JPH0680712A - Production of polystyrene resin - Google Patents

Abstract

PURPOSE:To obtain the title resin excellent in heat resistance and mechanical strengths, good in injection moldability, extrusion moldability and vacuum formability and also in moldability into a foamed sheet. CONSTITUTION:An aromatic vinyl compound or a mixture thereof with a copolymerizable compound is polymerized in the presence of an organic peroxide of the formula (wherein R<1> and R<2> are each hydrogen or 1-2 C alkyl; and R<3> is 1-5 C alkyl or phenyl) to obtain a resin having an Mz/Mw ratio (wherein Mz is the Z-average molecular weight as determined by gel permeation chromatography, and Mw is the weight-average molecular weight) of 1.7-2.5, an Mw/Mn ratio (wherein Mn is the number-average molecular weight) of 2.0-3.0 and a weight-average molecular weight 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 relates to a method for producing a polystyrene resin which is excellent in heat resistance and mechanical strength, has good injection molding and extrusion moldability, and is particularly excellent in heat secondary moldability.

[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 as a partition for confectionery boxes, etc., but it is required to have excellent secondary heat moldability 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 No. 62-22834, the step of adding a catalyst, a chain transfer agent, etc. during the polymerization is complicated. In addition, generally the weight average molecular weight
In order to increase 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 present invention has been completed by finding a method for producing a polystyrene-based resin having excellent mechanical strength, excellent injection molding and extrusion moldability, and particularly excellent secondary moldability when used as a foamed sheet. .

[0008]

That is, the present invention provides an aromatic vinyl compound or an aromatic vinyl compound and an aromatic vinyl compound using an organic peroxide polymerization initiator represented by the following general formula [Chemical formula 2]. A mixture of a vinyl compound and a copolymerizable compound is polymerized, and in the value measured by gel permeation chromatography, the ratio Mz / Mw of the Z average molecular weight Mz and the weight average molecular weight Mw is 1.7 to 2. 5, weight average molecular weight Mw
And a number average molecular weight Mn ratio Mw / Mn of 2.0 to 3.0 and a weight average molecular weight Mw of 200,000 to 600,000.

[0009]

[Chemical 2] (Wherein 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, a compound represented by the general formula:
By using as a polymerization initiator, the ratio Mz / Mw of the Z average molecular weight Mz and the weight average molecular weight Mw is in the range of 1.7 to 2.5 without decreasing the productivity by the known polymerization method, and the weight average A polystyrene resin characterized in that the ratio Mw / Mn of the 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 in the range of 200,000 to 600,000. can get.

The polystyrene foam obtained from this polystyrene resin is excellent in mechanical strength because the raw material resin has a large weight average molecular weight. Further, since the ratio Mz / Mw of the Z-average molecular weight Mz and the weight-average molecular weight Mw is larger than 1.7, the ratio of the high-molecular weight polymer is higher than that of the conventional polystyrene resin, and the mechanical strength is not impaired. In particular, it exhibits excellent formability during deep drawing, especially when used as a foamed sheet.

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, as the vinyl monomer copolymerizable with the above-mentioned aromatic vinyl compound, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, and acrylic ester compounds such as methyl acrylate and ethyl acrylate are used. , Methacrylic acid ester compounds such as methyl methacrylate, ethyl methacrylate and propyl methacrylate, and allyl amide 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.

In the production method of the present invention, as the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methylethylketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

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 [Chemical Formula 3].

[0018]

[Chemical 3] (Wherein 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 this polymerization initiator used is 1% by weight of the aromatic vinyl compound and a mixture of the compound and a compound copolymerizable therewith.
0.001-0.1 parts by weight, preferably 0.00, relative to 00 parts by weight
It is preferable to use 2 to 0.05 parts by weight, and more preferably 0.005 to 0.05 parts 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. Mz / Mw exceeding 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 achieve the target weight average molecular weight Mw.
The mechanical strength of the obtained foam 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 with two or more kinds of peroxides represented by the general formula [Chemical Formula 3].

The weight average molecular weight Mw of the polystyrene resin of the present invention is 200,000 to 600,000, preferably 250,000 to 500,000, and more preferably 280 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.

The production method of the present invention uses a known polymerization method such as suspension polymerization, a combination of bulk polymerization and suspension polymerization, emulsion polymerization, suspension emulsion polymerization, and continuous polymerization with a continuous polymerization apparatus. A system resin can be polymerized.

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.

