JP4332786B2 - Heat-sealable polypropylene film and method for producing the same - Google Patents

Description

  The present invention is excellent in low-temperature heat-sealability with little odor and elution of additives and deteriorated substances and less migration, which are preferably used in fields where clean packaging materials and containers such as food, medical and electronic materials are required. In particular, the present invention relates to a heat-sealable polypropylene film having small thickness spots and a method for producing the same.

  Polypropylene films are excellent in low-temperature heat sealability, tear strength, impact resistance, transparency, heat resistance, and the like, and are used in a wide range of fields as packaging materials and containers for food, medicine, electronic materials, and the like. In recent years, with the maturity of society, in the above-mentioned fields, market requirements have become extremely advanced with regard to odor, elution and migration of additives and deteriorated products, and so-called clean materials with improved properties are strongly strengthened. I'm waiting. Polyolefin resins such as polypropylene are inferior in stability, such as thermal stability, to polyester resins and the like, and various stabilizers such as antioxidants are blended for the purpose of improving these. The stabilizer is useful in terms of expressing the intended effect, but the stabilizer itself or its degradation product causes odor or contamination of the packaging object, and a resin not containing these stabilizers is used as a raw material. There is a need for molded bodies.

  In response to the above market requirements, for example, high-pressure low-density polyethylene is used for paper containers and packaging materials that are packaging materials for milk, dairy products, etc., as packaging materials that comply with the Ministerial Ordinance Notification No. 52, etc. It has been. However, the high-pressure method low-density polyethylene has a problem that heat resistance, waist strength and the like are inferior. The development of a clean molded body made of polypropylene that can satisfy these characteristics has been desired. Recently, there has been a demand for a clean molded body in the field of electronic materials for masking applications. However, since polypropylene has a higher molding temperature than the high-pressure method low-density polyethylene, it is necessary to add an antioxidant for preventing deterioration of the resin, and the catalyst residue is a halogen element such as chlorine. Therefore, since it is necessary to add a halogen absorbent (acid neutralizer) such as calcium stearate and hydrotalcite, there is a problem in the migration of odors and contaminants.

A linear low density polyethylene resin in which specific parameters are optimized, additive is not blended, the amount of the halide is reduced, and the additive does not substantially transfer to the contacted object, and clean molding using the resin as a raw material The body is disclosed (for example, refer patent documents 1-4).
JP 2001-342306 A JP 2002-52669 A JP 2003-64191 A JP 2003-341249 A

  However, these methods are formed by the inflation method or the extrusion laminating method, and the thickness unevenness of the film is large. On the other hand, it is necessary to extrude at 210 to 270 ° C. with respect to the film forming temperature of 160 to 200 ° C., which is the film forming temperature of the above-mentioned inflation method, in order to obtain a product with a small thickness variation, and an additive is contained When a raw material resin not used is used, the stability of the resin is inferior, and the odor due to deterioration is strong and the market demand cannot be satisfied. The inflation method requires a high extrusion viscosity for stabilization of balloon formation, and is generally advantageous in obtaining a clean molded product because it is extruded at a low temperature, but has the problem that the thickness unevenness of the film becomes large. ing. On the other hand, in the T-die method, when high melt viscosity extrusion is performed at a low temperature, flow spots are likely to occur and the thickness spots are increased, and thus extrusion molding is performed at a high temperature. For this reason, the above market requirements are not answered.

  In addition, all of the above-described known techniques relate to polyethylene resins, and it has been difficult to apply them to fields that require high heat resistance.

  The present invention was made against the background of the problems of the prior art, has good heat resistance, excellent heat sealability, less odor and elution and migration of additives and deteriorated products, and food with small thickness spots, An object of the present invention is to provide a heat-sealable polypropylene film suitably used in fields where clean packaging materials such as medical and electronic materials, containers and the like are required, and a method for producing the same.

  As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention is a heat-sealable film made of a polypropylene-based resin whose main constituent is polypropylene that does not contain an additive that migrates to an object to be contacted, and the thickness unevenness in the width direction of the film is within 10%. It is a heat-sealable polypropylene film characterized by being. In the T-die extrusion film formation, the heat-sealable polypropylene film production method is characterized in that a T-slot die is used.

