A cold drawing protective film and a preparation method and application thereof

Abstract

The application discloses a cold-drawing protective film and a preparation method and application thereof, and relates to the technical field of packaging materials. The cold-drawing protective film has a three-layer structure, and the three layers are an inner layer, a middle layer and an outer layer in sequence. The inner layer and the outer layer can play the roles of opening and heat sealing, and the middle layer plays the role of drawing and rebounding. The preparation raw materials of the inner layer and the outer layer are the same, and the preparation raw materials include metallocene polyethylene, polyethylene and an additive master batch. The middle layer is metallocene polyethylene and a block copolymer. The obtained protective film has excellent tensile strength, forging crack elongation performance and breakdown resistance. More importantly, the protective film has good tensile rebounding elasticity and rebounding speed at normal temperature, and has good wrapping performance on the protected material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of packaging materials, B32B27 / 32, and in particular to a cold-stretching protective film and a preparation method and application thereof. BACKGROUND

[0002] A protective film is a film material with a protective effect arranged on the surface of an entity to be protected, which mainly functions to avoid damage to the protected material, such as scratching, dust pollution, gas corrosion, microbial corrosion, and the like, during manufacturing, transportation, storage, and secondary processing, thereby reducing the use value of the protected material. At present, the raw materials for preparing protective films mainly include polyethylene film, polypropylene film, polyethylene terephthalate film, and the like. Among them, the polyethylene film has the characteristics of softness, good toughness, large elongation, easy bending processing, and good adhesion, and thus occupies a large market share in protective films. However, the traditional protective film is mainly a heat-shrinkable film, which needs to be heated to realize the shrinkage function, and thus is complicated to use, needs to be heated, and has high energy consumption.

[0003] Chinese Patent Application CN105328958A discloses a high-transparency polyethylene film for a protective film, which is made into a composite film by melt co-extrusion blown film. The inner layer includes low-density polyethylene, metallocene linear low-density polyethylene, PPA masterbatch, transparent nucleating agent masterbatch, and slip agent masterbatch. The middle layer includes low-density polyethylene, metallocene linear low-density polyethylene, PPA masterbatch, and transparent nucleating agent masterbatch. The outer layer includes low-density polyethylene, metallocene linear low-density polyethylene, PPA masterbatch, transparent nucleating agent masterbatch, and SEBS. The composite film has good transparency, low haze, and is easy to unwind and peel off, and is commonly used for adding points and electronic products. However, the protective film obtained by the above technical solution has poor mechanical properties such as breaking tensile strength and breaking elongation. Chinese Patent Application CN101758960B discloses a biaxially-stretched polyethylene protective film, which includes a functional layer, a core layer, and a secondary functional layer. The material of the functional layer is composed of low-density polyethylene, metallocene polyethylene, anti-sticking agent, and slip agent. The material of the core layer is metallocene polyethylene. The material of the functional layer is composed of ethylene-vinyl acetate copolymer (EVA) and metallocene polyethylene. The polyethylene protective film has good toughness and can prevent cutting and bruising. However, the protective film obtained by the above technical solution cannot realize normal-temperature shrinkage, and can only be better wrapped around the product through hot processing. SUMMARY

[0004] To solve the above problems, the present application provides a cold-stretching protective film in the first aspect, which sequentially includes an inner layer, a middle layer, and an outer layer.

[0005] In some preferred embodiments, the same metallocene polyethylene is contained in the preparation raw materials of the inner layer, the middle layer, and the outer layer.

[0006] In some preferred embodiments, the metallocene polyethylene is selected from at least one of metallocene polyethylene elastomer, metallocene polyethylene plastomer, metallocene ultra-low density polyethylene, metallocene linear low density polyethylene, metallocene low density polyethylene, metallocene medium density polyethylene; preferably metallocene linear low density polyethylene.

