JPH1160784A - Styrene-based expandable resin particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain styrene-based expandable particles capable of being dried and evaporating an excessive expanding agent on the surfaces of the particles at relatively high temperatures, viz., under an industrially advantageous condition, excellent in productivity, very small in the difference between the internal cell size and surface cell size thereof, and apart from generating any melt in the expanded mold, and to provide a producing method therefor. SOLUTION: The styrene-based expandable resin particles comprises a cell size-controlling agent and expanding agent, wherein the cell size-controlling agent is of a copolymer of styrene and monomer having a hydroxyl or epoxy group and double bond and is contained in the ratio of >=1 wt.ppm and <10,000 ppm based on a row material of styrene-based monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for obtaining pre-expanded particles having a very uniform cell size in which the internal cell size does not become coarse and the surface cell size does not become fine even under relatively high temperature conditions. The present invention relates to expandable styrene-based resin particles and a method for producing the same.

[0002]

2. Description of the Related Art The size (cell size) of small cells constituting a styrenic resin foam molded article is an important factor which determines the quality characteristics of the molded article such as surface gloss, mechanical strength properties, heat insulation properties, and the like. . Such characteristics generally depend on the cell size of the pre-expanded particles. In addition, the cell size of the pre-expanded particles is also an important factor that determines the heat resistance and molding time, especially the cooling time, during in-mold molding.

In order to adjust the cell size, various cell size adjusting agents have been proposed. For example, U.S. Pat. No. 3,389,097, JP-B-53-29.
No. 10, JP-A-59-168037, JP-A-59-1
There are amides described in each of the publications of 66538.

Further, Japanese Patent Application Laid-Open No. 57-96029 and Japanese Patent Application Laid-Open
There are surfactants described in JP-A-7-119934 and JP-A-57-141533. Also, Japanese Unexamined Patent Publication No.
Japanese Patent Laid-Open No. 207941 and Japanese Patent Laid-Open No. 3-192134. Further, there is a polymer described in JP-A-6-122781.

[0005]

However, even with the use of these cell size modifiers, none of them has a sufficient cell conditioning effect in industrially producing styrene-based expandable resin particles. Generally, styrene-based foamed resin particles are produced by suspension polymerization. Therefore, the drying process for separating water and the treatment for dispersing excess foaming agent on the surface of the styrene-based foamed resin particles are performed with hot air. Will be implemented. And the temperature of this hot air is usually 20 ° C to 5 ° C.
Although it is in the range of 0 ° C., when the temperature of the hot air is high, the temperature of the styrene-based foamed resin particles also increases.

[0006] Therefore, even when the cell size regulator conventionally proposed is used, a phenomenon occurs in which the cell size inside the pre-expanded particles increases in the styrene-based expandable resin particles. When a compact is manufactured using such pre-expanded particles whose internal cells are coarse, sufficient strength cannot be obtained.

If a large amount of a conventional cell size adjusting agent is used to prevent this phenomenon, a phenomenon occurs in which only the cell size near the surface becomes smaller. When molding is performed using such pre-expanded particles, there is a defect that a so-called “melting” surface melting phenomenon occurs, and the obtained expanded molded article is partially depressed. Therefore, the drying step of the styrene-based expandable resin particles and the step of dissipating the excess foaming agent on the surface of the particles need to be carried out over a long period of time at the lowest possible temperature.

[0008] For this reason, the drying and blowing agent dissipating equipment had to be large-scale in order to increase the residence time. Therefore, productivity was low and cost was high.

The present invention has been made in view of the above-mentioned conventional problems, and has made it possible to dry moisture and dissipate excess foaming agent on the particle surface under relatively high temperature conditions, that is, industrially advantageous conditions.
An object of the present invention is to provide styrene-based expandable resin particles which are excellent in productivity, have a very small cell size difference between the inside and the vicinity of the surface, and do not cause melting of the foamed molded article, and a method for producing the same.

[0010]

According to a first aspect of the present invention, there is provided a styrene-based expandable resin particle containing a cell size adjusting agent and a foaming agent, wherein the cell size adjusting agent comprises a hydroxyl group or an epoxy group and a secondary group. It is a copolymer of a monomer having a heavy bond and styrene, and the cell size modifier is added in a range of 1 ppm by weight or more and less than 10000 ppm based on a styrene monomer as a raw material. Styrene-based expandable resin particles.

The most remarkable point in the present invention is that the above specific copolymer is used as the above cell size regulator,
This is a styrene-based expandable resin particle as a pre-expanded particle, which is added to the styrene-based monomer as a raw material of the styrene-based expandable resin particle in the above-described specific range.

