JPH0120176B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a thermoplastic resin-coated polyolefin film having excellent antistatic properties and coating adhesion. A polyolefin film, especially a biaxially oriented polypropylene film coated on one side with a thermoplastic resin, has excellent optical and mechanical properties, and by selecting the thermoplastic resin to be coated, it can be improved in terms of water vapor barrier properties and ease of use. Since it has excellent heat sealability, it is used for a variety of purposes including food packaging and textile packaging. However, these coated polyolefin films are susceptible to the generation and accumulation of static electricity, especially on the uncoated surface, and workability is reduced due to static electricity during bag making or filling operations, and dust and There are problems such as adhesion of dust. Conventionally, as a method for preventing static electricity on a biaxially oriented polyolefin film (uncoated film), a polyolefin resin film kneaded with an antistatic agent has been biaxially stretched and then subjected to corona discharge treatment in air. When the film obtained by this method is coated with a thermoplastic resin, the adhesion of the film is poor, and the film becomes even worse when boiled in hot water. Although the details of this cause are not clear, it is certain that the antistatic agent mixed in inhibits the adhesion between the coating and the biaxially oriented polyolefin film. The inventor of the present invention has arrived at the present invention as a result of extensive research into poor adhesion when coating such an antistatic agent-mixed polyolefin film with a thermoplastic resin. That is, one side of a polyolefin in-film containing an antistatic agent is treated with corona discharge in a nitrogen atmosphere with an oxygen concentration of 0.3 V/V% or less, and this side is coated with a thermoplastic resin, such as vinylidene chloride copolymer, and the other side is coated with vinylidene chloride copolymer, which is a thermoplastic resin. By subjecting it to corona discharge treatment in air, it has become possible to produce a thermoplastic resin-coated polyolefin film with excellent film adhesion and antistatic properties. The present invention is based on the discovery that corona discharge treatment produces different effects depending on the atmosphere in which it is performed, and therefore the characteristics of the treated surface vary. Specifically, a polyolefin film with an antistatic agent mixed in has one side with a high oxygen concentration.
By performing corona discharge treatment in a substantially nitrogen atmosphere of 0.3V/V% or less, the adhesion when coating the thermoplastic resin is improved, and by further performing corona discharge treatment on the other side in air. Antistatic performance is improved. As mentioned above, the corona discharge treatment according to the present invention is carried out under different atmospheres in order to give different surface properties to both sides of the antistatic agent-infused polyolefin film. This method is desirable from the viewpoint of adhesion and antistatic performance of the vinylidene chloride copolymer-coated film. That is, rather than first performing two corona discharge treatments in different atmospheres and then coating the vinylidene chloride copolymer, we first perform a corona discharge treatment on one side in a nitrogen atmosphere, and then coat that side with the vinylidene chloride copolymer. A preferred method is to coat the vinylidene chloride copolymer and then subject the opposite side to a corona discharge treatment in air. The corona discharge treatment machine used in the present invention is one that is currently commercially available and has a frequency of about 5 KHz to 110 KHz. The electrical energy applied to the polyolefin film during the corona discharge treatment in air and the chrona discharge treatment in nitrogen is ²⁰ to 120 watt-minutes of alternating current electrical energy per square meter of film. The polypropylene preferably used in the present invention is solid in normal state and has a portion insoluble in boiling n-heptane.
