JPH1160785A - 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 polyethylene wax in which the summed amount of heat of fusion in the range of 75 to 150 deg.C (B) is beyond 80% of that in the range of 0 to 150 deg.C (A+B) and the agent is contained in the ratio of 11 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. Japanese Patent Application Laid-Open Nos. 57-96029 and 57-11
There are surfactants described in JP-A-9934 and JP-A-57-141533. Also, JP-A-59-207 describes
941 and JP-A-3-192134.
Further, there is a polymer described in JP-A-6-122781.

[0004]

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.

[0005] Therefore, even when the cell size adjuster 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 fine. 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.

[0007] For this reason, the drying and blowing agent dissipating equipment must 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 excessive 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 and a method for producing the same, 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" in the foamed molded article. is there.

[0009]

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 is 75 ° C. to 1 ° C.
The accumulated heat of fusion (B) in the temperature range of 50 ° C is 0 ° C to 150 ° C.
A polyethylene wax exceeding 80% of the accumulated heat of fusion (A + B) in the temperature range of 1 ° C., and the cell size modifier is 1 ppm by weight based on the styrene monomer as the raw material.
Styrene-based expandable resin particles characterized by being added in an amount of less than 10,000 ppm by weight.

The most remarkable point in the present invention is that the above-mentioned specific polyethylene wax is used as the above-mentioned cell size regulator, and the above-mentioned polyethylene wax is used with respect to the above-mentioned styrene-based monomer as a raw material of the styrene-based expandable resin particles. Styrene-based expandable resin particles as pre-expanded particles added in a 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.

The styrenic foamable resin particles of the present invention are
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. In addition, even when a foamed molded article is manufactured using this material, "melting" does not occur on the surface of the foamed molded article.

Therefore, according to the present invention, it is possible to dry water 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 styrene-based expandable resin particles and a method for producing the same, in which the difference in cell size between the inside and the vicinity of the surface is extremely small and "melting" does not occur in the expanded molded article.

[0014] The foamed styrene resin 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 in the third aspect of the invention. In the method for producing a styrene-based expandable resin particle by adding a foaming agent during or after the suspension polymerization, the cell size modifier has an integrated heat of fusion (B) in a temperature range of 75 ° C to 150 ° C. A polyethylene wax exceeding 80% of the integrated heat of fusion (A + B) in the temperature range of 0 ° C. to 150 ° C., and the cell size modifier is added in an amount of 1 wt ppm or more and less than 10,000 wt ppm based on the styrene monomer. There is a method for producing styrene-based expandable resin particles, which is characterized in that:

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

Next, the raw material components and the like common to the styrene-based expandable resin particles and 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 suspension-polymerizing a styrene-based monomer 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 The 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, as the cell size adjusting agent, the integrated heat of fusion (B) in the temperature range of 75 ° C. to 150 ° C. is the integrated heat of fusion (A + B) in the temperature range of 0 ° C. to 150 ° C. ) Is used in the styrene-based foamable resin particles.

If the ratio of the former accumulated heat of fusion (B) to the latter accumulated heat of fusion (A + B), ie, the accumulated heat of fusion ratio B / (A + B), is less than 80%, the effect of adjusting the cell size becomes weak. In addition, a large amount of the cell size adjusting agent must be used when producing the styrene-based expandable resin particles. In addition, when the styrene-based expandable resin particles are dried at a temperature exceeding 40 ° C. or when the excess foaming agent on the surface of the particles is subjected to dissipation treatment, the pre-expanded particles have a large cell size difference between the inside and the vicinity of the surface. Will be generated. For this reason, drying in a very short time and dissipating treatment of the foaming agent become impossible, which is industrially disadvantageous.

Next, as in the second and fourth aspects of the present invention, it is preferable to use a polyethylene wax having an integrated heat of fusion ratio of more than 90%. In this case, the cell size adjusting effect is particularly high, and the difference between the surface and internal cell sizes of the pre-expanded particles is further reduced, so that the cell uniformity is greatly improved. Note that the upper limit of the above-mentioned cumulative heat of fusion ratio is 100%.

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, even when the content exceeds 10,000 ppm by weight, the effect of reducing the cell size reaches its limit. The polyethylene wax can be dispersed in the styrene monomer before starting the suspension polymerization or added to the aqueous phase of the suspension polymerization to be contained in the styrene foamable resin particles. .

It is possible to add the polyethylene wax during the suspension polymerization. However, the polyethylene wax may be unevenly present in the styrene-based expandable resin particles, and may easily cause cell unevenness or the like. Not preferred. 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, polyvinyl pyrrolidone, 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, an electrolyte such as an inorganic salt such as lithium chloride, potassium chloride, sodium chloride, magnesium chloride, calcium chloride, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, etc. at the start of polymerization or during polymerization. Organic acid salts such as sodium acetate, disodium succinate, sodium behemate, sodium benzoate and the like can also be added.

Polymerization initiator; Examples of the polymerization initiator include polymerization initiators generally used for radical polymerization of styrene monomers, such as benzoyl peroxide, butyl perbenzoate, and the like.
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 expandable 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.

[0031]

Embodiments of the present invention and comparative examples will be described below.

