TW201815922A - Method for producing thermoplastic polyurethane foamed particles - Google Patents

Abstract

A method for producing foamed particles according to the present invention is a method for producing thermoplastic polyurethane foamed particles having an apparent density of 100 to 300 kg/m3 by impregnating thermoplastic polyurethane particles dispersed in an aqueous medium inside a sealed container with a foaming agent under heat, and then discharging the thermoplastic polyurethane particles containing the foaming agent from the sealed container together with the aqueous medium to foam the particles, wherein the foaming agent is a physical foaming agent containing carbon dioxide as the main component, the thermoplastic polyurethane particles contain 300 to 2,000 ppm by mass of an inorganic powder, and the pressure inside the container during the discharge exceeds 2.5 MPa (G) but is not more than 4.0 MPa (G).

Description

Manufacturing method of thermoplastic polyurethane foamed particles

The present invention relates to a method for producing thermoplastic polyurethane (Thermoplastic Polyurethane; hereinafter sometimes referred to as TP U) expanded particles.

TPU is a thermoplastic elastomer, which exhibits characteristics close to vulcanized rubber, and has excellent wear resistance, cold resistance and resilience. In addition, it has high mechanical strength, so it is classified as an engineering elastomer, and is used in various applications such as cushioning materials, shock-proof materials, sporting goods, and automotive parts.

The foamed molded body obtained by foaming the TPU maintains the superior characteristics of TPU such as abrasion resistance and resilience, and can achieve weight reduction and softening. Therefore, it will be used in subsequent applications such as sports goods and automotive parts. Development department can be expected. However, the manufacturing method of TPU foamed particles is actually still in the process of development and has not yet been established. As a method for producing TPU foamed particles, a method described in Patent Documents 1 and 2 is known. Patent Document 1 describes a method for producing TPU expanded particles by foaming TPU particles impregnated with carbon dioxide in a supercritical state. Specifically, first, TPU particles and water were added to the reaction kettle, and then carbon dioxide was added. Then, the temperature and pressure in the reaction kettle are controlled so that the carbon dioxide assumes a supercritical state, and then the temperature in the reaction kettle is raised to 90 to 140 ° C and maintained at this temperature. Then, TPU particles impregnated with carbon dioxide in a supercritical state are discharged from the reaction kettle into a pressure-holding pressure tank, and the temperature is lowered to 70 ° C. or lower, and the first stage of foaming is performed to obtain TPU primary foamed particles. Then, a method for manufacturing TPU expanded particles by performing second-stage normal pressure foaming with respect to the TPU primary expanded particles is described.

Patent Document 2 describes a method for manufacturing TPU foamed particles. TPU particles mixed with 0.1 to 5 phr of a bubble nucleating agent are mixed with a foaming agent and water into a pressure-resistant container, and the temperature and pressure in the container are increased to 11 After maintaining at 0 to 135 ° C, 10 to 25 bar (1.0 to 2.5 MPa), the contents in the container are released into the atmosphere, thereby manufacturing the TPU particles impregnated with the foaming agent by foaming. [Prior Patent Literature] [Patent Literature]

[Patent Document 1] Chinese Patent Publication No. 104130439 [Patent Document 2] Chinese Patent Publication No. 104231592

[Problems to be Solved by the Invention] However, as in Patent Document 1, if carbon dioxide in a supercritical state is used as a foaming agent, the impregnation amount of carbon dioxide in the TPU particles becomes excessive. Therefore, when TPU foamed particles of 100 to 300 kg / m ³ are to be manufactured in one stage, the temperature during foaming needs to be greatly reduced to suppress foaming, so residual stress is easily left in the TPU foamed particles. Furthermore, since the difference between the pressure in the container during foaming and the pressure in the release environment is too large, the foaming speed of the TPU particles becomes too fast, and as a result, the TPU crystals are easily aligned in the TPU foamed particles. Therefore, in order to obtain a good molded body by performing in-mold molding of the TPU expanded particles, a problem arises in that it is necessary to raise the molding steam pressure to a relatively high level. In addition, when the pressure difference during foaming is too large, not only the foaming speed is too fast, but also the bubbles of the TPU foamed particles tend to be finer. As a result, the problem of in-mold moldability is reduced, and the obtained TPU foamed particle formed body Physical properties such as compression set. Therefore, in Reference 1, the TPU particles are foamed under a certain pressure to produce TPU foamed particles with a low expansion ratio, and then further foamed in other steps, and foamed in two stages (two stages Foam). However, such a two-stage foaming method has problems such as poor productivity, and problems such as a decrease in the uniformity of the bubbles of the TPU foamed particles.

