JP2000053116A - Resin for food container, and resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a sanitary food container by providing a resin for forming the container and its resin composition so as to obtain the food container in which the color of a food is not transferred to the container, that is, the food pollution resistance is excellent. SOLUTION: A food container excellent in food pollution resistance can be manufactured by using a highly crystalline polypropylene of not less than 96% in isotactic pentad index. When a phosphoric antioxidant is added to the polypropylene or polycarbonate, the container manufactured therefrom is improved in food pollution resistance. In particular, the composition in which the phosphoric antioxidant is blended in the highly crystalline polypropylene further improves the food pollution resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a resin and a resin composition suitable for producing a food container having excellent resistance to food contamination.

[0002]

2. Description of the Related Art Plastics can be sterilized at high temperatures due to their heat resistance, can be easily molded into various shapes and desired designs because of their excellent moldability, and are not easily broken due to their high mechanical strength. It is widely used as a resin for food containers at present because of its characteristics such as being able to be provided at low cost.

[0003] However, plastic containers also have the disadvantage that the color of the food is easily transferred or stained with the color of the food at the same time, so that the container with the color of the food is not hygienic. Therefore, the work of washing the used container requires a lot of trouble and care, so that it is difficult to machine.

[0004]

Therefore, the present inventor has proposed:
A review of a series of manufacturing processes from the raw material to the molding method to improve the food contamination of plastic containers resulted in finding a resin and a resin composition for food containers with excellent food contamination resistance. Was. The food contamination resistance is
After placing the actual coloring material on the food container and leaving it for a certain period of time, it can be determined by examining the presence or absence of coloring.

[0005]

That is, the present invention relates to a resin for a food container characterized by using a highly crystalline polypropylene having an isotactic pentad fraction of 97% or more. In the present invention, a phosphorus-based antioxidant is added to 100 parts by weight of polypropylene or polycarbonate.
The present invention relates to a resin composition for food containers, which is contained in an amount of from 0.01 to 1 part by weight. In particular, the use of a highly crystalline polypropylene having an isotactic pentad fraction of 96% or more as the polypropylene is more preferable as a resin composition for food containers.

[0006]

Next, the present invention will be described in detail. Resins that can be used in the production of food containers in the present invention are polypropylene and polycarbonate. As the polypropylene, propylene homopolymer, propylene and an α-olefin having 2 to 20 carbon atoms, for example, ethylene, butene-
1, random copolymers of pentene-1, hexene-1, 4-methyl-pentene-1, octene-1, decene-1 or the like, or block copolymers of propylene and the α-olefin having 2 to 20 carbon atoms. It is a polymer.

The polycarbonate is, for example, a thermoplastic resin having a carbonate bond in the main chain, which is produced by using a dihydroxy compound such as bisphenol A as a raw material and reacting it with phosgene or the like.

Among these resins, a propylene homopolymer, a propylene random copolymer having an ethylene content of 0.1 to 5% by weight, and a propylene block copolymer having an ethylene content of 3 to 20% by weight have high heat resistance. Therefore, when molded into a food container, high-temperature sterilization necessary for hygiene becomes possible.
Among them, polypropylene having a stereoregularity (isotacticity) of 95% or more is preferable from the viewpoint of mechanical strength because it has high rigidity as well as heat resistance.
In particular, the propylene random copolymer and block copolymer obtained by copolymerizing a small amount of ethylene are high in heat resistance as well as impact resistance and surface hardness. As excellent. Polycarbonate resin is also preferable as a resin for food containers because it has excellent heat resistance and impact resistance.

A more preferred polypropylene as a resin for food containers is a so-called highly crystalline polypropylene having an isotactic pentad fraction of 97% or more, preferably 98% or more. Here, the isotactic pentad fraction was measured using ¹³ C-NMR,
It is a ratio of isotactic chains in pentad units in a polypropylene molecular chain, and indicates a fraction of propylene monomer units at the center of a chain in which five propylene monomer units are successively meso-bonded. Specifically, ¹³ C-
It is a value obtained as a mmmm peak fraction in all absorption peaks in the methyl carbon region of the NMR spectrum.

Here, the fact that the isotactic pentad fraction has the above-mentioned value means that the polypropylene is a highly crystalline material, and because of its regular crystal structure, special additives are specially required at the time of molding. Without adding, an excellent food stain resistance in addition to high mechanical strength and heat resistance can be obtained. Of course, an additive such as an antioxidant may be appropriately added according to a request from molding conditions or use conditions, or according to a use.

