JPH07278218A - Production of polystyrene resin - Google Patents

Abstract

PURPOSE:To produce a polystyrene resin having excellent heat resistance and mechanical strengths, good injection moldability, extrusion moldability and also excellent moldability into expanded sheets. CONSTITUTION:An aromatic vinyl compound or a mixture thereof with a compound copolymerizable therewith is polymerizded in a suspension by using an organic peroxide represented by the formula (R1 and R2 are each hydrogen or 1 or 2C alkyl, and R3 is 1-5C alkyl or phenyl) as the polymerization initiator to produce a polystyrene resin having an Mz/Mn ratio (Mz is the Z-average molecular weight as determined by gel permeation chromatography, and Mw is the weight-average molecular weight) in the range of 1.8-2.5, an Mw/Mn (Mw is the weightaverage molecular weight), and Mn is the number-average molecular weight) in the range of 2.0-3.0, and a weight-average molecular weight Mw in the range of 200000-600000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a polystyrene-based material which is excellent in heat resistance and mechanical strength, and is excellent in injection molding and extrusion moldability, and is particularly excellent in secondary molding by heating when used as a foamed sheet. The present invention relates to a method for producing a resin, and a foamed sheet and a foamed molded product made of a polystyrene resin obtained by the method.

[0002]

2. Description of the Related Art Polystyrene resins are generally transparent,
It has excellent heat resistance and mechanical strength, and because it has good moldability, it is used in many fields such as household products and electric appliances. Further, the foam of polystyrene resin has characteristics such as surface gloss, lightness, heat insulating property and cushioning property, and its field of use varies depending on the thickness of the foam. A sheet of polystyrene-based resin foam with a thickness of about 3 mm or less is called polystyrene paper (PSP). It is easy to mold, and features such as cushioning and heat insulation are used for pre-packaging. It is widely used mainly for lunch boxes, bowls, cups and confectionery boxes, etc., but it is required to have excellent heat-secondary formability from the viewpoint of improving productivity.

A polystyrene-based resin foam sheet is a foamable polystyrene-based resin impregnated with a foaming agent composed of an aliphatic hydrocarbon such as butane and pentane, and a halogenated aliphatic hydrocarbon such as trichloromonofluoromethane and methyl chloride. It is produced by a method of directly extruding particles into a sheet by an extruder or a method of extruding the particles into a sheet while pressing the above-mentioned foaming agent into a polystyrene resin melted in the extruder. The polystyrene-based resin foam sheet thus obtained is secondarily foamed by a heater and then vacuum-molded by a plug assist method, pressure-molded or press-molded to be used as a container. In general, polystyrene-based resin, when secondary processing of the extruded sheet, when the heating distribution state to the sheet is non-uniform and when the molding is performed with insufficient heating, the sheet is torn or the uneven thickness portion is generated. If it occurs, the strength of the molded product will be insufficient, and the appearance will be impaired.

In particular, when molding a foam using a foamed sheet, in the heating secondary foam molding step, there is a temperature distribution in the heating furnace and the fluctuation of the outside air temperature causes the sheet Insufficient heating of all or part of the sheet may cause the sheet to break during molding, the mold regularity may deteriorate, or conversely, excessive heating may cause the surface of the molded product to become keloid-like, or the thickness of the molded product may fluctuate. The phenomenon occurs. In order to prevent the occurrence of such keloid-like burns, there are known methods such as increasing the molecular weight of the raw material polystyrene-based polymer, sticking a film on the surface of the sheet, and forming a layer having a high resin density, a so-called skin layer. ing. However, such a method may lead to a decrease in productivity, and may cause defects such as vibration of a die and a mandrel at the time of extruding a sheet and scratches on the sheet surface. Further, when such a polymer is used for deep drawing, sheet breakage is likely to occur.

Further, in order to obtain a foam having good moldability during molding, a method is known in which the molecular weight of the raw polystyrene polymer is reduced or a plasticizer and a lubricant are added to the raw polystyrene polymer. . However, this method has a problem that the mechanical strength of the sheet is lowered and the heat resistance is lowered. On the other hand, it has excellent injection molding and extrusion moldability,
Moreover, regarding the molding of the foamed sheet, as a measure for improving the heating secondary processability, for example, a foam made of a resin having a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 3.0 or more is used. Are described in JP-A-62-22834.