On the other hand, as cited in Document 2, when the pressure in the pressure vessel is set to 2.5 MPa or less (gauge pressure is 2.4 MPa (G) or less) to produce TPU foamed particles, when carbon dioxide is used as the blowing agent, TPU particles The amount of carbon dioxide impregnated will be too small. Therefore, when producing TPU foam particles of 100 ~ 300kg / m ³ , it is necessary to increase the temperature during foaming to increase the expansion ratio, and use TPU raw materials with extremely small molecular weight (high melt flow rate) to increase the expansion ratio. . As a result, the TPU hydrolysis is promoted in the foaming step, and problems such as the problem that only TPU foamed particles having poor surface properties can be obtained, and the mechanical properties of the obtained TPU foamed particle molded body are reduced. Furthermore, the technique cited in Document 2 also has a problem that the bubbles of the obtained TPU foamed particles tend to become uneven.

This invention is made in order to solve the said subject, and an object is to provide the manufacturing method of the TPU foamed particle which can obtain the molded object which is excellent in mold moldability and surface property. [Means for solving problems]

That is, the present invention provides the following [1] to [9]. [1] A method for manufacturing thermoplastic polyurethane foamed particles is to impregnate a foaming agent with thermoplastic polyurethane particles dispersed in an aqueous medium in a closed container under heating, and mix the thermoplastic polyurethane particles containing the foaming agent with the aqueous medium. A method for producing foamed thermoplastic polyurethane particles having an apparent density of 100 to 300 kg / m ³ by releasing them from a closed container together to produce foam; the foaming agent is a physical foaming agent containing carbon dioxide as a main component. The thermoplastic polyurethane particles contain 300 to 2000 mass ppm of inorganic powder, and the pressure in the container at the time of discharging is more than 2.5 MPa (G) and less than 4.0 MPa (G). [2] The method for producing thermoplastic polyurethane expanded particles according to [1], wherein the inorganic powder is talc, and the 50% volume average particle diameter of the talc is 1 to 15 μm. [3] The method for producing thermoplastic polyurethane foamed particles according to [1] or [2], wherein the temperature of the aqueous medium when the foaming agent is impregnated is set to 80 ° C or higher and the melting temperature Tm of the thermoplastic polyurethane particles Under 20 ° C, the physical foaming agent is pressed into the closed container under the temperature condition, until the pressure in the closed container exceeds 2.5 MPa (G) and below 7.0 MPa (G), thereby making the physical development The foaming agent is impregnated with the thermoplastic polyurethane particles. [4] The method for producing thermoplastic polyurethane foamed particles according to any one of [1] to [3], wherein the temperature of the aqueous medium at the time of release is the melting temperature Tm-60 ° C of the thermoplastic polyurethane particles and is The melting temperature of thermoplastic polyurethane particles is below Tm-20 ° C. [5] The method for producing thermoplastic polyurethane expanded particles according to any one of [1] to [4], wherein the pressure in the container at the time of discharging is 2.6 to 3.4 MPa (G). [6] The method for producing thermoplastic polyurethane expanded particles according to any one of [1] to [5], wherein the thermoplastic polyurethane-based ether-based thermoplastic polyurethane constituting the thermoplastic polyurethane particles. [7] The method for producing thermoplastic polyurethane expanded particles according to any one of [1] to [6], wherein the thermoplastic polyurethane particles contain 300 to 950 ppm by mass of inorganic powder. [8] The method for producing thermoplastic polyurethane expanded particles according to any one of [1] to [7], wherein the melt flow rate of the thermoplastic polyurethane expanded particles at 190 ° C and a load of 10 kg is 10 to 50 g / 10 minutes . [9] The method for producing thermoplastic polyurethane foamed particles according to any one of [1] to [8], wherein the hardness of the A-type durometer of the thermoplastic polyurethane constituting the thermoplastic polyurethane particles is 90 or less. [Effect of the invention]

According to the method for producing TPU expanded particles of the present invention, expanded particles having a molded body having excellent in-mold formability and excellent surface properties can be obtained.

