JP3574297B2 - Method for producing polystyrene resin foam and polystyrene resin foam produced by the method - Google Patents

Description

【００６７】
表１に示された結果から、実施例１〜１０で得られた発泡体は、主発泡剤として二酸化炭素を用い、樹脂温度１００℃という低温で押出発泡させたにも関わらず、いずれも高発泡倍率および高独立気泡率を有し、圧縮強度、表面性の優れ、かつ発泡助剤の残存率の低い発泡体であることがわかる。
【００６８】
【発明の効果】
本発明によってえられたポリスチレン系樹脂発泡体は、二酸化炭素を主発泡剤として用いるにもかかわらず、高発泡倍率および高独立気泡率を有し、外観が美麗なものである。
【００６９】
したがって、本発明のポリスチレン系樹脂発泡体は、たとえば各種断熱材、各種緩衝剤、各種ディスプレイ板、各種浮板などとして好適に使用しうるものである。
【図面の簡単な説明】
【図１】Ａはポリスチレン１００重量部に添加された塩化メチルの量と該塩化メチルが添加されたポリスチレンの溶融剪断粘度との関係を表わすグラフ、Ｂはポリスチレン１００重量部に添加された塩化エチルの量と該塩化エチルが添加されたポリスチレンの溶融剪断粘度との関係を表すグラフ、Ｃはポリスチレン１００重量部に添加されたテトラヒドロフランの量と該テトラヒドロフランが添加されたポリスチレンの溶融剪断粘度との関係を表わすグラフ、Ｄはポリスチレン１００重量部に添加されたアセトンの量と該アセトンが添加された溶融剪断粘度との関係を表すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a polystyrene-based resin foam which can be used mainly as a material for building and civil engineering, and a polystyrene-based resin foam produced by the method.
[0002]
[Prior art]
In the production of extruded polystyrene resin foam, which is often used for building materials, a method of using a physical foaming agent for foaming the resin using the volume expansion from the liquid phase or solid phase to the gas phase is used for the polystyrene resin. Many are used.
[0003]
However, the physical foaming agent does not only mean that the polystyrene resin foams due to volume expansion, but also the bubble size in the foam, the growth rate of the foam, and the foaming agent in the foam of the manufactured foam. It has been clarified that the thermal properties of the foam greatly affect the mechanical properties of the foam. For this reason, in developing the extrusion foaming technique, selection of a physical foaming agent has been a main research topic in order to obtain desired performance.
[0004]
In recent years, as a physical type foaming agent, the chlorine atom-containing fluorocarbon used conventionally has a small greenhouse effect with respect to the chlorine atom-containing fluorocarbon from the viewpoint of protection of the ozone layer and from the viewpoint that it is inexpensive. Attempts have been made to use carbon dioxide as a physical foaming agent in view of the fact that there is no problem in terms of safety (JP-A-51-7068, JP-B-6-41161, No. 81346).
[0005]
However, when using carbon dioxide alone as a foaming agent, the extrusion temperature may be relatively high and the cooling rate may be slow, and the resulting foam has poor surface properties and a low closed cell rate or a low magnification. (For example, JP-A-3-81346).
[0006]
On the other hand, in the production of polystyrene resin foam, chlorine-containing compounds such as methyl chloride and ethyl chloride reduce the melt viscosity of the polystyrene resin, form a gel that can be foamed at a lower temperature, and have a closed cell rate and It is widely used as a physical foaming agent which is expected to improve the magnification (Japanese Patent Publication No. 41-672). Thus, it is also known that use of methyl chloride or the like improves the appearance.
[0007]
However, since the above-mentioned methyl chloride, ethyl chloride and the like are chlorine-containing blowing agents, it is desired that a good foam can be obtained by using a chlorine-free compound if possible.
[0008]
In this connection, as an attempt to lower the melt viscosity of the polystyrene resin, it has been studied to mix a polystyrene resin homopolymer with another copolymer, and to add a plasticizer for the polystyrene resin. (Tokuhyo Hei 8-510495, etc.). However, the foam obtained by these attempts to lower the melt viscosity of the resin in advance, the physical properties such as compressive strength are reduced because the plasticizer etc. remains in the resin forming the cells of the foam, and the heat resistance Tend to be inferior.