However, the fact that the ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn of the resin is wide means that the definition of the average molecular weight means that the broadening of the molecular weight mainly extends to the low molecular weight side. This means that the polystyrene resin foam having a wide distribution in the low-molecular region has a drawback that its strength is essentially low. Moreover, in the description of JP-A-62-22834, the process of adding a polymerization initiator, a chain transfer agent, etc. during the polymerization is complicated. Further, generally, in order to increase the weight average molecular weight Mw, it is necessary to carry out polymerization at a low temperature for a long time, which is not advantageous in terms of productivity. Further, JP-A-3-111434 and JP-A-3-111435 propose the use of a polystyrene resin polymerized with an initiator containing a long-chain alkyl. However, the decomposition temperature of this initiator is as low as around 80 ° C., and the polymerization temperature has to be lowered for commercial use, and the viscosity of the polymerization solution becomes high, and it is long as in Examples. It requires polymerization time and has a difficulty in productivity, which is not practical.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves these drawbacks, and the object of the present invention is to:
The mechanical strength was excellent, and the injection molding and extrusion moldability were good, and in particular, a method for producing a polystyrene-based resin having excellent heat-secondary moldability when forming a foamed sheet was found, and the present invention was completed. It was

[0008]

[Means for Solving the Problems] That is, the present invention provides polystyrene by suspension polymerization of an aromatic vinyl compound or a mixture of an aromatic vinyl compound and a compound copolymerizable with the aromatic vinyl compound in water. In the method for producing a resin-based resin, the Z-average molecular weight is measured by gel permeation chromatography after polymerization using an organic peroxide represented by the following general formula 1 as a polymerization initiator.
The ratio Mz / Mw of Mz to the weight average molecular weight Mw is 1.8 to 2.5, the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 2.0 to 3.0,
Moreover, the present invention relates to a method for producing a polystyrene-based resin having a weight average molecular weight Mw of 200,000 to 600,000, a foamed sheet made of the polystyrene-based resin obtained by this production method, and a foamed molded article obtained from the foamed sheet.

[0009]

[Chemical 2] (In the formula, R ₁ and R ₂ represent hydrogen or an alkyl group having 1 to 2 carbon atoms, and R ₃ represents an alkyl group having 1 to 5 carbon atoms or a phenyl group)

According to the production method of the present invention, by using the compound of the general formula 1 as a polymerization initiator, the ratio Mz of the Z-average molecular weight Mz and the weight-average molecular weight Mw can be obtained without lowering the productivity by the known polymerization method. / Mw is in the range of 1.8 to 2.5, the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn is in the range of 2.0 to 3.0, and the weight average molecular weight Mw is 20. A polystyrene resin characterized by being in the range of 10,000 to 600,000 is obtained.

The injection-molded article, extrusion-molded article and foam obtained from the polystyrene resin are excellent in mechanical strength because the raw material resin has a large weight average molecular weight.
Moreover, since the ratio Mz / Mw of the Z-average molecular weight Mz and the weight-average molecular weight Mw of this polystyrene-based resin is larger than 1.8, the ratio of high-molecular weight polymer is higher than that of the conventional polystyrene-based resin. It exhibits excellent formability, especially in deep drawing when forming a foamed sheet, without impairing the mechanical strength.

The present invention will be described in detail below. Examples of the aromatic vinyl compound of the present invention include styrene and α-
Nuclear alkyl-substituted styrenes such as methylstyrene, p-methylstyrene and p-tert-butylstyrene, and nuclear halogenated styrenes such as o-chlorostyrene, p-bromostyrene and 2,4-dibromostyrene, which may be used alone or in combination with 2
It can be used as a mixture of two or more species.

Further, examples of the compound copolymerizable with the above-mentioned aromatic vinyl compound include vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, acrylic ester compounds such as methyl acrylate and ethyl acrylate, and methacrylic acid. Methacrylic acid ester compounds such as methyl, ethyl methacrylate and propyl methacrylate, and arylamide derivatives can be used. These compounds may be used alone or in combination of two or more.

Further, a so-called rubber-like substance typified by polybutadiene or styrene-butadiene block copolymer may be dissolved and used in these monomers.

