JPS6338062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to expandable styrenic resin particles.
Styrenic resin particles containing 1 to 20 parts by weight of an easily volatile blowing agent such as propane, butane, pentane, methyl dichlorofluoromethane chloride, etc. are known as expandable styrenic resin particles. These expandable styrenic resin particles are generally produced by aqueous suspension polymerization, but when they are heated with water vapor or the like, a large number of small bubbles (cells) are generated therein, resulting in pre-expanded particles. When the pre-expanded particles are filled into a closed mold cavity and heated, the pre-expanded particles are fused to each other, making it possible to easily produce a foamed styrenic molded article according to the mold. Molded foams made in this way can be used as food containers, cushioning materials,
It is used for insulation materials, fishing boxes, floats, etc., and product characteristics such as molding time, strength, and surface condition are greatly influenced by the number of bubbles during foaming. Therefore, it is necessary to arbitrarily adjust the number of cells in the foam in order to impart properties suitable for the intended use to the molded product. However, the factors governing the number of bubbles are influenced by the type, content, and impregnation temperature of the blowing agent, as well as the degree of polymerization of the styrene resin and other factors, and some of these factors are not clearly defined. Therefore, it is extremely difficult to arbitrarily adjust the number of bubbles. Therefore, conventional expandable styrenic resin particles generally have the following drawbacks. 1. When resin particles are foamed immediately after production, the number of cells in the cross section of the foam is not small and their sizes are non-uniform. Therefore, after production, a long aging period is required until the size of the bubbles becomes uniform. 2. When foaming is performed after aging, the size of the bubbles becomes uniform, but the number of bubbles is small (in the case of a bulk ratio of approximately 60 times, the number of bubbles per 1 mm ² on the cut surface of the foamed particle is 50 or less). Furthermore, since the bubbles are coarse, the bubble film is thick, and residual gas within the bubbles is slow to dissipate during molding, causing expansion and deformation if the molded product is taken out without being completely cooled. Therefore, it takes a long time to cool down, resulting in poor work efficiency. Further, since the bubbles are coarse, the surface of the molded product is not smooth, and the cut surface of the cut product molded product also becomes rough. 3. If the manufactured resin particles are stored at a temperature around summer temperature and then foamed, the bubbles on the cut surface of the foam will become rough, so it is necessary to store it in a cold storage at a temperature below summer temperature. The present inventor investigated the relationship between the number of cells in expandable styrene resin foam obtained by a conventional method, the aging period after production, and the properties of the molded product (molding time, strength, surface condition, etc.). The bulk multiple of is approximately
When compared at 60x magnification, 1 mm ² at the cut surface of expanded particles
Those with a number of bubbles in the range of 50 to 300 are excellent as molded products, such as short aging period after production, short molding time, strong molded product, smooth and beautiful surface, and clean cut surface. It was confirmed that it has the following characteristics. Therefore, we found a method to arbitrarily adjust the number of bubbles in the foam, increasing the number of bubbles in 1 ^mm2 from 50 to 300.
