CN116080236B

CN116080236B - Light-blocking shrink film and preparation method thereof

Info

Publication number: CN116080236B
Application number: CN202310124634.7A
Authority: CN
Inventors: 李彬; 冯益强; 贺海峰
Original assignee: Shandong Shenghe Film New Material Co ltd
Current assignee: Shandong Shenghe Film New Material Co ltd
Priority date: 2023-02-16
Filing date: 2023-02-16
Publication date: 2023-12-15
Anticipated expiration: 2043-02-16
Also published as: CN116080236A

Abstract

The invention relates to a light-resistant shrink film and a preparation method thereof, and belongs to the technical field of heat-shrinkable polyester films. The light-blocking shrink film comprises a three-layer structure, wherein: a first polymer a layer comprising a white pigment as a white masking layer for the dark light blocking layer; a second polymer B layer comprising a dark pigment as a dark light blocking layer; the third polymer C layer, comprising a white pigment, serves as a white shading print layer for the dark light blocking layer. The invention not only has excellent light blocking effect, but also has excellent palm closing effect and attractive shrink appearance; meanwhile, the invention provides a preparation method of the light-resistant shrink film, which is low in cost. The light-blocking shrinkage film before printing is obviously rolled to the printing layer, so that the light-blocking shrinkage film is rolled to the third polymer C layer after printing, and the shrinkage time mark label is rolled to the outer side of the label sleeving object in a targeted manner. The shrink film has excellent production efficiency and attractive effect in the use process.

Description

Light-blocking shrink film and preparation method thereof

Technical Field

The invention relates to a light-resistant shrink film and a preparation method thereof, and belongs to the technical field of heat-shrinkable polyester films.

Background

The polyester heat-shrinkable film (PET heat-shrinkable film for short) is a novel heat-shrinkable packaging material, has low self-shrinkage rate, is relatively storage-resistant, and particularly accords with the characteristics of environmental protection, and the like in recent years, and is used for successfully replacing a polyvinyl chloride (PVC) heat-shrinkable film in developed countries, so that the polyester heat-shrinkable film becomes an optimal shrink packaging material.

In the use process of the common polyester shrink film, the light barrier property is very small due to the transparent material, so that the bottle body and substances in the bottle, which are sensitive to light, cannot be protected, and the bottle body is designed into a light barrier material in the market at present, so that the bottle body is difficult to recycle due to the addition of a large amount of light barrier agent.

The white shrink film and the ultraviolet ray blocking shrink film products sold in the market at present still have insufficient light blocking performance for visible light and other longer wavelength, but the damage of the light to the products to be protected is still quite large, and the requirements of the products on quality guarantee period cannot be met.

Patent number CN 108290395a discloses a light-tight shrink packaging film, the invention relates to a heat shrink film comprising a first polymer layer a containing at least one dark pigment and a second polymer layer B containing at least one white pigment, wherein the thickness ratio between the first polymer layer a and the second polymer layer B is in the range of 5:95 to 50:50, the film thickness is 20-100 μm, the light transmittance of the film is not more than 12%. And it is disclosed that the heat-shrinkable film may be composed of the first polymer layer a and the second polymer layer B, or may contain one or more additional layers other than the first polymer layer a and the second polymer layer B. An example of such a layer is a repetition of the first polymer layer a and/or the second polymer layer B.

As the use amount of the heat-shrinkable film is larger and larger, the application field is wider and wider. The development process of the heat shrinkage film also develops towards the direction of energy conservation and environmental protection, which is a necessary way for green development in the plastic industry. At present, the thickness of the shrink film is generally 30-50 mu m, and in order to ensure that the dark light-blocking layer contains enough light-blocking shrink film reclaimed materials produced by the formula, the thickness ratio of the dark light-blocking layer is further improved, so that the thickness of the white shielding layer of the dark light-blocking layer is greatly reduced, the content of white pigment is required to be improved, and white scraps are generated due to the corrosion and friction effects of palm-closing glue in the palm-closing process of the shrink packaging film due to the higher content of the white pigment. And the opaque shrink packaging film is easy to generate wrinkling phenomenon in the label sleeving process of shrink film labels.

