JP5603629B2 - Method for producing thermoplastic resin pre-expanded particles, method for producing thermoplastic resin foam molding - Google Patents

Description

  The present invention relates to thermoplastic resin pre-foamed particles used for the production of a thermoplastic resin foam molded article such as a polystyrene resin foam molded article and a method for producing the same, and more specifically, a molten foaming agent-containing thermoplastic resin is used as a die. In the manufacturing process of foamable thermoplastic resin particles by the so-called melt extrusion method, which is extruded through a small hole into a cooling medium such as water and then cut to produce resin particles, the cut resin particles are foamed in the cooling medium. The present invention relates to a technique for directly producing thermoplastic resin pre-expanded particles used for producing a foamed molded product.

As one of the methods for producing expandable polystyrene resin particles, a foaming agent is press-fitted and kneaded into polystyrene resin melted in an extruder, and a small hole in a die provided with a foaming agent-containing molten resin at the tip of the extruder A so-called melt extrusion method in which extrudates are extruded directly into a cooling liquid from the same time, and at the same time the extrudate is cut with a high-speed rotary blade and the extrudate is cooled and solidified by contact with the liquid to obtain expandable polystyrene resin particles Are known.
Conventionally, for example, techniques disclosed in Patent Documents 1 and 2 have been proposed regarding a method for producing expandable polystyrene resin particles by a melt extrusion method.

  In Patent Document 1, a thermoplastic resin is melted using an extruder, a foaming agent is mixed, subsequently cooled and extruded, so that the diameter is 1.5 to 10.5 times the nozzle diameter of the extrusion die. A method for producing pre-foamed particles of thermoplastic resin, characterized by cutting an extruded foam before or after foaming obtained by completing foaming into pre-foamed particles. It is disclosed.

  Patent Document 2 includes a resin composition containing 100 parts by mass of a mixed resin of 70 to 90% by mass of a styrene resin and 10 to 30% by mass of an olefin resin, and 0 to 15 parts by mass of a styrene elastomer. , Foamable particles obtained by simultaneously extruding a mixture with a volatile foaming agent into a liquid and cutting, and having a foaming ratio of 1.5 times or less and a volatile organic other than the volatile foaming agent A styrenic resin expandable particle characterized by a compound content of 500 ppm or less is disclosed. In Patent Document 2, 100 parts by mass of a mixed resin of 70 to 90% by mass of a styrene resin and 10 to 30% by mass of an olefin resin and 0 to 15 parts by mass of a styrene elastomer are supplied to an extruder. After heating and melting to obtain a resin composition, 3 to 15 parts by mass of a volatile blowing agent is injected into 100 parts by mass of the resin composition from the middle of the extruder, and then the blowing agent-containing molten resin is extruded from a porous die into a liquid. The resin is cut in the liquid simultaneously with extrusion while suppressing the foaming of the resin to 1.5 times or less to obtain expandable particles having a content of volatile organic compounds other than the volatile foaming agent of 500 ppm or less. A method for producing a styrene resin expandable particle is disclosed.

Japanese Patent Laid-Open No. 7-11041 JP 2004-244529 A

However, the prior art has the following problems.
The method of producing the pre-expanded particles in Patent Document 1 is to obtain the pre-expanded particles by cutting the foamed foam so as to have a diameter of 1.5 to 10.5 times the diameter of the nozzle of the extrusion die. When the nozzle shape is circular, the foamed body is cut, and the pre-expanded particles obtained are not spherical but columnar. Such columnar pre-expanded particles are harder to fill than spherical particles, and are difficult to fill sufficiently when filled into the cavity of the mold, and gaps are likely to occur. There is a possibility that a dent will be formed in the foamed molded product thus obtained, resulting in a poor appearance or poor mechanical strength.

  The production method of Patent Document 2 includes (1) a step of obtaining expandable resin particles by a melt extrusion method, (2) a step of heating the obtained expandable resin particles to obtain pre-expanded particles, (3) The production efficiency of the foamed molded product is obtained in order to produce the foamed molded product through the steps of filling the obtained pre-expanded particles into the cavity of the molding die, heating and in-mold foam molding to obtain the foamed molded product. In addition, there is a problem that storage space for expandable resin particles and pre-expanded particles is required.