Next, the present invention will be specifically described based on examples, but these do not limit the scope of the present invention. Example 1 Production of Raw Polystyrene A first reactor which is a complete mixing type stirring tank with a volume of about 20 liters, a second reactor which is a complete mixing stirring tank with a volume of about 15 liters, and a stirrer with a volume of about 7 liters The polymerization process was constituted by connecting a third reactor consisting of a plug flow type reactor in series. 83 parts by weight of styrene monomer and ethylbenzene
2,2-bis (4,4-ditertiary butylperoxycyclohexyl) propane was added to a mixture of 17 parts by weight.
0.013 parts by weight and 0.013 parts by weight of tertiary butyl peroxyisopropyl carbonate were mixed to prepare a raw material solution. This raw material solution was continuously fed to the first reactor at a rate of 4.3 liters per hour. The reaction temperature in each reactor was adjusted to 111 ℃ in the first reactor and 125 ℃ in the second reactor, and in the third reactor from 125 ℃ to 14 ℃ along the flow direction.
It was adjusted so that a gradient of 5 ° C was created. 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.
%Met. The polymer solution continuously taken out from the third reactor was separated into unreacted monomer and ethylbenzene from the polymer under a high temperature and reduced pressure according to a conventional method, then extruded in a strand form and cooled, and then cut into pellets. Table 1 shows the polymerization conditions, and Table 2 shows the gel permeation chromatography measurement results of the obtained pellets and the physical property evaluation results. The above polymer was 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. Table 2 shows the results of evaluation of the cracked state, keloid-shaped generation state and brittleness strength of the foamed sheet of the obtained container.

Example 2 The same polymerization process as in Example 1 was utilized. Styrene monomer
2,2-based on 80 parts by weight and 20 parts by weight of ethylbenzene
A mixture of 0.01 parts by weight of bis (4,4-ditertiarybutylperoxycyclohexyl) propane was used as a raw material solution and fed to the first reactor at a rate of 4.4 liters per hour. The reaction temperature in each reactor is 116 ℃ in the first reactor,
The second reactor was adjusted to 135 ° C, and the third reactor was adjusted to have a gradient of 135 ° C to 150 ° C along the flow direction. The conversion of styrene monomer to polymer at the outlet of each reactor was about 30% in the first reactor, about 62% in the second reactor and about 78% in the third reactor. The polymerization liquid continuously taken out from the third reactor was treated in the same manner as in Example 1 to obtain polystyrene pellets. The foam was molded in the same manner as in Example 1 below. The polymerization conditions are shown in Table 1, and the evaluation of the obtained pellets and foamed molded products is shown in Table 2.

Example 3 A jacket having an inner volume of 30 liters, a reactor equipped with a stirrer, and 12 parts of styrene monomer and 100 parts by weight of styrene monomer were used as a suspension stabilizer, and 0.05 part by weight of calcium triphosphate was added as a suspension stabilizer.
120 parts by weight of water containing 0.005 parts by weight of sodium dodecylbenzenesulfonate was charged as a surfactant, and the solution was suspended with stirring. Add styrene monomer 100 to this suspension.
2,2, -bis (4,4 as a polymerization initiator relative to parts by weight
4-ditertiary butylperoxycyclohexyl)
0.045 parts by weight of propane, 0.08 parts by weight of 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, 0.02 parts by weight of ethyl 3,3-di (tert-butylperoxy) butyrate, Further, 0.03 part by weight of alpha methyl styrene dimer was added as a chain transfer agent. The suspension was heated with stirring at 105 ° C. for 4 hours and at 130 ° C. for 3 hours to polymerize. The obtained bead-like resin was filtered off, dried with hot air, and then pelletized using an extruder. The foam was molded in the same manner as in Example 1 below. The polymerization conditions are shown in Table 1, and the evaluation of the obtained pellets and foamed molded products is shown in Table 2.

Example 4 The same polymerization process as in Example 1 was utilized. Styrene monomer
88.6 parts by weight, ethylbenzene 9.0 parts by weight and paraffin
0.01% of 2,2-bis (4,4-ditertiarybutylperoxycyclohexyl) propane to 2.4 parts by weight
The mixture of parts by weight was fed as a raw material solution to the first reactor at a rate of 3.0 liters per hour. The reaction time in each reactor was adjusted so that it was 119 ° C in the first reactor and 117 ° C in the second reactor, and the reaction time in the third reactor was 117 ° C along the flow direction.
The gradient was adjusted from ℃ to 151 ℃. The conversion of styrene monomer to polymer at the outlet of each reactor was about 47% in the first reactor, about 67% in the second reactor, and about 76% in the third reactor. The polymerization liquid continuously taken out from the third reactor was treated in the same manner as in Example 1 to obtain polystyrene pellets. The foam was molded in the same manner as in Example 1 below. Also, using an injection molding machine, length 120 mm
A three-stage plate having a width of 40 mm, a height of 1, 2 and 3 mm was molded. Polymerization conditions are shown in Table 1, and evaluations of the obtained pellets, foamed molded products and plates are shown in Table 2.