[0009]
[Problems to be solved by the invention]
In view of the above, the present invention has no problems in terms of occupational health and environmental hygiene, has a high expansion ratio and a high closed cell ratio, and has a method for producing a polystyrene resin foam having a beautiful appearance and a method for producing the same. It is an object to provide a manufactured polystyrene resin foam.
[0010]
[Means for Solving the Problems]
The inventors of the present invention have conducted intensive studies to solve the above-described problems.As a result of extruding and foaming a polystyrene-based resin, a compound containing no chlorine atom is used as a foaming agent and a foaming aid having no chlorine atom. A foaming agent containing carbon dioxide in an amount of more than 60% by weight and less than 80% by weight based on the total weight of the foaming agent. By using a foaming aid that has a low amount remaining in the foam after production, the ozone layer destruction and global warming tend to be small, environmental compatibility is excellent, and heat insulation and mechanical properties are improved. It has been found that an extruded polystyrene resin foam having excellent and excellent appearance can be obtained, and the present invention has been completed.
[0011]
That is, in the present invention, (1) a polystyrene resin is heated and melted, a foaming agent is blended to form a foamable gel substance, and the gel substance is cooled to a temperature suitable for foaming, and the gel substance is cooled. In a method for producing a polystyrene resin foam comprising extruding through a die to a lower pressure region and forming a foam, a foaming agent containing no chlorine atom in the molecule and a foaming containing no chlorine atom in the molecule Use auxiliaries,
As the blowing agent, one containing more than 60% by weight and less than 80% by weight of carbon dioxide based on the total weight of the blowing agent,
As the foaming aid, the following properties (a) to (c):
(A) 5 parts by weight were added to 100 parts by weight of a polystyrene resin, and the shear rate was 122 s at 170 ° C. ^-1 The melt viscosity measured in the above is less than half the melt viscosity measured under the same conditions for only the polystyrene resin,
(B) a permeation rate at 25 ° C. for a membrane made of the polystyrene resin is higher than an air permeation rate under the same conditions;
(C) the critical temperature is equal to or higher than the resin temperature at the time of extrusion;
The present invention relates to a method for producing a polystyrene-based resin foam, characterized by using a material having:
[0012]
Further, the present invention is characterized in that (2) the foaming auxiliary is at least one selected from the group consisting of ethers, ketones and esters having a boiling point of 30 to 90 ° C. The present invention relates to a method for producing a polystyrene-based resin foam as described in the above item.
[0013]
Further, the present invention provides a foam produced by the method according to the above (1) or (2), wherein the foaming aid contains 0.01% by weight or more and 1% by weight or less based on the total weight of the foam. And a polystyrene resin foam.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The polystyrene resin used in the present invention is not particularly limited as long as it can be foamed.
[0015]
Representative examples of the polystyrene resin include, for example, styrene; methylstyrenes such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, trimethylstyrene; Chlorostyrenes such as -chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene and trichlorostyrene; α-bromostyrene, β-bromostyrene, o-bromostyrene, Bromostyrenes such as m-bromostyrene, p-bromostyrene, dibromostyrene and tribromostyrene; α-fluorostyrene, β-fluorostyrene, o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, difluorostyrene, Trif Fluorostyrenes such as fluorostyrene; nitrostyrenes such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxy Vinylphenols such as styrene and trihydroxystyrene; divinylbenzenes such as o-divinylbenzene and p-divinylbenzene; styrenes such as diisopropenylbenzenes such as o-diisopropenylbenzene and m-diisopropenylbenzene. Homopolymers of the compounds, copolymers of two or more of the styrene compounds, copolymers of the styrene compounds with copolymerizable monomers such as methyl methacrylate, acrylonitrile, butadiene, and the like. The polystyrene resins are used alone or in combination of two or more.