  The present invention has been made in view of the above circumstances, and is capable of directly producing pre-foamed particles used in the production of a foamed molded article by a melt extrusion method, and is excellent in filling ability into a cavity of a mold and excellent in strength. It is an object of the present invention to provide a method for producing pre-expanded thermoplastic resin particles capable of obtaining the above.

  In order to achieve the above-mentioned object, the present invention immediately melts and kneads a thermoplastic resin and a foaming agent in a resin supply device, and immediately extrudes the molten foaming agent-containing thermoplastic resin through a small hole of a die into a cooling medium. Cutting and foaming in the cooling medium to obtain thermoplastic resin pre-expanded particles having a bulk expansion ratio of 1.6 times or more, and then separating the expanded particles from the cooling medium to obtain thermoplastic resin pre-expanded particles A method for producing pre-expanded thermoplastic resin particles is provided.

  In the method for producing pre-expanded thermoplastic resin particles of the present invention, the bulk expansion ratio of the pre-expanded thermoplastic resin particles is preferably in the range of 1.6 to 50 times.

  In the method for producing pre-expanded thermoplastic resin particles of the present invention, the foaming agent-containing thermoplastic resin preferably contains 1 to 10 parts by mass of a foaming agent with respect to 100 parts by mass of the thermoplastic resin.

  In the method for producing pre-expanded thermoplastic resin particles of the present invention, the foaming agent is preferably a mixture of one or both of isopentane and normal pentane.

  In the method for producing pre-expanded thermoplastic resin particles of the present invention, the thermoplastic resin is preferably a polystyrene resin.

  Moreover, this invention provides the thermoplastic resin pre-expanded particle obtained by the manufacturing method of the said thermoplastic resin pre-expanded particle.

  The present invention also provides thermoplastic resin foam molding by filling the thermoplastic resin pre-foamed particles obtained by the method for producing thermoplastic resin pre-foamed particles in a cavity of a mold and heating and molding in-mold foam. A method for producing a thermoplastic resin foam-molded article is provided.

  Moreover, this invention provides the thermoplastic resin foam molded object obtained by the manufacturing method of the said thermoplastic resin foam molded object.

  The thermoplastic resin pre-foamed particle manufacturing method of the present invention is obtained by melt-kneading a thermoplastic resin and a foaming agent in a resin supply apparatus, and extruding the molten foaming agent-containing thermoplastic resin into a cooling medium through a small hole in a die. The thermoplastic resin pre-expanded particles used for the production of the foam molded article are melt-extruded by cutting immediately after foaming in the cooling medium to obtain thermoplastic resin pre-expanded particles having a bulk expansion ratio of 1.6 times or more. Since it can be produced directly by the method, it is possible to produce foamed molded products with fewer steps compared to the conventional method of producing expandable resin particles and heating them to obtain pre-foamed particles. There is an advantage that the efficiency is increased and the storage space for the expandable resin particles can be reduced.

  The thermoplastic resin pre-expanded particles obtained by the method of the present invention are spherical or substantially spherical, and have better filling properties in the mold cavity than the column-shaped pre-expanded particles, and the cavity is filled without any gaps. In addition, the foamed particles are well fused at the time of in-mold foam molding, and a foam molded article having excellent strength can be obtained.

It is a block diagram which shows an example of the manufacturing apparatus used for the manufacturing method of the thermoplastic resin pre-expanded particle of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The method for producing pre-expanded thermoplastic resin particles (hereinafter referred to as pre-expanded particles) of the present invention is obtained by melt-kneading a thermoplastic resin and a foaming agent in a resin supply device, and then adding the molten foam-containing thermoplastic resin to a die. After extruding into the cooling medium through the small holes of, and cutting immediately after that, it is foamed in the cooling medium to obtain pre-expanded particles having a bulk expansion ratio of 1.6 times or more, and then the pre-expanded particles are separated from the cooling medium. The pre-expanded particles are directly produced by a melt extrusion method.

