KR20200115818A - High functional multi-layer film by simultaneous bi-axial orientation process - Google Patents

Abstract

The present invention relates to a multi-layer oriented film, and more specifically, to a high functional multi-layer coextruded and simultaneously and biaxially oriented film, which has excellent molding properties at room temperature as well as gas barrier properties and high shrinkage by installing a polyester resin layer with a special composition on a surface layer of the film, and thus exhibits excellent properties especially when used for packaging fresh meat.

Description

{High functional multi-layer film by simultaneous bi-axial orientation process}

The present invention relates to a multi-layered film composed of a thermoplastic resin, in particular, excellent heat shrinkage and gas barrier properties, so when used for direct packaging fresh growth such as beef, pork, fish and poultry, a packaging material that exhibits excellent long-term storage Its purpose is to provide. It has excellent heat adhesion, gas barrier properties, toughness, transparency or heat shrinkability, as well as printability and moldability, which are essential for fresh meat packaging, so it has excellent effects to suppress browning of meat quality and drip loss, so it has long-term refrigeration storage. It is intended to provide this excellent gas barrier heat shrinkable film.

In the case of packaged food, a method of sterilization treatment is mainly used for long-term preservation. For example, in the case of processed foods, long-term storage is mainly used by providing long-term storage through high-temperature sterilization after packaging and preventing spoilage by blocking the contents from oxygen. Since packaging materials for packaging of processed foods require dimensional stability as well as barrier properties, they are heat-treated after stretching and have excellent dimensional stability, such as biaxially oriented polyester film (BOPET), biaxially oriented polyamide film (BOPA), or biaxially oriented polypropylene film ( BOPP) or by laminating two or more films depending on the application to manufacture a packaging material. In addition, in order to further improve the gas barrier property, it is possible to further extend the storage period by laminating an aluminum-deposited film or aluminum foil layer using each biaxially stretched film as a base material to make the gas barrier property more excellent. This packaging material is the most widely used method because retort sterilization is possible by sterilizing for 10 to 40 minutes using high-temperature steam of 125°C to 150°C.

On the other hand, unlike processed foods, fresh meat such as growing meat cannot be sterilized at high temperature for a long time in the same way as a retort. Therefore, it requires a packaging function for long-term storage in refrigerated conditions without sterilization treatment. The storage period tends to be shortened due to various problems that occur during storage of growth. One is browning. Browning is a phenomenon in which the quality of meat changes to brown in the process of oxidation when proteins meet with oxygen. Also, over time, the effusion occurs. Juicy exudation is a phenomenon in which the juice inside the flesh leaks to the outside. All of these phenomena reduce the value of growth and cause a significant drop in distribution prices. Therefore, methods such as vacuum packaging or gas barrier vacuum shrinkage packaging have been used for a long time as a method to suppress this phenomenon and extend the storage and distribution period. In the case of vacuum packaging, the packaging material price is relatively inexpensive and has been widely used, but has a problem that loss is liable to occur due to deterioration if it is not distributed and consumed as fast as several days of storage period. The trend of using the gas barrier vacuum shrink packaging method as a more improved method is steadily increasing. Sufficient gas barrier properties are required to suppress browning. In addition, in order to suppress the effusion of meat juice, adhesion between the packaging film and growth is required, and the characteristics of the packaging material to impart such adhesion are shrinkage characteristics and room temperature molding characteristics. In other words, the most important properties required of packaging materials to extend the storage and shelf life of growth are excellent gas barrier properties, high shrinkage at a low temperature of around 70°C, and moldability at room temperature. In addition to these essential characteristics, additionally required characteristics require sufficient transparency in order to be able to check the quality of meat without disassembling the packaging and to facilitate quality inspection, and sufficient toughness to withstand external shocks that may occur during distribution. . In other words, it requires properties such as gas barrier properties, shrinkage, moldability and transparency and toughness. In order to impart such various characteristics, it is common to select resins having the required characteristics, coextrusion to be composed of multiple layers, and obtain them by uniaxial stretching or sequential or simultaneous biaxial stretching.

In addition, in terms of the distribution of the shrink film itself, the shrink film has characteristics that are likely to cause natural shrinkage depending on the manufacturing method. Natural shrinkage is a property that shrinks even at room temperature, and is a property caused by internal residual stress caused by stretching a polymer resin. When the natural shrinkage rate is high, the size of the film decreases during storage and distribution of the final film, so when the contents such as growth are contained, the content becomes insufficient and cannot be used. The shrinkage rate is insufficient in the shrinkage process after packaging, so the shelf life is shortened than the design value. A problem occurs. The final shrinkage rate of the film is proportional to the natural shrinkage property. For example, as the shrinkage rate of the final film increases, the natural shrinkage rate increases. Therefore, in order to suppress the natural shrinkage rate, a method of reducing the shrinkage rate through heat setting and relaxation in the film manufacturing process is applied. Therefore, it is a limiting factor to sufficiently increase the final shrinkage rate of the film. In conclusion, it is necessary to suppress the natural shrinkage rate at the same time for the storage and distribution stability of the film itself, as well as the properties of the shrink film for growing packaging for a long period of time.

