A heat-shrinkable film for HDPE containers and a method for preparing the same

Abstract

The application belongs to the field of heat-shrinkable film preparation, and particularly relates to a heat-shrinkable film special for HDPE material container and a preparation method thereof. The heat-shrinkable film special for HDPE material container is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom. The surface layer and the bottom layer are prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol modified PET 88-99.2%, toughening agent 0-8% and anti-blocking agent 0.8-4%. The intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol modified PET 68.5-91.2%, additive 8-28% and reactive compatibilizer 1.3-3.5%. The additive is a mixture of triallyl isocyanurate, azodicarbonamide and HDPE. The heat-shrinkable film disclosed in the application has a thermal expansion coefficient matched with the HDPE material container, low shrinkage force, high low-temperature shrinkage rate and excellent application when used for packaging the HDPE material container.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of heat-shrinkable film preparation, and particularly relates to a heat-shrinkable film special for HDPE material container and a preparation method thereof. BACKGROUND

[0002] HDPE (high-density polyethylene) containers have the characteristics of high rigidity, strong chemical resistance, and high thermal expansion coefficient (about 150-200 x 10 -6 / ℃), but have the following packaging pain points: heat deformation sensitivity, the HDPE melting point is about 130-135℃, and the bottle body is easily softened due to high temperature during filling or sterilization, so the label shrinkage temperature needs to be strictly controlled below 90℃ to avoid damaging the bottle body. Poor dimensional stability, HDPE starts to expand at 50℃ or above, and the volume shrinks after cooling, which leads to the problem of label shrinkage and loosening after shrinkage, and the label shrinkage rate needs to be dynamically matched with the HDPE expansion rate. At the same time, most of the cleaning and washing packaging products adopt the process of first wrapping the label and then shrinkage, so there is a higher requirement for the shrinkage force of the label.

[0003] Early heat-shrinkable labels for HDPE containers are mainly PVC, but they have the defects of low shrinkage rate (40%-60% ultimate shrinkage rate), poor environmental protection (release of dioxin by burning), and poor recycling performance. With the expansion of the application scenarios of HDPE containers and the evolution of the material system towards high performance and environmental protection, OPS (oriented polystyrene) has the advantages of low initial shrinkage temperature and smooth shrinkage curve, and has started to be applied to HDPE container packaging, but it has a high natural shrinkage rate and needs to be transported in a cold chain and use special ink, which has a relatively high cost and low market acceptance. PETG heat-shrinkable labels have started to be applied, and they have a high ultimate shrinkage rate (80%) and good printing effect, but they require a high shrinkage temperature of more than 75℃ to meet the packaging requirements, and the bottle body is easily deformed at the shrinkage temperature, which cannot meet the packaging requirements.

[0004] With the development of environmental protection concepts and policy requirements, different proportions of recycled materials (rPE) will be added to HDPE containers. rPE is mainly obtained by melting and recycling waste plastics, and the thermal oxidation during the processing process will cause the molecular chain to break, the molecular weight to decrease, the branching degree to increase, and LDPE and other materials to be mixed in, which will destroy the original regular molecular structure of HDPE, reduce the crystallinity, and further reduce the heat resistance of the HDPE bottle body. At the same time, it will cause the thermal expansion coefficient (CTE) of the container to increase, the dimensional stability to decrease, and the thermal expansion and cold contraction phenomenon to be more significant. The change in the properties of the HDPE container increases the performance requirements of the heat-shrinkable film for packaging. Due to the large difference in thermal expansion coefficient between ordinary heat-shrinkable PETG film and HDPE container, the low low-temperature shrinkage rate and the large shrinkage force, the shrinkable container is deformed and the "loosening" problem after shrinkage occurs. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to obtain a heat-shrinkable film special for HDPE material containers and a preparation method thereof. The heat-shrinkable film disclosed in the present application has a thermal expansion coefficient matched with the HDPE material container, low shrinkage force, high low-temperature shrinkage rate, and excellent application when used for special packaging of the HDPE material container.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0007] In one aspect, the present application provides a heat-shrinkable film special for HDPE material containers, which is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom. The surface layer and the bottom layer are both prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol modified PET 88-99.2%, toughening agent 0-8% and functional masterbatch 0.8-4%; the intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol modified PET 68.5-91.2%, additive 8-28% and reactive compatibilizer 1.3-3.5%; wherein the additive is a mixture of triallyl isocyanurate, azodicarboxamide and HDPE.

