JPS62201942A - Production of polypropylene foam - Google Patents

Abstract

PURPOSE:To obtain the titled foam which has uniform, fine cells and excellent appearance and heat resistance and is highly expanded, by extrusion-expanding a compsn. consisting of a PP resin, a main chain breakage inhibitor, a blowing agent and a peroxide under specified conditions. CONSTITUTION:A material 2 obtd. by pre-blending 100pts.wt. PP resin (A) having an MFI of 0.5-10 with 0.02-2.0pts.wt. main chain breakage inhibitor (B) (e.g., p,p'-dibenzoylquinone dioxime), etc. is fed through a hopper 1 to an extruder 3, wherein the temp. of a die 5 is set at about 150 deg.C to melt it. 0.05-2.0pts.wt. peroxide (D) having a one-min half-life temp. higher than the m.p. of the compo nent A [e.g., 2,5-dimethyl-2,5-di(t-butylperoxide)hexane], diluted with a volatile blowing agent (C) (e.g., butane) is fed through pressure inlets 4 and 6 to the extruder under pressure. The component d is used in an amount of 0.1-2.0 times that of the component B. While the mixture is reacted and the gel fraction is kept at 0%, it is thoroughly kneaded and extruded through the die 5 to obtain the titled foam having an expansion ratio of 1.5-60.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for making polypropylene foam.

(Prior art and its problems) Conventionally, polypropylene and a blowing agent such as a gas such as nitrogen or carbon dioxide, a hydrocarbon such as propane or butane, or a volatile liquid such as fluorocarbon are forced into an extruder and then kneaded. Extrusion foaming techniques are known. However, using these foaming agents to produce highly foamed polypropylene with uniform, fine cells and appearance with a foaming degree of several times to several tens of times requires advanced technology, especially the temperature and temperature during extrusion foaming. Since it is extremely difficult to control the viscosity, it has not yet been achieved industrially.

The viscosity of polypropylene changes significantly with temperature compared to polyethylene and the like, and it is particularly difficult to maintain the viscosity within an appropriate range to obtain a closed-cell foam.

Although it is possible to improve the properties of this polypropylene by mixing other resins, in this case, the excellent properties of the polypropylene itself, such as heat resistance, are deteriorated.

JP-A No. 57-24221 discloses a method of extruding polypropylene with a gel fraction of 60% or less by slightly crosslinking, but in this case, the presence of the gel component causes large heat generation in the extruder. However, there are disadvantages in that it is not possible to obtain a suitable foaming temperature and a good foam cannot be obtained, or the extrusion volume is limited to an extremely low extrusion volume. If this was to be avoided at all, it would be necessary to add cooling equipment such as a large separate extruder designed to have a very large cooling capacity to the extruder described above. It was also inconvenient to produce a thin film-like product or an irregularly shaped product with a narrow nozzle. It also has the disadvantage that the extrudates tend to have bumps and melt fractures.

OBJECTS OF THE INVENTION The present invention provides a method for producing polypropylene foams that do not have the disadvantages of "biped", especially polypropylene foams having an expansion ratio of 1.5 to 60 times.

(Structure and Effect of the Invention) That is, the present invention has an MFI (melt blow index) of 0.
．． Polypropylene extrusion foaming characterized by extruding and foaming a composition consisting of a polypropylene resin having a polypropylene resin of 5 to 10%, a main chain scission inhibitor, a blowing agent, and a peroxide in an extruder with a gel fraction of substantially 0%. Provides body preparation methods.

The MFI (melt flow index) of the polypropylene used in the present invention is 0.5 to 10. Preferably 1-5
It is. When MFI exceeds 10, gel content is practically 0%
However, adding peroxide to the extrudate under pressure does not improve the foaming properties sufficiently, and if too much peroxide is added to the point where a gel can be detected, the extrudate will have spots and streaks. This appears as unevenness, making it impossible to obtain a satisfactory foam. MFIh<
If it is less than 0.5, the essential melt viscosity of the resin is high, and uniform kneading and reaction with the injected peroxide will not occur, and cooling to the appropriate foaming temperature will be difficult.
Requires special and expensive equipment.

As mentioned above, it is difficult to adjust the viscosity of polypropylene to an appropriate level for forming a foam. In the present invention, a main chain scission inhibitor is used to suppress the gel fraction to substantially 0%, thereby facilitating viscosity adjustment.

Normally, when peroxide is added to plastics to generate radicals, there are two types of plastics: those that crosslink and those that disintegrate, and polypropylene belongs to the type that disintegrates. Therefore, if a peroxide is added and reacted without adding a main chain cleavage inhibitor, the main chain of the polypropylene will be cleaved, resulting in a lower molecular weight and a starch syrup-like appearance. The main chain scission inhibitor of the present invention suppresses the main chain scission reaction,
A substance that plays a role in increasing crosslinking efficiency.

Examples of main chain cleavage inhibitors include polyfunctional monomers such as triallyl cyanurate, triallyl isocyanurate, ethylene glycol dimethacrylate, trimedylolpropane trimethacrylate, divinylbenzene,
diallyl phthalate, etc.; monofunctional monomers, such as vinyltoluene, ethylvinylbenzene, etc.; oxime compounds and nitrone compounds, such as quinone dioxime, penzoquinone dioxom, etc.; maleimide compounds, such as N,
Among them, quinone dioxime compounds such as quinone dioxime, penzoquinone dioxom, and p,I)'-dibenzoylquinone dioxime are particularly effective. It can be used for. Also, hydroquinone diacrylate, p, p″-bis(methacryloyloxy) phenyl ether, p, p
'-bis(acryloyloxy)benzophenone, 1.
4-bis(methacryloyloxy)cyclohexane, p
, p'-bis(allyloxy)phenyl ether, diallylbutene tricarboxylate, triallyl trimellitate, or bis(β-acryloyloxyethyl)
Adipate and the like can also be suitably used.

The amount of the main chain scission inhibitor is usually 1 part polypropylene resin.
For 00 parts by weight, 0.05 to 2.0 parts by weight, preferably 0.05 to 1 parts by weight, is suitable. If it exceeds 2 parts by weight, the m required for the reaction of the present invention is exceeded, and the inhibitor is not sufficiently compatible with the polypropylene resin, resulting in poor dispersion and appearing as fine lumps on the foam, impairing its appearance. If the amount is less than 0.05 parts by weight, the polypropylene resin will have a low molecular weight and become syrupy-like.

The foaming agents of the present invention include gases such as nitrogen gas and helium-11, easily volatile liquids such as fluorocarbons and pro-Jbanbutane, and gases generated by thermal decomposition of strondium azonocarboxylate and hydrazinocarbonamide. Agents can be used.

The liquid blowing agent cools the niboripropylene at the same time it is press-fitted into the polypropylene, has the effect of plasticizing the polypropylene, lowering its viscosity, and has the advantage of being easy to dissolve uniformly, so it is most suitable for the present invention. be.

The peroxide used in the present invention preferably has the following properties.

■Effective in crosslinking polypropylene.

■Creating a uniform dispersion state with the easily volatile blowing agent or solvent to be diluted. Desirably, it should be compatible with the solvent to be diluted.

(2) In order to carry out a stable and uniform reaction, the 1-minute half-life temperature must not be lower than the melting point of polypropylene by more than 15°C. Preferably, the temperature is higher than the melting point of pyrene.

In particular, regarding (2), when injecting peroxide as a crosslinking agent, the small amount of peroxide necessary for the present invention is stabilized (7) Since it is supplied from the middle of the extruder, dilution can make the reaction more gradual. This is necessary in order to ensure uniform mixing of the resin and peroxide (C), and dilution can of course also be expected to have the effect of making unstable peroxide more stable.

Regarding (2), although it is also related to (2), it relates to the dispersion of crosslinking points, which is an important condition in the present invention. In other words, peroxide is normally diluted and press-injected into the extruder midway through the extruder, but the guideline for crosslinking reaction time with peroxide is 5 to IO times the half-life. 1 at the position where peroxide is forced into the extruder from the middle.
! The temperature of the ribropylene melt is higher than the melting point of polypropylene, and the reaction time is generally longer due to dilution injection. The reaction occurs almost instantaneously, resulting in reduced crosslinking efficiency or insufficient mixing with the resin, resulting in intensive crosslinking. Therefore, the effects of the present invention cannot be obtained.

Furthermore, during press-fitting, there is a possibility that a decomposition reaction occurs before press-fitting. By using a peroxide with a high 1-minute half-life temperature, stable press-in and the necessary time for kneading are secured, and uniform dispersion of crosslinking points can be expected, resulting in the effects of the present invention. be.

There are various examples of peroxides, but for example, if the melting point of polypropylene is 165°C, dicumyl peroxide (DC), t-butylcumyl peroxide, di-L-butyl peroxide, 2. 5-dimethyl-
2,5-di(t-butylperoxide)hexane, 2.
5-dimethyl-2,5-di(t-butylperoxide)
Examples include hexane, 1,3-di(L-butylperogindoisobrobyl)benzene, and the like.

The amount of peroxide used is 0.1 to 1 times the amount used if the main chain scission inhibitor is a quinonediochytum compound, and 0.1 to 1 times the amount used for polypropylene 100I (!n parts).
0.005 to 2.0 parts by weight, preferably 0.025 to 0.025 parts by weight.
5 parts by weight is preferred.

If the amount is less than 0.005 parts by weight, an appropriate crosslinking reaction will not occur. If it exceeds 2.0 parts by weight, the crosslinking reaction will occur beyond the limit necessary for the present invention, resulting in gel formation, which may appear as a lump in the foam, or cause problems such as extrusion (1) and (2) problems such as a decrease in extrusion. It has the following disadvantages.

In the present invention, the polypropylene foam is produced by the following method: 100 parts by weight of a polypropylene resin having an MFI of 0.5 to 10 and 0.05 to 2.0 parts by weight of a main chain scission inhibitor (limited quinone dioxime compound). 0.1 to 1.0 m of peroxide (1 minute half-life temperature higher than the melting point of polypropylene) was added to the extruder, and 0.1 to 1.0 m of peroxide was added to the main chain scission inhibitor. ) is diluted and dissolved in an easily volatile foaming agent with a boiling point of 100°C or less, and injected into the extruder from the middle. Alternatively, if the easily volatile blowing agent used does not dissolve the peroxide, a portion of the already dissolved peroxide is injected into the easily volatile foaming agent.
After kneading, peroxide decomposition, and reaction in an extruder, it is extruded from a mold attached to the tip of the extruder 111, and the gel fraction (hot toluene method) is essentially 0%. A polypropylene foam is obtained.

In the present invention, the gel fraction of polypropylene (hot toluene method)
Virtually kept at 0%. By setting the gel fraction to virtually 0%, there is little decrease in extrusion rate and there are no other extrusion problems.
Greatly improves foamability to +jy.

(Example) The present invention will be explained in more detail.

Sumitomo Noblen ll501 (
MF I = 3.5) l 0.3 parts by weight of p, p'-dibenzoylquinone dioxime (Kawaguchi Kagaku [Acta-DQJ)] as a main chain scission inhibitor and talc as a nucleating agent. After adding 0.5 parts and stirring well (2), transfer it to the hopper (1) of the single extruder (3) shown in Figure 1.
(The diameter of the cylinder of the extruder in Fig. 1 is 65 mm.
1III11, and the length was 35 times the diameter. ).

The temperature of the die (5) of the extruder (3) was set at 150°C. Through the injection port (4), 15 parts by weight of butane as a blowing agent and a composition having a half-life temperature of about 193°C (1 min. , 10 wt% ethanol solution of 5-dimethyl-2゜5-di([-butylperoxo)hequin-3 (NOF Verhekin 25B) was added to 1.0 mold assembly (0.1 heavy end as peroxide amount). was press-fitted from (6), sufficiently kneaded, reacted, and extruded through a die with a slit of 0.5t x I 90w while cooling the temperature of the foamable melt, resulting in a density of 0.14 g/ A foam with a closed cell ratio of 50% or more was obtained.

Comparative Example 1 When extruded under the same conditions as in Example without adding the main chain scission inhibitor, a foam with a density of 0.8 g/ee and almost open cells was obtained.

When extruded under the same conditions without adding the composition, severe cell splitting occurred near the die, resulting in an open cell foam with a density of 0.6 g/CC.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the present invention. The symbols in the figure are as follows: (1)...Hopper, (2)...Material made by pre-blending polypropylene with a main chain scission inhibitor, a nucleating agent such as talc, and others, (3)...・
・Extruder, (4)...Blowing agent, peroxide injection port, (5)...
Thailand. Figure 1

Claims (1)

[Claims] 1. MFI (melt flow index) 0.5 to 10
A method for producing an extruded polypropylene foam, which comprises extruding and foaming a composition comprising a polypropylene resin having the following, a main chain scission inhibitor, a blowing agent, and a peroxide in an extruder at a gel fraction of substantially 0%. . 2. The method according to item 1, wherein the main chain scission inhibitor is a quinone dioxime compound. 3. The method according to item 1, wherein the 1-minute half-life temperature of the peroxide is higher than the melting point of polypropylene. 4. The manufacturing method according to item 1, wherein the blowing agent is a volatile blowing agent. 5. After melt-mixing the main chain scission inhibitor into the polypropylene resin in advance, the first step is to add peroxide diluted with a blowing agent.
Manufacturing method described in section.