JPS6227091B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a propylene copolymer for sheet molding which has excellent thermoformability and impact resistance.
Conventionally, thermoforming sheets for food containers, including cups for tofu, tsukudani, ice cream, margarine, etc., and trays for meat, pickles, etc., have been made of vinyl chloride resin, high-impact polystyrene, polyprolene, etc. Resins are used extensively and in large quantities. Polypropylene has particularly excellent heat resistance compared to vinyl chloride resin and high-impact polystyrene, and is suitable for retort sterilization of whole food containers filled with food. It is also preferable that polypropylene has excellent oil resistance and does not generate harmful gases even when incinerated. However, polypropylene sheets have a large sheet sag during thermoforming, so the sheet width is 700 mm.
Continuous thermoforming is possible up to the order of mm, but
When a 1200 mm wide sheet is continuously thermoformed, the central part becomes overheated due to large sagging, which causes overlapping wrinkles called bridges and uneven wall thickness on the molded container, making it difficult to use as a product. loses its value. Therefore, when molding such a wide width, it is necessary to significantly increase the distance between the sheet and the heater and heat it slowly, but in this case the heating time is longer, so compared to vinyl chloride resin and high impact polystyrene. However, the disadvantage is that the molding cost is 2 to 3 times higher. An object of the present invention is to provide a sheet-forming polypropylene sheet that exhibits less sag during thermoforming, which reduces the cost of thermoforming, and that also has impact resistance even when used as a thin-walled container. 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 Chigu-Natsuta type activated titanium catalyst, the first
In the stage polymerization, the raw gas is 100% propylene by weight, or the ethylene content is 20% by weight in the copolymer.
The propylene-ethylene mixed gas adjusted to be less than 5% by weight is copolymerized in a range of 50 to 95% by weight of the total amount of olefin polymerized. 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
Let's call it the A-part generation [η] _A. Furthermore, [η]
is the viscosity of the tetralin solution (135℃, 50mg/50c.c.)
It was measured from Subsequently, in the second stage of polymerization, the above copolymer molecules are grown. In the second stage, a propylene-ethylene mixed gas is added at a rate of 50% to 50% of the total amount of olefin polymerized so that the ethylene content is 20% 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 and second stage polymerizations, or may be changed intermittently during the polymerization. [η] can be changed by adjusting the amount of the molecular weight regulator. In addition, in the method for producing polypropylene in the present invention, part A of the first polymerization and part B of the second stage polymerization are each further divided into two or more stages,
For example, part A is A-1, A-2..., part B is B-
Even if parts 1, B-2, etc. are polymerized separately, it is sufficient that parts A and B have the specific composition and specific production [η] of the present invention 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
M.1.) is based on the method described in ASTMD1238-62T, and is measured at a temperature of 230°C and a load of 2160g. The melt index of the copolymer used in the present invention is 0.01 to 0.8.
g/10 minutes, especially from 0.05 to
0.5g/10 minutes is preferred. melt index
If it exceeds 0.8 g/10 minutes, the sheet will sag more during thermoforming. Also, the melt index is 0.01g/
It is extremely difficult to produce polypropylene that lasts less than 10 minutes using normal methods, and even if it could be produced, the actual sheet forming temperature would be abnormally high, and the melting inside the forming machine would be extremely difficult. If the pressure of the resin is abnormally high, the molding machine equipment will be heavily equipped, which is 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]. Furthermore, the melt index referred to in the present invention can be measured in the form of polypropylene powder or pellets, but usually polypropylene powder is mixed with a certain antioxidant,
Add a certain amount of hydrochloric acid scavenger, make pellets using an extruder, and measure. The present invention was also carried out in this manner. Part A of the block copolymer of the present invention is a propylene homopolymer or has an ethylene content of 20% by weight.
The ethylene content is particularly preferably between 3 and 8% by weight. If the ethylene content exceeds 20% by weight, the properties of the slurry will deteriorate during the polymerization of part A, causing problems such as clogging of pipes during slurry transfer. Even when actually polymerizing the average composition of Part A to have an ethylene content of 3 to 8% by weight, propylene is prepolymerized in an amount of 5 to 20% by weight of the total amount of olefin polymerized in order to improve the slurry properties. Another method has been used in which a crystalline homopolymer is made and then a copolymerized portion is made using a propylene-ethylene mixed gas. 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 block copolymer of the present invention must be 20% by weight or more. When the ethylene content is less than 20% by weight, the impact strength is extremely reduced, making it impossible to obtain a sheet 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 total copolymer decreases, and the sheet sag during thermoforming increases somewhat. 50% by weight
If it exceeds this value, it becomes extremely soft and sticky during sheet molding, making it difficult to mold a good sheet. Moreover, the rigidity of the container obtained by thermoforming from the sheet decreases, making it impractical. The relationship between [η] _A and [η] _B in the present invention is
It is necessary that [η] _B − [η] _A ≧0.5. Preferably [η] _B - [η] _A = 0.8 to 15. If [η] _B - [η] _A is less than 0.5, the impact strength of the sheet will decrease and sag during thermoforming will tend to increase, making it impractical. 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 sheet using the copolymer of the present invention, a known method commonly referred to as the T-die method can be used. At this time, as in the usual case, there is no problem in adding additives used in ordinary polypropylene, such as antioxidants, lubricants, pigments, and other additives, if necessary. Sheets produced from the copolymer of the present invention include general sheets obtained by the above-mentioned T-die method (sometimes referred to as solid sheets or single-layer sheets in comparison with those described below), uniaxially oriented sheets, and melting point sheets. Excellent quality products can also be obtained in the case of the solid phase molding method in which thermoforming is performed below. Furthermore, foamed sheets obtained by adding known foaming agents (on the other hand, the aforementioned non-foamed sheets are referred to as solid sheets) also have good impact resistance and thermal stability. Also, in the case of sheets made by laminating films or sheets of other resins (for example, nylon, polyvinylidene chloride) using known methods, or sheets obtained by coextrusion with other resins (this is called a multilayer sheet), effective. 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, 10 hebutane 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 internal pressure of the autoclave when the temperature was raised to 55℃ 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% 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). Obtained. [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 4.41 dl/g and 5.77 dl/g, respectively.
From this, part B is generated [η] _B is [η] _B = 5.77-4.41×0.816/0.18
It can be calculated as 4=11.79 (dl/g). Also, [η] _B − [η] _A = 11.79−
4.41=7.38. 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.
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 Gaiki) 0.05
% by weight and 0.15% by weight of calcium stearate were uniformly mixed and formed into a pellet at 250°C. The MI of this Beret was 0.13 g/10 minutes. These results are summarized in Table-1. (2) Evaluation of sheet molding and thermoformability impact resistance The propylene copolymer pellets obtained above were put into a T-die extrusion sheet molding machine (L/D = 28, 280° setting). A sheet with a thickness of 0.5 mm was manufactured. This sheet was thermoformed using a vacuum forming machine (Cosmic FL-213-1 model manufactured by Asano Research Institute) to obtain a box-shaped vacuum-formed container with an inner volume of 500 c.c. and a wall thickness of 0.2 mm. At this time, the sag of the sheet was small and the thermoformability was good, the inner thickness of each part of the container was uniform, there were no overlapping wrinkles called bridges, and the appearance was extremely good. To simply measure sheet sag, the obtained sheet was placed between 400 x 400 mm frames and heated at 210℃.
The length of the sheet's sagging was measured 20 seconds after it was placed in a constant temperature room. In addition, the box-shaped container described above was filled with water, and the lid was heat-sealed with the main body to perform a drop impact test. These results are shown in Table 3. Example 2 A method for producing propylene copolymer
The gas phase hydrogen concentration of each part and part B, the ethylene content of the propylene-ethylene mixed gas (part A is a homopolymer of propylene) and A,
The same procedure as in Example 1 was carried out except that the polymerization ratio of part B was changed, and the results shown in Table 1 were obtained. Alternatively, 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 3 were obtained. Comparative Examples 1 to 5 A for the production method of propylene copolymer
Part, the gas phase hydrogen concentration of Part B, the ethylene content of the propylene-ethylene mixed gas, and A,
The procedure was carried out in exactly the same manner as in Example 1 except that the polymerization ratio of part B was changed, and the results shown in Table 1 were obtained. Further, sheet molding was carried out in exactly the same manner as in Example 1, and the performance of the obtained sheet was evaluated, and the results shown in Table 3 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 .
Propylene and hydrogen were charged so that the hydrogen concentration in the gas phase 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 ³ ·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 removed by suction to 40 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.
A propylene-ethylene mixed gas with an ethylene content of 77.2% by weight was continuously charged at a polymerization temperature of 55°C,
Keep the autoclave internal pressure at 0.5Kg/ ^cm2・G.
Polymerization was continued for 30 minutes. 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 polymerization ratio 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, B-
A very small amount of the polymerization slurry at the end of step 2 was taken out, a large excess of methanol was added thereto, it was filtered and dried to obtain a powdery polymer. This A-1, A-2,
When we measured [η] of the powder at the end of B-1 and B-2, they were 3.81 dl/g and 3.97 dl/g, respectively.
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) - 3.8
1 x 6.0/77.7 = 3.98 The production of B-1 part [η] ([η] _B-1 ) is [η] _B-1 = 4.14 x (6.0 + 77.7 + 7.0) - 3.97×(6.0+77.7)/7.0
= 6.17 The production 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 B part average including B-1 and B-2 [η]
([η] _B ) is [η] _B = 4.22×100−3.97×(6.0+7
7.7)/(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 specified value of monomer partial pressure at each stage.
The ethylene content of each part was 2.7% by weight, 77.1% by weight, and 97.8% by weight, respectively (Table-
2). The subsequent pellet manufacturing method and sheet molding were carried out in exactly the same manner as in Example 1. The results are shown in 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 (Table 2). The sheet was formed in exactly the same manner as in Example 1. The results are shown in Table-3.

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Claims (1)

[Scope of Claims] 1. In a propylene-ethylene copolymer for sheet molding, (a) the copolymer has a melt index of 0.01 to 0.8;
(b) the copolymer has an ethylene content of 50% by weight or less; (c) the copolymer has an ethylene content of less than 20% by weight (including propylene homopolymer). A
It is a block copolymer consisting of 50 to 95% by weight of part B and 50 to 5% by weight of part B having an ethylene content of 20% by weight or more, (d) Further formation of part _A [η] A propylene copolymer for sheet molding having excellent thermoformability and impact resistance, characterized by having a relationship between formation [η] _B and [η] _B ≧ [η] _A +0.5.