JP5032718B2 - Multi-layer sheet and container - Google Patents

Description

【００３８】
【表２】

【００３９】
表１、２より、比較例で得られた多層シート及び容器は、スチレン２量体と３量体の合計量が多く、食品への移行の可能性が高いものであったり、成形性、強度、臭気の何れかが劣ることがわかる。
【００４０】
【発明の効果】
以上の通り、本発明の多層シート及び容器は低分子量成分を少なく制御した場合であっても、成形性、強度のバランスに優れ、かつ臭気が少なく、食品容器等に最適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer sheet and a container that are excellent in balance between moldability and strength and have little odor.
[0002]
[Prior art]
Styrenic 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 large quantities in the sheet field including foamed sheets, utilizing its excellent foaming properties and sheet processability. Recently, however, when a styrene resin sheet is put into practical use as a food container, problems have been pointed out that low molecular weight components are transferred to foods and odors at the time of opening. In order to deal with these problems, Japanese Patent Application Laid-Open No. 2000-95888 describes an example in which the content of styrene dimer and styrene trimer is reduced. However, there is a problem in that moldability and strength are reduced by reducing low molecular weight components. It was.
[0003]
[Problems to be solved by the invention]
The present invention relates to a multilayer sheet and a container that are excellent in moldability and strength balance and have little odor even when the amount of low molecular weight components is controlled to be small.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that at least one layer composed mainly of a rubber-modified styrenic resin having a low molecular weight component and a methanol-soluble content in a specific range is at least the outermost layer. The present inventors have found that the multilayer sheet and container having the layers are excellent in balance of moldability and strength and have little odor, and have completed the present invention.
[0005]
That is, the present invention provides a rubber-modified styrene resin having a styrene monomer of 500 ppm or less, a total of styrene dimer and styrene trimer of 2000 ppm or less, and a methanol-soluble content of 1.5 to 5% by mass. The present invention relates to a multilayer sheet and a container having at least one outermost layer.
[0006]
The present invention is described in detail below. The rubber-modified styrene resin in the present invention is obtained by dissolving butadiene rubber in a styrene monomer and polymerizing it. As the styrene monomer, known monomers such as styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, and p-methyl styrene can be used, and styrene is preferable. Styrenic monomers can be used alone or as a mixture. In addition, monomers other than styrenic monomers such as acrylonitrile, (meth) acrylic acid, (meth) acrylic acid ester and the like that can be copolymerized with these styrenic monomers can also improve the performance of rubber-modified styrenic resins. It may be added and polymerized as long as it is not impaired, that is, 5 parts by mass or less with respect to 100 parts by mass of the styrene monomer. Further, in the present invention, a crosslinking agent such as divinylbenzene may be polymerized by adding less than 1 part by mass to 100 parts by mass of the styrene monomer.
[0007]
The butadiene rubber used for the rubber-modified styrene resin in the present invention is not particularly limited as long as it is a known one. Further, styrene-butadiene rubber can be used in place of butadiene rubber or in part.
[0008]
There is no restriction | limiting in particular as a polymerization method of a styrene-type monomer, Although a well-known method is employable, The radical polymerization method using an organic type polymerization initiator is preferable. Moreover, well-known methods, such as suspension polymerization, block polymerization, solution polymerization, and emulsion polymerization, can be employed, and they may be continuous or batch-type.
[0009]
As the organic polymerization initiator, those having a one-hour half-life temperature of 70 to 150 ° C. are preferable. For example, benzoyl peroxide, azoisobutyl nitrile, t-butyl peroxybenzoate, 1,1-bis (t-butyl) Peroxy) -3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, and the like. The polymerization temperature is preferably 90 ° C. or less until the conversion rate exceeds 95%.
[0010]
The styrene monomer remaining in the rubber-modified styrene resin in the present invention is 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less. If the styrene monomer exceeds 500 ppm, the odor is inferior or the possibility of transfer to food is increased, which is not preferable. The amount of the styrenic monomer can be adjusted by the type, addition amount, temperature and the like of the organic polymerization initiator. Moreover, it can also adjust by devolatilization conditions, such as a vacuum degree, and water injection devolatilization.
[0011]
The total of the styrene dimer and styrene trimer contained in the rubber-modified styrene resin in the present invention is 2000 ppm or less, preferably 1800 ppm or less, more preferably 1600 ppm or less. When the total of the dimer and the styrene trimer exceeds 2000 ppm, the odor is inferior or the possibility of transfer to food is increased, which is not preferable. Adjustment of the total amount of a dimer and a styrene trimer can be adjusted by the kind, addition amount, temperature, etc. of an organic polymerization initiator. Moreover, it can also adjust by devolatilization conditions, such as a vacuum degree, and water injection devolatilization.