Disclosure of Invention

The invention aims to provide a light-blocking shrink film which has excellent light-blocking effect, palm closing effect and attractive shrink appearance; meanwhile, the invention provides a preparation method of the light-resistant shrink film, which is low in cost. The light-blocking shrinkage film before printing is obviously rolled to the printing layer, so that the light-blocking shrinkage film is rolled to the third polymer C layer after printing, and the shrinkage time mark label is rolled to the outer side of the label sleeving object in a targeted manner. The shrink film has excellent production efficiency and attractive effect in the use process.

The light-blocking shrink film comprises a three-layer structure, wherein:

a first polymer a layer comprising a white pigment as a white masking layer for the dark light blocking layer;

a second polymer B layer comprising a dark pigment as a dark light blocking layer;

the third polymer C layer, comprising a white pigment, serves as a white shading print layer for the dark light blocking layer.

The thickness of the light-blocking shrinkage film is 30-50 mu m, wherein:

the thickness of the first polymer A layer accounts for 10% -30% of the total thickness;

a second polymer layer B, the thickness of which is 30% -60% of the total thickness;

the thickness of the third polymer C layer accounts for 30% -60% of the total thickness, and the absolute value of the thickness is more than or equal to 15 mu m.

The polymers of the first polymer a layer, the second polymer B layer, and the third polymer C layer all comprise a polyester raw material.

The polyester raw material is generated by esterification reaction of dibasic acid and dihydric alcohol and comprises homo-polyester and/or copolyester.

The homo-polyester is polymerized from terephthalic acid (TPA) and Ethylene Glycol (EG).

The copolyester is formed by copolymerizing one or more of terephthalic acid (TPA) and Ethylene Glycol (EG) and other dibasic acids or dihydric alcohols. Wherein other dibasic acids or dihydric alcohols are modified components of the polyester raw material.

The total content of other dibasic acids of the copolymerization component accounts for 7-50% of the total dibasic acid molar content of the copolyester, and the total content of other dihydric alcohols of the copolymerization component accounts for 7-50% of the total dihydric alcohol molar content of the copolyester.

Wherein the other dibasic acids as copolymerization components include: one or more of terephthalic acid (IPA), phthalic anhydride (OPAn), 1, 4-cyclohexanedicarboxylic acid (1, 4-CHDA), succinic anhydride (SuAn), adipic acid (AdA); other diols as a copolymerization component include: diethylene glycol (DEG), neopentyl glycol (NPG), 1, 4-Cyclohexanedimethanol (CHDM), 1, 3-Propanediol (PG), 1, 4-Butanediol (BD), 1, 6-Hexanediol (HD).

The intrinsic viscosity of the polyester raw material is 0.6 to 1.2dl/g.

The invention realizes that the shrinkage rate of the light-resistant shrinkage film in the main shrinkage direction is more than 30 percent, even more than 50 percent, even more than 70 percent, even more than 75 percent after the light-resistant shrinkage film is kept in a water bath with the temperature of 90 ℃ for 10 seconds by adjusting the types and the content of the modified components.

The first polymer a layer comprises: 25-50% of white pigment (omega), 45-75% of polyester raw material, and 0-5% of opening slipping agent. By adjusting the total content and thickness of the white pigment of the first polymer A layer, the shading of the dark color of the second polymer B layer by the first polymer A layer is realized, and the L value of the first polymer A layer is more than 80.

The second polymer B layer comprises: 0.1-10% of dark pigment, 0-30% of white pigment, 60-99.9% of polyester raw material, and 0-50% of light-blocking shrink film reclaimed material produced by the formula. The light transmittance of the light-blocking shrinkage film is less than 1%, even less than 0.5% by adjusting the total content and thickness of the dark pigment of the layer B.

The third polymer C layer comprises: 25-50% of white pigment, 45-74.9% of polyester raw material and 0.1-5% of opening slipping agent. The dark color shielding of the third polymer C layer to the second polymer B layer is realized by adjusting the total content and thickness of the white pigment of the third polymer C layer, and the L value of the third polymer C layer of the light-blocking shrink film is more than 90.

The white pigment, the dark pigment or the open slipping agent in the first polymer layer A, the second polymer layer B and the third polymer layer C are respectively mixed with polyester raw materials to form high-concentration master batches, and then the mixed master batches are mixed according to the content of the formula.

