A method for preparing a three-layer co-extruded film for soft pack cigarette packaging

Abstract

The application discloses a preparation method of a three-layer co-extrusion film for cigarette soft box packaging and belongs to the technical field of biaxially oriented polypropylene film. The application provides a film prepared by adopting a three-layer co-extrusion biaxial stretching process, which has a three-layer structure, i.e., an inner layer, a core layer and an outer layer, and the core layer is located between the inner layer and the outer layer. According to 100% of the mass percentage of each layer, the inner layer comprises heat-sealing material 50%-95%, stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5% and degradation agent 0%-10%; the core layer comprises propylene homopolymer 50%-90%, ethylene acrylic acid copolymer 10%-30%, stiffening agent 5%-35%, antistatic agent 1%-10% and degradation agent 0%-10%; and the outer layer comprises heat-sealing material 50%-95%, stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5% and degradation agent 0%-10%; the heat-sealing material is composed of ionic polymer, polybutylene resin and ethylene acrylic acid copolymer at a mass ratio of (4-6):(2-4):2. The cigarette soft packaging film provided by the application has high heat-sealing strength, high softness, good optical performance and degradable performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing a three-layer co-extruded film for soft box cigarette packaging, belonging to the technical field of biaxially oriented polypropylene film. BACKGROUND

[0002] Currently, the cigarette packaging film used at home and abroad is mainly biaxially oriented polypropylene film, but domestic customers have more stringent requirements for this film than foreign customers. The focus of foreign countries on this film is its smooth running on the packaging equipment. As long as the film can stably pass through the packaging machine without problems such as jamming, it is usually considered to meet the requirements. However, in the domestic market, in addition to requiring the film to run smoothly on the packaging equipment, customers are particularly concerned about the sealing performance of the film. This is because domestic cigarette factories hope to ensure that each pack of cigarettes has excellent sealing performance to reduce the risk of air leakage and prevent the products in the package from being affected by the external environment (such as moisture, oxygen, and microbial invasion) to maintain the taste and freshness of the cigarettes.

[0003] The smooth running and good sealing performance of the film are directly related to the packaging quality of the cigarette product. The packaging quality not only affects the appearance of the cigarette, but also affects the preservation effect during storage. The sealing performance of the packaging film represents whether the original aroma of the cigarette can be effectively maintained during storage and transportation after leaving the factory. Good sealing performance can prevent the loss of aroma components in the cigarette and avoid the fading of the aroma during storage, which is crucial for the consumer experience. Therefore, sealing performance has become a core technical indicator of domestic cigarette packaging materials. Packaging materials with good sealing performance can not only improve the sensory experience of consumers for cigarettes, but also protect product quality and reduce complaints caused by poor packaging.

[0004] Soft packaging refers to a form of packaging cigarettes with soft paper materials. Compared with hard packaging, the main feature of soft packaging is that the packaging material is soft and comfortable to the touch. Therefore, if soft box cigarettes are to be packaged, not only the sealing performance needs to be guaranteed, but also the softness of the film needs to be considered. At the same time, hard box cigarettes have obvious buffer pressure, which can help the film seal better during heat sealing. Soft box cigarette packaging is different, as the soft box has no buffer pressure and the box body is soft and lacks elasticity, so it is much more difficult to achieve good sealing effect than hard box packaging. Currently, only polyethylene film can achieve good sealing performance, but the use of polyethylene material is limited by its low softness, and its high heat shrinkage rate is not suitable for soft box packaging of cigarettes.

[0005] In addition, the existing cigarette packaging film is usually a film prepared by a three-layer co-extrusion polypropylene biaxial stretching process, the three-layer structure includes an inner layer, a core layer and an outer layer, and the optical performance of the film is determined by the inner layer, the core layer and the outer layer together. For soft pack film, higher gloss and lower haze are required to provide good appearance. However, both the existing polyethylene film and the polypropylene film have poor optical performance.

[0006] In summary, the present application aims to develop a preparation method of a soft pack film for cigarettes, which can be smoothly put on the machine, has good sealing performance, and has softness and good optical performance. SUMMARY

[0007] To solve the above problems, the present application provides a preparation method of a three-layer co-extrusion film for cigarette soft box packaging, which realizes good sealing performance while making the biaxial stretching film have good softness, optical performance and degradable characteristics through the synergistic effect of different formula components and processes.

[0008] The first object of the present application is to provide a preparation method of a three-layer co-extrusion film, comprising the following steps:

[0009] S1, respectively preparing each layer raw material according to the inner layer formula, the core layer formula and the outer layer formula;

[0010] S2, preparing the three-layer structure film from the raw materials of each layer in step S1 by using a three-layer co-extrusion biaxial stretching process, wherein the core layer is located between the inner layer and the outer layer;

[0011] According to 100% of the mass percentage of the inner layer, the inner layer formula comprises: heat sealing material 50%-95%, first additive 7%-50%;

[0012] According to 100% of the mass percentage of the core layer, the core layer formula comprises: propylene homopolymer 50%-90%, ethylene acrylic acid copolymer 10%-30%, second additive 6%-40%;

[0013] According to 100% of the mass percentage of the outer layer, the outer layer formula comprises: heat sealing material 50%-95%, third additive 7%-50%;

[0014] The heat sealing material is composed of ionomer, polybutylene resin and ethylene acrylic acid copolymer in a mass ratio of (4-6):(2-4):2.

