A polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels and its preparation method

Abstract

A polyester heat-shrinkable film capable of replacing PVC labels with high shrinkage at low temperature and a preparation method thereof belongs to the technical field of polymer packaging materials. The polyester heat-shrinkable film capable of replacing PVC labels with high shrinkage at low temperature and a preparation method thereof comprises raw materials of modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening lubricant. The obtained polyester heat-shrinkable film has a thickness of 30.0-100.6 μm, a TD tensile strength of 127-153 MPa, an MD tensile strength of 33-41 MPa, a TD elongation of 26-34%, an MD elongation of 220-313%, a TD shrinkage of 45-56% (70°C, 10s) and 68-80% (100°C, 10s), an MD shrinkage of 1-10% (70°C, 10s) and 1-14% (100°C, 10s), a haze of 3.6-5.8%, and a dynamic friction coefficient of 0.30-0.53 μs.

Description

Technical Field

[0001] The invention relates to a polyester heat shrinkable film with low temperature and high shrinkage capable of replacing a PVC label and a preparation method thereof, belonging to the technical field of polymer packaging materials. Background Art

[0002] Walking into any supermarket, you'll notice increasingly attractive packaging on the shelves, especially in the beverage section. Integrated packaging labels are prevalent and increasingly sleek. These labels, collectively known as heat-shrink labels, are specialized film labels printed with ink on plastic film or tubing.

[0003] From a market perspective, there are currently three main types of plastic films used for heat shrink labels: polyvinyl chloride (PVC), polyester (primarily PET), and oriented polystyrene (OPS). Of these three materials, PVC film has the lowest shrinkage temperature, generally beginning to shrink horizontally at around 53°C and longitudinally at 60°C. Polyester heat shrink film, on the other hand, generally has a higher shrinkage temperature, with shrinkage rates below 70°C, typically less than 40%. The heat shrink process typically uses temperatures of 80-90°C or even higher, making it difficult to use for packaging labels for heat-sensitive products. While OPS has many advantages, its cost is the highest of the three materials, and its corresponding market share is also the lowest. For packaged materials that are heat-sensitive, such as milk powder, protein, beverages, liquid yogurt containing probiotics, etc., the high temperature during the heat shrinkage process will damage the heat-sensitive materials, which can easily lead to product deterioration or shortened shelf life. In consideration of cost and heat shrinkage temperature, PVC or polyester materials can only be selected. However, the biggest disadvantage of PVC is that it cannot be recycled and contains chlorine, which poses a great environmental risk. Especially in the EU countries, PVC heat shrink film has been completely banned. Therefore, the development of low-temperature, high-shrinkage polyester heat shrink film that can replace PVC material, especially polyester heat shrink film that can achieve high shrinkage at 70℃ or even below 70℃, is a research direction with great market prospects.

[0004] To achieve high shrinkage at low temperatures, commercialized products are currently primarily provided by Eastman. Eastman developed polyester heat-shrinkable films using diethylene glycol (DEG) copolyester as a modified resin as early as 2000, which can reduce the heat shrinkage temperature to around 70°C. However, there is an upper limit on the amount of DEG copolyester-modified polyester resin added when physically blended with other polyester resins to prepare polyester heat-shrinkable films. When the mass fraction of DEG in the polyester mixture exceeds 7.5%, the heat-shrinkable film generally becomes brittle. Therefore, additional toughening methods are required to improve the brittleness caused by DEG copolymerization modification. Eastman subsequently developed a toughening agent called AAPE to improve the toughness of the DEG copolymer resin and polyester resin mixture system. Using AAPE toughening technology, the DEG copolymer modified polyester heat shrinkable film can achieve a minimum heat shrinkage temperature below 70°C. However, there is currently no report of large-scale commercialization of low-temperature, high-shrinkage polyester heat shrinkable film at 70~80°C or even below 70°C in China. Therefore, there is an urgent need to develop low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC material to fill the gap in the domestic market segment in this field.

[0005] Chinese patent CN102285184A discloses a low-temperature, high-shrinkage polyester film for bottle labels and its preparation method. The film comprises a shrink base layer and two heat-shrink layers composited on the upper and lower surfaces of the shrink base layer. The film is made from nano-SiO2-modified amorphous polyester and graft-modified copolyester as the raw materials for the heat-shrink layer, and from modified low-melting-point PET polymer and low-melting-point PTT polymer as the raw materials for the shrink base layer. These are melted separately and then co-extruded. After preheating, they are stretched longitudinally and transversely, then heat-set and subjected to secondary stretching. The resulting polyester heat-shrink film requires a temperature of 90°C to achieve a shrinkage of more than 75%, and the heat-shrinkage temperature remains at 90°C.

