High temperature cooking is an efficient and thorough sterilization process, which is widely used in the disinfection of meat, bean products, some medical supplies and medical injections. In recent years, this process has also been gradually used in the sterilization of cooked chestnut, cereal juice beverage, baby fruit and vegetable puree and other foods. The sterilization temperature range of high temperature cooking is generally between 121-135 ℃. At present, there are also researches on flexible packaging materials which can meet the requirements of ultra-high temperature sterilization at 145 ℃. The research data show that the most heat-resistant Bacillus botulinum can be completely killed under the condition of 145 ℃ for about 3 min. the composite flexible packaging materials are also widely used. According to the disinfection and sterilization conditions of the package contents, this paper focuses on how to meet the requirements of high-temperature cooking for the structural design and processing technology of 121 ℃ high-temperature packaging bags.
The structural design of composite flexible packaging materials should meet the process requirements of high temperature sterilization. In addition to ensuring the function of packaging materials in the production process, more consideration should be given to the requirements of contents. At the same time, the influence of sterilization treatment process conditions, flow storage conditions and sales and use links on the performance of packaging materials should be taken into account. The following will be discussed one by one.
1、 Purpose of cooking sterilization and classification of cooking packaging bags
There are two main purposes of sterilization
1. It can completely eliminate harmful bacteria and meet the requirements of asepsis, such as sterilization of medical supplies.
2. After thorough sterilization, it can inhibit the growth of bacteria and prolong the shelf life of the contents with little or no preservatives, so that the contents can keep the original design flavor for a long time at room temperature, such as all kinds of food high-temperature cooking products.
According to the current internationally recognized classification of heat-resistant and bactericidal treatment packaging bags are as follows:
1. It can endure 121 ℃ cooking bag, and the time of high temperature is 30-60min.
2. It can endure 135 ℃ cooking bag for 15-30 min.
3. It can endure 145 ℃ ultra-high temperature cooking bag, which is the highest level of cooking bag at present, and the temperature resistance time is less than 5min.
At present, the domestic market is widely used in high-temperature cooking bags which can withstand 121 ℃, and the general solid substances such as meat high-temperature cooking packaging must meet the vacuum requirements.
2、 Requirements of high temperature cooking bag on film substrate and chemical materials
The film substrate used in the production of high-temperature cooking bag is the basis to meet the cooking conditions. Generally, it is necessary to determine which substrate, specification, combination sequence, and type of ink and glue to be used according to the cooking conditions and the characteristics of the contents of the high-temperature cooking bag. Commonly used film substrates are: BOPET At present, there are also new types of coextrusion films, such as PP / AC / ev0h / AC / PP, PP / AC / PA / ev0h / PA / AC / PP; in addition, there are also copolymerized nylon MXD6, ceramic evaporation coating such as sioxpet12um, multi-layer coextrusion film and ceramic evaporation coating, which are currently used on high-temperature cooking bags due to technical process and price constraints Applications are rare.

According to the order of surface layer (or substrate), barrier layer and heat seal layer, the structure of composite packaging materials can be combined. There are also single-layer materials that can be used as both the substrate layer and the barrier layer. Therefore, the packaging bag can be designed as two-layer, three-layer, four-layer or more layers according to the needs, such as: BOPET / / rcpp, BOPA / / rcpp, BOPET / / BOPA / / rcpp, BOPET / / A1 / / rcpp, BOPET / / A1 / / BOPA / / rcpp, etc. The substrate thickness is usually selected as bopet12um, bopa15um, al7um or al9um, rcpp50um, rcp70um, rcp80um, rcp100um, etc. for the barrier layer, BOPA and Al are usually selected. According to the actual needs, bopa25um and al12um are also selected. For high-temperature cooking bags with large capacity and special requirements, the thickness of rcpp is more than 100um. In order to overcome the falling resistance of liquid packaging bags, additives are usually added into the film to enhance its anti dropping 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 separate layer after cooking, and some colors will change. High temperature cooking ink should be based on two-component reactive polyurethane as binder. It has good printing adhesion fastness. After crosslinking and curing reaction, it can resist high temperature cooking and form a very strong adhesion with glue. At the same time, for large areas of spot color and white pattern, but also choose the matching ink curing agent. When selecting ink, special attention should be paid to distinguish ordinary ink, boiling ink below 100 ℃ and cooking ink above 121 ℃ to avoid misuse. It is generally considered that the glue should meet the cooking requirements above 121 ℃ at least. After compounding, it must have good adhesion fastness, high temperature medium resistance and heat resistance. At present, the most commonly used glue is two-component polyurethane glue. The solvent should be well matched with the ink and glue, which can meet the process requirements, but can not affect the high temperature cooking performance of the ink and glue.
3、 Requirements of high temperature cooking bag on production process
In order to control the quality of high-temperature cooking products, in addition to the production requirements of ordinary products, special requirements should be put forward for individual places. In order to simplify the process clearly, here are only a few points for attention in each process.
1. Printing process
The following problems should be paid attention to in actual production
(1) Bopet12um and bopa15um are the most commonly used printing substrates for high-temperature cooking bags. The grade of substrates should be high and the quality should be guaranteed, including corona value of more than 52 dyne and even corona; uniform thickness, no lotus leaf edge, no foreign matter pollution, etc. Bopa15um (including composite) cooked at high temperature is different from ordinary bag. It is better to choose synchronous stretching to ensure isotropy in all directions, fixed longitudinal tensile ratio and special mechanical properties.
(2) Select the ink according to the technical data of the ink manufacturer, at least select the "R" grade ink, the high temperature cooking ink of different manufacturers can not be mixed, and the proportion of mixed solvent used with the ink must be appropriate, and the purity of the effective components should be more than 99%. In order to meet the health requirements, note that solvents and inks do not contain benzene, toluene, xylene, ketones or other high boiling point solvents. The suitable ink should be selected according to the characteristics of the substrate material and the composite membrane structure. For example, BOPA is selected as the substrate. The pigment may penetrate into the BOPA when the ink of individual colors is in the cooking state. Similarly, for the cooking bag with only two layers of substrate and heat seal layer, the ink may also penetrate into the rcpp, thus bringing the risk of contamination to the contents.
(3) Need to use a large area of spot color and white ink to add 1% - 3% of the ink curing agent, must be based on the ink manufacturers to provide technical information to determine the amount of addition, not too much or too little. The remaining ink recovered from the ink tray can not be used for printing high-temperature cooking products no matter how long it is stored.
(4) In order to minimize the residual solvent content of printing materials and improve the ink adhesion fastness, standard production process parameters must be selected, such as oven temperature, air volume and machine speed. For large area ink added with ink curing agent, the oven temperature should be 10-15 ℃ higher than that of other inks.
(5) After printing, BOPA film must be wrapped tightly with Al foil composite film to prevent moisture shrinkage and performance change.
(6) It is better to rewind the printing materials added with the ink curing agent, and the storage time shall not exceed three days, that is, the printing layer shall be compounded at least within three days.
2. Compound process
At present, the drying process is mainly used in the high-temperature cooking bag. How to control this process is the key to the success or failure of the high-temperature cooking bag
(1) The use of high-temperature cooking glue must be in accordance with the manufacturer's instructions, such as the ratio, aging temperature and time, etc., and the purity of ethyl acetate solvent used for dilution should reach 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, in addition to meeting its mechanical performance parameters, the surface of Al foil should be dry, and the cleanliness must meet the A-level standard, that is, when inspected with distilled water, all materials should be able to be soaked, and the less pinholes, the better. The storage time before use should not exceed three months. In order to enhance the composite fastness, the composite BOPA should be double-sided corona, and the corona value should not be less than 50 dyne.
(3) Glue coating should be uniform. According to the characteristics of different manufacturers and different types of glue, the dry base weight should be generally 3.5-4.8g/m2. When the minimum coating amount standard is reached, the coating deviation at the left, middle and right positions should not exceed 0.3g/m2. The curing agent should be added according to the requirements. If the ambient humidity of the drying workshop exceeds 80%, the addition amount of curing agent should be appropriately increased, generally 5% - 10% on the original basis. If there are more yellow, white and other light color areas in the printing pattern of the product, the coating amount should be increased by about 0.3g/m2 compared with the dark color pattern design to prevent obvious spots after cooking.