  The heat-sealable polypropylene film of the present invention has properties of polypropylene film such as sealability and heat resistance, and is made from a resin not containing an additive such as an antioxidant as a raw material. There are few odors, elution, migration, etc. due to additives such as inhibitors and their degradation, and the contamination of the contacted objects is suppressed, and the thickness unevenness is small, so clean packaging materials such as food, medical and electronic materials, It can be suitably used in fields where containers and the like are required. In addition, the production method of the present invention has an advantage that the high-quality heat-sealable polypropylene film can be produced stably and economically.

Hereinafter, the present invention will be described in detail.
The polypropylene resin used in the present invention is not limited as long as it has a polypropylene structure as a main component, and may be any of a homopolymer, a copolymer, and a mixture thereof. The copolymer may be random, block or graft. The copolymerization component in the case of the copolymer is not limited, and examples thereof include lower α-olefins such as ethylene, butene, heptene, hexene, octene and methylpentene, and dienes such as butadiene and isoprene. In the case of a copolymer, it may be a binary system with the component or a multi-element system of a ternary system or higher. The stereoregularity is not limited, and any of isotactic, syndiotactic and atactic can be used. What is necessary is just to select suitably according to the required characteristic of a market.
The density is preferably 870 to 912 kg / m ³ . Furthermore, the density is preferably 880 to 905 kg / m ³ . If the density is less than 870 kg / m ³ , rigidity, heat resistance and blocking resistance are lowered, which is not preferable. Conversely, when the density exceeds 912 kg / m ^{3, the} low temperature heat sealability is deteriorated, which is not preferable. Moreover, it is preferable to use a melt mass flow rate (hereinafter referred to as MFR) within a range of 1 to 100 g / 10 minutes (230 ° C.).
The thing of the range of 2-50 g / 10min (230 degreeC) is more preferable, More preferably, it exists in the range of 5-20 g / 10min (230 degreeC). If the MFR is less than 1 g / 10 min (230 ° C.), the melt viscosity becomes high in film molding, the load on the motor of the extruder increases, and the thickness accuracy of the film decreases, which is not preferable. On the other hand, if it exceeds 100 g / 10 min (230 ° C.), the melt viscosity becomes too low and film formation becomes difficult, and the mechanical properties of the obtained film deteriorate, which is not preferable.

  The method for producing the above polypropylene resin is not particularly limited, and for example, a so-called metallocene catalyst such as a Ziegler-Natta catalyst or a cyclopentadienyl metal compound or a complex catalyst such as a nonmetallocene complex is used. , Solution polymerization method, slurry polymerization method, bulk polymerization method, gas phase polymerization method, and the like.

  In the present invention, it is important that the polypropylene-based resin does not contain an additive that shifts to a contacted object. That is, those that are not blended with migratory additives composed of relatively low molecular weight organic substances such as antioxidants, lubricants, neutralizers, antistatic agents, processability improvers, ultraviolet absorbers, and antifogging agents, Or even if this additive is mix | blended, it is necessary for this mix | blended additive to transfer to the to-be-contacted object, such as the content, and to have the quantity which does not have a bad influence with respect to odor and taste.

The standard as the amount is that the [odor evaluation] value is 120 or less in the odor evaluation described below. In this case, 100 or less is preferable, and 80 or less is particularly preferable.
[Odor evaluation]
The measurement environment is 23 ° C. A hot-wire semiconductor gas sensor (manufactured by Keyence: NS720, NS710) is used as a portable odor sensor. After completion of the instrument adjustment, place the sensor in a flask containing the sample to be measured and read the value after 2 minutes.
The sample for evaluation is an A4 size film cut in the flow direction, divided into 16 pieces in the flow direction and put into a 400 ml flask, covered with an aluminum foil at the mouth, and heated at 60 ° C for 30 minutes. After heating with a circulating hot air dryer (model: 102.S.01), the sample is allowed to stand at 23 ° C. × 50% RH × 2 hours and then measured.