Hereinafter, the present invention will be described in detail based on the embodiments. In the following description, the description of "A ~ B" indicating a numerical range represents a numerical range including the endpoints A and B, "A is greater than A and B is less" (in the case of A <B) or "A is greater than B and B" ( A> B)). In addition, parts by mass and% by mass are synonymous with parts by weight and% by weight, respectively. [Thermoplastic polyurethane (TPU)] The TPU constituting the TPU foamed particles (hereinafter, simply referred to as foamed particles) produced by the present invention has a structure in which hard segments and soft segments are interactively bonded, and the hard Segmented diisocyanate and chain extender (diol compounds such as short-chain diols) are polymerized by urethane bonding. The soft segment is composed of a polymer chain containing an ether group, an ester group, and a carbonyl group. . Moreover, in the normal temperature region, the soft segment exhibits elasticity, and the hard segment generates a strong hydrogen bond as a physical crosslinking point, thereby exhibiting elasticity similar to rubber.

In the TPU, the soft segment type has a significant impact on the characteristics of the TPU. Ester-based TPU is particularly excellent in mechanical strength and heat resistance. On the other hand, ether-based TPU is particularly excellent in cold resistance, hydrolysis resistance, and antibacterial properties. Therefore, the type of TPU to be used can be appropriately selected according to the characteristics required for the TPU expanded particle molded article.

The constituent elements of the TPU are not particularly limited, and can be appropriately selected in accordance with the physical properties required for a TPU expanded particle molded body (hereinafter, also simply referred to as a foamed molded body) obtained by in-molding expanded particles. Ether-based TPU has better hydrolysis resistance than ester-based TPU. Therefore, by using ether-based TPU as a raw material, even if the manufacturing method of the present invention is a foaming method using an aqueous medium, it is not easy to cause molecular weight drop due to hydrolysis. During foaming, bubbles are not easy to break and can maintain a good bubble structure, so it is easy to obtain foamed particles with good in-mold formability.

In addition, according to the use and purpose of the foamed molded body, other polymers such as polyolefin resin, polystyrene resin, and styrene elastomer can be mixed and used in the TPU as long as the object of the present invention is not hindered. . The amount of the other polymer used is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less based on 100 parts by weight of the TPU. It is particularly desirable that the expanded particles do not contain polymers other than TPU.

The melting temperature of the TPU used in the production of the expanded particles is preferably 140 to 170 ° C. When the melting temperature of the TPU is within the above range, foamed particles having more excellent in-mold formability can be obtained. Considering this viewpoint, the melting temperature is more preferably 150 to 170 ° C. The melting temperature is adjusted in accordance with JIS K7121-1987 by "measurement of the melting temperature after a certain heat treatment" (the heating and cooling rates of the state adjustment of the test piece are both 10 ° C / min), And according to the heat flux differential scanning thermal analysis method, the peak top temperature of the melting peak of the DSC curve obtained at a heating rate of 10 ° C./min is the value obtained. When the DSC curve has a plurality of melting peaks, the peak temperature of the highest melting peak is used as the melting temperature.

The hardness of the A-type durometer of the TPU is preferably A90 or less. When the hardness is A90 or less, a good foamed molded body can be obtained without excessively increasing the steam pressure (molding pressure) during molding. In addition, when the hardness is too low, depending on the molding conditions and the shape of the foamed molded body, after the foamed molded body is released from the molding die, the foamed molded body significantly shrinks and deforms, so that so-called sink marks are likely to occur. ). Therefore, the hardness of A-type hardness tester is preferably A70 ~ A90, more preferably A80 ~ A88. The A-type durometer hardness means the hardness of the durometer measured using the A-type durometer in accordance with JIS K6253-3: 2012. The measurement time was 3 seconds.

[Manufacturing method of TPU foamed particles] The manufacturing method of the foamed particles of the present invention is to impregnate a foaming agent with TPU particles dispersed in an aqueous medium under heating in a closed container, and TPU particles are released together with an aqueous medium from a closed container to be foamed, and a method for manufacturing TPU foamed particles with an apparent density of 100 to 300 kg / m ³ is used. The foaming agent is a physical foaming agent that uses carbon dioxide as its main component. The TPU particles contain 300 to 2000 mass ppm of inorganic powder, and the pressure in the container at the time of discharging is more than 2.5 MPa (G: gauge pressure) and less than 4.0 MPa (G).

