JPH0867762A - Pre-expanded thermoplastic resin particles having a low thermal conductivity and a molded article comprising the pre-expanded thermoplastic resin particles - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a molded article composed of thermoplastic resin pre-expanded particles, which does not cause a significant decrease in thermal conductivity even when a part of the surface layer of the molded article is broken or cracked. thing. [Constitution] The thermal conductivity at 20 ° C. is 0.015 Kcal /
A molded article formed from thermoplastic resin pre-expanded particles obtained by coating a surface of a thermoplastic resin particle containing a foaming agent of m · h · ° C. or less with a gas barrier resin.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to a thermoplastic resin pre-expanded particle having a low thermal conductivity and a molded article formed from the thermoplastic resin pre-expanded particle, and particularly to a thermoplastic resin having a low thermal conductivity for a long period of time. The present invention relates to a molded article molded from resin pre-expanded particles and thermoplastic resin pre-expanded particles.

2. Description of the Related Art In the bead molding method, a step of pre-expanding to produce expanded particles by heating expandable particles by heating, and the expanded particles thus obtained are put into a mold and heated again to expand the particles. Two steps are required: a molding and foaming step of fusing and forming a molded body. Further, in order to obtain a good foam, it was necessary to leave the foamed particles in the atmosphere for a while to be aged after the pre-foaming step and before entering the molding and foaming step. Due to the aging after such pre-expansion, a large amount of air will penetrate into the pre-expanded particles, so that the foam obtained by subsequent molding and foaming only could contain a large amount of air. Therefore, as seen in JIS A9511 standards for polystyrene foam heat insulating materials, the lowest standard of thermal conductivity is the class A heat insulating plate special number 0.029 or less by the bead method (bead method: Table 3), the class B heat insulating material. 3 types of board 0.024 or less,
With the bead molding method, only foams having high thermal conductivity could be obtained. By the way, Japanese Patent Application Laid-Open No. 63-71335 discloses a foamed molded article having a lower thermal conductivity, that is, an improved heat insulating property, and a method for producing the same. That is, after the foamable synthetic resin is heat-molded in the mold, the inside of the foam-molded body is not replaced with air, that is, the foaming agent having a low thermal conductivity is not replaced with air, and the decompressed state is kept in a depressurized state. The feature is that surface treatment is applied to protect the condition. This surface treatment is intended to prevent substitution and invasion with air, and for example, painting, plating, film coating, etc. on the surface of the molded body container is used alone or in combination. The coating is a coating having air barrier properties, such as alkyd resin, aminoalkyd resin, epoxy resin, unsaturated polyester resin, polyurethane resin,
A synthetic resin paint such as acrylic resin or vinyl resin is suitable,
Epoxy resins, polyurethane resins, vinyl resin paints, etc. are particularly preferable because they have excellent chemical resistance. In addition to chemical and electrical plating, vacuum deposition is used for plating, and it is necessary to form the plating layer to the extent that it has an air barrier property. For film coating, a gas barrier film such as polyvinylidene chloride or polyester film is preferable. And the film coating should be done through an adhesive or by a method such as heat shrinking. Etc. are disclosed.

However, in the above-mentioned molded body, the coating, plating, film coating and other treatments for preventing substitution and invasion with air are applied only to the surface of the molded body. Therefore, if some part of the coating layer is damaged or cracked due to some unexpected external force, deterioration of the surface layer, surface treatment failure, etc., the air blocking property at the location is significantly reduced. As a result, there has been a problem that the thermal conductivity of the foamed molded product is lowered as a whole. Further, when a molded product such as a plate is scraped or used after being cut into several pieces, the air cutoff property is significantly reduced due to the cut opening or cut surface, resulting in a foamed molded product. There is a problem that the thermal conductivity is lowered as a whole. The present invention has been made in view of the above, an object thereof is a thermoplastic resin pre-expanded particles having a low thermal conductivity and a molded article molded from the thermoplastic resin pre-expanded particles, particularly a low thermal conductivity state. Is to provide a molded product formed from thermoplastic resin pre-expanded particles and thermoplastic resin pre-expanded particles that continue for a long period of time, and due to some unexpected external force, deterioration of the surface layer, surface treatment failure, etc. Even if a part is damaged or cracked, the thermal conductivity of the molded body does not significantly decrease, and even if it is cut or cut according to the intended use, the thermal conductivity of The present invention also provides a molded product that does not significantly decrease.

