CN113895120B - Shrink film and preparation method thereof - Google Patents

Shrink film and preparation method thereof Download PDF

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Publication number
CN113895120B
CN113895120B CN202111155843.5A CN202111155843A CN113895120B CN 113895120 B CN113895120 B CN 113895120B CN 202111155843 A CN202111155843 A CN 202111155843A CN 113895120 B CN113895120 B CN 113895120B
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layer
shrink film
ldpe
density
10min
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CN113895120A (en
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林城
黄思淇
杨连坚
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Dongguan Zhengxin Packaging Product Co ltd
South China University of Technology SCUT
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Dongguan Zhengxin Packaging Product Co ltd
South China University of Technology SCUT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D7/00—Producing flat articles, e.g. films or sheets
    • B29D7/01—Films or sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/24—All layers being polymeric
    • B32B2250/246—All polymers belonging to those covered by groups B32B27/32 and B32B27/30
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2270/00—Resin or rubber layer containing a blend of at least two different polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/56—Damping, energy absorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/582—Tearability
    • B32B2307/5825—Tear resistant

Abstract

The invention provides a shrink film and a preparation method thereof. The shrink film comprises an outermost layer, an intermediate layer, an inner layer and an innermost layer which are sequentially arranged, the thickness ratio of the outermost layer to the inner layer is (1.5-2.5): (0.3-0.7): (3~6): (0.3-0.7): (1.5-2.5), the outermost layer and the innermost layer are composed of 10-30% of LDPE or LLDPE and 70-90% of mLLDPE in percentage by weight, the intermediate layer is composed of 45-70% of HDPE, 20-40% of LDPE and 10-15% of MDPE, and the outer layer and the inner layer are composed of 67-80% of ethylene-vinyl alcohol copolymer, 17-30% of ethylene-vinyl acetate or ethylene-propylene copolymer and 0.5-3% of tackifying additive. It is a high-toughness, flexible-resistant shrink film.

Description

Shrink film and preparation method thereof
Technical Field
The invention relates to the technical field of multilayer structures, in particular to a film, and more particularly relates to a shrink film and a preparation method thereof.
Background
The shrink film as industrial film product has high tensile strength, high elongation, high self adhesion, high transparency and other features, and may be used as hand winding film and machine winding film for concentrated packing of various goods. The most important is that the wrapping film package enables the packaged articles to be stressed evenly, and the articles are prevented from being damaged due to uneven stress, which cannot be achieved by the traditional packaging mode (bundling, packaging, adhesive tape packaging and the like). Meanwhile, the product is wound and packaged by virtue of the retraction force after the winding film is stretched to form a compact and space-saving unit whole body, so that each tray of the product is tightly wrapped together, the mutual dislocation and movement of the product in the transportation process can be effectively prevented, meanwhile, the adjustable stretching force can enable the hard product to be tightly attached, the soft product is contracted, and the soft product has a unique packaging effect particularly in the tobacco industry and the textile industry. The shrink film is used for packaging products, so that the use cost can be effectively reduced, the labor intensity of workers can be reduced, and the packaging efficiency and the packaging grade can be improved.
However, in some special fields, such as packaging beverages or other rolling objects, the toughness requirement of the shrink film is high, the currently common shrink film cannot meet the toughness requirement, and the shrink film is prevented from being pulled and deformed or even torn due to the movement of the beverages or other rolling objects in the transportation process, so that the shrink film cannot be used. Meanwhile, a shrink film is generally a multi-layer structure, which is generally a three-layer structure or a five-layer structure, formed by co-extrusion blow molding, has poor flexibility resistance, and is delaminated due to external forces such as pulling and rubbing during transportation or use, thereby affecting the use thereof.
Therefore, in order to meet the demands of special fields for high toughness and delamination resistance of shrink films, a new high toughness, flexibility resistant shrink film is sought.
Disclosure of Invention
In order to achieve the above object, a first aspect of the present invention provides a shrink film comprising an outermost layer, a second outer layer, an intermediate layer, a second inner layer and an innermost layer, which are sequentially disposed, wherein the outermost layer, the second outer layer, the intermediate layer, the second outer layer and the second inner layer are symmetrically distributed about the intermediate layer, the thickness ratio of the outermost layer, the second outer layer, the intermediate layer, the second inner layer and the innermost layer is (1.5-2.5): (0.3-0.7): (3-6): (0.3-0.7): (1.5-2.5), in weight percentage, the outermost layer and the innermost layer consist of 10-30% of LDPE or LLDPE and 70-90% of mLLDPE, the intermediate layer consists of 45-70% of HDPE, 20-40% of LDPE and 10-15% of MDPE, and the second outer layer and the second inner layer consist of 67-80% of ethylene-vinyl alcohol copolymer, 17-30% of ethylene-vinyl acetate or ethylene-propylene copolymer and 0.5-3% of an additive.
Compared with the prior art, the outermost layer and the innermost layer, and the secondary outer layer and the secondary inner layer are symmetrically distributed by taking the middle layer as an axis, namely the whole shrink film is of a symmetrical structure, and when the shrink film is influenced by external force, all layers in the shrink film can keep the uniformity of stress to prevent local deformation and even tearing caused by uneven stress. Meanwhile, the middle layer has the highest density, the highest stiffness and the largest thickness, the outermost layer and the innermost layer have the lowest density and the best and thinner toughness, the secondary inner layer and the secondary outer layer are based on the high-content ethylene-vinyl alcohol copolymer and are supplemented with flexible resin ethylene-vinyl acetate or ethylene-propylene copolymer, so that the secondary inner layer and the secondary outer layer have excellent stretchability, flexibility and flexing resistance, the secondary inner layer and the secondary outer layer are clamped between the outermost layer/the innermost layer and the middle layer to serve as thin buffer layers, and the interlayer adhesiveness is improved through the tackifying additive, so that the influence of external force on the high-toughness outermost layer and the high-toughness inner layer can be effectively relieved, the high toughness of the shrink film in the long-term use process can be effectively maintained, the layering phenomena such as tearing and the like cannot occur, and the use requirement of the shrink film for packaging beverages or other rolling objects can be met.
A second aspect of the present invention provides a method for producing a shrink film, comprising: the raw materials of the outermost layer, the secondary outer layer, the middle layer, the secondary inner layer and the innermost layer are uniformly mixed according to a formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing unit, and then the film is blown, cooled, pulled and coiled to obtain the film. The preparation method can be formed by carrying out coextrusion blow molding on the five layers of raw materials, and the preparation method is convenient to process and form and has better performance.
Drawings
Fig. 1 is a schematic view of a 5-layer structure of a shrink film of the present invention.
Detailed Description
The technical solutions of the present invention are further described below by way of specific embodiments, but the present invention is not limited thereto.
For convenience of description, some materials of the present invention are abbreviated, for example, the ethylene-vinyl alcohol copolymer is EVOH, the ethylene-vinyl acetate copolymer is EVA, the ethylene-propylene copolymer is EPM, the low density polyethylene is LDPE, the high density polyethylene is HDPE, the medium density polyethylene is MDPE, the linear low density polyethylene is LLDPE, the metallocene linear low density polyethylene is mLLDPE, the metallocene polyethylene is mPE, and the ethylene-vinyl acetate copolymer is EVA.
As shown in figure 1, the shrink film comprises an outermost layer 1, a secondary outer layer 2, an intermediate layer 3, a secondary inner layer 4 and an innermost layer 5 which are sequentially arranged, wherein the outermost layer 1, the innermost layer 5, the secondary outer layer 2 and the secondary inner layer 4 are symmetrically distributed by taking the intermediate layer 3 as an axis, and the thickness ratio of the outermost layer 1, the secondary outer layer 2, the intermediate layer 3, the secondary inner layer 4 and the innermost layer 5 is (1.5-2.5), (0.3-0.7), (3-6), (0.3-0.7) and (1.5-2.5). Preferably (1.5-2) to (4.5-2) from (1.5-0.3).
The outermost layer 1 and the innermost layer 5 consist of 10 to 30% by weight of LDPE or LLDPE and 70 to 90% by weight of mLLDPE, the content of LDPE or LLDPE may be, but not limited to, 10%, 15%, 20%, 25%, 30%, and the content of mLLDPE may be, but not limited to, 70%, 75%, 80%, 85%, 90%.
The middle layer 3 consists of 45-70% HDPE, 20-40% LDPE and 10-15% MDPE, preferably the middle layer 3 consists of 50-65% HDPE, 25-40% LDPE and 10% MDPE. The content of HDPE may be, but is not limited to, 45%, 47%, 50%, 52%, 55%, 58%, 60%, 64%, 65%, 68%, 70%. The content of LDPE may be, but is not limited to, 20%, 22%, 25%, 27%, 29%, 30%, 32%, 34%, 35%, 38%, 39%, 40%. The content of MDPE may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%.
The secondary outer layer 2 and the secondary inner layer 4 consist of 67 to 80 percent of ethylene-vinyl alcohol copolymer, 17 to 30 percent of ethylene-vinyl acetate or ethylene-propylene copolymer and 0.5 to 3 percent of tackifying additive. The adhesion promoting additive is an alkali metal salt and/or a boride. Specifically, the alkali metal salt is potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, potassium hydrogen phosphate or sodium hydrogen phosphate. The boride is orthoboric acid, metaboric acid, pyroboric acid, triethyl borate or trimethyl borate. Preferably, the secondary outer layer 2 and the secondary inner layer 4 are composed of 67 to 80% of ethylene-vinyl alcohol copolymer, 17 to 30% of ethylene-vinyl acetate copolymer, 1 to 1.5% of alkali metal salt and 0.5 to 1.5% of boride. The content of the ethylene-vinyl alcohol copolymer may be, but is not limited to, 67%, 68%, 70%, 72%, 74%, 75%, 78%, 80%, the content of the ethylene-vinyl acetate or ethylene-propylene copolymer may be, but is not limited to, 17%, 18%, 20%, 22%, 24%, 25%, 27%, 28%, 29%, 30%, and the content of the tackifier additive may be, but is not limited to, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.7%, 3.0%.
Preferably, the LDPE has a density of from 0.910 to 0.930g/cm 3 The melt index is 0.25-0.30 g/10min, the density of HDPE is 0.950-0.960 g/cm 3 Melt index<0.21g/10min, density of MDPE 0.930-0.950 g/cm 3 A melt index of<0.8g/10min, LLDPE density of<0.920g/cm 3 A melt index of<2.0g/10min, the density of the mLLDPE is<0.920g/cm 3 A melt index of<1.0g/10min。
That is, the shrink film comprises an outermost layer 1, a secondary outer layer 2, an intermediate layer 3, a secondary inner layer 4 and an innermost layer 5 in sequence by taking the surface contacting the article to be shrunk as the inner side, and the thickness of the shrink film is 35-55 um.
The shrink film of the present invention can be prepared by a method comprising: the raw materials of the outermost layer, the secondary outer layer, the middle layer, the secondary inner layer and the innermost layer are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer co-extrusion film blowing machine set, and then the film is blown, cooled, pulled and coiled to obtain the film.
The following will describe the shrink film of the present invention in detail by way of specific examples, but the scope of the present invention is not limited thereto.
Example 1
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
a secondary outer layer: the thickness is 1.5um, and the composite material consists of 70 percent of EVOH, 28 percent of EVA, 1 percent of sodium bicarbonate and 1 percent of metaboric acid;
an intermediate layer: has a thickness of 24um and consists of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an innermost layer: the thickness is 10um, and the composite material consists of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE: the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
Example 2
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material consists of 20% of LLDPE and 80% of mLLDPE;
a secondary outer layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an intermediate layer: has a thickness of 24um and consists of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an innermost layer: the thickness is 10um, and the composite material consists of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE: the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
LLDPE: the density is 0.918g/cm 3 The melt index is 1.8g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
Example 3
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material consists of 20% of LDPE and 80% of mLLDPE;
a secondary outer layer: 1.5um thick, consisting of 70% EVOH, 28% EVA and 2% sodium bicarbonate;
an intermediate layer: has a thickness of 24um and consists of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an innermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE (Low-Density polyethylene): the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
Example 4
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material consists of 20% of LDPE and 80% of mLLDPE;
a secondary outer layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA and 2% of metaboric acid;
intermediate layer: thickness 24um, consisting of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 1.5um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an innermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE: the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and the five-layer coextrusion film blowing machine set is prepared by film blowing, cooling, traction and coiling.
Example 5
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 44um, and the performance parameters of each layer are as follows:
outermost layer: 11um thick, consisting of 20% LDPE and 80% mLLDPE;
a secondary outer layer: the thickness is 2um, and the film is composed of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
intermediate layer: thickness 18um, consisting of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 2um, and the composite material consists of 70% of EVOH, 28% of EVA, 1% of sodium bicarbonate and 1% of metaboric acid;
an innermost layer: 11um thick, consisting of 20% LDPE and 80% mLLDPE;
the parameters for each material were:
LDPE (Low-Density polyethylene): the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density was 0.955g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
Example 6
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: 11um thick, consisting of 25% LDPE and 75% mLLDPE;
a secondary outer layer: 1.5um thick, consisting of 75% EVOH, 22% EPM, 1% potassium carbonate and 2% triethyl borate;
intermediate layer: thickness 22um, consisting of 65% HDPE, 20% LDPE and 15% MDPE.
A secondary inner layer: 1.5um thick, consisting of 75% EVOH, 22% EPM, 1% potassium carbonate and 2% triethyl borate;
an innermost layer: 11um thick, consisting of 25% LDPE and 75% mLLDPE;
the parameters for each material were:
LDPE (Low-Density polyethylene): the density is 0.930g/cm 3 The melt index is 0.3g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
Comparative example 1
The shrink film comprises an outermost layer, a middle layer and an innermost layer in sequence, the total thickness of the shrink film is 44um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
an intermediate layer: the thickness is 24um, and the composite material consists of 60% of HDPE, 30% of LDPE and 10% of MDPE;
an innermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE (Low-Density polyethylene): the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The three layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a three-layer co-extrusion film blowing unit, and then the film is blown, cooled, drawn and coiled to obtain the film.
Comparative example 2
The shrink film comprises an outermost layer, a secondary outer layer, a middle layer, a secondary inner layer and an innermost layer in sequence, the total thickness of the shrink film is 47um, and the performance parameters of each layer are as follows:
outermost layer: the thickness is 10um, and the composite material is composed of 20% of LDPE and 80% of mLLDPE;
a secondary outer layer: the thickness is 1.5um, and the composite material consists of 30 percent of LDPE, 30 percent of HDPE, 30 percent of MDPE and 10 percent of LLDPE;
intermediate layer: thickness 24um, consisting of 60% HDPE, 30% LDPE and 10% MDPE.
A secondary inner layer: the thickness is 1.5um, and the composite material consists of 30 percent of LDPE, 30 percent of HDPE, 30 percent of MDPE and 10 percent of LLDPE;
an innermost layer: the thickness is 10um, and the composite material consists of 20% of LDPE and 80% of mLLDPE;
the parameters for each material were:
LDPE (Low-Density polyethylene): the density is 0.920g/cm 3 The melt index is 0.28g/10min;
HDPE: the density is 0.950g/cm 3 The melt index is 0.20g/10min;
MDPE (medium density polyethylene): the density is 0.940g/cm 3 The melt index is 0.7g/10min;
LLDPE: the density is 0.918g/cm 3 The melt index is 1.8g/10min;
mLLDPE: the density is 0.918g/cm 3 The melt index was 0.9g/10min.
The five layers of corresponding raw materials are uniformly mixed according to the formula ratio, and are respectively sent to an extruder of a five-layer coextrusion film blowing machine set, and then the film is blown, cooled, drawn and coiled to obtain the film.
It should be noted that all the components in the examples and comparative examples are in weight percent. The shrink films prepared in examples 1 to 6 and comparative examples 1 to 2 were respectively tested for dart impact property, tensile property and tear property to characterize toughness, and the test means were as follows:
falling mark impact performance: and (3) testing the falling-mark impact performance by adopting a testing method of a GB9639-1988 plastic film free falling dart impact tester and obtaining a corresponding falling-mark impact strength value.
And (3) testing tensile property: the tensile properties were tested using the tensile properties test method of GB13022-1991 and corresponding tensile strength values were obtained.
Tear performance: and (3) carrying out tearing performance test by using a measuring method of the tearing resistance of the GB/T16578.1-2008 plastic film and the thin sheet, and obtaining a corresponding tearing strength value.
The falling mark impact strength values, tensile strength values and tear strength values of the shrink films of examples 1 to 6 and comparative examples 1 to 2 are shown in the following table.
TABLE 1 Properties of shrink films of examples 1-6 and comparative examples 1-2
Examples Falling label impact strength (g) Tensile Strength (MPa) Tear Strength (KN/m)
Example 1 400 73 710
Example 2 403 74 715
Example 3 380 69 670
Example 4 385 71 695
Example 5 410 77 718
Example 6 405 75 720
Comparative example 1 320 57 530
Comparative example 2 340 60 600
As is apparent from the results in Table 1, examples 1 to 6 are superior in all of impact strength, tensile strength and tear strength to comparative examples 1 to 2, that is, examples 1 to 6 are superior in toughness property to comparative examples 1 to 2, mainly because in examples 1 to 6, the outermost and innermost layers are composed of 10 to 30% of LDPE or LLDPE and 70 to 90% of mLLDPE, the intermediate layer is composed of 45 to 70% of HDPE, 20 to 40% of LDPE and 10 to 15% of MDPE, and the second outer and inner sub-layers are composed of 67 to 80% of ethylene-vinyl alcohol copolymer, 17 to 30% of ethylene-vinyl acetate or ethylene-propylene copolymer and 0.5 to 3% of tackifier. The middle layer has the highest density, the highest stiffness and the largest thickness, the outermost layer and the innermost layer have the lowest density and the best and thinner toughness, the secondary inner layer and the secondary outer layer are based on the high-content ethylene-vinyl alcohol copolymer and are supplemented with flexible resin ethylene-vinyl acetate or ethylene-propylene copolymer, so that the secondary inner layer and the secondary outer layer have excellent stretchability, flexibility and flexing resistance, the secondary inner layer and the secondary outer layer are clamped between the outermost layer/the innermost layer and the middle layer to be used as thin buffer layers, and the interlayer adhesiveness is improved through tackifying additives, so that the influence of external force on the high-toughness outermost layer and the high-toughness inner layer can be effectively relieved, and the high toughness of a shrinkable film in the long-term use process can be effectively maintained.
In the comparative example 1, the middle layer with high stiffness and the outermost layer and the innermost layer with high toughness are directly combined, and the middle layer has no buffer layer, so that bending or other deformation is easily caused when external force is applied, and the toughness is greatly reduced. In comparative example 2, although the intermediate layer was formed using polyethylene of various densities, the buffering effect was significantly inferior to that of the buffer layer formed by combining ethylene-vinyl alcohol copolymer and ethylene-vinyl acetate or ethylene-propylene copolymer.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles disclosed herein.

Claims (8)

1. The application of the shrink film in the rolling object packaging is characterized in that the outermost layer, the secondary outer layer, the middle layer, the secondary inner layer and the secondary inner layer are symmetrically distributed by taking the middle layer as an axis, the thickness ratio of the outermost layer, the secondary outer layer, the middle layer, the secondary inner layer and the innermost layer is (1.5-2.5) - (0.3-0.7) - (3-6) - (0.3-0.7) - (1.5-2.5), the outermost layer and the innermost layer consist of 10-30% of LDPE or LLDPE and 70-90% of mLLDPE in percentage by weight, the middle layer consists of 45-70% of HDPE, 20-40% of LDPE and 10-15% of MDPE, and the secondary outer layer and the secondary inner layer consist of 67-80% of ethylene-vinyl alcohol copolymer, 17-30% of ethylene-vinyl acetate or ethylene-propylene copolymer and 0.5-3% of tackifying additive.
2. Use of a shrink film according to claim 1 for the wrapping of objects that are to be rolled, wherein said adhesion promoting additive is an alkali metal salt and/or a boride.
3. Use of a shrink film according to claim 2 for the packaging of rolling objects, wherein the alkali metal salt is potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, potassium hydrogen phosphate or sodium hydrogen phosphate.
4. Use of a shrink film according to claim 2 in the wrapping of a rolling object, wherein said boride is orthoboric acid, metaboric acid, pyroboric acid, triethyl borate or trimethyl borate.
5. Use of a shrink film in the wrapping of rolling objects according to claim 1, wherein the ratio of the thickness of the outermost layer, the second outer layer, the intermediate layer, the second inner layer and the innermost layer is (1.5-2): 0.3-0.5): 4-6: (0.3-0.5): 1.5-2.
6. Use of a shrink film according to claim 1 for the wrapping of objects with rolling properties, wherein said intermediate layer consists of 50-65% HDPE, 25-40% LDPE and 10% MDPE.
7. Use of a shrink film according to claim 2 for wrapping a rollable object, wherein said secondary outer layer and said secondary inner layer consist of 67-80% ethylene-vinyl alcohol copolymer, 17-30% ethylene-vinyl acetate copolymer, 1-1.5% alkali metal salt and 0.5-1.5% boride.
8. Use of a shrink film according to claim 1 for the packaging of objects with rolling properties, wherein the LDPE has a density of 0.910 to 0.930g/cm 3 The melt index is 0.25-0.30 g/10min, and the density of the HDPE is 0.950-0.960 g/cm 3 Melt index of<0.21g/10min, the density of the MDPE is 0.930-0.950 g/cm 3 A melt index of<0.8g/10min, the LLDPE having a density of<0.920g/cm 3 A melt index of<2.0g/10min, the density of the mLLDPE being<0.920g/cm 3 A melt index of<1.0g/10min。
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