  In the present invention, the type of thermoplastic resin is not limited. For example, a polystyrene resin, a polyethylene resin, a polypropylene resin, a polyester resin, a vinyl chloride resin, an ABS resin, an AS resin, or the like can be used alone or in combination. Can be used. Furthermore, it is possible to use a recovered resin of a thermoplastic resin obtained after being used once as a resin product. In particular, polystyrene resins such as amorphous polystyrene (GPPS) and high impact polystyrene (HIPS) are preferably used.

  Examples of polystyrene resins include homopolymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, or copolymers thereof. A polystyrene-based resin containing 50% by mass or more of styrene is preferable, and polystyrene is more preferable. Further, the polystyrene resin may be a copolymer of the styrene monomer and a vinyl monomer copolymerizable with the styrene monomer, the main component of which is the styrene monomer. As, for example, alkyl (meth) acrylate such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cetyl (meth) acrylate, (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl In addition to fumarate and ethyl fumarate, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate are exemplified.

  If a polystyrene resin is the main component, other resins may be added. Examples of the resin to be added include polybutadiene, styrene-butadiene copolymer to improve the impact resistance of the foam molded article. Examples thereof include rubber-modified polystyrene resins to which a diene rubbery polymer such as a polymer, ethylene-propylene-nonconjugated diene three-dimensional copolymer is added, so-called high impact polystyrene. Alternatively, a polyethylene resin, a polypropylene resin, an acrylic resin, an acrylonitrile-styrene copolymer, an acrylonitrile-butadiene-styrene copolymer, and the like can be given. In addition, as a polystyrene resin as a raw material, a polystyrene resin (virgin polystyrene) that is not a recycled raw material, such as a commercially available ordinary polystyrene resin, a polystyrene resin newly produced by a method such as a suspension polymerization method, or the like is used. In addition to being usable, it is possible to use a recycled material obtained by regenerating a used polystyrene resin foam molded article. As this recycled material, used polystyrene-based resin foam moldings such as fish boxes, household appliance cushioning materials, food packaging trays, etc. are collected, and recycled materials that are regenerated by the limonene dissolution method or heating volume reduction method are used. Can do. Recyclable raw materials that can be used include home appliances (eg, TVs, refrigerators, washing machines, air conditioners) and office work, in addition to those obtained by reprocessing used polystyrene-based resin foam moldings. A non-foamed polystyrene resin molded product that has been separated and collected from an industrial machine (for example, a copying machine, a facsimile machine, a printer, etc.), pulverized, melt-kneaded, and repelletized can be used.

The foaming agent used in the pre-expanded particles of the present invention is not particularly limited, but examples thereof include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, and cyclopentane, and ethers such as dimethyl ether and diethyl ether. Various alcohols such as methanol and ethanol, carbon dioxide gas, nitrogen, water and the like can be used. Of these, aliphatic hydrocarbons are preferred, and normal butane, isobutane, normal pentane, isopentane alone or a mixture thereof is more preferred. Further, normal pentane, isopentane, neopentane, cyclopentane, cyclopentadiene alone or a mixture thereof, which is a hydrocarbon having 5 carbon atoms, is particularly suitable. Of these, a mixture of one or both of isopentane and normal pentane is preferable. Further, it mainly comprises the hydrocarbon having 5 carbon atoms and has a boiling point of 20 ° C. or higher, and may contain a blowing agent other than the hydrocarbon having 5 carbon atoms (for example, normal butane, isobutane, propane, carbon dioxide gas, etc.). .
The amount of the foaming agent added is preferably in the range of 1 to 15 parts by mass, more preferably in the range of 1 to 10 parts by mass, and particularly preferably in the range of 2 to 6 parts by mass with respect to 100 parts by mass of the thermoplastic resin.

  In the method for producing pre-expanded particles of the present invention, the thermoplastic resin includes, as a foam nucleating agent, talc, calcium silicate, synthetically or naturally produced silicon dioxide, ethylene bis-stearic acid amide, methacrylate ester copolymer. It is desirable to add inorganic or organic fine powder such as coalescence. The amount of the foam nucleating agent added is preferably 1.5 parts by mass or less, more preferably 0.1 to 1.0 part by mass with respect to 100 parts by mass of the thermoplastic resin.

  In the method for producing the pre-foamed particles of the present invention, the thermoplastic resin includes, in addition to the foaming agent and the foam nucleating agent, a binding inhibitor, a cell conditioner, and the like within a range that does not impair the physical properties of the pre-foamed particles obtained. You may add additives, such as a crosslinking agent, a filler, a flame retardant, a flame retardant adjuvant, a lubricant, and a coloring agent.

  FIG. 1 is a configuration diagram showing an example of a production apparatus used in the method for producing pre-expanded particles of the present invention. The manufacturing apparatus of this example includes an extruder 1 as a resin supply device, a die 2 attached to the tip of the extruder 1 and having a large number of small holes, and a raw material supply hopper 3 for charging a resin raw material into the extruder 1. And a high pressure pump 4 for press-fitting the foaming agent into the molten resin in the extruder 1 through the foaming agent supply port 5 and a resin discharge surface in which a small hole of the die 2 is made to contact the cooling water, A cutting chamber 7 in which cooling water is circulated and supplied to the room, a cutter 6 rotatably provided in the cutting chamber 7 so as to cut the resin extruded from the small hole of the die 2, and the cooling water from the cutting chamber 7 The pre-expanded particles carried along with the water flow are separated from the cooling water and dehydrated and dried to obtain the pre-expanded particles, and the solid-liquid separation function-equipped dehydration dryer 10 and the solid-liquid separation function-equipped dehydration dryer 10 are separated. The collected cooling water A tank 8, a high-pressure pump 9 that sends cooling water in the water tank 8 to the cutting chamber 7, and a storage container 11 that stores the pre-expanded particles dehydrated and dried by the dehydration dryer 10 with a solid-liquid separation function. It is configured.

  As the extruder 1, either an extruder using a screw or an extruder not using a screw can be used. Examples of the extruder using a screw include a single-screw extruder, a multi-screw extruder, a vent-type extruder, and a tandem extruder. Examples of the extruder that does not use a screw include a plunger type extruder and a gear pump type extruder. Moreover, any extruder can use a static mixer. Among these extruders, an extruder using a screw is preferable from the viewpoint of productivity. Moreover, the conventionally well-known thing used in the granulation method by melt extrusion of resin can also be used for the cutting chamber 7 which accommodated the cutter 6. FIG.

  In order to produce pre-foamed particles using the production apparatus shown in FIG. 1, first, a desired additive such as a thermoplastic resin such as a polystyrene-based resin as a raw material, a foam nucleating agent, a flame retardant added if necessary, etc. Are weighed and put into the extruder 1 from the raw material supply hopper 3. The raw material thermoplastic resin may be mixed in advance in the form of pellets or granules and then charged from one raw material supply hopper. For example, when a plurality of lots are used, the supply amount for each lot may be reduced. A plurality of adjusted raw material supply hoppers may be charged and mixed in an extruder. Also, when using a combination of recycled materials from multiple lots, mix the raw materials from multiple lots in advance and remove foreign matter using appropriate sorting methods such as magnetic sorting, sieving, specific gravity sorting, and air blowing sorting. It is preferable to keep it.

  After supplying thermoplastic resin resin, foaming aid and other additives into the extruder 1, the resin is heated and melted, and the molten resin is transferred to the die 2 side, while being fed from the foaming agent supply port 5 by the high pressure pump 4. The foaming agent is pressed into the melted resin, and the foaming agent is mixed with the melted resin. Through the screen for removing foreign matter provided in the extruder 1 as necessary, the melt is further kneaded and moved to the tip side, and the foaming agent is added. The melted product is extruded through a small hole in the die 2 attached to the tip of the extruder 1.

  The resin discharge surface in which the small hole of the die 2 is formed is disposed in the cutting chamber 7 in which cooling water is circulated and supplied into the chamber, and the resin extruded from the small hole can be cut in the cutting chamber 7. Thus, the cutter 6 is rotatably provided. When the melt with the blowing agent added is extruded through a small hole in the die 2 attached to the tip of the extruder 1, the melt is cut into granules and rapidly cooled in contact with cooling water. It expands before solidification, and becomes a pre-expanded thermoplastic resin particle having a bulk expansion ratio of 1.6 times or more.

The bulk expansion ratio of the pre-expanded particles thus obtained is preferably in the range of 1.6 to 50 times, and more preferably in the range of 1.6 to 40 times.
In the present invention, the bulk expansion ratio of the pre-expanded particles refers to a value obtained by the following measurement method after measuring the bulk density in accordance with JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. .
<Bulk expansion ratio of pre-expanded particles>
First, pre-expanded particles are filled in a measuring cylinder to a scale of 500 cm ³ . However, the graduated cylinder is visually observed from the horizontal direction, and if at least one pre-expanded particle reaches the scale of 500 cm ³ , the filling is finished. Next, the mass of the pre-expanded particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, and the mass is defined as W (g). The bulk density of the pre-expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500
Next, the bulk expansion ratio of the pre-expanded particles is calculated by the following formula.
Bulk foam multiple (times) = 1 / bulk density (g / cm ³ )

  The bulk expansion ratio of the pre-expanded particles can be adjusted by the pressure and temperature of the cooling water. When producing pre-expanded particles with a low bulk expansion ratio (high bulk density), foaming should be performed under conditions of high pressure and low water temperature. Manufacture while suppressing. On the other hand, when producing pre-expanded particles having a high bulk expansion ratio (low bulk density), the pre-expanded particles are produced while being expanded to some extent under conditions of low pressure and high water temperature. The pressure of the cooling water is, for example, a part of the circulation path of the cooling water that passes through the cutting chamber 7 from the discharge side of the high-pressure pump 9 and reaches the inlet side of the dehydrating dryer 10 with a solid-liquid separation function. It is desirable to pressurize by the discharge pressure of the high-pressure pump 9 and adjust the pressure appropriately. The pressure is not particularly limited. Usually, the pressure is applied under no pressure condition, or when the pressure is applied, the pressure is 1.7 MPa or less, preferably 1.5 MPa or less. The water temperature is preferably adjusted by attaching a heater (or both a heater and a cooler) to one of the circulation channels of the cooling water. Although the water temperature is not particularly limited, it is usually within a range of 20 to 80 ° C, preferably within a range of 30 to 70 ° C.

  The formed pre-expanded particles are transferred from the cutting chamber 7 to the flow of cooling water and carried to the dehydrating dryer 10 with a solid-liquid separation function, where the pre-expanded particles are separated from the cooling water and dehydrated and dried. The dried pre-expanded particles are stored in the storage container 11.

  The obtained pre-expanded particles may be coated on the surface with powdered metal soaps such as zinc stearate as necessary. Thereby, blocking of the pre-expanded particles can be prevented, and the handling of the pre-expanded particles, in particular, the filling property into the cavity of the mold can be kept good.

  The obtained pre-expanded particles are spherical or substantially spherical, have better filling properties into the cavity of the mold than the column-shaped pre-expanded particles, and can be filled without gaps in the cavity. The foamed particles are well fused at the time of inner foam molding, and a foam molded article having excellent strength can be obtained.

  The method for producing the pre-foamed particles of the present invention is as follows: a thermoplastic resin and a foaming agent are melt-kneaded in a resin feeder, and the molten foaming agent-containing thermoplastic resin is extruded into a cooling medium through a small hole of a die. By cutting and foaming in the cooling medium to obtain pre-expanded particles having a bulk expansion ratio of 1.6 times or more, the pre-expanded particles used for the production of the foam molded article can be directly produced by the melt extrusion method. Compared with the conventional method of producing expandable resin particles and heating them to obtain pre-expanded particles, it is possible to manufacture foamed molded products with fewer steps, increasing the production efficiency of foamed molded products, and expanding the foamed resin There is an advantage that the storage space for particles can be reduced.

The pre-expanded particles of the present invention are filled in a cavity of a mold using a well-known apparatus and method in the field of manufacturing a foamed resin molded body, heated by steam heating or the like, and subjected to in-mold foam molding, and foamed thermoplastic resin. A molded body (hereinafter referred to as a foam molded body) is produced.
The density and expansion ratio of the foamed molded product of the present invention are the same as the bulk density and bulk expansion ratio of the pre-expanded particles, and the density is 0.625 g / cm ³ or less (expanding ratio is 1.6 times or more). Is preferably in the range of 0.020 to 0.625 g / cm ³ (foaming factor 1.6 to 50 times).

In the present invention, the density and expansion ratio of the foamed molded product are the density of the foamed molded product measured by the method described in JIS K7122: 1999 “Measurement of foamed plastic and rubber-apparent density”.
<Density of foam molding>
A test piece of 50 cm ³ or more (100 cm ³ or more in the case of semi-rigid and soft materials) was cut so as not to change the original cell structure of the material, its mass was measured, and calculated by the following formula.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
The test specimen for measurement was cut out from a sample that had passed 72 hours or more after molding, and was subjected to atmospheric conditions of 23 ° C. ± 2 ° C. × 50% ± 5% or 27 ° C. ± 2 ° C. × 65% ± 5% for 16 hours or more. It is what was left.

<Folding multiple of foamed molded product>
Further, the expansion factor of the foamed molded product is a numerical value calculated by the following equation.
Foaming factor = 1 / density (g / cm ³ )

  Hereinafter, the effects of the present invention will be demonstrated by examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited by the description of the following examples.

[Example 1]
(Manufacture of pre-expanded particles)
0.3 parts by mass of fine powder talc was added to 100 parts by mass of polystyrene resin (trade name “HRM10N” manufactured by Toyo Styrene Co., Ltd.), and these were continuously supplied to a single screw extruder having a diameter of 90 mm at 130 kg per hour. As the temperature inside the extruder, the maximum temperature was set to 210 ° C., and after melting the resin, 3 parts by mass of pentane (isopentane: normal pentane = 20: 80 (mass ratio)) with respect to 100 parts by mass of the resin as a foaming agent. Was press-fitted from the middle of the extruder. In the extruder, the resin and the foaming agent are kneaded and cooled, the resin temperature at the extruder tip is maintained at 170 ° C., the pressure at the resin introduction part of the die is maintained at 15 MPa, the diameter is 0.6 mm, and the land length is 3. Simultaneously extruding the foaming agent-containing molten resin into a cutting chamber set at a water pressure of 0.05 MPa through 40 ° C. water circulating from a die having 200 small holes of 0 mm connected to the discharge side of this die. The extrudate was cut at 3000 rpm with a rotary cutter having 10 blades in the circumferential direction. While the cut particles were cooled with circulating water, they were conveyed to a particle separator, and the particles were separated from the circulating water. Further, the collected particles were dehydrated and dried to obtain pre-expanded particles. The obtained pre-expanded particles are almost spherical with no deformation or beard, and have a bulk density of 0.6 g / cm ³ , a bulk expansion ratio of 1.7 times, and an average particle diameter of about 1.3 mm. there were.
With respect to 100 parts by mass of the pre-expanded particles obtained, 0.03 parts by mass of polyethylene glycol was uniformly coated on the entire surface of the particles.

(Manufacture of foam moldings)
After leaving the pre-expanded particles obtained at room temperature for 24 hours, the pre-expanded particles are filled into a mold having a rectangular cavity of length 400 mm × width 300 mm × height 25 mm, The mold cavity is heated with water vapor at a gauge pressure of 0.08 MPa for 20 seconds, then cooled until the pressure in the mold cavity reaches 0.01 MPa, and then the mold is opened, A rectangular foam molded body having a length of 400 mm, a width of 300 mm, and a height of 25 mm was taken out.
The obtained foamed molded product had a density of 0.6 g / cm ³ (foaming factor 1.7 times).