For example, I would like to look at the technique of Jongrye.

According to Korean Patent Publication No. WO1999044824, the innermost layer directly in contact with food has a specified melting point and a polyolefin-based resin layer with excellent thermal adhesion properties in order to satisfy the above-described characteristics, and the outermost layer has a specified melting point range. It is based on placing a polyester-based resin layer that contains terephthalic acid in a certain amount and has a melting point of 200°C to 260°C as a gas barrier material between the inner layer and the outer layer.Ethylene vinyl alcohol copolymer (EVOH) or heat resistance Polyvinylidine chloride (PVdC) and other resins that contain additives for improving thermal stability and have a certain range of melting points of 160°C or less for the purpose of improving toughness. A multilayer coextrusion film having a resin layer selected from the Amamide (PA) system and having an adhesive resin layer when necessary to improve the adhesion of each resin layer is proposed. It is suggested that the film provided by this technology provides gas barrier properties, toughness, internal heat adhesion, and high heat adhesion temperature in the case of an outer surface having a polyester-based resin layer and provides superposition heat adhesion workability.

However, the type of polyester resins proposed in the above patents lack flexibility, so after putting food inside using the packaging bag provided therefrom, vacuum is applied to remove the air from the inside. There are limitations to completely removing air or to impart perfect adhesion between the packaging material and the contents surface, for example the packaging material and the fleshy surface of the growth. In other words, in the case of a film stretched using polyesters presented in the above patents as a raw material, the mechanical modulus is very high, so it lacks flexibility and has poor formability even when heated to near the glass transition temperature as well as room temperature. For example, when trying to package hard or irregular contents such as growth including bones, it causes a problem that the adhesion between the contents and the film is insufficient because the contents are not sufficiently molded in the shape of the contents even if a vacuum is applied. In this case, there is a disadvantage in terms of maintaining long-term storage properties due to a problem in which the effect of inhibiting the effusion of meat is inferior and bubbles remain inside, causing partial browning.

Moreover, since the glass transition temperature (Tg) measured using the differential scanning calorimeter of the polyester resin presented in the above patent has a value from 70°C to 125°C, the glass transition temperature of the other resin layers coextruded together Compared to that, since it is significantly higher, it may be limited in the method of manufacturing the film. In the case of a resin having a glass transition temperature that is much higher than room temperature, stretching at a temperature generally higher than the glass transition temperature is generally the most uniform and desirable stretching result can be obtained. For example, in the method of manufacturing a stretched film, in the method of stretching before cooling, such as the one-stage blow method, the correlation between the glass transition ion and the elongation is insignificant, so a laminate of resins with a large difference in glass transition temperature is also a relatively problem. Although a film can be obtained without a film, it cannot be said to be stretched in a practical sense because molecular orientation does not occur, and the shrinkage rate is also insignificant, making it unsuitable as a method for producing a shrink film. As a film manufacturing method that realizes shrinkage by inducing molecular orientation and retaining internal residual stress due to the effect of stretching, it is extruded and quenched into an unstretched sheet or tube, preheated and heated again, and stretched in 2nd to 3rd steps. There are a bubble blown method and a stretching method using a tenter. In the case of the stretching method that induces such practical molecular orientation, the glass transition temperature is very closely related to the stretchability. Therefore, if the difference in the glass transition temperature is large, the appropriate stretching conditions for the resins constituting each layer do not match. Even if it is impossible to impart or it is possible to manufacture a film, it becomes very difficult to obtain the desired film properties.

In the present invention, the method of manufacturing the film is not particularly limited, but it is essential to perform at least uniaxial stretching in order to impart shrinkage, and more preferably, it is more preferable to manufacture through biaxial stretching for use as a packaging material. Do. In particular, for the purpose of uniformity of physical properties in both directions and convenience of processing to the final packaging material, a method of simultaneous biaxial stretching in a blowing (or inflation) method is more preferable than a simultaneous or sequential biaxial stretching method according to the tenter method. As for the blowing method, it is not necessary to limit any method of the 1-stage bubble, 2-stage bubble, or 3-stage bubble method, but it can be said that the 3-stage bubble method is more preferable to suppress the natural contraction rate and improve the residual contraction rate. Hereinafter, the present invention will be described in detail.

As the polyolefin resin positioned in the layer A, the α-olefin co-polymerized polyethylene resin having a specific gravity in the range of 0.880 to 0.910 g/cm ³ can obtain low-temperature thermal adhesiveness to secure sealability. In particular, in the case of growing packaging, good thermal adhesion can be obtained even against moisture or contamination resulting from growth. When the specific gravity is less than 0.880, there is a problem that bubble stability is poor in the blown drawing method. Conversely, when it exceeds 0.910, not only the heat bonding temperature increases, but also the transparency tends to deteriorate, and the puncture resistance strength is lowered, which is not preferable. More preferably, it is required to have a range of 0.895 to 0.905 g/cm ³ . As an example of the α-olefin copolymerized polyethylene-based resin, one obtained by copolymerizing a monomer such as 1-hexene or 1-octene may be selected as an α-olefin, and a 1-octene copolymer is particularly preferred from the viewpoint of commercial production. In addition, in order to reduce the load of the extrusion process, it is also possible to add a slip agent, and a direct injection method or a method of mixing a master batch form and introducing it is also possible. It is also possible to mix a certain amount of an aonomer (IONOMER) or ethylene vinyl acetate (EVA).

As for the polyester resin located in the B layer, a trimethylene terephthalate repeating unit obtained from 1,3-propanediol and terephthalic acid or dimethyl terephthalate, an ester product thereof, and 1,4-butanediol and terephthalic acid, or In the manufacturing process of a film by placing a layer formed from a polyester resin having a glass transition temperature of 60°C or less and at least one type of butylene terephthalate repeating unit obtained from dimethyl terephthalate, its ester product, contains at least 60 mol%. It is possible to improve the stretch stability of the product and the room temperature moldability and shrinkage characteristics in the final product. Since the trimethylene terephthalate repeating unit or the butylene terephthalate repeating unit is derived from a relatively long diol and has excellent flexibility, has a low glass transition temperature, and is derived from an aromatic terephthalic acid, and has a higher melting point than that of olefin resins. It is easy to control the shrinkage characteristics, which is a characteristic characteristic of polyester, as well as thermal properties with a low glass transition temperature required for the manufacture of films and a melting point for overlapping sealing of the finished product, and at the same time it is easy to control the natural shrinkage rate. Confirmed. In addition, excellent optical properties such as surface printability, transparency, and gloss can be simultaneously satisfied. When the sum of the repeating unit of trimethylene terephthalate and the repeating unit of butylene terephthalate is 60 mol% or less, flexibility is deteriorated, and thus low temperature moldability and impact resistance are not sufficiently exhibited, which is not preferable. In addition, when the sum of one or more of the two repeating units is less than 60 mol%, in order to limit the glass transition temperature to less than 60°C, there is a problem that a repeating unit that is difficult to select commercially must be selected in the composition, which is not preferable. . More preferably, 70 mol% or more is preferable. In addition, the reason that the glass transition temperature of the polyester resin is required to be in the range of 60°C or less is that when the glass transition temperature is 60°C or higher, the difference in stretching conditions between the olefin resin coextruded together and the resins constituting other layers is too large. As a result, it is difficult to maintain a stable stretching process, so that the production tablet is significantly lowered, and it is difficult to obtain a uniform quality. More preferably, it is 50 degrees C or less.

It is better to lower the coefficient of friction of the surface of the B layer as the surface layer for workability in film production or post-processing. Therefore, the surface friction coefficient is controlled by adding an appropriate amount of inorganic particles such as silica, calcium carbonate, alumina, zinc oxide, etc. or organic particles insoluble in the polyester to the level B to form appropriate projections on the surface of the surface layer. It is also possible to do. In addition, depending on the use of the film, it is possible to prepare a white film capable of imparting a UV blocking effect when an appropriate amount of inorganic particles such as titanium oxide is added.

The polyester resin is described in more detail. In the method containing 1,3-propanediol or 1,4-butanediol, each diol component can be added as a raw material at the same time in the polymerization step and airborne. In addition, terephthalic acid and ethylene glycol are used as raw materials. Polyethylene terephthalate (PET) polymerized, and polybutylene terephthalate (PTT), a condensation polymer from terephthalic acid and 1,3-propane diol, and polybutyl condensation polymerized using terephthalic acid and 1,4-butanediol as raw materials Each lenterephthalate (PBT) may be dry blended at an appropriate ratio before melt extrusion or re-pelletized through compounding and used in the form of a single resin.

Others may contain naphthalic acid residues, isophthalic acid residues, ethylene glycol residues, propanol residues, neopentylglycool residues, hexanediol residues, cyclohexanediol residues, etc., within the range that does not affect the properties of the present invention. Do.

In addition, when polyester is located on the outer layer surface, it is recommended to lower the film surface friction coefficient in order to improve the winding property and post-processability of the film. Therefore, in order to lower the coefficient of friction of the film surface, it is possible to contain an appropriate amount of inorganic or organic particles having an average particle diameter of 0.5 μm to 10 μm as needed.

