JP2015172099A - Polypropylene-based film, production method thereof, and laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene-based film that is bondable without using adhesive, and is thermally fusible at a relatively low temperature of not more than a melting point.SOLUTION: A polypropylene-based film surface (adhesive surface) is subjected to low-temperature plasma processing by a plasma processing machine 1 of an internal electrode type. Processing strength (E-value) in this case is in a range of 150 W min/m2 to 1200 W min/m2. A value (O/C) of a composition ratio of the number of oxygen atoms (O) and the number of carbon atoms (C) in the film surface after the plasma processing is in a range of not less than 0.1 and not more than 0.5.

Description

  The present invention relates to a polypropylene film that can be heat-sealed at a temperature below the melting point, a method for producing the same, and a laminate using the polypropylene film.

  For example, as a film for food packaging such as a snack confectionery bag, a so-called dry laminate product in which a polypropylene film and a polyester (PET) film are bonded together with an adhesive is used. For example, Patent Document 1 discloses a technique for performing ultraviolet treatment in order to improve the adhesiveness and the like of a polypropylene resin composition.

JP-A-8-41226

  Conventionally, it was considered difficult to heat-seal a polypropylene film at a temperature below the melting point (for example, 165 ° C.). Therefore, in order to obtain a laminated film including a polypropylene film, an adhesive is generally used. It was used. On the other hand, in order to realize cost reduction and the like, it is desired that the polypropylene film can be heat-sealed at a relatively low temperature below the melting point without using an adhesive. In addition, since a biaxially stretched polypropylene film has a thickness of about 80 μm at most and cannot be produced with a large thickness, it is desirable to bond a plurality of biaxially stretched polypropylene films in order to obtain a large thickness.

  The present invention has been made in view of the above circumstances, and the object thereof is a polypropylene film that can be bonded without using an adhesive, and that can be heat-sealed at a relatively low temperature below the melting point, and a method for producing the same, and And providing a laminate using the polypropylene film.

  In order to achieve the above-mentioned object, that is, the present inventor conducted various tests and researches in order to impart heat-fusibility at a relatively low temperature without using an adhesive in a polypropylene film. As a result, it has been found that heat-fusibility at a relatively low temperature below the melting point can be imparted by performing low-temperature plasma treatment on the film surface to accomplish the present invention. .

  That is, the polypropylene-based film of the present invention is characterized in that the film surface is subjected to low-temperature plasma treatment so that heat fusion can be performed at a temperature below the melting point (invention of claim 1). As a result, it is possible to perform heat fusion between the same kind of films or metal foils or different kinds of plastic films at a low temperature below the melting point (165 ° C.), for example, 120 to 140 ° C. without using an adhesive. is there. This is because low temperature plasma treatment is performed on the film surface, oxygen atoms are taken into the film surface, specifically, COOH groups and OH groups are added to the film surface. It is presumed that the polypropylene film is imparted with low temperature heat-fusibility.

  Moreover, it became clear that the average surface roughness Ra after the plasma treatment is smaller in the polypropylene film of the present invention than in the untreated one. Furthermore, in the polypropylene film of the present invention, it has also been clarified that the effect of being able to be heat-sealed at a temperature below the melting point is maintained over a long period (several years to several tens of years).

  The polypropylene film in the present invention may be a homopolymer having a melting point of around 165 ° C. obtained by polymerizing propylene alone, a random copolymer or terpolymer obtained by copolymerizing ethylene or butene, and the like. . In this case, the film may contain, for example, additives for improving properties such as durability and adhesion (such as organic or inorganic fillers), and may be pure without them. Of course.

  The low temperature plasma treatment in the present invention means that the substrate to be treated is exposed to a discharge that starts and continues by applying a high voltage of direct current or alternating current between electrodes, for example, corona discharge under atmospheric pressure or glow discharge in vacuum. Refers to the processing performed by At this time, although not particularly limited, processing in a vacuum with a wide selection of processing gas is preferable. Although it does not specifically limit as process gas, He, Ne, Ar, nitrogen, oxygen, a carbon dioxide gas, air, water vapor | steam etc. are used in the state of individual or mixed. Especially, water vapor and oxygen were able to obtain particularly good results. The treatment pressure is not particularly limited, but glow discharge treatment that sustains discharge in a pressure range of 0.1 Pa to 1330 Pa, so-called low temperature plasma treatment, is preferable in terms of treatment efficiency. More preferably, it is in the range of 1 Pa to 266 Pa.

