JP2002079622A - Multilayered sheet and container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayered sheet and a container excellent in the balance between moldability and strength, even if a low molecular weight component is controlled small, and reduced in offensive smell. SOLUTION: The multilayered sheet and the container excellent in the balance between moldability and strength and reduced in offensive smell is obtained by providing at least one layer based on a styrenic resin of which the methanol soluble component is within a specific range as the outermost layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer sheet and a container which are excellent in balance between moldability and strength and have low odor.

[0002]

2. Description of the Related Art Styrene resins are widely used because they are inexpensive and have excellent properties such as moldability and rigidity. Particularly, in recent years, it has been used in a large amount in a sheet field such as a foamed sheet, utilizing excellent foaming characteristics and sheet processability. However, recently, when a styrene-based resin sheet is put to practical use as a food container, problems such as the transfer of low molecular weight components to food and the problem of odor upon opening have been pointed out. To solve these problems, JP-A-2000-9
5888 describes an example in which the content of styrene dimer and styrene trimer is reduced, but there is a problem that if the low molecular weight components such as styrene dimer and styrene trimer are reduced, the moldability and strength are reduced.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a multilayer sheet and container excellent in balance between moldability and strength and low in odor even when a low molecular weight component is controlled to be small.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, even when the low molecular weight component is reduced, the styrene-based compound having a methanol-soluble content within a specific range is used. The present inventors have found that a multilayer sheet and a container having at least one outermost layer mainly composed of a resin have excellent moldability, excellent balance of strength, and low odor, and have completed the present invention.

That is, according to the present invention, the styrene monomer
00 ppm or less, a total of 1300 ppm or less of styrene dimer and styrene trimer, and at least one outermost layer mainly composed of a styrene resin having a methanol-soluble content of 0.5 to 3% by mass. The present invention relates to a multilayer sheet and a container characterized by the following.

Hereinafter, the present invention will be described in detail. The styrenic resin in the present invention is obtained by polymerizing a styrenic monomer such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and is preferably styrene. The styrenic monomers can be used alone or as a mixture. Further, monomers other than styrene monomers such as acrylonitrile, (meth) acrylic acid, and (meth) acrylate copolymerizable with these styrene monomers do not impair the performance of the styrene resin. To the extent, that is, 5 parts by mass or less based on 100 parts by mass of the styrene-based monomer, it may be added and polymerized. Further, in the present invention, a polymer obtained by adding less than 1 part by mass of a crosslinking agent such as divinylbenzene to 100 parts by mass of the styrene monomer may be used.

The styrene resin in the present invention may be a high impact polystyrene obtained by dissolving butadiene rubber or styrene-butadiene rubber in a styrene monomer and polymerizing the same.

The method of polymerizing the styrene monomer is not particularly limited, and a known method can be employed, but a radical polymerization method using an organic polymerization initiator is preferable. In addition, known methods such as suspension polymerization, bulk polymerization, solution polymerization, and emulsion polymerization can be adopted, and a continuous system or a batch system may be used.

The organic polymerization initiator preferably has an one-hour half-life temperature of 70 to 150 ° C., for example, benzoyl peroxide, azoisobutylnitrile, t-butylperoxybenzoate, 1,1-bis ( t-butylperoxy) -3,3,5-trimethylcyclohexane, t
-Butyl peroxyisopropyl carbonate, dicumyl peroxide, t-butyl peroxyacetate,
t-butyl peroxy-2-ethylhexanoate and the like. The polymerization temperature is preferably 90 ° C. or lower until the conversion exceeds 95%.

The styrenic monomer remaining in the styrenic resin in the present invention is 300 ppm or less, preferably 2 ppm or less.
It is 50 ppm or less, more preferably 200 ppm or less. If the styrene-based monomer exceeds 300 ppm, the odor becomes inferior and the possibility of transfer to food increases, which is not preferable. The amount of the styrene-based monomer can be adjusted by the type, the added amount, and the temperature of the organic polymerization initiator. It can also be adjusted by devolatilization conditions such as the degree of vacuum or water devolatilization.

The total amount of the styrene dimer and styrene trimer contained in the styrene resin in the present invention is 1300.
ppm or less, preferably 1200 ppm or less, more preferably 1100 ppm or less. If the total of the dimer and the styrene trimer exceeds 1300 ppm, the odor becomes inferior and the possibility of transfer to food becomes high, which is not preferable. The adjustment of the total amount of the dimer and the styrene trimer can be adjusted by the type and the amount of the organic polymerization initiator, the temperature and the like. It can also be adjusted by devolatilization conditions such as the degree of vacuum or water devolatilization.

In the present invention, the styrene dimer refers to 2,4-diphenyl-1-butene and 1,2-diphenylcyclobutane. Styrene trimer refers to 1-phenyl-4- (1′-phenylethyl) and 2,4,6-triphenyl-1-hexene.

