JP5119348B2 - Method for producing foamed molded article having voids - Google Patents

Description

  The present invention relates to a method for producing a foamed molded article having voids. More specifically, the present invention relates to a method for producing a foamed molded article having voids having excellent heat resistance, light weight and sound absorption, and having significantly improved chemical resistance and bending strength. The foamed molded product obtained by the present invention can be suitably used as an industrial member such as an automobile interior material or a construction material.

  In general, a foam of a polyethylene resin is used as a packaging material because it has high elasticity and excellent impact resistance. However, it has disadvantages such as low rigidity and low compressive strength. On the other hand, styrene resin foams are excellent in rigidity but have the disadvantage of being brittle.

  As methods for improving such defects, Japanese Patent Publication No. 51-46138 (Patent Document 1), Japanese Patent Publication No. 52-10150 (Patent Document 2), Japanese Patent Publication No. 58-53003 (Patent Document 3), Japanese Laid-Open Patent Publication No. 62-59642 (Patent Document 4) proposes a method in which a polyethylene resin is impregnated with a styrene monomer and polymerized to obtain styrene-modified polyethylene resin expanded particles.

  Moreover, as a foaming molding obtained by heat-foaming a styrene-modified polyethylene resin foam piece in a mold and fusing the pieces together, the pieces have a gap of 10 to 40% between the pieces. A fused styrene-modified polyolefin resin foam molded article is described in JP-A-7-80873 (Patent Document 5).

Japanese Patent Publication No.51-46138 Japanese Patent Publication No.52-10150 Japanese Patent Publication No.58-53003 JP-A-62-59642 Japanese Patent Laid-Open No. 7-80873

  In the modified resin particles obtained by the method described in Japanese Patent Publication No. 51-46138, the ratio of the polyolefin resin tends to be less than 50% by weight particularly in the vicinity of the surface portion thereof. Such modified resin particles tend to be those that cannot exhibit sufficient chemical resistance.

  In addition, the foamed molded article described in JP-A-7-80873 can obtain a desired porosity as well as a compressive strength that can sufficiently withstand the use as a culvert drainage material. Has been. A foam-molded product having such a porosity can also exhibit good sound absorption performance.

  However, even the foamed molded article of this publication has insufficient chemical resistance as described above, and is a foamed molded article provided with a desired porosity, so that it is used as an industrial member such as an automobile interior material. Has been found to be insufficient in strength (for example, bending strength) and cannot be used.

  The present invention has been made to solve the above-described problems, and is a foam molded article that improves chemical resistance, further provides a desired porosity, exhibits good sound absorption performance, and also improves bending strength. The purpose is to provide.

Thus, according to the present invention, the bulk density of 0.012~0.20g / cm ^3, 698cm ^-1 and 2850 cm ^-1 obtained from an infrared absorption spectrum of the measured particle surface by ATR method infrared spectroscopy The light absorption ratio (D ₆₉₈ / D ₂₈₅₀ ) is in the range of 0.1 to 2.5, the amount of polyolefin on the particle surface is 51 to 90% by weight, and styrene-based with respect to 100 parts by weight of the polyolefin resin component A foam-molded article having voids, wherein a foam-molded article having a porosity of 5 to 50% is obtained by foam-molding styrene-modified polyolefin resin pre-expanded particles containing 100 to 1000 parts by weight of a resin component A manufacturing method is provided.

The foam molded article obtained in the present invention is a foam molded article obtained from styrene-modified polyolefin resin particles having the following configuration. That is, the foamed molded product is obtained from pre-expanded particles having an absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) in the range of 0.1 to 2.5. For this reason, the proportion of the polyolefin resin in the vicinity of the surface of the pre-expanded particles can be about 50% by weight or more, although it varies depending on the types of the polyolefin resin and the styrene resin. Considering that the amount of polyolefin resin in the entire pre-expanded particles is less than the amount of styrene resin, polyolefin resin is more abundant than styrene resin on the surface of pre-expanded particles. I understand.

  Thus, since the proportion of the polyolefin-based resin is about 50% by weight or more on the particle surface portion, the chemical resistance of the foam molded product can be improved, and even a foam molded product provided with a desired porosity can be used. In addition, the fusion strength between the particles can be increased. Therefore, the foaming molding which has the space | gap provided with the chemical resistance and high bending strength which were not able to be exhibited conventionally can be obtained.

2 is an electron micrograph of the surface of styrene-modified polyolefin resin pre-expanded particles obtained in Example 1 taken using an SEM. 2 is an electron micrograph of a cross-section of the vicinity of the surface of the styrene-modified polyolefin resin pre-expanded particles obtained in Example 1, taken using a TEM. 2 is an electron micrograph of a cross-section of the vicinity of the surface of the styrene-modified polyolefin resin pre-expanded particles obtained in Example 1, taken using a TEM. 2 is an electron micrograph of a cross section of a central portion of styrene-modified polyolefin resin pre-expanded particles obtained in Example 1 using a TEM. It is the electron micrograph which image | photographed the surface of the styrene modified polyolefin resin pre-expanded particle (Example 1) after performing the extraction process of styrene resin using SEM. 2 is a schematic cross-sectional view of a polymerization vessel used in Example 1. FIG. 6 is a schematic cross-sectional view of a polymerization vessel used in Example 5. FIG. It is a calibration curve showing the relationship between the amount of styrene-based resin and the absorbance ratio. It is the schematic of a foam molding machine.

  In the present invention, the foam-molded product is obtained by foam-molding styrene-modified polyolefin resin pre-expanded particles (hereinafter referred to as pre-expanded particles), and has a porosity of 5 to 50%.

  The pre-expanded particles contain 100 to 1000 parts by weight of a styrene resin component with respect to 100 parts by weight of the polyolefin resin component.

First, pre-expanded particles for producing a foamed molded product will be described.
The pre-expanded particles are obtained by impregnating the modified resin particles with a volatile foaming agent to form expandable resin particles, and foaming the expandable resin particles.

  Here, the term “styrene-modified polyolefin resin” means a resin obtained by modifying a styrene resin with a polyolefin resin.

The polyolefin resin is not particularly limited, and a resin obtained by a known polymerization method can be used. Moreover, it is preferable to use resin which does not contain a benzene ring in a structure for polyolefin resin. Furthermore, the polyolefin resin may be cross-linked. For example, polyethylene resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers And polypropylene resins such as propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. Of these, branched low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer are preferable. These low-density polyethylene preferably has a density of 0.91~0.94g / cm ^3, and more preferably has a density of 0.91~0.93g / cm ^3.

  Examples of the styrene resin include resins derived from styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, and t-butylstyrene. Furthermore, the styrene resin may be a copolymer of a styrene monomer and another monomer copolymerizable with the styrene monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene, and (meth) acrylic acid alkyl esters that do not contain a benzene ring in the structure such as butyl (meth) acrylate. You may use these other monomers in the range which does not exceed 5 weight% substantially with respect to a styrenic resin.

  The z-average molecular weight of the styrene resin as measured by GPC is preferably 350,000 to 1,100,000, and more preferably 450,000 to 950,000. If the z-average molecular weight is lower than 350,000, the strength of the foamed molded product obtained by foam-molding the pre-foamed particles may decrease, which is not preferable. On the other hand, if it is higher than 1,100,000, the secondary foamability of the pre-foamed particles is lowered, the fusion property between the pre-foamed particles is lowered, and the strength of the foamed molded product may be lowered.

  The styrene resin is formed from a styrene monomer in the range of 100 to 1000 parts by weight with respect to 100 parts by weight of the polyolefin resin. The compounding quantity of a preferable styrene-type monomer is 120-800 weight part, and 130-700 weight part is more preferable.