  In the present invention, more specifically, the composition ratio value (O / C) between the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface subjected to the low temperature plasma treatment is 0. By being set to 1 or more and 0.5 or less, good heat-fusibility can be imparted (invention of claim 2).

  Here, the composition ratio refers to the value (O / C) of the ratio between the number of carbon atoms (C) and the number of oxygen atoms (O) measured on the film surface by XPS (X-ray electron light spectroscopy). In this case, since the molecular formula of polypropylene is (C3H6) n, oxygen atoms should not originally exist, but it is considered that oxygen atoms were added by the low temperature plasma treatment as described above. According to the study of the present inventor, when the composition ratio value (O / C) is 0.1 or more and 0.5 or less, it is possible to obtain good heat-fusibility at low temperatures. did it. When the composition ratio is less than 0.1, good heat-fusibility at low temperatures cannot be obtained, and when it exceeds 0.5, good heat-fusibility at low temperatures cannot be obtained. It was. More preferably, it is 0.25 or more and 0.4 or less.

  As a method for producing the polypropylene film as described above, a method can be adopted in which the surface of the polypropylene film is subjected to a low temperature plasma treatment with an internal electrode type low temperature plasma treatment machine (the invention of claim 3). ). Thereby, the polypropylene film which has the heat-sealing property in the comparatively low temperature below melting | fusing point can be manufactured easily.

  At this time, in the case where low temperature plasma processing is performed using an internal electrode type plasma processing machine, the processing strength (E value) of the low temperature plasma processing for the polypropylene film is set to 150 W · min / m 2 to 1200 W · min. / M @ 2 is preferable (Invention of Claim 4). Thereby, the favorable heat-sealing property in the comparatively low temperature below melting | fusing point is obtained. More preferably, it is in the range of 250 W · min / m 2 to 1000 W · min / m 2.

  The laminate according to the present invention is characterized in that the polypropylene film according to claim 1 or 2 and a dissimilar material are bonded together by thermal fusion (invention of claim 5). At this time, as the dissimilar material, a dissimilar plastic film such as metal foil, glass, ceramics, or a biaxially stretched saturated polyester film can be employed (invention of claim 6).

  According to this, since the polypropylene-based film has a heat-sealing property at a relatively low temperature below the melting point, the polypropylene-based film and the dissimilar material are, for example, 120 ° C. to 140 ° C. without using an adhesive. Bonding can be performed at a relatively low heating temperature of ° C. In this case, for example, since an organic solvent-based adhesive or the like is not necessary, facilities and processes for recovering the solvent are not required for environmental protection, and it is possible to obtain advantages such as easy recovery and regeneration of the film. .

  By the way, for example, since a biaxially stretched polypropylene film has a relatively thin thickness (about 80 μm), there is a situation where a single biaxially stretched polypropylene film cannot obtain a target thickness. Therefore, the laminate of the present invention can be configured to have an arbitrary thickness by laminating a plurality of the polypropylene-based films according to claim 1 or 2 by heat-sealing (the invention of claim 7). ). Thereby, since the polypropylene-based film has heat fusion properties at a relatively low temperature below the melting point, a plurality of films can be relatively bonded to each other, for example, at 120 ° C. to 140 ° C. without using an adhesive. Bonding can be performed at a low heating temperature. A thick sheet (plate) of a polypropylene film can be obtained by bonding a large number of the same type of polypropylene film.

  The method for obtaining the laminate of the present invention is not particularly limited, and a known method such as a method using a hot press or a method using a hot roll may be appropriately selected according to the purpose. Thereby, each above-mentioned laminated body can be manufactured easily. In addition, surface treatment (corona treatment, etc.) for improving adhesion to the dissimilar material (metal foil or dissimilar plastic film) or the surface of the same kind of film (lamination surface) ) Or having a surface treatment layer. In the case of a metal foil, a rust prevention treatment can be applied.

  According to the polypropylene film of the present invention, the method for producing the same, and the laminate, the film surface of the polypropylene film can be joined without using an adhesive because of the low-temperature plasma treatment, and the comparison is below the melting point. It has an excellent effect that heat fusion is possible at a low temperature.

The figure which shows embodiment of this invention and shows the structure of a low-temperature plasma processing machine typically Figure showing the results of the 180 ° C peel strength test The figure which shows the relationship between the processing intensity (E value) of low temperature plasma processing, and the value (O / C) of a composition ratio

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in Table 1 which will be described later, Examples 1 to 6 are polypropylene-based films according to the present invention, and have the structure as described in the claims, and the claims. It was manufactured by the manufacturing method as described in 1. Examples 1 to 6 are made of, for example, a non-filler biaxially stretched polypropylene film having a thickness of 60 μm, and the surface (adhesion surface) is subjected to low-temperature plasma treatment. The surface to be subjected to the low temperature plasma treatment may be one side or both sides of the film.

  At this time, the polypropylene films of Examples 1 to 6 have a composition ratio value (O / C) between the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface after the plasma treatment. It exists in the range of 0.1 or more and 0.5 or less. The value of this composition ratio means the value (O / C) of the ratio between the number of carbon atoms (C) and the number of oxygen atoms (O) measured on the film surface by XPS (X-ray electron light spectroscopy).

  In these Examples 1 to 6, the surface of the biaxially stretched polypropylene film was subjected to low-temperature plasma treatment by changing the treatment strength (E value) with the internal electrode type low-temperature plasma treatment machine 1 as described later. Is. The processing intensity (E value) in this case is in the range of 150 W · min / m 2 to 1200 W · min / m 2, and in the order of Example 1 to Example 6, 200, 390, 490, 670, 850, 1080 (W · min / m @ 2).

  Here, FIG. 1 schematically shows a state in which the low temperature plasma processing is performed on the polypropylene film F by the internal electrode type low temperature plasma processing machine 1. The low-temperature plasma processing machine 1 is configured to have a process chamber 2 that can be sealed, and a processing roller 3 is provided in the processing chamber 2, and an upper portion of the processing roller 3 is surrounded by the processing chamber 2. An electrode 4 is provided so as to surround a slight gap. A high frequency power source 5 is connected to the electrode 4 and, although not shown, the processing roller 3 is grounded. The inside of the processing chamber 2 is depressurized by opening the valve 6 connected to the vacuum pump, and the processing gas is discharged to the processing (discharge) portion by opening the valve 7 connected to the gas supply source. (E.g. CO2) is supplied. A pressure gauge 8 for measuring the pressure in the processing chamber 2 is also provided.

  Then, the unprocessed polypropylene film (raw material) F wound in a roll shape is drawn out from the supply unit 9 and guided around the processing roller 3 while being guided by the plurality of guide rollers 10 in the processing chamber 2. After being processed in the vicinity of the electrode 4 so as to be wound, the plasma processing is performed here, and then the winding portion 11 is wound again while being guided by the guide roller 10. In the present embodiment, for example, the pressure in the processing chamber 2 is 35 Pa, the supply amount of gas is 20 cc / min, and the feeding speed of the film F is 2 m / min.

  Thereby, as for the polypropylene film of Example 1- Example 6, the value (O / C) of the composition ratio of the number of oxygen atoms (O) and the number of carbon atoms (C) of the film surface after a plasma treatment is in order. , 0.2, 0.25, 0.31, 0.35, 0.27, and 0.45. These polypropylene films of Examples 1 to 6 are the same kind of films or metal foils or different kinds of plastic films at a low temperature below the melting point (165 ° C.), for example, 120 to 140 ° C., without using an adhesive. It became possible to heat-seal.

  In this case, since the molecular formula of polypropylene is (C3H6) n, there should be essentially no oxygen atoms on the film surface, but oxygen atoms are taken into the film surface by the low temperature plasma treatment. It is thought that a COOH group or an OH group was added to the above. And as mentioned above, it is presumed that oxygen atoms were taken into the film surface, thereby giving the polypropylene film heat fusion at a low temperature.

  On the other hand, Comparative Example 1 to Comparative Example 4 do not perform low-temperature plasma treatment on the polypropylene film equivalent to the example, or perform plasma treatment with a treatment strength outside the above range. It is out of range. Of these, Comparative Example 1 does not perform the low-temperature plasma treatment. In Comparative Examples 2 to 4, low-temperature plasma processing is performed by the low-temperature plasma processing machine 1, and the processing intensity (E value) is set to 120, 1330, and 1960 (W · min / m 2) in this order. . Thereby, as for the polypropylene film of the comparative example 1-the comparative example 4, the value (O / C) of the composition ratio of the number of oxygen atoms (O) and the number of carbon atoms (C) of a film surface is 0, 0.00 in order. 03, 0.55, and 0.62.

  Now, in order to verify the suitability of the present invention, the present inventor conducted a 180 ° C. peel strength test for examining the adhesive strength of the polypropylene films of Examples 1 to 6 and Comparative Examples 1 to 4 described above. In conducting the test, a biaxially stretched polyester film as an adherend, for example, a PET film having a thickness of 100 μm, is used as the adherend in each of the films of Examples 1 to 6 and Comparative Examples 1 to 4 (thickness 60 μm) without using an adhesive. The laminated film (laminated body) was laminated by heat fusion.

