JPH0471418B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Object of the Invention The present invention relates to a method for easily producing spherical expandable styrenic resin particles uniformly containing carbon. (Field of Application of the Invention) The carbon-containing expandable styrenic resin particles obtained by the manufacturing method of the present invention are spherical expandable resin particles that uniformly contain carbon, so they are used in the mold cavity. By filling the inside of the foam, expanding it with steam, and fusing it together, you can obtain a foamed resin molded product with good appearance and fusion rate, which is uniformly colored black to the inside, and has good antistatic properties and conductivity. It will be done. (Prior Art) Conventionally, a method of applying a black paint to the surface of a foamed polystyrene molded product has been used to blacken the foamed polystyrene molded product. However, this method has the disadvantage that if the epidermis is scratched or damaged, a white surface appears, and the coloring process is expensive, so it is difficult to produce expandable polystyrene particles that are uniformly colored black with carbon. It was wanted. In addition, in order to easily produce foamed polystyrene molded bodies having conductivity and antistatic properties, there has been a demand for the production of foamed polystyrene particles uniformly containing carbon. As a method for uniformly incorporating carbon into styrene-based foamable resin particles, there is a method in which polystyrene is heated and mixed with carbon and a blowing agent (expansion agent) in an extruder, and then pelletized by rapid cooling. After heating and mixing to form pellets, the pellets and a foaming agent are placed in a sealed container and heated to impregnate the foaming agent;
A method has been known in which a styrene monomer in which carbon is dispersed is subjected to suspension polymerization in an aqueous medium, and a blowing agent is added during or after the polymerization process to impregnate the polymer. However, in the methods of (2) and (2), small particles generate fewer large particles and relatively uniform particles of the desired size can be easily obtained, but because the particles are pellet-like in shape, it is difficult to form them during molding. The disadvantages are that the filling properties are poor and the surface appearance of the foamed molded product is poor. Although this method yields truly spherical foamable resin particles, it is unavoidable that unnecessary small particles and large particles are generated, which must be sieved and contamination between product grades can be prevented. for,
A large amount of equipment, such as a mixing and dispersing tank for monomers and carbon, a drying line for resin particles, a sieve, etc., must be dedicated for each product, resulting in increased equipment costs. Furthermore, a significant drawback of the method is that during polymerization, the carbon dispersed in the monomer migrates into the aqueous phase of the polymerization medium, resulting in loss of carbon;
Another disadvantage is that not only wastewater treatment becomes troublesome, but also the suspension polymerization system becomes unstable, resulting in delayed or incomplete polymerization (increase in the amount of unreacted monomers). As an improvement method of the method described above, by using a so-called polymer graft carbon, which is a product in which monomers such as styrene, acrylic acid ester, methacrylic acid ester, acrylonitrile, etc. are graft-polymerized on the surface of carbon, instead of carbon, polymerization can be delayed and polymerized. A method for preventing incomplete completion was proposed (Japanese Patent Application Laid-Open No. 59-217715,
Publication No. 31536). However, the method using such polymer-grafted carbon is industrially extremely disadvantageous in that it requires a special polymer-grafted carbon. In addition, JP-A-60-31536 discloses that the polymerization reaction in the presence of such polymer-grafted carbon is as follows:
Although it has been described that using an initiator having a benzene ring such as benzoyl peroxide as a polymerization initiator causes polymerization delay or incomplete polymerization, there is thought to be some error in this point.
