JPH0925355A - Heat-resistant foamed container for food - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foamed resin container which has a smooth molded surface and an improved brittleness and sufficiently withstands heating in a microwave oven. SOLUTION: This container has a density of 0.03-0.5g/cc and is obtd. from a styrene-methacrylic acid compolymer which is formed from 90-96wt.% styrene and 10-4wt.% methacrylic acid and has a wt. average mol.wt. (Mr) measured by differential angular refractometric detection by gel permeation chromatography(GPC) of 200,000-400,000 in terms of linear s tandard polystyrene, an absolute wt. average mol.wt. (Mabs) measured by Rayleigh small-angle scattering method of 240,000-800,000, and a ratio of Mabs/Mr of 1.2-2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a container having sufficient heat resistance so that it can be cooked in a microwave oven.

[0002]

2. Description of the Related Art Foams are used for instant ramen, miso soup containers, etc. due to their heat retention. In this case, since the material is polystyrene, if the content temperature is continued at 100 ° C. for 1 minute or more, the container is often softened and deformed. From this point of view, the polystyrene foam is not suitable for heating food containing water in a microwave oven, such as rice or side food.

As a microwave oven that can withstand heating,
Foams of polypropylene and modified PPO have been investigated, but they are not suitable for heat insulation containers because the foam container has a low stiffness and has a problem of odor. In addition, polypropylene is mixed with inorganic flakes for sheeting,
Although a molded heat-resistant container is on the market, it is inconvenient to handle when heated in a microwave oven because the container is heated.

Further, a container molded from a foamed sheet of styrene-methacrylic acid copolymer has excellent heat resistance, but since a usual container is brittle, it is improved by adding a thermoplastic elastomer. Thermal stability is not sufficient and there is a problem in terms of unit price.

[0005]

To provide a structure of a resin foam container having a smooth molded surface, improved brittleness, and capable of sufficiently withstanding heating in a microwave oven, and a foam container having excellent heat resistance. is there.

[0006]

The present invention is directed to styrene 90.
A styrene-methacrylic acid-based copolymer composed of ˜96 wt% and methacrylic acid 10-4 wt%, which is directly measured by a differential angle refractive index detection method by gel permeation chromatography (hereinafter referred to as GPC). The weight average molecular weight (hereinafter referred to as Mr) based on the chain standard polystyrene is 200,000 or more and 400,000 or less, and the absolute weight average molecular weight (hereinafter referred to as Mabs) measured by the Rayleigh small angle scattering method is 240,000 to 80.
And Mabs / Mr is 1.2 or more and 2 or less,
A foamed food container having a density of 0.03 g to 0.5 g / cc.

A styrene-methacrylic acid type copolymer comprising 90 to 96% by weight of styrene and 10 to 4% by weight of methacrylic acid, which is measured by a differential angle refractive index detection method by GPC, based on a linear standard polystyrene. Having a weight average molecular weight Mr of 200,000 to 400,000, and a glass transition temperature of 100 to 1 measured from tan δ obtained from dynamic viscoelastic behavior.
A foamed food container having two points of 10 ° C. and 120 to 130 ° C. and having a density of 0.03 g to 0.5 g / cc is preferable, and further, a molecular weight measured by the Rayleigh small angle scattering method. Mabs is 100,000 to 2,000,000, M
Abs / Mr is 1.2 or more and 2 or less, and the glass transition temperature measured from tan δ obtained from the dynamic viscoelastic behavior is 1
A foamed food container having two points of 00 to 110 ° C. and 120 to 130 ° C. and having a density of 0.03 g to 0.5 g / cc is preferable.

Further, styrene-methacrylic acid type copolymer 9
0 to 99% by weight and 1 to 10% by weight of a thermoplastic elastomer having at least one terminal composed of a styrene unit, and its density is 0.03 g to 0.
A foamed food container characterized by having 5 g / cc is preferable. Further, as a foamed food container of the styrene-methacrylic acid-based copolymer or the styrene-methacrylic acid-based copolymer and the thermoplastic elastomer resin composition in the present invention, the area of the parallel surfaces gradually increases from the opening surface to the bottom surface. The shape is reduced and has an edge on the opening surface, the ratio of the maximum opening diameter / depth is 0.4 to 1.5, and the ratio of the edge width / maximum opening diameter is 0.015 to 0. .09, and the ear thickness of 3 to 6 mm is more excellent in heat resistance, which is particularly convenient when the main container containing food is heated in a microwave oven.

The present invention will be described in more detail below. The present invention provides a container made of a foamed styrene-methacrylic acid copolymer having excellent heat resistance and improved brittleness and having a good surface texture. The styrene-methacrylic acid copolymer in the present invention is styrene 90-96.
% By weight, 10 to 4% by weight of methacrylic acid. If it exceeds 10% by weight, the resin itself is crosslinked due to a dehydration reaction due to heat during polymerization, and the appearance of the surface of the container is significantly deteriorated.
If it is less than 4% by weight, the heat resistance of the container is poor.

It is important that the styrene-methacrylic acid type copolymer has a weight average molecular weight Mr of 200,000 to 400,000 when formed into a molded product. When it is less than 200,000, the molded product becomes brittle, and when the container is held by hand, it may be broken. If it exceeds 400,000, it becomes difficult to control the operation during the production of the foam. The molecular weight Mabs measured by the Rayleigh small angle scattering method is 240,000 to 800,000.

The absolute weight average molecular weight Mabs measured by the Rayleigh small angle scattering method is different from the molecular weight obtained by the differential angle refractive index method and counts the number of constituent units in the polymer. Therefore, the polymer becomes larger due to the branched or syndiotactic structure, and Mabs / Mr
Is 1 or more. This can be confirmed by measuring the monodisperse polymer that has been pre-branched by anionic living polymerization.

The tan δ obtained from the dynamic viscoelastic behavior is obtained from the ratio of the storage elastic modulus to the loss elastic modulus,
The glass transition temperature measured from this tan δ is 100 to 1
It is preferable to have 2 points of 10 degreeC and 120-130 degreeC. When two distinct glass transition temperatures appear, the heat resistance and surface condition of the container are good. The reason why there are two glass transition temperatures is unknown, but it is considered that the styrene-methacrylic acid copolymer is partially blocked although it is not a perfect type. To be One point of the glass transition temperature is 100
It is preferably in the range of 110 ° C. When the glass transition temperature of the resin component constituting the container is lower than 100 ° C., the adhesive force at the ear of the container is too strong and the container is broken when peeled off, which is not preferable. On the other hand, if the temperature exceeds 110 ° C, the adhesive interface strength will be weak. The other glass transition temperature is 120 to 130 ° C.
Is preferred. This glass transition temperature is related to the heat resistance of the container. Therefore, it is preferable to adjust the balance of the glass transition temperature to 100 to 110 ° C and 120 ° C to 130 ° C.

In order to fully bring out the performance of this foam container, M of the styrene-methacrylic acid copolymer as the base material is used.
When abs / Mr is 1.1 to 2.0, the appearance is good,
It is preferably 1.2 or more and 2 or less, and more preferably 1.5 to 2.0. If this value is too close to 1, the foamed cell diameter becomes large and the foaming becomes uneven. Also, Ma
When the bs / Mr ratio of 1.1 to 2.0 is foamed with butane gas, the brittleness of the obtained sheet and the molded product obtained after the secondary molding is sufficiently improved without adding the thermoplastic elastomer. It On the other hand, when Mabs / Mr exceeds 2, intramolecular cross-linking occurs and gloss streaks and lumps are generated on the sheet or the molded product, resulting in poor appearance. In addition, the cell diameters of the foam become uneven, and the heat insulation of the foam decreases.

