WO2012155859A1

WO2012155859A1 - Polyolefin film for packaging and preparation method therefor

Info

Publication number: WO2012155859A1
Application number: PCT/CN2012/075709
Authority: WO
Inventors: 陈大魁; 黄旭生
Original assignee: 浙江众成包装材料股份有限公司
Priority date: 2011-05-18
Filing date: 2012-05-18
Publication date: 2012-11-22
Also published as: CN102248735A; CN102248735B

Abstract

A coextrusion polyolefin two-way stretching film, comprising a composite layer, an intermediate layer, and a heat-sealing layer. The composite layer, the intermediate layer, and the heat-sealing layer are of a coextrusion structure, and each layer independently comprises propylene polymer, ethylene polymer, blends thereof, or mixture thereof. The ratio of the vertical elongation rate to the horizontal elongation rate of the polyolefin two-way stretching film is smaller than 1.6. Furthermore, the vertical and horizontal shrinkage rate is smaller than 8% at 90 degrees Celsius. The polyolefin two-way stretching film can be used in different daily packaging or food packaging. Also provided are a composite packaging structure having substrates and the polyolefin two-way stretching film and a preparation method for the polyolefin two-way stretching film.

Description

Polyolefin film for packaging and preparation method thereof

[0001] The present application claims the priority of the Chinese patent application filed on May 18, 2011, the application number is 201110127215. 6, the invention is entitled "polyester film for packaging and its preparation method", the entire contents of which are incorporated by reference. Combined in this application. Technical field

The present invention relates to a multilayer coextruded polyolefin biaxially oriented film for packaging and a process for the preparation thereof. Background technique

[0003] Polyethylene film (PE fi lm) has the advantages of light weight, non-toxicity, moisture resistance, and excellent heat sealing performance, and is widely used for packaging of food, medicine, daily light labor, sanitary products and the like. One of the main uses of polyethylene film is to provide heat sealability, physical strength, such as puncture resistance and drop resistance, as a composite substrate film and other materials in the flexible packaging industry.

[0004] Composite structures are widely used in the flexible packaging industry. Biaxially oriented polypropylene film (B0PP), biaxially oriented polyester film (PET), biaxially stretched nylon film (B0PA), aluminum foil (A1 foil), aluminized PET (M-PET), polyethylene film (PE) Membrane) and CPP film (cast polypropylene film) are the most common composite packaging materials. For example, the B0PP/PE two-layer structure can be used for packaging of washing powder, sugar, salt, and the like. BOPP/CPP; PET/M-PET/CPP is commonly used for the packaging of biscuits and dried foods. PET/PE, B0PA/PE is commonly used for condiments, liquid foods, frozen foods and liquid daily necessities (shampoos, etc.). PET/AL/PE or PET/M-PET/PE can be used for foods that require a long shelf life, such as milk powder, meat, etc.

[0005] The reason why the composite structure adopts two or more layers is because different materials have different properties, and the composite materials can be used to produce packaging materials with different properties to meet the packaging requirements of different packaging materials in practical applications. For example, B0PP has high gloss and good dimensional stability, which is very suitable for printing. However, B0PP cannot be heat-sealed and has poor toughness, such as drop and puncture resistance. The PE film has good heat sealability and also has excellent drop resistance and puncture resistance. Therefore, through the compounding of B0PP/PE, it is possible to produce a composite packaging structure which is beautifully printed, firmly sealed, and has a certain physical strength. A1 foil and aluminized film have good oxygen and moisture barrier properties, which can extend the shelf life of the product, so it is often used for product packaging that is easy to degrade. B0PA combines printability, low temperature resistance and toughness, and a certain physical strength, so it is often used for food packaging with high quality requirements. [0006] Composite heat sealing substrate films commonly used in the flexible packaging industry mainly include PE film and CPP (cast polypropylene) film. The advantages of CPP film are high stiffness and high transparency, but its physical properties are poor, especially drop resistance and low temperature performance. In addition, the heat sealing performance of CPP film is also poor. PE film is generally produced by blow molding and casting. It has better heat sealing performance and physical properties than CPP, but the stiffness is much lower than that of CPP film. The transparency of blown PE film is also lower than that of PE film. CPP film.

[0007] Therefore, there is a need in the industry for a film having both transparency and stiffness of a CPP film, physical properties of a PE film, heat sealing properties and low temperature resistance.

[0008] At present, the most common method for improving the stiffness of PE films is to add high density polyethylene (HDPE) to the formulation, but HDPE has a great negative impact on the physical properties and heat sealing properties of the film, and HDPE is stiff. Improvement is also extremely limited. Coextrusion of PP and PE improves the stiffness of the film, but negatively affects the transparency and physical properties of the film.

