JP2006007490A - Film excellent in printability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film reduced in the lowering of a corona treatment effect with the elapse of time even in a flexible film made of a polypropylene resin and excellent in aqueous ink printability. <P>SOLUTION: In this film, an ethylene-propylene copolymer of which the molecular weight distribution is 4.5 or below as weight average molecular weight (Mw)/number average molecular weight (Mn) or an ethylene-propylene-butene terpolymer is laminated as a surface layer. After the film is formed, corona treatment is applied to the film to form a film with a thickness of 100 μm or below of which the surface tension three days after corona treatment is 80% or above of that immediately after corona treatment. The extract of this film obtained after the film is immersed in diethyl ether for two days is set to 3,000 ppm or below. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film or sheet excellent in flexibility, transparency, and gloss excellent in printability of water-based ink.

  Recently, due to the need to consider safety in the global environment, working environment or food packaging, VOC (volatile organic compound) emission regulations for toluene, ethyl acetate, and methyl ethyl ketone used in solvent-based inks have been examined. As a result, water-based inks that use water and alcohol as a medium have been actively adopted in printing converters.

  In general, a printed film or sheet (hereinafter referred to as a film) needs to be subjected to corona treatment on the printing surface in order to exhibit hydrophobic properties. In particular, a film using a polypropylene resin as a surface layer is difficult to get a water-based ink neatly because the surface tension tends to be reduced due to aging even when corona treatment is performed. The cause is considered to be that the surface tension is reduced due to the fact that the antioxidant, lubricant, catalyst neutralizing agent, and low molecular weight component contained in the polypropylene film easily migrate to the surface. When the homopolypropylene resin is used as the surface layer, it is considered that the surface migration of the extract due to crystals in the resin is inhibited, so that it has an effect of suppressing a decrease in surface tension, but is inferior in flexibility. On the other hand, when a copolymer such as a flexible ethylene-propylene copolymer resin is used, the surface tension tends to decrease over time even if corona treatment is performed because the degree of crystallinity is lower than that of homopolypropylene resin. It is in. Accordingly, it has been difficult to use a flexible film made of ethylene-propylene copolymer resin for water-based ink printing due to lack of printability of water-based ink.

  The present invention solves the conventional problems as described above, and provides a flexible film with little deterioration of the corona treatment effect with time and excellent water-based ink printability.

  In order to achieve the object of the present invention, an ethylene-propylene copolymer or ethylene-propylene-butene having a molecular weight distribution defined by weight average molecular weight (Mw) / number average molecular weight (Mn) of 4.5 or less. A laminated film having a terpolymer as a surface layer, the surface tension of the surface layer 3 days after corona treatment being 80% or more immediately after corona treatment, and extraction obtained by being immersed in diethyl ether for 2 days It is set as the laminated film excellent in the printability characterized by the thing being 3000 ppm or less.

  A film that can maintain a high surface tension for a long period of time with little change in corona treatment effect over time, when the molecular weight distribution of the ethylene-propylene copolymer or ethylene-propylene-butene terpolymer is 4.5 or less. It becomes.

  Moreover, the film has excellent gloss by using a surface layer by using an ethylene-propylene copolymer, an ethylene-butene copolymer, an ethylene-propylene-butene terpolymer, etc. as the surface layer. It will be a thing.

  Furthermore, the surface layer is subjected to corona treatment, and the surface tension after 3 days after corona treatment is 80% or more immediately after corona treatment, so that water-based ink is not repelled on the film surface and can be printed beautifully. It becomes.

  Furthermore, the amount of the extract contained in the film, which is converted from the extract obtained by being immersed in diethyl ether for 2 days, is 3000 ppm or less, so that the amount of the extract contained in the film is less transferred to the corona-treated surface. As a result, the water-based ink is not repelled on the film surface, and the printing can be finished beautifully.

  Examples of the extract contained in the film include, for example, antioxidants, lubricants, catalyst neutralizers, etc., but are not particularly limited, and the amount extracted with diethyl ether is small. is important.

  The fact that the extract is easily extracted with diethyl ether means that the surface migration of the extract is large. If the extraction is difficult, the surface migration of the extract is low. Therefore, in order to increase the surface adhesion of the water-based ink, it is necessary to reduce the extract that tends to migrate to the surface in order to keep the surface tension of the film surface high.

  When the extract in the film converted from the extract obtained by being immersed in diethyl ether for 2 days exceeds 3000 ppm, the surface tension immediately after the corona treatment is lowered over time. The surface tension after 3 days of corona treatment of the present invention is 80% or more immediately after corona treatment. When the surface tension after 3 days from the corona treatment is 80% or more immediately after the corona treatment, the printability of the water-based ink is improved.

  Next, the layer structure of the film excellent in printability of the present invention will be described. In the present invention, an ethylene-propylene copolymer or an ethylene-propylene-butene terpolymer having a molecular weight distribution of 4.5 or less is laminated on the center layer as a surface layer. The center layer is not particularly limited as long as it is a flexible material. For example, it is preferable to employ a resin that is the same as or more flexible than the surface layer.

Examples of the flexible resin include an ethylene-propylene copolymer, an ethylene-propylene-butene terpolymer, an ethylene-α-olefin copolymer having a density of 0.920 g / cm ³ or less, and a styrene copolymer. Examples thereof include polymerized elastomers.

  If the film having excellent printability according to the present invention is used for bag making, the melt macroflow rate of the surface layer (MFR, unit g / 10 min, resin temperature 230 ° C.) for the purpose of improving the heat seal strength. Is preferably set to 2.0 to 9.0. If it exceeds 9.0, stringing of the molten resin may occur during heat sealing, and if it is less than 2.0, it is difficult to stably form a film.

  When the thickness of the film excellent in printability of the present invention exceeds 100 μm, the rigidity is too high and deviates from the original purpose of providing a flexible film. Therefore, the thickness is preferably 100 μm or less, and minimum if the strength of the packaging film is required. However, it is preferably 15 μm or more.

  The melt macroflow rate of the ethylene-α-olefin copolymer used for the center layer is more preferably 0.5 to 3.5. This not only improves the heat seal strength, but also prevents the molten resin stringing phenomenon at the time of heat sealing, so that a film having no pinholes and excellent appearance can be obtained.

  The method for producing a film excellent in printability of the present invention is not particularly limited, and examples thereof include a simple method such as an inflation molding method by melt extrusion utilizing the properties of a thermoplastic resin and a T-die molding method. In particular, for the purpose of obtaining transparency and gloss in the film, it is preferable to cool the molten resin with a cooling roll in which the inside of the roll is water-cooled by a T-die molding method. Co-extrusion method as a method for obtaining the laminated structure of the surface layer and the center layer, and a method of extruding and laminating a film once formed by the above method, dry laminating three or more films having surface layers on both sides of the center layer However, the method is not limited, and the selection may be made according to the cost and the required quality as appropriate.

  A laminated film having an ethylene-propylene copolymer or ethylene-propylene-butene terpolymer having a molecular weight distribution of 4.5 or less as a surface layer, and the surface tension after 3 days of corona treatment of the surface layer is corona treated. It is possible to provide a flexible film excellent in water-based ink printing suitability by setting the extract to be 80% or more immediately after, having a thickness of 100 μm or less and being immersed in diethyl ether for 2 days to 3000 ppm or less. became.

Examples are shown below.
Example 1
Melt macroflow rate (MFR) 6.0 g / 10 min (190 ° C.) as a central layer, density 0.900 g / cm ³ , and molecular weight distribution of 3.6 in terms of weight average molecular weight (Mw) / number average molecular weight (Mn). An ethylene-propylene-butene terpolymer is used, and an ethylene-propylene copolymer having an MFR of 7.5 g / 10 min (230 ° C.), a density of 0.900 g / cm ³ , and a molecular weight distribution of 4.4 as both surface layers. The polymer is blended with 600 ppm of erucic acid amide lubricant and 500 ppm of silicone-based antiblocking agent, multi-layered by a feed block coextrusion method, formed into a T-die at 250 ° C, and roll-cooled at 30 ° C for layer thickness. A multilayer film with a thickness of 80 μm having a composition of surface layer / center layer / surface layer in a ratio of 1: 3: 1 was obtained.

(Example 2)
A multilayer film was prepared in the same manner as in Example 1 except that the central layer was a linear low density polyethylene having an MFR of 2.0 g / 10 min (190 ° C.) and a density of 0.915 g / cm ³ .

Example 3
As a surface layer, an ethylene-propylene copolymer having a molecular weight distribution of 4.4, a density of 0.900 g / cm ³ , and an MFR of 7.5 g / 10 minutes (230 ° C.) is mixed with 600 ppm of an erucamide amide lubricant and 500 ppm of a silicone antiblocking agent. A multilayer film was prepared in the same manner as in Example 1 except that was added.

(Comparative Example 1)
A multilayer film was produced in the same manner as in Example 1 except that erucic acid amide-based lubricant was blended in 4000 ppm on both surface layers.

(Comparative Example 2)
A multilayer film was prepared in the same manner as in Example 1 except that the condition for performing the corona treatment was reduced to 1 kW and the surface tension after 1 hour was 38 mmN / m.

(Comparative Example 3)
A multilayer was formed in the same manner as in Example 1 except that an ethylene-propylene copolymer having a molecular weight distribution of 6.0, a density of 0.900 g / cm ³ and an MFR of 7.5 g / 10 min (230 ° C.) was used for the surface layer. A film was created.

The performance of the obtained multilayer film was evaluated by the following measuring method.
(Evaluation methods)
(1) Extraction amount: The obtained laminated film was subjected to corona treatment in-line to produce a multilayer film having a surface tension of 54 mmN / m. The obtained multilayer film was finely cut, immersed in 300 ml of diethyl ether at room temperature for 2 days, filtered, concentrated with an evaporator, dried, and then dried, and the extract concentration was calculated from the original film weight. .
(2) Measurement of surface tension immediately after treatment and after 3 days: Measurement was performed according to the wettability test method of JIS-K6768.
(3) Water-based ink repellency: After 1 ml of water-based ink was dropped on the film surface, the liquid state after 5 seconds was evaluated visually.
○: Water-based ink spreads thinly.
X: State in which water-based ink is repelled.

Tables 1 and 2 summarize the measurement results for Examples and Comparative Examples.

A flexible polypropylene resin film capable of water-based ink printing that can be used for bag making is provided.

Claims (1)

Lamination having an ethylene-propylene copolymer or ethylene-propylene-butene terpolymer having a molecular weight distribution defined by weight average molecular weight (Mw) / number average molecular weight (Mn) of 4.5 or less as a surface layer Printing characterized in that the surface tension of the surface layer after 3 days of corona treatment is 80% or more immediately after corona treatment, and the extract obtained by being immersed in diethyl ether for 2 days is 3000 ppm or less. Laminated film with excellent suitability.