Comparative Example 1 The same polymerization process as in Example 1 was used. Styrene monomer
To 85 parts by weight and 15 parts by weight of ethylbenzene, 0.03 of tertiary butyl peroxyisopropyl carbonate was added.
A mixture of 0 parts by weight was fed as a raw material solution to the first reactor at a rate of 3.9 liters per hour. The reaction temperature in each reactor was adjusted to be 112 ° C in the first reactor and 124 ° C in the second reactor, and 12 ° C in the third reactor along the flow direction.
The gradient was adjusted from 4 ° C to 147 ° C. The conversion of styrene monomer to polymer at the outlet of each reactor was about 30% in the first reactor, about 64% in the second reactor and about 77% in the third reactor. The polymerization liquid continuously taken out from the third reactor was treated in the same manner as in Example 1 to obtain polystyrene pellets. The foam was molded in the same manner as in Example 1 below. Polymerization conditions are shown in Table 3, and evaluations of the obtained pellets and foamed molded products are shown in Table 4.

Comparative Example 2 The same polymerization process as in Example 1 was used. Styrene monomer
88 parts by weight and 12 parts by weight of ethylbenzene are mixed, and a raw material solution is added without adding a polymerization initiator such as a peroxide, and every hour 4.
The first reactor was fed at a rate of 0 liter. The reaction temperature in each reactor was 120 ° C in the first reactor and 135 ° C in the second reactor.
The temperature was adjusted so that the temperature became ℃, and the third reactor was adjusted so that there was a gradient of 135 ℃ to 155 ℃ along the flow direction. The conversion of styrene monomer to polymer at the outlet of each reactor was about 30% in the first reactor, about 64% in the second reactor,
About 82% in the third reactor. The polymerization liquid continuously taken out from the third reactor was treated in the same manner as in Example 1 to obtain polystyrene pellets. The foam was molded in the same manner as in Example 1 below. Polymerization conditions are shown in Table 3, and evaluations of the obtained pellets and foamed molded products are shown in Table 4.

Comparative Example 3 The same polymerization process as in Example 1 was used. Styrene monomer
93.1 parts by weight, 4.5 parts by weight of ethylbenzene and 2.4 parts by weight of liquid paraffin were used as raw material solutions and fed to the first reactor at a rate of 2.9 liters per hour. The reaction temperature in each reactor was adjusted to 122 ° C in the first reactor and 118 ° C in the second reactor, and 118 ° C along the flow direction in the third reactor.
The temperature was adjusted so that a gradient of 1 to 153 ° C could be obtained. The conversion of styrene monomer to polymer at the outlet of each reactor is
It was about 48% in the first reactor, about 65% in the second reactor, and about 78% in the third reactor. The polymerization liquid continuously taken out from the third reactor was treated in the same manner as in Example 1 to obtain polystyrene pellets. The foam was molded in the same manner as in Example 1 below. Also, using an injection molding machine, length 120 mm × width
A three-stage plate having a size of 40 mm × height 1, 2, and 3 mm was molded.
Polymerization conditions are shown in Table 3, and evaluations of the obtained pellets, foamed molded products and plates are shown in Table 4.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

The polymerization initiator is as follows. Initiator I: 2,2-bis (4,4-ditert-butylperoxycyclohexyl) propane Initiator II: Tertiarybutylperoxyisopropyl carbonate Initiator III: 1,1-bis (tert-butylperoxy) 3,3 3,5-Trimethylcyclohexane Initiator IV: Ethyl-3,3-di (tert-butylperoxy) butyrate α-MSD: Alphamethylstyrene dimer

Measurement of molecular weight and molecular weight distribution The molecular weight and molecular weight distribution by gel permeation chromatography were measured under the following conditions using HLC-802A type GPC manufactured by Toray Industries, Inc. Column: Toray column Mobile phase: Tetrahydrofuran Sample concentration: 0.3 wt% Measurement temperature: 38 ° C Detector: Differential refractometer

Measurement of physical properties 1) Plate brittleness strength: length 120 mm × width 40 mm × height 1, 2 and 3 mm 3-stage plate 3 mm weight 50 at the central part
The weight of g dropped at different heights and the plate broke 50
% Destruction height was indicated. 2) 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. 3) 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. There are no cracks or keloids ... 5 Almost no cracks or keloids.-4 Some cracks or keloids ... 3 Many cracks or keloids ... 2 Very many cracks or keloids. Many ... 1

[0039]

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 (2)

[Claims] 1. An aromatic vinyl compound or an aromatic vinyl compound and a compound copolymerizable with an aromatic vinyl compound using a polymerization initiator of an organic peroxide represented by the following general formula [Chemical Formula 1] In the value measured by gel permeation chromatography by polymerizing a mixture with and, the ratio Mz / Mw of Z average molecular weight Mz and weight average molecular weight Mw is 1.7 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. A method for producing a polystyrene resin, which has a weight average molecular weight Mw of 200,000 to 600,000. [Chemical 1] (Wherein 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 use amount of the organic peroxide represented by the general formula [Chemical Formula 1] is such that an aromatic vinyl monomer or an aromatic vinyl monomer and an aromatic vinyl monomer are copolymerized. The method for producing a polystyrene resin according to claim 1, wherein the content is in the range of 0.001 to 0.1 part by weight with respect to 100 parts by weight of the mixture with the possible compound.