JPH05239253A - Expandable thermoplastic polymer particle and its production - Google Patents

Abstract

PURPOSE:To obtain the subject particles shortened in a cooling time in molding and improved in molding productivity. CONSTITUTION:The production process comprises adding 0.05-1.0wt.% based on the particles, nonionic surfactant of an HLB of 9 or below to an aqueous medium containing suspended thermoplastic polymer particles and impregnating the particles with an easily volatile blowing agent. The objective particles are obtained by coating the surfaces of the obtained polymer particles with a normally solid fatty acid triglyceride.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to expandable thermoplastic polymer particles and a method for producing the same. More specifically, the present invention relates to expandable thermoplastic polymer particles and a method for producing the same, in which a cooling time during a molding step of a foamed molded product having a cell structure is short and a good foamed molded product is obtained.

[0002]

2. Description of the Related Art Usually, in order to obtain a foamed molded article from thermoplastic polymer particles, thermoplastic polymer particles containing a foaming agent in a liquid or gaseous state at room temperature are first prepared by steam heating to an arbitrary specific gravity. Foam. Then, the pre-expanded particles are left to mature for an arbitrary time, then filled in a mold and heated with steam to secondary-expand to fuse the pre-expanded particles to each other to obtain a desired homogeneous expansion. Use as a molded body. In the molding of this secondary foaming, it is necessary to hold the molded body in the mold while cooling it for a certain period of time after heating with steam. This is because if the molded product is taken out of the mold immediately after heating with steam, the molded product will expand or distort, and the desired accurate shape cannot be obtained. The time for which the molded body is held in the molding die in order to obtain the molded body having a satisfactory shape is called the cooling time, which is one of the important factors in the molding process. That is, if the cooling time can be shortened, the cycle for producing the molded product will be shortened, and the production amount per unit time can be increased. Many techniques have been reported to reduce the cooling time, and attempts have been made to add various substances into the expandable thermoplastic polymer particles or to the surface thereof.

For example, Japanese Unexamined Patent Publication (Kokai) No. 52-127968 discloses a technique in which a fatty acid triglyceride is present on the surface and / or inside other than the center of expandable styrene resin particles, and in Japanese Unexamined Patent Publication No. 53-97060, fatty acid carboxylic acid and fatty acid alcohol. Is applied to the surface of the expandable styrene resin particles, and JP-B-46-29486 discloses a polyoxyethylene monoester of a fatty acid having an HLB value of 15 or more,
Disclosed is a technique of impregnating a styrene polymer particle with a foaming agent in a suspension in which a polyoxyethylene sorbitan monoester of a fatty acid having an HLB value of 15 or more is present.

[0004]

However, in Japanese Patent Laid-Open No. Sho 5
In the technologies of No. 2-127968 and JP-A-53-97060, although the cooling time at the time of molding is shortened, it is difficult to increase the prefoaming ratio at the time of molding because the coating agent used corrodes the particle surface. There are problems that a large amount of water is taken into the inside of the molded body and the strength of the obtained molded body is significantly reduced. On the other hand, a technique such as Japanese Patent Publication No. 46-29486 has a problem that not only a great effect of shortening the cooling time is not obtained but also the suspension stability at the time of impregnation with the foaming agent is remarkably deteriorated.

[0005]

In view of such circumstances, the inventors of the present invention have conducted diligent research, and as a result, solved the above problems of the prior art and shortened the cooling time, and obtained a good foamability of a molded product. The present invention has provided a thermoplastic polymer particle and a method for producing the same. That is, the present invention, after adding a nonionic surfactant having an HLB value of 9 or less to the aqueous medium in which the thermoplastic polymer particles are suspended in an amount of 0.05 to 1.0% by weight based on the particles, The present invention relates to a method for producing expandable thermoplastic polymer particles, which comprises adding an easily volatile foaming agent to impregnate the particles, and the expandable thermoplastic polymer particles produced thereby.

The thermoplastic polymer particles referred to in the present invention include, for example, styrene polymers, copolymers of styrene and other vinyl monomers, methyl methacrylate polymers, copolymers of methyl methacrylate and other vinyl monomers. Examples thereof include polymers obtained by impregnating or graft-polymerizing a monomer having styrene or methyl methacrylate as a main component in an ethylene polymer or a propylene polymer, and these are used alone or in combination of two or more kinds.

When the fatty acid bisamide is contained in these thermoplastic polymer particles, immediately after the foaming agent is impregnated into the expandable thermoplastic polymer particles, that is, the aging period before foaming which is usually required. Not only a molded product having uniformly fine foam cells can be obtained by foam molding without undergoing the above, but also the effect of shortening the cooling time is improved. Examples of the fatty acid bisamide exhibiting such an effect include methylene bis-stearamide, ethylene bis-stearamide, etc. These may be used alone or in combination of two or more kinds.