  When the blending amount is more than 1000 parts by weight, the chemical resistance and impact resistance of the foamed molded article obtained by secondary foaming of the pre-foamed particles are unfavorable. On the other hand, when the blending amount is less than 100 parts by weight, the rigidity of the foamed molded product obtained by secondary foaming of the pre-foamed particles is unfavorable.

The pre-expanded particles have a bulk density of 0.012 to 0.20 g / cm ³ . A preferred bulk density is 0.014 to 0.15 g / cm ³ .

If the bulk density is less than 0.012 g / cm ³ , the closed cell ratio of the expanded particles is decreased, and the strength of the expanded molded product obtained by foaming the pre-expanded particles is not preferable. On the other hand, if it is larger than 0.20 g / cm ³ , the weight of the foamed molded product obtained by foaming the pre-foamed particles increases, which is not preferable. In addition, the measuring method of a bulk density is demonstrated in the column of an Example.

Additionally, pre-expanded particles, the surface, ATR method infrared absorption spectrum obtained by measurement by infrared spectroscopic analysis, the absorbance ratio of 698cm ^-1 and 2850 cm ^-1 in the range of 0.1 to 2.5 ( D ₆₉₈ / D ₂₈₅₀ ). A preferable absorbance ratio is 0.2 to 2.0, and 0.4 to 2.0 is more preferable. The particle surface includes a region from the surface to a depth of several μm.

  When the absorbance ratio is higher than 2.5, the ratio of the polyolefin resin on the surface of the pre-foamed particles is lowered. As a result, the chemical resistance and impact resistance of the foamed molded product obtained by foaming the pre-expanded particles are unfavorable. When the absorbance ratio is lower than 0.1, the foaming agent dissipates significantly from the surface of the pre-foamed particles, resulting in poor fusion between the particles during molding in the mold, resulting in a decrease in impact resistance. Or the finished appearance of the foamed molded product tends to deteriorate due to shrinkage or the like. In addition, when the pre-expanded particles are produced, the time required for impregnation and polymerization of the styrene monomer into the polyolefin resin particles is increased, and the production efficiency is lowered, which is not preferable.

  Here, the ATR method infrared spectroscopic analysis in the present invention is an analysis method in which an infrared absorption spectrum is measured by a single reflection type ATR method using total reflection absorption (Attenuated Total Reflectance). This analysis method is a method in which an ATR prism having a high refractive index is brought into close contact with a sample, infrared light is irradiated to the sample through the ATR prism, and light emitted from the ATR prism is spectrally analyzed.

  ATR infrared spectroscopic analysis includes organic materials such as polymer materials because of the simplicity of being able to measure the spectrum simply by bringing the sample and the ATR prism into close contact with each other, and the ability to perform surface analysis up to a depth of several μm. It is widely used for surface analysis of various substances.

The absorbance D _{698 at 698} cm ⁻¹ obtained from the infrared absorption spectrum refers to the height of a peak appearing in the vicinity of 698 cm ⁻¹ derived from the out-of-plane deformation vibration of the benzene ring mainly contained in the styrene resin. .

Further, the absorbance D _{2850 at 2850} cm ⁻¹ obtained from the infrared absorption spectrum is a peak appearing in the vicinity of 2850 cm ⁻¹ derived from the C—H stretching vibration of the methylene group contained in both the polyolefin resin and the styrene resin. The height of

  It is possible to determine the composition ratio of the styrene resin and the polyolefin resin from the absorbance ratio. That is, a plurality of types of standard samples obtained by uniformly mixing a styrene resin and a polyolefin resin at a predetermined composition ratio are prepared as described below. Each standard sample is subjected to particle surface analysis by ATR infrared spectroscopy to obtain an infrared absorption spectrum. The absorbance ratio is calculated from each of the measured infrared absorption spectra.

  A calibration curve is drawn by taking the composition ratio (weight ratio of styrene resin in the standard sample) on the horizontal axis and the absorbance ratio on the vertical axis. Based on this calibration curve, the approximate composition ratio of the styrene resin and the polyolefin resin can be determined from the absorbance ratio of the pre-expanded particles.

  For example, when the polyolefin resin is an ethylene-vinyl acetate copolymer (trade name “LV-121” manufactured by Nippon Polychem Co., Ltd.) and the styrene resin is polystyrene (trade name “MS142” manufactured by Sekisui Chemical Co., Ltd.), FIG. By using the calibration curve shown, the approximate composition ratio can be known. For example, when the absorbance ratio is 1.0, the polyolefin resin is about 76 to 82% by weight, the styrene resin is about 24 to 18% by weight, and when the absorbance ratio is 2.5, the polyolefin resin is about It can be calculated that 51 to 57% by weight and the styrene resin is about 49 to 43% by weight. The calibration curve is created by the following method.

The standard sample is obtained by the following method. First, a total of 2 g of styrene resin and polyolefin resin are precisely weighed so that the composition ratio (styrene resin / polyolefin resin) is the following ratio. This is heated and kneaded in a small injection molding machine under the following conditions and molded into a cylindrical shape having a diameter of 25 mm and a height of 2 mm to obtain a standard sample. In addition, as a small-sized injection molding machine, what is sold with the brand name "CS-183" from CSI can be used, for example.
Injection molding conditions: heating temperature 200 to 250 ° C., kneading time 10 minutes composition ratio (styrene resin / polyolefin resin; weight ratio):
0.5 / 9.5, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 9/1
The calibration curve of FIG. 8 is obtained by measuring the absorbance ratio of the standard sample with the above ratio and graphing the relationship between the polystyrene amount and the absorbance ratio.

  The pre-expanded particles have an absorbance ratio of 0.1 to 2.5. Therefore, the ratio of the polyolefin resin in the vicinity of the surface of the pre-expanded particles is about 50% by weight or more, although it varies depending on the types of the polyolefin resin and the styrene resin. In the entire pre-expanded particles, the amount of polyolefin resin is less than or equal to the amount of styrene resin, so that the polyolefin resin is more abundant than the styrene resin on the surface of the pre-expanded particles. Recognize. In addition, the weight% of the polyolefin resin with respect to the total amount of the polyolefin resin and the styrene resin in the entire pre-expanded particles is 9 to 50 wt%. Further, since the absorbance ratio is 0.1 or more, styrene resin is present on the surface of the pre-foamed particles, and the polyolefin resin does not reach 100% by weight.

  As described above, pre-expanded particles having a large amount of styrene resin and a large amount of polyolefin resin on the surface have a special structure that cannot be obtained by conventional methods.

  The form of the pre-expanded particles is not particularly limited as long as it does not affect the subsequent secondary expansion. For example, a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, a prismatic shape and the like can be mentioned. Of these, true spheres and elliptical spheres that can be easily filled into the mold are preferred.

  The average weight of each pre-expanded particle is preferably 0.5 to 5.0 mg, more preferably 0.5 to 3.0 mg. If it is lighter than 0.5 mg, it may be difficult to achieve high foaming, which is not preferable. On the other hand, if it is heavier than 5.0 mg, the pre-foamed particles become too large, and the filling property into the mold is lowered, which is not preferable. In addition, the weight of each pre-expanded particle means the average weight of 200 pre-expanded particles arbitrarily selected.

  The pre-expanded particles may contain an additive. Additives include foaming nucleating agents such as talc, calcium silicate, ethylene bis-stearic acid amide, methacrylic acid ester copolymers, fillers such as synthetic or naturally produced silicon dioxide, hexabromocyclododecane, triallyl Flame retardants such as isocyanurate hexabromide, diisobutyl adipate, liquid paraffin, glycerin diacetomonolaurate, plasticizers such as coconut oil, colorants such as carbon black and graphite, ultraviolet absorbers, antioxidants, etc. .

Next, a method for producing pre-expanded particles will be described.
First, polymerization is performed while impregnating polyolefin resin particles with styrene monomer (100 to 1000 parts by weight with respect to 100 parts by weight of polyolefin resin particles used) in an aqueous medium in which polyolefin resin particles are dispersed. Polymerization is performed in the presence of an initiator to obtain styrene-modified polyolefin resin particles (hereinafter also referred to as modified resin particles) (step (a)).

  The styrenic monomer can be continuously or intermittently added to the aqueous medium in order to impregnate the polyolefin resin particles. The styrenic monomer is preferably added gradually to the aqueous medium.

  Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol).

  Further, the average weight of each polyolefin-based resin particle is preferably 0.10 to 1.5 mg in view of ease of filling into the mold at the time of molding the pre-expanded particles to be produced. The average weight of polyolefin resin particles refers to the average weight of 100 arbitrarily selected polyolefin resin particles. The form of the polyolefin resin particles is not particularly limited. For example, a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, a prismatic shape and the like can be mentioned.

  When the blending amount of the styrene monomer is more than 1000 parts by weight, the polyolefin resin particles are not impregnated and particles of the styrene resin alone are generated, which is not preferable. In addition, the chemical resistance and impact resistance of the foamed molded product obtained by secondary foaming of the pre-expanded particles are not preferable. On the other hand, when the blending amount of the styrene monomer is less than 100 parts by weight, the time required for the impregnation and polymerization of the polyolefin resin particles is shortened, but the ability to retain the foaming agent of the resulting styrene modified polyolefin resin particles is It is not preferable because it decreases and cannot be highly foamed. In addition, the rigidity of the foamed molded product obtained by secondary foaming of the pre-expanded particles is not preferable.

  In addition, it is preferable to add a dispersant to the aqueous medium. Examples of such a dispersant include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose, magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, and magnesium phosphate. And inorganic dispersants such as magnesium carbonate and magnesium oxide. Of these, inorganic dispersants are preferred.

  When an inorganic dispersant is used, it is preferable to use a surfactant in combination. Examples of such surfactants include dodecyl benzene sulfonic acid soda and α-olefin sulfonic acid soda.

  Here, the impregnation and polymerization steps of the styrenic monomer may be performed separately as long as the impregnation is performed first, but it is preferable to proceed simultaneously.

  When proceeding simultaneously, impregnation and polymerization are carried out by adjusting the addition rate of the styrene monomer or adjusting the polymerization temperature so that the content of the styrene monomer in the polyolefin resin particles is maintained at 0 to 35% by weight. It is preferable to do. When the addition, impregnation and polymerization steps are carried out continuously, the content is preferably 0.5 to 35% by weight, more preferably 0.5 to 30% by weight.

  In addition, the polyolefin resin particle in the case of calculating said content means the particle | grains comprised from the polyolefin resin, the styrene-type monomer impregnated, and the styrene-type resin already impregnated and impregnated.

  When the content of the styrenic monomer is more than 35% by weight, pre-expanded particles having an absorbance ratio in a predetermined range may not be obtained even if the required power for stirring (Pv) is adjusted within the range described later. Absent.

An aqueous medium containing the polyolefin resin particles and the styrene monomer is stirred under predetermined conditions. Specifically, the power required for stirring (Pv) required to stir the aqueous medium 1m ³ including the polyolefin resin particles, the styrene monomer, and, if necessary, other dispersion and dissolved matter is 0.06. It is the stirring conditions adjusted so that it might become -0.8kw / m < ³ >. The power required for stirring is preferably 0.08 to 0.7 kw / m ³ . This required power for stirring corresponds to the net energy per unit volume received by the contents in the reaction vessel.

Conventionally, when a polyolefin resin particle is impregnated with a styrene monomer in an aqueous medium and polymerized, the stirring of the aqueous medium is not noted, and it is performed under conditions that allow the aqueous medium to be sufficiently stirred. The conventional stirring power is estimated to be about 1 to 2 kw / m ³ . On the other hand, in the above production method, the polyolefin power is localized in the vicinity of the surface of the modified resin particles with the polymerization of the styrene monomer by lowering the power required for stirring compared to the conventional method. Surprisingly, it has been found that modified resin particles containing a rich resin are obtained.

  By adjusting the power required for stirring to a predetermined range and adjusting the content of the styrene monomer in the polyolefin resin particles to a predetermined amount, the styrene monomer is sufficiently impregnated near the center of the polyolefin resin particles. It becomes possible to make it. As a result, it is possible to obtain a state in which a large amount of styrene monomer is present at the center of the polyolefin resin particles, and to gradually reduce the amount of styrene monomer from the center of the polyolefin resin particles toward the surface.

  Furthermore, since the styrene-based monomer produced in the polyolefin-based resin particles is polymerized while the styrene-based monomer is sequentially absorbed, the polyolefin-based resin particles are closer to the center as the styrene-based resin is generated. The larger the styrene resin, the larger the diameter.

  As a result, the pre-expanded particles obtained in the manner described later contain a high proportion of styrene resin at the center, and the polyolefin resin is dispersed in layers in the styrene resin. On the other hand, in the vicinity of the surface, the polyolefin resin is contained in a high ratio and the styrene resin is in a state of being finely dispersed in the polyolefin resin while gradually decreasing and decreasing the ratio as it approaches the particle surface. The particle surface is in a state where there is almost no styrene resin and polyolefin resin is present at a higher ratio.

If the power required for stirring is lower than 0.06 kw / m ^3, the dispersion of the styrene monomer in the aqueous medium becomes insufficient, and it is difficult to sufficiently impregnate the styrene monomer in the center of the polyolefin resin particles. is there. Therefore, the polymerization of the styrene monomer proceeds in the vicinity of the surface of the polyolefin resin particles, and the composition ratio of the polyolefin resin in the vicinity of the surface of the resulting modified resin particles decreases. As a result, the chemical resistance and impact resistance of the foamed molded article obtained by foaming the modified resin particles are lowered.

On the other hand, when the power required for stirring is higher than 0.8 kw / m ³ , the mixing of the styrene monomer and the polyolefin resin in the modified resin particles proceeds, and the modified resin containing the polyolefin resin rich in the vicinity of the surface Particles are difficult to obtain. In addition, the polyolefin resin particles impregnated with the styrene monomer and softened may be deformed into a flat shape. In that case, it becomes difficult to obtain pre-expanded particles having sufficient secondary foaming power.

Here, the power required for stirring refers to that measured in the following manner.
That is, an aqueous medium containing polyolefin resin particles, styrene monomers, and other dispersions and dissolved substances as necessary is supplied into a polymerization vessel of a polymerization apparatus, and a stirring blade is rotated at a predetermined rotational speed to form an aqueous medium. Stir the medium. At this time, the rotational driving load necessary to rotate the stirring blade is measured as a current value A ₁ (ampere). A value obtained by multiplying the current value A ₁ by an effective voltage (volts) is defined as P ₁ (watts).

Then, the stirring blade of the polymerization apparatus is rotated at the same rotation speed as described above in an empty state of the polymerization vessel, and the rotational driving load required to rotate the stirring blade is measured as a current value A ₂ (ampere). The value obtained by multiplying the current value A ₂ by the effective voltage (volt) is P ₂ (watts), and the required power for stirring can be calculated by the following equation 2. V (m ³ ) is the volume of the entire aqueous medium including the polyolefin resin particles, the styrene monomer, and other dispersions and dissolved substances as required.

Power required for stirring (Pv) = (P ₁ −P ₂ ) / V Equation 2
The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for the polymerization of styrene monomers.

  The stirring blade is not particularly limited as long as the power required for stirring can be set within a predetermined range. Specifically, paddle blades such as V-type paddle blades, inclined paddle blades, flat paddle blades, fiddler blades, pull margin blades, turbine blades such as turbine blades and fan turbine blades, propeller blades such as marine propeller blades, etc. Can be mentioned. Of these stirring blades, paddle blades are preferable, and V-type paddle blades, inclined paddle blades, flat paddle blades, Ferdler blades, and pull margin blades are more preferable. The stirring blade may be a single-stage blade or a multi-stage blade.

Also, the size of the stirring blade is not particularly limited as long as the required power for stirring can be set within a predetermined range.
Furthermore, you may provide a baffle plate (baffle) in the superposition | polymerization container.

  Moreover, as a polymerization initiator, the polymerization initiator currently used widely for superposition | polymerization of a styrene-type monomer can be used. For example, benzoyl peroxide, lauroyl peroxide, t-amyl peroxy octoate, t-butyl peroxybenzoate, t-amyl peroxybenzoate, t-butyl peroxybivalate, t-butyl peroxyisopropyl carbonate, t- Butyl peroxyacetate, t-butylperoxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t-butylperoxybutane, dicumyl peroxide And an azo compound such as azobisisobutyronitrile and azobisdimethylvaleronitrile. In addition, a polymerization initiator may be used independently or may be used together.

  The method for adding the polymerization initiator to the aqueous medium is not particularly limited, but is preferably performed according to the following procedure. That is, the polymerization initiator may be added in an amount of 0.02 to 2.0% by weight of the total amount of polyolefin resin particles and styrene monomer used until the amount of styrene monomer used reaches 90% by weight of the total amount used. preferable. The polymerization initiator is more preferably added until it reaches 85% by weight, particularly 80% by weight of the total amount used. Moreover, the more preferable addition amount of a polymerization initiator is 0.10-1.50 weight% with respect to the total amount used.

  According to the said addition point, the polymerization rate of the styrene-type monomer in polyolefin-type resin particle can be improved, and the composition ratio of polyolefin-type resin in the surface vicinity part of the modified resin particle obtained can be increased. As a result, it is possible to improve the strength of the foam molded body obtained by foam molding the modified resin particles.

  Furthermore, the addition of the polymerization initiator is preferably performed up to the predetermined amount via a styrene monomer containing the polymerization initiator. As the remaining styrenic monomer, a monomer containing no polymerization initiator can be used.

  The reason why the styrene monomer containing the polymerization initiator is used is considered as follows.

  That is, by allowing the styrene monomer to contain the polymerization initiator and absorbing it in the polyolefin resin particles, the polymerization initiator and the styrene monomer can be effectively impregnated in the center of the polyolefin resin particles. Therefore, from the early stage of the styrene monomer polymerization process, a polymerization initiator in an amount necessary for the polymerization of the styrene monomer can be preferentially supplied to the central part of the polyolefin resin particles. As a result, the styrene monomer can be preferentially polymerized at the center of the polyolefin resin particles.

  Next, when a styrene monomer that does not contain a polymerization initiator is added to the aqueous medium, the styrene monomer is sequentially absorbed by the styrene resin formed at the center of the polyolefin resin particles, and the polyolefin resin. Polymerization is smoothly performed under a polymerization initiator that is abundant in the center of the particle. Therefore, the resulting modified resin particles are in a state rich in styrene-based resin in the center from the vicinity of the surface.

  The amount of the styrene monomer not containing the polymerization initiator is preferably 10 to 60% by weight, more preferably 15 to 60% by weight, and particularly preferably 20 to 55% by weight of the total amount of the styrene monomer used. If the addition amount is less than 10% by weight, the ratio of the styrene resin in the vicinity of the surface of the modified resin particles may increase, which is not preferable. In this case, the impact resistance and chemical resistance of the foamed molded product obtained by secondary foaming of pre-expanded particles obtained from the modified resin particles may decrease. On the other hand, when the amount is more than 60% by weight, the polymerization rate of the styrene monomer is decreased, and a large amount of the styrene monomer may remain in the modified resin particles.

Various methods are mentioned as a method of adding the styrene monomer containing a polymerization initiator to an aqueous medium. For example,
(1) A method in which a polymerization initiator is dissolved and contained in a styrene monomer in a container different from the polymerization container, and the styrene monomer is supplied into an agitated aqueous medium in the polymerization container.
(2) A polymerization initiator is dissolved in a part of a styrene monomer, a solvent or a plasticizer to prepare a solution. A method of simultaneously supplying this solution and a predetermined amount of a styrenic monomer to a stirred aqueous medium in a polymerization vessel;
(3) A dispersion in which a polymerization initiator is dispersed in an aqueous medium is prepared. Examples thereof include a method of simultaneously supplying the dispersion and the styrene monomer to the stirred aqueous medium in the polymerization vessel.

  Further, the temperature of the aqueous medium when polymerizing the styrene monomer in the polyolefin resin particles is not particularly limited, but is preferably in the range of −30 to + 10 ° C. of the melting point of the polyolefin resin. More specifically, 70-140 degreeC is preferable and 80-130 degreeC is more preferable. Furthermore, the temperature of the aqueous medium may be a constant temperature from the start to the end of the polymerization of the styrenic monomer, or may be increased stepwise. When raising the temperature of the aqueous medium, it is preferable to raise the temperature stepwise at a rate of temperature rise of 0.1 to 2 ° C./min.

  Furthermore, when using particles comprising a crosslinked polyolefin resin, the crosslinking may be performed in advance before impregnating the styrene monomer, or by impregnating and polymerizing the styrene monomer in the polyolefin resin particles. It may be performed while the polyolefin resin particles are impregnated with a styrene monomer and polymerized.

  Examples of the crosslinking agent used for crosslinking the polyolefin resin include 2,2-di-t-butylperoxybutane, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy. An organic peroxide such as hexane may be mentioned. In addition, a crosslinking agent may be individual or may use 2 or more types together. Moreover, the usage-amount of a crosslinking agent has preferable 0.05-1.0 weight part normally with respect to 100 weight part of polyolefin resin particles.

  As a method for adding a crosslinking agent, for example, a method in which a crosslinking agent is directly added to a polyolefin resin, a method in which a crosslinking agent is dissolved in a solvent, a plasticizer, or a styrene monomer, and a crosslinking agent is dispersed in water. For example, a method of adding after adding them. Among these, the method of adding after dissolving a crosslinking agent in a styrene-type monomer is preferable.

  The modified resin particles are impregnated with a foaming agent (step (b)). The method of impregnating the modified resin particles with the foaming agent can be appropriately changed according to the type of the foaming agent. For example, a method in which a foaming agent is pressed into an aqueous medium in which the modified resin particles are dispersed to impregnate the modified resin particles with the foaming agent, the modified resin particles are supplied to a rotary mixer, Examples thereof include a method in which a foaming agent is injected and the modified resin particles are impregnated with the foaming agent. In addition, the temperature which makes a modified resin particle impregnate a foaming agent is 50-140 degreeC normally.

  Here, examples of the foaming agent include volatile foaming agents such as propane, butane, pentane, and dimethyl ether. A foaming agent may be used independently or may be used together. The addition amount of the foaming agent is preferably 5 to 25 parts by weight with respect to 100 parts by weight of the modified resin particles.

  Furthermore, you may use a foaming adjuvant with a foaming agent. Examples of such foaming aids include solvents such as toluene, xylene, ethylbenzene, cyclohexane, and D-limonene, and plasticizers (high boiling point solvents) such as diisobutyl adipate, diacetylated monolaurate, and coconut oil. . In addition, as addition amount of a foaming adjuvant, 0.1-2.5 weight part is preferable with respect to 100 weight part of modified resin particles.

  Further, a surface treatment agent such as a binding inhibitor, a fusion accelerator, an antistatic agent, or a spreading agent may be added to the modified resin particles.

  The anti-bonding agent plays a role of preventing coalescence of the pre-expanded particles when the modified resin particles are pre-expanded. Here, coalescence means that a plurality of pre-expanded particles are united and integrated. Specific examples include talc, calcium carbonate, zinc stearate, aluminum hydroxide, ethylene bis stearamide, tricalcium phosphate, dimethylpolysiloxane and the like.

  The fusion accelerator plays a role of promoting fusion between the pre-foamed particles when the pre-foamed particles are subjected to secondary foam molding. Specific examples include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, sorbitan stearate, and the like.

  Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride.

  Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.

  The total amount of the surface treatment agent is preferably 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the modified resin particles.

  If the modified resin particles impregnated with the volatile foaming agent are heated using a heating medium such as water vapor and pre-foamed to a predetermined bulk density, pre-foamed particles can be obtained (step (c)).

  Further, pre-expanded particles are filled in a mold of a foam molding machine, and heated again to foam the pre-expanded particles, and the foamed particles are heat-sealed to form a foam having a porosity of 5 to 50%. A molded body can be obtained. When the porosity is less than 5%, the foamed molded article does not have sufficient sound absorption. On the other hand, if it is larger than 50%, the bending strength is insufficient, and sound absorption is not obtained because sound waves pass. A preferable porosity is in the range of 5 to 30%.

  The foam molding machine is not particularly limited, and any known foam molding machine can be used. FIG. 9 is an example of a foam molding machine. This foam molding machine has a female mold 2 and a male mold 3, and the cavities 1 a are formed by combining both the molds 2 and 3. The molds 2 and 3 have steam chambers 2a and 3a, respectively, and are provided with a plurality of steam ejection slit holes 2b and 3b communicating with the steam chambers 2a and 3a and the cavity 1a, respectively. . On the other hand, steam supply pipes 2c and 3c for supplying steam to the respective steam chambers 2a and 3a and steam discharge pipes 2d and 3d for discharging the steam are arranged. A steam controller 4 is disposed in each of the steam supply pipes 2c and 3c, and a drain valve 5 is disposed in each of the steam discharge pipes 2d and 3d.

  Further, the female die 2 is provided with a filling device 7 for filling the pre-expanded particles 6 in the cavity 1a, and in addition, a pressure detection device for detecting the foaming pressure of the pre-expanded particles 6 in the cavity 1a. 9 is installed. And the control means 10 which controls the pressure detection apparatus 9, each steam controller 4, the drain valve 5, etc. is provided.

  The foam molding method using pre-expanded particles can be roughly divided into a heating step and a cooling step. The heating step is usually (1) mold heating step, (2) one heating step, and (3) reverse one heating. Step (4) It is often carried out in a subdivided manner, such as a double-sided heating step, and a cooling step is performed after the heating step to take out the molded product. An example will be described with reference to FIG.

(1) In the mold heating step, the molds 2 and 3 are mainly heated. Specifically, after the pre-expanded particles 6 are filled in the cavity 1a between the molds by the filler 7, the steam supply pipes are respectively connected to the steam chambers 2a and 3a of both the female mold 2 and the male mold 3. Steam is introduced from 2c and 3c, and air existing in the steam chamber is discharged from the drain valve 5 provided in each of the steam discharge pipes 2d and 3d.

(2) The one heating step is performed for the purpose of preheating for re-foaming the pre-expanded particles 6 or eliminating air in the cavity 1a. This is a step of flowing from the vapor chamber 3a into the gap between the pre-expanded particles 6 filled in the cavity 1a and discharging it out of the system through the vapor chamber 2a of the other mold (female mold 2). Usually, the end point of this process is the time when the pressure of the introduced steam becomes equal to the foaming pressure in the cavity.

(3) The reverse one-side heating step is a step for equilibrating the temperature gradient of the pre-expanded particles 6 generated by the previous one-side heating step, and the steam is discharged from the vapor chamber 2a of the female mold 2 through the reverse route. The pre-expanded particles 6 are introduced into 1 a and heated, and the steam is discharged from the steam chamber 3 a side of the male mold 3.

(4) The double-sided heating process is a process in which the pre-expanded particles 6 are secondarily expanded and finally the expanded particles are fused, and steam is fed into the steam chambers 2a and 3a of both molds 2 and 3. This is done by boosting.
If the molding is carried out along the heating steps (1) to (4), a foamed molded article in which the foamed particles are fused with each other with no voids between the particles can be obtained. It has voids and is required to leave a space between particles during foam molding. Therefore, it is preferable to perform foam molding by the following method.

(A) The mold heating step can be performed in the same manner as in the normal foam molding method. In addition, it is preferable to perform this process for about 3 to 12 seconds.
(B) On the other hand, the air between expanded particles is excluded by a heating process. In this step, heating is continued until the vapor pressure to be introduced is equal to the foaming pressure in the cavity, and the space between the foamed particles can be appropriately filled by further heating. Therefore, this step is preferably performed for 5 to 25 seconds.

Note that the reverse one-side heating step may be performed in order to balance the temperature gradient of the pre-expanded particles 6 as long as the porosity can be maintained within a predetermined range. Specifically, it is preferable to carry out for about 0 to 1 second. The reverse one heating step may be performed before the one heating step.
(C) Since the double-sided heating has an effect of rapidly filling the space between the expanded particles, the double-sided heating may not be performed, or the double-sided heating may be performed for a short time of 3 seconds or less.

  By the molding method as described above, it is possible to strengthen the adhesion between the foamed particles, so that a foamed molded product having voids with improved strength can be obtained.

  As described above, the pre-expanded particles contain a high proportion of styrene resin at the center and a high proportion of polyolefin resin near the surface.

  Accordingly, when the pre-expanded particles are subjected to secondary foaming, the pre-expanded particles can be strongly heat-bonded and integrated with each other by the polyolefin resin contained in a large amount on the surface thereof. In addition, the excellent foam moldability resulting from the styrene resin contained in a large amount at the center of the pre-expanded particles can be exhibited.

  The entire surface of the obtained foamed molded article contains a high proportion of polyolefin resin derived from the polyolefin resin in the vicinity of the surface of the pre-foamed particles. In other words, the foamed molded article has excellent chemical resistance and bending strength because it has a surface containing a high percentage of polyolefin resin.

  Moreover, the inside of each foamed particle constituting the foamed molded body is formed by foaming the central part of the pre-foamed particle and contains a high proportion of styrene resin, so that the foamed molded body has excellent rigidity. Is also provided.

Furthermore, since it has a specific porosity, it is excellent in heat insulation, light weight and sound absorption.
The foamed molded body obtained as described above is used for various purposes such as vehicle bumper core materials, vehicle cushioning materials such as door interior cushioning materials, electronic parts, various industrial materials, food containers and the like. Can do. In particular, it can be suitably used as a vehicle cushioning material.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the following examples, bulk density, absorbance ratio, maximum content of styrene monomer, z-average molecular weight by GPC measurement of styrene resin, porosity, bending strength, sound absorption, and chemical resistance are measured as follows. .
(Maximum content of styrene monomer)
A portion of the polyolefin resin particles impregnated with styrene monomer and polymerizing is taken out from the polymerization vessel and separated from the aqueous medium, and then the moisture on the surface of the polyolefin resin particles is removed with gauze to obtain a measurement sample. .

  Then, 0.08 g was precisely weighed from the measurement sample and immersed in 40 ml of toluene for 24 hours to extract the styrene monomer. Titrate the sample by adding 10 ml of Wis reagent, 30 ml of 5 wt% potassium iodide aqueous solution and about 30 ml of 1 wt% starch aqueous solution to the styrene monomer extracted solution, and titrating with N / 40 sodium thiosulfate solution. A number (milliliter). The Wies reagent was prepared by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.

  Further, the measurement sample was titrated in the same manner as described above without immersing the sample in toluene to obtain a blank titer (milliliter). And content of the styrene-type monomer in polyolefin-type resin particle was computed based on the following formula.

Styrenic monomer content (% by weight) = 0.1322 × (blank drop constant−sample drop constant) / weight of measurement sample (g)
The above measurement was performed every 20 minutes from the start of adding the styrenic monomer to the aqueous medium, and the content of the most styrenic monomer was defined as the maximum content of the styrenic monomer.

(The bulk density)
The bulk density of the pre-expanded particles is measured as follows.
First, pre-expanded particles are filled in a 500 cm ³ graduated cylinder to a scale of 500 cm ³ .

When the graduated cylinder is visually observed from the horizontal direction and any pre-expanded particles reach a scale of 500 cm ³ , the filling of the pre-expanded particles into the graduated cylinder is terminated at that point.

Next, the weight of the pre-expanded particles filled in the measuring cylinder is weighed with two significant figures after the decimal point, and the weight is defined as W (g). Then, the bulk density of the pre-expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500

(Absorbance ratio)
The absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is measured as follows. That is, the surface of each of 10 randomly selected pre-expanded particles is subjected to particle surface analysis by ATR infrared spectroscopy to obtain an infrared absorption spectrum. An absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is calculated from each infrared absorption spectrum, and the minimum absorbance ratio and the maximum absorbance ratio are excluded. The arithmetic average of the remaining 8 absorbance ratios is taken as the absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ). The absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is measured using, for example, a measuring apparatus sold by Nicolet under the trade name “Fourier transform infrared spectrophotometer MAGMA 560”.
(Z-average molecular weight of styrene resin)
About 60 mg of pre-expanded particles were collected, and each pre-expanded particle was divided into two using a cutter, and then immersed in 10 ml of chloroform at room temperature for 24 hours.

Thereafter, chloroform was filtered through a non-aqueous 0.45 μm chromatographic disk, and the polystyrene-equivalent z-average molecular weight was measured using GPC (gel permeation chromatograph).
Measuring apparatus: Product name “HPLC Detector 484, Pump 510” manufactured by Water
Measurement conditions Column: Showa Denko Co., Ltd., trade name “Shodex GPC K-806L (diameter 8.0 × 300 mm)” Column temperature: 40 ° C., mobile phase: chloroform, mobile phase flow rate: 1.2 ml / min Pump temperature: room temperature, measurement time: 25 minutes, detection: ultraviolet 254 nm
Injection amount: 50 microliters Standard polystyrene for calibration curve Product name “Shodex” molecular weight: 1030000 made by Showa Denko KK
Tosoh Corporation molecular weight: 5480000, 3840000, 355000, 102000, 37900, 9100, 2630, 495

(Porosity)
The foamed molded body having an apparent bulk volume (V1) is immersed in a graduated cylinder filled with a certain amount of water, the increased volume (V2) at that time is measured, and the porosity is obtained by the following equation.
Porosity = {(V1-V2) / V1} × 100

(Bending strength)
The maximum bending strength is measured according to the method described in JIS K9511: 1999 “Foamed plastic heat insulating material”. That is, using a Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.), the specimen size is 75 × 300 × 15 mm, the compression speed is 10 mm / min, the tip jig is a pressure wedge 10R, and a support base 10R. The distance between fulcrums is measured as 200 mm.

(Sound absorption rate)
The sound absorption coefficient is measured by the method described in JIS A 1405: 1998 “Acoustics—Measurement of sound absorption coefficient and impedance by impedance tube—standing wave ratio method”. That is, a sound absorption coefficient of 1 kHz is measured using a normal incidence sound absorption coefficient measuring device TYPE10041 (Frobe Probe Microphone) manufactured by Electronic Instruments. The sample is 30 mm thick and is measured in close contact with the back plate of the sample holder.

(chemical resistance)
Three flat rectangular plate-shaped test pieces having a length of 100 mm, a width of 100 mm, and a thickness of 20 mm were cut out from the foamed molded article and allowed to stand for 24 hours at 23 ° C. and a humidity of 50%. In addition, the following test is performed using the molding surface of a foaming molding.

Next, 1 g of different chemicals (gasoline, kerosene, dibutyl phthalate (DBP)) was uniformly applied to each molding surface of the three test pieces, and left for 60 minutes at 23 ° C. and 50% humidity. Then, the chemical | medical agent was wiped off from the molding surface of the test piece, the molding surface of the test piece was observed visually, and it judged based on the following reference | standard.
○: Good No change △: Slightly bad Surface softening ×: Bad Surface depression (shrinkage)

Example 1
Ethylene-vinyl acetate copolymer (EVA) (trade name “NUC-3221” manufactured by Nippon Unicar Co., Ltd., vinyl acetate content: 5 wt%, melting point: 107 ° C., melt flow rate: 0.5 g / 10 min, density: 0.93 g / cm ³ ) 100 parts by weight and 0.5 parts by weight of synthetic hydrous silicon dioxide are supplied to an extruder, melt-kneaded, granulated by an underwater cutting method, and oval (egg-like) polyolefin resin particles Got. The average weight of the polyolefin resin particles was 0.60 mg. In addition, the melt flow rate and density of an ethylene-vinyl acetate copolymer are the values measured based on JIS K6992-2.

In a polymerization vessel 3 having an inner diameter of 1800 mm, a straight body length of 1890 mm, and an internal volume of 6.4 m ³ , a V-type paddle blade 14 (3 stirring blades, stirring blade radius d ₁ : 585 mm, stirring blade width d ₂ : 315 mm) was prepared. In the polymerization vessel of this polymerization apparatus, 100 parts by weight of water at 70 ° C., 0.8 part by weight of magnesium pyrophosphate and 0.02 part by weight of sodium dodecylbenzenesulfonate were supplied while stirring with a V-type paddle blade 14 to form an aqueous solution. The medium. Thereafter, 40 parts by weight of the polyolefin-based resin particles were suspended in an aqueous medium while stirring with the V-type paddle blade 14. Then, after the aqueous medium was heated to 85 ° C., the rotation speed of the V-type paddle blade 14 was adjusted so that the power required for the subsequent stirring was maintained at 0.20 kw / m ³ .

  As shown in FIG. 7, the polymerization vessel 13 of the polymerization apparatus has a cylindrical peripheral wall portion 32 projecting upward from the outer peripheral edge of the bottom surface portion 31 having a convex arcuate cross section. Further, the upper end opening of the peripheral wall 32 is closed by a ceiling 33 having a convex arcuate cross section. A V-shaped paddle blade 14 is attached as a stirring blade to the lower end portion of the rotating shaft 33a suspended from the ceiling portion 33 of the polymerization vessel 3.

  The V-shaped paddle blade 14 includes a mounting portion 41 for mounting on the rotating shaft 33a and three side parallelogram stirring blades integrally provided at equal intervals in the horizontal direction on the outer peripheral surface of the mounting portion 41. 42. Each stirring blade 42 is directed obliquely outward at the top.

  In FIG. 7, 61 is a motor for rotating the V-type paddle blade 14, 62 is an inverter for controlling the rotational speed of the motor, 63 is an ammeter for measuring the load current value of the motor, and 64 is a power source. Means.

  On the other hand, 0.15 parts by weight of benzoyl peroxide and 0.01 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and 0.25 parts by weight of dicumyl peroxide as a crosslinking agent and 20 parts by weight of styrene monomer (St). The first styrene-based monomer was prepared by dissolving in the solution. In addition, a second styrene monomer was prepared by dissolving 0.05 parts by weight of ethylenebisstearic acid amide as a bubble regulator in 40 parts by weight of styrene monomer (St).

  The first styrene monomer is continuously dropped into the aqueous medium at a rate of 10 parts by weight per hour, and the styrene monomer, the polymerization initiator and the crosslinking agent are impregnated in the polyolefin resin particles, Was polymerized in polyolefin resin particles.

  Next, after the addition of the first styrene monomer to the aqueous medium is completed, the second styrene monomer is continuously dropped into the aqueous medium at a rate of 20 parts by weight per hour to adjust the styrene monomer and the bubbles. While impregnating the agent into the polyolefin resin particles, the styrene monomer was polymerized in the polyolefin resin particles.

  Further, while stirring the aqueous medium, the dropping of the second styrene monomer to the aqueous medium was allowed to stand for 1 hour, and then the aqueous medium was heated to 140 ° C. and held for 3 hours. Thereafter, the polymerization vessel was cooled to obtain modified resin particles.

Subsequently, 100 parts by weight of the modified resin particles, 1.0 part by weight of water, 0.15 part by weight of stearic acid monoglyceride and 0.5 part by weight of diisobutyl adipate are supplied to a pressure-resistant V-type rotary mixer having an internal volume of 1 m ^3. Then, 14 parts by weight of butane was press-fitted at room temperature while rotating. Then, the inside of the rotary mixer was heated to 70 ° C. and held for 4 hours, and then cooled to 25 ° C. to obtain expandable modified resin particles.

The obtained foamable modified resin particles are immediately supplied to a pre-foaming machine (trade name “SKK-70” manufactured by Sekisui Koki Seisakusho Co., Ltd.) and pre-foamed using steam at a pressure of 0.02 MPa to obtain a bulk density. 0.06 g / cm ³ of pre-expanded particles were obtained.

  Next, after leaving the pre-expanded particles at room temperature for 7 days, the pre-expanded particles are filled in a mold of a foam molding machine, using steam with a steam pressure of 0.08 MPa, heating time: (1) 7 seconds of mold heating, (2) One heating for 17 seconds, (3) reverse one heating for 0.5 seconds, and (4) double-sided heating for 0.5 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.

The following foam molding machine was used for foam molding.
Molding machine used: ACE-3SP (manufactured by Sekisui Koki Co., Ltd.)
Mold size: 300 × 400 × 30mm
The obtained foamed molded product was a foamed molded product having voids.

(Example 2)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that the power required for stirring was maintained at 0.50 kw / m ³ .

(Example 3)
15 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.25 parts by weight of benzoyl peroxide and 0.02 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.15 parts by weight of dicumyl peroxide in 30 parts by weight of styrene monomer, and the first styrene monomer was dropped into the aqueous medium at a rate of 10 parts by weight per hour. Then, 0.14 parts by weight of ethylene bis-stearic acid amide as a foam regulator is dissolved in 55 parts by weight of styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 15 parts by weight per hour. Pre-expanded particles were obtained in the same manner as in Example 1 except that it was dropped into the medium.

  Next, after leaving the pre-expanded particles at room temperature for 7 days, the pre-expanded particles are filled in a mold of a foam molding machine, using steam with a steam pressure of 0.08 MPa, heating time: (1) 7 seconds of mold heating, (2) One heating for 17 seconds, (3) reverse one heating for 0.5 seconds, and (4) double-sided heating for 2 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.

Example 4
100 parts by weight of linear low density polyethylene (LLDPE) (trade name “TUF-2032” manufactured by Nippon Unicar Co., Ltd., melting point: 126 ° C., melt flow rate: 0.9 g / 10 min, density: 0.923 g / cm ³ ) And 0.3 parts by weight of talc was supplied to an extruder, melted and kneaded, and granulated by an underwater cutting method to obtain oval (egg-like) polyolefin resin particles. The average weight of the polyolefin resin particles was 0.50 mg. The melt flow rate and density of the linear low density polyethylene were measured according to JIS K6767.

Using the same polymerization apparatus as in Example 1, 100 parts by weight of water at 70 ° C., 0.8 part by weight of magnesium pyrophosphate and 0.02 part by weight of sodium dodecylbenzenesulfonate were added to the polymerization vessel 13 of this polymerization apparatus. An aqueous medium was supplied by stirring with a mold paddle blade 14. Thereafter, 35 parts by weight of the polyolefin-based resin particles were suspended in an aqueous medium while stirring with the V-type paddle blade 14. Then, after heating the aqueous medium to 125 ° C., the rotation speed of the V-type paddle blade 14 was adjusted so that the power required for stirring after that would be maintained at 0.20 kw / m ³ .

  On the other hand, 0.15 part by weight of dicumyl peroxide as a polymerization initiator was dissolved in 20 parts by weight of styrene monomer to prepare a first styrene monomer.

  Then, the first styrene monomer is continuously dropped into the aqueous medium at a rate of 10 parts by weight per hour, and the styrene monomer and the polymerization initiator are impregnated in the polyolefin resin particles, while the styrene monomer is added to the polyolefin system. Polymerization was performed in the resin particles.

  Next, after the addition of the first styrene monomer to the aqueous medium is completed, 45 parts by weight of the styrene monomer is continuously dropped into the aqueous medium at a rate of 20 parts by weight per hour, and the styrene monomer is added to the polyolefin-based medium. While impregnating the resin particles, the styrene monomer was polymerized in the polyolefin resin particles. This styrene monomer is shown in the column of the second styrene monomer for convenience in Table 1.

  Further, while stirring the aqueous medium, the dropping of the styrene monomer to the aqueous medium was allowed to stand for 1 hour, and then the aqueous medium was heated to 140 ° C. and held for 1 hour. Thereafter, the polymerization vessel was cooled to obtain modified resin particles.

Subsequently, 100 parts by weight of the modified resin particles, 0.15 parts by weight of stearic acid monoglyceride and 0.5 parts by weight of diisobutyl adipate are supplied to a pressure resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated at room temperature. 14 parts by weight of butane was press-fitted. Then, the inside of the rotary mixer was heated to 80 ° C. and held for 3 hours, and then cooled to 25 ° C. to obtain expandable modified resin particles. The foamed modified resin particles were immediately pre-foamed using water vapor to obtain pre-foamed particles having a bulk density of 0.06 g / cm ³ .

  Next, after leaving the pre-expanded particles at room temperature for 7 days, the pre-expanded particles are filled in a mold of a foam molding machine, using steam with a steam pressure of 0.1 MPa, heating time: (1) mold heating for 7 seconds, (2) One heating for 17 seconds, (3) reverse one heating for 0.5 seconds, and (4) double-sided heating for 0.5 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.

In addition, the same foam molding machine as Example 1 was used for foam molding.
The obtained foamed molded product was a foamed molded product having voids.

(Example 5)
100 parts by weight of branched low density polyethylene (LDPE) (trade name “DFDJ-6775” manufactured by Nippon Unicar Co., Ltd., melting point: 112 ° C., melt flow rate: 0.2 g / 10 min, density: 0.92 g / cm ³ ) 0.5 parts by weight of synthetic hydrous silicon dioxide was supplied to an extruder, melted and kneaded, and granulated by an underwater cutting method to obtain elliptical spherical (egg-like) polyolefin resin particles. The average weight of the polyolefin resin particles was 0.75 mg. The melt flow rate and density of the branched low density polyethylene were measured according to JIS K6767.

Next, in the polymerization vessel, instead of the V-shaped paddle blade, a downflow type 45 ° inclined paddle blade 15 (4 stirring blades, stirring blade radius d ₁ : 550 mm, stirring blade as shown in FIG. 8) Width d ₂ : 280 mm) using a polymerization apparatus provided in two upper and lower stages, and the rotational speed of the inclined paddle blade 15 immediately before the first styrene monomer is dropped into the aqueous medium. The pre-expanded particles and the expanded molded body were obtained in the same manner as in Example 1 except that the sample was kept constant until the process was completed.

  Here, the polymerization vessel 13 of the polymerization apparatus has the same structure as that of Example 1, and each of the lower end portion of the rotation shaft 33a suspended from the ceiling portion 33 of the polymerization vessel 3 and the central portion in the vertical direction. Further, a downflow type 45 ° inclined paddle blade 15 is attached as a stirring blade.

  The downflow type 45 ° inclined paddle blade 15 includes an attachment portion 51 for attachment to the rotating shaft 33a and four laterally long rectangular shapes integrally provided on the outer peripheral surface of the attachment portion 51 at equal intervals in the horizontal direction. And a stirring blade 52 in the form of a ring. Each agitating blade 52 is oriented in the horizontal direction and is inclined by 45 ° obliquely forward from the upper end toward the lower end with respect to the rotational traveling direction.

  Further, a baffle plate 17 is installed in the polymerization container 13. The baffle plates 17 are installed on the side wall of the polymerization vessel 13 so as to be in a positional relationship of 90 ° with each other when viewed from the upper surface of the polymerization vessel 13. The baffle plate 17 has a width of 100 mm and a length of 1890 mm.

The power required for stirring immediately before dropping the first styrene monomer into the aqueous medium (initial power required for stirring) is 0.20 kw / m ³ , and stirring is required when the production of the modified resin particles is completed. The power (final stirring required power) was 0.29 kw / m ³ .

(Comparative Example 1)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that the power required for stirring was 0.04 kw / m ³ .

(Comparative Example 2)
8 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.32 parts by weight of benzoyl peroxide and 0.02 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.10 parts by weight of dicumyl peroxide in 30 parts by weight of a styrene monomer, and the first styrene monomer was dropped into an aqueous medium at a rate of 10 parts by weight per hour. Then, 0.12 part by weight of ethylenebisstearic acid amide as a foam regulator is dissolved in 62 parts by weight of styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 21 parts by weight per hour. Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that it was dropped into the medium.

(Comparative Example 3)
Expandable polystyrene particles (trade name “Eslen Beads HDS” manufactured by Sekisui Plastics Co., Ltd.) were pre-expanded to a bulk density of 0.06 g / cm ³ in the same manner as in Example 1 to obtain polystyrene pre-expanded particles. Then, the polystyrene pre-expanded particles were subjected to secondary foaming in the same manner as in Example 1 to obtain a foam molded article. In Table 1, polystyrene was expressed as “PSt”.

(Comparative Example 4)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 5 except that the initial power required for stirring was adjusted to 0.04 kw / m ³ . The final power required for stirring was 0.06 kw / m ³ .

In Examples 1 to 5 and Comparative Examples 1 to 4, the absorbance ratio of the pre-expanded particles (D ₆₉₈ / D ₂₈₅₀ ), the z-average molecular weight by GPC measurement of the styrene resin in the pre-expanded particles, and during the polymerization of the styrene monomer Table 1 shows the maximum content of the styrene monomer in the polyolefin resin particles, the porosity of the foamed molded product, the bending strength, the sound absorption coefficient, and the chemical resistance.

Table 1 shows the following.
(1) According to Examples 1 to 5 and Comparative Example 2, if the blending amount of the styrene resin is in the range of 1 to 10 times the blending amount of the polyolefin resin, a foam molded article having good characteristics can be obtained. You can see that
(2) From Examples 1 to 5 and Comparative Examples 1 and 4, it can be seen that if the absorbance ratio is in the range of 0.1 to 2.5, foamed molded articles having good characteristics can be obtained.
(3) It can be seen from Examples 1 to 5 that foam molded articles having good characteristics can be obtained even if the type of polyolefin resin particles is changed.
(4) From Examples 1 to 5 and Comparative Example 3, it can be seen that pre-expanded particles made of a styrene resin modified with a polyolefin resin can provide a foam molded article having good characteristics.

(Electron micrograph)
FIG. 1 is an electron micrograph obtained by photographing the surface of the pre-expanded particles obtained in Example 1 using a SEM at a magnification of 1500 times.

  FIG. 2 is an electron micrograph obtained by photographing the cross-section near the surface of the pre-expanded particles obtained in Example 1 at a magnification of 20,000 using a TEM.

  FIG. 3 is an electron micrograph of a cross section near the surface of the pre-expanded particles obtained in Example 1 taken at a magnification of 100,000 using a TEM.

  FIG. 4 is an electron micrograph of a cross section of the central portion of the pre-expanded particles obtained in Example 1 taken at a magnification of 20,000 using a TEM.

  FIG. 5 is an electron micrograph of the pre-expanded particles obtained in Example 1 taken with a styrene-based resin extracted, and then the surface of the pre-expanded particles after processing was photographed at a magnification of 1500 times using an SEM. .

2 to 4 were taken as follows.
That is, the pre-expanded particles obtained in Example 1 were divided into two. Then, the cross-section of the pre-expanded particles was entirely covered with a room temperature curing type epoxy resin (embedding resin) and then dyed with ruthenium tetroxide (RuO ₄ ).

  Next, the pre-expanded particles were sliced into a thin film using an ultramicrotome to prepare a test piece. This test piece was photographed at a predetermined magnification using a TEM.

Moreover, in FIG. 5, the extraction process of the styrene resin was performed as follows.
The pre-expanded particles were immersed in 40 ml of tetrahydrofuran and stirred at 23 ° C. for 3 hours to extract a styrene resin from the pre-expanded particles.

  Next, the pre-expanded particles after extraction were taken out from the tetrahydrofuran, and the tetrahydrofuran adhering to or penetrating the surface of the pre-expanded particles was removed by natural drying to obtain pre-expanded particles from which the styrene resin was extracted.

  As shown in FIG. 2 and FIG. 3, in the vicinity of the surface of the pre-expanded particles, the polyolefin resin 1 is contained in a high ratio, while the styrene resin 2 gradually decreases as it approaches the particle surface. And the size is getting smaller. The surface of the pre-expanded particles is generally formed from the polyolefin resin 1.

  Further, as shown in FIG. 4, in the cell membrane at the center of the pre-expanded particles, the styrene resin 2 is contained in a high ratio, and the polyolefin resin 1 is dispersed in a layered manner in the styrene resin 2. It has become.

  Furthermore, FIG.1 and FIG.5 represents the particle | grain surface before and behind extracting the styrene resin from the pre-expanded particle | grains of Example 1. FIG.

  1 and 5, it can be seen that slight gaps are formed on the surface of the pre-expanded particles of Example 1 after extraction with the styrene-based resin.

1a Cavity 2 Female mold 2a, 3a Steam chamber 2b, 3b Steam ejection slit hole 2c, 3c Steam supply pipe 2d, 3d Steam discharge pipe 3 Male mold 4 Steam controller 5 Drain valve 6 Pre-foamed particle 7 Filler 9 Pressure detector 10 Control means 13 Polymerization vessel 14 V-type paddle blade 15 Inclined paddle blade 17 Baffle plate 31 Bottom surface portion 32 Peripheral wall portion 33 Ceiling portion 33a Rotating shaft 41, 51 Mounting portion 42, 52 Stirring blade 61 Motor 62 Inverter 63 Ammeter 64 power supply

Claims (1)

With a bulk density of 0.012~0.20g / cm ^3, the absorbance ratio at 698cm ^-1 and 2850 cm ^-1 obtained from an infrared absorption spectrum of the measured particle surface by ATR method infrared spectroscopy (D ₆₉₈ / D ₂₈₅₀ ) is in the range of 0.1 to 2.5, the amount of polyolefin on the particle surface is 51 to 90% by weight, and 100 to 1000 parts by weight of the styrene resin component with respect to 100 parts by weight of the polyolefin resin component. A method for producing a foam-molded article having voids, wherein a foam-molded article having a porosity of 5 to 50% is obtained by foam-molding pre-foamed styrene-modified polyolefin resin particles contained in a part.