[0009] Biaxial stretching of PE and PP increases the stiffness and transparency of the film. However, PE is very easy to shrink after biaxial stretching, so it is mainly used for heat shrinkable film, which will shrink at the heat seal when applied to a packaged composite film. The PP stretch film has extremely poor physical and heat seal properties and is therefore mainly used for printing a substrate film. Summary of the invention

The present invention provides a polyolefin biaxially oriented film comprising a composite layer (also referred to as a corona layer), an intermediate layer (also referred to as a core layer), and a heat seal layer. The composite layer is used to form a composite packaging structure by various composite processes with a printed or non-printed substrate, the surface of which is treated by corona or the like to change the surface tension. The intermediate layer (i.e., the core layer) is of sufficient thickness to provide stiffness and strength. The heat seal layer provides low temperature heat sealing properties. The composite layer of the polyolefin biaxially oriented film of the present invention, the intermediate layer and the heat seal layer are coextruded structures, and each layer comprises a film-forming polyolefin polymer selected from the group consisting of ethylene polymers (also known as polyethylene). A propylene polymer (also known as polypropylene) or a mixture thereof. The polyolefin biaxially oriented film of the present invention has high transparency, high stiffness and high strength, has excellent heat sealing properties, and has low shrinkage. Compared with traditional packaging films such as PE and CPP, it combines the stiffness, transparency, physical strength of PE and heat sealing properties of CPP, so it can greatly reduce the thickness of packaging film. It is a new type of energy saving and environmental protection. Olefin packaging film. The polyolefin biaxially oriented film of the present invention can be used for a heat seal layer of a composite package, or can be used alone for daily necessities or food packaging. The polyolefin biaxially oriented film of the present invention can be prepared by a simultaneous tube film biaxial stretching process and subjected to heat setting treatment to attain the effects and objects of the present invention.

[0011] The present invention provides a coextruded polyolefin biaxially oriented film having a composite layer, an intermediate layer and a heat seal a layer, the composite layer, the intermediate layer and the heat seal layer are coextruded structures, and each layer independently comprises a propylene polymer, an ethylene polymer, a blend thereof or a mixture thereof, and the surface tension of the composite layer is greater than 38 because.

[0012] The polyolefin biaxially oriented film of the present invention has a film longitudinal elongation to transverse elongation ratio of less than 1.6, preferably less than 1.3. Further, the polyolefin biaxially oriented film of the present invention has a longitudinal and transverse shrinkage ratio at 90 ° C of less than 8%, preferably less than 5%. The shrinkage test and calculation method of the film can be carried out by a method known in the art and commonly used. One of the tests and calculations is as follows:

[0013] Shrinkage = (L1-L2) / L1 x 100. L1 is the strength of the sample before heat treatment, and L2 is the length of the sample after it has been placed in the oven for 10 minutes at the specified temperature. Usually the sample has a size of 10 cm _X 5 _Cm (i.e., Ll = 10 cm) before heat treatment.

[0014] The polyolefin biaxially oriented film of the present invention can be produced by a synchronous tube film simultaneous stretching process, and the film is subjected to surface treatment and heat setting treatment before winding to achieve the surface tension and vertical and horizontal directions required by the present invention. Shrinkage.

[0015] The ethylene polymer used in the film of the present invention may be an ethylene homopolymer or a copolymer of ethylene and other olefin monomers, such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), Very low density polyethylene (VLDPE, or ULDPE), low density polyethylene (LDPE), ethylene plastomer, mixtures thereof and blends thereof. Ethylene polymers also include copolymers of ethylene and other non-olefinic monomers.

[0016] HDPE has no or a small amount of comonomer, and has a density of about 0. 941 g / cm ³ or higher (for example, about 0. 952 g / cm ³ to about 0. 968 g / cm ³ ), for example a melting point of from about 266 °F to about 299 °F (about 130 ° C to about 148 ° C), and a melt index of less than 1 to 50 g/10 minutes (eg, 1 to 50 g/10 minutes) (190 degrees Celsius, 2 16 kg measured according to ASTM D1238). The common HDPE on the market is Sinopec's 5000S, Dow Chemical's 6200, and Exxon's 108TA.

[0017] LDPE is a homopolymer and has a density in the range of from 0.912 g/cm ³ to 0.94 g/cm ³ (eg, from 0.915 g/cm ³ to 0.928 g/cm ³ ) And a melt index of 0. 2 to 50 g/10 min (eg 1 to 10 g/10 min) (190 degrees Celsius, 2.16 kg measured according to ASTM D1238). LDPE is produced using a free radical initiator in a high pressure process. Common LDPEs on the market include Yanshan Petrochemical's IF7B, 100AC, Dow Chemical's 640, 1321, and Exxon's 165W.