In the present invention, the aqueous medium in which the TPU particles are dispersed is not particularly limited, and a medium such as water can be used. The foaming agent impregnated in the TPU particles is a physical foaming agent containing carbon dioxide as a main component. Carbon dioxide was used as the blowing agent. By controlling the pressure in the pressure vessel, the carbon dioxide does not become supercritical, and TPU foamed particles can be obtained without excessively miniaturizing the bubbles. In addition to carbon dioxide, other physical foaming agents and chemical foaming agents can be used in combination as the foaming agent. Examples of other physical blowing agents include aliphatic hydrocarbons such as propane, butane, hexane, pentane, and heptane; chlorochloromethane, trifluoromethane, 1,1-difluoroethane, 1,1 , 1,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride and other halogenated hydrocarbons, dimethyl ether, diethyl ether and other organic physical blowing agents. Examples of the inorganic physical foaming agent include nitrogen, argon, air, and water. In this case, the blending ratio of carbon dioxide in the foaming agent is preferably 50% by mass or more, more preferably 70% by mass or more, and more preferably 90% by mass or more.

Carbon dioxide used as a foaming agent is preferably pressed into a closed container so that the pressure in the closed container is not more than 7.0 MPa (G) in consideration of the point that the bubble size of the obtained foamed particles is not excessively reduced. This means that the impregnation pressure is preferably below 7.0 MPa (G), more preferably below 5.0 MPa (G), and even more preferably below 4.0 MPa (G). Furthermore, from the viewpoint of easy control of the pressure during foaming described later, the impregnation pressure is particularly preferably 3.4 MPa (G) or less. On the other hand, considering the viewpoint that the foaming agent is sufficiently impregnated in the TPU particles, the impregnation pressure is preferably 0.5 MPa (G) or more, and more preferably 1.0 MPa (G) or more. Further, it is considered that it is easy to control the pressure during foaming described later. From a viewpoint, more than 2.5 MPa (G) is more preferable, and 2.6 MPa (G) or more is especially preferable. From the viewpoint of the impregnation of the TPU particles with the foaming agent, it is preferable to impregnate under heating. The temperature for impregnation under heating (hereinafter referred to as the impregnation temperature) is preferably 20 ° C or higher and the melting temperature of TPU particles Tm ° C or lower, and more preferably 80 ° C or higher (Tm-20) ° C or lower. In addition, the impregnation time can be appropriately set in accordance with the pressure in the closed container, the type and quality of the TPU particles, but as a time for the foaming agent to be fully impregnated in the TPU particles, productivity is also considered in terms of 0.05 to 3 hours. For ideal, 0.1 ~ 1 hour is more ideal.

In particular, when the temperature of the aqueous medium is set to 80 ° C or higher and the melting temperature Tm-20 ° C or lower of the TPU particles, the physical blowing agent of carbon dioxide as the main component is pressed into the closed container under the temperature conditions, Until the pressure in the closed container exceeds 2.5 MPa (G) or more and 7.0 MPa (G) or less, the physical foaming agent is preferably impregnated into the TPU particles. In addition, the melting temperature is adjusted according to JIS K7121-1987, "measurement of the melting temperature after a certain heat treatment" (the heating and cooling rates of the state adjustment of the test piece are both 10 ° C / min), The peak temperature of the melting peak of the DSC curve obtained at a heating rate of 10 ° C./min was determined by a heat flux differential scanning thermal analysis method. When the DSC curve has a plurality of melting peaks, the peak temperature of the highest melting peak is used as the melting temperature.

In the present invention, the TPU particles contain 300 to 2000 mass ppm of inorganic powder. When the content of the inorganic powder in the TPU particles is too small, wrinkles are easily generated on the surface of the foamed particles, and the bubbles tend to become uneven, and sometimes a good formed body cannot be formed. Considering this viewpoint, the lower limit of the content of the inorganic powder in the TPU particles is preferably 400 ppm by mass. In addition, when the content of the inorganic powder is too large, the bubbles of the foamed particles become too small and the foaming speed becomes too fast, which may cause a drop in the in-mold molding. Taking this point of view into consideration, the upper limit of the content of the inorganic powder in the TPU particles is preferably 1500 mass ppm, 1,000 mass ppm is more desirable, and 950 mass ppm is more desirable. Although the inorganic powder is not particularly limited, it is preferable to use talc, and it is more preferable to use talc having a 50% volume average particle diameter (d50) of 1 to 15 μm. When the d50 of the talc is 1 μm or more, the bubble diameter of the foamed particles will not be excessively fined, so that foamed particles having excellent in-mold formability can be obtained, and there is no permanent compression deformation of the obtained foamed molded body. And other physical deterioration. On the other hand, when the d50 of the talc is 15 μm or less, bubbles are not excessively enlarged, and thus foamed particles having excellent in-mold formability can be obtained.

In the manufacturing method of the present invention, the pressure inside the container (hereinafter referred to as the foaming pressure) when the TPU particles are discharged needs to exceed 2.5 MPa (G) and be 4.0 MPa (G) or less. When the foaming pressure is 2.5 MPa (G) or less, wrinkles are generated on the surface of the foamed particles, and the bubble diameter becomes uneven. When the foaming pressure exceeds 4.0 MPa (G), the foaming speed of the TPU particles becomes too fast. As a result, the TPU crystals are easily aligned in the foamed particles. Therefore, in order to obtain such a molded body by performing in-mold molding of such foamed particles, it is necessary to increase the molding steam pressure. Considering this viewpoint, the foaming pressure is preferably 2.6 to 3.4 MPa (G).

In the production method of the present invention, the temperature (hereinafter referred to as foaming temperature) of the aqueous medium at the time of discharging is preferably (T m-60) ° C or higher and (Tm-20) ° C or lower. When the foaming temperature is in the range of (Tm-60) ° C or more and (Tm-20) ° C or less, expanded particles having more excellent in-mold formability can be obtained. In consideration of this viewpoint, the temperature (foaming temperature) of the aqueous medium at the time of the discharge is preferably (Tm-40) ° C or more and (Tm-25) ° C or less.

The mass of one of the TPU particles needs to be appropriately set according to the size of the expanded particles and the expansion ratio, but it is preferably 0.5 to 30 mg. When the content is within the above range, the foaming agent can be sufficiently impregnated into the TPU particles, and the foamed particles can be well-balanced with the filling property and the moldability in the mold. Considering this point of view, the lower limit of the mass of the TPU particles is more preferably 1 mg, and 3 mg is more desirable. On the other hand, the upper limit is more preferably 20 mg, 15 mg is more desirable, and 12 mg is particularly desirable. The method for producing TPU particles is not particularly limited, and can be obtained by a known method. For example, the raw material TPU can be melted in an extruder, and the molten material of the TPU can be extruded from a small hole of a die attached to the front end of the extruder into a strand shape, and cut into a predetermined weight Strand cut metho d, UPU under water cut method that cuts the TPU melt immediately after it is squeezed from the small hole into the water, and extrudes the TPU melt from the small hole A hot-cut method of cutting into the bubble phase, thereby obtaining TPU particles. The quality of TPU particles can be adjusted by adjusting the pore diameter, the amount of extrusion, and the pelletizing speed.

In addition to TPU particles, in addition to inorganic powders used as bubble regulators, generally used antistatic agents, conductivity imparting agents, lubricants, antioxidants, ultraviolet absorbers, and flame retardants can be appropriately blended as needed. Additives, metal deactivators, crystal nucleating agents, fillers, colorants and other additives. The amount of these various additives may vary depending on the purpose of the expanded particle molding, but it is preferably 25 parts by mass or less, more preferably 15 parts by mass or less, and 10 parts by weight or less based on 100 parts by mass of the raw material TPU. Still more preferred is 5 parts by weight or less.

The apparent density of the foamed particles obtained by the production method of the present invention is 100 to 300 kg / m ³ . According to the manufacturing method of the present invention, foamed particles having uniform bubbles, excellent in-mold formability, and an apparent density of 100 to 300 kg / m ³ can be manufactured in one stage of foaming. If the apparent density of the foamed particles is too low, when the foamed particles are subjected to in-mold molding, the obtained molded body is liable to be severely deformed and shrunk. Taking this point into consideration, the apparent density of the expanded particles is preferably 150 kg / m ³ or more, and more preferably 200 kg / m ³ or more. On the other hand, if the apparent density is too high, secondary foaming of foamed particles becomes difficult during in-mold molding, and voids are likely to remain between the foamed particles of the obtained molded body, and ideal cushioning properties cannot be obtained. The fear of shaped bodies. The apparent density of the expanded particles is a value obtained by dividing the weight of the expanded particles by the volume of the expanded particles. The volume of the expanded particles can be obtained by a drainage method.

In the present invention, the average bubble diameter of the foamed particles is preferably 100 to 500 μm. If the average bubble particle diameter is 100 μm or more, bubbles will not be easily broken during in-mold molding, and a foamed molded article having particularly excellent surface properties will be easily obtained. In addition, if the average bubble particle diameter is 500 μm or less, steam will easily penetrate into the inside of the foamed particles during in-mold molding, so the foamed particles will be sufficiently secondary foamed, and a foamed molded body having particularly excellent surface properties can be obtained. . Taking this point into consideration, it is more preferable that the average cell size of the expanded particles is 150 to 400 μm.

The average cell size of the expanded particles is a value measured in accordance with ASTM D3576-77 as follows. The foamed particles were cut and divided into two parts so as to pass through the center thereof. On the cross section of one side of each of the cut foamed particles, four line segments are drawn at an equal angle from the outermost surface of the foamed particles through the center to the outermost surface on the opposite side. Calculate the number of bubbles crossing each line segment, and divide the total length of the four line segments by the number of all bubbles crossing the line segment to obtain the average chord length of the bubble, and then divide by 0.616 to obtain the average bubble of the foamed particles Particle size.

In the foamed particles of the present invention, the melt flow rate (MFR) at 190 ° C and a load of 10 kg is preferably 10 to 50 g / 10 minutes. When the MFR is 10 g / 10 minutes or more, the secondary foamability during in-mold molding becomes good, and a foamed particle molded body having a good surface can be obtained in particular. Considering this point of view, the lower limit of MFR should preferably be 15g / 10 points, and 20g / 10 points is more desirable. In addition, if the MFR is 50 g / 10 minutes or less, the recoverability of the obtained foamed molded article is excellent. Considering this point of view, the upper limit of MFR is more preferably 45g / 10 points, and 40g / 10 points is more desirable. This MFR is a value measured in accordance with JIS K7210-2: 2014 at 190 ° C and a load of 10 kg.

[Foamed Molded Body] The foamed particles obtained by the production method of the present invention are molded in-mold to obtain a foamed molded body. The in-mold forming method may employ a conventional method. [Example]

Although the present invention will be described in detail using examples below, the present invention is not limited thereto. <Examples 1 to 6 and Comparative Examples 1 to 2> The raw materials used in the examples are as follows. [Raw materials] ‧TPU TPU1 (manufactured by Covestro, ether-based thermoplastic polyurethane, grade name: Desmopan DP9385A, MFR [190 ° C, load 10Kg]: 17g / 10min, A-type hardness tester hardness: 86, melting temperature: 164 ° C) TPU2 (Manufactured by Covestro, ether-based thermoplastic polyurethane, grade name: Desmopan DP9386A, MFR [190 ° C, load 10Kg]: 26g / 10min, A-type hardness tester hardness: 86, melting temperature: 165 ° C) ‧ bubble nucleating agent (inorganic Powder) Talc 1 (manufactured by Lim Kasei Corporation, grade name: KFP-125B, d50: 8 μm) Talc 2 (manufactured by Lin Kasei Corporation, grade name: PK-S, d50: 12 μm) Talc 3 (manufactured by Matsumura Industries, grade Name: Hi-Filler # 12, d50: 3μm)

[Production of TPU particles] TPU and talc as a bubble regulator (inorganic powder) of the type and amount shown in Table 1 relative to 100 parts by mass of the TPU were supplied to a biaxial extruder with an inner diameter of 20 mm, and They are heated and kneaded into a molten TPU composition. The molten TPU composition was extruded from a small hole attached to a die at the front end of the extruder into water and cut at the same time to obtain TPU particles with an average weight of 10 mg and L / D = 1.0.

[Production of foamed particles] 50 kg of the TPU particles obtained above and 270 liters of water as a dispersion medium were charged into a 400 liter autoclave equipped with a stirrer, and 100 parts by mass of TPU particles was used as a dispersant. 0.2 parts by mass of kaolin and 0.008 parts by mass of sodium alkylbenzenesulfonate as a surfactant were added to the dispersion medium. Stir the contents of the autoclave and raise the temperature at the same time. After the temperature (impregnation temperature) shown in Table 1 is reached, carbon dioxide as a foaming agent is pressed into the autoclave until the pressure in the closed container becomes as shown in Table 1. The pressure (impregnation pressure) is indicated, and after the predetermined pressure is reached, the pressure is maintained at the same temperature for 15 minutes. After that, back pressure was applied using carbon dioxide, and the pressure in the container was adjusted to be constant according to the pressure (foaming pressure) shown in Table 1. At the same time, the foam was impregnated with the temperature of the dispersion medium (foaming temperature) shown in Table 1. The TPU particles of the agent were released to atmospheric pressure together with the dispersion medium, and foamed particles were obtained. The obtained foamed particles were placed in a closed container, and subjected to a pressure treatment at 30 ° C for 12 hours with compressed air of 0.3 MPa (G), and then the pressure was released, and the resultant was left to stand at 40 ° C for 48 hours. The method for measuring the apparent density, MFR, and average bubble diameter of the obtained expanded particles, and the surface properties and presence or absence of bubbles of the expanded particles were evaluated. The results are shown in Table 1. The test method is shown below. In addition, these measurements were performed by leaving the obtained expanded particles under conditions of relative humidity of 50%, 23 ° C., and 1 atm for 2 days and adjusting the state.