[0015] Further, at least one of the following is contained:

[0016] (1) the ionomer is selected from Surlyn 1706 of Chemours company;

[0017] (2) the molecular weight of the polybutylene resin is 150000-250000; preferably, Innovene PB-1 of INEOS Company;

[0018] (3) the molecular weight of the ethylene acrylic acid copolymer is 80000-150000; preferably, Nucrel of DuPont Company;

[0019] (4) the molecular weight of the propylene homopolymer is 300000-400000; preferably, PP520L of Sabic Company.

[0020] Further, at least one of the following is included:

[0021] (1) the first additive includes stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5%, degradation agent 0%-10% by mass percentage of the inner layer;

[0022] (2) the second additive includes stiffening agent 5%-35%, antistatic agent 1%-10%, degradation agent 0%-10% by mass percentage of the core layer;

[0023] (3) the third additive includes stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5%, degradation agent 0%-10% by mass percentage of the outer layer.

[0024] Further, at least one of the following is included:

[0025] (1) the stiffening agent contains 40-70wt% of hydrogenated petroleum resin and 30-60wt% of propylene homopolymer;

[0026] (2) the slip agent includes polydimethylsiloxane;

[0027] (3) the anti-blocking agent includes at least one of silica, polymethyl methacrylate and polymethylsilsesquioxane;

[0028] (4) the antistatic agent includes at least one of fatty acid ester, ethoxylated alkyl amine, diethanolamide and ethoxylated alcohol;

[0029] (5) the degradation agent includes TDPA degradation agent.

[0030] Further, the thickness ratio of the inner layer, the core layer and the outer layer is (0.5-3):(11-21):(0.5-3).

[0031] Further, the three-layer co-extrusion biaxial stretching process includes a three-layer co-extrusion process and a biaxial stretching process;

[0032] The three-layer co-extrusion process comprises the steps of heating each layer of raw material to form molten raw material and simultaneously extruding;

[0033] The bidirectional stretching step comprises the steps of longitudinal stretching preheating, longitudinal stretching, longitudinal stretching setting, transverse stretching preheating, transverse stretching, and transverse stretching setting.

[0034] Further, at least one of the following is included:

[0035] (1) The temperature of longitudinal stretching preheating is 100-150 DEG C; most preferably, it is between 105-145 DEG C;

[0036] (2) The temperature of longitudinal stretching is 90-130 DEG C; most preferably, it is between 96-121 DEG C;

[0037] (3) The temperature of longitudinal stretching setting is 100-155 DEG C; most preferably, it is between 110-146 DEG C;

[0038] (4) The longitudinal stretching ratio is 4.0-6.0; most preferably, it is between 5.0-5.4;

[0039] (5) The temperature of transverse stretching preheating is 150-180 DEG C;

[0040] (6) The temperature of transverse stretching is 130-175 DEG C;

[0041] (7) The temperature of transverse stretching setting is 105-125 DEG C.

[0042] The second object of the present application is to provide a three-layer co-extrusion film prepared by the above preparation method.

[0043] The third object of the present application is to provide the application of the three-layer co-extrusion film in preparing packaging materials.

[0044] The fourth object of the present application is to provide a film for cigarette soft box packaging, which comprises at least one layer of the three-layer co-extrusion film.

[0045] The beneficial effects of the present application are:

[0046] The present application provides a cigarette packaging film, which has the following advantages:

[0047] (1) By improving the use of heat-sealing material, the heat-sealing temperature is reduced, the heat-sealing temperature range is expanded, and the heat-sealing strength is significantly improved, thereby providing good sealing performance after heat-sealing of the soft box packaging;

[0048] (2) Through the improvement of raw materials of different layers, especially the innovation of raw materials of the core layer, the prepared film has better softness, can be more attached to the surface of the cigarette box, can adapt to cigarette boxes of different shapes and sizes, ensures the tightness and uniformity of the package, and the soft film can also reduce friction and loss in the processing process;

[0049] (3) Through the cooperation of different layer formulas and processes, the improvement of the interface and internal uniformity is realized, the film has good optical performance, can provide clearer bottom showing effect, enhances the visual brightness, and improves the sensory experience of consumers;

[0050] (4) The degradation agent is added in the formula, and the adverse effects caused by the introduction of the degradation agent are greatly reduced by optimization, so that the film has degradable performance. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 It is a schematic diagram of the film structure of the present application.

[0052] Figure 2 It is a processing schematic diagram. DETAILED DESCRIPTION

[0053] The present application will be further described below in combination with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not as a limitation on the present application.

[0054] The materials involved in the present application are as follows:

[0055]

[0056] The scheme involved in the present application is as follows:

[0057] The present application provides a high-sealing soft box packaging film for cigarettes, comprising an inner layer, a core layer and an outer layer, the core layer is arranged between the inner layer and the outer layer, wherein

[0058] The inner layer comprises propylene modified heat-sealing material and additives, comprising:

[0059] The modified heat-sealing material accounts for 50% to 95%,

[0060] The stiffening agent accounts for 5% to 50%,

[0061] The slip agent accounts for 1% to 5%,

[0062] The anti-blocking agent accounts for 1% to 5%,

[0063] The degradation agent accounts for 0% to 10%;

[0064] The core layer comprises propylene homopolymer and additives, comprising:

[0065] propylene homopolymer 50% to 90%,

[0066] ethylene acrylic acid copolymer 10% to 30%,

[0067] stiffening agent 5% to 35%,

[0068] antistatic agent 1% to 10%,

[0069] degradation agent 0% to 10%,

[0070] The outer layer includes a modified heat seal material and additives, including:

[0071] modified heat seal material 50% to 95%,

[0072] stiffening agent 5% to 50%,

[0073] slip agent 1% to 5%,

[0074] antiblocking agent 1% to 5%,

[0075] degradation agent 0% to 10%.