When the styrene-based expandable resin particles of the present invention are heated by a heating means such as steam or hot air, a large number of small air bubbles are generated in the particles to become pre-expanded particles. Then, when the pre-expanded particles are filled in a mold and heated again, the pre-expanded particles are secondarily foamed and fused to each other to form a foam molded article faithful to the mold.

[0013] The styrene-based expandable resin particles of the present invention comprise 4
Under relatively high temperature conditions of 0 ° C. to 50 ° C., it is possible to carry out drying of water adhering at the time of suspension polymerization and dissipation treatment of excess foaming agent on the particle surface. Even in the drying and dissipation treatment, the cell size does not increase and the mechanical strength is high.

Therefore, according to the present invention, it is possible to dry moisture and to dissipate excess foaming agent on the surface of particles under relatively high temperature conditions, that is, industrially advantageous conditions, and to obtain excellent productivity. Further, it is possible to provide styrenic foamable resin particles which have a very small cell size difference between the inside and the vicinity of the surface and do not cause melting of the foamed molded article.

The styrenic resin foam molded article thus produced can be used as a food container, a cushioning material, a heat insulating material, and the like.

Next, as a method for producing the styrene-based expandable resin particles, a styrene-based monomer is subjected to suspension polymerization in the presence of a cell size adjusting agent, as described in the fifth aspect of the present invention. In the method for producing styrene-based expandable resin particles by adding a foaming agent during or after suspension polymerization, the cell size adjusting agent is a copolymer of styrene with a monomer having a hydroxyl group or an epoxy group and a double bond. A polymer, and the cell size modifier is not less than 1 ppm by weight and not more than 10000 ppm based on the styrene monomer.
There is a method for producing styrene-based expandable resin particles characterized by being added in an amount less than the range described below.

According to this production method, excellent styrene-based expandable resin particles as described above can be easily produced.

Next, the styrene-based expandable resin particles and raw material components common to the method for producing the same will be described below.

(1) Raw material component Styrene-based monomer The styrene-based expandable resin particles of the present invention are prepared by subjecting a styrene-based monomer to suspension polymerization, and adding a blowing agent during the polymerization, or terminating the polymerization step. It is manufactured by impregnating the polymer particles with a foaming agent later. As the styrene monomer, styrene,
It is mainly composed of styrene monomers such as α-methylstyrene and vinyltoluene, and a part (50% by weight or less) of styrene monomers is converted to other vinyl monomers such as acrylonitrile. It can be replaced with a monomer copolymerizable with a styrene monomer such as a vinyl cyanide monomer, an acrylate monomer such as butyl acrylate, or a methacrylate monomer such as methyl methacrylate.

(2) Compounding agents Compounding agents used for producing the styrene-based expandable resin particles include a cell size adjusting agent, a foaming agent suspending agent, a polymerization initiator, and if necessary, a dispersing aid, a plasticizer. Etc. can be used.
When drying and dissipating excess foaming agent on the particle surface, an antistatic agent, an antiblocking agent, a fusion improver, etc. are added to the styrene-based foamable resin particles after suspension polymerization. You may.

Cell size adjusting agent: In the present invention, a copolymer of a monomer having a hydroxyl group or an epoxy group and a double bond and styrene is used as the cell size adjusting agent. To be contained. The above-mentioned monomer having at least one of the above-mentioned hydroxyl group or epoxy group and a double bond can be used in the present invention as long as it can be copolymerized with styrene.

Examples of monomers having a hydroxyl group and a double bond include polyhydric alcohol monoesters of acrylic acid or methacrylic acid. Examples of polyhydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and butanediol.

Examples of monomers having an epoxy group and a double bond include esters of glycidyl alcohol and acrylic acid or methacrylic acid. As for the method of copolymerizing these monomers with styrene, any method can be used.

Next, as in the second and sixth aspects of the present invention, the monomer having a hydroxyl group or an epoxy group and a double bond is a polyhydric alcohol and a monoester of acrylic acid or methacrylic acid. Preferably, there is.

In this case, it is preferable because the cell regulator can be produced by radical polymerization under relatively simple and mild conditions. Examples of the method for producing the copolymer of the above combination include:
Suspension polymerization can be used. The following suspending agents and polymerization initiators can be used for the production of this copolymer.

Next, as in the third and seventh aspects of the present invention, the polyhydric alcohol is any one or more dihydric alcohols of butanediol, propylene glycol and ethylene glycol. Is preferred.
In this case, the dihydric alcohol and the monoester of acrylic acid or methacrylic acid are easily copolymerized with styrene by suspension polymerization, and the copolymer becomes soluble in the styrene monomer. It is preferred.