[0018] The LLDPE may be an ethylene-butene copolymer, an ethylene-hexene copolymer and an ethylene-octene copolymer, and has a melt index of less than 1 to 50 g/10 minutes (eg, 1 to 10 g/10 minutes). (190 ° C, 2. 16 kg measured according to ASTM D1238) and a density in the range of from 0.910 to 0.940 g/cm, preferably from 0.15 to 928 g/cm ³ . Conventional LLDPE is formed by a vapor phase or liquid phase reaction of a Ziegler-Natta catalyst. in the market Common LLDPEs are Sinopec's 7042, Dow Chemical's 2045G, and Exxon's 1002.

[0019] Another class of LLDPEs is ultra low density or very low density LLDPE, also known as ULDPE or VLDPE. 912. 912 g/cm The singularity of the singularity of the singularity of the singularity of the singularity of the singularity of the singularity. Between ³ Such products commonly found on the market include Dow Chemical's ATTANE4203, FLEX0MER1085 and the like.

[0020] The latest generation of LLDPE products is metallocene LLDPE, which has a single point of reaction compared to conventional Ziegler-Natta catalysts, so that the LLDPE produced has a more uniform comonomer distribution and, therefore, Physical and mechanical properties and heat seal performance are stronger than traditional LLDPE. Common metallocene LLDPE on the market are Dow Chemical's ELITE5400G, AFFINITY1881, ±Zexen's EXCEED1018, Japan's Mitsui's EV0LUE1520, 2520 and so on.

The propylene polymer used in the film of the present invention may be a homopolypropylene or a copolymer of propylene and other olefins. Homopolymer polypropylene has the characteristics of low cost, high melting point and high stiffness. Copolymerized polypropylene has a lower melting point and stiffness, but has a lower heat sealing temperature, which facilitates rapid packaging. PP has a density of about 0. 89-0. 91 g/cm ³ , and a melt index of less than 1 to 50 g/10 min (for example, 1 to 50 g/10 min) (230 ° C, 2. 16 kg, according to ASTM D1238 measurement). The common homopolymer PP on the market is T38F of Lanzhou Petrochemical Co., Ltd. PP is PP-M800E of Jinshan Petrochemical, 6612 of TPC, ADSYL5C37 of Basel.

[0022] Further, in the film of the present invention, the composite layer, the intermediate layer and the heat seal layer may further contain a usual additive. Commonly used additives are anti-blocking agents, slip agents, antistatic agents, nucleating agents, cavitation agents or sunscreens. Sunscreens include iron oxide, carbon black, titanium dioxide, talc, and combinations thereof. One or more hydrocarbon resins may further be included in each layer. The hydrocarbon resin may be a low molecular weight hydrocarbon compatible with the film forming polymer of the base layer. This or these hydrocarbon resins may be hydrogenated. Specific examples include, but are not limited to, petroleum resins, terpene resins, styrene resins, and cyclopentadiene resins. 01%_5% of one or more additives may be added to the material of the present invention in the form of a masterbatch.

[0023] The process for producing a biaxially stretched plastic film is a double bubble and a tenter frame. The tube film method is to stretch the film longitudinally and transversely while stretching the bubble tube. The method for producing a biaxially stretched plastic film by a tubular film stretching method generally comprises the following steps: a polyolefin raw material compounding, processing into a melt and extruding, forming a circular first tube film, and shaping the first tube film with cooling water, heating The first tube film is stretched to a suitable stretching temperature, and the first tube film is simultaneously stretched to a suitable thickness to form a second tube film, which is then wound and slit to obtain a finished film.

[0024] The polyolefin biaxially stretched film of the present invention can be produced by a synchronous tube film method, and the second tube film is advanced. Heat setting. The heat setting can be achieved by stretching the sheet by a heating roller or by a third bulb, and the heat setting temperature used in the present invention is about 80 to 120 degrees.

[0025] In one aspect of the invention, the film-forming polymer of the composite layer, the intermediate layer and the heat seal layer of the polyolefin biaxially oriented film is mainly an ethylene polymer. Here, "mainly" means that it does not contain other film-forming polymers, or contains a small amount of additives commonly used in the art, or contains a small amount of other film-forming polymers which do not substantially affect the chemical and physical properties of the film formation. In one aspect of the invention, the composite layer of the polyolefin biaxially oriented film, the film-forming polymer of the intermediate layer and the heat seal layer are independently composed of an ethylene polymer. In still another aspect of the invention, the polyolefin biaxially oriented film of the above film-forming polymer, which is mainly an ethylene polymer, is subjected to a crosslinking treatment. The cross-linking method can be online cross-linking or offline cross-linking. In the other hand, the cross-linking strength is such that the melt index (Ml) of the film is 0.1 to 5.0 g/10 minutes according to ASTM D-1238 (230 ° C, 10 kg). In another aspect of the present invention, the polyolefin film a density of between ^{0. 918 g / cm 3 -0.} 935g / cm between ^3, preferably ^{0. 922 g / cm 3 -0.} 928 g / cm 3 .