When higher levels of white pigment and/or dark pigment are desired, a polyester raw material having a higher level of modifying component is selected to meet shrinkage requirements.

When higher levels of white pigment and/or dark pigment are desired, resulting in reduced mechanical properties of the shrink film, a polyester starting material of higher intrinsic viscosity is selected, preferably having an intrinsic viscosity of greater than or equal to 0.8.

The second polymer B layer the dark pigment comprises one or more of an inorganic black pigment or an organic black dye. Carbon black, graphite, fine metal, and fine metal compound or aniline black are preferable, and carbon black is more preferable. The particle size of the dark pigment is less than 1 mu m. The present invention does not create voids around these particles during the stretching process to produce a light blocking shrink film.

The white pigment of the first polymer A layer, the second polymer B layer and the third polymer C layer is one or more of inorganic white pigment or organic white dye; titanium dioxide, calcium carbonate or barium sulfate is preferred, titanium dioxide is more preferred, and the particle size is < 1. Mu.m. The present invention does not create voids around these particles during the stretching process to produce a light blocking shrink film.

The opening slipping agent of the first polymer A layer, the second polymer B layer and the third polymer C layer is silicon dioxide, mica powder, aluminum oxide, kaolin or paraffin, preferably silicon dioxide.

In the 3-layer raw material for forming the light-blocking shrink film of the present invention, additives, preferably one or more of waxes, antioxidants, antistatic agents, nucleating agents, viscosity reducers, tackifiers, chain extenders, heat stabilizers, pigments for coloring, coloring resists or ultraviolet absorbers, are added or coated as needed.

The invention has carried on the deep verification to the use of the light-blocking shrink film. As a use method, the shrink film is generally used with the thickness of 30-50 mu m at present, but in order to ensure that the dark light-blocking layer contains enough light-blocking shrink film reclaimed materials produced under the formula, the thickness of the dark light-blocking layer is increased, so that the thickness of the white shielding layer of the dark light-blocking layer is greatly reduced, the shielding effect can be achieved only by increasing the content of white pigment, but after the content of the white pigment is higher, white scraps can be generated due to the corrosion and friction effects of palm-closing glue in the palm closing process of the shrink packaging film.

The palm closing process refers to that the printed shrink film is glued together through organic solvent glue to form a longitudinal cylinder shape, so as to form the shrink film label. When the third polymer C layer is thin and (1) the white pigment content is low, for example, 0% to 25%, a phenomenon of hiding the dark layer occurs; (2) When the white pigment content is high, for example, more than 25%, even higher, good hiding effect on the dark layer occurs, but white chips are generated due to corrosion and friction of the palm closing glue during the palm closing process of the shrink wrap film due to the high white pigment content. The white scraps can seriously influence the palm closing effect, so that the shrink film label has a flanging phenomenon in the subsequent labeling process, and cannot be suitable for the palm closing process, for example, the palm closing effect is poor after the palm closing process after printing is more than or equal to 4000 meters, even more than or equal to 2000 meters, even more than or equal to 1000 meters.

In order to solve the problems, a transparent layer without any pigment is added as a printing layer on the basis of the third polymer C layer, so that the chipping problem in the palm combining process can be effectively solved, but the phenomenon that the edge of laser coding is broken easily occurs in the laser coding process due to the fact that the white pigment of the transparent layer and the white pigment layer are too different.

And adding a fourth polymer D layer containing white pigment outside the third polymer C layer. The white pigment content of the fourth polymer D layer is 5-15%, preferably 6-12%, preferably 8-10%. The invention aims to avoid the chipping problem in the palm closing process, and simultaneously, the phenomenon of laser coding edge blurring does not occur. And adding a fourth polymer D layer containing white pigment outside the third polymer C layer. However, the proportion of the white pigment needs to be controlled, and the white pigment is obtained through experimental verification, (1) when the content of the white pigment is low, for example, the phenomenon of laser coding edge blurring occurs in 0 to 5 percent; (2) When the white pigment content is high, for example, 15% to 25%, even higher, chipping problems during the palm closing process occur. The white pigment content of the fourth polymer D layer is therefore 5 to 15%, preferably 6 to 12%, preferably 8 to 10%. The effect of the light-blocking shrink film is good in palm closing process of at least 4000 m after printing, even 6000 m or 8000 m.