Next, as in the invention according to claims 4 and 8, the composition ratio of styrene units in the copolymer of the dihydric alcohol, the monoester of acrylic acid or methacrylic acid, and styrene. Is preferably 50% by weight or more and less than 99% by weight.

When the styrene unit is less than 50% by weight,
The solubility of the dihydric alcohol and the monoester in the styrene monomer may be deteriorated. In addition, the suspension stability during the production of the styrene-based expandable resin particles is reduced, and the particles are easily aggregated. On the other hand, when the content is 99% by weight or more, the cell size adjusting effect is weakened, so that a large amount of the cell size adjusting agent must be used in the production of the styrene-based expandable resin particles.

If necessary, the copolymer may be used as a third component copolymerizable with styrene as other vinyl monomers, for example, vinyl cyanide monomers such as α-methylstyrene and acrylonitrile, and butyl acrylate. It is also possible to copolymerize acrylate monomers such as methacrylate monomers such as methyl methacrylate.

The molecular weight of the copolymer is not particularly limited. However, if the molecular weight is low and the composition ratio of styrene units is low, the copolymer may become particles during suspension polymerization for producing styrene-based expandable resin particles. Bleeding out to the surface is easy, so the suspension stability is reduced and it is easy to agglomerate. When pre-expanded particles are used, the phenomenon that only the cell size near the surface becomes fine tends to occur.

On the other hand, if the molecular weight is high, it takes time to dissolve the styrene monomer, which is not preferable. In consideration of these, it is preferable that the molecular weight of the copolymer be in the range of 10,000 to 500,000 in terms of the molecular weight equivalent to polystyrene by GPC (gel permeation chromatography).

If the amount of the cell size adjusting agent is less than 1 ppm by weight based on the styrene monomer as the main raw material of the styrene expandable resin particles, a sufficient cell size adjusting effect cannot be obtained. . On the other hand, if the content exceeds 10,000 ppm by weight, the effect of reducing the cell size is small.

Regarding the method of incorporating the cell size adjusting agent into the styrene foamable resin particles, it is preferable to dissolve the cell size adjusting agent in the styrene monomer before starting the suspension polymerization. Although it is possible to add the copolymer during suspension polymerization, the copolymer may be unevenly present in the styrene-based expandable resin particles, which is likely to cause cell unevenness or the like. The cell size adjusting agent may be used in combination with a conventionally known cell size adjusting agent, if necessary.

Foaming agents: As foaming agents, volatile foaming agents having a boiling point of 100 ° C. or less such as aliphatic hydrocarbons such as propane, butane, pentane and hexane and alicyclic hydrocarbons such as cyclopentane and cyclohexane are used. it can.

Suspending agents: Suspending agents used in suspension polymerization for producing styrene-based expandable resin particles include polymer dispersants (protective colloid agents) such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylamide, and water. Soluble inorganic salts such as calcium phosphate, hydroxyapatite,
A combination of magnesium pyrophosphate and the like with a surfactant, for example, sodium dodecylbenzenesulfonate can be mentioned.

If necessary, at the start of polymerization or during polymerization, electrolytes such as inorganic salts such as lithium chloride, potassium chloride, sodium chloride, magnesium chloride, calcium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, etc. Organic acid salts such as sodium acetate, disodium succinate, sodium behemate, sodium benzoate and the like can also be added.

Polymerization initiator: As the polymerization initiator, polymerization initiators generally used for radical polymerization of styrene monomers, for example, benzoyl peroxide, butyl perbenzoate,
Oil-soluble polymerization initiators such as tertiary butyl peroxy 2-ethylhexanoate, tertiary butyl peroxy 2-ethylhexyl carbonate, tertiary butyl peroxy isopropyl carbonate, azobisisobutyronitrile and the like can be used. If necessary, a water-soluble polymerization initiator such as an alkali metal salt of persulfuric acid and an alkali metal salt of bisulfite may be used in combination.

Plasticizer: Examples of the plasticizer include toluene, xylene, ethylbenzene, dioctyl adipate, and dioctyl phthalate.

(3) Polymerization and Post-Treatment The suspension polymerization in the present invention, the dehydration treatment of the styrene-based foamable resin particles obtained by the suspension polymerization, the drying of water and the escape treatment of excess foaming agent are described below. Well-known techniques for producing styrene-based expandable resin particles can be applied.

[0040]

Embodiments of the present invention and comparative examples will be described below. Embodiment 1 [Production of Cell Size Control Agent] In a 3 L (liter) autoclave equipped with a rotary stirrer, 1000 g of distilled water, 4 g of tribasic calcium phosphate as a suspending agent and 0.03 g of sodium dodecylbenzenesulfonate as a suspending aid were placed. I charged.

Then, 80 g of 2-hydroxypropyl methacrylate as a monomer having a hydroxyl group and a double bond and 720 g of styrene, 2.4 g of tertiary butyl peroxy 2-ethylhexanoate and tertiary butyl peroxy as an initiator were used. 0.8 g of isopropyl carbonate was charged. Next, the temperature was raised to 90 ° C. and maintained at the same temperature for 7 hours. Thereafter, the temperature was raised to 110 ° C, kept at the same temperature for 6 hours, and cooled to 40 ° C.

Hydrochloric acid was added to the obtained slurry until the pH reached 2, and the tertiary calcium phosphate component on the surface of the polymer particles was removed. Then, most of the water was removed while washing with a centrifuge. The thus obtained copolymer as a cell size adjusting agent was treated with hot air at 60 ° C. for 10 minutes and completely dried.

2. [Production of styrene foamable resin particles] In a 50 L autoclave equipped with a rotary stirrer, distilled water 1 was added.
6 kg, 40 g of tricalcium phosphate as a suspending agent and 0.64 g of sodium dodecylbenzenesulfonate as a suspending aid were charged.

Then, 1.7 g of the above copolymer as a cell size regulator, 50 g of tertiary butyl peroxy 2-ethylhexanoate and tertiary butyl as an initiator were added to 17 kg of styrene as a styrene monomer. A solution in which 15 g of peroxyisopropyl carbonate and 300 g of cyclohexane as a foaming agent were dissolved was added. Then, the temperature was raised to 90 ° C and 5
The temperature was raised over time.

Next, mixed butane 120 as a blowing agent was used.
0 g was pressed into the above solution, heated to 110 ° C. over 1 hour, and kept at the same temperature for 1 hour, then 30 ° C. over 4 hours.
Cooled down. Hydrochloric acid was added to the obtained slurry until the pH became 2, and the tertiary calcium phosphate component on the surface of the styrene-based expandable resin particles was removed.

Thereafter, most of the water was removed while washing with a centrifuge. Next, diethanolalkylamine as an antistatic agent was sprayed on the styrene-based foamable resin particles at a rate of 0.01% by weight, and then treated with warm air at 50 ° C. for 10 minutes and completely dried.

Next, the particle diameter is changed from 0.8 mm to 1.2 m.
m of styrene-based foamable resin particles, and 100% by weight of the styrene-based foamable resin particles, 0.1% by weight of zinc stearate as an antiblocking agent, and glycerin monostearate as a fusion improving agent 0.05% by weight was coated on the surface. Further, in order to dissipate excess foaming agent adhering near the surface of the styrene-based foamable resin particles, the particles were treated with warm air at 50 ° C. for 2 hours.

3. [Production of Pre-expanded Particles] The hot-air-treated styrene-based expandable resin particles obtained as described above were immediately pre-expanded to a bulk magnification of 60 times with a batch type foaming machine. The cells of the pre-expanded particles were almost uniform, the average cell size (diameter) near the surface was 90 μm, and the average cell size inside was 80 μm.

4. [Measurement of Properties of Pre-expanded Particles] That is, the number of cells and the cell uniformity of the pre-expanded particles were evaluated by the following methods. Cell size: Pre-expanded particles having a bulk magnification of 60 times are cut in half by a razor, and the number of cells of the pre-expanded particles is determined by an optical microscope (the portion partitioned between the walls of the resin portion is defined as one unit). Was measured at three arbitrary points and averaged.

(1) Surface cell size; As shown in FIGS. 1 and 2, a distance L1 (μ1) from the surface A to the center and from the cell wall A1 to An + 1 within a range of 0.2 mm.
The value obtained by dividing the distance L1 by the number n of cells in m) was rounded off to one decimal place to obtain the cell size. In the example shown in FIG. 1, L1 = 120 μm, and the number of cells n during this period is two. Therefore, the average cell size is 1
20 μm / 2 (pieces) = 60 μm.

