A special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology and a preparation method thereof

Abstract

A special environmentally friendly, light, low-density white shrink film formed based on micro-pore forming technology and a preparation method thereof, belonging to the technical field of polymer packaging materials. The specific formula of the polyester heat shrink film is composed of pore-forming agent composite modified polyethylene terephthalate, diol-modified polyethylene terephthalate, polybutylene terephthalate, opening lubricant, and filler. The white shrink film obtained by the invention has a thickness of 30-100 μm and a volume density of 1.04-1.17 g / cm 3 TD tensile strength is 125~132MPa, MD tensile strength is 35~48MPa, TD elongation at break is 36~40%, MD elongation at break is 209~236%, TD shrinkage is 42~73%, MD shrinkage is 1~12%, light transmittance is 16.4~19.2%, UV blocking rate is 99.1~99.5%, and dynamic friction coefficient is 0.42~0.47μs.

Description

Technical Field

[0001] The present invention relates to a special environmental protection light and thin low-density white shrink film formed by a micro-hole forming technology and a preparation method thereof, belonging to the technical field of polymer packaging materials. Background Art

[0002] In recent years, the shortage of petroleum resources has become increasingly obvious. Plastic products are one of the main consumption methods of petroleum resources. However, the disposal process after a large amount of plastic products are used brings environmental pollution problems, which have seriously affected the development and living space of various regions, countries, and even mankind. The research and application of green plastic products materials are imminent.

[0003] With the increasing use amount and wider application fields of PETG heat shrinkable films, the development of PETG heat shrinkable films should also be towards the direction of energy conservation and environmental protection, which is an inevitable way for the green development of the plastic industry. Because world resources have always been a hot topic for mankind, the slogan of saving resources has gradually penetrated into people's hearts. Therefore, the development of shrink films in the direction of environmental protection is also an inevitable trend.

[0004] The density of common polyethylene terephthalate is 1.38 - 1.41 g / cm 3 It belongs to a kind of polymer material with a relatively large density. PETG heat shrinkable film belongs to a copolyester modified material, and its density is about 1.25 - 1.35 g / cm 3 . The relatively large density results in a small use area per unit weight, which increases the use cost and the difficulty of waste treatment. In order to reduce costs and environmental pollution, modern green environmental protection packaging has put forward the development concept of being thinner and lighter, which poses new requirements for polyester heat shrinkable films.

[0005] Chinese Patent CN115742517A discloses a micro-porosity adjustable low-density PETG heat-shrinkable film and its preparation method. The micro-porosity adjustable low-density PETG heat-shrinkable film includes a core layer and upper and lower surface layers. It is characterized in that the upper and lower surface layers mainly include 100 parts by mass of modified polyethylene terephthalate glycol (PETG) polyester chips and 1 to 3 parts of an antiblocking agent, and the core layer mainly includes 100 parts by mass of PETG polyester chips, 0 to 30 parts of a white masterbatch, 10 parts of PET polyester chips, and 2 to 5 parts of a foaming agent. For the preparation method of the above heat-shrinkable film, each raw material is mixed, extruded and melt-plasticized, cast into a film through a die head, biaxially stretched, cooled and shaped, photo-cured, drawn, trimmed, and wound to obtain the composite film. Only the core layer film of this patent has a micro-porous structure. This is mainly because the use of a foaming agent to create pores in this patent causes great damage to the mechanical properties of the polyester film. Therefore, two upper and lower surface layers without foaming and pore-forming treatment are needed to enhance the overall mechanical properties. In addition, for the core layer film foamed by the foaming agent, the pore size is relatively large and the light transmittance is relatively large. Therefore, the micro-porosity adjustable low-density PETG heat-shrinkable film obtained by this patent does not have a high ultraviolet light barrier rate and is thus difficult to apply in the field of high-ultraviolet-barrier packaging films.

[0006] Chinese Patent CN116198202A discloses a recyclable micro-porous PETG heat-shrinkable film and its preparation method. The recyclable micro-porous PETG heat-shrinkable film has a 5-layer structure, and the A-layer surface layer and the B-layer intermediate layer are arranged on both sides of the C-layer core layer; the A-layer surface layer uses recyclable PETG polyester chips, polyglycolic acid (PGA), a multi-epoxy chain extender ADR, and a silica antiblocking and slip masterbatch; the B-layer intermediate layer uses recyclable PETG polyester chips and a cycloolefin-based pore-forming agent; the C-layer core layer uses recyclable PETG polyester chips. The micro-porous PETG heat-shrinkable film prepared by this patent has a 5-layer structure, which is very complex. Moreover, the cycloolefin-based pore-forming agent is only added to one of the 5 layers. The reduction of the overall density can only rely on the density of the micro-porous layer being reduced to a very low state. In this way, the mechanical properties of the micro-porous layer decline too much, and it is also difficult to obtain good high-ultraviolet-barrier performance as a whole.

[0007] As can be seen above, there are still disadvantages in current PETG heat-shrinkable films, such as high density, poor thinness and lightness, and low ultraviolet barrier rate. Therefore, it is of great significance to develop a white shrinkable film with good environmental protection, the characteristics of being thin, light and low-density, and at the same time having a high ultraviolet barrier rate for enriching the selectivity of film materials in the packaging field. Summary of the Invention

[0008] In view of the deficiencies of the above-mentioned existing technologies, the present invention provides a special environmental protection lightweight low-density white shrink film formed by micro-poration technology and a preparation method thereof, achieving the following invention objectives: preparing a white shrink film with light weight, low density, good mechanical properties, and high ultraviolet barrier rate based on micro-poration technology.

