JP5253119B2 - Method for producing thermoplastic resin expanded particles - Google Patents

Description

  The present invention relates to a method for producing thermoplastic resin expanded particles. More specifically, for example, the present invention relates to a method for producing thermoplastic resin foam particles that can be suitably used as a raw material for an in-mold foam molded article.

  Conventionally, thermoplastic resin particles are dispersed in an aqueous dispersion medium together with a foaming agent, and the temperature is raised and the resin particles are impregnated with the foaming agent at a constant pressure and constant temperature, and then released into a low-pressure atmosphere to obtain foamed particles. The method is known. Examples of the blowing agent include a method using a volatile organic blowing agent such as propane and butane (for example, Patent Document 1) and a method using an inorganic gas such as carbon dioxide, nitrogen, and air (for example, Patent Documents 2 and 3). It is disclosed.

  However, volatile organic blowing agents are substances whose global warming potential is larger than that of carbon dioxide, and volatile organic blowing agents such as propane and butane have the effect of plasticizing thermoplastic resins and are highly foamed. Although it is easy to obtain the magnification, it is difficult to control the expansion ratio and crystal state of the expanded particles due to its plasticizing action. In addition, since it is a flammable substance, it is necessary to make the equipment explosion-proof, which has the disadvantage of increasing the equipment cost.

  On the other hand, when an inorganic gas such as nitrogen or air is used, the impregnation ability into the thermoplastic resin is very low, and there is a problem that a sufficient impregnation amount for high foaming cannot be obtained even at high pressure.

  As a method for solving these drawbacks and economically producing polyolefin resin expanded particles that can be suitably used for the production of in-mold foam molded articles, a method using water used as a dispersion medium as a blowing agent has been proposed. ing.

  As a method using water as a foaming agent, crystalline polyolefin polymer particles containing 10 to 70% by weight of an inorganic filler are dispersed in water as a dispersion medium in a sealed container, and a pressure equal to or higher than the saturated vapor pressure of the dispersion and The dispersion is maintained in a high pressure region below the melting point of the crystalline polyolefin polymer particles and under a temperature condition where the crystallization of the polymer particles proceeds, and impregnated with water as a dispersion medium, There has been proposed a method for producing crystalline polyolefin polymer foamed particles by releasing the polymer (Patent Document 4). However, since the expanded particles obtained by this method contain a large amount of inorganic filler, the cell diameter tends to be fine and the open cell ratio tends to be high. Mechanical properties such as wear, surface appearance and compressive strength are not sufficient. In this way, attempts have been made to add water-absorbing minerals, water-soluble inorganic substances, etc. to the thermoplastic resin and to allow water to act as a foaming agent, but a large amount of addition is required compared to hydrophilic polymers. Also, since it itself has the function of a foam nucleating agent, it tends to be foamed particles with small bubbles, and the moldability is poor.

  In a closed container, polyolefin resin particles containing a hydrophilic polymer and an inorganic filler are dispersed in water, heated to a temperature equal to or higher than the softening temperature of the resin particles to obtain water-containing polyolefin resin particles, and then the dispersion is reduced to a low pressure region. A method for producing a polyolefin resin foamed particle by releasing it into a resin has been proposed (for example, Patent Documents 5 to 7). In this method, polyolefin-based resin expanded particles having a high expansion ratio can be obtained at a low container internal pressure while using environmentally friendly water as a foaming agent. However, the foamed particles obtained tend to be fine or non-uniform, and in-mold foam molding using the foamed particles obtained there can be obtained a molded product with no particular problems with a low-magnification molded product. However, if the molding conditions of the high expansion ratio molded product are shortened due to the recent increase in production costs, and the curing time after molding is shortened, the surface of the molded product may be wrinkled, Problems such as large dimensional shrinkage and distortion of the shape of the molded product are observed, resulting in a decrease in the commercial value of the molded product and a deterioration in the productivity of the molded product.

  Further, the polyolefin resin foam particles produced from the polyolefin resin particles containing the hydrophilic polymer and the inorganic filler are added with a hydrophilic polymer in order to use water as a foaming agent. Due to the poor dispersibility in polyolefin resins, there are also disadvantages in which the variation in the magnification of the expanded particles is likely to occur and the fusion between the particles when formed into a molded product tends to be poor.

  And the manufacturing method which obtains the polyolefin-type resin expanded particle using the ionomer resin which is a specific hydrophilic polymer using water and a carbon dioxide gas for a foaming agent is proposed (patent document 8). Attempts have been made to improve the foam uniformity of foamed particles and improve the moldability by this method, but the foam uniformity is insufficient, and the surface properties and dimensional accuracy at the time of obtaining the molded product are somewhat. Inferior, and ionomers are very expensive materials, which makes them unsuitable for industrial use.

Also disclosed is a method for producing foamed particles in which carbon dioxide gas is used as a foaming agent, polymer particles containing polypropylene glycol / polyethylene glycol polymer together with inorganic substances are foamed, and bubbles are not refined (patent) Reference 9). Since this method has low compatibility with polyolefin resin, it is easy to cause troubles such as strand breakage due to poor dispersion in the process of creating polymer particles and fluctuation of molten resin feed in the extruder. Since only a small amount could be added and water absorption was low, it was necessary to rely on foaming with carbon dioxide gas. Moreover, since the one having a large average molecular weight is used, the fusion rate between the foamed particles when formed into a molded body is easily reduced, and the heat resistance and strength are disadvantageously reduced.
Japanese Patent Publication No.56-1344 Japanese Patent Publication No. 4-64332 Japanese Examined Patent Publication No. 4-64334 Japanese Patent Publication No.49-2183 JP-A-10-298338 Japanese Patent Laid-Open No. 10-306179 JP-A-11-106576 Japanese Patent Laid-Open No. 10-152474 Japanese Patent Laid-Open No. 5-163381

  The present invention relates to a method for producing foamed thermoplastic resin particles using water as a foaming agent. An object of the present invention is to provide foamed thermoplastic resin particles that can provide an in-mold foam-molded article having good properties and surface properties and high dimensional accuracy.

