JP2001206436A - Styrene based resin food container and wrapping material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a food container or wrapping material made of a styrene based resin which is excellent in stability in secondary elaboration and contains a small content of monomers and oligomers. SOLUTION: The food container or wrapping material comprises a styrene based resin wherein (a) the resin contains a styrene monomer, a cyclic dimer and a cyclic trimmer, (b) a content of the styrene monomer is 150 ppm or less and (c) a total content of the styrene monomer, the cyclic dimer and the cyclic trimmer is 2,500 ppm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food container or packaging material using a styrene resin having a low content of a styrene monomer or the like suitable for food applications.

[0002]

2. Description of the Related Art Styrene-based resins have many advantages such as excellent moldability, excellent resistance to water and excellent electrical properties. In addition, various types of molded articles can be easily mass-produced. It is molded by molding methods and is used in large quantities as electrical product materials, sundries, food containers, and packaging materials.

[0003] Among those uses, for those which come into direct contact with foods, such as constituent materials for food containers and packaging, styrene resins having reduced residual monomers are strongly demanded. It has been a demand of the times to reduce the content of the monomer, dimer and trimer of the present invention.

[0004] Styrene resins are mainly produced by a thermal polymerization or a radical polymerization method using an initiator. There are two main production processes, bulk polymerization and suspension polymerization, but the bulk polymerization method, which is less susceptible to impurities and is cost effective, is mainly used.

[0005] Review articles (Encyclopedia o
f Chemical Technology, Kir
k-Othmer, Third Edition, Jo
hnWiley & Sons, vol. 21, p. 817), styrene dimer,
Oligomer by-products such as styrene trimer are produced, and the amount thereof becomes about 1% by weight.
(1′-phenylethyl) tetralin and 1,2-diphenylcyclobutane, and other components such as 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1
Hexene and the like are said to be present.

In the bulk polymerization process, polymerization is usually carried out at 80 to 180 ° C., and then a low molecular weight component such as a solvent or unreacted monomer is subjected to heat devolatilization in a recovery step, and the unreacted monomer and solvent are recovered and recycled. You. The by-product dimer and trimer are partially recycled together with the unreacted monomer, but eventually reach an equilibrium concentration in the system, and the amount generated during polymerization is contained in the styrene-based resin and goes out of the devolatilization step. Will go.

[0007] The styrene-based resin thus produced includes ethylbenzene, styrene, α-methylstyrene, n
-Propylbenzene, iso-propylbenzene, 1,
3-diphenylpropane, 2,4-diphenyl-1-butene, 1,2-diphenylcyclobutane, 1-phenyltetralin, 2,4,6-triphenyl-1-hexene, 1,3,5-triphenylbenzene, Analysis revealed that it contained 1-phenyl-4- (1-phenylethyl) tetralin and the like.

[0008] The content of the main oligomer in the product pellets of the thermally polymerized styrenic resin is approximately 1 in the dimer region.
3-diphenylpropane 50 ppm, 2,4-diphenyl-1-butene 200 ppm, 1,2-diphenylcyclobutane 660 ppm, 1-phenyltetralin 10p
pm, 2,4,6-triphenyl-1- in the trimer region
Hexene 1800 ppm, 1-phenyl-4- (1′-
(Phenylethyl) tetralin 13000 ppm and the like.

Examination of the thermal stability of these compounds and the effect as a radical source when contained in a styrene resin reveals that 1,2-diphenylcyclobutane has the largest effect, followed by 2,4,6- They were triphenyl-1-hexene and 2,4-diphenyl-1-butene, and the effect of 1-phenyl-4- (1′-phenylethyl) tetralin on the thermal stability was smaller than these. For example, the amount of thermal decomposition at 280 ° C. for 10 minutes is about 50% for 1,2-diphenylcyclobutane, and about 1% for 2,4,6-triphenyl-1-hexene and 2,4-diphenyl-1-butene. Thus, the other components were relatively stable.

In the present invention, the cyclic dimer is 1,2-diphenylcyclobutane represented by the following formula (1), and the cyclic trimer is 1-phenyl-4-butyl represented by the following formula (2).
Representative of (1′-phenylethyl) tetralin.

[0011]

Embedded image

[0012]

Embedded image

G, Jones, II, V, Chew, J,
Org, Chem, 1974, vol. 39, p. 1447, describes the thermal decomposition of 1,2-diphenylcyclobutane to a monomer in a tetrachloroethylene solvent at 230 ° C. Therefore, to achieve the object of the present invention,
Styrene monomer in styrene resin, cyclic dimer,
The content of cyclic trimers is low, and further, high stability to secondary processing is required.

