JPH0113487B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a propylene copolymer for film forming. Conventional polypropylene films have been produced using either a casting method or an inflation method, and polypropylene suitable for each method and use is already commercially available. However, when trying to mold extremely thin films using the above-mentioned molding method, especially using the air-cooled inflation molding method, these polypropylenes tend to tear as the film thickness decreases to about 30 microns. There are drawbacks such as reduced strength and impact strength, and poor stability of the tube during film forming (more wrinkles, uneven wall thickness, and uneven fold diameter), and improvements are needed. It is being These films are made into bags and used in place of plastic bags, garbage bags, standard bags, and other materials that used to be made of paper. It is necessary to withstand the load of the contents, not to be easily torn even if a part of the bag is damaged by touching a sharp corner of the contents, and to withstand some impact. In particular, conventional polypropylene has a drawback in that the film has strong directionality and is prone to vertical tearing. In addition, when forming a film using the air-cooled inflation method, when forming a tubular film by melt extrusion from an annular die, this tubular part (hereinafter referred to as the tube) is unstable, and if it shakes from side to side, it may become wrinkled or The thickness may become uneven, and in extreme cases, the folded diameter may change, resulting in loss of value as a product. The object of the present invention is to improve the tear strength and impact strength of this film, and to improve the stability of the tube during film molding. In order to accomplish these tasks, the present inventors
The molecular weight of polypropylene is much larger than conventional ones, and each part of the block copolymer (each block)
The present invention can be achieved by using an ethylene-propylene block copolymer in which the composition has a specific ethylene content and the molecular chain size of each part (represented by the intrinsic viscosity [η] described below) has a specific relationship. completed. This special polypropylene used in the present invention is produced, for example, by the following method. That is, using a Ziegler-Natsuta type activated titanium catalyst, propylene is produced in the first stage of polymerization.
Copolymerize 100% by weight raw material gas or a propylene-ethylene mixed gas adjusted so that the ethylene content is less than 20% by weight in the copolymer in a range of 50 to 95% by weight of the total olefin polymerization amount. . The part of the polymer molecule grown by this polymerization is called part A. The intrinsic viscosity number [η] (dl/g) of the polyolefin obtained by taking a sample and stopping the polymerization by destroying the catalyst at the stage where this part A is produced is defined as [η] _A. [η] _A will be referred to as A part generation [η] _A. Note that [η] was measured from the viscosity of the tetralin solution (135°C, 50 mg/50 c.c.). Subsequently, in the second stage of polymerization, the above copolymer molecules are grown, and in the second stage, a propylene-ethylene mixed gas is added to 50% to 50% of the total olefin polymerization amount so that the ethylene content is 35% by weight or more. Copolymerization is carried out in a range of 5% by weight. The part of the copolymer grown at this stage is referred to as Part B. A typical copolymer molecule obtained through both steps has a so-called block copolymer structure in which part A and part B are joined. At this time, if [η] of the overall average (measured value) of the copolymer consisting of the A part produced in the first stage and the B part produced in the second stage is [η] _AB , then the B part [η] _B of the part of the copolymer produced in (B part formed [η] _B
There is a relationship between the measured value [η] _A and the following equation. [η] _AB = [η] _A ×a + [η] _B ×b where a and b are the weight percent of the mixed gas polymerized in parts A and B, respectively. In this case, the mixing ratio of propylene ethylene and [η] may be gradually increased or decreased in the first-stage polymerization and the second-stage polymerization, or may be changed intermittently during the polymerization. To change [η],
The amount of molecular weight regulator may be adjusted. In addition, in the method for producing polypropylene in the present invention, part A in the first stage polymerization and part B in the second stage polymerization are each further divided into two or more stages, for example, part A is A-1, A-2, and part B is Even if B-1 and B-2 are polymerized separately, A
Part B is the specific composition and specific formation [η] of the present invention.
It is sufficient to have as an average. Next, each constituent feature of the copolymer of the present invention will be explained. First, the melt index (hereinafter referred to as
MI (abbreviated as MI) is based on the method described in ASTM D1238-62T, and is measured at a temperature of 230° C. and a load of 2160 g. The melt index of the copolymer used in the present invention is 0.01 to 0.5.
g/10 minutes, especially from 0.05 to
0.2 g/10 minutes is preferred. melt index
If it exceeds 0.5 g/10 minutes, the stability of the tube during molding will decrease, causing wrinkles and uneven wall thickness. Conventional polypropylene for film forming has a melt index of approximately 8, and the large difference in melt index from that of the copolymer of the present invention seems to be related to the performance of the film. In addition, it is extremely difficult to produce polypropylene with a melt index of less than 0.01 g/10 minutes using normal methods, and even if it were possible to produce it, the actual film forming temperature would be abnormally high. Also, the pressure of the molten resin inside the molding machine becomes abnormally high, making the molding machine equipment heavy and impractical. The melt index decreases as the molecular weight of the polymer increases. Furthermore, the larger the molecular weight of the polymer, the larger the [η] of the polymer. That is, melt index has an inverse correlation with molecular weight and [η]. The melt index referred to in the present invention can be measured in the form of polypropylene powder or pellets, but it is usually measured by adding a certain amount of antioxidant and hydrochloric acid scavenger to polypropylene powder and turning it into pellets using an extruder. do. The present invention was also carried out in this manner. Part A of the present invention consists of a homopolymer of propylene or a copolymer with an ethylene content of less than 20% by weight, particularly preferably an ethylene content of 3 to 20% by weight.
It is 8% by weight. If the ethylene content exceeds 20% by weight, the properties of the slurry will deteriorate during polymerization of part A, causing problems such as clogging of pipes during slurry transfer. Actually, the average composition of part A is ethylene content 3
Even when polymerizing to 8% by weight, in order to improve the slurry properties, propylene is polymerized in advance by 5 to 20% by weight of the total amount of olefin polymerized to create a highly crystalline homopolymer, and then propylene-ethylene is mixed. A method of creating a copolymerization region using gas has also been used. The present invention also includes such cases. At this time, if the proportion of the portion polymerized only with propylene is reduced in advance, large fluctuations in [η] _A of the entire A part will not occur. The ethylene content of Part B of the present invention must be 35% by weight or more. Ethylene content is 20
If the weight percentage is less than this, the impact strength will be extremely reduced, making it impossible to obtain a film of practical use. This part B needs to be in a range of 50 to 5% by weight based on the total copolymer. When the amount is less than 5% by weight, not only the impact strength decreases, but also the proportion of the high molecular weight polyolefin portion in the entire copolymer decreases, resulting in a decrease in the stability of the tube during film molding. If it exceeds 50% by weight, it becomes extremely soft and sticky during film molding, making it difficult to mold a good film. The relationship between [η] _A and [η] _B in the present invention is 10>
It is necessary that [η] _B ≧ [η] _A +0.5. Preferably [η] _B - [η] _A = 0.8 to 9. [η] _B − [η] When _A is less than 0.5, the tear strength of the film tends to decrease significantly, and the impact strength and stability of the tube during film forming also tend to decrease. The stability of the tube during forming is influenced more by the MI value than by the value of [η] _B − [η] _A. In the present invention, [η] _B is 0.5 dl/g from [η] _A
In order to increase the molecular weight above, the amount of hydrogen used as a molecular weight regulator in the polymerization of part B may be extremely reduced, or the amount of hydrogen used as a molecular weight regulator may be extremely reduced, or the amount may be polymerized without using it at all. As a method for forming a film using the copolymer of the present invention, a known method commonly referred to as an air-cooled inflation method can be used. At that time, as in normal cases, use antioxidants, lubricants, etc. as necessary.
There is no problem in adding various additives commonly used in polypropylene, such as pigments and other additives. The ultra-thin reinforced film obtained in the present invention has good tear strength and impact strength even if it has a small wall thickness, so it is expected to have a wide range of uses from the viewpoint of resource saving. In addition, the stability of the tube during molding is good, and there are few wrinkles and uneven wall thickness, so it is highly satisfactory in practice.
Although it is an unexpected effect, when inflation molding is performed using this propylene copolymer, in addition to the above-mentioned objective, there is a technical effect in that high-speed molding is possible. In other words, high quality films can be obtained even if the molding speed is faster than before.
This is useful for reducing film manufacturing costs. Next, the present invention will be explained in more detail with reference to Examples. Example 1 (1) Production of propylene copolymer In a SUS-27 autoclave with an internal volume of 20 ml, 10 g of heptane was charged under a nitrogen atmosphere, and 5 g of activated titanium trichloride and 8 g of diethylaluminium chloride were charged as catalysts. . The ethylene content was 3.7% by weight so that the autoclave internal pressure when the temperature was raised to 55°C was 4Kg/cm ² in gauge pressure (hereinafter the symbol is abbreviated as Kg/cm ² G) and the gas phase hydrogen concentration was 0.3% by volume. of propylene-ethylene mixed gas and hydrogen were charged. The autoclave contents were heated to 55°C and
The above propylene-ethylene mixed gas and hydrogen were continuously charged to maintain the internal pressure at 4 Kg/cm ² G and the hydrogen concentration at 0.3% by volume at ℃, and the polymerization was continued for 2.4 hours (first stage polymerization). . Next, after completely purging unreacted monomer while keeping the catalyst active, 0.5% of a propylene-ethylene mixed gas containing hydrogen and ethylene with a content of 43.5% by weight is added so that the gas phase hydrogen concentration is 1% by volume. Bulk charging up to Kg/cm ² G, polymerization temperature 55℃
When the temperature was maintained, polymerization started again. There the internal pressure
0.5Kg/cm ² G, a propylene-ethylene mixed gas with an ethylene content of 89.7% by weight and hydrogen were continuously charged to maintain a gas phase hydrogen concentration of 1.1% by volume.
Polymerization was continued for 1.6 hours (second stage polymerization). At the end of the polymerization, methanol 2 was added to stop the polymerization, and the product was purified and dried using the usual method to yield 3.9Kg.
A powdery polymer was obtained. The polymerization ratio in the first stage polymerization and the second stage polymerization was 81.6:18.4. Also, as a sample, the first
A very small amount of the polymerization slurry at the end of stage polymerization is taken out from the side pipe at the bottom of the autoclave, charged with a large excess of methanol, filtered, and dried to obtain a powdery polymer (i.e., a polymer consisting only of part A). Ta. [η] _A of the sample at the end of this first stage polymerization and the second
[η] _AB of the powder at the end of stage polymerization was measured to be 4.43 dl/g and 5.40 dl/g, respectively.
From this, the generation of part B [η] _B is [η] _B = 5.40−4.43×0.816/0.184=9.70 (dl/g
) can be calculated. Also, [η] _B − [η] _A = 9.70−4.43
= 5.27. In addition, the ethylene content of each part A and B, obtained by calculating the mass balance from the measured values of monomer partial pressure at each stage, was 4.8% by weight, respectively.
It was 89.7% by weight. This powdery polymer was added with 0.5% by weight of 2,6-di-t-butyl-p-cresol, tetrakis[methylene 3-(3',5'-di-t-butyl-4'-
Hydroxyphenyl) propionate] methane (Irganox 1010 manufactured by Ciba Geigy) 0.05
% by weight and 0.15% by weight of calcium stearate were uniformly mixed and pelletized at 250°C. The MI of this pellet was 0.13 g/10 min. These results are summarized in Table-1. (2) Forming of ultra-thin reinforced film The propylene copolymer pellets obtained above were placed in a cylinder with an inner diameter of 50 mm and a screw L/
Using a D=28 extruder, tubular films with wall thicknesses of 30 μm and 15 μm were formed by melt extrusion through a spiral-type annular die and air-cooled inflation method. The air-cooled inflation molding conditions are as follows:
The temperature of the annular die was set to 220℃, and the take-up speed of the tubular film was 15 m/min when the wall thickness was 30 μ.
The speed was set at 30m/min. The stability of the tube was good, and wrinkles and wall thickness unevenness were good without any practical problems. The thus obtained tubular film was measured for Elmendorf tear strength in the longitudinal and transverse directions and the longitudinal/lateral ratio according to the method of JIS Z1702, and the impact strength of the film was measured using an impact tester manufactured by Toyo Seiki. The results are shown in Table 2, and the Elmendorf tear strength in the longitudinal and lateral directions and the balance in the longitudinal and lateral directions were good, and the impact strength was also sufficiently strong. Example 2 The method for producing a propylene copolymer is described in Part A.
Same as Example 1 except that the gas phase hydrogen concentration of each part B, the ethylene content of the propylene-ethylene mixed gas (part A is a homopolymer of propylene), and the polymerization ratio of parts A and B were changed. The same procedure was carried out, and the results shown in Table 1 were obtained. Furthermore, the ultrathin reinforced film was molded in exactly the same manner as in Example 1, and the performance of the obtained film was evaluated and the results shown in Table 2 were obtained. Comparative Examples 1 to 5 A for the production method of propylene copolymer
Gas phase hydrogen concentration of Part and Part B, ethylene content of propylene-ethylene mixed gas, and A and B
The procedure was carried out in exactly the same manner as in Example 1 except that the polymerization ratio of parts was changed, and the results shown in Table 1 were obtained. Further, the molding of an ultra-thin reinforced film was carried out in exactly the same manner as in Example 1, and the performance of the obtained film was evaluated as shown in Table 2.
The results were obtained. Example 3 (1) Production of propylene copolymer In a SUS-27 autoclave with an internal volume of 20, 10 heptane was charged under a nitrogen atmosphere, and 5 g of activated titanium trichloride and 8 g of diethylaluminium chloride were charged as catalysts. . When the nitrogen in the autoclave was replaced with propylene and the temperature was raised to 50℃, the pressure inside the autoclave was 1Kg/
cm ² ·G, and propylene and hydrogen were charged so that the gas phase hydrogen concentration was 0.15% by volume. Part A was polymerized in two stages, A-1 and A-2. In A-1, the temperature of the contents of the autoclave was raised to 50°C, and polymerization was continued for 40 minutes while blowing propylene to maintain an internal pressure of 1 kg/cm ² G at 50°C, and then the internal temperature was raised to 55°C. It was warm. In A-2, the ethylene content was increased at the same time as the temperature was raised to 55℃.
A 2.3% by weight propylene-ethylene mixed gas was continuously charged, and the polymerization was continued for 2.3 hours while maintaining the internal pressure at 4 kg/cm ² ·G and the gas phase hydrogen concentration at 0.37% by volume. Part B was polymerized in two stages, B-1 and B-2. In B-1, after the polymerization of part A was completed, the residual monomer was immediately purged to normal pressure, and then the monomer was further suctioned and removed to 540 mmHg using a vacuum pump.
Next, hydrogen and ethylene were charged at once to 0.5 kg/cm ² G so that the gas phase hydrogen concentration was 3% by volume.
At a polymerization temperature of 55 DEG C., a propylene-ethylene mixed gas having an ethylene content of 77.2% by weight was continuously charged, and polymerization was continued for 30 minutes while maintaining the autoclave internal pressure at 0.5 kg/cm ² ·G. In B-2, after completely removing unreacted monomers using a vacuum pump, a propylene-ethylene mixed gas with a hydrogen and ethylene content of 80.0% by weight was added at 0.5Kg/cm ² so that the gas phase hydrogen concentration was 19% by volume. G
Polymerization temperature: 55℃, internal pressure: 0.5Kg/
Propylene-ethylene mixed gas with an ethylene content of 97.8% by weight and hydrogen were continuously charged so as to maintain a gas phase hydrogen concentration of 19% by volume at cm ² ·G, and polymerization was continued for 1 hour. After the polymerization is completed, methanol 2 is charged to stop the polymerization, and purified and dried using the usual method.
Kg of powdered polymer was obtained. The ratio of polymerization amounts in A-1, A-2, B-1, and B-2 was (6.0:77.7:7.0:9.3). In addition, samples A-1, A-2, B-1,
A very small amount of the polymerization slurry at the end of B-2 was taken out, and a large excess of methanol was charged, filtered and dried to obtain a powdery polymer. This A-1, A
-2, B-1, and B-2, the powder [η] was measured at the end of 3.81 dl/g, respectively.
They were 3.97 dl/g, 4.14 dl/g, and 4.22 dl/g.
From this, the generation of part A-2 [η] ([η] _A-2 ) is [η] _A-2 = 3.97 x (6.0 + 77.7) - 3.81 x 6.0 / 77.7 = 3
.98 The production of part B-1 [η] ([η] _B-1 ) is [η] _B-1 = 4.14 × (6.0 + 77.7 + 7.0)
−397 × (6.0 + 77.7) / 7.0 = 6.17 The generation of the B-2 part [η] ([η] _B-2 ) is [η] _B-2 = 4.22 × 100 − 4.14 × (6.0 + 77.7
+7.0)/9.3=5.00 Generation of the B part average including B-1 and B-2 [η] ([η] _B ) is [η] _B = 4.22×100−3.97×(6.0+77.7) /(7.0+9.
3) = 5.50. In addition, part A-2, part B-1, and part B-2 were obtained by calculating the material balance from the measured values of monomer partial pressure at each stage.
The ethylene content of each part is 2.7% by weight, respectively.
They were 77.1% by weight and 97.8% by weight. The subsequent steps for producing pellets and molding of an ultra-thin reinforcing film were carried out in exactly the same manner as in Example 1. The results are shown in Table-2 and Table-3. Example 4 A- for the production method of propylene copolymer
1, the gas phase hydrogen concentration of each of A-2, B-1, and B-2, the ethylene content of the propylene-ethylene mixed gas, and the polymerization ratio of A-1, A-2, B-1, and B-2. The procedure was carried out in exactly the same manner as in Example 3 except for the changes. The ultrathin reinforced film was molded in exactly the same manner as in Example 1. The results are shown in Table-2 and Table-3. Example 5 A method for producing propylene copolymer
The process was carried out in exactly the same manner as in Example 1, except that the gas phase hydrogen concentration, propylene-ethylene content of parts A and B, the propylene-ethylene content (part A is a propylene homopolymer), and the polymerization ratio of parts A and B were changed. and then table-
1 result was obtained. Furthermore, molding of an ultra-thin reinforced film was carried out in exactly the same manner as in Example 1, and the performance of the obtained film was evaluated and the results shown in Table 2 were obtained.

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Claims (1)

[Scope of Claims] 1. In an ethylene-propylene copolymer for film molding, (a) the copolymer has a melt index of 0.01 to 0.5;
g/10 minutes, (b) the ethylene content of the copolymer is 50% by weight or less, and (c) the copolymer has an ethylene content of less than 20% by weight (including propylene homopolymer). Part 50~
It is a block copolymer consisting of 95% by weight and 50 to 5% by weight of B part having an ethylene content of 35% by weight or more, (d) Further formation of part A [η] _A and part B [η] _B A film-forming propylene copolymer characterized by having a relationship of 10>[η] _B ≧ [η] _A +0.5.