In another aspect of the invention, the ethylene polymer in the polyolefin biaxially oriented film in which the film-forming polymer is mainly an ethylene polymer is a linear polyethylene (LLDPE), preferably ethylene octene. Copolymer, ethylene hexene copolymer, blends thereof or mixtures thereof. In still another aspect of the invention, the above linear polyethylene has a melting point of less than 128 degrees Celsius, preferably less than 125 degrees Celsius, according to a differential scanning calorimetry (DSC) test. In still another aspect of the invention, the linear polyethylene has a comonomer distribution index CDBI of <60%, preferably CDBI <50%, and a molecular weight distribution (Mw/Mn) of preferably between 3 and 8, more preferably 3 Between 5-6. Mw / Mn can be determined by GPC gel permeation chromatography.

CDBI is an indicator of the uniformity of comonomer distribution. The larger the CDBI, the more uniform the comonomer is distributed in the main chain. CDBI is determined by temperature fractionation extraction (TREF), its definition and test method Wi l d, et al. at J« rafl of Polymer

Science, Poly. Phys. Ed, , Vol. 20, 441 (1982); is described in U.S. Patent Nos _. 4,798,081, and 5,008,204.

In another aspect of the invention, in the polyolefin film of the invention, the composite layer, the intermediate layer and the heat seal layer independently contain a propylene polymer and/or an ethylene polymer. Wherein the polyethylene melt index (Ml) is 0. 5-10 g/10 minutes according to ASTM D-1238 (190 degrees Celsius, 2.16 kg), and the polypropylene melt index (Ml) is according to ASTM D- 1238 (230 ° C, 2. 16 kg) The test was 1. 0_15 g/10 minutes. In one aspect of the invention, in the polyolefin film of the present invention, at least one of the composite layer, the intermediate layer and the heat seal layer mainly contains polypropylene, and at least one layer mainly contains polyethylene.

[0028] Preferably, in the non-heat seal layer (ie, the core layer and the composite layer), a film-forming polymer having a relatively high melting point is generally used. (ie ethylene polymer or propylene polymer or a mixture thereof, etc.) to improve the stiffness of the film.

On the other hand, the film-forming polymer used in the heat seal layer is generally composed of polyethylene or copolymerized polypropylene having a relatively low melting point to provide low-temperature heat-sealing properties.

[0030] Additives may be added to the heat seal layer to change properties such as openness, friction coefficient, and the like. Although the heat seal layer material is mostly polyethylene or polypropylene, it may be a polyethylene derivative or a composition thereof, or a blend of these derivatives with polyethylene and polypropylene.

In one aspect of the invention, the heat seal layer of the polyolefin biaxially oriented film contains a polyethylene derivative or a blend thereof. Polyethylene derivatives include ethylene-ethyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA) and ionic polar ethylene polymers.

[0032] Polyethylene derivatives include copolymers of ethylene and other non-olefinic monomers, such as ethylene-ethyl acetate copolymers

(EVA), ethylene-acrylic acid copolymer (EAA) and ionic polar ethylene polymer. Ethylene-vinyl acetate copolymer (EVA) reduces the high crystallinity due to the introduction of vinyl acetate monomer in the molecular chain. The content of vinyl acetate (VA) in the EVA is from about 5% to 40% by weight. Common EVAs on the market include Taiwanese Formosa Plastics (TAISOX®) 7350F, 7130F, 7140F, etc., Japan's C Company's 8450, etc., and DuPont's (ELVAX®) 3130, 3190, etc. Ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate copolymer

The properties of (EEA) polar ethylene copolymers have many similarities to EVA. Common EAAs are Primacore (registered trademark) of Dow Chemical, such as 1410, 3003, 3002, etc. The common EMAA is NUCREL (registered trademark) of DuPont, USA, such as 3990, 0910, etc. Common EEAs are Amplify (registered trademark) 101, 103, etc. of Dow Chemical. The ionic polar ethylene polymer is a type of ethylene polymer formed by substituting hydrogen ions on an acid bond in a resin such as EAA with zinc or sodium ions. Zinc and sodium ions form intermolecular crosslinks at normal temperature, thus greatly improving the physical properties of the polymer. Common ionic polymers on the market are DuPont's Surlyn (registered trademark), such as 1650, 1610 and the like.

In one aspect of the invention, the polyolefin biaxially oriented film of the invention has a heat-off temperature of less than 125 degrees, preferably less than 110 degrees. The heat-sealing temperature is defined as a pressure of 0. 275 N/mm ² and a heat-sealing time of 0.5 Nsec.

In one aspect of the invention, the polyolefin biaxially oriented film of the present invention may be provided with high density polyethylene (HDPE) or high pressure low density polyethylene (LDPE) having a melting point of greater than 128 degrees Celsius.

[0035] The polyolefin biaxially oriented film structure of the present invention comprises a composite layer (also referred to as a corona composite layer or a corona layer), one or more (eg two or three) core layers and one or more ( For example two or three) heat seal layers, each of which The layers are the same or different. The core layer of the polyolefin biaxially oriented film of the present invention may be in direct contact with the heat seal layer or may have a subsurface layer between the core layer and the heat seal layer. The polymer of the sub-surface layer may be the same as or different from the heat seal layer.