[0008] In some embodiments of the present application, the thickness ratio of the surface layer, the intermediate layer and the bottom layer is 5-15%, 70-90% and 5-15%, respectively, in a thickness ratio of 100%.

[0009] In some embodiments of the present application, the toughening agent is styrene-butadiene block copolymer or acrylate-butadiene-styrene.

[0010] Preferably, the melt index of the styrene-butadiene block copolymer is 10-15 g / 10 min (200℃, 2.16 kg).

[0011] Preferably, the melt index of the acrylate-butadiene-styrene is 8-12 g / 10 min (200℃, 2.16 kg).

[0012] In some embodiments of the present application, the anti-blocking agent is SiO2.

[0013] In some embodiments of the present application, the diol modified PET is neopentyl glycol and hexanediol co-modified PET.

[0014] In some embodiments of the present application, the glass transition temperature of the diol modified PET is 63-72℃.

[0015] In some embodiments of the present application, the additive comprises the following raw materials in a mass percentage of 100%: 12-14% triallyl isocyanurate, 16-18% azodicarbonamide and 68-72% HDPE.

[0016] Preferably, the melt index of the HDPE is 8-10 g / 10 min (200℃, 2.16 kg).

[0017] In some embodiments of the present application, the reactive compatibilizer is PE-g-GMA.

[0018] Preferably, the density of the PE-g-GMA is 0.93-0.95 g / cm3, and the GMA grafting rate is 1.0-1.2 wt%.

[0019] The present application achieves a thermal expansion coefficient close to that of HDPE material by blending chemical modification, which can synchronize the volume change of the HDPE material container when the label is preheated or precooled, thereby ensuring the shrinkage effect and meeting the requirements of HDPE container empty bottle packaging, avoiding the problem of compression deformation of the HDPE container caused by improper shrinkage force.

[0020] Specifically, the present application prepares a heat-shrinkable film by three layers of surface layer, middle layer and bottom layer, wherein the preferred raw materials of the middle layer ensure the polarity matching of the three-layer contact surface, improve the interlayer bonding force, and are not prone to sealing layer problems; at the same time, the mixture of triallyl isocyanurate, azodicarbonamide and HDPE is added as an additive to the raw materials of the middle layer, which is conducive to the formation of a uniform and controllable closed pore structure, and improves the polarity and expansion coefficient matching, avoiding the problems of overall haze reduction of the film and possible label "back loose" caused by excessively large pore structure; and the heat-shrinkable film prepared from the specific raw materials has a low initial shrinkage temperature, effectively avoiding deformation and other problems caused by the softening of the HDPE container when heated; at the same time, the present application can realize efficient separation from the HDPE material container, which is conducive to the classification and recycling of the HDPE material container and the label, and has a wide application prospect.

[0021] The present application also provides a preparation method of a heat-shrinkable film special for HDPE material containers, comprising the following steps:

[0022] S1: uniformly mix the neopentyl glycol modified PET, toughening agent and functional masterbatch for preparing the surface layer and bottom layer to obtain a surface layer mixture and a bottom layer mixture;

[0023] S2: uniformly mix the diol modified PET, additive and reactive compatibilizer for preparing the middle layer to obtain a middle layer mixture;

[0024] S3: melt plasticize, melt extrude, and cool form the mixtures of the surface layer, the intermediate layer and the bottom layer to obtain a cast sheet according to the thickness ratio of each layer;

[0025] S4: sequentially stretch the cast sheet of step S3 in the longitudinal direction, in the transverse direction and draw and wind, to obtain the HDPE material container special heat shrinkable film.

