JP2637201B2 - Processing method for expanded polypropylene resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] Foamed polypropylene resin particles obtained by carrying out the present invention include packaging containers, heat-insulating building materials, toys, floating tools, automobile bumper cores, helmet cores, and packaging. The present invention relates to a method for treating foamed particles, which provides foamed particles suitable for producing foamed molded articles useful as cushioning materials and the like.

(Prior art)

Polypropylene resin foam moldings are used as bumper cores and packaging containers because they have better heat resistance, impact resistance, and compression elastic recovery than polystyrene foam moldings.

In order to mold this foamed molded article, crystalline polypropylene-based resin foamed particles are used as a raw material, and the particles themselves do not have secondary foaming ability. Gas pressure of 0.18 kg / cm ² G or more is applied to the foamed particles with compressed air in the foamed particle cell, and the foamed particles are filled in a pair of male and female mold cavities having steam holes, and then heated and foamed with steam. Pressure aging method to form an in-mold foamed product by fusing (Japanese Patent Publication No. 51-22951, 59-23731)
Nos. 59-43490, 59-43493, 63-44780, etc.) (ii). The foamed particles are compressed by 40 to 70% with pressurized air and filled into the mold cavity with steam holes, then evacuated with steam, and the pressure inside the mold is returned to atmospheric pressure. In-mold compression-filled bead fusing method in which foamed particles are fused by heating to form a foamed molded product (Japanese Patent Laid-Open No. 63-1780).
No. 29) is known.

As a method for producing the expanded polypropylene resin particles as a raw material, the polypropylene resin particles are dispersed in water in a closed container, a volatile expanding agent is supplied to the dispersion, and the dispersion is then dispersed in the polypropylene resin. After heating to a temperature higher than the softening point of the resin and lower than the melting point (peak end temperature Mp of the DSC curve) and maintaining the same temperature for a certain period of time, open the nozzle or slit provided at the lower end of the container,
A method in which resin particles impregnated with a volatile expander along with water are released to a lower pressure range (usually atmospheric pressure) than a closed container to obtain expanded particles (JP-B-56-1344, JP-B-63-24615, JP-A-61-115940 and JP-A-61-103944) are known.

The aqueous dispersion containing the polypropylene-based resin particles containing these volatile expanders is discharged from the high-pressure region to the low-pressure region at a temperature equal to or higher than the softening point of the polypropylene-based resin as the base resin of the particles to form expanded particles. Can be obtained without blocking the expanded polypropylene resin particles. In these methods, when the expansion ratio of the particles is less than 30 times (when the specific gravity of polypropylene is 0.90 and the bulk density of the expanded particles is 30 g / or more), wrinkles are observed on the surfaces of the obtained expanded particles. However, when the expansion ratio of the particles is as high as 30 times or more, wrinkles due to shrinkage are generated on the surface of the expanded particles, and the degree of the wrinkles is more remarkable as the expansion ratio is higher.

In the case of a crystalline polypropylene resin, the generation of the wrinkles occurs when the particles are released into the low-pressure region and foamed because the holding power of the foaming agent (volatile expanding agent or pressurized air) in the foaming cell is poor. The foaming agent is dissipated relatively early, the internal pressure of the cells in the expanded particles is reduced, and the particles having a high expansion ratio have a small cell wall and low strength, so that the entire expanded particles contract,
It seems that wrinkles occur on the surface.

In addition, in order to produce foamed particles with higher foaming, the amount of the volatile expanding agent used is increased, and the degree of pressure reduction in the cells of the foamed particles after release becomes higher, so that the degree of shrinkage is also large.

[Problems to be solved by the invention]

In the in-mold bead molding method for obtaining a foamed product of a polypropylene-based resin, the pressure aging method (i) needs to perform pressure aging over about 2 days in order to impart secondary foaming ability to the foamed particles. Yes, a large-capacity aging tank is required, and the equipment cost is high (Japanese Patent Publication No. 59-23731).

The in-mold compression-filled bead fusing method (ii) does not require an aging step and has the advantage of a short molding time. Further, since molding can be performed even when the cell internal pressure of the foamed particles is 0 kg / cm ² G, there is an advantage that it is not necessary to pay attention to storage so that the internal pressure does not decrease unlike the pressure aging method.