In the present invention, the methanol-soluble content of the styrenic resin is 0.5 to 3% by mass, preferably 0.55 to 2% by mass.
%, More preferably 0.6 to 1.5% by mass. If the methanol soluble content is less than 0.5% by mass or 3
If the amount is more than mass%, the moldability and the strength will be reduced. The methanol-soluble matter can be adjusted by adding mineral oil or the like.

The weight average molecular weight (Mw) of the styrene resin in the present invention is preferably from 280,000 to 600,000, more preferably from 300,000 to 500,000. If Mw is less than 280,000, the strength is inferior, and if it exceeds 600,000, the moldability decreases. The number average molecular weight (Mn) is preferably at least 80,000, more preferably at least 100,000. If it is less than 80,000, the strength is inferior. The ratio between the Z average molecular weight (Mz) and the weight average molecular weight (Mw) is preferably Mz / Mw =
It is 1.8-3.5, more preferably 2.0-3.0. If the ratio is less than 1.8 or exceeds 3.5, the strength is inferior.

The styrenic resin of the present invention may optionally contain higher fatty acids, higher fatty acid salts, higher fatty acid amides, mineral oils, antioxidants, weathering agents, antistatic agents, flame retardants, sliding agents, foaming agents, foaming agents, Known additives such as auxiliaries may be added.

The multilayer sheet of the present invention has at least one outermost layer mainly composed of a styrene resin. The layer mainly composed of a styrene-based resin may be in the form of a foam or a film, but is preferably a foam. As long as there is at least one outermost layer mainly composed of a styrene resin, the other layers are not particularly limited, and known layers can be employed. The thickness is not particularly limited, but is preferably 0.1 to 10 mm as a multilayer sheet.

Known methods can be used for the method of manufacturing the multilayer sheet. For example, a method of manufacturing using a multilayer sheet extruder provided with a feed block, a method of fusing a film to a sheet manufactured by a sheet extruder or the like, and the like can be adopted.

The multilayer sheet is formed into a container by molding such that a layer mainly composed of a styrene resin is located inside the container. The method of molding is not particularly limited, and vacuum molding, compressed air molding and the like can be adopted.

[0019]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. First, the evaluation method in the present invention will be described below.

Measurement of Styrene-Based Monomer in Styrene-Based Resin 500 mg of styrene-based resin was dissolved in 10 ml of DMF containing cyclopentane as an internal standard substance, and the measurement was performed using a gas chromatography GC12A manufactured by Shimadzu Corporation.

Measurement of styrene dimer and styrene trimer in styrene resin. After dissolving 200 mg of the styrene-based resin in 2 ml of 1,2-dichloromethane and adding 2 ml of methanol to precipitate the styrene-based resin, and allowing it to stand, the supernatant was subjected to gas chromatography HP-5890 manufactured by Hewlett-Packard Company. It measured using. The detailed conditions are described below. (A) Column: DB-1 (ht) 0.25 mm × 30
m Film thickness 0.1 mm (b) Injection temperature: 250 ° C (c) Column temperature: 100-300 ° C (2) Detector temperature: 300 ° C (e) Split ratio: 50/1 (f) Internal standard substance: n -Eikosan

The methanol-soluble matter The styrene resin (Pg) whose mass was measured was dissolved in methyl ethyl ketone, and the solution was added to methyl ethyl ketone in 30 g.
The mixture was poured into twice the volume of methanol to precipitate methanol-insoluble components, and filtered to remove the methanol-insoluble components.
C., dried at 1.3 kPa (abs) for 15 hours, cooled in a desiccator for 20 minutes, and the mass of the dried precipitate was measured (Ng) and determined by the following formula. MS (%) = (P−N) / P × 100

Molecular weight and weight average molecular weight The molecular weight and the weight average molecular weight were measured under the following conditions using HLC-802A type gel permeation chromatography (GPC) manufactured by Tosoh Corporation. (B) Column: Tosoh Corporation column (b) Mobile phase: tetrahydrofuran (c) Sample concentration: 0.3% by weight (d) Measurement temperature: 38 ° C (e) Detector: differential refractometer

Formability: The multilayer sheet is heated in an oven at 170 ° C. for 25 seconds, and has a diameter of 110 mm and a depth of 121 mm.
A bowl-shaped container was molded. At this time, molding was performed so that the styrene resin was on the inside. The molded container was judged according to the following criteria.・ ・ ・: Good appearance △: Cracks generated or thin side walls ×: Perforated or non-container

Strength: The container obtained in the above was compressed from the bottom at a speed of 400 mm / min using a Tensilon measuring machine,
The strength at the time when the container buckled was indicated.