[0016]
The blowing agent used in the present invention is a mixture of carbon dioxide as a main blowing agent and a physical blowing agent containing no chlorine atom in other molecules.
[0017]
Examples of the physical foaming agent other than carbon dioxide include hydrocarbons having a boiling point of 30 ° C. or lower, fluorinated hydrocarbons, ethers, and the like, which are generally suitably used for polystyrene resin extrusion foaming. As the hydrocarbons, for example, propane (-42.1 ° C (indicating the boiling point, the same applies hereinafter)), n-butane (-0.5 ° C), i-butane (-11.7 ° C), i- Examples of fluorinated hydrocarbons such as pentane (27.9 ° C) include difluoromethane (HFC-32, -51.7 ° C), trifluoromethane (HFC-23, -82.0 ° C), 1,1-difluoroethane. (HFC-152a, −24.1 ° C.), 1,1,1-trifluoroethane (HFC-143a, −47.3 ° C.), 1,1,1,2-tetrafluoroethane (HFC-134a, − Ethers such as dimethyl ether (-24.8 ° C.) and methyl ethyl ether (6.6 ° C.).
[0018]
The amount of carbon dioxide in the total foaming agent is preferably more than 60% by weight and less than 80% by weight, which is the amount used as the main foaming agent, from the viewpoint of occupational health and environmental hygiene. When the content is 60% by weight or less, the effect of using carbon dioxide having high environmental compatibility is reduced, and the flammability of the flammable foaming aid tends to appear in the foam, and the industrial application field is likely to be restricted. . If the content is 80% by weight or more, carbon dioxide is too much, so that deterioration in surface properties and decrease in closed cell rate cannot be sufficiently solved.
[0019]
Further, the total weight of the blowing agent is 2 parts by weight or more, especially 5 parts by weight, based on 100 parts by weight of the polystyrene resin in order to produce a foam having a high expansion ratio using a blowing agent mainly composed of carbon dioxide. In order to improve the distribution of cell diameters, improve the heat insulating property by preventing the breakage of the cells and improve the heat insulation, the weight is preferably 20 parts by weight or less, more preferably 15 parts by weight, per 100 parts by weight of the polystyrene resin. Parts or less.
[0020]
Further, in the present invention, as a foaming aid, those containing no chlorine atom in the molecular structure,
(A) 5 parts by weight were added to 100 parts by weight of a polystyrene resin, and the shear rate was 122 s at 170 ° C. ^-1 The melt viscosity measured in the above is less than half the melt viscosity measured under the same conditions for only the polystyrene resin,
(B) a permeation rate at 25 ° C. for a membrane made of the polystyrene resin is higher than an air permeation rate under the same conditions;
(C) the critical temperature is equal to or higher than the resin temperature at the time of extrusion;
It is a great feature that a foaming aid having the following properties (hereinafter referred to as a non-chlorine foaming aid) is used simultaneously with a foaming agent containing carbon dioxide in extrusion foaming of a polystyrene resin as described above. .
[0021]
Here, the use of the non-chlorine-based foaming aid as described above is based on the present inventors' studies on the melt shear viscosity of the resin as described below.
[0022]
As described above, in extrusion foaming of a polystyrene resin, generally, a physical foaming agent is injected under pressure into a molten polystyrene resin, mixed under high pressure, and extruded from the die of an extruder into the atmosphere and rapidly extruded. And a method of expanding the foam into a foam.
[0023]
When extruding a foamable gel from a die, when the temperature is high, the foamed gel is solidified, that is, the time until the foam film is fixed is long, and the state where the elastic modulus is low for a relatively long time is maintained, The air bubbles that have been generated will be broken.
[0024]
On the other hand, when methyl chloride or the like is added, the viscosity of the foamable gel can be achieved at a low temperature, and this phenomenon can be avoided.
[0025]
Curve A in FIG. 1 shows the amount of methyl chloride added to 100 parts by weight of polystyrene and the melt shear rate of the polystyrene to which the methyl chloride was added (resin temperature: 170 ° C., shear rate: 122 s). ^-1 And curve B represent the amount of ethyl chloride added to 100 parts by weight of polystyrene, the amount of ethyl chloride added to 100 parts by weight of polystyrene to which the ethyl chloride was added, and the curve B. Shear viscosity of polystyrene to which is added (resin temperature: 170 ° C., shear rate: 122 s) ^-1 3) shows a graph representing the relationship with (). The polystyrene was used in Examples described later, and details of the measurement of the melt shear rate are shown in Examples.
[0026]
As is clear from graphs A and B in FIG. 1, methyl chloride or ethyl chloride, which is usually used in the production of an extruded polystyrene resin foam, is added in an amount of, for example, 4 parts by weight or more based on 100 parts by weight of polystyrene. In such a case, the melt shear viscosity is halved compared to the melt shear viscosity of polystyrene alone, and a viscosity suitable for foaming can be achieved at a relatively low temperature.
[0027]
However, when the viscosity is too low, the obtained foam may shrink or the heat resistant temperature of the foam may decrease.
[0028]
The amount of the non-chlorine foaming aid depends on the amount of the foaming aid remaining when the foam is formed, the state of dissipation from the foam or the speed, and therefore the viscosity reduction performance of the non-chlorine foaming aid. Although it is difficult to determine the amount of addition in the case of estimating the total, 170 ° C. and a shear rate of 122 s when approximately 5 parts by weight are added ^-1 It is preferable that the decrease in the viscosity measured in step 1 becomes about 1/2 or less as compared with the case where the foaming aid is not added.
[0029]
The performance of reducing the viscosity of the non-chlorine foaming aid is evaluated by assuming the kneading state of the polystyrene resin and the non-chlorine foaming aid, the state of the extruder outlet, and the temperature decrease in the extruder, This is the evaluation with the highest industrial utility value. From this point, in the case of extrusion, 170 ° C. and a shear rate of 122 s ^-1 Is suitable for evaluating the state of the die portion of the extruder, and the melt viscosity can be easily measured with a capillograph device or the like.
[0030]
Further, other than the viscosity reducing performance, important characteristics that the non-chlorine foaming auxiliary should have are also found.
[0031]
In order for bubbles to be stably fixed, they must be quickly solidified from a molten state and form a strong film. In order to achieve rapid solidification, the heat of vaporization when the foaming agent or foaming aid undergoes a phase change from liquid or solid to gas during extrusion foaming is effectively applied. To do so, it is necessary that the critical temperature is, for example, 100 ° C. or higher, preferably the resin temperature at the time of extrusion.
[0032]
Also, when a foaming aid is contained in a foam in a large amount, mechanical properties such as compressive strength and bending strength are reduced, and viscosity tends to decrease as the temperature increases. Physical property deterioration becomes remarkable. For this reason, the foaming aid remaining in the foam should be reduced to such an extent that no problem occurs immediately. Further, by rapidly dispersing the foam out of the foam, the viscosity increases, and the same effect as when the temperature of the foam is lowered can be provided. However, a trace amount of residue is generally preferable for a hard and brittle foam in terms of the development of flexibility.
[0033]
The dissipation rate of the substance out of the foam is evaluated based on the magnitude relationship between the permeation rate of the substance through the polystyrene resin membrane and the permeation rate of the air. That is, the permeation rate of the air is compared with the permeation rate of the substance. If the permeation rate of the substance is higher, the substance is quickly discharged out of the foam. The permeation rate is determined by measuring the amount of the measurement substance leaking to the inert gas side by joining a chamber filled with a measurement substance on one side and an inert gas, for example, at 25 ° C. with a polystyrene resin film exposed. It is quantified by a gas chromatograph or the like at regular intervals, and the speed can be easily calculated from the time and amount from the start of leakage to the inert gas side to the stable state. At this time, since a substance having a boiling point higher than 25 ° C. does not reach 1 atm, it is sufficient to use saturated steam in a mixed gas with air and evaluate the magnitude of the speed with air based on the partial pressure of steam.