A method of providing another resin layer between the layer A and the layer B is also possible in order to further improve the function of the film, if necessary. For example, in order to obtain more improved barrier properties, the layer C between the A layer and the B layer is selected from vinylidine chloride (VdC) and methyl acrylate (MA) copolymer resins or ethylene vinyl alcohol copolymer (EVOH) resins. It is possible to place more than one resin layer. However, since polyvinylidene chloride resin contains a large amount of chlorine, there is a problem of discharging environmental pollutants including chlorine such as dioxin during incineration, so an ethylene vinyl alcohol copolymer resin that does not cause such problems is selected. It can be said that it is more preferable to do it. In particular, an adhesive resin layer is used to secure the adhesion between the polyester layer (B layer) and the barrier resin layer (C layer) and between the α-olefin copolymerized polyethylene resin layer (A layer) and the barrier carrier layer (C layer). Thus, it is possible to place a polyethylene-based resin in which maleic anhydride, which is generally well known, is graft-polymerized. In this case, for example, the layer structure of the film consists of a polyester layer (B)/adhesive layer/barrier resin layer (C)/adhesive layer/α-olefin co-polymerized polyethylene resin layer (A) from the surface layer. I can do it with a structure.

In addition, sufficient toughness can be secured from only the B and A layers, but in the case where toughness is required for packaging hard contents such as meat including bones, the polyamide layer is placed as the D layer. It is also possible to let. The most common polyamide 6 exhibits the best toughness, so it is possible to use it alone, but polyamide 6 resin has a very fast crystallization rate, so if it is placed in the inner layer of the coextrusion resin, film production Since it is difficult to control the degree of crystallization in the process, it may be very difficult to manufacture a stretched film, and it may become difficult to obtain the required heat shrinkage properties. Therefore, it is more preferable to mix and use a copolymerized polyamide in order to control the crystallinity of the polyamide 6 resin. Polyamide 6/66, or polyamide 6I/6T as a copolymerized polyamide resin, as well as polyamide 6/66/12 as a terpolymer, and it is possible to mix and extrude one or two or more. In particular, polyamide 6I/6T is the most effective in controlling crystallinity, but if an excessive amount is mixed, there is a problem that the toughness of the polyamide resin layer is significantly lowered and the meaning of positioning the polyamide resin layer may be lost. It is required to do. In this case, the polyamide resin layer can be positioned on one or both sides of the vinyl alcohol copolymer (layer C). For this reason, in the case of polyamide resin, when it absorbs moisture, the toughness slightly increases, but there is a problem that the barrier property of oxygen and moisture is significantly reduced, and an adhesive resin layer must be additionally placed, but a vinyl alcohol copolymer ( When placed adjacent to the layer C), the adhesive strength between the two resin layers is excellent, so there is no need to position the adhesive resin layer, as well as the effect of supporting the gas barrier property of the vinyl alcohol copolymer (layer C). This is because it has the advantage of obtaining barrier properties. In this case, for example, the overall layer composition is polyester layer (B) / adhesive layer / polyamide resin layer (D) / barrier resin layer (C) / adhesive layer / α-olefin copolymerized polyethylene resin layer (A) or polyester Layer (B) / adhesive layer / polyamide resin layer (D) / barrier resin layer (C) / polyamide resin layer (D) / adhesive layer / α-olefin co-polymerized polyethylene resin layer (A) consisting of a total of 6 layers It can be a seven-layer structure.

In addition, by placing one or two additional layers of low-density polyethylene resin (LDPE) at a level where there is no particular problem in the quality according to the use, it is possible to further improve the problem of moisture and reduce the cost of raw materials while improving the film stretch stability. It is possible. In this case, for example, the overall layer composition is polyester layer (B) / adhesive layer / polyamide resin layer (D) / barrier resin layer (C) / polyamide resin layer (D) / adhesive layer / low density polyethylene resin layer / 8-layer structure like α-olefin copolymerized polyethylene resin layer (A) or polyester layer (B) / adhesive layer / low density polyethylene resin layer / adhesive layer / polyamide resin layer (D) / barrier resin layer (C) / poly It can also have a 10-layer structure composed of an amide resin layer (D) / adhesive layer / low density polyethylene resin layer / α-olefin co-polymerized polyethylene resin layer (A).

