JP2000017104A - Olefin-based resin foam and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an olefin-based resin foam excellent in surface wettability and hardly producing any blocking by forming fine concaves on at least one surface of the foam. SOLUTION: This foam of an olefin-based resin (suitably ethylene-based or propylene-based resin, esp. pref. containing >=20 wt.% of ethylene-vinyl acetate copolymer) is provided with fine concaves (having a mean diameter of pref. 1 to 10.more pref. 10 to 50.) formed on at least one surface of the foam. The ratio of fine concaves to surface cells of the foam is pref. 1 to (1 to 10). The other objective method is pref. conducted by meltably kneading an olefin- based resin and pyrolyzable foaming agent, extruding it for obtaining the resultant foam and then contacting the foam with brush rolls.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an olefin resin foam and a method for producing the same.

[0002]

2. Description of the Related Art An olefin resin foam is widely used as a base material of an adhesive tape, but has poor surface wettability as it is.
When performing printing or the like, the surface is usually treated to improve the surface wettability.

[0003] As a surface treatment method, a method using corona discharge is generally used. However, in this method, the surface wettability decreases over time. Therefore, in order to ensure sufficient surface wettability during actual use, corona discharge is required. It is necessary to increase the initial surface wettability immediately after the treatment. However, if the initial surface wettability is increased, blocking tends to occur when the foam is wound up in a roll shape for storage, transportation, etc., and the expansion force of the foam is increased, and the foam becomes There were problems such as wrinkles and tears. Particularly, in the pressure-sensitive adhesive tape substrate, since the ethylene-vinyl acetate copolymer, which easily causes blocking, is used as the olefin-based resin in order to improve flexibility, the above-described blocking problem is likely to occur.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an olefin resin foam having excellent surface wettability and hardly causing blocking. Another object of the present invention is to provide a production method capable of easily obtaining the olefin resin foam with good productivity.

[0005]

The olefin resin foam of the invention according to claim 1 comprises an olefin resin,
Further, a minute concave portion is formed on at least one surface.

As the olefin resin used in the first aspect of the present invention, any olefin resin conventionally used for foams can be used. In particular, ethylene resins and propylene resins are preferably used.

Examples of the ethylene resin include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component, and ethylene as a main component. Ethylene-ethyl acrylate copolymer, etc., which may be used alone or in combination of two or more. In particular, when an ethylene-vinyl acetate copolymer is used, the effect of preventing blocking increases, so that the ethylene-vinyl acetate copolymer preferably contains 20% by weight or more. The vinyl acetate content of the ethylene-vinyl acetate copolymer is usually from 5 to 40% by weight. The linear low-density polyethylene is obtained by copolymerizing ethylene with an α-olefin other than ethylene.
Examples of the olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like.

As the propylene resin, for example,
Polypropylene, ethylene mainly composed of propylene
Examples thereof include a propylene copolymer and an ethylene-propylene-butene terpolymer containing propylene as a main component, and these may be used alone or in combination of two or more.

[0009] The minute recess is a depression formed on the surface of the foam, and its shape is not particularly limited.
The size of the minute concave portion may be appropriately determined according to the application to be used, but as the size decreases, the effect of preventing blocking decreases, and as the size increases, the mechanical strength of the foam decreases.
The average diameter is preferably from 1 to 100 μm, more preferably from 20 to 50 μm.

The average diameter referred to in the present invention is an average value of the maximum diameter of the minute concave portion existing per unit area (mm ² ), which is measured by magnifying the surface of the foam 20 to 30 times with a microscope.

When the proportion of the minute recesses is reduced, the effect of preventing blocking is reduced, and when the proportion is increased, the mechanical strength of the foam is reduced. Since it becomes worse, it is preferable that one foam cell is formed at a rate of 1 cell per 1 to 10 surface cells. In addition, the diameter of the surface cell of the olefin-based foam is generally 100 to 800 μm.

The olefin resin foam of the invention according to claim 1 may be appropriately crosslinked, and the degree of crosslinking is
When the size is smaller, the resin cannot retain bubbles during foaming, and gas is likely to escape.Therefore, the appearance is deteriorated or the strength is reduced, and when the size is larger, the resin cannot follow the foaming during foaming, and bubbles are not generated. 3 to 70% is preferable because it becomes uniform,
More preferably 15 to 60%, even more preferably 20 to 60%
50%.

The degree of crosslinking referred to in the present invention is a value measured by the following method. The foam was sliced in the thickness direction, and about 100 mg was precisely weighed and used as a sample. The foam was crushed, immersed in 100 ml of xylene at 120 ° C. for 24 hours, and filtered through a 200-mesh stainless steel wire mesh. ,
The insoluble matter on the wire mesh is vacuum dried. Next, the weight of the insoluble portion is precisely weighed, and the degree of crosslinking is calculated as a percentage by the following equation. Degree of crosslinking (%) = {b / a} × 100 where a: weight of sample (mg), b: weight of insoluble matter (mg)}

The apparent density of the olefin-based resin foam may be appropriately determined according to the intended use. However, as the apparent density decreases, the mechanical strength decreases, and as it increases, the flexibility decreases. / Cm ³ , more preferably 0.020 to 0.200 g / cm ³ . The apparent density referred to in the present invention is JIS K 6767.
It is a value measured in accordance with.

The thickness of the olefin resin foam may be appropriately determined according to the application. For example, when the foam is used as a pressure-sensitive adhesive sheet substrate, the thickness is usually 0.25 to 10 mm, preferably 0.1 to 10 mm. 3-5 mm, more preferably 0.5
２2 mm.

According to a fourth aspect of the present invention, there is provided a method for producing a single-screw extruder, a twin-screw extruder, and the like. After being extruded by an extruder or the like, crosslinking is performed as necessary, foaming is performed by a conventionally known arbitrary method, and the obtained foam is brought into contact with a brush roll, and the micro concave portion is formed by friction. I do.

As the above-mentioned pyrolytic foaming agent, any conventionally known one can be used. Examples thereof include azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine and the like. Two or more kinds may be used in combination. The addition amount of the pyrolytic foaming agent is adjusted according to the desired apparent density, but generally, 1 to 5 parts by weight based on 100 parts by weight of the olefin resin.
0 parts by weight, preferably 4 to 25 parts by weight.

The crosslinking aid is added when crosslinking is performed,
For example, divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, etc., may be used alone or in combination of two or more. The amount of the crosslinking aid added is in accordance with the desired degree of crosslinking, and is generally 0.5 to 10 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight of the olefin resin.
8 to 6 parts by weight.

As a method of crosslinking, any conventionally known method may be employed, and for example, a method of irradiating with ionizing radiation may be mentioned. Examples of the ionizing radiation include an electron beam, α-ray, β-ray, and γ-ray, and the irradiation amount is generally 1 to 20 Mrad.

As the above-mentioned brush roll, any conventionally known brush roll can be used. For example, a brush roll formed on a generally used metal roll surface perpendicular to the roll surface can be mentioned. As the material of the brush hair,
For example, nylon, pig hair, horse hair, and the like in which carbon, an antistatic agent and the like are mixed, and the like, may be appropriately determined depending on the resin composition of the foam, the thickness, the degree of crosslinking, the expansion ratio, and the like.

The diameter and length of the brush bristles are not particularly limited, and may be appropriately determined according to the resin composition, thickness, degree of crosslinking, expansion ratio, etc. of the foam. Further, the formation density of the brush bristles is not particularly limited and may be determined as appropriate.However, if the formation density is too high, the frictional force between the brush bristles and the foam increases, and the foam tends to wrinkle. If too much, the surface treatment becomes uneven.

The pressing force of the brush roll, the relative speed to the foam, and the like are not particularly limited, and the resin composition of the foam,
Thickness, degree of crosslinking, may be appropriately determined depending on the expansion ratio, etc.,
If the pressing force is too strong, a friction mark that can be visually confirmed is left on the foam surface, so that the appearance of the foam deteriorates. If the pressing force is too weak, the effect of preventing blocking is reduced.
kg / m ² . The direction of rotation of the brush may be the same as or opposite to the line traveling direction of the foam sheet.

Also, instead of the friction by the brush roll, the foam surface flowing through the line is brought into contact with the fixed brush bristles, and the foam surface is rubbed with a cloth or the like.
A method of rubbing may be adopted, and after obtaining a foam,
Friction may be applied in a separate step.

Further, in order to improve the surface wettability,
It is preferable to perform a corona discharge treatment after the formation of the minute concave portions. The strength of the corona discharge treatment may be appropriately determined depending on the desired surface wettability, but if it is too strong, blocking tends to occur.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of 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.

[0026]

EXAMPLES (Examples 1, 3 and 4) LDPE (MI = 4 g / 10 min, density = 0.921 g /
cm ³ , low-density polyethylene having a melting point of about 110 ° C.), E
VA (ethylene-vinyl acetate copolymer having a vinyl acetate content of 14% by weight) and azodicarbonamide were added in an amount of about 140.
After melting and kneading at ℃, 0.4mm thick by twin screw extruder
After extruding the sheet with a total of 2.2 Mrad from both sides of the sheet to perform cross-linking, foaming is performed in a heating furnace maintained at about 210 ° C., and the obtained foamed sheet is
After moving and cooling by flowing at a line speed of 5 m / min,
Next, a nylon roll having a length of 40 mm and a diameter of 0.25 mm was uniformly formed on a metal roll having an outer diameter of 300 mm at a ratio of 50 hairs / cm ² , and 100 in the direction opposite to the line advancing direction.
The brush roll rotating at m / min was brought into contact with the foam sheet so that the distance between the foam sheet surface and the metal roll surface was 30 mm. At this time, the average diameter and the formation ratio (the number of surface cells per minute recess) of the formed minute recesses were as shown in Table 1. Next, a corona discharge treatment machine (manufactured by Kasuga Electric Co., Ltd., model “thyristor inverter method, H
FS402 "), the output voltage is 130 V, and the processing speed is 2
Corona discharge treatment was performed at 0 m / min to obtain a foamed olefin resin sheet having a thickness of about 1 mm.

Example 2 After a foamed sheet was obtained in the same manner as in Example 1, the brush roll was formed in the same manner as in Example 1 except that the distance between the foamed sheet surface and the metal roll surface was 35 mm. Contacted. At this time, the average diameter and the formation ratio of the formed minute concave portions were as shown in Table 1.
Next, corona discharge treatment was performed in the same manner as in Example 1 to obtain an olefin resin foam sheet having a thickness of about 1 mm.

(Comparative Examples 1 to 3) After a foamed sheet was obtained in the same manner as in Example 1, a corona discharge treatment was carried out in the same manner as in Example 1 without contacting with a brush roll to obtain an olefin having a thickness of about 1 mm. A resin foam sheet was obtained.

(Comparative Example 4) After a foamed sheet was obtained in the same manner as in Example 1, the foamed sheet was obtained without contact with a brush roll.
Output voltage 180V,
Perform corona discharge treatment at a treatment speed of 15 m / min.
mm olefin resin foam sheet was obtained.

(Comparative Example 5) After obtaining a foamed sheet in the same manner as in Example 1, without contact with a brush roll and without performing corona discharge treatment, an olefin-based resin foamed sheet having a thickness of about 1 mm I got

The degree of crosslinking, apparent density, and surface wettability (initial value) of the foamed olefin resin sheets obtained in Examples and Comparative Examples were as shown in Table 1. The surface wettability referred to in the present invention is a value of surface tension measured according to JIS K6768.

The olefin resin foam sheet 300
After winding m in a roll, the surface wettability and the developing force were measured as follows. (Measurement of Surface Wettability) The surface tension of the rolled olefin-based resin foam sheet after leaving it to stand at room temperature for 2 weeks was measured.

(Measurement of developing force) A roll-shaped olefin resin foam sheet was left at 50 ° C. for 24 hours (Example 1,
2, Comparative Examples 1, 4, 5) or left at 27 ° C. for one week (Examples 3, 4, Comparative Examples 2, 3), and then the central position of the roll-shaped olefin resin foam sheet is rotatably positioned. In the fixed state, the expansion force when the olefin-based resin foam sheet was expanded at 15 m / min was measured by a spring balance, and the maximum value of the expansion force is shown in Table 1.

[0034]

[Table 1]

[0035]

According to the first aspect of the present invention, the olefin resin foam according to the first aspect has the above-described structure, and thus has excellent surface wettability,
In addition, it does not cause blocking, and can be easily developed or peeled even after being wound up in a roll or stacked. In addition, even when an olefin-based resin containing an ethylene-vinyl acetate copolymer is used, blocking is unlikely to occur, development after winding in a roll is easy, and even when the thickness is reduced, the film is torn. Therefore, it can be suitably used as a pressure-sensitive adhesive sheet substrate. In the production method according to the fourth aspect of the present invention, after the olefin-based resin foam is produced, the foam is brought into contact with the brush roll before winding, so that the process is simple, the productivity is excellent, and the foam surface is easily micro-sized. A recess can be formed.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) // B29K 23:00 105: 04 C08L 23:04 F term (Reference) 4F073 AA01 BA06 BA07 BA11 BB04 CA21 CA42 4F074 AA16 AA20 AA22 BA01 BA13 BB25 CA22 CA29 CC08Z 4F212 AA03 AA07 AA10 AB02 AG01 AG20 UA09 UB02 UN06 UP03 UP04

Claims (4)

[Claims] 1. An olefin-based resin foam comprising an olefin-based resin and having at least one surface formed with minute concave portions. 2. The olefin resin foam according to claim 1, wherein one minute recess is formed for every 1 to 10 surface cells. 3. The olefin resin according to claim 1, wherein the olefin resin contains at least 20% by weight of an ethylene-vinyl acetate copolymer.
Or the olefin-based resin foam according to 2. 4. The method according to claim 1, wherein the olefin resin and the pyrolytic foaming agent are melt-kneaded, extruded, foamed to form a foam, and then contacted with a brush roll. A method for producing an olefin-based resin foam according to any one of the preceding claims.