Low-temperature high-shrinkage polyester heat shrinkage film capable of replacing PVC label and preparation method of low-temperature high-shrinkage polyester heat shrinkage film

Abstract

The invention relates to a low-temperature high-shrinkage polyester heat shrinkage film capable of replacing a PVC label and a preparation method thereof, and belongs to the technical field of polymer packaging materials, the low-temperature high-shrinkage polyester heat shrinkage film capable of replacing the PVC label comprises the following raw materials: modified polyethylene glycol terephthalate, polybutylene terephthalate, a reinforcing and toughening agent and an opening and slipping agent; the thickness of the obtained polyester heat shrink film is 30.0-100.6 [mu] m, the TD tensile strength is 127-153 MPa, the MD tensile strength is 33-41 MPa, the TD elongation at break is 26-34%, the MD elongation at break is 220-313%, the TD shrinkage rates are 45-56% (70 DEG C, 10 s) and 68-80% (100 DEG C, 10 s), the MD shrinkage rates are 1-10% (70 DEG C, 10 s) and 1-14% (100 DEG C, 10 s), the haze is 3.6-5.8%, and the dynamic friction coefficient is 0.30-0.53 [mu] s.

Description

Technical Field

[0001] The present invention relates to a polyester heat - shrinkable film that can replace PVC labels with low temperature and high shrinkage and a preparation method thereof, belonging to the technical field of polymer packaging materials. Background Art

[0002] Walking into major supermarkets, it is not difficult to find that the packages on the shelves are becoming more and more beautiful. Especially in the beverage area, such integrated packaging labels are abundant and showing a more and more bright and beautiful development trend. This kind of packaging is collectively called heat - shrinkable labels, which are film labels specially printed with ink on plastic films or plastic tubes.

[0003] From the market perspective, currently, the plastic films used as heat - shrinkable labels mainly have three types of materials: polyvinyl chloride (PVC), polyester (mainly PET), and oriented polystyrene (OPS). Among these three materials, the PVC film has the lowest shrinkage temperature. Generally, it starts to shrink horizontally at about 53°C and longitudinally at 60°C. While the shrinkage temperature of polyester heat - shrinkable films is generally relatively high. Below 70°C, the shrinkage rate of polyester heat - shrinkable films is relatively low, usually less than 40%. Usually, the temperature used in the heat - shrinkage process of polyester heat - shrinkable films is 80 - 90°C or even higher, making it difficult to be used for packaging labels of heat - sensitive products. Although OPS also has many advantages, the cost of OPS materials is the highest among the three materials, and its corresponding market share is also the lowest. For the objects to be packaged that are heat - sensitive substances, such as milk powder, protein, beverages, liquid yogurt containing probiotics, etc., the relatively high temperature during the heat - shrinkage process will damage the heat - sensitive substances, easily leading to product spoilage or shortened shelf life. Considering cost and heat - shrinkage temperature, only PVC or polyester materials can be selected. However, the biggest disadvantage of PVC materials is that they cannot be recycled and contain chlorine, posing too great an environmental protection risk. Especially in European Union countries, the use of PVC heat - shrinkable films has been completely prohibited. Therefore, developing a low - temperature and high - shrinkage polyester heat - shrinkable film that can replace PVC materials, especially a polyester heat - shrinkable film that can achieve high shrinkage at 70°C or even below 70°C, is a very promising research direction.

[0004] To obtain a polyester heat-shrinkable film with low temperature and high shrinkage, the currently commercialized products are mainly provided by Eastman. As early as around 2000, Eastman developed a polyester heat-shrinkable film with diethylene glycol (DEG) copolyester as the modified resin. Its heat shrinkage temperature can be reduced to about 70 °C. However, when the polyester resin modified by DEG copolyester is physically blended with other polyester resins to prepare a polyester heat-shrinkable film, there is an upper limit on the addition amount. After the mass fraction of DEG in the polyester mixture is greater than 7.5%, the heat-shrinkable film generally becomes brittle. Therefore, additional toughening means are needed to improve the brittleness problem brought by DEG copolymer modification. Subsequently, Eastman developed a toughening agent called AAPE to improve the toughness of the mixture system of DEG copolymer resin and polyester resin. Using the technology of toughening with AAPE, the lowest heat shrinkage temperature of the polyester heat-shrinkable film modified by DEG copolymer can be achieved below 70 °C. However, there is still no large-scale commercial report on low-temperature and high-shrinkage polyester heat-shrinkable films in the range of 70-80 °C or even below 70 °C in China. Therefore, it is urgent to develop a polyester heat-shrinkable film with low temperature, high shrinkage and capable of replacing PVC material to meet the blank in the domestic sub-market in this field.

