JPH0524932B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a foamable sheet suitable for obtaining a crosslinked polypropylene foam. More specifically, the present invention relates to a method for producing a foamable sheet suitable for obtaining a polypropylene crosslinked foam having an expansion ratio of 2 times or more, having closed cells, and having a good skin of a molded product. [Prior Art] Polypropylene foam has superior heat resistance, strength, rigidity, etc. compared to polyethylene foam, and is expected to be used as high-temperature insulation materials, packaging materials, building materials, lightweight structural materials, etc. Polypropylene (hereinafter abbreviated as PP) has extremely low viscoelasticity when melted compared to polyethylene, especially high-pressure low-density polyethylene, so it cannot resist the pressure of foaming gas during melting and foaming, and most of the foaming gas escapes, resulting in a good foam. Therefore, in the production of PP foam, a method has been proposed in which appropriate crosslinking is performed to increase the melt viscoelasticity (for example, Japanese Patent Publication No. 31754/1983). However, as described in Japanese Patent Publication No. 46-31754, PP alone lacks foamability, has a low foaming ratio, and results in coarse cells. Furthermore, the publication
Although it is stated that other polymers such as polyethylene, ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, ethylene/propylene copolymer, etc. may be added to PP, such polymers Compared to PP, the crosslinking reaction by the radical generator is faster, and when mixed with PP, crosslinking proceeds rapidly by itself due to the radical generator used in combination, so the amount of such polymer is small compared to the amount of PP. When added, the cross-linked polymer portion becomes merely scattered in the PP, which not only fails to improve the foamability of the PP component, but also worsens the foamability due to lack of affinity at the interface with the PP component. . [Problems to be Solved by the Invention] In view of the above circumstances, the present inventors have developed a crosslinked polypropylene foam that has an excellent expansion ratio and has closed cells with a uniform cell distribution, and a molded product with a good skin. As a result of various studies to obtain a foamable sheet, we found that in addition to polypropylene, a radical generator, and a crosslinking aid, a specific 1-butene polymer was added to crosslink, and then a foaming agent was added and kneaded. It was found that the above object could be achieved by foaming the sheet, and the present invention was completed. [Means for solving the problems] That is, the present invention provides: (a) Melt flow rate: 0.1 to 50 g/
10min polypropylene (A): 60 to 95 parts by weight, (b) Melt flow rate: 0.05 to 50g/
1-Butene polymer (B) with 10 min, 1-butene content: 70 mol% or more and heat of crystal fusion: 20 Joule/g or more based on thermal analysis using a differential scanning calorimeter:
5 to 40 parts by weight, (c) (A) + (B) = 100 parts by weight, radical generator (C): 0.05 to 0.5 parts by weight, and (d) (A) + (B) = 100 Crosslinking aid (D) based on weight part: 0.1
After performing a crosslinking reaction by melt-kneading a mixture consisting of from 1 to 1 part by weight at a temperature higher than the decomposition temperature of the radical generator (C),
Such a crosslinking composition: blowing agent (E) per 100 parts by weight
A cross-linked polypropylene having closed cells with excellent expansion ratio and cell uniformity, characterized by adding 0.5 to 5 parts by weight of the foaming agent (E) and then kneading at a temperature below the decomposition temperature of the blowing agent (E) to obtain a sheet. The present invention provides a method for manufacturing a foamable sheet suitable for obtaining a foam. [Function] The polypropylene used in the method of the present invention (hereinafter referred to as
(sometimes abbreviated as PP) (A) means melt flow rate (MFR: ASTM D 1238, L) of 0.1 or more.