Further, as the chain transfer agent, aliphatic mercaptan, aromatic mercaptan, pentaphenylethane,
α-Methylstyrene dimer and terpinolene can also be used.

The polymerization initiator used in the production method of the present invention is
It is an organic peroxide represented by the general formula 1.

[0017]

[Chemical 3] (In the formula, R ₁ and R ₂ represent hydrogen or an alkyl group having 1 to 2 carbon atoms, and R ₃ represents an alkyl group having 1 to 5 carbon atoms or a phenyl group)

And as a concrete organic peroxide,
Examples include 2,2-bis (4,4-ditertiarybutylperoxycyclohexyl) propane and 2,2-bis (4,4-ditertiaryoctylperoxycyclohexyl) propane, but are not limited thereto. Instead, they may be used alone or in combination of two or more.

The amount of the polymerization initiator used is 0.001 to 0.1 part by weight, preferably 100 to 100 parts by weight of the mixture of the aromatic vinyl compound and the compound copolymerizable with the compound.
It is preferable to use 0.002 to 0.1 part by weight, more preferably 0.005 to 0.1 part by weight. If it is less than 0.001 part by weight, the effect is small, and if it exceeds 0.1 part by weight, it becomes difficult to control the molecular weight and the polymerization rate of the resulting polymer, and the ratio of Z average molecular weight Mz to weight average molecular weight Mw Mz / Mw. Will exceed 2.5. The fact that Mz / Mw exceeds 2.5 means that the molecular weight distribution of not only the high molecular weight region but also the low molecular weight region is widened in order to make the weight average molecular weight Mw the target size. Mechanical strength is impaired.

The present invention also provides a so-called monofunctional compound represented by azo compounds represented by azobisisobutyronitrile, benzoyl peroxide, tertiary butyl peroxybenzoate and tertiary butyl peroxycyclohexyl isopropyl carbonate. Peroxides and 2 such as 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane
As a polymerization initiator, a functional peroxide can be used alone or in combination of two or more kinds in combination with the peroxide represented by the general formula 1.

The polystyrene-based resin of the present invention has a weight average molecular weight Mw of 200,000 to 600,000, preferably 250,000 to 500,000, and more preferably 280,000 to 400,000. If the Mw is less than 200,000, the mechanical strength of the molded product will be weak and a molded product that can be used practically cannot be obtained. Further, if it exceeds 600,000, the load when extruding the raw material resin pellets is large and the productivity is remarkably reduced, and further, the sheet to be extruded and the foamed sheet are imprinted on the mold when the secondary molding is performed by heating. The remarkably poor quality.

In the production method of the present invention, an aromatic vinyl compound monomer or a monomer mixture comprising an aromatic vinyl compound monomer and a compound copolymerizable with the aromatic vinyl compound monomer is used. The polymerization is carried out by a so-called suspension polymerization method of suspending in water and polymerizing, and it is desirable that at least the final polymerization conversion rate is 95% or more. If the final polymerization conversion rate is less than 95%, the heat resistance of the obtained polystyrene may be insufficient, a malodor may be generated during molding, and the appearance of the surface of the molded product may be impaired. Further, when the final polymerization conversion rate is less than 95%, unreacted monomers can be devolatilized by an extruder, but the yield of products is deteriorated, which is not economical. In order to make the final polymerization conversion rate 95% or more, it can be carried out by a method of lengthening the polymerization time or adding a polymerization initiator, but the reaction temperature is 80 to 1
A method is preferred in which the polymerization conversion rate is at least 60% or more in the range of 20 ° C., and then the reaction temperature is increased to 120 ° C. or more so that the final polymerization conversion rate is 95% or more. If the reaction temperature is less than 80 ° C. until the polymerization conversion rate is at least 60%, the polymerization time becomes long and the productivity becomes low.
When the temperature is 0 ° C. or higher, it is difficult to obtain the desired molecular weight, and it is difficult to control the reaction rate. If the reaction temperature is lower than 120 ° C. after the polymerization conversion rate becomes 60% or more, the polymerization time becomes extremely long and the productivity is remarkably lowered.

The polystyrene resin produced by the production method of the present invention is excellent in injection moldability, extrusion moldability and vacuum moldability, and is also excellent in performance as a foam containing a foaming agent. is there.

