JPH025181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer film that is easy to open. More specifically, high-density polyethylene is used as the core material, a propylene/α-olefin random copolymer layer is formed on one side, and a propylene/α-olefin random copolymer layer or ethylene/α-
The present invention relates to a multilayer film formed by laminating olefin copolymer layers and having excellent low-temperature impact strength, transparency, low-temperature heat sealability, and easy opening. In general, packaging for relatively hard contents such as boxed cigarettes, confectionery, and pharmaceuticals is done using polyvinylidene chloride, high-pressure low-density polyethylene, or propylene on both sides of a base material that is mainly made of strong biaxially oriented polypropylene film or cellophane. A three-layer film made by laminating ethylene random copolymers is used as an overwrap packaging film. However, the stiff three-layer film is not suitable as a packaging material for soft contents such as bread and toilet paper, and instead,
A three-layer film in which high-pressure low density polyethylene or ethylene-vinyl acetate copolymer is laminated on both sides of an unstretched polypropylene film, or a single film of high-pressure low density polyethylene is used. Among these, the three-layer film based on unstretched polypropylene film has excellent low-temperature heat-sealability and easy-opening properties, so that the contents can be easily removed, making it suitable as an overlap packaging film. However, since the three-layer film is based on polypropylene, it has poor cold resistance, and at low temperatures, the bag easily breaks due to impact or pinholes occur. Therefore, in order to improve the low-temperature impact strength, polyethylene or ethylene/α-olefin copolymer is added and mixed to polypropylene.
A method has been proposed that uses a so-called propylene random copolymer in which propylene is copolymerized with a small amount of ethylene. However, as long as polypropylene is the main component, there is a limit to the improvement in low-temperature impact strength. On the other hand, for the purpose of improving the low-temperature impact strength, a film has been proposed in which an ethylene/vinyl acetate copolymer is laminated on both sides of a base material made of a composition of high-density polyethylene and high-pressure low-density polyethylene, or high-pressure low-density polyethylene. However, on the contrary, it had the disadvantage that it was too soft and the film was not easy to cut with a bag making machine, and the heat sealing strength was strong and there was a risk of damaging the contents when taking it out. Therefore, the present inventors used high-density polyethylene as a core material, had a propylene/α-olefin random copolymer layer on one side, and a propylene/α-olefin random copolymer layer or ethylene/α-olefin random copolymer layer on the other side.
-By laminating olefin copolymer layers,
It was found that a multilayer film having appropriate stiffness, excellent low-temperature impact strength, transparency, low-temperature heat-sealability, and easy-to-open properties could be obtained, and the present invention was achieved. That is, the present invention has a melt flow rate (ASTM D1238:E) of 0.3 to 15.0g/10min,
The core material is high-density polyethylene (A) with a density ranging from 0.950 to 0.970 g/ ^cm3 , and one side has a melt flow rate (ASTM D1238: L) of 0.1 to 40 g/cm3.
10 min, propylene content 43 to % by weight, heat of crystal fusion 10 to 80 Joule/g based on thermal analysis with differential scanning calorimeter, and carbon number 4.
Random copolymer with 1 to 10 α-olefins
(B) layer on the other side of the propylene/α-olefin random copolymer (B) layer or melt flow rate (ASTM D1238:E) 0.5 to 20 g/
10min, density 0.910 to 0.940g/ ^cm3 and melting point
The present invention provides a multilayer film characterized by laminating layers of a copolymer (C) of ethylene and α-olefin having 4 to 20 carbon atoms at a temperature in the range of 115 to 130°C. High-density polyethylene as the core material used in the present invention
(A) means melt flow rate (ASTM D1238:
E) is 0.3 to 15.0g/10min, preferably 0.5
or 7.0g/10min, density 0.950 or 0.970
g/cm ³ , preferably in the range of 0.950 to 0.965 g/cm ³ and a homopolymer of ethylene or ethylene and up to 2 mol % of other α-olefins, such as propylene, 1-butyne, 1-pentene, 1 - It is a copolymer with hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc. If the melt flow rate is less than 0.3 g/10 min, the melt viscosity is high and molding is difficult, and the surface of the base material becomes rough, making it difficult to laminate the propylene/α-olefin random copolymer (B) layer described below. However, a multilayer film with good appearance cannot be obtained. On the other hand, those with a melt flow rate exceeding 15.0 g/10 min have low melt viscosity and poor moldability. If the density is less than 0.950 g/cm ³ , the rigidity is low, and when made into a multilayer film, the stiffness is weak, and the suitability for packaging machines is poor. The propylene/α-olefin random copolymer (B) laminated on at least one side of the core material made of high-density polyethylene (A) has a melt flow rate (ASTM D1238: L) of 0.1 to 40 g/10 min,
Preferably 1 to 20g/10min, propylene content 43 to 80% by weight, preferably 53 to 75%.
Weight %, heat of crystal fusion based on thermal analysis with differential scanning calorimeter is 10 to 80 Joule/g, preferably 20
A random copolymer of propylene and an α-olefin having 4 to 10 carbon atoms in a range of 70 to 70 Joule/g, preferably a random copolymer of propylene and 1-butene. Melt flow rate is 0.1
If it is less than 40 g/10 min, the melt viscosity is high and the moldability is poor, and if it exceeds 40 g/10 min, the melt viscosity is low and the moldability is poor. If the propylene content is less than 43% by weight, the melting point of the copolymer will be low, the heat resistance of the film will be poor, and blocking will occur easily.
If the film exceeds this value, it will have poor transparency and flexibility as a film, and will have a high melting point and poor low-temperature heat sealability. The heat of crystal fusion is a value that correlates with the degree of crystallinity of the polymer, but propylene/α-olefin random copolymers with a heat of fusion exceeding 80 Joule/g have a small amount of α-olefin, which is a copolymerization component. Or, since it is a block copolymerization of α-olefin, it has poor transparency and flexibility. On the other hand, propylene/α-olefin random copolymers with a heat of fusion of 10 Joule/g or less have poor mechanical properties and heat resistance, and have a sticky feel. The heat of fusion of the polymer in the present invention is measured by measuring the specific heat curve of the copolymer in a completely molten state (preferably the specific heat curve shown at 160°C or higher and 240°C or lower) using a differential scanning calorimeter directly to the low temperature side. This is a value calculated using the straight line obtained by interpolation as the baseline. The heat of fusion is measured under the following measurement conditions. In other words, after leaving the sample at 200℃ for 5 minutes,
Cool to -40°C at a rate of min and leave at -40°C for 5 minutes. Then -40℃ at a heating rate of 20℃/min.
Measurement is carried out from 200℃ to 200℃. Propylene content with the above properties
43 to 80% by weight of the propylene/α-olefin random copolymer is, for example, (a) a composite containing at least magnesium, titanium, and a halogen, (b) an organometallic metal of Group 1 to Group 3 of the periodic table. It is obtained by random copolymerization of propylene and α-olefin using a catalyst formed from a compound and (c) an electron donor. Part or all of the electron donor (c) may be immobilized in part or all of the complex (a), or may be pre-contacted with the organometallic compound (b) prior to use. Good too. Particularly preferred is an embodiment in which a part of the electron donor (c) is immobilized on the complex (a), and the remainder is added to the polymerization system as it is or is used after being brought into preliminary contact with the organometallic compound (b). be. In this case, the electron donor immobilized on the complex (a) and the electron donor used by directly adding it to the polymerization system or by pre-contacting it with (b) may be the same or different. It's okay. In addition, the propylene/α-olefin random copolymer (B) may include, within the range that does not impair the purpose of the present invention, a melt polypropylene that falls within the category of polypropylene commercially available as a so-called ordinary propylene random copolymer. Flow rate is 0.1 to 40g/
For 10 min, polypropylene with a propylene content in the range of 93 to 99 mol% and homogeneous polypropylene may be added. The propylene/α-olefin random copolymer (B) layer must be laminated on at least one side of the high-density polyethylene (A) that is the core material of the multilayer film of the present invention, and the other side is made of propylene. - An ethylene/α-olefin copolymer (C) layer may be laminated in place of the α-olefin random copolymer (B) layer. The ethylene/α-olefin copolymer (C) used in the present invention has a melt flow rate (ASTM
D1238:E) is 0.5 to 20g/10min, preferably 1.0 to 10g/10min, density is 0.910 to
0.940g/cm ³ , preferably 0.915 to 0.935g/cm ³
and ethylene having a melting point in the range of 115 to 130°C, preferably 115 to 125°C, and a carbon number of 4 to 20,
Preferably, it is a copolymer with 5 to 18 α-olefins. Melt flow rate is 0.5g/
If it is less than 10 min, the melt viscosity is high and the moldability is poor, and if it exceeds 20 g/10 min, the melt viscosity is low and the moldability is poor. If the density is less than 0.910g/10min, when made into a film, the surface will be sticky and the oil resistance will be poor, while if it exceeds 0.940g/ ^cm3 , the transparency
Poor low temperature heat sealability. The melting point is the highest temperature at a point showing a sharp endothermic peak determined from an endothermic curve measured by a differential scanning calorimeter at a heating rate of 10° C./min. The ethylene/α-olefin copolymer (C) has one or more sharp endothermic peaks, often two or three, and the maximum temperature of the sharp endothermic peak, that is, the melting point, is between 115 and 115.
It is in the range of 130℃. Those with a melting point of less than 115°C have poor heat resistance, and those with a melting point of over 130°C have poor low-temperature heat sealability. Also, α- with 4 to 20 carbon atoms
Specifically, olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-pentene,
1-octene, 1-decene, 1-hexadecene,
1-octadecene or a mixture thereof, and α-olefin having 5 to 18 carbon atoms is particularly preferred. Copolymers with propylene have poor mechanical strength. The ethylene/α-olefin copolymer (C) having the above properties used in the present invention is obtained by polymerizing ethylene and α-olefin in a ratio to obtain the required density by a so-called medium/low pressure method using a transition metal catalyst. It can be obtained by letting In this case, a molecular weight regulator such as hydrogen may be used to obtain the desired melt flow rate. Polymerization can be carried out by various methods such as slurry polymerization, gas phase polymerization, and high temperature solution polymerization. The ethylene/α-olefin copolymer (C) used in the present invention may include a low-crystalline ethylene/propylene random copolymer, an ethylene/1-butene random copolymer, within a range that does not impair the purpose of the present invention. etc. may be blended. Although the thickness of each layer of the multilayer film of the present invention is not particularly limited, the thickness of the propylene/α-olefin random copolymer (B) layer or the ethylene/α-olefin copolymer layer, which is the coating layer, is usually 1 to 20 μm. , preferably 1 to 10μ, particularly preferably 1 to 5μ. If the thickness exceeds 20 μm, low temperature heat sealing properties and easy opening properties tend to be poor. On the other hand, the high-density polyethylene (A) layer that serves as the core material is not particularly limited, but it is usually
The thickness is 100μ, preferably in the range 5 to 50μ. As a method for obtaining the multilayer film of the present invention, that is, the multilayer film consisting of (B)/(A)/(B) or (C)/(A)/(B), the method for obtaining the multilayer film consisting of (B)/(A)/(B) is as follows: A propylene/α-olefin random copolymer (B) layer on both sides, or a propylene/α-olefin random copolymer (B) layer on one side, and an ethylene/α-olefin copolymer (C) layer on the other side. There is a method of extrusion lamination using a die with a three-layer structure, and a method of coextrusion molding using a die with a three-layer structure. C) It is preferable to use a coextrusion molding method because the layer can be made thinner. Coextrusion molding methods include a T-die method using a flat die and an inflation method using a circular die. The flat die may be either a single manifold type using black boxes or a multi-manifold type. Any known die can be used for the die used in the inflation method. The multilayer film of the present invention is made of high-density polyethylene (A)
By laminating a propylene/α-olefin random copolymer (B) layer on at least one side of the layer,
A multilayer film suitable for overwrap packaging, which has appropriate stiffness, is transparent, has low-temperature heat-sealability, and is easy to open, can be obtained. In addition, by making one side of the high-density polyethylene (A) layer an ethylene/α-olefin copolymer (C) layer, it has the above-mentioned performance.
When the layers are heat-sealed, a multilayer film with strong heat-sealing strength is created.
It is also suitable as a material for bags such as those shown in No. 55-217. However, both sides of the high-density polyethylene (A) layer are covered with something other than the propylene/α-olefin random copolymer (B) layer, such as an ethylene/α-olefin copolymer (C) layer or an ethylene/vinyl acetate copolymer layer. Otherwise, a multilayer film with strong heat sealing strength and easy opening cannot be obtained. The multilayer film of the present invention includes high-density polyethylene.
(A) layer, propylene/α-olefin random copolymer (B) layer, and ethylene/α-olefin copolymer (C) layer. Various compounding agents such as antifogging agents, anti-fogging agents, anti-blocking agents, slip agents, lubricants, pigments, dyes, droplet agents, nucleating agents, etc., which are usually added to polyolefins, may not be used without impairing the purpose of the present invention. It may be added within a certain range. The multilayer film of the present invention has moderate stiffness, excellent low-temperature impact strength, transparency, and low-temperature heat sealability,
Moreover, since it is easy to open, it can be used in a wide range of fields, such as square bag packaging and overlap packaging. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way unless the gist of the invention is exceeded. Example 1 As core material, melt flow rate 1.0g/
High-density polyethylene (hereinafter referred to as HDPE-I) with a density of 10 min and a density of 0.953 g/cm ³ , a melt flow rate of 7.0 g/10 min as a coating layer, a propylene content of 70% by weight, a heat of crystal fusion of 50 Joule/g, and a melting point.
Using propylene/1-butene random copolymer (hereinafter abbreviated as PBR-I) at 110℃, HDPE-I
), HDPE-I was put into a 65mmφ extruder (cylinder temperature 240℃), and PBR-I was put into two 40mmφ extruders (cylinder temperature: 240°C).
PBR-
A three-layer film consisting of I/HDPE-I/PBR-I=3μ/14μ/3μ was obtained. Next, performance was evaluated using the following method. Haze (%): ASTM D1003 Tensile test: According to ASTM D638, yield point stress (hereinafter abbreviated as YS) and break point tensile strength (hereinafter referred to as YS)
TB) was measured in the longitudinal direction (hereinafter referred to as MD) and the transverse direction (hereinafter referred to as TD). Bending rigidity (Kg/cm ² ): Prepare a 140mm x 140mm sample and measure it with a Handle-o-Meter (Thwing
A bending stress was applied to the sample using a slit width of 5 mm, and the maximum stress was determined and the value divided by the thickness of the sample was defined as the bending rigidity (Kg/cm ² ). The bending stiffness of the sample is
Two points, MD and TD, were determined. Impact strength (Kg/cm/cm): ASTM D3420 Peel strength of heat-sealed part (g/15mm): Overlapping film surfaces, 90℃, 100℃, 110℃,
After heat-sealing with a sealing bar having a width of 5 mm at temperatures of 120°C, 130°C, and 140°C and a pressure of 2 kg/cm ² for 1 second, the pieces were allowed to cool. Cut a 15 mm wide test piece from this and set the crosshead speed.
The strength is shown as the strength when the heat-sealed part is peeled off at 200 mm/min. The results are shown in Table 1. Example 2 One layer of PBR-I used in Example ¹ was mixed with ethylene/4-methyl-1-pentene copolymer (hereinafter referred to as EMC- Example 1 was carried out in the same manner as in Example 1, except that 1) was used. The results are shown in Table 1. The peel strength of the heat-sealed portion is a value measured by heat-sealing the PBR-I layers together. Comparative Example 1 Instead of HDPE-I used in Example 2, polypropylene with a melt flow rate of 7 g/10 min (Product name: Mitsui Petrochemical Polypro F631, manufactured by Mitsui Petrochemical Industries KK; hereinafter abbreviated as PP-I) was used. Table 1 shows the results obtained in the same manner as in Example 2. Comparative Example 2 PP-I used in Comparative Example 1 was substituted for HDPE-I used in Example 1, and PBR-I used in Example 1 was replaced with PBR-I used in Example 1.
Instead of I, use ethylene/vinyl acetate copolymer (product name: EVAFLEX P1405, Mitsui Polychemical Co., Ltd.)
The same procedure as in Example 1 was conducted except that EVA-I (manufactured by KK, hereinafter abbreviated as EVA-I) was used. The results are shown in Table 1. Comparative Example 3 Instead of HDPE-I used in Example 2, PP-I used in Comparative Example 2 and a melt flow rate of 4 g/
10min (ASTM D1238:E), ethylene content 91
Example except that a composition (PP-I/EBR-I = 70/30 weight ratio) consisting of an ethylene/1-butene random copolymer (hereinafter abbreviated as EBR-I) with mol% and a melting point of 73°C was used. I did the same as 1. The results are shown in Table 1. Comparative Example 4 EVA-I used in Comparative Example 2 was used instead of PBR-I used in Example 1, HDPE-I used in Example 1 was used as the core material, and the melt flow rate was 4.8.
A composition (HDPE-I/LDPE=70/30 weight ratio) consisting of high-pressure low-density polyethylene (trade name Mirason ^24H , manufactured by Mitsui Polychemicals KK; hereinafter abbreviated as LDPE) with g/10 min and density 0.921 g/cm 3 ) was carried out in the same manner as in Example 1 except for using. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. Melt flow rate (ASTM D1238:E)
0.3 to 15.0g/10min, density 0.950 to 0.970
g/ ^cm3 high-density polyethylene (A) as the core material, one side has a melt flow rate (ASTM D1238:
L) 0.1 to 40g/10min, propylene content
A random copolymer (B) layer of propylene and α-olefin having 4 to 10 carbon atoms with a heat of crystal fusion of 10 to 80 Joule/g based on thermal analysis using a differential scanning calorimeter. On the other side, the propylene/α-olefin random copolymer (B) layer or melt flow rate (ASTM D1238: E) 0.5 to 20 g/10 min,
A multilayer film comprising laminated layers of a copolymer (C) of ethylene and α-olefin having 4 to 20 carbon atoms and having a density of 0.910 to 0.940 g/cm ³ and a melting point of 115 to 130°C.