50g/10min, preferably 0.5 to 20g/10min
propylene homopolymer or propylene and 30
Mol% or less of ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene,
It is a crystalline copolymer with other α-olefins such as 1-decene. If the MFR is less than 0.1g/10min, it will be difficult to knead and extrude during the crosslinking process, making it unsuitable for industrial use.On the other hand, if it exceeds 50g/10min, the amount of crosslinking aid required to improve foaming properties will be too large. , impractical. The 1-butene polymer (B) used in the method of the present invention has a melt flow rate (MFR: ASTM D
1238, L) is 0.05 to 50 g/10 min, preferably 0.1 to 20 g/10 min, and the 1-butene content is
70 mol% or more, preferably 75 mol% or more and
The heat of crystal fusion based on DSC thermal analysis is 20Joule/
g or more, preferably 30 Joule/g or more, or a random copolymer of 1-butene and an α-olefin having 2 to 20 carbon atoms, preferably a melting point of 70°C or more, more preferably teeth
The temperature is 80℃ or higher. If the MFR is less than 0.05g/10min, it is difficult to uniformly disperse it in PP(A), while if it is more than 50g/10min, it is necessary to mix with PP(A) and co-crosslink to improve foamability. The amount of crosslinking auxiliary agent becomes too large, making it impractical. If the 1-butene content is less than 70 mol% and the heat of crystal fusion is less than 20 Joule/g, it is PP.
The difference in melting point from (A) is too large, which not only results in insufficient uniform dispersion by heating and kneading, but also causes the radical generator (C) and crosslinking aid (D) to be absorbed into the 1-butene polymer (B) There is a strong tendency for the co-crosslinking efficiency with PP(A) to decrease, resulting in coarse bubbles and no improvement in foamability. In the 1-butene polymer (B), the α-olefin copolymerized with 1-butene has 2 or more carbon atoms.
20 α-olefins, specifically, for example, ethylene, propylene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene,
Examples include 1-tetradecene and 1-octadecene. In addition, the measurement of the heat of fusion of the 1-butene polymer (B) in the present invention is calculated using the area of the endothermic part based on crystal melting of the copolymer using a differential scanning calorimeter, and based on the heat of fusion of indium. is the value. The heat of fusion and melting point are measured under the following measurement conditions. That is, after leaving the sample at 200℃ for 5 minutes,
Cool down to -35℃ at a rate of ℃/min, and cool down to 1 at -35℃.
Leave for a minute. After that, at a heating rate of 10℃/min -
Measurements are taken from 35℃ to 200℃. 1-butene content having the above-mentioned properties
70 mol% or more of the 1-butene polymer (B) is, for example, (a)
(b) a complex containing at least magnesium, titanium and halogen;
It can be obtained by random copolymerization of 1-butene and α-olefin or by homopolymerization of 1-butene using a catalyst formed from an organometallic compound of group metal and (c) an electron donor. Part or all of the electron donor (c) may be immobilized on part or all of the complex (a), or may be brought into preliminary contact with the organometallic compound (b) prior to use. Good too. Particularly preferred is an embodiment in which a part of the electron donor (c) is immobilized on the complex (a), and the remainder is added to the polymerization system as it is or is used after being brought into preliminary contact with the organometallic compound (b). be. In this case, the complex
The electron donor immobilized in (a) and the electron donor used by directly adding it to the polymerization system or by making preliminary contact with (b) may be the same or different. As the radical generator (c) used in the method of the present invention, organic peroxides and organic peroxy esters are mainly used, and the decomposition temperature for obtaining a half-life of 1 minute is higher than that of the 1-butene polymer (B). It is preferably higher than the melting point, and more preferably higher than the melting point of the PP(A). Note that it is practically preferable that the decomposition temperature of the radical generator (C) to obtain a half-life of 100 hours (hr) is 40° C. or higher. Specific examples of these organic peroxides include 3,5,5-trimethylhexanoyl peroxide (1), octanoyl peroxide (2),
Decanoyl peroxide (3), lauroyl peroxide (4), succinic peroxide (5), acetyl peroxide 6, tert-butyl peroxide (2)
