JPS60221440A - Production of foamed particles of propylene resin - Google Patents

Abstract

PURPOSE:A dispersion of a specific propylene-ethylene random copolymer is pressurized with an inorganic gas to a specific pressure, then heated up to a specific temperature to give foamed particles of uniform particle size which have been foamed more than 5 times the original volume without use of inorganic filler and a volatile swelling agent. CONSTITUTION:In a tightly sealed vessel, 100pts.wt. of particles of propylene- ethylene random copolymer which has 1-12wt% of ethylene content and a weight of 0.01-20mg every particle is dispersed in 200-100pts.wt. of water using, as a dispersing agent, a mixture of calcium phosphate and sodium dodecylbenzenesulfonate, an inorganic gas such as nitrogen gas is introduced into the vessel to pressurize the inside over 5kg/cm<2>G. Then, they are heated over the melting point to 25 deg.C higher than the melting point and the temperature is kept for more than 30min. At this time, the pressure in the vessel is set to 10-45kg/ cm<2>G and the polymer is discharged out of the outlet in an atomosphere of a lower pressure than the inside to give foamed particles of 0.03-0.18g/cm<3> bulk density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing propylene copolymer resin foam particles. A foam product obtained by filling the mold cavity of a mold having steam holes with the foam particles produced by the method of the present invention, and heating the foam particles with steam to fuse the foam particles together. It is strong and has excellent mechanical strength, making it useful as a heat insulating material for hot spring piping, a heat insulating material for solar water heaters, and a packaging material for refrigerators and televisions.

[Conventional technology]

Polystyrene foam is excellent as insulation material and packaging cushioning material.
Used in a wide range of fields. However, this polystyrene foam has a low compression strain ratio and a heat resistance of 70 to 80°C at most.

These drawbacks can be solved by using polypropylene foam, but it is difficult to produce foam particles as a raw material for forming polypropylene foam, and even if obtained, the bulk density is low at most. is 9.1~0.5y
There was a drawback that only a product with low foaming of /cl could be obtained.

As a method to solve this drawback, inorganic filler
Polypropylene resin particles containing ~70% by weight were dispersed in water as a dispersion medium in a sealed container, and this dispersion was heated to a pressure higher than the saturated vapor pressure of the dispersion and a temperature higher than the softening point of polypropylene and lower than the melting point. Water, which is a dispersion medium, is infiltrated into the polypropylene resin particles by maintaining high pressure under temperature conditions, and then this dispersion liquid is ejected from a high-pressure sealed container into atmospheric pressure until the bulk density is 0.05-0. 07? /
A method for producing CJ and highly foamed polypropylene foam particles was proposed (Japanese Patent Publication No. 49-2183).

This method uses water as a dispersion medium as a blowing agent.
This method has the advantage that foam particles can be produced at a lower cost than the extrusion foaming method using an organic expansion agent such as dichlorodifluoromethane, butane, or hexane. However, the presence of a large amount of σ inorganic filler is not preferable because it inhibits the fusion of the foam particles during molding.

On the other hand, polyolefin resin particles are dispersed in water in a sealed container, then a volatile organic swelling agent is supplied into the sealed container, and the pressure inside the sealed container is maintained at the vapor pressure of the swelling agent or higher. After heating the polyolefin resin particles to a temperature higher than the softening temperature of the polyolefin resin particles, the temperature and pressure are maintained for a certain period of time, and then the discharge port provided below the water surface in the sealed container is opened, and the polyolefin resin containing a volatile swelling agent is A method for producing polyolefin resin foam particles by simultaneously releasing particles and water into an atmosphere at a lower pressure than in a container is known (Japanese Patent Laid-Open Nos. 57-12035 and 57-25336).
No. 57-90027, No. 57-195131,
No. 58-1732, No. 58-23834, No. 58-
No. 25334, No. 58-33435, No. 58-552
No. 31, No. 58-76229, No. 58-76231, No. 58-76232, No. 58-76233, No. 5
No. 8-76234 and No. 58=87027).

[Problems with conventional technology]

These methods use non-crosslinked polypropylene to
It has the advantage of providing highly foamed particles that are expanded up to 50 times.

However, the use of volatile blowing agents increases the cost of the foam particles.

The present inventors have proposed the above-mentioned Japanese Patent Publication No. 4, which does not use a volatile swelling agent.
In the method described in Publication No. 9-2183, we conducted additional tests to see if it was possible to obtain polypropylene resin foam particles with a uniform particle size that expanded 5 to 20 times even without the addition of a hydrophilic inorganic filler. It has been found that it is difficult to foam with highly homogeneous polypropylene, and with propylene/ethylene random copolymer, foam particles that are only 2 to 3 times more foamed can be obtained. Further, the particle size and shape of the obtained foam particles were also irregular. Irregular shapes of foam particles cause uneven filling rates during molding, making it impossible to obtain molded products with consistent mechanical properties.

[Structure of the invention]

In order to obtain economical resin foam particles of 5 times or more, the inventors conducted experiments under various conditions and found that (a) propylene with an ethylene content of 1 to 12% by weight was used as the resin particles;・Using an ethylene random copolymer, (b) The dispersion liquid is treated with an inorganic gas so that the pressure inside the sealed container is 5.
(3) The holding temperature of the dispersion must be between the melting point of the resin particles and 25°C higher than the melting point, and the inorganic filler must not necessarily be incorporated into the resin particles. The inventors have discovered that it is possible to produce foam particles that expand five times or more and have a uniform particle size without using a volatile expansion agent, and have thus arrived at the present invention.

That is, in the present invention, the ethylene content is 1 to 12 in a closed container.
1ii Disperse 1% propylene/ethylene random copolymer resin particles in water, then introduce an inorganic gas into a sealed container to increase the pressure inside the sealed container to 5 breasts/JG or more, and then heat to lower the temperature of the dispersion liquid. The temperature exceeds the melting point of the copolymer resin particles and is 25°C higher than the melting point. Then, the discharge port provided below the water surface in the sealed container is opened, and the copolymer resin particles are dispersed into water, which is a dispersion medium. The present invention provides a method for producing propylene-based random copolymer resin foam particles by discharging the mixture into an atmosphere having a lower pressure than that in a closed container.

In the practice of the present invention, the propylene/ethylene random copolymer particles dispersed in water are obtained by copolymerizing propylene and ethylene, and optionally other α-olefins such as butene-1,4-methylpentene. These are propylene-based random copolymer particles having an ethylene content of 1 to 12% by weight. The amount of other α-olefins is up to 15% by weight.

Homopolypropylene has a high degree of crystallinity (for example, isotoughness of 95 to 99%) and it is difficult for water, which is a dispersion medium, to penetrate into the resin particles, so foams with an expansion ratio of 5 times or more are used. In order to obtain this, it is necessary to increase the pressure and heating temperature of the dispersion chamber and to extend the holding time, which tends to cause blocking among the resin particles, and the shape of the resulting foam particles is also irregular.

In order to facilitate the penetration of water into the copolymer particles, ethylene is mixed with propylene so that the unit concentration of ethylene in the copolymer is 1% by weight or less in order to reduce the crystallinity of the copolymer particles. Copolymerize.

On the other hand, if the ethylene unit concentration in the copolymer exceeds 12% by weight, the heat resistance of the foam product obtained by molding the obtained foam particles into a mold using steam will be low.

Furthermore, when a propylene/ethylene block copolymer is used, only a foam product with low cushioning properties (low repulsion against compression) can be obtained.

The preferred ethylene content is 2-10% by weight.

In addition to propylene/ethylene random copolymers, polyethylene, ethylene/vinyl acetate copolymers, resins with low crystallinity such as Surlyn, amorphous resins such as polystyrene and ABS, and rubbers such as SBR and ethylene/propylene rubber. can be added to facilitate water penetration. These additive resins can be present in an amount of at most 20% by weight in the resin component.

Furthermore, the resin may contain inorganic fillers such as zeolite, silica, and talc, wood flour, pigments, heat stabilizers, dyes, lubricants, and antistatic agents. These should be less than 5% by weight, preferably less than 2% by weight, in order to achieve good fusion when the foam particles are heated with steam to fuse them together to form a foam product. .

The weight of one propylene random copolymer particle is 0.0
1 to 201 Fg.

As a dispersant for dispersing propylene resin particles in water, a poorly water-soluble inorganic dispersant such as titanium oxide, aluminum oxide, calcium carbonate, basic magnesium carbonate, zinc carbonate, or tribasic calcium phosphate is used. Dispersants play a role in preventing propylene resin particles dispersed in water from fusing together when heated above their softening point. Inorganic dispersants are stable at high temperatures, so polyvinyl alcohol, It is more commonly used than water-soluble polymeric protective colloid agents with poor thermal stability such as methylcarboxycellulose and N-polyvinylpyrrolidone.

When tricalcium phosphate is used as a dispersant, a suspension aid may be used in combination. Such suspension aids include anionic surfactants such as sodium dodecylbenzene sulfonate, sodium alkanesulfonate, sodium alkyl sulfate, sodium olefin sulfate, acylmethyl taurine, sodium dialkyl sulfosuccinate; polyoxyethylene alkyl ether,
Examples include nonionic surfactants such as polyoxyethylene fatty acid ester, polyoxyethylene alkylphenol ether, sorbitan fatty acid ester, and polyoxyethylene rubitan fatty acid ester; amphoteric surfactants such as alkyl betaine and alkyl diethylene triaminoacetic acid.

Particularly preferred is a solution in which a water-soluble salt is formed by mixing an aqueous solution of calcium hydroxide and an aqueous phosphoric acid solution, and the suspending agent is made of sodium dodecylbenzenesulfonate as a suspending agent. be.

The suspending agent (2) above is obtained by reacting phosphoric acid in an aqueous solution at a ratio of 0.60 to 0.67 mol with respect to 1 mol of calcium hydroxide, and is an aqueous solution containing a poorly water-soluble salt thereof. The pH of is 8.5 to 11.5. The aqueous solution of the poorly water-soluble salt contains hydroxyapartite ([Ca5(PO4)+
)s ・Ca(OH)g ).

The aqueous solution containing the poorly water-soluble salt (4) can be used as a dispersion medium for propylene resin particles by adjusting the content of the poorly water-soluble salt to 0.01 to 2% by weight. 0.
If the amount is less than 0.01% by weight, blocking between propylene resin particles tends to occur. On the other hand, if the amount exceeds 2% by weight, the fusion properties of the resulting foam particles will be inhibited. A water-soluble medium such as methanol, ethanol, glycerin, or ethylene glycol can also be blended with water as a dispersion medium.

A surfactant such as sodium dodecylbenzenesulfonate, which is a suspension aid, has a 0.0001 to 0.0 concentration of water, which is a dispersion medium.
When used at a ratio of less than 0.0001% by weight, there is a problem that blocking of propylene resin particles tends to occur under heating and pressure. Conversely, 0.005% by weight
Even if it exceeds 200 to 1,000 parts by weight, preferably 250 parts by weight, the amount of water in the dispersion medium per 100 parts by weight of propylene resin particles is economically disadvantageous because the anti-blocking effect cannot be further improved.
~500 parts by weight. If the amount is less than 200 parts by weight, propylene resins tend to block each other during heating and pressurization.

If it exceeds 1,000 parts by weight, the productivity of the propylene resin foam particles decreases and is not economical.

In an aqueous dispersion of propylene resin particles dispersed in water using a fine water-repelling salt of tricalcium phosphate with an average particle size of 01 to 0.8 microns as a suspending agent and a surfactant as a dispersion aid, After supplying an inorganic gas such as air, nitrogen gas, or argon, and setting the pressure in the closed container to 5 kg/- or more, preferably 10 to 30 V4/cJG, this aqueous dispersion is heated in a closed container with a propylene resin. The aqueous dispersion is heated to a temperature above the melting point but not more than 25°C higher than the melting point, and then the aqueous dispersion is heated at the temperature for at least 30 minutes, preferably from 1 to 1
It is held for 2 hours to ensure the penetration of water into the resin particles.

Next, the propylene resin particles are discharged from the sealed container into a low pressure region, generally atmospheric pressure, along with water as a dispersion medium through a discharge port such as a slit or nozzle provided at the bottom of the sealed container, thereby reducing the bulk density to 0. 026~o, 2t/alr
propylene resin foam particles can be produced.

By heating the dispersion, the pressure inside the closed container increases, water permeates into the propylene resin particles, and the resin particles become expandable resin particles. Due to heating, the pressure inside the sealed container is 10 to 5.
The inorganic gas introduced into the sealed container, which is as high as 0 Kf/cJG, facilitates the release of the aqueous dispersion into the atmosphere, and also causes propylene resin particles to remain in the sealed container after the dispersion is discharged. It is meaningful to prevent the above problems and to obtain propylene resin foam particles having fine and uniform cells.

However, it is necessary to pressurize the dispersion liquid with an inorganic gas to 5 Kf/dG or more in order to obtain foam particles that are more than 5 times foamed. Foaming occurs only partially, and the window portion of the particle does not foam.

It is presumed that water permeates into the resin particles selectively into the amorphous portions of the resin rather than the crystalline portions.The heating temperature was determined by differential thermal analysis (DSC) of the propylene resin particles.
The peak of the crystal melting temperature in the DSC chart shown in Figure 1 (
The so-called melting point, a), is approximately 2 to 3 points below this peak temperature.
It is sufficient to select a temperature approximately 10°C higher than the temperature (b) at which this peak descends from a temperature higher than 10°C and reaches the bottom of the DSC chart. Preferably, the temperature in (b) is good. For example, in the case of a propylene copolymer with a melting point of 140°C, the heating temperature is set to 145 to 160°C. Also,
When the melting point is a propylene-ethylene-butene-1 copolymer of 135°C, the temperature is set at 137 to 160°C.

When the heating temperature is below the melting point of the resin particles, the resulting foam particles contain 2 to 8% of irregularly shaped foam particles. In addition, if an attempt is made to increase the foaming ratio, it is necessary to lengthen the holding time, which is not economical.

If the heating temperature is too high, resin particles may fuse together in the dispersion (
Therefore, the upper limit of the temperature should be set at 25° C. above the melting point of the resin, and the holding time should be adjusted to prevent blocking.

The time period for which the dispersion is maintained at a temperature exceeding the melting point of the resin depends on the pressure applied, the holding temperature, and the desired expansion ratio.
The time is 30 minutes to 12 hours, preferably 1 to 3 hours. During this holding time, when the dispersion liquid is released into the atmosphere, the pressure of the water that has permeated into the resin particles is suddenly released, and the volume of the water expands by a hundred times, causing the resin particles to foam. The release speed of the dispersion liquid is fast from the point of view of increasing the expansion ratio, for example, 200 to 500 m/sec, but 30' to 200 m/s is good.
It may be m7 seconds. When the release rate is high, there is a high-pitched popping sound, so noise countermeasures should be taken for sealed containers.

The discharge of the dispersion liquid from the high pressure region to the low pressure region is carried out through a single-hole, multi-hole, slit-like or other shaped outlet.

The foam particles thus obtained are dried in a room at 30 to 65° C. to remove water adhering to the surface, and then used to mold cushioning materials, containers, and the like.

As the molding method, various conventionally known methods can be used. An example is shown below.

■ After filling the mold with propylene resin foam particles, compress the foam particles to reduce their volume by 15 to 50%,
Next, steam of 1 to 5 Kf/c+#G is introduced to fuse the foam particles together, and then the mold is cooled to obtain a product.

(7) The foam particles are pre-impregnated with a volatile expansion agent to impart secondary foamability to the foam particles, which are then filled into a mold and steam-molded.

■1 Foam particles are placed in a closed chamber, and then inorganic gas such as air or nitrogen gas is injected into the chamber to increase the pressure within the foam particles and give secondary foamability. The foam particles imparted with foamability are filled into a mold and steam-molded.

Φ　Combination with two or more of the above ■～■.

The propylene resin foam product molded in this manner has excellent fusion between foam particles and high mechanical strength.

Hereinafter, the present invention will be further explained in detail with reference to Examples. Note that parts and percentages in the examples are based on weight.

Example 1 When an aqueous solution of 0.859 parts of calcium hydroxide dissolved in 1,200 parts of water and 4.46 parts of an aqueous solution of 17% phosphoric acid were mixed, the particle size was 0.05 to 0.3 microns. 0.1% of the salt was precipitated (pH 9,2). Sodium dodecylbenzenesulfonate was added to this to prepare the following dispersion.

Water release salt concentration 0.1 - pH of dispersion 9.2 Dodecylbenzenesulfonic acid concentration 0.003% After transferring 1,200 parts by weight of this dispersion (temperature 20°C) into an autoclave equipped with a discharge nozzle at the bottom, particle 1
The weight of the piece is about 1119, and the calcium stearate is 0.
Ethylene containing 0.03% by weight and 0.5% by weight of stabilizer (
4%), propylene (96%) random copolymer particles (
Add 400 parts (melting point 137°C) into an autoclave,
Nitrogen gas was supplied into the autoclave so that the internal pressure within the autoclave was 10 kg/2G.

Next, the dispersion was heated in the autoclave to 150° C. over about 100 minutes, and further maintained at the same temperature for 20 minutes. The pressure inside the autoclave at this time was approximately 21 kg/cJG.

Thereafter, the dispersion was further heated to 150° C. and held at the same temperature for 2 hours, and then the valve of the discharge nozzle at the bottom of the autoclave was opened to discharge the dispersion into atmospheric pressure for 2 seconds to cause foaming. (According to water heat analysis, the expandable propylene copolymer particles before release contained approximately 4% water within the particles). The internal pressure of the autoclave was approximately 9 Ky/cJG at the moment when the dispersion liquid was discharged from the autoclave, in other words, at the moment when the gas phase began to be discharged.

Also, during dispersion release, the temperature of the autoclave was 150°C.
It was ℃.

The bulk density of the propylene copolymer foam particles thus obtained was about 0.13 t/cl.

Further, the granularity of the foam particles was almost the same, and no blocking between the foam particles was observed.

After leaving the foam particles in a room at 40°C for 2 days to dry the moisture, they were placed in a sealed room and the 3Kf/cIRG
Air was injected for 48 hours to impart secondary foamability to the particles (pressure aging).

The foam particles imparted with secondary foamability are filled into a mold cavity having steam holes, and then 4, sV4/cJ
G steam is introduced to perform secondary foaming, fuse the foam particles together, and then cool it until the bulk density is approximately 0.
．． 11 y/cr! A propylene copolymer foam product having a length of 200 vans, a width of 300 vans, and a height of 50 III+11 was obtained.

When this product was broken in half by hand and the degree of fusion of the foam particles was examined, it was found to be 74 degrees.

The degree of fusion is defined as 0 when all the foam particles have peeled off at the interface between them when the product is broken, and the degree of fusion is defined as 0 when all the foam particles have peeled off due to cohesive failure. Wear degree 1
It was set as 00chi.

Examples 2 to 8, Comparative Examples 1 to 3 A dispersion having the same composition as the dispersion of Example 1 was pressurized with nitrogen gas at a pressure of 10/cJGs and the holding temperature of the pressurized liquid after pressurization was 150. The foam particles shown in Table 1 were obtained in the same manner as in Example 1, except that the temperature and holding time were changed as shown in Table 1.

A molded foam product was obtained in the same manner as in Example 1 using these foam particles.

The degree of fusion of this product is shown in the same table.

Examples 9 to 11, Comparative Example 4 Using the propylene resin particles shown in Table 1 as the resin particles, foam particles were obtained under the manufacturing conditions of pressurization conditions, heating temperature, and holding time shown in the table.

The results are shown in the same table.

Reference Example The following foam particles were obtained in the same manner as in Example 1, except that resin particles containing 10% by weight of talc in the propylene/ethylene random copolymer particles were used.

Expansion ratio: 15 Presence of blocking: Non-uniformity of particle size: Poor The degree of fusion of a molded foam product obtained in the same manner as in Example 1 using these foam particles was 30%.

(Margin below)

[Brief explanation of the drawing]

FIG. 1 is a chart of differential thermal analysis of the resin. Patent applicant: Yuka Baichi Datessie Co., Ltd. Agent: Patent attorney: Hidetoshi Furukawa Agent: Patent attorney: Masahisa Hase Figure 1 Temperature (°C)

Claims (1)

[Claims] 1) Propylene/ethylene random copolymer resin particles having an ethylene content of 1 to 12 times are dispersed in water in a closed container, and then an inorganic gas is introduced into the closed container. After increasing the internal pressure to 5Kf/dG or higher, the temperature of the dispersion is raised to exceed the melting point of the copolymer resin particles and 2Kf/dG below the melting point.
The temperature was lowered to 5°C higher than that, and then the discharge port provided below the water surface in the sealed container was opened, and the copolymer resin particles and water as a dispersion medium were released into an atmosphere with a lower pressure than in the sealed container. A method for producing propylene random copolymer resin foam particles. (2) After setting the temperature of the dispersion liquid to a temperature above the softening temperature of the copolymer resin particles and below a temperature 25°C higher than the melting point, the dispersion liquid is copolymerized until the dispersion liquid is discharged out of the closed container. A method for producing resin foam particles according to claim 1, characterized in that the resin foam particles are maintained at a temperature equal to or higher than the melting point of the combined resin for 30 minutes or more; 3) the pressure in the closed container immediately before releasing the zero dispersion; is 10
45 Kg/cJ G. The method for producing resin foam particles according to claim 1. 4) Production of resin foam particles according to claim 1, characterized in that the resin foam particles of a propylene-based random copolymer have a bulk density of 0.03 to 0.18 f/cJ. Method. 5), the weight of the copolymer resin particles dispersed in water is 0.0
1 to 20 ■ Claim 1
The manufacturing method described in Section 1. 6), the manufacturing method according to claim 1, characterized in that the inorganic gas is nitrogen gas; 7), tricalcium phosphate and dodecylbenzenesulfone as a dispersant for dispersing the copolymer resin particles in water; A method according to claim 1, characterized in that a mixture of acid soda is used.