JP2011202110A - Method for pre-expanding expandable thermoplastic resin particle, pre-expanded particle, and expanded molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for pre-expanding expandable thermoplastic resin particles, in which the time of pre-expansion is drastically shortened without causing cohesion of the pre-expanded particles.SOLUTION: The method for pre-expanding expandable thermoplastic resin particles is characterized in that pre-expanded particles are obtained by pre-expanding expandable thermoplastic resin particles containing 100 to 400 pts.wt of a polystyrene resin relative to 100 pts.wt of a polyolefin resin having a melting point of 117 to 145°C, in a closed pre-expansion tank under a gauge pressure of 0.02 to 0.15 MPa in the pre-expansion tank.

Description

  The present invention relates to a pre-foaming method for foamable thermoplastic resin particles, and pre-foamed particles and a foam-molded product obtained by the pre-foaming method. More specifically, the present invention relates to a pre-foaming method of expandable thermoplastic resin particles that does not cause coalescence of pre-foamed particles during pre-foaming, and can greatly shorten the pre-foaming time, and the pre-foaming method The present invention relates to pre-expanded particles and a foam-molded product obtained by

  A foam molded article obtained from expandable thermoplastic resin particles (also referred to as expandable thermoplastic resin particles in the present invention) containing a polyolefin resin and a polystyrene resin is a foam molded article obtained from conventional polystyrene single resin particles. Since it is excellent in formability, heat resistance, etc., compared with the body, it is widely used as a returnable box for automobile parts, etc., and as a buffer packaging material for electrical products.

  In addition, as a method for producing the foamed molded article, a foamed molded article producing method is generally used in which foamable thermoplastic resin particles are prefoamed to a predetermined magnification, and then the obtained prefoamed particles are foam-molded in a mold. ing.

The batch method is widely used from the viewpoint of maintaining the quality of the pre-foamed particles as the pre-foaming method, specifically,
Injecting foamable thermoplastic resin particles into the prefoaming tank;
In the pre-foaming tank, the foamed thermoplastic resin particles are heated and foamed with stirring while circulating unpressurized steam or substantially unpressurized steam of about 0.01 MPa under atmospheric pressure. Let;
When the expandable thermoplastic resin particles are expanded to a desired expansion ratio, the flow of steam is stopped, and then the pre-expanded particles are cooled and dried by blowing air;
A method of recovering the obtained prefoamed particles from the prefoaming tank is generally used.

However, the pre-foaming has been found to have problems in the production process, such as the time required for the pre-foaming process being extremely long. The above problems lead to a decrease in the amount of foaming treatment per unit time, which is not preferable in terms of manufacturing cost, production efficiency, and the like.
Therefore, as a method for solving these problems, Patent Document 1 proposes a pre-foaming method using pressurized steam having a predetermined gauge pressure.

Japanese Patent No. 4105195 Japanese Patent No. 4085835 Japanese Patent No. 4090932 JP 2008-308668 A

  Patent Document 1 discloses a pre-foaming method for foamable thermoplastic resin particles in which pressurized steam having a gauge pressure of 0.01 to 0.10 MPa is circulated. However, although the invention described in Patent Document 1 uses pressurized steam having the gauge pressure described above, pre-foaming of expandable thermoplastic resin particles is performed in an open pre-foaming tank as in the conventional method. It is done in For this reason, the inside of the preliminary foaming tank is not substantially under the pressurized condition, and the gauge pressure in the preliminary foaming tank is the same as in the case of the conventional batch method. Therefore, even in this case, although a slight shortening of the prefoaming time was confirmed, a satisfactory effect of shortening the prefoaming time compared with the prior art was not recognized.

  Patent Document 2 and Patent Document 3 disclose high-quality pre-expanded particles by performing pre-expansion under slightly pressurized conditions (steam pressure (gauge pressure) of 0.03 MPa or less in the pre-foaming tank). Specifically, a method for pre-expanding expandable polystyrene resin particles is disclosed.

  However, when the expandable polystyrene resin particles are replaced with expandable thermoplastic resin particles and prefoaming is performed under the same conditions, a long time is required for the prefoaming process, which is preferable from the viewpoint of manufacturing cost and the like. There wasn't. In addition, it is sometimes impossible to obtain sufficiently expanded pre-expanded particles, which is not preferable in terms of quality. Furthermore, since the invention described in Patent Document 2 performs the pre-foaming process in two or more steps, the pre-foaming process becomes complicated, and the productivity and the like are not satisfactory.

  On the other hand, Patent Document 4 discloses a foamable polyolefin resin particle that produces high-quality pre-expanded particles by performing under a predetermined pressure condition (internal pressure (gauge pressure) 0.27 to 0.54 MPa). A pre-foaming method is specifically disclosed.

  Similarly, when the expandable polyolefin resin particles are replaced with expandable thermoplastic resin particles and pre-expanded under the same conditions, the pre-expanded particles are bonded to each other due to the extremely high pressure conditions (in the present invention). (Also referred to as blocking). The blocking described above causes a cavity during the production of the foamed molded product, bridging of pre-expanded particles in the hopper, and the like, which is not a preferable phenomenon in terms of production. Moreover, it leads to generation | occurrence | production of the aggregate of a pre-expanded particle, and it is not preferable also in terms of the quality of a pre-expanded particle and a foaming molding.

  Accordingly, there is provided a pre-foaming method for foamable thermoplastic resin particles that does not cause blocking at the time of pre-foaming, and can significantly shorten the pre-foaming time, and pre-foamed particles and foam molded articles obtained by the pre-foaming method. It is requested to do.

  Thus, according to the present invention, expandable thermoplastic resin particles containing 100 to 400 parts by weight of a polystyrene resin with respect to 100 parts by weight of a polyolefin resin having a melting point of 117 to 145 ° C. are placed in a sealed prefoaming tank. There is provided a pre-foaming method of foamable thermoplastic resin particles, wherein pre-foamed particles are obtained by pre-foaming under a gauge pressure in a pre-foaming tank of 0.02 to 0.15 MPa.

Moreover, according to this invention, the pre-expanded particle obtained by the said pre-expansion method is also provided.
Furthermore, according to this invention, the foaming molding obtained by carrying out in-mold shaping | molding of the said pre-expanded particle is provided.

  In the present invention, blocking of the foamable thermoplastic resin particles during pre-foaming can be suppressed, and the pre-foaming time can be greatly shortened.

  In the present invention, the pre-foaming step can be a single step. Also in this case, the preliminary foaming method of the present invention does not require a multi-step process, and is excellent in productivity, manufacturing cost, and the like.

