JPS6046009B2 - Biaxially oriented styrene-butadiene copolymer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxially oriented styrene-putadiene copolymer film that has a high stretching ratio and stable elongation rate and is excellent in various physical properties after stretching.

In recent years, biaxially oriented polystyrene films have attracted attention as packaging films, and the demand for them is rapidly expanding.

However, the commonly used polystyrene films do not necessarily have satisfactory performance as a raw material resin for biaxial stretching, and the development of further improved biaxially stretched films using resins with excellent performance. was required.

Generally, the condition required for thermoplastic resins used in biaxially stretched films is that they have excellent tensile stretching properties at the temperature at which the resin is stretched (in the case of styrene resins, in the range of 800 to 160°C). .

However, it is not enough just to be able to stretch to a high magnification, but in consideration of its use as a packaging film, the physical properties of the film obtained by stretching to a high magnification, such as tensile strength, tear strength, and impact strength, are significantly improved. What is important is that it has been improved. Conventionally, improved radically polymerized polystyrenes with large average molecular weights have been provided in order to obtain styrenic resins suitable for biaxial stretching, but even with these, biaxially stretched polystyrene films with satisfactory physical properties have not been produced. I couldn't get it. A styrene-butadiene copolymer has also been proposed in which the brittleness of styrene is improved by copolymerizing styrene with butadiene, but a copolymer with satisfactory properties after biaxial stretching has not been obtained. As a result of research on styrene-putadiene copolymer resin suitable for biaxial stretching, the present inventors found that the monomer ratio of styrene and putadiene is not just a block copolymer, but that the monomer ratio of styrene and putadiene is Using a block copolymer with a continuously changing tapered structure, Mw/Mn (weight average molecular weight/
It was discovered that films with a small molecular weight (number average molecular weight), particularly films of 2.0 or less, are superior in stretching ratio as well as physical and physical properties of stretched films, and in order to complete the present invention. I've reached it.

That is, the present invention provides a film with excellent physical properties obtained by biaxially stretching a styrene-butadiene tapered copolymer having a sharp molecular weight distribution with Mw/straightness of 2.0 or less. It is.

The styrene-butadiene tapered block copolymer according to the present invention is Mi/? A film having a value of 2.0 or less has extremely excellent stretching properties, and has a wide range of applications, such as a high stretching ratio over a wide temperature range, a uniform film thickness distribution, and little uneven thickness.

The present invention will be explained in detail below.

The styrene-butadiene copolymer in the present invention is composed of styrene or α-methylstyrene and butadiene, has a styrene or α-methylstyrene content of 5% by weight or more, and has a tapered block structure. be.

The tapered block structure is a block structure in which the composition ratio of each monomer unit of styrene and butadiene changes continuously along the polymer chain. 53-41
6).

Such a tapered block structure is contrasted with a clear cut structure in which the proportion of each monomer unit changes rapidly along the polymer chain. That is, even if the monomer ratio and degree of polymerization are the same, the tapered block copolymer is significantly different from the clear cut structure in its physical properties. Styrene-butadiene tapered block copolymer. To synthesize a union,
Usually, after a portion of styrene or butadiene is charged to complete the polymerization, a mixture of styrene monomer and butadiene monomer is charged to continue the polymerization reaction.

In this way, butadiene with higher polymerization activity will be polymerized first! Finally, a book consisting of a single monomer of styrene is formed. For example, first, styrene is homopolymerized, and after the polymerization is completed, a mixture of styrene monomer and butadiene monomer is charged and the polymerization is continued. Polymer sites are formed and a tapered block copolymer can be obtained. When polymerizing the styrene-butadiene copolymer having an Aura of 2.0 or less according to the present invention, an anionic polymerization method is preferable.

In other words, it is a polymerization method that uses an alkali metal or an organic alkali metal compound as a polymerization initiator.The most commonly used alkali metal or its organic compound is an organic lithium compound, followed by an organic sodium compound. has been done. According to the anionic polymerization method, it is possible to synthesize materials whose Mj/Mj ratio is almost close to 1.0. The present invention will be specifically explained below with reference to Examples.

Example 1 Synthesis of styrene-butadiene tapered block copolymer Purified in a 150e reaction vessel dried in a nitrogen stream.
Charge dry benzene 100e.

Next, 8k9 of dried and deoxidized styrene monomer was charged, and 10y of n-butyllithium was added at 30°C with stirring.
Insert. Polymerization started immediately and the temperature reached 57°C.
Next, a mixture of 8k9 dried and deoxidized styrene monomer and 4 kg of butadiene was charged, and polymerization was carried out at 65°C. When the polymer was collected using a crumb former and dried, a block copolymer with a tapered structure was obtained. The average molecular weight and elongation rate of this block copolymer were measured and shown in Table 1.

Furthermore, the stretching performance as a biaxially stretched resin is shown in Table 1.
In addition, =, elongation rate, and maximum stretching rate were measured by the following method.

M? measurement method Measured by light scattering method.

Measurements are made at four points between the solvent cyclohexane, room temperature 25°C, wavelength 436μ, and concentration 0.05 to 0.2 Da/100ml, and extrapolation to the concentration 0.

Nagi's measurement method Measured by light scattering method.

Solvent toluene, temperature 37°C, concentration 0.2y-0.8y/
Measure 4 points between 100 mL of solvent and extrapolate to a concentration of 0.

How to measure elongation rate Measured according to JISK687l.

The film was pulled at a speed of 50 wn/min. Measuring method for maximum stretch ratio The maximum stretch ratio that does not cause film tearing when stretched at a stretching speed of 5 m/min after preheating for 2 minutes using a biaxial stretch measuring machine.

Production of biaxially oriented styrene-butadiene tapered block copolymer film 90W1.17nφ L/D=29
The film raw material was extruded using a general vented extruder.

The vacuum degree of the ventro is 30T0rr, the cylinder temperature is 160~2000C1, the die temperature is 175~195
I did it at ℃. The lip width of the die is 275m. 1771.
The screw rotation speed is 30 to 80 r'. P. m
I drove. After the extruded film passed through a casting roll at 70°C, it was first stretched by a longitudinal stretching roll for 10
It was stretched 3 times at a temperature of 5° C. and subsequently stretched 3 times transversely at a temperature of 115° C. using a tenter. The stretched film was fixed in its stretching by heat treatment with a width of 130 cm and 108', and then wound up with a take-up roll. The physical properties of the obtained film were measured and the results are shown in Table 1.

In the following tests, tensile strength was determined by JISK6732, elongation (%) was determined by JISK6732, Elmendorf tear was determined by JISK6732, and Tartt impact strength was determined by ASTM D17O9, a weight was dropped from a height of 10 cm, and each sample was tested 100 times. The weight of the weight that causes 50% destruction was determined by repeating the steps above and expressed in y-Cm.

Comparative Example 1 Using the same equipment as in Example 1, dehydrated and purified benzene 100' and dehydrated and purified styrene monomer 8k9 were charged, and then 11.5f of n-methyllithium was added at 300C with stirring. Polymerized.

After completion of heavy duty, 4kg of purified butadiene was added, and 60
] was polymerized. Then purified styrene monomer 8k9
was charged and polymerized at 65°C. Recovery of the polymer and performance evaluation as a film were carried out in the same manner as in Example 1.
The results are shown in Table 1 together with Example 1.

Claims (1)

[Claims] 1 Biaxially stretched styrene-butadiene copolymer having a molecular weight distribution (@Mw@/@Mn@) of 2.0 or less, having a dart impact strength of 600 g cm or more, and having a dart impact strength of 600 g cm or more. A styrene-butadiene copolymer film characterized in that the polymer has a tapered block structure in which the composition ratio of each monomer unit of styrene and butadiene changes continuously along the polymer chain.