As a use method, the opaque shrink packaging film in the prior art is easy to generate wrinkling in the label sleeving process of shrink film labels. The labeling process is to sleeve the cylindrical shrink film labels on the object one by one after the palm is closed, and shrink the shrink film labels after high temperature, so that the shrink film labels are tightly and attractive attached to the surface of the object. The phenomenon of wrinkling is a phenomenon that a plurality of layers of wrinkles are laminated together, which occurs at local positions in the process of labeling the finger stall. The reason that wrinkling phenomenon easily occurs in the label sleeving process is that the shrinkage rate of one side of the shrink film close to the printing ink is smaller than that of one side far from the printing ink due to the influence of the organic ink used in the printing process, and the phenomenon that the shrink film label curls towards a non-printing surface occurs. However, the printed surface of the light-blocking shrink film label is arranged on the outer side of the label sleeving object, after the label is curled towards the non-printed surface, the label is rolled towards the inner side of the label sleeving object, air between the label and the bottle body is not removed, and the process of shrinking from outside to inside is generated, so that the problem of wrinkling is easy to occur.

The light-blocking shrink film of the present invention is realized in the transverse direction (i.e., perpendicular to the machine winding direction) to solve the above-described problems. The light-blocking shrink film is obviously rolled to the printing layer before printing and is used for counteracting the influence of printing ink, so that the shrink film label is still curled to the printing surface, and the light-blocking shrink film is rolled to the third polymer C layer after printing, and the label is curled to the outer side of the label sleeving object in a targeting manner during shrinkage. The shrink film has excellent production efficiency and attractive effect in the use process.

The light-blocking shrink film realizes directional curling in the transverse direction (namely, perpendicular to the rolling direction of a machine). The shrinkage rate of the first polymer A layer, the second polymer B layer and the third polymer C layer is different by adjusting the content or the type of the polymer modified components of each layer. Thereby achieving directional curling of the light blocking shrink film in the transverse direction (i.e., perpendicular to the machine's winding direction) and thus achieving rolling to the third polymer C layer before and after printing.

The content of the modified component of the third polymer layer C is more than 0.5 percent, preferably more than 3 percent, even more than 6 percent of the mass content of the modified component of any one of the first polymer layer A or the second polymer layer B.

The content of the modified component of the third polymer layer C is 0.5-40%, preferably 3-30% and even 6-20% of the mass content of the modified component of any one of the first polymer layer A or the second polymer layer B.

The specific modified component content is compared as follows:

the first polymer A layer is less than the second polymer B layer is less than the third polymer C layer;

or first polymer a layer = second polymer B layer < third polymer C layer;

or the second polymer B layer < the first polymer A layer < the third polymer C layer.

Experiments prove that the difference of the thickness ratio of each layer is too large, the difference of the shrinkage rates of each layer is too small, the curl caused by the difference of the thickness ratio which counteracts the difference of the shrinkage rates is not obvious and even the curl is curled in the opposite direction, and the aim of directional curl is realized by reducing the difference of the thickness ratio of each layer or improving the difference of the shrinkage rates of each layer.

The light-blocking shrink film realizes directional curling in the longitudinal direction (namely the winding direction of a machine). The directional curling of the shrink film is realized by adjusting the temperature and the speed of the quenching roller and the calendaring roller, and the principle is that the directional curling of the shrink film is realized by different intermolecular orientation forces of two surface layers of the shrink film.

The preparation method of the light-resistant shrink film is characterized by comprising the following specific steps:

(1) The raw materials of the first polymer A layer, the second polymer B layer and the third polymer C layer are respectively fed according to the proportion, plasticized and extruded by respective extruders, and fused together at a die to form flaky molten resin with a multi-layer structure, wherein the temperature of the flaky molten resin is higher than the melting point range of the raw materials of the layers;

(2) Cooling the exiting sheet-like molten resin on a chill roll to form an unstretched sheet;

(3) Stretching unidirectionally or bidirectionally at a temperature 10-50 ℃ higher than the softening point, wherein the stretching multiplying power is 1-7 times;

(4) And after trimming, rolling into a large-volume light-resistant shrink film.

