Expanded thermoplastic polyurethane beads and preparation method and application thereof

Abstract

The present invention relates to expanded thermoplastic polyurethane beads, a preparation method for same, and an application thereof. The expanded thermoplastic polyurethane beads consists of components of the following parts by weight: 100 parts of a thermoplastic polyurethane, 1-10 parts of a cell size stabilizer, and 1-35 parts of a melt viscosity modifier. The preparation method for the expanded thermoplastic polyurethane beads is also disclosed. The bead is produced by employing a volatile blowing agent to immerse the thermoplastic polyurethane, comprising the pore size stabilizer and the melt viscosity modifier, in an aqueous suspension, and is then followed by the foaming process. Utilization of the expanded thermoplastic polyurethane beads of the present invention allows for preparation of a foam product. The expanded thermoplastic polyurethane beads prepared per the present invention has uniform cell sizes and a high product yield. At the same time, the expanded thermoplastic polyurethane bead provides a great sintering performance even at a relatively low vapor pressure, a molded foam product has a small deformation, a low dimensional shrinkage ratio relative to a mold, great dimensional stability, and an aesthetically appealing appearance.

Claims

1. A process comprising: (1) mixing 100 parts by weight of a thermoplastic polyurethane, 1-10 parts by weight of a cell size stabilizer, and 1-35 parts by weight of a melt viscosity modifier to form a mixture; introducing the mixture into an extruder to obtain a melt which is then extruded to provide extruded strips; obtaining thermoplastic polyurethane particles by cooling and then cutting the extruded strips, or by performing underwater pelletizing after the melt is extruded via a die to provide extruded strips; and (2) adding the thermoplastic polyurethane particles obtained in step (1), a volatile foaming agent, and water into a pressure vessel; raising the temperature to 115-118 C.; maintaining the pressure in the pressure vessel at 18-26 bar; maintaining constant temperature and pressure in the pressure vessel for 20 minutes to obtain a suspension, discharging the suspension from the pressure vessel, and obtaining expanded thermoplastic polyurethane beads wherein the expanded thermoplastic polyurethane beads comprise: 100 parts by weight of the thermoplastic polyurethane, 1-10 parts by weight of the cell size stabilizer, and 1-35 parts by weight of the melt viscosity modifier, wherein the cell size stabilizer is selected from the group consisting of: sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and a sucrose fatty acid ester, and mixtures thereof, and wherein the melt viscosity modifier is chosen from: an ethylenevinyl acetate copolymer, a polypropylene-butadiene-styrene resin, a polystyrene-polyethylene-polybutylene-polystyrene resin, or mixtures thereof.

2. The process of claim 1, wherein the melt viscosity of the expanded thermoplastic polyurethane beads at 180 C. is 8000-15000 poise.

3. The process of claim 1, wherein the expanded thermoplastic polyurethane beads possess a Shore hardness of 55-95 A.

4. The process of claim 1, wherein the melt flow rate of the thermoplastic polyurethane is 5-50 g/10 minutes.

5. The process of claim 1, wherein the volatile foaming agent is one or more of propane, n-butane, isobutane, n-pentane, and isopentane; and the amount added of the volatile foaming agent is 1-40 parts by weight.

6. The process of claim 1 further comprising expanding and sintering the expanded thermoplastic polyurethane beads with steam at a pressure of 1-3 bar.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Description of the principles and features of the present invention are given in what follows. The listed examples are only used for the explanation of the present invention, and are not intended to limit the scope of the present invention.

(2) The raw material thermoplastic polyurethane elastomer particle is usually prepared by mixing isocyanate, an active hydrogen-containing compound with a molar mass of 500-10000 g/mol, and a chain extender with a molar mass of 50-500 g/mol, wherein a catalyst is added during the production.

(3) Preferred starting raw materials for producing the thermoplastic polyurethane particles in the present invention are described by way of examples as follows:

(4) The isocyanate includes aliphatic, alicyclic, aromatic, and araliphatic series diisocyanate is preferred, such as toluene diisocyanate (TDI), diphenyl methane-2,2-diisocyanate (MDI) (where 2,2- can be replaced with 2,4- or 4,4-), 3-isocyanatomethylene-3,5,5-trimethylcyclohexyl isocyanate (IPDI), hexamethylene diisocyanate (HDI), dicyclohexyl methane diisocyanate (HMDI), 1,5-naphthalene diisocyanate (NDI), p-phenylene diisocyanate (PPDI), 1,4-cyclohexane diisocyanate (CHDI), or cyclohexane dimethylene diisocyanate HXDI), and especially preferably diphenyl methane-4,4-diisocyanate (MDI).

(5) The active hydrogen-containing compound includes polyester polyol, polyether polyol, and polycarbonate polyol. Polyester polyol having a molar mass of 800-1200 g/mol and polyether polyol having a molar mass of 500-2000; g/mol are preferred. Polyether polyol is especially preferred, wherein the average number of functionality is 1.8-2.5, preferably 1.9-2.0, and 2 is especially preferred. Examples include polyethylene glycol adipate (PEA), polydiethylene glycol adipate (PDA), polybutylene glycol adipate (PBA), polypropylene glycol adipate (PPA), polyoxypropylene glycol, polytetramethylene ether glycol (PTMEG), and especially preferred are polybutylene glycol adipate (PBA) and polytetramethylene ether glycol (PTMEG).

(6) The chain extender includes an aliphatic, aromatic, or alicyclic diol compound having a molar mass of 50-500 g/mol. Examples include ethylene glycol (EG), 1,4-butanediol (BDO), 1,2-propylene glycol (PG), 1,6-hexanediol (HD), hydroquinone bis(2 hydroxyethyl) ether (HQEE), resorcinol bis (hydroxyethyl) ether (HER), dipropylene glycol (DPG), 1,4-cyclohexanedimethanol (CHDM), and especially preferred is ably 1,4-butanediol (BDO).

(7) The catalyst raises the reaction rate between isocyanate group and hydroxyl group. The commonly used catalyst includes triethylene diamine, dimethyl cyclohexyl amine, triethylamine (N,N,N, N-tetraethylmethylenediamine), 1,4-dimethyl piperazine, dibutyltin dilaurate, potassium isooctanoate, tetrabutyl titanate, and tetraisopropyl titanate.

(8) The thermoplastic polyurethane elastomer particle is continuously produced using a conventional method, such as extrusion reaction type of extruder, or through the one-pot or a prepolymer method.

(9) Types of the thermoplastic polyurethane beads used in examples and control examples, and the proportions added of each component are shown in Table 1.

(10) TABLE-US-00001 TABLE 1 Melt viscosity Cell size stabilizer modifier Bead MI Amount Amount Amount type (g/10 min) added Type added Type added T1 20 100 Dihydroxypropyl 5 EVA 10 stearate T2 25 100 Sorbitan 3 PVC 15 monolaurate T3 30 100 Sucrose fatty acid 2 ABS 10 ester T4 20 100 Dihydroxypropyl 5 stearate T5 25 100 PVC 15 T6 20 100

Example 1

(11) 100 parts of TPU particle having an MI of 20 g/10 min, 5 parts by weight of dihydroxypropyl stearate, 10 parts by weight of EVA were uniformly mixed via a high speed mixer; and then the mixture was put into a twin-screw extruder for melt mixing. The melted mixture was extruded into strips using an extruder with a die having a diameter of 2 mm; the strips were cooled for shaping in a water tank, and pelletized by a granulation and pelletizing machine to obtain thermoplastic polyurethane particles.

(12) 100 parts by weight of the above obtained thermoplastic polyurethane particles and 400 parts by weight of water were added into a 10 L autoclave; and 30 parts by weight of a foaming agent n-butane was added while stirring. The autoclave was heated to 118 C. and maintained at this temperature for 20 minutes; a discharge valve at the bottom of the autoclave was opened to discharge the mixture from the autoclave into the atmospheric environment to obtain expanded thermoplastic polyurethane particles. The obtained expanded thermoplastic polyurethane beads have a foam density of 0.16 g/cm.sup.3, and a cell diameter of 550 m.

(13) The obtained expanded thermoplastic polyurethane beads were filled into a mold with the length of 300 mm, the width of 250 mm, and the thickness of 50 mm. The particles are sintered and compressed 10 percent into the mold by the steam with the pressure of 1.4 bar. An expanded thermoplastic polyurethane molded foam product was then obtained. After standing for 2 hours at 50 C.50% RH, the foam product is dried for 2 hours in a thermostatic chamber at 80 C. After being maintained for 2 hours at 25 C.50% RH, its performance was evaluated, as shown in Table 2.

Example 2

(14) Sorbitan monolaurate, used as a cell size stabilizer, was added into 100 parts of TPU having an MI of 25 g/10 min. PVC was used as a melt viscosity modifier. The foaming temperature was set to 116 C., and n-pentane was used as a foaming agent. Other than those described above, expanded thermoplastic polyurethane beads and an expanded thermoplastic polyurethane molded foam product were obtained using the same method described in Example 1. The evaluation of the performance is shown in Table 2.

Example 3

(15) Sucrose fatty acid ester, used as a cell size stabilizer, was added into 100 parts of TPU having an MI of 30 g/10 min. ABS was used as a melt viscosity modifier. The foaming temperature was set to 115 C., and n-butane was used as a foaming agent. The steam molding pressure was 1.2 bar. Other than those described above, expanded thermoplastic polyurethane beads and an expanded thermoplastic polyurethane molded foam product were obtained using the same method described in Example 1. The evaluation of the performance is shown in Table 2.

Comparative Example 1

(16) Expanded thermoplastic polyurethane beads and an expanded thermoplastic polyurethane molded foam product were obtained using the same method described in Example 1, except that dihydroxypropyl stearate was added alone into 100 parts of a TPU particle having an MI of 20 g/10 min as a cell size stabilizer. The evaluation of the performance is shown in Table 2.

Comparative Example 2

(17) Expanded thermoplastic polyurethane beads and an expanded thermoplastic polyurethane molded foam product were obtained using the same method described in Example 2, except that PVC was added along into 100 parts of a TPU having an MI of 25 g/10 min as a melt viscosity modifier. The evaluation of the performance is shown in Table 2.

Comparative Example 3

(18) Expanded thermoplastic polyurethane beads and an expanded thermoplastic polyurethane molded foam product were obtained using the same method described in Example 2, except that no cell size stabilizers or melt viscosity modifiers were added into 100 parts of a TPU particle having an MI of 20 g/10 min. The evaluation of the performance is shown in Table 2.

(19) Production process conditions and physical properties of the expanded thermoplastic polyurethane particles and the performance evaluation of the molded foam products are shown in Table 2.

(20) TABLE-US-00002 TABLE 2 Foaming agent Amount Foaming Particle Cell Molding Deformation of Surface properties Bead Type added temperature density diameter pressure foam product of foam product Example 1 TI n-butane 30 118 0.16 550 1.4 Example 2 T2 n-pentane 35 116 0.12 600 1.3 Example 3 T3 n-butane 28 115 0.18 620 1.2 Comparative T4 n-pentane 30 118 0.16 570 1.4 x Example 1 Comparative T5 n-pentane 35 116 0.13 625 1.3 x Example 2 Comparative T6 n-butane 30 118 0.15 680 1.4 x Example 3

(21) Various evaluations were implemented according to the following methods.

(22) 1. Deformation of Foam Product

(23) The appearance of the foam molded product was observed by macroscopic method. The foam product in which no shrinkage and wrinkles (stripes above 1 cm) are observed is evaluated as , whereas the foam product in which only wrinkles exist but no shrinkage is observed is evaluated as ; and the foam molded product having many wrinkles and an irregular overall shape is evaluated as x.

(24) 2. Surface Properties of Foam Product

(25) The surface of the molded foam product is observed. An average number of gaps between expanded beads of above 1 cm.sup.2 per 10 cm.sup.2 area is calculated. The following observation is determined as follows:

(26) indicates the number being less than 100; and

(27) indicates the number being more than 100.

(28) As can be seen from the above examples and Comparative examples, the expanded thermoplastic polyurethane beads prepared in Examples 1 to 3 have a uniform cell size and a high production yield rate. Compared with the Comparative Examples 1 to 3, the molded foam products obtained in Examples 1 to 3 have a limited deformation, and no observable shrinkages or wrinkles (strips above 1 cm); the gaps between the expanded beads are small; the shrinkage ratio is low, and the dimensional stability and surface appearance are excellent.

(29) The examples above were merely preferred embodiments of the present invention, and they are not intended to limit the present invention. Any modification, equivalent substitution, and improvement made within the spirit and principle of the present invention shall fall into the protection scope of the claims of the present invention.