Copolymers containing at least 90 w/w% of propylene with an intrinsic viscosity of 1.3 to 4.2 in the polymer chain, and 10 w/w% or less of ethylene can also be used. be. These crystalline polypropylenes may contain stabilizers, inorganic lubricants, etc. that are usually added. The antistatic agent used in the present invention is a known anionic, cationic, amphoteric and nonionic antistatic agent, and in particular, the nonionic antistatic agent is an alkyl diethanolamine monofatty acid represented by the following general formula: esters, difatty acid esters of alkyldiethanolamines, and mixtures thereof,
It is desirable from the viewpoint of antistatic effect and film slipperiness, and the amount added is preferably about 0.6 to 1.5 w/w%. General formula: (In the formula, R is an alkyl group having 12 to 18 carbon atoms,
( _R1 is an alkyl group having 11 to 17 carbon atoms) Furthermore, in order to improve the slipperiness of the film, 0.2 w/w% or less of higher fatty acid amides such as oleic acid amide, stearic acid amide, erucic acid amide, etc. May be used in combination with an inhibitor. The antistatic agent and higher fatty acid amide are kneaded into the polypropylene resin by a conventional method. As the thermoplastic resin of the present invention, known coating resins such as vinylidene chloride copolymer, acrylic acid ester copolymer, and vinyl acetate-ethylene copolymer can be used. Among these, vinylidene chloride copolymer is most preferable from the point of view of gas barrier properties, but examples of vinylidene chloride copolymer include vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, and vinylidene chloride-vinyl acetate copolymer. polymer,
Known materials such as vinylidene chloride-acrylic acid ester copolymers and those containing a small amount of tertiary copolymer component are used. Note that the vinylidene chloride content in the vinylidene chloride copolymer is particularly preferably 80 w/w % or more in terms of gas barrier properties and the like. Further, the acrylic acid ester copolymer disclosed in JP-A-52-155633 is also suitably used since it has easy heat-sealability. For coating the thermoplastic resin as described above, an organic solvent solution or an aqueous dispersion thereof is used, and the coating is applied by a known method. In addition, regarding these coatings,
21230, Special Publication Showa 43-16316, Special Publication Showa-46-19876,
Known adhesives disclosed in Japanese Patent Publication No. 43-26085 and Japanese Patent Application Laid-Open No. 48-40828 are used, and these are preferably added to the coating solution or used as an undercoat for the coated surface. Further, commonly used inorganic or organic lubricants, waxes, etc. can be added to these coating solutions. Next, the present invention will be explained in more detail with reference to Examples. Example 1 (1) Production of biaxially oriented polypropylene film containing an antistatic agent First, 100 parts by weight of powdered polypropylene with an n-heptane extraction residue of 96 w/w% and a melting index of 2.0 was mixed with silica (trade name: Thyroid) as an inorganic lubricant. 244) Composition (A) to which 0.06 parts by weight and 1.0 parts by weight of N-stearyldiethanolamine monostearate as an antistatic agent were added, and 0.06 parts by weight of silica and 1.0 parts by weight of N-stearyldiethanolamine monostearate based on the powdered polypropylene. 1 part by weight, and a composition (B) containing 0.2 parts by weight of stearamide as an organic lubricant. After supplying these resin compositions (A) and (B) to an extruder with a diameter of 65 m/mφ connected to a T-die,
It was melted at 280°C and extruded onto a polishing roll at 35°C to obtain an unstretched film with a thickness of 800 μm. This was stretched in the longitudinal direction using a roll stretching machine at a stretching temperature of 140°C and a stretching ratio of 5, and then laterally stretched in a tenter at a stretching temperature of 160°C and a stretching ratio of 7, and then heat set with the film width fixed. After getting old,
The ears at both ends were cut to obtain a film with a thickness of approximately 20 μm. (2) Corona discharge treatment of the surface coated with vinylidene chloride copolymer Corona discharge treatment was carried out under the following conditions under nitrogen gas substitution. A Purity of nitrogen gas used: 99.999v/v%, humidity
0.05%RH or less B Clearance between electrode and film: 1 mm C Processing roll temperature: 60℃ D Applied electrical energy: 15 to 50 W・min/m ² E Oxygen concentration in processing atmosphere: 0.05 to 21 v/v% F Equipment used 1 Oxygen Concentration meter: Beckman “Fieldlab” oxygen concentration meter 2 Generator: Vacuum tube type manufactured by Kasuga Denki Co., Ltd.
