JPH0362543B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a propylene copolymer resin foam molded product having rebound resilience. Synthetic resin foam moldings have been known for a long time.
For example, they are used in a wide range of applications such as cushioning materials, packaging materials, insulation materials, and construction materials, and the demand for them has increased greatly in recent years. Foamed polystyrene and foamed polyethylene are known as molded products of this type, but the former has the fatal drawback of being brittle and has poor chemical resistance, while the latter has the disadvantage of being difficult to obtain with low density. However, when attempting to obtain a product with a low density, the cell structure becomes open and the shrinkage is large, making it difficult to obtain a molded product that can be used for practical purposes. In addition, research has recently been underway to produce polypropylene foam moldings by bead molding, and the applicant has already proposed a method for producing pre-expanded particles (Japanese Patent Publication No. 1344/1983). The foamed molded product obtained using the pre-expanded particles obtained by this method has superior heat resistance, chemical resistance, dimensional stability, rebound resilience, etc. compared to conventional foamed polystyrene, foamed polyethylene, etc., and is practical. However, it is difficult to obtain a product that satisfies all the properties required when used in cushioning materials, packaging materials, etc., such as heat resistance, impact resilience, surface protection, compression hardness, and dimensional stability. However, there is still room for improvement. The purpose of the present invention is to provide a propylene-based copolymer resin foam molded product that is further improved over the above-mentioned conventional technology. We discovered that a propylene ^- based copolymer resin foam molded product had excellent physical properties such as excellent cushioning properties, impact resilience, and low residual strain by specifying the relationship between The present invention has now been completed. That is, the present invention provides a foam molded product obtained by filling a mold that can be closed but cannot be closed with pre-expanded particles of a propylene copolymer resin, and heating and foaming the molded product, the density of the molded product being 0.006 to 0.06. 0.018g/ ^cm3
When the density is d (g/cm ³ ) and the number of bubbles per 1 mm ² of cross section is n (pieces), the following formula: 2<n ^1/2 /d ^1/3 <
The gist of the present invention is a propylene copolymer resin foam molded product having rebound resilience characterized by having the relationship shown by 40. Examples of the propylene copolymer resin that is the base resin of the foam molded product of the present invention include ethylene-propylene random copolymers, ethylene-propylene block copolymers, and mixtures thereof. These may be crosslinked or non-crosslinked, but non-crosslinked ones are preferred. The density of the molded article of the present invention is 0.006 to 0.018 g/cm ³ , preferably 0.006 to 0.010 g/cm ³ . Density is 0.006
If it is less than g/cm ³ , the mechanical strength such as compressive hardness of the molded product will be low, and for example, when used as a cushioning material, the appropriate cushioning range will be narrow, and it will be difficult to obtain good dimensional stability. On the other hand, if the density exceeds 0.018 g/cm ³ , for example, when used as a cushioning material, there is a problem in the surface protection of the product, there is a risk of scratching the product, and it is difficult to obtain sufficient flexibility. Further, in the molded article of the present invention, when the density is d and the number of bubbles is n, the relationship between the two is expressed by the following formula: 2<n ^1/2 /d ^1/3 <40. The inventors believe that this relationship shows that as the density value changes, the preferred range for the number of bubbles changes accordingly, resulting in an exponential correlation between the density and the number of bubbles. It was discovered by et al. and defined based on it. If n ^1/2 / d ^1/3 is less than 2, the surface unevenness of the molded product will be significant and it will be difficult to obtain good surface protection, whereas if n ^1/2 / d ^1/3 is 40 or more, good dimensional stability will be achieved. Sex is hard to come by. In addition, the number of bubbles is 0.13 to 110/ ^mm2 ,
Preferably it is 0.3 to 43 pieces/ ^mm2 . The propylene copolymer resin foam molded product of the present invention can be produced, for example, by the method shown below.
First, pre-expanded propylene copolymer resin particles can be produced, for example, by the following pre-expanding method. That is, a step of incorporating a volatile blowing agent into the polymer particles, a step of dispersing the polymer particles in a dispersion medium in a closed container and heating it to a predetermined temperature, and a step of opening one end of the container and simultaneously dispersing the particles and the dispersion medium. It can be produced by a pre-foaming method comprising a step of releasing the foam into an atmosphere at a lower pressure than that in the container. Examples of volatile blowing agents used here include aliphatic hydrocarbons such as propane, butane, pentane, and hexane, cycloaliphatic hydrocarbons such as cycloptane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, Examples include halogenated hydrocarbons such as dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc., and these include resin particles.
It is usually used in an amount of 10 to 40 parts by weight per 100 parts by weight.
As the dispersant, fine particles of aluminum oxide and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, etc. can be used. The amount of this dispersant added is usually 0.01 to 10 parts by weight per 100 parts by weight of the resin particles. The dispersion medium may be any solvent that does not dissolve the resin particles, such as one or two of water, ethylene glycol, glycerin, methanol, ethanol, etc.
Although a mixture of more than one species is exemplified, water is usually preferred. The pre-expanded particles thus obtained usually have a density of 0.3 to 0.024 (g/cm ³ ), although it varies depending on the temperature, pressure, amount of volatile blowing agent, etc. during foaming. The pre-expanded particles can be further heated to obtain highly expanded pre-expanded particles. At that time, the pre-expanded particles may be heated as they are, but they may be heated after applying a predetermined internal pressure with an inorganic gas, a volatile blowing agent, or a mixed gas of an inorganic gas and a volatile blowing agent. It is preferable to carry out foaming (hereinafter referred to as two-stage foaming). Further, by repeating the above operation, pre-expanded particles with even higher degree of foaming can be obtained. Next, the above pre-expanded particles are aged at room temperature and pressure for a predetermined time, and then heated to a predetermined pressure using an inorganic gas such as nitrogen or air, or a mixed gas of an inorganic gas and a volatile blowing agent. Maturing under pressure for a predetermined period of time. Pre-expanded particles with internal pressure applied as above,
The particles are filled into a mold that can be closed but cannot be sealed, for example, a mold having small holes on the mold surface through which a heating medium such as steam passes, and heated with 2 to 5 kg/cm ² (G) of steam. By expanding the foam and causing fusion between the particles, it is possible to obtain a foam molded article of the present invention that is molded according to a mold. In the present invention, the density d of the pre-expanded particles is determined by the following formula: d (g/cm ³ )=W/V ₁ −V ₀ (where W is the weight of the pre-expanded particles, and V ₀ is the weight of the pre-expanded particles placed in the measuring cylinder in advance. The volume of water placed in the container, _V1 , is the volume when the pre-expanded particles are immersed in the water in the graduated cylinder.) The propylene copolymer resin foam molded product of the present invention can be used for packaging materials, cushioning materials, heat insulating materials, heat insulating materials, building materials, vehicle parts, flotation materials, etc. Among them, packaging materials, cushioning materials, heat insulating materials, etc. It is suitable for use as a heat insulating material, and is particularly effective when used as a cushioning material or packaging material due to its excellent cushioning properties and surface protection properties. As explained above, the propene-based copolymer resin foam molded product with rebound resilience of the present invention has a relatively small density, so it is an excellent molded product made of highly foamed foam, and is superior to conventional foamed polystyrene. It has more rebound resilience than molded products, and has much better heat resistance and surface protection, and it also has better heat resistance and dimensional stability than low-density polyethylene foam molded products. In addition, the foam molded product of the present invention has a specific density and a specific relationship between the density and the number of cells, so it has excellent impact resilience, heat resistance, dimensional stability, surface protection, etc. When used as a cushioning material or packaging material, it exhibits sufficient volatilization properties. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 8 and Comparative Examples 1 to 11 100 parts by weight of ethylene-propylene random copolymer particles or low-density polyethylene particles, a volatile blowing agent in the amount shown in Table 1, finely divided aluminum oxide, and water were placed in a closed container. After heating the container to the temperature shown in Table 1 while stirring, one end of the container is opened, and while maintaining the pressure inside the container at a predetermined level, the polymer particles and water are released into the atmosphere at the same time for pre-foaming. Particles were obtained. For Examples and Comparative Examples 1 to 4, 6, and 8 to 11, the pre-expanded particles were subjected to a predetermined internal pressure with air, heated, and subjected to two-stage foaming to obtain various densities shown in Table 1. Pre-expanded particles were obtained. For Examples 1, 5, and 8 and Comparative Examples 1, 3, 9, and 10, pre-expanded particles obtained by two-stage foaming were further subjected to a predetermined internal pressure with air, heated, and then subjected to three-stage foaming. Pre-expanded particles of various densities shown in Table 1 were obtained by foaming. After applying an internal pressure of 1 to 2 kg/cm ² (G) to the pre-expanded particles obtained in this way, the length
Filling a mold of 300 mm, width 300 mm, and thickness 50 mm, the case of ethylene-propylene random copolymer is 3.2
Kg/cm ² (G), 1.4Kg/ for low density polyethylene
Molding was carried out at a vapor pressure of cm ² (G). Polyethylene also uses commercially available expanded polystyrene (EPS) particles.
The foam was foamed to a predetermined expansion ratio using a pre-foaming machine for EPS, and the vapor pressure was 1.2 Kg/cm ² (G). Various physical property tests were conducted on the obtained molded body. The results are shown in Table 2. Further, FIG. 1 shows the results of plotting data regarding the density: d and the number of cells: n of the foamed molded products obtained in each of the above Examples and Comparative Examples. In Figure 1, straight line A represents an (exponential function) straight line with n ^1/2 / d ^1/3 = 2, and straight line B represents an (exponential function) straight line with n ^1/2 / d ^1/3 = 40. , straight line C is a line indicating d=0.006,
Straight line D is a line indicating d=0.018.

【table】

The numbers in [Table] indicate molar ratios.
(Note) The ethylene content of the base resin ethylene-propylene random copolymer is 2.8%.

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram in which the data of the density: d and the number of cells: n of the foamed molded products obtained in Examples 1 to 8 and Comparative Examples 1 to 11 are plotted on a logarithmic graph.

Claims (1)

[Scope of Claims] 1. A foam molded product obtained by filling pre-expanded particles of a propylene copolymer resin into a mold that can be closed but cannot be closed, heated and foamed, the density of the molded product being 0.006. ~0.018g/ ^cm3 , and the density is d
(g/cm ³ ), and when the number of bubbles per 1 mm ² of cross section is n (pieces), it is characterized by having the relationship shown by the following formula: 2<n ^1/2 /d ^1/3 <40 A propylene copolymer resin foam molded product with rebound resilience. 2. The propylene copolymer resin foam molded article having impact resilience as claimed in claim 1, having a density of 0.006 to 0.010 g/cm ³ .