[0076] Wherein:

[0077] The modified heat seal material is a specially formulated material, obtained by mixing three raw materials in a specific ratio. It includes three raw materials: ionic polymer (MFI = 0.5-0.9 g / 10 min @ 190°C, 2.16 kg), polybutene resin (MFI = 2.8-3.2 g / 10 min @ 190°C, 2.16 kg), and ethylene acrylic acid copolymer (MFI = 5.8-6.2 g / 10 min @ 190°C, 2.16 kg), with a mass ratio of (4-6):(2-4):2.

[0078] The stiffening agent is prepared from 40-70 wt% hydrogenated petroleum resin and 30-60 wt% propylene homopolymer, with a melt mass flow rate MFR ≥ 25 g / 10 min. The propylene homopolymer has an MFI value of 2.5-9.0 g / 10 min and an isotacticity of over 95%.

[0079] The slip agent is polydimethylsiloxane, with a melt mass flow rate MFR = 2.5-9.0 g / 10 min.

[0080] The antiblocking agent is synthetic silica, polymethyl methacrylate, or polymethylsilsesquioxane, with a melt mass flow rate MFR = 2.5-9.0 g / 10 min.

[0081] The antistatic agent is a fatty acid ester, an ethoxylated alkyl amine, a diethanolamide, or an ethoxylated alcohol, with a melt mass flow rate MFR = 15-50 g / 10 min.

[0082] The degradation agent can be any degradation agent that does not affect film formation, preferably a metal salt, as used in the present application.

[0083] The MFI (Melt Flow Index) of the heat-sealant referred to above is an important parameter for measuring the flow performance of a material in a molten state, also known as MFR. The higher the MFI value, the better the flow performance of the material in a molten state, which is very important for the heat-sealing process. Good flow performance ensures that the heat-sealant flows uniformly and closely during heat-sealing, thereby forming a firm seal.

[0084] The present application improves the heat-sealant by compounding a certain proportion of ionic polymer, polybutene resin and ethylene acrylic acid copolymer to form a brand new heat-sealant formula. The film prepared by melt extrusion and stretching with the formula can at least take into account the heat-sealing performance and softness. Among them, the ionic polymer selected by the present application has excellent melt strength, definition, softness and toughness, and can exhibit superior heat-sealing performance even at a lower heat-sealing starting temperature. The polybutene resin has excellent heat resistance, transparency and non-toxicity. The ethylene acrylic acid copolymer (EAA) has good heat-sealing performance and can achieve effective heat-sealing at a lower temperature. Moreover, EAA has extremely high adhesion to a variety of materials, making it an ideal choice for packaging applications.

[0085] The present application finds that, whether it is a commonly used polypropylene film, or a polyethylene film or an ethylene acrylic acid copolymer film, its sealing performance is relatively good, but it has limitations when applied to soft cigarette packaging, especially in terms of optical performance and softness. The present application realizes the compromise of these several performances through appropriate combination and proportioning and appropriate process. Specifically:

[0086] It is well known that when preparing a film, the first consideration is whether the selected formula can form a film. Whether a film can be formed depends at least on several aspects: formula and process conditions, and the matching of raw materials and process. (1) If the formula design is unreasonable, including but not limited to the types of raw materials, the proportion of raw materials, the types and proportions of additives, etc., it may lead to the failure to form a film. When the raw materials in the formula are unreasonable, not only will the optical performance of the film deteriorate, but also the film may drop or even break during the stretching process. (2) The parameters in the film-forming process, especially the stretching process in the three-layer co-extrusion process, will affect the formation of the film. The stretching process includes longitudinal preheating, longitudinal stretching, transverse preheating, transverse stretching, etc. Proper process will make the originally disordered high molecular materials in the formula rearrange during the stretching process. Various interactions between the high molecular chains will play a role in this process, promoting the alignment, and different raw materials can achieve different stretching effects, thereby affecting the performance of the film.

[0087] Secondly, the optical performance of the film is determined by the inner layer, the core layer and the outer layer together, therefore, the present application adjusts the formula of different layers to improve the optical performance of the film. The optical performance is not only related to the connection at the interface of each layer, but also affected by the uniformity of each layer, such as the above-mentioned stretching process and the movement of the polymer chain therein.

[0088] The present application provides a preparation method of a three-layer co-extrusion film, comprising the following steps:

[0089] S1, mixing the raw materials of each layer according to the inner layer formula, the core layer formula and the outer layer formula respectively;

[0090] S2, using a three-layer co-extrusion biaxial stretching process to prepare the raw materials of each layer in step S1 into a film with a three-layer structure, wherein the core layer is located between the inner layer and the outer layer;

[0091] According to 100% of the mass percentage of the inner layer, the inner layer formula comprises: heat sealing material 50%-95%, first additive 7%-50%;

[0092] According to 100% of the mass percentage of the core layer, the core layer formula comprises: propylene homopolymer 50%-90%, ethylene acrylic acid copolymer 10%-30%, second additive 6%-40%;

[0093] According to 100% of the mass percentage of the outer layer, the outer layer formula comprises: heat sealing material 50%-95%, third additive 7%-50%;

[0094] The heat sealing material is composed of ionomer, polybutylene resin and ethylene acrylic acid copolymer with a mass ratio of (4-6):(2-4):2.

[0095] Preferably, at least one of the following is contained:

[0096] (1) the ionomer is selected from Surlyn 1706 of Chemours company;

[0097] (2) the molecular weight of the polybutylene resin is 150000-250000; preferably, it is Innovene PB-1 of INEOS company;

[0098] (3) the molecular weight of the ethylene acrylic acid copolymer is 80000-150000; preferably, it is Nucrel of DuPont company;

[0099] (4) the molecular weight of the propylene homopolymer is 300000-400000; preferably, it is PP520L of Sabic company.

[0100] Preferably, the first additive includes stiffening agent 5-50%, slip agent 1-5%, anti-blocking agent 1-5%, degradation agent 0-10%, based on 100% by mass of the inner layer.

[0101] The stiffening agent is 5-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc., including but not limited to the percentages listed above, preferably 10-30%.

[0102] The slip agent is 1-5%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc., including but not limited to the percentages listed above.

[0103] The anti-blocking agent is 1-5%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc., including but not limited to the percentages listed above.

[0104] The degradation agent is 0-10%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, etc., including but not limited to the percentages listed above, preferably 1-5%.

[0105] As understood by those skilled in the art, in order to make the material more convenient to process and to meet the general performance required of the material, stiffening agent, slip agent and anti-blocking agent are generally added to the inner layer, and the present application adds degradation agent in line with the concept of green environmental protection. However, it has been found through experiments that the addition of degradation agent can increase the degradation speed, but will affect the performance of the film, such as changing the mechanical properties of the film and reducing the thermal stability of the film. In order to improve the influence of the degradation agent on the heat sealing performance of the film, the present application selects metal salt degradation agent from TDPA on the one hand, and adjusts the formula to reduce the adverse effects of the degradation agent on the other hand.

[0106] Preferably, the second additive includes stiffening agent 5-35%, antistatic agent 1-10%, degradation agent 0-10%, based on 100% by mass of the core layer.

[0107] The stiffening agent is 5-35%, such as 10%, 15%, 20%, 25%, 30%, etc., including but not limited to the percentages listed above, preferably 15-25%.

[0108] The anti-static agent is 1-10%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, etc., including but not limited to the percentages listed above, preferably 3-8%.

[0109] The degradation agent is 0-10%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, etc., including but not limited to the percentages listed above, preferably 1-5%.

[0110] Preferably, the third additive comprises a stiffening agent 5-50%, a slip agent 1-5%, an anti-blocking agent 1-5%, and a degradation agent 0-10%, based on 100% by mass of the outer layer.

[0111] The stiffening agent is 5-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc., including but not limited to the percentages listed above, preferably 10-30%.

[0112] The slip agent is 1-5%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc., including but not limited to the percentages listed above, preferably 1-4%.

[0113] The anti-blocking agent is 1-5%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc., including but not limited to the percentages listed above, preferably 1-4%.

[0114] The degradation agent is 0-10%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, etc., including but not limited to the percentages listed above, preferably 1-5%.

[0115] Preferably, the hot-seal material is 50%-95% in the inner layer formula, and 50%-95% in the outer layer formula. For example, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc., including but not limited to the percentages listed above, preferably 60%-80%, and most preferably 60%-70%. The hot-seal material provides the film with heat-seal effect, which is mainly achieved by adding a certain amount of hot-seal material to the inner and outer surfaces of the film. Upon heating, the hot-seal material, due to its low melting point, multiple chain segments and branches, will first melt and flow, and after a certain pressure, the surface hot-seal molecules of the film will entangle with each other and change their arrangement through molecular motion to form a heat-sealed state. The selection of appropriate hot-seal material formula can improve the heat-seal strength, seal initiation temperature and heat-seal temperature range of the film.

[0116] Preferably, the propylene homopolymer (ternary) is 50%-90% in the core layer formula, for example, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc., including but not limited to the percentages listed above, and preferably 50%-60%. Increasing the propylene homopolymer in the core layer not only increases the overall strength and stiffness of the film, but also has good flow characteristics, which helps the extrusion processing of the film.

[0117] Preferably, the ethylene acrylic acid copolymer is 10%-30% in the core layer formula, for example, 15%, 20%, 25%, etc., including but not limited to the percentages listed above. The addition of ethylene acrylic acid copolymer in the core layer of the present application not only because EAA has good adhesion and heat-seal performance, but also because: the present application adds a certain proportion of EAA in the inner and outer layers, which can promote the compatibility between the core layer and the inner and outer layers during processing due to molecular motion and intermolecular forces (such as hydrogen bonding), and the interface is more smooth, achieving the purpose of improving the interface, concentrating light reflection, and improving gloss; at the same time, the distribution of components in each layer is more uniform, reducing internal unevenness, reducing light scattering, reducing haze, thereby providing the film with good optical and heat-seal performance.

[0118] Preferably, the thickness ratio of the inner layer, core layer and outer layer is (0.5-3):(11-21):(0.5-3), for example, 1:15:1, 1:15:2, 2:15:1, etc., including but not limited to the ratios listed above, and the thickness of each layer can be controlled by adjusting the weight of the formula. Most preferably, the inner layer is 0.5-3.0 μm thick, the core layer is 11-21 μm thick, and the outer layer is 0.5-3.0 μm thick, and the thickness of the film ranges from 17 μm to 28 μm.

[0119] The three-layer co-extrusion bidirectional stretching process described in the present application is a plastic processing technology, which is to extrude and tightly combine three different molten materials (i.e. the inner layer formula, the core layer formula and the outer layer formula in the present application) through a co-extrusion head at the same time, to form a composite material product with specific functions (such as Figure 2 )。

[0120] Preferably, the present application specifically includes the following steps:

[0121] (1) Melt extrusion: the raw materials are heated to melt in the extruder, and then extruded out through the screw of the extruder;

[0122] (2) Stretching into a film: the extruded product is introduced into a stretching orientation machine, and the film is stretched by adjusting the temperature and speed, so as to change the mechanical properties, physical properties, etc. of the film;

[0123] (3) Setting: the stretched and oriented film needs to be quickly cooled to solidify. During the cooling and setting process, the width and thickness of the film can be controlled by adjusting the temperature of the cooling water tank and the stretching speed.

[0124] The multi-layer co-extrusion extruder described in the present application can be a wide step stretching BOPP machine, or a synchronous stretching BOPP machine. In the above process, the specification of the BOPP auxiliary extruder extruder is particularly required: the extruder screw used for auxiliary extrusion belongs to a double screw, the screw diameter is 60 mm, and the length-diameter ratio = 35. The materials of the longitudinal stretching preheating roller and the stretching roller are thickened Teflon, and the total thickness is 100 μm.

[0125] Preferably, the three-layer co-extrusion biaxial stretching process comprises a three-layer co-extrusion step and a biaxial stretching step, and the biaxial stretching step comprises: longitudinal stretching preheating, longitudinal stretching, longitudinal stretching setting, transverse stretching preheating, transverse stretching, and transverse stretching setting. The biaxial stretching process affects the softness, heat sealing performance, and optical performance of the film, and the key lies in the matching of the parameters of the longitudinal stretching section (MDO) and the transverse stretching section (TDO), so this process is particularly important in preparation. Specifically: (1) Softness is an index for evaluating the performance of a soft package film. In the stretching process, the molecules are oriented along the longitudinal direction (MD) and the transverse direction (TD), and with the change of the formula, the orientation parameters of the molecules along different directions will change accordingly, thereby adjusting the softness of the film. In the present application, it is found that the Young's modulus of the final product is significantly reduced by the synergistic combination of different substances, thereby providing the required softness. (2) In addition to the formula of the heat sealing material, the temperature also has a significant effect on the heat sealing strength. The process steps include melt extrusion, film stretching, and setting. As mentioned above, the stretching process involves the movement and arrangement of molecular chains, and the temperature in the stretching process will undoubtedly affect the movement of the molecular chains, and the setting temperature is the same. The combination of the two determines the heat sealing performance of the film. (3) Similarly, the temperature in the preheating and stretching process will affect the movement and arrangement of the molecular chains, and will affect the uniformity between the interface and the layers, thereby affecting the optical performance of the film.

[0126] Preferably, at least one of the following is included:

[0127] (1) The temperature of the longitudinal stretching preheating is 100-150°C; most preferably between 105-145°C;

[0128] (2) The temperature of the longitudinal stretching is 90-130°C; most preferably between 96-121°C;

[0129] (3) The temperature of the longitudinal stretching setting is 100-155°C; most preferably between 110-146°C;

[0130] (4) The longitudinal stretching ratio is 4.0-6.0; most preferably 5.0-5.4;

[0131] (5) The temperature of the transverse stretching preheating is 150-180°C;

[0132] (6) The temperature of the transverse stretching is 130-175°C;

[0133] (7) The temperature of the transverse stretching setting is 105-125°C.

[0134] The application also provides a film for soft box cigarette packaging, which comprises at least one three-layer co-extrusion film prepared by the above preparation method. The film has good softness and heat shrinkage performance, and does not cause extrusion to the cigarette box in the packaging when used for cigarette packaging, so that the requirement for the material of the cigarette box is more relaxed, and the film is suitable for the packaging of soft box cigarette.

[0135] Example 1

[0136] (1) The formula of each layer of the soft box packaging film is as follows (by mass ratio):

[0137] The sticking roller layer (inner layer) comprises 66% of modified heat sealing material, 20% of stiffening agent, 4% of slip agent, 5% of anti-blocking agent and 5% of TDPA degrading agent, wherein the MFI of the modified heat sealing material is 2.0 g / 10 min, the MFI of the stiffening agent is 40 g / 10 min, and the MFI of the slip agent is 5.2 g / 10 min.

[0138] The core layer comprises 55% of propylene homopolymer, 15% of ethylene acrylic acid copolymer (molecular weight 80000), 20% of stiffening agent, 5% of antistatic agent and 5% of TDPA degrading agent, wherein the MFI of the propylene homopolymer is 3.0 g / 10 min.

[0139] The air knife layer (outer layer) comprises 66% of modified heat sealing material, 20% of stiffening agent, 5% of slip agent, 4% of anti-blocking agent and 5% of TDPA degrading agent, wherein the MFI of the modified heat sealing material is 2.0 g / 10 min, the MFI of the stiffening agent is 40 g / 10 min, and the MFI of the slip agent is 5.2 g / 10 min.

[0140] In the application, the modified heat sealing material comprises 50% of ionic polymer (MFI = 0.7 g / 10 min@190℃, 2.16 kg), 30% of polybutene resin (MFI = 3.0 g / 10 min@190℃, 2.16 kg, molecular weight 200000) and 20% of ethylene acrylic acid copolymer (MFI = 6.0 g / 10 min@190℃, 2.16 kg, molecular weight 80000).

[0141] The modified heat sealing material is prepared by mixing the above components in a mass ratio of 50:30:20 and extruded by a mixing extruder.

[0142] The stiffening agent is a mixture of 50% of hydrogenated petroleum resin and 50% of propylene homopolymer.

[0143] The slip agent is polydimethylsiloxane.

[0144] The anti-blocking agent is synthetic silicon dioxide.

[0145] The antistatic agent is a fatty acid ester.

[0146] (2) Prepared by three-layer co-extrusion polypropylene biaxial stretching process, the process flow includes: mixing of raw materials, extrusion, longitudinal stretching preheating, longitudinal stretching (MDO), setting, transverse stretching preheating, transverse stretching (TDO), setting, winding. Among them, the production process parameters are:

[0147] MDO preheating temperature: 120°C; MDO stretching temperature: 97°C; MDO setting temperature: 120°C; MDO total stretching ratio is 5.2;

[0148] TDO preheating temperature: 172°C; TDO stretching temperature: 145°C; TDO setting temperature: 110°C; TDO speed set value 170 m / min.

[0149] Finally, the soft package film product with a total thickness of 21 μm, a roller layer thickness of 0.9 μm, a core layer thickness of 18.9 μm, and a air knife layer thickness of 1.2 μm is obtained.

[0150] Example 2

[0151] Adjust the three-layer co-extrusion polypropylene biaxial stretching process parameters, the rest is the same as example 1. The production process parameters of three-layer co-extrusion polypropylene biaxial stretching process for preparation are:

[0152] MDO preheating temperature: 115°C; MDO stretching temperature: 98°C; MDO setting temperature: 110°C; MDO total stretching ratio is 5.0;

[0153] TDO preheating temperature: 172°C; TDO stretching temperature: 145°C; TDO setting temperature: 110°C; TDO speed set value 170 m / min.

[0154] Finally, the soft package film product with a total thickness of 21 μm, a roller layer thickness of 1.2 μm, a core layer thickness of 18.3 μm, and a air knife layer thickness of 1.5 μm is obtained.

[0155] Example 3

[0156] Adjust the three-layer co-extrusion polypropylene biaxial stretching process parameters, the rest is the same as example 1. The production process parameters of three-layer co-extrusion polypropylene biaxial stretching process for preparation are:

[0157] MDO preheating temperature: 105°C; MDO stretching temperature: 98°C; MDO setting temperature: 110°C; MDO total stretching ratio is 4.5;

[0158] TDO preheating temperature: 172°C; TDO stretching temperature: 146°C; TDO setting temperature: 110°C; TDO speed set value 170 m / min.

[0159] The final soft pouch film product has a total thickness of 21 μm, a roll lamination layer thickness of 1.5 μm, a core layer thickness of 17.7 μm, and a air knife layer thickness of 1.8 μm.

[0160] Example 4

[0161] The formulation of each layer of the soft pouch packaging film was adjusted, and the rest was the same as in Example 2. The formulation of each layer of the soft pouch packaging film was as follows (by mass ratio):

[0162] Roll lamination layer (inner layer): modified heat sealant 50%; stiffening agent 47%; slip agent 1%; anti-blocking agent 1%; TDPA degrading agent 1%.

[0163] Core layer: propylene homopolymer 79%; ethylene acrylic acid copolymer 10% (molecular weight 80000); stiffening agent 9%; antistatic agent 1%; TDPA degrading agent 1%.

[0164] Air knife layer (outer layer): modified heat sealant 80%; stiffening agent 10%; slip agent 4%; anti-blocking agent 4%; TDPA degrading agent 2%.

[0165] wherein:

[0166] Modified heat sealant: made of 50% ionic polymer (MFI = 0.7 g / 10 min @ 190°C, 2.16 kg), 30% polybutene resin (MFI = 3.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 200000), and 20% ethylene acrylic acid copolymer (MFI = 6.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 80000) by mass percentage, and extruded using a mixing extruder.

[0167] Stiffening agent: made of 50% hydrogenated petroleum resin and 50% propylene homopolymer.

[0168] Slip agent is polydimethylsiloxane.

[0169] Anti-blocking agent is synthetic silica.

[0170] Antistatic agent is fatty acid ester.

