JPH1143567A - Polystyrene-based resin composition and molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition, having antimicrobial properties, excellent in transparency and useful as a part, a container, etc., in a refrigerator or a laminating film, etc., for food packaging or an expanded tray by including a specific antimicrobial agent in a polystyrene-based resin. SOLUTION: This composition is obtained by uniformly premixing, e.g. a styrene-based monomer with a copolymerizable compound, copolymerizing the resultant mixture at 140-200 deg.C polymerizing temperature until the final conversion rate attains >=60 wt.% and recovering the unreacted monomer and uniformly mixing the resultant polystyrene-based resin with 0.005-1 wt.% antimicrobial agent having 1.5-1.7 refractive index (especially -0.05 to +0.10 based on the refractive index of the polystyrene-based resin) and <=5 μm weight-average particle diameter (an inorganic antimicrobial agent obtained by supporting silver, copper and zinc, etc., having antimicrobial effects in combination thereon) and kneading the resultant mixture at about 200 deg.C with a granulator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polystyrene resin composition having antibacterial properties and excellent transparency, and a molded article comprising the resin composition.

[0002]

2. Description of the Related Art Polystyrene resins, especially general-purpose polystyrene (GPPS) containing no rubber component, are widely used in various molding applications because of their rigidity and excellent transparency. In the field of injection molding, it is used in various fields related to refrigerator interior parts, containers and miscellaneous goods. In the field of extrusion molding, it is widely used as a film for laminating food packaging and foam trays. Injection molded products and films made using such polystyrene,
Since there are so many uses that come into direct contact with foods, regulations on the resin itself are also set based on the Food Sanitation Law. In recent years, food poisoning accidents observed in O-157 have been reported one after another, and interest in hygiene has been increasing, and attempts have been made to impart antibacterial properties to injection molded articles and films that are in direct contact with food. .

As an attempt to meet such demands, there has been proposed a method of applying or vapor-depositing an antibacterial agent to an injection-molded product or film. However, these methods require additional antibacterial treatment after molding, which is troublesome and not economical in terms of cost. In order to save such labor, Japanese Patent Publication No. 63-54013 discloses a method in which an antibacterial agent is mixed into a resin to impart bactericidal properties to the resin itself. However, in the method disclosed in this patent, the transparency of the resin is hindered by the addition of an antibacterial agent, and the resulting resin composition is not suitable for applications that require transparency in particular.

[0004]

In such a situation,
The problem to be solved by the present invention is to provide a polystyrene resin composition having antibacterial properties and excellent transparency, and a molded article comprising the resin composition.

[0005]

According to a first aspect of the present invention, an antibacterial agent having a refractive index of 1.5 to 1.7 and a weight average particle diameter of 5 μm or less is contained at 0.005 to 1% by weight. It relates to a characteristic polystyrene resin composition. In the second aspect of the present invention, the antimicrobial agent has a refractive index of 1.
The present invention relates to the polystyrene resin composition of the first invention, which is 55 to 1.70. The third invention of the present invention is the polystyrene resin according to the first invention, wherein the refractive index of the antibacterial agent is in the range of -0.05 to +0.10 with respect to the refractive index of the polystyrene resin. The present invention relates to a resin composition. The fourth invention of the present invention relates to a molded article comprising the polystyrene resin composition of the first invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
Examples of the styrene-based monomer of the polystyrene-based resin used in the present invention include nucleus-substituted alkylstyrenes such as styrene, α-methylstyrene, and p-methylstyrene. The polystyrene resin used in the present invention is generally obtained by radical polymerization of the above styrene monomer. A styrene-only polymer (GPPS) has a refractive index of 1.5
It is around 9.

In the polystyrene resin used in the present invention, a copolymerizable compound such as acrylonitrile, together with the styrene monomer during polymerization, is used.
Methacrylonitrile, methacrylic acid, ester derivatives such as methyl methacrylate, maleic anhydride, maleimide, nucleus-substituted maleimide, etc. may be used in combination.However, when the ratio increases, the refractive index greatly differs from that of GPPS. When the antibacterial agent used in the present invention is added, transparency may be poor. The polystyrene-based resin used in the present invention preferably has a weight average molecular weight of 100,000 to 2,000,000, preferably 100,000 to 500,000.

