JPH0432861B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene resin composition that has excellent transparency, rigidity, impact resistance, and stress whitening resistance. Polypropylene resin is used in various molded products due to its excellent rigidity, processability, heat resistance, mechanical properties, etc. However, polypropylene resin has poor transparency due to its high crystallinity and poor impact resistance, making it difficult to use it in applications that require all of transparency, rigidity, and impact resistance. . Therefore, in order to improve transparency, a method was adopted in which propylene was randomly copolymerized with a small amount of α-olefins such as ethylene, butene-1, hexene-1, etc., but these methods had a certain degree of transparency. Although the improvement effect was recognized, it could hardly be called sufficient. In addition, although the impact resistance has been improved to some extent, the decrease in rigidity is significant, and as the degree of improvement in transparency and impact resistance is increased, the amount of by-product of amorphous polymers with poor commercial value increases. There was a problem in which the production of random copolymers suddenly became difficult. In addition, from the perspective of additive formulation, it is known that transparency and rigidity can be simultaneously improved by incorporating dibenzylidene sorbitol or bis(alkylbenzylidene) sorbitol into propylene homopolymer. The impact resistance of the product tended to be lower than that of the propylene homopolymer before blending. Furthermore, propylene-based random copolymers, for example, are formed into sheets and then cut out or bent to make containers such as boxes, but at that time, they withstand the impact of bending due to the impact force of a box-making machine. In order to make the material, a material was used in which ethylene-propylene copolymer rubber was added to a random copolymer resin of propylene and a small amount of ethylene to the extent that the transparency was not impaired as much as possible. Since the copolymer resin and the rubber lack compatibility, the two form a non-uniform morphology, which, despite improving impact resistance, also causes significant stress whitening. This drawback significantly impairs the commercial value and is a problem that must be solved. In view of this situation, the present inventors have conducted intensive research and have found that by blending specific additives into a propylene block copolymer with a specific structure, a product with excellent transparency, rigidity, and impact resistance can be obtained. The present inventors have also discovered that a polypropylene resin composition can be obtained in which whitening that occurs when stress is applied is suppressed, and the present invention has been completed. That is, the present invention uses a propylene homopolymer block of 15 to 85 parts by weight and an ethylene content of 2 to 15% by weight.
To 100 parts by weight of a propylene block copolymer consisting of 85 to 15 parts by weight of a propylene/ethylene random copolymer block and having a melt flow rate (MFR) of 0.1 to 100 g/10 minutes, the following formula [] was added. This is a polypropylene resin composition characterized by comprising 0.05 to 0.5 parts by weight of a compound. (R is an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogen atom, or a hydroxyl group; m and n are 0 to 3
an integer; R may be different in the same compound,
m and n may be the same in the same compound. ) The propylene block copolymer used in the present invention has a propylene homopolymer block of 15 to 85 parts by weight and an ethylene content of 2 to 15% by weight (preferably
2.5-13% by weight, more preferably 3-10% by weight)
It consists of 85 to 15 parts by weight of a propylene/ethylene random copolymer block, and has an MFR of
0.1-100g/10 minutes is suitable. The proportion of the propylene homopolymer block and the propylene/ethylene random copolymer block can be selected from a wide range depending on the balance of desired physical properties, but in general, propylene alone is the most suitable for achieving a balance of physical properties that emphasizes rigidity. If the proportion of the polymer block is high and the physical property balance with emphasis on impact resistance is desired, the proportion of the propylene/ethylene random copolymer block can be set high. Any deviation from the above ratio range will disrupt the balance between rigidity and impact resistance. Propylene homopolymer block and propylene
When the proportion of the ethylene random copolymer blocks is kept constant, by increasing the ethylene content in the random copolymer blocks, the impact resistance can be significantly improved with almost no decrease in the rigidity of the block copolymer. is possible. However, a parallel decrease in transparency and stress whitening resistance was found. However, as long as the ethylene content is within the above range, transparency can be improved by adding specific additives, as described below, without significantly reducing the impact resistance once increased. It is possible to significantly improve stress whitening resistance. Furthermore, advantageously, the stiffness is also slightly improved at the same time. If the ethylene content exceeds the above range, not only will the transparency deteriorate to an extent that cannot be recovered even by adding specific additives, but the amount of amorphous polymer produced as a by-product during block copolymer production will deteriorate. increases rapidly, deteriorating productivity. Such block copolymers are generally produced by directly applying the production techniques for propylene homopolymers or random or block copolymers of propylene and ethylene. That is, it is produced by a multistage polymerization method including a propylene homopolymerization step and a propylene/ethylene random polymerization step using a Ziegler type stereospecific polymerization catalyst in the presence or absence of an inert solvent. Molecular weight is controlled by hydrogen. As the Ziegler type stereospecific polymerization catalyst, a catalyst system containing various titanium trichloride or magnesium chloride supported titanium-containing catalysts and an organic aluminum compound such as diethylaluminium chloride or triethylaluminum as the main components can be suitably used. The composition containing the block copolymer of the present invention is different from the composition obtained by using a mechanical blend of a propylene homopolymer and a propylene/ethylene random copolymer instead of the block copolymer. It has the following advantages in terms of physical properties and economy. Generally, when a propylene/ethylene random copolymer is produced using a Ziegler-type stereospecific catalyst, an amorphous rubber-like copolymer is produced as a by-product at the same time as copolymer particles that retain crystallinity. The amount of copolymer by-products tends to increase rapidly as the ethylene content in the copolymer increases, so the ethylene content in the copolymer must be carefully controlled in order to ensure stable operation of the process and economical constraints. The upper limit is considered to be about 5% by weight. However, when a propylene homopolymer block is produced and then a propylene/ethylene random copolymer block is produced by a two-stage polymerization method, surprisingly, the ethylene content in the random copolymer block is reduced to 15%. It was found that the amount of rubbery copolymer by-product was within an acceptable range even if the amount was increased to about % by weight. This means that a polymer structure that cannot be realized industrially using the blending method can be realized for the first time using the block copolymerization method.How does this contribute to improving the physical property balance of the final composition? can be easily understood from the explanations given so far. If the MFR of the propylene block copolymer thus obtained is less than 0.1 g/10 minutes, moldability will be extremely difficult, while if it exceeds 100 g/10 minutes, it will be unfavorable in terms of mechanical strength. Note that MFR is a value measured under the conditions of 230°C and a load of 2.16 kg. Furthermore, dibenzylidene sorbitol or bis(substituted benzylidene) sorbitol used in the present invention has the general formula (R is an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogen atom, or a hydroxyl group; m and n are 0 to 3
an integer; R may be different in the same compound,
m and n may be the same in the same compound. ) is a compound represented by Specifically, for example, dibenzylidene sorbitol, 1,3,2,
4-di(p-methylbenzylidene) sorbitol 1,3,2,4-di(p-chlorobenzylidene)
Examples include sorbitol 1,3,2,4-di(p-methoxybenzylidene) sorbitol. This compound is blended in an amount of 0.05 to 0.5 parts by weight, preferably 0.1 to 0.3 parts by weight, per 100 parts by weight of the propylene block copolymer. If it is less than 0.05 parts by weight, there will be almost no improvement in transparency or stress whitening resistance, and if it exceeds 0.5 parts by weight, there will be problems in addition to bleeding.
Economic efficiency is also not favorable. In addition, various additives can be appropriately blended into the composition of the present invention within a range that does not impair the effects of the invention. Specifically, antioxidants, light stabilizers,
Examples include ultraviolet absorbers, nucleating agents, antistatic agents, pigments, pigment dispersants, lubricants, neutralizing agents, and acid scavengers. In particular, it is preferable to add antioxidants to maintain the stability of granulation and molding processes, and neutralizing or hydrochloric acid scavengers such as metal soaps and hydrotalcites exhibit the effects of this patent. This is more preferable. Example 1 After sufficiently replacing the inside of a stainless steel reactor with an internal volume of 200 mm equipped with a stirring blade with propylene gas,
Heptane 80 was added as a polymerization solvent. The temperature inside the vessel was maintained at 50° C., and 50 g of diethyl aluminum chloride (DEAC) and 10 g of titanium trichloride (TMB-07, manufactured by Marubeni Solvay Chemical Co., Ltd.) were added as catalysts. Propylene was then fed at a rate of 5.83 Kg/hr for 15 minutes. During this time, the concentration of hydrogen in the gas phase was 2.0.
% by volume. Next, increase the temperature inside the vessel to 60℃.
The hydrogen concentration was increased to 3.5% by volume, and propylene was continuously fed at a rate of 5.83 kg/hour for 185 minutes. The total amount of propylene supplied during this period was 18.0 kg (the above is a propylene homopolymer block). Ethylene was newly fed at a rate of 0.333 kg/hour while maintaining the internal temperature, hydrogen concentration, and propylene feed rate, and propylene and ethylene were each fed for 175 minutes. The total amount of propylene and ethylene supplied during this period was 17.0Kg and
It weighed 0.97Kg. At this point, the internal pressure was 3.9Kg/
cm ² (gauge pressure), but at this point the supply of propylene and hydrogen was stopped, and ethylene was 0.233 cm2 (gauge pressure).
While feeding at a rate of kg/hour, the pressure inside the vessel was lowered to 2.0 kg/cm ² (gauge pressure) over 30 minutes to complete the reaction. The total amount of ethylene supplied during this period was 0.12 kg (propylene/ethylene random copolymer block). Butanol was added to the obtained block copolymer at 1.1
After the catalyst was decomposed at 68° C. for 3 hours, the catalyst was removed by washing with water. After further centrifugation and drying steps, 32.0 kg of product copolymer was obtained. The amount of amorphous copolymer produced as a by-product after being solubilized in the polymerization solvent was 1.12 kg. The proportion of the propylene homopolymer block and the propylene-ethylene random copolymer block in the block copolymer is calculated by subtracting the amount of unreacted monomer and the amount of by-product amorphous polymer from the total amount of monomer supplied. It was calculated by allocating it to the ratio of the amount of monomers supplied to produce the polymer block. The ethylene content of the propylene/ethylene random copolymer block portion was calculated from the ratio of both blocks calculated above and the ethylene content in the product block copolymer. To 100 parts by weight of the block copolymer thus obtained, tetrakis[methylene (3,5-di-t-
-butyl-4-hydroxyhydrocinnamate)]
Butane (antioxidant) 0.1 part by weight, calcium stearate (neutralizing agent) 0.1 part by weight and 1,3,
0.1 part by weight of 2,4-dibenzylidene sorbitol was added and mixed, followed by granulation at 260°C. The block copolymer composition pellets were sandwiched between hard chrome-plated iron plates and heated to 230°C.
The mixture was press-molded using a hot plate press-molding machine, and after being cooled and solidified using a cooling press-molding machine at 30° C., it was taken out to produce sheets with a thickness of 1 mm and 2 mm. For each of these sheets, the degree of haze (based on ASTM-D1003) and stress whitening resistance were measured using a 1 mm thick sheet, and the flexural modulus (based on ASTM-D747) was measured using a 2 mm thick sheet. ) and Charpy impact strength (based on JIS-K7111) were measured. The results are shown in Table 1. The stress whitening resistance was measured using a Dupont impact tester (manufactured by Toyo Seiki Seisakusho) by dropping a load of 300 g from heights of 5, 10, 20, 30, and 40 cm to apply impact stress to the sheet. After the application, the whitening state of the sheet was visually evaluated. The evaluation was carried out as 5th grade if all whitening was observed after being dropped at each height, and 0 grade if no whitening was observed at all. Examples 2 to 4 1,3,2,4-di(paramethylbenzylidene) sorbitol, 1,3,2,4-di(parachlorbenzylidene) sorbitol instead of 1,3,2,4-dibenzylidene sorbitol A block copolymer was produced and a sheet was formed in the same manner as in Example 1, except that 1,3,2,4-di(paramethoxybenzylidene)sorbitol was used. The evaluation results are the first
Shown in the table. Example 5 The propylene supply time in the propylene homopolymer block manufacturing stage after the temperature in the polymerization vessel reached 60°C was 250 minutes (therefore, the total amount of propylene supplied was 24.3 kg), and the gas phase during this period was The hydrogen concentration in the block was set at 4.2% by volume, the ethylene supply rate at the propylene-ethylene random copolymer block manufacturing stage was set at 0.530 kg/hour, and the supply time during simultaneous supply of propylene and ethylene was set at 110 minutes (therefore, , the total supply of propylene and ethylene during this period was 10.7Kg and 0.97Kg, respectively), and the ethylene supply rate and time after stopping the propylene supply were 0.675Kg/hour