JP4238418B2 - Olefin resin foam and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has no adverse effect of bleed out of the stabilizer during sheet molding when producing olefin resin foam, particularly polyethylene resin foam, and the foaming temperature is limited to a certain limit due to insufficient heat stability during foaming. The present invention relates to an olefin-based resin foam that can solve the problem that it cannot be raised more than that, and further has no coloring and excellent long-term heat stability.
[0002]
[Prior art]
Olefin-based resin foam has excellent cushioning properties, cushioning properties, water resistance, and chemical properties, so it can be used as insulation for electrical appliances such as coolers, packaging cushioning materials for high-end products, packing for containers, adhesive tape, or long. It has been widely used as a heat insulating material for a scale roof or a pipe heat insulating material processed into a pipe shape. In the production of such an olefin resin foam, particularly a polyethylene resin foam, an antioxidant has generally been added as a heat stabilizer to prevent thermal degradation due to heat during processing or mechanical shearing force. . Such antioxidants are roughly classified into radical chain inhibitors and peroxide decomposition products in terms of their functions, and have been used in combination from the viewpoint of long-term thermal stability.
[0003]
[Problems to be solved by the invention]
As described above, heat stabilizers have also been applied in the production of olefin-based resin foams. However, the heat stabilizer bleeds out and adheres to the transport roll when it is made into a sheet. As a result, there was a problem that a dent defect occurred. Furthermore, when cross-linking with an electron beam, the stabilizer is modified by the electron beam, and the desired effect cannot be fully exhibited in the foaming process receiving a lot of heat, and the foaming temperature can be raised to a certain limit or more. In addition, there was a problem that when the temperature was raised, the edge portion was particularly hot and colored. In addition, various processes are performed in the above-mentioned various application fields to produce products. However, when heat is applied, there are disadvantages that heat resistance is poor, molding defects are increased, and long-term thermal stability is lacking.
[0004]
The present invention improves the heat resistance of such a foam, eliminates the bleed-out problem at the time of forming a sheet, does not burn even at high temperature foaming, has no color, and has excellent long-term heat resistance. The purpose is to provide.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an olefin resin foam having closed cells, which contains 0.05 to 1.0% by weight of a hindered phenol antioxidant having a melting point of 150 ° C. or higher. It consists of a resin foam.
Further, the present invention is an olefin resin foam having closed cells, 0.05 to 1.0% by weight of a hindered phenol antioxidant (A) having a melting point of 150 ° C. or higher, and a molecular weight of 500 or higher. The thioether-based antioxidant (B) is contained in an amount of 0.05 to 1.0% by weight, and the ratio of (B) / (A) is 0.5 to 2.0.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be described below.
Examples of the olefin resin constituting the olefin resin foam of the present invention include a polyethylene resin alone, and a polyethylene-based resin blended with a polyethylene resin obtained by copolymerizing vinyl acetate, ethylene / ethyl acrylate, or the like with a polyethylene resin. Alternatively, a polypropylene resin alone or a mixed resin of a polypropylene resin and a polyethylene resin is exemplified.
[0007]
Examples of the polyethylene resin include polyethylene resins having a density of 0.90 to 0.965 g / cm ³ manufactured by a low pressure method, a medium pressure method, and a high pressure method, ethylene, butene, pentene, hexene, octene, 4-methylpentene, and the like. Illustrative examples include linear polyethylene resins copolymerized with olefins, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and the like. These polyethylene resins may be used alone or in combination of two or more.
[0008]
Examples of polypropylene resins include propylene homopolymers, block copolymers of α-olefins such as ethylene and butene with propylene, random copolymers, random-block copolymers, and the like. These polypropylene resins may be used alone or in combination of two or more.
A preferred example of the olefin resin used in the present invention is a foam made of the polyethylene resin because of its particularly good cold resistance.
[0009]
In order to improve heat resistance, the olefin resin foam used in the present invention contains 0.05 to 1.0% by weight of a hindered phenol antioxidant having a melting point of 150 ° C. or higher based on the olefin resin. It is necessary.
[0010]
Examples of the hindered phenol antioxidant having a melting point of 150 ° C. or higher include 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane (melting point: 186 ° C.), 1,1. -Bis (2-methyl-4-hydroxy-5-t-butylphenyl) butane (melting point: 210 ° C.), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t- Preferable examples include those having a molecular skeleton composed of only carbon and hydrogen such as butyl-4-hydroxybenzyl) benzene (melting point: 244 ° C.). These are all registered on the positive list of the Sanitation Council for Polyolefins, etc., and are excellent in safety that has been attracting attention in recent years.
[0011]
The content of the hindered phenol antioxidant in the foam needs to be 0.05 to 1.0% by weight with respect to the olefin resin. If it is less than 0.05% by weight, it is difficult to achieve the intended effect of the present invention. Further, even if the amount exceeds 1.0% by weight, there is almost no effect of increasing the amount.
[0012]
Examples of thioether antioxidants having a molecular weight of 500 or more include didodecyl thiodipropionate (molecular weight: 517), ditetradecyl thiodipropionate (molecular weight: 571), dioctadecyl thiodipropionate (molecular weight: 683), pentae. Examples include thylitol tetrakis 3-dodecyl thiopropionate (molecular weight 1162), among which dioctadecyl thiodipropionate is preferable. The content of the thioether antioxidant in the foam is preferably 0.05 to 1.0% by weight with respect to the olefin resin.
[0013]
In the present invention, even if the hindered phenolic antioxidant alone is used, the effect of the present invention is sufficiently exhibited. However, the combined use with a thioether antioxidant is preferable because long-term thermal stability is further enhanced. If the content of the thioether-based antioxidant exceeds 1.0% by weight, it tends to bleed out during the production of the foam and is transferred to a roll during the production process, which tends to cause stain defects and the like. In addition, as a mixing ratio (B) / (A) of a hindered phenol type antioxidant (A) and a thio type antioxidant (B), the range of 0.5-2.0 is preferable.
[0014]
The olefin resin foam of the present invention is mixed with a predetermined amount in the above resin in combination with a foaming agent, an additive such as a pigment, and the above-mentioned hindered phenol antioxidant, or further a thioether antioxidant. And after extruding into a sheet form with an extruder and bridge | crosslinking with an electron beam, the foam of a desired shape can be manufactured by making the said foaming agent foam. As the foaming agent, for example, a thermally decomposable foaming agent such as azodicarbonamide can be used.
[0015]
Prior to or simultaneously with foaming, polyolefin resin is subjected to silanol condensation using an ionizing radiation crosslinking method, a chemical crosslinking method using a peroxide such as dicumyl peroxide, or bilnimethoxysilane. Crosslinking can be performed by means such as a so-called silane crosslinking method or ultraviolet crosslinking by ultraviolet irradiation, but the crosslinking method by electron beam irradiation is desirable from the viewpoint of ease of process control.
For crosslinkability, divinyl hensen, diallyl phthalate, hydroquinone dimethacrylate, and the like may be appropriately blended and used in the resin composition as a crosslinking aid.
[0016]
The apparent density of the olefin resin foam of the present invention can be appropriately selected according to the purpose of use. However, when used as various packings, the range of 0.05 to 0.25 g / cm ³ is particularly in strength and handling. This is preferable. When the apparent density is small, the strength of the foam is small, and it is difficult to say that it is easy to use for the intended application, and the density, in other words, the expansion ratio may be selected in consideration of the tensile strength.
[0017]
In addition, as a thickness of a foam, the thing of the range of 0.2-5 mm is used preferably, However It does not specifically limit and should just set suitably according to a use aspect.
The cell structure of the olefin resin foam of the present invention is a closed cell structure because high shear strength is obtained, and the foam having such a closed cell structure is produced by the above-described method using a pyrolytic foaming agent. Can do.
[0018]
【Example】
Hereinafter, the present invention will be described in detail by way of examples.
In addition, the characteristic of an olefin resin foam is measured based on JISK6767.
[0019]
[Example 1, Comparative Example 1]
Two compositions prepared by adding 10.5 parts by weight of azodicarbonamide as a foaming agent to 100 parts by weight of a low density polyethylene resin having a resin density of 0.92 g / cm ³ were prepared. , 1-bis (2-methyl-4-hydroxy-5-butylphenyl) butane (melting point: 210 ° C.) (Asahi Denka Mark AO-40) was added in an amount of 0.3 part by weight (Example 1). Was added 0.3 parts by weight of tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (melting point: 120 ° C.) (Irganox 1010 manufactured by Ciba Geigy) (Comparative Example) 1) A sheet having a thickness of 1.8 mm was prepared using an extruder. Next, the two sheets were irradiated with an electron beam to crosslink the resin, and then the temperature of a small foaming furnace was set to 245 ° C., and foaming was performed. The sheet of Example 1 was placed in a foaming furnace for 5 minutes. Neither thermal deterioration nor discoloration was observed, and the heat resistance was excellent. On the other hand, the sheet of Comparative Example 1 started to thermally deteriorate at about 2 minutes and 30 seconds after the start of foaming, and discoloration was recognized.
Furthermore, the sheet of Example 1 was foamed by setting the temperature of the foaming furnace as high as 270 ° C., but it was excellent in heat resistance without any thermal deterioration or discoloration in the foaming furnace for 5 minutes.
[0020]
[Example 2]
50 parts by weight of low-density polyethylene resin with a resin density of 0.92 g / cm ³ and 50 parts by weight of linear polyethylene resin copolymerized with butylene, 2.5 parts by weight of azodicarbonamide as a foaming agent, and oxidation as a colorant 0.21 parts by weight of 1,1-bis (2-methyl-4-hydroxy-5-butylphenyl) butane (melting point: 210 ° C.) (Mark AO-40, manufactured by Asahi Denka) as a titanium heat stabilizer, dioctadecylthio 0.2 parts by weight of dipropionate (molecular weight: 683) (trademark: Cynox DS) was added to prepare a resin composition for a foam.
[0021]
The obtained resin composition for foam was mixed with a Henschel mixer and then extruded by a T-die method using an extruder to obtain a sheet-like product having a thickness of 1.4 mm. During the sheet formation, the stabilizer did not bleed out to the roll. Thereafter, the sheet-like material was irradiated with an electron beam, the resin was previously crosslinked, and then foamed in a hot air foaming furnace at 280 ° C. to produce a sheet-like foam.
The obtained foam is a crosslinked foam having a closed cell structure, the thickness is 2.0 mm, the apparent density is 0.20 g / cm ³ , the gel fraction representing the degree of crosslinking is 35%, A beautiful white foam sheet was obtained without the end portion being heated and colored yellow.
[0022]
Next, the foamed sheet was punched into a circular shape of 50 mmφ to prepare a packing member.
Thereafter, a linear polyethylene resin is used as a cap member, and after the packing member is mounted in a mold, the packing member is integrally molded by an insert molding method in which the resin is injected at an injection temperature of 180 ° C. A cap part was created. The packing part of the obtained cap part was in a good finished state without being melted by heat, lacking in shape, or roughening the surface. Also, no molding defects were observed.
[0023]
[Comparative Example 2]
Instead of the antioxidant of Example 2, tetrakis [methylene-3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (melting point: 120 ° C.) (Irganox 1010 manufactured by Ciba Geigy) was 0.5. A sheet-like foam was produced in the same manner as in Example 1 except that the addition by weight was added. At the time of sheeting, the stabilizer bleeded out and had to be manufactured with roll cleaning.
Further, the obtained foamed product of Comparative Example 2 was not only burnt and yellowed at the ends, but also had a smooth surface at the center and was yellowish and inferior in commercial value.
[0024]
【The invention's effect】
The olefin resin foam of the present invention has the following effects.
(1) Bleed-out at the time of sheet molding in the foam production process is eliminated.
(2) The foam can have a clean surface quality without yellowing due to heat burn.
(3) The foam is excellent in long-term heat resistance and can reduce the molding defect rate in various molding processes.

Claims (4)

An olefin resin foam having closed cells and containing 0.05 to 1.0% by weight of a hindered phenol antioxidant having a melting point of 150 ° C. or higher. An olefin resin foam having closed cells, 0.05 to 1.0% by weight of a hindered phenol antioxidant (A) having a melting point of 150 ° C. or higher, and a thioether antioxidant having a molecular weight of 500 or higher An olefin-based resin foam containing 0.05 to 1.0% by weight of (B) and having a ratio of (B) / (A) of 0.5 to 2.0. The olefin resin foam according to claim 1 or 2, wherein the olefin resin foam is an electron beam crosslinked foam. After adding and mixing 1 to 20 parts by weight of a heat decomposable foaming agent and 0.05 to 1.0 parts by weight of a hindered phenol antioxidant having a melting point of 150 ° C. or more with respect to 100 parts by weight of the olefin resin, a sheet A process for producing an olefin-based resin foam, which is extruded into a shape and irradiated with an electron beam, and then the foaming agent is decomposed and foamed at a high temperature of 200 ° C. or higher.