Further, the above-mentioned highly crystalline polypropylene is
More preferably, it has a broad molecular weight distribution. In general,
The values of Mw / Mn and Mz / Mw as indices of the molecular weight distribution were determined by gel permeation chromatography (GP
It is a value calculated from the weight average molecular weight (Mw), number average molecular weight (Mn), and Z average molecular weight (Mz) measured by C). The index value of this molecular weight distribution is Mw /
Mn is 5 or more, preferably 10 or more, and Mz / Mw
Is 3 or more, preferably 4 to 5 means that the polypropylene has a broad molecular weight distribution on the high molecular weight side, excellent moldability, and a resin having high mechanical strength for producing food containers. Become.

The GPC can be measured, for example, by attaching a column (PL mixed B) manufactured by Polymer Laboratories to a Model 150C manufactured by Waters and using o-dichlorobenzene as a solvent at 135 ° C. In calculating the molecular weight, a calibration curve prepared with standard polystyrene can be used.

The highly crystalline polypropylene may be a homopolymer of propylene or a small amount of, for example, 3% by weight or less of an α-olefin such as ethylene or 1-butene. Such a crystalline polypropylene is, for example, a Ziegler-Natta catalyst mainly composed of titanium trichloride and an alkylaluminum compound, or a magnesium compound used as a carrier, or a third component such as an electron donor is added. It can be produced by polymerizing propylene under ordinary polymerization conditions in the presence of a composite catalyst, if necessary, together with another α-olefin. Also, a small amount of another polymer may be mixed and used in the high crystalline polypropylene.

[0014] Since these polypropylenes or polycarbonates are usually formed into the shape of a food container by adopting the injection molding method, the melt flow rate of the polypropylene is 1.0 to 150 (g / 10
Min), preferably 5 to 50 (g / 10 min) (ASTM D
(Measured at 230 ° C. under a load of 2.16 kg) according to No. 1238) in order to increase the molding cycle and maintain excellent mechanical strength.

When a phosphorus-based antioxidant is added to polypropylene or polycarbonate to improve the food container's resistance to food contamination, the effect can be further enhanced. The chemical structure of the phosphorus-based antioxidant that enhances the resistance to food contamination is not particularly limited, but the following compounds are suitable.

1) Triphenyl phosphite 2) Triisooctyl phosphite 3) Trilauryl phosphite 4) Trinonyl phenyl phosphite 5) Trioctadecyl phosphite 6) Tris (2,4-di-tert-butyl phenyl phosphite) 7) trilauryl dithiophosphite 8) trilauryl trithiophosphite 9) distearyl pentaerythritol diphosphite

10) Bis (2,4-di-tertiary)
Butylphenyl) pentaerythritol diphosphite 11) bis (2,6-di-tert-butyl-4-)
Methylphenyl) pentaerthritol di-phosphite 12) 2-[[2,4,8,10-tetrakis (1,1-dimethylethyl) dibenzo [d, f] [1,3,2] dioxaphos Phethyn-6-yl] oxy] -N, N-bis [2-[[2,4,8,10-tetrakis (1,1-dimethylmethyl)] benzo [d, f]
[1,3,2] dioxaphosphen-6-yl] oxy] -ethyl] ethanamine

Of these compounds, the use of tris (2,4-di-tert-butylphenyl phosphite) and bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite is particularly preferred. The phosphorus-based antioxidant is used in an amount of 0.1 to 100 parts by weight of polypropylene or polycarbonate.
It is added in an amount of 0.01 to 1 part by weight, preferably 0.05 to 0.8 part by weight. If the amount is within this range, the effect of food contamination resistance can be sufficiently exerted. In particular, it is desirable to mix this phosphorus-based antioxidant with the above-mentioned highly crystalline polypropylene, since a high food stain resistance can be obtained.

Prior to molding a food container from these resin compositions, various additives can be blended with polypropylene or polycarbonate without departing from the object of the present invention. For the purpose of enhancing the food contamination resistance of food containers, it is sufficient to add the above-mentioned phosphorus-based antioxidant, but the phenol-based antioxidant generally used to prevent oxidation of the resin at the time of molding or at the time of use is sufficient. And a sulfur-based antioxidant can be added and blended.

The resin composition may contain a filler, for example, up to 50 parts by weight of barium sulfate, talc, mica or calcium carbonate per 100 parts by weight of polypropylene or polycarbonate. Within this range, the rigidity and heat resistance can be increased without increasing the specific gravity too much and without decreasing the surface hardness. In addition, additives such as a hydrochloric acid absorbent, a slip agent, an antistatic agent, a weather stabilizer, and a pigment can be blended.

The above resin composition is uniformly mixed using a mixing device such as a Henschel mixer, an extruder, a Banbury mixer and the like, and then molded into a desired food container shape using an injection molding machine. The molding conditions can be changed in a wide range. When polypropylene is used, for example, molding can be performed at a cylinder temperature of an injection molding machine of 200 ° C., an injection pressure of 600 kg / cm ² , and a mold temperature of 40 ° C.