For example, antioxidants include 2,6-di-t-butyl-p-cresol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, n- Phenol stabilizer represented by octadecyl-3- (4′-hydroxy-3,5′-di-t-butylphenyl) propionate, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite And phosphite stabilizers represented by the above.
Examples of the lubricant include higher fatty acid derivatives represented by higher fatty acid amides and higher fatty acid esters.
Examples of the catalyst residue neutralizing agent include fatty acid metal salts such as calcium stearate and hydrotalcite.
Examples of the antistatic agent include hydrophilic compounds represented by glycerin esters, sorbitan acid esters, polyethylene glycol esters, and the like of fatty acids having 8 to 22 carbon atoms.
Examples of the processability improver include fatty acid metal salts such as calcium stearate.
Examples of UV absorbers include organic UV absorbers typified by 2-hydroxybenzophenone, 2-hydroxyphenylbenzotriazole, salicylate, and cyanoacrylate. Examples of antifogging agents include glycerin fatty acid ester and sorbitan. Examples include hydrophilic compounds typified by fatty acid esters, polyoxyethylene fatty alcohol ethers, polyethylene glycol fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.
Therefore, an additive that elutes to the outside, for example, when the contents are liquid, an additive that elutes into the liquid, an additive that migrates odors, or the film surface over time. Due to the fact that additives that are unevenly distributed are not contained in the resin, for example, when used as a packaging material or container for food, it is hygienic with little change in odor and taste, and it is also used for packaging medical and electronic materials. When used as a material or container, a clean film that does not contaminate the contents can be obtained.

Among polyolefin resins, polypropylene resins have poor oxidation resistance stability because the propylene skeleton contains tertiary hydrogen, and the above-mentioned antioxidant is indispensable. However, in recent years, the progress of the polymerization catalyst technology for polypropylene resins has made it possible to significantly reduce the amount of residual catalyst in the resin. It has become possible to dramatically improve the properties without having to add the above-mentioned antioxidant.

  In the present invention, an additive that does not substantially transfer to an object to be contacted may be added within a range that does not substantially impair the properties of the clean film of the present invention. Examples include inorganic fillers and fillers made of organic, inorganic, and inorganic / organic hybrid polymers. Inorganic fillers include silica, calcium carbonate, talc, clay, kaolin, alumina, aluminum hydroxide, magnesia, magnesium hydroxide, calcium sulfate, calcium sulfite, barium sulfate, aluminum silicate, calcium silicate, sodium silicate, potassium silicate, carbonic acid Examples thereof include magnesium, barium carbonate, calcium oxide, titanium oxide, zinc oxide, mica, glass flake, zeolite, diatomaceous earth, perlite, fly ash, and glass beads. Examples of the filler made of an organic polymer include those made of polymethylmethacrylate cross-linked resin, polyester cross-linked resin, phenol resin, powders of other synthetic resins, fine beads, and the like. Examples of the filler made of an inorganic polymer include those made of a silicone resin, and examples of the filler made of an organic / inorganic hybrid polymer include those made of a composite resin of silicone and an organic polymer.

  The roll characteristics of the film obtained by improving the slipperiness of the film and the workability when using the obtained film can be improved by blending the filler.

  In the present invention, a resin comprising ultra-low density polyethylene, linear low-density polyethylene, high-pressure polyethylene, ultra-high molecular weight polyethylene, olefin-based elastomer and the like is within a range not departing from the gist of the present invention. It is also recommended as a preferred embodiment to add% to prevent blocking, impart slipperiness, impact resistance or improve heat seal characteristics. As a matter of course, it is preferable to use a resin that does not contain an additive that migrates to a contacted object, as in the case of the polypropylene resin.

  It is also a preferred embodiment to incorporate means such as embossing on the surface of the film for the purpose of improving slipperiness or preventing blocking.

  As the polypropylene resin, resins and resin blends that are commercially available as additive-free grades may be used, or those specially designed so that the effects of the present invention can be expressed more greatly.

In the present invention, it is important that the thickness unevenness in the width direction of the film is within 10%. Within 8% is more preferred, and within 6% is even more preferred. If it exceeds 10%, the tension generated by the tightening phenomenon that occurs when the film is stored in a roll shape will fluctuate in the width direction of the film due to thickness spots, and deformation such as partial sagging of the film will occur. For this reason, in the case of a film with a large thickness unevenness, for example, when used as a laminate material, deformation such as sagging during laminating processing may cause wrinkles and air entrainment, resulting in reduced processing operability, and the resulting product wrinkles. This is not preferable because it may lead to poor appearance such as transparent spots and fluctuations in laminate strength. In recent years, the heat-sealable film is also an important characteristic because the market demand for the thickness unevenness of the film has increased.
In addition, it is preferable that the said thickness variation in this invention is satisfy | filled in the roll whose film width is 400 mm or more and whose film length is 1000 m or more. A film roll having a width of less than 400 mm may be used industrially in some cases, but in many cases, it is of low utility value, and a film roll having a length of less than 1000 m is used in the present invention. The effect is difficult to express. The width of the film roll in the present invention is more preferably 400 mm or more, and further preferably 600 mm or more. The length of the film roll is more preferably 1000 m or more, and further preferably 2000 m or more. The upper limit of the width and winding length of the film roll is not particularly limited, but generally it is 2000 mm or less in width for ease of handling, and the winding length is about 2000 m or less when the film thickness is 150 μm. In addition, the winding core in the present invention refers to a paper tube of 3 inches, 6 inches, 8 inches, or the like, a plastic core, or a metal core that serves as a core of a film roll.

  In the present invention, it is necessary to form a film by the T-die method as described in claim 3. As described above, the conventional T-die film formation has been extruded at a temperature of 200 ° C. or higher. However, in the present invention, it is necessary to use a polypropylene resin that does not contain a stabilizer such as an antioxidant as a raw material. When extrusion molding is performed at a conventionally known temperature, the polypropylene resin undergoes thermal deterioration and is the object of the present invention. Since a clean film cannot be obtained, countermeasures are required. Means for solving this problem is not limited, but as described in claim 4, it is a preferred embodiment that the resin temperature at the die outlet is extruded at 150 to 200 ° C. 155-195 degreeC is more preferable, and 160-190 degreeC is further more preferable. If it is less than 150 ° C., the melt viscosity of the raw material resin becomes too high, and the thickness unevenness of the film that can deteriorate the flow characteristics increases. Conversely, when the temperature exceeds 200 ° C., the deterioration increases, which is not preferable. The resin temperature at the die outlet in the present invention is measured using an infrared thermometer with an accuracy within ± 5 ° C. Examples of the infrared thermometer include IR-CAM type for polyethylene film manufactured by Chino Corporation.

  As an achievement means for molding at the above extrusion temperature, there is a method of increasing the MFR of the raw material polypropylene resin, which is not preferable because the mechanical properties of the obtained film are not satisfied. Therefore, it is necessary to use a MFR of 1 to 100 g / 10 min (230 ° C.), preferably 2 to 80 g / 10 min (230 ° C.), more preferably 5 to 20 g / 10 min (230 ° C.). Using the MFR polypropylene resin, molding at the extrusion temperature of 150 to 200 ° C. can reduce the deterioration, but it is difficult to make the film thickness unevenness within the above range. Therefore, in order to bring the properties of the obtained film within the scope of the present invention, it is essential to improve the thickness unevenness even if extrusion is performed at the above-described extrusion temperature. For this purpose, it is necessary to optimize the film forming machine, particularly the die structure and film forming conditions. The measures are mentioned.

One of the means for achieving the above is optimization of the die shape. Coat hanger dies, which are commonly used in the plastic industry today, had a clamshell problem. This clamshell phenomenon is a deformation of the die in which a large force is applied to the central portion of the die body and the deformation is greater than the end portion of the die. This non-uniform deformation is likely to cause unevenness in thickness because the resin pressure constantly changes due to changes in viscosity and discharge amount. Further, the coat hanger die has a pressure adjustment mechanism in the pre-land portion as a result of the arrangement of the manifold, and has a triangular shape (a shape like a hanger for applying a coat). It is usually impossible to match the change in viscosity at the straight preland portion with respect to the different viscosity of the resin. As a result, there is a problem that a part that is called W pattern and flows early and slows at the die exit is generated and the flow is not uniform. This was the cause of deterioration due to uneven thickness and thermal history. On the other hand, in recent years, a T-slot die has attracted attention as a measure for overcoming the problems of the coat hanger die. The T-slot die is, for example, Gary D.C. Oliver, "Latest Coextrusion Technology and Market Accompanying", Convertech, December 1996, Vol. 24, No. 12, P14-19 and Koyama, "Extrusion Technology for Functional Multilayer Films", Plastic Age, 2003 June, Vol. 49, No. 595, P93-97 and the like.
Characteristic 1 is a linear manifold in which the aspect ratio of the T-slit die is increased, whereby the thickness uniformity can be improved. Furthermore, since a force is uniformly applied to the surface through which the resin flows, a clamshell is not generated. Characteristic 2 is that the pre-land is made up of two steps and the shape of the stepped portion is made curved so that the flow is balanced and uniform throughout the die. It has been improved to be able to. Therefore, it is important to use a T-slot die as described in claim 3.

  Just using the above-mentioned T-slot type die as it is is not effective as a measure for reducing film thickness unevenness, and in the present invention, since the extrusion temperature is low, the shear viscosity of the molten resin in the die slip increases. Additives that are added to the polypropylene resin, such as inorganic fillers that do not dissolve in the resin, are ejected out of the fluid by a die slip and precipitate around the lip mouth to form a stain that is usually referred to as “eyes”. Detrimental effects on thickness spots and contamination. Therefore, it is a preferred embodiment to increase the lip opening of the die in order to solve the problem.

  A manifold with such a large aspect ratio can be extruded uniformly and accurately. The T-slot of this clawlene can be simplified by using a T-slot die that has been devised for higher accuracy, such as a two-stage pre-land. In the prior art, for example, coat hanger type dies, thickness adjustment and quality uniformization with the die were insufficient, so it was necessary to perform thickness adjustment and quality uniformization assistance with the feed block, but it had a complicated shape In the case of the above T slot type die, the flow of the molten resin in the die is made uniform, so that the feed block can be simplified. Since the dead space can be reduced by the simplification, it is effective in reducing thermal degradation.

  It is a preferred embodiment to optimize because the direction of air flow around the T-stood die affects film thickness spots. It is important to eliminate the wind that is the air flow perpendicular to the molten resin sheet coming out of the T-slot die. When this receives a vertical wind in a molten state, the molten resin sheet is shaken, and a thickness change or a partial cooling spot occurs in the shaken part, which leads to a thickness spot. As one of the countermeasures, it is possible to make an enclosure with a sheet, a plate, etc., surround the die and surround the die so that the above-mentioned unfavorable wind does not hit the die outlet. Furthermore, it is also a preferred embodiment to positively create a wind flow that does not disturb the flow of the molten resin sheet at the die outlet.

  Since temperature spots around the T-slot die also affect thickness spots, it is important to make the temperature spots as small as possible. For example, surrounding the die is recommended as a preferred embodiment because it leads to improvement of the phenomenon. Moreover, since a temperature spot becomes small by making it the state which raised humidity with the humidity raised, it is a preferable embodiment.

  Improvement of the adhesion method of the molten resin sheet extruded from the T-slot die to the cooling roll is also an important factor for improving the film thickness accuracy. For example, an air nozzle method, an air chamber method, an air knife method, a vacuum chamber method, or the like is widely used as a method for closely contacting the cooling roll with air, but the above three methods are simultaneously operated as described in claim 5. Is a preferred embodiment. That is, at the time of adhesion of the molten resin sheet to the cooling roll, both ends are fixed by the air nozzle method, and the molten resin sheet is pressed to the cooling roll of the full width by the air chamber method or the air knife method, and the vacuum chamber method is simultaneously applied. The thickness unevenness is reduced by preventing the entrainment of air between the molten resin sheet and the cooling roll. Also in this method, the air knife or air chamber wind is applied uniformly to the molten resin sheet so that the flow is not disturbed, and the vacuum chamber suction force is uniform in the width and flow direction. It is also important to optimize the structure, mounting position, air flow rate and direction of air knife and air chamber, vacuum chamber suction and suction direction, etc. This makes it possible to reduce the deflection of the molten resin sheet, leading to an improvement in thickness accuracy, and is recommended as an effective means.

  The selection of the air chamber method and the air knife method in the contact method may be appropriately selected in relation to the space volume of the place where the apparatus is installed and the performance of the vacuum chamber.

  Although the film formation in the temperature range of the extrusion temperature can suppress thermal deterioration, in the present invention, since the raw material polypropylene resin is not blended with an antioxidant, the extrusion temperature is optimized. It is difficult to stabilize the thermal degradation only with this. Reference will be made to other preferable means for achieving the reduction in thermal degradation.

  The raw material polypropylene resin pellets used in the present invention are preferably used after the inert gas replacement when dried. Oxidation decomposition is suppressed when deoxygenated by inert gas replacement and enters the extruder and melts, leading to reduction of thermal degradation. It is also a preferred embodiment that the hopper of the extruder for film formation and the silo for containing the raw material are replaced with an inert gas so that the oxygen does not enter, so that the raw material is not oxidized. This method has an effect of suppressing the mixing of oxygen into the extruder together with the raw material resin, and leads to the suppression of deterioration in physical properties. Adoption of this measure can not only suppress the deterioration of physical properties but also exhibit the effect of suppressing the generation of degradation products that affect odor and taste. The inert gas used includes noble gas elements such as helium, neon, argon, krypton, xenon, and radon, but it is not practical because it is expensive. Nitrogen gas that is inexpensive and easily available is preferred.

  In recent years, twin screw extruders are often used for the purpose of improving the kneading effect of the raw material blend. However, in the present invention, low temperature extrusion is necessary, and in the twin screw extruder, resin deterioration due to local heat generation is caused. Since this may occur, it is recommended as a preferred embodiment to use an extruder with a single screw. The disadvantages of the single screw are that mixing and kneading defects occur as the screw rotation speeds up, and that proper operation is limited due to an excessive increase in the resin temperature. In order to solve this problem, for example, Sakagami, “Experimental research of mixing screw [2] I. Experimental research of single screw (2)”, Plastic Age, April 2003, Vol. 49, Vol. 593 No., P146-157, the preferred embodiment is the three-stage screw structure. That is, it is preferable to adopt a three-stage screw structure in which a mixing element is provided in the middle portion of the screw, the front is a first stage, the mixing element is a second stage, and the third is a subsequent stage. It is a more preferable embodiment that the mixing and kneading performance is enhanced by the mixing element at the middle part, the groove depth at the tip is deepened to suppress excessive heat generation, the cooling capacity is reinforced, and the extrusion amount is also increased. It is. Even the biaxial type is possible by adjusting the screw design appropriately and is not excluded.

  The recovered raw material is also an important factor for suppressing thermal degradation. In many cases, products, incisions, etc. are reused and mixed with raw materials. A method in which products, cutting waste, etc. are melted into resin pellets. A method of making these products, incisions, etc. into pellets or plates by pressure. A method of forming a pellet in a semi-molten state is known. In the method of melting and pelletizing, since it is melted and pelletized by heat, thermal degradation occurs. The method of forming pellets by pressure is not suitable for soft films, and even when pellets are used, the force to return to the original film shape is strong, and the shape may change over time, and management is difficult. The method of forming a pellet in a semi-molten state is preferable because it is uniform without changing with the passage of time and heat deterioration is unlikely to occur.

In the present invention, as described in claim 2, it is a preferred embodiment that the seal start temperature is 80 to 190 ° C.
90-185 degreeC is more preferable, and 100-180 degreeC is further more preferable. If the sealing start temperature is less than 80 ° C., the blocking resistance is lowered and the suitability for secondary processing is lowered. On the other hand, when the temperature exceeds 140 ° C., the low-temperature sealability is deteriorated, which leads to a decrease in seal strength in high-speed heat seal processing, which is not preferable.

  The film thickness used in the present invention is 5 to 300 μm. Preferably, it is 10-200 micrometers.

  The heat-sealable polypropylene film obtained in the present invention is made from a polypropylene-based resin that does not contain an additive that migrates to an object to be contacted, such as an antioxidant, and is formed by extrusion at a low temperature. Therefore, because the odor, elution and migration due to the additive and its degradation products are low and contamination of the contacted materials is suppressed, fields that require clean packaging materials, containers, etc. for food, medical, electronic materials, etc. Can be suitably used. In addition, when used for food, the effect that the taste change of the food is small can be exhibited. For example, the effect of odor can be quantitatively evaluated by using not only sensory evaluation but also a hot-wire semiconductor gas sensor.

  Next, the present invention will be specifically described using examples and comparative examples. The film properties obtained in each example were measured and evaluated by the following methods.

[Seal start temperature]
The film is sandwiched between polyethylene terephthalate films (12 μm) so that the sealing surfaces face each other, and the sealing surfaces are sealed with a thermal inclined sealer (manufactured by Toyo Seiki Co., Ltd.) at 0.2 MPa × 1 second. The strength (N / 15 mm) at a width of 15 mm is evaluated at a speed of 200 mm / min with a tensile tester (Shimadzu Autograph, model: S-100-D). As polyethylene terephthalate, Toyobo Co., Ltd. product: E5100 (12 micrometers) is used. The seal start temperature is a temperature at which the seal strength reaches 4.9 N (500 g) / 15 mm.

[Thickness spot evaluation]
A film roll wound with a film having a length of 1000 m and a width of 400 mm obtained in Examples and Comparative Examples described later is evaluated according to JIS K7130: 1999. Details of the differences in some methods will be described below. The measurement environment is 23 ° C. × 50% RH room. The measuring instrument to be used has a minimum reading of 0.001 mm. The accuracy shall be equal to or better than the dial gauge specified in JIS B7503: 1997.
Measurement is 15 cm in the above-mentioned film roll MD direction, full width in the TD direction, two portions of the surface layer part peeled off from the wrinkle part and two parts from the winding core part from the wrinkle-free part, about 2 turns, Three samples are taken in succession, and the average value of the six samples is obtained.
Measurement of each sample is performed by cutting 5 cm at both ends of each sample film, dividing the sample with both ends cut into 40 equal parts in the width direction, and marking the measurement positions. The dial gauge is used for the place where the mark portion is removed at the mark position. Thickness unevenness is obtained by the following formula.
Thickness unevenness (%) = (maximum thickness−minimum thickness) ÷ average value of 6 samples × 100

[Die outlet resin temperature]
The resin temperature at the die outlet in the present invention is measured using an infrared thermometer having an accuracy within ± 5 ° C. Five locations equally divided in the width direction of the T die are measured at n = 3, and the average value is obtained. Using an IR-CAM type for polyethylene film manufactured by Chino Co., Ltd., measurement is performed at a position of 10 to 15 cm from the molten resin.

[Odor evaluation]
The measurement environment is 23 ° C. A hot-wire semiconductor gas sensor (manufactured by Keyence: NS720, NS710) is used as a portable odor sensor. After completion of the instrument adjustment, place the sensor in a flask containing the sample to be measured and read the value after 2 minutes.
The sample for evaluation is an A4 size film cut in the flow direction, divided into 16 pieces in the flow direction and put into a 400 ml flask, covered with an aluminum foil at the mouth, and heated at 60 ° C for 30 minutes. After heating with a circulating hot air dryer (model: 102.S.01), the sample is allowed to stand at 23 ° C. × 50% RH × 2 hours and then measured.

[MFR]
According to JIS K 7210: 1999, the evaluation conditions evaluated the viscosity of the raw material resin at 2.16 kg at 230 ° C.

[Resin density]
The density was evaluated according to JIS K 7112: 1999.

[Example 1]
Anti-oxidant, neutralizer, lubricant, antistatic agent and other stabilizers added to ordinary polypropylene resins and additives for imparting functionality such as slipperiness are not added at all Resin density 899kg Using a three-stage type single screw extruder having a screw diameter of 250 mm and a block-copolymerized polypropylene-based resin (rubber amount 12 mass%) of / m ³ and MFR 6 g / 10 min, using a T-slot die having a width of 3000 mm, Extrusion was performed at a resin temperature of 180 ° C. at the die outlet. The molten resin sheet coming out of the die was cooled with a cooling roll at 30 ° C. to obtain a polypropylene film having a thickness of 40 μm. The raw material polypropylene resin was dried by substituting nitrogen gas. The silo and hopper for supplying to the extruder were also replaced with nitrogen gas. When cooling with the cooling roll, both ends of the film on the cooling roll are fixed with an air nozzle, and the entire width of the molten resin sheet is pressed against the cooling roll with an air knife, and at the same time, the vacuum chamber is operated to cool the molten resin sheet and the cooling roll. Air entrainment between rolls was prevented. The die was surrounded by a sheet so that the molten resin sheet was not blown by the wind. Film formation was continuously performed over 1000 m after adjusting the thickness at a speed of 100 m / min.
The obtained film was slit to a width of 1000 mm and a length of 1000 m, and wound on a 3-inch paper tube to obtain a heat-shrinkable film roll.
Table 1 shows the characteristic values of the obtained film.