[0171] Example 5

[0172] The formulation of each layer of the soft pouch packaging film was adjusted, and the rest was the same as in Example 2. The formulation of each layer of the soft pouch packaging film was as follows (by mass ratio):

[0173] Roll lamination layer (inner layer): modified heat sealant 85%; stiffening agent 12%; slip agent 1%; anti-blocking agent 1%; TDPA degrading agent 1%.

[0174] Core layer: propylene homopolymer 60%; ethylene acrylic acid copolymer 30% (molecular weight 80000); stiffening agent 8%; antistatic agent 1%; TDPA degradant 1%.

[0175] Air knife layer (outer layer): modified heat sealable material 50%; stiffening agent 40%; slip agent 4%; anti-blocking agent 4%; TDPA degradant 2%.

[0176] wherein:

[0177] Modified heat sealable material: made of 50% ionomer (MFI = 0.7 g / 10 min @ 190°C, 2.16 kg), 30% polybutene resin (MFI = 3.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 200000), 20% ethylene acrylic acid copolymer (MFI = 6.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 80000) by mass percentage, and extruded using a compound extruder.

[0178] Stiffening agent: made of 50% hydrogenated petroleum resin and 50% propylene homopolymer.

[0179] Slip agent is polydimethylsiloxane.

[0180] Anti-blocking agent is synthetic silica.

[0181] Antistatic agent is fatty acid ester.

[0182] Example 6

[0183] The composition of the modified heat sealable material is adjusted, and the rest is the same as Example 2. Wherein: the modified heat sealable material is made of 40% ionomer (MFI = 0.7 g / 10 min @ 190°C, 2.16 kg), 40% polybutene resin (MFI = 3.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 200000), 20% ethylene acrylic acid copolymer (MFI = 6.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 80000) by mass percentage, and extruded using a compound extruder.

[0184] Example 7

[0185] The composition of the modified heat sealable material is adjusted, and the rest is the same as Example 2. Wherein: the modified heat sealable material is made of 60% ionomer (MFI = 0.7 g / 10 min @ 190°C, 2.16 kg), 20% polybutene resin (MFI = 3.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 200000), 20% ethylene acrylic acid copolymer (MFI = 6.0 g / 10 min @ 190°C, 2.16 kg, molecular weight 80000) by mass percentage, and extruded using a compound extruder.

[0186] Example 8

[0187] The polybutene resin in the modified heat sealant was replaced with a polybutene resin having an average molecular weight of 150,000, and the remaining steps were the same as in Example 2.

[0188] Example 9

[0189] The ethylene acrylic acid copolymer in the modified heat sealant was replaced with an ethylene acrylic acid copolymer having an average molecular weight of 150,000, and the remaining steps were the same as in Example 2.

[0190] Comparative Example 1

[0191] The modified heat sealant in the kiss roll layer was replaced with a propylene homopolymer, the ethylene acrylic acid copolymer in the core layer was replaced with a propylene homopolymer, and the modified heat sealant in the air knife layer was replaced with a propylene homopolymer, and the remaining steps were the same as in Example 2.

[0192] Comparative Example 2

[0193] The ionic polymer in the modified heat sealant was replaced with a propylene homopolymer, and the remaining steps were the same as in Example 2.

[0194] Comparative Example 3

[0195] The ethylene acrylic acid copolymer in the modified heat sealant was replaced with a propylene homopolymer, and the remaining steps were the same as in Example 2.

[0196] Comparative Example 4

[0197] The modified heat sealant in the kiss roll layer was replaced with an ethylene acrylic acid copolymer, the ethylene acrylic acid copolymer in the core layer was replaced with an ethylene acrylic acid copolymer, and the modified heat sealant in the air knife layer was replaced with an ethylene acrylic acid copolymer, and the remaining steps were the same as in Example 2.

[0198] Comparative Example 5

[0199] The modified heat sealant in the kiss roll layer was replaced with polyethylene, the ethylene acrylic acid copolymer in the core layer was replaced with polyethylene, and the modified heat sealant in the air knife layer was replaced with polyethylene, and the remaining steps were the same as in Example 2.

[0200] Comparative Example 6

[0201] The ethylene acrylic acid copolymer in the core layer was replaced with a propylene homopolymer, and the remaining steps were the same as in Example 2.

[0202] Comparative Example 7

[0203] The amounts of the propylene homopolymer and the ethylene acrylic acid copolymer in the core layer were adjusted to 30% propylene homopolymer and 40% ethylene acrylic acid copolymer, and the remaining steps were the same as in Example 2.

[0204] Comparative Example 8

[0205] The polybutene resin in the modified heat-sealing material was replaced by a polybutene resin with an average molecular weight of 10000, and the remaining steps were the same as in Example 2.

[0206] Comparative Example 9

[0207] The polybutene resin in the modified heat-sealing material was replaced by a polybutene resin with an average molecular weight of 500000, and the remaining steps were the same as in Example 2.

[0208] Comparative Example 10

[0209] The ethylene acrylic acid copolymer in the modified heat-sealing material was replaced by an ethylene acrylic acid copolymer with an average molecular weight of 10000, and the remaining steps were the same as in Example 2.