The preferred preparation method of the light-resistant shrink film comprises the following steps:

The processing method of the light-resistant shrink film preferably comprises the following steps:

(1) The raw materials of the layers of the first polymer A layer, the second polymer B layer, the third polymer C layer and the like are respectively fed according to a set proportion, are plasticized and extruded by respective extruders, are fused together at a die at a temperature higher than the melting point range of the raw materials of the layers, and form the flaky molten resin with a multilayer structure.

(2) The exiting sheet-like molten resin is cooled on a chill roll to form an unstretched sheet.

(3) Stretching in one or two directions at 10-50 ℃ above the softening point, comprising: longitudinal unidirectional stretching or transverse unidirectional stretching, longitudinal bidirectional stretching and transverse bidirectional stretching are performed firstly, synchronous bidirectional stretching is performed, and stretching multiplying power is 1-7 times.

(4) After longitudinal stretching, one or both sides of the film may be coated as needed, and the coating may be a slip coating, an antistatic coating, an antibacterial coating, an adhesion improving coating, or the like.

(5) And (3) trimming and rolling into a large rolled film, and carrying out corona treatment before rolling.

(6) Cutting into specifications required by customers, and packaging.

(7) The light-blocking shrink film is obtained.

When the fourth polymer layer D exists in the raw materials of the light-resistant shrink film, the raw materials of the first polymer layer A, the second polymer layer B, the third polymer layer C and the fourth polymer layer D are respectively fed according to a set proportion, plasticizing and extruding are carried out by using respective extruders, the temperature is 30+/-5 ℃ higher than the melting point range of the raw materials of the layers, and the raw materials are fused together at a die to form the flaky molten resin with a multilayer structure.

The light-blocking shrink film also comprises a hose after the heat shrink film is folded or a corresponding hose after heat shrink.

The light blocking shrink film or hose can be used to wrap an object for shrinking and adapting to the contour of the object by heat treatment.

The light-blocking shrinkage film has light transmittance less than 1%.

-the shrinkage of the light-blocking shrink film in the main shrinkage direction is > 30% after being kept in a water bath at a temperature of 90 ℃ for 10S.

-the first polymer a layer of the light-blocking shrink film has an L value > 80 and the third polymer C layer has an L value > 90.

The photo-blocking shrinkage film has good palm closing effect in the palm closing process after printing, wherein the palm closing process is at least more than or equal to 4000 meters.

The light-blocking shrink film is rolled to a third polymer C layer after printing, and no obvious wrinkling phenomenon exists in the labeling process.

Compared with the prior art, the invention has the following beneficial effects:

(1) The invention realizes excellent light-blocking rate, light transmittance less than 1%, even less than 0.5%, and meets the requirements of products on warranty period. In particular, the transparent bottle has a certain protection function on substances sensitive to light in the content, and plays a role in prolonging the shelf life.

(2) The shrinkage rate of the light-resistant shrinkage film in the main shrinkage direction after the light-resistant shrinkage film is kept for 10 seconds in a water bath at 90 ℃ is more than 30%, even more than 50%, even more than 70%, even more than 75%. Meeting the shrinkage requirements of different objects.

(3) The white shading layer of the light-blocking shrinkage film has excellent shading effect on a dark light-blocking layer, and the mass fraction of white pigment is 25-50 parts, so that the L value of a printing layer is more than 90. Has better beautiful appearance and good printing effect.

(4) According to the light-blocking shrink film, the fourth polymer D layer containing the white pigment is additionally arranged as the printing layer, so that the chipping problem in the palm closing process is avoided, and the phenomenon of edge blurring caused by laser coding is avoided. The effect of the light-blocking shrink film is good in palm closing process of at least 4000 m after printing, even 6000 m or 8000 m.

(5) The light-blocking shrink film provided by the invention has the advantages that the light-blocking shrink film before printing has obvious rolling-to-printing layer phenomenon by including but not limited to the following scheme, and the light-blocking shrink film is used for counteracting the influence of printing ink, so that the shrink film label is still curled towards a printing surface, and no obvious wrinkling phenomenon of the light-blocking shrink film in the label sleeving process is realized.