[0007] In some preferred embodiments, the metallocene linear low density polyethylene has a melt index of 190℃ / 2.16kg of 0.2-1.5g / 10min, a tensile strength at yield MD of 3-15MPa, a tensile strength at yield TD of 4-15MPa; preferably, the metallocene linear low density polyethylene has a melt index of 190℃ / 2.16kg of 0.50g / 10min, a tensile strength at yield MD of 6.8MPa, a tensile strength at yield TD of 6.7MPa.

[0008] In some preferred embodiments, the metallocene linear low density polyethylene has a dart drop impact value of 750-1000g, a puncture force of 50-75N; preferably, the metallocene linear low density polyethylene has a dart drop impact value of 900g, a puncture force of 60N.

[0009] In some preferred embodiments, the metallocene polyethylene is added in the inner layer and the outer layer in an amount of 65-85 parts by weight, and in the middle layer in an amount of 75-95 parts; preferably, the metallocene polyethylene is added in the inner layer and the outer layer in an amount of 70-80 parts by weight, and in the middle layer in an amount of 80-95 parts.

[0010] The metallocene linear low density polyethylene has excellent optical properties and puncture resistance, and the addition of the metallocene linear low density polyethylene in the inner layer and the outer layer can increase the puncture resistance of the protective film. The applicant has found that the metallocene linear low density polyethylene with a melt index of 190℃ / 2.16kg of 0.2-1.5g / 10min, a tensile strength at yield MD of 3-15MPa, and a tensile strength at yield TD of 4-15MPa has high melt strength and superior mechanical and optical properties, good flowability, good compatibility with the polyethylene, the additive master batch, and the block copolymer in the middle layer in the system, can be uniformly mixed in the system, and the processing performance is improved. Under specific process parameters in the later stage, the metallocene linear low density polyethylene can be well extruded and blown, and in particular, the metallocene linear low density polyethylene with a melt index of 190℃ / 2.16kg of 0.50g / 10min, a tensile strength at yield MD of 6.8MPa, and a tensile strength at yield TD of 6.7MPa can also improve the anti-bending crack performance of the protective film and increase the opening and sealing performance of the inner and outer layers of the protective film.

[0011] In some preferred embodiments, the inner layer and the outer layer further comprise polyethylene and additive master batch.

[0012] In some preferred embodiments, the inner layer and the outer layer further comprise, by weight parts, polyethylene 17-35 parts and an auxiliary master batch 1-7 parts; preferably, further comprise polyethylene 20-30 parts and an auxiliary master batch 2-5 parts.

[0013] In some preferred embodiments, the polyethylene is selected from at least one of low pressure polyethylene, high pressure polyethylene, linear low density polyethylene; preferably, the polyethylene is linear low density polyethylene.

[0014] In some preferred embodiments, the linear low density polyethylene has a melt index of 0.5-5 g / 10 min, a dart impact strength of 400-550 g, and a tensile strength at break in the range of 20-40 MPa at 190℃ / 2.16 kg; preferably, the melt index is 0.6-3 g / 10 min, the dart impact strength is 420-500 g, and the tensile strength at break is in the range of 23-35 MPa at 190℃ / 2.16 kg; further preferably, the melt index is 1 g / 10 min, the dart impact strength is 450 g, and the tensile strength at break is in the range of 27.6-33.8 MPa.

[0015] In some preferred embodiments, the auxiliary master batch contains a functional master batch of an opening and smooth component.

[0016] Preferably, the opening and smooth component is selected from at least one of (Z)-13-docosenamide, erucyl stearate amide, polyethylene oxide, polyethylene wax, silicone oil, organosilicon, polyethylene glycol oleyl palmitamide, silicon dioxide, oleic acid amide; preferably, the opening and smooth component is (Z)-13-docosenamide.

[0017] In some preferred embodiments, the auxiliary master batch has a density of 820-910 kg / m 3 at 90℃, and a bulk density of 520-630 kg / m 3 at 20℃; preferably, the auxiliary master batch has a density of 850 kg / m 3 at 90℃, and a bulk density of 570 kg / m 3 at 20℃.

[0018] In some preferred embodiments, the preparation raw material of the middle layer further comprises a block copolymer.

[0019] In some preferred embodiments, the preparation raw material of the middle layer further comprises, by weight percentage, a block copolymer 3-27 parts; preferably, further comprises a block copolymer 5-20 parts.

[0020] In some preferred embodiments, the block copolymer is selected from at least one of styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-butadiene block copolymer, polyether-polyolefin block copolymer, and ethylene-propylene block copolymer; and preferably is hydrogenated styrene-butadiene block copolymer.

[0021] In some preferred embodiments, the hydrogenated styrene-butadiene block copolymer has a melt flow rate of 8-20 g / 10 min, a tensile strength of 380-500 kg / cm 2 , and a molding shrinkage of 1-3%; preferably, the melt flow rate is 16 g / 10 min, the tensile strength is 450 kg / cm 2 , and the molding shrinkage is 2% (Japan Asahi SEBS S1613).

[0022] The addition of a polymer material having excellent resilience to the middle layer material of the protective film can increase the cold-stretching recovery shrinkage performance of the protective film. The present inventor has found that the addition of a hydrogenated styrene-butadiene block copolymer, particularly a hydrogenated styrene-butadiene block copolymer having a melt flow rate of 8-20 g / 10 min, a tensile strength of 380-500 kg / cm 2 , and a molding shrinkage of 1-3% to the above system is advantageous for the obtained protective film to be wrapped around the protected object after being stretched from the normal temperature range. It is presumed that the possible reason is that the hydrogenated styrene-butadiene block copolymer has a molecular chain with a high-reactivity functional group, which can be uniformly mixed with the polyethylene material in the system, increase the mechanical strength of the protective film without reducing its flowability, and make it have good resilience, tear resistance, and electrical properties, while its permanent deformation is small, and it can quickly recover after being stretched at normal temperature, and the wrapping is strong, which further increases the sealing protection of the material. The present inventor has unexpectedly found that when the amount of the block copolymer added in the middle layer preparation raw material is 3-27 parts, the toughness and tensile strength of the protective film can be better improved, while its excellent wrapping force is maintained.

[0023] In some preferred embodiments, the weight ratio of the inner layer, the middle layer, and the outer layer is 1:(2-3.5):1; preferably is 1:(2-3):1; and further preferably is 1:3:1.

[0024] The weight ratio of the preparation raw materials of the inner layer, the middle layer and the outer layer can be adjusted to effectively improve the blowing film processing stability of the final protective film. When the weight ratio of the inner layer, the middle layer and the outer layer is 1:(2-3.5):1, especially 1:3:1, the thickness of the obtained protective film is uniform, and the tear resistance and the puncture strength of the obtained protective film can be improved, the tensile strength is above 37 MPa, the breaking nominal strain is above 780%, the puncture strength is 5 N, and the surface impact damage mass is 1100 g.

[0025] The second aspect of the present application provides a preparation method of a cold-drawing protective film, comprising:

[0026] S1. The preparation raw materials of the inner layer, the middle layer and the outer layer are respectively fed into three extruders, and are respectively mixed and plasticized in the screw rods;

[0027] S2. The mixture obtained in S1 is fed into the same three-layer blowing film die, and the inner layer, the middle layer and the outer layer are sequentially hot-bonded together;

[0028] S3. The film obtained in S2 is extruded and blown through the three-layer co-extrusion blowing film die, is then cooled by the inner and outer cooling air, and finally is adjusted in thickness uniformity by automatic thickness measurement and automatic air ring.

[0029] In S1, the temperature of the screw rod is 150-200°C; preferably 150-190°C; and further preferably 175°C.

[0030] In S3, the temperature of the three-layer co-extrusion blowing film die is 160-195°C, preferably 170-190°C; and further preferably 180°C.

[0031] In some preferred embodiments, the diameter of the three-layer co-extrusion blowing film die is 140-450 mm, which can be adjusted according to the obtained protective film.