45KHz (3) Coating treatment of vinylidene chloride copolymer resin 100 parts by weight of vinylidene chloride-acrylonitrile copolymer resin (vinylidene chloride content 92w/w%),
Chlorinated polypropylene (chlorine content 30w/w%) 1
Parts by weight, reaction product of tolylene diisocyanate and hexanetriol (trade name: Coronate L)
A resin composition consisting of 4 parts by weight of N-stearoyl-aminoethyl-stearate as an organic lubricant and 0.1 part by weight of silica as an inorganic lubricant was added to a mixed solvent of methyl ethyl ketone/toluene (1:1) at 90°C. It was dissolved to make a 20w/w% solution. This solution was applied to a polypropylene film using a gravure roll coater in an amount of 2.5 g/m ² and dried for 30 seconds in a drying zone at 120°C. (4) Corona discharge treatment in air After coating with vinylidene chloride copolymer resin, the uncoated surface of the film that came out of the drying zone was immediately treated with corona discharge in air, and then wound onto a roll. The corona discharge treatment conditions are as follows. A Generator: Vacuum tube type 45K manufactured by Kasuga Electric Co., Ltd.
Hz B Electrode-film clearance: 1 mm C Processing roll temperature: 60°C D Applied electrical energy: 15 to 50 W・min/m ² (5) Method for evaluating the obtained coated film The film obtained in (4) was After being left in an atmosphere of 40°C and 70% RH for 5 days, the following evaluations were performed. A. Antistatic Property (Charge Attenuation Property) Using a rotary star charge honesty meter, the time required for the charge applied to the film to be reduced by half was measured. Neostometer: Startetsu Honestometer (manufactured by Shishido Shokai) Applied voltage: 10KV Application time: 30 seconds Measurement atmosphere: 20℃, 65% RH B Lamination strength To evaluate the adhesive strength between the film and the polypropylene base film, Extrusion laminated with low density polyethylene. The anchoring agent for extrusion laminate is urethane-isocyanate adhesive, and the thickness of the polyethylene is 50 μm. This laminated film was left at room temperature and humidity, and it was boiled in boiling water at 90℃ for 30 minutes.The laminated strength was measured using a Schottspur universal tensile tester at 180° peeling and at a tensile speed of 200°.
Measured in mm/min. (6) Evaluation results Table 1 shows the evaluation results. First, if no antistatic agent is added to the polypropylene base film, even if the coated surface is subjected to corona discharge treatment in air with an oxygen concentration of 21v/v%, as long as the applied electrical energy is 30W.min/ ^m2 or more,
The laminate strength shows a high value at room temperature and humidity, and further increases when boiled in hot water, and the adhesion of the coating to the base film is sufficiently high, but in this case, the uncoated surface remains strong even after corona discharge treatment. Antistatic properties cannot be expected. However, by adding an antistatic agent to the base film, the uncoated surface is exposed to oxygen concentration.
Applied electrical energy 25W in air at 21v/v%
When subjected to corona discharge treatment at a concentration of min/m ² or more, the half-life of the honest meter is 200 seconds or less, showing good antistatic properties with no practical problems. v% air, the applied electrical energy is 30W・min/
m ² or more, the lamination strength is significantly lower than that without the antistatic agent added at room temperature and humidity, and furthermore, when boiled in hot water at 90° C., adhesiveness is completely lost. From these results, it is clear that the antistatic agent inhibits the adhesion between the coating and the base film. However, when the oxygen concentration in the atmosphere in which the coated surface is treated with corona discharge is reduced by nitrogen gas replacement,
The laminate strength gradually increases, and the oxygen concentration increases.
At 0.3v/v% or less, it became possible to obtain laminate strength comparable to that without the addition of antistatic agent. If the lamination strength is 100 g/cm or more, the film can be used practically without any problems. As described above, by subjecting the coated surface of a polypropylene film containing an antistatic agent to a corona discharge treatment in a substantially nitrogen atmosphere with an oxygen concentration of 0.3v/v% or less, it is possible to As a result, the adhesion of the film increased at normal temperature and humidity, and a large adhesion was obtained even during boiling. Furthermore, by subjecting the non-coated surface to a corona discharge treatment in air, a film having antistatic properties on the non-coated surface could be obtained.

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[Table] Example 2 (1) Preparation of biaxially oriented polypropylene film containing antistatic agent The same method as in Example 1 was performed except that the addition of the antistatic agent and organic lubricant was changed as follows. Antistatic agent N-stearyldiethanolamine distearate 1.0 parts by weight Organic lubricant Erucic acid amide 0.2 parts by weight (2) Corona discharge treatment of vinylidene chloride copolymer coated surface The same method as in Example 1 was performed. (3) Coating treatment of vinylidene chloride copolymer resin Performed in the same manner as in Example 1 except that vinylidene chloride-vinyl chloride copolymer resin (vinylidene chloride content 90 w/w%) was used as the vinylidene chloride copolymer resin. Summer. (4) Corona discharge treatment in air The same method as in Example 1 was used. (5) Evaluation method The same method as in Example 1 was used. (6) Evaluation results Table 2 shows the evaluation results.

[Table] Regarding the antistatic properties on the uncoated surface, a good film with an honest meter half-life of 200 seconds or less with no practical problems was obtained when the applied electrical energy was 35 W min/m ² or more. In addition, the adhesion between the coating and the base film can be improved by making the atmosphere during the corona discharge treatment of the coated surface a substantially nitrogen atmosphere with an oxygen concentration of 0.3v/v% or less. A good film with no practical problems was obtained. Example 3 In order to further prove the effectiveness of the present invention, the adhesion to a heat-sealable polymer coating that imparts heat-sealability to polypropylene film was evaluated. (1) Preparation of biaxially oriented polypropylene containing an antistatic agent The type and amount of the antistatic agent and organic lubricant added were the same as in Example 2, and the process was otherwise the same as in Example 1. (2) Corona discharge treatment of the surface coated with easily heat-sealable polymer This was carried out in the same manner as in Example 1. (3) Application of easily heat-sealable polymer A Application of acrylic ester copolymer Acrylic ester copolymer (methyl methacrylate/ethyl acrylate/
An aqueous dispersion (20w/w% liquid) of methacrylic acid = 55/36/9) was applied using the air knife method so that the coating amount after drying was 1g/m2, and 1g/ ^m2 was applied in a drying zone at 100℃. Dry for a minute. B Application of vinyl acetate polymer Vinyl acetate polymer aqueous dispersion (30w/w% liquid)
0.5w/w% polyethyleneimine was added to the solid content, and this was applied using the air knife method so that the coating amount after drying was 1g/ ^m2 ,
Dry for 1 minute in a drying zone at 100°C. (4) Corona discharge treatment in air The same method as in Example 1 was used. (5) Evaluation method The adhesion between the coated film and the polypropylene film was evaluated using a cellophane tape test and heat seal strength. A. Cellophane tape test A 24 mm wide pressure-sensitive adhesive cellophane tape was firmly attached to the coated surface, then the tape was suddenly peeled off at a 90° angle and the state of peeling of the coated film was observed. We graded the results. Peeling of the film Not at all...Excellent Peeling area of the film 10% or less...Good 10% to 20%...Possible 20% or more...Poor B Heat seal strength Align the coated surfaces of the film with a bar type heat sealer. Heat sealing was performed under the conditions of a heater temperature of 120°C, a crimping pressure of 0.5 Kg/cm ² , and a crimping time of 0.5 seconds.The heat seal was then pulled from a sample of 15 mm width x 100 mm length using a tensilon at a tensile speed of 100 mm/min. Peel strength was measured. (6) Evaluation results Table 3 shows the evaluation results for the acrylic ester copolymer coated film, and Table 4 shows the evaluation results for the vinyl acetate polymer coated film. By subjecting a polypropylene film containing an antistatic agent to a corona discharge treatment in a substantially nitrogen atmosphere with an oxygen concentration of 0.1 v/v%, the adhesion of the acrylic ester copolymer and vinyl acetate polymer film was improved. , and a coated film with good heat sealability could be obtained.

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Claims (1)

[Claims] 1 One side of a polyolefin in-film containing an antistatic agent is subjected to corona discharge treatment in a nitrogen atmosphere with an oxygen concentration of 0.3V/V% or less, this side is coated with a thermoplastic resin, and the other side is subjected to corona discharge treatment in air. A method for producing a thermoplastic resin-coated polyolefin film, characterized by: