A method for recycling heat-shrinkable film and its preparation method

Abstract

A recycled heat-shrinkable film and a preparation method thereof. The recycled heat-shrinkable film is composed of an A-layer surface layer, a B-layer core layer, and a C-layer bottom layer formed by extrusion molding. The A layer and the C layer are respectively disposed on both sides of the B layer and are both made of polyester for ordinary films. The B layer is made of a recycled material with 5wt% - 95wt% of the total mass of the core layer and polyester for ordinary films. The recycled material is prepared by mixing 60 - 80wt% of polyester recycled particles and 20 - 40wt% of a functional masterbatch. The polyester recycled particles are prepared from recycled PET bottles or heat-shrinkable film labels. The functional masterbatch is composed of a polyester carrier, diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate, and magnesium carbonate. In this application, by adding a functional masterbatch to the polyester recycled particles for melt modification treatment, the obtained recycled material can be directly used to prepare a heat-shrinkable film. The prepared heat-shrinkable film has excellent properties, can meet environmental protection requirements, and has the same quality as ordinary heat-shrinkable films.

Description

Technical Field

[0001] This application relates to the field of plastic product recycling, particularly to the technical field of preparing heat shrinkable films from waste plastic products, and especially to a recycled heat shrinkable film and its preparation method. Background Art

[0002] Plastic recycling and regeneration is a technology for recycling and regenerating waste plastic products. Due to the diverse sources of waste plastics, the components of different plastic products vary greatly, and there are problems such as aging and discoloration. Therefore, the plastic products prepared from recycled materials are usually of relatively low grade and have limited applications in consumer fields with high-quality requirements.

[0003] For example, heat shrinkable film is an outer packaging material that can significantly reduce its size after heating and is widely used as the outer packaging of various consumer and industrial products. As an outer packaging material, heat shrinkable film usually requires good mechanical properties, a large transverse elongation rate, high transparency, and fire resistance. The heat shrinkable film prepared from recycled waste plastics usually has defects such as visible transparency and can only be used as a low-grade packaging material in the industrial field.

[0004] For example, CN 100493903 C discloses a heat shrinkable polyester-based film. This shrinkable polyester-based film is a multi-layer structure, where one layer uses recycled PET bottle raw materials and the other layers do not contain recycled raw materials. In this prior art, it is considered that the recycled PET bottle raw materials are various PETs with different melt viscosities, molecular weights, molecular weight distributions, monomer compositions, degrees of crystallinity, and the presence or absence of additives such as polymerization catalysts, and their physical properties deviate greatly in each batch of recycled raw materials. Directly manufacturing a heat shrinkable film using such recycled raw materials cannot obtain stable and uniform products. In addition, in films using more than 45% by mass of recycled raw materials, sufficient mechanical strength or heat shrinkability cannot be obtained. Therefore, this prior art adopts a multi-layer structure heat shrinkable film and uses the layer without recycled raw materials to provide the required mechanical strength and heat shrinkability to avoid the defects of insufficient performance of recycled raw materials.

[0005] Similarly, CN 101155689 B discloses a heat-shrinkable polyester film which also has good printability even when using recycled materials such as polyethylene terephthalate bottles. This prior art is a heat-shrinkable polyester film in which at least one single surface layer of a base layer containing recycled polyethylene terephthalate bottle materials is laminated with a layer not containing recycled polyethylene terephthalate bottle materials, and the layer not containing PET recycled materials is used as the printing surface, or a heat-shrinkable polyester film in which a base layer containing 45 to 80% by weight of recycled polyethylene terephthalate bottle materials and front and back layers mainly composed of amorphous materials are laminated. Among them, the heat shrinkage rate in the main shrinkage direction after being immersed in warm water at 80°C for 10 seconds and then taken out is 30% or more, and the heat shrinkage rate in the direction perpendicular to the main shrinkage direction is 10% or less. In addition, in this prior art, it is considered that since recycled polyethylene terephthalate bottle materials have problems such as the mixing of different raw materials or impurities such as sand, and also have various substances composed of polyethylene terephthalate bottles with different melt viscosities, molecular weights, molecular weight distributions, monomer compositions, crystallinities, types or addition amounts of polymerization catalysts, etc., these physical properties deviate widely in each production batch of recycled materials. Therefore, there is a large deviation in the quality of films containing 40% by weight or more of such recycled materials, and it is impossible to obtain the required heat shrinkage rate or mechanical strength as a heat-shrinkable label.

[0006] The above prior art uses a method of treating recycled plastics by separating the recycled materials from the conventional raw materials in layers to cover up the defects of the recycled material layer. However, if there are problems such as discoloration, turbidity, and peculiar smell in the recycled layer, they cannot be completely removed, and further improvement is still needed. Summary of the Invention

[0007] The technical problem to be solved by this application is to provide a recycled heat-shrinkable film and its preparation method to reduce or avoid the problems mentioned above.

