JPH0665308A - Production of vinyl polymer particle and expandable vinyl polymer particle - Google Patents

Abstract

PURPOSE:To produce polymer particles which give a molded foam having an improved appearance without detriment to the foaming characteristics of the particles including particle size distribution. CONSTITUTION:Vinyl polymer particles are produced by the suspension polymn. of a polymerizable mixture comprising a vinyl monomer and a polymn. initiator in an aq. medium contg. a hardly sol. phosphate and an anionic surfactant. The polymn. is started after the temp. of the suspension is raised to 80-90 deg.C and continued at 80-90 deg.C until the conversion reaches 40wt.%. Then, the temp. is raised by at least 5 deg.C and the polymn. is continued at 90-100 deg.C until the conversion reaches 95wt.%.

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 vinyl polymer particles excellent in quality and moldability and a method for producing expandable vinyl polymer particles excellent in surface smoothness of a molded product.

[0002]

2. Description of the Related Art In recent years, various types of printing have been frequently performed on the surface of foam molded articles, and foam molded articles having excellent surface smoothness have been demanded. This is because if the surface of the foamed molded product has irregularities, the concave portions are not printed and remain white, and the appearance of the printed appearance deteriorates. In particular, in expanded polystyrene using expandable polymer particles, it is difficult to sufficiently fill the gaps between expanded particles, and therefore it is further required to improve the surface smoothness. In order to obtain the polymer particles for expanded polystyrene, peroxide type initiators such as benzoyl peroxide and lauroyl peroxide and azo compound type initiators such as azobisisobutyronitrile have been conventionally used. However, with the expandable polymer particles using these initiators, it was difficult to obtain a foamed molded product having excellent surface smoothness of the molded product.

JP-A-58-222121, JP-A-62-11740, JP-A-61-214544, JP-A-63-69844 and JP-A-1-28.
No. 9841 and Japanese Patent Application Laid-Open No. 1-299843 disclose a foam-molded article in which a non-foaming layer is provided on the surface layer by coating the surface of polymer particles for expanded polystyrene impregnated with a foaming agent with a surface additive that corrodes the skin. Although a method for improving the surface smoothness of the foamed product is described, this method improves the surface smoothness of the foamed molded product, but the gas that is the foaming agent easily dissipates as a product of the expandable polystyrene polymer particles. It has the drawback of shortening the life of the.

Further, in JP-A-3-39334, for the purpose other than the present invention, a polymerization batch is subjected to a maximum of several hours at 80 ° C. to 9 ° C.
Polymerization is initiated by rapid heating to 0 ° C, and the reaction temperature is 8 ° C / hr.
100 degrees Celsius, increasing by 17 degrees Celsius from 120 degrees Celsius to 130 degrees Celsius
The exchange rate is 30% to 60% when reaching the maximum temperature, and the conversion rate is at least 80% when the maximum temperature is reached.
A method of obtaining a pearl-like polymer by maintaining the residual monomer content in the polymer at a temperature of 00 ° C to 130 ° C until it is reduced to less than 0.1% is described. Although the reaction time can be reduced, there is a problem in the quality reproducibility of the expandable polymer particles to be obtained, there is a drawback that the industrially operable range is very narrow, and further, the polymer particles having a narrow particle size distribution. There is a problem such as not being able to obtain.

[0005]

As a result of various studies on the surface smoothness of the foamed molded product, it was found that the above-mentioned drawbacks are eliminated and the surface smoothness is improved by increasing the polymerization temperature in the latter stage of the polymerization. Came to. That is, the present invention provides a method for suspension polymerization of a polymerizable monomer mixture containing a vinyl monomer and a polymerization initiator in an aqueous medium containing a sparingly soluble phosphate and an anionic surfactant. The polymerization temperature from the start to the polymerization conversion rate of less than 40% by weight is 80 ° C to 9 ° C.
The temperature is in the range of 0 ° C., and the polymerization conversion rate is 40% by weight to 95%.
Increase the polymerization temperature by at least 5 ° C or more between 90% by weight and 90%.
The present invention relates to a method for producing vinyl polymer particles, characterized in that the temperature is in the range of 100 to 100 ° C. The present invention also relates to a method for producing expandable vinyl polymer particles, which comprises impregnating a foaming agent during or after polymerization in the method for producing vinyl polymer particles.