-ethylhexanoate) (7), meta-toluoyl peroxide (8), benzoyl peroxide (9), tert-butyl peroxyisobutyrate (10),
1,1-bis(tert-butylperoxy)
3,3,5-trimethylcyclohexane (11), 1,
1-bis(tertiary-butylperoxy)cyclohexane (12), tertiary-butylperoxymaleic acid (13), tertiary-butylperoxylaurate (14), tertiary-butylperoxy 3,
5,5-trimethylhexanoate (15), cyclohexanone peroxide (16), tert-butylperoxyisopropyl carbonate (17), 2,5-
Dimethyl-2,5-di(benzoylperoxy)
Hexane (18), tertiary-butyl peroxyacetate (19), 2,2-bis(tertiary-butylperoxy)butane, tertiary-butylperoxybenzoate (21), n-butyl-4,4-
Bis(tert-butylperoxy)valerate (22), di-tert-butyl peroxyisophthalate (23), methyl ethyl ketone peroxide (24), α,α′-bis(tert-butylperoxyisopropyl)benzene (25), dicumyl Peroxide (26), 2,5-dimethyl-
2,5-di(tert-butylperoxy)hexane (27), tert-butyl cumyl peroxide (28), diisopropylbenzene hydroperoxide (29), di-tert-butyl peroxide (30), para-menthane hydroperoxide (31) ), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3
(32), 1,1,3,3-tetramerbutyl hydroperoxide (33), 2,5-dimethylhexane 2,5-dihydroperoxide (34), cumene hydroperoxide (35), tert-butyl peroxide (36) ). Among these, (12) to (36) are preferred. As the crosslinking aid (D) used in the composition of the present invention,
An unsaturated compound, an oxime compound, a nitroso compound, a maleimide compound, etc. having one or more double bonds;
The polymer radicals generated by hydrogen abstraction of PP (A) react with the crosslinking co-agent (D) faster than the cleavage reaction, thereby stabilizing the polymer radicals and simultaneously converting the 1-butene polymer ( B) and the PP(A)
It works to increase the mutual crosslinking efficiency with each other and the crosslinking efficiency of each individual. Specifically, these compounds include triallyl cyanurate, triallyl isocyanurate,
Ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, pentaerythritol triacrylate, neopentyl glycol diacrylate,
Polyfunctional monomers such as 1,6-hexanediol dimethacrylate and divinylbenzene, oxime compounds such as quinone dioxium and benzoquinone dioxium, paranitrosophenol, N,N
-meta-phenylene bismaleimide, and mixtures of two or more thereof. Among these, neopentyl glycol diacrylate, 1,6-hexanediol dimethacrylate, divinylbenzene, and mixtures thereof are preferred. The blowing agent (E) used in the method of the present invention is a chemical substance that is liquid or solid at room temperature and decomposes when heated to generate gas, and is particularly limited if it has a decomposition temperature equal to or higher than the melting point of PP (A). Not allowed. Such blowing agents (E) include azodicarbonamide, barium azodicarboxylate, N,N'-dinitrosopentamethylenetetramine, 4,4-oxybis(benzenesulfonylhydrazide), diphenylsulfone-3,3-disulfonylhydrazide. , p-toluenesulfonyl semicarbazide, trihydrazinotriazine, biurea, zinc carbonate, and the like. Among these, azodicarbonamide, N,N'-dicarbonamide, which generates a large amount of gas, and whose gas generation end temperature is sufficiently lower than the thermal deterioration start temperature of the PP(A)/1-butene polymer (B) mixed system. Nitrosopentamethylenetetramine and trihydrazinotriazine are preferred. The method for producing a foamable sheet of the present invention is based on the PP
(A): 60 to 95 parts by weight, preferably 70 to 90 parts by weight, the 1-butene polymer (B) 5 to 40 parts by weight, preferably 10 to 30 parts by weight, (A) + (B) = 100
Radical generator (C) 0.05 to 0.5 per part by weight
parts by weight, preferably 0.1 to 0.3 parts by weight and (A)+
A mixture of 0.1 to 1 part by weight, preferably 0.2 to 0.5 parts by weight of crosslinking aid (D) to 100 parts by weight of (B) is heated at a temperature higher than the decomposition temperature of the radical generator (C), preferably at 300 parts by weight. After performing a crosslinking reaction by melt-kneading at a temperature below °C, preferably a crosslinking reaction such that the gel fraction becomes 0.5 to 30% by weight, 0.5 parts by weight of the blowing agent (E) is added to 100 parts by weight of the crosslinked composition. or 5
This method involves adding parts by weight, preferably 1 to 3 parts by weight, followed by kneading at a temperature below the decomposition temperature of the blowing agent (E), and then producing a sheet. If the amount of the 1-butene polymer (B) is less than 5 parts by weight, the dispersibility of the radical generator (C) and the crosslinking aid (D) will not be improved when they are melt-kneaded and crosslinked.
Furthermore, the decomposition of PP (A) by the radical generator (C) is not suppressed, making it impossible to obtain a foamable sheet that provides a good foam. If the amount of the radical generator (C) is less than 0.05 parts by weight, it will not contribute to increasing the melt viscoelasticity of the crosslinked composition, and gas will escape when foaming the foamable sheet.
A foam with good closed cells cannot be obtained. On the other hand, if it exceeds 0.5 parts by weight, the amount of radicals generated will be excessive, and the excess radicals exceeding the amount of radicals required for crosslinking will cause cleavage in the polymer chain portion derived from PP (A) and/or 1-butene polymer (B). ,
The melt viscoelasticity of the PP(A)/1-butene polymer (B) mixed system decreases again, and a foamable sheet that provides a good foam cannot be obtained. If the amount of the crosslinking aid (D) is less than 0.1 part by weight, the crosslinking reaction of the PP(A)/1-butene polymer (B) system by the radical generator (C) will be insufficient, and the contribution to the increase in melt viscoelasticity will be insufficient. few. On the other hand, if it exceeds 1 part by weight, the foaming agent (E)
It becomes difficult to produce a foamable sheet by mixing and extrusion molding, or the appearance and skin of the foaming sheet deteriorates, impairing the appearance of the product after foaming and impairing its practicality. When melt-kneading the PP (A), 1-butene polymer (B), radical generator (C) and crosslinking aid (D), a phenolic heat stabilizer (F) having an oxygen number of 30 or more is added. (A)+(B)
By adding 0.05 to 1 part by weight, or even 0.1 to 0.5 part by weight, per 100 parts by weight, the concentration of polymer radicals generated can be controlled to increase crosslinking efficiency, and the foamable sheet can be heated and foamed. When letting
and prevention of thermal oxidative deterioration during thermal processing of foam;
In addition, it is preferable in terms of improving the heat aging resistance of the foamed product during practical use. Examples of the heat stabilizer (F) include n-ocdecyl-3-(4'-hydroxy-3',
5'-shaributylphenyl) propionate,
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,
1,3,tris(4-tert-butyl-3-
Hydroxy-2,6-dimethylbenzyl)-S-
Triazine-2,4,6-(1H,3H,5H)trione, 1,3,5-5-trimethyl-2,4,6
-Tris(3,5-ditertiarybutyl-4-
hydroxyphenyl)benzylbenzene, 1,
3,5-Tris(3,5-ditertiarybutyl-4'-hydroxybenzyl)-S-triazine-
Examples include 2,4,6-(1H,2H,5H)trione, tetrakis[methylene-3(3,5-ditertiarybutyl-4-hydroxyphenyl)propionate]methane, and mixtures of two or more of these. It will be done. When mixing the crosslinked composition and the blowing agent (E),
The above PP(A) powder was added to 100 parts by weight of the crosslinking composition.
Adding 15 to 50 parts by weight, or even 15 to 30 parts by weight, improves dispersibility and suppresses the formation of giant bubbles even when the blowing agent (E) is a cohesive substance. . Furthermore, if the blowing agent (E) to be added is mixed in advance with an additive (G) that has a function of preventing secondary agglomeration of the blowing agent (E), the blowing agent (E) It is possible to obtain a foamable sheet that improves the uniform dispersion of fine particles in the foamable sheet and provides a good foamed product free of coarse bubbles. Such additives (G) include metal soaps and surfactants, and specifically, metal salts of stearic acid, the crosslinking composition such as stearyl monoglyceride, blowing agents (E), etc. are mixed. Substances that are solid at the temperatures at which they are used are preferred. The method of kneading the crosslinked composition and the blowing agent (E) to form a sheet is to add the blowing agent to the crosslinked composition heated and melted in a twin-screw kneader such as a Brabender, disperse it, and then knead it with a calendar roll. Examples include a method of forming into a sheet, a method of forming a sheet with a press molding machine, a method of kneading using an extruder and then forming a sheet through a T-die or an annular die. The method of extrusion molding using a T-die at a temperature below the decomposition temperature of is preferred because the process is short, the amount of energy required and the time required are small, and the flatness and extrusion surface of the resulting sheet are also good, so foaming is preferred. The latter product is also preferable because it provides a foamed sheet with a good appearance. A foamed body can be obtained from the foamable sheet of the present invention by various known methods, such as placing the trimmed foamable sheet in a pressure press mold, closing the mold, and heating the mold to decompose the foaming agent (E). Pressure press foaming method, in which the mold is heated to a temperature that generates gas, and after the gas has been generated, the mold is opened to foam, and normal pressure foaming, in which a foamable sheet is placed on a heated hot plate and heated to foam. law,
A method in which a foamable sheet is placed on a hot plate and then further heated and foamed from above with a radiant heat beam, or a foamable sheet is suspended at both ends and heated from above and/or below with a radiant heat ray and/or high frequency. A method of foaming, or a method of placing a foamable sheet in an oven heated to the decomposition temperature of the blowing agent (E) and foaming by heating with hot air, and a method of foaming in a molten salt bath heated to a temperature above the decomposition temperature of the blowing agent (E). Alternatively, a method of heating and foaming in a bath can be used. [Effects of the Invention] The method for manufacturing a foamable sheet of the present invention is based on a conventional composition for a crosslinked foam made solely of polypropylene, or polypropylene mixed with an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, or an ethylene-acrylic acid composition. Compared to the method of manufacturing a foamable sheet using a crosslinked foam composition containing a copolymer, etc., this method has an excellent expansion ratio, and has closed cells with a uniform cell distribution, and has excellent heat resistance, strength, rigidity, etc. This is a method for producing a foamable sheet suitable for obtaining a crosslinked polypropylene foam with a beautiful appearance, and the process includes a step of producing a crosslinked polypropylene composition with excellent foamability, and a step of producing a foamable sheet by mixing a foaming agent. By separating the steps, the manufacturing conditions for the crosslinked polypropylene composition can be widened, and unnecessary volatile components that may pose health and safety hazards to foamed products can be easily removed. The appearance of the foam sheet becomes uniform,
It has the advantage of being able to easily produce a foamable sheet that provides a polypropylene crosslinked foam with good skin texture, which provides a highly practical polypropylene cross-linked foam with good post-processability and product finish. Example 1, Comparative Examples 1 to 8 (These examples show the differences in the foamability improvement effects of the modifying resins.) Polypropylene resin (manufactured by Mitsui Petrochemical Industries, Ltd., brand name B200, MFR = 0.5) pellets
55 parts by weight, 15 parts by weight of the above resin powder, 1st
30 parts by weight of the modifying resin shown in the table, 0.2 parts by weight of dicumyl peroxide as a crosslinking agent, 0.5 parts by weight of divinylbenzene as a crosslinking aid, and tetrakis[methylene-3(3,
5-ditertiarybutyl-4-hydroxyphenyl)propionate] methane (manufactured by Ciba Geigy, trade name Irganox 1010), n-octadecyl-
0.1 parts by weight of each of 3-(4′-hydroxy-3′,5′-ditertiarybutylphenyl)propionate (manufactured by Ciba Geigy, trade name Irganox 1076) and calcium stearate were mixed in a high-speed mixer (Mitsui Miike Manufacturing Co., Ltd.). The mixture was mixed using a Henschel mixer (manufactured by Henschel). (Hereinafter, referred to as crosslinkable mixture) The above crosslinkable mixture was extruded using an extruder (manufactured by Thermoplastics, cylinder diameter 20 mm, L/D = 26).
Using a screw equipped with a dalmage part, the maximum temperature was 250℃ and the screw rotation speed.
The mixture was heated and kneaded at 60 rpm, extruded into a strand shape, cooled with water, and finely granulated using a rotary cutter. (Hereinafter referred to as crosslinked fine particles) 100 parts by weight of the crosslinked fine particles, 15 parts by weight of the resin powder, and 100 parts by weight of azodicarbonamide and 5 parts by weight of stearyl monoglyceride as blowing agents were mixed in advance in a low-speed mixer ( 2 parts by weight of the mixture mixed using My Mixer MX-M2 (manufactured by Matsushita Electric Industrial Co., Ltd.) was mixed using the high-speed mixer. (Hereinafter, referred to as foamable mixture) The above foamable mixture was produced using the extruder equipped with a full-flight screw and a die having an approximately fishtail-shaped flow path with an opening width of 50 mm and an opening thickness of 1 mm. , resin temperature 190℃,
It was extruded at a screw rotation speed of 40 rpm and formed into a long sheet. (Hereinafter, referred to as a foamable sheet) The foamable sheet was cut into approximately disk shapes weighing 2.2 g (hereinafter referred to as foamable sheet pieces), and subjected to press foam molding described below. As a press foam mold, the opening diameter is 50mm,
A metal mold with a truncated cone-shaped recess with a tapered periphery and a depth of 2 mm and a bottom diameter of 44 mm was placed facing another metal mold with a smooth surface, and the two molds were brought into contact. A cavity was constructed that could be closed airtight by pressing. Each mold was provided with a cooling medium flow path for cooling the periphery of the cavity. The foaming mold is heated and pressure molded using a heating and pressure molding machine (manufactured by Shinto Metal Industry Co., Ltd., product name: One-cycle automatic molding machine SFA-
Each mold was suspended between the upper and lower mold plates of the 50-inch model, allowing them to be opened and closed freely. Thickness 0.1mm, width 100mm on the top and bottom of the foam sheet piece
Rectangular sheets made of tetrafluoroethylene with a length of 100 mm and a length of 100 mm are stacked on top of each other and placed on a 0.2 mm thick aluminum plate that has been previously formed to fit the recess of the mold.
The foaming mold was heated to 180° C. and inserted into the open recess. Next, the foam molds were placed close to each other so that the interval was 5 mm, and the foam sheet was preheated for 1 minute to soften or melt, and then the mold was closed by pressing and the mold temperature was lowered.
After raising the temperature to 205℃ and keeping it airtight for about 7 minutes,
The mold was opened, and the contents together with the tetrafluoroethylene sheet were taken out from the mold and allowed to cool at room temperature. After natural cooling, the tetrafluoroethylene sheet was removed and the molded product was taken out. The specific volume of the molded article was measured by the air comparison method and the external dimension measurement method, and the results are shown in the "Specific volume of foam" column of Table 1. The measurement method and unit of the specific volume mentioned here are as follows. Air comparison method: Air comparison hydrometer (manufactured by Beckman,
Air Comparison Pycnometer
Model 930), 1-0.5-1
The volume of the molded article was measured by the air pressure operation method, and the value divided by the weight of the molded article was defined as the "specific volume by air comparison method." Units,
cm ³ /g. (Hereinafter, abbreviated as cc/g.) External dimension measurement method: Using calipers, measure the thickness, width, and
The length was measured, the apparent volume was calculated, and the value divided by the weight of the molded product was defined as the "specific volume by external dimension measurement method." The unit is cm ³ /g. (Hereafter, cc/
It is abbreviated as g. )

【table】

[Table] The types of modifying resins in Table 1 are as follows. BPR: 1-butene/propylene random copolymer MFR: 7.4g/10min, 1-butene content 75 mol%, heat of crystal fusion:
36Joule/g EPR: Ethylene-propylene random copolymer
MFR: 0.8 g/10 min, ethylene content: 80.0 mol% EPT: Ethylene-propylene-diene terpolymer (product name Mitsui EPT1071; manufactured by Mitsui Petrochemical Industries, Ltd.) TPE: Thermoplastic elastomer (product name Milastomer 8530N; manufactured by Mitsui Petrochemical Industries, Ltd.) HDPE: High-density polyethylene (trade name: Hi-Zex 5000S; manufactured by Mitsui Petrochemical Industries, Ltd.) LDPE: Low-density polyethylene (trade name: Mirason M)
-9; Mitsui Dupont Polychemical Co., Ltd.
EVA: Ethylene-vinyl acetate copolymer (product name: Evaflex V-5274; manufactured by Mitsui DuPont Polychemical Co., Ltd.) EEA: Ethylene-vinyl acrylate copolymer (product name: Mitsui-EEA A-702; Mitsui Dupont Polychemical Co., Ltd.) (manufactured by DuPont Polychemical Co., Ltd.) As shown in Table 1, it can be seen that the foamability of the foamable sheet produced by the method of the present invention is significantly superior to that of conventional methods and methods other than the present invention. Examples 2 to 3, Comparative Examples 9 to 10 (In these examples, the influence of the 1-butene content of the 1-butene/α-olefin random copolymer will be described.) In Example 1, 1-butene/propylene The 1-butene content of the random copolymer was changed as shown in Table 2, and the amount of PP resin pellets mixed was 65%.
Parts by weight, 20 parts by weight of the 1-butene/propylene random copolymer, 1 part by weight of the blowing agent,
Table 2 shows the results of evaluating the foamability in the same manner as in Example 1 except that the foaming temperature was 210°C.

[Table] As shown in Table 2, the 1-butene/α-olefin random copolymer or 1-butene homopolymer used in the method of the present invention has the following properties: 1-butene content, melting point, heat of fusion, and It can be seen that foamability is excellent when the MFR has physical properties within a specific range. Examples 4 to 7 (These examples discuss the effect of the type of PP resin.) In Example 2, the type of PP resin was changed as shown in Table 3, and the blowing agent mixture was changed to 2 parts by weight,
Table 3 shows the results of evaluating the foamability in the same manner as in Example except that the weight of the foamable sheet piece was changed to 2.1 g and the time for keeping the mold airtight was changed to 4 minutes.

[Table] As shown in Table 3, the method of the present invention includes PP
It will be appreciated that a wide variety of resin types can be used. Examples 8 to 13, Comparative Examples 11 to 12 (In these examples, the effects of the mixing amount of the blowing agent and the foam molding conditions will be described.) In Example 5, the mixing amount of the blowing agent and the foam molding conditions are shown in Table 4. Table 4 shows the results of evaluating the foamability in the same manner as in Example 5, except that the weight of the foamable sheet piece was changed as shown in .

[Table] As shown in Table 4, the preferred mixing amount of the blowing agent in the method of the present invention is 1 to 3 parts by weight,
In particular, when it is intended to increase the foaming temperature and shorten the heating time, it is understood that the amount is 1 to 2 parts by weight. Examples 14 to 18, Comparative Example 13 (In these examples, the influence of the mixing amount of 1-butene polymer will be described.) In Example 5, the mixing amount of 1-butene polymer and the mixing of PP resin pellets Table 5 shows the results of evaluating the foamability in the same manner as in Example 5, except that the amount was changed as shown in Table 5 and the mixing amount of the blowing agent mixture was changed to 1 part by weight.