The present inventors have found the present invention as a result of intensive research for solving the above problems. That is, the first aspect of the present invention is that the surface of thermoplastic resin particles containing a foaming agent having a thermal conductivity at 20 ° C. of 0.015 Kcal / m · h · ° C. or less is coated with a gas barrier resin. It is a thermoplastic resin pre-expanded particle characterized. The second aspect of the present invention is that the thermal conductivity at 20 ° C. is 0.01.
A molded article characterized by being formed from thermoplastic resin pre-expanded particles obtained by coating the surface of a thermoplastic resin particle containing a foaming agent of 5 Kcal / m · h · ° C or less with a gas barrier resin. . It is a more preferable embodiment that the thermoplastic resin is a polystyrene resin and the gas barrier resin is a polyvinylidene chloride resin.
In the present invention, the foaming agent has a thermal conductivity of 0.0 at 20 ° C.
It is necessary to use those having a temperature of 15 Kcal / m · h · ° C or less. From the chemical structure, such a foaming agent is an aliphatic hydrocarbon, an alicyclic hydrocarbon, a specific one of halogenated aliphatic hydrocarbons, sulfur hexafluoride, or carbon dioxide. Of these, particularly preferred is CF3 CHF2.
(Freon 125), CF3 CH2 F (Freon 134)
a), CHF2CH3 (Freon 152a), CF2 HC
HFC Freon such as F2 CFH2 (Freon 245ca), C3 H8 (Propane), C4 H10 (Normal butane and isobutane), C5 H12 (Normal pentane and isopentane), C5 H10 (Cyclopentane) and other aliphatic and alicyclic groups Hydrocarbons, SF6, CO2, etc. Other,
The second best blowing agent after that is CF3 CHCl2.
(Freon 123), CF3 CHClF (Freon 12)
4), CCl2 FCH3 (CFC 141b), CClF
2 CH3 (Freon 142b), CF3 CF2 CHCl2
(Freon 225ca), CClF2 CF2 CHClF
(Freon 225cb), CHClF2 (Freon 22), etc. These can be used alone or as a mixture. CFC-based CFCs are said to be the cause of ozone layer depletion in the stratosphere, and are currently subject to regulation in Japan as well, so they are not preferred as blowing agents. As the thermoplastic resin used in the present invention, polystyrene resin, polyethylene resin, polypropylene resin, polyester resin, polyvinylidene chloride resin, etc. are used. Among them,
A polystyrene resin is particularly preferable in terms of versatility and economy. As the polystyrene resin, in addition to a homopolymer of a styrene monomer, a graft polymer containing a copolymer of a styrene monomer and another monomer, and further containing a styrene monomer is used. It also includes. Here, the styrene-based monomer includes, in addition to styrene, α-methylstyrene, α-chlorostyrene and the like. Examples of the copolymer are a copolymer of styrene and maleic anhydride, a copolymer of styrene and acrylonitrile, an acrylonitrile / styrene / butadiene copolymer and the like. An example of the graft polymer is a graft polymer of styrene on an ethylene / vinyl acetate copolymer. The copolymer and the graft polymer are
It must contain 50% by weight or more of a styrene monomer. The shape of the styrene resin foam may be a flat shape or an irregular shape, for example, a box shape and a depression on the surface. The expansion ratio is not particularly limited, but is preferably 15
It is foamed up to 50 times. It is desirable that the cells in the foam are uniform and fine. Particularly preferable bubble size is 50 to 300 μm. Further, it is preferable that the bubbles have independent shapes. Examples of the gas barrier resin used in the present invention include polyvinylidene chloride, ethylene / vinyl alcohol copolymer, gas barrier nylon such as MXD nylon, polyimide, polyvinyl alcohol, polyamide, polyester, polyolefin and polyacrylonitrile. These resins have a nitrogen permeability coefficient at 23 ° C of 5 cc / m 2 ·
Those satisfying day · atm or less are particularly preferable from the viewpoint of gas barrier property. The expandable particles used in the present invention are the same as those used in the bead molding method so far. The expandable particles are resin particles having a particle size of about 0.1 to 1.5 mm, and contain 1 to 20% by weight of a foaming agent. Steam is used to heat the expandable particles to pre-expand them. The pre-expanded particles (thermoplastic resin pre-expanded particles, sometimes simply referred to as pre-expanded particles hereinafter) are swollen to a bulk ratio of 15 to 50 times depending on the content of the foaming agent and heating conditions. The foamed particles thus obtained have been molded in a molding die after being left in the atmosphere for at least one day, usually several days. This neglect is generally called aging. In fact, it is believed that air enters the expanded particles during aging. That is, since the foamed particles are cooled immediately after the pre-expansion, the foaming agent is condensed in the bubbles, and as a result, the inside of the bubbles is decompressed, but during the aging, air enters the bubbles and the bubbles are The inside becomes isobaric. In general, air has much higher thermal conductivity than blowing agents. So in the present invention,
Before the air is replaced with the blowing agent, it is coated with a gas barrier resin. However, if the gas barrier resin is coated immediately after the pre-foaming, the pre-foamed particles will be in a reduced pressure state, and when the molded product is molded, the foaming force may be insufficient and molding may not be successful. It is necessary to impregnate more than usual. When the amount of impregnating gas in the expandable particles is Y (mol / kg) and the desired compact ratio is X (times), Y ≧ 0.027X (10 ≦ X ≦ 50) is satisfied. Good. In addition, the amount of the foaming agent contained in the pre-expanded particles immediately after foaming should be 50% or more of the amount of the foaming agent contained in the expandable particles before pre-foaming, and the expansion ratio of the pre-expanded particles should be 50% or more. It is preferable to control the above. By satisfying the above conditions, it becomes possible to mold even if the resin is coated with the gas barrier resin immediately after pre-foaming.

According to the above construction, the surface of the thermoplastic resin pre-expanded particles is coated with the gas barrier resin, so that the foaming agent in the pre-expanded particles is less likely to be replaced with air, and the pre-expanded particles are molded with a molding die. It becomes possible to leave it in the state of pre-expanded particles for many days until it is molded into a body. Also,
Since the molded article molded from the pre-expanded particles is composed of the individual pre-expanded particles coated with the gas barrier resin, even if a part of the surface layer of the molded article is damaged or cracked, Protected by the gas barrier properties of individually coated pre-expanded particles, no significant decrease in thermal conductivity occurs,
It has the excellent feature that Next, the present invention will be described in detail based on examples.

【Example】

Example 1 (Foaming Agent Impregnation Step) A particle size of 0.7 was set in an autoclave.
100 parts by weight of styrene spherical polymer particles (manufactured by Sekisui Plastics Co., Ltd.) classified to about mm to 1.0 mm,
CClF2 CH3 as a foaming agent in a closed autoclave
(Freon 142b) was press-fitted until the entire amount of the resin particles was soaked and left at 50 ° C. for 24 hours for impregnation. Then, it cooled to 20 degreeC and took out the expandable resin particle. The expandable resin particles contained 14.7% by weight of a foaming agent. CClF2
CH3 has a thermal conductivity of about 0.0107 Kcal at 20 ° C.
/ M · h · ° C. (Pre-expansion step, gas barrier resin coating step) The expandable resin particles obtained in the above step are heated with steam at 105 ° C. to be pre-expanded to a bulk ratio of 30 times, and immediately thereafter, the pre-expanded particles are made of Saran latex. L111 (Asahi Kasei Kogyo Co., Ltd., a synthetic resin latex obtained by emulsion polymerization using vinylidene chloride as a main monomer) was pre-expanded by mixing with a small mixer about 20 wt% (solid content ratio 10 wt%) based on the weight of the pre-expanded particles. After adhering to the particle surface, the pre-expanded particles were spread and placed on a wire mesh with a mesh of 2 mm so as not to overlap with each other, and dried in an atmosphere at 50 ° C. for 10 minutes to coat the surface of the pre-expanded particle with vinylidene chloride resin. (Molding step) The pre-expanded particles after the coating are filled in a closed mold and heated with steam to obtain 200 mm × 200 mm
A foamed product having a beautiful appearance of × 20 mm was obtained.
The apparent magnification was about 34 times. Thermal conductivity (measurement method
JISA1412) is 0.0 at 20 ° C.
It was 181 Kcal / m · h · ° C. The thermal conductivity after 9 days is 0.0207 Kcal / m ・ h ・
° C. The thermal conductivity after 30 days was 0.0223 Kcal / m · h · ° C at 20 ° C. The thermal conductivity after 120 days is 0.0239 Kcal at 20 ° C.
/ M · h · ° C.

[Example 2] Saran latex L111 was used as the pre-expanded particles.
Was coated once, and then all were coated under the same conditions except that coating was further performed. About 40% by weight (solid content ratio 20% by weight) is coated with respect to the weight of the pre-expanded particles. The thermal conductivity (measurement method according to JIS A1412) was 0.0180 Kcal / m · h · ° C at 20 ° C. The thermal conductivity after 9 days is 0.0196 Kcal at 20 ° C.
/ M · h · ° C. The thermal conductivity after 30 days is 20 ° C.
Was 0.0212 Kcal / m · h · ° C.
The thermal conductivity after 120 days is 0.0227 at 20 ° C.
It was Kcal / m · h · ° C.

Example 3 (Foaming Agent Impregnation Step) A particle size of 0.7 was set in the autoclave.
1% of copolymer resin containing 76% by weight of styrene and 24% by weight of acrylonitrile classified into about mm to 1.0 mm
00 parts by weight was added, and CF3 CH2 F (Freon 134a) as a foaming agent was pressure-inserted into the autoclave under a closed condition until the entire amount of the resin particles was immersed, and the mixture was allowed to stand at 80 ° C. for 48 hours for impregnation. Then, it cooled to 20 degreeC and took out the expandable resin particle.
The expandable resin particles contained 13.2% by weight of the foaming agent. CF3 CH2 F has a thermal conductivity of about 0.00 at 20 ° C.
94 Kcal / m · h · ° C. (Pre-expansion step, gas barrier resin coating step) The expandable resin particles obtained in the above step are heated with steam at 105 ° C. to pre-expand to a bulk ratio of 30 times, and immediately thereafter, the pre-expanded particles are provided with Saran latex. L111 (a synthetic resin latex produced by Asahi Kasei Kogyo Co., Ltd. by emulsion polymerization using vinylidene chloride as the main monomer) was mixed with a small mixer in an amount of 20% by weight (solid content ratio of about 10% by weight) based on the weight of the pre-expanded particles. After adhering to the particle surface, the pre-expanded particles were spread and placed on a wire mesh with a mesh of 2 mm so as not to overlap with each other, and dried in an atmosphere at 50 ° C. for 10 minutes to coat the surface of the pre-expanded particle with vinylidene chloride resin. (Molding step) The pre-expanded particles after the coating are filled in a closed mold and heated with steam to obtain 200 mm × 200 mm
A foamed product having a beautiful appearance of × 20 mm was obtained.
The apparent magnification was about 34 times. Thermal conductivity (measurement method
JISA1412) is 0.0 at 20 ° C.
It was 178 Kcal / m · h · ° C. The thermal conductivity after 9 days is 0.0188 Kcal / m · h · at 20 ° C.
° C. The thermal conductivity after 30 days was 0.0196 Kcal / m · h · ° C at 20 ° C. The thermal conductivity after 120 days is 0.0215 Kcal at 20 ° C.
/ M · h · ° C.

[Comparative Example 1] The same procedure as in Example 1 was repeated except that the surface of the pre-expanded particles was not coated with the gas barrier resin. The thermal conductivity (measurement method according to JIS A1412) is 0.0183 Kcal / m.
It was h.degree. The thermal conductivity after 9 days was 0.0228 Kcal / m · h · ° C at 20 ° C. The thermal conductivity after 30 days is 0.0248 Kcal / at 20 ° C.
It was m · h · ° C. Thermal conductivity after 120 days is 20 ° C
Was 0.0276 Kcal / m · h · ° C.

According to the present invention, a gas barrier resin is coated on the surface of thermoplastic resin pre-expanded particles containing a foaming agent having a thermal conductivity at 20 ° C. of 0.015 Kcal / m · h · ° C. or less. As a result, the ingress of air into the pre-expanded particles is suppressed, the escape of the foaming agent is suppressed, and the pre-expanded particles remain in the state of the pre-expanded particles until the time when the pre-expanded particles are molded into a molded body by a molding die. It is possible to leave it alone. Further, if a large amount of a foaming agent is impregnated, the gas barrier resin can be coated immediately after prefoaming. Therefore, there is an effect that no aging period is required. In addition, since the molded product molded from the pre-expanded particles is composed of the individual pre-expanded particles coated with the gas barrier resin, when the surface layer of the molded product is damaged or cracked. However, it has an excellent feature that the gas barrier property of the individually-expanded pre-expanded particles is protected and the thermal conductivity does not significantly decrease. An excellent feature that even when a molded product such as a plate is cut or used after being cut into several pieces, the air blocking property is not significantly deteriorated due to the cut opening or cut surface. Also has In addition, since the gas barrier resin is coated on the surface of the thermoplastic resin pre-expanded particles having a uniform shape and size, when the gas barrier resin is coated on the surface of the molded body having different shapes and sizes. Compared with the above, it has an extremely excellent effect that it is easy to handle in the coating and drying steps and the productivity is good and it is economical. Further, if the entire molded body is further covered with a gas barrier resin after being molded, a low thermal conductivity can be maintained for a longer period of time. In addition, the obtained molded product has a thermal conductivity of 0.024 Kcal / m · h · at20 which cannot be achieved by the conventional foamed product.
The state of ℃ or less can be maintained for a long time. By utilizing this excellent heat insulating property, it can be suitably used for various molded articles such as various containers, packaging materials, building construction members, and heat insulating members for electric devices.

Claims (3)

[Claims] 1. The thermal conductivity at 20 ° C. is 0.015 Kca.
Pre-expanded thermoplastic resin particles, characterized in that the surface of thermoplastic resin particles containing a foaming agent of 1 / m · h · ° C or less is coated with a gas barrier resin. 2. The thermal conductivity at 20 ° C. is 0.015 Kca.
A molded article formed from thermoplastic resin pre-expanded particles obtained by coating the surface of a thermoplastic resin particle containing a foaming agent of 1 / m · h · ° C. or less with a gas barrier resin. 3. The thermoplastic resin is a polystyrene resin,
The thermoplastic resin pre-expanded particles according to claim 1 and the molded article according to claim 2, characterized in that the gas barrier resin is a polyvinylidene chloride resin.