  When the polyolefin resin is either a polyethylene resin or a polypropylene resin, and the polystyrene resin is a polystyrene homopolymer, good pre-expanded particles with less blocking can be obtained.

  When the foamable thermoplastic resin particles contain 8 to 20 parts by weight of a readily volatile foaming agent with respect to 100 parts by weight of the foamable thermoplastic resin, it is possible to obtain pre-foamed particles having more excellent foamability.

  Expandable thermoplastic resin particles are produced by impregnating and polymerizing a polyolefin resin with a styrene monomer to produce thermoplastic resin particles containing a polyolefin resin and a polystyrene resin, and then readily volatile to the thermoplastic resin particles. In the case of impregnating the foaming agent, the ratio of the polyolefin resin in the surface layer of the thermoplastic polymerizable resin particles and the pre-expanded particles can be increased, and as a result, the moldability and heat resistance of the obtained foamed molded product can be further improved.

  In addition, by performing the pre-foaming method of the present invention, pre-foamed particles with less quality such as blocking and excellent quality can be obtained.

  In the present invention, when the ratio of the polystyrene resin on the surface of the pre-foamed particle is 40% by mass or less, the pre-foamed particle surface is suppressed from being unnecessarily softened, and further, pre-foamed with excellent quality in terms of blocking and the like. Particles can be obtained.

  In addition, the pre-expanded particles obtained in the present invention have an extremely small amount of blocked expandable thermoplastic resin particles and are excellent in quality such as heat resistance, so that a foamed molded article excellent in moldability and heat resistance is obtained. You can also.

It is the schematic which shows a preliminary | backup foaming tank. It is a graph which shows the analytical curve for measuring the polystyrene-type resin ratio of the pre-expanded particle surface layer containing a polypropylene-type resin.

  The present invention provides a foamed thermoplastic resin particle containing 100 to 400 parts by weight of a polystyrene resin to 100 parts by weight of a polyolefin resin having a melting point of 117 to 145 ° C. A pre-foaming method for foamable thermoplastic resin particles, wherein pre-foaming is performed under a gauge pressure in a pre-foaming tank of 02 to 0.15 MPa.

  In the present invention, the sealed pre-foaming tank can be a closed space inside the pre-foaming tank by adjusting an on-off valve or the like as shown in FIG. It means a pre-foaming tank that can pre-foam plastic resin particles. Since the pre-foaming tank can maintain the system under a constant gauge pressure condition, a large amount of readily volatile foaming agent is not released from the foamable thermoplastic resin particles, and the quality is superior. Pre-expanded particles can be obtained. Moreover, softening of the resin particles can be promoted, and as a result, the pre-foaming time can be further shortened.

In the present invention, the inside of the preliminary foaming tank is 0.02 to 0.15 MPa, preferably 0.03.
The preliminary foaming is performed under a gauge pressure of ˜0.08 MPa, more preferably 0.04 to 0.06 MPa. When pre-foaming is performed under a gauge pressure lower than 0.02 MPa, the above-mentioned readily volatile foaming agent may be released. On the other hand, when prefoaming is performed under a gauge pressure higher than 0.15 MPa, the resin particles soften more than necessary, which may cause blocking.
In the present invention, the gauge pressure means a pressure indicated by a pressure gauge provided in the preliminary foaming tank. Therefore, the preliminary foaming of the present invention is performed under a combined pressure of the atmospheric pressure and the gauge pressure.

The expandable thermoplastic resin particles used in the present invention will be described below.
The expandable thermoplastic resin particles of the present invention are particles in which a polystyrene resin is contained in a polyolefin resin.

  In the present invention, the polyolefin resin refers to a resin obtained by polymerizing an olefin polymerizable monomer having a double bond. Examples of polyolefin resins include branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, Polypropylene resins such as cross-linked polyethylene resins, polypropylene homopolymers, ethylene-propylene random copolymers, propylene-1-butene copolymers, ethylene-propylene-butene random copolymers, polypropylene homopolymers, etc. Can be mentioned.

  In the present invention, from the correlation between the gauge pressure at the time of pre-foaming and the melting point of the polyolefin resin, either a polyethylene resin or a polypropylene resin is preferable as the polyolefin resin.

In the present invention, the above polyolefin resins may be used alone or in combination of two or more as long as they do not affect the preliminary foaming step and the like. Incidentally, in the illustration, it is preferred that the low density, which is 0.91~0.94g / cm ^3, more preferably 0.91~0.93g / cm ^3. Preferably high density and is 0.95~0.97g / cm ^3, more preferably 0.95~0.96g / cm ^3. The medium density is an intermediate density between the low density and the high density.

  The polyolefin resin of the present invention has a melting point of 117 to 145 ° C, preferably 125 to 140 ° C, more preferably 138 to 142 ° C. By using the polyolefin-based resin having the above melting point, it is possible to harmonize with the gauge pressure at the time of pre-foaming, and as a result, it is possible to more easily solve the shortening of pre-foaming time and prevention of blocking, which are the problems of the present invention. it can.

  In the present invention, when the melting point is lower than 117 ° C., the foamable thermoplastic resin particles may be too soft to cause blocking. Moreover, since the retention capability of a readily volatile foaming agent falls, adjustment of a preliminary foaming time may not be performed stably. On the other hand, when the melting point is higher than 145 ° C., the expandable thermoplastic resin particles may not be sufficiently softened to obtain a predetermined expansion ratio. Details of the melting point measurement method and the like will be described in detail in Examples.

The polystyrene-based resin is a polystyrene homopolymer or a copolymer of styrene as a main component and another monomer copolymerizable with styrene. Here, styrene as a main component means that styrene accounts for 70% by weight or more of all monomers. Examples of other monomers include α-methylstyrene, p-methylstyrene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, alkyl acrylate ester, alkyl methacrylate ester, divinylbenzene, and polyethylene glycol dimethacrylate. The In the examples, alkyl means alkyl having 1 to 8 carbon atoms.
In the present invention, a polystyrene homopolymer capable of stably pre-foaming expandable thermoplastic resin particles is preferable.

  Polyolefin resin and polystyrene resin are vinyl group, carbonyl group, aromatic group, ester group, ether group, aldehyde group, amino group, nitrile group, nitro group, etc. These functional groups may be contained, may be cross-linked by a cross-linking agent having two or more vinyl groups, and may be used alone or in combination of two or more.

  The polystyrene resin is contained in the foamable thermoplastic resin particles in the range of 100 to 400 parts by weight with respect to 100 parts by weight of the polyolefin resin. Moreover, the compounding quantity of the raw material styrene-type monomer of the polystyrene-type resin with respect to 100 weight part of polyolefin-type resin particles is also 100-400 weight part similarly to a polystyrene-type resin. When the content of the polystyrene-based resin is more than 400 parts by weight, the heat resistance of the pre-expanded particles and the foamed molded product is lowered, and blocking may occur. On the other hand, if the amount is less than 100 parts by weight, the volatile foaming agent is rapidly dissipated from the surface layer of the foamable thermoplastic resin particles and the desired foamability cannot be obtained, and the retention of the easily volatile foaming agent is not possible. May decrease. Moreover, even if it is a case where it is a case where the vapor | steam pressure (gauge pressure) in a preliminary foaming tank is kept at 0.02-0.03 MPa when it is in the said range, there is little blocking, without requiring a long process time. Desired pre-expanded particles can be obtained.

  In this invention, 125-240 weight part is preferable with respect to 100 weight part of polyolefin resin, and, as for content of polystyrene resin, 140-190 weight part is more preferable. On the other hand, since good pre-expanded particles with less blocking may be obtained, a combination of either a polyethylene resin or a polypropylene resin and a polystyrene homopolymer is preferable as a combination of a polyolefin resin and a polystyrene resin. .

  As the readily volatile foaming agent, various known volatile foaming agents can be used. In particular, it is preferable to use butane from the viewpoint of imparting foaming performance. Examples of butane include normal butane and isobutane. A small amount of other hydrocarbons such as propane, pentane, hexane, cyclohexane and cyclopentane may be used in combination. In the readily volatile blowing agent, the butane content is preferably 80% by weight or more. Further, a foaming aid may be used. Examples of the foaming aid include solvents such as toluene, xylene, cyclohexane, and d-limonene, and plasticizers (high-boiling solvents) such as diisobutyl adipate, glycerin, diacetylated monolaurate, and palm oil. The readily volatile foaming agent and the foaming aid are vinyl group, carbonyl group, aromatic group, ester group, ether group, aldehyde group, amino group, nitrile group as long as they do not affect the preliminary foaming process. And may contain a functional group such as a nitro group.

  The content of the readily volatile foaming agent is preferably 8 to 20 parts by weight, more preferably 10 to 17 parts by weight, and even more preferably 12 to 15 parts by weight with respect to 100 parts by weight of the foamable thermoplastic resin particles. is there. If the content of the easily volatile foaming agent is lower than 8 parts by weight, the foamability of the foamable thermoplastic resin particles may be lowered. When foamability is lowered, it becomes difficult to obtain low-bulk density pre-expanded particles having a high bulk ratio, and the foam-molded product obtained by in-mold molding of the pre-expanded particles has a low coalescence rate and is resistant to cracking May decrease. On the other hand, when the content is higher than 20 parts by weight, the moldability may be lowered and the strength characteristics such as compression and bending of the obtained foamed molded article may be lowered.

  Moreover, as long as a desired pre-expanded particle can be obtained, the pre-expanded particle may contain the additive etc. Specific additives include flame retardants, flame retardant aids, coating agents, chain transfer agents, light stabilizers, UV absorbers, pigments, dyes, antifoaming agents, thickeners, heat stabilizers, leveling agents. , Lubricants, antistatic agents and the like.

A method for producing expandable thermoplastic resin particles used at the time of preliminary foaming will be described below.
A known polymerization method, that is, a suspension polymerization method, an emulsion polymerization method, a solution polymerization method, a seed polymerization method, or the like may be used as appropriate for the production of the thermoplastic resin particles used in the production of the expandable thermoplastic resin particles. it can. In the present invention, it is preferable to use a suspension polymerization method as a polymerization method because thermoplastic resin particles can be more easily and safely produced while suppressing excessive heat generation and pressure increase during polymerization.

  In particular, the suspension polymerization method is preferably an impregnation polymerization method in which thermoplastic resin particles are produced by impregnating and polymerizing a styrene monomer in an aqueous medium in polyolefin resin particles. By the impregnation polymerization, the ratio of the polyolefin resin in the surface layer of the thermoplastic polymerizable resin particles and the pre-expanded particles may be higher.

Next, the thermoplastic resin particles obtained are impregnated with a readily volatile foaming agent, whereby foamable thermoplastic resin particles can be obtained. The impregnation of the readily volatile blowing agent can be carried out in the presence of an easily volatile blowing agent, in the presence or absence of an aqueous medium. The impregnation corresponds to impregnating the thermoplastic resin particles with the volatile foaming agent by contacting and immersing the thermoplastic resin particles in an excessive amount of the volatile foaming agent.
As an example of impregnation method,
A method of mixing the readily volatile foaming agent and the thermoplastic resin particles with stirring;
Circulating a readily volatile blowing agent in a container holding thermoplastic resin particles;
Examples thereof include a method of injecting a foaming agent into an aqueous medium in which thermoplastic resin particles are dispersed and impregnating the thermoplastic resin particles with the foaming agent.

A method for pre-foaming the expandable thermoplastic resin particles will be described below.
In the present invention, the foamed thermoplastic resin particles are prefoamed in a prefoaming tank in which the inside of the system is closed by an on-off valve or the like as shown in FIG. 1 and the gauge pressure in the system can be constant. However, the present invention is not limited to the pre-foaming tank of FIG.

In FIG. 1, reference numeral 1 denotes a line for sending steam to the preliminary foaming tank, and the pressure of the sent steam can be adjusted by opening and closing the valve.
Reference numeral 2 denotes a line for sending steam to the jacket of the pre-foaming tank. Like 1, the pressure of the steam sent to the jacket can be adjusted by a valve.
Reference numeral 3 denotes a preliminary foaming tank for performing preliminary foaming.
Reference numeral 4 denotes a stirring blade for preventing coalescence of the pre-foamed particles during pre-foaming.
Reference numeral 5 denotes a line for discharging the steam sent from 1 into the preliminary foaming tank, and the degree of opening and closing can be adjusted by operating the valve.
Reference numeral 6 denotes a charging port used when foaming thermoplastic resin particles are placed in the preliminary foaming tank.
Reference numeral 7 denotes an outlet for taking out the pre-foamed particles after the pre-foaming is completed.
Reference numeral 8 denotes a measuring instrument for measuring the gauge pressure and temperature in the preliminary foaming tank.
Reference numeral 9 denotes a measuring instrument for measuring the gauge pressure and temperature of the pressurized steam in the steam pipe.
The pre-foaming tank can be arbitrarily adjusted to a gauge pressure in the pre-foaming tank of 8 to a gauge pressure equivalent to the vapor pressure of the steam pipe by adjusting the opening / closing degree of the steam discharge valve of 5 Can do.

  In the present invention, as described above, the inside of the system is adjusted to be sealed under atmospheric pressure by opening and closing the valve, etc., and then pressurized steam is introduced, and the inside of the preliminary foaming tank is under a gauge pressure of 0.02 to 0.15 MPa. To perform pre-foaming. When pre-foaming is performed under a gauge pressure lower than 0.02 MPa, release of a readily volatile foaming agent may be caused. On the other hand, when pre-foaming is performed under a gauge pressure higher than 0.15 MPa, the resin particles may soften more than necessary and cause blocking.

The gauge pressure P (MPa) in the pre-foaming tank is expressed by the formula:
0.02 <P <10 ^{(8.027-1705 / (T + 220))} × 1.33 × 10 ⁻⁴ −0.1013 MPa
It is preferable that

The above formula is the Antoine formula:
log10P [mmHg] = AB / (t [° C.] + C)
Is calculated by A, B, and C mean Antoine constants.
If the above formula is not satisfied, the pre-expanded particles may cause blocking.

  In the present invention, since the inside of the pre-foaming tank may be brought to a more uniform temperature condition, it is preferably pressurized steam having a gauge pressure of 0.02 to 0.15 MPa, more preferably 0.02 to 0.06 MPa. Is used to heat the pre-foaming tank. When pressurized steam with a gauge pressure lower than 0.02 MPa is used, the temperature in the tank may not be uniform. On the other hand, when pressurized steam having a gauge pressure higher than 0.15 MPa is used, there may be a problem in terms of manufacturing cost.

  Moreover, 105-127 degreeC is preferable and the temperature in a preliminary foaming tank has more preferable 109-114 degreeC. When pre-foaming is performed at a temperature lower than 105 ° C., the foamable thermoplastic resin particles may not be sufficiently pre-foamed. On the other hand, when pre-foaming is performed at a temperature higher than 127 ° C., the resin particles may soften more than necessary and cause blocking. Further, from the viewpoint of preventing blocking, it is preferable to add gentle stirring to the preliminary foaming tank.

  By performing the pre-foaming of the present invention, the pre-foaming time can be preferably 120 seconds or shorter, more preferably 65 seconds or shorter. Further, the foamable thermoplastic resin particles having a composition capable of being prefoamed with a prefoaming time of 120 seconds or less without using the present invention can further reduce the prefoaming time to one half or less by using the present invention. May also be possible. These mean that the pre-foaming time can be greatly shortened as compared with the prior art, and the batch method is extremely preferable from the viewpoint of production cost and the like. The pre-foaming time refers to the time from when the expandable thermoplastic resin particles are introduced into the system and the introduction of pressurized steam into the pre-foaming tank is started until the bulk multiple of the pre-foamed particles becomes 35 times. This is the time required. The method for measuring the pre-foaming time will be described in detail in Examples.

  After the pre-foaming time has elapsed, the pressure in the pre-foaming tank is released by adjusting the opening and closing of the valve, whereby the pre-foamed particles obtained are recovered from the pre-foaming tank under atmospheric pressure in the system.

  In the present invention, it is preferable in terms of productivity and production cost that the preliminary foaming step is performed in one step. Moreover, as long as the preliminary foaming process, quality, etc. are not affected, the preliminary foaming process may be performed in two or more stages, with the prefoaming conditions such as pressurization conditions, heating conditions, and heating time being multistage.

  In the present invention, expandable thermoplastic resin particles are used in which the ratio of the polystyrene-based resin in the surface layer of the pre-expanded particles is preferably 40% by mass or less, more preferably 25% by mass or less. When the said ratio is higher than 40 mass%, a preliminary resin particle may soften more than necessary and may cause blocking. Therefore, in this invention, blocking can also be effectively reduced by adjusting the ratio of the polystyrene-type resin in the surface layer of a pre-expanded particle. The surface layer refers to a region from the surface of the pre-foamed particles to a depth of several μm, and the method for calculating the ratio will be described in detail in the examples.

The pre-expanded particles of the present invention preferably have a bulk ratio of 25 to 80 times (bulk density of 0.04 to 0.0125 g / cm ³ ), more preferably a bulk ratio of 35 to 60 times (bulk density of 0.029 to 0.017 g). / Cm ³ ). If the bulk multiple is greater than 80 times, the strength of the resulting foamed molded product may be reduced. On the other hand, if it is less than 25 times, the weight of the obtained foamed molded product may increase.

  Further, the average particle diameter of the pre-expanded particles is preferably 8.4 mm or less, and more preferably 6.0 mm or less. When the average particle diameter is larger than 8.4 mm, the filling property of the pre-expanded particles in the foam molding machine may be lowered, and the strength of the obtained foam molded product may be lowered.

  Furthermore, the pre-expanded particles are filled into a mold of a molding machine, heated and subjected to secondary foaming, and the pre-expanded particles are fused and integrated with each other, whereby a foam-molded article having a desired shape can be obtained. As the molding machine, there can be used an EPS molding machine or the like used when producing a foam molded body from polystyrene resin pre-foamed particles.

  Since the foamed molded product obtained by the present invention uses pre-expanded particles with reduced blocking, it has excellent moldability and a beautiful surface. Therefore, the foamed molded product obtained can be used for applications such as cushioning materials (cushion materials) for home appliances, electronic parts, various industrial materials, food containers and the like. In particular, it can be suitably used as a return packaging box for automobile parts and the like, and a shock-absorbing packaging material for electrical products and the like.

The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. Various manufacturing conditions and evaluation methods will be described below.
<Melting point of polyolefin resin>
The melting point of the polyolefin-based resin is measured according to the method described in JIS K 7122: 1987 “Method for measuring the transition heat of plastic”. Specifically, a differential scanning calorimeter DSC220 type (manufactured by Seiko Denshi Kogyo Co., Ltd.) is used. The temperature is raised, lowered, and raised repeatedly at an ascending / descending speed per minute, and the melting peak temperature of the DSC curve at the second raising temperature is taken as the melting point. Further, when there are two or more melting peaks, the lower peak temperature is taken as the melting point.

<Easily volatile foaming agent inclusion amount of foamable thermoplastic resin particles>
Weigh accurately the amount of about 20 mg of expandable thermoplastic resin particles, set it at the decomposition furnace entrance of the pyrolysis furnace PYR-1A manufactured by Shimadzu Corporation, and purge with helium for about 15 seconds to discharge the mixed gas at the time of sample setting . After sealing, the sample is inserted into a 200 ° C. core and heated for 120 seconds to release the gas, and this released gas is quantified using a gas chromatograph GC-14B (detector: TCD) manufactured by Shimadzu Corporation. The measurement conditions were: Polapack Q (80/100) 3 mmf × 1.5 m manufactured by GL Sciences Inc., column temperature (100 ° C.), carrier gas (helium), carrier gas flow rate (1 ml / min), inlet temperature (120 ° C.) and detector temperature (120 ° C.).

<Prefoaming time>
In the present invention, after the foamable thermoplastic resin particles are introduced into the system, the time from when the introduction of pressurized steam into the prefoaming tank is started until the bulk multiple of the prefoamed particles becomes 35 times is 65 seconds. When it becomes the following, it determines with a pass ((circle)). The pre-foaming time refers to the time required for the total volume of the pre-foamed particles in the pre-foaming tank to reach a predetermined volume corresponding to 35 times the bulk multiple of the pre-foamed particles. By evaluating the bulk multiple of the pre-expanded particles, it is confirmed that the bulk multiple of the pre-expanded particles is actually 35 times. The end of the introduction of the pressurized steam was judged using a level sensor that detects the end of foaming provided in the preliminary foaming tank. In addition, when the said predetermined volume is not reached at the time of preliminary foaming, and when it takes a long time from 65 seconds, it determines with disqualification (x).

<Blocking of pre-expanded particles>
The presence or absence of blocking of two or more particles is confirmed by visually confirming the pre-foamed particles after the pre-foaming. Next, the obtained pre-foamed particles are foamed using a known foam molding machine equipped with a filling device for filling the pre-foamed particles in the cavities without performing classification or the like, regardless of the presence or absence of blocking. Perform molding. Here, when filling the pre-expanded particles in the cavity, it is confirmed whether or not the pre-expanded particles are satisfactorily filled without causing a bridge or the like.
The evaluation of blocking is determined according to the following criteria.
1. Blocking is not confirmed and can be filled well: ○ (pass)
2. Although blocking was confirmed, it can be filled well: △ (pass)
3. Blocking is confirmed and cannot be filled well: x (failed)

<Bulk density and bulk multiple of pre-expanded particles>
Filling the pre-expanded particles in a measuring cylinder of 500 cm ³ to the scale of 500 cm ^3. Here, the graduated cylinder is visually observed from the horizontal, and if any pre-expanded particles reach the scale of 500 cm ³ , the filling of the pre-expanded particles into the graduated cylinder is terminated at that point. Next, the mass of the pre-expanded particles filled in the graduated cylinder is measured with the second significant figures after the decimal point, and the mass is defined as W (g).
The bulk density and bulk multiple of the pre-expanded particles are calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500
Bulk multiple = 1 / bulk density

<Average particle diameter of pre-expanded particles>
The average particle diameter of the pre-expanded particles is calculated by taking the average particle diameter of the pre-expanded particles. That is, the average particle size of the pre-expanded particles of the present invention means the volume average particle size. The average particle size of the pre-expanded particles can be measured, for example, using a measuring apparatus commercially available from Beckman Coulter, Inc. as a product name “Coulter Multisizer II”.

<Ratio of polystyrene-based resin on the surface of pre-expanded particles>
The surface layer of the particle refers to a region from the surface of the pre-foamed particle to a depth of several μm, and the ratio of the polystyrene resin in the surface layer of the pre-foamed particle can be calculated by the following measurement.
As a method for obtaining the composition ratio of polystyrene resin and polypropylene resin from the absorbance ratio, a plurality of types of standard samples prepared by uniformly mixing polystyrene resin and polypropylene resin at a predetermined composition ratio are prepared as described below. Then, 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 obtained infrared absorption spectra. A calibration curve is drawn by taking the composition ratio (polystyrene resin ratio (% by mass) in the standard sample) on the vertical axis and the absorbance ratio (D698 / D1376) on the horizontal axis. Based on this calibration curve, the composition ratio of the polystyrene resin and the polypropylene resin in the pre-expanded particles of the present invention can be determined.
For example, when the polypropylene resin is made by Sun Allomer, trade name “PC540R”, and the polystyrene resin is polystyrene (made by Sekisui Chemical Co., Ltd., trade name “SS142”), the composition ratio is obtained by using the calibration curve shown in FIG. Can know. For example, when the absorbance ratio (D698 / D1376) is 10.0, the polypropylene resin is 20.2 mass%, the polystyrene resin is 79.8 mass%, and the absorbance ratio is 15.0, the polypropylene resin is It can be calculated that 8.1% by mass and the polystyrene resin is 90.9% by mass.

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 the polystyrene resin and the polypropylene resin are precisely weighed so that the composition ratio (polystyrene resin / polypropylene resin) becomes 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 (polystyrene resin / polypropylene resin; mass ratio):
0/10, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 8/2, 9/1, 10/0
The calibration curve of FIG. 2 is obtained by measuring the absorbance ratio of the standard sample of the previous ratio and graphing the relationship between the polystyrene resin ratio (mass%) and the absorbance ratio (D698 / D1376).
In FIG. 2, when the polystyrene resin ratio is 40% by mass or less, the calibration curve is approximated by the following formula (1).
Y = −2.5119X ² + 22.966X (1)
In FIG. 2, when the polystyrene resin ratio is 40% by mass or more, the calibration curve is approximated by the following formula (2).
Y = 27.591Ln (X) +16.225 (2)
In the above formula, X represents an absorbance ratio (D698 / D1376), and Y represents a polystyrene resin ratio. The polystyrene resin ratio (mass%) of the pre-expanded particles is calculated based on the calibration curve in FIG.

  Similarly, as a method for obtaining the composition ratio of the polystyrene resin and the polyethylene resin from the absorbance ratio, the horizontal axis represents the absorbance ratio (D698 / D2850), and a similar calibration curve is drawn. The composition ratio of polystyrene resin and polyethylene resin in can also be obtained.

Example 1
<Preparation of polyolefin resin particles>
100 parts by weight of polyolefin resin (polypropylene resin, manufactured by Prime Polymer Co., Ltd., product name F-744NP, melting point 140 ° C.) is supplied to an extruder, melted and kneaded, granulated by an underwater cutting method, and oval (egg-like) ) Polyolefin-based resin particles. The average mass of the polyolefin resin particles at this time was adjusted to 74 mg per 100 grains.

<First polymerization>
Next, 800 g of the polyolefin resin particles are put into a 5 L autoclave equipped with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in the aqueous medium. Held for 10 minutes, and then heated to 60 ° C. to obtain an aqueous suspension. Next, 0.344 kg of a styrene monomer in which 0.7 g of dicumyl peroxide was dissolved in this suspension was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes to allow the polyolefin resin particles to absorb the styrene monomer. Next, the temperature of the reaction system was raised to 140 ° C., the same as the melting point of the polyolefin resin, and maintained for 2 hours, and the styrene monomer was polymerized in the polyolefin resin particles.

<Second polymerization>
Next, the reaction liquid for the first polymerization was set to 120 ° C., which is 20 ° C. lower than the melting point of the polyolefin resin, and 1.5 g of sodium dodecylbenzenesulfonate was added to this suspension, and then dicumyl parsene was used as a polymerization initiator. Polymerization was carried out while 0.856 kg of a styrene monomer in which 3.6 g of oxide was dissolved was dropped over 4 hours and absorbed in polyolefin resin particles. After the completion of the dropping, the temperature was kept at 120 ° C. for 1 hour, and then the temperature was raised and kept for 3 hours to complete the polymerization to obtain thermoplastic resin particles.

<Impregnation of volatile foaming agent>
Thereafter, the temperature of the reaction system was set to 60 ° C., and in this suspension, 60 g of tri (2,3-dibromopropyl) isocyanurate (manufactured by Nippon Kasei Co., Ltd.) as a flame retardant, and 2, 30 g of 3-dimethyl-2,3-diphenylbutane (manufactured by Kayaku Akzo) was added, and after the addition, the temperature of the reaction system was raised to 130 ° C. and stirring was continued for 2 hours to obtain thermoplastic resin particles. . Subsequently, it cooled to normal temperature and took out the thermoplastic resin particle from the 5L autoclave. 2 kg of the thermoplastic resin particles after removal and 2 L of water were again put into a 5 L autoclave with a stirrer, and 520 ml (300 g) of butane as a volatile foaming agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours. Then, after cooling to normal temperature and taking out from the 5 L autoclave, dehydrating and drying, expandable thermoplastic resin particles were obtained. The content of the readily volatile foaming agent was 13 parts by weight with respect to 100 parts by weight of the foamable thermoplastic resin particles.

<Pre-foaming>
Next, 1000 g of the obtained expandable thermoplastic resin particles was put into a pre-foaming machine (product name: PSX40, manufactured by Kasahara Kogyo Co., Ltd.), the system was sealed, and pressurized steam was introduced into the PSX pre-foaming tank and PSX Pre-expanded particles pre-expanded to a bulk multiple of 35 times were obtained while maintaining the gauge pressure in the pre-expansion tank at 0.14 MPa. When the gauge pressure in the preliminary foaming tank was kept at 0.14 MPa, the temperature in the preliminary foaming tank rose to 126 ° C.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk magnification of the pre-expanded particles was 35.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 21% by mass.
The average particle diameter of the pre-expanded particles was 5.0 mm.

Example 2
100 parts by weight of polyolefin resin (polypropylene resin, manufactured by Prime Polymer Co., Ltd., product name F-744NP, melting point 140 ° C.) at the time of preparation of polyolefin resin particles is supplied to an extruder, melted and kneaded, and manufactured by an underwater cutting method. It was granulated to obtain an oval (egg-like) polyolefin resin particle, and the average mass of the polyolefin resin particle was adjusted to 74 mg per 100 particles.
100 parts by weight of polyolefin resin (linear low density polyethylene, manufactured by Nippon Unicar Co., Ltd., product name TUF-2032, melting point 126 ° C.) is supplied to an extruder for granulation, and polyolefin having L / D = 0.9 System resin particles were obtained, and the same procedure as in Example 1 was carried out except that the average mass of the polyolefin resin particles was adjusted to 40 mg per 100 grains.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 13% by mass.
The average particle diameter of the pre-expanded particles was 4.1 mm.

Example 3
It implemented like Example 2 except the gauge pressure in the preliminary foaming tank at the time of preliminary foaming having been 0.08 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 13% by mass.
The average particle diameter of the pre-expanded particles was 4.1 mm.

Example 4
It implemented like Example 1 except the gauge pressure in the preliminary foaming tank at the time of preliminary foaming having been 0.025 Mpa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk magnification of the pre-expanded particles was 35.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 21% by mass.
The average particle diameter of the pre-expanded particles was 5.0 mm.

Example 5
It implemented like Example 2 except the gauge pressure in the preliminary foaming tank at the time of preliminary foaming having been 0.025 Mpa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 13% by mass.
The average particle diameter of the pre-expanded particles was 4.1 mm.

Example 6
(1) 800 g of polyolefin resin particles at the time of the first polymerization is 600 g;
(2) 0.7 g of dicumyl peroxide during the first polymerization is 0.6 g;
(3) 0.344 kg of styrene monomer in the first polymerization is set to 0.3 kg;
(4) 3.6 g of dicumyl peroxide in the second polymerization is changed to 4.2 g;
(5) 1.1 kg of 0.856 kg of styrene monomer in the second polymerization
The same procedure as in Example 1 was performed except that.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 25% by mass.
The average particle diameter of the pre-expanded particles was 5.5 mm.

Example 7
(1) 400 g of the polyolefin resin particles 800 g during the first polymerization;
(2) 0.7 g of dicumyl peroxide in the first polymerization is 0.4 g;
(3) 0.344 kg of styrene monomer in the first polymerization is 0.2 kg;
(4) 3.6 g of dicumyl peroxide in the second polymerization is changed to 4.8 g;
(5) 1.4kg of 0.856 kg of styrene monomer in the second polymerization
The same procedure as in Example 1 was performed except that.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 32% by mass.
The average particle diameter of the pre-expanded particles was 6.3 mm.

Example 8
(1) 400 g of the polyolefin resin particles 800 g during the first polymerization;
(2) 0.7 g of dicumyl peroxide in the first polymerization is 0.4 g;
(3) 0.344 kg of styrene monomer in the first polymerization is 0.2 kg;
(4) 3.6 g of dicumyl peroxide in the second polymerization is changed to 4.8 g;
(5) 1.4kg of 0.856 kg of styrene monomer in the second polymerization
The same procedure as in Example 2 was performed except that.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Example 9
The same operation as in Example 8 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was set to 0.05 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Example 10
The same operation as in Example 7 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was set to 0.025 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle diameter of the pre-expanded particles was 6.3 mm.

Example 11
The same operation as in Example 8 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was set to 0.025 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Comparative Example 1
It implemented like Example 1 except the gauge pressure in the preliminary foaming tank at the time of preliminary foaming having been 0.17 MPa.
Many blockings were confirmed during pre-foaming, and subsequent molding was difficult.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 21% by mass.
The average particle diameter of the pre-expanded particles was 5.0 mm.

Comparative Example 2
It implemented like Example 2 except the gauge pressure in the preliminary foaming tank at the time of preliminary foaming having been 0.17 MPa.
Many blockings were confirmed during pre-foaming, and subsequent molding was difficult.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 13% by mass.
The average particle diameter of the pre-expanded particles was 4.1 mm.

Comparative Example 3
The same operation as in Example 7 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was 0.17 MPa.
Many blockings were confirmed during pre-foaming, and subsequent molding was difficult.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 32% by mass.
The average particle diameter of the pre-expanded particles was 6.3 mm.

Comparative Example 4
The same operation as in Example 8 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was 0.17 MPa.
Many blockings were confirmed during pre-foaming, and subsequent molding was difficult.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Comparative Example 5
The same operation as in Example 8 was performed except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was 0.01 MPa.
However, although the preliminary foaming time was 120 seconds, the foamable thermoplastic resin particles could not be prefoamed to a predetermined multiple.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk magnification of the pre-expanded particles was 21.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Comparative Example 6
Pre-foaming is performed in a state where the obtained foamable thermoplastic resin particles are put into a pre-foaming machine (product name SKK-70, manufactured by Sekisui Koki Seisakusho Co., Ltd.), and the system is not sealed and opened to atmospheric pressure. Then, the same procedure as in Example 8 was performed except that pressurized steam having a pressurized steam pressure of 0.05 MPa was introduced into the PSX prefoaming tank and then prefoaming was performed in a state where the steam was released under atmospheric pressure.
82 seconds were required to obtain 35 times pre-expanded particles, and the time required for the foaming time was longer than that in Example 8.
During the pre-foaming step, the gauge pressure in the pre-foaming tank was substantially equal to atmospheric pressure.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk magnification of the pre-expanded particles was 35.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 22% by mass.
The average particle size of the pre-expanded particles was 5.1 mm.

Comparative Example 7
(1) 800 g of polyolefin resin particles during the first polymerization are set to 1200 g;
(2) 0.7 g of dicumyl peroxide at the time of the first polymerization is 0.96 g;
(3) 0.38 kg of styrene monomer at the time of the first polymerization is changed to 0.48 kg;
(4) 3.6 g of dicumyl peroxide in the second polymerization is changed to 2.4 g;
(5) 0.32 kg of 0.856 kg of styrene monomer in the second polymerization
The same procedure as in Example 1 was performed except that.
However, even when the pre-foaming time was 120 seconds, good pre-foaming could not be caused.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 18 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particle was 11% by mass.
The average particle diameter of the pre-expanded particles was 4.4 mm.

Comparative Example 8
100 parts by weight of polyolefin resin (linear low density polyethylene, manufactured by Nippon Unicar Co., Ltd., product name TUF-2032, melting point 126 ° C.) is supplied to an extruder for granulation, and polyolefin having L / D = 0.9 System resin particles were obtained, and the average mass of polyolefin resin particles was adjusted to 40 mg per 100 grains. Next, 200 g of the polyolefin resin particles are put into a 5 L autoclave equipped with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in the aqueous medium. Held for 10 minutes, and then heated to 60 ° C. to obtain an aqueous suspension. Subsequently, 0.1 kg of a styrene monomer in which 0.2 g of dicumyl peroxide was dissolved in this suspension was dropped in 15 minutes. After dropping, the mixture was held for 30 minutes to allow the polyolefin resin particles to absorb the styrene monomer. Next, the temperature of the reaction system was raised to 140 ° C., which is 17 ° C. higher than the melting point of the polyolefin resin, and held for 2 hours, and the styrene monomer was polymerized (first polymerization) in the polyolefin resin particles.

  Next, the reaction liquid of the first polymerization was set to 120 ° C. which was 3 ° C. lower than the melting point of the polyolefin resin, and 1.5 g of sodium dodecylbenzenesulfonate was added to this suspension, and then dicumyl was used as a polymerization initiator. 1.7 kg of styrene monomer in which 5.4 g of peroxide was dissolved was dropped over 5 hours, and polymerization (second polymerization) was performed while absorbing the polyolefin resin particles.

  Subsequently, it cooled to normal temperature and took out the thermoplastic resin particle from the 5L autoclave. 2 kg of the thermoplastic resin particles after removal and 2 L of water were again put into a 5 L autoclave with a stirrer, and 520 ml (300 g) of butane as a volatile foaming agent was poured into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours. Then, after cooling to normal temperature and taking out from the 5 L autoclave, dehydrating and drying, expandable thermoplastic resin particles were obtained.

Next, 1000 g of the obtained expandable thermoplastic resin particles was put into a pre-foaming machine (product name PSX40, manufactured by Kasahara Kogyo Co., Ltd.), the system was hermetically sealed, and then the PSX pre-foaming tank had a pressurized vapor pressure of 0.08 MPa. While introducing the pressurized steam, the gauge pressure in the PSX pre-foaming tank was maintained at 0.08 MPa, and pre-foamed particles pre-foamed to a bulk multiple of 35 times were obtained. When the gauge pressure in the preliminary foaming tank was kept at 0.08 MPa, the temperature in the preliminary foaming tank rose to 115 ° C.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-expanded particles was 29% by mass.
The average particle diameter of the pre-expanded particles was 6.4 mm.

Comparative Example 9
<Preparation of polyolefin resin particles>
Polyolefin resin (ethylene-vinyl acetate copolymer (EVA)) (manufactured by Nippon Unicar Co., Ltd., product name NUC-3221, vinyl acetate content: 5 wt%, melting point 107 ° C., density: 0.93 g / cm ³ ) 100 Part by weight and 0.5 part by weight of synthetic hydrous silicon dioxide were supplied to an extruder, melt-kneaded, and granulated by an underwater cutting method to obtain elliptical (egg-like) polyolefin resin particles. The average weight of one polyolefin resin particle was 0.60 mg.

<First polymerization>
In a 5 L autoclave with a stirrer, 2000 kg of 70 ° C. water, 16 g of magnesium pyrophosphate and 0.4 g of dodecylbenzenesulfonic acid were used as an aqueous medium while stirring. Next, 800 g of the polyolefin resin particles were suspended in an aqueous medium while stirring. Next, the aqueous medium was heated to 85 ° C. to obtain an aqueous suspension. As a polymerization initiator, 3 g of benzoyl peroxide, 0.2 g of t-butylperoxybenzoate and 5 g of dicumyl peroxide were dissolved in 400 g of styrene monomer to prepare a first styrene monomer. In addition, 2 g of ethylenebisstearic acid amide as a bubble regulator was dissolved in 800 g of styrene monomer to prepare a second styrene monomer.
Next, the first styrene monomer is continuously dropped into the aqueous medium at a rate of 200 g per hour, and the polyolefin resin particles are impregnated with the styrene monomer, the polymerization initiator, and the crosslinking agent. A styrene monomer was polymerized into the polyolefin resin particles.

<Second polymerization>
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. Next, the polymerization vessel was cooled to obtain expandable thermoplastic resin particles.

Subsequently, impregnation with a volatile foaming agent and preliminary foaming were performed in the same manner as in Example 1 except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was 0.08 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 27% by mass.
The average particle diameter of the pre-expanded particles was 5.0 mm.

Comparative Example 10
In 100 parts by weight of a mixed resin of 40 parts by weight of a polystyrene resin (product name: HRM10N, manufactured by Toyo Styrene Co., Ltd.) and 60 parts by weight of a polyolefin resin (polypropylene resin, manufactured by Sun Allomer, product name: PF734S, melting point: 150 ° C.) It was supplied to the extruder together with 0.2 parts by weight of fine powder talc as a regulator and mixed with the solution. As the extruder, a meshing type co-rotating twin screw kneader (screw outer diameter: 37 mm, L / D ratio: 31.1) was used. Next, the melt-kneaded product was extruded into a strand shape and pelletized to obtain thermoplastic resin particles having a weight per 100 particles of 200 mg.

Subsequently, impregnation with a readily volatile foaming agent and preliminary foaming were performed in the same manner as in Example 1 except that the gauge pressure in the preliminary foaming tank at the time of preliminary foaming was set to 0.07 MPa.
The preliminary foaming time and blocking evaluation results are shown in Table 1.

The bulk expansion ratio of the pre-expanded particles was 35 times.
The ratio of the polystyrene resin in the surface layer of the pre-foamed particles was 27% by mass.
The average particle diameter of the pre-expanded particles was 4.6 mm.

  Table 1 shows the raw material species of the examples and comparative examples.

  From Table 1, the pre-foaming method of the expandable thermoplastic resin particles performed in Examples 1 to 10 can obtain good pre-foamed particles without requiring a long process time and without causing blocking. It shows what you can do. In particular, in the pre-foaming of the expandable thermoplastic resin particles having the same composition by the pre-foaming method performed in Examples 8, 9, and 11, the pre-foaming time was 2 minutes compared to the case of not using the present invention. It can be shortened to 1 or less. This is because the pre-expanded particles of the present invention are composite expandable thermoplastic resin particles containing 100 to 400 parts by weight of polyolefin resin with respect to 100 parts by weight of polyolefin resin having a melting point of 117 to 145 ° C. Even if the gauge pressure (MPa) in the pre-foaming tank, which could not be performed by the prior art, is 0.02 to 0.03 MPa, it shows that the desired pre-foaming can be performed without causing the above problem. Yes.

Further, the gauge pressure (MPa) in the preliminary foaming tank and the melting point of the polyolefin resin T (° C.) are expressed by the formula:
0.02 <P <10 ^{(8.027-1705 / (T + 220))} × 1.33 × 10 ⁻⁴ −0.1013 MPa
When satisfy | filling, it has shown that a particularly favorable pre-expanded particle can be obtained.

  Furthermore, the present invention can be applied to any expandable thermoplastic resin particles containing 100 parts by weight of a polyolefin resin having a melting point of 117 to 145 ° C. and 100 to 400 parts by weight of a polyolefin resin. It shows that you can.

Example 12
In the case of producing a foamed molded article using the pre-expanded particles obtained in Examples 1 to 11, the pre-expanded particles can be stably introduced into the molding machine without causing a bridge or the like in the molding machine during foam molding. did it.
Therefore, the foamed molded article obtained by using the pre-foaming method of the present invention was excellent in heat resistance and the appearance was beautiful.

1 Line for sending steam to the pre-foaming tank and its open / close valve 2 Line for sending steam to the jacket of the pre-foaming tank and its open / close valve 3 Pre-foaming tank 4 Stirring blade 5 Line for discharging the steam sent to the pre-foaming tank and The opening / closing valve 6 Pre-foamed particle inlet 7 Pre-foamed particle outlet 8 Pre-foaming tank meter 9 Line meter for feeding steam to the pre-foaming tank

Claims (8)

  The foamable thermoplastic resin particles containing 100 to 400 parts by weight of a polystyrene-based resin with respect to 100 parts by weight of a polyolefin-based resin having a melting point of 117 to 145 ° C. in a sealed pre-foaming tank are 0.02 to 0.0. A pre-foaming method for foamable thermoplastic resin particles, wherein pre-foamed particles are obtained by pre-foaming under a gauge pressure in a 15 MPa pre-foaming tank.   The preliminary foaming method according to claim 1, wherein the preliminary foaming is performed in one step.   The pre-foaming method according to claim 1 or 2, wherein the polyolefin resin is one of a polyethylene resin and a polypropylene resin, and the polystyrene resin is a polystyrene homopolymer.   The pre-foaming according to any one of claims 1 to 3, wherein the foamable thermoplastic resin particles include 8 to 20 parts by weight of a readily volatile foaming agent with respect to 100 parts by weight of the foamable thermoplastic resin particles. Method.   The foamable thermoplastic resin particles are produced by impregnating and polymerizing the polyolefin resin with a styrene monomer to produce thermoplastic resin particles containing the polyolefin resin and the polystyrene resin, and then the thermoplastic resin particles. The pre-foaming method according to any one of claims 1 to 4, wherein the pre-foaming method is produced by impregnating the easily volatile foaming agent with the foaming agent.   Pre-expanded particles obtained by the method according to any one of claims 1-5.   The pre-expanded particles according to claim 6, wherein the pre-expanded particles have a polystyrene resin ratio of 40% by mass or less on the surface layer thereof.   A foam-molded product obtained by molding the pre-foamed particles according to claim 6 or 7 in a mold.

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