According to the present invention, a vinyl monomer and a polymerization initiator soluble in a vinyl monomer are contained in an aqueous medium containing a sparingly soluble phosphate and an anionic surfactant as a suspension stabilizer. Suspension polymerization is started by adding the polymerizable monomer mixture, and the particle size distribution and foaming characteristics of the expandable polymer particles are not deteriorated by increasing the polymerization temperature in the latter stage of the polymerization, and an excellent molded product is obtained. The present invention provides expandable vinyl polymer particles that provide surface smoothness. If the polymerization conditions of the present invention cannot be satisfied, a molded product having an excellent appearance cannot be obtained even if the particle size distribution of the polymer particles and the foaming property are good.

Generally, a foamed molded article using beads is obtained by impregnating vinyl polymer particles polymerized by suspension polymerization with a foaming agent, pre-foaming the expandable vinyl polymer particles with steam or the like, and then Fill the mold with pre-expanded particles,
It is manufactured by foaming this again with steam or the like. The surface smoothness of the foam-molded article thus obtained strongly depends on the properties of the pre-expanded particles. As a result of various studies on the surface smoothness of the foamed molded product, it was found that the surface smoothness is surprisingly greatly influenced by the polymerization temperature in the latter stage of the polymerization.
That is, when the polymerization temperature in the latter half of the polymerization is increased, when the expandable vinyl polymer particles are pre-expanded, the film thickness of the cells (air bubbles) on the surface of the expanded particles becomes larger than the film thickness of the internal cells, It was found that the heat resistance to steam during steam forming was increased and the surface smoothness was improved. The pre-expanded particles obtained from the expandable vinyl polymer particles polymerized at a constant temperature from the beginning to the end of the polymerization as in the conventional case have the same thickness of the surface cell and the inner cell or the surface cell Since the film thickness is thinner, the surface smoothness of the molded product after foam molding is poor. In the method of the present invention, the cell structure of the pre-expanded particles can be changed to a structure having excellent heat resistance by increasing the polymerization temperature by at least 5 ° C. or more after the weight conversion of 40% by weight or more.

In the present invention, an aqueous medium suspension of a polymerizable monomer and a polymerization initiator is first heated to a temperature of 80 ° C. to 90 ° C. to initiate polymerization, and at least the polymerization conversion rate is less than 40% by weight. The polymerization temperature is set to a temperature of 80 ° C to 90 ° C (note that, of course, the polymerization proceeds to some extent during the temperature increase to 80 ° C to 90 ° C). The preferred polymerization temperature is 83 ° C to 86 ° C. It is preferable that the polymerization temperature at which the polymerization conversion rate is less than 40% by weight after the temperature is raised to start the polymerization is constant from the viewpoint of controlling the production process and stabilizing the quality. If the polymerization temperature in this range exceeds 90 ° C., the effect of the present invention cannot be obtained, and there is a problem that the particle size distribution becomes broad depending on the kind of the peroxide type polymerization initiator. Especially t-butylperoxy-2
-When ethylhexanoate is used as an initiator, there is a problem that the particle size distribution of polymer particles obtained is broad. When the polymerization temperature in this range is less than 80 ° C., the polymerization time becomes extremely long and the particle size distribution of the polymer particles becomes broad. The rate of temperature increase from the polymerization temperature of 80 ° C to 90 ° C is preferably 0.5 ° C / min to 2 ° C / min. If the heating rate is slower than this, the synthesis time will be long, while if it is faster, it will be difficult to control the polymerization temperature. According to such a heating rate, the heating can be completed while the polymerization conversion rate is 5% by weight or less.