The pre-expanded particles produced as described above were subjected to measurement / evaluation as described in <Evaluation of mold filling property> below, and the mold filling property was evaluated.
In addition, the foamed molded article produced as described above was measured and evaluated as described below in <Evaluation of appearance of foamed molded article> and <Measurement of fusion rate>.
Further, based on the results of <Evaluation of mold filling property>, <Appearance evaluation of foamed molded product>, and <Measurement of fusion rate>, comprehensive judgment was made in light of the judgment criteria of <Comprehensive judgment> below. The results are shown in Table 1.

<Evaluation of mold filling property>
The bulk density of the obtained pre-expanded particles and the density of the foamed molded product were obtained, the fillability was calculated according to the following formula, and the fillability was evaluated according to the following criteria.
Mold filling property = density of foamed molded article / bulk density of pre-expanded particles The evaluation criteria for this mold filling property were as follows.
Good (O): When mold filling property is 0.95 or more Poor (X): When mold filling property is less than 0.95

<Appearance evaluation of foam molding>
The pre-expanded particles were filled in a mold of a foam molding machine and subjected to in-mold foam molding using water vapor, thereby obtaining a rectangular solid foam molded body having a length of 400 mm, a width of 300 mm, and a thickness of 25 mm. The appearance of the obtained foamed molded product was visually observed and evaluated based on the following criteria.
Good (O): When the fused part between the expanded particles is smooth. Poor (X): When unevenness occurs at the fused part between the expanded particles.

<Measurement of fusion rate>
First, a cutting line having a depth of 1 mm is formed on an arbitrary surface of the foamed molded body using a cutter knife, and the foamed molded body is divided into two by a hand or a hammer along the cutting line. Thereafter, in any 100 to 150 expanded particles exposed on the fracture surface of the expanded molded body, the number of particles (a) broken in the expanded particles and the thermal fusion interface between the expanded particles was broken. The number (b) of particles present was counted, and the fusion rate of the foamed molded product was calculated based on the following formula.
Fusion rate of foamed molded product (%) = 100 × number of particles (a) / (number of particles (a) + number of particles (b))
The evaluation criteria for this fusion rate were as follows: Good: When the fusion rate is 70% or more Poor: When the fusion rate is less than 70%

<Comprehensive judgment>
Based on the three evaluation results of <Evaluation of mold filling property>, <Appearance evaluation of foamed molded article>, and <Measurement of fusion rate>, a comprehensive determination was made in light of the following criteria.
Good (O): When there is no defect (x) in the three evaluation results Defect (x): When there are one or more defects (x) in the three evaluation results

[Example 2]
The same procedure as in Example 1 was performed except that the amount of pentane added was 5 parts by mass and the water temperature was 50 ° C. The obtained pre-expanded particles were almost spherical without deformation, beard, etc., with a bulk density of 0.2 g / cm ³ , a bulk expansion factor of 5.1 times, and an average particle size of about 1.9 mm. there were. The results are shown in Table 1.

[Example 3]
Example 1 except that a die having a small hole with a diameter of 0.5 mm and a land length of 2.5 mm was used, the amount of pentane added was 7 parts by mass, and the water temperature was 50 ° C. Went to. The obtained pre-expanded particles are almost spherical without deformation, whiskers, etc., have a bulk density of 0.03 g / cm ³ , a bulk expansion ratio of 33.7 times, and an average particle diameter of about 3.2 mm. there were. The results are shown in Table 1.

[Comparative Example 1]
The same procedure as in Example 1 was conducted except that the amount of pentane added was 5 parts by mass, the water temperature was 85 ° C., and the rod-shaped foam was extruded into the cutting chamber and cut after foaming. The obtained pre-expanded particles have a cylindrical shape, the bulk density is 0.04 g / cm ³ , the bulk foaming factor is 27.3 times, the diameter of the cylinder is about 2.5 mm, and the height of the cylinder is about 1.7 mm. there were. The results are shown in Table 1.

  From the results in Table 1, the pre-expanded particles obtained in Examples 1 to 3 according to the present invention had a spherical particle shape and good mold filling properties. Moreover, the external appearance of the foam molded body obtained in Examples 1 to 3 was good, the fusion rate of the foamed particles was high, and a high quality foam molded body was obtained.

  On the other hand, in Comparative Example 1, since the molten resin extruded into water was cut after being in a foamed state, the shape of the obtained pre-expanded particles became a columnar shape. The pre-expanded particles of Comparative Example 1 had poor mold filling properties, and the appearance and fusion rate of the obtained foamed molded product were poor.

The present invention relates to thermoplastic resin pre-foamed particles used for the production of a thermoplastic resin foam molded article such as a polystyrene resin foam molded article and a method for producing the same, and more specifically, a molten foaming agent-containing thermoplastic resin is used as a die. In the manufacturing process of foamable thermoplastic resin particles by the so-called melt extrusion method, which is extruded through a small hole into a cooling medium such as water and then cut to produce resin particles, the cut resin particles are foamed in the cooling medium. The present invention relates to a technique for directly producing thermoplastic resin pre-expanded particles used for producing a foamed molded product.
According to the present invention, since the thermoplastic resin pre-expanded particles used for the production of the foamed molded product can be directly produced by the melt extrusion method, the conventional method obtains the expandable resin particles and heats them to obtain the pre-expanded particles. Compared with the method, there are advantages that a foamed molded product can be produced with fewer steps, the production efficiency of the foamed molded product becomes higher, and the storage space for the expandable resin particles can be reduced. The thermoplastic resin pre-expanded particles obtained by the method of the present invention are spherical or substantially spherical, and have better filling properties in the mold cavity than the column-shaped pre-expanded particles, and the cavity is filled without any gaps. In addition, the foamed particles are well fused at the time of in-mold foam molding, and a foam molded article having excellent strength can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Extruder (resin supply apparatus), 2 ... Die, 3 ... Raw material supply hopper, 4 ... High pressure pump, 5 ... Foam supply port, 6 ... Cutter, 7 ... Cutting chamber, 8 ... Water tank, 9 ... High pressure pump, 10: Dehydration dryer with solid-liquid separation function, 11: Storage container.

Claims (5)

Using a manufacturing apparatus comprising a resin supply device, a die provided at the tip of the resin supply device, and a cutting chamber to which the cooling medium is supplied so that the cooling medium contacts the discharge surface of the die, a thermoplastic resin and a blowing agent were melted and kneaded in the resin supply device, extruded while cutting the molten foaming agent-containing thermoplastic resin in the cooling medium of the cutting chamber through the small holes of the die, during the cooling medium Of the thermoplastic resin pre-expanded particles to obtain a thermoplastic resin pre-expanded particle having a bulk expansion ratio of 1.6 to 50 times , and then separating the expanded particle from the cooling medium to obtain a thermoplastic resin pre-expanded particle. A manufacturing method comprising:
The said cooling medium is 40-80 degreeC, and is the manufacturing method of the thermoplastic resin pre-expanded particle pressurized to 1.7 Mpa or less and supplied to the said cutting chamber . The said foaming agent containing thermoplastic resin is a manufacturing method of the thermoplastic resin pre-expanded particle of Claim 1 which contains 1-10 mass parts of foaming agents with respect to 100 mass parts of thermoplastic resins. The method for producing pre-expanded thermoplastic resin particles according to claim 1 or 2 , wherein the foaming agent is a mixture of one or both of isopentane and normal pentane. Method for producing a thermoplastic resin pre-expanded particles according to any one of claims 1-3 wherein the thermoplastic resin is a polystyrene resin. Obtaining a by Rinetsu thermoplastic resin pre-expanded particles to the production method of the thermoplastic resin pre-expanded particles according to any one of claims 1-4, resulting in the mold the thermoplastic resin pre-expanded particles and filled into the cavity, producing a thermoplastic resin foam molded body characterized by having a step of obtaining a thermoplastic resin foamed molded by mold foaming by heating.

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