[0009] To achieve the above invention objectives, the present invention adopts the following technical solutions:

[0010] A special environmental protection lightweight low-density white shrink film formed by micro-poration technology and a preparation method thereof. The raw material formula of the special environmental protection lightweight low-density white shrink film formed by micro-poration technology is as follows, by weight:

[0011] 60 - 120 parts of pore-forming agent compound modified polyethylene terephthalate,

[0012] 10 - 40 parts of polyethylene terephthalate modified by diol,

[0013] 5 - 13 parts of polybutylene terephthalate,

[0014] 1 - 3 parts of anti-blocking and slip agent,

[0015] 0 - 15 parts of filler;

[0016] The polyethylene terephthalate modified by diol is polyethylene terephthalate co-modified by neopentyl glycol and diethylene glycol, wherein the molar percentage of neopentyl glycol is 25 - 35%, and the molar percentage of diethylene glycol is 5 - 15%;

[0017] The polyethylene terephthalate modified by diol has a glass transition temperature of 70 - 83°C, a melting temperature of 220 - 260°C, an intrinsic viscosity of 0.4 - 1.0 dl / g, and a number average molecular weight of 17000 - 21000 g / mol;

[0018] The polybutylene terephthalate has a glass transition temperature of 43 - 50°C, a melting temperature of 220 - 240°C, an intrinsic viscosity of 0.6 - 1.0 dl / g, and a number average molecular weight of 35000 - 40000 g / mol;

[0019] The anti-blocking and slip agent is silica, with a particle size of 1 - 5 μm;

[0020] The filler is one of titanium dioxide and calcium carbonate, with a particle size of 0.5 - 2 μm;

[0021] The following is a further improvement of the above technical solution:

[0022] Step 1. Preparation of pore-forming agent compound modified polyethylene terephthalate

[0023] (1) Preparation of modified nano-sepiolite

[0024] After the nano-sepiolite is dried at high temperature, it is put into a high-speed dispersion kettle, and then acetone is added. After being dispersed evenly at a high-speed dispersion rate, the dispersion rate is reduced to a low-speed dispersion rate, and an amino-silane coupling agent is added. After the low-speed dispersion stirring reaction is completed, the modified nano-sepiolite is obtained after filtration, washing with absolute ethanol, and drying at low temperature;

[0025] The particle size of the nano-sepiolite is 10~100nm;

[0026] The amino-silane coupling agent is one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane;

[0027] The mass ratio of the nano-sepiolite, acetone, and amino-silane coupling agent is 10~35:140~260:1~6;

[0028] For the high-temperature drying, the drying temperature is 85~110°C, and the drying time is 8~15 hours;

[0029] The high-speed dispersion rate is 9000~14000 revolutions per minute;

[0030] The low-speed dispersion rate is 1000~2500 revolutions per minute;

[0031] For the low-speed dispersion stirring reaction, the dispersion rate is 1000~2500 revolutions per minute, and the reaction time is 5~10 hours;

[0032] For the washing with absolute ethanol, the number of washing times is 2~4 times. Each time of washing, the amount of absolute ethanol used is 1~1.3 times the mass of the solid obtained by filtration;

[0033] For the low-temperature drying, the drying temperature is 60~80°C, and the drying time is 5~9 hours.

[0034] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate

[0035] Add the modified nano-sepiolite and fluorinated solvent into a high-speed dispersion kettle. After dispersing them evenly at high speed, reduce the dispersion rate to low speed, and then add polyethylene terephthalate and epoxy chain extender. Heat up and keep the temperature constant at the boiling point temperature of the fluorinated solvent. Under the condition of condensation reflux, react fully until the viscosity of the liquid in the kettle no longer changes. Then transfer the liquid in the kettle to a centrifugal scraping thin-film evaporator. After evaporating the fluorinated solvent, the obtained solid is the pore-forming agent composite modified polyethylene terephthalate;

[0036] The fluorinated solvent is one of hexafluorobutanol and hexafluoroisopropanol;

[0037] The epoxy chain extender is an oligomer of BASF Joncryl® ADR series, and the specific grade is one of ADR-4400, ADR-4468, ADR-4380, and ADR-4385;

[0038] The glass transition temperature of the polyethylene terephthalate is 75 - 85 °C, the melting temperature is 250 - 270 °C, the intrinsic viscosity is 0.5 - 0.7 dl / g, and the number average molecular weight is 15000 - 20000 g / mol;

[0039] The mass ratio of the modified nano-sepiolite, fluorinated solvent, polyethylene terephthalate, and epoxy chain extender is 4 - 9:260 - 580:45 - 120:0.5 - 4;

[0040] For the high-speed dispersion, the dispersion rate is 8000 - 12000 revolutions per minute;

[0041] The low-speed dispersion rate is 1500 - 2600 revolutions per minute.

[0042] Step 2: Preparation of a special environmental protection lightweight low-density white shrink film formed based on micro-porous technology

[0043] (1), Melting and extrusion

[0044] According to the raw material formula of the special environmental protection lightweight low-density white shrink film formed based on micro-porous technology, dry all the raw materials involved in the formula at 110 - 140 °C for 2 - 4 hours, and then cool them to room temperature in a dry environment. Then, according to the raw material formula of the special environmental protection lightweight low-density white shrink film in parts by weight, mix the raw materials and put them into a twin-screw extruder. Heat all the heating zones of the twin-screw extruder to 240 - 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. By adjusting the number of twin-screw extruders and the matching die head, cast sheets with single-layer, double-layer co-extrusion, and three-layer co-extrusion structures are prepared;

[0045] (2), Stretching

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

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

[0048] The biaxial stretching process first performs longitudinal stretching and then transverse stretching;

[0049] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film, the stretching temperature is 85-100°C, the ratio is 1-3:1, and the tensile strength is 20-90MPa; the longitudinally stretched base film is heat-set on the surface of a group of cooling rollers, the setting temperature is 75-140°C, and the setting time is 2-4 seconds;

[0050] The transverse stretching is carried out on a transverse stretching machine, the stretching temperature is 75-135°C, the transverse stretching ratio is 2-5:1, the tensile strength is 180-200MPa, and the stretched base film is heat-set and then cooled, the setting temperature is 50-90°C, and the setting time is 1-3 seconds;

[0051] (3) Traction, trimming and winding

[0052] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then it is pulled to the winder to wind the base film, obtaining a large roll of special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology.

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

[0054] ​​1. The present invention utilizes nano-scale sepiolite as a micro pore-forming agent to promote the formation of a microporous structure during the stretching process of a polyester film. To ensure the nano-scale dispersion of nano-scale sepiolite in the polyester matrix, first, the surface of sepiolite is modified by an amino-silane coupling agent to reduce the surface polarity of nano-sepiolite. Second, through a high-speed solvent dispersion process, the modified nano-sepiolite is first dispersed into a fluorinated solvent to ensure that the modified nano-sepiolite is dispersed into the solvent system in the form of nano-scale single particles. Then, polyester resin and an epoxy chain extender are added. In the fluorinated solvent environment, during the reaction process of the polyester polymer chain and the epoxy chain extender, the nano-scale sepiolite is adsorbed on the polyester polymer chain segment in the form of nano-scale single particles. Moreover, there is a strong hydrogen bond between the amino group on the surface of the modified sepiolite and the carboxyl group at the end of the polyester molecular chain, and the modified nano-sepiolite will preferentially adsorb at the end of the polyester polymer chain. The hydroxyl functional group formed after the opening of the epoxy group during the chain extension reaction of the epoxy chain extender will also adsorb the modified nano-sepiolite by the hydrogen bond effect. In the above processes, under the induction of the hydrogen bond adsorption effect, the modified nano-sepiolite will be relatively orderly dispersed in the polyester resin in the form of nano-scale single particles. During the subsequent hot-melt film stretching process, this hydrogen bond adsorption effect will enhance the binding force between the polyester molecular chain and the nano-sepiolite. The stronger binding force will induce the formation of small and uniform ultra-microporous structures, avoiding the appearance of larger micropores during the stretching process, thereby avoiding too much damage to the mechanical properties of the film. Moreover, the ultra-microporous structure will also improve the ultraviolet light barrier rate of the film while reducing the light transmittance of the film;

[0055] 2. The present invention improves the molecular weight of the polyester resin by adding an epoxy chain extender, and thus can greatly improve the mechanical properties of the polyester film. To promote the full and thorough chain extension reaction between the epoxy chain extender and the polyester resin, the present invention avoids the melting reaction method in the conventional technology and designs a solvent reaction system to enable the two polymers, polyester and epoxy chain extender, to carry out the chain extension reaction in a state where the molecular chain segments are fully stretched. This can ensure the high reaction rate, the completeness of the reaction, and to a certain extent, realize the controllable adjustment of the chain extension reaction. In addition, during this reaction process, the modified nano-sepiolite will also be directionally adsorbed in the polyester molecular chain segment by using the strong hydrogen bond adsorption effect, realizing the nano-scale dispersion of nano-sepiolite in the polyester matrix resin;

[0056] 3. The special environmentally friendly, light, thin, low-density white shrink film formed by the present invention based on the micro pore-forming technology has a thickness of 30 - 100 μm and a bulk density of 1.04 - 1.17 g / cm 3, the TD tensile strength is 125 - 132 MPa, the MD tensile strength is 35 - 48 MPa, the TD elongation at break is 36 - 40%, the MD elongation at break is 209 - 236%, the TD shrinkage rate is 42 - 73%, the MD shrinkage rate is 1 - 12%, the light transmittance is 16.4 - 19.2%, the ultraviolet light barrier rate is 99.1 - 99.5%, and the dynamic friction coefficient is 0.42 - 0.47 μs. Detailed implementation manners

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

[0058] Example 1: A preparation method of a special environmental protection thin and lightweight low-density white shrink film formed based on micro-hole forming technology

[0059] Step 1: Preparation of pore-forming agent composite modified polyethylene terephthalate

[0060] (1) Preparation of modified nano-sepiolite

[0061] After the nano-sepiolite is dried at high temperature, it is put into a high-speed dispersion kettle, and then acetone is added. After being dispersed evenly at a high-speed dispersion rate, the dispersion rate is reduced to a low-speed dispersion rate, and an amino silane coupling agent is added. After the low-speed dispersion stirring reaction is completed, it is filtered, washed with absolute ethanol, and dried at low temperature to obtain modified nano-sepiolite;

[0062] The particle size of the nano-sepiolite is 30 nm;

[0063] The amino silane coupling agent is 3-aminopropylmethyldimethoxysilane;

[0064] The mass ratio of the nano-sepiolite, acetone, and amino silane coupling agent is 25:200:3;

[0065] For the high-temperature drying, the drying temperature is 100 °C and the drying time is 11 hours;

[0066] The high-speed dispersion rate is 12,000 revolutions per minute;

[0067] The low-speed dispersion rate is 2,000 revolutions per minute;

[0068] For the low-speed dispersion stirring reaction, the dispersion rate is 2,000 revolutions per minute and the reaction time is 8 hours;

[0069] For the absolute ethanol washing, the washing times are 3 times, and each time, the amount of absolute ethanol used is 1.2 times the mass of the solid obtained by filtration;

[0070] For the low-temperature drying, the drying temperature is 70 °C and the drying time is 8 hours.

[0071] (2) Preparation of Porogen Composite Modified Polyethylene Terephthalate

[0072] Add the modified nano-sepiolite and fluorinated solvent into a high-speed dispersion kettle. After dispersing evenly at high speed, reduce the dispersion rate to low speed, and then add polyethylene terephthalate and epoxy chain extender. Heat up and keep the temperature constant at the boiling point temperature of the fluorinated solvent. Under the condition of condensation reflux, react fully until the viscosity of the liquid in the kettle no longer changes. Then transfer the liquid in the kettle to a centrifugal scraping thin-film evaporator. The solid obtained after evaporating the fluorinated solvent is the porogen composite modified polyethylene terephthalate;

[0073] The fluorinated solvent is hexafluorobutanol;

[0074] The epoxy chain extender is an oligomer of BASF Joncryl® ADR series, and the specific grade is ADR-4400;

[0075] The glass transition temperature of the polyethylene terephthalate is 80 °C, the melting temperature is 260 °C, the intrinsic viscosity is 0.6 dl / g, and the number average molecular weight is 18000 g / mol;

[0076] The mass ratio of the modified nano-sepiolite, fluorinated solvent, polyethylene terephthalate, and epoxy chain extender is 6:380:100:2;

[0077] For the high-speed dispersion, the dispersion rate is 10000 revolutions per minute;

[0078] The low-speed dispersion rate is 2000 revolutions per minute.

[0079] Step 2. Preparation of Special Environmental Protection Lightweight Low-Density White Shrink Film Molded Based on Micro-Pore Formation Technology

[0080] The raw material formula of the special environmental protection lightweight low-density white shrink film molded based on micro-pore formation technology is as follows, by weight:

[0081] 100 parts of porogen composite modified polyethylene terephthalate,

[0082] 20 parts of polyethylene terephthalate modified by diol,

[0083] 8 parts of polybutylene terephthalate,

[0084] 2 parts of anti-blocking and slip agent,

[0085] 6 parts of filler;

[0086] The ethylene glycol-modified polyethylene terephthalate is a polyethylene terephthalate co-modified with neopentyl glycol and diethylene glycol, wherein the molar percentage of neopentyl glycol is 30% and the molar percentage of diethylene glycol is 11%;

[0087] The ethylene glycol-modified polyethylene terephthalate has a glass transition temperature of 78 °C, a melting temperature of 240 °C, an intrinsic viscosity of 0.7 dl / g, and a number average molecular weight of 19,000 g / mol;

[0088] The polybutylene terephthalate has a glass transition temperature of 48 °C, a melting temperature of 230 °C, an intrinsic viscosity of 0.7 dl / g, and a number average molecular weight of 38,000 g / mol;

[0089] The antiblocking and slip agent is silica with a particle size of 3 μm;

[0090] The filler is titanium dioxide with a particle size of 1 μm;

[0091] (1), Melting and extrusion

[0092] According to the raw material formula of the special environmental protection lightweight low-density white shrink film formed based on the micro-porous forming technology, all the raw materials involved in the formula are dried at 120 °C for 3 hours, and then cooled to room temperature in a dry environment. Then, according to the raw material formula of the special environmental protection lightweight low-density white shrink film in parts by weight formed based on the micro-porous forming technology, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are all heated to 260 °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. By adjusting the number of twin-screw extruders and the matching die head, cast sheets with single-layer, double-layer co-extrusion, and three-layer co-extrusion structures are prepared;

[0093] (2), Stretching

[0094] For the stretching, the cast sheet is stretched by a unidirectional stretching process to obtain a base film;

[0095] The unidirectional stretching process is longitudinal stretching;

[0096] For the longitudinal stretching, it is stretched into a base film on a longitudinal stretching machine. The stretching temperature is 90 °C, the stretching ratio is 2:1, and the stretching strength is 60 MPa; The base film after longitudinal stretching is heat-set on the surface of a set of cooling rolls. The setting temperature is 100 °C and the setting time is 3 seconds;

[0097] (3), Traction, trimming, and winding

[0098] The stretched base film enters the traction station, where the edge device in the traction station trims the edges of the base film with a trimming knife, and then it is pulled to the winder to wind up the base film, obtaining a large roll of special environmentally friendly, thin, light, low-density white shrink film formed based on the micro-porous technology.

[0099] Example 2: A preparation method of a special environmentally friendly, thin, light, low-density white shrink film formed based on the micro-porous technology

[0100] Step 1: Preparation of pore-forming agent composite modified polyethylene terephthalate

[0101] (1) Preparation of modified nano-sepiolite

[0102] After drying the nano-sepiolite at high temperature, it is put into a high-speed dispersion kettle, and then acetone is added. After being dispersed evenly at a high-speed dispersion rate, the rate is reduced to a low-speed dispersion rate, and an amino-silane coupling agent is added. After the low-speed dispersion stirring reaction is completed, it is obtained after filtration, washing with absolute ethanol, and drying at low temperature;

[0103] The particle size of the nano-sepiolite is 10 nm;

[0104] The amino-silane coupling agent is 3-aminopropylmethyldiethoxysilane;

[0105] The mass ratio of the nano-sepiolite, acetone, and amino-silane coupling agent is 10:140:1;

[0106] For the high-temperature drying, the drying temperature is 85 °C and the drying time is 8 hours;

[0107] The high-speed dispersion rate is 9000 revolutions per minute;

[0108] The low-speed dispersion rate is 1000 revolutions per minute;

[0109] For the low-speed dispersion stirring reaction, the dispersion rate is 1000 revolutions per minute and the reaction time is 5 hours;

[0110] For the washing with absolute ethanol, the number of washing times is 2 times. Each time when washing, the amount of absolute ethanol used is 1 time the mass of the solid obtained by filtration;

[0111] For the low-temperature drying, the drying temperature is 60 °C and the drying time is 5 hours.

[0112] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate

[0113] Add the modified nano-sepiolite and fluorinated solvent into a high-speed dispersion kettle. After dispersing evenly at high speed, reduce the dispersion rate to low speed, and then add polyethylene terephthalate and epoxy chain extender. Heat up and keep the temperature constant at the boiling point temperature of the fluorinated solvent. Under the condition of condensation reflux, react fully until the viscosity of the liquid in the kettle no longer changes. Then transfer the liquid in the kettle to a centrifugal scraping thin-film evaporator. The solid obtained after evaporating the fluorinated solvent is the pore-forming agent composite modified polyethylene terephthalate;

[0114] The fluorinated solvent is hexafluoroisopropanol;

[0115] The epoxy chain extender is an oligomer of BASF Joncryl® ADR series, and the specific grade is ADR-4468;

[0116] The glass transition temperature of the polyethylene terephthalate is 75 °C, the melting temperature is 250 °C, the intrinsic viscosity is 0.5 dl / g, and the number average molecular weight is 15000 g / mol;

[0117] The mass ratio of the modified nano-sepiolite, fluorinated solvent, polyethylene terephthalate, and epoxy chain extender is 4:260:45:0.5;

[0118] For the high-speed dispersion, the dispersion rate is 8000 revolutions per minute;

[0119] The low-speed dispersion rate is 1500 revolutions per minute.

[0120] Step 2. Preparation of a special environmental protection thin, light, low-density white shrink film formed based on micro-porous technology

[0121] The raw material formula of the special environmental protection thin, light, low-density white shrink film formed based on micro-porous technology is as follows, by weight:

[0122] Pore-forming agent composite modified polyethylene terephthalate 60 parts,

[0123] Neopentyl glycol and diethylene glycol co-modified polyethylene terephthalate 10 parts,

[0124] Polybutylene terephthalate 5 parts,

[0125] Opening and lubricating agent 1 part;

[0126] The neopentyl glycol and diethylene glycol co-modified polyethylene terephthalate is a polyethylene terephthalate co-modified by neopentyl glycol and diethylene glycol, where the molar percentage of neopentyl glycol is 25% and the molar percentage of diethylene glycol is 5%;

[0127] The diol-modified polyethylene terephthalate has a glass transition temperature of 70°C, a melting temperature of 220°C, an intrinsic viscosity of 0.4 dl / g, and a number average molecular weight of 17000 g / mol;

[0128] The polybutylene terephthalate has a glass transition temperature of 43°C, a melting temperature of 220°C, an intrinsic viscosity of 0.6 dl / g, and a number average molecular weight of 35000 g / mol;

[0129] The opening lubricant is silicon dioxide with a particle size of 1 μm;

[0130] (1) Melt extrusion

[0131] According to the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology, all the raw materials involved in the formula are dried at 110°C for 2 hours, and then placed in a dry environment to cool to room temperature, and then according to the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology in parts by weight, the raw materials are mixed and put into a twin-screw extruder, and the heating zones of the twin-screw extruder are heated to 240°C to melt and extrude the mixed raw materials, and the melt extruded from the die head is cooled and solidified on the surface of the casting roll to form a casting sheet, and the casting sheets of single-layer, double-layer co-extrusion and three-layer co-extrusion structures are prepared by adjusting the number of twin-screw extruders and matching die heads;

[0132] (2) Stretch

[0133] The stretching comprises stretching the cast sheet using a uniaxial stretching process to obtain a base film;

[0134] The unidirectional stretching process is transverse stretching;

[0135] The transverse stretching is carried out on a transverse stretching machine, the stretching temperature is 75°C, the transverse stretching ratio is 2:1, the tensile strength is 180MPa, and the stretched base film is heat-set and then cooled, the setting temperature is 50°C, and the setting time is 1 second;

[0136] (3) Traction, trimming and winding

[0137] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then it is pulled to the winder to wind the base film, obtaining a large roll of special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology.

[0138] Example 3: A method for preparing a special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology

[0139] Step 1, Preparation of pore-forming agent composite modified polyethylene terephthalate

[0140] ​​​​​​​(1) Preparation of modified nano-sepiolite

[0141] After drying the nano-sepiolite at high temperature, it is put into a high-speed dispersion kettle, and then acetone is added. After being dispersed evenly at a high-speed dispersion rate, the dispersion rate is reduced to a low-speed dispersion rate, and an amino-silane coupling agent is added. After the low-speed dispersion and stirring reaction is completed, the modified nano-sepiolite is obtained after filtration, washing with absolute ethanol, and drying at low temperature;

[0142] The particle size of the nano-sepiolite is 100 nm;

[0143] The amino-silane coupling agent is 3-aminopropyltrimethoxysilane;

[0144] The mass ratio of the nano-sepiolite, acetone, and amino-silane coupling agent is 35:260:6;

[0145] For the high-temperature drying, the drying temperature is 110 °C and the drying time is 15 hours;

[0146] The high-speed dispersion rate is 14,000 revolutions per minute;

[0147] The low-speed dispersion rate is 2,500 revolutions per minute;

[0148] For the low-speed dispersion and stirring reaction, the dispersion rate is 2,500 revolutions per minute and the reaction time is 10 hours;

[0149] For the washing with absolute ethanol, the number of washing times is 4 times. Each time during washing, the amount of absolute ethanol used is 1.3 times the mass of the solid obtained by filtration;

[0150] For the low-temperature drying, the drying temperature is 80 °C and the drying time is 9 hours.