[0014] Even in a styrene resin produced by a known thermal radical polymerization method, the styrene monomer and the like contained in the resin can be reduced to some extent by making the operating conditions in the devolatilization step stricter. . However, even when a styrene-based resin having a low monomer content is produced, when the styrene-based resin is subjected to secondary processing, the generation of a monomer occurs again by thermal decomposition. As a result, there is naturally a limit to the amount of styrene monomer and the like in the styrene resin material constituting the molded article.

[0015]

DISCLOSURE OF THE INVENTION The present invention relates to a food container or packaging material comprising a styrene resin which is excellent in stability during secondary processing and has a low content of styrene monomer and the like and is suitable for food applications. The task is to provide.

[0016]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies on styrene resins suitable for food containers and packaging materials. As a result, styrene monomers and dimers in the styrene resins have been studied. Of the present invention, characterized in that the content of is less than a certain amount.

That is, the present invention a) contains a styrene monomer, a cyclic dimer and a cyclic trimer, and b) has a styrene monomer content of 150 ppm or less, and c) a total content of the styrene monomer, the cyclic dimer and the cyclic trimer. The present invention provides a food container or packaging material comprising a styrene resin having a styrene content of 2500 ppm or less.

Preferably, the content of the cyclic dimer is 250 ppm or less. 250p of the dimer content
pm or less can suppress the production of monomers after the secondary processing.

The method for producing the styrene resin used in the present invention is not particularly limited, and a known method can be used. For example, a method for producing a styrene-based resin by bulk polymerization can be used, and as a method for producing the styrene resin, besides heat-initiated polymerization, a method using a polymerization initiator can be used. Styrene resin produced by initiator polymerization,
Generally, it has improved performances such as less generation and mixing of dimers and trimers as compared with styrene resins by thermal polymerization, and can be preferably used.

The styrene resin obtained by the anionic polymerization method has higher thermal stability of the resin itself than the styrene resin obtained by the radical polymerization method. In addition, the anionic polymerization method hardly generates an oligomer such as a dimer or a trimer due to its polymerization mechanism. Further, the conversion of the styrene monomer during the polymerization is usually almost 100%, and the residual monomer in the obtained styrene resin is extremely small.

Therefore, the styrene resin produced by the anionic polymerization method can be particularly preferably used. By using these styrene resins, food containers,
The content of styrene monomer, dimer, trimer and the like of the styrene resin constituting the packaging material can be suppressed.

For the production of a styrene resin by the initiator radical polymerization method preferably used in the present invention, a known radical initiator can be used. Generally, the 10-hour half-life temperature is in the range of 30 to 170 ° C. Preferred initiators are AIBN, BPO, 1,1-bis (t-
(Butylperoxy) -3,5,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate and the like.

Known methods can also be used for producing a styrene resin by anionic polymerization. For example, the monomer can be dissolved in an inert solvent at 10 to 130 ° C., and polymerization can be performed using an alkyl alkali metal or the like as a polymerization initiator.

The inert solvent is capable of dissolving the polymerization initiator and the resulting styrene resin.
For example, hydrocarbons such as cyclohexane, methylcyclohexane, decalin, tetralin, benzene, toluene, xylene and ethylbenzene, and ethers such as tetrahydrofuran, dioxane and ethylene glycol dimethyl ether can be preferably used. These solvents may be mixed and used.

As the polymerization initiator, alkyl lithiums are preferably used. In order to increase the polymerization rate, an ether compound such as dioxane or an amine compound such as tetramethylethylenediamine can be added. Further, after the polymerization is completed, it can be reacted with a compound having active hydrogen such as methanol to deactivate the polymerization active terminal. At this time, by using a coupling agent, the anion active terminal can be coupled to have a branched structure.

The weight average molecular weight of the styrene resin obtained by anionic polymerization of the present invention is from 60,000 to 800,000, preferably from 70,000 to 500,000. If the weight average molecular weight is 60,000 or less, the mechanical strength of the styrene resin is insufficient, and if it is 800,000 or more, there is a problem in fluidity. Further, the molecular weight distribution is not particularly limited, but it is preferable that the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) be 1.5 or less and sharp.

