JPH089708B2 - Adhesive tape base material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive tape substrate made of a cross-linked ethylene-based resin closed-cell foam.

(Prior Art) An adhesive tape based on a flexible foam is used for fixing side moldings of automobiles, electric parts and the like. As this kind of adhesive tape base material, low-density polyethylene of high pressure method, ethylene-vinyl acetate copolymer, density 0.915 ~
A pressure-sensitive adhesive tape base material made of a closed-cell type foam of a crosslinked ethylene resin using 0.40 g / cm ³ of linear low-density polyethylene is widely used.

However, the pressure-sensitive adhesive tape base material using low-density polyethylene is particularly insufficient in mechanical strength and flexibility. Further, the pressure-sensitive adhesive tape base material using the ethylene-vinyl acetate copolymer has good flexibility, but particularly insufficient mechanical strength and heat resistance.

Further, the adhesive tape base material using a linear low density polyethylene having a density of 0.915 to 0.940 g / cm ³ has good mechanical strength, elongation at break, and heat resistance, but particularly insufficient flexibility, In addition, there is a problem that fine irregularities such as mandarin skin are generated on the surface. Further, the linear low-density polyethylene as described above has a problem that due to its characteristics, a large amount of shear heat is generated and heat is generated during extrusion molding, and the pyrolytic foaming agent contained therein tends to undergo primary decomposition.

Therefore, it is also attempted to compensate for the defects of the respective resins by blending these resins. However, as the adhesive tape base material made of this kind of foam, the mechanical strength, the elongation at break, the flexibility, and the excellent heat resistance have not been obtained. Is being used as is. Therefore, the amount used is also stagnant.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned problems, and an object thereof is to have a fine cell structure and a smooth surface, mechanical strength, elongation at break, An object of the present invention is to provide a pressure-sensitive adhesive tape substrate made of a cross-linked ethylene-based resin closed-cell foam having excellent flexibility and heat resistance.

(Means for Solving the Problems) The pressure-sensitive adhesive tape substrate of the present invention is a closed-cell type foam of a crosslinked ethylene resin containing 10% by weight or more of linear ultra-low density polyethylene having a density lower than 0.915 g / cm ^3. It consists of a body, which achieves the above objectives.

The linear ultra-low density polyethylene used in the present invention means, for example, ethylene, butene-1, hexene-1, 4-methylpentene-1, octene-1, etc. by a polymerization reaction using a Ziegler type catalyst under medium and low pressure. By copolymerizing α-olefins with 4 or more carbon atoms, the crystallinity is controlled by introducing an appropriate number of short chain branches into the linear trunk polymer, and the density is lower than 0.915 g / cm ^3. It is a set polymer.

The linear ultra-low density polyethylene has a density of 0.
890 to less than 0.915 g / cm ³ , melt index 0.5 to ³⁰ g /
10 minutes is preferable, especially density 0.890 to 0.910 g / cm ³ ,
It is more preferable that the melt index is 2 to 10 g / 10 minutes. In addition, the melting point peak measured with a differential calorimeter is 80-12.
Those in the range of 0 ° C. are preferable, and those in the range of 110 to 120 ° C. are particularly preferable. For example, Ultzex UZ- manufactured and sold by Mitsui Petrochemical Industries, Ltd.
1520L, UZ-1020L, UZ-1030L, and Excellen VL-200 and VL-700 manufactured and sold by Sumitomo Chemical Co., Ltd.

The above-mentioned linear ultra-low density polyethylene is used alone or as a mixture with an ethylene resin. In any case,
10% by weight or more of linear ultra-low density polyethylene, preferably
20 to 90% by weight, and more preferably 30 to 80% by weight. When the content of the linear ultra-low density polyethylene is less than 10% by weight, it is difficult to obtain a foam having excellent mechanical strength, elongation at break, flexibility and heat resistance.

Examples of the ethylene-based resin mixed with the linear ultra-low density polyethylene include polymers of ethylene monomers such as low-density polyethylene, medium-density polyethylene, and high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-chloride. Vinyl copolymer, ethylene-ethyl acrylate copolymer,
Copolymers mainly composed of ethylene monomers such as ethylene-methyl methacrylate copolymers and ethylene-propylene copolymers, modified polyethylenes such as chlorinated polyethylenes, and mixtures thereof are used.

Particularly, low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer are preferable.

Low-density polyethylene is a conventional high-pressure method low-density polyethylene that has been widely used, and has a density of 0.910-
It preferably has a melt index of 0.930 g / cm ³ and a melt index of 0.5 to 30 g / 10 min, and more preferably a density of 0.918 to 0.925 g / cm ³ and a melt index of 2.0 to 10 g / 10 min.

Medium-density and high-density polyethylene is a high-density polyethylene of ordinary medium and low pressure method which has been generally used, and has a density of 0.940 to 0.965 g / cm ³ and a melt index of 0.5 to ³⁰ .
g / 10 min is preferable, especially density is 0.945 to 0.960 g / cm
^3. Those having a melt index of 2.0 to 10 g / 10 minutes are more preferable.

The ethylene-vinyl acetate copolymer has a density of 0.925 to 0.9.
70 g / cm ³ , a melt index of 0.5 to 30 g / 10 minutes, and a vinyl acetate content of 5 to 30% by weight are preferable from the viewpoints of the flexibility and adhesiveness of the foam, and particularly the density is 0.930 to 0.950 g / cm
³ , more preferably those having a melt index of 2.0 to 20 g / 10 minutes and a vinyl acetate content of 5 to 20% by weight.

The ethylene-ethyl acrylate copolymer has a density of 0.92
5 ~ 0.975g / cm ³ , melt index 0.5 ~ 30g / 10min,
It is preferable that the content of ethyl acrylate is 7 to 25% by weight from the viewpoint of the flexibility and adhesiveness of the foam, and especially the density of 0.
930 to 0.950g / cm ³ , melt index from 2.0 to 10g / 10
It is more preferable that the content of ethyl acrylate is 7 to 25% by weight.

The ethylene-methyl methacrylate copolymer has a density of 0.
930 ~ 0.950g / cm ³ , melt index 0.5 ~ 30g / 10
Minutes, the content of methyl methacrylate is preferably 10 to 25% by weight from the viewpoint of the flexibility of the foam, adhesiveness, etc., especially density 0.930 to 0.940 g / cm ³ , melt index of 2.0 to 10 g /
It is more preferable that the content of methyl methacrylate for 10 minutes is 7 to 20% by weight.

In the present invention, the closed-cell foam of a crosslinked ethylene-based resin by crosslinking and foaming an ethylene-based resin containing 10% by weight or more of linear ultra-low density polyethylene having a density lower than 0.915 g / cm ³ described above. To produce an adhesive tape substrate. The thickness of the adhesive tape substrate is preferably about 0.5 to 3 mm, the expansion ratio is about 5 to 30 times, and the gel fraction is preferably about 25 to 50% by weight.

Such a pressure-sensitive adhesive tape substrate is specifically, for example, a mixture obtained by blending a decomposable foaming agent with the above-mentioned ethylene resin and uniformly mixing it using a ribbon blender or the like, and foaming the mixture with an extruder or a calendar roll. The agent is kneaded and melted at a temperature and pressure at which it does not substantially decompose to form a sheet, which is crosslinked by irradiating the sheet-like molded article with ionizing radiation, and then heated to a temperature above the decomposition temperature of the foaming agent to foam. It can be manufactured.

Further, the ethylene-based resin is blended with a decomposable foaming agent and a cross-linking agent, and a mixture obtained by uniformly mixing the same is used at a temperature and pressure at which the foaming agent and the cross-linking agent are not substantially decomposed by an extruder or a calender roll. It can be produced by kneading, melting, and shaping into a sheet, heating this to a temperature at which the cross-linking agent decomposes to cross-link, and further heating at a temperature not lower than the decomposition temperature of the foaming agent to foam.

Decomposition type foaming agents include azodicarbonamide, N,
N'-dinitrosopentamethylenetetramine and the like are preferable. These decomposable foaming agents are generally used in the range of 2 to 20 parts by weight based on 100 parts by weight of the above-mentioned ethylene resin, depending on the expansion ratio.

When ionizing radiation is used as a means for crosslinking the resin, β rays, γ rays, neutrons, electron beams and the like are used, and the irradiation amount thereof is preferably in the range of 1 to 20 Mrad. When a cross-linking agent is used as a means for cross-linking the resin, dicumyl peroxide, 1,3-bis (t-
Organic peroxides such as butylperoxyisopyropyl) benzene and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane are used. These cross-linking agents are generally used in the range of 0.1 to 5 parts by weight with respect to 100 parts by weight of the above ethylene resin.

In addition, the above-mentioned ethylene-based resin composition includes divinylbenzene, a cross-linking accelerator composed of a polyfunctional monomer such as trimethylolpropane triacrylate, a foaming aid such as zinc stearate and calcium stearate, talc, and an oxidation agent. You may mix | blend various additives, such as zinc, titanium oxide, and a nucleating agent for controlling air bubbles, a coloring agent, such as carbon black.

(Function) The adhesive tape substrate made of the closed cell foam of the crosslinked ethylene resin of the present invention has a linear ultra-low density polyethylene having a density lower than 0.915 g / cm ³ in an amount of 10% by weight or more,
With this linear ultra-low density polyethylene, the surface of the foam is smooth, and the foam has excellent mechanical strength, elongation at break, and
Flexibility and heat resistance are given.

(Example) Hereinafter, the Example and comparative example of this invention are shown.

Example 1 70 parts by weight of linear ultra-low density polyethylene having a density of 0.905 g / cm ³ , a melt index of 10.0 g / 10 min, and a density of 0.930 g / cm ³ ,
30 parts by weight of ethylene-vinyl acetate copolymer having a melt index of 3.5 g / 10 minutes and a vinyl acetate content of 14% by weight, 6 parts by weight of a foaming agent (azodicarbonamide), 1.0 part by weight of carbon black, and 1.0 part by weight of zinc oxide. Parts and mix it with an extruder at 135 ° C, which is the temperature at which the blowing agent does not decompose.
It was formed into a 0.5 mm sheet. The obtained sheet had a smooth surface and had no bubbles and was good.

Next, 2.5 sheets from both sides of this sheet with an electron beam irradiator.
Cross-linking was performed by irradiating an electron beam of ad to cross-link, and then continuously passing through a heating furnace at 250 ° C. to foam, to obtain a cross-linked foamed sheet having a thickness of about 1.0 mm. The obtained crosslinked foamed sheet had a smooth surface and had uniform closed cells.

Example 2 70 parts by weight of linear ultra-low density polyethylene having a density of 0.900 g / cm ³ and a melt index of 2.0 g / 10 min, and a density of 0.930 g / cm ³ ,
Ethylene-methyl methacrylate copolymer having a melt index of 7.0 g / 10 minutes and a methyl methacrylate content of 15% by weight
30 parts by weight, 6 parts by weight of a foaming agent (azodicarbonamide), 1.0 part by weight of titanium oxide, and 1.0 part by weight of zinc oxide were mixed, and the mixture was mixed with an extruder at a temperature not decomposing the foaming agent.
It was formed into a sheet having a thickness of 0.5 mm at 135 ° C. The obtained sheet had a smooth surface and had no bubbles and was good.

Next, using an electron beam irradiator on this sheet, 3.0 Mr.
Cross-linking was performed by irradiating an electron beam of ad to cross-link, and then continuously passing through a heating furnace at 250 ° C. to foam, to obtain a cross-linked foamed sheet having a thickness of about 1.0 mm. The obtained crosslinked foamed sheet had a surface close to white and smooth, and had uniform closed cells.

Example 3 100 parts by weight of linear ultra-low density polyethylene having a density of 0.905 g / cm ³ and a melt index of 10.0 g / 10 min, 6 parts by weight of a foaming agent (azodicarbonamide), 1.0 part by weight of titanium oxide, and zinc oxide. 1.0 part by weight was mixed, and this mixture was molded into a sheet having a thickness of 0.5 mm at 135 ° C. at a temperature at which the foaming agent was not decomposed by an extruder. The obtained sheet had a smooth surface and had no bubbles and was good.

Next, this sheet is exposed to 4.0 Mr.
Cross-linking was performed by irradiating an electron beam of ad to cross-link, and then continuously passing through a heating furnace at 250 ° C. to foam, to obtain a cross-linked foamed sheet having a thickness of about 1.0 mm. The obtained crosslinked foamed sheet had a surface close to white and smooth, and had uniform closed cells.

Comparative Example 1 In Example 1, 70 parts by weight of a linear ultra-low density polyethylene and 30 parts by weight of an ethylene-vinyl acetate copolymer were added to obtain a density.
The same procedure as in Example 1 was repeated except that 100 parts by weight of low-density polyethylene having a melt index of 0.921 g / cm ³ and a melt index of 4.0 g / 10 min was used.

Comparative Example 2 Example 1 was repeated except that 70 parts by weight of linear ultra-low density polyethylene was replaced with 70 parts by weight of low density polyethylene having a density of 0.921 g / cm ³ and a melt index of 4.0 g / 10 minutes. It carried out similarly to.

Comparative Example 3 30 parts by weight of linear low-density polyethylene having a density of 0.920 g / cm ³ and a melt index of 8.0 g / 10 minutes, a density of 0.94 g / cm ³ , a melt index of 10.0 g / 10 minutes, and a vinyl acetate content of 15% by weight. 70 parts by weight of ethylene-vinyl acetate copolymer, 6 parts by weight of a foaming agent (azodicarbonamide), 1 part by weight of zinc oxide, and 1 part by weight of carbon black were mixed, and the mixture was mixed with an extruder to give a thickness of 0.5. It was formed into a sheet of mm. The obtained sheet had a smooth surface and was good.

Next, this sheet was irradiated with an electron beam of 2.5 Mrad from both sides with an electron beam irradiator to be crosslinked, and then continuously passed through a hot air oven at 250 ° C for foaming to obtain a crosslinked foamed sheet with a thickness of 1.0 mm. It was The surface of the obtained sheet was smooth at first glance, but fine irregularities such as mandarin skin were observed over the entire surface. The cells had fine closed cells.

Comparative Example 4 In Example 3, instead of 100 parts by weight of the linear ultra-low density polyethylene, the density was 0.920 g / cm ³ , and the melt index was 80.
Extrusion was attempted with a mixture having the same formulation as in Example 3, except that 100 parts by weight of linear low-density polyethylene of g / 10 min was used, but the resin temperature at the extrusion screw head portion increased and the foaming agent An extruded sheet from which primary decomposition occurred and a foam was obtained was not obtained.

Regarding the crosslinked foamed sheets obtained in the above Examples 1 to 3 and Comparative Examples 1 to 3, by a method according to JIS K 6767, breaking strength (indicative of mechanical strength), breaking elongation, bending strength (flexibility). , And the heat shrinkage ratio (indicating heat resistance) were measured.
The results are summarized in Table 1.

(Effects of the Invention) As described above, the pressure-sensitive adhesive tape substrate of the present invention has a crosslinked structure of fine closed cells, has a smooth surface, and is excellent in mechanical strength, elongation at break, flexibility, and heat resistance. It also has excellent performance.

Therefore, it can be suitably used as a side molding of automobiles and an adhesive tape substrate for fixing electric parts, and can also be used in a wide range of applications.

Claims (1)

[Claims] 1. A pressure-sensitive adhesive tape substrate comprising a closed cell foam of a crosslinked ethylene-based resin, which contains a linear ultra-low density polyethylene having a density lower than 0.915 g / cm ^{3 in an} amount of 10% by weight or more.