JP4218992B2 - Styrenic resin and its foam - Google Patents

Description

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【表３】

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【発明の効果】
本発明のスチレン系樹脂は、発泡性能が良好で軽量化や生産性の向上が可能となり、従来のスチレン系樹脂に比べコストダウンが可能である。また、これからなる発泡体は、強度、外観性に優れ、臭気が少なく、食品包装材、建材、緩衝材等の発泡分野で有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a styrenic resin having good foaming performance and capable of reducing weight and improving productivity, and its styrenic resin foam having excellent strength and appearance and less odor.
[0002]
[Prior art]
Since styrene resins are inexpensive and have good moldability, they are widely used in the foaming field of food packaging materials, building materials, cushioning materials, etc., in addition to molding materials such as various containers, toys and sundries. Recently, the weight reduction of the foam for the purpose of cost reduction and the improvement of the productivity at the time of foam production have been studied, and the demand for higher performance of the styrene resin for this purpose is increasing.
[0003]
However, the conventional styrenic resin was obtained by reducing the foaming performance by reducing the closed cell ratio when the foaming ratio was increased by increasing the foaming ratio or when the foam was manufactured by increasing the productivity. The strength and appearance of the foam were not good.
For example, Japanese Patent Laid-Open No. 6-80712 discloses a method for producing a polystyrene-based resin having excellent foam sheet moldability. However, the strength, appearance, odor, etc. of the foam when weight is reduced or productivity is increased. There was no suggestion about.
[0004]
On the other hand, foams of styrenic resins are strongly oriented toward increasing strength, and technologies such as adding a butadiene component or increasing the molecular weight have been proposed, but all of these results in increased costs and reduced productivity. It was not preferable.
[0005]
[Problems to be solved by the invention]
As a result of various studies to solve such problems, the present inventors have found that a styrene resin having a specific molecular weight and molecular weight distribution, a specific loss on heating, a specific residual styrene monomer amount, and a residual benzaldehyde amount has a foaming performance. It has been found that the foam can be reduced in weight and productivity can be improved, and the obtained foam is excellent in strength and appearance, and has a low odor.
[0006]
[Means for Solving the Problems]
That is, the present invention is a styrene resin having a weight average molecular weight (Mw) of 150,000 to 600,000 and a Z average molecular weight (Mz) ratio Mz / Mw of 1.8 to 3.5, and (A) nitrogen Foam formed by foaming a styrene resin with a weight loss of less than 0.5% by weight when heated at a rate of 10 ° C / min from 200 ° C to 300 ° C under an air stream, and (B) the remaining benzaldehyde is less than 50 ppm. It relates to food packaging material consisting of body .
[0007]
The present invention is described in detail below.
The styrenic resin of the present invention is obtained by polymerizing a styrenic monomer.
As the styrenic monomer, styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, t-butylstyrene or the like can be selected alone or as a mixture.
In addition, monomers other than styrene monomers such as acrylonitrile, methacrylic acid ester, acrylic acid ester, etc., do not impair the performance of the styrene resin, that is, 5 parts by weight or less with respect to 100 parts by weight of styrene monomer. If so, it may be added and polymerized.
Further, in the present invention, at the time of polymerization of the styrene monomer, a polymer obtained by adding less than 1 part by weight of a crosslinking agent such as divinylbenzene to 100 parts by weight of the styrene monomer may be used.
[0008]
As the polymerization method, a known method such as a suspension polymerization method, a bulk polymerization method, a solution polymerization method or an emulsion polymerization method can be used, and a continuous polymerization method or a batch polymerization method may be used. A known polymerization initiator can be used during the polymerization, but a tetrafunctional polymerization initiator such as 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane is particularly preferable. Furthermore, it can also superpose | polymerize by adding a well-known chain transfer agent.
[0009]
The weight average molecular weight (Mw) of the styrene resin of the present invention is 150,000 to 600,000, preferably 200 to 500,000, and more preferably 250,000 to 400,000. A styrene resin having an Mw of less than 150,000 has a remarkably low strength and cannot produce a foam, and a styrene resin having an Mw of more than 600,000 has a remarkably low productivity and cannot achieve the purpose of cost reduction.