[0006] From the above, we can see that when polyester heat shrinkable film is used as packaging label, it still has the disadvantage of too high heat shrinkage temperature, which is difficult to compare with PVC material in heat shrinkage temperature. Therefore, the development of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels has very important practical value and realistic significance. Summary of the Invention

[0007] In view of the shortcomings of the above-mentioned prior art, the present invention provides a polyester heat shrinkable film with high shrinkage at low temperature and capable of replacing PVC labels, and a preparation method thereof, to achieve the following invention objectives: to prepare a polyester heat shrinkable film with a shrinkage rate of more than 40% at 70°C and a shrinkage rate of more than 65% at 100°C and excellent mechanical properties that can replace PVC labels.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0009] A polyester heat shrinkable film with high shrinkage at low temperature and capable of replacing PVC labels and a preparation method thereof, wherein the raw materials of the polyester heat shrinkable film with high shrinkage at low temperature and capable of replacing PVC labels include modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening lubricant;

[0010] The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels is 70-150 parts by weight of modified polyethylene terephthalate, 10-35 parts of polybutylene terephthalate, 8-20 parts of reinforcing and toughening agent, and 1-3 parts of opening slip agent.

[0011] The opening lubricant is silicon dioxide with a particle size of 1 to 5 μm;

[0012] The following are further improvements to the above technical solution:

[0013] Step 1, preparation of modified polyethylene terephthalate

[0014] Adding terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into a reaction kettle, passing nitrogen to maintain the reaction pressure, and heating to the esterification reaction temperature while maintaining the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stopping the nitrogen passing, turning on the vacuum pump to evacuate the kettle to a first vacuum degree, heating to a pre-polycondensation temperature to carry out a pre-polycondensation reaction, and continuing to evacuate to a second vacuum degree, while simultaneously heating to a high vacuum polycondensation reaction temperature, increasing the stirring rate to the second stirring rate, and after the high vacuum polycondensation reaction is completed, passing nitrogen to pressurize the material, water-cooling, pelletizing, and drying to obtain modified polyethylene terephthalate;

[0015] The hydroxyl-terminated compound is any one of ricinoleic acid, monoricinoleic acid glyceride, 2-methyl-2,4-pentanediol, 3-hydroxycyclopentanecarboxylic acid, 4-hydroxymethyl-1-cyclohexanecarboxylic acid, azelaic acid, dodecanedioic acid, and adipic acid, or a mixture of any two of them in any mass ratio, or a mixture of any two or more of them in any mass ratio;

[0016] The mass ratio of terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide is 60-150:50-140:9-16:0.2-0.5;

[0017] The reaction pressure is 0.01-0.02 MPa;

[0018] The first stirring rate is 40 to 65 rpm;

[0019] The esterification reaction temperature is 180-235°C;

[0020] The esterification reaction is completed, and the esterification reaction time is 4 to 6 hours;

[0021] The first vacuum degree is 100~130Pa;

[0022] The pre-condensation temperature is 240-255°C;

[0023] The pre-polycondensation reaction is completed, and the pre-polycondensation reaction time is 1 to 2 hours;

[0024] The second vacuum degree is 30~60Pa;

[0025] The high vacuum polycondensation reaction temperature is 270-280°C;

[0026] The second stirring rate is 70-100 rpm;

[0027] The high vacuum polycondensation reaction is completed, and the high vacuum polycondensation reaction time is 2.5~4h.

[0028] Step 2: Preparation of reinforcing and toughening agent

[0029] An unsaturated organosilicon compound and an organic solvent are added to a reaction kettle, stirred and dissolved, and then heated to a constant temperature under condensation reflux. A mixture of glycidyl methacrylate and an initiator is then added dropwise. After the addition is complete, the reaction is continued at a constant temperature until all the unsaturated organosilicon reacts. The reaction is then cooled to room temperature, acetone is added to precipitate the precipitate, and the precipitate is filtered, washed with alcohol, and dried to obtain a reinforcing and toughening agent.

[0030] The unsaturated organosilicon compound is one of vinyl MQ silicone resin and vinyl-terminated silicone oil;

[0031] The vinyl MQ silicone resin has a viscosity of 4000-9000 mPa·s at 25° C. and a vinyl content of 2-4 wt %.

[0032] The vinyl-terminated silicone oil has a viscosity of 500-3000 mPa·s at 25° C. and a vinyl content of 0.2-0.5 wt %.

[0033] The organic solvent is one of toluene and xylene;

[0034] The mixed solution of glycidyl methacrylate and initiator is prepared by mixing glycidyl methacrylate and initiator, and the mass ratio of glycidyl methacrylate to initiator is 80-150:3;

[0035] The initiator is one of benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile;

[0036] The mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and the initiator, and acetone is 20-60:190-400:8-18:100-230;

[0037] The stirring dissolution has a stirring rate of 100 to 400 rpm;

[0038] The mixture of glycidyl methacrylate and initiator is added dropwise at a rate of 1 to 20 g / min;

[0039] The reaction temperature is 70-95°C;

[0040] The alcohol washing is performed 3 times with anhydrous ethanol, and the amount of anhydrous ethanol used in each washing is equal to the mass of the washed solid;

[0041] The drying temperature is 60-85° C. and the drying time is 4-9 hours.