Embodiment 1 [Measurement of integrated heat of fusion of polyethylene wax]
For each type of polyethylene wax shown in the following examples (Table 1), 2010 Instruments DSC manufactured by TA Instruments
Using a measuring instrument, follow the standard method in air at -50 ° C to 15 ° C.
The mixture was heated to 0 ° C. at a rate of 10 ° C./min, and the heat of fusion (joules / g) was measured (see FIG. 1).

The integrated heat of fusion was obtained by drawing a linear baseline from 0 ° C. to 150 ° C. in the plot in FIG.
Calculated values were obtained by dividing the range into an integrated heat of fusion (A) of 75 ° C. and an integrated heat of fusion (B) of 75 ° C. to 150 ° C. From these values, the integrated heat of fusion ratio [B / (A + B)]
I asked.

[Production of styrene-based expandable resin particles] 50
L in an autoclave with a rotary stirrer, distilled water 16k
g, 40 g of tricalcium phosphate as a suspending agent and 0.64 g of sodium dodecylbenzenesulfonate as a suspending aid.

Then, to 17 kg of styrene as a styrene monomer, 1.7 g of the above copolymer as a cell size regulator, 50 g of tertiary butyl peroxy 2-ethylhexanoate as an initiator and tertiary butyl 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 foaming agent is 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.

[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 substantially uniform, the average cell size (diameter) near the surface was 90 μm, and the internal average cell size was 100 μm.

[Measurement of Properties of Pre-expanded Particles] That is, the number of cells and 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. 2 and 3, distance L1 (μm) from cell A to cell walls A1 to An + 1 in a range of 0.2 mm from surface A toward the center.
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. 2, 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. 2, 900 (μm) / 9 (pieces) =
It becomes 100 μm. In addition, 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.

[Production of foamed molded article] Next, the pre-expanded particles were aged at room temperature for 1 day, and the inner dimensions were 300 mm × 75 mm.
80 × 25mm
It was heated for 20 seconds with water vapor of Pa to obtain a foam molded article. No so-called "melting" was observed on the surface of the obtained foam molded article. After one day at room temperature, JIS-A9511
The maximum strength was 282
kPa.

Cell uniformity: The obtained foam molded article was cut with a slicer, and the distribution of the number of cells observed on the cut surface was visually judged. Physical properties of polyethylene wax as the cell size modifier, ie, the cumulative heat of fusion (A),
Table 1 shows (B), the integrated heat of fusion ratio [B / (A + B)%], the molecular weight, and the cell size and cell uniformity on the surface and inside of the pre-expanded particles.

Embodiments 2 to 4 The same procedures as in Embodiment 1 were carried out, except that the polyethylene wax was variously changed as shown in Table 1.

Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that the polyethylene wax was variously changed as shown in Table 1.

Comparative Example 3 The same procedure as in Example 1 was carried out except that no polyethylene wax was added.

As can be seen from Table 1, in Examples 1 to 4 according to the present invention, the cell size of the pre-expanded particles is almost the same both on the surface and inside, and the cell uniformity is high. On the other hand, Comparative Examples 1 and 2 have a low cell uniformity because the integrated heat of fusion ratio is 80% or less, and Comparative Example 3 does not use polyethylene wax as a cell size adjuster.

[0049]

[Table 1]

[0050]

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 achieve excellent productivity. Further, it is possible to provide a styrene-based foamable resin particle having a very small cell size difference between the inside and the vicinity of the surface, and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between temperature and heat of fusion of polyethylene wax in Embodiment 1;

FIG. 2 is an explanatory diagram of property measurement of pre-expanded particles.

FIG. 3 is an overall explanatory diagram of FIG. 2;

Claims (4)

[Claims] 1. A styrene-based expandable resin particle containing a cell size adjuster and a foaming agent, wherein the cell size adjuster has an integrated heat of fusion (B) of 0 to 75 ° C. to 150 ° C. It is a polyethylene wax exceeding 80% of the integrated heat of fusion (A + B) in the temperature range of 150 ° C. to 150 ° C., and the cell size modifier is at least 1 ppm by weight and less than 10000 ppm by weight with respect to the styrene monomer as a raw material. Styrene-based expandable resin particles characterized by being added. 2. The method according to claim 1, wherein the temperature is from 75 ° C. to 150 ° C.
The integrated heat of fusion (B) in the temperature range of 0 ° C is 0 ° C to 150 ° C.
Styrene-based expandable resin particles, wherein the styrene-based expandable resin particles exceed 90% of the integrated heat of fusion (A + B) in the above temperature range. 3. 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 adjusting agent and adding a foaming agent during or after the suspension polymerization. At 75 ° C.
The integrated heat of fusion (B) in the temperature range of ~ 150 ° C is 0 ° C ~ 1
A polyethylene wax exceeding 80% of the integrated heat of fusion (A + B) in a temperature range of 50 ° C., and the cell size modifier is added in an amount of 1 wt ppm or more and less than 10000 wt ppm to the styrene monomer. A method for producing styrene-based expandable resin particles, comprising: 4. The method according to claim 3, wherein the temperature is from 75 ° C. to 150 ° C.
The integrated heat of fusion (B) in the temperature range of 0 ° C is 0 ° C to 150 ° C.
Characterized by exceeding 90% of the integrated heat of fusion (A + B) in the above temperature range.