[Comparative Example 1]
In the method of Example 1, except that the extruder is changed to a single stage type, the die is changed to a coat hanger type, and the close contact with the cooling roll is changed to only the air chamber, so that the enclosure around the die is eliminated. A polypropylene film of Comparative Example 1 was obtained in the same manner as Example 1. Table 1 shows the characteristic values of the obtained film.

[Comparative Example 2]
In the method of Comparative Example 1, a polypropylene film of Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that the extrusion temperature was 240 ° C. Table 1 shows the characteristic values of the obtained film.
[Comparative Example 3]
In the method of Comparative Example 1, a polypropylene film of Comparative Example 3 was obtained in the same manner as Comparative Example 1 except that a resin containing an additive was used as the polypropylene resin. As additives, Irganox 1010: 1500 ppm (manufactured by Ciba Specialty Chemicals), Irgaphos 168: 1000 ppm, (manufactured by Ciba Specialty Chemicals), calcium stearate S: 1000 ppm, (Nippon Oils and Fats) As a lubricant, Armoslip E: 800 ppm (manufactured by Lion Corporation) and Silicia 450: 5000 ppm (manufactured by Fuji Silysia Chemical Co., Ltd.) were added. Table 1 shows the characteristic values of the obtained film.

[Comparative Example 4]
Air-cooled inflation method, Plako extruder (screw diameter 55 mm), resin temperature 190 ° C., film width 300 mm, blow ratio 2.7, single layer extrusion was performed to form a film. The resin used was the same density as in Example 1 with an MFR of 2 g / 10 min. Table 1 shows the characteristic values of the obtained film.

[Example 2]
In the method of Example 1, a polypropylene resin is added to a normal polypropylene resin to provide functionalities such as stabilizers such as antioxidants, neutralizers, lubricants, antistatic agents, and improvement of slipperiness. Except for changing the extrusion temperature to 170 ° C. and the film thickness to 50 μm to a random copolymer polypropylene resin (density 895 kg / m ³ , MFR 6 g / 10 min) copolymerized with 2 mol% of ethylene not added at all. Obtained a polypropylene film of Example 2 in the same manner as Example 1. Table 1 shows the characteristic values of the obtained film.

  The films obtained in Examples 1 and 2 were good in both odor and thickness spots. On the other hand, the films obtained in Comparative Examples 1 and 4 were inferior in thickness spots, and the films obtained in Comparative Examples 2 and 3 were inferior in both odor and thickness spots.

  The heat-sealable polypropylene film of the present invention has properties of polypropylene film such as low-temperature sealability, impact resistance and heat resistance, and also uses a resin containing no additives such as an antioxidant as a raw material. In addition, there are few odors, elution, migration, etc. due to the additives such as antioxidants and their degradation products, and the contamination of the contacted objects is suppressed, and the thickness spots are small. Can be suitably used in a field where a simple packaging material, container or the like is required. In addition, the high-quality low-temperature heat-sealable polypropylene film can be stably and economically produced by the production method of the present invention. Therefore, it is important to contribute to the industry.

Claims (3)

A step of extruding from a T-slot die a polypropylene resin having a polypropylene as a main component, which does not contain an additive that migrates to an object to be contacted, such as an antioxidant, at a die outlet resin temperature of 150 to 200 ° C .; Nozzle method, air chamber method or air knife method and vacuum chamber method are heat-sealable films formed by the process of bringing the extruded film into close contact with a cooling roll. A heat-sealable polypropylene film characterized by being within 10%.   The heat-sealable polypropylene film according to claim 1, wherein a sealing start temperature is 80 to 190 ° C. A step of extruding from a T-slot die a polypropylene resin having a polypropylene as a main component, which does not contain an additive that migrates to an object to be contacted, such as an antioxidant, at a die outlet resin temperature of 150 to 200 ° C .; No more than 10% of thickness unevenness in the width direction of the film, characterized by having a step in which the nozzle method, the air chamber method or the air knife method and the vacuum chamber method are simultaneously applied to bring the extruded film into close contact with the cooling roll A method for producing a heat-sealable polypropylene film.