A double layer packaging film, its preparation method and use

Abstract

The application discloses a double-layer packaging film, which is a double-layer BOPP film; the inner-layer BOPP film and the outer-layer BOPP film are both BOPP films prepared by using a step-by-step bidirectional stretching method in a flat film method. The application further discloses a preparation method of the double-layer packaging film and an application of the double-layer packaging film to a cigarette box or a cigarette carton packaging film.

Description

Technical Field

[0001] This invention belongs to the field of tobacco technology, specifically relating to a double-layer BOPP film, its preparation method, and its use in cigarette packaging film. Background Technology

[0002] Sealing is a packaging process that prevents the exchange of gases, liquids, and other substances between the inside and outside of the box, and is one of the main effective measures to prevent mold growth. Good sealing of cigarette packaging not only effectively prevents the loss of aroma during long-term storage, but also reduces the impact of external temperature and humidity on the moisture content of the cigarettes, minimizing the risk of mold growth and extending the shelf life. Preliminary project research shows that after 8 months of storage in an open environment, the number of microbial communities in well-sealed cigarette products showed no significant change, while the total number of colonies in poorly sealed products increased from 10... 3 Growth to 10 5 The number of xerophilic molds increased from 10¹ to 10², making airtightness a crucial quality indicator in cigarette packaging. Furthermore, the sealing performance of cigarette box packaging significantly impacts the moisture retention of cigarettes under various environmental conditions. This quality requirement reflects new demands arising from changes in the consumer market, represents a new challenge in market upgrading, and necessitates improvement in the cigarette quality control system. Many factors influence cigarette moisture retention. From a packaging perspective, under certain conditions, improvements in factors such as the squareness of the unopened cigarette box, the unit dimensions of paper materials and BOPP thin materials, and the dimensions of key forming stations on the equipment can positively impact the cigarette consumer experience. Therefore, the goal is to improve cigarette box packaging to achieve "squareness and airtight moisture retention," thereby enhancing the cigarette quality control system.

[0003] BOPP film is colorless, odorless, tasteless, and non-toxic, possessing high tensile strength, impact strength, rigidity, toughness, and excellent transparency. Its surface energy is low, requiring corona treatment before coating or printing. After corona treatment, it exhibits good printability, allowing for multi-color printing to achieve exquisite visual effects, thus making it suitable as a composite substrate for composite films. Its drawbacks include a tendency to accumulate static electricity and poor heat-sealing properties. On high-speed production lines, BOPP film is prone to generating static electricity, necessitating the installation of static eliminators. BOPP film coating technology has matured significantly, and the film's applications are expanding rapidly, from simple packaging to printing, plate making, and some specialized industries, with polypropylene film rapidly permeating every aspect of human life.

[0004] BOPP film undergoes biaxial stretching during its manufacturing process, resulting in excellent tensile strength, impact resistance, high stiffness, and high transparency. Its high melting point (above 160℃) also provides good high-temperature resistance. BOPP film also exhibits certain barrier properties, particularly good water vapor barrier performance. Therefore, it is a commonly used printing material in the packaging industry. However, BOPP film has poor heat-sealing properties and cannot be used as a heat-sealing layer in composite films. Furthermore, polypropylene has a high glass transition temperature, resulting in generally poor low-temperature resistance, and its oxygen barrier properties are also relatively poor. When used as a composite substrate, a common thickness is around 20 micrometers. BOPP can be chosen as a printing composite material for most products whose packaging requirements are not high.

[0005] Biaxial stretching is a technology developed for the subsequent or simultaneous orientation of thermoplastic materials. Currently, there are two main production processes for BOPP film: tubular film and flat film. Biaxial stretching methods are further divided into progressive biaxial stretching and simultaneous biaxial stretching. Simultaneous biaxial stretching in the flat film method produces products with isotropic properties; however, due to complex equipment, manufacturing difficulties, and high costs, it has not been widely adopted. Progressive biaxial stretching is the method used by most manufacturers. Although the resulting products show some differences in tensile strength, breaking productivity, and heat shrinkage between the longitudinal and transverse directions, the impact on product quality is minimal. It offers advantages such as high output, fast speed, wide range of applications, and stable product quality. The process flow is roughly as follows: 1: Batching; 2: Melting; 3: Plasticizing extrusion; 4: Filtration; 5: Longitudinal stretching; 6: Transverse stretching; 7: Corona treatment; 8: Winding; 9: Aging treatment; 10: Slitting; 11: Finished product. The tubular membrane method requires relatively simple equipment, occupies little space, has low cost, quick results, and moderate output, which initially made it popular with many manufacturers; however, due to its low output, uneven film thickness, and large heat shrinkage rate, its development has slowed down in recent years.

[0006] Research on the test method of cigarette box sealing. The commonly used method for testing the sealing of cigarette boxes in the industry has always been YC / T 140-1998 "Determination of the sealing of cigarette boxes by air-filling method". This standard was abolished in 2015. This standard method has certain limitations: (1) Narrow scope of application. This method is only applicable to the sealing of soft-pack cigarette boxes. However, for hard-pack cigarette boxes, the air-filling method cannot be applied to the sealing of such cigarette boxes because the cigarette box packaging film and the packaging box are in close contact and the air circulation is poor. (2) Large detection error. Two packs of cigarettes with obvious differences in sealing may produce opposite results. (3) Blind spots in detection. This method is more effective for detecting leakage at both ends of the joint. However, it is less effective for detecting leakage at the pull line or side damage of the cigarette box. It is often difficult to detect. (4) Limited guidance for production improvement. The test result of this method is only the numerical value of the sealing degree. It cannot intuitively judge the leakage point and cannot guide the improvement and optimization of the production process in a timely manner.

[0007] Currently, commonly used methods for testing sealing performance include visual inspection, talc powder method, bubble method, sealing performance tester method, differential pressure air leakage detection method, and the gas filling method for determining the sealing performance of cigarette packs. Among these, visual inspection, talc powder method, and bubble method are qualitative measurement methods, while sealing performance tester method, differential pressure air leakage detection method, and the gas filling method for determining the sealing performance of cigarette packs are quantitative measurement methods. For quantitative measurement methods, the three methods mentioned above are not suitable for determining the sealing performance of cigarette packaging. For the differential pressure air leakage detection method, due to the relatively high filling pressure, it is generally suitable for testing the sealing performance of rigid packaging. For the sealing performance tester method and the gas filling method, because the airflow cannot pass through the four edges of the cigarette pack, this method is only suitable for measuring the sealing performance of the top and bottom seals of soft packs, and cannot detect the sealing performance of the sides of soft packs or hard packs. In addition, other methods for testing packaging sealing performance include displacement leakage detection, ultrasonic detection, helium mass spectrometry leak detection, and novel gas tracer methods. Based on the characteristics of small-pack cigarettes, the main methods for testing leaks include volume change method, buoyancy method, water immersion weighing method, negative pressure method, negative pressure water immersion method, and negative pressure air extraction method. Among these, the negative pressure air extraction method is the most feasible method for testing the sealing performance and has good test repeatability, while the negative pressure water immersion method can locate the leakage point of small-pack cigarettes.

[0008] The moisture content of tobacco shreds inside cigarette packs is generally 12.5% ​​(equilibrium moisture content at 22℃ and 60% relative humidity), while the moisture content of cigarette paper upon delivery is 4.5%, inner lining paper 4.0%, frame paper 6.0%, and carton packaging paper 5.5%. When the cigarette pack has good sealing stability, meets the required sealing requirements, and has high humidity, moisture in the tobacco shreds will diffuse into the cigarette paper and carton packaging paper, forming a humidity equilibrium system. When the cigarette pack's sealing stability is poor, the tobacco shreds, cigarette paper, frame paper, and other materials inside the pack are in contact with the external environment for a long time. When the external environment is too dry or too humid, it will inevitably affect the moisture content of the tobacco shreds, cigarette paper, and other materials inside the pack, thus affecting the quality of the cigarettes. Summary of the Invention

[0009] This invention proposes a double-layer packaging film and its preparation method. The double-layer packaging film of this invention is a double-layer BOPP film; both the inner and outer BOPP films are BOPP films prepared using the stepwise biaxial stretching method in the flat film process. The double-layer BOPP film of this invention has a high sealing degree and is suitable for use in cigarette packaging. The sealing degree of soft cigarette pack packaging is no more than 50 mL at -1.00 kPa; the sealing degree of hard cigarette pack packaging is no more than 10 mL at -8.00 kPa.

[0010] The technical solution of the present invention is as follows:

[0011] The first aspect of this invention discloses a double-layer packaging film, wherein the packaging film is a double-layer BOPP film; both the inner BOPP film and the outer BOPP film are BOPP films prepared by the stepwise biaxial stretching method in the flat film process.

[0012] Preferably, the inner BOPP membrane has a thickness of 15μm-18μm and an activated carbon layer is coated on its inner surface; the outer BOPP membrane has a thickness of 18μm-22μm.

[0013] Preferably, the double-layer BOPP film is tested using the negative pressure vacuum method: the sealing degree of the soft box packaging is no more than 50 mL at -1.00 kPa, and the sealing degree of the hard box packaging is no more than 10 mL at -8.00 kPa.

[0014] Preferably, the folding and heat-sealing positions of the inner and outer BOPP films are the same, and the tear heads are in the same or different positions.

[0015] Preferably, the folding and heat-sealing positions of the inner and outer BOPP films are different, and the tear heads are also different.

[0016] A second aspect of this invention discloses a method for preparing the double-layer packaging film, comprising the following steps:

[0017] (1) Use a ceramic soldering iron to heat seal the inner BOPP film: keep the soldering iron temperature at 340℃±5℃, use a "U" shaped knife to cut the BOPP film online, and complete the folding and heat sealing of the inner BOPP film according to the shape of the package.

[0018] (2) Use a ceramic soldering iron to heat seal the outer BOPP film: keep the soldering iron temperature at 330℃±5℃, and use a "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the outer BOPP film.

[0019] Preferably, both the inner and outer BOPP membranes are BOPP membranes prepared by the stepwise biaxial stretching method in the flat film process; the thickness of the inner BOPP membrane is 15μm-18μm, and the inner surface is coated with an activated carbon layer; the thickness of the outer BOPP membrane is 18μm-22μm.

[0020] Preferably, the folding and heat-sealing positions of the inner and outer BOPP film layers are the same, and the tear heads are in the same or different positions.

[0021] Preferably, the folding and heat-sealing positions of the inner and outer BOPP films are different, and the tear heads are also different.

[0022] The third aspect of this invention discloses the use of the double-layer packaging film for cigarette boxes or cigarette cartons.

[0023] The beneficial effects of this invention are:

[0024] 1. The double-layer packaging film of the present invention is a double-layer BOPP film; both the inner and outer BOPP films are BOPP films produced by the progressive biaxial stretching method in the flat film process. The double-layer BOPP film of the present invention has a high sealing degree. When used for cigarette packaging, the sealing degree of soft cigarette pack packaging is no more than 50 mL at -1.00 kPa; the sealing degree of hard cigarette pack packaging is no more than 10 mL at -8.00 kPa.

[0025] 2. In existing technologies, the moisture content of tobacco shreds in cigarette packs is generally 12.5% ​​(equilibrium moisture content, 22°C, 60% relative humidity); while the moisture content of cigarette paper is 4.5%, inner lining paper 4.0%, frame paper 6.0%, and carton packaging paper 5.5%. Using the double-layer packaging film of this invention for cigarette packaging ensures good sealing stability, keeping the cigarette pack isolated from the outside environment; the moisture in the tobacco shreds in the cigarette pack diffuses into the cigarette paper and carton packaging paper, forming a humidity balance system that effectively meets tobacco packaging requirements. The double-layer packaging film of the present invention is used for cigarette packaging film. Preferably, an activated carbon layer is coated on the inner surface of the inner BOPP film. The activated carbon can ensure that the moisture content of the tobacco is about 12.5%. Below 12.5%, the activated carbon can release moisture, and above 12.5%, the activated carbon can release and absorb moisture. That is, the activated carbon can absorb excess moisture diffused from the inside, and when the internal moisture decreases, it can diffuse the moisture into the carton packaging paper and tobacco, thereby maintaining the moisture balance in the cigarette pack.

[0026] 3. The double-layer packaging film of the present invention is used for cigarette packaging. Besides considering the sealing effect, it also takes into account the ease with which consumers can tear the film to open the packaging. When the folding and heat-sealing positions of the inner and outer BOPP films are the same, and the tear head positions are also the same, the tearing effect is the same as with a single-layer film, but the sealing effect is slightly worse because the tear head is a leakage point. When the folding and heat-sealing positions of the inner and outer BOPP films are the same, but the tear head positions are different (e.g., the tear head is on the left or right side), two tears are required to open the packaging, but the sealing effect is better. When the folding and heat-sealing positions of the inner and outer BOPP films are different, the tear head positions are also different, requiring two tears to open the packaging (the outer packaging must be opened before the inner packaging), but the sealing effect is the best. The double-layer packaging film of the present invention is used for cigarette packaging. To save costs, the double-layer packaging film of the present invention can be used in either cigarette boxes or cigarette cartons; preferably, the double-layer packaging film is used in cigarette boxes.

[0027] 4. The double-layer packaging film of this invention uses a ceramic soldering iron to heat-seal the inner and outer BOPP films. Existing packaging machines typically use either cast iron or ceramic soldering irons. During operation, cast iron soldering irons are often used at high temperatures, which can cause unevenness on the iron surface, negatively impacting the heat-sealing tightness of the cigarette film. This invention uses a ceramic soldering iron, which significantly improves the heat-sealing tightness (better sealing) of the double-layer packaging film. Furthermore, the soldering iron temperature for heat-sealing the outer BOPP film is approximately 10°C lower than that for the inner BOPP film, thus avoiding damage to the inner BOPP film and ensuring the cigarette box's seal. Detailed Implementation

[0028] The following description, in conjunction with embodiments, is provided. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention. Other advantages, objectives, and features of the invention will be set forth in the following embodiments and will be apparent to those skilled in the art to some extent, or may be learned by practice of the invention.

[0029] This invention discloses a double-layer packaging film, wherein the packaging film is a double-layer BOPP film; both the inner and outer BOPP films are BOPP films produced using the stepwise biaxial stretching method in the flat film process. The thickness of the inner BOPP film is 15μm-18μm, and the thickness of the outer BOPP film is 18μm-22μm. The sealing performance of the double-layer BOPP film for flexible box packaging, measured using a negative pressure vacuum method, is no greater than 50mL at -1.00kPa. The sealing performance of the double-layer BOPP film for rigid box packaging, measured using a negative pressure vacuum method, is no greater than 10mL at -8.00kPa.

[0030] Example 1: Preparation of double-layer packaging film and its use in cigarette hard pack packaging.

[0031] Both the inner and outer BOPP membranes were prepared using the stepwise biaxial stretching method in the flat film process; the thickness of the inner BOPP membrane was 18 μm, and the thickness of the outer BOPP membrane was 22 μm; the inner surface of the inner BOPP membrane was coated with an activated carbon layer.

[0032] (1) Keep the temperature of the ceramic soldering iron at 345℃ and use the "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the top, bottom corners and sides of the inner layer of the cigarette box BOPP film;

[0033] (2) Keep the temperature of the ceramic soldering iron at 335℃ and use the "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the top, bottom corners and sides of the outer BOPP film of the cigarette box; the folding and heat sealing positions are the same as the inner BOPP film positions, and the tear head positions are the same.

[0034] The airtightness of the rigid box packaging was measured using the negative pressure vacuum method. The negative pressure was -8.00 kPa, and the result was 8 mL.

[0035] The cigarettes remained unchanged in quality after being stored for 6 months. When smoking, the tearing action of the double-layer BOPP film was essentially the same as that of the single-layer film.

[0036] Example 2: Preparation of double-layer packaging film and its use in cigarette soft pack packaging.

[0037] Both the inner and outer BOPP membranes were prepared using the stepwise biaxial stretching method in the flat film process; the thickness of the inner BOPP membrane was 15 μm, and the thickness of the outer BOPP membrane was 20 μm; the inner surface of the inner BOPP membrane was coated with an activated carbon layer.

[0038] (1) Keep the temperature of the ceramic soldering iron at 340℃ and use the "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the top, bottom corners and sides of the inner layer of the cigarette box BOPP film;

[0039] (2) Keep the temperature of the ceramic soldering iron at 330℃ and use the "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the top, bottom corners and sides of the outer BOPP film of the cigarette box; the folding and heat sealing positions are the same as the inner BOPP film positions, but the tear head positions are different.

[0040] The airtightness of the rigid box packaging was measured using the negative pressure vacuum method. The negative pressure was -1.00 kPa, and the result was 30 mL.

[0041] The cigarettes remained unchanged in quality after being stored for 6 months. When smoking, the tearing action of the double-layer BOPP film was essentially the same as that of the single-layer film.

[0042] Example 3: Preparation of double-layer packaging film and its use in packaging cigarette hard packs, same as in Example 1. However, the packaging of the cigarette hard packs uses ordinary single-layer BOPP film.

[0043] When smoking, the double-layered BOPP film on the cigarette pack is torn in the same position. The cigarette quality remains unchanged after 6 months of storage.

[0044] Example 4: Same as Example 2, except that the positions of folding and heat sealing are different from the positions of the inner BOPP film, and the positions of the tear heads are different.

[0045] The airtightness of the rigid box packaging was measured using the negative pressure vacuum method. The negative pressure was -1.00 kPa, and the result was 20 mL.

[0046] The quality of the cigarettes remained unchanged after being stored for 6 months.

[0047] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A double-layer packaging film, characterized in that, The packaging film is a double-layer BOPP film; both the inner and outer BOPP films are made using the stepwise biaxial stretching method in the flat film process; the thickness of the inner BOPP film is 15μm-18μm, and the inner surface is coated with an activated carbon layer; the thickness of the outer BOPP film is 18μm-22μm; the folding and heat-sealing positions of the inner and outer BOPP films are different, and the tear heads are also different; the double-layer packaging film is used for cigarette boxes or cigarette carton packaging.

2. The double-layer packaging film according to claim 1, characterized in that, The double-layer BOPP film was tested using the negative pressure vacuum method: the sealing degree of the soft box packaging was no more than 50 mL at -1.00 kPa, and the sealing degree of the hard box packaging was no more than 10 mL at -8.00 kPa.

3. A method for preparing a double-layer packaging film according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Use a ceramic soldering iron to heat seal the inner BOPP film: keep the soldering iron temperature at 340℃±5℃, use a "U" shaped knife to cut the BOPP film online, and complete the folding and heat sealing of the inner BOPP film according to the shape of the package. (2) Use a ceramic soldering iron to heat seal the outer BOPP film: keep the soldering iron temperature at 330℃±5℃, and use a "U" shaped knife to cut the BOPP film online to complete the folding and heat sealing of the outer BOPP film.

4. The preparation method according to claim 3, characterized in that, Both the inner and outer BOPP membranes are made using the stepwise biaxial stretching method in the flat film process; the thickness of the inner BOPP membrane is 15μm-18μm, and the inner surface is coated with an activated carbon layer; the thickness of the outer BOPP membrane is 18μm-22μm.

5. The preparation method according to claim 3, characterized in that, The folding and heat-sealing positions of the inner and outer BOPP film are different, and the tear heads are also in different positions.

6. The use of the double-layer packaging film according to any one of claims 1-2 for packaging film of cigarette boxes or cigarette cartons.