[0005] Chinese Patent CN102285184A discloses a low-temperature and high-shrinkage polyester film for bottle labels and its preparation method. The film includes a shrinkage base layer and two heat-shrinkable layers compounded on the upper and lower surfaces of the shrinkage base layer. The film uses nano-SiO2 modified amorphous polyester and graft-modified copolyester as the raw materials for the heat-shrinkable layers, and uses modified low-melting-point PET polymer and low-melting-point PTT polymer as the raw materials for the shrinkage base layer. After melting respectively, they are formed by co-extrusion compounding, preheated and then longitudinally and transversely stretched respectively, and then secondarily stretched after heat setting, and then cooled to obtain a low-temperature and high-shrinkage polyester film for bottle labels. The polyester heat-shrinkable film obtained by this patent needs a high temperature of 90 °C to reach a shrinkage degree of more than 75%. The heat shrinkage temperature has not been reduced and still remains at 90 °C.

[0006] As can be seen above, when the polyester heat-shrinkable film is used as a packaging label at present, there are still disadvantages such as too high heat shrinkage temperature and it is difficult to compare with PVC material in terms of heat shrinkage temperature. Therefore, developing a polyester heat-shrinkable film with low temperature, high shrinkage and capable of replacing PVC labels has very important practical value and practical significance. Summary of the Invention

[0007] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a polyester heat-shrinkable film with low temperature, high shrinkage and capable of replacing PVC labels and its preparation method, and realizes the following invention objectives: to prepare a polyester heat-shrinkable film with a shrinkage rate of more than 40% at 70 °C, a shrinkage rate of more than 65% at 100 °C and excellent mechanical properties and capable of replacing PVC labels.

[0008] To achieve the above-mentioned invention objectives, the present invention adopts the following technical solutions: A polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage and its preparation method. The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage includes modified polyethylene terephthalate, polybutylene terephthalate, an enhancing and toughening agent, and an antiblocking and slip agent; The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage is formulated in parts by weight as 70 - 150 parts of modified polyethylene terephthalate, 10 - 35 parts of polybutylene terephthalate, 8 - 20 parts of an enhancing and toughening agent, and 1 - 3 parts of an antiblocking and slip agent; The antiblocking and slip agent is silica, with a particle size of 1 - 5 μm; The following is a further improvement to the above technical solution: Step 1: Preparation of modified polyethylene terephthalate Add terephthalic acid, ethylene glycol, a hydroxyl-terminated compound, and antimony trioxide into the reaction kettle. Pass nitrogen to maintain the reaction pressure. Raise the temperature to the esterification reaction temperature at the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stop passing nitrogen, open the vacuum pump to evacuate the kettle to the first vacuum degree, raise the temperature to the pre-polycondensation temperature to carry out the pre-polycondensation reaction. After the pre-polycondensation reaction is completed, continue to evacuate to the second vacuum degree, and at the same time raise the temperature to the high-vacuum polycondensation reaction temperature, increase the stirring rate to the second stirring rate. After the high-vacuum polycondensation reaction is completed, pass nitrogen to pressurize and discharge the material. After water cooling, pelletizing, and drying, modified polyethylene terephthalate is obtained; The hydroxyl-terminated compound is any one or any two of ricinoleic acid, glycerol monoricinoleate, 2-methyl-2,4-pentanediol, 3-hydroxycyclopentanecarboxylic acid, 4-hydroxymethyl-1-cyclohexanecarboxylic acid, azelaic acid, dodecanedioic acid, adipic acid, or a mixture composed of any two or more in any mass ratio; 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; The reaction pressure is 0.01 - 0.02 MPa; The first stirring rate is 40 - 65 revolutions per minute; The esterification reaction temperature is 180 - 235 °C; When the esterification reaction is completed, the esterification reaction time is 4 - 6 h; The first vacuum degree is 100 - 130 Pa; The pre-polycondensation temperature is 240 - 255 °C; When the pre-polycondensation reaction is completed, the pre-polycondensation reaction time is 1 - 2 h; The second vacuum degree is 30 - 60 Pa; The high - vacuum polycondensation reaction temperature is 270 - 280 °C; The second stirring rate is 70 - 100 revolutions per minute; After the high - vacuum polycondensation reaction is completed, the high - vacuum polycondensation reaction time is 2.5 - 4 h.

