JPH0361574B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention produces a film with a thickness of 30 μm that has a well-balanced tear strength and suppresses orientation, which is obtained by processing a copolymer of ethylene and α-olefin into a film.
The present invention relates to a method for producing the following novel ultra-high impact resistant film. To be more specific, the density is 0.895 to 0.935
g/ ^cm3 and melt index is 0.5g/10
Ethylene of 3 or less and α- with carbon number of 3 to 18
A film obtained by processing a copolymer with olefin (hereinafter referred to as ethylene-α-olefin copolymer resin) has an orientation function fβ of the b-axis of the crystal lattice based on the machine direction during film processing of -0.1 or more The present invention relates to a method for producing an ultra-high impact resistant film having a thickness of 30 μm or less, which has a c-axis orientation function fε of 0.1 or less, has a suppressed orientation, and has a well-balanced tear strength. Ethylene-α-olefin copolymer resins are industrially produced by various processes using so-called Ziegler type catalysts and Phillips type catalysts. One of these is the linear low-density polyethylene commercially available these days. Ethylene-α-olefin copolymer resins generally have very good mechanical properties such as tensile properties and impact resistance when used in heated press sheets, but they require high torque during processing and have low strength when melted. (hereinafter abbreviated as melt tension) is small, resulting in poor processing stability. Regarding the ethylene-α-olefin copolymer resin, the effects of melt index, density, etc. on the impact resistance and processability of the press sheet are as follows. The smaller the melt index and density, the better the impact resistance. On the other hand, the smaller the melt index, the higher the torque during processing and the higher the melt tension, which means that the motor consumes more power during processing, but on the other hand, processing stability is improved. Therefore, in order to reduce the torque of products with a small melt index, methods such as blending resins with different melt indexes or polymerizing using special catalysts to widen the molecular weight distribution are generally taken. There is. Furthermore, the impact resistance of a molded article of ethylene-α-olefin copolymer resin varies greatly depending on the thickness of the molded article and the molding method. That is, in thick molded products such as sheets, pipes, molds, etc., the MD/TD balance of mechanical properties is good and good impact resistance inherent to the resin can be obtained. However, in thin molded products such as T-die films and inflation films, due to the unique molecular orientation during the molding process, the mechanical properties of MD/
The TD balance is poor, and the good impact resistance inherent to the resin cannot be obtained. This tendency is remarkable in thin films of 30 μm or less. Here, MD represents the machine direction during molding, and TD represents the direction perpendicular to it. The MD/TD balance of mechanical properties is
The smaller the melt index and the higher the density of the ethylene-α-olefin resin, the worse it becomes, and as a result, the original good impact resistance cannot be obtained. To solve these problems, high-density polyethylene with a small melt index (hereinafter abbreviated as high-molecular-weight high-density polyethylene) has been developed up to now.
Various film processing methods have been proposed for this purpose, and it is known that good impact resistance inherent to resins can be obtained in thin films. One example of the manufacturing technology for this high molecular weight high density polyethylene film is known as the ultra-thin reinforced film forming method.
Explanations have been made in various literature. (For example, Kinoshita, “Plastics”, Vol. 29, No. 12, p. 70~
78, 1978) This ultra-thin reinforced film has recently been widely used in standard packaging, garbage bags, plastic shopping bags, etc. The present inventors have conducted extensive studies on the impact resistance of such ethylene-α-olefin copolymer resin films, and have found that they have a density of 0.895 to 0.935 g/cm ³ and a melt index of 0.5 g/10 minutes or less. MD obtained by processing an ethylene-α-olefin copolymer into a film using the method described below.
The orientation function fβ of the crystal lattice b axis based on the direction is −
We have discovered the surprising fact that a film with a thickness of 30 μm or less with suppressed orientation and a c-axis orientation function fε of 0.1 or more and 0.1 or less exhibits a well-balanced tear strength and ultra-high impact resistance, leading to the present invention. It is ivy. That is, the present invention uses ethylene having a density of 0.895 g/cm ³ or more and 0.935 g/cm ³ or less and a melt index of 0.5 g/10 min or less and a carbon number of 3 or more.
A copolymer with an α-olefin of 18 or less is extruded from a die by melt extrusion to obtain a tubular melt, and the tubular melt is transferred to the mandrel using a conical internal mandrel concentric with the die. By making the constriction smaller than the diameter of the die in a shape that corresponds to the diameter of the die, then expanding it to a blow-up ratio of 3 or more to form a bubble, and cooling with air so that the solidification position is at least 5 times the diameter of the die from the die exit. The present invention relates to a method for producing an ultra-high impact resistant film, which is characterized by obtaining a film having an orientation function fβ of -0.1 or more, an orientation function fε of 0.1 or less, and a thickness of 30μ or less. Here, the orientation function of each lattice axis is according to Stein et al.
It is obtained from the polarized infrared absorption spectrum using the following formula with MD as a reference. (RERead.R.Stein.
Macromolecules.1.116 (1968)) fα=(D730-1)/(D730+2) =(3cos ² α-1)/2 (1) fβ=(D720-1)/(D720+2) =(3cos ² β-1)/2 (2) fε=−(fα+fβ) (3) D730=A(730cm ^-1 )/A⊥(730cm ^-1 ) (4) D720=A(720cm ^-1 )/A⊥( 720cm ^-1 ) (5) The meaning of each symbol is as follows. fα, fβ, and fε are orientation functions of the a-axis, b-axis, and c-axis of the crystal lattice, respectively. D730 and D720 are wave numbers respectively
Infrared dichroic ratio at 730 cm ^-1 and 720 cm ^-1 ,
Expression (4) as the ratio of absorbance A and A⊥ of each polarized infrared spectrum of MD and TD at the indicated wave number
and (5). Further, α and β are angles formed by the a-axis and the b-axis, respectively, and MD. In the most advanced state of orientation in the inflation film, the crystal lattice c
The axis and MD match, α=β=90°, and fα=−0.5,
fβ=−0.5, fε=1. In actual inflation film, fα, fβ＞−0.5, fε＜
1, and these values express the state in which the orientation of the blown film is suppressed. (As an example of calculating the orientation of an inflation film using a model, see Matsumura and Nagasawa, “Collection of Polymer Papers”, Vol. 33, 4).
No., p171 (1976). ) The ethylene-α-olefin copolymer used in the present invention is a copolymer of ethylene and α-olefin having 3 to 18 carbon atoms, and the α-olefin as a copolymerization component has the general formula R-CH
= _CH2 (In the formula, R represents an alkyl group having 1 to 16 carbon atoms.) Specific examples thereof include propylene, butene-1, pentene-1, hexene-1, heptene-1, and octene. -1, nonene-1, decene-1, 4-methyl-pentene-1,
4-Methyl-hexene-1,4,4-dimethyl-
Examples include pentene-1. Such ethylene-
The α-olefin copolymer is obtained by copolymerizing ethylene and α-olefin using a transition metal catalyst. The density is controlled by the type and amount of copolymerization of the α-olefin, and the melt index is controlled by the type and amount of the chain transfer agent. There are no particular restrictions on the catalyst or polymerization method, and examples of the catalyst include so-called Ziegler type catalysts and Phillips type catalysts, and examples of the polymerization method include so-called slurry polymerization, solution polymerization, gas phase polymerization, and the like. As the ethylene-α-olefin copolymer,
Those with a density of 0.895 to 0.935 g/cm ³ and a melt index of 0.5 g/10 minutes or less are used, particularly those with a density of 0.910 to 0.920 g/cm ³ and a melt index of 0.3 g/10 minutes or less. Preferably.
If the density is less than 0.895 g/cm ³ , film blocking is large and therefore cannot be used practically. If the weight exceeds 0.935 g/cm ³ , the film will not have sufficient impact resistance and cannot be used. If the melt index exceeds 0.5 g/10 minutes, the film will not have sufficient impact resistance, and the bubble stability will not be sufficient in the air-cooled inflation film processing described below, so it cannot be used. This ethylene-α-olefin copolymer is processed using the film processing method according to the present invention, and the orientation function fβ of the crystal lattice b axis with respect to the MD direction is -
If the orientation function fε of the c-axis is controlled to be 0.1 or more and 0.1 or less, the tear strength is well balanced with orientation suppressed.