[0008] To solve the above technical problems, this application proposes a recycled heat-shrinkable film, which is composed of an extruded A-layer surface layer, a B-layer core layer, and a C-layer bottom layer. The A layer and the C layer are respectively arranged on both sides of the B layer and are both made of polyester for ordinary films. The B layer is made of a mixture of recycled materials with 5 wt% - 95 wt% of the total mass of the core layer and polyester for ordinary films; the recycled materials are prepared by mixing 60 - 80 wt% of polyester recycled particles and 20 - 40 wt% of a functional masterbatch. The polyester recycled particles are prepared from recycled PET bottles or heat-shrinkable film labels. Among them, the functional masterbatch is composed of a polyester carrier, diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate, and magnesium carbonate.

[0009] Preferably, the contents of the components in the functional masterbatch are as follows: 100-150 parts by weight of polyester carrier, 25-30 parts by weight of diethyl phenylphosphonate, 5-10 parts by weight of sodium dodecylbenzenesulfonate, 15-20 parts by weight of tridecyl stearate, and 5-10 parts by weight of magnesium carbonate.

[0010] Preferably, the polyester carrier is polyethylene terephthalate and its copolymers.

[0011] Preferably, the particle size of the polyester recycled particles is 50-200 µm.

[0012] This application also provides a method for preparing the above-mentioned recycled heat-shrinkable film, which includes the following steps: Weigh the polyester chips for ordinary film by an electronic scale and put them into the mixing bin for mixing, and then put them into the first twin-screw extruder and the third twin-screw extruder respectively; At the same time, weigh the polyester chips for ordinary film and 5 wt% - 95 wt% of the recycled material of the total core layer mass by an electronic scale, put them into the mixing bin for mixing, and then put them into the second single-screw extruder; Then, adjust the temperature of the first and third twin-screw extruders to 270°C - 280°C, and the temperature of the second single-screw extruder to 265°C - 280°C; After melting, filter, use the materials extruded from the first and third twin-screw extruders as the A layer and the C layer, and the material extruded from the second single-screw extruder as the B layer, and make a three-layer composite thick sheet through a multi-layer co-extrusion process; After obtaining the thick sheet, preheat the above-mentioned thick sheet at a temperature of 50°C - 90°C, enter the infrared heating zone at 300°C - 500°C, and perform longitudinal stretching at a linear speed of 40 - 150 m / min, and the longitudinal stretching ratio is 3.0 - 4.5 to obtain a stretched sheet; Then, preheat the stretched sheet at a temperature of 90°C - 120°C, and perform transverse stretching at a temperature of 100°C - 160°C, and the transverse stretching ratio is 3.0 - 4.5; Then, perform shaping at a temperature of 165°C - 250°C, and then cool at a temperature of 100°C - 50°C, perform shaping, cooling, and winding to obtain the heat-shrinkable film.

[0013] Preferably, the preparation of the recycled material respectively includes the preparation steps of the functional masterbatch, the preparation steps of the polyester recycled particles, and the steps of mixing the polyester recycled particles and the functional masterbatch to prepare the recycled material. Among them, the preparation steps of the functional masterbatch include: First, dry 100-150 parts by weight of the polyester carrier at 65°C-75°C for 4 hours, grind 5-10 parts by weight of magnesium carbonate to a particle size of 0.3-0.5 μm, and dry it at 65°C-75°C for 4 hours. Dry 5-10 parts by weight of sodium dodecylbenzenesulfonate at 65°C-75°C for 4 hours; Then, add the dried polyester carrier, magnesium carbonate, sodium dodecylbenzenesulfonate, 25-30 parts by weight of diethyl phenylphosphonate, and 15-20 parts by weight of tridecyl stearate to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1000-1500 rpm for 15-30 minutes to form a mixed material; Then, melt-extrude the mixed material through a single-screw extruder. The temperature of the heating zone of the extruder is 265°C-275°C, and then water-cooled granulation is carried out to obtain the functional masterbatch.

[0014] Preferably, the preparation steps of the polyester recycled particles include: using the transparent particles obtained by crushing, decolorizing, and cleaning the recycled PET bottles or heat shrink film labels as the polyester recycled particles.

[0015] Preferably, the preparation method further includes the following steps: crushing the recycled PET bottles or heat shrink film labels, and drying them while crushing. After drying, remove the low-density and high-density impurities by air separation; The material after air separation is decolorized by a solvent.

[0016] Preferably, the preparation method further includes the following steps: drain the liquid after decolorization treatment, then inject clear water and let it stand, and remove the activated carbon by flotation cleaning; The material after flotation cleaning is dried, and polyester recycled particles with a particle size of 100-150 μm are separated for standby.

[0017] Preferably, 1.5-3% of the total mass of the clear water of sodium hydroxide and 0.5-1.0% of the total mass of the clear water of ethanolamine are added to the injected clear water.

[0018] Preferably, the steps of mixing the polyester recycled particles and the functional masterbatch to prepare the recycled material include: uniformly mixing the prepared polyester recycled particles with an average particle size of 100-150 μm and the prepared functional masterbatch in proportion, then inputting them into a single-screw extruder, filtering out impurities through melt filtration and then extruding. The temperature of the heating zone of the extruder is 265°C-275°C, and then water-cooled granulation is carried out, and finally the recycled material is prepared.

[0019] By adding a functional masterbatch to polyester recycled particles for melt modification treatment, the recycled material obtained can be directly used to prepare a heat shrinkable film. The prepared heat shrinkable film has excellent properties, meets environmental protection requirements, and has the same quality as ordinary heat shrinkable films. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following drawings are only intended to illustrate and explain the present application schematically and do not limit the scope of the present application.

[0021] Figure 1 Shows a schematic cross-sectional structure diagram of a recycled heat shrinkable film according to a specific embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] For a clearer understanding of the technical features, objectives, and effects of the present application, the specific embodiments of the present application are now described with reference to the drawings. Among them, the same components are denoted by the same reference numerals.

[0023] As shown in the figure, it shows a schematic cross-sectional structure diagram of a recycled heat shrinkable film according to a specific embodiment of the present application. The heat shrinkable film shown in the figure is composed of an A-layer surface layer, a B-layer core layer, and a C-layer bottom layer formed by extrusion molding. The A-layer and the C-layer are respectively arranged on both sides of the B-layer and are both made of ordinary film-grade polyester. The B-layer is made of a recycled material and ordinary film-grade polyester, where the recycled material accounts for 5 wt% - 95 wt% of the total mass of the core layer.

[0024] Specifically, the recycled material of the present application is prepared from polyester recycled particles that have been melt-modified. Among them, the polyester recycled particles can be transparent particles obtained by crushing, decolorizing, and cleaning recycled PET bottles or heat shrinkable film labels. The present application performs melt modification treatment on the polyester recycled particles by adding a functional masterbatch to the polyester recycled particles, thereby obtaining the recycled material. By adding a certain proportion, for example, 5% - 95%wt of the total mass of the recycled material, to the film-grade polyester, it can be used to produce the core layer of a heat shrinkable film with recycled material.

[0025] In a specific embodiment, the recycled material of the present application is prepared by mixing 60 - 80 wt% of polyester recycled particles with 20 - 40 wt% of a functional masterbatch. The polyester recycled particles are prepared from recycled PET bottles or heat shrinkable film labels. Among them, the functional masterbatch is composed of a polyester carrier and diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate, and magnesium carbonate. In a specific embodiment, the recycled material of the present application can be prepared by the following method: taking the transparent particles obtained by crushing, decolorizing, and cleaning recycled PET bottles or heat shrinkable film labels as polyester recycled particles, selecting polyester recycled particles with an average particle size of 100 - 150 μm and uniformly mixing them with the prepared functional masterbatch, and then melting and extruding through an extruder and pelletizing to obtain the recycled material.

[0026] Among them, the functional masterbatch of the present application can be prepared by the following method: uniformly mix granular polyester carrier, diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate and magnesium carbonate, and then melt-extrude and pelletize through an extruder to obtain the functional masterbatch of the present application. Among them, the content of each component in the functional masterbatch is preferably: 100-150 parts by weight of polyester carrier, 25-30 parts by weight of diethyl phenylphosphonate, 5-10 parts by weight of sodium dodecylbenzenesulfonate, 15-20 parts by weight of tridecyl stearate, and 5-10 parts by weight of magnesium carbonate.

[0027] The polyester carrier in the functional masterbatch of the present application is preferably polyethylene terephthalate (PET), polybutylene terephthalate, polypropylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate, polybutylene naphthalate, polypropylene naphthalate and their copolymers. Particularly preferably polyethylene terephthalate (PET) and its copolymers.

[0028] Taking PET as an example, the preparation method of the polyester carrier of the present application is as follows. The preferred preparation method includes the following steps: First, bis(2-hydroxyethyl) terephthalate is prepared by esterification or transesterification of terephthalic acid or dimethyl terephthalate with ethylene glycol. Then, under high temperature and vacuum conditions, a polycondensation reaction is carried out using a catalyst to polycondense bis(2-hydroxyethyl) terephthalate into polyethylene terephthalate (PET). In a specific embodiment, terephthalic acid, ethylene glycol, cyclohexanedimethanol, a catalyst and a heat stabilizer can be used as raw materials for the esterification reaction; or terephthalic acid, ethylene glycol, isophthalic acid, a catalyst and a heat stabilizer can be used as raw materials for the esterification reaction. The catalyst can be selected from any one of Ti / Si-based non-heavy metal catalysts and antimony trioxide, and its addition amount is 0.01-0.09% of the polyester quality. The heat stabilizer can be selected from phosphoric acid compounds, such as any one of phosphoric acid, phosphorous acid, polyphosphoric acid, trimethyl phosphate, triphenyl phosphate, and triethyl phosphate, and its addition amount is 0.0003-0.030% of the polyester quality.

