JP2000169618A - Production of polyolefin-based resin foamed grain secondarily foamed in high magnification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject foamed grains capable of preventing the decrease in the foamability of the primarily foamed grains by the use of a compact and inexpensive device by impregnating the specific primarily foamed grains with a foaming agent in a gaseous phase in a pressure vessel, heating the foamed grains, while maintaining the same vessel in a pressurized state, and then releasing the primarily foamed grains outside the pressure vessel. SOLUTION: This method for producing the polyolefin-based resin foamed grains secondarily foamed in a high magnification comprises impregnating (A) low magnification polyolefin-based resin foamed grains preferably having a magnification of 3-20 times with (B) a foaming agent such as air in a pressure vessel preferably at a pressure of 5-30 kg/cm2 (abc) at a temperature of 60-100 deg.C for 60-360 min in the gaseous phase, heating the foamed grains preferably at the softening temperature +5 to 30 deg.C for 0.5-5 min, while maintaining the inner pressure of the same vessel in the pressurized state, and then releasing the foamed grains outside the pressure vessel. The base material resin of the component A includes propylene-ethylene random copolymer. The foaming magnification of the foamed grains is preferably 5-40 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expanded polyolefin-based resin particles obtained by imparting foaming ability to low-magnification polyolefin-based resin expanded particles, heating the expanded particles, and secondary-expanding the expanded particles at a high magnification. .

[0002]

2. Description of the Related Art Expanded polyolefin resin particles are frequently used in in-mold foam molding, and these expanded particles range in size from low to high. In particular, high-magnification foamed particles are often obtained by imparting foaming power to low-magnification foamed particles and performing secondary foaming by heat treatment or the like, and various secondary foaming methods have been proposed (Japanese Patent Laid-Open No. Sho 58-58). -1366
No. 34, JP-A-58-65734, JP-A-58-65734
1-291107, JP-A-10-237212).

In these secondary foaming methods, low-expanded foamed particles are impregnated with a foaming agent to impart foaming capability, and then the foamed particles are subjected to secondary foaming by heat treatment or the like. The device used for the secondary foaming is different from the device used for the secondary foaming. The foamed particles provided with the foaming ability are fed into the secondary foaming device through processes such as transportation and measurement.

[0004] However, the above-mentioned processes such as transportation and measurement are often performed under atmospheric pressure, and if these processes are interposed, a part of the foaming agent impregnated to impart the foaming capability to the foamed particles may be removed from the atmosphere. Has the disadvantage that the foaming ability is reduced.
The amount of decrease in the foaming ability is not uniform but varies among the foamed particles, and the magnification of the foamed particles after secondary foaming also varies. In addition, a foaming ability providing step, a transport / weighing step,
If the subsequent foaming steps are separately provided, the apparatus will not be compact and the equipment cost will be high.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, the process of imparting foaming ability to low-magnification foamed particles and the secondary foaming process have been carried out using the same equipment. The present invention has been found to prevent the reduction of the foaming ability of the foamed particles, which is a conventional drawback, by omitting the transportation and weighing of the foamed particles between both steps, and to find that the apparatus is compact and inexpensive. It was completed.

That is, according to the present invention, a foaming agent is imparted to a low-magnification polyolefin resin foamed particle by impregnating a foaming agent in a gas phase in a pressure-resistant container, and then the foaming is performed while maintaining the same container in a pressurized state. The present invention relates to a method for producing expanded polyolefin resin particles which have been subjected to secondary expansion at a high magnification, wherein the particles are heated and then the expanded particles are discharged out of a pressure vessel.

[0007]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, low-magnification polyolefin resin expanded particles (hereinafter also referred to as low-magnification PO expanded particles) are charged into a pressure-resistant container, a blowing agent is impregnated in a gas phase, and foaming ability is imparted. You.

The polyolefin resin constituting the low-magnification PO expanded particles can be used without particular limitation as long as it is generally used for producing polyolefin resin expanded particles.

Specific examples of the polyolefin resin include, for example, an ethylene-propylene random copolymer,
Ethylene-propylene-butene random terpolymer,
Ethylene-propylene block copolymer, polypropylene resin such as homopolypropylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer,
Examples include polyethylene resins such as ethylene-methyl methacrylate copolymer, as well as polybutene and polypentene. These polyolefin-based resins may be used in a non-crosslinked state, or may be used after being crosslinked by peroxide or radiation. Among them, the ethylene-propylene random copolymer (the ethylene unit content is about 1 to 10% by weight) makes it easy to obtain high-expanded secondary expanded particles, and the mechanical strength and heat resistance of the obtained molded article. Is preferred in that it is good.