A thermoplastic elastomer may be mixed in order to improve the brittleness. 90 to 99% by weight of styrene-methacrylic acid-based copolymer, and thermoplastic elastomer 1
10% by weight is good. If the addition amount is less than 1% by weight, the effect of adding the elastomer is not sufficient, and if it is 10% by weight or more, the gas injection pressure is extremely increased during foam extrusion, resulting in poor foam stability. Specific examples of the thermoplastic elastomer include Tahprene 125, 126 or Tuftec 1081, manufactured by Asahi Kasei Kogyo Co., Ltd., manufactured by Nippon Synthetic Rubber Co., Ltd., T
R2000 etc. are mentioned.

Before making the container, the resin is passed through a circular die to make an expanded polystyrene sheet. At this time, the foaming viscosity of the resin containing the foaming agent may be too high or too low. The gas injection amount is preferably 4 to 5.5 parts by weight with respect to 100 parts by weight of the resin. When talc is used as the foam nucleating agent, the foaming efficiency is 0.8 to 1.0% by weight. The linear polymer, that is, the value of Mabs / Mr is 1.
When one having a size of 0 to 1.05 is used, the shape of the foamed cells becomes large and becomes uneven, so that the appearance of the molded product is deteriorated and the texture is bad. Further, if the skin layer existing on the foamed surface is too thick, the sheet and the molded product become brittle.

The density of the foam container of the present invention is 0.03 to 0.
5 g / cc is preferred. More preferably 0.08-0.
It is 3 g / cc. If the density exceeds 0.5 g / cc,
Poor heat insulation. When food is put in a container and heated in a microwave oven, if the density is higher than 0.5 g / cc, it is difficult to hold it with bare hands. If the density is less than 0.03 cc / g, the heat resistance of the molded product is poor and it is not practical.

The shape of the foamed resin container is such that the area of the parallel surface gradually decreases from the opening surface to the bottom surface, and the opening surface has ears, and the maximum opening diameter / depth ratio is 0.4 to 1. 5, and the ratio of the edge width / maximum opening diameter is 0.015 to 0.0
9. It is preferable that the foam container has the ear thickness of 3 to 6 mm. The maximum opening diameter / depth ratio is preferably 0.4 to 1.5.
If it is less than 0.5, it is difficult to hold the container with one hand and it is not suitable as a food container. If it exceeds 1.5, the heat resistance becomes poor, and it is particularly unsuitable as a container for heating in a microwave oven.

By attaching an ear to the container, heat resistance is improved. The ratio of edge width / maximum opening diameter is 0.015 to 0.
09 is preferable. More preferably 0.015 to 0.0
7, more preferably 0.02 to 0.05. Larger ears reduce thermal deformation, but on the other hand, increase the heat-sealing area and increase the force of peeling off the lid, which may destroy the container.

The thickness of the ear is preferably 3 to 6 mm. The thickness of the ear is a factor that increases heat resistance. If it is less than 3 mm, the deformation during heating in a microwave oven is remarkable, and if it exceeds 6 mm, it becomes brittle. Naho, maximum opening diameter is the maximum inner diameter of the container,
The depth is the distance from the opening surface to the lowest bottom surface. The shape of the container may be circular, oval, elliptical, quadrangular, polygonal or the like when viewed from the opening, but the area of the opening is larger than the area of the bottom. Specific examples include containers for instant noodles, hot water bowls, bonito bowls, parent and child bowls, catered lunch boxes, etc., or deep-draw containers for Oden-like items.

The method for polymerizing the styrene-methacrylic acid copolymer in the present invention is described in JP-A-6-279612.
As shown in Japanese Patent Publication No. 2,87,82.5% by weight of styrene, 9-3.5% by weight of methacrylic acid, and 14% by weight of ethylbenzene, 100 parts by weight of a polymerization solution is used for 2,2 bis (4,4,4). -Ditertiary butylperoxycyclohexyl propane It is produced by continuously charging a polymerization solution added in an amount of 0.01 to 0.03 part by weight into an integral type reactor.
The temperature of the inlet of the polymerization reactor is 130 ° C, the middle stage is 140 ° C, and the last stage is 155 ° C. At this time, the conversion rate of the monomer is 70.
-80%, then unreacted monomer was vacuum degassed. The weight average molecular weight was 300,000.