Next, the present invention will be described through examples and comparative examples, but the present invention is not limited to the examples. (Example 1) Polypropylene (MFR 10 g / 10 min,
Density 0.91 g / cm ³ , isotactic pentad fraction 96%) 100 parts by weight, 0.1 parts by weight of Irgafos 168 which is a phosphorus-based antioxidant, 360.1 parts by weight of PEP which is also a phosphorus-based antioxidant Parts and 0.05 parts by weight of calcium stearate as a neutralizing agent. The resin temperature is 200 ° C and the injection pressure is 600kg / c.
Injection molding was performed under the conditions of m ² to form a dish-shaped container. This container was subjected to a food contamination resistance test, and the results are shown in Table 1.

Comparative Example 1 0.1 parts by weight of Irganox 1010 as a phenolic antioxidant, 0.1 parts by weight of DSTP as a sulfuric antioxidant, and 0 parts by weight of calcium stearate were added to the polypropylene used in Example 1 0.05 parts by weight, and injection-molded in the same manner as in Example 1 to obtain a dish-shaped container. Table 1 also shows the results of the food stain resistance test.

Example 2 Highly crystalline polypropylene (M
FR 10 g / 10 min, density 0.91 g / cm ³ , isotactic pentad fraction 98.6%), 100 parts by weight, 0.2 parts by weight of Irganox 1010, DSTP
0.15 parts by weight and calcium stearate 0.0
5 parts by weight were blended and injection-molded in the same manner as in Example 1,
A dish-shaped container was obtained. Table 1 also shows the results of the food stain resistance test.

Example 3 The polypropylene described in Example 2 was further added to Irgafos 16 which is a phosphorus antioxidant.
8 0.1 parts by weight of PE, also a phosphorus antioxidant
Performed in the same manner as in Example 1 except that 0.1 part by weight of P36 and 0.05 part by weight of calcium stearate were added,
A dish-shaped container was obtained by injection molding. A food stain resistance test was performed, and the results are shown in Table 1.

Comparative Example 2 Irganox 10100.02 was added to 100 parts by weight of the polypropylene used in Example 1.
Parts by weight, 0.15 parts by weight of DSTP, and 0.05 parts by weight of calcium stearate were blended and injection-molded in the same manner as in Example 1 to obtain a dish-shaped container. Table 1 also shows the results of the food stain resistance test.

In the food contamination resistance test, Chinese cabbage, kimchi, orange, and ginseng were each put on a polypropylene dish in a fixed amount in separate dishes, kept at 80 ° C. for 24 hours, and then the food was removed. Washed. The coloring of the dishes with these foods was examined visually and by microscopic observation. In Table 1, ○ is not colored, Δ is slightly colored,
X shows that there is coloring.

[0028]

[Table 1]

In Table 1, IP represents the isotactic pentad fraction in%. The antioxidants used in Examples and Comparative Examples are the following compounds. (1) Phenolic antioxidant: Irganox 101
0; tetrakis (methylene-3 (3,5-di-tert-leafyl-4-human-peroxyphenyl) fluorodionate) methane (2) Sulfur-based antioxidant: DSTP; Agent (A): Irgafos 168;
Tris (2,4-di-tert-butylphenyl) phosphite (4) Phosphorus antioxidant (B): PEP36; bis (2,6-
(Tert-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphite

[0030]

According to the present invention, since highly crystalline polypropylene is used as a resin for a food container, the color of the food does not shift to the food container manufactured therefrom, and a sanitary container can be obtained. In addition, this highly crystalline polypropylene has high heat resistance, excellent mechanical strength, and is particularly resistant to scratches due to its high surface hardness, and is suitable for manufacturing a wide range of food containers.

Further, in the present invention, a resin composition for a food container is prepared by mixing a phosphorus-based antioxidant with polypropylene or polycarbonate. Was not transferred, and a hygienic food container could be obtained. In particular, it was found that when a phosphorus-based antioxidant was added to the highly crystalline polypropylene, the food stain resistance was further improved, and a clean and hygienic food container could be provided.

Claims (3)

[Claims] An isotactic pentad fraction of 97%.
A resin for a food container, wherein the highly crystalline polypropylene is used. 2. Polypropylene or polycarbonate 1
A resin composition for food containers, wherein 0.01 to 1 part by weight of a phosphorus-based antioxidant is added to 00 parts by weight. 3. An isotactic pentad fraction of 97%.
A resin composition for food containers, comprising 0.01 to 1 part by weight of a phosphorus-based antioxidant with respect to 100 parts by weight of the above highly crystalline polypropylene.