JPH0649336B2 - Method for thermoforming styrenic polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for thermoforming a styrene-based polymer, and more particularly to a method for thermoforming a belt-shaped member containing a styrene-based polymer having a syndiotactic structure as a main component. .

[Problems to be Solved by Prior Art and Invention]

In general, styrene polymers, particularly polystyrene, having an atactic structure produced by radical polymerization are used and are widely used as films and sheets in food packaging, miscellaneous goods packaging, industrial materials, and the like. However, the products obtained from polystyrene having an atactic structure of stereoregularity have the drawbacks of poor heat resistance, chemical resistance, and mechanical strength, so that their fields of use have been limited.

On the other hand, the group of the present inventor conducted research to solve the above drawbacks, and succeeded in developing a styrene polymer having a syndiotactic structure (Japanese Patent Laid-Open No. 62-104818). .

However, this styrene-based polymer having a syndiotactic structure (hereinafter sometimes abbreviated as SPS).
Because of its characteristic of having a crystalline structure, it is unavoidable that the extrusion temperature be higher than that of a general styrene-based polymer, and when the produced belt-shaped member such as a film or sheet is thermoformed into a container or the like. There were various problems in the equipment and conditions such as large drawdown and defective molding phenomenon.

Therefore, in order to solve the above-mentioned problems, the present inventor has conducted various studies on various practical conditions for a specific manufacturing apparatus, and has conducted earnest studies to develop an efficient thermoforming method.

As a result, they have found that a band-shaped member such as a film or sheet containing SPS as a main component is heated under a specific condition to perform pressure molding, whereby a molded product having excellent physical properties can be efficiently manufactured. The present invention has been completed based on such findings.

[Means for Solving the Problems]

That is, in the present invention, a belt-shaped member containing a styrene-based polymer having a syndiotactic structure as a main component is heated by bringing it into contact with a heating surface heated to a temperature 11 ° C lower than the glass transition temperature or melting point of the belt-shaped member. The present invention also provides a method for thermoforming a styrene-based polymer, which is characterized in that it is thereafter pressure-molded.

In the present invention, a styrene polymer (SPS) having a syndiotactic structure is used as a main constituent of the material. Here, the syndiotactic structure in the styrene-based polymer having the syndiotactic structure,
The stereochemical structure is a syndiotactic structure, that is, it has a stereostructure in which a phenyl group or a substituted phenyl group, which is a side chain with respect to the main chain formed from carbon-carbon bonds, is alternately located in opposite directions. Tacticity is quantified by a nuclear magnetic resonance method ( ¹³ C-NMR method) using isotope carbon. ^The tacticity measured by ¹³ C-NMR method is the existence ratio of a plurality of continuous structural units, for example, 2
The number of styrene-based polymers having a syndiotactic structure referred to in the present invention is usually a racemic diad of 75. % Or more, preferably 85% or more, or 30% with racemic pentad
Above, preferably polystyrene having a syndiotacticity of 50% or more, poly (alkylstyrene), poly (halogenated styrene), poly (alkoxystyrene),
It refers to poly (vinyl benzoate), hydrogenated polymers thereof and mixtures thereof, or copolymers containing these as the main components. Here, as poly (alkylstyrene), poly (methylstyrene), poly (ethylstyrene), poly (isopropylstyrene), poly (tertiarybutylstyrene), poly (phenylstyrene), poly (phenylstyrene),
(Vinylnaphthalene), poly (vinylstyrene), and the like, and poly (halogenated styrene) includes poly (chlorostyrene), poly (bromostyrene), poly (fluorostyrene), and the like. Further, examples of poly (halogenated alkyl styrene) include poly (chloromethyl styrene). Further, as poly (alkoxystyrene),
(Methoxystyrene), poly (ethoxystyrene), etc. Further, as the comonomer component of the copolymer containing these structural units, in addition to the above-mentioned styrene-based polymer monomers, olefin monomers such as ethylene, propylene, butene, hexene, and octene, diene monomers such as butadiene and isoprene, and cyclic compounds. Olefin monomer, cyclic diene monomer, methyl methacrylate, maleic anhydride,
Examples include polar vinyl monomers such as acrylonitrile.

