JP2000007019A - Food packaging material suitable for recycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the quantity of a limonene volume-reducing agent to be repeatedly used during the recycling by setting the content of styrene monomer and styrene dimer to be not more than a specified value, respectively. SOLUTION: The content of styrene monomer is set not more than 200 ppm. When it exceeds approximately 200 ppm, the contamination of a recovered limonene volume-reducing agent becomes remarkable, and the quality of the agent is unpreferably degraded. The content of styrene dimer is set approximately not more than 300 ppm. The styrene dimer here includes the total amount of the linear dimer and the cyclic dimer. The contamination of the limonene volume-reducing agent is suppressed to a minimum. Since the recycling frequency of the agent itself is remarkably improved, the life time of the limonene volume- reducing agent itself can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a food packaging material suitable for recycling. More specifically, when dissolving, recovering and recycling using a limonene-based volume reducing agent, which is one of the recycling techniques for food packaging materials molded from a styrene-based polymer, a limonene-based volume reduction mainly composed of d-limonene is used. The present invention relates to a food packaging material whose recyclability is greatly improved in repeated use of the volume reducing agent without lowering the quality of the agent.

[0002]

2. Description of the Related Art In recent years, foam trays for fresh foods widely used as packaging materials for meat and fresh fish in supermarkets, transparent containers such as cucumbers and cracked radish, instant noodle containers, convenience stores and the like. Food packaging materials that make use of the advantages of light, durable, water-resistant, etc. As is consumed in large quantities.

[0003] Until a few years ago, these were used up and disposed of as waste by incineration, landfill, and the like. on the other hand,
Once collected, the value of these food packaging materials is very high, and in conjunction with the growing awareness of environmental issues in recent years, recycling for processing into building materials, daily necessities and the like is also active. In the past, the biggest bottleneck in this recycling was the bulk of these food packaging materials, especially expanded polystyrene mainly made of foam trays for fresh foods.
Still facing this problem. Poor logistics efficiency during the recovery process accounted for most of the recovery costs, and was an obstacle to the growing trend of recycling.

On the other hand, "d" extracted from the skin of citrus fruits
"Limonene" is known to be an excellent solubilizer of polystyrene. In recent years, polystyrene focused on this,
In particular, expanded polystyrene recovery and recycling systems are in the spotlight. The technology uses limonene, a natural component, to dissolve foamed polystyrene, thereby reducing its volume to several tens to hundreds of hundreds, and reducing recovery costs, thereby increasing recovery efficiency. The purpose is to improve it. Of course, in this technique, if the material to be recycled is a styrene-based polymer centered on a polystyrene resin, it can be preferably dissolved, recovered, and recycled.

[0005] Further, d-limonene itself is also extracted from the pomace of citrus beverages, so it is a completely natural raw material and has both environmentally and human-friendly merits. On the other hand, there is also a recycling technology that compresses the volume by applying heat and recovers it.However, by applying heat, polystyrene causes a change in its chemical structure, such as cutting the main chain and generating styrene monomer due to decomposition, and is recycled. From the point of view,
It can be said that the dissolution and recovery technique using a limonene-based volume reducing agent is superior. Another feature of the dissolution and recovery technology using a limonene-based volume reducer is that the limonene-based volume reducer can also be collected and reused when recovering food packaging and producing recycled resin pellets. It is possible.

However, styrene polymers used for food packaging materials usually contain 300 to 1000 ppm of residual styrene monomer. Since the styrene monomer and limonene have relatively close boiling points, this styrene monomer is mixed in when the limonene-based volume-reducing agent is recovered, and as the limonene-based volume-reducing agent is repeatedly recycled and used, it becomes a volume-reducing agent. There was a problem that the quality of the product extremely deteriorated. Further, the styrenic polymer has a
It contains about 2000 ppm of dimer, which is a slightly high-boiling compound itself. However, if it is present in a large amount in the recovered food packaging material, as in the case of the styrene monomer, this dimer is collected when the limonene-based volume reducing agent is recovered. Or in some cases, the dimer is further decomposed into a styrene monomer and mixed into the limonene-based volume reducing agent as a styrene monomer. It was one.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a food packaging material comprising a styrene-based polymer widely used in modern life, which is used repeatedly when recycling using a limonene-based volume reducing agent. An object of the present invention is to provide a food packaging material which is greatly improved from the viewpoint of maintaining the quality of a limonene-based volume reducing agent and which is excellent in recyclability and can further reduce the recycling energy.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above points, and as a result, the following food packaging materials have been obtained.
The present inventors have found that all of the above problems can be solved, and have reached the present invention. That is, the present invention is a food packaging material which is a styrene-based polymer and has a styrene monomer content of 200 ppm or less and a styrene dimer content of 300 ppm or less. Hereinafter, the present invention will be described in detail.

The styrene polymer in the present invention refers to a polymer obtained mainly from styrene. For example, non-rubber reinforced polystyrene (GPPS), styrene-methacrylic acid copolymer (SMAA), rubber reinforced polystyrene (HIPS), and styrene-butadiene copolymer (SBC) correspond to this. As an example, GPPS is suitable for a foam molded container such as a tray for fresh food, an instant noodle container, a natto container, or the like, or a food packaging material formed by secondary molding of a biaxially stretched extruded sheet. For applications requiring higher heat resistance, such as in a range,
MAA is preferred. On the other hand, in the case of a beverage cup, any of these materials can be used by combining these depending on the use and characteristics thereof.

The method for molding a food packaging material according to the present invention comprises:
It is manufactured through any of the methods of foam extrusion molding, non-stretched extrusion sheet molding, biaxially stretched extrusion sheet molding, injection hollow molding, and injection molding, and if necessary, through secondary molding. For example, in the case of foam extrusion, a tray for fresh food, or an instant noodle container in the shape of a donburi or square,
Before molding into a natto container or the like, first, a molten resin is impregnated with a gas as a foaming agent to form a foamed polystyrene sheet. By subjecting the obtained foamed sheet to secondary molding into a desired shape, the food packaging material intended for the present invention can be obtained.

[0011] In addition, bento containers and side dish containers used in convenience stores and the like, lids thereof, food packages used in fried noodles in stalls, and the like are also provided.
After forming the sheet once or not through the stretching step, secondary molding is performed to obtain the intended food packaging material. On the other hand, lactic acid bacteria beverage containers and beverage cups obtained by injection blow molding, and yogurt containers and beverage cups obtained by injection molding are also included in the category of food packaging materials.

The styrene monomer contained in the food packaging material proposed in the present invention is at most 200 ppm, more preferably at most 100 ppm. 200p
If it exceeds pm, contamination of the limonene-based volume reducer after recovery becomes remarkable, and the quality of the limonene-based volume reducer is undesirably reduced. 2 styrene monomer
Since the contamination of the limonene-based volume reducer is suppressed to a minimum by setting the content to be less than or equal to 00 ppm, the number of reuses of the volume reducer itself is dramatically improved, and the lifetime of the volume reducer itself is reduced. Prolongation is achieved. Furthermore, the styrene dimer contained in the food packaging material proposed in the present invention is 300 ppm or less. The styrene dimer described here indicates the total amount of a linear dimer and a cyclic dimer. The chemical structure of each dimer is shown below by structural formulas (1) to (3).

[0013]

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It is known that the linear dimers represented by the formulas (1) and (2) are mainly formed in the early stage of the polymerization, for example, in the case of bulk radical polymerization. Since it is also generated from molecular chain breakage due to factors, it is possible in some cases that a small amount is contained in the anionic polymer. On the other hand, it is known that the cyclic dimer represented by the formula (3) has a dimer structure peculiar to radical polymerization, and hardly exists in a styrene-based polymer obtained by anionic polymerization.

Further, EPS, which is generally used as a cushioning material for home appliances and the like, so-called “styrene foam” uses the same polystyrene resin as the raw material,
It can be collected and recycled at the same time. Also in this case, in consideration of the gist of the present invention, the amount of the residual monomer in the expanded polystyrene is also preferably 200 ppm or less. Styrofoam is unique in its manufacturing method.
It is known that the styrene dimer content is extremely low as compared with the bulk radical polymerized styrene-based polymer. 200 ppm or less residual styrene monomer in the present invention,
As the polymerization technique and the production technique for controlling the amount of the styrene dimer to 300 ppm or less, any of the known existing techniques may be used.

For example, regarding the residual monomer,
In the styrene-based resin production process by bulk radical polymerization, devolatilization is performed by a flash tank in the final finishing stage, but unreacted residual styrene monomer is reduced by increasing the degree of vacuum and extending the residence time.
It is possible to make it below 00 ppm. Further, after or after the flash tank process, the residual styrene monomer can be removed to 200 ppm or less using a twin-screw extruder or a kneader under high vacuum conditions.

Here, the radical polymerization includes bulk radical polymerization, emulsion polymerization, and suspension polymerization. Furthermore, a method of reducing the residual styrene monomer to 200 ppm or less is also possible by using a solvent such as cyclohexane and increasing the conversion rate to a polymer by an anionic polymerization method using an organolithium initiator. Is known. The lower limit of the styrene monomer is ideally preferably as close as possible to 0 ppm, but it is extremely difficult to achieve 0 ppm completely industrially.

Further, with respect to the styrene dimer, reduction can be achieved by using a radical initiator such as a peroxide compound in the bulk radical polymerization or by using an anionic polymerization process. The method for quantifying the styrene monomer and the styrene dimer is not particularly limited in the present invention, but it is generally preferable to use gas chromatography. As an example, the resin constituting the container is dissolved in a good solvent such as methyl ethyl ketone, the polymer content is removed with a poor solvent such as methanol, and the remaining solution is quantified by gas chromatography. At this time, if the internal standard sample is previously added to the solvent, the styrene monomer and styrene dimer can be easily and reproducibly quantified.

[0019]

Embodiments of the present invention will be described below. Here, the present invention is not limited at all by the examples and the like. The evaluation method adopted in the examples is described.
The styrene monomer concentration (ppm) was determined by gas chromatography using p-methylstyrene and the styrene dimer concentration (ppm) using triphenylmethane as an internal standard sample.

[0020]

Examples 1-2, Comparative Example 1 Bulk radical polymerization was carried out using styrene as a monomer, ethylbenzene as a chain transfer agent, and pertetra A (trade name, manufactured by NOF Corporation) as a radical initiator. Carried out. Furthermore, by changing the degree of vacuum in the devolatilization step as needed, three types of GPPS having different styrene monomer and styrene dimer contents can be obtained.
I got Using these molding materials, a foam extruded sheet was formed, and then subjected to secondary molding to prepare a large number of foam trays for fresh food. The weight was 6.0 g per piece. The styrene monomer content in these containers is the average value (n = 5) of random samples from each foam tray
And 80 ppm, 170 ppm, 280 ppm,
Similarly, the styrene dimer content was 120 ppm and 17
It was 0 ppm and 220 ppm.

Each foaming tray having a different styrene monomer content was charged into each dissolving tank (containing 500 ml in total) containing d-limonene and dissolved therein. After dissolving 30 foaming trays, d-limonene and polystyrene were separated by a distillation separator. Each of the recovered d-limonene was returned to the original dissolving tank again, and 30 foaming trays having the same styrene monomer content were again dissolved, and separated again by the distillation separator. These series of cycles were repeated 50 times, and the amount of styrene monomer in each d-limonene was analyzed by gas chromatography to evaluate the degree of maintenance of the quality of d-limonene. Table 1 shows the results.

[0022]

Examples 3 and 4, Comparative Example 2 From the foamed extruded sheets prepared in Examples 1 and 2, secondary molding was performed to prepare a large number of instant noodle containers. The weight was 5.0 g per piece.
The styrene monomer content in these containers was 80 ppm, 180 ppm, 280 ppm, as in Example 1, and the styrene dimer content was 120 ppm,
170 ppm and 220 ppm. The same test as in Example 1 was carried out except that 36 pieces were dissolved at a time and d-limonene was separated by a distillation separator.
The quality maintenance of limonene was similarly evaluated. Table 1 shows the results
Are shown together.

[0023]

Examples 5 to 6, Comparative Example 3 From the foamed extruded sheets prepared in Examples 1 and 2, secondary molding was performed to produce a large amount of natto containers. The weight was 3.0 g per piece. The styrene monomer content in these containers was 80 ppm, 170 ppm, 300 ppm, as in Example 1.
Similarly, the styrene dimer content was 120 ppm, 17
It was 0 ppm and 220 ppm. The same test as in Example 1 was conducted except that 60 pieces were dissolved at a time and d-limonene was separated by a distillation separator, and the degree of maintenance of the quality of d-limonene after the test was similarly evaluated. The results are shown in Table 1.

[0024]

Example 7, Comparative Example 4 Polybutadiene (NF35: trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.) was dissolved in a polymerization solution using styrene as a monomer, and ethylbenzene was used as a chain transfer agent and a radical initiator was used. Without performing bulk radical polymerization. Furthermore, two kinds of HIPS having different styrene monomer and styrene dimer contents were obtained by changing the degree of vacuum in the devolatilization step as needed. HI
The amount of rubber in PS was 6.0%. Using this molding material, a non-stretched extruded sheet having a thickness of 0.5 mm was molded, and then subjected to secondary molding to prepare a large amount of bento / delivery containers. The weight was 15 g per piece. The styrene monomer content in these containers was 90 ppm as the average value (n = 5) of the randomly extracted samples in each lunch box / side dish container,
180 ppm, and the styrene dimer content was 260 ppm and 500 ppm, respectively. The same test as in Example 1 was carried out except that 12 pieces were dissolved at a time and d-limonene was separated by a distillation separator.
The degree of maintenance of limonene quality was similarly evaluated. Table 1 shows the results
Are shown together.

[0025]

Example 8, Comparative Example 5 A biaxially stretched extruded sheet having a thickness of 0.3 mm was formed using two points of the molding materials polymerized in Examples 1 and 2, and then subjected to secondary molding. A large number of transparent food packages with a lid container suitable for a takoyaki or yakisoba container are prepared. The weight was 15 g per piece. The styrene monomer content in these containers was 80 ppm and 280 as in Examples 1-2.
ppm, and the styrene dimer content was 12
It was 0 ppm and 220 ppm. Except having melt | dissolved 12 pieces at a time and isolate | separating d-limonene with a distillation separator, the same test as Example 1-2 was performed, and the maintenance degree of the quality of d-limonene after a test was evaluated similarly. . The results are shown in Table 1.

[0026]

Example 9 As a styrene-based polymer, HIPS, Styrone H9407 (trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.)
, A large number of lactic acid bacteria beverage containers were molded by injection blow molding (injection blow molding). The weight was 6.0 g per piece. The styrene monomer content in this lactic acid bacterium beverage container was 150 ppm as an average value (n = 5) of any extracted sample in the container, and similarly, the styrene dimer content was 100 ppm. The same test as in Example 1 was performed, except that 30 pieces were dissolved at a time and d-limonene was separated by a distillation separator, and the degree of maintenance of the quality of d-limonene after the test was similarly evaluated.
The results are shown in Table 1.