[0009] Step 2: Preparation of the reinforcing and toughening agent Add the unsaturated organosilicon compound and the organic solvent into the reaction kettle. After stirring and dissolving, under the condition of condensation reflux, heat up and keep the temperature constant at the reaction temperature. Then, dropwise add the mixed solution of glycidyl methacrylate and the initiator. After the dropping is completed, continue the constant - temperature reaction until all the unsaturated organosilicon has reacted. Then, cool down to room temperature, add acetone to precipitate the precipitate, and then obtain the reinforcing and toughening agent after filtration, alcohol washing, and drying; The unsaturated organosilicon compound is one of vinyl MQ silicone resin and terminal vinyl silicone oil; The viscosity of the vinyl MQ silicone resin at 25 °C is 4000 - 9000 mPa·s, and the vinyl mass content is 2 - 4 wt%; The viscosity of the terminal vinyl silicone oil at 25 °C is 500 - 3000 mPa·s, and the vinyl mass content is 0.2 - 0.5 wt%; The organic solvent is one of toluene and xylene; The mixed solution of glycidyl methacrylate and the initiator is composed of glycidyl methacrylate and the initiator, and the mass ratio of glycidyl methacrylate to the initiator is 80 - 150:3; The initiator is one of benzoyl peroxide, di - tert - butyl peroxide, azobisisobutyronitrile, and azobisisoheptonitrile; The feeding 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; For the stirring and dissolving, the stirring rate is 100 - 400 revolutions per minute; For the dropping of the mixed solution of glycidyl methacrylate and the initiator, the dropping rate is 1 - 20 grams per minute; The reaction temperature is 70 - 95 °C; For the alcohol washing, wash with anhydrous ethanol 3 times, and the amount of anhydrous ethanol used for each washing is equal to the mass of the solid to be washed; For the drying, the drying temperature is 60 - 85 °C, and the drying time is 4 - 9 hours.

[0010] Step 3: Preparation of the polyester heat - shrinkable film for low - temperature high - shrinkage PVC - replaceable labels (1), Melt extrusion According to the raw material composition of the polyester heat shrinkable film that can replace PVC labels with low temperature and high shrinkage, all raw materials are dried at 120 - 140 °C for 3 - 5 hours, then cooled to room temperature in a dry environment. Then, according to the weight ratio of the raw material composition of the polyester heat shrinkable film that can replace PVC labels with low temperature and high shrinkage, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are all heated to 255 - 280 °C to melt and extrude the mixed raw materials. The melt extruded from the die head is cooled and solidified into a cast sheet on the surface of the casting roll; (2), Stretching For the stretching, the cast sheet is stretched using one of the unidirectional stretching process and the biaxial stretching process to obtain a base film; The unidirectional stretching process is one of longitudinal stretching and transverse stretching; For the biaxial stretching process, first perform longitudinal stretching and then transverse stretching; For the longitudinal stretching, it is stretched into a base film on a longitudinal stretching machine. The stretching temperature is 80 - 105 °C, the stretching ratio is 1 - 2.5:1, and the stretching strength is 22 - 86 MPa; The base film after longitudinal stretching is heat-set on the surface of a set of cooling rollers. The setting temperature is 70 - 140 °C, and the setting time is 2 - 6 seconds; For the transverse stretching, it is carried out on a transverse stretching machine. The stretching temperature is 80 - 135 °C, the transverse stretching ratio is 2.5 - 5.5:1, the stretching strength is 190 - 205 MPa, and the stretched base film is heat-set and then cooled. The setting temperature is 55 - 85 °C, and the setting time is 1.5 - 4 seconds; (3), Traction, edge trimming and winding The stretched base film enters the traction station. The edge device in the traction station trims the edges of the base film with a trimming knife, and then it is tractioned to a winder to wind the base film, obtaining a large roll of polyester heat shrinkable film that can replace PVC labels with low temperature and high shrinkage.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses hydroxyl-terminated compounds with asymmetric molecular chains or long chains. Among the hydroxyl-terminated compounds with asymmetric molecular chains, there are mainly oleic acid, glycerol monocastor oilate, 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. These substances are used for modified copolymerization of polyethylene terephthalate. After forming copolyesters with terephthalic acid and ethylene glycol, compared with pure polyethylene terephthalate, the regularity of the polymer chains becomes worse. This will affect the crystallization performance of polyethylene terephthalate to a certain extent, and then reduce the glass transition temperature of pure polyethylene terephthalate. Therefore, the modified polyethylene terephthalate has a lower glass transition temperature compared with pure polyethylene terephthalate, and thus is prone to thermal deformation at low temperatures, and finally exhibits the characteristics of high shrinkage at low temperatures; 2. Although the modified polyethylene terephthalate prepared by the present invention has the characteristics of high shrinkage at low temperatures, the decline in 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 reduction in mechanical properties, the present invention uses unsaturated silicone compounds, namely vinyl MQ silicone resin or vinyl-terminated silicone oil, to undergo a free radical reaction with glycidyl methacrylate under the action of an initiator, so that the double bonds at the ends of the vinyl MQ silicone resin or vinyl-terminated silicone oil become epoxy groups. This mainly has two purposes. First, the compatibility between silicone and polyester is not very good. After being terminated with epoxy groups, the polarity of the short-chain compound formed by silicone and glycidyl methacrylate will increase. This promotes the compatibility between the silicone molecular chains and the polyester polymer chains, causing the silicone molecular chains to entangle with the polyester polymer chain segments. Since the silicone molecular chains have very good elasticity, the entanglement of the silicone molecular chain segments and the polyester molecular chain segments can increase the toughness of the polyester resin matrix and improve the elongation at break of the polyester heat shrinkable film. Second, the epoxy functional groups at the ends can react with the hydroxyl or carboxyl groups at the ends of the modified polyethylene terephthalate polymer chains during the melt extrusion step, causing a certain degree of cross-linking reaction of 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 silicone and glycidyl methacrylate can enhance and toughen the polyester film; 3. The polyester heat-shrinkable film obtained by the present invention, which 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 at break of 26 - 34%, an MD elongation at break of 220 - 313%, a TD shrinkage rate of 45 - 56% (70 °C, 10 s) and 68 - 80% (100 °C, 10 s), an MD shrinkage rate of 1 - 10% (70 °C, 10 s) and 1 - 14% (100 °C, 10 s), a haze of 3.6 - 5.8%, and a dynamic friction coefficient of 0.30 - 0.53 μs. Detailed implementation manners

[0012] The following are descriptions of the preferred embodiments of the present invention. It should be understood that the preferred embodiments described herein are only for illustrating and explaining the present invention, and are not used to limit the present invention.

[0013] Example 1: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1: Preparation of modified polyethylene terephthalate Add terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide into the reaction kettle, introduce nitrogen to maintain the reaction pressure, heat up to the esterification reaction temperature at the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stop introducing nitrogen, open the vacuum pump to evacuate the kettle to the first vacuum degree, heat up to the pre-polycondensation temperature to carry out the pre-polycondensation reaction. After the pre-polycondensation reaction is completed, continue to evacuate to the second vacuum degree, and at the same time heat up to the high-vacuum polycondensation reaction temperature, increase the stirring rate to the second stirring rate. After the high-vacuum polycondensation reaction is completed, introduce nitrogen to pressurize and discharge the material, cool with water, pelletize, and dry to obtain modified polyethylene terephthalate; The hydroxyl-terminated compound is ricinoleic acid; The mass ratio of terephthalic acid, ethylene glycol, hydroxyl-terminated compound, and antimony trioxide is 100:90:11:0.4; The reaction pressure is 0.016 MPa; The first stirring rate is 50 revolutions per minute; The esterification reaction temperature is 200 °C; When the esterification reaction is completed, the esterification reaction time is 5 h; The first vacuum degree is 110 Pa; The pre-polycondensation temperature is 245 °C; When the pre-polycondensation reaction is completed, the pre-polycondensation reaction time is 1.6 h; The second vacuum degree is 40 Pa; The high-vacuum polycondensation reaction temperature is 276 °C; The second stirring rate is 80 revolutions per minute; The high-vacuum polycondensation reaction is completed, and the high-vacuum polycondensation reaction time is 3 h.

[0014] Step 2: Preparation of the reinforcing and toughening agent An unsaturated organosilicon compound and an organic solvent are added to a reaction kettle. After stirring and dissolving, while in a state of condensation reflux, the temperature is raised and kept constant at the reaction temperature. Then, a mixed solution of glycidyl methacrylate and an initiator is added dropwise. After the dropwise addition is completed, the reaction is continued under constant temperature until all the unsaturated organosilicon has reacted. Then, the temperature is lowered to room temperature, acetone is added to precipitate a precipitate, and after filtration, alcohol washing, and drying, the reinforcing and toughening agent is obtained; The unsaturated organosilicon compound is vinyl MQ silicone resin; The viscosity of the vinyl MQ silicone resin at 25 °C is 4000 mPa·s, and the vinyl mass content is 2 wt%; The organic solvent is toluene; The mixed solution of glycidyl methacrylate and an initiator is composed of glycidyl methacrylate and an initiator, and the mass ratio of glycidyl methacrylate to the initiator is 120:3; The initiator is benzoyl peroxide; The feeding mass ratio of the unsaturated organosilicon compound, the organic solvent, the mixed solution of glycidyl methacrylate and an initiator, and acetone is 30:300:10:160; For the stirring and dissolving, the stirring rate is 200 revolutions per minute; For the dropwise addition of the mixed solution of glycidyl methacrylate and an initiator, the dropping rate is 15 g / min; The reaction temperature is 80 °C; For the alcohol washing, it is washed 3 times with absolute ethanol, and the amount of absolute ethanol used for each washing is equal to the mass of the solid being washed; For the drying, the drying temperature is 70 °C, and the drying time is 6 hours.

[0015] Step 3: Preparation of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage (1). Melting and extrusion According to the raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, all the raw materials are dried at 135 °C for 4 hours, and then cooled to room temperature in a dry environment. Then, according to the weight ratio of the raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are all heated to 270 °C, so that the mixed raw materials are melted and extruded, and the melt extruded from the die head is cooled and solidified into a cast sheet on the surface of the casting roll; The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage includes modified polyethylene terephthalate, polybutylene terephthalate, reinforcing and toughening agent, and anti-blocking and slip agent; The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, by weight, is 120 parts of modified polyethylene terephthalate, 20 parts of polybutylene terephthalate, 12 parts of reinforcing and toughening agent, and 2 parts of anti-blocking and slip agent; The anti-blocking and slip agent is silicon dioxide with a particle size of 4 μm; (2), stretching For the stretching, the cast film is processed by a biaxial stretching process; For the biaxial stretching process, longitudinal stretching is carried out first and then transverse stretching; For the longitudinal stretching, it is carried out on a longitudinal stretching machine to form a base film. The stretching temperature is 100 °C, the stretching ratio is 2:1, and the stretching strength is 70 MPa; the base film after longitudinal stretching is heat-set on the surface of a set of cooling rollers, the setting temperature is 120 °C, and the setting time is 4 seconds; For the transverse stretching, it is carried out on a transverse stretching machine. The stretching temperature is 100 °C, the transverse stretching ratio is 3:1, the stretching strength is 200 MPa, and the stretched base film is heat-set and then cooled. The setting temperature is 70 °C, and the setting time is 3 seconds; (3), traction, trimming and winding The stretched base film enters the traction station. The edge device in the traction station trims the edges of the base film with a trimming knife, and then it is tractioned to a winding machine to wind the base film, obtaining a large roll of polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage.

[0016] Example 2: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1, preparation of modified polyethylene terephthalate Add terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide into the reaction kettle, introduce nitrogen to maintain the reaction pressure, raise the temperature to the esterification reaction temperature at the first stirring rate to carry out the esterification reaction. After the esterification reaction is completed, stop introducing nitrogen, open the vacuum pump to pump the kettle to the first vacuum degree, raise the temperature to the pre-polycondensation temperature to carry out the pre-polycondensation reaction. After the pre-polycondensation reaction is completed, continue to pump vacuum to the second vacuum degree, and at the same time raise the temperature to the high-vacuum polycondensation reaction temperature, increase the stirring rate to the second stirring rate. After the high-vacuum polycondensation reaction is completed, introduce nitrogen to pressurize and discharge the material, cool with water, pelletize and dry to obtain modified polyethylene terephthalate; The hydroxyl-terminated compound is monoglyceryl ricinoleate; The mass ratio of terephthalic acid, ethylene glycol, hydroxyl-terminated compound, and antimony trioxide is 60:50:9:0.2; The reaction pressure is 0.01 MPa; The first stirring rate is 40 revolutions per minute; The esterification reaction temperature is 180 °C; When the esterification reaction ends, the esterification reaction time is 4 h; The first vacuum degree is 100 Pa; The pre-polycondensation temperature is 240 °C; When the pre-polycondensation reaction is completed, the pre-polycondensation reaction time is 1 h; The second vacuum degree is 30 Pa; The high-vacuum polycondensation reaction temperature is 270 °C; The second stirring rate is 70 revolutions per minute; When the high-vacuum polycondensation reaction is completed, the high-vacuum polycondensation reaction time is 2.5 h.

[0017] Step 2: Preparation of the strengthening and toughening agent Add the unsaturated organosilicon compound and the organic solvent into the reaction kettle. After stirring and dissolving, under the condition of condensation reflux, heat up and keep the temperature constant at the reaction temperature. Then, dropwise add the mixed solution of glycidyl methacrylate and the initiator. After the dropping is completed, continue the constant-temperature reaction until all the unsaturated organosilicon has reacted. Then, cool down to room temperature, add acetone to precipitate the precipitate, and then obtain the strengthening and toughening agent after filtration, alcohol washing, and drying; The unsaturated organosilicon compound is vinyl MQ silicone resin; The viscosity of the vinyl MQ silicone resin at 25 °C is 9000 mPa·s, and the vinyl mass content is 4 wt%; The organic solvent is xylene; The mixed solution of glycidyl methacrylate and the initiator is composed of glycidyl methacrylate and the initiator, and the mass ratio of glycidyl methacrylate to the initiator is 80:3; The initiator is di-tert-butyl peroxide; The feeding 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; For the stirring and dissolving, the stirring rate is 100 revolutions per minute; For the dropping of the mixed solution of glycidyl methacrylate and the initiator, the dropping rate is 1 g / minute; The reaction temperature is 70 °C; For the alcohol washing, wash with anhydrous ethanol 3 times, and the dosage of anhydrous ethanol for each washing is equal to the mass of the solid to be washed; For the drying, the drying temperature is 60 °C and the drying time is 4 hours.

[0018] Step 3: Preparation of polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels (1) Melt extrusion According to the raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels, all the raw materials are dried at 120° C. for 3 hours, and then placed in a dry environment to cool 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° 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 casting sheet; The raw material composition of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels includes modified polyethylene terephthalate, polybutylene terephthalate, a reinforcing and toughening agent, and an opening lubricant; 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 lubricant; The opening lubricant is silicon dioxide with a particle size of 1 μm; (2) Stretching The stretching comprises stretching the cast sheet using a biaxial stretching process to obtain a base film; The biaxial stretching process first performs longitudinal stretching and then transverse stretching; The longitudinal stretching is performed on a longitudinal stretching machine to form a base film, the stretching temperature is 80°C, the ratio is 1:1, and the tensile strength is 22MPa; the longitudinally stretched base film is heat-set on the surface of a group of cooling rollers, the setting temperature is 70°C, and the setting time is 2 seconds; The transverse stretching is carried out on a transverse stretching machine, the stretching temperature is 80°C, the transverse stretching ratio is 2.5:1, the tensile strength is 190MPa, and the stretched base film is heat-set and then cooled, the setting temperature is 55°C, and the setting time is 1.5 seconds; (3) Traction, trimming and winding The stretched base film enters the traction station, and the edge device in the traction station trims the edge of the base film with a trimming knife, and then pulls it to the winder to wind the base film to obtain a large roll of low-temperature and high-shrink polyester heat shrinkable film that can replace PVC labels.

[0019] Example 3: A method for preparing a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels Step 1, preparation of modified polyethylene terephthalate Add terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide into the reaction kettle, introduce nitrogen to maintain the reaction pressure, heat up to the esterification reaction temperature at the first stirring rate, and carry out the esterification reaction. After the esterification reaction is completed, stop introducing nitrogen, turn on the vacuum pump to pump the kettle to the first vacuum degree, heat up to the pre-polycondensation temperature for pre-polycondensation reaction. After the pre-polycondensation reaction is completed, continue to pump the vacuum to the second vacuum degree, and at the same time heat up to the high-vacuum polycondensation reaction temperature, increase the stirring rate to the second stirring rate. After the high-vacuum polycondensation reaction is completed, introduce nitrogen to pressurize and discharge the material, and obtain modified polyethylene terephthalate after water cooling, pelletizing and drying; The hydroxyl-terminated compound is 2-methyl-2,4-pentanediol; The mass ratio of terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide is 150:140:16:0.5; The reaction pressure is 0.02 MPa; The first stirring rate is 65 revolutions per minute; The esterification reaction temperature is 235 °C; When the esterification reaction is completed, the esterification reaction time is 6 h; The first vacuum degree is 130 Pa; The pre-polycondensation temperature is 255 °C; When the pre-polycondensation reaction is completed, the pre-polycondensation reaction time is 2 h; The second vacuum degree is 60 Pa; The high-vacuum polycondensation reaction temperature is 280 °C; The second stirring rate is 100 revolutions per minute; When the high-vacuum polycondensation reaction is completed, the high-vacuum polycondensation reaction time is 4 h.

[0020] Step 2: Preparation of the reinforcing and toughening agent Add the unsaturated organosilicon compound and the organic solvent into the reaction kettle, stir and dissolve them. Under the condition of condensation reflux, heat up and keep the temperature constant at the reaction temperature, then dropwise add the mixed solution of glycidyl methacrylate and the initiator. After the dropping is completed, continue the constant-temperature reaction until all the unsaturated organosilicon has reacted, then cool down to room temperature, add acetone to precipitate the precipitate, and then obtain the reinforcing and toughening agent after filtration, alcohol washing and drying; The unsaturated organosilicon compound is vinyl-terminated silicone oil; The viscosity of the vinyl-terminated silicone oil at 25 °C is 500 mPa·s, and the vinyl mass content is 0.2 wt%; The organic solvent is toluene; The mixed solution of glycidyl methacrylate and the initiator is composed of glycidyl methacrylate and the initiator, and the mass ratio of glycidyl methacrylate to the initiator is 150:3; The initiator is azobisisobutyronitrile; The feeding mass ratio of the unsaturated organosilicon compound, organic solvent, the mixed solution of glycidyl methacrylate and initiator, and acetone is 60:400:18:230; For the stirring and dissolving, the stirring rate is 400 revolutions per minute; For the dropping of the mixed solution of glycidyl methacrylate and initiator, the dropping rate is 20 grams per minute; The reaction temperature is 95 °C; For the alcohol washing, it is washed 3 times with absolute ethanol, and the amount of absolute ethanol used for each washing is equal to the mass of the solid being washed; For the drying, the drying temperature is 85 °C and the drying time is 9 hours.

[0021] Step 3. Preparation of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage (1). Melting and extrusion According to the raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, all raw materials are dried at 140 °C for 5 hours, then cooled to room temperature in a dry environment. Then, according to the weight ratio of the raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are all heated to 280 °C to melt and extrude the mixed raw materials. The melt extruded from the die head is cooled and solidified into a cast sheet on the surface of the casting roll; The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage includes modified polyethylene terephthalate, polybutylene terephthalate, reinforcing and toughening agent, antiblocking and slip agent, filler; The weight ratio of the raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage is 150 parts of modified polyethylene terephthalate, 35 parts of polybutylene terephthalate, 20 parts of reinforcing and toughening agent, 3 parts of antiblocking and slip agent; The antiblocking and slip agent is silica with a particle size of 5 μm; (2). Stretching For the stretching, the cast sheet is subjected to a biaxial stretching process; For the biaxial stretching process, longitudinal stretching is carried out first and then transverse stretching; For the longitudinal stretching, it is stretched into a base film on a longitudinal stretching machine. The stretching temperature is 105 °C, the stretching ratio is 2.5:1, and the stretching strength is 86 MPa; The base film after longitudinal stretching is heat-set on the surface of a set of cooling rolls. The setting temperature is 140 °C and the setting time is 6 seconds; The transverse stretching is carried out on a transverse stretching machine. The stretching temperature is 135 °C, the transverse stretching ratio is 5.5:1, the stretching strength is 205 MPa. After the stretched base film is heat-set, it is cooled. The setting temperature is 85 °C and the setting time is 4 seconds. (3), Traction, edge trimming and winding The stretched base film enters the traction station. The edge device in the traction station trims the edges of the base film with a trimming knife, and then it is tractioned to a winding machine to wind the base film, obtaining a large roll of polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage.

[0022] Example 4: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1, Preparation of modified polyethylene terephthalate The hydroxyl-terminated compound is 3-hydroxycyclopentanecarboxylic acid, and other operations are the same as in Example 1; Step 2, Preparation of the reinforcing and toughening agent The unsaturated organosilicon compound is vinyl-terminated silicone oil; The viscosity of the vinyl-terminated silicone oil at 25 °C is 3000 mPa·s, and the mass content of vinyl is 0.5 wt%; The initiator is azodiisobutyronitrile; Other operations are the same as in Example 1; The operation of Step 3 is the same as in Example 1.

[0023] Example 5: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1, Preparation of modified polyethylene terephthalate The hydroxyl-terminated compound is 4-hydroxymethyl-1-cyclohexanecarboxylic acid, and other operations are the same as in Example 1; The operations of Steps 2 and 3 are the same as in Example 1.

[0024] Example 6: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1, Preparation of modified polyethylene terephthalate The hydroxyl-terminated compound is azelaic acid, and other operations are the same as in Example 1; The operations of Steps 2 and 3 are the same as in Example 1.

[0025] Example 7: A preparation method of a polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage Step 1, Preparation of modified polyethylene terephthalate The hydroxyl-terminated compound is dodecanedioic acid, and other operations are the same as in Example 1; The operations of Steps 2 and 3 are the same as in Example 1.

[0026] Example 8: Preparation method of a polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels Step 1: Preparation of modified polyethylene terephthalate The hydroxyl-terminated compound is adipic acid, and other operations are the same as in Example 1; Steps 2 and 3 are the same as in Example 1.

[0027] Comparative Example 1: Based on Example 1, without performing Step 2, preparation of the reinforcing and toughening agent, and Step 3, preparation of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels. In the melt extrusion of (1), 12 parts of the reinforcing and toughening agent are replaced with 12 parts of modified polyethylene terephthalate in equal amounts. The specific operations are as follows: Step 1 is the same as in Example 1; Do not perform Step 2, preparation of the reinforcing and toughening agent; Step 3: Preparation of the polyester heat shrinkable film with low temperature and high shrinkage that can replace PVC labels (1). Melt extrusion Replace 12 parts of the reinforcing and toughening agent with 12 parts of modified polyethylene terephthalate in equal amounts, and other operations are the same as in Example 1; (2). Stretching and (3). Traction, trimming, and winding operations are the same as in Example 1.

[0028] Performance test: The polyester heat shrinkable films obtained in Examples 1, 2, 3, 4, 5, 6, 7, 8 and Comparative Example 1 are tested for the following performance indicators: 1. Thickness: The thickness value of the film is measured using a thickness tester (Millimar1240) produced by Mahr Company in Germany according to ASTM D374; 2. Mechanical strength: Tensile strength and elongation at break are in accordance with the ASTM D882 standard; 3. Shrinkage rate: Tested according to the ASTM D1204 standard; 4. Haze: Measured using a haze tester (BS 2782) produced by Diffusion System Company in the UK according to ASTM D1003 for the haze of the film; 5. Dynamic friction coefficient: The dynamic friction coefficient (μs) of the film is measured using a friction coefficient tester produced by Blbert Instrument Company in the US according to ASTM D 1894; The test data are shown in Table 1: Table 1

[0029] As can be seen from the test results in Table 1, the tensile strength in the TD direction of Examples 1-8 is above 120 MPa, the tensile strength in the MD direction is above 30 MPa, the elongation at break in the TD direction exceeds 25%, the elongation at break in the MD direction is above 200%, the thermal shrinkage rate in the TD direction is above 45% at 70 °C and above 65% at 100 °C, the thermal shrinkage rate in the MD direction is 1-10% at 70 °C and 1-14% at 100 °C. At the same time, the haze is less than 7% and the dynamic friction coefficient is less than 0.55. This shows that the polyester heat shrinkable film obtained by the present invention, which can replace PVC labels with low-temperature high shrinkage, has the characteristics of low-temperature high shrinkage, and its mechanical properties, haze and surface dynamic friction properties are all very excellent; in Comparative Example 1, without adding a reinforcing and toughening agent, the mechanical properties of Comparative Example 1 decreased significantly, and the thermal shrinkage rates at 70 °C and 100 °C also increased significantly, while the haze and dynamic friction coefficient did 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 it also has a certain influence on the thermal shrinkage rate, but the influence is relatively limited. At 70 °C, Examples 1-8 with the addition of the reinforcing and toughening agent can still maintain a relatively high thermal shrinkage rate.

[0030] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage, characterized in that: The raw material composition of the polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage includes modified polyethylene terephthalate, polybutylene terephthalate, reinforcing and toughening agent, and anti-blocking and slip agent; For the modified polyethylene terephthalate, its preparation method is as follows: Add terephthalic acid, ethylene glycol, hydroxyl-terminated compound and antimony trioxide into the reaction kettle, pass nitrogen to maintain the reaction pressure, heat up to the esterification reaction temperature at the first stirring rate, and carry out the esterification reaction. After the esterification reaction is completed, stop passing nitrogen, open the vacuum pump to pump the kettle to the first vacuum degree, heat up to the pre-polycondensation temperature for pre-polycondensation reaction. After the pre-polycondensation reaction is completed, continue to pump vacuum to the second vacuum degree, and at the same time heat up to the high-vacuum polycondensation reaction temperature, increase the stirring rate to the second stirring rate. After the high-vacuum polycondensation reaction is completed, pass nitrogen to pressurize and discharge the material, cool with water, pelletize, and dry to obtain modified polyethylene terephthalate; The hydroxyl-terminated compound is any one or any two of castor oil acid, glycerol monoricinoleate, 2-methyl-2,4-pentanediol, 3-hydroxycyclopentanecarboxylic acid, 4-hydroxymethyl-1-cyclohexanecarboxylic acid, azelaic acid, dodecanedioic acid, adipic acid, or a mixture composed of any two or more in any mass ratio; For the reinforcing and toughening agent, its preparation method is as follows: Add unsaturated organosilicon compound and organic solvent into the reaction kettle, stir and dissolve, then heat up and keep the temperature constant at the reaction temperature under the condition of condensation reflux. Then dropwise add a mixture of glycidyl methacrylate and initiator. After the dropping is completed, continue the constant-temperature reaction until all the unsaturated organosilicon reacts, then cool to room temperature, add acetone to precipitate the precipitate, and then obtain the reinforcing and toughening agent after filtration, alcohol washing, and drying; The unsaturated organosilicon compound is one of vinyl MQ silicone resin and vinyl-terminated silicone oil.

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

3. The polyester heat-shrinkable film that can replace PVC labels with low temperature and high shrinkage according to claim 1, characterized in that: 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.

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

3.

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

6. The preparation method of the polyester heat shrinkable film for low-temperature high-shrinkage PVC label substitution according to claim 1, characterized in that: The preparation method of the polyester heat shrinkable film for low-temperature high-shrinkage PVC label substitution includes three steps: melt extrusion, stretching, and traction trimming and winding. For the melt extrusion, according to the raw material composition of the polyester heat shrinkable film for low-temperature high-shrinkage PVC label substitution, all raw materials are dried at 120 to 140°C for 3 to 5 hours, then cooled to room temperature in a dry environment, and then, according to the ratio of the raw material composition of the polyester heat shrinkable film for low-temperature high-shrinkage PVC label substitution 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 all heated to 255 to 280°C to melt and extrude the mixed raw materials, and the melt extruded from the die head is cooled and solidified into a cast sheet on the surface of the casting roll.

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

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

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