JPH04296338A - Crosslinked and foamed material - Google Patents

Abstract

PURPOSE:To provide a crosslinked and foamed material having excellent antistaticity, formability and uniformity. CONSTITUTION:The objective crosslinked and foamed material is made of a resin composition composed of 20-75wt.% of an ionomer of an ethylene- unsaturated carboxylic acid copolymer containing potassium as the ion source and having an average neutralization degree of >=50% and 80-25wt.% of an olefin polymer. The ionomer containing 18-35wt.% of unsaturated carboxylic acid accounts for >=10wt.% in the above composition and the expansion ratio of the material is <20%. The crosslinked and foamed material produced by this process is easily formable and has excellent cushioning property, heat- resistance and antistaticity and is useful as a cushioning material for electric and electronic parts, etc.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides homogeneity, compression recovery,
This invention relates to a crosslinked foam with excellent cushioning properties, heat resistance, and non-static properties.

0002

[Prior Art] Regarding cross-linked ionomer foams,
JP-A-57-135837 and JP-A-63-18235
There are proposals such as No. 9. These proposals mention the possibility of using a wide variety of ionomers, specifically sodium ionomers and zinc ionomers; these crosslinked foams are susceptible to charging unless they are formulated with special additives, and therefore Field of use is limited. Although it is known that ionomers containing a high concentration of potassium ions exhibit non-static properties, it has been recognized that there are several problems when such ionomers are crosslinked and foamed according to the disclosure of the above proposal. In other words, when crosslinking and foaming a potassium ionomer alone according to the former proposal, or a potassium ionomer composition containing a small amount of ethylene/vinyl acetate copolymer according to the latter proposal, there is a marked tendency to stick to the mold. Therefore, there was a problem in that the molding process was restricted. Moreover, the surface hardness of the resulting crosslinked foam was too high, making it unsuitable for uses such as cushioning materials.

0003

[Problems to be Solved by the Invention] Therefore, the present inventors conducted studies in order to obtain a crosslinked foam that has non-static properties, does not have a tendency to stick to molds, and has an appropriate surface hardness. As a result, they found that the objective could be achieved by crosslinking and foaming a blend of a specific potassium ionomer and an olefin polymer in a specific ratio. However, even in this case, it has been recognized that a uniform foam cannot be obtained when foaming is carried out 20 times or more, and that the mechanical strength of the obtained foam is not sufficient, leading to the development of the present invention. Therefore, an object of the present invention is to provide a crosslinked foam that is easy to manufacture and has excellent homogeneity and non-static properties, and has an appropriate surface hardness. Another object of the present invention is to provide a crosslinked foam having excellent mechanical strength, compression recovery properties, cushioning properties, and heat resistance.

0004

[Means for Solving the Problems] The present invention provides 20 to 75% by weight of an ionomer of an ethylene/unsaturated carboxylic acid copolymer using potassium as an ion source and 80 to 75% by weight of an olefin polymer.
A crosslinked foam of a resin composition comprising 25% by weight,
Non-static, the average degree of neutralization of the ionomer is 50% or more, the ionomer with an unsaturated carboxylic acid content of 18 to 35% by weight accounts for at least 10% by weight or more, and the expansion ratio is less than 20 times. Regarding crosslinked foam.

The ionomer used in the present invention is an ionomer of an ethylene/unsaturated carboxylic acid copolymer using potassium as an ion source. Such an ionomer may, of course, contain unneutralized unsaturated carboxylic acid copolymerized units, and may also contain other polymerized units such as unsaturated esters, but unsaturated carboxylic acid copolymerized units may also be included. The average degree of neutralization by potassium ions per unit is 50% or more, particularly preferably 70 to 90%. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic anhydride, monoethyl maleate, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Further, the unsaturated ester which is an optional polymerization component may be an alkyl ester of the above-mentioned unsaturated carboxylic acid or a vinyl ester such as vinyl acetate. Specific examples of the former include methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, and 2-acrylate.
Examples include ethylhexyl, methyl methacrylate, and dimethyl fumarate.

The ionomer contains 18 to 35% by weight, preferably 18 to 30% by weight of neutralized and unneutralized unsaturated carboxylic acid polymer units, and this is 10% by weight of the polymer component. As long as the unsaturated carboxylic acid polymer units occupy less than 18% by weight, for example, 1 to 17% by weight, preferably 2 to 16% by weight, may be used in combination. In particular, such a combination system is more preferable in consideration of cost, water absorption, adhesion to a mold, dispersion-mixability with an olefin polymer, etc. The unsaturated ester polymerized unit, which is an optional polymerization component, can be present in the ionomer in an amount such as, for example, up to 40% by weight, preferably up to 30% by weight. Considering moldability and mechanical strength of the foam, the ionomer has a melt flow rate of 0.05 to 200 g/10 min at 190°C and 2160 g load, especially 0.1 to 200 g/10 min.
It is preferable to use 20 g/10 minutes.

[0007] In the present invention, the olefin polymer is
A general term for olefin homopolymers, copolymers of two or more olefins, copolymers of olefins and unsaturated esters, etc., and these can be highly crystalline, low crystalline, or amorphous. It may be of. Examples of olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, butadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, etc. can be exemplified. More specifically, the olefin polymer includes high, medium, or low density polyethylene, linear low density polyethylene, low crystalline or amorphous ethylene/α-olefin copolymer, or ethylene/α-olefin copolymer.
Examples include α-olefin/diene copolymer, polypropylene, poly-1-butene, and poly-4-methyl-1-pentene.

[0008] Further, as the unsaturated ester component in the copolymer of olefin and unsaturated ester, for example, vinyl esters such as vinyl acetate and vinyl propionate,
Esters such as acrylic acid, methacrylic acid, maleic acid, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-acrylate
Examples include ert-butyl, isooctyl acrylate, 2-ethylhexyl acrylate, and methyl methacrylate. The proportion of the unsaturated ester component in the copolymer is, for example, 1 to 60% by weight, preferably 5 to 60% by weight.
It may be 50% by weight. More specific examples of copolymers include ethylene/vinyl acetate copolymer, ethylene/methyl acrylate copolymer, ethylene/methyl methacrylate copolymer, ethylene/ethyl acrylate copolymer, and ethylene/acrylic copolymer. Examples include n-butyl acid copolymer and ethylene/isobutyl acrylate copolymer.

The blending ratio of the ionomer and the olefin polymer is 20 to 75% by weight, preferably 25 to 70% by weight of the former, and 80 to 25% by weight, and preferably 7% by weight of the latter.
At least 1 potassium ionomer of the ethylene/unsaturated carboxylic acid copolymer is 5 to 30% by weight and contains 18 to 35% by weight of unsaturated carboxylic acid.
It is blended in a proportion of 0% by weight or more, preferably 25 to 40% by weight. If the amount of the ionomer is greater than the above range, it will tend to stick to the mold and will not be easy to mold. In addition, if the blending amount is less than the above range, or if the amount of the ionomer of a copolymer with an unsaturated carboxylic acid content of 18 to 35% by weight is less than the above range, the antistatic property will not be sufficient. .

In the present invention, the above-mentioned composition is crosslinked and foamed at a crosslinking ratio of less than 20 times, preferably 4 to 8 times. If the expansion ratio is 20 times or more, a homogeneous foam cannot be obtained and a foam with high mechanical strength cannot be obtained. In addition, without crosslinking, a foam with excellent heat resistance cannot be obtained.
Otherwise, it is not preferable because it does not form closed cells. In addition, mold adhesion is severe and molding becomes difficult.

[0011] In order to obtain such a foam, a crosslinking agent and a chemical foaming agent may be blended with the resin component, and crosslinking and foaming may be carried out by a conventional method. As a crosslinking agent, dicumyl peroxide, t-butylcumyl peroxide, di-t-butyl peroxide, 1,3-di(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(t It is preferred to use organic peroxide crosslinking agents such as -butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3. Two or more of these may be used in combination. The appropriate amount of these crosslinking agents to be used is usually about 0.1 to 5 parts by weight per 100 parts by weight of the resin component.

As the chemical blowing agent, it is preferable to use, for example, azodicarbonamide, dinitrosopentamethylenetetramine, or a mixture thereof. Although these vary depending on the desired expansion ratio, 0.1 to 10 parts by weight, preferably 0.5 to 1 part by weight, per 100 parts by weight of the resin component.
It is preferable to add about 0 parts by weight.

[0013] During foaming, various other additives used in this technical field may be added, if necessary. Examples of such other additives include crosslinking accelerators, foaming aids,
Antioxidants, light stabilizers, ultraviolet absorbers, antistatic agents, lubricants, antiblocking agents, organic or inorganic pigments, dyes, etc. can be mentioned.

[0014] In order to uniformly blend these components, kneading, which is conventionally used in the process of molding crosslinked foams of thermoplastic resins or synthetic rubbers, using mixing rolls, calender rolls, Banbury mixers, kneaders, etc., is carried out simultaneously or sequentially. They may be melted and mixed using a machine. Thereafter, it is formed into a sheet using a T-die extruder, rolls, etc., and then cross-linked and foamed by heating using a heat press, a foaming furnace, a foaming bath, etc. The temperature conditions for crosslinking and foaming vary depending on the type of chemical crosslinking agent, chemical foaming agent, foaming aid, etc., but are generally set at about 150°C to 250°C. As another means of crosslinking and foaming, instead of using a chemical crosslinking agent, a method of crosslinking with electron beams and foaming may be adopted.

[0015]

[Examples] Next, the present invention will be explained with reference to Examples. Example 1 Ethylene-based potassium ionomer resin (MFR 0.7 g/10 min) in which 70% of methacrylic acid in ethylene/methacrylic acid copolymer (methacrylic acid content 20% by weight) is neutralized with potassium ions (MFR 0.7 g/10 min) 50 weight and vinyl acetate copolymer (Mitsui DuPont Polychemical Co., Ltd. product Evaflex P-2505 vinyl acetate content 25%, M
FR2.0g/10min) 50 parts by weight and vinylhole SE#3 whose main component is azodicarbonamide as a blowing agent.
0 (manufactured by Eiwa Chemical Industries, Ltd.) and 0.8 parts by weight of Mitsui DCP (manufactured by Mitsui Petrochemical Industries, Ltd.) as a crosslinking agent, without decomposing the crosslinking agent. The mixture was kneaded for 5 minutes using a 10-inch mixing open roll to prepare a portioned sheet. 500 g of the thus obtained dispensed sheets were stacked and placed in the mold (2) of a crosslinking foam press molding machine.
00 x 200 x 11.5 mm) and heated at 160℃ for 20 minutes.
After heating under pressure for a minute, the mold was opened to obtain a crosslinked foam. The resulting foam was a white crosslinked foam with very dense cells. Foam density is 0.260g/cm3,
The cross-sectional hardness (Asker C) was 75, and the surface specific resistance value of the foam 7 days after molding was 7×10 10 Ω. (Hiresta IP measuring device manufactured by Mitsubishi Yuka Co., Ltd.). Also,
Even when the foam was strongly rubbed with a cotton cloth, cigarette ash did not adhere to it and it was uncharged.

Example 2 A polymer consisting of 50% ethylene/methacrylic acid copolymer A (methacrylic acid content 20% by weight) and 50% ethylene/methacrylic acid copolymer B (methacrylic acid content 10% by weight) 60 with an average degree of neutralization of methacrylic acid by potassium ions of 80% (MFR 0.2 g/10 min)
A crosslinked foam obtained in the same manner as in Example 1 using 40 parts by weight of vinyl acetate copolymer P-2505 and 25% vinyl acetate content had a foam density of 0.263 g/cm3,
The foam had a cross-sectional hardness (Asker C) of 77 and a surface resistivity value of 7×10 11 Ω 7 days after molding. Further, even when the foam was strongly rubbed with a cotton cloth, cigarette ash did not adhere to it and it was non-electrified.

Comparative Example 1 In Example 1, the amount of ethylene potassium ionomer resin used was 10 parts by weight, and the amount of vinyl acetate resin was 9 parts by weight.
A cross-linked foam obtained in the same manner as in Example 1 except that the weight was changed to 0.0 weight had a foam density of 0.223 g/cm3, a cross-sectional hardness (Asker C) of 55, and the foam was obtained 7 days after molding. The surface resistivity value was measured using Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd., and it was found to be 1013Ω or more. In addition, when the foam was strongly rubbed with a cotton cloth, cigarette ash adhered to it.

Comparative Example 2 When molding was carried out using the same formulation as in Example 1, except that 90 parts by weight of the ethylene-based potassium ionomer resin and 10 parts by weight of the vinyl acetate resin were used,
It adhered strongly to the mixing roll and was difficult to knead. Furthermore, it was not possible to obtain a homogeneous foam due to mold adhesion in the crosslinking foam press. The above results are shown in the lower column of Table 1.

[0019]

[Table 1]

[0020]

According to the present invention, it is possible to provide a crosslinked foam that is easy to mold and has excellent homogeneity, compression recovery properties, cushioning properties, heat resistance, and non-static properties. For example, the surface resistivity measured according to JISK-6705 is 1013Ω or less, preferably 10
A crosslinked foam with a resistance of 12Ω or less can be provided. Taking advantage of these properties, the crosslinked foam of the present invention can be used for applications such as buffering materials for electrical and electronic components, storage cases, transportation boxes, automobile parts, heat insulating materials, and protectors for sporting goods.

Claims (1)

[Claims] [Claim 1] Ionomer 20 of ethylene/unsaturated carboxylic acid copolymer using potassium as an ion source
-75% by weight of a resin composition and 80-25% by weight of an olefin polymer, the average degree of neutralization of the ionomer is 50% or more, and the content of unsaturated carboxylic acid in the composition is is 18 to 35% by weight of an ionomer at least 10% by weight, and has an expansion ratio of less than 20 times.