[0151] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate

[0152] The modified nano-sepiolite and a fluorinated solvent are added to a high-speed dispersion kettle. After being dispersed evenly at a high speed, the dispersion rate is reduced to a low speed, and then polyethylene terephthalate and an epoxy chain extender are added. The temperature is raised and kept constant at the boiling point temperature of the fluorinated solvent. Under the condition of condensation reflux, the reaction is carried out until the viscosity of the liquid in the kettle no longer changes. Then the liquid in the kettle is transferred to a centrifugal scraping thin-film evaporator, and the solid obtained after evaporating the fluorinated solvent is the pore-forming agent composite modified polyethylene terephthalate;

[0153] The fluorinated solvent is 1,1,1,3,3,3-hexafluorobutanol;

[0154] The epoxy chain extender is an oligomer of BASF Joncryl® ADR series, and the specific grade is ADR-4380;

[0155] The glass transition temperature of the polyethylene terephthalate is 85 °C, the melting temperature is 270 °C, the intrinsic viscosity is 0.7 dl / g, and the number average molecular weight is 20,000 g / mol;

[0156] The mass ratio of the modified nano-sepiolite, fluorinated solvent, polyethylene terephthalate, and epoxy chain extender is 9:580:120:4;

[0157] For the high-speed dispersion, the dispersion rate is 12,000 revolutions per minute;

[0158] The low-speed dispersion rate is 2,600 revolutions per minute.

[0159] Step 2, Preparation of a special environmentally friendly thin, lightweight, low-density white shrink film formed based on micro-porous technology

[0160] The raw material formula of the special environmentally friendly thin, lightweight, low-density white shrink film formed based on micro-porous technology is as follows, by weight:

[0161] 120 parts of pore-forming agent composite modified polyethylene terephthalate,

[0162] 40 parts of polyethylene terephthalate modified with diol,

[0163] 13 parts of polybutylene terephthalate,

[0164] 3 parts of anti-blocking and slip agent,

[0165] 15 parts of filler;

[0166] The polyethylene terephthalate modified with diol is polyethylene terephthalate co-modified with neopentyl glycol and diethylene glycol, where the molar percentage of neopentyl glycol is 35% and the molar percentage of diethylene glycol is 15%;

[0167] The polyethylene terephthalate modified with diol has a glass transition temperature of 83 °C, a melting temperature of 260 °C, an intrinsic viscosity of 1.0 dl / g, and a number average molecular weight of 21,000 g / mol;

[0168] The polybutylene terephthalate has a glass transition temperature of 50 °C, a melting temperature of 240 °C, an intrinsic viscosity of 1.0 dl / g, and a number average molecular weight of 40,000 g / mol;

[0169] The anti-blocking and slip agent is silica with a particle size of 5 μm;

[0170] The filler is calcium carbonate with a particle size of 2 μm;

[0171] (1), Melting and extrusion

[0172] According to the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology, all the raw materials involved in the formula are dried at 140°C for 4 hours, and then placed in a dry environment to cool to room temperature, and then according to the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology in parts by weight, the raw materials are mixed and put into a twin-screw extruder, and the heating zones of the twin-screw extruder are heated to 280°C to melt and extrude the mixed raw materials, and the melt extruded from the die head is cooled and solidified on the surface of the casting roll to form a casting sheet, and the casting sheets of single-layer, double-layer co-extrusion and three-layer co-extrusion structures are prepared by adjusting the number of twin-screw extruders and matching die heads;

[0173] (2) Stretch

[0174] The stretching comprises stretching the cast sheet using a biaxial stretching process to obtain a base film;

[0175] The biaxial stretching process first performs longitudinal stretching and then transverse stretching;

[0176] The longitudinal stretching is performed on a longitudinal stretching machine to form a base film, the stretching temperature is 100°C, the ratio is 3:1, and the tensile strength is 90MPa; the longitudinally stretched base film is heat-set on the surface of a group of cooling rollers, the setting temperature is 140°C, and the setting time is 4 seconds;

[0177] The transverse stretching is carried out on a transverse stretching machine, the stretching temperature is 135°C, the transverse stretching ratio is 5:1, the tensile strength is 200MPa, and the stretched base film is heat-set and then cooled, the setting temperature is 90°C, and the setting time is 3 seconds;

[0178] (3) Traction, trimming and winding

[0179] The stretched base film enters the traction station, where the edge device trims the edge of the base film with a trimming knife, and then it is pulled to the winder to wind the base film, obtaining a large roll of special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology.

[0180] Comparative Example 1: Based on Example 1, in step 1, in the preparation of the composite modified polyethylene terephthalate with a pore former, (1) the preparation of modified nano sepiolite is not performed, and in the step (2) of preparing the composite modified polyethylene terephthalate with a pore former, 6 parts of modified nano sepiolite are replaced by 6 parts of nano sepiolite. The specific operation is as follows:

[0181] Step 1, Preparation of pore-forming agent composite modified polyethylene terephthalate

[0182] Not carrying out (1) preparation of modified nano-sepiolite;

[0183] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate​​​​​

[0184] Replace 6 parts of modified nano-sepiolite with 6 parts of nano-sepiolite in equal amounts, and other operations are the same as in Example 1;

[0185] The particle size of the nano-sepiolite is 30 nm;

[0186] Step 2: Preparation of a special environmental protection thin and light low-density white shrink film formed based on micro-porous technology

[0187] The operation is the same as in Example 1.

