JP3418081B2 - Expanded resin particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expanded resin particles, and more particularly, it has excellent fusion-bonding properties, and therefore the molding temperature for obtaining an in-mold molded article can be lowered, The present invention relates to expanded resin particles having excellent mechanical properties and thermal properties.

[0002]

2. Description of the Related Art Expanded resin particles can have any shape and have a low thermal conductivity based on a closed cell structure. Therefore, they are widely used as a molding raw material for heat insulating materials, cushioning materials, core materials and the like. . As the thermoplastic resin forming the expanded resin particles, polyethylene, polypropylene, polystyrene or the like is usually used.

However, when the expanded resin particles are high melting point resin represented by polypropylene resin, the melting point is 1
Since the temperature is as high as 35 ° C. or higher, high pressure steam exceeding ² kg / cm ² G is required as the pressure required for fusion of the foamed resin particles during in-mold molding. Therefore, there are disadvantages that the cost for molding becomes high and the molding cycle becomes long. Further, in the case of expanded resin particles composed of the above-mentioned high melting point resin, it cannot be molded by the in-mold expansion molding machine for expanded polystyrene that is widely used, so a molding machine equipped with a high-pressure steam control system and having a high clamping pressure. Is required.

On the other hand, in the case of polyethylene resin, since the melting point is as low as 125 ° C. or lower, the vapor pressure for fusing the expanded resin particles to each other may be a low pressure of less than ² kg / cm ² G. This molding machine has the advantage that molding can be performed without changing the specifications. However, the foamed molded product of polyethylene resin has low heat resistance because of its low melting point, and in particular, the foamed molded product of high foaming is
Energy absorption performance is small. Therefore, the foamed molded product of polyethylene resin can be used only in low foaming, as compared with the foamed molded products of other thermoplastic resins.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to use expanded thermoplastic resin particles having a high melting point even when molded by a general-purpose molding machine having a low mold clamping pressure. It is an object of the present invention to provide a foamed resin particle which has substantially the same physical properties as those of the conventional molded product described above and which can provide a molded product having a high heat resistant temperature.

[0006]

That is, the gist of the present invention is to provide a foamed core layer made of a crystalline thermoplastic resin,
Foaming characterized by comprising a coating layer having a melting point lower than that of the thermoplastic resin or having substantially no melting point, and a coating layer which is substantially in a non-foaming state. Exists in resin particles.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The expanded resin particles of the present invention have a composite structure composed of a core layer and a coating layer. The core layer is made of a crystalline thermoplastic resin. Specific examples of such a thermoplastic resin include:
Polypropylene resin, polybutene resin, polymethylpentene resin, polyester resin, polyamide resin, fluorine resin, crystalline styrene resin and the like, propylene homopolymer, propylene and α-other than propylene Random copolymers and block copolymers with olefins are preferred.

The coating layer is composed of an ethylene polymer having a melting point lower than that of the thermoplastic resin or having substantially no melting point. Such low-melting point ethylene polymers include high-pressure process low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, vinyl acetate, unsaturated carboxylic acid ester, unsaturated carboxylic acid, and vinyl. Examples thereof include copolymers of alcohol and ethylene.

Further, examples of the above-mentioned ethylene polymer having substantially no melting point include, for example, ethylene / propylene rubber, ethylene / propylene / diene rubber, and ethylene / propylene rubber.
Examples thereof include rubber elastomers such as acrylic rubber, chlorinated polyethylene rubber, and chlorosulfonated polyethylene rubber. These ethylene-based polymers are used alone and in addition to 2
It can be used as one or more compositions.

Among the above-mentioned ethylene polymers, high-pressure low-density polyethylene, linear low-density polyethylene, and linear ultra-low-density polyethylene are preferable. Among them, linear low-density polyethylene polymerized using a metallocene catalyst,
Most preferred is linear ultra low density polyethylene. Further, in the present invention, an ethylene polymer composition comprising an ethylene polymer and the same crystalline thermoplastic resin as the core layer can be preferably used as the coating layer. According to such an ethylene polymer composition, there is an advantage that the adhesiveness between the core layer and the coating layer is improved.

The proportion of the thermoplastic resin used is selected from the range of 1 to 100 parts by weight with respect to 100 parts by weight of the ethylene polymer. If the proportion of the thermoplastic resin used exceeds 100 parts by weight, the sea-island morphology of the coating layer will change, and the thermoplastic resin will form a continuous sea phase, and the steam pressure for in-mold molding will not drop so much. . The preferable ratio of the thermoplastic resin is in the range of 1 to 50 parts by weight.