In the method of manufacturing a film, either a tenter method or an unfavorable method can be used. In the case of the tenter method, it is advantageous in terms of obtaining thickness uniformity, but when stretching by coextruding different resins into multiple layers, due to the characteristics of each resin, coextrusion of heterogeneous resins with a large difference in the stretching conditions, especially the stretching temperature, When stretching the unstretched sheet obtained through the T-die, if the difference in the inherent thermal characteristics of each resin is too large, stretching may be very difficult, so there is a limited disadvantage in the type of resin to be coextruded. In addition, when the unfavorable method is selected, the 3-stage bubble method is more preferable than the direct unfavorable method or the two-stage bubble method to control the shrinkage. In the case of the three-stage bubble method, an unstretched tube is manufactured through the first circular die, and in the second bubble step, simultaneous biaxial stretching is performed in both directions to achieve a sufficient shrinkage rate. Then, in the third bubble, the heat setting step is performed simultaneously with relaxation. By roughing, it is possible to adjust the necessary shrinkage rate according to the application, and it is also possible to manufacture a non-shrinkable film when the shrinkage rate is completely removed. In the present invention, it is easy to control the shrinkage rate and also used a three-stage bubble method that can suppress the natural shrinkage rate.

The film manufacturing process will be described in more detail. In an embodiment of the present invention, a 3-stage bubble blowing method stretching equipment capable of controlling the shrinkage rate of the film was used. The manufacturing process of FIG. 1 will be described in more detail as follows. Using 9 extruders (1), each resin is melt-extruded and discharged in the form of a molten tube through a circular die (2) connected to the extruder, and then rapidly cooled and solidified using cooling water controlled at about 15℃, amorphous and lead-free. A new tube is manufactured and then passed through a pressing roll to form a sleeve and moved to the upper part of the stretching part (②). In the stretching section, while moving the film in a downward direction, it passes through the preheating radiator heater (5-1) at the top of the stretching section, and then is stretched by sufficiently heating it using a hotter stretching radiator heater (5-2). At this time, the draw ratio in the circumferential direction can obtain a draw ratio of the required level by the pressure inside the bubble, and at the same time, the drawing was performed in the machine direction using the difference in circumferential speed between the upper and lower compression rolls. In this way, after performing simultaneous biaxial stretching in the circumferential direction and in the machine direction at a certain ratio, move it to the top of the heat treatment unit (③) to control the shrinkage, and the pressure inside the bubble is maintained at a pressure lower than the stretching pressure, while the heat treatment radiation heater ( When passing through 5-3), heat treatment was performed at the same time as relaxation to obtain a final film, which was wound up in the winding unit (④) to obtain a film product in the form of a roll.

The properties of the raw resin or each film obtained through the examples were evaluated by the following measurement method.

(1) Glass transition temperature of the polymer (Tg): The glass transition temperature of the polyester-based resin was measured while heating at a rate of 20°C/min using DSC manufactured by TA Corporation.

(2) Contents of trimethylene terephthalate and butylene terephthalate: Based on the area of each characteristic peak obtained by using a nuclear magnetic resonance analyzer (H-NMR), the content of each component is calculated as mole% relative to terephthalic acid, and each content Got it.

(3) Natural shrinkage rate of film: After measuring the dimensional change of the film cut into squares of 10cm each in width and length when stored for 60 minutes in hot water maintained at 50°C, the natural shrinkage rate of the film is evaluated using the following equation. I did.

40℃ Natural Shrinkage Rate (%) = [(Dimensions before heat treatment-Dimensions after heat treatment)/Dimensions before heat treatment] x 100

(4) Thermal shrinkage rate of film: After immersing the film cut into squares of 10 cm each in width and length in a thermostat maintained at 70°C for 5 seconds, measure the dimensional change before and after immersion, and measure the thermal contraction rate of the film using the following equation. Evaluated.

Hot water shrinkage (%) = [(Dimension before contraction-Dimension after contraction)/Dimension before contraction] x 100

(5) Formability of film: In accordance with the ASTM D 882 measurement standard, a strain-stress curve was obtained by testing under a tensile speed condition of 200 mm/min using a universal testing machine (UTM) and a modulus value using a computer program associated with the device. Got it. Measurement samples were collected at the positions of 5 sites, the average value was calculated, and determined according to the values as follows.

Excellent moldability: Modulus less than 2000MPa

Formability Moderate: Modulus of 2000 MPa or more and 3000 MPa or less

Lack of formability: Modulus of 3000 MPa or more

(6) Toughness of the film: The puncture resistance was measured in compression mode using a universal testing machine (UTM) in accordance with the ASTM D5748-95 measurement standard. Measurement samples were collected at the positions of 5 sites, the average value was calculated, and determined according to the values as follows.

Excellent toughness: more than 200 N puncture resistance

Toughness Moderate: Modulus less than 200 N and more than 150 N

Lack of toughness: puncture resistance less than 150 N

(7) Oxygen barrier properties: The model 8003 oxygen permeability of Systech illinoise was measured according to ASTM D3985 measurement standard using a measuring instrument.

(8) Film manufacturing processability: After measuring the thickness at a dense interval of 10 mm in the width direction of the film using a micro gauge, the thickness uniformity was calculated and wavelength was calculated by the following equation.

Thickness uniformity (%) = (maximum thickness-minimum thickness)/(2x average thickness)x100

Very good fairness: less than 7% thickness uniformity

Excellent fairness: thickness uniformity of 7% or more and less than 10%

Poor fairness: thickness uniformity of 10% or more and less than 15%

Film processing impossible: thickness uniformity of more than 15% and poor productivity due to fracture

Resins used in the examples are as follows.

As the polyethylene crab resin (layer A), LF100, an alpha olefin copolymer of LG Chem, was used. LF100F had a density of 0.902g/cm ³ and a melt index (MFR) of 1.2g/10min measured at 190°C, which was the most suitable kind for inflation film.

As the polyester resin (B layer), at least one of polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT) was selected, or two types were mixed at a predetermined ratio. The polybutylene terephthalate resin was LUPOX GP1000S manufactured by LG Chem, and SORONA PTT manufactured by DuPont was used as the polytrimethylene terephthalate resin.

In addition, as the barrier resin (layer C), an ethylene vinyl alcohol copolymer (EVOH) was used as a barrier resin that does not emit environmental pollutants such as dioxins. In particular, a product with an ethylene copolymerization amount of 44 mol% with the product name SP292B of Kuraray was used.

The polyamide resin used for the purpose of further improving the toughness was C40L, a polyamide 6/66 copolymer (PA6/66 Copolyamide) manufactured by BASF, and DuPont Corporation for the purpose of controlling crystallinity. (DuPont) Selar AT3426 product was mixed with C40L in a certain amount and used.

When adhesive strength between layers was required, Mitsui's ADMER AT1995E product was used as a polyethylene grafted with male anhydrad.

The present invention provides a multi-layer co-extrusion stretched film of thermoplastic plastic capable of extending the storage and distribution period of fresh meat after the packaging process and packaging by exhibiting excellent properties, especially when used as a fresh meat packaging material.

In order to compensate for the shortcomings of the conventional technology, as a result of extensive research, it was confirmed that not only the disadvantages but also more various functions can be given by installing a polyester resin having a special composition on the surface layer as a difference from the conventional technology. And completed the present invention. In other words, a polyester having a special composition is installed on the surface layer, and a resin with excellent heat adhesion is installed on the inner layer where the contents come into contact, and a barrier layer between the surface layer and the inner layer and a barrier layer between the surface layer and the inner layer to satisfy the required characteristics such as gas barrier properties and mechanical strength Accordingly, a functional layer is installed to provide a coextrusion stretched film having a multilayer structure.

The present inventors have carefully studied to solve the conventional problems as described above. As a result, the inner thermal bonding layer (layer A) is mainly made of α-olefin co-polymerized polyethylene resin having a specific gravity in the range of 0.880 to 0.910 g/cm ³ , and the outer surface layer (layer B) is a repeating unit of trimethylene terephthalate. Or butylene terephthalate repeating units, containing at least 60 mol% or more and at the same time having a polyester resin layer having a glass transition temperature of 60°C or less, as required between the A and B layers In the case of manufacturing a gas barrier heat-shrinkable film consisting of 5, 7 or 9 layers of resin by positioning, the optimum packaging material can be provided according to the use, and excellent properties are exhibited especially when applied for growth packaging. And completed the present invention.

The present invention has excellent productivity due to its easy film manufacturing process, excellent gas barrier properties and toughness in the properties of the final film, excellent surface printability and optical properties, and particularly low natural shrinkage in terms of shrinkage properties, so the packaging material is stored. On the other hand, it is possible to provide a multilayer biaxial stretching having excellent properties when the contents are used for food packaging such as heat-sensitive growth due to the high temperature shrinkage rate of 70°C or higher.

Figure 1 Multi-layer coextrusion simultaneous biaxial stretching manufacturing process diagram
Layer structure of Fig. 2 film

[Example 1]

The heat-adhesive layer (layer A) is extruded by mixing 99% by weight of LG Chem's LF100 as the main raw material and 1.0% by weight of a master compound containing 2000 ppm of SiO2 as an anti-blocking agent in linear low-density polyethylene (LLDPE) resin. As a polyester resin, polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT) are mainly used in 79% and 20% by weight, respectively, and a polytrimethylene terephthalate master containing 2000 ppm SiO2 as an anti-blocking agent. 1% by weight of the chips were mixed, vacuum dried at 150° C. for about 3 hours using a rotary vacuum dryer, and then extruded through a separate extruder. The glass transition temperature of the resin mixed with 80% by weight of PTT and 20% by weight of PBT was 41°C, and as a result of NMR analysis, it was confirmed that the repeating unit of trimethylene terephthalate was 81 mol% and the repeating unit of butylene terephthalate was 19 mol%.

In addition, for the purpose of improving the gas barrier properties of the film, an ethylene vinyl alcohol copolymer (EVOH) having an ethylene content of 44 mol% was extruded as the C layer through another separate extruder. Polyethylene resins graft copolymerized with maleic anhydride (MAH) were extruded through separate extruders in order to impart adhesion between layers A and C and B and C. In this way, each of the resins extruded from each extruder was extruded in a laminated form through a circular die. The melted resin extruded into a tube through a circular die was quenched and solidified using cooling water controlled at about 15°C to suppress crystallization. Subsequently, in the drawing process, in the drawing section maintained at 480℃, which is a higher temperature after preheating, while passing through the preheating section maintained at 285℃ according to the radiator heater, pressurized holes are made to have a pressure of 4 Bar inside, resulting in a blow of 3.2 times. At the same time as drawing at the up-ratio (BUR), by using the difference in circumferential speed between the upper lip roll and the lower lip roll, drawing at a drawdown ratio (DDR) of 3.0 times in the machine direction, it went through a process of simultaneously stretching in the biaxial direction. Immediately after stretching, it was cooled using an air ring and then moved to a heat setting process, and the temperature of the radiator heater was set to 220°C to perform heat setting while relaxing by 12%. The total thickness of the film thus obtained was 51um, and as a result of cross-sectional cutting and layer analysis, it was found that it had a thickness distribution of A layer (11) / adhesive layer (4) / C layer (5) / adhesive layer (4) / B layer (27). Confirmed. The results of the characteristic analysis of the film are shown in Table 1.

[Example 2]

The composition of the layer B in Example 1 was polytrimethylene terephthalate (PTT) containing 49% by weight of polytrimethylene terephthalate (PTT) and 50% by weight of polybutylene terephthalate (PBT) and 2000 ppm of SiO2 as an anti-blocking agent. A film was obtained in the same manner, except that 1% by weight of the master chip was mixed. The total thickness of the film was 53um, and as a result of the layer analysis, it was confirmed that it had a thickness distribution of layer A (12)/adhesive layer (4)/layer C (5)/adhesive layer (4)/layer B (28). The glass transition temperature of the resin obtained by mixing 50% by weight of PTT and 50% by weight of PBT was 38°C, and as a result of NMR analysis, it was confirmed that the repeating unit of trimethylene terephthalate was 52 mol% and the repeating unit of butylene terephthalate was 52 mol%. The results of characteristic analysis of the obtained film are shown in Table 1.

[Example 3]

The composition of the layer B in Example 1 was polytrimethylene terephthalate (PTT) containing 29% by weight of polytrimethylene terephthalate (PTT) and 50% by weight of polybutylene terephthalate (PBT) and 2000 ppm of SiO2 as an anti-blocking agent. A film was obtained by the same method except that 1% by weight of the master chip and 20% by weight of polyethylene terephthalate (PET) were mixed. The total thickness of the film was 53um, and as a result of the layer analysis, it was confirmed that it had a thickness distribution of layer A (12)/adhesive layer (4)/layer C (5)/adhesive layer (4)/layer B (28). The glass transition temperature of the resin in which 50% by weight of PTT and 50% by weight of PBT was mixed was 51°C, and as a result of NMR analysis, the repeating unit of trimethylene terephthalate was 31 mol%, the repeating unit of butylene terephthalate was 48 mol%, and ethylene terephthalate. It was confirmed that the repeating unit was 21 mol%. The results of characteristic analysis of the obtained film are shown in Table 1.

[Example 4]

A film was obtained in the same manner as in Example 1, except that the A layer, the B layer, and the C layer were formed, and the polyamide layer (D layer) was symmetrically positioned on both sides adjacent to the C layer. At this time, the polyamide forming the D layer was crystallized in the cooling process to obtain an undrawn tube by mixing 85% by weight of polyamide 6/66 (PA6/66) copolymer and 15% by weight of polyamide 6I/6T copolymer. I tried to suppress it. The thickness of the film thus obtained is 50 μm, and as a result of layer analysis, layer A (9) / adhesive layer (5) / layer D (5) / layer C (5) / layer D (5) / adhesive layer (4) / layer B ( It was confirmed that it had a thickness distribution of 22). The results of the characteristic analysis of the film are shown in Table 1.

[Comparative Example 1]

In Example 1, the composition of the layer B was polytrimethylene terephthalate (PTT) 49% by weight, polyethylene terephthalate (PET) 50% by weight, and a polytrimethylene terephthalate (PTT) master chip containing 2000 ppm of SiO2 as an anti-blocking agent. Except for mixing 1% by weight, film formation was performed in the same manner. The film was not formed at a low temperature during the film formation process, and at a high temperature sufficient for stretching the polyester layer, the film was not spread out in a tube shape in the heat treatment process due to fusion bonding between the inner heat bonding layers, and thus heat treatment was impossible. The glass transition temperature of the resin obtained by mixing 50% by weight of PTT and 50% by weight of PET was 63°C, and as a result of NMR analysis, it was confirmed that the repeating unit of trimethylene terephthalate was 48 mol% and the repeating unit of ethylene terephthalate was 52 mol%. The results of characteristic analysis of the obtained film are shown in Table 1.

[Comparative Example 2]

In Example 1, the composition of the layer B was polytrimethylene terephthalate (PTT) 49% by weight, polybutylene terephthalate (PBT) 20% by weight, and polytrimethylene terephthalate (PTT) containing 2000 ppm of SiO2 as an anti-blocking agent. A film was obtained in the same manner, except that 1% by weight of the master chip and 30% by weight of polyethylene terephthalate (PET) were mixed. The total thickness of the film was 53um, and as a result of the layer analysis, it was confirmed that it had a thickness distribution of A layer (12)/adhesive layer (4)/C layer (5)/adhesive layer (4)/B layer 28. The glass transition temperature of the resin in which 50% by weight of PTT and 50% by weight of PBT was mixed was 62°C, and as a result of NMR analysis, the repeating unit of trimethylene terephthalate was 50 mol%, the repeating unit of butylene terephthalate was 19 mol%, and ethylene terephthalate. It was confirmed that the repeating unit was 31 mol%. The results of characteristic analysis of the obtained film are shown in Table 1.

[Comparative Example 3]

A film was obtained in the same manner as in Example 3, except that the B layer, which is the surface layer, was placed with the same alpha-olefin copolymerized polyethylene resin as the D layer instead of the polyester resin. The thickness of the film thus obtained is 55 um, and as a result of layer analysis, layer A (11) / adhesive layer (5) / layer D (5) / layer C (5) / layer D (5) / adhesive layer (4) / layer B ( It was confirmed that it had a thickness distribution of 20). The results of the characteristic analysis of the film are shown in Table 1.

nature
Shrinkage rate
(%) 70℃
Heat shrinkage
(%) Formability
(Modulus, MPa) Toughness
(My puncher strength,N) Oxygen barrier properties
(cc/m ² ·atm·day) Film manufacturing processability
(Thickness uniformity,%) Judgment Example 1 4 38 1820 327 11.3 6 ○ Example 2 5 41 1740 291 12.1 4 ○ Example 3 3 37 2070 253 11.5 5 ○ Example 4 6 35 2350 251 10.2 7 △ Comparative Example 1 - - - - - Impossible X Comparative Example 2 9 22 4380 215 11.2 13 X Comparative Example 3 8 26 1870 146 12.5 17 X

① Extruded part
② Extension part
③ Heat treatment part
④ Winding part
1. Extruder (composed of several extruders to enable co-extrusion)
2. Circular die
3-1. Unstretched film tube (1 layer bubble)
3-2 Stretched film tube (2-stage bubble)
3-3 Heat treatment film tube (3-stage bubble)
4. Raw material input port
5-1. Preheating Radiation Heater
5-2. Stretch Heating Radiation Heater
5-3. Heat Treatment Radiation Heater
6. Collapsing frame
7. Water cooling system
8. Film ladle
① External surface layer (B layer)
② Inner floor (A floor)
③ Inner layer

Claims (6)

The inner thermal bonding layer (layer A) is mainly made of α-olefin co-polymerized polyethylene resin having a specific gravity in the range of 0.880 to 0.910 g/cm ³ , and the outer surface layer (layer B) is a repeating unit of trimethylene terephthalate or butyl Based on a structure having a polyester resin layer containing at least one or more of the repeating units at least 60 mol% and at the same time having a glass transition temperature of 60°C or lower, a functional resin is placed between the A and B layers as needed. The gas barrier heat-shrinkable multilayer film manufactured by biaxial stretching. The gas barrier property of claim 1, characterized in that an ethylene vinyl alcohol copolymer (layer C) having an ethylene content of 28% to 44% is placed as a barrier resin layer between the A layer and the B layer. Multilayer film. The gas barrier heat shrinkable multilayer film according to claim 1, wherein a polyamide resin (D) is positioned between the A layer and the B layer for the purpose of reinforcing mechanical toughness. The gas barrier heat-shrinkable multilayer film according to claim 1, characterized in that it is positioned between layers A, B, C, and D made of each resin in order to improve adhesion between resin layers. According to claim 2, at least one resin selected from polyamide 6, polyamide 6/66, or PA6/66/12 terpolymer and PA6I/6T, an amorphous polyamide copolymer, are mixed in an amount of 30% by weight or less. Heat-shrinkable multilayer film made by doing this A packaging pouch or bag processed using the heat-shrinkable multilayer film of claims 1 to 5.

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