[0188] Comparative Example 2: On the basis of Example 1, in Step 1, the preparation of pore-forming agent composite modified polyethylene terephthalate, without performing (1) the preparation of modified nano-sepiolite, (2) in the step of preparing pore-forming agent composite modified polyethylene terephthalate, do not add modified nano-sepiolite, and replace 6 parts of modified nano-sepiolite with 6 parts of fluorinated solvent in equal amounts. The specific operation is as follows:

[0189] Step 1: Preparation of pore-forming agent composite modified polyethylene terephthalate

[0190] Do not perform (1) the preparation of modified nano-sepiolite;

[0191] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate

[0192] Replace 6 parts of modified nano-sepiolite with 6 parts of fluorinated solvent in equal amounts, and other operations are the same as in Example 1;

[0193] Step 2: Preparation of a special environmental protection thin and light low-density white shrink film formed based on micro-porous technology

[0194] The operation is the same as in Example 1.

[0195] Comparative Example 3: On the basis of Example 1, in Step 1, the preparation of pore-forming agent composite modified polyethylene terephthalate, in (2) the step of preparing pore-forming agent composite modified polyethylene terephthalate, do not add epoxy chain extender, and replace 2 parts of epoxy chain extender with 2 parts of fluorinated solvent in equal amounts. The specific operation is as follows:

[0196] Step 1: Preparation of pore-forming agent composite modified polyethylene terephthalate

[0197] (1) Preparation of modified nano-sepiolite, the operation is the same as in Example 1;

[0198] (2) Preparation of pore-forming agent composite modified polyethylene terephthalate

[0199] Replace 2 parts of epoxy chain extender with 2 parts of fluorinated solvent in equal amounts, and other operations are the same as in Example 1;

[0200] Step 2: Preparation of a Special Environmental Protection Lightweight Low-Density White Shrink Film Formed by Micro-Pore Forming Technology

[0201] The operation is the same as that in Example 1.

[0202] Performance Test:

[0203] The special environmental protection lightweight low-density white shrink films obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 are tested for the following performance indicators:

[0204] 1. Thickness: The thickness value of the film is measured using a thickness tester (Millimar1240) produced by Mahr, Germany in accordance with ASTM D374.

[0205] 2. Bulk density: The bulk density of the film is calculated by the mass-volume method.

[0206] 3. Mechanical strength: Tensile strength and elongation at break are in accordance with the ASTM D882 standard.

[0207] 4. Shrinkage rate: Tested in accordance with the ASTM D1204 standard.

[0208] 5. Transmittance: Tested using a UV-2600 ultraviolet spectrophotometer produced by Shimadzu, Japan in accordance with ASTM D1003.

[0209] 6. Ultraviolet light barrier rate: Tested using an NDH-5000 produced by Nippon Denshoku in accordance with ASTM D1003.

[0210] 7. Dynamic friction coefficient: The dynamic friction coefficient (μs) of the film is measured using a friction coefficient tester produced by Blbert Instrument Company, USA in accordance with ASTM D 1894.

[0211] The test data are shown in Table 1:

[0212] Table 1

[0213]

[0214] From the data in Table 1, it can be seen that the thickness of Examples 1-3 is 30-100 μm, and the bulk density is 1.2 g / cm 3Hereinafter, the TD tensile strength is greater than 120 MPa, the MD tensile strength is greater than 35 MPa, the TD elongation at break is above 35%, the MD elongation at break is above 200 MPa, the TD shrinkage rate is above 40%, the light transmittance is less than 20%, the ultraviolet light barrier rate is greater than 99%, and the dynamic friction coefficient is below 0.5 μs. From the test data of the above three examples, it can be seen that the low-density white shrink film obtained by the present invention has remarkable advantages such as being thin, light in density, good in mechanical properties, low in light transmittance, and high in ultraviolet light barrier rate; in Comparative Example 1, the added nano-sepiolite was not surface-modified, and the bulk density of Comparative Example 1 increased to 1.28 g / cm 3 , and the tensile strength, elongation at break, and shrinkage rate in the TD and MD directions all decreased sharply. At the same time, the light transmittance of Comparative Example 1 increased, and the ultraviolet light barrier rate decreased significantly. This shows that without surface modification of nano-sepiolite, it is difficult to achieve nano-scale dispersion in the polyester film matrix, so it is difficult to form micropores in the film during the stretching process. Moreover, the aggregation of nano-sepiolite will lead to a serious decline in the mechanical properties of the polyester film, and the light transmittance and ultraviolet barrier rate also increase and decrease respectively due to the ineffective construction of the microporous structure; in Comparative Example 2, no modified nano-sepiolite was added, and the bulk density of Comparative Example 2 increased to 1.31 g / cm 3 , and the tensile strength, elongation at break, and shrinkage rate in the TD and MD directions all increased to some extent, the light transmittance increased, and the ultraviolet light barrier rate decreased to 31.2%. This shows that without adding modified nano-sepiolite, the polyester film did not form a microporous structure, resulting in a significant increase in bulk density, an increase in mechanical properties, an increase in light transmittance, and a decrease in ultraviolet light barrier rate; in Comparative Example 3, no epoxy chain extender was added, the bulk density of Comparative Example 3 increased slightly, and the tensile strength, elongation at break, and shrinkage rate in the TD and MD directions all decreased to a certain extent. Compared with Example 1, the light transmittance and ultraviolet light barrier rate changed little. This shows that the main function of the epoxy chain extender is to improve the mechanical properties of the polyester film and has little effect on the light transmittance and ultraviolet light barrier rate of the film.

[0215] 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 within the protection scope of the present invention.