The polyolefin biaxially oriented film of the present invention is usually in a three-layer or five-layer structure.

[0037] The core layer of the polyolefin biaxially oriented film of the present invention may be one or more layers, for example, two or three layers. When the core layer is a two-layer or multi-layer structure, the materials of the respective core layers are the same or different.

[0038] The heat seal layer of the polyolefin biaxially oriented film of the present invention may have a one-layer structure. The heat seal layer of the polyolefin biaxially oriented film of the present invention may also have a multilayer structure such as two or three layers, the components of which are the same or different.

[0039] In one aspect of the invention, there is provided a polyolefin biaxially oriented film comprising a composite layer, one, two or three core layers, a heat seal layer, and optionally, a core layer A subsurface between the heat seal layer and the heat seal layer.

[0040] In one aspect of the invention, the polyolefin biaxially oriented film is a three-layer structure comprising a composite layer, a core layer and a heat seal layer.

[0041] In one aspect of the invention, the polyolefin biaxially oriented film is a five-layer structure comprising a composite layer, two or three core layers and a heat seal layer; or a composite layer, two a core layer and two heat seal layers; or a composite layer, two core layers, a subsurface layer between the core layer and the heat seal layer, and a heat seal layer.

In another aspect of the invention, the polyolefin biaxially oriented film of the invention is characterized in that the film has a total thickness of from about 10 μm to 80 μm, preferably from 20 to 50 μm. The polyolefin biaxially oriented film heat seal layer of the present invention is generally 1 to 15 μm thick.

The polyolefin biaxially oriented film of the present invention can be directly used for various packaging purposes, for example, for daily necessities packaging or food packaging. The polyolefin biaxially oriented film can be used for various commodity packaging or food packaging after printing.

The polyolefin biaxially oriented film of the present invention may also be composited with various substrates by a composite process to form a composite packaging structure in which the composite layer of the polyolefin biaxially oriented film of the present invention is composited with the substrate. The substrate comprises a printed or non-printed biaxially oriented polypropylene film (BOP), a biaxially oriented polyester film (B0PET), a biaxially oriented polyamide film (B0PA), an aluminum foil, a PE film, a paper, and the like. In one aspect of the invention, there is provided a composite packaging structure comprising a substrate and the aforementioned polyolefin biaxially oriented film comprising a biaxially oriented polypropylene film (BOP), biaxially oriented Polyester film (B0PET), biaxially stretched polyamide film (B0PA), aluminum foil, ordinary PE film and paper, etc., wherein the polyolefin biaxially stretched film is composited with these substrates through a composite layer thereof to form a composite packaging structure. The composite packaging structure may have one or more layers of a polyolefin biaxially oriented film or one or more layers of the substrate. The substrate may be an ink-printed material. In the composite package structure of the present invention, the composite layer of the polyolefin biaxially stretched film may be composited with the surface of the substrate with an ink. The present invention also provides a method of preparing the above-described polyolefin biaxially oriented film of the present invention.

The present invention provides a method of preparing a polyolefin biaxially oriented film having a coextruded composite layer, an intermediate layer and a heat seal layer, wherein each layer independently contains a propylene polymer, ethylene a polymer or a mixture thereof, the composite layer has a surface tension of more than 38 dynes, and the ratio of the longitudinal elongation to the transverse elongation of the polyolefin biaxially oriented film is less than 1.6, preferably less than 1.3, and the film is The longitudinal and transverse shrinkage at 90 degrees Celsius is less than 8%, preferably less than 5%. The method of the present invention treats a polyolefin raw material by a tubular film simultaneous stretching process, and heat-sets the obtained film to obtain a polyolefin biaxially stretched film of the present invention. In one aspect of the invention, the method processes the polyolefin raw material by a synchronous tube film simultaneous stretching process, and then heat-sets the formed second tube film to obtain a longitudinal elongation and a transverse elongation of the film. The ratio of less than 1.6, preferably less than 1.3, and the transverse and transverse shrinkage at 90 degrees Celsius is less than 8%, preferably less than 5% of the polyolefin biaxially oriented film. The method also treats the surface of the composite layer to have a surface tension greater than 38 dynes. Preferably, the treatment is corona treatment.

[0047] In the method of the invention, the heat setting can be shaped by a heated roll after stretching or by a third tube. The heat setting temperature used in the present invention is about 80 to 120 degrees.

[0048] In one method of the present invention, a method of preparing a polyolefin biaxially oriented film includes the following steps:

a) according to the composite layer of the film, the composition of the intermediate layer and the heat seal layer, the polyolefin raw material is batched, processed into a melt and extruded;

b) forming a circular first tube film through the annular head, and shaping the first tube film with cooling water;

c) heating the first film to a suitable stretching temperature;

d) simultaneously stretching the first film to a suitable thickness to form a second film;

e) heat setting the second film;

f) surface treatment of the second film to adjust the surface tension of the composite layer to 38 dynes or more;

g) Winding.

In one aspect of the invention, the above polyolefin film produced by the present invention consists essentially of an ethylene polymer. The ethylene polymer is selected from the group consisting of ethylene copolymers or ethylene homopolymers, such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), low density polyethylene (LDPE). ), ethylene plastomer. In still another aspect of the invention, the polyolefin film mainly composed of an ethylene polymer is subjected to a crosslinking treatment. 1-5. 0 g/10分钟。 The strength of the treatment of the film after the melt index (Ml) according to ASTM D-1238 (230 degrees Celsius, 10 kg) was tested to 0. 1-5. 0 g/10 minutes. The crosslinking can be online crosslinking or offline crosslinking. For example, in steps b) and c) The first film film may be cross-linked online, or may be cross-linked after step g).

[0050] In step c), the usual stretching temperature is from 95 to 120 degrees.

[0051] In step b), the thickness of the first tubular film is generally from 300 micrometers to 2400 micrometers, preferably from 600 to 1800 micrometers.

[0052] In step d), the thickness of the second tubular film is generally from 10 micrometers to 80 micrometers, preferably from 20 to 50 micrometers.

[0053] In the present invention, step f) may be subjected to surface tension adjustment using corona treatment. The surface tension can also be adjusted by flame treatment or plasma treatment, or by conventional methods such as chemical treatment, mechanical roughing, and coating.

The present invention also provides a polyolefin biaxially oriented film prepared according to the above method. detailed description

The invention has been described in connection with the preferred embodiments thereof. Example:

[056] A B0PE tensile composite film was produced on a 5-layer co-extrusion film biaxial stretching apparatus, and its structure is shown in Table 1 below. Films 9 and 10 are PE films produced by conventional blow molding, and the structure is shown in Table 2.

[0057] The film of the present invention (total thickness: 35μ) has the structure shown in Table 1:

Table 1: The film structure of the present invention

Film-7 D0WLEX2645G D0WLEX2645G ADSYL5C37 D0WLEX2645G D0WLEX2645G Non-crosslinked film-8 DOWLEX2045G DOWLEX2045G ADSYL5C37 ATTANE 4203 ATTANE4203 Non-crosslinking

Table 2: Comparative film (total thickness: 50 microns) structure

[0060] The details of the materials used are as shown in Table 3:

Table 3: Use of raw materials

[0061] The production of the film 1-8 is produced on the tube film biaxial stretching process production line, and the specific process is as follows:

1. Extrusion of polyolefin raw materials;

2. Forming a circular first tube film through the annular head;

3. The cooling water is shaped on the first film;

4. Cross-linking the first tube film on the electron beam;

5. Heat to the first film to a suitable stretching temperature;

6. Synchronously stretching the first tube film to a suitable thickness to form a second tube film;

7. Heat setting the second film; 8. Corona treatment of the second film;

9. Rewinding;

10. Cut.

[0062] The detailed production process and parameters are shown in Table 4:

Table 4: Invention film processing technology and parameters

[0063] The production of films 9-10 is produced using a conventional multilayer coextrusion topblowing line. The specific process parameters are:

Table 5: Film properties

Tensile strength Impact strength Secant modulus Elongation % 90 degrees Fog Heat seal strength N/25mm degrees (g) MD/CD (MD/CD) Shrinkage % degrees 100 110 120 130

MD/CD (Mpa) (MD/CD) °c "C "C "C (Mpa )

Test ASTM ASTM D882 ASTM D882 oven 10 seconds ASTM heat seal pressure: D. 2N/mm ² ; Method ASTM D1709 D100 Heat seal time: D. 5 seconds;

D882 3

Film -l 111/93 550 422/418 122/98 5/4 7. 6 10. 16 29 41

5

Film-2 110/94 743 369/410 108/92 4/3 8. 7 13 21 32 39 Film-3 98/96 732 372/390 112/120 3/3 11 16 28 35 36 Film-4 92/98 644 367/387 125/119 3/4 8 11 18 28 43 Film-5 109/107 632 387/364 98/102 3/3 10. 7 18 25 31 38.

5 Film -6 92/98 453 430/457 120/85 4/5 4. 5 0. 2 0. 5 4. 6 21.

5 Film-7 119/89 520 442/453 118/100 5/3 7. 3 8 15 25 20 Film-8-105/91 612 423/411 136/92 3/3 6. 7 18 20 26 19 Film-9 45/43 282 240/255 650/852 0/0 30 8 15 15 5

(Compared)

Film -10 42/41. 5 350 205/222 623/786 0/0 22 9 13 17 3

(Compared)

The film structure-1 and film-4 of the present invention have the same formulation structure and ratio, but due to the unique process of the film of the present invention, the film of the present invention is nearly 30% thinner than the comparative film. However, the tensile strength, impact strength, and stiffness (positive modulus) of the inventive film were more than double that of the comparative film. In addition, the haze of the inventive film is also much lower than that of the comparative film, and the film of the invention is more than twice as high as the heat sealing strength of the comparative film, and the heat sealing interval of the inventive film is much wider than that of the comparative film.