In other words, according to the research of the present inventors, polymerization delay and incomplete polymerization in this type of suspension polymerization are not due to the presence of a benzene ring in the polymerization initiator, but due to the presence of a benzene ring as an initiator, even though the initiator does not generate tertiary alkoxy radicals. It is believed that this is caused by the use of carboxy radicals, especially those that generate carboxy radicals. (Problems to be Solved by the Invention) The present invention provides a spherical foam that uniformly contains carbon, without using special carbon such as polymer grafted carbon, and without causing polymerization delay or incomplete polymerization. The present invention aims to provide a method for easily producing polystyrene-based resin particles. (b) Structure of the Invention (Means for Solving the Problems) As a result of repeated research in order to solve the above-mentioned problems, the present inventor has discovered that carbon-containing styrene resin can be used instead of carbon in the above-mentioned method. If particles are used and a styrenic monomer is suspension polymerized in an aqueous medium in the presence of the carbon-containing styrenic resin particles and using a specific polymerization initiator,
The present invention was achieved by discovering that spherical expandable styrenic resin particles uniformly containing carbon can be easily obtained without using special carbon such as polymer-grafted carbon. That is, the method for producing carbon-containing expandable styrenic resin particles of the present invention involves using a styrenic monomer containing styrene as a main component in an aqueous medium in the presence of carbon-containing styrenic resin particles and generating tertiary alkoxy radicals. It is characterized by carrying out suspension polymerization using a polymerization initiator containing an initiator as a main component, and impregnating it with an organic blowing agent having a boiling point lower than the softening temperature of the styrenic resin during or after the polymerization reaction. This is the way to do it. The carbon-containing styrenic resin particles used in the present invention are simply particles of a mixture of carbon and styrene resin, such as those obtained by heating and mixing carbon and styrene resin in an extruder to form pellets. This does not include styrenic resin particles containing polymer-grafted carbon. Carbon used in the production of the carbon-containing styrenic resin used in the present invention includes, for example, furnace black, channel black,
Examples include summer black, acetylene black, graphite, and carbon fiber. In addition, examples of the styrene resin containing such carbon include homopolymers of styrene monomers such as styrene, α-methylstyrene, and p-methylstyrene, copolymers of these styrene monomers, and styrenic resins of these styrene monomers. Examples include copolymers of 50% by weight or more of monomers and 50% by weight or less of other vinyl monomers (eg, acrylonitrile, acrylic esters, methacrylic esters, butadiene, etc.). The carbon content in the carbon-containing styrenic resin used in the present invention varies depending on the required degree of blackness and conductivity of the foam molded product, and is usually 1 to 40% by weight, preferably 1 to 40% by weight. 2
It is appropriately selected from the range of ~30% by weight. Also,
The size of the carbon-containing styrenic resin particles used in the present invention is not particularly limited, but is usually 0.1
The size is preferably about 1 mg/piece. The styrenic monomer used in the suspension polymerization of the present invention has styrene as its main component, and may be styrene alone, or may contain other vinyl monomers such as α-methylstyrene in a proportion of less than 50% by weight. , p-methylstyrene, acrylonitrile, acrylic ester, methacrylic ester, butadiene, etc. may be used. A preferable styrenic monomer is one having the same or similar composition to the monomer composition used in the production of the styrenic resin in the carbon-containing styrenic resin used. The amount of the styrene monomer used in the present invention is preferably 10% by weight or more based on the carbon-containing styrenic resin particles. When the amount of the styrene monomer used is 10% by weight or less, the resulting expandable styrenic resin particles are less likely to be spheroidized.
In addition, the amount of styrene monomer used is determined so that the carbon content of the foamed styrene resin particles is 0.1 to 30.
It is desirable that the amount is 1 to 10% by weight. If the carbon content in the expandable styrenic resin particles is too low, the blackness, conductivity, and antistatic properties of the foamed molded product will be insufficient, and if it is too high, the mechanical strength of the foamed molded product will be insufficient. descend. The polymerization initiator used in the suspension polymerization of the present invention is an initiator that generates a tertiary alkoxy radical (〓CO.), preferably an initiator that generates a tertiary alkoxy radical and a carboxy radical (RCOO.).
This is an initiator whose main component is an initiator that does not generate. This is because an initiator that generates tertiary alkoxy radicals does not cause polymerization retardation or polymerization incompleteness, whereas using an initiator that generates carboxy radicals causes polymerization retardation or polymerization incompleteness. Examples of initiators that generate tertiary alkoxy radicals used in the present invention include t-butylperoxybenzoate, t-butylperoxybenzoate, and t-butylperoxybenzoate.