[0024]

EXAMPLES Next, the present invention will be specifically described based on examples, but these do not limit the scope of the present invention. Example 1 12 kg of styrene monomer and 100 parts by weight of this styrene monomer in a jacket with an internal volume of 30 liters, a reactor equipped with a stirrer, 0.05 parts by weight of calcium triphosphate as a suspension stabilizer, and dodecylbenzenesulfonic acid as a surfactant. 120 parts by weight of water containing 0.005 parts by weight of sodium was charged, and the solution was suspended with stirring. Styrene monomer in this suspension
0.045 parts by weight of 2,2, -bis (4,4-ditertiarybutylperoxycyclohexyl) propane as a polymerization initiator to 100 parts by weight of 1,1-bis (tertiarybutylperoxy) 3,3,3 0.08 parts by weight of 5-trimethylcyclohexane, 0.02 parts by weight of ethyl 3,3-di (tertiarybutylperoxy) butyrate, and 0.2 parts of α-methylstyrene dimer as a chain transfer agent.
03 parts by weight was added. The suspension was heated with stirring at 105 ° C. for 4 hours and at 130 ° C. for 3 hours to polymerize. After the polymerization was completed, hydrochloric acid was added to the suspension to neutralize the suspension stabilizer tricalcium phosphate. The obtained bead-like resin was filtered off, dried with hot air, and then pelletized using an extruder. Table 1 shows the results of gel permeation chromatography measurement and the results of physical property evaluation of the obtained pellets.

Further, using a 2 ounce in-line screw injection molding machine manufactured by Niigata Iron Works Co., Ltd., a molding temperature of 230
A three-step step plate having a length of 120 mm, a width of 40 mm, a thickness of 1, 2, and 3 mm was molded at ℃, and the brittle strength was measured.
Further, the above pellets were extruded and foamed using butane gas as a foaming agent to obtain a foamed sheet having a thickness of about 2.5 mm and a density of about 0.07 g / cc. This foam sheet was subjected to secondary foaming by heating, and a container was immediately molded by a vacuum molding machine. The cracked state of the obtained container, the state of occurrence of keloids, and the brittle strength of the foamed sheet were evaluated, and the results are also shown in Table 1.

Example 2 12 kg of styrene monomer in a reactor having an inner volume of 30 liters, a reactor equipped with a stirrer, and 0.05 part by weight of calcium triphosphate as a suspension stabilizer, and dodecyl as a surfactant, based on 100 parts by weight of this styrene monomer. 120 parts by weight of water containing 0.005 part by weight of sodium benzenesulfonate was charged, and the solution was suspended with stirring. Styrene monomer in this suspension
0.09 parts by weight of 2,2, -bis (4,4-ditertiarybutylperoxycyclohexyl) propane as a polymerization initiator, and 1,1-bis (tert-butylperoxy) 3,3,100 parts by weight. 0.06 parts by weight of 5-trimethylcyclohexane, 0.02 parts by weight of ethyl 3,3-di (tert-butylperoxy) butyrate, and
0.06 parts by weight of α-methylstyrene dimer was added as a chain transfer agent. The suspension was heated at 105 ° C. for 3 hours, heated at 115 ° C. for 2 hours, and heated at 130 ° C. for 2 hours to polymerize the suspension. The obtained bead-shaped resin was treated in the same manner as in Example 1 to obtain polystyrene pellets. Hereinafter, Example 1
The pellets obtained in the same manner as above were evaluated for physical properties and the foam was evaluated, and the results are shown in Table 1.

Comparative Example A jacket having an inner volume of 30 liters, 12 kg of styrene monomer in a reactor equipped with a stirrer, and 0.05 part by weight of calcium triphosphate as a suspension stabilizer, and dodecylbenzene as a surfactant with respect to 100 parts by weight of this styrene monomer. 120 parts by weight of water containing 0.005 parts by weight of sodium sulfonate was charged, and the solution was suspended with stirring. Styrene monomer in this suspension
As a polymerization initiator, 100 parts by weight of tert-butyl peroxybenzoate 0.1 part by weight of ethyl 3,3-
Di (tertiary butyl peroxy) butyrate 0.01
In addition, 0.04 part by weight of α-methylstyrene dimer was added as a chain transfer agent. While stirring this suspension
Polymerization was carried out by heating at 117 ° C. for 5 hours and 130 ° C. for 2 hours. The obtained bead-shaped resin was treated in the same manner as in Example 1 to obtain polystyrene pellets. The physical properties of the pellets and the foam obtained in the same manner as in Example 1 were evaluated, and the results are shown in Table 1.