[0042] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0043] (1) Melt extrusion

[0044] According to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, all raw materials are dried at 120-140° C. for 3-5 hours, then placed in a dry environment and cooled to room temperature, and then the raw materials are mixed according to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels in parts by weight, and then put into a twin-screw extruder, and the heating zones of the twin-screw extruder are heated to 255-280° C., so that the mixed raw materials are melted and extruded, and the melt extruded from the die head is cooled and solidified on the surface of the casting roller to form a cast sheet;

[0045] (2) Stretching

[0046] The stretching comprises stretching the cast sheet using one of a uniaxial stretching process and a biaxial stretching process to obtain a base film;

[0047] The unidirectional stretching process is one of longitudinal stretching and transverse stretching;

[0048] The biaxial stretching process is performed by first performing longitudinal stretching and then transverse stretching;

[0049] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film at a stretching temperature of 80-105°C, a ratio of 1-2.5:1, and a tensile strength of 22-86 MPa; the longitudinally stretched base film is heat-set on a surface of a set of cooling rollers at a setting temperature of 70-140°C and a setting time of 2-6 seconds;

[0050] The transverse stretching is carried out on a transverse stretching machine at a stretching temperature of 80-135°C, a transverse stretching ratio of 2.5-5.5:1, and a tensile strength of 190-205 MPa. The stretched base film is heat-set and then cooled at a setting temperature of 55-85°C and a setting time of 1.5-4 seconds.

[0051] (3) Traction, trimming and winding

[0052] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film, obtaining a large roll of low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC labels.

[0053] Compared with the prior art, the present invention achieves the following beneficial effects:

[0054] 1. The present invention uses hydroxyl-terminated compounds with asymmetric or long molecular chains, wherein the hydroxyl-terminated compounds with asymmetric molecular chains mainly include oleic acid, monoricinoleic acid glyceride, 2-methyl-2,4-pentanediol, 3-hydroxycyclopentanecarboxylic acid, and 4-hydroxymethyl-1-cyclohexanecarboxylic acid; the long-chain hydroxyl-terminated compounds include azelaic acid, dodecanedioic acid, and adipic acid, to modify and copolymerize polyethylene terephthalate. After these substances form copolyesters with terephthalic acid and ethylene glycol, the regularity of the polymer chain is deteriorated compared with pure polyethylene terephthalate, which will affect the crystallization properties of polyethylene terephthalate to a certain extent, thereby reducing the glass transition temperature of pure polyethylene terephthalate. Therefore, the modified polyethylene terephthalate has a lower glass transition temperature than pure polyethylene terephthalate, and is subsequently more susceptible to thermal deformation at low temperatures, ultimately exhibiting the characteristics of high shrinkage at low temperatures;

[0055] 2. Although the modified polyethylene terephthalate prepared by the present invention has the characteristics of high shrinkage at low temperature, the decline of its crystallization performance will have a serious negative impact on the mechanical properties of the final heat shrinkable film. In order to avoid a significant decrease in mechanical properties, the present invention uses an unsaturated organic silicon compound, that is, vinyl MQ silicone resin or vinyl-terminated silicone oil, and glycidyl methacrylate to react with a free radical under the action of an initiator, so that the double bond at the end of the vinyl MQ silicone resin or vinyl-terminated silicone oil is converted into an epoxy group. This has two main purposes. First, the compatibility of organic silicon and polyester is not very good. After being capped with epoxy groups, the polarity of the short chain compound formed by organic silicon and glycidyl methacrylate will increase, thereby promoting the The compatibility of the silicone molecular chain and the polyester polymer chain allows the silicone molecular chain to entangle with the polyester polymer chain segments. Because the silicone molecular chain has excellent elasticity, the entanglement of the silicone molecular chain segments with the polyester molecular segments can increase the toughness of the polyester resin matrix and improve the elongation at break of the polyester heat-shrinkable film. Secondly, the end-capped epoxy functional group can react with the hydroxyl or carboxyl group at the end of the modified polyethylene terephthalate polymer chain during the melt extrusion step, causing a certain degree of cross-linking reaction in the polyester polymer chain segments. This will greatly enhance the tensile strength of the polyester polymer resin matrix. Therefore, the short-chain compound formed by the silicone and glycidyl methacrylate can play a role in strengthening and toughening the polyester film.