  As the bonding conditions, for example, a heat roller is used. In this case, the surface temperature of the heat roller is 130 ° C., the feed rate is 0.5 m / min, and the linear pressure is 2.5 kg / cm. Moreover, the plasma processing for improving adhesiveness is also performed to the surface of the adherent PET film. Each laminated film is a sample cut to a width of 10 mm and a length of 120 mm, and for each of these samples, the end of the lower PET film and the end of the upper polypropylene film are respectively used using a Tensilon tester. Clamping was performed, and a 180 ° C. peel strength test (peel strength test) was performed at a tensile speed of 100 m / min.

  The results of the 180 ° C. peel strength test are shown in Table 1. In addition, in the table, the evaluation items for practicality are as follows: “Good” (2.0 N / cm or more) for a circle “◯”, Normal (0.7 N / cm or more and less than 2.0 N / cm) for a triangle “ “△”, impossibility (less than 0.7 N / cm) and impossibility of evaluation “×”. Further, this result is shown by a bar graph in FIG.

  As is clear from these results, the polypropylene films of Examples 1 to 6 which were subjected to low-temperature plasma treatment at an appropriate treatment strength on the film surface were deposited at a low temperature (130 ° C.) below the melting point (165 ° C.). Heat fusion with the body (PET film) was possible, and high peel strength (adhesive strength) could be obtained. In this case, the value (O / C) of the composition ratio between the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface is in the range of 0.1 to 0.5, so It is presumed that good heat-fusibility at a relatively low temperature was imparted.

  On the other hand, the value (O / C) of the composition ratio between the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface is out of the range of 0.1 to 0.5. In the polypropylene film No. 4, good heat-fusibility was not obtained.

  Further, FIG. 3 shows the processing strength (E value) of the low-temperature plasma treatment for the polypropylene film and the composition ratio value (O / C) between the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface. The test result which investigated the relationship is shown. In this case, the case where CO2 and Ar are employed as the processing gas is shown. Also from this result, in order to set the composition ratio value (O / C) on the film surface to an appropriate value, it is desirable that the treatment intensity (E value) of the low temperature plasma treatment is within a relatively low predetermined range. Can understand. Even if the treatment strength (E value) is increased, it does not lead to an improvement in heat-fusibility.

  In addition to the above-described PET film, the polypropylene film of the present invention can be heat-sealed at a relatively low temperature with the same type of polypropylene film and different materials such as metal foil, glass, ceramics, or another plastic film. It has been confirmed that various laminates can be obtained. Not only the lamination of two sheets but also the lamination of a film of three layers (three kinds) or more is possible. A thick polypropylene film (sheet) can also be obtained by laminating a large number of the same type of polypropylene film by heat fusion.

  In the above-described embodiment, the polypropylene film and the adherend are heat-sealed using a hot roll, but can be heat-sealed using a hot press machine. It is also possible to adopt the method by. The heating temperature at this time is not limited to 130 ° C, and an appropriate temperature can be selected in the range of 120 to 140 ° C. In addition, various modifications can be made to the configuration of the low-temperature plasma processing machine, and the present invention can be implemented with appropriate modifications within a range not departing from the gist.

  In the drawings, 1 is a low-temperature plasma treatment machine, 2 is a treatment chamber, 4 is an electrode, and F is a polypropylene film.

Claims (7)

  A polypropylene-based film characterized in that the film surface is subjected to low-temperature plasma treatment, so that heat fusion can be performed at a temperature below the melting point.   The composition surface ratio (O / C) of the number of oxygen atoms (O) and the number of carbon atoms (C) on the film surface subjected to the low-temperature plasma treatment is 0.1 or more and 0.5 or less. The polypropylene-based film according to claim 1, wherein: A method for producing a polypropylene film according to claim 1 or 2,
A process for producing a polypropylene film, characterized in that the surface of the polypropylene film is subjected to a low temperature plasma treatment with an internal electrode type low temperature plasma treatment machine.   4. The method for producing a polypropylene film according to claim 3, wherein the intensity (E value) of the low temperature plasma treatment in the low temperature plasma treatment machine is in the range of 150 W · min / m 2 to 1200 W · min / m 2.   A laminate comprising the polypropylene film according to claim 1 and a different material bonded together by heat fusion.   6. The laminate according to claim 5, wherein the dissimilar material is a dissimilar plastic film such as metal foil, glass, ceramics or a biaxially stretched saturated polyester film.   A laminate comprising a plurality of the polypropylene-based films according to claim 1 or 2 bonded together by heat fusion.

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