After the polymerization of these styrenic resins is completed, a devolatilization process is performed to recover unreacted monomers and a solvent. As a devolatilizing apparatus, a method of flashing in a vacuum tank and a method of extrusion evaporation are known, and both methods can be used. Generally, the temperature is from 180 to 260
Volatile components such as unreacted monomers are volatilized at a temperature of 1 ° C. and a degree of vacuum of 1 to 50 Torr. It is also known to connect devolatilizers in series and arrange them in two stages. There is also a method in which water is added between the first and second stages to increase the volatility of the second-stage monomer.

The styrenic resin material of the present invention is a radical chain inhibitor represented by a phenolic stabilizer, that is, a material having a function of terminating a radical chain. The radicals trapped in the agent are converted to the resulting peroxide ROOH
By adding together a so-called secondary antioxidant represented by a more stable compound, for example, a sulfur-based antioxidant having a function of decomposing into ROH, or a phosphorus-based antioxidant, a more advanced compound can be obtained. Stabilization can be achieved.

According to JP-A-7-292188, 2,4,6-trisubstituted phenol is advantageous as a method for stabilizing a styrenic resin, and 2,6-di-t-butyl-4-methylphenol is advantageous. It is stated that Examples of the phenolic antioxidant used in the present invention include, in addition to the 2,6-di-t-butyl-4-methylphenol,
Pentaerythritol tetrakis [3- (3,5-di-t
-Butyl-4-hydroxyphenyl) propionate]
IRGANOX1010, octadecyl-3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate IRGANOX1076, 2-t-butyl-6-
(3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate Sumiliz
erGM and the like. One or more of the above primary antioxidants of the present invention may be used.

The secondary antioxidant used in combination with the primary antioxidant used in the present invention has a function as a peroxide decomposer. Generally, there are sulfur-based antioxidants and phosphorus-based antioxidants, but even if a secondary antioxidant is used alone, autoxidation cannot be effectively prevented. The synergistic effect is obtained only when used in combination with the agent.

Specific examples of the sulfur-based antioxidant among the secondary antioxidants include 3,3'-thiobispropionic acid didodecyl ester IRGANOX PS800F
L, dilauryl 3,3 'thiopropionate Sumil
IserTPLR, dimistil 3,3 ′ thiodipropionate Sumilizer TPM, and the like.

Specific examples of the phosphorus-based antioxidant among the secondary antioxidants include trisnonylphenylphosphite Sumilizer TNP and tris (2,4-di-t
-Butylphenyl phosphite) ADK STAB2
112, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite ADKS
TAB PEP-36 and the like.

As the secondary antioxidant used in the present invention, one or more of sulfur-based and phosphorus-based antioxidants can be used. The content of the primary antioxidant and the secondary antioxidant contained in the styrene resin material of the present invention is preferably 50 to 1000 pp in total.
m, more preferably in the range of 100 to 500 ppm. A preferable ratio of the primary antioxidant and the secondary antioxidant in the total antioxidants contained is that the primary antioxidant is 5%.
0 to 90% by weight, and the secondary antioxidant is 50 to 10% by weight.

The styrenic resin material of the present invention may contain additives known to be blended with the styrenic resin, such as various stabilizers, flame retardants, antistatic agents and coloring agents, as long as the object of the present invention is not impaired. Can be contained in any amount. As described above, the styrene-based resin of the present invention has a very low content of styrene monomer or styrene oligomer, and by taking advantage of this feature, such as being in direct contact with food, can be preferably used for food containers and packaging materials. .

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, according to Examples and Comparative Examples,
Embodiments of the present invention will be specifically described, but it is needless to say that the scope of the present invention is not limited to these. The styrene-based resin used in the examples and comparative examples was prepared in the following Reference Example 1.
~ 4.

Reference Example 1 (Preparation of styrene resin P1 by anionic polymerization method) In an autoclave replaced with dry nitrogen, 60 kg of dehydrated cyclohexane and 10.0 kg of dehydrated styrene monomer were charged. Then, a 30% by weight cyclohexane solution containing 8 g of n-butyllithium was poured in, and a polymerization reaction was carried out with vigorous stirring.

After 5 minutes, the temperature inside the reactor rose to 85 ° C. 2
After reacting for 0 minutes, conv
When the area measurement was performed, it was 99.9%. After precipitating the styrenic resin in methanol,
It was devolatilized and dried in a volatilization furnace at 30 ° C. and 10 Torr for 20 minutes to obtain a styrene resin P1. The weight average molecular weight of the obtained styrene resin measured by GPC (gel permeation chromatography) is 105,000, and the number average molecular weight is 10.
It was 10,000.