[0066] Other inventive films (2, 3, 5, 6, 7, 8) also have high strength, high stiffness and low haze characteristics. These features contribute to the thinning and weight reduction of the film. In addition, the crosslinked inventive film has better heat seal strength and a wider heat seal interval than the non-crosslinked inventive film.

[0067] The inventive film 1 and the comparative film 9 were respectively made into a 200 mm x 100 mm package by a corona layer and a 12 micron biaxially stretched PET film, and then subjected to a drop damage test by charging 500 g of salt. The results are shown in the following table: 1. 2 m drop test breakage rate % (experimental 3 m drop test breakage rate % (experimental amount: quantity: 10 packs) 10 packs)

PET / invention film 1 0 30%

PET/contrast film 9 20% 100%

From the above experiments, it was found that the package made of the film of the present invention was 15 μm thinner than the package made of the comparative film, but the breakage rate in the breakage test was much lower than that of the comparative film. At the same time, since the stiffness of the inventive film 1 is much higher than that of the comparative film, even if the thickness is reduced by 15 μm, the feeling of the package made of the inventive film and the feeling of the package made of the comparative film 9 are substantially close.

[0069] In summary, the BOPE film of the present invention unexpectedly has high transparency, high stiffness, high physical strength, superior heat sealing performance and low shrinkage ratio, which is helpful compared with the prior art. The packaging industry is thinning the film and meeting the need for lightweight packaging. Compared with the conventional PE, CPP and other packaging films, the polyolefin biaxially stretched film of the present invention integrates the stiffness, transparency, physical strength of PE and heat sealing properties of the CPP, thereby greatly reducing the thickness of the film and The amount of raw materials used is a new type of polyolefin packaging film that is energy-saving and environmentally friendly. Conventional films, especially the polyethylene films produced by the double bubble method in the industry, have low surface tension, low adhesion to inks or adhesives, and high shrinkage at low temperatures. The purpose of shrink packaging. The film provided by the present invention has a high adhesion fastness to an ink or an adhesive, and greatly reduces the shrinkage ratio, thereby satisfactorily meeting the needs of printing and lamination.

[0070] Unless otherwise indicated, the practice of the present invention will employ conventional techniques of organic chemistry, polymer chemistry, etc., and it is apparent that the invention may be practiced otherwise than as specifically described in the foregoing description and examples. Other aspects and modifications within the scope of the invention will be apparent to those skilled in the art. Many variations and modifications are possible in light of the teachings of the invention and are therefore within the scope of the invention.

[0071] All patents, patent applications, and scientific papers referred to herein are hereby incorporated by reference.

[0072] Unless otherwise indicated, the unit "degree" of temperature appearing herein refers to degrees Celsius, ie. C.

Claims

A coextruded polyolefin biaxially oriented film having a composite layer, an intermediate layer and a heat seal layer, the composite layer, the intermediate layer and the heat seal layer being a coextruded structure, and each layer independently containing propylene a polymer, an ethylene polymer, a blend thereof, or a mixture thereof, wherein the composite layer has a surface tension greater than 38 dynes, characterized by a longitudinal elongation and a transverse elongation of the polyolefin biaxially oriented film The ratio is less than 1.6, preferably less than 1.3, and both the longitudinal and transverse shrinkage at 90 degrees Celsius are less than 8%, preferably less than 5%.

2. The polyolefin biaxially oriented film according to claim 1, wherein the ethylene polymer is an ethylene copolymer or an ethylene homopolymer such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), which is extremely low Density polyethylene

(VLDPE), low density polyethylene (LDPE), ethylene plastomer, and wherein the propylene polymer is a propylene copolymer or a propylene homopolymer.

The polyolefin biaxially oriented film according to claim 1 or 2, which is produced by a simultaneous tube film biaxial stretching process and which is subjected to heat setting treatment.

The polyolefin biaxially oriented film according to any one of claims 1 to 3, wherein the composite layer, the intermediate layer and the heat seal layer each independently mainly contain an ethylene polymer, and preferably, the polyolefin film is crosslinked. More preferably, the melt index (Ml) of the film after the crosslinking treatment is 0.1 to 5.0 g/10 minutes according to ASTM D-1238 (230 ° C, 10 kg).

Polyolefin biaxially stretched film of claim 4, wherein the density of said thin film is 0.918 g / between cm ^³ -0.935g / cm ^3, preferably 0.922 g / cm between ^{³ -0.928} g / cm ^3.