[0029] In another specific embodiment of the present application, the polyester carrier of the present application can be prepared by the following method: Add 5.0 kg of terephthalic acid, 2.2 kg of ethylene glycol, and 1.10 g of germanium dioxide into a 20 L general polymerization reaction kettle, carry out an esterification reaction at 230-265 °C and 0.2-0.3 Mpa (gauge pressure). When the water output reaches 1200 ml, release the pressure to atmospheric pressure, add 1.025 g of triphenyl phosphate, stir at atmospheric pressure for 10 minutes, raise the temperature and reduce the pressure to below 280 °C and the pressure is below 100 Pa. After 1-3 hours of reaction, extrude, pelletize and dry to finally obtain the polyester carrier.

[0030] In a specific embodiment of the present application, the functional masterbatch of the present application can be obtained synchronously with the preparation of the polyester carrier. For example, taking PET as the polyester carrier, the preparation method of the functional masterbatch of the present application can include the following steps: First, bis(2-hydroxyethyl) terephthalate is prepared by the esterification reaction of terephthalic acid or dimethyl terephthalate with ethylene glycol. Then, under high temperature and vacuum conditions, a polycondensation reaction is carried out using a catalyst to polycondense bis(2-hydroxyethyl) terephthalate into a PET polyester carrier. In the above steps, other components except the polyester carrier in the functional masterbatch can be added in the esterification reaction stage or in the polycondensation reaction stage. Finally, the melt of the functional masterbatch containing the PET polyester carrier and other components is generated, and the melt is extruded and pelletized to obtain the functional masterbatch of the present application. In this specific embodiment, terephthalic acid, ethylene glycol, cyclohexanedimethanol, a catalyst, and a heat stabilizer can be used as raw materials for the esterification reaction; or terephthalic acid, ethylene glycol, isophthalic acid, a catalyst, and a heat stabilizer can be used as raw materials for the esterification reaction. The catalyst can be selected from any one of Ti / Si-based non-heavy metal catalysts and antimony trioxide, and its addition amount is 0.01-0.09% of the polyester mass. The heat stabilizer can be selected from phosphoric acid compounds, such as any one of phosphoric acid, phosphorous acid, polyphosphoric acid, trimethyl phosphate, triphenyl phosphate, and triethyl phosphate, and its addition amount is 0.0003-0.030% of the polyester mass.

[0031] In another specific embodiment of the present application, the functional masterbatch of the present application can be prepared by the following method: Add terephthalic acid, ethylene glycol, and germanium dioxide into a general polymerization reactor, and carry out an esterification reaction at 230-265 °C and 0.2-0.3 Mpa (gauge pressure). After the esterification is completed, the pressure is released to atmospheric pressure, triphenyl phosphate and other components except the polyester carrier in the functional masterbatch are added, and stirred at atmospheric pressure for 10 minutes. Then, the temperature is raised and the pressure is reduced to below 280 °C and the pressure is below 100 Pa, and after a reaction of 1-3 hours, finally extruded, pelletized, and dried to obtain the functional masterbatch.

[0032] As described above, in a preferred embodiment of the present application, the functional masterbatch of the present application can be prepared by the following method: Uniformly mix granular polyester carrier, diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate, and magnesium carbonate, and then melt extrude and pelletize through an extruder to obtain the functional masterbatch.

[0033] More specifically, the preparation steps of the functional masterbatch of the present application include: First, dry 100-150 parts by weight of the polyester carrier at 65°C - 75°C for 4 hours, grind 5-10 parts by weight of magnesium carbonate to a particle size of 0.3-0.5 μm, and dry it at 65°C - 75°C for 4 hours, and dry 5-10 parts by weight of sodium dodecylbenzenesulfonate at 65°C - 75°C for 4 hours. Then, add the dried polyester carrier, magnesium carbonate, sodium dodecylbenzenesulfonate, 25-30 parts by weight of diethyl phenylphosphonate, and 15-20 parts by weight of tridecyl stearate to a high-speed mixer for pre-dispersion mixing at a rotation speed of 1000-1500 rpm for 15-30 minutes to form a mixed material. Then, melt-extrude the mixed material through a single-screw extruder, and the temperature of the heating zone of the extruder is 265°C - 275°C, and then water-cooled granulation is carried out. Finally, the functional masterbatch can be obtained.

[0034] As described above, the recycled material of the present application is prepared by mixing 60-80 wt% of polyester recycled particles with 20-40 wt% of the functional masterbatch. Therefore, the preparation method of the recycled material includes, in addition to the preparation steps of the functional masterbatch described above, the preparation steps of polyester recycled particles and the steps of mixing with the functional masterbatch to prepare the recycled material.

[0035] For example, the preparation steps of the polyester recycled particles of the present application are: using the transparent particles obtained by crushing, decolorizing, and cleaning the recycled PET bottles or heat-shrinkable film labels as the polyester recycled particles. Among them, the recycled PET beverage bottles usually have labels, most of which are heat-shrinkable film labels tightly bonded to the bottle body, and a small part are adhesive peelable labels. The density of the peelable labels is very small and it is easy to separate and remove them after crushing. The caps of the recycled PET bottles need to be removed, and only the bottle body is used. Most of the current PET beverage bottles usually adopt an integral molding process at the bottle mouth part, and the materials of the bottle mouth part and the bottle body are the same. For bottles in some special fields, such as injection bottles in the medical field, the materials of the bottle mouth and the bottle body are different and may carry germs, which need to be removed.

[0036] Therefore, the preparation steps of the polyester recycled particles of the present application further include: crushing the recycled PET bottles or heat-shrinkable film labels, and performing air drying while crushing. After air drying, remove low-density and high-density impurities by air separation. Since there may be residual liquid in the beverage bottles, it is necessary to perform air drying while crushing to avoid the particles sticking and being difficult to dry. After drying, the material is easy to perform air separation operation.

[0037] The materials after air separation need to be decolorized by a solvent. For example, a decolorizing solvent commonly used in the art can be selected for decolorization. In a specific embodiment, a decolorizing agent can be prepared from 20 - 30 wt% of propylene glycol diacetate, 50 - 60 wt% of dimethyl sulfoxide, and 10 - 30 wt% of activated carbon. The materials and the decolorizing agent are soaked in a volume ratio of 1:2 for 10 - 24 hours, while continuously stirring at a speed of 20 - 30 revolutions per minute.

[0038] After the decolorization treatment, the liquid is drained, and then clear water is injected and left to stand. The activated carbon is removed by flotation cleaning. The mass ratio of the materials to the clear water is preferably between 1:3 and 1:5. The activated carbon adsorbed with the liquid has a large density and sinks to the bottom, while the PET particles have a small density and float on the upper layer. Therefore, it is very easy to fish out the PET particles by flotation, thereby removing the activated carbon. In addition, the high-density impurities that were not completely removed by air separation before can also be further removed by flotation. The flotation process also has a cleaning effect and can be operated repeatedly (since the activated carbon has a dark color and it is easy to see whether it has been completely removed, the number of flotation times can be selected according to the observed situation).

[0039] During flotation, since the materials are also repeatedly cleaned, it is preferred to add 1.5 - 3% of the total mass of the clear water of sodium hydroxide and 0.5 - 1.0% of the total mass of the clear water of ethanolamine to the injected clear water for surface treatment of the materials, to remove the attached solvent as much as possible, and at the same time change the surface properties of the materials, which is convenient for subsequent modification treatment.

[0040] The materials after flotation cleaning need to be dried, and polyester recycled particles with a particle size of 100 - 150 μm are sorted out for standby. The moisture content of the prepared polyester recycled particles needs to be lower than 0.1%.

[0041] Finally, the steps of mixing the polyester recycled particles and the functional masterbatch to prepare the recycled material include: uniformly mixing the prepared polyester recycled particles with an average particle size of 100 - 150 μm and the prepared functional masterbatch in proportion, then inputting them into a single-screw extruder, filtering out impurities through melt filtration and then extruding. The temperature of the heating zone of the extruder is 265°C - 275°C, and then water-cooled pelletizing is carried out, and finally the recycled material is prepared.

[0042] Examples 1 - 3

[0043] The functional masterbatches 1 - 3 are prepared with the raw material ratios in parts by weight shown in the following table.

[0044] Example 1 Example 2 Example 3 Polyester carrier 100 (PET) 125 (PETG) 150 (PET) Diethyl phenylphosphonate 25 28 30 Sodium dodecylbenzenesulfonate 5 7 10 Tridecyl stearate 15 18 20 Magnesium carbonate 5 8 10

[0045] The polyester carrier in the above embodiment was dried at 65°C to 75°C for 4 hours, magnesium carbonate was ground to a particle size of 0.3 to 0.5 μm, and dried at 65°C to 75°C for 4 hours. Sodium dodecylbenzenesulfonate was dried at 65°C to 75°C for 4 hours. The dried polyester carrier, magnesium carbonate, sodium dodecylbenzenesulfonate and other components in the embodiment were added to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1000 to 1500 rpm for 15 to 30 minutes to form a mixture; then the mixture was melt-extruded through a single-screw extruder, and the temperature of the heating zone of the extruder was 265°C to 275°C, and then water-cooled granulated, and finally functional masterbatches 1-3 were prepared respectively.

[0046] Examples 4-6

[0047] The prepared polyester recycled particles with an average particle size of 100 to 150 μm were uniformly mixed with functional masterbatches 1-3 respectively, input into an extruder, filtered through a melt filter to remove impurities, and then extruded and pelletized to obtain recycled materials.

[0048] The prepared recycled materials were directly put into a twin-screw extruder, and the temperature of the twin-screw extruder was adjusted to 270°C to 280°C. After melting, it was filtered and extruded into a thick sheet. After the thick sheet was prepared, the above thick sheet was preheated at a temperature of 50°C to 90°C, entered an infrared heating zone of 300°C to 500°C, and longitudinally stretched at a linear speed of 40 to 150 m / min, and the longitudinal stretching ratio was 3.0 to 4.5 to obtain a stretched sheet. Then, the stretched sheet was preheated at a temperature of 90°C to 120°C and transversely stretched at a temperature of 100°C to 160°C, and the transverse stretching ratio was 3.0 to 4.5. Then it was shaped at a temperature of 165°C to 250°C, and then cooled at a temperature of 100°C to 50°C, shaped, cooled and wound up to obtain a heat-shrinkable film with a thickness of 50 μm.

[0049] Among them, in Example 4, the polyester recycled particles were mixed with functional masterbatch 1, and the weight ratio was 4:1 to obtain heat-shrinkable film 4. In Example 5, the polyester recycled particles were mixed with functional masterbatch 2, and the weight ratio was 3:1 to obtain heat-shrinkable film 5. In Example 6, the polyester recycled particles were mixed with functional masterbatch 3, and the weight ratio was 7:3 to obtain heat-shrinkable film 6. The prepared heat-shrinkable films 4-6 were stored sealed at room temperature for one week without obvious peculiar smell.

[0050] The performance parameters of heat-shrinkable films 4-6 were measured respectively as shown in the table.

[0051] Performance parameters Tensile strength MPa Transverse thermal shrinkage rate % at 120°C for 2 - 3 seconds Film surface friction coefficient Light transmittance % Flame retardant grade UL94V - 2 Heat shrinkable film 4 297 70 0.29 90 Pass Heat shrinkable film 5 289 65 0.35 89 Pass Heat shrinkable film 6 301 68 0.32 92 Pass

[0052] As can be seen from the above performance parameters, the recycled polyester particles can be directly used to prepare heat shrinkable films after adding the functional masterbatch of the present application and undergoing melt modification treatment. The prepared heat shrinkable films not only meet the environmental protection requirements but also can basically maintain the quality of the original heat shrinkable films.

[0053] Comparative Examples 1-3

[0054] For comparison, comparative functional masterbatches 1-3 were prepared with the raw material ratios in parts by weight shown in the following table.

[0055] Comparative example 1 Comparative example 2 Comparative example 3 Polyester carrier 100 (PET) 125 (PETG) 150 (PET) Diethyl phenylphosphonate 0 40 43 Sodium dodecylbenzenesulfonate 8 0 14 Tridecyl stearate 25 28 0 Magnesium carbonate 5 8 10

[0056] Comparative Examples 4-7

[0057] Through the same process, comparative heat shrinkable films 4-6 with a thickness of 50 μm were prepared. Among them, in Comparative Example 4, the recycled polyester particles were mixed with comparative functional masterbatch 1 in a weight ratio of 4:1 to obtain comparative heat shrinkable film 4. In Comparative Example 5, the recycled polyester particles were mixed with comparative functional masterbatch 2 in a weight ratio of 3:1 to obtain comparative heat shrinkable film 5. In Comparative Example 6, the recycled polyester particles were mixed with comparative functional masterbatch 3 in a weight ratio of 7:3 to obtain comparative heat shrinkable film 6. In Comparative Example 7, no functional masterbatch was added, and a comparative heat shrinkable film 7 with a thickness of 50 μm was directly prepared from the recycled polyester particles. The prepared comparative heat shrinkable films 4-7 were sealed and stored at room temperature for one week, and obvious peculiar smells could be detected.

[0058] The performance parameters of comparative heat shrinkable films 4-7 were measured respectively as shown in the table.

[0059] Performance parameters Tensile strength MPa Transverse thermal shrinkage rate % at 120°C for 2 - 3 seconds Film surface friction coefficient Light transmittance % Flame retardant grade UL94V - 2 Comparative heat shrinkable film 4 235 38 0.83 81 Fail Comparative heat shrinkable film 5 226 45 0.76 84 Fail Comparative heat shrinkable film 6 219 33 0.77 86 Fail Comparative heat shrinkable film 7 173 30 0.85 79 Fail

[0060] Comparative Examples 8-10

[0061] Through the same process, comparative heat shrinkable films 8-10 with a thickness of 50 μm were prepared. Among them, in Comparative Example 8, only sodium hydroxide was added during the sorting and cleaning of the recycled polyester particles. In Comparative Example 9, only ethanolamine was added during the sorting and cleaning of the recycled polyester particles. In Comparative Example 10, neither sodium hydroxide nor ethanolamine was added during the sorting and cleaning of the recycled polyester particles. Similar to the foregoing Examples 1-3, in Comparative Example 8, the recycled polyester particles were mixed with functional masterbatch 1 in a weight ratio of 4:1 to obtain comparative heat shrinkable film 8. In Comparative Example 9, the recycled polyester particles were mixed with functional masterbatch 2 in a weight ratio of 3:1 to obtain comparative heat shrinkable film 9. In Comparative Example 10, the recycled polyester particles were mixed with functional masterbatch 3 in a weight ratio of 7:3 to obtain comparative heat shrinkable film 10.

[0062] Performance parameters Tensile strength MPa Transverse thermal shrinkage rate % at 120°C for 2 - 3 seconds Film surface friction coefficient Light transmittance % Flame retardant grade UL94V - 2 Comparative heat shrinkable film 8 271 58 0.43 83 Pass Comparative heat shrinkable film 9 275 53 0.48 84 Pass Comparative heat shrinkable film 10 273 55 0.51 82 Pass

[0063] It can be seen by comparison that adding sodium hydroxide and ethanolamine during the cleaning process can appropriately improve the performance of the heat-shrinkable film.

[0064] The preparation method of the three-layer heat-shrinkable film of the present application will be further described below with reference to the accompanying drawings. Specifically, the preparation method of the heat-shrinkable film of the present application includes the following steps.

[0065] First, the ordinary film made of polyester chips is weighed by an electronic scale and enters the mixing bin for mixing, and then is respectively put into the first twin-screw extruder and the third twin-screw extruder.

[0066] At the same time, the ordinary film made of polyester chips and 5 wt% - 95 wt% of the recycled material of the total core layer mass are respectively weighed by an electronic scale, enter the mixing bin for mixing, and then enter the second single-screw extruder.

[0067] Then, adjust the temperature of the first and third twin-screw extruders to 270°C - 280°C, and the temperature of the second single-screw extruder to 265°C - 280°C; after melting, filter, and use the materials extruded from the first and third twin-screw extruders as the A layer and the C layer, and the material extruded from the second single-screw extruder as the B layer, and make a three-layer composite thick sheet through a multi-layer co-extrusion process.

[0068] After the thick sheet is made, preheat the above thick sheet at a temperature of 50°C - 90°C, enter the infrared heating zone of 300°C - 500°C, and perform longitudinal stretching at a linear speed of 40 - 150 m / min, and the longitudinal stretching ratio is 3.0 - 4.5 to obtain a stretched sheet. Then, preheat the stretched sheet at a temperature of 90°C - 120°C, perform transverse stretching at a temperature of 100°C - 160°C, and the transverse stretching ratio is 3.0 - 4.5. Then, set the shape at a temperature of 165°C - 250°C, and then cool at a temperature of 100°C - 50°C, set the shape, cool, and wind up to obtain the heat-shrinkable film of the present application.

[0069] Examples 11 - 13

[0070] The three-layer heat-shrinkable film is prepared by the above method, and the performance parameters are shown in the following table.

[0071] Example 11 Example 12 Example 13 Thickness of layer A μm 2.5 μm 3.5 μm 5 μm Thickness of layer B μm 15 μm 33 μm 50 μm Thickness of layer C μm 2.5 μm 3.5 μm 5 μm Tensile strength MPa 305 320 321 Transverse thermal shrinkage rate % at 120°C for 2 - 3 seconds 64 65 69 Film surface friction coefficient ≤0.5 ≤0.5 ≤0.5 Light transmittance % 90 92 91 Flame retardant grade UL94V - 2 Pass Pass Pass

[0072] Those skilled in the art should understand that although the present application is described in the form of multiple embodiments, not each embodiment only contains an independent technical solution. Such a narrative in the specification is only for clarity. Those skilled in the art should understand the specification as a whole and regard the technical solutions involved in each embodiment as ways that can be combined with each other to form different embodiments to understand the protection scope of the present application.

[0073] The above is only a schematic specific embodiment of the present application, and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principle of the present application shall fall within the scope of protection of the present application.

Claims

1. A heat-shrinkable film for recycling is composed of an A-layer surface layer, a B-layer core layer, and a C-layer bottom layer formed by extrusion molding. The A-layer and the C-layer are respectively disposed on both sides of the B-layer and are both made of polyester for ordinary films. The B-layer is made of recycled materials with 5 wt% to 95 wt% of the total core layer mass and polyester for ordinary films; it is characterized in that, The recycled material is prepared by mixing 60 - 80 wt% of polyester recycled particles and 20 - 40 wt% of functional masterbatch. The polyester recycled particles are prepared from recycled PET bottles or heat - shrinkable film labels. The functional masterbatch consists of a polyester carrier, diethyl phenylphosphonate, sodium dodecylbenzenesulfonate, tridecyl stearate, and magnesium carbonate. The contents of the components in the functional masterbatch are: 100 - 150 parts by weight of polyester carrier, 25 - 30 parts by weight of diethyl phenylphosphonate, 5 - 10 parts by weight of sodium dodecylbenzenesulfonate, 15 - 20 parts by weight of tridecyl stearate, and 5 - 10 parts by weight of magnesium carbonate.