[0010] The low magnification in the low-magnification PO expanded particles is as follows.
Further, it refers to a ratio at which secondary expansion can be performed at a high magnification, and even expansion ratios that fall within the category of high-magnification expanded particles are generally 2%.
This includes cases where higher magnification is achieved by subsequent foaming.
The low magnification ranges from 1.5 to 30 times, and more preferably 3 to 20 times. If the foaming ratio is too low, it is difficult to perform secondary foaming at a high ratio, and if it is too high, it is difficult to make the device which is a feature of the present invention compact.

Examples of the foaming agent to be impregnated with the gas phase include a gas containing nitrogen as a main component and an organic gas from a low-boiling organic compound such as butane.

When an inorganic gas such as air is used as the gas mainly containing nitrogen, it is advantageous at low cost.

When a mixed gas of an inorganic gas containing nitrogen as a main component and an organic gas from a low-boiling organic compound is used as a foaming agent, a processing time for imparting foaming ability is shortened, and However, since the foaming agent used is released into the atmosphere in the secondary foaming step, it is preferable to use air.

As the pressure-resistant container into which the low-magnification PO expanded particles are charged, the low-magnification PO expanded particles can be impregnated with a foaming agent in a gas phase to provide a foaming ability. Any pressure-resistant container capable of performing secondary foaming of the particles by heating in a pressure state and discharging the particles out of the container may be used.

The capacity of the pressure-resistant container is not particularly limited as long as it corresponds to the amount of the low-magnification PO expanded particles, and is not particularly limited. It is generally 10 times, and more preferably 2 to 5 times. For example, 30 to 200 liters when 20 liters of low-magnification PO expanded particles having an expansion ratio of 5 are input, and 60 to 400 liters when 40 liters of low-magnification PO expanded particles having an expansion ratio of 12 are input. Are usually used.

The shape of the pressure vessel is not particularly limited. When stirring is performed when the blowing agent is impregnated in the gas phase or when the particles are discharged, the shape is preferably suitable. Generally, a cylinder having a semi-elliptical or hemispherical head plate is used in consideration of pressure resistance, manufacturing cost, installation area, and the like.

The gas-phase impregnation may be performed by a conventional method after, for example, charging the low-magnification PO expanded particles into the pressure-resistant container, until the pressure required for gas-phase impregnation of the blowing agent is reached. It is done by introducing. At this time, a heated blowing agent may be circulated in order to promote the impregnation of the blowing agent. The stirring is preferably performed so that the temperature of the particles in the container becomes uniform.

The pressure required for gas-phase impregnation is not particularly limited as long as it is suitable for the type of low-magnification PO expanded particles, the desired secondary expansion ratio, and the like. Generally, 1.5 to 50 kg / cm ² (abs), and more preferably 5 to 30 kg / cm ²
It is preferably cm ² (abs). 1.5kg / cm ² (abs)
In the becomes insufficient foaming agent vapor impregnation under high magnification particles occurs tends to be difficult to obtain, 50kg / cm ² (ab
If s) is exceeded, it takes time to recover the low-magnification particles compressed by high pressure, and the gas-phase impregnation tends to be difficult.
The lower the expansion ratio of the low-expansion PO expanded particles, the higher the pressure and the higher the expansion ratio.

The temperature in the pressure vessel at the time of introduction of the foaming agent and after the introduction is preferably 30 to 1 to promote the impregnation of the foaming agent.
The temperature is preferably 20C, more preferably 60C to 100C.
If the temperature is lower than 30 ° C., the effect of accelerating the impregnation of the foaming agent tends to be hardly obtained.

The time required for the gas phase impregnation is 30 to 600 minutes after the introduction of the foaming agent, at a predetermined pressure and temperature, and more preferably 60 to 360 minutes, from the viewpoint of secondary foamability and productivity. preferable. In less than 30 minutes, the foaming agent is sufficiently reduced to a low magnification P.
O-foamed particles cannot be impregnated, and high-magnification PO-foamed particles tend to be difficult to obtain, and if it exceeds 600 minutes, there tends to be a problem in terms of productivity.

After the gas phase impregnation, the internal pressure of the foaming agent impregnated inside the low-magnification PO expanded particles provided with the foaming ability is generally 1.5 to 10 kg / cm ² (abs), and furthermore, It becomes 2-5 kg / cm ² (abs).

After imparting the expandability to the low-magnification PO expanded particles, the expanded particles are heated while keeping the same container in a pressurized state, and then the expanded particles are discharged to the outside of the pressure-resistant container. Polyolefin-based resin expanded particles which are secondarily expanded at a magnification are produced.

While the same container is maintained in a pressurized state, the pressure in the pressure-resistant container is maintained within a pressure range not lower than the internal pressure of the blowing agent impregnated in the low-magnification PO expanded particles. Means that the pressure does not exceed the internal pressure of the particles by 1 kg / cm ² (abs) or more.

The above-mentioned heating refers to heating the low-magnification PO expanded particles to the softening temperature or higher, preferably to the softening temperature +5 to 30 ° C., for example, supplying a heating medium into the pressure-resistant container while stirring the inside of the pressure-resistant container. What is necessary is just to do by doing. If the temperature is too high, fusion of the particles or the physical properties of the obtained secondary expanded particles tend to decrease, and if the temperature is too low, it tends to be difficult to obtain high magnification secondary expanded particles.

As the heating medium, steam may be used, and the foaming agent in the pressure vessel may be heated by using a heat exchanger, a blower, or the like to serve as a heating medium.

The time required for the heating may be 0.1 to 10 after reaching a predetermined temperature from the viewpoint of secondary foamability and productivity.
Minutes, more preferably 0.5 to 5 minutes. If the time is too long, the magnification of the secondary expanded particles does not increase any more, and the productivity tends to be deteriorated. If the time is too short, the heating is insufficient and it is difficult to obtain the high expanded secondary expanded particles. There is a tendency.

The low-expansion PO foamed particles thus imparted with the foaming ability and heated to the softening temperature or higher are not foamed in the pressure vessel because the foaming agent (gas) is under pressure, and the foaming agent is diffused. The foaming ability does not decrease.

Discharging of the heated foamed particles to which the foaming ability has been imparted and heated out of the pressure-resistant container is performed by instantaneously lowering the internal pressure of the pressure-resistant container to atmospheric pressure by opening the discharge valve of the pressure-resistant container. . The low-expansion PO expanded particles provided with the foaming ability discharged out of the pressure-resistant container and heated to a softening temperature or higher are subjected to secondary expansion, and polyolefin-based resin expanded particles secondary-expanded to a desired high magnification are formed. can get.

Since the discharge valve of the pressure-resistant container is usually connected to the storage tank by a pipe, at the same time when the discharge valve is opened, the particles are mainly sent to the storage tank by secondary foaming in the pipe. After the secondary foaming (dispensing), some of the secondary expanded particles remain in the pressure-resistant container, but by continuing to stir the pressure-resistant container and supplying a foaming agent or the like,
The remaining secondary expanded particles can be easily pumped to the storage tank.

Thus, the step of imparting the foaming ability to the low-magnification PO expanded particles and the secondary foaming step can be performed by the same equipment, and the low-magnification PO foamed particles provided with the foaming ability can withstand pressure even when heated. Since the pressure in the container is equal to or higher than the internal pressure of the particles, the particles do not undergo secondary foaming in the pressure container until the discharge valve is opened, and the volume of the pressure container is equal to the secondary pressure of the particles. A minimum volume that can be stirred and mixed before foaming is sufficient, and the apparatus becomes compact and cheap.

The expansion ratio of the obtained polyolefin-based resin particles secondary-expanded at a high magnification is generally 3 to 50.
Times, preferably 5 to 40 times. The expansion ratio is generally 1.25 of the expansion ratio of the low-expansion PO expanded particles.
３３33 times, furthermore 1.5１．５13 times.

[0032]

EXAMPLES Next, the production method of the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Example 1 FIG. 1 schematically shows an apparatus for performing the foaming ability imparting step and the secondary foaming step using the same equipment used in this example. FIG.
Inside, X is air, Y is steam, 1 is a pressure vessel, 2 is a stirrer, 3 is a raw material inlet, 4 is a pressure gauge, 5 is a thermometer, 6 is low-expansion polypropylene resin particles described later, 7 is Heat exchanger, 8 blower, 9 storage tank, 10a discharge valve, 1
0b is an air discharge valve, 10c is an air supply valve, 10d is an air circulation outlet valve, 10e is an air circulation inlet valve, 10f
Denotes a steam supply valve, and 11 denotes a pipe.

Expanded polypropylene resin particles having an expansion ratio of 12 times (base resin is propylene-ethylene random copolymer, density 0.90 g / cm ³ , MI = 10 g / 10 min,
Ethylene unit content 3% by weight) (hereinafter referred to as low-magnification PP expanded particles) was charged into the 160-liter pressure-resistant container 1 through the raw material inlet 3 in a volume of 40 liters. By supplying air X through the air supply valve 10c while circulating air through the heat exchanger 7, the internal pressure of the pressure-resistant container was set to 21 kg / cm ² (abs) and the internal temperature was set to 100 ° C. This state was maintained for 3 hours while continuing air circulation, and air was impregnated in the gas phase. The internal pressure of the air impregnated inside the low-magnification PP expanded particles after gas phase impregnation was 4 kg / cm ² (abs).

Next, the pressure in the pressure vessel is reduced to 4.2 kg / cm ² (abs) by opening the air discharge valve 10b, and then the inside of the pressure vessel is agitated using the stirrer 2 in the pressure vessel. The temperature was further heated to 130C. 5 in this state
After holding for 1 minute, the dispensing valve 10a was opened to release the pressure in the pressure-resistant container, thereby discharging the low-magnification PP expanded particles, and pressure-fed to the storage tank 9 while performing secondary expansion in the pipe 11. The secondary expanded particles partially remaining in the pressure vessel are air X
Was pressure-fed to the storage tank by additionally supplying from the air supply valve 10c.

The magnification of the secondary expanded particles thus obtained is 2
It was four times.

Example 2 Using the same apparatus as in Example 1, a magnification of 1 was used in the same manner as in Example 1.
2x low magnification polypropylene resin expanded particles (low magnification P
After charging 40 liters of P foamed particles into the pressure vessel 1 in bulk volume, the internal pressure of the pressure vessel was set to 11 kg / cm ² (abs) and the internal temperature was set to 100 ° C. in the same manner as in Example 1. This state was maintained for one hour while continuing the air circulation, and air was impregnated in the gas phase. The internal pressure of the air impregnated inside the low-magnification PP expanded particles after gas phase impregnation was 3 kg / cm ² (abs).

Next, after the air release valve 10b is opened to reduce the pressure in the pressure-resistant container to 3.2 kg / cm ² (abs), the air circulation is stopped, and then steam is supplied while stirring the inside of the pressure-resistant container. Water vapor Y is supplied into the pressure-resistant container through the valve 10f, the pressure in the pressure-resistant container is set to 5.6 kg / cm ² (abs) (air pressure + water vapor pressure), the temperature is set to 130 ° C., and after maintaining for 90 seconds, the steam is supplied. After closing the valve 10f and stopping the supply of water vapor, the discharging valve 10a is opened and the low-magnification PP expanded particles are secondary-foamed as in the first embodiment.
Pumped to

The magnification of the secondary expanded particles thus obtained was 27.
It was twice.

[0040]

By performing the foaming ability imparting step to the low-magnification PO expanded particles and the secondary foaming step with the same equipment, the conventional disadvantages of the foaming ability imparting step and the secondary foaming step can be eliminated. The reduction in the foaming ability of the low-magnification PO foamed particles after the foaming ability is generated can be prevented, and the apparatus can be made compact and cheap.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an apparatus for performing a foaming ability imparting step to a low-magnification PO foamed particle and a secondary foaming step, which are used in Examples, with the same equipment.

[Explanation of symbols]

 X Air Y Steam 1 Pressure vessel 2 Stirrer 3 Raw material inlet 4 Pressure gauge 5 Thermometer 6 Low magnification polypropylene resin foam particles 7 Heat exchanger 8 Blower 9 Storage tank 10a Discharge valve 10b Air release valve 10c Air supply valve 10d Air circulation Outlet valve 10e Air circulation inlet valve 10f Steam supply valve 11 Piping

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B29K 105: 04 F term (Reference) 4F074 AA17 AA22A AA24 AA25A AA25B AA26 BA33 BA35 BA37 BB02 CA24 CA30 CA34 CA35 4F201 AA03 AB02 AC01 AG20 BA02 BC01 BC12 BC37 BL01 BL47 BN01 BN36 4F212 AA09 AA11 AB02 AB03 AG20 UA01

Claims (1)

[Claims] 1. A foaming agent is imparted to a low-magnification polyolefin resin foam particle by impregnating a foaming agent in a gas phase in a pressure-resistant container, and then the foamed particle is heated while maintaining the same container in a pressurized state. Then, the foamed particles are discharged to the outside of the pressure-resistant container.