JPH10316778A - Production of foamed olefin resin sheet subjected to corona discharge treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foamed sheet which can retain a sufficient surface wettability for a long time and is suitable for a self-adhesive tape substrate, etc., by subjecting an unfoamed olefin resin sheet contg. a blowing agent to a corona discharge treatment with a specified amt. of energy applied, then foaming the sheet, and subjecting the foamed sheet again to a corona discharge treatment with a specified amt. of energy applied. SOLUTION: The sheet is subjected to a corona discharge treatment with an applied energy of 500-10.000 J/m<2> before the foaming and with an applied energy of 500-10,000 J/m<2> after the foaming. The blowing agent, pref. a thermally decomposable one. is added pref. in an amt. of 0.1-30 pts.wt. to 100 pts.wt. olefin resin. Pref., the corona discharge treatment is carried out at 0 deg.C or higher and not higher than the m.p. of the resin and in an inert atmosphere. The surface of the objective foamed sheet can be changed by embossing the sheet just after the foaming and before the surface is cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamed olefin resin sheet which is suitable for an adhesive tape substrate and the like and has excellent surface wettability.

[0002]

2. Description of the Related Art Although an olefin resin foam sheet is widely used as an adhesive tape base material or the like, it has poor surface wettability as it is, so that a surface treatment is performed when applying an adhesive or an adhesive. Is normal. As such a surface treatment for improving the surface wettability, for example, JP-A-2-255740 discloses that sodium or potassium remains on the surface by a treatment using nitrate or nitrite and subsequent washing. There is disclosed a technique for improving the surface wettability by using the method.

[0003] However, this technique merely improves the adhesiveness of the surface, and it is difficult to adjust the amount of residual sodium or potassium, so that sufficient surface wettability could not be obtained. Further, since a large amount of water is required for the cleaning treatment, environmental problems such as the generated wastewater treatment are inevitable.

The conventional corona discharge treatment has a disadvantage that its effect is lost with the passage of time after the treatment, and the effect is often insufficient, causing blisters and the like. Therefore, some measures have been taken to increase the discharge level. However, in the case of a long object, there is a possibility that blocking may occur or surface defects such as a large number of pinholes and avatars may occur.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a method for producing a foamed olefin resin sheet capable of maintaining sufficient surface wettability for a long time.

[0006]

According to the present invention, an olefin-based resin sheet containing a foaming agent is prepared before foaming.
Corona discharge treatment with an applied energy of 000 J / m ² ,
After that, it is made to foam, and then it is 500 to 10000J
/ M ² , wherein a corona discharge treatment is performed with an applied energy of / m ² . Hereinafter, the present invention will be described in detail.

In the present invention, an olefin resin sheet containing a foaming agent is used. The olefin-based resin used in the olefin-based resin sheet containing the blowing agent is not particularly limited, for example, olefin homopolymer,
Copolymers of olefins and other monomers, and the like, may be mentioned. Specifically, for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-octene copolymer, propylene- Butene copolymer, ethylene-propylene-butene copolymer, ethylene-vinyl acetate copolymer and the like. Among them, polyethylene, a copolymer containing ethylene as a main component, polypropylene, and a copolymer containing propylene as a main component are preferable. These may be used alone or in combination of two or more.

As the foaming agent used for the olefin resin sheet containing the foaming agent, a thermal decomposition type foaming agent which generates a decomposition gas by heating is preferable. Such foaming agents are not particularly limited, for example, azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide,
4,4-oxybis (benzenesulfonyl hydrazide)
And the like. These may be used alone or in combination of two or more.

The amount of the foaming agent is preferably 0.1 to 30 parts by weight based on 100 parts by weight of the olefin resin. If the amount is less than 0.1 part by weight, the expansion ratio becomes low, and if it exceeds 30 parts by weight, the obtained olefin-based resin foam sheet tends to be broken. More preferably,
It is 0.5 to 20 parts by weight.

[0010] If necessary, other additives can be added to the olefin resin. The additives are not particularly limited, and include, for example, polyfunctional compounds such as divinylbenzene, diallyl phthalate, and trimethylolpropane trimethacrylate. The amount of the additive is preferably 2 to 5 parts by weight based on 100 parts by weight of the olefin resin.

The olefin resin sheet containing the foaming agent can be obtained by a usual method. For example, the foaming agent or the additive is added to the olefin resin, and a single screw extruder or a twin screw extruder is used. Melt-kneading at a temperature lower than the decomposition temperature of the foaming agent using a mixer, a Banbury mixer, or the like, and then forming into a sheet and crosslinking. The method of crosslinking is not particularly limited, for example, α-ray, β-ray,
A method of irradiating with ionizing radiation such as γ-ray, electron beam, neutron beam and the like; a method of adding a peroxide or the like to the above-mentioned olefin resin in advance to chemically crosslink.

In the present invention, the olefin-based resin sheet containing the above-mentioned foaming agent is subjected to 500 to 1000 before foaming.
Corona discharge treatment is performed with an applied energy of 0 J / m ² . 5
When it is less than 00 J / m ² , the discharge effect is reduced, and
If it exceeds 00 J / m ² , the obtained olefin-based resin foam sheet will be deteriorated and cause a decrease in surface wettability, so that it is limited to the above range. Preferably, 2000-8
000 J / m ² .

The processing temperature at the time of the corona discharge processing is as follows:
It is preferably at least 0 ° C. and at most the melting point of the olefin resin. If it is too low, the discharging effect may be reduced.

The method of the corona discharge treatment is not particularly limited, and includes, for example, a method using a general corona discharge treatment machine for oxidizing the surface of an object by a high voltage to polarize the surface. The corona discharge treatment machine is not particularly limited, and includes, for example, a thyristor inverter type corona discharge treatment machine (HFS402, manufactured by Kasuga Electric Co., Ltd.).

The above-mentioned corona discharge treatment is preferably performed in an inert atmosphere. By performing the reaction in an inert atmosphere, the obtained olefin resin foam sheet has better surface wettability. The inert gas used in the inert atmosphere is not particularly limited, for example,
Examples include nitrogen, helium, and carbon dioxide. These may be used alone or in combination of two or more.

In the present invention, after the above-mentioned corona discharge treatment, the olefin resin sheet containing the above-mentioned foaming agent is treated.
Let it foam. The foaming method is not particularly limited,
For example, a method using hot air, an electric heater, a salt bath, or the like can be used.

In the present invention, after the foaming,
Corona discharge treatment is performed with an applied energy of 500 to 10000 J / m ² . The corona discharge treatment described above is employed for the corona discharge treatment.

In the second aspect of the present invention, the surface of the sheet is textured after the foaming of the first aspect. The method of the graining is not particularly limited. For example, immediately after the foaming agent-containing olefin-based resin sheet is foamed to form a foamed sheet, and before the surface of the foamed sheet is cooled, two embossing rolls are used. (Embossing roll) to change the shape of the foamed sheet surface by passing it through, and then wind the sheet through a cooling roll.

The grain shape of the grain roll is not particularly limited, and examples thereof include a pyramid shape (quadrangular pyramid), a cone, a fine pear ground pattern, and a silk grain shape. The size of the grain is such that the area of one protrusion is 0.2 to 1
0.0 mm ² is preferred. If less than 0.2 mm ² ,
Since the surface of the foam sheet itself is originally rough, it is difficult to obtain the effect of graining, and if it exceeds 10.0 mm ² , an anchor effect may not be expected in some cases.

The surface material of the sieve roll is not particularly limited as long as it has adhesiveness to the foamed sheet and good releasability. For example, hard chrome plating of mirror surface, Teflon plating, And the like.

The clearance between the two civolols is
The thickness is appropriately determined according to the thickness of the foamed sheet, but is preferably 60 to 90% of the thickness of the obtained olefin-based resin foamed sheet. If it is less than 60%, the bubbles of the foam sheet may be crushed, and if it is more than 90%, the effect of the graining may be lost.

In the graining process, the surface temperature of the foamed sheet is a temperature immediately after foaming and before cooling, and is appropriately determined according to the type of resin constituting the foamed sheet. (Melting point−50 ° C.) to (melting point of resin + 30 ° C.). If the melting point is less than (melting point of resin−50 ° C.), it is difficult to form a grain shape, and (melting point of resin + 30).
If the temperature exceeds (° C.), the foamed sheet may be entangled in rolls, or the bubbles of the foamed sheet may be reduced or broken. More preferably, it is (melting point of resin−40 ° C.) to (melting point of resin + 20 ° C.). Here, the melting point of the resin is a temperature at a crystal melting peak in a differential scanning calorimeter (DSC).

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Ethylene resin (MI: 2.0, density: 0.924 g / c)
m ³ , 100 parts by weight of Tm (resin melting point: 120 ° C.) and 9.5 parts by weight of azodicarbonamide as a foaming agent are supplied to a single screw extruder, kneaded at a resin temperature of 140 ° C., and a thickness of 1 A foamable sheet of 0.0 mm was obtained. Next, after irradiating the foamable sheet with an electron beam of 3.0 Mrad to crosslink, one side of the foamable sheet is subjected to a corona discharge treatment at a temperature of 20 ° C., an applied energy of 3000 J / m ² , and in air. Machine (thyristor inverter type, HFS40)
2, manufactured by Kasuga Electric Co., Ltd.).
Thereafter, the foamable sheet is placed in a hot blast stove adjusted to 280 ° C. and foamed, and has a density of 0.053 g / cm ³ ,
A 2.0 mm thick foam sheet was obtained. When the wetting index of the surface of the obtained foamed sheet was measured in accordance with JIS K 6768 (wetting test method for polyethylene and polypropylene films), it was 37 dyne / cm.

Next, a temperature of 20
℃, applied energy 3000J / m ^TwoUnder air conditions
Then, the corona discharge treatment is performed using the above-described corona discharge treatment machine.
went. The wetting index of the obtained foam sheet surface is the same as above.
It was measured in the same manner. After one month, the surface wetting index
It was measured in the same manner. Samples should be stored at room temperature.
The temperature was 30 ° C. and the humidity was 60%. The results are shown in Table 1.

Example 2 A foamed sheet was obtained in the same manner as in Example 1 except that the corona discharge treatment before and after foaming was performed in a nitrogen gas atmosphere, and the surface wetting index was measured. The results are shown in Table 1. The wetting index before corona discharge treatment after foaming was 3
It was 7 dyne / cm.

Comparative Example 1 A foamed sheet was obtained in the same manner as in Example 1 except that the corona discharge treatment before foaming was not performed, and the surface wetting index was measured. The results are shown in Table 1. The wetting index after foaming and before corona discharge treatment was 32 dyne / cm.

Comparative Example 2 A foamed sheet was obtained in the same manner as in Example 1 except that the corona discharge treatment before foaming was not performed and the corona discharge treatment after foaming was performed under the conditions of an applied energy of 6000 J / m ² . The surface wetting index was measured. The results are shown in Table 1. The wetting index before corona discharge treatment after foaming was 32 dyn.
e / cm.

[0029]

[Table 1]

Example 3 Ethylene resin (MI: 4.0, density: 0.924 g / c)
m ³ , 100 parts by weight of Tm (resin melting point: 110 ° C.) and 6 parts by weight of azodicarbonamide as a foaming agent are supplied to a single screw extruder, kneaded at a resin temperature of 140 ° C., and a thickness of 0.4 mm Was obtained. Next, the foamable sheet was irradiated with a 2.2 Mrad electron beam to crosslink, and then one side of the foamable sheet was subjected to a temperature of 20 ° C., an applied energy of 3000 J / m ² , a processing speed of 20 m / min, and a condition in air. Below, corona discharge treatment was performed using the above-mentioned corona discharge treatment machine. Thereafter, the foamable sheet was placed in a hot blast stove adjusted to a temperature of 230 ° C. and foamed to a density of 0.10 g.
/ Cm ³ and a 1.0 mm thick foam sheet.

Immediately after the foamed sheet was obtained, the surface of the obtained foamed sheet was subjected to graining by passing between two grain rolls, and then wound up by a winder. The shape of the crimp roll was a pyramid of 1 × 1 mm, and the interval between the two crimp rolls was 0.7 mm. The surface temperature of the foamed sheet when passing between the rolls was 90 ° C. (actually measured by a surface contact thermometer).

Next, a temperature of 20
℃, applied energy 3000J / m ^Two, Processing speed 20m
/ Min, using the above corona discharge treatment machine under air conditions
And a corona discharge treatment was performed. Obtained foam sheet surface
Was measured in the same manner as in Example 1. Also, 2
One day later, expand the roll of foam sheet and break the foam sheet.
The presence or absence of blocking was evaluated based on the presence or absence of a part. The result
The results are shown in Table 2.

Comparative Example 3 A foamed sheet was obtained in the same manner as in Example 3, except that the corona discharge treatment before foaming was not performed and the corona discharge treatment after foaming was performed under the conditions of an applied energy of 6000 J / m ² . The surface wetting index and the presence or absence of blocking were measured. The results are shown in Table 2.

Comparative Example 4 The corona discharge treatment before foaming was not performed, and the graining was not performed.
Corona discharge treatment after foaming was performed with an applied energy of 6000 J /
A foamed sheet was obtained in the same manner as in Example 3 except that the test was performed under the conditions of m ² , and the surface wetting index and the presence or absence of blocking were measured. The results are shown in Table 2.

Comparative Example 5 No corona discharge treatment was performed before foaming, and no graining was performed.
The corona discharge treatment after foaming was performed with an applied energy of 9700 J /
m ² , except that the processing speed was 17 m / min.
A foamed sheet was obtained in the same manner as in Example 3, and the surface wetting index and the presence or absence of blocking were measured. The results are shown in Table 2.

[0036]

[Table 2]

Example 4 A foamed sheet was obtained in the same manner as in Example 3 except that the corona discharge treatment was performed in a nitrogen gas atmosphere, and the surface wetting index and the presence or absence of blocking were measured. Table 3 shows the results
It was shown to.

Comparative Example 6 A foamed sheet was obtained in the same manner as in Comparative Example 3 except that the corona discharge treatment was performed in a nitrogen gas atmosphere, and the surface wetting index and the presence or absence of blocking were measured. Table 3 shows the results
It was shown to.

Comparative Example 7 A foamed sheet was obtained in the same manner as in Comparative Example 4 except that the corona discharge treatment was performed in a nitrogen gas atmosphere, and the surface wetting index and the presence or absence of blocking were measured. Table 3 shows the results
It was shown to.

Comparative Example 8 A foamed sheet was obtained in the same manner as in Comparative Example 5 except that the corona discharge treatment was performed in a nitrogen gas atmosphere, and the surface wetting index and the presence or absence of blocking were measured. Table 3 shows the results
It was shown to.

[0041]

[Table 3]

[0042]

As described above, the method for producing an olefin resin foam sheet subjected to corona discharge treatment of the present invention is as described above, so that the surface wettability of the obtained olefin resin foam sheet is maintained for a long time immediately after the corona discharge treatment. Is done. Therefore,
High degree of freedom in the production process and no defects such as adhesive drop-off. Further, the olefin-based resin foam sheet obtained by the present invention is excellent in surface wettability immediately after corona discharge treatment, surface wettability after lapse of time, and antiblocking property, and thus is suitable as a base material for an adhesive tape or the like. Things.

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Claims (2)

[Claims] 1. An olefin resin sheet containing a foaming agent is subjected to a corona discharge treatment with an applied energy of 500 to 10000 J / m ² before foaming, foamed, and then applied at a rate of 500 to 10000 J / m ² . A method for producing a foamed olefin resin sheet, comprising performing corona discharge treatment with energy. 2. An olefin resin sheet containing a foaming agent is subjected to a corona discharge treatment with an applied energy of 500 to 10000 J / m ² before foaming, then foamed, and then the sheet surface is embossed. 500-100
A method for producing a foamed olefin resin sheet, comprising performing corona discharge treatment with an applied energy of 00 J / m ² .