[0026] In some embodiments of the present application, the thickness of the HDPE material container special heat shrinkable film is 30-100 μm.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The heat expansion coefficient of the heat shrinkable film disclosed by the present application matches, the shrinkage force is low, the low-temperature shrinkage rate is high, and the application is excellent when used for HDPE material container special packaging;

[0029] (2) The heat expansion coefficient of the heat shrinkable film obtained by blending and chemical modification in the present application is close to that of HDPE material, which can synchronize the volume change of the HDPE material container when the label is preheated or precooled, thereby ensuring the shrinkage effect;

[0030] (3) The shrinkage force of the HDPE material container special heat shrinkable film obtained by the present application is less than 5N, which can meet the requirements of HDPE container empty bottle packaging, and avoid the problem of compression deformation of HDPE container caused by improper shrinkage force; and the initial shrinkage temperature of the film is low, which effectively avoids the deformation problem of the HDPE container caused by softening under low shrinkage temperature;

[0031] (4) The HDPE material container special heat shrinkable film obtained by the present application can realize efficient separation with the HDPE material container, which is beneficial to the classification and recycling of the HDPE material container and the label, and has wide application prospect. DETAILED DESCRIPTION

[0032] The various exemplary embodiments of the present application will now be described in detail, which should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present application. It should be understood that the terms described in the present application are only for the description of the particular embodiments, and are not used to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0033] Unless otherwise specified, the compounds and related reagents used in the following detailed description can be purchased from the market.

[0034] Unless otherwise specified, the process post-treatment operations used in the following detailed description are routine operations for those skilled in the art, which are selected by the actual operation.

[0035] As used in the following detailed description, unless otherwise specified, the neopentyl glycol modified PET is YH101 from Source High Polymer; the melt index of the styrene-butadiene block copolymer used is 12 g / 10 min (200°C, 2.16 kg); the melt index of the acrylate-butadiene-styrene used is 10 g / 10 min (200°C, 2.16 kg); the melt index of the HDPE used is 9 g / 10 min (200°C, 2.16 kg); the density of the PE-g-GMA used is 0.94 g / cm3, and the GMA grafting rate is 1.1 wt%; the glass transition temperature of the PETG used is preferably 65°C, and the viscosity is 0.80 dL / g.

[0036] Preparation Example 1

[0037] The preparation steps of the diol modified PET are as follows:

[0038] 2 mol of terephthalic acid, 0.00027 mol of ethylene glycol antimony and 2.2 mol of ethylene glycol were mixed, replaced with nitrogen, and heated to 240°C at 300 kPa. When the amount of esterification water was 90% of the theoretical value, 0.12 mol of neopentyl glycol was added at normal pressure. After 0.7 h, 0.05 mol of hexanediol was added. After 1.5 h, the temperature was raised to 278°C at 80 Pa, and reacted for 2 h, to obtain the product.

[0039] The glass transition temperature of the diol modified PET is 65°C.

[0040] Preparation Example 2

[0041] The preparation steps of the additive are as follows:

[0042] 13% of triallyl isocyanurate, 17% of azodicarbonamide and 70% of HDPE were mixed to be uniform, based on 100% by mass, to obtain the product.

[0043] Preparation Example 3

[0044] The preparation steps of the additive are as follows:

[0045] 19.5% of azodicarbonamide and 80.5% of HDPE were mixed to be uniform, based on 100% by mass, to obtain the product.

[0046] Preparation Example 4

[0047] The preparation steps of the additive are as follows:

[0048] 15.7% of triallyl isocyanurate and 84.3% of HDPE were mixed to be uniform, based on 100% by mass, to obtain the product.

[0049] Preparation Example 5

[0050] The preparation steps of the additive are as follows:

[0051] 43.3% triallyl isocyanurate and 56.7% azodicarbonamide are mixed to be uniform, namely, the additive is obtained.

[0052] Example 1

[0053] A heat-shrinkable film special for HDPE material containers is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom. The surface layer and the bottom layer are both prepared from the following raw materials in the amount of 100% by mass: neopentyl glycol modified PET 88%, styrene-butadiene block copolymer 8% and SiO2 4%; the intermediate layer is prepared from the following raw materials in the amount of 100% by mass: diol modified PET 68.5%, additive 28% and PE-g-GMA 3.5%.

[0054] The preparation method of the heat-shrinkable film special for HDPE material containers in this embodiment comprises the following steps:

[0055] S1: neopentyl glycol modified PET, styrene-butadiene block copolymer and SiO2 for preparing the surface layer and the bottom layer are dried to remove water and then mixed to be uniform, to obtain a surface layer mixture and a bottom layer mixture;

[0056] S2: diol modified PET, additive and PE-g-GMA for preparing the intermediate layer are dried to remove water and then mixed to be uniform, to obtain an intermediate layer mixture;

[0057] S3: the mixtures of the surface layer, the intermediate layer and the bottom layer are respectively fed into three double-screw extruders for melt plasticization, the screw diameter is selected to be 80 mm, the length-diameter ratio is 28, and the temperature is 230℃; the three extruders are co-extruded in the same die according to the thickness ratio of each layer of 10:80:10 (%) at a die temperature of 240℃; the extruded castings (the ratio of the linear speed of the quenching roller to the melt flow-out speed is less than or equal to 3, and the temperature of the quenching roller is controlled at 32℃±2℃);

[0058] S4: the castings of step S3 are sequentially subjected to longitudinal stretching (single-point stretching by infrared heating, longitudinal stretching of the castings at a stretching ratio of 1.11 times at 80℃ after preheating at 85℃, and cooling and setting at 45℃ after longitudinal stretching), transverse stretching (stretching by oil heating at a stretching ratio of 4.5 times at 80℃ after preheating at 100℃, and cooling and setting at 75℃ after transverse stretching) and traction and winding, to obtain the heat-shrinkable film special for HDPE material containers.

[0059] The diol-modified PET used in this example is obtained from Preparation Example 1, and the additive used is obtained from Preparation Example 2.

[0060] Example 2

[0061] A heat-shrinkable film special for HDPE material containers is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom. The surface layer and the bottom layer are both prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol-modified PET 88%, styrene-butadiene block copolymer 8% and SiO2 4%; the intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol-modified PET 68.5%, additive 28% and PE-g-GMA 3.5%.

[0062] The preparation method of the heat-shrinkable film special for HDPE material containers in this example comprises the following steps:

[0063] S1: neopentyl glycol-modified PET, styrene-butadiene block copolymer and SiO2 used for preparing the surface layer and the bottom layer are mixed uniformly after being dried to remove water, to obtain a surface layer mixture and a bottom layer mixture;

[0064] S2: diol-modified PET, additive and PE-g-GMA used for preparing the intermediate layer are mixed uniformly after being dried to remove water, to obtain an intermediate layer mixture;

[0065] S3: the mixtures of the surface layer, the intermediate layer and the bottom layer are respectively fed into three double-screw extruders for melt plasticization, with a screw diameter of 80 mm, a length-diameter ratio of 28 and a temperature of 230℃; the three extruders are co-extruded in the same die according to the thickness ratio of each layer of 10:80:10 (%) with a die temperature of 240℃; and the extruded castings are obtained (the ratio of the linear speed of the quenching roller to the melt flow-out speed is less than or equal to 3, and the temperature of the quenching roller is controlled at 32℃±2℃);

[0066] S4: the castings of step S3 are sequentially subjected to longitudinal stretching (single-point stretching by infrared heating, longitudinal stretching of the castings at a stretching ratio of 1.21 times at 80℃ after preheating at 85℃, and cooling and setting at 45℃ after longitudinal stretching), transverse stretching (oil heating, stretching conditions: preheating at 100℃, and stretching at a stretching ratio of 4.9 times at 80℃, and cooling and setting at 75℃ after transverse stretching), and traction and winding, to obtain the heat-shrinkable film special for HDPE material containers.

[0067] The diol-modified PET used in this example is obtained from Preparation Example 1, and the additive used is obtained from Preparation Example 2.