Odor: The container obtained in [1] was covered with aluminum foil, heated at 40 ° C. for 30 minutes, and then smelled when the lid was opened. ○ ・ ・ ・ No odor is felt △ ・ ・ ・ Slight odor is felt × ・ ・ ・ Smell is strongly felt

Example 1 100 kg of pure water, 400 g of tertiary calcium phosphate were placed in an autoclave equipped with a 200 L content jacket and a stirrer.
10 g of sodium dodecylbenzenesulfonate was added and stirred at 130 rpm. Then styrene 80k
g, 240 g of mineral oil (white oil) and 400 g of t-butylperoxy-2-ethyl-hexanoate,
80 g of dicumyl peroxide was charged, the autoclave was closed, and the temperature was raised to 60 ° C. After the polymerization was carried out while the temperature was raised from 60 ° C. to 90 ° C. over 12 hours, the temperature was raised to 120 ° C. for 2 hours, and further raised to 135 ° C. and held for 2 hours to complete the polymerization. The conversion was 98% when the temperature was raised from 60 ° C. to 90 ° C. over 12 hours while polymerizing. After the obtained beads were washed, dehydrated and dried, they were subjected to a pressure of 1.3 kPa (a) at a temperature of 210 ° C. using a single screw extruder.
Extrusion was carried out while degassing in bs) to obtain a pellet-shaped styrene resin. Using 100 parts by mass of the styrene resin, 0.05 parts by mass of talc as a nucleating agent and 3 parts by mass of butane gas as a foaming agent were used.
A double foam sheet was obtained. Further, a high-impact polystyrene E641N manufactured by Toyo Styrene Co., Ltd. was laminated with an extruder equipped with a T-die while extruding a 150 μm-thick film to obtain a multilayer sheet. Table 1 shows the evaluation results of the obtained multilayer sheet.

Example 2 The procedure of Example 1 was repeated, except that the polymerization was carried out while increasing the temperature from 60 ° C. to 90 ° C. over 15 hours. Table 1 shows the evaluation results of the obtained multilayer sheet.

Example 3 The procedure of Example 1 was repeated except that 200 g of t-butylperoxy-2-ethyl-hexanoate was used for polymerization. Table 1 shows the evaluation results of the obtained multilayer sheet.

Example 4 The temperature was raised from 60 ° C. to 90 ° C. in one hour,
The procedure was carried out in the same manner as in Example 1 except that the polymerization was carried out by holding at 0 ° C. for 11 hours. Table 1 shows the evaluation results of the obtained multilayer sheet.

Example 5 The procedure of Example 1 was repeated except that 480 g of mineral oil was used for polymerization. Table 1 shows the evaluation results of the obtained multilayer sheet.

Comparative Example 1 The procedure of Example 1 was repeated except that dicumyl peroxide was not charged. Table 2 shows the evaluation results of the obtained multilayer sheet.

Comparative Example 2 The procedure of Example 1 was repeated, except that the polymerization was carried out using 80 g of t-butylperoxy-2-ethyl-hexanoate.
Table 2 shows the evaluation results of the obtained multilayer sheet.

Comparative Example 3 The temperature was raised from 60 ° C. to 90 ° C. in one hour,
The procedure was performed in the same manner as in Example 1 except that the temperature was raised to 120 ° C. at 0.5 ° C./min without holding at 0 ° C., maintained at 120 ° C. for 2 hours, and further raised to 135 ° C. and maintained for 2 hours. Was.
Table 2 shows the evaluation results of the obtained multilayer sheet.

Comparative Example 4 The same operation as in Example 1 was carried out except that no mineral oil was charged. Table 2 shows the evaluation results of the obtained multilayer sheet.

Comparative Example 5 The procedure of Example 1 was repeated except that the polymerization was carried out using 2.6 kg of mineral oil. Table 2 shows the evaluation results of the obtained multilayer sheet.

[0037]

[Table 1]

[0038]

[Table 2]

As shown in Tables 1 and 2, the multilayer sheets and containers obtained in Comparative Examples have a large total amount of styrene dimer and trimer, and have a high possibility of being transferred to foods, or have a high possibility of molding. It can be seen that any of the properties, strength and odor are inferior.

[0040]

As described above, the multilayer sheet and the container of the present invention have an excellent balance of moldability and strength, have a low odor, and are optimal for food containers and the like, even when the low molecular weight component is controlled to be small. .

Continued on front page F term (reference) 3E033 BA22 BB01 BB04 BB08 CA03 CA08 4F100 AC10 AK12 AK12A AT00B BA02 BA07 CA01 DJ01A EH17 EH23 GB16 JC00 JL02 YY00A

Claims (3)

[Claims] (1) a styrenic monomer is 300 ppm or less;
Total of styrene dimer and styrene trimer is 1300p
pm or less and at least one outermost layer mainly composed of a styrene resin having a methanol-soluble content of 0.5 to 3% by mass. 2. The multilayer sheet according to claim 1, wherein the layer mainly composed of a styrene resin is a foam. 3. A container formed by molding the multilayer sheet according to claim 1 or 2, wherein a layer mainly composed of a styrene resin is inside the container.