In the present invention, it is preferable to select and use an ethylene polymer having a melting point lower than 15 ° C. with respect to the thermoplastic resin constituting the core layer. The melting point difference between the ethylene polymer and the thermoplastic resin is preferably 20 ° C to 6 ° C.
The temperature is 0 ° C, more preferably 20 ° C to 40 ° C. If the melting point difference is less than 15 ° C., the coating layer made of the ethylene polymer may foam under the condition of foaming the thermoplastic resin of the core layer.

Further, the melting point of the ethylene polymer is
It is selected from the range of 125 ° C or lower, preferably 100 to 125 ° C. When an ethylene polymer having a melting point of more than 125 ° C. is used, the vapor pressure required for molding the expanded resin particles tends to be high.

In the expanded resin particles of the present invention, the coating layer has a thickness of 1 to 150 μm, preferably 10 to 100 μm.
Is the range. When the thickness of the coating layer is less than 1 μm,
At the time of molding, the effect of sufficiently reducing the steam pressure is small.
On the other hand, when the thickness of the coating layer exceeds 150 μm, the vapor pressure can be lowered during molding, but the proportion of the non-foaming portion of the coating layer is substantially large and the mechanical strength of the molded body is high. It tends to be low for the expansion ratio.

The expanded resin particles of the present invention basically comprise a core layer made of a crystalline thermoplastic resin and an ethylene-based polymer having a melting point lower than that of the thermoplastic resin or substantially no melting point. It is obtained by impregnating the volatile foaming agent into the composite particles composed of the coating layer made of coalesced and then foaming by heating.

The above volatile blowing agent is propane,
Butane, pentane, heptane, cyclopentane, lower aliphatic hydrocarbons such as cyclohexane, dichlorodifluoromethane, halogenated hydrocarbons such as trichloromonofluoromethane, nitrogen, air, inorganic gases such as carbon dioxide, and the like, These are used alone or in combination of two or more.

Each of the following methods is used as a specific method for producing composite particles as a raw material for the expanded resin particles of the present invention. For example, Japanese Examined Patent Publication No. 41-16125 and No. 43-
The sheath-core type composite dies described in JP-A-23858, JP-A-44-29522 and JP-A-60-185816 are used. In this case, two extruders were used, one extruder melt-kneading the thermoplastic resin forming the core layer, and the other extruder melt-kneading the ethylene polymer composition forming the coating layer. After that, a sheath-core type composite is discharged by using a die with a thermoplastic resin as a core layer and an ethylene-based polymer composition as a coating layer with a die.

Next, the composite thus obtained is cut into 0.1 to 10 mg of composite particles. If the weight of the composite particles is less than 0.1 mg, the ratio of the coating layer that effectively lowers the vapor pressure of the molding process becomes high, and the mechanical strength of the obtained foamed molded product decreases. On the other hand, when the weight of the composite particles exceeds 10 mg, the moldability during molding tends to deteriorate.

As a method of heat-foaming after impregnating the above-mentioned sheath-core type composite particles with a volatile foaming agent, specifically, for example, JP-B-49-2183 and JP-A-56-1.
344, West German Patent No. 1285722,
The method described in Japanese Patent No. 2107683 can be used.

In this case, the sheath-core type composite particles are put in a closed container together with the volatile foaming agent and heated to a temperature not lower than the softening temperature of the crystalline resin of the core layer, and the composite particles are impregnated with the volatile foaming agent. Let Then, the foamed resin particles of the present invention are obtained by releasing the contents in the closed container from the closed container to a low-pressure atmosphere and then drying the contents.

The heating temperature for foaming the composite particles is usually
The temperature is not lower than the softening temperature of the thermoplastic resin of the core layer, but is preferably higher than the melting point of the ethylene polymer of the coating layer (the melting point of the main component in the case of a composition). Further, in the present invention, a stirring device is provided in order to prevent the composite particles from being fused to each other in the closed container.

At the time of foaming by heating, it is preferable to use water, alcohols or the like as a dispersion medium for the composite particles.
Furthermore, so that the composite particles are uniformly dispersed in the dispersion medium, a poorly water-soluble inorganic substance such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, and zinc oxide, water-soluble protection such as polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose. It is preferable to use anionic surfactants such as colloid, sodium dodecylbenzene sulfonate and sodium α-olefin sulfonate, either alone or in combination of two or more.

When releasing the composite particles into a low pressure atmosphere,
In order to facilitate the release, it is preferable to introduce the same inorganic gas or volatile foaming agent as described above from the outside into the closed container to keep the pressure in the closed container constant.

The expanded resin particles of the present invention are molded using molds under various conditions. For example, foamed resin particles are filled into a cavity formed by a pair of concave and convex molds under atmospheric pressure or reduced pressure, and then compressed so that the mold cavity volume is reduced by 5 to 70%, and then a heat medium such as steam is used. Is introduced into the cavity and the foamed resin particles are heated and fused (for example, Japanese Patent Publication No. 46-38359).

Further, the expanded resin particles are previously treated with one or more kinds of a volatile foaming agent or an inorganic gas to enhance the secondary expansion power of the expanded resin particles, and then the secondary expansion power is maintained. A pressure aging method in which a mold cavity is filled under atmospheric pressure or reduced pressure, and then a heating medium is introduced into the cavity for heat fusion (for example, Japanese Patent Publication No. 51-22951).
Is mentioned.

A compression-filling method in which a mold cavity pressurized to a pressure higher than atmospheric pressure with a compressed gas is filled with expanded resin particles pressurized to a pressure higher than the pressure, and then a heating medium is introduced into the cavity for heat fusion. (For example, Japanese Patent Publication No. 4-46217).

Using expanded resin particles having a high secondary expansion power obtained under special conditions, the expanded resin particles are filled into a cavity formed by a pair of concave and convex molds under atmospheric pressure or reduced pressure, and then the cavities Atmospheric pressure filling method in which a heat medium such as steam is introduced into the tee and heated and fused (for example, Japanese Patent Publication No. 6-49
No. 795). The molding method used in the present invention may be any of the above methods, or may be a combination of the above methods (for example, Japanese Patent Publication No. 6-2.
(See Japanese Patent No. 2919).

In the expanded resin particles of the present invention, the thermoplastic resin of the core layer exhibits a closed cell structure in an expanded state from the state of the cut cross section of the particles, while the ethylene polymer of the coating layer is substantially non-existent. It is in a foamed film state.

In the present invention, a molded body in which the expanded resin particles are sufficiently fused to each other can be obtained with a low vapor pressure by any of the above molding methods. Further, the molded product thus obtained has high mechanical strength and high heat resistance, and is useful as a heat insulating material, a structural member and a core material.

[0030]

The present invention is described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In addition, in each of the following examples, each physical property was determined as follows.

<Melting point> Measured by a differential scanning calorimeter (DSC). First, 3 to 5 mg of resin is heated to a temperature at which the crystals melt, and then cooled to room temperature at a rate of 10 ° C./min. Then, the temperature is increased by heating at a rate of 10 ° C./min, and the peak temperature of the endothermic curve obtained is taken as the melting point.

<Fusion test> Length 200 mm, width 30 m
A test piece having a thickness of 12.5 mm and a thickness of 12.5 mm was prepared, and the test piece was bent to 90 degrees along the circumference of a cylinder having a diameter of 50 mm and judged according to the following criteria.

[0033]

[Table 1] ◯: 80% or more of the total number of test pieces did not crack. X: More than 20% of the total number of test pieces break.

<Heat Resistance Test> According to JIS K 6767, the heat resistant dimensional change rate at 110 ° C. was measured according to the following criteria.

[0035]

[Table 2] ◯: The dimensional shrinkage ratio is less than 3%. Δ: The dimensional shrinkage ratio is 3 to 6%. X: The dimensional shrinkage exceeds 6%.

Example 1 An ethylene / propylene random copolymer having an ethylene content of 1.5% (melting point 153 ° C.) was kneaded using a single-screw extruder having an inner diameter of 40 mm, and a single-screw extruder having an inner diameter of 25 mm was used. And linear low-density polyethylene (melting point: 123 ° C.) having a density of 0.920 was kneaded. Then 1.5 mm in diameter
From the die having the die orifice, the strand was extruded with the ethylene / propylene random copolymer as the core layer and the linear low-density polyethylene as the coating layer.

Further, this strand was cooled through a water bath and then cut into 1.2 mg. When the cross section of the composite particles was observed by a phase contrast microscope, the thickness was 30 μm.
The linear low-density polyethylene of the above was coated with an ethylene / propylene random copolymer.

Next, the above composite particles 10 are placed in a closed container.
0 parts, 250 parts of water, 1.0 part of tribasic calcium phosphate having a particle size of 0.3 to 0.5 μm and 0.007 part of sodium dodecylbenzenesulfonate are charged, and then 20 parts of butane are stirred under a closed container. Supplied to. After the contents were filled at a filling rate of 62%, the temperature was raised to 145 ° C. over 1 hour and kept at the same temperature for 30 minutes.

After that, the valve of the discharge hole at the bottom of the closed container is opened, and nitrogen gas is introduced from the outside into the gas phase part of the closed container to release the contents under atmospheric pressure while maintaining the pressure inside the container. Thus, expanded resin particles were obtained. The expanded resin particles thus obtained had an average bulk density of 17 kg / m ³ and an average cell diameter of 12
It was 0 μm, and there was no blocking between the expanded resin particles.

Observation of the cross section of the foamed resin particles with a phase contrast microscope revealed that the ethylene-propylene copolymer of the core layer was in the foamed state of closed cells, while the linear low-density polyethylene was The ethylene / propylene random copolymer foam was covered in a substantially non-foamed film state.

The foamed resin particles were completely dried in a drying chamber at 40 ° C., compressed with 2.0 kg / cm ² G of compressed air to shrink the foamed resin particles, and then 1.5 kg / cm ^2.
Expanded resin particles by filling the inside of the cavity of a pair of concave and convex aluminum molds having steam holes under the atmosphere pressurized with G compressed air, and further introducing 1.0 kg / cm ² G steam. The two were heat fused.

Then, after cooling with water for 20 seconds, it is left to cool for 35 seconds,
When the surface pressure of the mold reached 0.3 kg / cm ² G, the mold was opened and the molded product was taken out. The molded body taken out from the mold has a density of 30 kg / cm ³ , a length of 200 mm, and a width of 30.
The thickness was 0 mm and the thickness was 25 mm, and the dimensional shrinkage ratio to the mold was 1.9%.

From the above molded body, length 200 mm, width 3
Twenty test pieces of 0 mm and a thickness of 12.5 mm were produced, wound around the circumference of a cylinder having a diameter of 50 mm and bent to an angle of 90 °, and 80% or more of the test pieces did not crack. Also,
From another molded body molded under the same molding conditions, length 50mm,
A test piece with a width of 50 mm and a thickness of 25 mm is produced and JISK
According to 6767, a compression test was carried out and found to be 50
The% compressive stress was 2.9 kg / cm ² . Furthermore, J
When a heat resistance test was performed at 110 ° C. according to IS K 6767, the dimensional shrinkage was less than 3%. The results are shown in Table 3.

Examples 2 to 9 and Comparative Examples 1 to 9 In Example 1, the particles shown in Tables 3 to 8 were used as the expanded resin particles, and foaming and molding were carried out under the conditions shown in Tables 3 to 8. The same procedure as in Example 1 was carried out except that the above was carried out. The results are shown in Tables 3-7. It has been found that the expanded resin particles and the molded product of the present invention exhibit excellent fusion bondability, high mechanical strength and heat resistance.

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

[Table 5]

[0048]

[Table 6]

[0049]

[Table 7]

[0050]

[Table 8]

[0051]

The expanded resin particles of the present invention described above are
In addition to exhibiting excellent fusion-bonding properties even when the heating steam pressure in in-mold molding is low, the resulting molded product has excellent mechanical properties and high heat resistance.

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Teruya Oguwa 1000 Kawajiri-cho, Yokkaichi-shi, Mie Mitsubishi Kagaku BSF Co., Ltd. (56) References JP-A-60-181139 (JP, A) JP-A-58 -145739 (JP, A) JP 60-235850 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/16

Claims (7)

(57) [Claims] 1. A foamed core layer made of a crystalline thermoplastic resin, and an ethylene-based polymer having a melting point lower than or substantially no melting point of the thermoplastic resin, A foamed resin particle comprising a non-foamed coating layer. 2. The coating layer contains 1 to 10 parts of the same crystalline thermoplastic resin as the core layer based on 100 parts by weight of the ethylene polymer.
The expanded resin particles according to claim 1, which is a composition obtained by blending 0 part by weight. 3. The expanded resin particles according to claim 1, wherein an ethylene polymer having a melting point lower than the melting point of the thermoplastic resin by 15 ° C. or more is used. 4. The expanded resin particles according to claim 1, wherein the ethylene polymer has a melting point of 125 ° C. or lower. 5. The expanded resin particle according to claim 1, wherein the coating layer has a thickness of 1 to 150 μm. 6. The expanded resin particles according to claim 1, wherein the weight of one particle is 0.1 to 10 mg. 7. A core layer made of a crystalline thermoplastic resin,
A volatile foaming agent is impregnated into the composite particles having a melting point lower than that of the thermoplastic resin or a coating layer made of an ethylene-based polymer having substantially no melting point, and then heat-foamed. The expanded resin particles according to claim 1, which are obtained.