When the polymerization conversion rate is between 40% by weight and 95% by weight, the polymerization temperature is increased by at least 5 ° C. to 90 ° C.-1.
It is necessary to set the temperature to 00 ° C. It is preferably 8 ° C. or higher. Specifically, the polymerization temperature is preferably 93 ° C to 97 ° C. If the increase in the polymerization temperature is less than 5 ° C when the polymerization conversion rate is between 40% by weight and 95% by weight, the cell structure of the pre-expanded particles cannot be changed to a structure having excellent heat resistance. The effect of the present invention is not obtained at a polymerization temperature of less than 90 ° C., which is increased between 40% by weight and 95% by weight, and the polymerization conversion is 40% by weight to 95% by weight.
If the polymerization temperature increased between 100 ° C. exceeds 100 ° C., the suspension system becomes unstable, resulting in problems such as formation of giant particles and increased adhesion of the polymer to the polymerization apparatus. When the polymerization temperature is increased by 5 ° C. or more, the polymerization conversion rate is 40% by weight or more, preferably the polymerization conversion rate is 50% by weight to 70% by weight, and particularly preferably the polymerization conversion rate is between 50% by weight and 65% by weight. . If the polymerization conversion rate is less than 40% by weight, not only the effect of the present invention cannot be obtained, but also the particle size distribution of the obtained polymer particles becomes wide. The polymerization temperature does not necessarily have to be increased at once, and may be increased stepwise or continuously. Finally, if there is a difference of 5 ° C. or more, the effect of the present invention can be obtained. For example, the temperature may be raised by 10 ° C. or higher within 30 minutes, or may be raised by 5 ° C. in two steps in 2 hours. The heating rate is not particularly limited, but is 0.2 ° C /
Minutes to 1 ° C./minute is preferred.

As the polymerization initiator soluble in the vinyl monomer, a polymerization initiator having a half-life temperature of 10 hours (hereinafter referred to as 10-hour half-life temperature) of 65 ° C. to 80 ° C. is preferable. Furthermore, the 10-hour half-life temperature is 70 ° C to 75 ° C.
Are preferred. As the polymerization initiator, a conventional organic peroxide-based polymerization initiator such as benzoyl peroxide, t-butylperoxy-2ethylhexanoate or methylbenzoyl peroxide can be used. Also, a peracid ester-based polymerization initiator is preferable because the effect of the present invention can be more remarkably obtained. With a polymerization initiator having a 10-hour half-life temperature outside this range, the particle size is uniform under the temperature conditions of the present invention, and it becomes difficult to obtain polymer particles with excellent surface smoothness. The polymerization initiator is generally used in the range of 0.05% by weight to 1% by weight based on the total amount of the vinyl-based monomer. Preferably 0.20
% By weight to 0.35% by weight. The polymerization initiators can be used in combination. Generally, when synthesizing expandable polystyrene polymer particles, a polymerization initiator as described in the present invention is used, but a polymerization that decomposes at a higher temperature in order to reduce residual monomers in the polystyrene polymer particles. An initiator is also used together. For example, t-butylperoxybenzoate or t-butylperoxyisopropyl carbonate can be used in combination.

As the sparingly soluble phosphate used in suspension polymerization, tricalcium phosphate, hydroxyapatite, magnesium phosphate, barium phosphate, strontium phosphate,
Aluminum phosphate, iron phosphate, cobalt phosphate, calcium pyrophosphate and the like can be used, but tricalcium phosphate and hydroxyapatite are generally used. The addition amount is preferably 0.1% by weight to 0.8% by weight, particularly 0.15% by weight to the total amount of the polymerizable monomer.
0.4% by weight is preferred.

