JPS6024933A - Pressurizing treatment of pre-expanded particle - Google Patents

Abstract

PURPOSE:To raise the bonding property of expanded grains as well as prevent the occurrence of sink by a method in which pre-expanded grains are put in a container, the internal pressure of the container is regulated to the same pressure as the internal pressure of the grains, the container is heated to a temperature at which no bonding and no contraction occur in the expanded grains to raise the internal pressure of the container, and the container is gradually cooled while keeping the internal pressure of the container. CONSTITUTION:Pre-expanded grains are put in an enclosed container, and the internal pressure of the container is regulated to the same pressure as the internal pressure of the grains. The container is gradually heated to a temperature enough to avoid the bonding and contraction of the grains, and the grains are slowly cooled while keeping the internal pressure of the container high. The pre-expanded grains are slowly cooled to room temperature, and the internal pressure of the container is lowered to ordinary pressure to obtain the pre-expanded grains whose internal pressure is 1.2-1.6 times higher than the original internal pressure of the grains. In the pressurizing treatment, the pre-expanded grains are treated in such a way as to avoid the contraction of the grains in order to provide an internal pressure necessary for molding for the grains. Therefore, the lowering of properties due to the breakage of bubble walls and occurrence of wrinkle, fawls, etc., on the surfaces of the grains do not occur. Since no contraction occurs in the grains, internal pressures necessary for molding can be provided for the grains in a short time.

Description

[Detailed description of the invention] The present invention relates to a method for pressurizing pre-expanded particles.

Generally, when pre-expanded particles are filled into a mold and molded indoors, it is known that a pressure treatment is performed before the molding process in order to apply an internal pressure suitable for forming the particles to the particles. usually,
In the pressurization treatment, the particles are placed in a pressurized container, and an inorganic gas such as air or nitrogen is supplied into the container to increase the pressure, and the inorganic gas is injected into the particles under osmotic pressure to give a constant gas pressure. It is something.

The conventional pressure treatment method is carried out by pressurizing pre-expanded particles under a certain pressure atmosphere for a certain period of time. Further, after holding the particles in a pressure atmosphere of 8 kg/d (G) or less, 0.5 to 3 kg/cd
A two-step pressurized treatment method is also known in which the material is maintained in a pressure atmosphere within the range (G) and lower than the above-mentioned pressure (Japanese Patent Publication No. 30304/1983).

However, in all conventional methods, after the particles are placed in a pressurized container, the pressure is rapidly applied and the pressure is maintained at a predetermined high pressure. The shrinkage destroys the cell walls of the particles, resulting in a disadvantage that the physical strength of the particles decreases and wrinkles, scratches, etc. occur on the particle surfaces. In addition, when particles contract, the volume of intraparticle air bubbles decreases and the internal pressure of the particles increases, so the pressure difference between the internal pressure and the pressurized atmospheric pressure becomes small4, which allows pressurized gas to enter the particles under osmotic pressure. As a result, there is a drawback that the internal pressure of the pre-expanded particles cannot be increased to a value required for molding when the pressurized atmosphere is removed and the original volume is restored. For this reason, even if molding is performed using pre-expanded particles that have been pressurized using the conventional method,
Shrinkage, sink marks, and poor fusion occurred in the resulting molded product, making it impossible to obtain a good foam molded product.

The inventors of the present invention have conducted extensive research in view of the above points, and have found that pressurization can be performed without shrinking the pre-expanded particles, and that the internal pressure necessary for molding can be applied to the pre-expanded particles in a short time. They found a method and completed the present invention.

That is, in the present invention, pre-expanded particles are placed in a closed container, and after adjusting the internal pressure of the container to approximately the same pressure as the internal pressure of the pre-expanded particles, the pre-expanded particles are gradually heated in a closed state to a temperature that does not cause melting or shrinkage of the pre-expanded particles. The temperature is raised to increase the internal pressure of the container, and then,
The gist of the present invention is a method for pressurizing pre-expanded particles, which is characterized by slow cooling while maintaining an elevated container internal pressure.

Although the present invention is applicable to any type of pre-expanded particles, polyolefin resins such as polypropylene homopolymer, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-butene copolymer, etc. It is particularly suitable for pressure treatment of pre-expanded particles that tend to shrink due to pressure, such as pre-expanded particles having a base material or pre-expanded particles having a base material of nylon or polyester elastomer.

In the present invention, first, the pre-expanded particles are placed in a closed container, and the internal pressure of the container is adjusted to approximately the same pressure as the internal pressure of the pre-expanded particles.

To adjust the internal pressure of the container, for example, an inorganic gas such as air, nitrogen, argon, helium, neon, carbon dioxide, or a mixed gas of the above-mentioned inorganic gas and a volatile blowing agent is used. Examples of volatile blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane;
Examples include halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, cyclotitrough, loloethane, methyl chloride, ethyl chloride, and methylene chloride.

It is economically preferable to use the above-mentioned inorganic gas or a mixed gas of the inorganic gas and a volatile blowing agent (usually air).

), the pressure inside the container is determined from the internal pressure of the pre-expanded particles to the internal pressure +0.
．． It is preferable to adjust the pressure to 5 ky/cl.

After adjusting the internal pressure of the container, the temperature is gradually raised in a closed state to a temperature that does not cause fusion or shrinkage of the pre-expanded particles. The temperature at the end of this heating is usually 50° C. to 130° C., although it varies depending on the type of base resin, etc., and the temperature increasing rate is preferably 0.5° C./min to 5° C./min. The internal pressure of the container at this time; P2 (atnl) is the temperature before heating up, which is TI (K).
, the internal pressure of the container is Pl (atm), and the temperature at the end of heating is T2 (K), the pressure is increased to the pressure given by .

Next, in the present invention, the pre-expanded particles are slowly cooled with tin while maintaining the increased container internal pressure: P.
By supplying the above-mentioned inorganic gas or a mixed gas of an airless gas and a volatile blowing agent into the container to compensate for the decrease in the container internal pressure due to the temperature drop, the container internal pressure is maintained at P until the slow cooling is completed. maintain it. The temperature decreasing rate in the above slow cooling step is 0.01℃
/min to 2°C/min is preferred. After slowly cooling the pre-expanded particles to room temperature, the pre-expanded particles obtained by lowering the internal pressure of the container to this pressure have an internal pressure that is about 1.2 to 1.6 times the internal pressure of the original pre-expanded particles. Further, the time required for the above-mentioned pressure treatment is usually about 2 hours to 24 hours.

In the present invention, the above-mentioned slow cooling may be performed at a constant temperature decreasing rate, or may be performed by changing the temperature decreasing rate in stages as the temperature decreases. Further, the pressure treatment in the present invention is not limited to one time, but may be repeated multiple times.

As explained above, the pressure treatment method of the present invention applies pressure treatment to the pre-expanded particles so as not to cause shrinkage, and gives the particles the internal pressure necessary for molding. There is no possibility that the particles will deteriorate in physical properties due to cell wall destruction or that wrinkles, scratches, etc. will occur on the particle surface. In addition, the pressure-treated particles shrink, and as a result, the internal pressure necessary for molding can be applied to the particles reliably and in a short time.

However, by filling a mold with pre-expanded particles that have been subjected to pressure treatment according to the present invention and heating and foaming them, the particles have excellent fusing properties, and shrinkage and sink marks do not occur. It is possible to obtain a molded product of high quality.

The present invention will be explained in more detail below by giving Examples and Comparative Examples. Note that μ indicates absolute pressure unless otherwise specified.

Example I Polypropylene pre-expanded particles (melting point 148°C
) sooy in a 201 autoclave and seal it.
After adjusting the internal pressure of the autoclave to 1.6 Ky/d with air, the autoclave was kept in a sealed state and heated at a heating rate of 1°C/min to 12
The temperature was raised to 7°C (400K). At this time, the autoclave internal pressure L was 2.1 sKy/crl. As a result of observing the state of the pre-expanded particles through the glass window of the autoclave,
No shrinkage was observed in the pre-expanded particles. Next, air is supplied into the autoclave to increase the autoclave internal pressure to 2. x
s from 127℃ to 77℃ while maintaining sKy/c11.
6”C/min, 0.3°C/min from 77°C to 52°C,
Slow cooling was performed at a temperature decreasing rate of 0.1°C/min from 52°C to 20°C (room temperature). No shrinkage was observed in the pre-expanded particles until the end of the slow cooling. The time required for the above pressure treatment was 10 hours. The surface condition and internal pressure of the pre-expanded particles after treatment were measured. The results are shown in Table 1. Further, the above pre-expanded particles were filled into a mold of 30 x 300 m* x 300 m (inner diameter) and heated with water vapor of 3.5 Kp/cra (G) to perform molding. The obtained molded body is
After drying in an open room at 0° C. for 20 hours, the shrinkage rate of the molded product was measured. The results are also shown in Table 1.

] Example 1 The same pre-expanded particles as in Example 1 were placed in an autoclave, and syringed with air at room temperature (20°C).

The autoclave internal pressure was adjusted to Kf/t4, and pressurization treatment was performed for 20 hours. The surface condition and internal pressure of the pre-expanded particles after treatment were measured. The results are shown in Table 1. Further, the pre-expanded particles were molded in the same manner as in Example 1. Table 1 shows the results of measuring the shrinkage of the molded product obtained.

Example 2 Expansion ratio 2 made of cross-linked polyethylene with gel fraction of 60 inches
0 times, internal pressure 1.24Kp/61 at 22℃ (room temperature)
800 g of pre-expanded particles having a particle size of 1.5 g were placed in a 201 autoclave, the autoclave was sealed, and the internal pressure of the autoclave was adjusted to 1.0 g with air.
It was adjusted to 24Kf/l:tl. Then, keep it in a closed state at 1℃.
The temperature was raised to 97"C (370K) at a rate of 1/min. The internal pressure of the autoclave at this time was x,5eKp,',1.The state of the pre-expanded particles was also observed through the glass window of the autoclave. No shrinkage was observed in the particles.Next, air was supplied into the autoclave to maintain the autoclave internal pressure at 1.56 Ky/d, and the particles were slowly cooled to room temperature over 8 hours at a constant cooling rate. Pre-expanded particles are 1-56 Kp/cffl at 22°C (room temperature)
It had an internal pressure of Furthermore, the IT autoclave in which these pre-expanded particles were placed was sealed again, and the internal pressure of the autoclave was adjusted to 9/6 d with air to 1.56, and then the temperature was raised and slowly cooled in the same manner as above ( The internal fan of the autoclave when the temperature rose to 97°C was 1°94Ky/
During slow cooling, the autoclave internal pressure was maintained at 1.94 Ky/crl with air. ) The time required for two pressurization treatments was 18 hours. The surface condition and internal pressure of the pre-expanded particles after the two pressurization treatments were measured. The results are shown in Table 1. Further, the above pre-expanded particles were molded in the same manner as in Example 1 (however, 25 Ky/
It was heated with crl (G) steam. ) The shrinkage rate of the molded body was measured. The results are also shown in Table 1.

Comparative Example 2 The same pre-expanded particles as in Example 2 were placed in an autoclave, and the internal pressure of the autoclave was replaced with air at room temperature (22°C).
Pressure treatment was performed for 32 hours with the pressure adjusted to Ky/cl. The surface condition and internal pressure of the pre-expanded particles after treatment were measured. The results are shown in Table 1. Further, the shrinkage rate of a molded product obtained by molding the pre-expanded particles in the same manner as in Example 2 was measured. The results are shown in Table 1.

*1 The surface condition of the pre-expanded particles was determined by observing the particle surface, and there were no wrinkles or scratches on the surface...○〃 Wrinkles or scratches...・It was judged as ×.

*2 The internal pressure is a value converted to 20℃.The internal pressure of the particles is calculated by taking an arbitrary amount (for example, 100 cc) of pre-expanded particles, accurately weighing its weight 1-W, (II), and using the following formula. The internal pressure of the pre-expanded particles was then increased.

However, Wo... Weight iIk (g) when the internal pressure of the pre-expanded particles (sample) is atmospheric pressure (i.e. latm).・・・・・・Pre-expanded particles at an internal pressure of 1 atm (
True volume (cc) of sample) ■.・・・・・・Value obtained by dividing Wo under the resin density (CC)
(In other words, the volume of the resin die forming the particles) M...Molecular weight of the pressurized gas R...Gas constant (0,082a tm-//m
ol -K)t...Temperature (℃) S...Conversion coefficient of pressure unit (1,0332Kf/cr/l/at m)*3
The shrinkage rate of the molded product in the plane direction of the mold was determined as follows: Shrinkage rate less than 5%: ○ 5% or more: ×.

0! 'f Applicant: Japan Styrene Paper Co., Ltd. Agent: Patent Attorney Isamu Hosoi 1C!

Claims (1)

[Claims] The pre-expanded particles are placed in a sealed container, and after adjusting the internal pressure of the container to approximately the same pressure as the internal pressure of the pre-expanded particles, the temperature is gradually raised in a closed state to a temperature that does not cause the pre-expanded particles to fuse or shrink. 1. A method for pressurizing pre-expanded particles, which comprises increasing the internal pressure of the container, and then slowly cooling the container while maintaining the increased internal pressure.