Among these, particularly preferable styrene-based polymers include polystyrene, poly (alkylstyrene), and poly (alkylstyrene).
(Halogenated styrene), hydrogenated polystyrene and copolymers containing these structural units.

A styrene-based polymer having such a syndiotactic structure can be obtained, for example, by using a titanium compound and a condensation product of water and a trialkylaluminum as a catalyst in an inert hydrocarbon solvent or in the absence of a solvent to form a styrene-based monomer. It can be produced by polymerizing the polymer (monomer corresponding to the above styrene-based polymer) (JP-A-62-18770).
No. 80). Further, poly (halogenated alkylstyrene) can be obtained by the method described in JP-A-1-46912, and these hydrogenated polymers can be obtained by the method described in JP-A-1-178505.

The styrene polymer is not particularly limited in molecular weight, but has a weight average molecular weight of 100,000 or more, preferably 30
It is more than 0,000. Further, the molecular weight distribution is not limited in width and width, and various kinds can be applied.

In the method of the present invention, the SPS is further added with a commonly used amorphous thermoplastic resin, rubber, inorganic filler,
Antioxidants, plasticizers, compatibilizers, colorants, nucleating agents, etc. can be added.

In the present invention, when thermoforming such a band-shaped member containing SPS as a main component, first, the band-shaped member is heated by directly contacting the surface (heating surface) heated to a predetermined temperature. The heating temperature at this time is 11 ° C lower than the glass transition temperature (Tg) to melting point (Tm) of the belt-shaped member (Tm-11 ° C), preferably (Tg + 10 ° C) to (Tg + 100 ° C).

When the heating temperature at this time is less than Tg, it is difficult to perform molding sufficiently, and good mold reproducibility cannot be obtained. Further, if it exceeds (Tm-11 ° C), a ridge may be generated, or the material may adhere to the heating surface.

Further, by making the heating surface a flat plate or a drum surface, it is possible to reduce the occurrence of wrinkles during heating, as compared with a surface having another shape. Further, the heating surface may be provided with small holes at predetermined intervals. That is, by providing such a small hole and connecting to a vacuum pump or the like and sucking the strip-shaped member from the back side of the heating surface, the strip-shaped member and the heating surface can be more surely brought into close contact with each other, and heating efficiency is improved. Can be made. There are no particular restrictions on the shape and arrangement of these small holes, but the small hole diameter is 0.3 to 1.0 mm, and the small hole arrangement interval is 5 mm.
It is preferably within a range of up to 50 mm, and it is preferable to arrange them at regular intervals.

Next, the band-shaped member heated by contacting with the heating surface as described above is pressure-molded using a mold having a desired shape. As the molding apparatus used at this time, a molding apparatus which has been generally used can be used as it is. Pressurization can be performed by appropriately combining a plug and vacuum, compressed air, or vacuum compressed air, and can be similarly performed even when there is no plug.

By heating by directly contacting the heating surface in this manner, it is possible to almost completely prevent drawdown, which is a problem in indirect heating using a heater or the like.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Reference Example (Production of Styrene Polymer) Toluene 2 as a solvent, 5 mmol of tetraethoxytitanium as a catalyst component and 500 mmol of methylaluminoxane as an aluminum atom were added to a reaction vessel, and styrene 15 was added thereto at 50 ° C. The polymerization reaction was carried out for a time.

After completion of the reaction, the product was cleaned with a hydrochloric acid-methanol mixed solution to decompose and remove the catalyst component. Then, it was dried to obtain 2.5 kg of a styrene polymer (polystyrene). Next, this polymer was subjected to Soxhlet extraction using methyl ethyl ketone as a solvent to obtain an extraction residue of 95% by weight. The weight average molecular weight of this product was 800,000. In addition, from the analysis by ¹³ C-NMR measurement using 1,2-dichlorobenzene as a solvent,
Absorption was observed at 143.35 ppm due to the syndiotactic structure, and the syndiotacticity in racemic pentad calculated from the peak area was 96%. The polystyrene thus obtained was added with bis (2,4-di-butylphenyl) pentaerythritol diphosphite and tetrakis [methylene (3,5-di-butyl-hydroxyhydrocinnamate)] methane as antioxidants. 0.1 part by weight of each was mixed and extruded by a twin-screw extruder having a diameter of 40 mm to form pellets.

The melting temperature (T) of the obtained styrene polymer (SPS)
m) was 270 ° C and the glass transition temperature (Tg) was 100 ° C.

Example 1 The SPS obtained in the above reference example was subjected to 2 at 120 to 150 ° C.
After drying for ~ 5 hours, a single screw extruder with a diameter of 30 mm (L / D = 26) was used as an extruder and the extrusion rate was 6.9 kg / hour.
Extruder temperature distribution is 290 ℃ near the inlet, 300 in the middle part
Width 170 ° C, tip 310 ° C, T-die 310 ° C
A strip-shaped member (sheet) having a thickness of 0.3 mm and a thickness of 0.3 mm was extruded and rapidly cooled with a cooling roll at a temperature of 60 ° C. The crystallinity of this product was 20%, and the thickness unevenness was + 3%.

Then, this sheet was heated by direct heating by bringing a flat plate having small holes of 0.5 mm at 15 mm intervals into contact with a hot plate heated to 120 ° C. (Tg + 20 ° C.). Next, a container was molded with a molding machine using a mold having an opening of 100 × 50 mm and a depth of 40 mm under a pressure of 3 kg / cm ² .

Table 1 shows evaluation results of mold reproducibility, presence / absence of defective phenomenon and heat resistance of the obtained container.

Example 2 and Example 3 A container was molded in the same manner as in Example 1 except that the heating temperature of the hot plate and the pressure applied during molding were set to the conditions shown in Table 1. Table 1 shows evaluation results of mold reproducibility, presence / absence of defective phenomenon and heat resistance of the obtained container.

Comparative Example 1 and Comparative Example 2 Instead of SPS as the resin material, polystyrene (aPS) having a general atactic structure was used, and the heating temperature and pressure of the hot plate were set to the conditions shown in Table 1, respectively. The container was molded in the same manner as in Example 1. Table 1 shows evaluation results of mold reproducibility, presence / absence of defective phenomenon and heat resistance of the obtained container.

Comparative Example 3 A container was molded in the same manner as in Example 1 except that the heating temperature of the hot plate and the pressure applied during molding were set to the conditions shown in Table 1. Table 1 shows evaluation results of mold reproducibility, presence / absence of defective phenomenon and heat resistance of the obtained container.

Comparative Example 4 A container was formed in the same manner as in Example 3 except that the sheet was heated by indirect heating with a heater without using a hot plate. Table 1 shows evaluation results of mold reproducibility, presence / absence of defective phenomenon and heat resistance of the obtained container.

[Effects of the Invention] As described above, according to the method of the present invention, a molded article having excellent heat resistance, chemical resistance, and mechanical strength can be efficiently manufactured at low cost.

The molded product manufactured in this manner is effectively used as a packaging material for various products including foods and industrial materials.

Claims (4)

[Claims] 1. A strip-shaped member containing a styrene-based polymer having a syndiotactic structure as a main component is brought into contact with a heating surface heated to a temperature 11 ° C. lower than the glass transition temperature or melting point of the strip-shaped member and heated. A method for thermoforming a styrene-based polymer, which comprises press-molding after that. 2. The thermoforming method according to claim 1, wherein the heating surface is a flat plate. 3. The thermoforming method according to claim 2, wherein the heating surface is provided with small holes at regular intervals. 4. The thermoforming method according to claim 1, wherein the heating surface is a drum surface.