  As a result of intensive studies, the present inventors have made a thermoplastic resin comprising a thermoplastic resin composition containing 0.05 to 2 parts by weight of polyethylene glycol and a foam nucleating agent with respect to 100 parts by weight of the thermoplastic resin. The inventors have found that the above problems can be solved by using particles, and have completed the present invention.

  That is, in the first aspect of the present invention, the thermoplastic resin particles are dispersed in an aqueous dispersion medium in a sealed container, heated and pressurized to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles, and then a pressure lower than the internal pressure of the sealed container. In the method for producing a thermoplastic resin foamed particle using water contained in an aqueous dispersion medium as a foaming agent to be released into the region, the thermoplastic resin particle is 0.05 part by weight of polyethylene glycol with respect to 100 parts by weight of the thermoplastic resin. The present invention relates to a method for producing foamed thermoplastic resin particles, comprising a thermoplastic resin composition comprising 2 parts by weight or less and a foam nucleating agent.

As a preferred embodiment,
(1) The thermoplastic resin is a polyolefin resin.
(2) The polyolefin resin is a polypropylene resin.
(3) The molecular weight of the polyethylene glycol is 200 or more and 9000 or less.
(4) The molecular weight of the polyethylene glycol is 200 or more and 600 or less.
(5) Carbon dioxide gas is used as a foaming agent.
The present invention relates to a method for producing the thermoplastic resin expanded particles described above.

  A second aspect of the present invention is a thermoplastic resin foam particle obtained by the above-described method for producing a thermoplastic resin foam particle, comprising 0.05% by weight or more and 2% by weight or less of polyethylene glycol, and the expansion ratio is 10 times. The present invention relates to thermoplastic resin foam particles having a crystal structure of 45 times or less, an average cell diameter of 50 μm or more and 800 μm or less, and having two or more melting points in measurement by differential scanning calorimetry.

  A third aspect of the present invention relates to an in-mold foam-molded product obtained by foam-molding the above-mentioned thermoplastic resin foam particles.

  According to the present invention, it is possible to obtain thermoplastic resin foam particles in which the foamed particles are less likely to be non-uniform and finer than those in the method for producing thermoplastic resin foam particles using water as a foaming agent. Further, when in-mold foam molding is performed using the thermoplastic resin foam particles obtained by the production method of the present invention, the in-mold foam molded article has good fusion property, good surface properties, and high dimensional accuracy. Is obtained. In particular, after the thermoplastic resin foam particles of the present invention are doubled by two-stage foaming, when molding an in-mold foam molded article, it is better in-mold foam molding than when conventional water is used as a foaming agent. It is possible to get a body.

  The method for producing the thermoplastic resin foamed particles of the present invention is obtained by dispersing thermoplastic resin particles in an aqueous dispersion medium in an airtight container, pressurizing and heating the thermoplastic resin particles to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles. The water contained in is discharged into a pressure region lower than the internal pressure of the sealed container as a foaming agent, and the thermoplastic resin particles are 0.05 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin. A thermoplastic resin composition comprising a polyethylene glycol and a foam nucleating agent.

  The polyethylene glycol used in the present invention is a nonionic water-soluble polymer having a structure in which ethylene glycol is polymerized, and has a molecular weight of approximately 50,000 or less. The polyethylene glycol used in the present invention preferably has an average molecular weight of 200 or more and 9000 or less, more preferably 200 or more and 600 or less. In general, glycols are slightly inferior in compatibility with thermoplastic resins, but if polyethylene glycol has an average molecular weight of 200 or more and 9000 or less, the thermoplastic resin and polyethylene glycol are kneaded with an extruder and strand cut. Even in the process of producing thermoplastic resin particles by the method, since the dispersion is relatively good, troubles such as occurrence of strand breakage and unstable feeding of molten resin tend to be small. Further, expanded thermoplastic resin particles having uniform bubbles and small variation in magnification can be obtained. An in-mold foam molded article obtained by in-mold foam molding using the thermoplastic resin foam particles has a high fusion rate, a beautiful surface, and a small dimensional shrinkage rate.

  In addition, polyethylene glycol having different molecular weights can be used in combination. However, a polypropylene glycol / polyethylene glycol polymer, which is a similar substance to glycols, is limited to addition in a very small amount because of its poor dispersibility in thermoplastic resins, and is not suitable for combined use because of its low water absorption. Further, when polyethylene glycol having an average molecular weight of 200 or more and 600 or less and having a small average molecular weight is selected, the carbon dioxide gas impregnation property, which is preferable when used in combination with water, is increased, and thus it is easy to obtain thermoplastic resin expanded particles having a high expansion ratio It is in. Moreover, although the crosslinked polyalkylene oxide is commercially available and available, when it is attempted to obtain the water content, a large amount of addition is necessary and the cost is very high because it is an expensive substance.

  Here, the average molecular weight of polyethylene glycol can be measured, for example, using a liquid chromatograph mass spectrometer such as LCQ Advantage manufactured by Thermo Fisher Scientific.

  The amount of polyethylene glycol added is 0.05 to 2 parts by weight, preferably 0.05 to 1 part by weight, more preferably 0.1 parts by weight, relative to 100 parts by weight of the thermoplastic resin. The amount is 0.5 parts by weight or less. However, the smaller the average molecular weight of polyethylene glycol, the higher the water content tends to be, and the higher the average molecular weight, the more the added amount tends to increase when trying to obtain an equivalent water content. The molecular weight and addition amount of polyethylene glycol used can be selected in balance with a desired expansion ratio, desired moisture content and physical properties. Here, the addition amount of polyethylene glycol refers to the weight of polyethylene glycol that has not absorbed water.

  When the addition amount of polyethylene glycol is less than 0.05 parts by weight, the expansion ratio of the thermoplastic resin expanded particles cannot be improved, or the effect of uniforming the bubbles is reduced. When the addition amount exceeds 2 parts by weight, shrinkage of the thermoplastic resin expanded particles is likely to occur, or dispersion of polyethylene glycol in the thermoplastic resin becomes insufficient.

  Polyethylene glycol is a substance having extremely low toxicity, and the thermoplastic resin foamed particles of the present invention can be used as a raw material for an in-mold foam molded article used for an application having contact with food.

  To include polyethylene glycol in the thermoplastic resin, for example, a pellet-shaped thermoplastic resin pre-blended with polyethylene glycol is melt-kneaded with an extruder, extruded from a die, cooled, and then chopped with a cutter By doing so, the particle shape can be obtained. Alternatively, polyethylene glycol may be added in a liquid state to the molten thermoplastic resin in the middle of the extruder and kneaded. When the liquid is added, polyethylene glycol having a molecular weight of 1000 or more and 3000 or less is waxy at room temperature, so it is preferable to add after heating and melting. Further, when the molecular weight is 4000 or less, it is desirable to lower the temperature of the cylinder and the die part of the extruder to 250 ° C. or less in order to reduce the transpiration of polyethylene glycol. If the average molecular weight is greater than 4000, a masterbatch with a thermoplastic resin may be prepared in advance and then melt-kneaded with the thermoplastic resin. Further, polyethylene glycol may be quantitatively supplied in a liquid state in a hopper portion where the thermoplastic resin is charged into the extruder.

  The foam nucleating agent used in the present invention refers to a substance that promotes the formation of cell nuclei during foaming. For example, talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide , Inorganic materials such as zeolite, fatty acid metal salts such as calcium stearate and barium stearate, high melting point organic materials such as melamine and melamine cyanurate, zinc borate, barium metaborate, calcium borate, Examples thereof include metal borate salts such as aluminum borate. These foam nucleating agents may be used alone or in combination of two or more. Among these, talc and calcium carbonate are preferable, and when using talc that is inexpensive and familiar with polyethylene glycol, the dispersibility of polyethylene glycol in the thermoplastic resin is improved, and a thermoplastic resin foam having uniform bubbles is obtained. It is preferable because particles are easily obtained.

  The amount of the foam nucleating agent varies depending on the foam nucleating agent to be used and cannot be generally determined, but is preferably 0.005 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin. More preferably, the content is 0.01 parts by weight or more and 1 part by weight or less. For example, when talc is used as the foam nucleating agent, the amount is preferably 0.005 parts by weight or more and 1 part by weight or less, more preferably 0.01 parts by weight or more and 0.001 part by weight or less with respect to 100 parts by weight of the thermoplastic resin. 5 parts by weight or less, more preferably 0.02 parts by weight or more and 0.2 parts by weight or less.

  When the addition amount of the foam nucleating agent is less than 0.005 parts by weight, the foaming ratio of the thermoplastic resin foam particles may not be increased or the uniformity of the bubbles may be deteriorated. When the amount of the foam nucleating agent added is more than 2 parts by weight, the average cell diameter of the thermoplastic resin expanded particles tends to be too small, and the in-mold foam moldability tends to be poor.

  Various additives such as a compatibilizing agent, an antistatic agent, a colorant, a stabilizer, a weathering agent, a flame retardant, and a copper damage preventing agent can be appropriately added to such an extent that the effects of the present invention are not impaired.

  The foaming nucleating agent and the additive that is added as necessary can be added when the thermoplastic resin is melt-kneaded, as in the method of adding polyethylene glycol.

  Examples of the thermoplastic resin used in the present invention include polyolefin resins, polystyrene resins, polymethyl methacrylate resins, polyester resins, polylactic acid resins, maleimide copolymer resins, and the like. Among these, polyolefin resins such as polypropylene and polyethylene are preferable.

  Examples of the polyethylene resin include high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene. These may be used alone or in combination of two or more.

  Examples of the polypropylene resin include a propylene homopolymer, an α-olefin-propylene random copolymer, an α-olefin-propylene block copolymer, and the like. These may be used alone or in combination of two or more. In particular, ethylene-propylene random copolymer, ethylene-propylene-butene-1 random copolymer, and propylene-butene-1 random copolymer can be used suitably because the foaming ratio can be easily controlled from low foaming to high foaming. Can do.

  The melting point of the polypropylene resin that can be used in the present invention is preferably 130 ° C. or higher and 165 ° C. or lower, and more preferably 135 ° C. or higher and 155 ° C. or lower. When the melting point is less than 130 ° C., heat resistance and mechanical strength tend to be insufficient. Moreover, when melting | fusing point exceeds 165 degreeC, there exists a tendency for it to become difficult to ensure the melt | fusion at the time of in-mold foam molding. Here, the melting point refers to a temperature of 10 to 10 mg of polypropylene-based resin raised from 40 ° C. to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter, and then cooled to 40 ° C. at a rate of 10 ° C./min. The peak temperature of the endothermic peak in the DSC curve obtained when the temperature is increased again to 220 ° C. at a rate of 10 ° C./min.

  The melt index (hereinafter referred to as MI value) of the polypropylene resin that can be used in the present invention is preferably 0.5 g / 10 min or more and 30 g / 10 min or less, and more preferably 2 g / 10 min or more and 20 g / 10 min. The following are preferred.

  When the MI value is less than 0.5 g / 10 minutes, it is difficult to obtain thermoplastic resin expanded particles having a high expansion ratio. When the MI value exceeds 30 g / 10 minutes, the bubbles of the thermoplastic resin expanded particles are likely to break, and the thermoplasticity The open cell ratio of the resin foam particles tends to increase. In the present invention, the MI value is a value measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  Among polyolefin-based resins, it is more preferable to use a polypropylene-based resin because it is easy to obtain thermoplastic resin expanded particles having a high expansion ratio even when water is used as a foaming agent.

  The thermoplastic resin particles containing 0.05 part by weight or more and 2 parts by weight or less of polyethylene glycol and 100 parts by weight of the thermoplastic resin and containing the foam nucleating agent are dispersed in an aqueous dispersion medium in a sealed container, and the thermoplastic resin In the method of producing thermoplastic resin foam particles by heating and pressurizing to a temperature higher than the softening temperature and then releasing into a pressure range lower than the internal pressure of the sealed container, the water contained in the aqueous dispersion medium becomes the foaming agent, and the low pressure Nitrogen or air is press-fitted before being discharged into the region, thereby increasing the internal pressure in the sealed container, adjusting the pressure release speed during foaming, and adjusting the foaming ratio and the average cell diameter. When a gaseous physical foaming agent such as carbon dioxide gas is used at room temperature, the physical foaming agent such as carbon dioxide gas may be introduced into the container after the thermoplastic resin particles and the aqueous dispersion medium are introduced into the sealed container.

  Water is preferable as the aqueous dispersion medium. A dispersion medium in which methanol, ethanol, ethylene glycol, glycerin, or the like is added to water can also be used as the aqueous dispersion medium.

  In the present invention, water is used as the foaming agent. In the present invention, “use water as a blowing agent” can be determined by measuring the moisture content described later. As another method, it is also possible to measure the expanded particles immediately after expansion with a polymer moisture meter or a Karl Fischer moisture meter.

  If water is used as a foaming agent, other physical foaming agents may be used in combination. Examples of other physical foaming agents include saturated hydrocarbons such as propane, butane and pentane, ethers such as dimethyl ether, alcohols such as methanol and ethanol, and inorganic gases such as air, nitrogen and carbon dioxide. Among them, it is desirable to use carbon dioxide gas in combination because it has a particularly low environmental load and no danger of combustion. By using water and carbon dioxide gas in combination, it is easy to increase the foaming power, so even when obtaining a high expansion ratio, the amount of foam nucleating agent added can be reduced, resulting in expanded particles having a large average cell diameter. And secondary foamability tends to be good.

  Specifically, for example, the following procedure can be used.

  After charging thermoplastic resin particles, water-based dispersion medium, and dispersing agent, if necessary, in a sealed container, the inside of the sealed container is evacuated and then 1 MPa (gauge pressure) to 2 MPa (gauge pressure). About carbon dioxide gas is introduced and heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin. By heating, the pressure in the sealed container rises to about 1.5 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure). Carbon dioxide gas is further added near the foaming temperature to adjust to a desired foaming pressure, and further the temperature is adjusted, and then released into a pressure range lower than the internal pressure of the sealed container to obtain thermoplastic resin foam particles.

  Alternatively, after preparing thermoplastic resin particles, an aqueous dispersion medium, and a dispersant as required in a sealed container, the inside of the sealed container is evacuated as necessary, and then heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin. Carbon dioxide gas may be introduced while being introduced.

  In addition, after preparing thermoplastic resin particles, an aqueous dispersion medium, and a dispersant as necessary in a sealed container, heating to near the foaming temperature, introducing air, nitrogen, etc., and then setting the foaming temperature, the sealed container The foamed thermoplastic resin particles are obtained by discharging into a pressure range lower than the internal pressure.

  There is no restriction | limiting in particular in the expansion ratio of the expanded particle obtained by the manufacturing method of this invention, Although the manufacture of the expanded particle exceeding 1 time and less than 10 times is also possible, 10 times or more are more preferable. The upper limit of the expansion ratio is preferably 45 times or less, more preferably 20 times or less, and most preferably 17 times or less.

  In the present invention, the foamed thermoplastic resin particles obtained by the above-described method are pressurized with an inorganic gas such as air in a pressure-resistant container, and after applying an internal pressure, further foaming is performed by heating, and further higher magnification. May be used.

  In the present invention, the thermoplastic resin particles are dispersed in an aqueous dispersion medium in a sealed container, impregnated with a foaming agent at high temperature and high pressure, and released into a pressure range lower than the internal pressure of the sealed container for foaming. This is referred to as “single-stage foaming”, and the foamed particles obtained by single-stage foaming may be referred to as “single-stage foamed particles”.

  Furthermore, pressurizing the first-stage foamed particles with an inorganic gas such as air in a pressure-resistant container, applying internal pressure, and then further foaming by heating is called “two-stage foaming” and is obtained by two-stage foaming. The obtained expanded particles may be referred to as “two-stage expanded particles”.

  In the present invention, when obtaining thermoplastic resin expanded particles having an expansion ratio of 20 times or more, the first-stage expanded particles obtained by the first-stage expansion can be further expanded in two stages.

  If the expansion ratio is less than 10 times, the advantages of weight reduction cannot be obtained, and the flexibility and buffering properties of the obtained in-mold foam molded product tend to be insufficient. There is a tendency that the dimensional accuracy, mechanical strength, heat resistance and the like of the in-mold foam-molded product are insufficient.

In the present invention, the expansion ratio of the foamed thermoplastic resin particles means that after measuring the weight w (g) of the foamed thermoplastic resin particles, the volume v (cm ³ ) is measured by a submerging method, and the foamed thermoplastic resin particles The true specific gravity ρb = w / v is obtained and is a ratio with the density ρr of the thermoplastic resin particles before foaming.

  The average cell diameter of the thermoplastic resin expanded particles of the present invention is preferably 50 μm or more and 800 μm or less, more preferably 100 μm or more and 600 μm or less, and further preferably 200 μm or more and 500 μm or less. When the average cell diameter is less than 50 μm, there are cases where the shape of the obtained in-mold foam molded product is distorted and the surface is wrinkled. When the average cell diameter exceeds 800 μm, the buffer properties of the in-mold foam molded product to be obtained May decrease.

  The average cell diameter is measured according to the theory of ASTM D3576 with respect to the cut surface of the thermoplastic resin foamed particles, except for the surface layer portion.

  The open cell ratio of the thermoplastic resin expanded particles of the present invention is preferably 0% or more and 12% or less, more preferably 0% or more and 8% or less, and further preferably 0% or more and 5% or less. When the open cell ratio exceeds 12%, when used for in-mold foam molding, the foamed particles are inferior in foaming property during steam heating in the mold, and the obtained in-mold foam molded product tends to shrink. It is in.

  The moisture content of the thermoplastic resin expanded particles of the present invention is preferably 0.7% or more and 10% or less, more preferably 1% or more and 8% or less, and further preferably 1% or more and 5% or less. When the moisture content is less than 0.7%, only low foaming ratio may be obtained. When the moisture content exceeds 10%, the foamed particles are easily shrunk because the foamed particles have a low internal pressure after foaming. Shrinkage may remain even after oven curing after foaming.

  The thermoplastic resin expanded particles of the present invention preferably have two melting peaks in a DSC curve obtained by differential scanning calorimetry. In the case of thermoplastic resin foam particles having two melting peaks, in-mold foam moldability is good, and there is a tendency to obtain an in-mold foam molded article having good mechanical strength and heat resistance.

  Here, the DSC curve obtained by differential scanning calorimetry of the thermoplastic resin foam particles is 40 ° C. to 220 ° C. at a temperature rising rate of 10 ° C./min with a differential scanning calorimeter of 1 mg to 10 mg of the thermoplastic resin foam particles. DSC curve obtained when the temperature is raised to.

  As described above, the foamed thermoplastic resin particles having two melting peaks can be easily obtained by setting the temperature in the closed container at the time of foaming to an appropriate value. When the thermoplastic resin is a polyolefin-based resin, the softening temperature of the polyolefin-based resin particles impregnated with the foaming agent is usually at least the melting point of the polyolefin-based resin that is the base material, preferably the melting point + 3 ° C. or more, preferably less than the melting end temperature. Is selected from a melting end temperature of −2 ° C. or lower.

  Here, the melting end temperature is a temperature of 10 to 10 mg of polyolefin resin from 40 ° C. to 220 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter, and then a rate of 10 ° C./min to 40 ° C. This is the temperature at which the bottom of the melting peak of the DSC curve obtained when the temperature is cooled again to 220 ° C. at a rate of 10 ° C./min returns to the baseline position on the high temperature side.

  The foamed thermoplastic resin particles obtained as described above can be formed into an in-mold foam molded body by a conventionally known in-mold foam molding. For example, a) The thermoplastic resin expanded particles are pressurized with an inorganic gas, such as air or nitrogen, impregnated with the inorganic gas in the pre-expanded particles to give a predetermined internal pressure of the pre-expanded particles, and then filled into the mold. B) Method of heat-sealing with steam, b) Method of compressing foamed thermoplastic resin particles with gas pressure, filling the mold, and heat-sealing with water vapor using the recovery power of the pre-foamed particles, c) In particular, a method such as a method of filling thermoplastic resin foam particles in a mold without heat treatment and heat-sealing with water vapor can be used.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to such examples. In addition, evaluation in Examples and Comparative Examples was performed by the following method.

(Foaming ratio)
After taking 3 g or more and 10 g or less of the expanded particles and drying at 60 ° C. for 6 hours, and measuring the weight w (g), the volume v (cm ³ ) is measured by the submersion method, and the true specific gravity of the expanded particles ρb = w / v was determined, and the expansion ratio K = ρr / ρb was determined from the ratio to the density ρr of the thermoplastic resin particles before foaming.

(Open cell rate)
Using an air comparative hydrometer (manufactured by Tokyo Science Co., Ltd., model 1000), the closed cell volume of the obtained foamed particles was obtained, and this was obtained by dividing this by the apparent volume obtained separately by the submerged method. The bubble rate (%) was determined by subtracting from 100.

(Bubble uniformity, average bubble diameter)
With careful attention not to break the cell membrane, the foamed particles are cut almost at the center, the cut surface is magnified with a microscope, and the portion (A) excluding the surface layer portion having a length of 5% of the diameter of the foamed particles, When a certain arbitrary direction is an x direction and a direction orthogonal to the x direction is a y direction, the ferret diameters of the cells in the x and y directions are measured as dx and dy, respectively, and one cell diameter di is obtained. This is measured for 40 or more cells adjacent to each other so that there is no deviation in the radial direction within the portion (A). Then, the standard deviation (σ) of the cell diameter variation, the average bubble diameter d, and the bubble uniformity u in one expanded particle were calculated. This was performed for three or more foamed particles, and the average of the foamed particles was defined as U to evaluate the uniformity of the bubbles.

di = (dx + dy) / (2 × 0.785)
d = Σ (di) / n
u = σ / d × 100
◎: U is 30 or less ○: U exceeds 30 and 35 or less ×: U is more than 35

(Moisture content)
Even when other foaming agents are used in combination, the foamed particles immediately after foaming at the same foaming temperature and foaming pressure using only water as the foaming agent are used. After the dehydration, the weight (W1) is measured, the weight (W2) when the foamed particles are dried in an oven at 80 ° C. for 12 hours is measured and calculated by the following formula. used.
Moisture content (%) = (W1-W2) / W2 × 100

(Two-stage foaming)
The foamed particles obtained by the two-stage foaming were visually observed and evaluated as follows.
○: No stick (with multiple foam particles attached) △: A small amount of stick is generated ×: High vapor pressure is required and many sticks are generated

(In-mold foam moldability)
In the molding evaluation, a mold having a molded body design outer dimension of 400 mm × 300 mm × 20 mm was used.

(In-mold foam molding fusion rate)
A crack with a depth of about 5 mm is made with a knife on the surface of the in-mold foam molded body, and then the molded body is divided along the crack, the fracture surface is observed, and the ratio of the number of fractured particles to the total number of particles on the fracture surface Was determined as the in-mold foam molding fusion rate.

(Surface properties of molded products)
After molding, the mixture was allowed to stand at 23 ° C. for 2 hours, then cured at 65 ° C. for 6 hours, and then allowed to stand in a room at 23 ° C. for 4 hours. .
◎: Wrinkles, less intergranular, beautiful ○: Slight wrinkles, intergranular but good x: Wrinkles, sink marks and poor appearance

(Dimension shrinkage of molded product)
After molding, it is allowed to stand at 23 ° C. for 2 hours, then cured at 65 ° C. for 6 hours, and then measured for the longitudinal dimension of the in-mold foam molded product obtained by leaving it in a room at 23 ° C. for 4 hours. The ratio of the difference between the mold dimension and the dimension of the in-mold foam molded body with respect to the mold dimension was defined as the mold dimension shrinkage rate, and was evaluated according to the following criteria.
◎: Dimensional shrinkage ratio against mold is 4% or less ○: Dimensional shrinkage ratio against mold exceeds 4% and 7% or less ×: Dimensional shrinkage ratio against mold is larger than 7%

Example 1
Polyethylene glycol (average molecular weight 300, manufactured by Lion Corporation) with respect to 100 parts by weight of polypropylene resin (propylene-ethylene random copolymer: ethylene content 3.0%, MI = 6 g / 10 min, melting point 143 ° C.) Next, 0.5 parts by weight of talc (manufactured by Hayashi Kasei Co., Ltd., Talcan Powder PK-S) was added and blended as a foam nucleating agent. After supplying to a 50φ single-screw extruder and melt-kneading, it was extruded from a cylindrical die having a diameter of 1.8 mm, cooled with water, and cut with a cutter to obtain cylindrical polyolefin resin particles (1.2 mg / particle).

  100 parts by weight of the obtained polyolefin-based resin particles were put into a pressure-resistant sealed container together with 200 parts by weight of pure water, 1.0 part by weight of tricalcium phosphate and 0.05 part by weight of sodium dodecylbenzenesulfonate, and then deaerated. While stirring, 6 parts by weight of carbon dioxide gas was placed in a sealed container and heated to 148 ° C. The pressure at this time was 3 MPa (gauge pressure). Immediately after opening the valve at the bottom of the sealed container, the aqueous dispersion (resin particles and aqueous dispersion medium) was discharged under atmospheric pressure through an orifice having a diameter of 4 mm to obtain expanded particles (single-stage expanded particles). At this time, during discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The obtained first-stage expanded particles showed two melting points at 138 ° C. and 157 ° C. in differential scanning calorimetry, and the expansion ratio, the open cell ratio, and the average cell diameter were measured. As a result, the expansion ratio was 19 times and the open cell ratio was 0. .6%, excellent bubble uniformity, and average bubble diameter of 340 μm. The water content was 3.3% when measured by foaming with water at 148 ° C., the same as above, in the sealed container.

  The single-stage expanded particles obtained here were dried at 60 ° C. for 6 hours and then impregnated with pressurized air in a pressure-resistant container to adjust the internal pressure to about 0.4 MPa (absolute pressure). Two-stage foaming was performed by contacting with steam of 08 MPa (gauge pressure) to obtain two-stage foamed particles having a foaming ratio of 30 times. The two-stage expanded particles showed two melting points in differential scanning calorimetry, and had excellent bubble uniformity with an open cell ratio of 1.3% and an average cell diameter of 435 μm. As a result of observing the surface of the two-stage expanded foam particles with an electron microscope, it was found that the foam diameter of the surface portion was uniform, the surface was not rough, and the thickness of the foam particle surface film was small. . Next, the two-stage foamed particles were again pressurized with air in a pressure-resistant container to obtain an air pressure of about 0.19 MPa (absolute pressure), and in-mold foam molding was performed. The surface of the obtained in-mold foam molded article has excellent smoothness, no wrinkles, small dimensional shrinkage of the in-mold foam molded article, little distortion of the in-mold foam molded article, and excellent fusion of particles. It was a beautiful in-mold foam molding.

（実施例２）
添加剤のポリエチレングリコール（平均分子量３００）を０．２重量部、タルクを０．１重量部とした他は実施例１と同様に発泡、二段発泡、型内発泡成形した。一段発泡粒子は２つの融点を示し、発泡倍率１５倍、連泡率０．７％、気泡の均一性に優れ、平均気泡径２７０μｍであった。含水率は２．０％であった。次に、実施例１と同様に発泡倍率３０倍の二段発泡粒子を得た。二段発泡粒子は、示差走査熱量計測定において２つの融点を示し、連泡率０．８％、平均気泡径３７５μｍで気泡の均一性に優れていた。型内発泡成形評価の結果、得られた型内発泡成形体の表面は平滑性に優れ、しわの発生も無く、型内発泡成形体の寸法収縮が小さく、型内発泡成形体の歪が少なく、粒子どうしの融着に優れ、美麗な型内発泡成形体であった。

(Example 2)
Foaming, two-stage foaming, and in-mold foaming were carried out in the same manner as in Example 1 except that the additive polyethylene glycol (average molecular weight 300) was 0.2 parts by weight and talc was 0.1 parts by weight. The first-stage expanded particles exhibited two melting points, the expansion ratio was 15 times, the open cell ratio was 0.7%, the cell uniformity was excellent, and the average cell diameter was 270 μm. The water content was 2.0%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in differential scanning calorimetry, and had excellent bubble uniformity with an open cell ratio of 0.8% and an average cell diameter of 375 μm. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molded article with excellent fusion between particles.

(Example 3)
Foaming, two-stage foaming, and in-mold foaming were performed in the same manner as in Example 1 except that the additive polyethylene glycol (average molecular weight 300) was 0.1 parts by weight. The single-stage expanded particles obtained by the single-stage expansion exhibited two melting points, an expansion ratio of 11 times, a continuous bubble ratio of 0.7%, excellent bubble uniformity, and an average cell diameter of 275 μm. The water content was 1.3%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in differential scanning calorimetry, and had excellent bubble uniformity with an open cell ratio of 0.8% and an average cell diameter of 420 μm. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molded article with excellent fusion between particles.

Example 4
Foaming, two-stage foaming, and in-mold foam molding were performed in the same manner as in Example 1 except that the additive polyethylene glycol (average molecular weight 6000) was 1.0 part by weight and talc was 0.1 part by weight. The first-stage expanded particles obtained by the first-stage expansion showed two melting points, the expansion ratio was 12 times, the open cell ratio was 1.3%, and the average cell diameter was 260 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The water content was 2.2%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement and had excellent bubble uniformity with an open cell ratio of 2.0% and an average cell diameter of 390 μm. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molding. In the fusion of the particles, a slightly unfused portion was observed as compared with Examples 1 to 3.

(Example 5)
Foaming, two-stage foaming, and in-mold foaming were carried out in the same manner as in Example 1 except that 0.05 part by weight of polyethylene glycol (average molecular weight 300) and 3 parts by weight of carbon dioxide gas were added. The single-stage expanded particles obtained by single-stage expansion exhibited two melting points, the expansion ratio was 6 times, the open cell ratio was 0.7%, and the average cell diameter d was 200 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The water content was 0.7%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement. The open cell ratio was 0.8%, the average bubble diameter d was 330 μm, and the bubble uniformity was good. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molded article with excellent fusion between particles.

(Example 6)
The additive polyethylene glycol (average molecular weight 300) was 0.5 parts by weight and talc 0.1 parts by weight. Carbon dioxide gas as a blowing agent was not used, nitrogen gas was introduced, and the mixture was heated to 151 ° C. Others were evaluated in the same manner as in Example 1, one-stage foaming, two-stage foaming, and in-mold foam molding. The internal pressure of the one-stage foamed sealed container was 3.0 MPa (gauge pressure). The expanded particles obtained by the single-stage expansion had two melting points, the expansion ratio was 12 times, the open cell ratio was 1.1%, and the average cell diameter was 235 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The water content was 3.3%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, and had excellent bubble uniformity with an open cell ratio of 2.3% and an average cell diameter of 355 μm. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molded article with excellent fusion between particles.

(Example 7)
One-stage foaming, two-stage foaming, and in-mold foam molding were evaluated in the same manner as in Example 6 except that the additive polyethylene glycol (average molecular weight 600) was 0.5 parts by weight. The internal pressure of the one-stage foamed sealed container was 3.0 MPa (gauge pressure). The expanded particles obtained by the single-stage expansion had two melting points, the expansion ratio was 10 times, the open cell ratio was 1.2%, and the average cell diameter was 225 μm. The uniformity of the bubbles was almost uniform, although somewhat inferior to Examples 1-3. The water content was 3.0%. Next, two-stage expanded particles having an expansion ratio of 30 times were obtained in the same manner as in Example 1. The two-stage expanded particles showed two melting points in differential scanning calorimetry, and had excellent bubble uniformity with an open cell ratio of 2.5% and an average cell diameter of 345 μm. In-mold foam molding. As a result of in-mold foam molding evaluation, the surface of the obtained in-mold foam molded article is excellent in smoothness, no wrinkles are generated, dimensional shrinkage of the in-mold foam molded article is small, and distortion of the in-mold foam molded article is small. It was a beautiful in-mold foam molded article with excellent fusion between particles.

(Example 8)
0.5 parts by weight of polyethylene glycol (average molecular weight 300, manufactured by Lion Corporation) is pre-blended with 100 parts by weight of a linear low-density polyethylene resin (MI = 1.9 g / 10 min, melting point 122 ° C.). Next, 0.1 part by weight of talc (manufactured by Hayashi Kasei Co., Ltd., Talcan Powder PK-S) was added and blended as a foam nucleating agent. After feeding to a 50φ single screw extruder, melt kneading, extrusion from a cylindrical die having a diameter of 1.8 mm, water cooling, cutting with a cutter, and cylindrical linear low density polyethylene resin particles (1.2 mg / particle) )

  After 100 parts by weight of the obtained linear low density polyethylene resin particles were put into a pressure-resistant sealed container together with 200 parts by weight of pure water, 1.0 part by weight of tricalcium phosphate and 0.05 part by weight of sodium dodecylbenzenesulfonate, While deaerated, 12 parts by weight of carbon dioxide gas was placed in a sealed container while stirring and heated to 123 ° C. The pressure in the pressure-resistant airtight container at this time was 4.5 MPa (gauge pressure). Immediately after opening the valve at the bottom of the sealed container, the aqueous dispersion (resin particles and aqueous dispersion medium) was discharged under atmospheric pressure through an orifice having a diameter of 3.6 mm to obtain expanded particles (single-stage expanded particles). At this time, during discharge, the pressure was maintained with carbon dioxide gas so that the pressure in the container did not decrease.

  The obtained first-stage expanded particles showed two melting points at 117 ° C. and 128 ° C. in differential scanning calorimetry, and the expansion ratio, the open cell ratio, and the average cell diameter were measured. As a result, the expansion ratio was 5 times and the open cell ratio was 0. .6%, excellent bubble uniformity, and average bubble diameter d was 160 μm. The moisture content was 2.4% when measured by foaming with water at the same internal temperature of 123 ° C. as described above.

  The single-stage expanded particles obtained here were dried at 60 ° C. for 6 hours and then impregnated with pressurized air in a pressure-resistant container to adjust the internal pressure to about 0.4 MPa (absolute pressure). Two-stage foaming was performed by contacting with steam of 03 MPa (gauge pressure) to obtain two-stage foamed particles having an expansion ratio of 20 times. The two-stage expanded particles showed two melting points in the differential scanning calorimeter measurement, the open cell ratio was 1.3%, the average cell diameter d was 270 μm, and the cell uniformity was excellent. As a result of observing the surface of the two-stage expanded foam particles with an electron microscope, it was found that the foam diameter of the surface portion was uniform, the surface was not rough, and the thickness of the foam particle surface film was small. . Next, in-mold foam molding was performed using the foamed particles obtained by two-stage foaming. The surface of the obtained in-mold foam molded product had slight wrinkles and intergranularity, but it was excellent in smoothness, the dimensional shrinkage of the in-mold foam molded product was relatively small, the in-mold foam molded product had less distortion, and the particles It was a beautiful in-mold foam molded article with excellent fusion between each other.

(Comparative Example 1)
Polyethylene glycol was not used, and foaming was performed in the same manner as in Example 1 under the conditions shown in the table. Only a low expansion ratio of 6 times was obtained, and the average bubble diameter was as small as 150 μm. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which the foamed particles adhere are observed. When the two-stage foamed particles were used and subjected to in-mold foam molding, the resulting in-mold foam molded article had a large dimensional shrinkage, wrinkles were observed, and the appearance was poor.

(Comparative Example 2)
One-stage foaming, two-stage foaming, and in-mold foam molding were performed in the same manner as in Example 1 except that 1 part by weight of a crosslinked polyalkylene oxide was used instead of polyethylene glycol. The obtained in-mold foam molded article was characterized by large dimensional shrinkage and inferior fusion between particles.

(Comparative Example 3)
One-stage foaming, two-stage foaming, and in-mold foam molding were performed in the same manner as in Example 1 except that 0.5 parts by weight of sodium polyacrylate was used instead of polyethylene glycol. The bubbles of the first-stage expanded particles were inferior in uniformity because large bubbles and small bubbles were mixed. When the two-stage expanded particles were used to obtain an in-mold foam molded product, wrinkles were observed on the surface of the in-mold foam molded product, the dimensional shrinkage was large, and the fusion between the particles was inferior. It was.

(Comparative Example 4)
Single-stage foaming, two-stage foaming, and in-mold foam molding were performed in the same manner as in Example 1 except that 0.3 parts by weight of sodium carboxymethylcellulose was used as an additive instead of polyethylene glycol and talc was 0.1 parts by weight. went. The bubbles of the first-stage expanded particles were inferior in uniformity because large bubbles and small bubbles were mixed. When the two-stage expanded particles were used to obtain an in-mold foam molded product, wrinkles were observed on the surface of the in-mold foam molded product, the dimensional shrinkage was large, and the fusion between the particles was inferior. It was.

(Comparative Example 5)
One-stage foaming, two-stage foaming, and in-mold foaming were performed in the same manner as in Example 1 except that 1.0 part by weight of zeolite A type was used instead of polyethylene glycol and talc was not used. The air bubbles of the first-stage expanded particles are a mixture of coarse and small bubbles, and are inferior in uniformity. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and a slight amount of adhesion between the expanded particles was observed. When the two-stage expanded particles were used to obtain an in-mold foam molded article, wrinkles were conspicuous on the surface of the in-mold foam molded article, and the dimensional shrinkage was large.

(Comparative Example 6)
One-stage foaming, two-stage foaming, and in-mold foam molding were performed in the same manner as in Example 1 except that 0.2 parts by weight of polypropylene glycol (average molecular weight 2000) and 0.1 parts by weight of talc were used as additives. Only a low expansion ratio of 9 times was obtained, and the average bubble diameter was as small as 160 μm. In the two-stage foaming, a high vapor pressure is required to increase the expansion ratio to 30 times, and many sticks to which the foamed particles adhere are observed. When the two-stage expanded particles were used and in-mold foam molding was performed, the dimensional shrinkage ratio of the in-mold foam molded article was large, wrinkles were observed, and the appearance was inferior.

Claims (8)

  An aqueous dispersion medium in which thermoplastic resin particles are dispersed in an aqueous dispersion medium in an airtight container, heated and pressurized to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles, and then released to a pressure range lower than the internal pressure of the airtight container. In the method for producing foamed thermoplastic resin particles using water contained in the foaming agent, the thermoplastic resin particles are 0.05 parts by weight or more and 2 parts by weight or less of polyethylene glycol with respect to 100 parts by weight of the thermoplastic resin. A method for producing foamed thermoplastic resin particles, comprising a thermoplastic resin composition comprising a nucleating agent.   The method for producing foamed thermoplastic resin particles according to claim 1, wherein the thermoplastic resin is a polyolefin resin.   The method for producing expanded thermoplastic resin particles according to claim 2, wherein the polyolefin resin is a polypropylene resin.   The molecular weight of the said polyethylene glycol is 200-9000, The manufacturing method of the thermoplastic resin expanded particle as described in any one of Claims 1-3.   5. The method for producing expanded thermoplastic resin particles according to claim 1, wherein the polyethylene glycol has a molecular weight of 200 or more and 600 or less.   The method for producing foamed thermoplastic resin particles according to any one of claims 1 to 5, wherein carbon dioxide gas is used in combination as a foaming agent.   A thermoplastic resin foam particle obtained by the method for producing a thermoplastic resin foam particle according to any one of claims 1 to 6, comprising 0.05% by weight to 2% by weight of polyethylene glycol, and having a foaming ratio of Thermoplastic resin foamed particles having a crystal structure of 10 or more and 45 or less, an average cell diameter of 50 μm or more and 800 μm or less, and having two or more melting points in measurement by differential scanning calorimetry.   An in-mold foam-molded article obtained by foam-molding the thermoplastic resin foam particles according to claim 7.