2. The recycled heat shrinkable film according to claim 1, characterized in that, The polyester carrier is polyethylene terephthalate and its copolymers.

3. The recycled heat-shrinkable film according to claim 1, characterized in that, The particle size of the polyester recycled particles is 50 - 200 µm.

4. A method for preparing the recycled heat - shrinkable film according to any one of claims 1 - 3, comprising the following steps: The polyester chips for ordinary films are metered by an electronic scale and enter the mixing bin for mixing, and then are respectively fed into the first twin - screw extruder and the third twin - screw extruder; Meanwhile, the polyester chips for ordinary films and 5 wt% - 95 wt% of the recycled material of the total core layer mass are respectively metered by an electronic scale, enter the mixing bin for mixing, and then enter the second single - screw extruder; Then, the temperatures of the first and third twin - screw extruders are adjusted to 270°C - 280°C, and the temperature of the second single - screw extruder is adjusted to 265°C - 280°C; after melting, through filtration, the materials extruded from the first and third twin - screw extruders are used as the A layer and the C layer, and the material extruded from the second single - screw extruder is used as the B layer, and a three - layer composite thick sheet is made through a multi - layer co - extrusion process; After obtaining the thick sheet, the above - mentioned thick sheet is pre - heated at a temperature of 50°C - 90°C, enters an infrared heating zone of 300°C - 500°C, and is longitudinally stretched at a linear speed of 40 - 150 m / min, and the longitudinal stretching ratio is 3.0 - 4.5 to obtain a stretched sheet; then, the stretched sheet is pre - heated at a temperature of 90°C - 120°C and is transversely stretched at a temperature of 100°C - 160°C, and the transverse stretching ratio is 3.0 - 4.5; then it is shaped at a temperature of 165°C - 250°C, and then cooled at a temperature of 100°C - 50°C, shaped, cooled, and wound up to obtain the heat - shrinkable film.

5. The preparation method according to claim 4, characterized in that The preparation of the recycled material respectively includes the preparation steps of the functional masterbatch, the preparation steps of the polyester recycled particles, and the steps of mixing the polyester recycled particles and the functional masterbatch to prepare the recycled material, characterized in that the preparation steps of the functional masterbatch include: First, dry 100 to 150 parts by weight of the polyester carrier at 65°C to 75°C for 4 hours, grind 5 to 10 parts by weight of magnesium carbonate to a particle size of 0.3 to 0.5 μm, and dry it at 65°C to 75°C for 4 hours, and dry 5 to 10 parts by weight of sodium dodecylbenzenesulfonate at 65°C to 75°C for 4 hours; Then, add the dried polyester carrier, magnesium carbonate, sodium dodecylbenzenesulfonate, 25 to 30 parts by weight of diethyl phenylphosphonate, and 15 to 20 parts by weight of tridecyl stearate to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1000 to 1500 rpm for 15 to 30 minutes to form a mixed material; Then, melt-extrude the mixed material through a single-screw extruder, and the temperature of the heating zone of the extruder is 265°C to 275°C, and then water-cooled granulation is carried out to obtain the functional masterbatch.

6. The preparation method according to claim 5, characterized in that, The preparation steps of the polyester recycled particles include: using the transparent particles obtained by crushing, decolorizing, and cleaning the recycled PET bottles or heat shrink film labels as the polyester recycled particles.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes the following steps: Crush the recycled PET bottles or heat shrink film labels, and perform air drying while crushing, and remove low-density and high-density impurities by air separation after air drying; The material after air separation is subjected to decolorization treatment with a solvent; The decolorization treatment step is: Obtain a decolorizing agent by mixing 20 to 30 wt% of propylene glycol diacetate, 50 to 60 wt% of dimethyl sulfoxide, and 10 to 30 wt% of activated carbon; Immerse the material and the decolorizing agent in a volume ratio of 1:2 for 10 to 24 hours, and continuously stir at a speed of 20 to 30 revolutions per minute.

8. The preparation method according to claim 7, characterized in that, The preparation method further includes the following steps: Drain the liquid after decolorization treatment, then inject clear water and let it stand, and remove the activated carbon by flotation cleaning; The material after flotation cleaning is dried, and polyester recycled particles with a particle size of 100 to 150 μm are sorted out for standby.

9. The preparation method according to any one of claims 5-8, characterized in that, The steps of mixing the polyester recycled particles and the functional masterbatch to prepare the recycled material include: uniformly mix the prepared polyester recycled particles with an average particle size of 100 to 150 μm and the prepared functional masterbatch in proportion, then input them into a single-screw extruder, filter out impurities through melt filtration and then extrude, the temperature of the heating zone of the extruder is 265°C to 275°C, and then water-cooled granulation is carried out, and finally the recycled material is prepared.

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