As the anionic surfactant, sodium dodecylbenzene sulfonate, sodium styrene sulfonate, sodium dodecyl sulfonate, sodium dioctyl sulfosuccinate and the like can be used. The amount added is 0.0001% by weight based on the total amount of the polymerizable monomer.
~ 0.01 wt% is preferred. Water is mainly used as the aqueous medium. Known soluble inorganic salts in aqueous medium,
For example, sodium chloride, sodium sulfate, sodium nitrate, etc. may be contained. These soluble inorganic salts have the effect of narrowing the particle size distribution of polymer particles.

Vinyl-based monomers include styrene and α-
Styrene and its derivatives such as methylstyrene, chlorostyrene, and vinyltoluene, acrylonitrile, vinylpyrrolidone, vinylpyridine, vinylcarbazole, polybutadiene, esters of alcohol having 1 to 8 carbon atoms and acrylic acid or methacrylic acid, and the like can be used. However, when forming the expandable vinyl polymer particles, it is preferable to use 50% by weight or more of styrene or a styrene derivative.

The monomer mixture added first is, in addition to the vinyl-based monomer and the polymerization initiator, ethylene vinyl acetate copolymer known as a cell-forming agent, ethylenebisstearylamide, methylenebisstearylamide, etc. May be included. Further, a plasticizer such as dioctyl adipate or dioctyl phthalate may be included.

The weight ratio of all vinyl monomers to the aqueous medium is preferably 0.8 / 1 to 1.2 / 1 (former / latter). The resulting vinyl-based polymer particles can be made into expandable vinyl-based polymer particles by using propane, butane, pentane, hexane,
It can be obtained by impregnating a blowing agent such as a hydrocarbon such as cyclopentane or cyclohexane, a halogen hydrocarbon such as methylene chloride, dichlorodifluoromethane or trifluoromethane, or a mixture thereof by a known method during or after the polymerization. . According to this method, it is possible to obtain expandable vinyl polymer particles which give a molded article having a smooth surface and excellent appearance. In the present invention, the polymerization conversion rate was obtained from the oil droplets during the polymerization by the specific gravity method.

[0016]

EXAMPLES The present invention will be described below with reference to examples. The surface smoothness of the molded product was determined by the following method to determine the quality of the surface smoothness. That is, the irregularities (the gaps between the foamed particles) on the surface of the molded product were measured by a non-contact type surface roughness meter, and the larger the depression depth, the worse the surface smoothness. The particle size distribution and average particle size of the polymer particles are indicated by the deviation coefficient Cv and the median diameter, respectively. That is, based on the cumulative weight distribution curve, the cumulative weight is 15%, 50%, 8
The deviation coefficient Cv was determined by the equation of Cv = (d ₈₅ −d ₁₅ ) / d ₅₀ , where the particle diameters of 5% were d ₁₅ , d ₅₀ , and d ₈₅ , respectively, and the breadth of the particle diameter distribution was judged. The larger the Cv value, the wider the particle size distribution, and the smaller the Cv value, the narrower the particle size distribution. The average particle size is the above d
_The median diameter represented by ₅₀ was adopted.

Example 1 10 wt% tricalcium phosphate dispersion liquid in a 4 l autoclave (manufactured by Nippon Kagaku Kogyo KK, trade name Super Tight 1)
0) 24 g, sodium dodecylbenzene sulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.048 g, 10 wt% sodium sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) 5 g, and ion-exchanged water 1176 g were added and well stirred. A homogeneous mixed solution was obtained. Next, 3.2 g of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name perbutyl O)
(0.28% by weight), t-butylperoxy-isopropyl carbonate (Nippon Oil & Fats Co., Ltd., trade name Perbutyl I) 0.40 g, and ethylene vinyl acetate copolymer (Nippon Gosei Co., Ltd., trade name So 1150 g of styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) in which 1.2 g of Alex CH) was dissolved was added with stirring, and the temperature was raised to 86 ° C. at a heating rate of 1 ° C./min to initiate polymerization. When the polymerization conversion rate reached 40% by weight, 12 g of 10% tricalcium phosphate dispersion was added,
After 40 minutes (polymerization conversion of 52% by weight), 96 minutes over 20 minutes
The temperature was raised to ℃ and the polymerization proceeded. When the polymerization conversion rate reached 95% by weight, 35 g of a 10% by weight tricalcium phosphate dispersion was added, and then 11 g of cyclohexane and 5 parts of butane were added.
0 g was introduced in 1 hour. Thereafter, the temperature was raised to 120 ° C. over 2 hours, the temperature was maintained at 120 ° C. for 5 hours, and then cooled to room temperature to obtain the target expandable polystyrene polymer particles. The expandable polystyrene polymer particles obtained had an average diameter d ₅₀ of 0.91 mm and a deviation coefficient Cv value of 0.40. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin portion of the pre-expanded particles was 2.2 μm, and the cell thickness inside was 1.0 μm. 2 pre-expanded particles
It was aged for 4 hours, and heat-molded at a steam pressure of 0.078 MPa for 5 seconds. The maximum depression depth of the surface of the obtained molded product was 77 μm. The cell film thickness was determined by cutting the pre-expanded particles with a razor and observing a cross-section SEM photograph (× 100).
The cell film thickness was measured at 10 locations arbitrarily selected from 0) and calculated from the average value.

Example 2 In the process of Example 1, during the polymerization (at a polymerization conversion rate of 40% by weight, 1
40 minutes after adding 0 wt% tricalcium phosphate) 9
Suspension polymerization was performed in the same manner as in Example 1 except that the temperature was raised to 3 ° C. to obtain expandable polymer particles. The expandable polystyrene polymer particles thus obtained had an average diameter d ₅₀ of 0.92 mm and a deviation coefficient C.
The v value was 0.41. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin portion of the pre-expanded particles was 1.8 μm, and the cell thickness inside was 1.1 μm. The pre-expanded particles were aged for 24 hours and subjected to the same molding conditions as in Example 1. The maximum depression depth of the surface of the obtained molded product was 80 μm.

Comparative Example 1 Foamable polymer particles were obtained by carrying out suspension polymerization in the same manner as in Example 1 except that the temperature was not raised during the polymerization (at the same time as in Example 2). . The expandable polystyrene polymer particles thus obtained had an average diameter d ₅₀ of 0.93 mm and a deviation coefficient Cv value of 0.40. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin portion of the pre-expanded particles was 0.9 μm, and the cell thickness inside was 1.4 μm. The pre-expanded particles were aged for 24 hours and molded under the same molding conditions as in Example 1. The maximum depth of depression on the surface of the obtained molded product was 90 μm.

Comparative Example 2 In Example 1, during polymerization (at the same time as Example 2), 9
Suspension polymerization was performed in the same manner as in Example 2 except that the temperature was raised to 0 ° C. to obtain expandable polymer particles. The expandable polystyrene polymer particles thus obtained had an average diameter d ₅₀ of 0.92 mm and a deviation coefficient C.
The v value was 0.41. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin portion of the pre-expanded particles was 1.1 μm, and the cell thickness inside was 1.2 μm. The pre-expanded particles were aged for 24 hours and molded under the same molding conditions as in Example 1. The maximum depression depth on the surface of the obtained molded product was 88 μm.

Comparative Example 3 Foaming polymer particles were obtained by carrying out suspension polymerization in the same manner as in Example 1 except that the polymerization temperature in the initial stage of polymerization was 91 ° C., but the particle size distribution was widened. It was The expandable polystyrene polymer particles obtained had an average diameter d ₅₀ of 0.92 mm and a deviation coefficient Cv value of 0.55. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin portion of the pre-expanded particles is 1.3 μm and the cell thickness inside is 1.2 μm.
Met. The pre-expanded particles were aged for 24 hours and molded under the same molding conditions as in Example 1. The maximum depression depth on the surface of the obtained molded product was 85 μm.