[0034]
Due to the cooling effect due to the heat of vaporization and dissipation to the outside of the foam, the foam film is rapidly solidified and fixed, so that the destruction of the bubbles can be prevented, and a foam having a high expansion ratio can be obtained stably. .
[0035]
As a result of the above examination, by adding to the polystyrene resin, the effect of lowering the viscosity with respect to the polystyrene resin is sufficiently exhibited, the dissipation to the outside of the foam is fast, and the critical temperature is higher than the resin temperature at the time of extrusion. As a substance which can be suitably used as a foaming auxiliary having the requirement that the compound does not contain a chlorine atom, ethers, ketones and esters having a boiling point of 30 to 90 ° C. are preferable.
[0036]
Examples of the ethers, ketones, and esters used as the foaming aid in the present invention include ethyl ether (34.6 ° C.), methylal (42.3 ° C.), isopropyl ether (68.3 ° C.), and furan. (31.3 ° C.), ethers such as 2-methylfuran (62 to 64 ° C.), tetrahydrofuran (66 ° C.) and tetrahydropyran (88 ° C.); acetone (56.2 ° C.), methyl ethyl ketone (79.6 ° C.) Ketones such as ethyl formate (54.3 ° C.), propyl formate (81.3 ° C.), methyl acetate (57.8 ° C.), ethyl acetate (77.1 ° C.), isopropyl acetate (89.0 ° C.), Esters such as methyl propionate (79.7 ° C.) are preferably exemplified, and these can be used alone or in combination of two or more.
[0037]
Among them, the use of a small amount of 5 parts by weight or less with respect to 100 parts by weight of the polystyrene resin is equivalent to the plasticizing effect of methyl chloride and ethyl chloride usually used in the production of an extruded polystyrene resin foam. Methylal, furan, 2-methylfuran, tetrahydrofuran, acetone, methyl ethyl ketone, and ethyl formate are more preferred from the viewpoint that the effect of (1) is exhibited, safety, and price.
[0038]
The amount of the foaming aid used is such that the heat resistance of the obtained foam is not adversely affected, that is, 5 parts by weight or less, preferably 3 parts by weight or less, per 100 parts by weight of the polystyrene resin. Further, the lower limit may be any amount as long as the effects of the present invention are exhibited, and for example, 0.5 parts by weight or more is preferable.
[0039]
As described above, the amount of carbon dioxide in the total foaming agent is an amount exceeding 60% by weight due to the requirements of occupational health and use restrictions as described above. Further, it is preferable that carbon dioxide is less than 80% by weight in the total foam. If the amount exceeds 80% by weight, the effect of improving the closed cell rate is small even if a small amount of the foaming aid is added, and therefore the mechanical properties are reduced.
[0040]
On the other hand, when the foaming assistant is used in an increased amount, the closed cell ratio is improved, but at the same time, the amount of the foaming assistant remaining in the foam increases. As described above, the heat resistance is lowered in this case. It is effective to use the foaming aid even when the amount of carbon dioxide is reduced to 60% by weight or less, but if the amount of carbon dioxide is reduced, other foaming agents become the main foaming agent, and the cost, flammability, etc. It can be problematic in point. Another feature of the present invention is that it overcomes the industrial disadvantages of carbon dioxide, which is excellent in price, occupational health, environmental compatibility, production equipment and management costs, and has high utilization, and therefore does not conform to the spirit of the present invention. .
[0041]
In particular, the optimum amount of carbon dioxide cannot be determined unconditionally because it is affected by the type and amount of the foaming aid used, but a range of 65 to 75% by weight provides a good foam having particularly good mechanical properties. .
[0042]
As described above, the present invention has a viscosity reducing effect on polystyrene-based resin without modifying a portion related to essential strength and physical properties such as resin modification, and has a boiling point of 30 to 90 ° C. It is one of the great features of the present invention to use at least one of ethers, ketones, and esters not containing as a foaming aid, and also uses carbon dioxide as a main foaming agent, and as a foaming aid. The use of at least one of the ethers, ketones, and esters in combination is also one of the great features of the present invention.
[0043]
Further, in the present invention, if necessary, within a range that does not inhibit the object of the present invention, an antioxidant, a metal deactivator, a phosphorus-based stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent brightener, Commonly used additives such as a stabilizer such as metal soap, a nucleating agent, a lubricant, a filler, a reinforcing agent, a pigment, a flame retardant, and an antistatic agent may be appropriately added.
[0044]
The extruded polystyrene resin foam of the present invention can be produced by a known extrusion foaming method itself in the foaming operation. For example, a predetermined amount of a polystyrene resin and, if necessary, an additive are mixed, heated and melt-kneaded, and then a foaming agent and a foaming aid are added or press-fitted to the foamable resin composition prepared at a high temperature and a high pressure. The foamed product of the present invention is obtained by mixing under the following conditions and then extruding to foam in a low pressure range.
[0045]
There are no particular restrictions on the heating temperature, melt-kneading time and melt-kneading means when the resin mixture is heated and melt-kneaded. The heating temperature may be equal to or higher than the temperature at which the polystyrene-based resin is melted, usually about 150 ° C. to 250 ° C. The melt-kneading time cannot be determined unequivocally because it differs depending on the extrusion amount per unit time, the melt-kneading means, and the like. However, usually, the time required for uniformly dispersing the polystyrene resin and, for example, the additive is selected. The melt-kneading means is not particularly limited as long as it is one used for ordinary extrusion foaming, such as a screw-type extruder.
[0046]
The foaming agent and the foaming assistant may be added or press-fitted into the heat-melt kneaded material at the same time, or may be dividedly added or press-fitted. The present invention is not limited by the method of adding or press-fitting such a foaming agent.
[0047]
The pressure at which the foaming agent and the foaming aid are pressed into the heat-melt kneaded material is not particularly limited, and may be any pressure as long as it is higher than the internal pressure of the extruder in order to press it into the extruder.
[0048]
The heat-melt kneaded product to which the foaming agent and the foaming aid have been added or press-fitted is then extruded through a commonly used foaming device such as a slit die into a low-pressure region such as under atmospheric pressure to be foamed. You. At that time, the resin temperature at the time of extrusion can be as low as 100 to 120 ° C., and varies depending on the type and amount of the foaming aid to be added. The extrusion temperature can be lowered by about 40 ° C., which is extremely useful industrially.
[0049]
Thus, as a foaming aid, it lowers the melt viscosity of the polystyrene-based resin, and easily escapes from the foam, is difficult to remain, has a high critical temperature, and has at least one of ethers, ketones, and esters having a boiling point of 30 to 90 ° C. By using one kind in combination with a foaming agent containing carbon dioxide as a main component, an effect equivalent to the effect of reducing the viscosity of the resin by adding a chlorine-containing compound such as methyl chloride or ethyl chloride can be obtained, and foam molding can be performed. Reduced the viscosity of the molten resin to the extent that it is possible, with little foaming aid remaining in the obtained foam, high foaming ratio and closed cell rate, and excellent appearance, excellent work hygiene environment A polystyrene resin foam is obtained.
[0050]
The residual ratio of the foaming aid in the foam (referred to as the content (% by weight) contained in the foam after several days (for example, three days) after the production of the foam) is 0.01% by weight or more and 1% by weight % Or less is preferable. If the residual ratio of the foaming aid exceeds the above range, the mechanical properties tend to decrease, while if it is less than the above range, the foam tends to become brittle.
[0051]
According to the method for producing a polystyrene resin foam of the present invention, a high expansion ratio, a high closed cell rate, and a beautiful appearance can be suitably used as various heat insulating materials, various cushioning materials, various display plates, various floating plates, and the like. A polystyrene resin foam is obtained. These foams can be used for any application that requires the above properties, but at present, construction materials, civil engineering materials, furniture and the like are preferred examples of their use.
[0052]
The polystyrene-based resin foam of the present invention uses carbon dioxide having no problem on occupational health and environmental hygiene as a main blowing agent, has a high expansion ratio and a high closed cell rate, and has a beautiful appearance. The fact that a foam having excellent properties was obtained is based on repeated studies to solve the problems of the prior art.
[0053]
【Example】
Next, the method for producing a polystyrene resin foam of the present invention and the obtained foam will be described in more detail based on Examples, but the present invention is not limited to only these Examples.
[0054]
In graph C of FIG. 1, tetrahydrofuran (THF) added to 100 parts by weight of a polystyrene resin (trade name: Estyrene G-17, manufactured by Nippon Steel Chemical Co., Ltd., melt index (MI): 3.1) And the melt shear viscosity of polystyrene to which the tetrahydrofuran was added (resin temperature: 170 ° C., shear rate: 122 s) ^-1 4 shows a graph representing the relationship with ()). The graph D in FIG. 1 shows the amount of acetone added to 100 parts by weight of the polystyrene resin and the melt shear viscosity of the polystyrene to which the acetone was added (resin temperature: 170 ° C., shear rate: 122 s). ^-1 3) shows a graph representing the relationship with (). The melt shear viscosity was measured by mounting a die having a diameter of 1 mm and a length of 10 mm on a Capillograph manufactured by Toyo Seiki Co., Ltd. As is clear from graphs C and D in FIG. 1, the addition of 5 parts by weight or less of both acetone and tetrahydrofuran reduces the melt shear rate by half compared to the melt shear rate of the polystyrene resin alone.
[0055]
Further, with respect to acetone and tetrahydrofuran, the above-mentioned polystyrene resin film (thickness: 50 μm) was fixed to a gas permeation amount measurement device (manufactured by LISY Corporation, GPM-200), and the amount of gas permeated through the film was measured by gas chromatography ( The permeation rate was calculated from the amount of permeation with respect to time using Fick's first and second laws, and Henry's law, as a result of the measurement using the 663-30 (manufactured by Hitachi, Ltd.). The permeation rate is more than twice as high as air and easily dissipates from the foam into the air.
[0056]
The respective critical temperatures are acetone 235 ° C. and tetrahydrofuran 267 ° C., which are higher than the resin temperature at extrusion (100 ° C.), and the heat of vaporization can be used.
[0057]
Examples 1 to 10
0.1 part by weight of talc as a nucleating agent, flame retardant per 100 parts by weight of a polystyrene resin (trade name: Estyrene G-17, manufactured by Nippon Steel Chemical Co., Ltd., melt index (MI): 3.1) And 3.0 parts by weight of hexabromocyclododecane was mixed for 15 minutes using a ribbon blender. This mixture is supplied to a tandem extruder (first-stage extruder: cylinder diameter 40 mm, second-stage extruder: cylinder diameter 50 mm), melted in the first-stage extruder at 210 ° C., and then subjected to first-stage extrusion. The foaming agent and foaming aid shown in Table 1 are press-fitted and kneaded from the pressure inlet provided in the latter half of the cylinder of the machine so that the resin temperature in the second-stage extruder becomes 100 ° C. After cooling, the orifice was extruded from a circular die having a diameter of 3 mm and a land length of 25 mm to obtain a round bar-shaped polystyrene resin foam.
[0058]
The expansion ratio, closed cell ratio, compressive strength, and residual ratio of the foaming aid of the obtained foam were measured in accordance with the following methods, and the appearance was visually evaluated based on the following evaluation criteria. Table 1 shows the evaluation results.
[0059]
(1) Expansion ratio
The approximate density of the mixture of the polystyrene resin, the nucleating agent and the flame retardant is set to 1.05 (g / cm ³ ) As the formula:
Expansion ratio (times) = 1.05 / density of foam (g / cm ³ )
Ask based on.
[0060]
The density of the foam is calculated from the weight of the foam and the volume obtained by the submersion method.
[0061]
(2) Closed cell rate
Using a multi-pycnometer (product name, manufactured by Yuasa Ionics Co., Ltd.), the measurement is performed according to ASTM D-2856.
[0062]
(3) Compressive strength
It is measured according to JIS A 9511 using an autograph (AG-2000 manufactured by Shimadzu Corporation).
[0063]
(4) Evaluation criteria for appearance
◎: A foam having very good appearance without unfoamed resin lumps and voids in the cross section and without wrinkles and protrusions on the surface.
：: A foam having a good appearance, though a little unfoamed resin mass or void is present in the cross section, or a few wrinkles or protrusions are present on the surface.
X: A foam having a poor appearance in which an unfoamed resin mass and voids are present in the cross section and wrinkles and protrusions are present on the surface.
[0064]
(5) Residual rate of foaming aid
The residual ratio of the foaming aid was determined by dissolving the foam in dimethylformamide one week after the production of the foam, and quantifying the extracted solution by gas chromatography.
[0065]
Comparative Examples 1-3
As a comparative example, an extruded foam was obtained under the same conditions as in Examples 1 to 10, except that only carbon dioxide was used as a foaming agent, or a foaming agent containing carbon dioxide as a main component was used, and no foaming aid was used. . Table 1 shows the magnification, closed cell ratio, compressive strength, appearance, and residual ratio of the foaming aid of the obtained foam.
[0066]
[Table 1]

[0067]
From the results shown in Table 1, all of the foams obtained in Examples 1 to 10 were extruded and foamed at a low temperature of 100 ° C. using carbon dioxide as a main foaming agent, and all were high in foam. It can be seen that the foam has an expansion ratio and a high closed cell ratio, has excellent compressive strength and surface properties, and has a low residual ratio of the foaming aid.
[0068]
【The invention's effect】
The polystyrene-based resin foam obtained according to the present invention has a high expansion ratio and a high closed cell ratio, and has a beautiful appearance, despite using carbon dioxide as the main blowing agent.
[0069]
Therefore, the polystyrene resin foam of the present invention can be suitably used as, for example, various heat insulating materials, various buffers, various display plates, various floating plates, and the like.
[Brief description of the drawings]
FIG. 1A is a graph showing the relationship between the amount of methyl chloride added to 100 parts by weight of polystyrene and the melt shear viscosity of polystyrene to which the methyl chloride is added, and B is the ethyl chloride added to 100 parts by weight of polystyrene. Is a graph showing the relationship between the amount of polystyrene and the melt shear viscosity of the polystyrene to which the ethyl chloride was added, and C is the relationship between the amount of tetrahydrofuran added to 100 parts by weight of the polystyrene and the melt shear viscosity of the polystyrene to which the tetrahydrofuran was added. And D is a graph showing the relationship between the amount of acetone added to 100 parts by weight of polystyrene and the melt shear viscosity to which the acetone was added.

Claims (3)

The polystyrene resin is heated and melted, a foaming agent is blended into a foamable gel material, the gel material is cooled to a temperature suitable for foaming, and the gel material is extruded through a die to a lower pressure region. In a method for producing a polystyrene-based resin foam including the steps of forming a foam, a foaming agent containing no chlorine atom in a molecule and a foaming aid containing no chlorine atom in a molecule are used,
As the blowing agent, one containing more than 60% by weight and less than 80% by weight of carbon dioxide based on the total weight of the blowing agent,
As the foaming aid, the following properties (a) to (c):
(A) 5 parts by weight were added to 100 parts by weight of a polystyrene resin, and the melt viscosity measured at 170 ° C. at a shear rate of 122 s ⁻¹ was one half of the melt viscosity of the polystyrene resin alone measured under the same conditions. Becomes
(B) a permeation rate at 25 ° C. for a membrane made of the polystyrene resin is higher than an air permeation rate under the same conditions;
(C) the critical temperature is equal to or higher than the resin temperature at the time of extrusion;
A method for producing a polystyrene-based resin foam, characterized by using one having: 2. The polystyrene resin foam according to claim 1, wherein the foaming aid is at least one selected from the group consisting of ethers, ketones and esters having a boiling point of 30 to 90 [deg.] C. Method. 3. A polystyrene resin produced by the method according to claim 1 or 2, wherein the foaming agent contains 0.01% by weight or more and 1% by weight or less based on the total weight of the foamed body. Foam.

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