(2) Internal cell size: From the point A ′ of 1.0 mm from the surface toward the center, the center of the pre-expanded particles O
With the number n 'of cells at a distance L2 (μm) from the cell walls A'1 to A'n' + 1 in the range up to The cell size was determined. In the example of FIG. 1, 900 (μm) / 9 (pieces) =
It becomes 100 μm. Aa, Bb, C- in FIG.
c indicates three arbitrary measurement positions. The above (1),
According to the method (2), the surface size and the internal cell size measured along each of the axes Aa, Bb, and Cc were averaged to obtain measured values.

5. [Production of foamed molded article] Next, the pre-expanded particles were aged at room temperature for one day, filled in a mold cavity having an inner size of 300 mm x 75 mm x 25 mm, and heated with 80 kPa steam for 20 seconds. A foam molded article was obtained. No so-called "melting" was observed on the surface of the obtained foam molded article. Further, a bending test according to JIS-A9511 was performed one day after the room temperature, and the maximum strength was 282 kPa. Table 1 shows the conditions of the cell size adjusting agent, the pre-expanded particles, and the measurement results of the expanded molded product in the first embodiment.

Embodiments 2 to 9, Comparative Examples 1 to 2 Same as Embodiment 1 except that the type, composition and amount of the copolymer used as the cell size modifier were changed as shown in Table 1. Operation and measurement were carried out. In Table 1, the amount of “styrene and a monomer having a hydroxyl group or an epoxy group and a double bond and styrene” in the “copolymer” serving as a cell size adjuster is “100% by weight” in total.

As shown in Table 1, the pre-expanded particles obtained from the styrene-based expandable resin particles according to the present invention are. It can be seen that the difference between the cell size in the vicinity of the surface and the cell size in the inside is small, and that the foamed article obtained by this has no "melting" on the surface and has excellent strength.

[0055]

[Table 1]

[0056]

According to the present invention, it is possible to dry moisture and to dissipate excess foaming agent on the particle surface under relatively high temperature conditions, that is, industrially advantageous conditions, to provide excellent productivity, and to improve the inside and the vicinity of the surface. The present invention can provide a styrene-based expandable resin particle having an extremely small cell size difference and which does not cause melting of a foam molded article, and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of property measurement of pre-expanded particles.

FIG. 2 is an overall explanatory diagram of FIG. 1;

Continued on the front page (72) Inventor Tomomichi Ito 1000 Kawajiri-cho, Yokkaichi-shi, Mie Prefecture Mitsubishi Chemical BSF Inc.

Claims (8)

[Claims] 1. A styrene-based expandable resin particle containing a cell size adjusting agent and a foaming agent, wherein the cell size adjusting agent is a copolymer of styrene and a monomer having a hydroxyl group or an epoxy group and a double bond. A polymer,
The styrene foamable resin particles are characterized in that the cell size modifier is added in a range of 1 ppm by weight or more and less than 10000 ppm with respect to the styrene monomer as a raw material. 2. The styrenic foaming resin according to claim 1, wherein the monomer having a hydroxyl group or an epoxy group and a double bond is a monoester of a polyhydric alcohol and acrylic acid or methacrylic acid. particle. 3. The styrene-based expandable resin particles according to claim 2, wherein the polyhydric alcohol is at least one dihydric alcohol among butanediol, propylene glycol and ethylene glycol. . 4. The composition according to claim 3, wherein the composition ratio of the styrene unit in the copolymer of the dihydric alcohol, the monoester of acrylic acid or methacrylic acid, and styrene is 50% by weight or more and less than 99% by weight. Styrene-based foamable resin particles. 5. A method for producing styrene-based expandable resin particles by subjecting a styrene-based monomer to suspension polymerization in the presence of a cell size modifier and incorporating a foaming agent during or after the suspension polymerization. The cell size adjusting agent is a copolymer of a monomer having a hydroxyl group or an epoxy group and a double bond with styrene, and the cell size adjusting agent is at least 1 ppm by weight based on the styrene monomer. 1
A method for producing styrene-based expandable resin particles, characterized by being added in a range of less than 0000 ppm. 6. The styrenic foaming resin according to claim 5, wherein the monomer having a hydroxyl group or an epoxy group and a double bond is a monoester of a polyhydric alcohol and acrylic acid or methacrylic acid. Method for producing particles. 7. The styrene foamable resin particles according to claim 6, wherein the polyhydric alcohol is at least one dihydric alcohol among butanediol, propylene glycol and ethylene glycol. Manufacturing method. 8. The composition according to claim 7, wherein the composition ratio of the styrene unit in the copolymer of the dihydric alcohol, the monoester of acrylic acid or methacrylic acid, and styrene is 50% by weight or more and less than 99% by weight. A method for producing styrene-based expandable resin particles, comprising: