CN115674626A - A kind of preparation method of biodegradable heat-shrinkable film - Google Patents

Abstract

The invention discloses a preparation method of a biodegradable heat shrinkable film. The preparation method comprises the following steps: heating the biodegradable heat shrinkable film material to a molten state, casting and cooling; then, sequentially carrying out stretching treatment twice to obtain a biodegradable heat shrinkable film; the stretching treatment is preheating, transverse stretching or longitudinal stretching, and cold setting treatment; the biodegradable heat shrinkable film material comprises the following components in parts by weight: 30-95 parts of aliphatic biodegradable copolyester or aliphatic-aromatic biodegradable copolyester and 5-70 parts of polylactic acid; the longitudinal stretching ratio is (1-6): 1, transverse stretching ratio of (3-10): 1, the ratio of the longitudinal stretching ratio to the transverse stretching ratio is 1: (1-10); the temperature of cold setting treatment is 1-25 ℃. The biodegradable heat shrinkable film not only maintains higher heat shrinkage rate and tear strength in the longitudinal and transverse directions, but also is more balanced in heat shrinkage rate and tear strength in the longitudinal and transverse directions.

Description

A kind of preparation method of biodegradable heat-shrinkable film

technical field

The invention belongs to the technical field of completely biodegradable materials, and more specifically relates to a preparation method of a biodegradable heat shrinkable film.

Background technique

Heat-shrinkable film is widely used in the packaging of beverages, food, industrial products and other contents (heat shrinkage to prevent the contents of the package from separating from each other, as well as the covering and protection of the contents), as well as plastic bottle labels and other packaging purposes. The main materials of existing commonly used plastic heat shrinkable films are traditional petroleum-based plastics such as PE, PP, PVC, PET, PETG, etc., because they are not degradable and are used in a large amount as packaging for daily necessities and industrial products, there is a risk of damage in the natural environment after being discarded. It has long been difficult to handle and there is a lot of pollution after residues. In addition, due to the need for packaging effects of traditional plastic shrink films such as PE, the thickness is thicker, and it is difficult to separate from the contents or containers such as bottles and cans. The recycling method is complicated and the cost is too high, which also leads to It is difficult to promote the recycling scheme of heat shrinkable film.

Patent CN 102712766 B adopts the blown film preparation process of biodegradable aliphatic/aromatic copolyester (preferably PBST and PBAT)/polylactic acid composition to produce the method for heat-shrinkable film, wherein because the inflation ratio of blown film method is affected by film The limitation of the machinability of the foam support leads to the large anisotropy of the longitudinal and transverse heat shrinkage rate of the blown film heat shrinkable film, and the adjustment flexibility is extremely low; in addition, the blown film method has low transparency caused by low cooling efficiency of the product , the visibility of the package contents is greatly reduced.

The three-layer co-extrusion method used in the patent CN 103625061 A is used to prepare degradable heat-shrinkable films. The three-layer material is mainly polylactic acid, and the proportion of other materials is low. This material formula will lead to high stiffness and brittleness of the shrinkable film, but Insufficient flexibility makes it difficult to meet the shrink packaging requirements of bulk products; the three-layer co-extrusion process also has high equipment investment, complex product processing, shrinkage rate, transparency and other physical properties are greatly affected by the thickness ratio of each of the three layers; in addition , the patent only involves the transverse stretching process, and the prepared degraded heat shrinkable film also has the problem that the shrinkage rate varies greatly in the vertical and horizontal directions and is difficult to control.

In the patent CN 106519599 B, polyethylene terephthalate and other fillers and additives are used as the main material formula, and the heat-shrinkable film method prepared by the biaxial stretching process. The formula materials in this patent are all non-biodegradable materials, which do not have the functionality of environmental protection and degradation. After being discarded, there are environmental problems such as difficulty in landfill and recycling, and white pollution.

In summary, there are various defects in existing products, and it is difficult to meet the requirements of high balanced shrinkage and complete biodegradation at the same time, and the existing patents on biodegradable heat shrinkable films also have defects in materials and preparation methods. The preparation method and necessity of novel biodegradable shrink film material.