The nonionic surfactant used in the present invention has the effect of shortening the cooling time during molding,
The HLB value needs to be 9 or less, and is preferably 4.5 to 8.0. Examples of the nonionic surfactant having an HLB value of 9 or less used in the present invention include sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and glycerin fatty acid ester. These may be used alone or in combination of two or more. Although used, a sorbitan fatty acid ester is preferably used, and a sorbitan fatty acid monoester is more preferably used, because it has a large effect of reducing the cooling time. The HLB value here is defined as the hydrophilic-lipophilic equilibrium [W. C. WC Griffin: Journal of Society Cosmetics Chewists 1, 311 (194)
9)]. The HLB value is determined empirically by the method described by Griffin, but can also be calculated using various equations. For example, HLB = 20
The formula (1-S / A) is used, where S is the saponification value of the ester and A is the acid value of the acid.

The amount of nonionic surfactant is 0.05 to 1.0% by weight, preferably 1.
It is 0 to 0.5% by weight. If it is less than 0.05% by weight, a good cooling time shortening effect cannot be obtained, and if it is added in an amount of more than 1.0% by weight, the cooling time effect does not change,
It is not preferable because it will impair suspension stability.

The addition timing of the nonionic surfactant is preferably from the time when the thermoplastic polymer particles are suspended in the aqueous medium to the time before the blowing agent is added, and the thermoplastic polymer particles are prepared by suspension polymerization. When the same polymerization machine used for the production and polymerization was continuously impregnated with the blowing agent, the polymerization conversion rate was 50%.
It may be performed from the time when the so-called so-called equal particle point is passed and before the addition of the foaming agent. As a method of addition, the nonionic surfactant powder may be added directly to the aqueous medium, or may be added after being suspended or dissolved in water, a solvent or the like.

As the suspending agent used for suspending the thermoplastic polymer particles in water in the present invention, generally known suspending agents can be generally used, and examples thereof include polyvinyl alcohol, polyvinylpyrrolidone and methyl cellulose. Examples thereof include organic polymer compounds such as polyacrylamide, hardly water-soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate, and these may be used alone or in combination of two or more. When a poorly water-soluble inorganic compound is used, it is preferable to use an anionic surfactant such as sodium alkylbenzene sulfonate and sodium alpha-olefin sulfonate together. A combination preferably used for maintaining suspension stability is a combination of tricalcium phosphate and an anionic surfactant. On the other hand, it is not preferable to add a water-soluble inorganic salt such as calcium chloride or sodium chloride to an aqueous medium containing these suspending agents, because it disturbs the dissolution or dispersion of the nonionic surfactant. From the standpoint of suspension stability, the weight ratio of the thermoplastic polymer particles to be suspended to the aqueous medium is preferably 1 or less.

The easily volatile foaming agent in the present invention includes:
Primarily, lower aliphatic hydrocarbons such as propane, butane, and pentane are preferably used, and in addition to halogenated hydrocarbons such as dichlorodifluoromethane and trichloromonofluoromethane, any commonly used blowing agent can also be used. , And these are used alone or in combination of two or more kinds.

The foamable thermoplastic polymer particles thus obtained may contain additives such as a flame retardant, a coloring agent and an antistatic agent, which are generally used, depending on the intended use of the particles. You can In addition, adding various surface additives to the surface of the particles, for example, an antiblocking agent, a fusion promoter, an antistatic agent, etc. is the same as applying to general expandable thermoplastic polymer particles. Can be done.

The expandable thermoplastic polymer particles obtained as described above, especially when a surface-temperature-solidified fatty acid triglyceride is applied to the surface thereof, can further reduce the cooling time by a very small amount. . In this case, since the coating amount is small, adverse effects such as extension of prefoaming time, increase of water content inside the molded product, and decrease of strength of the molded product are small. Examples of such fatty acid triglycerides include hydrogenated soybean oil, hydrogenated rapeseed oil, hydrogenated coconut oil, hydrogenated castor oil, and hydrogenated beef tallow, which may be used alone or in combination of two or more.

[0015]

EXAMPLES The present invention will be described below with reference to examples.
These do not limit the invention. Example 1 A polymerization machine equipped with a stirrer having a capacity of 180 liters weighs 56 kg.
100 parts by weight, pure water 110 parts by weight, tricalcium phosphate 0.155 parts by weight, alpha olefin sodium sulfonate 0.006 parts by weight, ethylene bisstearamide 0.14 parts by weight, and then peroxide 0.14 parts by weight of benzoyl, 0.2 parts by weight of 1,1-ditertiarybutyl 3,3,5 trimethylcyclohexane and 2.0 parts by weight of toluene were dissolved in 100 parts by weight of styrene monomer and charged with stirring. Then, the internal temperature of the polymerization machine was raised to 98 ° C., and 1 hour and 45 minutes after the temperature was raised, 0.15 parts by weight of calcium triphosphate was added. The polymerization temperature was kept at 98 ° C. for 3 hours to continue the polymerization.

After adding 0.2 parts by weight of sorbitan monostearate into the suspension of the styrene polymer particles thus obtained, 0.8 parts by weight of cyclohexane and 7.
5 parts by weight was added and the temperature was raised to 115 ° C. After maintaining at this temperature for 2 hours and 30 minutes, it was cooled, particles were taken out, washed with water and dried. From the obtained particles, a particle size of 71 is obtained by sieving.
Particles of 0 to 1000 μm are selected, and zinc stearate powder is added to the surface of these particles in an amount of 0.1 per 100 parts by weight of the particles.
4 parts by weight were attached. The particles were heated with steam in a pre-expanding machine to be expanded to form pre-expanded particles having an apparent magnification of 60 times, and then aged at room temperature for 24 hours. Using the TH90-VM molding machine (manufactured by Toyo Kikai Kinzoku Co., Ltd.), the pre-expanded particles were subjected to a pressure of 0.6 kg / cm in a slit mold which gives a molded body having a length of 45 cm, a width of 30 cm and a thickness of 5 cm. ² G
It was heated for 12 seconds with water vapor and then cooled. While observing the expansion force of the molded body with the surface pressure gauge attached to the mold,
The time from the start of cooling until the surface pressure dropped to 0.2 kg / cm ² G was evaluated as the cooling time. The results are shown in Table 1.

Examples 2 to 5 Particles were obtained in the same manner as in Example 1 except that the addition amount of sorbitan monostearate was changed as shown in Table 1.
The evaluation results are shown in Table 1.

Examples 6 to 8 Example 1 except that 0.16 parts by weight of the nonionic surfactant shown in Table 1 was used instead of sorbitan monostearate.
Particles were obtained in the same manner as in. The evaluation results are shown in Table 1.

Comparative Example 1 Particles were obtained in the same manner as in Example 1 except that sorbitan monostearate was not used. The evaluation results are shown in Table 1.

Comparative Examples 2 to 4 Example 1 except that 0.16 parts by weight of the nonionic surfactant shown in Table 1 was used in place of sorbitan monostearate.
Particles were obtained in the same manner as in. The evaluation results are shown in Table 1.

Example 9 73 kg of styrene monomer was used as 100 parts by weight, and pure water was added to 7 parts.
Polymerization and foaming agent impregnation were carried out in the same use ratio and method as in Example 1 except that 0 parts by weight and 0.2 parts by weight of initial calcium triphosphate were used. 30% by weight of the particles obtained are
The shape was such that two or more particles were attached. When these particles were evaluated in the same manner as in Example 1, the cooling time was 82 seconds.

Example 10 Particles were obtained in the same manner as in Example 1 except that ethylenebisstearoamide was not used. When the particles were pre-expanded after 1 day, the cells inside the expanded particles were very coarse and could not be molded.
Since good cells were obtained after pre-expansion after storage for a week, molding evaluation was carried out in the same manner as in Example 1. Cooling time is 9
It was 5 seconds.

Examples 11 and 12 Hardened soybean oil was applied to the surface of 100 parts by weight of the particles obtained in Example 1 in the amounts shown in Table 2 and evaluated. The pre-foaming time is indicated by the heating time by steam required to obtain the expansion ratio of 60 times. In addition, the water content of the molded product is 40 ° C.
The weight decreased by drying for 24 hours was calculated as the weight% with respect to the weight of the molded product immediately after molding, and less than 5% by weight was evaluated as low, 5-10% by weight as slightly high, and more than 10% as high. The results are shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

INDUSTRIAL APPLICABILITY As described above, according to the production method of the present invention using a specific nonionic surfactant, foamable thermoplastic polymer particles having a short cooling time during molding and good productivity in molding can be obtained. The particles obtained by coating fatty acid triglyceride on the surface of the particles have a shorter cooling time.

Claims (9)

[Claims] 1. A non-ionic surfactant having an HLB value of 9 or less is added to an aqueous medium in which thermoplastic polymer particles are suspended in an amount of 0.05 to 1.0% by weight based on the particles, and then easily added. A method for producing expandable thermoplastic polymer particles, wherein a volatile foaming agent is added to impregnate the particles. 2. The method according to claim 1, wherein the thermoplastic polymer particles are styrene polymer particles. 3. The method according to claim 2, wherein the styrenic polymer particles contain a fatty acid bisamide. 4. The production method according to claim 1, wherein the weight ratio of the thermoplastic polymer particles to the aqueous medium is 1 or less. 5. The method according to claim 1, wherein the suspending agent in the aqueous medium comprises calcium triphosphate and an anionic surfactant. 6. The nonionic surfactant has an HLB value of 4.5.
It is-8.0, The manufacturing method of Claims 1-5. 7. The method according to claim 1, wherein the nonionic surfactant is a sorbitan fatty acid ester. 8. The method according to claim 7, wherein the nonionic surfactant is a fatty acid monoester of sorbitan. 9. Expandable thermoplastic polymer particles obtained by coating a surface of expandable thermoplastic polymer particles produced by the production method according to claim 1 with a fatty acid triglyceride in a solid state at room temperature.