The antimicrobial agent used in the present invention has a refractive index of 1.
5 to 1.7, preferably 1.55 to 1.70, and -0.00 to the refractive index value of the polystyrene resin.
It is preferably in the range of 5 to +0.10. If the refractive index of the antimicrobial agent is too small or too large, the injection molded article or film obtained from the polystyrene resin composition containing the antibacterial agent becomes cloudy and has poor appearance and transparency. The antibacterial agent used in the present invention has a weight average particle diameter of 5 μm.
It is as follows. If the weight average particle size of the antibacterial agent is too large, the surface of the obtained injection-molded product or film becomes rough, and the appearance and the transparency are also inferior. The refractive index of the antibacterial agent is measured, for example, by the following method. That is,
The antimicrobial agent is dispersed in a solution having a known refractive index, sandwiched by a glass slide, observed with a polarizing microscope, and determined by comparing with the refractive index of the solution.For details, for example,
It is described in the book "How to Use a Polarizing Microscope" (by Kenya Hamano, Gihodo). The weight average particle size of the antibacterial agent is, for example,
It is measured by the following method. That is, it is a method of dispersing particles in an appropriate medium and determining by measuring the change in particle concentration when light is transmitted.
For example, it is described in the book "Powder Properties Illustration" (powder engineering research society, edited by Japan Powder Industry Association, Industrial Technology Center, 1975). In addition, it can be measured by the following method. That is, a transmission electron micrograph of an ultrathin section of an injection molded product or film is taken, and the particle size of the antibacterial agent in the photograph is measured. The weight average particle size is calculated by the following equation. Weight average particle diameter = ΣniDi ² / ΣniDi where ni is the number of particles having a particle diameter Di. The particle size of the antibacterial agent is the length of one side when the antibacterial agent is a cuboid, the length of the long side when the antibacterial agent is a cuboid,
When it is spherical, it refers to its diameter, and when it is elliptical, it refers to the length of its major axis.

The amount of the antibacterial agent used in the present invention is 0.00
It is 5 to 1% by weight, preferably 0.005 to 0.5% by weight. If the amount is too small, the antibacterial properties of the injection-molded article or film molded using the obtained resin composition are inferior. If the amount is too large, the surface of the injection-molded article or film becomes rough. Poor in appearance and transparency.

The antibacterial agent used in the present invention refers to an inorganic antibacterial agent carried in combination with silver, copper, zinc and the like having an antibacterial effect. For example, zeolite solid particles, silver,
It can be produced by carrying ions of a metal selected from copper or zinc by an ion exchange method. As an example, a method for producing an antibacterial agent carrying silver ions is described below. An aqueous solution of silver nitrate is added to the dried fine powder of zeolite, and ion exchange is performed while stirring and maintaining the mixture at room temperature. Next, the silver-zeolite obtained by the ion exchange is filtered and washed with water to remove excess silver ions. Thereafter, the silver-zeolite is dried and pulverized to obtain an antibacterial agent having a desired particle size. Note that zeolite is generally an aluminosilicate having a three-dimensionally developed skeletal structure.

[0011] The polystyrene resin used in the present invention can be produced by a batch suspension polymerization or a continuous bulk polymerization method. For example, it can be suitably manufactured by the following method. That is, the styrene monomer and the copolymerizable compound are uniformly mixed in advance, and the mixture is continuously supplied to the polymerization tank. Polymerization temperature 140-200
At 200C, the polymerization is carried out until the final conversion is 60% by weight or more, and the unreacted monomer is recovered by passing the polymerization mixture through a vacuum degassing tank at 200 to 280C. The polystyrene-based resin thus obtained and the antibacterial agent are uniformly mixed at a specific ratio, and kneaded at about 200 ° C. with a granulator to obtain a target polystyrene-based resin composition.

The polystyrene resin composition of the present invention comprises:
If necessary, a lubricant, an antistatic agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, and the like may be added, and, as long as the effects of the present invention are not impaired, using a plasticizer such as a mineral oil. Is also good.

The method for forming the polystyrene resin composition of the present invention into an injection molded article is not particularly limited. For example, a resin temperature of 210 ° C., an injection rate of 100 cm ³ / sec, and
Molding can be performed at an injection pressure of 400 kg / cm ² and a mold temperature of 50 ° C. The method for forming the polystyrene resin composition of the present invention into a film is not particularly limited.
The polystyrene resin composition of the present invention is passed through a screw heated to 60 ° C. to 230 ° C., and while the molten resin extruded into a tube from an extruder equipped with a circular die is taken up in the vertical direction, immediately expanded by air pressure and folded. With a thickness of 100 with a diameter larger than the diameter of the die
A method for producing a cylindrical film having a size of μm or less can be given. Furthermore, the film after the inflation processing may be stretched 2 to 5 times in the TD direction (direction perpendicular to the winding direction) at 100 to 150 ° C. to form a biaxially stretched film.

[0014]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In addition, among the evaluation methods, the items other than the items described above were implemented as follows. (1) Transparency (Haze) As an index of transparency, haze (Haze) was used. J
Haze was measured with a direct-reading Haze meter (manufactured by Suga Test Instruments Co., Ltd.) in accordance with IS K7105. (2) Antibacterial test Based on the film adhesion method determined by the Silver and Other Inorganic Antibacterial Agents Study Group, it was measured by the following method. First, a normal broth medium (N
B medium) was diluted 500-fold with sterile purified water and adjusted to pH 7.0.
Test bacteria (Escherichia coli IFO-3972 or Staphylococcus aureus IFO-12732) pre-cultured in 1 / 500NB medium adjusted to ± 0.2
Is uniformly dispersed to obtain a bacterial solution for inoculation. Next, on the test piece, 0.5 ml of the inoculum bacterial solution prepared by the above method was used.
(In the case of Escherichia coli, the number of bacteria is 4.6 × 10 ⁵ , in the case of Staphylococcus aureus, the number of bacteria is 8.6 × 10 ⁵ ). save. Thereafter, the bacteria adhering to the film are sufficiently washed out in a Petri dish using SCDLP medium (10 ml), and the number of viable bacteria in 1 ml of the washed liquid is measured by an agar plate culture method. When the residual bacterial count when tested using the antimicrobial-containing resin composition is 2 or more logarithmically smaller than the residual bacterial count when tested using the antimicrobial-free resin composition, It is determined that there is sex.

Examples 1 and 2 and Comparative Examples 1 to 4 Pellets of polystyrene (manufactured by Nippon Polystyrene Co., Ltd., trade name "Nippon Polysty" G757X, melt flow rate 1.8) obtained by a continuous bulk polymerization method Antibacterial agents having a refractive index and a weight average particle size described in Tables 1 and 2 are uniformly mixed in proportions shown in Tables 1 and 2,
The mixture was re-granulated at 200 ° C. with a granulator and kneaded completely. Using the obtained polystyrene-based resin composition, a resin temperature of 210 ° C. and an injection rate of 100 cm ³ / sec were measured using a PS40E5ASE non-vent injection molding machine manufactured by Nissei Plastic Industry Co., Ltd.
c, A 50 mm × 90 mm × 2.5 mmt flat plate was injection molded at an injection pressure of 400 kg / cm ² and a mold temperature of 50 ° C. Transparency (HAZE) and antibacterial tests were performed using test pieces cut out from the injection molded flat plate to a size of 50 mm square. The conditions and results are shown in Tables 1 and 2.

The following can be understood from the results. All examples satisfying the conditions of the present invention show excellent results in transparency and antibacterial properties. On the other hand, Comparative Example 1 in which the addition amount of the antibacterial agent is too small is inferior in antibacterial properties. Comparative Example 2 with an excessive amount of antibacterial agent
Is inferior in transparency. Comparative Example 3, in which the weight average particle size of the antibacterial agent is excessively large, is excellent in antibacterial properties, but inferior in transparency, and has a poor surface state of the obtained injection molded product. Comparative Example 4, in which the refractive index of the antibacterial agent is extremely lower than that of polystyrene, which is 1.59, has excellent antibacterial properties but extremely poor transparency.

[0017]

[Table 1]

[0018]

[Table 2]

The polystyrene resin composition of the present invention is
Excellent antibacterial properties while maintaining a satisfactory level of transparency.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08J 5/00 CET C08J 5/00 CET

Claims (4)

[Claims] (1) a refractive index of 1.5 to 1.7, and a weight average particle size of 5;
A polystyrene-based resin composition containing 0.005 to 1% by weight of an antimicrobial agent having a particle size of μm or less. 2. The polystyrene resin composition according to claim 1, wherein the antibacterial agent has a refractive index of 1.55 to 1.70. 3. The polystyrene resin composition according to claim 1, wherein the refractive index of the antibacterial agent is in the range of -0.05 to +0.10 with respect to the refractive index of the polystyrene resin. 4. A molded article comprising the polystyrene resin composition according to claim 1.