[0068] Comparative Example 1

[0069] The HDPE material container special heat shrinkage film is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom, and the surface layer and the bottom layer are prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol modified PET 97.8% and SiO2 2.2%; and the intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol modified PET 90%, acrylate-butadiene-styrene 6% and PE-g-GMA 4%.

[0070] The preparation method of the HDPE material container special heat shrinkage film comprises the following steps:

[0071] S1: neopentyl glycol modified PET, styrene-butadiene block copolymer and SiO2 for preparing the surface layer and the bottom layer are mixed uniformly after being dried to remove water, to obtain a surface layer mixture and a bottom layer mixture;

[0072] S2: diol modified PET, additives and PE-g-GMA for preparing the intermediate layer are mixed uniformly after being dried to remove water, to obtain an intermediate layer mixture;

[0073] S3: the mixtures of the surface layer, the intermediate layer and the bottom layer are respectively fed into three double-screw extruders for melting and plasticizing, the screw diameter is selected to be 80 mm, the length-diameter ratio is 28, and the temperature is 230℃; the three extruders are co-extruded in the same die according to the thickness ratio of each layer of 10:80:10 (%) with a die temperature of 240℃; and the extruded castings (the ratio of the linear speed of the quenching roller rotation to the melt flow-out speed is less than or equal to 3, and the temperature of the quenching roller is controlled at 32℃±2℃);

[0074] S4: the castings of step S3 are sequentially subjected to longitudinal stretching (single-point stretching by infrared heating, the castings are longitudinally stretched at a stretching ratio of 1.12 times at 80℃ after preheating at 85℃, and are cooled and set at 45℃ after longitudinal stretching), transverse stretching (stretching by oil heating, the stretching ratio is 4.6 times at 80℃ after preheating at 100℃, and the castings are cooled and set at 75℃ after transverse stretching), and traction and winding, to obtain the HDPE material container special heat shrinkage film.

[0075] The diol modified PET used in the present example is obtained from Preparation Example 1.

[0076] Comparative Example 2

[0077] The HDPE material container special heat shrinkage film is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom, and the surface layer and the bottom layer are prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol modified PET 95.7% and SiO2 4.3%; and the intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol modified PET 68.5%, additive 28% and PE-g-GMA 3.5%.

[0078] The preparation method of the HDPE material container special heat shrinkage film of the present comparative example comprises the following steps:

[0079] S1: neopentyl glycol modified PET and SiO2 of the surface layer and the bottom layer are mixed uniformly after being dried to remove water, to obtain a surface layer mixture and a bottom layer mixture;

[0080] S2: diol modified PET, additive and PE-g-GMA of the intermediate layer are mixed uniformly after being dried to remove water, to obtain an intermediate layer mixture;

[0081] S3: the mixtures of the surface layer, the intermediate layer and the bottom layer are respectively put into three double-screw extruders for melting and plasticizing, the screw diameter is selected to be 80mm, the length-diameter ratio is 28, and the temperature is 230℃; the three extruders are co-extruded in the same die according to the thickness ratio of each layer of 10:80:10 (%) with a die temperature of 240℃; and the extruded castings (the ratio of the linear speed of the quenching roller rotation to the melt flow-out speed is less than or equal to 3, and the temperature of the quenching roller is controlled at 32℃±2℃);

[0082] S4: the castings of step S3 are sequentially subjected to longitudinal stretching (single-point stretching by infrared heating, the castings are longitudinally stretched, the stretching conditions are: preheated at 85℃, stretched at 80℃ to reach a stretching ratio of 1.11 times, and cooled and set at 45℃ after longitudinal stretching), transverse stretching (oil heating is adopted, the stretching conditions are: preheated at 100℃, stretched at 80℃ to reach a stretching ratio of 4.5 times, and cooled and set at 75℃ after transverse stretching), and traction and winding, to obtain the HDPE material container special heat shrinkage film.