[0056] 3. The low-temperature, high-shrinkage polyester heat-shrinkable film obtained by the present invention can replace PVC labels, has a thickness of 30.0-100.6 μm, a TD tensile strength of 127-153 MPa, an MD tensile strength of 33-41 MPa, a TD elongation of 26-34%, an MD elongation of 220-313%, a TD shrinkage of 45-56% (70°C, 10s) and 68-80% (100°C, 10s), an MD shrinkage of 1-10% (70°C, 10s) and 1-14% (100°C, 10s), a haze of 3.6-5.8%, and a dynamic friction coefficient of 0.30-0.53 μs. DETAILED DESCRIPTION

[0057] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0058] Example 1: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0059] Step 1, preparation of modified polyethylene terephthalate

[0060] Adding terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into a reaction kettle, passing nitrogen to maintain the reaction pressure, and heating to the esterification reaction temperature while maintaining the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stopping the nitrogen passing, turning on the vacuum pump to evacuate the kettle to a first vacuum degree, heating to a pre-polycondensation temperature to carry out a pre-polycondensation reaction, and continuing to evacuate to a second vacuum degree, while simultaneously heating to a high vacuum polycondensation reaction temperature, increasing the stirring rate to the second stirring rate, and after the high vacuum polycondensation reaction is completed, passing nitrogen to pressurize the material, water-cooling, pelletizing, and drying to obtain modified polyethylene terephthalate;

[0061] The hydroxyl-terminated compound is ricinoleic acid;

[0062] The mass ratio of terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide is 100:90:11:0.4;

[0063] The reaction pressure is 0.016 MPa;

[0064] The first stirring rate is 50 rpm;

[0065] The esterification reaction temperature is 200°C;

[0066] The esterification reaction is completed, and the esterification reaction time is 5h;

[0067] The first vacuum degree is 110 Pa;

[0068] The pre-condensation temperature is 245°C;

[0069] The pre-polycondensation reaction is completed, and the pre-polycondensation reaction time is 1.6h;

[0070] The second vacuum degree is 40Pa;

[0071] The high vacuum polycondensation reaction temperature is 276°C;

[0072] The second stirring rate is 80 rpm;

[0073] The high vacuum polycondensation reaction was completed, and the high vacuum polycondensation reaction time was 3 hours.

[0074] Step 2: Preparation of reinforcing and toughening agent

[0075] An unsaturated organosilicon compound and an organic solvent are added to a reaction kettle, stirred and dissolved, and then heated to a constant temperature under condensation reflux. A mixture of glycidyl methacrylate and an initiator is then added dropwise. After the addition is complete, the reaction is continued at a constant temperature until all the unsaturated organosilicon reacts. The reaction is then cooled to room temperature, acetone is added to precipitate the precipitate, and the precipitate is filtered, washed with alcohol, and dried to obtain a reinforcing and toughening agent.

[0076] The unsaturated organosilicon compound is vinyl MQ silicone resin;

[0077] The vinyl MQ silicone resin has a viscosity of 4000 mPa·s at 25° C. and a vinyl content of 2 wt %.

[0078] The organic solvent is toluene;

[0079] The mixed solution of glycidyl methacrylate and initiator is prepared by mixing glycidyl methacrylate and initiator, and the mass ratio of glycidyl methacrylate to initiator is 120:3;

[0080] The initiator is benzoyl peroxide;

[0081] The mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and the initiator, and acetone is 30:300:10:160;

[0082] The stirring dissolution is performed at a stirring rate of 200 rpm;

[0083] The mixture of glycidyl methacrylate and initiator is added dropwise at a rate of 15 g / min;

[0084] The reaction temperature is 80°C;

[0085] The alcohol washing is performed 3 times with anhydrous ethanol, and the amount of anhydrous ethanol used in each washing is equal to the mass of the washed solid;

[0086] The drying temperature is 70° C. and the drying time is 6 hours.

[0087] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0088] (1) Melt extrusion

[0089] According to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, all raw materials are dried at 135° C. for 4 hours, then placed in a dry environment and cooled to room temperature. Then, according to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels in parts by weight, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are heated to 270° C., and the mixed raw materials are melted and extruded. The melt extruded from the die head is cooled and solidified on the surface of the casting roller to form a cast sheet.

[0090] The raw materials of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels include modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening slip agent;

[0091] The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels is 120 parts by weight of modified polyethylene terephthalate, 20 parts of polybutylene terephthalate, 12 parts of reinforcing and toughening agent, and 2 parts of opening slip agent;

[0092] The opening lubricant is silicon dioxide with a particle size of 4 μm;

[0093] (2) Stretching

[0094] The stretching is to apply a biaxial stretching process to the cast sheet;

[0095] The biaxial stretching process is performed by first performing longitudinal stretching and then transverse stretching;

[0096] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film at a stretching temperature of 100° C., a ratio of 2:1, and a tensile strength of 70 MPa; the longitudinally stretched base film is heat-set on a surface of a set of cooling rollers at a setting temperature of 120° C. and a setting time of 4 seconds;

[0097] The transverse stretching is carried out on a transverse stretching machine at a stretching temperature of 100°C, a transverse stretching ratio of 3:1, and a tensile strength of 200 MPa. The stretched base film is heat-set and then cooled at a setting temperature of 70°C and a setting time of 3 seconds.

[0098] (3) Traction, trimming and winding

[0099] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film, obtaining a large roll of low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC labels.