(Apparent density of foamed particles) First, foamed particles of mass W1 were sunk in a graduated cylinder filled with water at a temperature of 23 ° C using a metal mesh. Then consider the volume of the metal mesh, measure the volume V1 [L] of the expanded particles based on the rising water level, and divide the weight W1 [g] of the expanded particles by the volume V1 (W1 / V1) to convert the unit into [kg / m ³ ], thereby obtaining the apparent density of the expanded particles.

(Average cell diameter of foamed particles) From the obtained foamed particle group, 50 foamed particles were randomly selected. The foamed particles were cut and divided into two parts so as to pass through the center thereof. On the cross section of one side of each of the cut expanded particles, 4 line segments were drawn at an equal angle from the outermost surface of the expanded particles through the center to the outermost surface on the opposite side. Measure the number of bubbles crossing each line segment, divide the total length of the 4 line segments by the number of all bubbles crossing the line segment to obtain the average chord length of the bubble, and then divide by 0.616 to obtain the average bubble of the foamed particles Particle size. Then, the arithmetic mean of the values was calculated to obtain the average cell size of the foamed particles. (MFR of foamed particles) Measured under the conditions of a temperature of 190 ° C and a load of 10 Kg in accordance with JIS K7210-2: 2014. After drying at a temperature of 80 ° C. for 4 hours, foamed particles having a moisture content of 500 mass ppm or less were used as samples for measurement.

(Surface property of foamed particles) Visual evaluation was performed based on the following criteria. ○: No wrinkles on the surface of the foamed particles and good surface properties ×: Wrinkles were confirmed on the surface of the foamed particles, and the surface properties were uneven (bubble uniformity). Ten foamed particles were randomly selected from the obtained foamed particle group. The foamed particles were cut and divided into two parts so as to pass through the center thereof. On one side cross section of each of the cut foamed particles, bubbles were observed and evaluated according to the following criteria. ○: No excessively large bubbles or excessively small bubbles ×: Excessive or excessively small bubbles

[Production of Foamed Molded Body] The foamed particles produced in the above were filled into cavities of a molding die having a length of 200 mm, a width of 250 mm, and a thickness of 20 mm, and were heated with steam until the molding pressure shown in Table 1 was reached. After cooling, the molded body was taken out from the molding die to obtain a plate-like foamed molded body.

(Surface property) The voids between the foamed particles on the surface of the obtained foamed molded body were evaluated as "○" if they were filled, and "x" if they were not filled.

(Weldability) In order to evaluate the weldability of the obtained foamed molded body, the weldability was measured. When the weldability was 90% or more, the evaluation was “○”, and when the weldability was less than 90%, the evaluation was “×”. The welding rate of the foamed molded body was measured by the following method. A test piece having a length of 170 mm, a width of 30 mm, and a thickness equal to the original thickness was cut out of the foamed molded body. On one of the surfaces of the test piece, a notch was cut at a position equal to 2 on the long side of the test piece, a notch having a depth of about 10 mm was cut in the thickness direction, and the formed body was bent from the cut portion to break it. The ratio (m / n × 100 [%]) of the number m of foamed particles destroyed by the material existing on the fracture surface to the number n of all foamed particles existing on the fracture surface was calculated. When the foamed molded body does not break even when it is bent, the fusion rate is defined as 100%. The aforementioned measurement was performed 5 times using different test pieces, and the respective material failure rates were determined, and the arithmetic average was calculated as the fusion rate.

(Resilience) When the thickness of the central portion and the four corner portions of the obtained foamed molded body were measured separately, when the ratio of the thickness of the central portion to the thickest portion of the four corner portions was 90% or more, the evaluation was "○" When it is less than 90%, it is evaluated as "×".

The apparent density of the obtained foamed molded article was measured. The results are shown in Table 1. The method for measuring the apparent density is shown below. In addition, these measurements were performed after the obtained foamed molded article was left to stand for two days under conditions of a relative humidity of 50%, 23 ° C., and 1 atm, and the state was adjusted.

(Apparent density of foamed molded product) The foamed molded product was sunk in ethanol, and the apparent volume of the molded product was obtained from its rising water level component. The apparent density [kg / m ³ ] of the foamed molded body was obtained by dividing the mass of the foamed molded body by the apparent volume.

【Table 1】

According to the evaluation results shown in Table 1, in Examples 1 to 6, foamed particles having good surface properties and uniformity of bubbles were produced. When the foamed particles were subjected to in-mold molding, the molding range was wide, and it was possible to obtain Good foam molding. In contrast, in Comparative Example 1 where foamed particles were produced under a small amount of inorganic powder, the obtained foamed particles had poor surface properties and extremely uneven cell diameters, and a good foamed molded body could not be obtained by in-mold molding. . Further, in Comparative Example 2 where foamed particles were produced under conditions where the foaming pressure was as low as 2.0 MPa (G), although the obtained foamed particles were subjected to in-mold molding to obtain a foamed molded body, the moldable The range is narrow. In addition, the bubble particle size of the foamed particles is not uniform, so that the obtained foamed molded body also becomes non-uniform in the bubble particle size, and the portion having too small a bubble particle size is whitened, so that only a defective foamed molded body having an appearance of marble shape can be obtained.

Claims (9)

A method for manufacturing thermoplastic polyurethane foamed particles, in which a foaming agent is impregnated with thermoplastic polyurethane particles dispersed in an aqueous medium in a closed container under heating, and the thermoplastic polyurethane particles containing the foaming agent are sealed from the aqueous medium together with the aqueous medium. The container is released and foamed to produce thermoplastic polyurethane foam particles with an apparent density of 100-300 kg / m ³ ; It is characterized by: The foaming agent is a physical foaming agent containing carbon dioxide as the main component, and the thermoplastic polyurethane particles contain 300 ~ The inorganic powder with a mass of 2000 ppm has a pressure in the container at the time of discharging exceeding 2.5 MPa (G) and below 4.0 MPa (G). For example, the method for manufacturing thermoplastic polyurethane foamed particles in the scope of application for the first item, wherein the inorganic powder is talc, and the 50% volume average particle diameter of the talc is 1 to 15 μm. For example, the method for manufacturing thermoplastic polyurethane foamed particles in the scope of application for patents 1 or 2, wherein the temperature of the aqueous medium when the foaming agent is impregnated is set to 80 ° C or higher and the melting temperature Tm-20 ° C of the thermoplastic polyurethane particles Hereinafter, the physical foaming agent is pressed into the closed container under the temperature conditions until the pressure in the closed container exceeds 2.5 MPa (G) and less than 7.0 MPa (G), thereby making the physical foaming agent The thermoplastic polyurethane particles are impregnated. For example, the method for producing thermoplastic polyurethane foamed particles according to any one of claims 1 to 3, wherein the temperature of the aqueous medium at the time of release is the melting temperature of the thermoplastic polyurethane particles Tm-60 ° C or higher and is a thermoplastic polyurethane. The melting temperature of the particles is below Tm-20 ° C. For example, the method for producing thermoplastic polyurethane foamed particles according to any one of claims 1 to 4, wherein the pressure in the container at the time of discharging is 2.6 to 3.4 MPa (G). The method for producing thermoplastic polyurethane expanded particles according to any one of claims 1 to 5, wherein the thermoplastic polyurethane-based ether-based thermoplastic polyurethane constituting the thermoplastic polyurethane particles. For example, the method for manufacturing thermoplastic polyurethane foamed particles according to any one of the claims 1 to 6, wherein the thermoplastic polyurethane particles contain 300 to 950 mass ppm of inorganic powder. For example, the method for manufacturing thermoplastic polyurethane expanded particles according to any one of the claims 1 to 7, wherein the thermoplastic polyurethane expanded particles have a melt flow rate of 10 to 50 g / 10 minutes at 190 ° C and a load of 10 kg. For example, the method for producing thermoplastic polyurethane foamed particles according to any one of claims 1 to 8, wherein the hardness of the type A hardness tester of the thermoplastic polyurethane constituting the thermoplastic polyurethane particles is 90 or less.