We believed that if we could adjust the amount within a range, we could obtain a foamable styrenic resin with excellent molded properties.As a result of extensive research, we found that by copolymerizing maleimide with a styrene monomer, we could obtain a foamable styrenic resin with excellent molded properties. The drawbacks of the styrene-based resin particles have been improved and the desired objective has been achieved. That is, the present invention provides expandable styrenic resin particles containing a styrenic resin and an organic blowing agent, in which the styrenic resin contains a styrenic monomer and a styrenic monomer in the presence or absence of a styrenic polymer. General formula () (However, in the formula, R is an aliphatic hydrocarbon group having 1 to 24 carbon atoms.) The present invention relates to styrenic resin particles. The styrenic monomer in the present invention refers to a vinyl monomer containing 50% by weight or more of a styrene derivative such as styrene, α-methylstyrene, vinyltoluene, or chlorostyrene, and other vinyl monomers containing cyanide vinyl monomers such as acrylonitrile. methacrylate monomers such as methyl methacrylate, acrylate monomers such as butyl acrylate, vinyl acetate,
It may contain a monomer copolymerizable with styrene or a styrene derivative of vinyl chloride. When using two or more of these monomers, they are not necessarily used in combination, but may be used separately. The styrenic polymer is a polymer of styrene monomers, and there are no restrictions on its manufacturing method or shape. For example, there are those obtained by suspension polymerization, and the shape of the resin includes spherical particles, pellets, etc. The organic blowing agent used in the present invention has the property of not dissolving the styrene resin or only slightly swelling it, and its boiling point is lower than the softening point of the above-mentioned polymer, so it is normally liquid. A liquid or a gaseous substance can be used. Examples include aliphatic hydrocarbons such as propane, butane, and pentane, and cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane. The styrenic resin in the present invention is obtained by polymerizing a styrene monomer and a maleimide represented by the general formula () in the presence or absence of a styrene polymer. Here, the maleimide is 0.01~
2% by weight, preferably 0.05-1% by weight. If the amount of maleimide is too small, the number of cells in the expanded particles cannot be increased, and if it is too large, the number of cells becomes too large, leading to a reduction in heat resistance such as thermal shrinkage of the molded product. In the general formula (), R is a saturated alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a capryl group, a lauryl group, or a stearyl group, or an alkenyl group such as a myristole group, a palmitoleyl group, or an oleyl group. and so on. As the method for the above polymerization, aqueous suspension polymerization is preferred. In aqueous suspension polymerization, a sparingly soluble inorganic substance or a water-soluble polymer compound is present as a dispersant in an aqueous medium. Generally well-known materials can be used as the poorly soluble inorganic substance. Examples include calcium phosphate, hydroxyapatite, magnesium phosphate, magnesium pyrophosphate, and the like. The poorly soluble inorganic substance means the total amount of the obtained styrenic resin (the charged styrenic monomer and maleimide or the charged styrenic monomer, styrene resin and maleimide) in an aqueous medium.Hereinafter,
(similar) is used in a range of 0.01 to 3% by weight. If less than 0.01% by weight is used, it will hardly function as a dispersant. In addition, if the amount exceeds 3% by weight, the effect as a dispersing agent will be too high, and the particles produced will be small, making it difficult to obtain the desired particle size (0.1 to 4 mm) in a good yield, and in some cases. may also emulsify. Further, it is preferable that an anionic surfactant be present at the same time as the poorly soluble inorganic substance. The presence of the anionic surfactant makes the poorly soluble inorganic substance easier to function as a dispersant. As the anionic surfactant, commonly known ones can be used. Examples include sodium alkylbenzenesulfonate, sodium α-olefinsulfonate, sodium alkylsulfonate, and the like. The anionic surfactant is used in an amount of 1.times.10.sup. ^-4 to 0.01% by weight based on the styrenic resin obtained in the aqueous medium. If it is used outside this range, it will hardly function as a dispersant. As the water-soluble polymer compound, generally well-known compounds can be used. Examples include partially saponified polyvinyl alcohol, alkylcellulose, hydroxyalkylcellulose, carboxyalkylcellulose, polyacrylamide, polyvinylpyrrolidone, and sodium polyacrylate. The water-soluble polymer-resistant dispersant is used in an aqueous medium in an amount of 1 x 10 ^-4 to 1% by weight based on the styrene resin obtained. If less than 1×10 ⁻⁴ weight % is used, it will hardly function as a dispersant. In addition, if it exceeds 1% by weight, the effect as a dispersant will be too strong, so the particles produced will be small, with a preferable particle size (0.1 to 4 mm).
Not only is it difficult to obtain in good yield, but also emulsification may occur in some cases, which is not preferable. In the above polymerization, when using a styrene polymer, 10% by weight based on the styrene monomer.
Preferably used below. The styrenic polymer may be used by being dissolved in the styrene monomer in advance, or if it is not dissolved in advance, the styrene monomer is sufficiently added to the styrene copolymer in an aqueous medium before the start of polymerization. Impregnation is preferred. In the above polymerization, there is no particular restriction on the timing of adding maleimide as long as it is before the completion of polymerization of the styrenic monomer, and there is no particular restriction on the method of addition. However, it is particularly preferable to add it before the start of polymerization or before the polymerization conversion rate is 50% by weight. Polymerization initiators used in the above polymerization include organic peroxides such as benzoyl peroxide and tertiary butyl perbenzoate, azo compounds such as azobisisobutylnitrile and azobisdimethylvaleronitrile, and generally styrene monomers. Polymerization initiators used for radical polymerization can be used. The polymerization initiator is used in an amount of about 0.1 to 4% by weight based on the total amount of the styrenic monomer and the maleimide. Further, the aqueous medium is used in an amount of about 80 to 300% by weight, preferably about 100% by weight or less, based on the styrenic resin obtained. The organic blowing agent used in the present invention may be added during the polymerization reaction or after the polymerization reaction is completed. Among the above blowing agents, when propane and butane are used alone or in combination, it is preferable to use a small amount of solvent necessary to soften the styrene resin to some extent. Examples of such solvents include ethylbenzene, benzene, toluene, xylene, ethylene dichloride, trichloroethylene, tetrachloroethylene, cyclohexane, and the like. The amount used is 0.1 to 4% by weight based on the styrene resin particles obtained. When adding a blowing agent during the polymerization process, add the blowing agent when the polymerization conversion rate is 50% by weight or more, especially 70% by weight.
It is preferable to carry out the above process by press-fitting into an aqueous medium. When adding after the completion of polymerization, it may be added under pressure into an aqueous medium following the polymerization process, or the once separated styrene resin particles may be resuspended in an aqueous medium and then press-fitted into this, or by other methods. This can be done using the following method. In addition, the polymerization conversion rate refers to the ratio of the styrenic polymer, styrenic monomer, and the above to the total amount of the styrenic polymer, the charged styrenic monomer, and the above maleimide when polymerizing in the presence of the styrenic polymer. This is the ratio of the total amount of polymerized maleimide. The expandable styrenic resin particles according to the present invention have the following features. 1. The cross-section of a foamed product expanded immediately after production has a large number of cells and is uniform in size. Therefore, the ripening period is extremely short. 2 When foaming after aging, the number of cells is large (approximately
When the bulk ratio is 60 times, the number of cells per 1 mm ² on the cut surface of the foamed particles is 50 to 300).Therefore, the cooling period during molding is short and the work efficiency is high. Furthermore, the surface of the molded product is smooth and beautiful, and the cut surface of the cut molded product is also clean. Next, examples of the present invention will be shown. Example 1 1100 g of ion-exchanged water, 22 g of tricalcium phosphate, and a 1% aqueous solution of sodium dodecylbenzenesulfonate were placed in an autoclave equipped with a rotary stirrer.
3.3g, styrene 1000g, N-laurylmaleimide
2 g, benzoyl peroxide, 3.0 g, and butyl perbenzoate, 0.5 g, and the temperature was raised to 90°C after 1 hour while stirring. Thereafter, polymerization proceeds while maintaining the temperature at 90°C. Occasionally sample a portion of the suspension,
Measure the specific gravity of the oil droplets using the specific gravity liquid method to examine the polymerization conversion rate. When the polymerization conversion rate reaches 95% or more, 16 g of ethylbenzene is added, and after another 20 minutes, 180 ml of butane gas is pressurized with nitrogen gas. After the injection of butane was completed, the temperature began to rise again, and after 2 hours, the temperature was raised to 120°C, and stirring was continued at this temperature for 4 hours. After this 30℃
The mixture is cooled to a temperature of 1.5 mm, excess gas in the system is discharged, and after drying, it is classified to obtain expandable styrene resin particles with a uniform particle size (0.71 to 1.00 mm). After aging this product at room temperature (25° C.) for 2 days, it was pre-foamed to a bulk ratio of 60 times, and the bubble state of the foamed particles was examined. twenty four
After a period of time, the mixture was filled into a mold and molded using a steam molding machine under certain conditions. Example 2 Same as Example 1 except that the amount of N-laurylmaleimide used in Example 1 was increased to 10 g. Example 3 Ion-exchanged water in an autoclave with a rotating stirrer
1200g, 24g of tricalcium phosphate, 3.6g of 1% aqueous solution of sodium dodecylbenzenesulfonate,
Charge 1000g of styrene, 3.0g of benzoyl peroxide, and 0.5g of butyl perbenzoate, and raise the temperature to 90°C after 1 hour while stirring, then keep it at 90°C.