Claims

1. A special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology, characterized by: The raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology is, in parts by weight: 60-120 parts of pore-forming agent composite modified polyethylene terephthalate, 10-40 parts of glycol-modified polyethylene terephthalate, 5-13 parts of polybutylene terephthalate, 1~3 parts of opening lubricant, Filler 0~15 parts; The diol-modified polyethylene terephthalate is polyethylene terephthalate co-modified with neopentyl glycol and diethylene glycol, wherein the molar percentage of neopentyl glycol is 25-35%, and the molar percentage of diethylene glycol is 5-15%; The diol-modified polyethylene terephthalate has a glass transition temperature of 70-83° C., a melting temperature of 220-260° C., an intrinsic viscosity of 0.4-1.0 dl / g, and a number average molecular weight of 17000-21000 g / mol; The polybutylene terephthalate has a glass transition temperature of 43-50° C., a melting temperature of 220-240° C., an intrinsic viscosity of 0.6-1.0 dl / g, and a number average molecular weight of 35000-40000 g / mol; The opening lubricant is silicon dioxide with a particle size of 1 to 5 μm; The filler is one of titanium dioxide and calcium carbonate, and the particle size is 0.5-2 μm; The pore-forming agent composite modified polyethylene terephthalate is prepared by: adding modified nano sepiolite and a fluorine-containing solvent into a high-speed dispersion kettle, dispersing the mixture evenly at high speed, reducing the dispersion rate to a low speed, adding polyethylene terephthalate and an epoxy chain extender, heating and maintaining the temperature to the boiling point of the fluorine-containing solvent, reacting the mixture fully under condensation reflux until the viscosity of the liquid in the kettle no longer changes, transferring the liquid in the kettle to a centrifugal scraper film evaporator, and removing the fluorine-containing solvent to obtain a solid, which is the pore-forming agent composite modified polyethylene terephthalate; The fluorinated solvent is one of hexafluorobutanol and hexafluoroisopropanol; The modified nano-sepiolite is prepared by: drying the nano-sepiolite at high temperature, placing it in a high-speed dispersion kettle, adding acetone, dispersing it uniformly at a high-speed dispersion rate, reducing the dispersion rate to a low-speed dispersion rate, adding an aminosilane coupling agent, and after the low-speed dispersion and stirring reaction is completed, filtering, washing with anhydrous ethanol, and drying at low temperature to obtain the modified nano-sepiolite; The special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology has a thickness of 30-100 μm and a volume density of 1.04-1.17 g / cm 3 TD tensile strength is 125~132MPa, MD tensile strength is 35~48MPa, TD elongation at break is 36~40%, MD elongation at break is 209~236%, TD shrinkage is 42~73%, MD shrinkage is 1~12%, light transmittance is 16.4~19.2%, UV blocking rate is 99.1~99.5%, and dynamic friction coefficient is 0.42~0.47μs.

2. The special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 1, characterized in that: The epoxy chain extender is an oligomer of the BASF Joncryl® ADR series, and the specific brand is one of ADR-4400, ADR-4468, and ADR-4380; The aminosilane coupling agent is one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane and 3-aminopropyltrimethoxysilane.

3. The special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 1, characterized in that: The particle size of the nano sepiolite is 10-100 nm; The mass ratio of the nano-sepiolite, acetone and aminosilane coupling agent is 10-35:140-260:1-6.

4. The special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 1, characterized in that: The polyethylene terephthalate has a glass transition temperature of 75-85° C., a melting temperature of 250-270° C., an intrinsic viscosity of 0.5-0.7 dl / g, and a number average molecular weight of 15000-20000 g / mol; The mass ratio of the modified nano-sepiolite, the fluorine-containing solvent, the polyethylene terephthalate and the epoxy chain extender is 4-9:260-580:45-120:0.5-4.

5. The method for preparing a special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 1, characterized in that: The method for preparing the special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology comprises three steps of melt extrusion, stretching, and traction, trimming, and winding; The melt extrusion is based on the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on the micro-pore forming technology. All the raw materials involved in the formula are dried at 110-140° C. for 2-4 hours, and then placed in a dry environment to cool to room temperature. Then, according to the raw material formula of the special environmentally friendly, thin, low-density white shrink film formed based on the micro-pore forming technology in parts by weight, the raw materials are mixed and put into a twin-screw extruder. The heating zones of the twin-screw extruder are heated to 240-280° C. to melt and extrude the mixed raw materials. The melt extruded from the die is cooled and solidified on the surface of the casting roller to form a casting sheet. By adjusting the number of twin-screw extruders and matching die heads, casting sheets with single-layer, double-layer co-extrusion and three-layer co-extrusion structures are prepared.

6. The method for preparing a special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 5, characterized in that: The stretching comprises stretching the cast sheet using one of a uniaxial stretching process and a biaxial stretching process to obtain a base film; The uniaxial stretching process is one of longitudinal stretching and transverse stretching; 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 85-100°C, the ratio is 1-3:1, and the tensile strength is 20-90 MPa; the longitudinally stretched base film is heat-set on the surface of a group of cooling rollers, the setting temperature is 75-140°C, and the setting time is 2-4 seconds; The transverse stretching is carried out on a transverse stretching machine, the stretching temperature is 75-135°C, the transverse stretching ratio is 2-5:1, the tensile strength is 180-200MPa, and the stretched base film is heat-set and then cooled, the setting temperature is 50-90°C, and the setting time is 1-3 seconds.

7. The method for preparing a special environmentally friendly, thin, low-density white shrink film formed based on micro-pore forming technology according to claim 6, characterized in that: The traction, trimming and winding are carried out, and the stretched base film enters the traction station. The edge device in the traction station trims the edge of the base film through a trimming knife, and then the base film is pulled to the winding machine to be wound up to obtain a large roll of special environmentally friendly, thin and low-density white shrink film formed based on micro-pore forming technology.

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