[0100] Example 2: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0101] Step 1, preparation of modified polyethylene terephthalate

[0102] Adding terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into a reaction kettle, passing nitrogen to maintain the reaction pressure, and heating to the esterification reaction temperature while maintaining the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stopping the nitrogen passing, turning on the vacuum pump to evacuate the kettle to a first vacuum degree, heating to a pre-polycondensation temperature to carry out a pre-polycondensation reaction, and continuing to evacuate to a second vacuum degree, while simultaneously heating to a high vacuum polycondensation reaction temperature, increasing the stirring rate to the second stirring rate, and after the high vacuum polycondensation reaction is completed, passing nitrogen to pressurize the material, water-cooling, pelletizing, and drying to obtain modified polyethylene terephthalate;

[0103] The hydroxyl-terminated compound is glyceryl monoricinoleate;

[0104] The mass ratio of the terephthalic acid, ethylene glycol, hydroxyl-terminated compound, and antimony trioxide is 60:50:9:0.2;

[0105] The reaction pressure is 0.01 MPa;

[0106] The first stirring rate is 40 rpm;

[0107] The esterification reaction temperature is 180°C;

[0108] The esterification reaction is completed, and the esterification reaction time is 4 hours;

[0109] The first vacuum degree is 100 Pa;

[0110] The pre-condensation temperature is 240°C;

[0111] The pre-polycondensation reaction is completed, and the pre-polycondensation reaction time is 1 hour;

[0112] The second vacuum degree is 30 Pa;

[0113] The high vacuum polycondensation reaction temperature is 270°C;

[0114] The second stirring rate is 70 rpm;

[0115] The high vacuum polycondensation reaction was completed, and the high vacuum polycondensation reaction time was 2.5 h.

[0116] Step 2: Preparation of reinforcing and toughening agent

[0117] An unsaturated organosilicon compound and an organic solvent are added to a reaction kettle, stirred and dissolved, and then heated to a constant temperature under condensation reflux. A mixture of glycidyl methacrylate and an initiator is then added dropwise. After the addition is complete, the reaction is continued at a constant temperature until all the unsaturated organosilicon reacts. The reaction is then cooled to room temperature, acetone is added to precipitate the precipitate, and the precipitate is filtered, washed with alcohol, and dried to obtain a reinforcing and toughening agent.

[0118] The unsaturated organosilicon compound is vinyl MQ silicone resin;

[0119] The vinyl MQ silicone resin has a viscosity of 9000 mPa·s at 25° C. and a vinyl content of 4 wt %.

[0120] The organic solvent is xylene;

[0121] The mixed solution of glycidyl methacrylate and initiator is prepared by mixing glycidyl methacrylate and initiator, and the mass ratio of glycidyl methacrylate to initiator is 80:3;

[0122] The initiator is di-tert-butyl peroxide;

[0123] The mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and the initiator, and acetone is 20:190:8:100;

[0124] The stirring dissolution has a stirring rate of 100 rpm;

[0125] The mixture of glycidyl methacrylate and initiator is added dropwise at a rate of 1 g / min;

[0126] The reaction temperature is 70°C;

[0127] The alcohol washing is performed 3 times with anhydrous ethanol, and the amount of anhydrous ethanol used in each washing is equal to the mass of the washed solid;

[0128] The drying temperature is 60° C. and the drying time is 4 hours.

[0129] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0130] (1) Melt extrusion

[0131] According to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, all raw materials are dried at 120° C. for 3 hours, then placed in a dry environment and cooled to room temperature. Then, according to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels in parts by weight, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are heated to 255° C., and the mixed raw materials are melted and extruded. The melt extruded from the die head is cooled and solidified on the surface of the casting roller to form a cast sheet.

[0132] The raw materials of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels include modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening slip agent;

[0133] The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels is 70 parts by weight of modified polyethylene terephthalate, 10 parts of polybutylene terephthalate, 8 parts of reinforcing and toughening agent, and 1 part of opening slip agent;

[0134] The opening lubricant is silicon dioxide with a particle size of 1 μm;

[0135] (2) Stretching

[0136] The stretching comprises stretching the cast sheet using a biaxial stretching process to obtain a base film;

[0137] The biaxial stretching process is performed by first performing longitudinal stretching and then transverse stretching;

[0138] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film at a stretching temperature of 80°C, a ratio of 1:1, and a tensile strength of 22 MPa; the longitudinally stretched base film is heat-set on a surface of a set of cooling rollers at a setting temperature of 70°C and a setting time of 2 seconds;

[0139] The transverse stretching is carried out on a transverse stretching machine at a stretching temperature of 80°C, a transverse stretching ratio of 2.5:1, and a tensile strength of 190 MPa. The stretched base film is heat-set and then cooled at a setting temperature of 55°C and a setting time of 1.5 seconds.

[0140] (3) Traction, trimming and winding

[0141] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film, obtaining a large roll of low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC labels.

[0142] Example 3: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0143] Step 1, preparation of modified polyethylene terephthalate

[0144] Adding terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into a reaction kettle, passing nitrogen to maintain the reaction pressure, and heating to the esterification reaction temperature while maintaining the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stopping the nitrogen passing, turning on the vacuum pump to evacuate the kettle to a first vacuum degree, heating to a pre-polycondensation temperature to carry out a pre-polycondensation reaction, and continuing to evacuate to a second vacuum degree, while simultaneously heating to a high vacuum polycondensation reaction temperature, increasing the stirring rate to the second stirring rate, and after the high vacuum polycondensation reaction is completed, passing nitrogen to pressurize the material, water-cooling, pelletizing, and drying to obtain modified polyethylene terephthalate;

[0145] The hydroxyl-terminated compound is 2-methyl-2,4-pentanediol;

[0146] The mass ratio of the terephthalic acid, ethylene glycol, hydroxyl-terminated compound, and antimony trioxide is 150:140:16:0.5;

[0147] The reaction pressure is 0.02 MPa;

[0148] The first stirring rate is 65 rpm;

[0149] The esterification reaction temperature is 235°C;

[0150] The esterification reaction is completed, and the esterification reaction time is 6 hours;

[0151] The first vacuum degree is 130 Pa;

[0152] The pre-condensation temperature is 255°C;

[0153] The pre-polycondensation reaction is completed, and the pre-polycondensation reaction time is 2h;

[0154] The second vacuum degree is 60Pa;

[0155] The high vacuum polycondensation reaction temperature is 280°C;

[0156] The second stirring rate is 100 rpm;

[0157] The high vacuum polycondensation reaction was completed, and the high vacuum polycondensation reaction time was 4 hours.

[0158] Step 2: Preparation of reinforcing and toughening agent

[0159] An unsaturated organosilicon compound and an organic solvent are added to a reaction kettle, stirred and dissolved, and then heated to a constant temperature under condensation reflux. A mixture of glycidyl methacrylate and an initiator is then added dropwise. After the addition is complete, the reaction is continued at a constant temperature until all the unsaturated organosilicon reacts. The reaction is then cooled to room temperature, acetone is added to precipitate the precipitate, and the precipitate is filtered, washed with alcohol, and dried to obtain a reinforcing and toughening agent.

[0160] The unsaturated organosilicon compound is vinyl-terminated silicone oil;

[0161] The viscosity of the vinyl-terminated silicone oil at 25° C. is 500 mPa·s, and the vinyl content is 0.2 wt %;

[0162] The organic solvent is toluene;

[0163] The mixed solution of glycidyl methacrylate and initiator is prepared by mixing glycidyl methacrylate and initiator, and the mass ratio of glycidyl methacrylate to initiator is 150:3;

[0164] The initiator is azobisisobutyronitrile;

[0165] The mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and the initiator, and acetone is 60:400:18:230;

[0166] The stirring dissolution is performed at a stirring rate of 400 rpm;

[0167] The mixture of glycidyl methacrylate and initiator is added dropwise at a rate of 20 g / min;

[0168] The reaction temperature is 95°C;

[0169] The alcohol washing is performed 3 times with anhydrous ethanol, and the amount of anhydrous ethanol used in each washing is equal to the mass of the washed solid;

[0170] The drying temperature is 85° C. and the drying time is 9 hours.

[0171] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0172] (1) Melt extrusion

[0173] According to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, all raw materials are dried at 140° C. for 5 hours, then placed in a dry environment and cooled to room temperature. Then, according to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels in parts by weight, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are heated to 280° C., and the mixed raw materials are melted and extruded. The melt extruded from the die head is cooled and solidified on the surface of the casting roller to form a cast sheet.

[0174] The raw materials of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels include modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, an opening lubricant, and a filler;

[0175] The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels is 150 parts by weight of modified polyethylene terephthalate, 35 parts of polybutylene terephthalate, 20 parts of reinforcing and toughening agent, and 3 parts of opening slip agent.

[0176] The opening lubricant is silicon dioxide with a particle size of 5 μm;

[0177] (2) Stretching

[0178] The stretching is to apply a biaxial stretching process to the cast sheet;

[0179] The biaxial stretching process is performed by first performing longitudinal stretching and then transverse stretching;

[0180] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film at a stretching temperature of 105°C, a ratio of 2.5:1, and a tensile strength of 86 MPa; the longitudinally stretched base film is heat-set on a set of cooling rollers at a setting temperature of 140°C and a setting time of 6 seconds;

[0181] The transverse stretching is carried out on a transverse stretching machine at a stretching temperature of 135°C, a transverse stretching ratio of 5.5:1, and a tensile strength of 205 MPa. The stretched base film is heat-set and then cooled at a setting temperature of 85°C and a setting time of 4 seconds.

[0182] (3) Traction, trimming and winding

[0183] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film, obtaining a large roll of low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC labels.

[0184] Example 4: Preparation method of a low-temperature, high-shrink polyester heat-shrinkable film that can replace PVC labels

[0185] Step 1, preparation of modified polyethylene terephthalate

[0186] The hydroxyl-terminated compound is 3-hydroxycyclopentanecarboxylic acid, and the other operations are the same as in Example 1;

[0187] Step 2: Preparation of reinforcing and toughening agent

[0188] The unsaturated organosilicon compound is vinyl-terminated silicone oil;

[0189] The viscosity of the vinyl-terminated silicone oil at 25° C. is 3000 mPa·s, and the vinyl content is 0.5 wt %;

[0190] The initiator is azobisisoheptanonitrile;

[0191] Other operations are the same as in Example 1;

[0192] The operation of step 3 is the same as that of embodiment 1.

[0193] Example 5: Preparation method of a low-temperature high-shrink polyester heat shrinkable film that can replace PVC labels

[0194] Step 1, preparation of modified polyethylene terephthalate

[0195] The hydroxyl-terminated compound is 4-hydroxymethyl-1-cyclohexanecarboxylic acid, and the other operations are the same as in Example 1;

[0196] The operations of steps 2 and 3 are the same as those in Example 1.

[0197] Example 6: Preparation method of a low-temperature, high-shrink polyester heat-shrinkable film that can replace PVC labels

[0198] Step 1, preparation of modified polyethylene terephthalate

[0199] The hydroxyl-terminated compound is azelaic acid, and the other operations are the same as in Example 1;

[0200] The operations of steps 2 and 3 are the same as those in Example 1.

[0201] Example 7: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0202] Step 1, preparation of modified polyethylene terephthalate

[0203] The hydroxyl-terminated compound is dodecanedioic acid, and the other operations are the same as in Example 1;

[0204] The operations of steps 2 and 3 are the same as those in Example 1.

[0205] Example 8: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0206] Step 1, preparation of modified polyethylene terephthalate

[0207] The hydroxyl-terminated compound is adipic acid, and the other operations are the same as in Example 1;

[0208] The operations of steps 2 and 3 are the same as those in Example 1.

[0209] Comparative Example 1: Based on Example 1, step 2, preparation of the reinforcing and toughening agent, was omitted. Step 3, preparation of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels (1) During melt extrusion, 12 parts of the reinforcing and toughening agent were replaced with 12 parts of modified polyethylene terephthalate. The specific operation was as follows:

[0210] The operation of step 1 is the same as that of Example 1;

[0211] Step 2, preparation of the reinforcing and toughening agent, is not performed;

[0212] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels

[0213] (1) Melt extrusion

[0214] The 12 parts of reinforcing and toughening agent were replaced by 12 parts of modified polyethylene terephthalate, and the other operations were the same as in Example 1;

[0215] The operations of (2) stretching and (3) pulling, trimming and winding are the same as those in Example 1.

[0216] Performance testing:

[0217] The polyester heat shrinkable films with high shrinkage at low temperature and capable of replacing PVC labels obtained in Examples 1, 2, 3, 4, 5, 6, 7, 8 and Comparative Example 1 were tested for the following performance indicators:

[0218] 1. Thickness: According to ASTM D374, the film thickness was measured using a thickness tester (Millimar 1240) produced by Mahr, Germany.

[0219] 2. Mechanical strength: tensile strength and elongation at break shall comply with ASTM D882 standard;

[0220] 3. Shrinkage: Tested according to ASTM D1204 standard;

[0221] 4. Haze: According to ASTM D1003, using the British Diffusion System company

[0222] The haze tester (BS 2782) produced by the company measures the haze of the film;

[0223] 5. Dynamic friction coefficient: The dynamic friction coefficient of the film (μs) was measured using a friction coefficient tester produced by Blbert Instrument Company, USA, in accordance with ASTM D 1894.

[0224] The test data is shown in Table 1:

[0225] Table 1

[0226] From the test results in Table 1, it can be seen that the tensile strength in the TD direction of Examples 1-8 is all above 120 MPa, the tensile strength in the MD direction is all above 30 MPa, the elongation at break in the TD direction exceeds 25%, the elongation at break in the MD direction is all above 200%, the heat shrinkage in the TD direction is all above 45% at 70°C and above 65% at 100°C, the heat shrinkage in the MD direction is 1-10% at 70°C and 1-14% at 100°C, the haze is less than 7%, and the dynamic friction coefficient is less than 0.55, which shows that the low-temperature high-shrinkage obtained by the present invention can replace PVC. The polyester heat-shrinkable film of the label has the characteristics of high shrinkage at low temperature, and its mechanical properties, haze and surface dynamic friction properties are very excellent. In Comparative Example 1, no reinforcing and toughening agent is added. The mechanical properties of Comparative Example 1 are greatly reduced, and the heat shrinkage rates at 70°C and 100°C are also significantly increased. The haze and dynamic friction coefficient do not change much. This shows that the reinforcing and toughening agent has a very good reinforcing and toughening effect on the modified polyethylene terephthalate, and also has a certain effect on the heat shrinkage rate, but the effect is relatively limited. At 70°C, Examples 1-8 with the addition of the reinforcing and toughening agent can still maintain a relatively high heat shrinkage rate.