[0210] Test Example

[0211] The heat-sealing starting temperature, heat-sealing strength, haze, gloss, and softness of the film products prepared in the above examples and comparative examples were detected, respectively. Among them, the detection conditions of the inside-out heat-sealing starting temperature and the outside-out heat-sealing starting temperature were: force 150N, time 0.5 seconds; the inside-out heat-sealing strength, the inside-out heat-sealing strength, the outside-out heat-sealing strength were all detected according to the detection method of YC / T 266; the haze was detected according to the method in GB 2410; the gloss was detected according to the method in GB 8807; the softness was detected according to YC / T 266-2008. The results are as follows:

[0212]

[0213] During the preparation process, Comparative Example 8 occurred material dropping during the stretching process, Comparative Examples 2 and 8 could not form films, and the film in Comparative Example 1 appeared whitening.

[0214] The films prepared in Examples 1-3 and Comparative Example 1 were subjected to 100 hours of 500nm wavelength UV light, and their tensile strength and elongation at break were detected, and the results are as follows:

[0215]

[0216] The degradation performance of different films was detected by the simulated light irradiation method, the film occurred oxidative chain scission during the photo-degradation process, the molecular structure changed, and the properties such as tensile strength and elongation at break changed with the increase of light irradiation time. From the above table, it can be seen that the tensile strength and elongation at break of the film prepared in the present application after 100 hours of UV light irradiation are obviously lower than those of the existing polypropylene film, indicating that it has good degradability.

[0217] Obviously, the above embodiments are merely example for clearly illustrating, and are not limitation to the embodiments. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments need not and can not be exhausted. The obvious changes or variations derived therefrom are still within the scope of the present invention.

Claims

1. A process for the production of a three-layer co-extruded film, characterized in that, The method comprises the following steps: S1, preparing raw materials of each layer according to the inner layer formula, the core layer formula and the outer layer formula respectively; S2, preparing the raw materials of each layer in step S1 into a film with a three-layer structure by a three-layer co-extrusion and biaxial stretching process, wherein the core layer is located between the inner layer and the outer layer; The inner layer formula comprises, taking the mass percentage of the inner layer as 100%, heat seal material 50%-95%, and first additive 7%-50%; the first additive comprises stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5%, and degradation agent 0.5%-10%; The core layer formula comprises, taking the mass percentage of the core layer as 100%, propylene homopolymer 50%-90%, ethylene acrylic acid copolymer 10%-30%, and second additive 6%-40%; the second additive comprises stiffening agent 5%-35%, antistatic agent 1%-10%, and degradation agent 0.5%-10%; The outer layer formula comprises, taking the mass percentage of the outer layer as 100%, heat seal material 50%-95%, and third additive 7%-50%; the third additive comprises stiffening agent 5%-50%, slip agent 1%-5%, anti-blocking agent 1%-5%, and degradation agent 0.5%-10%; The heat seal material is composed of ionic polymer, polybutene resin and ethylene acrylic acid copolymer in a mass ratio of (4-6):(2-4):2; the ionic polymer is Surlyn 1706 of Chemours Company; the molecular weight of the polybutene resin is 150000-250000; the molecular weight of the ethylene acrylic acid copolymer is 80000-150000; and the molecular weight of the propylene homopolymer is 300000-400000; The three-layer co-extrusion film prepared by the preparation method has heat sealing performance, optical performance and degradation performance.

2. The production method according to claim 1, characterized by, At least one of the following features is included: (1) the polybutene resin is Innovene PB-1 of INEOS Company; (2) the ethylene acrylic acid copolymer is Nucrel of DuPont Company; (3) the propylene homopolymer is PP520L of Sabic Company.

3. The preparation method according to claim 1, characterized in that At least one of the following features is included: (1) the stiffening agent contains 40-70wt% of hydrogenated petroleum resin and 30-60wt% of propylene homopolymer; (2) the slip agent comprises polydimethylsiloxane; (3) the anti-blocking agent comprises at least one of silica, polymethyl methacrylate and polymethylsilsesquioxane; (4) the antistatic agent comprises at least one of fatty acid ester, ethoxylated alkyl amine, diethanolamide and ethoxylated alcohol.

4. The preparation method according to claim 1, characterized in that The thickness ratio of the inner layer, the core layer and the outer layer is (0.5-3):(11-21):(0.5-3).

5. The preparation method according to claim 1, characterized in that The three-layer co-extrusion and biaxial stretching process comprises a three-layer co-extrusion process and a biaxial stretching process; The three-layer co-extrusion process comprises the steps of heating the raw materials of each layer to form molten raw materials and simultaneously extruding; The biaxial stretching process comprises the steps of longitudinal stretching preheating, longitudinal stretching, longitudinal stretching setting, transverse stretching preheating, transverse stretching, and transverse stretching setting.

6. The production method according to claim 5, characterized by, At least one of the following features is included: (1) the temperature of the longitudinal stretching preheating is 100-150°C; (2) the temperature of the longitudinal stretching is 90-130°C; (3) the temperature of the longitudinal stretching setting is 100-155°C; (4) the longitudinal stretching ratio is 4.0-6.0; (5) the temperature of the transverse stretching preheating is 150-180°C; (6) the temperature of the transverse stretching is 130-175°C; (7) the temperature of the transverse stretching setting is 105-125°C.

7. The three-layer co-extruded film prepared by the preparation method of any one of claims 1-6.

8. The use of the three-layer co-extruded film of claim 7 in the preparation of packaging materials.

9. A film for soft pack cigarette packaging, characterized in that, The film comprises at least one three-layer co-extruded film of claim 7.

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