Reference Example 2 (Preparation of Styrenic Resin R1 by Initiator Radical Polymerization) In an autoclave equipped with a temperature controller, 9.0 kg of styrene monomer, 1.0 kg of purified ethylbenzene, 1,1 as an initiator -Bis (t-butylperoxy)
1.0 g of -3,5,5-trimethylcyclohexane was charged, and a polymerization reaction was carried out at 140 ° C. for 8 hours while stirring under a nitrogen atmosphere.

Thereafter, unreacted styrene monomer and ethylbenzene were distilled off at 250 ° C. under a reduced pressure of 5 Torr. The obtained styrene-based resin R1 had a weight average molecular weight of 260,000 by GPC measurement, and a molecular weight distribution (Mw / Mn) represented by a ratio of the weight average molecular weight to the number average molecular weight of 2.4.

Reference Example 3 (Preparation of Rubber-Modified Styrenic Resin R2 by Initiator Radical Polymerization) Polybutadiene (Nippon 1220, ZEON CORPORATION)
SL) was dissolved in styrene, and then a small amount of ethylbenzene and t-butylperoxyisopropyl carbonate were added to prepare a polymerization stock solution having the following composition. (Unit: parts by weight) ・ polybutadiene 9.8 ・ styrene 76.8 ・ ethylbenzene 13.0 ・ t-butylperoxyisopropyl carbonate
0.04 ・ α-methylstyrene dimer 0.02 ・ Polydimethylsiloxane 0.10

The polymerization stock solution was continuously fed at a rate of 2.2 L / hr to a 6.2 L, 3-tank reactor equipped with a stirrer.
The reactor internal temperature was adjusted so that the solid content concentration at the reactor outlet of the first tank was 38% by weight. At the same time, the reactor internal temperature was adjusted so that the solid concentration at the outlet of the reactor in the final tank was 80% by weight. Then, the mixture is fed into a devolatilizer under vacuum at 230 ° C. to remove unreacted styrene and ethylbenzene, and granulated by an extruder to obtain a pelletized rubber-modified styrene resin R2.
I got

The polybutadiene content was 1
2.3% by weight. The weight-average molecular weight and number-average molecular weight of the continuous phase determined by GPC measurement of the methyl ethyl ketone-soluble component were 254,000 and 92,000, respectively. The average rubber particle diameter of the dispersed phase is 1.5 μm,
The swelling index for toluene was 9.8.

[0043]

Example 1 100 g of the styrene resin P1 prepared by the anionic polymerization method prepared in Reference Example 1 was used as a primary antioxidant as pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-). Hydroxyphenyl) propionate] IR
GANOX1010 and bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite ADK STAB PE as a phosphorus-based secondary antioxidant
An 8/2 (weight) mixture of P-36 was dispersed and dissolved in methanol, and a total of 50
0 ppm was added and dispersed sufficiently. Next, the mixture was melt-kneaded at 200 ° C. for 10 minutes using a Labo Plastomill.

1.00 g of the styrene resin material thus obtained was precisely weighed, and 20 ml of toluene was added thereto to prepare 1
Dissolve using a time shaker. This was centrifuged at 20,000 rpm for 1 hour in a centrifuge, and 10 ml of the supernatant was collected. To this solution was added 10 ml of methanol to precipitate a styrene resin, which was filtered using a 0.2 μm filter, and the filtrate was analyzed by gas chromatography.

The column was TC-1 manufactured by GL Sciences (inner diameter 0.25 mm, thickness 0.25 μm, length 30 m). The column temperature was maintained at 50 ° C. for 5 minutes, and then 32 ° C. at 20 ° C./min.
The temperature was raised to 0 ° C. and kept for 3 minutes. The equipment is Shimadzu GC-
Injection is 260 with 14B (FID detector)
° C, and the detector was set at 330 ° C. Anthracene was used as the internal standard.

The content of the styrene monomer, the cyclic dimer and the cyclic trimer in the styrene resin material after processing by melt kneading assuming the secondary processing described above is 70 pp, respectively.
m, 1 ppm or less, 170 ppm, a total amount of 24 ppm
It was extremely low, less than 1 ppm, and was excellent in thermal stability.

The MFR was 8.5 g / 10 min. The fluidity of the styrene resin material was evaluated. Melt flow rate (MFR value) is ASTM D12
It was measured under the condition G (200 ° C., 5 kg load) in accordance with No. 38.