[0227] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, characterized by: The raw materials of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels include modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening slip agent; The modified polyethylene terephthalate is prepared by the following method: adding terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into a reaction kettle, introducing nitrogen to maintain the reaction pressure, heating the kettle to an esterification reaction temperature while maintaining a first stirring rate, and performing an esterification reaction; after the esterification reaction is completed, stopping the introduction of nitrogen, turning on a vacuum pump to evacuate the kettle to a first vacuum degree, heating the kettle to a pre-polycondensation temperature, and performing a pre-polycondensation reaction; after the pre-polycondensation reaction is completed, continuing to evacuate the kettle to a second vacuum degree, while simultaneously heating the kettle to a high-vacuum polycondensation reaction temperature, increasing the stirring rate to a second stirring rate, introducing nitrogen to pressurize the discharge, and water-cooling, pelletizing, and drying to obtain the modified polyethylene terephthalate; The hydroxyl-terminated compound is any one of ricinoleic acid, monoricinoleic acid glyceride, 2-methyl-2,4-pentanediol, 3-hydroxycyclopentanecarboxylic acid, 4-hydroxymethyl-1-cyclohexanecarboxylic acid, azelaic acid, dodecanedioic acid, and adipic acid, or a mixture of any two or more of the above in any mass ratio; The reinforcing and toughening agent is prepared by adding an unsaturated organosilicon compound and an organic solvent into a reaction kettle, stirring and dissolving the mixture, heating the mixture to a reaction temperature under condensation reflux, and then dripping a mixture of glycidyl methacrylate and an initiator. After the dripping is complete, the mixture is kept at a constant temperature until the unsaturated organosilicon is completely reacted, cooling the mixture to room temperature, adding acetone to precipitate the precipitate, and filtering, washing with alcohol, and drying the mixture to obtain the reinforcing and toughening agent. The unsaturated organic silicon compound is one of vinyl MQ silicone resin and vinyl-terminated silicone oil.

2. The polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 1, characterized in that: The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels is 70-150 parts by weight of modified polyethylene terephthalate, 10-35 parts of polybutylene terephthalate, 8-20 parts of reinforcing and toughening agent, and 1-3 parts of opening slip agent. The opening lubricant is silicon dioxide with a particle size of 1 to 5 μm.

3. The polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 1, characterized in that: The mass ratio of the terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide is 60-150:50-140:9-16:0.2-0.

5.

4. The polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 1, characterized in that: The vinyl MQ silicone resin has a viscosity of 4000-9000 mPa·s at 25° C. and a vinyl content of 2-4 wt %. The vinyl-terminated silicone oil has a viscosity of 500-3000 mPa·s at 25° C. and a vinyl content of 0.2-0.5 wt %. The organic solvent is one of toluene and xylene; The mixed liquid of glycidyl methacrylate and initiator is prepared by mixing glycidyl methacrylate and initiator, and the mass ratio of glycidyl methacrylate to initiator is 80-150:

3.

5. The polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 1, characterized in that: The initiator is one of benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile; The mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and the initiator, and acetone is 20-60:190-400:8-18:100-230.

6. The method for preparing a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 1, characterized in that: The method for preparing the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels comprises three steps: melt extrusion, stretching, and traction, trimming, and winding; The melt extrusion comprises the following steps: drying all raw materials at 120-140° C. for 3-5 hours according to the raw material composition of the polyester heat shrinkable film that can replace PVC labels with high shrinkage at low temperature; cooling the raw materials to room temperature in a dry environment; mixing the raw materials according to the raw material composition of the polyester heat shrinkable film that can replace PVC labels with high shrinkage at low temperature in parts by weight; and then feeding the raw materials into a twin-screw extruder; heating the heating zones of the twin-screw extruder to 255-280° C. to melt and extrude the mixed raw materials; and cooling the melt extruded from the die head on the surface of a casting roller to form a cast sheet.

7. The method for preparing a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 6, characterized in that: The stretching comprises stretching the cast sheet using one of a uniaxial stretching process and a biaxial stretching process to obtain a base film; The unidirectional stretching process is one of longitudinal stretching and transverse stretching; The biaxial stretching process is performed by first performing longitudinal stretching and then transverse stretching; The longitudinal stretching is performed on a longitudinal stretching machine to form a base film at a stretching temperature of 80-105°C, a ratio of 1-2.5:1, and a tensile strength of 22-86 MPa; the longitudinally stretched base film is heat-set on a surface of a set of cooling rollers at a setting temperature of 70-140°C and a setting time of 2-6 seconds; The transverse stretching is carried out on a transverse stretching machine at a stretching temperature of 80-135°C, a transverse stretching ratio of 2.5-5.5:1, and a tensile strength of 190-205 MPa. The stretched base film is heat-set and then cooled at a setting temperature of 55-85°C and a setting time of 1.5-4 seconds.

8. The method for preparing a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels according to claim 7, characterized in that: The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film, obtaining a large roll of low-temperature, high-shrinkage polyester heat shrinkable film that can replace PVC labels.

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