as the condition parameters 121 °C, 40min, 0.2-0.24MPa ) Test for high-temperature cooking resistance.

(6) According to the size and weight of the bag to select the appropriate number of packages, pay attention to protection against mechanical damage to the bag.

The above points for the bagging process should be paid attention to. At present, there are also standing bags and organ bags on the market for high-temperature cooking straws, and the control focuses on the material of the pipe to be matched with the material of the bag sealing layer to ensure a good sealing effect. After cooking and during use, leakage will not occur. In addition, the combination of the tube and the lid can ensure the sealing before and after cooking. According to the expansion and contraction of the material, it is necessary to ensure that the opening moment after cooking can not be changed too much to ensure smooth opening but good sealing.

During the production process, all control items must be inspected according to requirements. This is the basic measure to verify whether the quality meets the standards. Therefore, the entire process from raw materials to finished products must be strictly conducted, especially the high-temperature cooking inspection that validates the function of the bags. careless.

Fourth, how to adapt to the contents of high temperature cooking bag packaging and sterilization process requirements

The high-temperature cooking bag finally has to withstand the test of the contents packaging process and the subsequent sterilization process, so this condition has a great influence on it. The final packaged and sterilized finished products must be flat on the surface of the bag, and the package itself should be free from shrinkage, wrinkling, blistering, no separation, no leakage, etc. The following are the key points to pay attention to:

1, according to the content of the form and nature of the selection of suitable materials and structures, such as solid, liquid or solid-liquid mixed state to use different material structure, bone, barbed meat content before and after high-temperature cooking can not puncture the bag . If there is a difference in the acidity and alkalinity of the contents, the structure of the bag material and the specifications of the material should also be adjusted as required.

2. Before the food company uses the cooking bag in batches, the performance of the cooking bag should be confirmed through simulation tests. Due to the physical and chemical properties of the contents, new materials may be produced at high temperatures and may infiltrate between the layers of cooking pouches, thereby causing a drop in the packaging performance of the cooking pouch.

3, choose the appropriate sealing temperature to make the seal firmly, to prevent leakage during the cooking process here, in the cooling process to prevent bacterial contamination in the cooling water.

4. If it is not vacuum-packed, pay attention to controlling the amount of residual gas in the package. The proportion can be moderate, and the residual amount is basically the same. Otherwise, even if there is back pressure during the cooking process, the bag with more residual gas will burst.

5, determine the stable high temperature sterilization process conditions, such as the standard cooking conditions for 121 °C temperature 40min, the production of various types of cooking bag materials reached 121 °C has been able to withstand the limit, if the temperature and time exceeded too much This process conditions, it is difficult to ensure that certain properties of the cooking bag are not damaged, such as discoloration of light-colored ink, severe attenuation of composite strength, and reduced heat-seal strength.

6. Pay attention to the influence of material changes on the packaging, such as the hardening of RCPP after cooking, the precipitation of additives in the material, etc., assess the influence of changes in the physical properties after cooking and before cooking, and pay attention to the influence on the hygienic properties of the contents.

7. Prevent leakage of bag breaks during storage and transportation, especially vacuum cooking bags. Generally, the RCPP after cooking will harden, and the problem of air leakage will occur at the place where the vacuum crease is formed. This needs to be resolved from the material selection and process.

8. For products packaged in high-temperature cooking bags, avoid harsh handling, loading and unloading, and store them in a clean, dry, ventilated, cool place. The unreliable heat sources are too close to ensure the physical and chemical properties of the bags and contents are as stable as possible. Products that have bulges and leaks during storage and sale are prohibited from being sold and eaten. If there are many adverse conditions in the sales process, it will seriously affect the image of the product, and it may even destroy a brand. Enterprises that use high-temperature cooking bags must make full assessments.

9, after high-temperature cooking of the contents and bags to determine a reasonable shelf life, such as cooked meat products are rich in protein, microorganisms are very easy to breed, and meat products in the storage of easily oxidized fat deterioration, the general shelf life within one year Even if the AL membrane structure is not more than 24 months. Moreover, after high-temperature cooking, certain additives in the packaging material will accelerate to the surface under high temperature conditions. For example, the opening agent, antistatic agent, and slip agent added in the plastic film will slowly seep out and slowly The risk of contaminating food, and plastic products will have a gradual aging process, will continue to affect the performance of the bag, so it should not be stored for a long time.

Although according to the structure of the composite material, theoretically the shelf life of the content can be calculated based on the moisture permeability, oxygen permeability data, and the aging time, the theoretical shelf life can be two years or even more than five years, but there are too many uncertainties in practical applications. The characteristics of the material itself and the uncertainty of the content nature, the shelf life can not be determined only relying on moisture permeability, oxygen permeability data and sealability of the package material, so it is lack of factual basis for the high temperature cooking food to determine the shelf life of more than two years.

10, can not ignore the special requirements, such as more than 500ml high temperature cooking infusion bags infusion side customer requirements must meet the requirements of 1.8m high natural drop without breaking the bag, then can not be applied in accordance with national standards, only by increasing the thickness of the material or The heat seal layer is added with anti-broken additives to meet this requirement.

The above analysis of high-temperature cooking bag in the production and use of the process to pay attention to the problem, different from the ordinary bag is: high temperature cooking bag not only meet the standards before cooking, after cooking and shelf life also in the appearance, function and hygiene In terms of meeting the requirements for use, the actual requirement may even be much higher than a national standard for high-temperature cooking bags.

Fifth, the high-temperature cooking package structure design needs comprehensive consideration

Whether the packaging material meets the requirements or not, both packaging material users and producers are very concerned. In particular, the user must consider the nature of the contents of the package, the size of the package, the type of sterilizing conditions to be subjected to the package, and the environment in which it is stored. Shelf life and so on. The requirements for different contents will have different requirements for the quality of cooking bags. The choice of material structure, adhesives, and inks will also be different. There will also be differences in the production process control, as well as different costs.

Before you determine which structure to use, be sure to do a full assessment, such as a 150g capacity, the same size size of high-temperature cooking chestnut composite upright bag, the structure can be PET12um//AL7um//RCPP70um, it can be PET12um //AL7um //BOPA15um//CPP70um, which one is selected, should be determined according to the user's specific requirements, choose a structure with BOPA15 um, the bag will have better sealing strength, better puncture resistance, extrusion resistance , anti-leakage and anti-breakdown performance, while the barrier performance is stronger, suitable for long-distance transportation, multiple turnover and long-distance sales (such as exports to foreign countries). If the above two structures can meet their functional requirements, price may be the focus of consideration, and the use of BOPA15um will certainly be eliminated.

In addition, there are printed high-temperature cooking bags, try not to choose PET / RCPP or BOPA / / RCPP two-layer structure, because in the high-temperature cooking ink pigments will accelerate the penetration of RCPP, the content will cause pollution, to prevent this For risk, it is necessary to add an appropriate thickness of AL foil before RCPP. After the structure is determined, it is necessary for the producers to strictly select materials and strictly follow the process requirements to ensure that the safe use of high-temperature cooking bags is the common responsibility of both producers and users.