[0027]

Example 10, Comparative Example 6 As a styrenic polymer, G
Stylon 685 as PPS and Asaflex 845 as SBC (both manufactured by Asahi Kasei Kogyo Co., Ltd .: trade name)
Were blended at a ratio of 50:50, and a large number of beverage cups were formed from a non-stretched extruded sheet through a secondary molding process. On the other hand, Stylon 475D (trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.), which is a HIPS, similarly formed a large number of beverage cups from non-stretched extruded sheets. Weight is 6.0 per piece
g. Each styrene monomer content is the average value (n = 5) of random samples from each, and the former HI
150 ppm for PS / SBC system, 2 for HIPS system
70 ppm, and the styrene dimer content was 130 ppm and 280 ppm, respectively. The same test as in Example 1 was carried out except that 30 pieces were dissolved at a time and d-limonene was separated by a distillation separator.
The quality maintenance of limonene was similarly evaluated. Table 1 shows the results
Are shown together.

[0028]

Example 11 Anionic polymerization was carried out using styrene as a monomer, a styrene concentration of 33% by volume using cyclohexane as a solvent, and n-butyllithium as an initiator, and GPPS was obtained after removing the solvent. . Using these molding materials, a foam extruded sheet was molded and subjected to secondary molding to prepare a large number of foam trays for fresh food. The weight was 6.0 g per piece. The styrene monomer content in these containers was the mean (n = 5) of the random sample and was 10%.
ppm, and the styrene dimer content is 40 pp.
m. Dissolve 30 at a time and use a distillation separator
-The same test as in Example 1 was performed except that limonene was separated, and the degree of maintenance of the quality of d-limonene after the test was similarly evaluated. The results are shown in Table 1.

[0029]

[Table 1]

As is clear from the results, it is clear that the food packaging material provided by the present invention is excellent in recyclability from the viewpoint of maintaining the quality of d-limonene in recycling with d-limonene. .

[0031]

According to the present invention, the quality of the limonene-based volume reducer to be used is improved by recovering and recycling the specific food packaging material proposed in the present invention using the dissolution, collection and recycling technology using the limonene-based volume reducer. With little reduction, the quality is largely maintained by repeated use of the volume reducing agent,
It is possible to greatly contribute to prolonging the lifetime of the volume reducing agent. As a result, an excellent recycling technology using a limonene-based volume reducing agent becomes a recycling technology that is more environmentally friendly in terms of energy and resources, and is extremely effective from the viewpoint of protecting the global environment.

Claims (17)

[Claims] 1. A food packaging material comprising a styrene-based polymer, having a styrene monomer content of 200 ppm or less and a styrene dimer content of 300 ppm or less. 2. The food packaging material according to claim 1, wherein the food packaging material is formed by molding an extruded foam. 3. The food packaging material according to claim 2, wherein the food packaging material is a foam tray for fresh food. 4. The food packaging material according to claim 2, wherein the food packaging material is an instant noodle container. 5. The food packaging material according to claim 2, wherein the food packaging material is a natto container. 6. The food packaging material according to claim 1, wherein the food packaging material is formed by molding a non-stretched extruded sheet. 7. The food packaging material according to claim 6, wherein the food packaging material is a lunch box or a side dish container. 8. The food packaging material according to claim 1, wherein the food packaging material is formed by forming a biaxially stretched extruded sheet. 9. The food packaging material according to claim 8, wherein the food packaging material is a lunch box or a lid of a side dish container. 10. The food packaging material according to claim 8, wherein the food packaging material is a food package. 11. The food packaging material according to claim 1, wherein the food packaging material is formed by injection blow molding. 12. The food packaging material according to claim 11, wherein the food packaging material is a lactic acid bacteria beverage container. 13. The food packaging material according to claim 1, wherein the food packaging material is formed by injection molding. 14. The food packaging material according to claim 13, wherein the food packaging material is a yogurt container. 15. The food packaging material according to claim 6, wherein the food packaging material is a beverage cup. 16. A styrene monomer content of 100 p
The food packaging material according to any one of claims 1 to 15, which is not more than pm. 17. The styrene polymer according to claim 1, wherein the styrene polymer is any one of a radically polymerized styrene-based polymer and an anionic polymerized styrene-based polymer, or an arbitrary mixture thereof. Food packaging material according to any of the above.