Contents of the invention

For the above-mentioned existing technical problems, the primary purpose of the present invention is to provide a kind of preparation method of biodegradable heat-shrinkable film, by optimizing longitudinal stretch ratio and transverse stretch ratio and draw aspect ratio (longitudinal stretch ratio and transverse stretch ratio) Ratio of elongation ratio) and cold setting treatment after stretching, so that the prepared biodegradable heat shrinkable film not only maintains a high thermal shrinkage rate and tear strength in the longitudinal and transverse directions, but also maintains a high thermal shrinkage rate in the longitudinal and transverse directions. Shrinkage and tear strength are more balanced.

The second object of the present invention is to provide the biodegradable heat-shrinkable film prepared by the above preparation method.

The third object of the present invention is to provide the application of the above-mentioned biodegradable heat-shrinkable film in the preparation of shrink-wrapped products.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

A preparation method of a biodegradable heat-shrinkable film, comprising the following steps:

S1. After putting the biodegradable heat-shrinkable film material into the extruder and heating it to a molten state, it is cast to a chilled roll for cooling to form a cast sheet;

S2. After preheating the cast sheet described in S1, perform longitudinal stretching, and then cold-setting treatment, and then preheat the cold-setting cast sheet, perform transverse stretching, and cold-setting treatment to obtain the biodegradable heat shrinkable film; or

After preheating the cast sheet described in S1, perform transverse stretching, and then cold-setting treatment, and then preheat the cold-setting cast sheet, perform longitudinal stretching, and cold-setting treatment to obtain the biodegradable heat-shrinkable film;

In parts by weight, the biodegradable heat-shrinkable film material includes: 30-95 parts of biodegradable copolyester, 5-70 parts of polylactic acid; the biodegradable copolyester is an aliphatic biodegradable copolymer Esters or aliphatic-aromatic biodegradable copolyesters; the longitudinal stretch ratio is (1-6):1, the transverse stretch ratio is (3-10):1, the longitudinal stretch ratio and transverse stretch ratio The stretching ratio is 1:(1-10); the temperature of the cold setting treatment is 1-25°C.

The degradable sheet film flows down from the die during the casting process and then stretches through all subsequent rollers from traction to transition to winding to achieve the required thickness. This process will achieve a certain degree of longitudinal stretching, that is There is a certain longitudinal stretching ratio. After preheating, it is stretched in both transverse and longitudinal directions. The molecular chains of the film have undergone more complex cooling crystallization, crystal region slippage, and longitudinal and transverse bidirectional preferential arrangement of molecular chains. Cloth orientation will eventually show different heat shrinkage and balance, as well as isotropic changes in mechanical properties including tear strength. A small stretch ratio shows a small shrinkage rate, and a large stretch ratio does the opposite. It is generally believed that the closer the stretch aspect ratio is to 1, the more uniform the vertical and horizontal orientation of the film will be. However, the inventors have found through long-term studies that for specific systems of biodegradable materials (such as polybutylene adipate terephthalate/polylactic acid (PBAT/PLA) system biodegradable materials), the biodegradable materials In the presence of polylactic acid, the unique molecular chain structure and crystal arrangement of polylactic acid have a decisive influence on the thermal shrinkage rate (both longitudinal and transverse). The conventional stretching ratio and stretching aspect ratio cannot achieve the film's High heat shrinkage and balance.

The inventor changed the direction and degree of molecular chain orientation in the formation of a specific system of biodegradable material film by optimizing the range of specific longitudinal stretch ratio, transverse stretch ratio and stretch aspect ratio, and improved the isotropy, making the aspect ratio The two directions not only have higher heat shrinkage and tear strength, but also have more balanced heat shrinkage and tear strength. At the same time, the inventors have found through long-term research that the heat-setting treatment of a specific system of biodegradable materials after stretching will lead to a tendency to de-orientate, and due to the specific ester bonds and part of the special benzene ring structure in the biodegradable materials, The degree of molecular disorientation is particularly obvious, and the biodegradable shrink film after heat setting treatment almost loses the heat shrinkage rate. Based on this, the inventors cold-set the heat-shrinkable film after stretching treatment, and the cold-setting treatment after stretching reduces the disorientation tendency of the biodegradable heat-shrinkable film in the longitudinal and transverse directions, so that the prepared biodegradable heat The heat shrinkage rate of the shrink film does not decrease, and a high heat shrinkage rate is maintained.

Preferably, the biodegradable copolyester is selected from polybutylene adipate terephthalate, polybutylene sebacate terephthalate, polyhydroxyalkanoate or polybutylene succinate One or more of diesters. More preferably, it is polybutylene adipate terephthalate.

Preferably, the longitudinal stretch ratio is (2-4):1, the transverse stretch ratio is (4-8):1, and the ratio of the longitudinal stretch ratio to the transverse stretch ratio is 1:(2～ 4).

Preferably, the longitudinal stretch ratio is (2-3):1, the transverse stretch ratio is (6-8):1, and the ratio of the longitudinal stretch ratio to the transverse stretch ratio is 1:(2～ 3).

Most preferably, the longitudinal stretch ratio is 2:1, the transverse stretch ratio is 6:1, and the ratio of the longitudinal stretch ratio to the transverse stretch ratio is 1:3. Under this preferred range, the biodegradable heat-shrinkable film prepared by the present invention has higher and more balanced heat shrinkage rate and tear strength.

Further preferably, when the preferred temperature of the cold setting treatment is 10-14°C, the biodegradable heat-shrinkable film prepared by the present invention can obtain a higher heat shrinkage rate.

Preferably, in the cold setting treatment, 4 to 6 groups of cooling and setting rollers are connected in succession, preferably 6 groups; the front and rear distances of all the cold setting rollers are 4 to 10 meters, preferably 6 to 10 meters.

Preferably, the temperature of the longitudinal stretching is 50-80°C; the temperature of the transverse stretching is 70-110°C.

Preferably, the cooling temperature of the chill roll is 1-20°C. The molecular chains of biodegradable polyester materials (such as polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS) and polylactic acid (PLA), etc.) are relatively long, and There are sterically hindered functional groups such as benzene rings, ester bonds, and hydroxyl groups, and the regularity is poor. During the melt cooling and crystallization process, there are situations such as slow crystallization speed, mixed crystal forms, and uneven crystallinity. The inventor optimizes the cooling temperature of the chilling roll, so that the biodegradable heat-shrinkable material is rapidly cooled at a low temperature in the two chilling rolls after the melt casting, so that the melt can preferentially generate uniform fine crystals and uniform crystals during the cooling process. The γ-crystal form, after uniform growth, reaches a regular and uniform crystallization degree, which can significantly optimize and improve the light transmittance of the biodegradable heat-shrinkable film, reduce the haze of the biodegradable heat-shrinkable film; and improve the mechanical strength.

Preferably, the cooling of the chilled rolls can be cooled by double chilled rolls, the cooling efficiency is higher, the time is longer, the cooling effect is better, and the light transmittance of the biodegradable heat shrinkable film can be better improved and the haze can be reduced.

Preferably, the preheating temperature is 40-80°C.

Preferably, in parts by weight, the biodegradable heat-shrinkable film material further contains: 0.1-20 parts of filler, and 0.001-20 parts of auxiliary agent.

Preferably, the filler includes an organic filler and/or an inorganic filler; the organic filler is selected from one or more of starch, natural fiber, straw, wood powder or bamboo powder; the inorganic filler is selected from talcum powder, Montmorillonite, kaolin, chalk, calcium carbonate, graphite, gypsum, conductive carbon black, calcium chloride, iron oxide, dolomite, silica, wollastonite, titanium dioxide, silicates, mica, glass fibers or mineral fibers one or more of.

Preferably, the auxiliary agent is selected from lubricants, slip agents, blocking agents, nucleating agents, surfactants, antistatic agents, pigments, anti-hydrolysis agents, anti-UV agents, antioxidants, chain extenders, cross-linking agents, etc. One or more of joint agent or antifogging agent.

Preferably, the biodegradable heat-shrinkable film material can be put into a single-layer extruder, a double-layer co-extrusion extruder or a three-layer co-extrusion extruder in any proportion of a single-layer, double-layer or three-layer structure middle.

Further, the present invention also protects the biodegradable heat shrinkable film prepared by the above preparation method.

Preferably, the average thickness of the biodegradable heat-shrinkable film is 20 μm-80 μm.

Further, the present invention also provides the application of the above-mentioned biodegradable heat-shrinkable film in the preparation of shrink-wrapped products. Specifically, the products may be beverages, mineral water, alcohol, resin packaging, toys, tableware, food, health care products, paper products, photo frame products, books, audio-visual products, stationery, handicrafts, building materials, cosmetics, electronic products, daily Chemicals and other products.

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

(1) The present invention not only makes the biodegradable heat-shrinkable film obtained in the longitudinal and transverse directions by optimizing the range of specific longitudinal stretch ratio, transverse stretch ratio, stretch aspect ratio and cold setting treatment after stretching. The heat shrinkage rate in both directions is maintained at more than 55%, and the heat shrinkage rate and tear strength in the longitudinal and transverse directions are more balanced, which improves the actual packaging shrinkage protection and tear resistance effect of the biodegradable heat shrinkable film.

(2) By optimizing the cooling temperature of the chill roll, the present invention enables the biodegradable heat-shrinkable material to be rapidly cooled at a low temperature after the melt casting, thereby significantly optimizing and improving the light transmittance of the biodegradable heat-shrinkable film , reducing the haze of the biodegradable heat shrinkable film.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

Embodiment and comparative example raw material description:

PLA: 4032D, Natureworks, USA;

PBAT: A400, Kingfa Technology Co., Ltd.;

Filler: talcum powder, 3000 mesh, from commercially available;

Additive: smooth agent, derived from commercially available;

Antioxidant, 1010, comes from commercially available;

The chain extender, glycidyl methacrylate, was obtained commercially.

The test method of concrete parameter in following embodiment is as follows:

Average thickness (μm): Tested by GB/T 6672-2001 test method.

Tear strength (mN): Tested by GB/T 16578.2-2009 test method.

Heat shrinkage rate (120°C, 10s): Tested by GB/T 34848-2017 test method.

Light transmittance: Tested by GB/T 2410-2008 test method.

Haze: Tested by GB/T 2410-2008 test method.

The preparation of embodiment 1 biodegradable heat-shrinkable film

The biodegradable heat-shrinkable film adopts AB double-layer co-extrusion structure. According to parts by weight, the A-layer formula: 50 parts of PLA, 50 parts of PBAT, 5 parts of talcum powder, 0.5 parts of slip agent, 0.2 parts of antioxidant, 0.1 parts of chain extender B layer formula: 70 parts of PLA, 30 parts of PBAT, 5 parts of talcum powder, 0.5 part of slip agent, 0.2 part of antioxidant, 0.1 part of chain extender.

A preparation method for a biodegradable heat-shrinkable film, comprising the steps of:

(1) After mixing the formula components of layer A evenly, put them into a twin-screw extruder, extrude at 140-190°C, and granulate to obtain biodegradable heat shrinkable film material A; mix the formula components of layer B evenly Finally, put it into a twin-screw extruder, extrude at 140-190°C, and granulate to obtain biodegradable heat-shrinkable film material B;

(2) Put the biodegradable heat-shrinkable film material A and the biodegradable heat-shrinkable film material B into the corresponding single-screw extruder, plasticize and melt at 120°C to 180°C, and enter the die head through a filter and a melt metering pump;

(3) The melt is melted and plasticized and then cast to the chilled rolls for cooling after being merged by the die heads. The cooling temperature of the double-channel chilled rolls is 12 ° C, and the cast sheets are formed by rotation;

(4) The cast sheet undergoes preheating, longitudinal stretching, and cold setting treatment sequentially through different traction rollers of the longitudinal stretching unit, wherein the preheating temperature is 60°C; the longitudinal stretching is realized by 4 sets of stretching rollers, and the The temperature is 70°C, and the longitudinal stretch ratio is 2:1; 6 sets of cooling and setting rollers are used for cold setting, and the cold setting temperature is 12°C.

(5) The cast sheet after longitudinal stretching enters the transverse stretching unit for preheating, transverse stretching, and cold setting treatment, and then the prepared biodegradable heat shrinkable film is cut and rolled to obtain a heat shrinkable film with a thickness of 45 μm. Shrink film; wherein, the preheating temperature is 60°C; the transverse stretching temperature is 90°C, and the transverse stretching ratio is 6:1; the cold setting temperature is 12°C.

The preparation of embodiment 2 biodegradable heat-shrinkable films

The difference between this embodiment and embodiment 1 is: the difference between this embodiment and embodiment 1 is: the longitudinal stretch ratio is 3:1; the transverse stretch ratio is 4:1; the stretch aspect ratio is 1:1.33.

Preparation of embodiment 3 biodegradable heat-shrinkable film

The difference between this embodiment and embodiment 1 is: the difference between this embodiment and embodiment 1 is: the longitudinal stretch ratio is 4:1; the transverse stretch ratio is 7:1; the stretch aspect ratio is 1:1.75.

The preparation of embodiment 4 biodegradation heat-shrinkable film

The difference between this embodiment and Embodiment 1 is that: the longitudinal stretch ratio is 6:1; the transverse stretch ratio is 6:1; and the stretch aspect ratio is 1:1.

The preparation of embodiment 5 biodegradation heat-shrinkable film

The difference between this embodiment and Embodiment 1 is that: the longitudinal stretch ratio is 1:1; the transverse stretch ratio is 10:1; and the stretch aspect ratio is 1:10.

Embodiment 6 The preparation of biodegradable heat-shrinkable film

The difference between this embodiment and Embodiment 1 is that: the longitudinal stretch ratio is 3:1; the transverse stretch ratio is 3:1; and the stretch aspect ratio is 1:1.

Embodiment 7 The preparation of biodegradable heat-shrinkable film

The difference between this embodiment and Embodiment 1 is that: the longitudinal stretch ratio is 6:1; the transverse stretch ratio is 10:1; and the stretch aspect ratio is 1:1.67.

Embodiment 8 Preparation of biodegradable heat-shrinkable film

The difference between this example and Example 1 is that the cold setting treatment temperature during longitudinal stretching is 1°C, and the cold setting treatment temperature during transverse stretching is 1°C.

Embodiment 9 The preparation of biodegradable heat-shrinkable film

The difference between this example and Example 1 is that the cold setting treatment temperature during longitudinal stretching is 25°C, and the cold setting treatment temperature during transverse stretching is 25°C.

The preparation of embodiment 10 biodegradable heat-shrinkable film

The difference between this example and Example 1 is that the mass fraction of the layer A formula is 100% (that is, only contains the components of layer A).

Embodiment 11 Preparation of biodegradable heat-shrinkable film

The difference between this example and Example 1 is that the mass fraction of the layer B formula is 100% (that is, only layer B components are contained).

Embodiment 12 Preparation of biodegradable heat-shrinkable film

The difference between this example and Example 1 is: the formula of layer A: 30 parts of PLA, 70 parts of PBAT, 5 parts of talcum powder, 0.5 part of slip agent, 0.2 part of antioxidant, and 0.1 part of chain extender; the formula of layer B is the same.

Embodiment 13 Preparation of biodegradable heat shrinkable film

The difference between this example and Example 1 is: the formula of layer A: 5 parts of PLA, 95 parts of PBAT, 5 parts of talcum powder, 0.5 part of slip agent, 0.2 part of antioxidant, and 0.1 part of chain extender; the formula of layer B is the same.

Example 14-15 Optimization of forced cooling of double-channel chilled rolls

The difference between Example 14 and Example 1 is that the cooling temperature of the double-pass chilling rolls is 25°C.

The difference between Example 15 and Example 1 is that the cooling temperature of the double-pass chilling rolls is 40°C.

The performances of the biodegradable heat-shrinkable films tested in the above-mentioned Examples 1-15 are as follows in Table 1:

Table 1

From Table 1, Examples 1 to 7, it can be seen that Example 1 (stretched aspect ratio 1:3) is compared with Examples 2 to 7 (stretched aspect ratio is outside the range of 1: (2 to 4)), the embodiment 1 The thermal shrinkage rate of the prepared biodegradable heat shrinkable film is greater than 70% in the longitudinal direction and the transverse direction, which not only has a high thermal shrinkage rate, but also is very balanced. This is because in the biaxial stretching process, there is a certain longitudinal orientation in the melt casting to the chilled roll and the subsequent drawing process, so the longitudinal stretching and transverse stretching processes need to meet a certain stretching aspect ratio. To achieve a balanced and high shrinkage rate, otherwise it is easy to cause anisotropy, which makes the orientation in one direction too strong, so that a certain degree of molecular chain relaxation occurs in the other vertical direction, resulting in shrinkage balance deviation and overall numerical value. On the low side.

In Example 4 and Example 6, under the condition of stretching aspect ratio of 1:1, the longitudinal stretching ratio and transverse stretching ratio are respectively the same, and Example 5 is in the case of low stretching aspect ratio. It can be seen from the comparison that under the same condition of longitudinal stretch ratio and transverse stretch ratio, the longitudinal shrinkage rate will be significantly higher than the transverse shrinkage rate.

From the test results of Examples 8 and 9, it can be seen that when the cold-setting treatment temperature of longitudinal stretching and transverse stretching is 1-25°C, the heat shrinkage ratio of the prepared biodegradable heat-shrinkable film is above 55%.

It can be known from Examples 10 to 13 that among the biodegradable heat shrinkable film materials, when the biodegradable copolyester is in the range of 30 to 95 parts and the polylactic acid is in the range of 5 to 70 parts, the single layer biodegradable heat shrinkable film can also be used. Achieving a balanced high heat shrinkage rate.

It can be seen from Table 1 above that the longitudinal and transverse heat shrinkage rates of the biodegradable heat shrinkable films prepared in Examples 1 to 15 of the present application are not only greater than 55%, but also the longitudinal tear strength is 1200-2500mN, and the transverse tear strength can be maintained at 3000～4200mN; light transmittance ≥ 65%; haze < 32. Further preferably, the biodegradable heat-shrinkable film prepared in Examples 1-13 has a more balanced longitudinal and transverse tear strength, the longitudinal tear strength can be maintained at 1900-2500mN, and the transverse tear strength can be maintained at 3800-4200mN; It has more excellent optical properties, light transmittance ≥ 80%; haze < 5.5.

Comparative Example 1-2 Preparation of biodegradable heat shrinkable film by blown film method

Comparative example 1: Add the formula in Example 1 into a single-screw machine for melting and curing, and form a heat-shrinkable film by the blown film process, wherein the extrusion temperature is 130-170°C, the die head temperature is 150°C, and the blown film is blown. The expansion ratio is 3:1.

Comparative example 2: Add the formula in Example 10 into a single-screw machine for melting and curing, and form a heat-shrinkable film by blown film process, wherein the extrusion temperature is 130-170°C, the die head temperature is 150°C, and blown The expansion ratio is 3:1.

The biodegradable heat-shrinkable film with a nominal thickness of 45 μm was prepared from Comparative Examples 1 and 2, and the performance of the biodegradable heat-shrinkable film was tested in the following table 2:

Table 2

It can be seen from the above table 2 that the biodegradable shrink film of the same formula prepared by the blown film method in Comparative Examples 1-2 has insufficient cooling efficiency due to the cooling method, and the inflation process of blown film forming is not suitable for both longitudinal and transverse directions. Due to the limitation of the orientation degree, the longitudinal tear strength and optical properties are lower than those of the biodegradable shrink film prepared by the biaxial stretching method in Example 1 and Example 10, respectively.

However, the biodegradable heat-shrinkable film prepared by the biaxial stretching method in Example 1 and Example 10 not only has excellent light transmittance and extremely low haze, but also exhibits good optical properties; it also has excellent longitudinal, The transverse heat shrinkage rate is relatively excellent, and its balance is also relatively excellent, especially the transverse heat shrinkage rate in Comparative Examples 1-2 is far from the transverse heat shrinkage rate in Example 1 and Example 10.

Different longitudinal stretch ratios, transverse stretch ratios and stretch aspect ratio optimizations of comparative examples 3 to 7

The difference between Comparative Example 3 and Example 1 is that: the longitudinal stretch ratio is 2:1; the transverse stretch ratio is 2:1; the stretch aspect ratio is 1:1.

The difference between Comparative Example 4 and Example 1 is that: the longitudinal stretch ratio is 8:1; the transverse stretch ratio is 8:1; the stretch aspect ratio is 1:1.

The difference between Comparative Example 5 and Example 1 is that: the longitudinal stretch ratio is 3:1; the transverse stretch ratio is 15:1; the stretch aspect ratio is 1:5.

The difference between Comparative Example 6 and Example 1 is that: the longitudinal stretch ratio is 15:1; the transverse stretch ratio is 3:1; the stretch aspect ratio is 5:1.

The difference between Comparative Example 7 and Example 1 is that: the longitudinal stretch ratio is 6:1; the transverse stretch ratio is 3:1; the stretch aspect ratio is 2:1.

Biodegradable heat-shrinkable films with a nominal thickness of 45 μm were prepared from Comparative Examples 3 to 7. The properties of the film tests are as follows in Table 3:

table 3

It can be seen from the above Table 3 that compared with Comparative Examples 3-7, the thermal shrinkage rate of the biodegradable heat shrinkable film prepared in Example 1 can reach more than 55% in the longitudinal and transverse directions, and has excellent shrink wrap protection; in addition , the thermal shrinkage rate is also greatly affected by the stretching aspect ratio. In the case of cooling the casting melt to a certain longitudinal stretching ratio during the winding process, Example 1 (the stretching aspect ratio is 1:3) The balance (isotropy) of the thermal shrinkage rate of the prepared biodegradable heat shrinkable film is significantly better than that of Comparative Examples 3 to 7 (the stretching aspect ratios are 1:5, 1:1, 5:1 and 2:1 respectively). ) prepared biodegradable heat shrinkable film.

In addition, the inventors have found that when the stretch aspect ratio coefficient is too small or too large, that is, when the longitudinal stretch ratio is too large or the transverse stretch ratio is too large, the shrinkage in the other direction tends to decline (as in Comparative Examples 6 and Comparative example 7), the main reasons are: firstly, there is a certain initial longitudinal stretching behavior in the entire casting process, and the superposition of the longitudinal stretching ratio will lead to a larger actual longitudinal stretching ratio, and secondly, the more important thing is that the biodegradable polyester material In the stretching and orientation process of molecular chains, when the one-way orientation is too large, the molecular chains will relax in the other direction, resulting in disorientation, which will lead to a decrease in the thermal shrinkage rate in the other direction.

The above data show that the longitudinal stretch ratio, transverse stretch ratio, and stretch aspect ratio all need to be controlled within an appropriate range in order to achieve high thermal shrinkage and balance in the longitudinal and transverse directions.

Optimization of different shaping methods after stretching treatment in comparative examples 8-10

The difference between Comparative Example 8 and Example 1 is that in step (3) and step (4), cold setting treatment is not carried out after longitudinal stretching and transverse stretching.

The difference between Comparative Example 9 and Example 1 is that the temperature of the cold setting treatment is 30°C.

The difference between Comparative Example 10 and Example 1 is that in steps (3) and (4), after longitudinal stretching and transverse stretching, 6 sets of heat setting rollers are used for processing, and the setting temperature is 45°C.

Biodegradable heat-shrinkable films with a nominal thickness of 45 μm were prepared from Comparative Examples 8-10. The properties of the film tests are as follows in Table 4:

Table 4

It can be seen from the above table 4 that whether it is longitudinal stretching or transverse stretching, crystallization and setting by active forced cooling after molecular chain orientation help to avoid deorientation. In Comparative Example 8, no cold setting treatment was carried out after the longitudinal stretching and transverse stretching, the molecular chain deorientation was obvious, and the longitudinal and transverse heat shrinkage rates of the prepared biodegradable heat-shrinkable film were relatively low. The bidirectional heat shrinkage rate of the biodegradable heat-shrinkable film prepared in Example 1 (cold-setting treatment temperature is 12°C) is also significantly better than that of the biodegradable heat-shrinkable film in Comparative Example 9 (cooling temperature is 30°C). In comparison example 10, the thermal setting process obviously caused the molecular chain relaxation of the biodegradable heat-shrinkable film, the de-orientation was obvious, and the thermal shrinkage rate was almost lost.

Preparation of biodegradable heat-shrinkable films of different biodegradable materials in comparative examples 11-13

The difference between Comparative Example 11 and Example 10 is: A-layer formula: 2 parts of PLA, 98 parts of PBAT, 5 parts of talcum powder, 0.5 part of slippery agent, 0.2 part of antioxidant, and 0.1 part of chain extender.

The difference between Comparative Example 12 and Example 10 is: PPC (polymethylethylene carbonate, commercially available film grade) is 95 parts, PLA is 5 parts, talcum powder is 5 parts, smooth agent 0.5 part, antioxidant 0.2 parts, chain extender 0.1 parts.

The difference between Comparative Example 13 and Example 10 is: PET (polyethylene terephthalate, commercially available film grade) is 95 parts, PLA is 5 parts, talcum powder is 5 parts, smooth agent 0.5 part, anti- 0.2 part of oxygen agent, 0.1 part of chain extender; melt at 220-270°C.

Biodegradable heat-shrinkable films with a nominal thickness of 45 μm were prepared from Comparative Examples 11 to 13. The properties of the film tests are shown in Table 5:

table 5

It can be seen from the above table 5 that the unique molecular chain structure and crystal form arrangement of polylactic acid have an important influence on the heat shrinkage rate (both longitudinal and transverse), and the biological shrinkage can be adjusted by optimizing the number of PLA parts in the formula. The key index of heat shrinkage rate of degraded heat shrinkable film. In Comparative Example 11, a single-layer heat-shrinkable film with high PBAT content was used. Although its mechanical properties were higher than that of Example 1 in terms of flexibility, it had no heat shrinkability. In Comparative Examples 12 to 13, different polyester components did not show sufficient thermal shrinkage under the conditions of specific chill roll temperature, cold setting treatment, stretching aspect ratio, and longitudinal and transverse stretch ratios in Example 1. , and the light transmittance, haze and tear strength also have a large gap with Example 1. The comprehensive performance effect of the biodegradable heat-shrinkable films prepared in Comparative Examples 11-13 is much lower than that of Example 1.

The foregoing examples are illustrative only, and are used to explain some features of the methods described in the present invention. The appended claims are intended to have the broadest scope conceivable and the examples presented herein are evidenced by applicants' actual tests. Accordingly, it is the applicant's intention that the appended claims not be limited by the selection of examples which characterize the invention. Certain numerical ranges used in the claims also include sub-ranges therein, and changes within these ranges should also be construed as being covered by the appended claims where possible.

Claims (10)

1. A preparation method of biodegradable heat-shrinkable film, is characterized in that, comprises the following steps: S1. After putting the biodegradable heat-shrinkable film material into the extruder and heating it to a molten state, it is cast to a chilled roll for cooling to form a cast sheet; S2. After preheating the cast sheet described in S1, perform longitudinal stretching, and then cold-setting treatment, and then preheat the cold-setting cast sheet, perform transverse stretching, and cold-setting treatment to obtain the biodegradable heat shrinkable film; or After preheating the cast sheet described in S1, perform transverse stretching, and then cold-setting treatment, and then preheat the cold-setting cast sheet, perform longitudinal stretching, and cold-setting treatment to obtain the biodegradable heat-shrinkable film; In parts by weight, the biodegradable heat-shrinkable film material includes: 30-95 parts of biodegradable copolyester, 5-70 parts of polylactic acid; The biodegradable copolyester is an aliphatic biodegradable copolyester or an aliphatic-aromatic biodegradable copolyester; The longitudinal stretch ratio is (1-6):1, the transverse stretch ratio is (3-10):1, and the ratio of the longitudinal stretch ratio to the transverse stretch ratio is 1:(1-10); The temperature of the cold setting treatment is 1-25°C. 2. according to the described preparation method of claim 1, it is characterized in that, described biodegradable copolyester is selected from polybutylene adipate terephthalate, polybutylene sebacate terephthalate , one or more of polyhydroxyalkanoate or polybutylene succinate. 3. The preparation method according to claim 1, characterized in that, the longitudinal stretch ratio is (2-4): 1, and the transverse stretch ratio is (4-8): 1; the longitudinal stretch ratio and The ratio of the transverse stretch ratio is 1: (2-4). 4. The preparation method according to claim 1, characterized in that, the temperature of the cold setting treatment is 10-14°C. 5. The preparation method according to claim 1, characterized in that, the temperature of the longitudinal stretching is 50-80°C, and the temperature of the transverse stretching is 70-110°C. 6. The preparation method according to claim 1, characterized in that, the cooling temperature of the chill roll is 1-20°C. 7 . The preparation method according to claim 1 , wherein, in parts by weight, the biodegradable heat-shrinkable film material further contains: 0.1-20 parts of filler, and 0.001-20 parts of auxiliary agent. 8. The preparation method according to claim 7, wherein the filler comprises an organic filler and/or an inorganic filler; the organic filler is selected from one or more of starch, natural fiber, straw, wood powder or bamboo powder Multiple; the inorganic filler is selected from talcum powder, montmorillonite, kaolin, chalk, calcium carbonate, graphite, gypsum, conductive carbon black, calcium chloride, iron oxide, dolomite, silicon dioxide, wollastonite, titanium dioxide , silicate, mica, glass fiber or mineral fiber; the auxiliary agent is selected from lubricants, slippery agents, opening agents, nucleating agents, surfactants, antistatic agents, pigments, One or more of anti-hydrolysis agents, anti-UV agents, antioxidants, chain extenders, cross-linking agents or antifogging agents. 9. The biodegradable heat-shrinkable film prepared by the preparation method according to any one of claims 1-8. 10. The application of the biodegradable heat-shrinkable film according to claim 9 in the preparation of shrink-wrapped products.