(6) The preparation method of the light-resistant shrink film is simple and feasible and is beneficial to industrial production.

Detailed Description

The present invention will be further described with reference to examples, but the present invention is not limited to these examples.

Description of the raw materials of examples and comparative examples:

(1) PET: polyethylene terephthalate

(2) 30% molNPG modified PETG: 30% mole fraction neopentyl glycol modified polyethylene terephthalate copolyester

(3) 30% molchdm modified PETG: mole fraction 30%1, 4-cyclohexanedimethanol modified polyethylene terephthalate copolyester

(4) 30% molAdA modified PETG: 30% mole fraction adipic acid modified polyethylene terephthalate copolyester

(5) 30% molBD modified PETG: mole fraction 30%1, 4-butanediol modified polyethylene terephthalate copolyester

(6) 10% moldeg and 20% molnpg modified PETG: 10% mole fraction diethylene glycol and 20% mole fraction neopentyl glycol modified polyethylene terephthalate copolyester

(7) PET with 60% omega titanium dioxide: polyethylene terephthalate with 60% titanium dioxide pigment mass fraction

(8) PET with 30% omega carbon black: polyethylene terephthalate with 30% carbon black pigment mass fraction

(9) 50% omega titanium dioxide and 30% mol npg modified PETG: 50% by mass of titanium dioxide pigment and 30% by mole of neopentyl glycol-modified polyethylene terephthalate copolyester

(10) 50% omega titanium dioxide and 30% molchdm modified PETG: 50% by mass of titanium dioxide pigment and 30% by mole of 1, 4-cyclohexanedimethanol modified polyethylene terephthalate copolyester

(11) 50% omega titanium dioxide and 20% molnpg modified PETG: 50% by mass of titanium dioxide pigment and 20% by mole of neopentyl glycol-modified polyethylene terephthalate copolyester

(12) PET masterbatch containing 5% silica: polyethylene terephthalate master batch with mass fraction of 5% of silicon dioxide

Processing methods of examples 1-4 and comparative examples 1-5:

(1) The raw materials of each layer of the first polymer A layer, the second polymer B layer and the third polymer C layer are respectively fed according to a set proportion, are plasticized and extruded by respective extruders, are fused together at a die position at a temperature which is 30+/-5 ℃ higher than the melting point range of the raw materials of each layer, and form the flaky molten resin with a multilayer structure.

(2) The exiting sheet-like molten resin was cooled on a chill roll to an unstretched sheet.

(3) The transverse unidirectional stretching is carried out at the temperature 10+/-5 ℃ higher than the softening point, and the stretching multiplying power is 5.2 times.

(4) And (3) trimming and rolling into a large rolled film, and carrying out corona treatment before rolling.

(5) Cutting into specifications required by customers, and packaging.

(6) The light-blocking shrink film is obtained.

When the fourth polymer layer D exists in the embodiment, the step (1) is to respectively feed the raw materials of the first polymer layer A, the second polymer layer B, the third polymer layer C and the fourth polymer layer D according to a set proportion, plasticize and extrude the raw materials by using respective extruders at a temperature which is 30+/-5 ℃ higher than the melting point range of the raw materials of the layers, and fuse the raw materials together at a die to form the flaky molten resin with a multi-layer structure.

The test method is as follows:

1. tensile strength and elongation at break were carried out as specified in GB/T1040.3.

2. Haze and light transmittance were determined in accordance with GB/T2410.

3. The gloss was determined as specified in GB/T8807 (45 degrees).

4. The coefficient of friction is set according to GB/T10006.

5. The wetting tension is as specified in GB/T14216.

6. Shrinkage test:

(1) Using a shrinkage sampling plate, samples of about 100mm by 100mm in size were taken.

(2) The direction marks of TD and MD are drawn on the sample, and the numerical values are precisely measured in the directions of TD and MD of the sample and marked L0.

(3) On the whole of the banner from 5-10cm on the OS side to the DS side, 5 points were taken on average across the width of the film

(4) The temperature of the water bath kettle is regulated to be 90+/-0.5 ℃, and the test is carried out after the temperature is constant.

(4) The sample is immersed, one corner of the sample is clamped by forceps, and the sample is quickly placed into a water bath kettle to be kept for 10S

(5) After the predetermined time is reached, the sample is taken out and cooled to the test environment temperature, and then the longitudinal and lateral lengths L1 not gripped by the forceps are measured, respectively, to calculate the thermal shrinkage rate of the sample.

(6) The results were averaged over 5 points.

7. The color difference L value is carried out according to the specification of GB/T2913.

8. After the palm closing effect is pressed for a certain length after printing, whether the palm closing effect is good or not is observed.

9. The label covering effect is rolled to the printing surface after printing, and whether the label is rolled to the printing surface or not is observed.

TABLE 3 detection results for examples 1-4

TABLE 4 detection results for comparative examples 1-5

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Claims

1. A light blocking shrink film comprising a three layer structure wherein:

a third polymer C layer comprising a white pigment as a white mask printing layer of the dark light blocking layer;

the thickness of the third polymer C layer accounts for 30% -60% of the total thickness, and the absolute value of the thickness is more than or equal to 15 mu m;

the first polymer a layer comprises: 25-50% of white pigment, 45-75% of polyester raw material, and 0-5% of opening slipping agent;

the second polymer B layer comprises: 0.1-10% of dark pigment, 0-30% of white pigment, 60-99.9% of polyester raw material, and 0-50% of light-blocking shrink film reclaimed material produced by the formula;

the third polymer C layer comprises: 25-50% of white pigment, 45-74.9% of polyester raw material, and 0.1-5% of opening slipping agent;

the polymers of the first polymer a layer, the second polymer B layer, and the third polymer C layer all comprise a polyester raw material; the polyester raw material is generated by esterification reaction of dibasic acid and dihydric alcohol and comprises homo-polyester and/or copolyester;

the homo-polyester is polymerized by terephthalic acid and ethylene glycol; the copolyester is formed by copolymerizing one or more of terephthalic acid, ethylene glycol and other dibasic acid or dihydric alcohol; the total content of other dibasic acids of the copolymerization component accounts for 7-50% of the mole content of the total dibasic acids of the copolyester, and the total content of other dihydric alcohols of the copolymerization component accounts for 7-50% of the mole content of the total dihydric alcohols of the copolyester;

wherein other dibasic acids or dihydric alcohols are modified components of the polyester raw material;

the modified component content of the third polymer layer C is more than 0.5% of the modified component content of any one of the first polymer layer A or the second polymer layer B.

2. The light-blocking shrink film according to claim 1, wherein the third polymer C layer has a content of a modifying component greater than 3% by mass of any one of the first polymer a layer or the second polymer B layer.

3. The light-blocking shrink film according to claim 1, wherein the content of the third polymer C layer modifying component is more than 6% by mass of any one of the first polymer a layer or the second polymer B layer modifying component.

4. The light-blocking shrink film according to claim 1, wherein the other dibasic acid as a copolymerization component comprises: one or more of terephthalic acid, phthalic anhydride, 1, 4-cyclohexanedicarboxylic acid, succinic anhydride and adipic acid; other diols as a copolymerization component include: one or more of diethylene glycol, neopentyl glycol, 1, 4-cyclohexanedimethanol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol.

5. The light-blocking shrink film of claim 1, wherein the second polymer B layer of the dark pigment comprises one or more of an inorganic black pigment or an organic black dye; the white pigment of the first polymer A layer, the second polymer B layer and the third polymer C layer is one or more of inorganic white pigment or organic white dye; the opening slipping agent of the first polymer A layer and the third polymer C layer is silicon dioxide, mica powder, aluminum oxide, kaolin or paraffin.

6. The light-blocking shrink film of claim 1, wherein a fourth polymer D layer comprising white pigment is added to the third polymer C layer; the white pigment content of the fourth polymer D layer is 5-15%.

7. The light-blocking shrink film of claim 6, wherein the white pigment content of the fourth polymer D layer is 6-12%.

8. The light-blocking shrink film of claim 6, wherein the white pigment content of the fourth polymer D layer is 8-10%.

9. A method for preparing the light-blocking shrink film according to claim 1, which comprises the following specific steps: