JPS6135217B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for improving printability without impairing the antistatic properties imparted to polypropylene films. Polypropylene film (hereinafter also referred to as PP film) is widely used as a packaging material because of its excellent mechanical properties, chemical properties, transparency, water vapor barrier properties, etc. However, PP film has poor printability due to its surface characteristics, and has the disadvantage that printing with general-purpose printing inks such as cellophane ink, water-based ink, etc. is almost impossible. As a method to eliminate such drawbacks, the present inventors have already proposed a method in which a PP film containing a fatty acid amide is subjected to a corona discharge treatment in a nitrogen gas atmosphere with a low oxygen concentration. In the above method, a PP film with better printability can be obtained as the oxygen concentration in the nitrogen gas is lowered, but if the oxygen concentration becomes extremely low, less than 0.2% by volume, the antistatic agent may be Addition causes a problem in that the antistatic property imparted to the PP film is impaired. The present inventors have solved the above problem while preventing PP.
Further research was conducted to develop a method to improve the printability of the film. As a result, the oxygen concentration of PP film containing fatty acid amide and antistatic agent was 0.2.
It has been discovered that when corona discharge treatment is performed in a nitrogen gas atmosphere of less than % by volume, the desired objective can be achieved by subsequent corona discharge treatment in a nitrogen gas atmosphere having a specific oxygen concentration, and the present invention has been completed. It came to this. That is, in the present invention, at least one side of a polypropylene film containing a fatty acid amide and an antistatic agent is subjected to a corona discharge treatment in a nitrogen gas atmosphere with an oxygen concentration of less than 0.2% by volume, and then treated with a nitrogen gas atmosphere with an oxygen concentration of 0.2 to 1.0% by volume. This is a method for processing polypropylene film, which is characterized by subjecting it to corona discharge treatment. In the present invention, the PP film is a general term for a uniaxially stretched PP film, a biaxially stretched PP film, and a composite film having the above-mentioned PP film on at least one side. Polypropylene is a homopolymer of propylene: propylene, ethylene, and butene.
Copolymer with α-olefin other than propylene such as 1,4-methylpentene-1: polypropylene
polyethylene, ionomer, polybutene.
1, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, acrylic acid grafted polyethylene, acrylic acid grafted polypropylene, maleic anhydride grafted polypropylene,
Polypropylene compositions are generally used in which polymers and modifiers such as terpene resins, petroleum resins, rosins, coumaron resins, and plasticizers are added within the range that does not impair the properties of polypropylene. In the present invention, the PP film contains a fatty acid amide and an antistatic agent. Any known fatty acid amide can be used without any particular restriction. for example,
octylamide, nonylamide, decylamide,
undecylamide, laurylamide, tridecylamide, myristylamide, permitylamide,
Oleylamide, hexanecylamide, octacosylamide, etc. are commonly used. The content of the fatty acid amide in the PP film is 0.01 to 0.5% by weight,
Preferably, the content is in the range of 0.05 to 0.3% by weight because it can impart excellent printability to the PP film by the corona discharge treatment described below. Also, known antistatic agents can be used without any restrictions. Typical antistatic agents include glycerin fatty acid ester, pentaerythritol fatty acid ester, alkyl diethanolamine, sorbitan fatty acid ester, polyethylene glycol fatty acid ester, alkyl diethanolamine fatty acid ester, and alkylbenzene sulfonate. The content of the antistatic agent in the PP film may be the amount normally used to impart antistatic properties to the PP film. in general,
0.1-3.0% by weight in PP film, preferably
It is preferable to contain it in an amount of 0.2 to 2.0% by weight. Furthermore, in the present invention, the PP film may contain other additives that are normally added during the production of PP films, such as antioxidants, lubricants, antiblocking agents, ultraviolet absorbers, colorants, and the like. The greatest feature of the present invention is that at least one side of the PP film is subjected to corona discharge treatment in a nitrogen gas atmosphere with an oxygen concentration of less than 0.2% by volume (hereinafter also referred to as first stage treatment), and then Corona discharge treatment is performed in a nitrogen gas atmosphere (hereinafter also referred to as second stage treatment). By performing corona discharge treatment under the above specific conditions, the PP film has excellent printability due to the action with the fatty acid amide, without impairing the antistatic properties of the PP film imparted by the antistatic agent. It is possible to grant. That is, even if the order of the first stage treatment and the second stage treatment is changed, or even if the oxygen concentration is outside the range of the first stage treatment and the second stage treatment, the effects of the present invention cannot be exhibited. In the first stage treatment, the oxygen concentration is not particularly limited as long as it is less than 0.2% by volume, but it is particularly preferably less than 0.1% by volume.
In addition, in the second stage treatment, there are no restrictions on the oxygen concentration as long as it is within the range of 0.2 to 1.0% by volume, but in particular
It is preferably within the range of 0.3 to 0.8% by volume. In the present invention, the ratio of the first stage treatment to the second stage treatment is not particularly limited, but it is generally preferred that the first stage treatment accounts for 30 to 90% of the total, preferably 40 to 80%. In addition, the total of the first stage treatment and second stage treatment is 20 to 300 W/min per ¹ m2 of PP film.
It is preferable to perform the corona discharge treatment so that the power is preferably 40 to 150 W·min. That is, if the corona discharge treatment is weaker than the above range, the effect of imparting printability will be small, and if the corona discharge treatment is stronger than the above range, the PP film tends to be damaged by electric discharge shock. The first stage processing and the second stage processing may be performed independently or consecutively. Furthermore, there are no particular limitations on the manner in which the PP film is subjected to the corona discharge treatment in a nitrogen gas atmosphere having a predetermined oxygen concentration. for example,
Common methods include performing corona discharge treatment while spraying nitrogen gas having a predetermined oxygen concentration onto the surface of the PP film, and performing corona discharge treatment in a tank in which the nitrogen gas is present. In the treatment method of the present invention, other treatment conditions may be those in known corona discharge treatment without particular limitation. For example, the distance between the corona discharge treatment and the film to be treated is generally about 0.5 to 3 mm. Furthermore, any known corona discharge electrode may be used without any restriction. As can be understood from the above explanation, the processing method of the present invention can impart excellent printability without impairing the antistatic property imparted to the PP film, and can obtain a highly versatile PP film. . The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples. In addition, the characteristic values shown in the examples were obtained by the following method.
was measured. 1 Melt Index Measured using a melt indexer manufactured by Takara Kogyo Co., Ltd. according to ASTMD-1238. 2 Oxygen concentration Using a gas chromatograph model 636050 manufactured by Hitachi, carrier gas He, column length 2 m,
It was measured at room temperature using the filler Molecular Sieve 5A (manufactured by Gascro Industries). 3 Transparency (Haze) Measured using a haze meter manufactured by Toyo Seiki Seisakusho in accordance with JIS K-6714. The smaller this number is, the better the transparency is. 4 Slip property (coefficient of dynamic friction) Using a friction coefficient measuring device made by Uejima Seisakusho, stack two films front and back, place a 200-gram weight measuring 45 mm x 45 mm, and fix one side of the film while pulling the other at 30 mm/min. The coefficient of dynamic friction was measured when it was stretched. 5. Blocking resistance A 120 mm x 120 mm film was repeatedly subjected to corona discharge treatment, a 1 kg weight was placed on it, and the film was left at 40°C and 90% RH for 24 hours. A 30 mm wide sample was cut out and its tensile shear peel strength was measured. 6 Wetting index Measured according to JIS K-6768. 7. Odor The corona discharge treated surface was evaluated in three grades by a sensory test. ○: No odor at all. △: Slight odor. ×: Strong odor. 8 Antistatic effect (surface specific resistance) Using a micropotentiometer and film electrode manufactured by Yokogawa Heuretsu Packard, 23℃, 50%
Apply 500V DC voltage under RH atmosphere,
The surface resistivity of the corona discharge treated surface was measured after 5 minutes. 9 Printability Commercial cellophane printing ink Cellocolor ST “White” was applied to the corona discharge treated surface of PP film.
(manufactured by Toyo Ink Mfg. Co., Ltd.) and commercially available water-based ink Deitskusafe LS #4 "White" (manufactured by Dainippon Ink & Chemicals Co., Ltd.) were applied using a Mayer bar, dried in an oven at 80°C for 1 minute, and then dried at 23°C. , and left under 50% RH for 24 hours. B. Cellotape Peeling Test A 18 mm wide cellophane tape (manufactured by Nichiban Co., Ltd.) was attached to a printed PP film, and it was strongly peeled off, and the ink peeled area was evaluated in five grades as shown in the table below.

[Table] B. Rub test The printed PP film was rubbed vigorously 20 times and evaluated on a 5-grade scale in the same manner as the cellophane tape peel strength. Example 1 To powdered polypropylene with a melt index of 0.8 dg/min, fatty acid amide and antistatic agent of the type and amount shown in Table 1 were added and mixed in a super mixer, and then mixed using a twin screw extruder. and granulated at 230°C. The blended polypropylene pellets were heated and melted at 300°C using a 65mmφ single-screw extruder equipped with a T-die, extruded onto a cooling roll at 40°C, and cooled and solidified to produce an unstretched sheet with a thickness of 1.25mm. The unstretched sheet was stretched 5 times in the machine direction using a roll longitudinal stretching machine with a roll surface temperature adjusted to 155°C, and then 10 times in the transverse direction using an oven type horizontal stretching machine with an ambient temperature of 160°C. A biaxially stretched PP film with a thickness of 25μ was obtained. Further, while the biaxially stretched PP film was traveling at a speed of 30 m/min, nitrogen gas having the oxygen concentration shown in Table 1 was sequentially sprayed onto the film surface, and corona discharge treatment was continuously performed at the intensity shown in Table 1. After the obtained PP film was aged for 3 days at 30°C and 50% RH, its antistatic properties, haze, slipperiness, blocking resistance, wetting index, odor, and printability were evaluated, and the results are shown in Table 1. It was shown to. 〓〓〓〓〓

【table】

[Table] Example 2 Melt index 7dg/min, ethylene content
0.10% by weight of erucylamide and 0.3% by weight of pentaerythritol fatty acid ester (Daiichi Kogyo Seiyaku Co., Ltd.: Registat PE-139) were added to 2.5% by weight of powdered ethylene propylene random copolymer, mixed in a super mixer, and then uniaxially extruded. The mixture was granulated using a machine at 210°C. This blended pellet was heated and melted at 240°C using a 65mmφ extruder equipped with a T-die, and cold water at 20°C was flowed through the inside.
A PP film with a thickness of 30 μm was produced by extrusion at a film forming speed of 40 m/min onto a cooling roll coated with mirror-finished hard chrome plating and cooling and solidifying it. This PP
The film was run at 40 m/min, and the oxygen concentration was 0.04.
〓〓〓〓〓
The first stage treatment was carried out at a treatment intensity of 40 W min/m ² while spraying nitrogen gas at a concentration of 0.7 volume % onto the film surface, and then at a treatment intensity of 38 W min/m 2 while spraying nitrogen gas at a concentration of 0.7 volume % on the film surface. The second stage treatment was carried out continuously in m ² . The resulting PP film has a haze of 2.8%, slipperiness of 0.25, and blocking resistance of 10.
＞, Wetting index 44dyne/cm, surface specific resistance 2.2×
10 ¹¹ Ω, no odor, cellophane ink, cellophane ink peeling strength against water-based ink, and rubbing strength were all "5", showing excellent properties. 〓〓〓〓〓

Claims (1)

[Scope of Claims] 1 At least one side of a polypropylene film containing a fatty acid amide and an antistatic agent is subjected to corona discharge treatment in a nitrogen gas atmosphere with an oxygen concentration of less than 0.2% by volume, and then treated with nitrogen having an oxygen concentration of 0.2 to 1.0% by volume. A method for processing polypropylene film, characterized by corona discharge treatment in a gas atmosphere. 2 Polypropylene film absorbs fatty acid amide
The method according to claim 1, containing 0.01 to 0.5% by weight.