JPS6028855B2 - Pre-expanded polypropylene resin particles and their manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to pre-expanded polypropylene resin particles and a method for producing the same.

Polypropylene resin foam has traditionally been highly flexible (strong), heat resistant, oil resistant, etc. Taking advantage of these excellent properties, it has been used for various purposes such as cushioning materials, packaging materials, and insulation materials. It is being

Among polypropylene resin foams, polypropylene resin foam moldings can be obtained by a pre-expanded bead molding method using pre-expanded particles, and this technique has recently been developed by the present inventors. However, with pre-expanded polypropylene resin particles, it is difficult to obtain highly foamed particles compared to the commonly used polystyrene foam beads, and in order to obtain highly foamed particles, a large amount of blowing agent is required. It must be consumed and there is still room for improvement. The purpose of the present invention is to provide pre-expanded polypropylene resin particles and a method for producing the same that eliminate the drawbacks of the above-mentioned conventional techniques. The pre-expanded particles, which are obtained by foaming the intraparticle polymer obtained by graft polymerization of a mixture of resin particles and a small amount of vinyl aromatic monomer, have a dramatically high foaming rate while maintaining the excellent properties of polypropylene. In addition, they discovered that it has appropriate rigidity and succeeded in developing a method for manufacturing it, thereby completing the present invention.

That is, the present invention provides that an intraparticle polymer of a mixture consisting of polypropylene resin particles in an amount exceeding 7% by weight and a vinyl aromatic monomer in an amount less than 3% by weight is added to the polypropylene resin by a part or all of the vinyl aromatic monomer. The gist of the present invention is to provide pre-expanded polypropylene resin particles characterized by being a graft-polymerized polymer.

Another aspect of the present invention is to disperse polypropylene resin particles in an amount exceeding 7% by weight, a vinyl aromatic monomer in an amount less than 30% by weight, and a polymerization catalyst in a dispersion medium, and then add a portion of the vinyl aromatic monomer to the polypropylene resin. A step of graft polymerizing part or all of the particulate polymer to obtain an intraparticle polymer, a step of incorporating a volatile blowing agent into the intraparticle polymer in a closed container,
and a step of opening one end of the container and releasing the intragranular polymer containing the volatile blowing agent into a low-pressure atmosphere from inside the closed container. That is. In the present invention, as the polypropylene resin, propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene flock copolymer, etc. are used. Combination is preferred.

The amount of polypropylene resin added is more than 7% by weight in the mixture with vinyl aromatic monomer, and the amount added is more than 7% by weight.
If it is less than 0% by weight, the properties as a polypropylene resin will be impaired, and the flexibility, heat resistance, oil resistance, etc. of the pre-expanded particles will be reduced, which is not preferable. Also vinyl aromatic monomer
Examples include styrene, Q-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylxylene, isof. Ropylxylene and the like can be mentioned, and these can be used alone or in a mixture of two or more. The amount of vinyl aromatic monomer added is less than 30% by weight in the mixture with polypropylene resin, preferably 10% by weight.
~2% by weight. If the amount added exceeds 3% by weight, the properties of the resulting pre-expanded particles as a polypropylene resin will be impaired, and various properties such as flexibility, heat resistance, and oil resistance will decrease, and brittleness will increase, which is not preferable. In the present invention, polyfunctional monomers such as dipinylbenzene and (poly)ethylene glycol diacrylate may be used together with the vinyl aromatic monomer, if desired.

In that case, the amount of polyfunctional monomer used is usually 0.1 to 4 parts by weight based on the vinyl aromatic monomer. In the present invention, by polymerizing a mixture of polypropylene resin particles and a vinyl aromatic monomer, an intraparticle polymer in which the vinyl aromatic monomer is partially or completely graft-polymerized to the polypropylene is obtained. A polymerization catalyst is used in the present invention to polymerize the vinyl aromatic monomer.

Examples of the polymerization catalyst include penzoyl peroxide, lauroyl peroxide, azobisisobutyronitrile, di-t-
Examples include phtyl peroxide and dicumyl peroxide. The amount of the polymerization catalyst added is usually 0.5 to 4 parts by weight based on 10 parts by weight of the vinyl aromatic monomer. Examples of volatile blowing agents used in the present invention include aliphatic hydrocarbons such as propane, butane, bentane, hexane, and hebutane; cycloaliphatic hydrocarbons such as cyclobutane and cyclobentane; and Halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. are used. The amount of the blowing agent added is usually 5 to 3 parts by weight based on the intraparticulate polymer 10 parts by weight. In the present invention, polypropylene resin particles, etc. are dispersed in dispersed soot. At this time, if necessary, a dispersant is used, such as finely divided aluminum oxide and titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, phosphoric acid, etc. Tricalcium etc. can be used.

The amount of this dispersant added is usually 0.01 to 10 parts by weight per 10 parts by weight of the intragranular polymer. Further, the dispersion medium may be any solvent that does not dissolve the above mixture, such as water,
Examples include one or a mixture of two or more of ethylene glycol, glycerin, methanol, ethanol, etc., but water is usually preferred. Further, an aqueous solution containing a small amount of a surfactant such as sodium dodecylbenzenesulfonate is more preferred. Next, the method for producing the pre-expanded particles of the present invention will be described below.

The method of the present invention involves the steps of dispersing a polypropylene resin, a vinyl aromatic monomer, and a polymerization catalyst in a dispersion medium, and grafting some or all of the vinyl aromatic monomer onto the polypropylene resin, and intraparticle polymerization in a closed container. There is a method in which the step of incorporating a volatile blowing agent into the product is carried out separately or a method in which it is carried out simultaneously.

In a method in which the above steps are performed simultaneously, a polypropylene resin, a vinyl aromatic monomer, a polymerization catalyst, and a volatile blowing agent are dispersed in a dispersion medium in a closed container, and the temperature inside the container is usually 60 to 150 qo, which is about the vapor pressure of the blowing agent. The intragranular polymer is polymerized at a pressure of 100 mL, and a volatile blowing agent is incorporated into the intragranular polymer. Alternatively, in a separate method, after polymerizing a vinyl aromatic monomer at the above temperature using a polymerization catalyst, the obtained intragranular polymer is stored in a closed container, and the intragranular polymer is heated at a predetermined temperature and the above pressure. contains a volatile blowing agent. In the method of the present invention, preliminary foaming is performed by opening one end of the container and releasing the intragranular polymer containing the volatile foaming agent into a low-pressure atmosphere from inside the container.

The pressure inside the container at the time of release may be either higher than the vapor pressure of the volatile blowing agent or lower than the vapor pressure (0.7P or higher when vapor pressure is P), but pre-expanded particles with an appropriate average cell diameter may be used. Therefore, it is preferable to have a high vapor pressure, and the atmosphere to be released is usually an atmosphere at normal pressure. In the present invention, the vapor pressure of the volatile blowing agent refers to the vapor pressure of the volatile blowing agent in a state in which the volatile blowing agent is contained in the intraparticle polymer and the particles are dispersed in the dispersion medium. This does not necessarily correspond to the vapor pressure when a volatile blowing agent is present alone.

That is, it cannot be unambiguously determined because it depends on the degree of affinity between the blowing agent and the intragranular polymer, the content, and the combination of types of blowing agents. The pre-expanded particles of the present invention obtained as described above usually have an apparent expansion ratio of 5 to 10, although this varies depending on the temperature, pressure, etc. during pre-expansion, and the amount is smaller than that of polypropylene resin alone. Even if a foaming agent of

Further, the pre-expanded particles have a closed cell ratio of 75% or more. Further, the pre-expanded particles of the present invention are thermally formed, for example, at room temperature and pressure, and if necessary, pressure-ripened at a predetermined pressure for a predetermined time using an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent. Next, the pre-expanded particles are filled into a mold and heated and foamed to obtain a foam molded article according to the mold. The foam molded product thus obtained can be used, for example, as a cushioning material, a heat insulating material, a packaging material, a food container, a building material, a flotation material, a strong odor, and the like.

As explained above, the pre-expanded polypropylene resin particles of the present invention are an intraparticle polymer of more than 7% by weight of polypropylene resin particles and less than 3% by weight of a vinyl aromatic monomer; Since the base material is a polymer obtained by graft polymerization of part or all of a vinyl aromatic monomer, it maintains the excellent properties of a polypropylene resin such as flexibility, heat resistance, and oil resistance. It has even higher foaming properties and has appropriate rigidity (compression hardness) in addition to flexibility.

Furthermore, according to the production method of the present invention, since the intragranular polymer containing the volatile blowing agent is released into a low-pressure atmosphere from inside the container simultaneously with the dispersion medium, a portion of the vinyl aromatic monomer or Combined with the use of an intraparticle polymer that is entirely graft polymerized, it is possible to obtain pre-expanded particles with excellent foaming efficiency and high foaming rate compared to the case of polypropylene resin alone. When foaming,
Since the intraparticulate polymer is discharged from the container together with the dispersion medium, it has various advantages such as being able to prevent the pre-expanded particles from fusing together. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 3 Ethylene propylene random copolymer particles containing 2.5% by weight of ethylene component, styrene monomer, etc. in the formulation shown in Table 1, and 0.01% sodium dodecylbenzenesulfonate.
300 parts by weight of an aqueous solution and 2 parts by weight of tricalcium phosphate
．． The mixture was placed in a sealed container together with 5 parts by weight, and heated at 8500 Iso Azusa for 6 hours, and then further heated at 14000 for 4 hours to obtain an intragranular polymer.

Parts by weight of this intragranular polymer 10 and 0.3 parts by weight of finely divided aluminum oxide were placed in a pressure-tight airtight container together with 20 parts by weight of dichlorodifluoromethane, and the inside of the container was heated to 145% by weight.
One end of the container was opened while the container was held in an approximately 30k9'c tube (G), and the intragranular polymer and water were simultaneously discharged into the atmosphere to obtain pre-expanded particles having the magnification shown in Table 2.

Table 2 shows the physical properties of the foamed product obtained by molding the pre-expanded particles in a mold according to a conventional method.

Examples 4 to 5 An aqueous solution of 0.01% by weight of sodium dodecylbenzenesulfonate was prepared by mixing ethylene propylene block copolymer particles at 2% by weight of ethylene component, styrene monomer, dichlorodifluoromethane, etc. in the formulation shown in Table 1. 30 parts by weight of tricalcium phosphate and 2.5 parts by weight of tricalcium phosphate were placed in a closed container, heated at 85° C. for 6 hours under coagulation, and further heated at 14,000° C. for 4 hours to complete polymerization.

After that, the foaming temperature was adjusted to 155 qo, and the internal pressure of the container was approximately 3
While maintaining the temperature at 0k9' (G), one end of the container was opened and the intragranular polymer and water were simultaneously released under atmospheric pressure to obtain pre-expanded particles having the magnification shown in Table 2. Table 2 shows the physical properties of the foamed product obtained by molding the pre-expanded particles in a mold according to a conventional method.

Comparative Example 1 The same procedure as in Example 1 was conducted except for the formulation shown in Table 1.

Table 2 shows the magnification of the obtained pre-expanded particles and the physical properties of the foamed molded product. Comparative Example 2 10 parts by weight of ethylene-propylene random copolymer particles containing 2.5% by weight of ethylene component, 0.0 parts by weight of finely divided aluminum oxide. $ parts by weight, 25 parts by weight of dichlorodifluoromethane, and 30 parts by weight of water were poured into a pressure-tight airtight container, and while maintaining the inside of the container at 14500, approximately 30 kg' C), one end of the container was opened and the particles were collected. and water were simultaneously discharged under atmospheric pressure to obtain pre-expanded particles having the magnification shown in Table 2.

Table 2 shows the physical properties of the foamed product obtained by molding the pre-expanded particles in a mold according to a conventional method.

Table 1 Table 2 *1 Heat resistance The volumetric shrinkage rate when placed in an open environment at 100oC x 24hr was measured.

Less than 15% ○ 15% or more × *2 Oil resistance 2 ml in cooking oil Changes when soaked No change ○ Swelling× *3 Flexibility NDS (Defense Agency standard) Measured according to Z-0503.

No cracks ○ 〃 Yes × *4 Compression hardness Measured according to JISK6767.

0.8k9/more than carp 0 Less than 0.8k9/c beard ×

Claims (1)

[Scope of Claims] 1. The base resin is an intraparticle polymer of a mixture consisting of polypropylene resin particles in an amount exceeding 70% by weight and a vinyl aromatic monomer in an amount less than 30% by weight, and the intraparticle polymer is polypropylene. 1. Pre-expanded polypropylene resin particles, characterized in that they are polymers in which part or all of a vinyl aromatic monomer is graft-polymerized to a resin. 2 After dispersing more than 70% by weight of polypropylene resin particles, less than 30% by weight of a vinyl aromatic monomer, and a polymerization catalyst in a dispersion medium, a part or all of the vinyl aromatic monomer is graft-polymerized onto the polypropylene resin. A step of obtaining an intragranular polymer, a step of making the intragranular polymer contain a volatile blowing agent in a closed container, and a step of opening one end of the container and transferring the intragranular polymer containing the volatile blowing agent into a sealed container. A method for producing pre-expanded polypropylene resin particles, which comprises a step of discharging the particles from the inside into a low-pressure atmosphere.