[0083] The diol modified PET used in the present comparative example is obtained from the preparation example 1, and the additive used in the present comparative example is obtained from the preparation example 2.

[0084] Comparative example 3

[0085] A HDPE material container special heat shrinkage film and a preparation method thereof, the specific implementation manner is the same as that of the example 1, and the difference lies in that the additive of the intermediate layer in the present comparative example is obtained from the preparation example 3.

[0086] Comparative example 4

[0087] A kind of HDPE material container special heat shrinkable film and its preparation method, specific implementation same as example 1, the difference is that the additive of middle layer in this comparative example is obtained from preparation example 4.

[0088] Comparative example 5

[0089] A kind of HDPE material container special heat shrinkable film and its preparation method, specific implementation same as example 1, the difference is that the additive of middle layer in this comparative example is obtained from preparation example 5.

[0090] Comparative example 6

[0091] A kind of HDPE material container special heat shrinkable film, from top to bottom, it is composed of surface layer, middle layer and bottom layer in turn, the surface layer and bottom layer are prepared and contain the following raw materials by 100% of mass percentage: neopentyl glycol modified PET 97.8% and SiO2 2.2%;The middle layer is prepared and contains the following raw materials by 100% of mass percentage: diol modified PET 95.7% and PE-g-GMA 4.3%.

[0092] The preparation method of HDPE material container special heat shrinkable film in this comparative example, comprising the following steps:

[0093] S1: neopentyl glycol modified PET, styrene-diene block copolymer and SiO2 for preparing surface layer and bottom layer are mixed uniformly after being dried to remove moisture, to obtain surface layer mixture and bottom layer mixture;

[0094] S2: diol modified PET, acrylate-diene-styrene and PE-g-GMA for preparing middle layer are mixed uniformly after being dried to remove moisture, to obtain middle layer mixture;

[0095] S3: the above-mentioned surface layer, middle layer and bottom layer are respectively put into three double-screw extruders, screw diameter is selected as 80mm, length-diameter ratio is 28, temperature is 230℃;Three extruders are co-extruded in the same die according to the thickness ratio of each layer of 10:80:10 (%),Die temperature is 240℃;Extrusion casting piece (control the ratio of line speed of quenching roller rotation and melt flow speed less than or equal to 3, the temperature of quenching roller is controlled at 32℃±2℃);

[0096] S4: the casting piece of step S3 is sequentially stretched longitudinally (single point stretching is carried out by infrared heating, the casting piece is stretched longitudinally, the stretching conditions are: after preheating at 85℃, it is stretched at 80℃ to reach 1.12 times, after longitudinal stretching, it is cooled and shaped at 45℃), transversely stretched (using oil heating, the stretching conditions are: after preheating at 100℃, it is stretched at 80℃ to reach 4.6 times, after transverse stretching, it is cooled and shaped at 75℃), and traction winding, to obtain the HDPE material container special heat shrinkable film.

[0097] The diol-modified PET used in the present comparative example was obtained from Preparation Example 1.

[0098] Comparative Example 7

[0099] A heat-shrinkable film for HDPE material container, which is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom, wherein the surface layer and the bottom layer are both prepared from the following raw materials in the amount of 100% by mass: neopentyl glycol-modified PET 88%, styrene-butadiene block copolymer 8% and SiO2 4%; and the intermediate layer is prepared from the following raw materials in the amount of 100% by mass: diol-modified PET 71% and additives 29%.

[0100] The preparation method of the heat-shrinkable film for HDPE material container in the present comparative example comprises the following steps:

[0101] S1: dry and remove moisture from the neopentyl glycol-modified PET, styrene-butadiene block copolymer and SiO2 used for preparing the surface layer and the bottom layer, and then mix them uniformly to obtain a surface layer mixture and a bottom layer mixture;

[0102] S2: dry and remove moisture from the diol-modified PET and additives used for preparing the intermediate layer, and then mix them uniformly to obtain an intermediate layer mixture;

[0103] S3: melt and plasticize each of the mixtures of the surface layer, the intermediate layer and the bottom layer in three double-screw extruders, with the screw diameter being 80 mm, the length-diameter ratio being 28 and the temperature being 230℃; co-extrude the three extruders in the same die according to the thickness ratio of each layer of 10:80:10 (%) with the die temperature being 240℃; and extrude the cast sheet (control the ratio of the linear speed of the quenching roller rotation to the melt flow-out speed to be less than or equal to 3, and control the temperature of the quenching roller to be 32℃±2℃);

[0104] S4: sequentially perform longitudinal stretching (single-point stretching by infrared heating, longitudinally stretch the cast sheet at 85℃ after preheating, and then at 80℃ to make the stretching ratio reach 1.11 times, cool and set at 45℃ after longitudinal stretching), transverse stretching (oil heating, stretching conditions: preheat at 100℃, then at 80℃ to make the stretching ratio reach 4.5 times, cool and set at 75℃ after transverse stretching) and traction winding on the cast sheet of step S3, to obtain the heat-shrinkable film for HDPE material container.

[0105] The diol-modified PET used in the present comparative example was obtained from Preparation Example 1, and the additives used were obtained from Preparation Example 2.

[0106] Comparative Example 8

[0107] A kind of special heat-shrinkable film for HDPE container and its preparation method, specific embodiment is same as example 1, the difference is that in the present comparative example, intermediate layer is replaced by PETG in equal amount instead of diol modified PET.

[0108] Performance test

[0109] The thickness, tensile strength, elongation at break, heat shrinkage, haze, transparency, light transmittance, thermal expansion coefficient, wetting tension, shrinkage force and interlayer bonding force indexes of the special heat-shrinkable film for HDPE container prepared in examples 1-2 and comparative examples 1-8 are tested respectively; wherein the tensile strength and elongation at break are tested according to GB / T 1040.3-2006 method; the heat shrinkage is tested according to BB / T0070-2014 method; the light transmittance and haze are tested according to GB / T 2410-2008 method; the linear thermal expansion coefficient is tested according to ISO 11359-2 "Plastics Thermal Mechanical Analysis (TMA) Part 2: Determination of Linear Thermal Expansion Coefficient and Glass Transition Temperature"; the wetting tension is tested according to GB / T 14216-2008 / ISO 8296:2003 method; the shrinkage force is tested according to GB / T 34848-2017 "Test Method for Shrinkage Performance of Heat-shrinkable Film"; the interlayer bonding force testing method is as follows: take the film sample, cut the film into 15mm×100mm sample in TD direction of the film, fold the film at the middle position of the sample several times, tear the surface layer and core layer to separate the two layers, and then clamp the two layers on the electronic tensile testing machine respectively to test the tensile property; when the surface layer and core layer of the film are completely separated, the force value displayed by the sensor of the equipment is greater than 1N, which is determined as high interlayer bonding force; when the surface layer and core layer of the film are completely separated, the force value displayed by the sensor of the equipment is less than or equal to 1N, which is determined as low interlayer bonding force. The specific test results are shown in Table 1.

[0110] Table 1

[0111]

[0112] From the data in Table 1, it can be seen that the heat-shrinkable films disclosed in examples 1-2 and comparative examples 1 of the present application all have excellent comprehensive performance.

[0113] From the comparison between comparative example 2 and example 1, it can be seen that when no styrene-butadiene block copolymer is added to the surface layer and the bottom layer, the interlayer bonding force between the intermediate layer and the surface layer is poor due to the difference in polarity, and the problem of layer sealing is prone to occur.

[0114] From the comparison between comparative example 3 and example 1, it can be seen that when no triallyl isocyanurate is added during the preparation of the additive of the intermediate layer, the crosslinking effect may be affected during the high-temperature blending and melting process, which may result in the failure to form uniform closed pores, and the pore structure of the foaming cannot be uniformly controlled, the pore structure is too large, and the overall haze of the film is large.