[0028]

[Table 1]

Various physical properties were evaluated by the following methods. (1) Measurement of molecular weight and molecular weight distribution The molecular weight and molecular weight distribution by gel permeation chromatography are HLC-802A manufactured by Tosoh Corporation.
It was measured under the following conditions using a type GPC. (A) Column: Tosoh Corp. column (b) Mobile phase: Tetrahydrofuran (c) Sample concentration: 0.3 wt% (d) Measurement temperature: 38 ° C (e) Detector: Differential refractometer

(2) Measurement of physical properties (a) Plate brittleness strength: Length 120 mm × width 40 mm × thickness 1, 2 and 3 mm 3-step step plate 3 mm Drop a weight of 50 g on the central part at different heights. The plate showed a 50% fracture height at which it cracked. (B) Foamed sheet brittleness strength: A sphere having a weight of 300 g was dropped while changing the height, and the height at which the foamed sheet was broken at 50% was shown. (C) Cracks and keloids of molded product: molded container 1
With respect to 0, the state of cracks and the degree of occurrence of keloids were visually determined by the 5-step display method. (a) No cracks or keloids ... 5 (b) Almost no cracks or keloids. 4 (c) Some cracks or keloids ... 3 (d) Many cracks or keloids.・ ・ ・ ・ 2 (e) Very many cracks and keloids ・ ・ 1

(D) Tensile strength: Measured according to ASTM D-638. (E) Bending strength: Measured according to ASTM D-790. (F) Flexural modulus: measured according to ASTM D-790. (G) Melt flow rate (MFR): JIS K-7
According to 210, the test temperature was 200 ° C. and the load was 5 kgf. (H) Heat distortion temperature: Measured according to JIS K-6871. (I) Vicat softening point: The test load was measured at 5 kgf in accordance with JIS K-7206.

[0032]

As described above, the polystyrene resin produced by the method of the present invention has excellent mechanical strength and
Good injection moldability, extrusion moldability and vacuum moldability,
In particular, when it is used as a raw material for a foamed sheet, it has a very good moldability because of the characteristic of the molecular weight distribution of the polystyrene-based resin, and a molded product excellent in brittle strength and appearance can be obtained.

Claims (5)

[Claims] 1. A method for producing a polystyrene resin by suspension polymerization of a monomer mixture of an aromatic vinyl compound or an aromatic vinyl compound and a compound copolymerizable with an aromatic vinyl compound in water. In, the value obtained by polymerizing using the organic peroxide represented by the general formula 1 as a polymerization initiator and measuring by gel permeation chromatography is the ratio Mz / Mw of the Z average molecular weight Mz and the weight average molecular weight Mw.
Is 1.8 to 2.5, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn
Mw / Mn is 2.0-3.0, and weight average molecular weight Mw is 200,000-
A method for producing a polystyrene-based resin, which is 600,000. [Chemical 1] (In the formula, R ₁ and R ₂ represent hydrogen or an alkyl group having 1 to 2 carbon atoms, and R ₃ represents an alkyl group having 1 to 5 carbon atoms or a phenyl group) 2. The reaction temperature is in the range of 80 to 120 ° C., at least the polymerization conversion rate is 60% or more, and then the reaction temperature is raised to 120 ° C. or more, and the polymerization conversion rate is 95% or more. The method for producing a polystyrene resin according to claim 1. 3. The amount of the organic peroxide represented by the general formula 1 is 0.001 to 100 parts by weight based on 100 parts by weight of a mixture of an aromatic vinyl compound or the compound and a compound copolymerizable with the compound. The method for producing a polystyrene-based resin according to claim 1 or 2, wherein the content is in the range of 0.1 part by weight. 4. A foamed sheet comprising a polystyrene resin obtained by the method according to claim 1, 2 or 3. 5. A foamed molded product obtained from the foamed sheet according to claim 4.