[0032] Preferably, when used for chemical industry and building materials, the diameter of the three-layer co-extrusion blowing film die is 250-400 mm; and further preferably 310 mm.

[0033] Preferably, when used for household appliance film, the diameter of the three-layer co-extrusion blowing film die is 150-250 mm; and further preferably 200 mm.

[0034] In some preferred embodiments, the blowing ratio of the extrusion blowing is 2.5-3.5; and preferably 3.0.

[0035] In some preferred embodiments, the temperature of the cooling air is 10-25°C; and preferably 10-20°C.

[0036] In some preferred embodiments, the thickness uniformity is ≤ 7%; preferably ≤ 6%.

[0037] The third aspect of the present application provides an application of the cold-stretching protective film in the field of packaging protection film for chemical products, building materials and home appliance protection film.

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] (1) The cold-stretching protective film has a three-layer structure, including an inner layer, a middle layer and an outer layer in sequence, the inner layer and the outer layer can play the roles of opening and heat sealing, and the middle layer plays the role of stretching and rebounding. The preparation raw materials of the inner layer and the outer layer are the same, including metallocene polyethylene, polyethylene and additive master batch, and the middle layer is metallocene polyethylene and block copolymer. The obtained protective film has excellent tensile strength, cracking elongation performance and breakdown resistance. More importantly, the film has good stretching rebounding elasticity and fast rebounding speed at room temperature, and has good wrapping performance for the protected materials.

[0040] (2) The middle layer in the present application uses hydrogenated styrene-butadiene block copolymer which has good rebounding elasticity and tear resistance. The hydrogenated styrene-butadiene block copolymer has excellent tensile strength and electrical properties, small permanent deformation, good flexing and rebounding elasticity, and can also resist ozone and oxygen. The cold-stretching protective film produced by using the material has excellent clamping force and weather resistance, high packaging efficiency and low damage in use, and can better improve the production efficiency. Meanwhile, the hydrogenated styrene-butadiene block copolymer has good compatibility with polyethylene material, and the material can be recycled after use, which is friendly to the environment.

[0041] (3) The obtained cold-stretching protective film uses the material with elasticity added in each layer of the film to stretch the film in the normal temperature range, then puts the required packaging product into the tube film, and relies on the rebounding performance of the film to wrap the product. According to the needs, the film can also be heat sealed on the top of the product for waterproofing, or the film surface can be punched to increase the exhaust, which is a low-energy consumption protective film product.

[0042] (4) In the present application, the three-layer film material is mixed, plasticized, bonded and extruded by an extruder to obtain the cold-stretching protective film. The preparation process is simple, and the film blowing process in the preparation process is stable, the thickness uniformity of the film is good, and the performance is stable. DETAILED DESCRIPTION

[0043] Example 1

[0044] 1. A cold-stretching protective film, sequentially comprising an inner layer, a middle layer and an outer layer.

[0045] The preparation raw materials of the inner layer, the middle layer and the outer layer all contain the same metallocene polyethylene.

[0046] The metallocene polyethylene is a metallocene linear low-density polyethylene.

[0047] The metallocene linear low-density polyethylene at 190℃ / 2.16kg has a melt index of 0.50g / 10min, a yield tensile strength MD of 6.8MPa, and a yield tensile strength TD of 6.7MPa.

[0048] The metallocene linear low-density polyethylene has a dart impact value of 900g and a puncture force of 60N.

[0049] The metallocene linear polyethylene is ExxonMobil, mLLDPE 7052.

[0050] The metallocene polyethylene is added in 75 parts by weight in the inner and outer layers and in 90 parts by weight in the middle layer.

[0051] The raw materials used to prepare the inner and outer layers also include polyethylene and auxiliary masterbatch.

[0052] By weight, the raw materials for preparing the inner and outer layers also include: 22 parts of polyethylene and 3 parts of additive masterbatch.

[0053] The polyethylene is linear low-density polyethylene.

[0054] The linear low-density polyethylene has a melt index of 1 g / 10 min at 190℃ / 2.16 kg, a dart impact strength of 450 g, and a tensile strength at break ranging from 27.6 to 33.8 MPa (DowDuPont, LLDPE 5401G).

[0055] The additive masterbatch contains a functional masterbatch with an opening-slipping component.

[0056] Preferably, the slippery opening component is (Z)-13-eicosenoamide.

[0057] The density of the additive masterbatch at 90℃ is 850 kg / m³. 3 The bulk density at 20℃ is 570 kg / m³. 3 ( Formerly Aksu, QC-066).

[0058] The raw materials for preparing the middle layer also include block copolymers.

[0059] The raw materials for preparing the middle layer also include 10 parts of block copolymer by weight percentage.

[0060] The block copolymer is a hydrogenated styrene-butadiene block copolymer.

[0061] The melt flow rate of the hydrogenated styrene-butadiene block copolymer is 16 g / 10 min, the tensile strength is 450 kg / cm2, and the molding shrinkage is 2% (Japan Asahi SEBS S1613).

[0062] The weight ratio of the inner layer, the middle layer and the outer layer is 1:3:1.

[0063] 2. A method for preparing a cold-stretching protective film, comprising:

[0064] S1. feeding the raw materials for preparing the inner layer, the middle layer and the outer layer into three extruders respectively, and mixing and plasticizing in the screw rods respectively;

[0065] S2. feeding the mixture obtained in S1 into the same three-layer film blowing die, and sequentially hot-bonding the inner layer, the middle layer and the outer layer together;

[0066] S3. extruding and blowing the film obtained in S2 through the three-layer co-extrusion film blowing die, then cooling by inner and outer cooling air, and finally adjusting the thickness uniformity by automatic thickness measurement and automatic air ring, to obtain the cold-stretching protective film.

[0067] In S1, the temperature of the screw rod is 175°C.

[0068] In S3, the temperature of the three-layer co-extrusion film blowing die is 180°C.

[0069] The diameter of the three-layer co-extrusion film blowing die is 310 mm.

[0070] The blowing ratio of the extrusion blowing is 3.0.

[0071] The temperature of the cooling air is 10-20°C.

[0072] The thickness uniformity is ≤6%.

[0073] 3. Application of the cold-stretching protective film in the field of protective film for outer packaging of chemical products, building materials and home appliances.

[0074] Example 2

[0075] 1. A cold-stretching protective film, which is different from Example 1 in that:

[0076] The addition amount of the metallocene polyethylene in the middle layer is 80 parts.

[0077] The raw materials for preparing the middle layer further comprise 20 parts of block copolymer by weight percentage.

[0078] 2. A method for preparing a cold-stretching protective film, which is the same as Example 1.

[0079] 3. The application of the cold-stretching protective film in the field of packaging protection film for chemical products, building materials and household appliances.

[0080] Example 3

[0081] 1. A cold-stretching protective film, which is different from Example 1 in that:

[0082] The amount of the metallocene polyethylene added in the middle layer is 70 parts.

[0083] The preparation raw materials of the middle layer further include 30 parts of block copolymer by weight percentage.

[0084] 2. A preparation method of a cold-stretching protective film, which is the same as Example 1.

[0085] 3. The application of the cold-stretching protective film in the field of packaging protection film for chemical products, building materials and household appliances.

[0086] Example 4

[0087] 1. A cold-stretching protective film, which is different from Example 1 in that:

[0088] The weight ratio of the inner layer, the middle layer and the outer layer is 1:2:1.

[0089] 2. A preparation method of a cold-stretching protective film, which is the same as Example 1.

[0090] 3. The application of the cold-stretching protective film in the field of packaging protection film for chemical products, building materials and household appliances.

[0091] Example 5

[0092] 1. A cold-stretching protective film, which is different from Example 1 in that:

[0093] The weight ratio of the inner layer, the middle layer and the outer layer is 1:4:1.

[0094] 2. A preparation method of a cold-stretching protective film, which is the same as Example 1.

[0095] 3. The application of the cold-stretching protective film in the field of packaging protection film for chemical products, building materials and household appliances.

[0096] Performance test

[0097] 1. The performance test of the protective film obtained in Example 1 is carried out, and the specific results are shown in Table 1.

[0098] Table 1 Performance test results of the protective film obtained in Example 1

[0099] Report No.: Light Commission 2022-06-0387 Page 2 of 2

[0100]

[0101] 2. The following performance tests were conducted on the examples, and the results are shown in Table 1.

[0102]

[0103] As can be seen from Table 1, Examples 1 and 2 are preferred examples, which can meet the actual production requirements. The cold-drawing protective film obtained in Example 3 is relatively soft, easy to stretch, has slightly low wrapping force, and has high cost. Example 4 has poor tear resistance and slow rebound, and is easy to be torn during use. Example 5 has poor stability during the film blowing process, poor uniformity of film thickness, and unstable performance.

Claims

1. A cold stretch protection film, characterized by, It consists of an inner layer, a middle layer, and an outer layer, in that order. The inner, middle, and outer layers are all made from the same metallocene polyethylene; the metallocene polyethylene is metallocene linear low-density polyethylene; the metallocene linear low-density polyethylene has a melt index of 0.50 g / 10 min at 190℃ / 2.16 kg, a yield tensile strength MD of 6.8 MPa, and a yield tensile strength TD of 6.7 MPa; the metallocene linear low-density polyethylene has a dart impact value of 900 g and a puncture force of 60 N; the metallocene linear low-density polyethylene is ExxonMobil, mLLDPE 7052; The metallocene polyethylene is added in 75 parts by weight in the inner and outer layers and 90 parts by weight in the middle layer. By weight, the raw materials for preparing the inner and outer layers also include: 22 parts of polyethylene and 3 parts of additive masterbatch; The polyethylene is linear low-density polyethylene; the linear low-density polyethylene has a melt index of 1 g / 10 min at 190℃ / 2.16 kg, a dart impact strength of 450 g, and a tensile strength at break ranging from 27.6 to 33.8 MPa. The auxiliary master batch is a functional master batch containing an opening smooth component; the opening smooth component is (Z)-13-docosenamide; the density of the auxiliary master batch at 90°C is 850 kg / m 3 , and the bulk density at 20°C is 570 kg / m 3 . The middle layer is prepared from 10 parts by weight of a block copolymer; the block copolymer is a hydrogenated styrene-butadiene block copolymer; the hydrogenated styrene-butadiene block copolymer has a melt flow rate of 16 g / 10 min, a tensile strength of 450 kg / cm 2 , and a molding shrinkage of 2%. The weight ratio of the inner layer, middle layer and outer layer is 1:3:1; The method for preparing the cold-stretch protective film includes: S1. feeding the raw materials for the inner layer, middle layer, and outer layer into three extruders, and mixing and plasticizing them in the screws respectively; S2. feeding the mixture obtained in S1 into the same three-layer blown film die, and thermally bonding the inner layer, middle layer, and outer layer together in sequence; S3. extruding and blowing the film obtained in S2 through the three-layer co-extrusion blown film die, then cooling it with internal and external cooling air, and finally adjusting the thickness uniformity by automatic thickness measurement and automatic air ring, thus obtaining the final product. In S1, the temperature of the screw is 175°C; in S3, the temperature of the three-layer co-extrusion blown film die is 180°C. The diameter of the three-layer co-extrusion blown film die is 310 mm; the blow-up ratio of the extrusion blow-up is 3.0; the temperature of the cooling air is 10~20℃; and the thickness uniformity is ≤6%.

2. The application of the cold-stretched protective film according to claim 1 in the fields of protective film for outer packaging of chemical products, building materials, and protective film for household appliances.

Images