Example 2 Instead of 100 g of the styrene resin P1 prepared by the anionic polymerization method prepared in Reference Example 1, 50 g of the styrene resin P1 and 50 g of the styrene resin R1 prepared by the initiator radical polymerization method of Reference Example 2 were used. Was used. Further, the same treatment as in Example 1 was carried out using the same antioxidant as in Example 1. Styrene monomer in the styrene resin material after processing by melt kneading assuming secondary processing is 70 ppm, cyclic dimer 110 ppm, cyclic trimer 1020 ppm, a total of 1
It was 200 ppm. The MFR value is 5.2 g / 10
min.

Example 3 60 g of the styrene-based resin P1 prepared by the anionic polymerization method prepared in Reference Example 1 was obtained by using a commercially available thermally polymerized GPPS (Styrone 6).
85 Asahi Kasei Kogyo Co., Ltd.) and the same antioxidant as in Example 1 were treated in the same manner as in Example 1. 100 ppm of styrene monomer in styrene resin material after processing by melt-kneading assuming secondary processing, cyclic dimer 230
ppm, cyclic trimer 2080 ppm, total 2410 p
pm. The MFR value was 5.7 g / 10 min.

Example 4 30 g of the styrene resin P1 prepared by the anionic polymerization method prepared in Reference Example 1 and 70 g of the rubber modified styrene resin R2 prepared by the initiator radical polymerization method prepared in Reference Example 3 were used as primary antioxidants. 1,3,5-trimethyl-2,4
6/4 (weight) mixture of 6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene IRGANOX1330, distearyl 3,3'thiodipropionate Sumilizer TPS as sulfur secondary antioxidant Was dissolved in methanol, and a total of 400 ppm was added to the styrene-based resin, and sufficiently dispersed. Thereafter, the same processing as in Example 1 was performed. Styrene monomer 120 ppm in the styrene resin material after processing by melt kneading assuming secondary processing, cyclic dimer 200
ppm, cyclic trimmer 1630 ppm, total 1950p
pm. The MFR was 4.5 g / 10 min.

Example 5 20 g of the anionic polymerized styrene resin P1 prepared in Reference Example 1 and the rubber-modified polystyrene R2 prepared in Reference Example 3
And pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-) as a primary antioxidant.
Hydroxyphenyl) propionate] IRGANOX
1010 and bis (2,6-
Di-t-butyl-4-methylphenyl) pentaerythritol diphosphite ADK STAB PEP-36
And treated in the same manner as in Example 1 using 8/2 (weight).
The styrene-based resin material after processing by melt-kneading assuming secondary processing was 100 ppm of styrene monomer, 170 ppm of cyclic dimer, and 1780 ppm of cyclic trimer, for a total of 2,050 ppm. MFR is 3.5 g / 10
min.

Comparative Example 1 The same antioxidant as in Example 1 was added to 100 g of the rubber-modified styrenic resin R2 prepared by the radical polymerization method prepared in Reference Example 3, and treated in exactly the same manner. 150 ppm of styrene monomer and 220 pp of cyclic dimer in styrene resin material after processing by melt kneading assuming secondary processing
m, the cyclic trimer was 2300 ppm. As described above, when the rubber-modified styrene resin of the radical polymerization method is used,
It is difficult to reduce the content levels of monomers and oligomers to 2500 ppm or less. The MFR is 2.8 g /
It was 10 minutes. The results of these examples and comparative examples are summarized in Table 1.

[0053]

[Table 1]

[0054]

The food container or food packaging material made of a styrene resin of the present invention has excellent effects such as higher thermal stability and less content of styrene monomer and the like as compared with conventional ones. .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 5/5415 C08L 25/06 C08L 25/06 B65D 1/00 A

Claims (4)

[Claims] 1. A) It contains styrene monomer, cyclic dimer and cyclic trimer, and b) The content of styrene monomer is 150 ppm or less, c) The total content of styrene monomer, cyclic dimer and cyclic trimer is 2500 ppm or less A food container or packaging material comprising a styrene resin. 2. The food container or packaging material according to claim 1, wherein the content of the cyclic dimer is 250 ppm or less. 3. The container or packaging material for food according to claim 1, wherein the styrene resin is a styrene resin obtained by an anionic polymerization method. 4. The method according to claim 1, which comprises one or more phenolic antioxidants and one or more phosphorus or sulfur antioxidants in a total amount of 50 to 1000 ppm. A food container or packaging material as described.