(4) Determine the appropriate machining process parameters, especially the temperature of the three section oven is 5-10 ℃ higher than that of the ordinary products, the temperature of the composite heating roller is 70-80 ℃, the compound pressure is increased by 0.1-0.2mpa compared with the ordinary products of the same specification, and the machine speed is controlled below 120m / min according to the machine performance. The selection of the initial tension and taper is determined according to the type and specification of the material. The take-up tightness is moderate and the film is not wrinkled.
(5) The aging must be done according to different types of glue according to the manufacturer's use requirements. The temperature and time should not deviate from the requirements too much. The temperature deviation should be within 5 ℃ and the time deviation should not exceed 4 hours. It is not advisable for the aging time to be insufficient or too long.
(6) The aged materials should be cooled at room temperature for more than 12 hours before being cut into bags.
(7) The selection of composite high temperature cooking glue must be well matched with ink and film. If it is not properly matched, the layer separation phenomenon will occur after high temperature cooking. Therefore, sample test must be done before mass production.
(8) According to the characteristics of glue, each composite layer can be cured for 12-24h. After the last layer is finished, the final aging is completed according to the required curing time. It can also enter the curing room after the completion of multi-layer one-time compounding, and finish the final curing according to the curing time required by the glue. The advantages of layered ripening are stable quality, reducing the impact of compound wrinkling; the advantage of one-time completion is high production efficiency and easy management, but there is a potential risk of wrinkle.
3. Bag making process
Generally speaking, bag making is the final process of high-temperature cooking bag, which should be strictly controlled and controlled, otherwise it will fall short. The problems to be noticed in bag making are as follows:
(1) Before batch bag making, the sample test should be done to determine the processing parameters, including the temperature, pressure and machine speed of each section of the heat sealing knife, and these parameters can ensure that the heat sealing strength before and after cooking can reach the standard. In order to determine the conformity of material structure, the content with equal capacity is put into the high temperature cooking test machine for medium resistance test.
(2) Ensure that the roll film before bag making has been fully cooled, and the composite strength of each layer and solvent residue of roll film are all up to the standard after testing, and the first article inspection items are confirmed.
(3) During bag making, the width of hot sealing edge shall not be less than 5mm. In addition, in order to ensure that the heat sealing area is smooth and beautiful, the cooling mold should be kept low enough temperature, generally below 25 ℃.
(4) In the process of bag making, the adaptability evaluation of roll film should be done fully to ensure smooth film moving, good heat sealing condition and stable bag making quality. In particular, rcpp as a heat sealing layer, easy to cause the opening of the bag is not good, to prevent bad opening caused by the bag hardening.
(5) Due to the particularity of high-temperature cooking materials and processes, the proportion of sampling inspection of high-temperature cooking products should be appropriately increased in the process of bag making, so as to find out the quality abnormality in the process as soon as possible. The cooking test should be conducted once in a production shift, and the test method should be correct. The use conditions of customers should be simulated, that is, the contents with the same capacity and nature should be packed in according to the sterilization conditions of customers (main It is the cooking temperature, time, pressure, such as the condition parameters of 121 ℃, 40min, 0.2-0.24mpa).
(6) According to the size and weight of the bag, select the appropriate number of packaging, pay attention to protection, to prevent mechanical damage to the bag.
The above points should be paid attention to in the bag making process. At present, there are also high-temperature cooking vertical bags and organ bags connected with straw in the market. The key point of control is that the material of the tube should be matched with the material of the hot sealing layer of the bag, so as to ensure good sealing effect and prevent leakage after cooking and during use. In addition, the matching of tube and cover can ensure the sealing before and after cooking. According to the expansion and contraction of materials, the opening torque after cooking should not change too much, so as to ensure smooth opening and good sealing.
In the production process, each control item should be inspected according to the requirements, which is the basic measure to verify whether the quality meets the standard. Therefore, the inspection should be carried out strictly from the raw materials to the finished products, especially the high-temperature cooking test to verify the bag function should not be careless.