A thin film with ultra-high impact resistance of 30μ or less can be obtained. A thin film of 30 μm or less in which the b-axis orientation function fβ is less than −0.1 or the c-axis orientation function fε exceeds 0.1 cannot have the original ultra-high impact resistance.
Also, the b-axis orientation function fβ of a thin film of 30μ or less
Even if the c-axis orientation function fε is -0.1 or more and the c-axis orientation function fε is 0.1 or less, if the melt index of the raw material ethylene-α-olefin copolymer resin exceeds 0.5 g/10 minutes, it is inherently impact resistant. is low, making it impossible to obtain ultra-high impact resistant thin films. A typical air-cooled inflation film forming process involves extruding a molten material through a tubular slit (hereinafter referred to as die), blowing a certain volume of air into the interior to expand it, and then cooling it with air from the outside using a blower. However, the material is wound on a take-up winder at a constant take-up speed. The film processing method according to the present invention will now be described. When processing air-cooled inflation films, a conical internal mandrel that is concentric with the die is used, and the diameter of the tubular melt extruded from the die is aligned with the mandrel so that it is constricted to be smaller than the diameter of the die. In this method, the material is expanded to a blow-up ratio of 3 or more to form bubbles, and air-cooled to form a solidified portion at a position at least 5 times the diameter of the die from the die exit. The gist of the air-cooled inflation film processing method will be explained below with reference to the drawings. Figures 1-1 and 1-2 are 19μ or less according to the present invention and
FIG. 2 is a conceptual diagram showing a constricted bubble shape and the shape of a conical internal mandrel 4 used in air-cooled inflation film processing of a thin film of 20 to 30 μm. (Hereinafter, these processing methods will be abbreviated as processing method 1 and processing method 2, respectively.) FIG. 2 is a conceptual diagram showing the shape of a bubble in normal air-cooled inflation film processing. (Hereinafter, this processing method will be abbreviated as Processing Method 3.) The important point in processing the orientation-suppressed ultra-high impact resistant inflation film of the present invention with a thickness of 30 μm or less is that the film is extruded from the die 1. The diameter of the tubular melt is constricted to be smaller than the diameter of the die 1, and then expanded to a blow-up ratio of 3 or more to form a bubble, and the solidification position 3 is located at a position 5 times or more the diameter of the die from the die exit. Similarly, air cooling is performed using air ring 2. The conical internal mandrel 4 was used to maintain the stability of the bubble, but the ethylene-α-olefin copolymer resin with a melt index exceeding 0.5 g/10 minutes is Even if the bubble is used, the stability of the bubble cannot be maintained. In the normal air-cooled inflation processing method of processing method 3, in order to maintain bubble stability, the blow-up ratio should be less than 3, and the solidification position 3 should be 2 to 5 times the die diameter from the die exit. It is necessary to perform air cooling with the air ring 2, and in that case, the bubble shape as in processing method 1 or 2 cannot be obtained. In addition, in air-cooled inflation film processing by processing method 1 of low-density ethylene-α-olefin copolymer resin with a density of 0.920 g/cm ³ or less, the conical internal mandrel 4 of the cylindrical melt exits the die. Adhesion may occur irregularly and may impair the stability of the bubble. In this case,
As shown in Figure 3, by using a special conical internal mandrel 5 in combination with a minute air circulation system 6, it is possible to stabilize the constricted bubble and at the same time circulate air at a minute flow rate and minute pressure. Therefore, it is necessary to prevent the film from sticking to the internal mandrel. (Hereinafter, this processing method will be abbreviated as Processing Method 4.) The ultra-high impact resistant film obtained by the present invention is suitable for use as a thin film that requires impact resistance, such as agricultural polyethylene film, garbage bags, and standards. It is suitable for use in bags, etc., and can be made thinner than conventional films in order to exhibit the same performance, making it extremely valuable in terms of resource conservation. Next, definitions of physical property values used in the present invention are shown below. (1) Melt index According to the method specified in JIS K6760-1981. The measurement temperature is 190℃. (2)Density According to the method specified in JIS K6760-1981. (3) Tensile impact strength According to the method specified in ASTM D1822-61. (4) Orientation function using polarized infrared absorption spectroscopy
According to the method of R. Stein et al. (Macromoleules.1,
116 (1968)) (5) Tear strength Elmendorf tear strength, based on the method specified in JIS Z-1702. The larger the size, the better the tearability. (6) Tear strength balance MD value of tear strength
Expressed as a ratio to the TD value. The closer it is to 1, the better the balance is. (7) Falling weight impact strength Dirt impact
According to the method specified in ASTM D1709. Next, the present invention will be specifically explained using examples, but the present invention is not limited to the examples unless it departs from the gist. In the following examples, the following air-cooled inflation film processing conditions are used as common conditions. (1) Equipment: IFA−600− manufactured by Tomy Machine Industry Co., Ltd.
50 (2) Die: 75φ, gap 2.5mm, manispill die (3) Processing temperature: 200℃ (4) Extrusion rate: 15Kg/Hr (5) Cooling: Single stage air cooling Other conditions, (6) Blow-up ratio, (7) ) Solidification position and (8) film thickness will be described in individual examples. Examples 1 to 2, Comparative Example 1 Using various ethylene-butene-1 copolymers (raw material resins 1 to 3) as shown in Table 1 as ethylene-α-olefin copolymer resins, processing method 2 was carried out. air-cooled inflation film processing using
We evaluated the stability of the bubble. The processing method, blow-up ratio, solidification position, and film thickness processing conditions for each Example and Comparative Example are as shown in Table 1. As shown in Table 1, the melt index
Ethylene-butene-1 copolymer (raw material resins 1-2) at a rate of 0.5 g/10 minutes or less has good bubble stability (Examples 1-2), but the melt index is low.
Ethylene-butene-1 copolymer (raw material resin 3) exceeding 0.5 g/10 minutes does not have sufficient bubble stability. (Comparative Example 1) Examples 3 to 5, Comparative Examples 2 to 4 The ethylene-α-olefin copolymer resin had a melt index of 0.30 g/10 min and a density of
0.917 g/cm ³ of ethylene-butene-1 copolymer (raw material resin 4) was processed by the air-cooled inflation film processing method shown in the present invention (processing methods 1, 2, or 4) and by ordinary air-cooled inflation film processing. 10, 20 and 30μ, respectively, using the method (processing method 3).
A film was prepared and the physical properties of the film were compared. The processing method, blow-up ratio, solidification position, and film thickness processing conditions for each example and comparative example are as follows.
As shown in the table. Regarding the blow-up ratio, in the ordinary air-cooled inflation film processing method (Comparative Examples 2 to 4), a small condition of 2.3 was used in consideration of bubble stability. No matter which processing method is used, the smaller the film thickness, the more the crystal lattice c-axis is oriented, and the tear strength balance of the film becomes worse. The falling weight impact strength of films formed using the normal air-cooled inflation film processing method decreases significantly as the film thickness decreases (Comparative Examples 2 to 4), whereas the air-cooled inflation film shown in the present invention On the contrary, the film formed using the film processing method has a significant improvement. (Examples 3 to 5) Films of the present invention (Examples 3 to 5) in which the crystal lattice b-axis orientation function fβ is -0.1 or more and the c-axis orientation function is 0.1 or less meet the conditions for both orientation functions. It can be seen that the films having the same thickness as the unsatisfied ordinary air-cooled inflation films (Comparative Examples 2 to 4) have a significantly better tear strength balance and excellent falling weight impact strength. Example 6, Comparative Example 5 Ethylene-butene-1 copolymers (raw material resins 5 to 6) shown in Table 3 were used as the ethylene-α-olefin copolymer resin, and the material resin 5 was air-cooled as shown in the present invention. Using the inflation film processing method (processing method 2) and the ordinary air-cooled inflation film processing method (processing method 3) for raw resin 6, 30μ films were formed for both and the physical properties of the films were compared. . Processing method of each example and comparative example,
The processing conditions of blow-up ratio, solidification position and film thickness are as shown in Table 3. In the ordinary air-cooled inflation film processing (Comparative Example 5), the blow-up ratio was set to a low value of 2.3 in consideration of bubble stability. In Comparative Example 5, the orientation function fβ of the b-axis of the crystal lattice of the film is -
Although the conditions of 0.1 or more and c-axis orientation function of 0.1 or less are satisfied, the melt index is 0.5.
g/10 minutes, the tensile impact strength of the sheet is low, and the falling weight impact strength of the film is also low.
In Example 6, the film satisfies the above orientation function conditions and has a melt index of 0.5 g/
It takes less than 10 minutes, and the tensile impact strength of the sheet is high, and the falling weight impact strength of the film is also extremely high. The latter also has a better balance of tear strength. Examples 7 to 9, Comparative Examples 6 to 8 The ethylene-α-olefin copolymer resin had a melt index of 0.15 g/10 minutes and a density of
0.918 g/cm ³ of ethylene-butene-1 copolymer (raw material resin 7) and commercial product A were processed into an air-cooled inflation film processing method according to the present invention (processing methods 1 and 2).
Alternatively, 10, 20, and 30μ films were formed using 4) and the physical properties of the films were compared. The processing method, blow-up ratio, solidification position, and film thickness processing conditions for each example and comparative example are shown in Table 4. Raw material resin 7 of the present invention, 10, 20 and
The 30μ films (Examples 7, 8, and 9, respectively) had a blow-up ratio of 4.0 under air-cooled inflation film processing conditions, and the 10, 20, and 30μ films (Comparative Examples 6, 7, and 8, respectively) had a blow-up ratio of 5.0.
Although the processing is disadvantageous in terms of suppressing orientation compared to
The tear strength is well balanced and the falling weight impact strength is also significantly superior.

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【table】 [Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the constricted bubble shape and the shape of the conical internal mandrel used in air-cooled inflation film processing of a film of 19 μm or less according to the present invention. (Processing method 1) 1st
FIG. 2 is a conceptual diagram showing the constricted bubble shape and the shape of the conical inner mandrel used in the air-cooled inflation film processing of a 20 to 30 μm film according to the present invention. (Processing method 2) FIG. 2 is a conceptual diagram showing the shape of a bubble in normal air-cooled inflation film processing. (Processing method 3)
Figure 3 shows an air-cooled inflation film process used to prevent the cylindrical melt from sticking to the conical inner mandrel in the air-cooled inflation process of low-density films with a density of 0.925 g/cm ³ or less according to the present invention. It is a conceptual diagram of the system. Next, the symbols will be explained. 1: Die, 2: Air ring, 3: Assimilation position,
4: Conical internal mandrel, 5: Special conical internal mandrel, 6: Micro air circulation system, 4 conical internal mandrels are used to support the stabilization of constricted bubbles in air-cooled inflation film processing. It is the body. Furthermore, the special conical internal mandrel (5), together with the (6) minute air circulation system, stabilizes the constricted bubble and at the same time circulates air at a minute flow rate and pressure, thereby improving the film quality. This is intended to prevent adhesion to the internal mandrel. (Processing method 4) The arrows in the figure indicate the direction of air flow.

Claims (1)

[Claims] 1. The density is 0.895 g/cm ³ or more and 0.935 g/cm ³ or less,
A copolymer of ethylene with a melt index of 0.5 g/10 min or less and α-olefin with a carbon number of 3 to 18 is extruded through a die using a melt extrusion method to obtain a tubular melt. The molten material is constricted to a size smaller than the diameter of the die by using a conical internal mandrel that is concentric with the die, and then expanded to a blow-up ratio of 3 or more to form a bubble, and the solidification position is set at the die exit. By performing air cooling so that the position is at least 5 times the diameter of the die, the orientation function fβ is -0.1 or more,
A method for producing an ultra-high impact resistant film, characterized by obtaining a film having an orientation function fε of 0.1 or less and a thickness of 30μ or less. 2 The density of the copolymer is 0.910g/cm3 ^or more and 0.920g/cm3 or more.
cm ³ or less, and the melt index is 0.3
The manufacturing method according to claim 1, wherein the manufacturing method is 1 g/10 minutes or less.