[Table] As shown in Table 5, it can be seen that the preferred mixing amount of the 1-butene polymer in the method of the present invention is 10 to 30 parts by weight, particularly preferably 10 to 20 parts by weight. Examples 19 to 22 (In these examples, the effect of odor removal by vent suction will be described.) In Example 4, an extruder equipped with a vent section (manufactured by Thermoplastics Co., Ltd.,
Suction is applied to the vent section of the cylinder (cylinder diameter 25 mm, L/D = 28, equipped with three-stage screw for vent) using a vacuum suction pump, or the vent section is closed, and the maximum temperature of the kneading section upstream of the vent section is measured as shown in Table 6. Table 6 shows the results of evaluating odor and foamability in the same manner as in Example 4, except that crosslinked fine particles were prepared at the temperature shown in .

[Table] Here, the odor was evaluated using a sensory test, and the evaluation criteria were as follows.
○: Good (no odor), △: Fair (slight odor), ×: Impossible (with odor)
From Table 6, in the process of producing crosslinked fine particles in the method of the present invention, when the vent part is suctioned, the odor removal effect is remarkable, and when the vent part is closed, kneading at high temperature It is clear that it is preferable to do so. Examples 23 to 28 (These examples discuss the influence of the type of crosslinking aid.) In Example 4, the type of crosslinking aid was changed as shown in Table 7, and crosslinked granules were produced. Table 7 shows the results of evaluating the odor and foamability of the foam in the same manner as in Example 4, except that the kneading temperature in the process was lowered to 220°C.

【table】

[Table] From Table 7, when a foamable sheet is manufactured using an extruder without a vent suction section in the method of the present invention, it is abbreviated as TAIC, P-300, A-NPG, and NK-HD. When using a crosslinking auxiliary agent,
It has been found that this is preferable because the foam has a pleasant odor. Furthermore, it is particularly preferable to use a crosslinking aid abbreviated as NK-HD, since the MFR of the kneaded product is not too high, making it easy to form a foamable sheet in a molten state. Examples 29 to 31 (These examples indicate that the foamable sheet produced by the method of the present invention can be foamed under normal pressure.) Foam sheet pieces made by cutting into pieces,
Each was heated to 250℃ and inserted between a pair of opposing hot plates with a gap of 5 mm for the time shown in Table 8.
After foaming by heating under normal pressure using radiant heat, the foam was taken out, allowed to cool naturally, and cooled to room temperature to solidify to obtain a foam. Table 8 shows the results of measuring the specific volume of the foam using the external dimension measurement method in the same manner as in Example 4.

[Table] As shown in Table 8, the foamable sheet produced by the method of the present invention is approximately 3c.c./g even when heated at high temperature under normal pressure.
It can be seen that it has a high foaming property.

Claims (1)

[Claims] 1 (a) Melt flow rate: 0.1 to 50 g/
10min polypropylene (A): 60 to 95 parts by weight, (b) Melt flow rate: 0.05 to 50g/
1-Butene polymer (B) with 10 min, 1-butene content: 70 mol% or more and heat of crystal fusion: 20 Joule/g or more based on thermal analysis using a differential scanning calorimeter:
5 to 40 parts by weight, (c) (A) + (B) = 100 parts by weight, radical generator (C): 0.05 to 0.5 parts by weight, and (d) (A) + (B) = 100 Crosslinking aid (D) based on weight part: 0.1
After performing a crosslinking reaction by melt-kneading a mixture consisting of 1 to 1 part by weight at a temperature higher than the decomposition temperature of the radical generator (C),
Such a crosslinking composition: blowing agent (E) per 100 parts by weight
A method for producing a foamable sheet, which comprises adding 0.5 to 5 parts by weight of foaming agent (E) and then kneading at a temperature below the decomposition temperature of the foaming agent (E) to obtain a sheet.