[0012]
The styrene dimer in the present invention refers to 2,4-diphenyl-1-butene and 1,2-diphenylcyclobutane. The styrene trimer refers to 1-phenyl-4- (1′-phenylethyl), 2,4,6-triphenyl-1-hexene.
[0013]
The methanol-soluble content of the rubber-modified styrene resin in the present invention is 1.5 to 5% by mass, preferably 2 to 4% by mass, and more preferably 2.5 to 3.5% by mass. If the methanol-soluble content is less than 1.5% by mass or exceeds 5% by mass, the moldability and strength are lowered. The methanol-soluble component can be adjusted by adding mineral oil or the like.
[0014]
The weight average molecular weight (Mw) of the rubber-modified styrene resin in the present invention is preferably 240,000 to 500,000, and more preferably 250,000 to 400,000. If the Mw is less than 240,000, the strength is inferior, and if it exceeds 600,000, the moldability is lowered. The number average molecular weight (Mn) is preferably 60,000 or more, more preferably 80,000 or more. If it is less than 60,000, the strength is inferior.
The rubber content of the rubber-modified styrene resin in the present invention is not particularly limited, but is preferably 3 to 15% by mass, more preferably 4 to 10% by mass.
[0015]
The rubber-modified styrenic resin of the present invention may contain known additives such as higher fatty acids, higher fatty acid salts, higher fatty acid amides, mineral oils, antioxidants, antifungal agents, antistatic agents, flame retardants, and sliding agents as required. It may be added.
[0016]
The multilayer sheet of the present invention has at least one outermost layer mainly composed of a rubber-modified styrene resin. The shape of the layer mainly composed of the rubber-modified styrenic resin may be a foam or a film, but is most preferably a film having a thickness of 10 to 1000 μm. If there is at least one layer mainly composed of a rubber-modified styrene resin, the other layers are not particularly limited and a known layer can be adopted, but a foamed sheet of styrene resin is most preferable. . The thickness of the multilayer sheet is not particularly limited, but is preferably 0.1 to 10 mm.
[0017]
A known method can be adopted as a method for producing 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 can be employed.
[0018]
The multilayer sheet is formed into a container so that a layer mainly composed of rubber-modified styrene resin is inside the container. The molding method is not particularly limited, and vacuum molding, pressure molding, or the like can be employed.
[0019]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples. First, the evaluation method in the present invention will be described below.
[0020]
(1) Measurement of styrene monomer in rubber-modified styrene resin 500 mg of rubber-modified styrene resin was dissolved in 10 ml of DMF containing cyclopentane as an internal standard substance and measured using a gas chromatography GC12A manufactured by Shimadzu Corporation. .
[0021]
(2) Measurement of styrene dimer and styrene trimer in rubber-modified styrene resin 200 mg of rubber-modified styrene resin is dissolved in 2 ml of 1,2-dichloromethane, and 2 ml of methanol is added to the rubber-modified styrene resin. After depositing and allowing to stand, the supernatant was measured using a gas chromatography HP-5890 manufactured by Hewlett-Packard Company. 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 to 300 ° C
(2) Detector temperature: 300 ° C
(E) Split ratio: 50/1
(F) Internal standard substance: n-eicosane [0022]
(3) The rubber-modified styrene resin (Pg) whose methanol soluble mass was measured was dissolved in methyl ethyl ketone, and the solution was poured into 30 times the amount of methanol with respect to methyl ethyl ketone to precipitate the methanol insoluble matter, followed by filtration. The methanol-insoluble matter was taken out, dried at 70 ° C. and 1.3 kPa (abs) for 15 hours, cooled in a desiccator for 20 minutes, and then the mass of the dried precipitate was measured (Ng), and obtained by the following formula. .
MS (%) = (P−N) / P × 100
[0023]
{Circle around (4)} Molecular Weight and Weight Average Molecular Weight Using a HLC-802A type gel permeation chromatography (GPC) manufactured by Tosoh Corporation, measurement was performed under the following conditions.
(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 [0024]
(5) Formability: The multilayer sheet was heated in an oven at 170 ° C. for 25 seconds to form a bowl-shaped container having a diameter of 110 mm and a depth of 121 mm. At this time, the rubber-modified styrenic resin was molded to be inside. The molded container was determined according to the following criteria.
○: Appearance is good Δ: Cracks are generated or the side walls are thin ×: Holes are not formed or containers are not used [0025]
(6) Strength: The container obtained in (5) was compressed from the bottom using a Tensilon measuring machine at a speed of 400 mm / min and indicated by the strength when the container was buckled.
[0026]
(7) Odor: The container obtained in (5) was covered with aluminum foil, smelled when the lid was opened after heating at 40 ° C. for 20 minutes, and judged according to the following criteria.
○ ・ ・ ・ No odor can be felt △ ・ ・ ・ Small odor can be felt × ・ ・ ・ Odor can be felt strongly [0027]
Example 1
75.2 kg of styrene and 4.8 kg of polybutadiene (Diene 55A manufactured by Asahi Kasei Co., Ltd.) were charged into an autoclave with an internal volume of 100 L and a stirrer, and dissolved by stirring at 180 rpm. Subsequently, 1.6 kg of mineral oil (white oil), 80 g of benzoyl peroxide, and 40 g of t-dodecyl mercaptan were charged, the autoclave was sealed, the temperature was raised to 85 ° C., and polymerization was performed for 5 hours to obtain a prepolymer. Next, 100 kg of pure water, 400 g of tricalcium phosphate, and 10 g of sodium dodecylbenzenesulfonate were added to an autoclave with an internal volume of 200 L and a stirrer, and the mixture was stirred at 130 rpm. Subsequently, 70 kg of prepolymer, 210 g of t-butylperoxy-2-ethyl-hexanoate and 70 g of dicumyl peroxide were charged, the autoclave was sealed, and the temperature was raised to 60 ° C. Polymerization was carried out while raising the temperature from 60 ° C. to 90 ° C. over 12 hours, and then 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 obtained beads were washed, dehydrated and dried, and then extruded using a single screw extruder while degassing at a temperature of 210 ° C. and a pressure of 1.3 kPa (abs), to give a pellet-shaped rubber-modified styrene resin. Obtained. The conversion rate was 97% when polymerization was carried out while heating from 60 ° C. to 90 ° C. over 12 hours.
Next, the polystyrene HRM20 manufactured by Toyo Styrene Co., Ltd. was extruded with a tandem type extruder equipped with a circulator die using 0.05 parts by mass of talc as a nucleating agent and 3 parts by mass of butane gas as a blowing agent for 100 parts by mass To obtain a foam sheet having a thickness of 2 mm and an expansion ratio of 8 times, and laminating the rubber-modified styrenic resin while extruding an 80 μm-thick film with an extruder having a T-die attached to the foam sheet to obtain a multilayer sheet. It was. The evaluation results of the obtained multilayer sheet are shown in Table 1.
[0028]
Example 2
The same procedure as in Example 1 was conducted except that the polymerization was carried out while raising the temperature from 60 ° C. to 90 ° C. over 15 hours in the suspension polymerization. The evaluation results of the obtained multilayer sheet are shown in Table 1.
[0029]
Example 3
The same procedure as in Example 1 was repeated except that 140 g of t-butylperoxy-2-ethyl-hexanoate was polymerized. The evaluation results of the obtained multilayer sheet are shown in Table 1.
[0030]
Example 4
The suspension polymerization was carried out in the same manner as in Example 1 except that the polymerization was carried out by raising the temperature from 60 ° C. to 90 ° C. over 1 hour and further holding at 90 ° C. for 11 hours. The evaluation results of the obtained multilayer sheet are shown in Table 1.
[0031]
Example 5
The same procedure as in Example 1 was performed except that 800 g of mineral oil was polymerized. The evaluation results of the obtained multilayer sheet are shown in Table 1.
[0032]
Comparative Example 1
The same operation as in Example 1 was conducted except that dicumyl peroxide was not charged. The evaluation results of the obtained multilayer sheet are shown in Table 2.
[0033]
Comparative Example 2
The same procedure as in Example 1 was conducted except that 70 g of t-butylperoxy-2-ethyl-hexanoate was polymerized. The evaluation results of the obtained multilayer sheet are shown in Table 2.
[0034]
Comparative Example 3
In suspension polymerization, the temperature was raised from 60 ° C. to 90 ° C. over 1 hour, and further maintained at 90 ° C. without increasing the temperature at 120 ° C. at 0.5 ° C./min, held at 120 ° C. for 2 hours, Furthermore, it carried out like Example 1 except having heated up to 135 degreeC and hold | maintaining for 2 hours. The evaluation results of the obtained multilayer sheet are shown in Table 2.
[0035]
Comparative Example 4
The same procedure as in Example 1 was performed except that no mineral oil was charged. The evaluation results of the obtained multilayer sheet are shown in Table 2.
[0036]
Comparative Example 5
The same procedure as in Example 1 was performed except that the polymerization was performed as 3.2 kg of mineral oil. The evaluation results of the obtained multilayer sheet are shown in Table 2.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
From Tables 1 and 2, the multilayer sheet and the container obtained in the comparative example have a large total amount of styrene dimer and trimer, and are highly likely to be transferred to food, and have formability and strength. It can be seen that either odor is inferior.
[0040]
【Effect of the invention】
As described above, the multilayer sheet and container of the present invention are excellent in the balance between moldability and strength and have little odor even when the low molecular weight component is controlled to be small, and are optimal for food containers and the like.

Claims (3)

A rubber-modified styrene resin obtained by radical polymerization, in which a styrene monomer is 500 ppm or less, a total of styrene dimer and styrene trimer is 2000 ppm or less, and a methanol-soluble content is 1.5 to 5% by mass. The rubber-modified styrenic resin having a weight average molecular weight Mw of 240,000 to 500,000 and a number average molecular weight of 80,000 or more has at least one outermost layer,
A multilayer sheet in which the layer mainly composed of the rubber-modified styrene resin is a film having a thickness of 10 to 1000 μm. The multilayer sheet according to claim 1, which is formed into a sheet by extrusion molding. A container formed by molding the multilayer sheet according to claim 1 or 2 , wherein the layer mainly composed of the rubber-modified styrene resin is inside the container.