The ratio Mz / Mw of the Z average molecular weight (Mz) and Mw of the styrene resin of the present invention is 1.8 to 3.5, preferably 1.9 to 2.7, more preferably 2.0 to 2.3. is there. If a styrene resin having an Mz / Mw of less than 1.8 is used, the strength of the foam is reduced, and if a styrene resin exceeding 3.5 is used, the appearance of the foam is inferior.
Mw and Mz / Mw can be adjusted by adjusting polymerization conditions such as temperature, polymerization initiator, chain transfer agent, and crosslinking agent, and mixing of various styrene resins.
In addition, the measurement of Mw and Mz / Mw in this invention was performed on condition of the following using GPC (Shodex system-21) by Showa Denko KK.
(1) Column: PL MIXED-B 30 cm x 3 (2) Mobile phase: THF
(3) Concentration: 0.3% by weight
(4) Temperature: 38 ° C
[0010]
The styrenic resin of the present invention has a weight loss (heat loss) of less than 0.5% by weight, preferably 0.4% when heated to 10 ° C / min from 200 ° C to 300 ° C under a nitrogen stream. %, More preferably less than 0.3% by weight. When a styrene resin with a weight loss of 0.5% by weight or more is used, not only the odor of the foam becomes stronger, but also the foaming performance decreases, such as the reduction of the closed cell ratio in the foam. When it is improved, the foaming performance is remarkably lowered, and the strength and appearance of the obtained foam are inferior.
Adjustment of heat loss can be adjusted with additives such as plasticizers and lubricants, oligomers generated during polymerization, or thermal decomposition products during extrusion and molding.
The heating loss in the invention was measured under the following conditions using a thermal analyzer (SSC-5200) manufactured by Seiko Electronics Industry.
(1) Temperature rising rate: 10 ° C / min (2) Nitrogen: 100 mL / min (3) Sample amount: about 10 mg
[0011]
The styrene monomer remaining in the styrene resin of the present invention is less than 1000 ppm, preferably less than 700 ppm, more preferably less than 500 ppm. When the remaining styrene monomer is 1000 ppm or more, the odor of the foam becomes strong, and the foaming performance is also affected, the closed cell ratio in the foam is lowered, and the strength of the foam is inferior. The remaining amount of the remaining styrenic monomer can be adjusted by adding a high-temperature decomposable polymerization initiator, the degree of vacuum at the time of devolatilization, the heating temperature and the time.
The benzaldehyde remaining in the styrene resin of the present invention is less than 50 ppm, preferably less than 30 ppm, and more preferably less than 15 ppm. If the remaining benzaldehyde is 50 ppm or more, the odor is strong.
Benzaldehyde is produced as a by-product during the polymerization of the styrene monomer, and the residual amount can be adjusted by the amount of oxygen present in the system, the degree of vacuum during devolatilization, and the like.
The styrene monomer and benzaldehyde in the present invention were measured under the following conditions using GC (GC12A) manufactured by Shimadzu Corporation.
(1) Column: Glass column 3mmφ, 3m
(2) Mobile phase: Nitrogen (3) Injection volume: 1 μL (internal standard method)
(4) Temperature: 115 ° C
[0012]
The styrenic resin used in the present invention may be added with known additives such as mineral oil, higher fatty acid, higher fatty acid salt, higher fatty acid amide, antioxidant, weathering agent, antistatic agent, and sliding agent. There is no problem.
[0013]
The styrenic resin of the present invention can be made into a foam by a known method.
For example, volatile foaming agents such as propane, butane, pentane, etc. or a combination of bicarbonate and organic acid salt are used as blowing agents, talc, sodium bicarbonate, citric acid, etc. are used as nucleating agents. Examples thereof include a foam extrusion method. The foaming ratio of the foam is not particularly limited, but is preferably 1.5 to 50 times, more preferably 5 to 30 times.
Further, the foam may have any shape, and may be, for example, a sheet shape, a plate shape, or a shape obtained by molding these.
[0014]
【Example】
Next, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.
In addition, the physical property test method of an Example is described below.
(1) Strength: A sphere having a weight of 300 g was dropped at a different height to show a 50% fracture height at which the foam was broken.
(2) Appearance: When the appearance of the foam is visually observed and the surface bubbles are dense, “◯”. When the surface bubbles are rough and uneven or the surface bubbles are broken, “×” In the middle, “△” was used.
(3) Closed-cell ratio: Observe the cross section of the foam with a microscope, and mark “O” when almost all closed cells are observed, “△” when some open cells are observed, and when many open cells are observed. It was set as “x”.
{Circle around (4)} Odor: 10 g of foam was put into a 1 L sealed container, and the odor inside the container after 1 day was sniffed. When there was little odor, “◯” was given, and when there was much odor, “X” was given.
[0015]
Example 1
A reactor with an internal volume of 15 L, a reactor equipped with a stirrer was sufficiently purged with nitrogen, charged with 7 kg of pure water subjected to nitrogen bubbling, 5 g of tribasic calcium phosphate and 0.1 g of sodium dodecylbenzenesulfonate, and 7 kg of styrene monomer while stirring. 7 g of t-butyl peroxyacetate, 7 g of di- (t-butyl peroxide), 0.7 g of divinylbenzene, and 14 g of α-methylstyrene dimer were charged. Then, after enclosing nitrogen, heating was carried out at a temperature of 110 ° C. for 5 hours and at 135 ° C. for 2 hours to complete the polymerization. The obtained bead-shaped resin is neutralized, filtered and dried, and then extruded using a 40 mm single screw extruder while devolatilizing at a temperature of 230 ° C. and a pressure of 10 torr to obtain a pellet-shaped styrene resin. It was.
After adding 1 part by weight of talc as a cell nucleating agent and 0.1 part by weight of zinc stearate as a dispersion aid to 100 parts by weight of the styrenic resin, the mixture is mixed well with a mixer, and then placed in a hopper of a 40 mm single screw extruder. Supplied. It was melt-kneaded at a temperature of about 220 ° C. at the front stage of the screw of the extruder, and butane gas was continuously injected into the melt-kneaded product from a blowing agent injection hole provided in the middle stage of the extruder. It is cooled to a temperature of 160 ° C. at the subsequent stage of the extruder, extruded and foamed in a tubular shape from a cylindrical die at a discharge rate of 10 kg / h, and after cooling with a mandrel, one side of the tubular foamed sheet is cut open by a cutter, and the thickness is 2.5 mm and the density is 0. 072 g / cc of sheet-like foam A was obtained.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
Further, by adjusting the amount of butane gas and the screw rotation speed of the extruder, the discharge amount is 10 kg / h, the sheet-like foam B having a thickness of 2.5 mm and the density of 0.064 g / cc, and the discharge amount is 15 kg / h. A sheet-like foam C having a thickness of 2.5 mm and a density of 0.072 g / cc was obtained.
The physical properties of the obtained foam B and foam C are shown in Table 3.
[0016]
Example 2
Styrenic resin and foam A were obtained in the same manner as in Example 1 except that 14 g of α-methylstyrene dimer was not added.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0017]
Example 3
Styrenic resin and foam A were obtained in the same manner as in Example 1 except that 14 g of α-methylstyrene dimer was changed to 28 g.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0018]
Example 4
Styrenic resin and foam A were obtained in the same manner as in Example 1 except that 0.7 g of divinylbenzene was changed to 1.4 g and 14 g of α-methylstyrene dimer was changed to 28 g. Further, in the same manner as in Example 1, foam B and foam C were obtained.
Table 1 shows the physical properties of the obtained styrenic resin and foam A, and Table 3 shows the physical properties of foam B and foam C.