2-Ethylhexanoate, t-butylperoxyhexahydroterephthalate, n-butyl-
4,4-bis(t-butylperoxy)valerate, 1,1-bis(t-.butylperoxy)-
Examples include 3,3,5-trimethylcyclohexane, dicumyl peroxide, di-t-butylperoxybutane, and the like. Among these initiators, dicumyl peroxide, n-butyl-4,4-bis(t-butylperoxy)valerate, 1,1-bis(t-.butylperoxy)-3,3,5 -Trimethylcyclohexane is particularly preferred since it does not generate carboxy radicals. Examples of polymerization initiators include initiators that mainly generate carboxy radicals, such as benzoyl peroxide and lauroyl peroxide. It does not remain as an initiator for use in the present invention because it delays and increases the amount of unreacted monomer. However, initiators that mainly generate carboxy radicals and azo initiators such as azobisisobutyronitrile,
If it is used in a relatively small amount, it can be used in combination with the initiator that generates the tertiary alkoxy radical used in the present invention. The amount of the polymerization initiator used in the present invention is 0.05 to 2 parts by weight per 100 parts by weight of the styrene monomer.
Preferably it is 0.1 to 1.0 parts by weight. If the amount of initiator used is too small, the polymerization will not be completed and the amount of unreacted monomer will increase, while if it is too large, resin particles will be obtained that will give a brittle foam. The polymerization temperature in the present invention includes the decomposition temperature of the polymerization initiator used, the degree of polymerization of the polymer to be produced,
It is determined by considering the absorption rate of the monomer, etc.
Usually, the temperature is appropriately selected from the range of 60 to 150°C. The polymerization initiator in the present invention may be added to the polymerization system before the addition of the styrene monomer, or may be dissolved in the monomer and added together with the monomer. In the present invention, it is preferable to add the styrene monomer after the polymerization temperature has been reached, from the viewpoint of monomer absorption efficiency. A solvent such as toluene, xylene, cyclohexane, or a small amount of a polymerization inhibitor or chain transfer agent may be added to the styrene monomer. The polymerization reaction of the present invention is carried out in an aqueous medium. As a dispersion stabilizer, for example, a water-soluble polymer such as polyvinyl alcohol or polyvinylpyrrolidone, or a poorly water-soluble inorganic dispersant such as tricalcium phosphate, magnesium pyrophosphate, or calcium carbonate can be added to the aqueous medium. . When adding an inorganic dispersant, it is desirable to use a surfactant such as sodium dodecylbenzenesulfonate together. The amount of dispersant used is preferably 0.1% by weight or more based on water. However, although it is not inconvenient to use a large amount of 2% by weight or more, it is economically disadvantageous because the effect cannot be expected to improve commensurately with the use of a large amount. In the present invention, an organic blowing agent is added according to a conventional technique during or after the polymerization reaction step of suspension polymerization to impregnate the produced styrenic resin particles with the organic blowing agent. Examples of the organic blowing agent include those having a boiling point lower than the softening point of the styrene resin, such as hexane, pentane, butane, propane, trichloromonofluoromethane,
Dichlorodifluoromethane and the like are used. In the present invention, when adding the organic blowing agent during the polymerization process, it is desirable to add it after 70% by weight of the monomer has been polymerized, and also after the polymerization is complete.
It may be added at the time of completion of 99% or more to allow subsequent impregnation with a blowing agent. Further, an aqueous medium may be newly added to the styrenic resin particles obtained after the polymerization reaction is completed and dispersed, and a blowing agent may be added thereto to perform a blowing agent impregnation treatment. (Examples etc.) Below, Examples and Comparative Examples will be given and further explained in detail. Example 1 An aqueous medium was prepared by adding 900 g of pure water and 9 g of tribasic calcium phosphate and 0.027 g of sodium dodecylbenzenesulfonate as dispersants to an autoclave having an internal volume of 3. Next, polystyrene resin containing 8% by weight of carbon was extruded into strands using an extruder, cooled, and cut into pellets (approximately 0.5mg/piece), which were then extruded into strands of 400%
g, and heated to 93℃ while stirring at 400 rpm.
20 minutes after reaching the same temperature, a solution of 1.4 g of 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane dissolved in 200 g of styrene monomer was heated for 20 minutes. It was added continuously. After the addition was completed, the temperature was maintained at 93° C. for 8 hours, then the temperature was raised to 115° C. over 2 hours, 40 g of pentane was added, and the temperature was maintained for 6 hours to complete polymerization. After cooling, the polymer particles are separated by centrifugation,
After washing with nitric acid, washing with water and drying, the diameter is 1.0 to 1.2 mm.
True spherical carbon-containing expandable polystyrene particles with uniform particles were obtained. The polystyrene particles were pre-foamed to 50 g/particle by heating with steam at normal pressure. After leaving this for one day, it was filled into a mold with a cavity measuring 300 mm long, 300 mm wide, and 25 mm deep, and had steam permeation holes, and heated with steam at a pressure of 0.8 kg/cm ² G for 20 seconds. The pre-expanded particles were expanded, fused together, and cooled to form a foamed molded product. This molded product has good appearance and fusion condition,
The foam was colored uniformly black throughout. Table 1 shows the manufacturing conditions for the carbon-containing expandable polystyrene particles and an overview of the produced particles. Examples 2 to 7 Comparative Examples 1 to 2 Various expandable polystyrene particles were manufactured according to the method of Example 1, except that the conditions for manufacturing expandable polystyrene particles were variously changed as shown in Table 1. The results were as shown in Table 1.

[Table] Example 8 In Example 1, the polystyrene resin was replaced with styrene-acrylonitrile (styrene content 77% by weight).
The same procedure as in Example 1 was carried out except that the styrene monomer was changed to a copolymer and the styrene monomer was changed to a mixture of 154 g of styrene and 46 g of acrylonitrile.
True spherical carbon-containing expandable styrene-acrylonitrile copolymer particles with uniform particles of 1.0 to 1.2 mm were obtained. The unreacted monomer in the particles was 0.2% by weight. (c) Effects of the invention The present invention has the following effects. () Spherical expandable polystyrene resin particles uniformly containing carbon can be easily obtained, and the resin particles have excellent filling properties during foam molding. It is colored uniformly black, has excellent conductivity and antistatic properties, and has a good surface appearance. () Compared to the above-mentioned conventional method, the resin particles produced are spherical, so the filling properties during foam molding are excellent, and the surface appearance of the foam is good. () Compared to the conventional method described above, the produced resin particles are uniform and there is no need for sieving, the production equipment is simple, and there is no risk of polymerization delay or incomplete polymerization. () Compared to conventional methods that use polymer-grafted carbon, special polymer-grafted carbon is not required.

Claims (1)

[Scope of Claims] 1. A polymerization initiator containing a styrenic monomer containing styrene as a main component in an aqueous medium in the presence of carbon-containing styrenic resin particles and an initiator that generates tertiary alkoxy radicals as a main component. During or after the polymerization reaction, an organic blowing agent having a boiling point lower than the softening temperature of the styrenic resin is added to impregnate the produced styrenic resin particles with the organic blowing agent. A method for producing carbon-containing expandable styrenic resin particles. 2. The production method according to claim 1, wherein the polymerization initiator is an initiator that generates tertiary alkoxy radicals but does not generate carboxy radicals. 3 The polymerization initiator is dicumyl peroxide, n
-butyl-4,4-bis(t-butylperoxy)valerate, and at least one selected from 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane. The manufacturing method described in Scope 1. 4. Claims 1 and 2, wherein the carbon-containing styrenic resin particles are particles obtained by mixing styrene resin and carbon in an extruder and granulating the mixture.
The manufacturing method described in Section 3 or Section 3.