A foam product can be obtained by using any of the wrinkled foam particles and any of the molding methods (i) and (ii).

However, when trying to obtain a foamed molded product by in-mold compression-filled bead fusion using wrinkled foamed particles, fusion of the foamed particles in the center of the foamed molded product in the region where the compression ratio is somewhat high The degree of compression is low (see Comparative Example 4). On the other hand, in a region where the compression ratio is low, there are disadvantages that the molded product has a large surface gap and a large shrinkage.

An object of the present invention is to provide highly foamed polypropylene resin expanded particles which are not limited by the compressibility. The present invention also provides a curing method for further increasing the expansion ratio of wrinkled, highly expanded expanded polypropylene resin particles.

[Specific means to solve the problem]

To achieve the above object, in the present invention, the foamed polypropylene resin particles having wrinkles are stored in a pressurized state under a specific temperature condition, and then, by releasing the pressurized state, there are no wrinkles, and Expanded particles having a higher expansion ratio can be obtained.

That is, the present invention releases an aqueous dispersion containing polypropylene resin particles containing a volatile expander into a lower pressure region than a high pressure region at a temperature equal to or higher than the softening point of the polypropylene resin as the base resin of the particles. The foamed polypropylene resin particles having a bulk density of 30 g / or less are placed in a closed container, and the melting end temperature of the intrinsic peak of the DSC curve obtained by differential scanning calorimetry of the base resin of the particles is Mp. And Mp-12
The foamed particles are heated and pressurized at a temperature (T) of 0 ° C. <T <Mp−70 ° C. and a pressure of 1.0 kg / cm ² G or more in a closed container. A process for exposing polypropylene resin foam particles to a pressure atmosphere lower than the above pressure.

(Polypropylene Resin) The polypropylene resin as the base resin of the expanded particles of the present invention is mainly composed of propylene homopolymer and propylene, and ethylene, butene-1, pentene-1,
Random copolymers or block copolymers obtained by copolymerizing one or more α-olefins such as 4-methylpentene-1; vinylsilane-grafted polypropylene; low-density polyethylene, ethylene / acetic acid Those containing 0.5 to 20% by weight of a vinyl copolymer, a high-density polyethylene, an ethylene / propylene copolymer rubber or the like are used.

The melting point (Mp) of this resin is
~ 8 mg at a temperature rise rate of 10 ° C / min by a differential scanning calorimeter.
After the temperature was raised to 20 ° C and then lowered at a rate of 10 ° C / min to 40 ° C, the temperature was raised again to 220 ° C at a rate of 10 ° C / min and obtained by the second heating. The temperature when the end of the endothermic peak of the DSC curve returns to the baseline position on the high temperature side.

Dokan method for polypropylene-based foamed resin particles (Patent Office 63
Since the manufacturing method according to the IPC illustration, March, 2003, is described in the above-mentioned patent publications, the details are omitted here.

(Treatment method) Place a polypropylene resin with a wrinkle on the surface in a closed container, and keep the temperature (T) in the closed container at a temperature of 120 ° C. lower than the melting point (Mp) of the foamed particles from 70 ° C. to 70 ° C. 1
5 to 120 kg / cm ² or more of inorganic gas
Minutes, preferably 20-80 minutes, to allow the inorganic gas to penetrate into the cells of the foamed particles. The pressure of the inorganic gas at the time of infiltration may be the same pressure, may be gradually increased, or may be increased stepwise. The higher the pressure of the inorganic gas, the shorter the treatment time.However, if the pressure of the inorganic gas is too high, the expanded particles shrink, thereby reducing the volume of the expanded particles in the cell and allowing the inorganic gas to penetrate into the cell. Excessive high pressure is not preferred because it becomes difficult.

Therefore, the pressurization method in which the pressure is gradually increased from low pressure to high pressure or the pressure is gradually increased is preferable. In any case, when the pressure of the inorganic gas is 1 to 5 kg / cm ² G, even if the inorganic gas is pressurized at a constant pressure, the permeation of the inorganic gas into the expanded particle cell can be performed properly.

Accordance connexion, the pressure of inorganic gas 1 kg / cm ² G or more, preferably from 1~5kg / cm ² G. If it is less than 1 kg / cm ² G, the pressure treatment time of the expanded particles is too long.

The temperature (T) of the pressure treatment time of the expanded particles is Mp-120 ° C.
<T <Mp-70 ° C, preferably Mp-100 ° C <T <Mp-70
° C. If the temperature is too low, the pressure treatment time becomes too long, and there is no economical advantage. If the temperature is too high, the shrinkage of the expanded particles during pressurization is large, and there is almost no decrease in the bulk density of the expanded particles after the pressure is released by the pressurization treatment.

After the pressurization, the supply of the inorganic gas in the closed container is stopped, the pressure valve is opened, and the pressure in the closed container is reduced to a pressure lower than the pressure at the time of the pressurization, preferably to the atmosphere, or the lower portion of the closed container. The valve of the nozzle provided in the above is opened to discharge the foamed particles to a lower pressure region, preferably to the atmospheric pressure. The foamed particles are restored, and the foamed particles having no shrinkage and having a smooth surface can be obtained.

In a preferred embodiment, filling and restoring can be performed at once if the release zone is within the mold cavity.

The pressure inside the cell of the expanded and restored foam particles is 0k instantly
g / cm ² G.

(In-Mold Molding Method) The highly foamed particles without wrinkles may be subjected to pressure aging and in-mold bead foam molding (JP-B-59-43492). The adoption of the in-mold compression filling bead fusing method disclosed in the publication has the following advantages as compared with the pressure aging method.

(A). The sealed container to be cured needs to be small,
The equipment cost is lower than that of a large-sized closed vessel for pressurized ripening in the pressurized ripening method disclosed in Japanese Patent No. 731.

(B). Since the molding can be performed even when the cell internal pressure of the expanded particles is 0 kg / cm ² G, the pot life of the pressure-aged expanded particles when subjected to pressure aging (period until the cell internal pressure drops to 0.18 kg / cm ² G) Without having to worry about it, the manufacturer of foamed particles can also transport foamed particles to a long distance molding company.

In-mold molding, for example, as shown in JP-A-63-178029, pressurized foamed particles in a cavity pressurized by pressurized gas of a mold consisting of a fixed mold having a steam hole and a moving mold having a steam hole Filling while compressing with gas, while maintaining the above-mentioned cavity internal pressure in the cavity after filling the expanded particles, while suppressing the restoration of the expanded particles, a pressure higher than the internal pressure of the cavity by 0.2 kg / cm ² or more. Guide the degassing steam to the movable chamber and vent through the steam holes, cavities and fixed chambers, or vent to the fixed chamber and vent through the steam holes, cavities and mobile chambers Or both of the above-mentioned deflation and the above-mentioned deflation are performed (either deflation or the deflation may be performed first), and then the internal pressure of the cavity is returned to the atmospheric pressure and compressed. After restoring the foamed particles, the heating steam is introduced into the movable steam chamber and the fixed steam chamber to fuse the foamed particles together to form a molded product. Formula for foam particles to be compressed and filled [W, V and σ in the formula each represent the following.

W: Weight of molded article (g) V: Capacity of molded article () σ: Bulk density of expanded particles in air (g /)] Controlling the compression ratio to a value within the range of 40 to 70% I do.

Next, a typical embodiment in which a bead fusing method in a compression filling mold is performed using a molding apparatus shown in the accompanying drawings will be further described. The attached drawings show an example of a molding apparatus used for carrying out the present invention in a partial longitudinal sectional view, where A is a rotary feeder for compressing and filling expanded particles, and B is a mold apparatus. is there.

First, the mold apparatus B has a space formed by the fixed mold 11 or the movable mold 12, the frames 13, 13 ', and the back plates 14, 14'.
That is, it has steam chambers 16 and 16 ', but has a pressure P ₁ (eg,
A pressurized gas of 0.1 to 6.0 kg / cm ² G), for example, compressed air is press-fitted to pressurize the internal pressures of both steam chambers to the above-mentioned predetermined pressure.

Next, the rotation supply device A is mainly composed of the casing 2 and the rotor 3 as shown, and the rotor 3 is provided with a plurality of chambers 4, and one end of the chamber 4 is provided on the casing 2. Since the other end of the chamber 4 coincides with the suction port 7 of the decompression line 8 at the rotation position corresponding to the supply port 5 of the expanded particles, the expanded particles in the hopper 1 are transferred into the chamber 4 by the decompression force. Fill this up. Chiyanba 4 which is filled with foamed particles, the end of Chiyanba 4 reaches the expanded beads outlet 6 by rotating in a state where both ends were sealed, than the pressure P ₁ of the other end of the Chiyanba 4 above, For example, 0.5kg /
Since reaching cm ² or higher pressure P ₂ in the pressurized pressurized gas outlet 9, the expanded particles filled cancer 15 while being compressed by the pressurized gas pressure P ₂ in Chiyanba 4, wherein the pressure P ₁
The mold cavity 21 formed by the fixed mold 11 and the moving body 12 pressed into the mold is filled. Since a plurality of the above-described chambers 4 are provided on the rotor 3 of the rotation supply device A, the expanded particles in the hopper 1
By repeating the above operation, the mold cavity 21 is divided into a plurality of times and is sequentially filled in the mold cavity 21.

Next, when a predetermined amount of the foamed particles in the mold is compressed and filled, for example, steam for degassing is introduced from the steam pipe 17 ′ into the steam chamber 16 ′ of the movable mold 12, and the steam is transferred to the steam of the movable mold 12. Holes 20 ', 20' ..., cavity 21
Inside, through the steam holes 20, 20,... Of the fixed mold 11, and through the fixed steam chamber 16, air is evacuated (discharged) to the outside of the system from the bleed pipe 18 provided with a pressure regulating valve. Then, the gas (air or the like) existing in the gaps between the foamed particles filled in the cavity 21 is accompanied by the steam and is exhausted.
In this case, the bleed pipe 18 ′ and the drain discharge pipe 19 ′ of the movable mold 12, the steam pipe 17 and the drain discharge pipe 19 of the fixed mold 11 are provided.
Are closed by valves (not shown), and the valves (not shown) of the mobile steam pipe 17 'and the fixed vent pipe 18 are opened respectively. It should be noted that the vent tube 18 is provided with a pressure regulating valve as described above.

In addition, the degassing process is performed by introducing steam for degassing from the steam pipe 17 of the fixed mold 11 to the steam chamber 16 in the opposite manner as described above, and the steam holes 20, 20... , 20 '..., Through a steam chamber 16', and may be discharged out of the system from a vent tube 18 '.

Further, in the deaeration process, after introducing the deaeration steam in the first mode and performing the deaeration process, the valve is switched, and the deaeration steam is further introduced in the second mode. Can be treated. Conversely, the operation may be performed in the second mode and then in the first mode.

These degassing treatments have a pressure 0.2 kg / cm ² or more higher than the pressure P _{1 because} it is necessary to stably supply steam into the chamber against the internal pressure P ₁ of the steam chambers 16 and 16 ′. This is done by introducing steam for degassing.

After the degassing process, the pressure in the cavity 21 is returned to the atmospheric pressure by opening the pipes 19 and 19 'to restore the compressed expanded particles, and then the steam chambers 16 and 16'
Steam at a predetermined temperature is supplied into the inside and heated to fuse the foamed particles to form a molded foam. Next, water is sprayed from the cooling water pipes provided in the steam chambers 16 and 16 'to the concave mold 11 and the convex mold 12 to cool the air, and further, if necessary, air-cooled and allowed to cool, and then the mold is opened. Take out.

(Examples, etc.) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Production Example of Foam Particles Production Example 1 Water was added to an autoclave having an inner volume of 3 and a pressure resistance of 50 kg / cm ^2.
1400 parts (parts by weight, the same applies hereinafter), ethylene / propylene random copolymer (Mitsubishi Yuka Co., Ltd. trade name Mitsubishi Noblen FG3, ethylene content 3% by weight, melting point 160 ° C.) 600 parts,
15 parts of tricalcium phosphate as a suspending agent, 0.05 part of sodium dodecylbenzenesulfonate as a surfactant, 150 parts of butane as a foaming agent were charged, and the temperature was raised from room temperature to 135 ° C. over 1 hour under stirring at 430 rpm. When the same temperature was maintained for 10 minutes, the internal pressure of the autoclave reached 28 kg / cm ² G. The discharge nozzle valve at the bottom of the autoclave was opened, and the contents were discharged into the atmosphere in 180 seconds with stirring at 180 rpm to cause foaming. The obtained expanded particles had a particle size of about 4 mm, a bulk density of 17.5 g /, and had many wrinkles on the surface.

Production Example 2 Water was added to an autoclave having an inner volume of 3 and a pressure resistance of 50 kg / cm ^2.
1400 parts (parts by weight, hereinafter the same), 600 parts of butene-1 / propylene random copolymer (butene 1 content 5% by weight, melting point 162 ° C., manufactured by Mitsubishi Yuka Co., Ltd.), 15 parts of magnesium pyrophosphate as a suspending agent, surfactant The mixture was charged with 0.05 parts of sodium dodecylbenzenesulfonate and 45 parts of butane as a foaming agent. The temperature was raised from room temperature to 140 ° C. over 1 hour under stirring at 430 rpm, and maintained at the same temperature for 10 minutes. Reached 29 kg / cm ² G. The discharge nozzle valve at the bottom of the autoclave was opened, and the contents were discharged into the atmosphere in 180 seconds with stirring at 180 rpm to cause foaming. The resulting expanded particles had a particle size of about 4 mm, a bulk density of 16.4 g / surface wrinkles.

Production Example 3 In Production Example 1, ethylene (4.2 wt%)-propylene random copolymer was used, and the amount of butane used was 14
Except that the foaming temperature was 132 ° C. and 0 parts, foamed particles of an ethylene / propylene random copolymer were obtained in the same manner.

The expanded particles have a particle size of about 4 mm, a bulk density of 19.2 g /,
The particles were wrinkled on the surface.

Example 1 1.0 kg of the wrinkled foamed particles obtained in Production Example 1 was put into an autoclave, and pressurized air of 4 kg / cm ² G at 80 ° C. was introduced into the autoclave for 30 minutes to perform a pressure treatment (in an autoclave). The pressure was kept at 4 kg / cm ² G by a control valve during processing), and then the valve of the nozzle provided at the lower part of the autoclave was opened to release the foamed particles into the atmosphere.

Immediately after release, the foamed particles had an internal cell pressure of 0 kg / cm ² G, a high density of 13.5 g /, and wrinkles on the surface had disappeared.

In-mold molding was performed using the foamed particles from which the wrinkles disappeared. DAIYA-600LF (trade name of Daisen Industries Co., Ltd.) as a molding machine, and a mold with an inner volume of 4.5 that can obtain a molded product with a width of 300 mm × length of 300 mm × height of 50 mm. The feeder used was an apparatus as shown in the accompanying drawings with six chambers (each chamber was 35 mm in diameter x 52 mm in length and 50 cc in volume), and a filling gun with a diameter of 30 mm was used as the filling gun.

Further, the molding method, first closing the mold, obtained by boosting the mold internal pressure P ₁ to 2Kg / cm ² G with compressed air. Then, 4 Kg / cm ² the expanded beads bulk density 13.5 g / in or has been prepared as the number of supply of Chiyanba 4 of the rotary feeder for compressed packing as set pressurized gas pressure P ₂ in 190 Using compressed air having a pressure of G, filling was carried out sequentially in 0.1 second intervals. During filling, evacuate the tube so that the mold pressure P ₁ is maintained at ² kg / cm ² G.
The pressure regulating valves attached to 18 and 18 'were activated.

After filling is completed, the filling gun is closed, the steam pipe 17 'is opened, 2.5 kg / cm ² G steam is introduced into the movable chamber 16' for 15 seconds, and the pressure control device attached to the vent pipe 18 is turned on. It was turned off and degassing was performed while controlling the in-mold pressure P ₁ to 2.5 kg / cm ² G.

Then, the supply of steam was stopped by closing the valves 17 'and 17, the drain discharge pipes 19' and 19 were opened, and the pressure in the chambers 16 'and 16 and the cavity 21 was instantaneously returned to the atmospheric pressure.

Then, simultaneously on the convex (movable) side and the concave (11) side, that is, on the fixed type steam chambers 16 'and 16,
2.5 kg / cm ² G steam was introduced for 10 seconds, and the foamed particles were heated and fused together.

The mold was water-cooled for 50 seconds, then air-cooled in a tube for 8 seconds, and then cooled for 60 seconds, then taken out and dried to obtain a foamed molded product having a density of 24.5 g /. The compression ratio was 45%. The obtained foamed molded article was filled with foamed particles by chance, the gap between the particles was very small (display gap: 2 pieces / 25 cm ² ), and the fusion was excellent (85%).

Examples 2 to 4 and Comparative Examples 1 to 5 In Example 1, except that the temperature (T), the pressure of the compressed air and the processing time during the heating and pressurizing treatment of the wrinkled foamed particles were changed as shown in Table 1. Similarly, foamed particles from which wrinkles disappeared were obtained.

Using the expanded particles, the beads were fusion-molded in a compression filling mold in the same manner as in Example 1 except that the compression ratio was changed as shown in the same table to obtain a molded product having the physical properties shown in the same table.

Example 5 The foamed particles having a wrinkled bulk density of 17.5 g / obtained in Production Example 1 were first heated in an autoclave at 80 ° C and 4 kg / cm ² G air.
After pressurizing for 30 minutes and then at 80 ° C. and air of 6 kg / cm ² G for 30 minutes, the pressure in the autoclave was returned to atmospheric pressure to obtain wrinkled expanded particles having a bulk density of 12.4 g /.

Thereafter, a molded product having a bulk density of 21.8 g / was obtained in the same manner as in Example 1.

Examples 6 to 8 Using wrinkled foamed particles obtained in Production Example 2 or 3,
The heated and pressurized treatment shown in Table 2 was followed to obtain wrinkle-free expanded particles, and a molded product was obtained in the same manner as in Example 1 below.

(Effect) According to the method for treating expanded beads of the present invention, wrinkles of expanded polypropylene resin particles having a high expansion ratio can be easily and
It can be expanded in a short time, and can be a foamed particle having a smooth surface. The in-mold molded product obtained using the expanded particles has an excellent degree of fusion among the particles.

[Brief description of the drawings]

The accompanying drawings show an example of an in-mold compression-filling bead fusion-bonding apparatus in a partial longitudinal sectional view. A: a rotary feeder for compressing and filling expanded particles, B:
... Molding device, 1 ... Hopper for foam particles, 2 ... Casing, 3 ... Rotor, 4 ... Chamber, 5 ... Exposure particle supply port, 6 ... Exposure particle discharge port, 7 ... Suction of vacuum line Mouth, 8 ... Decompression line, 9 ... Pressurized gas outlet, 10 ...
… Pressurized gas line, 11 …… Fixed type, 12 …… Movable type, 13,1
3 ′… Frame, 14,14 ′… Back metal, 15… Filling gun,
16,16 '... Steam chamber, 17,17' ... Steam pipe, 18,18 '... Vented pipe, 19,19' ... Drain discharge pipe, 2
0,20 '... Steam hole, 21 ... Cavity.

Claims (1)

(57) [Claims] An aqueous dispersion containing polypropylene resin particles containing a volatile expanding agent is discharged from a high pressure region to a low pressure region at a temperature not lower than the softening point of the polypropylene resin as a base resin of the particles. The foamed polypropylene resin particles having a bulk density of 30 g / or less obtained in a closed container, the melting end temperature of the intrinsic peak of the DSC curve obtained by differential scanning calorimetry of the base resin of the particles is Mp. When done, Mp-120 ℃ <
The foamed particles are heated and pressurized at a temperature (T) where T <Mp−70 ° C. and the pressure in the closed container is 1.0 kg / cm ² G or more. A method for treating expanded polypropylene resin particles, comprising subjecting the resin to exposure to a lower pressure atmosphere.