[0019]
Example 5
A styrene resin and foam A were obtained in the same manner as in Example 1 except that 0.7 g of divinylbenzene and 14 g of α-methylstyrene dimer were not added.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0020]
Example 6
A styrene resin and foam A were obtained in the same manner as in Example 1 except that 7 g of t-butyl peroxyacetate was changed to 3.5 g.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0021]
Example 7
Styrenic resin and foam A were obtained in the same manner as in Example 1 except that 7 g of di- (t-butyl peroxide) was changed to 3.5 g.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0022]
Example 8
Styrenic resin and foam A were obtained in the same manner as in Example 1 except that nitrogen filling after the polymerization can was charged was not performed.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0023]
Example 9
A third reaction comprising a first reactor which is a fully mixed stirring tank having a capacity of about 20 L, a second reactor which is a fully mixing stirring tank having a capacity of about 15 L, and a column type plug flow reactor with a stirrer having a capacity of about 7 L. The reactor was connected in series, and two vacuum devolatilization tanks equipped with a preheater were connected in series to constitute a polymerization step. After sufficiently replacing the system with nitrogen, 85 parts by weight of styrene monomer, 15 parts by weight of ethylbenzene, 0.015 part by weight of 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane and t -A raw material solution prepared by mixing 0.015 parts by weight of butyl peroxyisopropyl monocarbonate under a nitrogen atmosphere was continuously supplied at a rate of 4.3 L / h, taking care not to allow air to enter the first reactor. The reaction temperature in each reactor is adjusted to be 111 ° C. in the first reactor and 125 ° C. in the second reactor, and the gradient from 125 ° C. to 145 ° C. along the flow direction in the third reactor. I adjusted it to be on. The conversion of styrene monomer to polymer at the outlet of each reactor was about 30% in the first reactor, about 65% in the second reactor, and about 80% in the third reactor. The polymerization liquid continuously led from the third reactor to the vacuum devolatilization tank was prepared by adding unreacted monomer and ethylbenzene at a temperature of 180 ° C. in the first devolatilization tank and a pressure of 400 torr in the second devolatilization tank and 3 torr at 250 ° C. in the second devolatilization tank. After separating from the polymer, it was extruded into a strand shape, cooled, cut, and pelletized to obtain a styrene resin. Further, a foam A was obtained in the same manner as in Example 1.
Table 1 shows the physical properties of the obtained styrenic resin and foam A.
[0024]
Comparative Example 1
Except that 0.015 part by weight of 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane was not added and 0.03 part by weight of t-butylperoxyisopropyl monocarbonate was used. Styrenic resin and foam A were obtained in the same manner as in Example 9. Further, in the same manner as in Example 1, foam B and foam C were obtained.
Table 2 shows the physical properties of the obtained styrenic resin and foam A, and Table 3 shows the physical properties of foam B and foam C.
Table 2 shows that the strength of the foam is inferior. Further, it can be seen from Table 3 that the appearance performance is slightly lowered due to weight reduction and productivity improvement.
[0025]
Comparative Example 2
A styrene resin and foam A were obtained in the same manner as in Example 1 except that 0.7 g of divinylbenzene and 70 g of α-methylstyrene dimer were changed to 70 g.
Table 2 shows the physical properties of the obtained styrenic resin and foam A. Table 2 shows that the appearance of the foam is inferior.
[0026]
Comparative Example 3
A styrene resin and foam A were obtained in the same manner as in Example 1 except that 7 g of t-butyl peroxyacetate was not added. Further, in the same manner as in Example 1, foam B and foam C were obtained.
Table 2 shows the physical properties of the obtained styrenic resin and foam A, and Table 3 shows the physical properties of foam B and foam C. From Table 2, it can be seen that the strength of the foam is inferior and the odor is strong, and from Table 3, the strength is further reduced by weight reduction and productivity improvement, and the appearance and the like are also inferior.
[0027]
Comparative Example 4
A styrene resin and foam A were obtained in the same manner as in Example 1 except that 7 g of di- (t-butyl peroxide) was not added.
Table 2 shows the physical properties of the obtained styrenic resin and foam A.
Table 2 shows that the odor of the foam is strong.
[0028]
Comparative Example 5
A styrene resin and foam A were obtained in the same manner as in Example 1 except that pure water that was not subjected to nitrogen bubbling was used.
Table 2 shows the physical properties of the obtained styrenic resin and foam A.
Table 2 shows that the odor of the foam is strong.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
[Table 3]

[0032]
【The invention's effect】
The styrenic resin of the present invention has good foaming performance, can be reduced in weight and productivity, and can be reduced in cost compared to conventional styrenic resins. In addition, the foamed body is excellent in strength and appearance, has little odor, and is useful in the foaming field of food packaging materials, building materials, cushioning materials and the like.

Claims (1)

A styrene resin having a weight average molecular weight (Mw) of 150,000 to 600,000 and a Z average molecular weight (Mz) ratio Mz / Mw of 1.8 to 3.5, and (A) a temperature of 200 under a nitrogen stream. Food packaging comprising a foam formed by foaming a styrenic resin having a weight loss of less than 0.5% by weight when heated from 10 ° C. to 300 ° C. at a rate of 10 ° C./min, and (B) the remaining benzaldehyde is less than 50 ppm Wood .