0.8-1 part by weight of a foam nucleating agent (talc) is mixed in a rotary mixer with respect to 99.2-99% by weight of the styrene-methacrylic acid type copolymer in the present invention. When the thermoplastic elastomer is mixed, it is advisable to carry out at the same time at this time. Furthermore, impregnating with a hydrocarbon having 3 to 5 carbon atoms,
The rotary cooler is set to 155 to 160 ° C. and the circular die is set to 145 to 155 ° C., and extrusion foaming is performed, and the sheet is adjusted so that the foaming density is 0.06 to 0.7 g / cc.

For the above-mentioned sheet, for example, a ceramic heater which is a heating plate is set at 350 ° C., and after heating for 4 to 10 seconds,
Secondary molding into a desired container with a match mold.

[0023]

EXAMPLES The evaluation methods used in the examples will be described. To evaluate the adhesion state of the heat-sealed surface of the container and the heat resistance in a microwave oven, heat-seal the mouth of the container as shown in FIG.
I peeled it off. The adhesive surface was observed. Next, after putting a solution of 80 parts of water, 18 parts of soy sauce, and 2 parts of salad oil in a 300 cc container and 30 g of dried noodles,
The container mouth is covered with Asahi Kasei Co., Ltd., trade name Saran Wrap, and after heating for 7 minutes with a Hitachi, Ltd., MRO-GT1 microwave oven, how the entire container is deformed depends on the opening diameter. When the degree of deformation h value, the diameter D ′ after heating, and the diameter D before heating were used, h value = D ′ / D was evaluated. In addition, it is visually determined whether the container can withstand practical use.

To evaluate the printability of the container, a wooden insert was put in the container, and an ink containing ethyl acetate as a solvent was added to the container (Xerox Co., Ltd., toner carbon 20% by weight, polystyrene resin 20% by weight, Solvent 60% by weight)
Is evenly applied to the surface of the rubber roll and transferred to the side surface of the molded product, and how the ink is applied is visually determined. The molecular weight is measured by the method described in Japanese Patent Application No. 5-278899. That is, a piece of a container was dissolved in a tetrahydrofuran solvent, a resin concentration was adjusted to 10 mg / 10 ml, talc was removed by centrifugation, and then a molecular weight Mr was measured by a differential angle refractive index method by GPC. At the same time, a Rayleigh small angle scattering method was performed. Absolute molecular weight Mabs is measured at to determine Mabs / Mr. HLC8020 manufactured by Tosoh Co., Ltd. is used as the measuring device body, and LS8000 manufactured by Tosoh Co., Ltd. is used as the absolute molecular weight measuring device.

To measure the glass transition temperature, a molded product is heated and compressed into a test piece, which is manufactured by Rheometrics RM.
The glass transition temperature is measured in S2500.

[0026]

Examples 1 to 4 and Comparative Examples 1 to 3 The monomer composition of the resin component was 93% by weight of styrene and 7% by weight of methacrylic acid, and the ratio of the edge width / maximum opening diameter (E value) shown in Table 1 was used. A container was made. The weight average molecular weight of the resin component of this container is 240,000, and the Mabs / Mr at a molecular weight of 100,000 to 1,000,000 is 1.2 to 1.8, and the glass transition temperature is 100 ° C.
5 ° C.

The evaluation results are shown in Table 1.

[0028]

[Table 1]

The ratio of the maximum opening diameter / depth is 0.4 to 1.5, and the ratio of the edge width / maximum opening diameter is

[0030]

Examples 5 to 7 and Comparative Examples 4 to 5 As the monomer composition of the resin component, 93% by weight of styrene and 7% by weight of methacrylic acid were used, and the maximum opening diameter / depth ratio (R value) and E shown in Table 2 were used.
Value containers were made. The resin component in this container has a weight average molecular weight of 240,000 and a molecular weight of 100,000 to 1,000,000.
Mr is 1.2 to 1.8, and the glass transition temperature is 100 ° C.
It was 125 ° C.

The evaluation results are shown in Table 2.

[0032]

[Table 2]

[0033]

Examples 8 to 10 and Comparative Examples 6 and 7 As for the monomer composition of the resin component, 93% by weight of styrene and 7% by weight of methacrylic acid were used, and Mabs / Mr was 1.68, which shows a relationship between the surface states. Table 3 shows the evaluation results.

[0034]

[Table 3]

[0035]

Examples 11 to 13 and Comparative Examples 8 and 9 As for the monomer composition of the resin component, 93% by weight of styrene and 7% by weight of methacrylic acid were used, and the R value was 0.7 and the E value was 0.04.
Mr is set to 1.68 and shows the relationship between the surface condition and the heat resistance in a microwave oven. Table 4 shows the evaluation results.

[0036]

[Table 4]

[0037]

EFFECTS OF THE INVENTION By using the container of the present invention, it is possible to obtain a heat-resistant container with little deformation even when heated in a microwave oven.

[Brief description of drawings]

FIG. 1 is a perspective view of a container used in an example.

[Explanation of symbols]

 D: Maximum opening diameter. L: Depth of the molded product. O: Ear width

Claims (5)

[Claims] 1. A styrene-methacrylic acid copolymer comprising 90 to 96% by weight of styrene and 10 to 4% by weight of methacrylic acid, which has a differential angle refractive index measured by gel permeation chromatography (hereinafter referred to as GPC). The weight average molecular weight (hereinafter referred to as Mr) based on the linear standard polystyrene of 200,000 or more and 400,000 or less measured by the detection method, and the absolute weight average molecular weight (hereinafter Ma
bs) is 240,000 to 800,000, and Mabs /
Mr is 1.2 or more and 2 or less, and its density is 0.03 g or more.
A foamed food container, which is 0.5 g / cc. 2. A styrene-methacrylic acid copolymer comprising 90 to 96% by weight of styrene and 10 to 4% by weight of methacrylic acid, which is a standard linear polystyrene measured by a differential angle refractive index detection method by GPC. The standard weight average molecular weight Mr is 200,000 or more and 400,000 or less, and the glass transition temperature measured from tan δ obtained from the dynamic viscoelastic behavior is 100 to
A foamed food container having two points of 110 ° C. and 120 to 130 ° C. and having a density of 0.03 g to 0.5 g / cc. 3. A styrene-methacrylic acid copolymer comprising 90 to 96% by weight of styrene and 10 to 4% by weight of methacrylic acid, which is a linear standard polystyrene measured by a differential angle refractive index detection method by GPC. The standard weight average molecular weight Mr is 200,000 or more and 400,000 or less, and the absolute weight average molecular weight Mabs measured by the Rayleigh small angle scattering method is 240,000 to 80.
And Mabs / Mr is 1.2 or more and 2 or less, and the glass transition temperature measured from tan δ obtained from the dynamic viscoelastic behavior is 100 to 110 ° C. and 120 to 130 ° C.
A foamed food container having points and having a density of 0.03 g to 0.5 g / cc. 4. The styrene-methacrylic acid copolymer according to claim 1, 2 or 3 and 90 to 99% by weight, and 1 to 10% by weight of a thermoplastic elastomer having at least one terminal composed of a styrene unit. A foamed food container comprising a resin composition and having a density of 0.03 g to 0.5 g / cc. 5. A shape of a foamed resin container having a parallel surface area gradually decreasing from an opening surface to a bottom surface and having an edge on the opening surface, and a maximum opening diameter / depth ratio of 0.4. ~ 1.
5, and the ratio of the edge width / maximum opening diameter is 0.015
A foam container having a thickness of 0.09 and an ear thickness of 3 to 6 mm. The density is 0.0, which is made of the styrene-methacrylic acid copolymer or the resin composition according to claim 1, 2, 3, or 4.
A foamed food container characterized in that it is 3 g to 0.5 g / cc.