Proceed with polymerization. Polymerization was proceeded by checking the polymerization conversion rate using the method described in Example 1, and the polymerization conversion rate was 50.
%, a solution of 2 g of N-lauryl maleimide dissolved in 4 g of styrene was added as a bubble regulator to further proceed with polymerization. The subsequent implementation method was the same as in Example 1. Example 4 1800 g of ion-exchanged water, 36 g of tricalcium phosphate, and a 1% aqueous solution of sodium dodecylbenzenesulfonate were placed in the autoclave equipped with a rotary stirrer in step 4.
5.4 g and 1500 g of polystyrene particles (with a diameter of 0.71 to 1.0 mm) copolymerized with 0.2% by weight of N-laurylmaleimide obtained by suspension polymerization in an aqueous medium with a relatively uniform particle size were charged and stirred. while raising the temperature to 80℃. After 10 minutes while maintaining the temperature at 80°C, 37.5 g of styrene as a plasticizer was added, and after another 20 minutes, 220 ml of butane gas was pressurized with nitrogen gas. After injecting butane gas, the temperature began to rise again, and after 1 hour it reached 100℃.
Thereafter, stirring was continued for 5 hours while maintaining this temperature. Thereafter, it is cooled to 30°C, excess gas in the system is discharged, and it is dried separately to obtain expandable styrene particles. After aging this product at 25°C for 2 days, it was pre-foamed to 60 times the bulk, and the foam state of the foamed particles was examined. After 24 hours, the mixture was filled into a mold and molded using a steam molding machine under certain conditions. Example 5 Expandable styrenic resin particles were produced by the method of Example 1, and then tested in accordance with Example 1 at an aging temperature of 40° C. and an aging period of 4 days. Example 6 1100g of ion-exchanged water, 0.01g of polyvinyl alcohol (Gohsenol KH-20, Nippon Gosei Kagaku Co., Ltd.), and styrene were placed in an autoclave equipped with a rotary stirrer.
1000g, N-laurylmaleimide 2g, benzoyl peroxide 3.0g, and butyl perbenzoate 0.5g were charged, and the temperature was raised to 90°C after 1 hour while stirring. Thereafter, polymerization proceeds while maintaining the temperature at 90°C. A portion of the suspension is sampled from time to time, and the specific gravity of the oil droplets is measured by the specific gravity liquid method to examine the polymerization conversion rate. 16g of ethylbenzene when the polymerization conversion rate reaches 95% or more.
After another 20 minutes, 180 ml of butane gas was injected with nitrogen gas. Thereafter, the same operation as in Example 1 was carried out. Comparative Example 1 Same as Example 1 except that N-laurylmaleimide as a cell regulator was not used. Comparative Example 2 Same as Example 5 except that the foam regulator N-laurylmaleimide was not used. Comparative Example 3 Same as Example 6 except that the foam regulator N-laurylmaleimide was not used. Table 1 summarizes the characteristics of the expandable styrenic resin particles obtained in each of the above Examples and Comparative Examples and the cell state of the expanded particles.

【table】

[Table] The expandable styrenic resin particles according to the present invention have a large number of cells when formed into a foam. The expandable styrenic resin particles made using conventional technology are approximately 60
In the case of a bulk multiple of times, 1 at the cross section of the expanded particle
The number of bubbles per mm ² was less than 50, but according to the present invention, the number of bubbles increased to 50 to 300. The increase in the number of cells adds the following features to expandable particles and foam molded products. 1. The aging period of expandable particles can be shortened. 2. Molding time can be shortened. 3. The strength of the foamed molded product increases. 4. The foam molding surface is smooth and beautiful.

Claims (1)

[Scope of Claims] 1. In expandable styrenic resin particles containing a styrenic resin and an organic blowing agent, the styrenic resin contains a styrenic monomer in the presence or absence of a styrenic polymer. and general expression () (However, in the formula, R is an aliphatic hydrocarbon group having 1 to 24 carbon atoms.) Styrenic resin particles.