and 22 minutes, respectively (therefore, the total supply of ethylene during this period was 0.675Kg/hour and 22 minutes, respectively). A block copolymer was produced in the same manner as in Example 1, except that the amount was changed to 0.248 kg). Further, a sheet was formed using the obtained block copolymer under the same conditions as in Example 1 and evaluated. The results are shown in Table 1. Comparative Examples 1 and 2 The block copolymers of Examples 1 and 5 were used in the same manner as in Examples 1 and 5, except that the additive 1,3,2,4-dibenzylidene sorbitol was not added. Each sheet was molded and evaluated. The results are shown in Table 1. Comparative Example 3 When the temperature inside the polymerization vessel reached 60°C, the process immediately proceeded to the random copolymerization stage of propylene and ethylene without further homopolymerizing propylene. The simultaneous supply time was set to 360 minutes, and the hydrogen concentration during this period was changed to 3.0% by volume, and the ethylene supply rate was changed to 0.186Kg/hour (therefore, the total amount of propylene and ethylene supplied during this period was set to 35.0Kg and 1.12Kg, respectively). In addition, the ethylene supply rate, supply time, and total supply amount after stopping the propylene supply are 0.130Kg/hour, respectively.
A block copolymer was produced in the same manner as in Example 1, except that the reaction time was 36 minutes and the weight was 0.078 kg.
This block copolymer was molded into a sheet in the same manner as in Example 1 and evaluated. The results are shown in Table 1. Comparative Example 4 The ethylene supply rate in the random copolymerization stage was 0.350 Kg/hour during the simultaneous supply of propylene and ethylene, and 0.245 Kg/hour after the propylene supply was stopped. The time period during which propylene and ethylene were simultaneously supplied was the same as in Comparative Example 3 (therefore, the total amount of ethylene supplied during this period was 2.10 kg),
The period after the propylene supply was stopped was set at 28 minutes (therefore, the total amount of ethylene supplied during this period was 0.114Kg).
A block copolymer was produced in the same manner as in Comparative Example 3, except that Further, using this block copolymer, Example 1
A sheet was formed and evaluated in the same manner as above. The results are shown in Table 1. Comparative Example 5 The same procedure as in Example 1 was carried out, except that 5 parts by weight of ethylene-propylene copolymer rubber having a Mooney viscosity of 70 and a propylene content of 27% by weight was added to 100 parts by weight of the block copolymer used in Comparative Example 3. A sheet was formed and evaluated. The results are shown in Table 1. Comparative Example 6 In Comparative Example 5, a block copolymer to which no rubber was added was similarly evaluated. The results are shown in Table 1.

【table】

[Table] In Table 1, bis(substituted benzylidene)
The sorbitol type symbols represent the following: A: 1,3,2,4-dibenzylidene sorbitol B: 1,3,2,4-di(p-methylbenzylidene) sorbitol C: 1,3,2,4-di(p-chlorobenzylidene) sorbitol D :1,3,2,4-di(p-methoxybenzylidene)sorbitol Examples 6 to 9 and Comparative Examples 7 to 11 Supply time of propylene in the propylene homopolymer block production stage, hydrogen concentration in the gas phase during this time, The ethylene supply rate in the propylene/ethylene random copolymer block production stage, the supply time during the simultaneous supply of propylene and ethylene, and the ethylene supply rate and time after stopping the propylene supply were respectively selected as in Example 1. Various block copolymers shown in Table 2 were produced by the method described above. Using the obtained block copolymer, a sheet was molded and evaluated under the same conditions as in Example 1. The results are shown in Table 2.

【table】

【table】

Claims (1)

[Scope of Claims] 1 Propylene homopolymer block with 15 to 85 parts by weight and an ethylene content of 2 to 15% by weight.
Consists of 85 to 15 parts by weight of ethylene random copolymer block, and has a melt flow rate of 0.1 to 100.
g/10 minutes of propylene block copolymer
A polypropylene resin composition comprising 0.05 to 0.5 parts by weight of a compound represented by the following formula [] to 100 parts by weight. (R is an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogen atom, or a hydroxyl group; m and n are 0 to 3
an integer; R may be different in the same compound,
m and n may be the same in the same compound. )