Comparative Example 4 In Example 1, the polymerization conversion was 30% by weight and the polymerization temperature was 8%.
Suspension polymerization was carried out in the same manner as in Example 1 except that the temperature was raised from 6 ° C to 92 ° C to obtain expandable polymer particles, but the particle size distribution was widened. The resulting expandable polystyrene polymer particles had an average diameter d ₅₀ of 0.94 mm and a deviation coefficient Cv value of 0.47. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin of the pre-expanded particles is 1.4 μm
The inner cell film thickness was 1.2 μm. The pre-expanded particles were aged for 24 hours and molded under the same molding conditions as in Example 1. The maximum depression depth of the obtained molded product surface is 86 μm.
Met.

Example 3 In Example 1, the polymerization conversion was 70% by weight and the polymerization temperature was 8%.
Suspension polymerization was carried out in the same manner as in Example 1 except that the temperature was raised from 6 ° C to 93 ° C to obtain expandable polymer particles. The expandable polystyrene polymer particles obtained had an average diameter d ₅₀ of 0.90 mm and a deviation coefficient Cv value of 0.41. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin of the pre-expanded particles is 1.6 μm, and the cell thickness inside is 1.2 μ.
It was m. The pre-expanded particles were aged for 24 hours, and Example 1 was used.
Molding was performed under the same molding conditions as. The maximum depression depth of the surface of the obtained molded product was 84 μm.

Comparative Example 5 Foamable polymer particles were obtained by carrying out suspension polymerization in the same manner as in Example 1 except that the temperature was raised to 102 ° C. at a polymerization conversion rate of 60% by weight. The expandable polystyrene polymer particles obtained had an average diameter d ₅₀ of 0.96 mm and a deviation coefficient Cv value of 0.
49, and some large particles were generated. The amount of the polymer deposited on the polymerizer increased about three times. The expandable polymer particles obtained were pre-expanded to 55 ml / g. The cell thickness of the skin part of the pre-expanded particles is 1.6 μm and the cell thickness inside is 0.8 μ.
It was m. The pre-expanded particles were aged for 24 hours, and Example 1 was used.
Molding was performed under the same molding conditions as. The maximum depression depth of the surface of the obtained molded product was 82 μm. Table 1 summarizes the polymerization conditions and particle characteristics of each of the above Examples and Comparative Examples.

[0025]

[Table 1]

[0026]

INDUSTRIAL APPLICABILITY The present invention provides a stable production method, and the vinyl-based polymer particles thus obtained are
A molded article having excellent surface smoothness can be formed without impairing the particle size distribution of the polymer particles and other foaming characteristics, and the present invention is industrially extremely useful in terms of productivity and quality.

Claims (4)

[Claims] 1. When suspension polymerizing a polymerizable monomer mixture containing a vinyl monomer and a polymerization initiator in an aqueous medium containing a sparingly soluble phosphate and an anionic surfactant, 80 ℃
Up to a temperature in the range of 90 ° C to start the polymerization, and the polymerization conversion rate until the polymerization conversion rate is less than 40% by weight is 80 ° C.
The temperature is in the range of ~ 90 ° C and the polymerization conversion rate is 40% by weight or more.
A method for producing vinyl polymer particles, characterized in that the polymerization temperature is increased by at least 5 ° C or more between 95% by weight to a temperature in the range of 90 ° C to 100 ° C. 2. The method for producing vinyl polymer particles according to claim 1, wherein a peroxide polymerization initiator having a half-life of 10 hours at a temperature in the range of 65 ° C. to 80 ° C. is used as the polymerization initiator. 3. The method for producing vinyl polymer particles according to claim 1, wherein t-butylperoxy-2-ethylhexanoate is used as a polymerization initiator. 4. The method for producing expandable vinyl polymer particles according to claim 1, 2 or 3, wherein a foaming agent is impregnated during or after the polymerization. .