JPS6140334A - Method of providing preliminarily expanded particle of polyolefinic resin with internal pressure - Google Patents

Abstract

PURPOSE:In permeating a gas into preliminarily expanded particles under pressure, to provide the particles with internal pressure in a short time efficiently without using a high pressure vessel, by setting a shrinkage factor at a specific value. CONSTITUTION:In providing preliminarily expanded particles of olefinic resin with internal pressure by permeating a gas into the particles under pressure, the gas is permeated into the particles under pressure while raising gradually the pressure of the gas in such a way that a shrinkage volume factor of the particles is 10-50%. Propylene-ethylene copolymer, or polyethylenic resin is preferable as the polyolefinic resin. The internal pressure of the particles is 1.18-4.00 atmospheric pressure (absolute pressure), preferably 1.40-2.60 atmospheric pressure (absolute pressure).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for applying internal pressure to pre-expanded polyolefin resin particles.

[Prior Art] Conventionally, in the in-mold molding of polyolefin resin particles, the pre-expanded polyolefin resin particles are treated in a pressurized gas atmosphere to increase the internal pressure before molding, and then the in-mold molding is performed. is publicly known. Which method usually involves filling pre-expanded polyolefin resin particles into a pressure-resistant container, and then introducing a pressurized inorganic gas into the pressure-resistant container to diffuse and permeate the pressurized gas into the particles. This method applies internal pressure to the

As a known conventional technique, there is a method described in Japanese Patent Laid-Open No. 49-85158.

In this method, the polyolefin resin pre-expanded particles are placed under fairly high gas pressure, so the degree of shrinkage of the particles is significantly large, and various problems arise, such as the need for a pressure-resistant container with structural strength that can withstand high-pressure gas. This poses problems, such as being economically disadvantageous and slowing down the rate of diffusion and permeation, probably because the surface area through which the pressurized gas diffuses and permeates is apparently reduced due to shrinkage of the particles.

Other conventional techniques include the method described in Japanese Patent Application Laid-Open No. 58-101025.

In this method, the pre-expanded polyolefin resin particles are held under pressure that does not cause them to shrink, and then the pressurizing pressure is gradually increased to give internal pressure to the particles so as not to cause their shrinkage. However, in this case, since the particles are press-fitted at a pressure that does not cause shrinkage, this pressure is extremely low, depending on the expansion ratio of the particles, and as a result, the time required to apply the specified internal pressure to the particles is very low. The disadvantage is that it is extremely long. Therefore, the volume of the container used to apply particle internal pressure becomes extremely large, or if a container of normal size is used, the number of containers increases, resulting in an economic disadvantage.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of the known techniques, namely, the degree of shrinkage of pre-expanded polyolefin resin particles as in the method described in JP-A-49-85158. There are problems such as being extremely large, slowing the rate of gas diffusion and permeation, and requiring a pressure-resistant container that can withstand high pressure. This is an attempt to solve problems such as the time required to apply an internal pressure of 100 mL to an extremely long time and the volume of the container used to be extremely large.

[Means for Solving the Problems] The present invention provides that when gas is injected into pre-expanded polyolefin resin particles to apply internal pressure to the particles, the volume shrinkage of the particles falls within a range of 10 to 50%. The present invention relates to a method for applying internal pressure to pre-expanded polyolefin resin particles, which is characterized by gradually increasing the pressure of gas and pressurizing it under such conditions.

That is, in the present invention, when injecting and infiltrating pre-expanded polyolefin resin particles under pressurized gas, internal pressure can be applied extremely efficiently to the particles by setting the shrinkage rate of the particles within a specific range. This is possible.

[Example] The polyolefin resin used in the present invention includes polypropylene, a random or block copolymer of propylene and ethylene, a terpolymer of propylene, ethylene, and butene, low density polyethylene, and linear low density polyethylene. , medium density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer, copolymer of ethylene and acrylic acid or acrylic acid metal salt, polybutene-
1, poly-4-methylpentene-1, etc., but are not limited thereto. These resins may be used alone or in combination of two or more.

Alternatively, a mixture of the resin and an inorganic or organic filler may be used.

Among the polyolefins and resins mentioned above, crosslinked or non-crosslinked propylene-ethylene copolymers and polyethylene resins are particularly preferred.

There are no particular limitations on the method for producing the pre-expanded polyolefin resin particles used in the present invention, and any method may be used to produce the pre-expanded polyolefin resin particles.
It doesn't matter if it's something you've been given.

For example, a volatile foaming agent, polyolefin resin particles, and a dispersant are dispersed and suspended in a pressure-resistant sealed container with water.
Then, after raising the temperature to a predetermined temperature and pressure, pre-expanded particles obtained by releasing the polyolefin resin particles and water into a low pressure region, or polyolefin resin particles impregnated with a volatile blowing agent or an inorganic gas, are prepared. Pre-expanded particles are obtained by placing them in a pressure-resistant container and heating them with steam or the like in the container. Examples include pre-foamed particles obtained by extruding a foamed strand through a perforated die and then cutting the foamed strand into an appropriate length with a cutter, etc., but pre-foamed particles having substantially closed cells are available. Particles obtained by any method can be used.

There is no particular limit to the density of the polyolefin resin pre-expanded particles, but for example, the density is 9.01 to 0.3 g.
/cmA, average bubble diameter 100-1000μ
About m is used.

Gases used in the method of the present invention include air, nitrogen,
Inorganic gases such as carbon dioxide, helium, and argon, aliphatic hydrocarbons such as methane, ethane, propane, butane, and pentane, whose boiling point under atmospheric pressure is 50°C or less, chlorodifluoromethane, dichlorodifluoro Examples include volatile organic gases such as halogenated hydrocarbons such as methane, dichlorotetrafluoroethane, methyl chloride, and methylene chloride, but air is preferably used from the viewpoint of economy and ease of handling. These gases may be used alone or in combination of two or more.

Next, the method of the present invention will be explained based on embodiments.

After filling a pressure tank with polyolefin pre-expanded particles, air pressure can be injected into the pre-expanded particles by introducing pressurized gas into the pressure tank, but when the pressurized gas is introduced into the pressure tank, It is necessary to gradually increase the gas pressure under conditions such that the volume shrinkage of the pre-expanded polyolefin resin particles falls within the range of 10 to 50%.

The volume shrinkage rate of the pre-expanded polyolefin resin particles in this case refers to the bulk volume shrinkage rate measured under various conditions of warm polishing and pressure after filling the pre-expanded particles into a graduated pressure-resistant glass container. .

The initial pressure of the pressurized gas varies depending on the type of pre-expanded polyolefin resin particles, expansion ratio, temperature when applying internal pressure, etc., but for example, when pre-expanded particles of ethylene-propylene random copolymer with an expansion ratio of 30 By the way,
The volume shrinkage rate becomes about 10-50% at about 0.5-1.
It is in the range of 4Kg/cdG.

After applying the initial pressure, the pressure of the gas is gradually increased.
It is necessary to do this so that the shrinkage rate does not fall outside the range of 10 to 50%, and in reality this can be determined by determining in advance the conditions under which the shrinkage rate does not fall outside the range of 10 to 50% for the scaled pressure-resistant glass container. For example, in the case of pre-expanded particles of ethylene-propylene lantum copolymer with an expansion ratio of 30 times, depending on the initial pressure value of the pressurized gas,
Usually 0.5Kg/a per hour! Below, preferably 0
．． The range is 09 to 0°48y/cd.

As a method for gradually increasing the pressurizing pressure, it may be increased continuously using an automatic control device or the like, or it may be increased stepwise at fixed time intervals.

When the volumetric shrinkage rate is less than 10% or more than 50%, the rate of applying internal pressure becomes slow, resulting in extremely poor efficiency.

When the shrinkage rate is less than 10%, the pressure of the pressurized gas is too low, and when it exceeds 50%, the particle shrinkage rate is too large and the particle interfacial area decreases, resulting in a low internal pressure application rate. It is considered to be.

The temperature of the pressure tank when applying internal pressure cannot be limited because it varies depending on the type of polyolefin resin, the expansion of the pre-expanded particles, the magnification, etc., but it is usually between room temperature and 80°C.
determined from the range of

According to the method of the present invention, pressurized gas diffuses into the interior of the pre-expanded polyolefin resin particles, and after a certain period of time, a -room pressure is achieved. This particle internal pressure varies depending on the type of polyolefin resin, the presence or absence of crosslinking of the resin, the expansion ratio of the pre-expanded particles, etc.
absolute pressure), preferably 1.40 to 2.60
This is the range of atmospheric pressure (absolute pressure).

In the present invention, the method for measuring the internal pressure of polyolefin resin particles after internal pressure application treatment is to store the polyolefin resin particles after internal pressure application treatment in a container connected to a gas buret, and then to measure the internal pressure of the polyolefin resin particles after internal pressure application treatment. The amount of gas can be measured using a gas buret, or the polyolefin resin particles after the internal pressure application process can be left at a desired temperature of 50 to 80°C for 2 to 3 hours, and the gas can be diffused from within the pre-expanded particles by the internal pressure application process. After all the permeated gas is expelled, the weight change of the particles is measured, and the weight change is calculated as pressure using the ideal gas equation of state. However, any method may be used.

In the present invention, pre-expanded polyolefin resin particles to which a predetermined internal pressure has been applied are transferred to an in-mold molding process, filled into a mold that can be closed but cannot be closed and is equipped with a steam heating device, and then heated with steam. The product is molded to produce an in-mold foamed product.

Next, the method of the present invention will be explained in more detail based on Examples and Comparative Examples.

Examples 1 to 8 and Comparative Examples 1 to 4 100 parts of ethylene-propylene random copolymer particles (ethylene content 4.5% (weight %, same hereinafter)) were added to 300 parts of water in a pressure container, and dichlorodifluoromethane was added. Approximately 3
0 parts and a small amount of dispersant. Next, the dispersion was heated to a prefoaming temperature of 134 to 136°C, and then dichlorodifluoromethane was newly added while maintaining the internal pressure of the container at a pressure of 26 to 27 9/ldG. After that, the 4sφ oriswiss hole provided at the bottom of the pressure container was opened and the dispersion was released into the atmosphere to achieve a foaming ratio of 30.
Two times as many ethylene-propylene random copolymer pre-expanded particles were produced.

An internal pressure application process was performed using pressurized air at the pre-foaming temperature shown in Table 1, and the volumetric shrinkage rate and internal pressure of the particles were measured by the following method to calculate the rate of increase in internal pressure of the particles per hour. The results are shown in Table 1.

(Particle internal pressure) After measuring the weight of the ethylene-propylene random copolymer particles after completion of the internal pressure application treatment, the particles were left to stand in an atmosphere at 60°C for 2 hours, and the air that had diffused and permeated through the particles due to the internal pressure application treatment was measured. is expelled, the weight of the particles is measured, and the amount of change is calculated as pressure using the ideal gas equation of state.

(rate of increase in particle internal pressure per hour) Calculated using the following formula.

Grains per hour = m particle internal pressure - ioo (atmospheric pressure/hr)
Prepressure 1 increase rate Internal pressure application time This is a measure of efficiency when internal pressure is applied to particles.

[Margins below] From the results in Table 1, the volumetric shrinkage rate is within the range of the present invention.
In the cases of Comparative Examples 1 to 4, which correspond to cases outside of 0 to 50%, the achieved particle internal pressure was approximately 40 to 50% lower than that of the Examples, and the benefits of the present invention gender has been revealed. It should be noted that the variation in shrinkage rate in these Examples and Comparative Examples indicates that the shrinkage rate of the particles changed during application of internal pressure.

[Effects of the Invention] By carrying out the method of applying internal pressure to pre-expanded polyolefin resin particles of the present invention, it is possible to efficiently apply internal pressure even at a low pressurizing pressure.
Compared to high-pressure processing methods such as those disclosed in Japanese Patent Application Laid-Open No. 58-101025, it is not necessary to use a container with high pressure resistance, so equipment costs can be reduced and the processing time can be reduced compared to that of JP-A-58-101025.
Compared with the extremely low pressure treatment method as disclosed in the above publication, the treatment method for applying internal pressure to polyolefin resin pre-expanded particles has extremely large benefits, such as requiring a considerably shorter treatment time.

Claims (1)

[Claims] 1. When pressurizing gas into pre-expanded polyolefin resin particles to apply internal pressure to the particles, gradually pressurize the gas under conditions such that the volume shrinkage of the particles is in the range of 10 to 50%. A method for applying internal pressure to pre-expanded polyolefin resin particles, the method comprising increasing the pressure and press-fitting the particles.