4、 How can high temperature cooking bag meet the requirements of content packaging and sterilization process
The high-temperature cooking bag will eventually withstand the test of the packaging process and subsequent sterilization process of the contents, so this condition has a great impact on it. The finished product after final packaging and sterilization treatment must be flat bag surface, and the packaging material itself shall be free from shrinkage, wrinkle, blister, separation layer and leakage. Here are the key points to pay attention to:
1. Select appropriate materials and structures according to the shape and properties of the contents. For example, different materials and structures should be selected for solid, liquid or mixed state. Meat contents with bones and thorns should not be punctured before and after high temperature cooking. If the acidity and alkalinity of the contents are different, the bag material structure and material specifications should also be adjusted according to the needs.
2. Before batch use of cooking bags in food enterprises, the performance of cooking bags should be confirmed by simulation test. Because of the physical and chemical properties of the contents, they may change at high temperature and produce new substances, which may penetrate between layers of cooking bags, resulting in the decline of packaging performance of cooking bags.
3. Select the appropriate sealing temperature to make the sealing firm, prevent the leakage of materials in the cooking process, and prevent the bacteria from penetrating into the cooling water during the cooling process.
4. If it is not vacuum packaging, we should pay attention to control the amount of residual gas in the package to achieve a moderate proportion, and the residual amount is basically the same. Otherwise, even if there is back pressure in the cooking process, the bag with more residual gas will burst.
5. Determine the stable high temperature sterilization process conditions, for example, according to the standard cooking conditions of 121 ℃ for 40 min, all kinds of materials for making cooking bags have reached the limit when they reach 121 ℃. If the temperature and time exceed the process conditions, it is difficult to ensure that some properties of the cooking bag will not be damaged, such as discoloration of light color ink, serious degradation of composite strength and reduction of heat sealing strength Etc.
6. Pay attention to the impact of material changes on the packaging materials, such as the hardening of rcpp after cooking, the precipitation of additives in the materials, etc., evaluate the impact of changes in physical properties after cooking and before cooking, and pay attention to the impact on the sanitation of the contents.
7. To prevent air leakage from bag breakage during storage and transportation, especially vacuum cooking bags. Generally, the rcpp will harden after cooking, and air leakage is easy to occur at the crease of vacuum pumping, which needs to be solved from the aspects of material selection and process.
8. For the products packed in high-temperature cooking bags, avoid rough handling, loading and unloading. At the same time, they should be stored in clean, dry, ventilated and cool places. The unreliable heat source is too close, so as to ensure the stability of the physical and chemical properties of the packaging bags and contents. It is forbidden to sell and eat the products with bulge and leakage during storage and sale. If there are more bad conditions in the sales process, it will seriously affect the image of the product, and even destroy a brand. Enterprises using high-temperature cooking bags should make a full evaluation.
9. For example, cooked meat products are rich in protein, microorganisms are easy to breed, and fat in meat products is easy to oxidize and deteriorate during storage. Generally, the shelf life is within one year, even if there is al membrane structure, it should not exceed 24 months. In addition, some additives in the packaging materials will accelerate to dissociate to the surface under high temperature conditions after high temperature cooking. For example, the mouth opening agent, antistatic agent and smoothing agent added in the plastic film will slowly exude, at the same time, there is a risk of slowly polluting the food, and the plastic products will have a step-by-step aging process, which will continue to affect the performance of the bag, so it is not suitable to store for a long time. Although according to the structure of the composite, the shelf life of the content can be calculated theoretically according to its moisture permeability, oxygen permeability data and aging time, and the theoretical shelf life can be more than two years or even more than five years, but there are too many uncertain factors in practical application. In view of the characteristics of the composite and the uncertainty of the properties of the content, the shelf life can not only rely on the moisture permeability, oxygen permeability data and density of the packaging materials Therefore, it is lack of factual basis to determine the shelf life of high-temperature cooking food for more than two years.
10. Special requirements can not be ignored. For example, the customer standard for the side sealed high-temperature cooking infusion bag of organ above 500ml must meet the situation that the height of the bag is 1.8m and there is no broken bag. At this time, it is not possible to carry the hard cover according to the national standard. Only by increasing the thickness of the material or adding anti breaking additives in the heat sealing layer can meet this requirement.
The above analysis of high temperature cooking bag in the production and use process should pay attention to the problem, different from the ordinary bag is: high temperature cooking bag not only before cooking to meet the standard, after cooking and shelf life, but also in the appearance, function and hygiene requirements, this actual requirement will be far higher than a certain national standard of high temperature cooking bag.
5、 The structural design of high temperature cooking packaging materials should be considered comprehensively
Whether the packaging materials meet the requirements or not, the packaging materials users and producers are very concerned. In particular, the user must consider the contents of the package, the nature of the article, the capacity of the package, the cooking and sterilization conditions to be endured after packaging, the environment in which it is stored, and the shelf life required. The requirements of different contents on the quality of cooking bag are different, the combination of material structure, the choice of adhesive and ink are also different, the production process control will be different, and the cost will also be different. Before determining which structure to use, we must make a full evaluation. For example, the structure of high-temperature cooking chestnut composite vertical bag with the same capacity and size of 150g can be pet12um / / al7um / / rcpp70um, or pet12um / / al7um / / bopa15um / / cpp70um. Which one should be selected should be determined according to the specific requirements of users Um structure, the bag will have better sealing strength, better puncture resistance, extrusion resistance, anti leakage and anti drop performance, and stronger barrier performance, suitable for long-distance transportation, multiple handling turnover and long-distance sales (such as export to foreign countries). If the above two structures can meet their functional requirements, the price may be the key point to be considered, and the use of bopa15um will definitely be cancelled. In addition, the two-layer structure of PET / rcpp or BOPA / / rcpp should not be selected for the high-temperature cooking bag with printing. Under the high-temperature cooking state, the ink and pigment will accelerate the penetration in the rcpp and cause pollution to the contents. In order to prevent this risk, it is necessary to add a layer of Al foil with appropriate thickness before the rcpp. After the structure is determined, it is necessary for the producer to select materials strictly and produce in strict accordance with the process requirements. It is the common responsibility of both producers and users to ensure the safe use of high-temperature cooking bags.

6、 Summary and Prospect
In order to ensure a higher safety factor, high temperature cooking bag must have appropriate "excess function" compared with ordinary bag. However, we advocate moderate packaging to prevent serious excess of function and quality of packaging, and maintain reasonable cost performance of packaging materials. Therefore, the structural design of packaging materials should first clarify the basic functional requirements of the contents for the bag, and do not exceed this requirement Too much. Manufacturers applying high-temperature cooking bags should also weigh the grade requirements of the contents. In addition to making the packaging meet the functional needs, it can also reflect the intrinsic value of the products. If the proportion of packaging materials in the cost of products is very small, they may as well appropriately upgrade the functional grade of packaging materials, so that the packaging materials show their uniqueness and add highlights to the products. For example, some foreign high-end food uses the very expensive si0xpet12 as a barrier layer of 121 ℃ high-temperature cooking bag. Therefore, the structural design of high-temperature cooking composite packaging materials must be based on the actual situation and take into account the needs of all aspects as far as possible.
Although it has been more than half a century since the high-temperature cooking bag was born, there are also more production and application of high-temperature cooking cover film, and the composite flexible packaging materials meeting the requirements of 121 ℃ cooking are also very mature, but in the domestic market, there are only a few mature products that can meet the requirements above 135 ℃ in the domestic market. In addition to the limitation of materials, especially the matching of film, ink and glue More importantly, the production process and sterilization process are unstable, and the users generally lack confidence. The success of 145 ℃ high temperature cooking products in the laboratory does not mean that they can be mass produced and put into practical application.
With the emergence of new materials and new technologies, as well as the continuous maturity and improvement of high-temperature sterilization process, the quality of domestic high-temperature cooking bags will become more and more stable, and the cooking resistance level will be gradually improved, which can better meet the requirements of high-temperature cooking process.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service. The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries. We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.