JPS587665B2 - Method for modifying propylene ethylene block copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a propylene-ethylene block copolymer which is excellent in processability, and also has excellent impact resistance, weld strength and surface gloss.

In order to improve the processability of a propylene/ethylene block copolymer with improved impact resistance at low temperatures, a method of adding an organic peroxide and heat-treating it at 180 to 270°C has already been reported in Japanese Patent Publication No. 51-30102. It is known by et al.

However, many of the propylene-ethylene block copolymers produced by these methods not only have considerably inferior gloss in the molded products, but also have poor gloss in the weld area, which has a large relationship with the impact strength of actual injection molded products. It had the disadvantage of low strength.

In addition, the low-temperature impact strength, especially when made highly fluid, is much higher than that of a propylene-ethylene copolymer with the same ethylene content that has the same fluidity without being treated with an organic peroxide. It wasn't.

As a result of intensive research into means for solving the above-mentioned problems, the inventors of the present invention discovered that the intrinsic viscosity of the copolymerized portion of a block copolymer was determined by using a material having a specific range of intrinsic viscosity as a base polymer. The present inventors have discovered that not only the above-mentioned drawbacks are solved, but also the low-temperature impact strength is greatly improved.

That is, in the present invention, the ethylene content of the entire polymer is 5 to 15% by weight, the ethylene content of the ethylene/propylene copolymer portion is 50 to 80% by weight, and the intrinsic viscosity of the copolymerization portion is 4 to 15%. Propylene/ethylene block copolymer is mixed with 0.005 to 0.2% by weight of organic peroxide based on the copolymer and melt-kneaded at 180 to 300°C. This is a method for modifying block copolymers.

Here, the concept of the intrinsic viscosity of the copolymerization part will be explained. This is not a value measured by actually cutting and taking out only the copolymerization part, but is a convenient concept calculated by the following calculation.

First, the intrinsic viscosity [η]p of the polypropylene polymerized portion that is polymerized in advance in the manufacturing process of the block copolymer is measured (in tetralin at 135° C., the same applies hereinafter).

Next, the block copolymerization portion is polymerized, and the intrinsic viscosity [η]C of the final copolymer obtained is measured.

At this time, if the polymerization ratio of the copolymerized portion in the block copolymer is a, then the intrinsic viscosity of the copolymerized portion [η]Rc and [η]C
, [η]p, and the following equation (1) is assumed to hold. Therefore, the intrinsic viscosity of the copolymerized portion [η)Rc is determined by equation (2).

[η, lc=a(η, lRc+(1-a)(η)p (
1) [η)Rc=-Cη,lc-(=1)(η,ip
(2) The melt-kneading treatment is carried out using equipment and methods commonly used for pelletizing thermoplastics, such as using a screw extruder type pelletizer.

The temperature may be that used for conventional polypropylene extrusion.

The propylene/ethylene block copolymer used in the method of the present invention is obtained by first polymerizing propylene to form a polypropylene portion using a Ziegler-Natsuta catalyst, and then copolymerizing a mixture of ethylene and propylene.

At this time, a small amount (5% or less) of ethylene may be copolymerized with the propylene portion.

There is also a method in which the polymerization of the copolymerization portion is carried out in multiple stages.

Methods for producing these block copolymers are described, for example, in Japanese Patent Application No. 53-91069 and Japanese Patent Application No. 53-11 filed by the present applicant.
It is also stated in No. 7107, etc.

The propylene/ethylene copolymer used in the present invention has a total ethylene content of 5 to 15% by weight, an ethylene content of the copolymerized part of 50 to 80% by weight, and an intrinsic viscosity of the copolymerized part of 4 to 15%. belongs to.

The ethylene content in the copolymer and the copolymerized portion is determined by the balance between rigidity and low-temperature impact resistance, but if the intrinsic viscosity of the copolymerized portion is 4 or less, the main effect of the present invention, which is the formation of molded products, is reduced. Impact resistance, weld part strength and gloss are insufficient.

Furthermore, if the intrinsic viscosity of the copolymerized portion exceeds 15, the amount of high-molecular-weight dispersed substances increases, which impairs the appearance of the molded product, which is not preferable.

Inorganic fillers, nucleating agents, pigments, etc. may be added to this block copolymer as additives within the range normally used.

In addition, in order to further improve impact resistance, 10% of ethylene-propylene elastic copolymer (so-called EPR or EPT) was added.
A block copolymer mixed up to about % may also be used.

The organic peroxides used in the present invention include dialkyl peroxides such as 2,5-dimethyl-2,5-t7'' tilperoxyhexene-3, 2,5-dimethylhexane-2,5-di Hydroperoxides, hydroperoxides such as P-menthane hydroperoxide, ketone peroxides, peroxy esters, etc., which have a half-life of more than 10 hours at 100°C, either alone or in combination. A combination of these is appropriate.

Among the polymers obtained by the method of the present invention, particularly useful ones are low-viscosity (i.e., high fluidity) polymers for injection molding with an intrinsic viscosity of 1.5 or less (corresponding to about 15 or more in M, FR). It is.

Such low-viscosity polymers make it possible to make injection-molded products thinner in response to market demands for energy saving and cost reduction, and also to reduce distortions such as warping and twisting due to crystalline orientation distortion of polypropylene, as well as crystallization shrinkage. This is useful for preventing deformation of injection molded products such as sink marks, prevention of polymer flow patterns in injection molded products, and shortening of molding cycles. The combination of effects such as strengthening the weld portion and improving impact resistance has made it possible to provide an extremely useful molding raw material.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Consisting of 133% ethylene/propylene copolymerized portion and 86.7% polypropylene polymerized portion, ethylene content in the ethylene/propylene copolymerized portion is 60%, intrinsic viscosity of the copolymerized portion is 7.5, and copolymerized A propylene/ethylene block copolymer powder having an ethylene content of 8% and a total intrinsic viscosity of 2.30 was obtained by polymerization, and 2,5-dimethyl-2,5-dimethyl was added as an organic peroxide to the powder. (
A homogeneous mixture of 0.06% by weight of t-butylperoxy)hexane and 0.1% by weight of BHT as an antioxidant was melt-kneaded in an extruder at 230°C to obtain pellets.

Its intrinsic viscosity had decreased to 1.36.

This pellet was injection molded to form a test piece of a predetermined shape, and the test piece was subjected to a test.

The results are shown in Table 1.

Comparative Example 1 The intrinsic viscosity of the copolymerized portion was 7.45, which is slightly lower than that of Example 1, and the total intrinsic viscosity was 1.38, which was low from the beginning. The same propylene/ethylene block copolymer was produced and pelletized through an extruder without adding any organic peroxide, and its physical properties were measured in the same manner as in Example 1.

The results are shown in Table 1. Comparative Example 2 The same propylene-ethylene copolymer as in Example 1 was used except that the intrinsic viscosity of the copolymerized part was low at 3.10 and the total intrinsic viscosity was slightly high at 2.31. In the same manner as above, an organic peroxide was added and the mixture was passed through an extruder to obtain pellets.

The intrinsic viscosity of this pellet was 1.35.

A test piece was prepared in the same manner, and various physical properties were measured.

The results are shown in Table 1. Comparative Example 3 The intrinsic viscosity of the copolymerized part is 3.05, which is the same as Comparative Example 2.
In addition, the overall intrinsic viscosity was as low as 1.36 from the beginning, as in Comparative Example 2. In the case of the propylene-ethylene copolymer, which was otherwise the same as in Comparative Example 1, the organic peroxide was Pelletization and molding were performed without adding any additives, and various physical properties were measured.

The results are shown in Table 1.

From the results of the above Examples 1 to Comparative Examples 3, the copolymer of Example 1 produced by the method of the present invention has a low viscosity from the beginning and is compared to the copolymers of Comparative Examples 1 and 3 that are not treated with peroxide. It can be seen that the impact strength and tensile elongation at the weld area are significantly superior.

In addition, compared to the copolymer of Comparative Example 2, which was treated with peroxide using a copolymer with a low intrinsic viscosity in the copolymerization part, impact resistance, weld elongation, and especially surface gloss were significantly improved. I can see that it is being done.

Example 2 The ratio of the propylene polymerization part to the ethylene/propylene copolymerization part, the ethylene content, etc. are the same as in Example 1, and the copolymerization part has an intrinsic viscosity of 6.0 and the total intrinsic viscosity is 1.80. Add 0.085% of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane as an organic peroxide to the block copolymer powder and add 0% of the antioxidant BHT.
．． Add 1%. The mixture was melt-kneaded in an extruder at 230°C to form pellets, and test pieces were molded in the same manner as in Example 1 to measure various physical properties.

The results are shown in Table 1.

Comparative Example 4 A propylene-ethylene copolymer powder with the same ethylene content as in Example 2 except that the overall intrinsic viscosity was low from the beginning at 1.12 and the intrinsic viscosity of the copolymerized part was slightly high at 6.1 was used as an organic powder. Pelletization was performed using an extruder without adding peroxide, and specimens were molded to measure various physical properties.

The results are shown in Table 1. Comparing the results of Example 2 and Comparative Example 4, the copolymer of Example 2 obtained by the method of the present invention has higher impact strength and weldability than the copolymer of Comparative Example 4 which is not treated with organic peroxide. It can be seen that the tensile elongation is significantly superior.

Example 3 The intrinsic viscosity of the copolymerized part is 13.0, and the total intrinsic viscosity is 4.0.
0, 93 parts of propylene/ethylene block copolymer having the same characteristics as in Example 1 and commercially available ethylene/propylene rubber (Mooney viscosity 60, ethylene content 79% by weight)
0.05% of organic peroxide 2,5-dimethyl-2,5-di;(t-butylperoxy)hexane and 0.1% of BHT were added to the mixture with 7 parts of 2.5-dimethyl-2,5-di;(t-butylperoxy)hexane. The mixture was melt-kneaded to obtain pellets.

Its intrinsic viscosity was 2.40.

The pellets were injection molded to prepare test pieces, and various physical properties were measured.

The results are shown in Table 1.

Comparative Example 5 Except for the lower overall intrinsic viscosity of 2.43 from the beginning, the intrinsic viscosity of the copolymerized part is slightly lower at 12.8 than in Example 3, but the other ethylene contents are the same. A mixture of 93 parts of pyrene-ethylene block copolymer and 7 parts of the same ethylene-propylene rubber used in Example 3 was pelletized using an extruder without adding organic peroxide, and test pieces were made by injection molding and various physical properties were determined. I measured it.

The results are shown in Table 1. Comparative Example 6 Except for the low intrinsic viscosity of the copolymerized portion of 3.6, the overall intrinsic viscosity was 3.90, which is slightly lower than that of the copolymer of Example 3, but the other ethylene content etc. were the same as that of Example 3. To 93 parts of the same propylene/ethylene block copolymer were added 7 parts of the same ethylene rubber used in Example 3, and in the same manner as in Example 3, peroxide was added and pelletized by extrusion.

The intrinsic viscosity of the pellets was 2.41.

This was injection molded to make predetermined test pieces and various physical properties were measured.

The results are shown in Table 1. Comparative Example 7 The intrinsic viscosity from the beginning was 2.42, which is almost the same value as the copolymer of Comparative Example 5, and the intrinsic viscosity of the copolymerized part was 3.58, which is slightly lower than that of Comparative Example 6, and the other ethylene contents etc., a mixture of 93 parts of the same propylene/ethylene block copolymer as the block copolymer of Example 3 and 7 parts of the ethylene/propylene rubber used in Example 3 was mixed with organic peroxide in the same manner as in Comparative Example 5. Pelletized by passing through an extruder without adding.

This was passed through an injection molding machine to make a test piece, and various physical properties were measured. The results are shown in Table 1.

Comparing the results of Example 3 and Comparative Examples 5 to 7, the improved block copolymer of the present invention has a lower impact than Comparative Example 5 and Comparative Example 7, which have the same intrinsic viscosity without peroxide treatment. It can be seen that the strength (especially Izod impact strength at low temperatures) and the tensile elongation at the weld area are significantly improved.

It can also be seen that even after peroxide treatment, impact resistance, weld area elongation, and gloss are significantly improved compared to the copolymer of Comparative Example 6, which has a low intrinsic viscosity in the copolymerized portion.

Claims (1)

[Claims] 1 The ethylene content of the entire polymer is 5 to 15% by weight, and the ethylene content of the ethylene/propylene copolymer part is 50% by weight.
A propylene/ethylene block copolymer containing ~80% by weight and an intrinsic viscosity of the copolymerized portion of 4 to 15 is mixed with 0.005 to 0.2% by weight of an organic peroxide based on the copolymer. A method for modifying a propylene/ethylene block copolymer, which comprises melt-kneading at 180 to 300°C.