[0115] From the comparison of Comparative Example 4 and Example 1, it can be seen that when the additive of the intermediate layer is prepared without adding azodicarbonamide, the bubble and microporous structure are insufficient during high-temperature blending and melting, which further affects the matching of the thermal expansion coefficient of the matrix and the HDPE, and the label "loose" problem may exist after the shrinkage of the heat-shrinkable film, affecting the packaging effect.

[0116] From the comparison of Comparative Example 5 and Example 1, it can be seen that when the additive of the intermediate layer is prepared without adding HDPE, the polarity difference between the heat-shrinkable film and the HDPE material container is large, and the expansion coefficient cannot be improved to completely close to the HDPE container, and the label "loose" problem may exist.

[0117] From the comparison of Comparative Example 6 and Example 1, it can be seen that when the intermediate layer does not add acrylate-butadiene-styrene, the distribution of the pore structure of the intermediate layer may be affected, and the insufficient olefin component leads to the decrease of the polarity matching with the HDPE material container, and the "loose" problem occurs.

[0118] From the comparison of Comparative Example 7 and Example 1, it can be seen that when the intermediate layer does not add PE-g-GMA, the heat-shrinkable film appears white and mist due to the influence of compatibility and interface distribution, which greatly affects the transparency and use effect of the heat-shrinkable film.

[0119] From the comparison of Comparative Example 8 and Example 1, it can be seen that when the intermediate layer is replaced by PETG instead of diol-modified PET, the overall shrinkage temperature of the heat-shrinkable film may be too high, and the overall shrinkage force is too high, which cannot meet the requirements of the HDPE container material for high shrinkage rate and low shrinkage force at low temperature, and the HDPE material container is squeezed and deformed by the label shrinkage.

[0120] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A heat shrinkable film for HDPE containers, characterized in that, The HDPE material container special heat shrinkable film is composed of a surface layer, an intermediate layer and a bottom layer from top to bottom, and the surface layer and the bottom layer are prepared from the following raw materials in a mass percentage of 100%: neopentyl glycol modified PET 88-99.2%, toughening agent 0-8% and anti-blocking agent 0.8-4%; the intermediate layer is prepared from the following raw materials in a mass percentage of 100%: diol modified PET 68.5-91.2%, additive 8-28% and reactive compatibilizer 1.3-3.5%; wherein the additive is a mixture of triallyl isocyanurate, azodicarboxamide and HDPE; The toughening agent is a styrene-butadiene block copolymer or an acrylate-butadiene-styrene; The diol modified PET is a neopentyl glycol and hexanediol co-modified PET; The additive contains the following raw materials in a mass percentage of 100%: 12-14% triallyl isocyanurate, 16-18% azodicarboxamide and 68-72% HDPE.

2. The heat shrinkable film for HDPE containers according to claim 1, wherein The thickness of the surface layer, the intermediate layer and the bottom layer accounts for 5-15%, 70-90% and 5-15%, respectively, in a thickness ratio of 100%.

3. The heat shrinkable film for HDPE containers according to claim 1, wherein The anti-blocking agent is SiO2.

4. The heat shrinkable film according to claim 1, wherein The glass transition temperature of the diol modified PET is 63-72℃.

5. The heat shrinkable film according to claim 1, wherein The reactive compatibilizer is PE-g-GMA.

6. A method for preparing a heat-shrinkable film for a HDPE container according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1: uniformly mix the neopentyl glycol modified PET, the toughening agent and the functional master batch for preparing the surface layer and the bottom layer, respectively, to obtain a surface layer mixture and a bottom layer mixture; S2: uniformly mix the diol modified PET, the additive and the reactive compatibilizer for preparing the intermediate layer to obtain an intermediate layer mixture; S3: melt plasticize, melt extrude and cool form the mixtures of the surface layer, the intermediate layer and the bottom layer according to the thickness ratio of each layer to obtain a cast sheet; S4: sequentially perform longitudinal stretching, transverse stretching and traction winding on the cast sheet of step S3 to obtain the HDPE material container special heat shrinkable film.

7. The method for preparing the heat-shrinkable film for HDPE containers according to claim 6, characterized in that, The thickness of the HDPE material container special heat shrinkable film is 30-100μm.

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