6. The polyolefin biaxially oriented film of claim 5, wherein the ethylene polymer is a linear polyethylene

(LLDPE), preferably ethylene octene copolymer, ethylene hexene copolymer, blends thereof or mixtures thereof, more preferably, according to differential scanning calorimetry (DSC) test analysis, the melting point of the ethylene polymer Below 128 degrees Celsius, preferably below 125 degrees Celsius, and the copolymer has a comonomer distribution index CDBI < 60%, preferably CDBI < 50%, and the molecular weight distribution (Mw / Mn) is preferably between 3-8, more It is preferably between 3.5 and 6.

The polyolefin biaxially oriented film according to any one of claims 1 to 3, wherein the composite layer, the intermediate layer and the heat seal layer each independently comprise a propylene polymer, an ethylene polymer, a mixture thereof or a blend thereof, Preferably, the ethylene polymer melt index is 0.5-10 g/10 min according to ASTM D-1238 (190 degrees C, 2.16 kg), and the propylene polymer melt index is according to ASTM D-1238 (230 degrees Celsius, 2.16). The kilogram) test is 1.0-15 g/10 minutes.

The polyolefin biaxially oriented film according to any one of claims 1 to 7, which has a heat-sealing temperature of less than 125 degrees, preferably less than 110 degrees, and the heat-sealing temperature is defined as a pressure of 0.275 N/mm ² , 0.5 second heat sealing time can reach the heat sealing temperature of 4N/25mm.

The polyolefin biaxially oriented film according to any one of claims 1 to 8, which is a three-layer, four-layer or five-layer structure comprising a composite layer, one or more core layers, and one or more heats The sealing layer, wherein each layer component is the same or different.

The polyolefin biaxially oriented film according to any one of claims 1 to 9, characterized in that the film has a total thickness of from 10 to 80 μm, preferably from 20 to 50 μm.

The use of the polyolefin biaxially oriented film according to any one of claims 1 to 10 for use in daily necessities packaging or food packaging.

A composite packaging structure comprising a substrate and the polyolefin biaxially oriented film according to any one of claims 1 to 10, wherein the substrate is selected from the group consisting of biaxially oriented polypropylene film (BOPP), biaxially oriented polyester Film (BOPET), biaxially stretched polyamide film (BOPA), aluminum foil, polyethylene film and paper, wherein the composite layer of the polyolefin biaxially stretched film is composited with the substrate by a composite process to form a composite packaging structure.

The method for producing a polyolefin biaxially oriented film according to any one of claims 1 to 10, wherein the polyolefin biaxially oriented film has a composite layer, an intermediate layer and a heat seal layer, wherein each layer independently contains a propylene polymer, a vinyl polymer or a mixture thereof, the composite layer having a surface tension greater than 38 dynes, and the longitudinal elongation of the polyolefin biaxially oriented film The ratio to the transverse elongation is less than 1.6, preferably less than 1.3, and both the longitudinal and transverse shrinkage at 90 degrees Celsius are less than 8%, preferably less than 5%.

Wherein, the method processes the polyolefin raw material by a synchronous tube film simultaneous stretching process, and then heat-forms the formed second film.

14. The method of claim 13 comprising the steps of:

a) polyolefin raw material ingredients, processed into melt and extruded;

c) heating the first film to a suitable stretching temperature;

e) heat setting the second film;

ΐ) Surface treatment of the second film to adjust the surface tension of the composite layer to 38 dynes or more; g) Winding.

15. The method of claim 13 or 14, wherein the composite layer, the intermediate layer and the heat seal layer of the polyolefin film are mainly composed of an ethylene polymer, preferably the ethylene polymer is a linear polyethylene (LLDPE), Preferred is an ethylene octene copolymer, an ethylene hexene copolymer, a blend thereof or a mixture thereof,

Preferably, according to differential scanning calorimetry (DSC) test analysis, the linear polyethylene has a melting point of less than 128 degrees Celsius, preferably less than 125 degrees Celsius, and the comonomer distribution index CDBI<60% in the copolymer. Preferably, the CDBI is <50%, and the molecular weight distribution (Mw/Mn) is preferably between 3 and 8, more preferably between 3.5 and 6.

16. The method of claim 15, wherein the polyolefin film is subjected to a crosslinking treatment, and more preferably, the melt index (Ml) of the film after the treatment is 0.1 according to ASTM D-1238 (230 degrees Celsius, 10 kg). -5.0 g/10 minutes.

17. The method of claim 16, wherein the crosslinking can be either online crosslinking or offline crosslinking, for example, the first tubular film can be cross-linked online after step b), or the film can be taken offline after step g) Cross-linking.

18. The method of claim 13 or 14, wherein step f) is treated with corona.

19. The method of claim 13 or 14, wherein the heat setting can be set by a heated roll or by a third bubble after stretching, and the setting temperature is from 80 to 120 degrees.