JP2005126680A - Heat-sealable linear low-density polyethylene film and process for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sealable linear low-density polyethylene film that has low odor, has good processing operability when processed into a packaging bag and a packaging container for packaging different goods, gives the manufactured article having small variations in sealing properties and having good appearance and therefore can be suitably used in the field such as a packaging material, a container or the like for food products, medical materials or the like where odor is undesirable, and to provide a process for producing the heat-sealable linear low-density polyethylene film. <P>SOLUTION: The film is a heat-sealable film formed from as a constituent component a linear low-density polyethylene comprising a copolymer of ethylene and a 3-12C α-olefin wherein thickness unevenness in the width direction of the film is 10% or less and the amount of volatile components in the film is 2,000 ppm or less. The film is produced by forming a film from a linear low-density polyethylene resin comprising a copolymer of ethylene and a 3-12C α-olefin and having an amount of the volatile components in the resin of 3,000 ppm or less by using a T-slot die at the resin temperature at the die opening of 150-200°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sealable linear low-density polyethylene film having a low odor, which is preferably used in the field of packaging materials, containers, etc., which are apt to be odored, such as foods and medical materials. The film thickness is small and the fish eyes are small, the operability of the folding process using the film to be processed into packaging bags and packaging containers for various packaging is good, and the sealing characteristics of the resulting product vary. The present invention relates to a heat-sealable linear low-density polyethylene film and a method for producing the same.

  The linear low density polyethylene film is excellent in low temperature heat sealability, tear strength, impact resistance, transparency and the like, and is used in a wide range of fields as packaging materials and containers for foods and medical materials. In recent years, with the maturity of society, market demand for odors in the above-mentioned fields has become extremely advanced, and so-called low odor materials with improved characteristics are strongly desired. Polyolefin resins such as linear low density polyethylene 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 the tear strength, impact resistance, waist strength, and the like are inferior. In addition, the low-temperature sealability is insufficient, and the development of a clean molded body made of linear low-density polyethylene that can satisfy these characteristics has been desired. However, since linear low density polyethylene has a molding temperature higher than that of the high pressure method low density polyethylene, it is necessary to add an antioxidant for preventing deterioration of the resin, and as a catalyst residue, chlorine, etc. 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.

  Low linearity with no additive added and optimized for density, melt flow rate, molecular weight distribution, elution fractionation characteristics, etc. A molded body having a low odor and a low migration property using a density polyethylene resin as a raw material is disclosed (for example, see Patent Documents 1, 2, 3, and 4).

JP 2001-342306 A JP 2002-52669 A JP 2003-64191 A JP 2003-341249 A

In recent years, the low-odor heat-sealable polyethylene film is also used for fold processing using the film into various packaging bags and packaging containers, as well as the variation and appearance of the sealing properties of the product. The demand for quality is increasing.
However, the above method is formed by the inflation method or the extrusion lamination method, and the film has a large thickness unevenness, and the tension generated by the tightening phenomenon that occurs when the film is stored in a roll shape is caused by the thickness unevenness. The film fluctuates in the direction, and deformation such as partial sagging of the film occurs. 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. In addition, there is a problem that it leads to poor appearance such as transparent spots and fluctuations in laminate strength. Moreover, there are many fish eyes, and these points do not meet the demands of the market. For example, the definition of fish eye is written in Polymer Editorial Board, Polymer Dictionary, Taiseisha, 2000, 6th edition, P337, etc. Fisheye refers to a small spherical mass that occurs in a film or sheet product. The name was given because there are many things that have transparency like fish eyes. There are various types such as unmelted lumps resulting from insufficient kneading of the molding material, lumps due to gelation of a part of the raw material, lumps due to partial deterioration of the material during molding, and those with foreign matter as the core. The fish eye here excludes those with foreign matter as the core. Examples of the foreign material include cellulose, dust, metal pieces, resin carbide, plastics of different types, lint, and pieces of paper.

For example, when the film is packaged with the film, the fish eye can be seen with the naked eye. With regard to the fish eye, in recent years, market demands have become stricter along with the increasing safety orientation of consumers. For example, even if it is not visible to the consumer under normal conditions, such as when used as an inner layer material for a paper pack, the paper pack will be cut out for collection to the consumer's eyes. As a result, phenomena such as raising anxiety about safety have begun to appear. In addition, when used as a transparent packaging bag, fish eyes may stand out as foreign matter depending on the color and form of the contents. These market demands require strict management, and market demands cannot be met.
The inflation method requires a high extrusion viscosity to stabilize balloon formation, and is generally advantageous in obtaining a molded product with low odor because extrusion is performed at a low temperature. Have. On the other hand, in the T-die method, if high melt viscosity extrusion is performed at a low temperature, flow spots tend to appear and the thickness spots become large, so 210 to 210 to 200 to 160 ° C. which is the film forming temperature in the inflation method. It is necessary to extrude at 270 ° C. It is said that when high temperature extrusion molding is carried out, the deterioration of the raw material resin increases, the odor worsens and the fish eye increases. Therefore, the addition of an antioxidant has been essential in the T-die method.

On the other hand, disclosed is a method for producing a low odor T-die cast film in which an ethylene polymer having a specific density and a melt index or a resin composition containing the ethylene polymer is melt-extruded to form a resin composition at a temperature of 210 ° C. or lower. (See Patent Document 5). However, in this patent document, there is no mention of an increase in film thickness unevenness due to low-temperature extrusion in T-die casting and countermeasures therefor, and there is no description of qualitative evaluation about the odor etc. of the film. There is no detailed description of the effect of the inhibitor.
Japanese Patent Laid-Open No. 10-329195

  Moreover, in the technique disclosed in the above-mentioned patent document, the measurement of odor is performed by sensory evaluation. The sensory evaluation has a problem in the accuracy of the judgment, such as the judgment is different among the examiners, or the judgment changes even by the physical condition etc., and the improvement is strongly envyed.

  On the other hand, a polypropylene resin with an improved odor in which the total amount of hydrocarbon components having 9 to 21 carbon atoms contained in the polypropylene resin is 30 ppm by weight or less is disclosed (see Patent Document 6). However, in this patent document, it is limited to a polypropylene resin, and no mention is made of a polyethylene resin. No mention is made of the specific contents and characteristics of the method for producing the film or sheet. Further, as a method of bringing the hydrocarbon content into the above range, in the pelletizing step, a degassing facility is provided in the extruder, and the pellet is dried under hot air by a method of degassing under reduced pressure when melt-extruding and a hopper dryer. However, there is no mention of a method of heat-treating the resin in a solid state under reduced pressure.

JP-A-5-194648

  The present invention has been made against the background of the problems of the prior art, and is a heat-sealable linear low-density polyethylene with a low odor that is suitably used in the field of packaging materials, containers, and the like that are disliked by odors such as food and medical materials. In relation to a system film, the film has little odor, the thickness unevenness of the film is small, and the operability of folding processing that is processed into packaging bags and packaging containers for various packaging using the film is obtained, and the product obtained It is an object of the present invention to provide a heat-sealable linear low-density polyethylene film and a method for producing the same, in which a product with a good appearance can be obtained with a small change in the sealing properties and a small number of fish eyes.

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 comprising a linear low-density polyethylene composed of a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, with a thickness variation of 10 in the width direction of the film. %, And the total amount of paraffins and olefins having 12 to 16 volatile carbon atoms quantified by gas chromatography mass spectrometry described in the specification is an n-tetradecane conversion value with respect to the film mass. It is a heat-sealable linear low-density polyethylene film characterized by being 2000 ppm or less.
In this case, it is preferable that the number of fish eyes having a maximum diameter of 0.1 mm or more in the film is 10 / 0.1 m ² or less.
In addition, the present invention provides the total amount of volatile carbon atoms having 12 to 16 carbon atoms and olefins quantified by gas chromatography mass spectrometry described in the specification in terms of n-tetradecane equivalent to the resin weight. Using a T-slot die, a linear low-density polyethylene resin made of a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms of 3000 ppm or less is formed at a resin temperature of 150 to 200 ° C. at the die outlet. This is a method for producing a heat-sealable linear low-density polyethylene film.
In this case, when the film extruded from the T-slot die is brought into close contact with the cooling roll, it is preferable that the air nozzle method, the air chamber method or the air knife method and the vacuum chamber method are simultaneously applied.
In this case, it is preferable to filter the resin melted in the melt-extrusion step with a filter having a filtration accuracy of 100 μm or less.
Furthermore, in this case, it is preferable to perform filtration in two stages.
Furthermore, in this case, the linear low density polyethylene resin comprising the copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms is heat-treated at a temperature of 50 ° C. or higher and lower than the softening point under reduced pressure. It is preferable that
Furthermore, in this case, it is preferable that the degree of vacuum is 13 hPa or less.
Furthermore, in this case, a linear low density polyethylene resin comprising a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms before the heat treatment is obtained by gas chromatography mass spectrometry described in the specification. It is preferable that the total amount of paraffins and olefins having a volatile carbon number of 12 to 16 to be quantified exceeds 3000 ppm in terms of n-tetradecane amount with respect to the resin mass.

  The heat-sealable linear low-density polyethylene film of the present invention has the characteristics of a linear low-density polyethylene film such as low-temperature sealability and impact resistance, and has less odor and good film thickness accuracy. In addition, since the fisheye is less mixed, the operability of folding processing using the film into a packaging bag or packaging container for various packaging is good, there is little variation in the sealing characteristics of the product obtained, and Since it has an advantage that a product with a good appearance can be obtained, it can be suitably used in the field of packaging materials, containers and the like where food and medical materials and other odors are disliked. In addition, the production method of the present invention has an advantage that the above-described high-quality heat-sealable linear low-density polyethylene film can be produced stably and economically.

Hereinafter, the present invention will be described in detail.
The linear low density polyethylene resin used in the present invention is composed of a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, and the carbon number is preferably selected in the range of 4 to 8. It is desirable. Specific examples of these copolymer components include propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, dodecene-1, 4-methyl-pentene. -1,4-methyl-hexene-1 and the like, but the present invention is not limited to the above compounds. Among these, butene-1, hexene-1, octene-1, and 4-methylpentene-1 are preferable. The density is preferably 880 to 950 kg / m ³ . 885 to 930 kg / m ³ is more preferable, and 890 to 920 kg / m ³ is more preferable. When the density is less than 880 kg / m ³ , rigidity, heat resistance and blocking resistance are lowered, which is not preferable. Conversely, when the density exceeds 950 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. The thing of the range of 2-80 g / 10min is more preferable, More preferably, it exists in the range of 2-50 g / 10min. If the MFR is less than 1 g / 10 minutes, the melt viscosity increases 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, the melt viscosity becomes too low and film formation becomes difficult, and the mechanical properties of the obtained film are deteriorated.

  The method for producing a linear low-density polyethylene resin comprising the above-mentioned copolymer of ethylene and α-olefin is not particularly limited. For example, so-called metallocene such as a Ziegler-Natta catalyst or a cyclopentadienyl metal compound is used. Solution polymerization method, slurry polymerization method, bulk polymerization method, gas phase polymerization method using bulk catalyst or non-metallocene complex catalyst, bulk polymerization method using radical initiator, solution polymerization method, etc. What was manufactured by the method is mentioned.

The heat-sealable linear low-density polyethylene film of the present invention is composed of linear low-density polyethylene having the above composition, and the thickness variation in the width direction of the film is within 10%. The total amount of paraffins and olefins having a volatile carbon number of 12 to 16 to be quantified needs to be 2000 ppm or less in terms of n-tetradecane amount with respect to the film mass.
[Gas chromatography mass spectrometry of volatile components in film]
(1) Setting of sample Weighing 2-3 mg of film sample, putting it in a sample tube for thermal desorption cold trap injector (TCT) (Chrompack, inner diameter: 3 mm), and TCT (GL Sciences: CP-4020) ) In the desorption oven.
(2) Heating of sample and introduction of volatile component into gas chromatography mass spectrometer The desorption oven in which the sample tube is set by the above method is heated at 80 ° C. for 10 minutes to volatilize the volatile component in the film. The generated volatile components are introduced into a cold trap cooled to −100 ° C. by a carrier gas (He: flow rate 14 cc / min). After 10 minutes, the cold trap is heated to 250 ° C. all at once, and the condensed volatile components are introduced into the gas chromatography mass spectrometer.
(3) Gas chromatography mass spectrometry a. Gas chromatograph: HP-6890 (manufactured by Agilent)
b. Mass spectrometer: HP-5993 (manufactured by Agilent)
c. Gas chromatography column: capillary column HP-1MS (diameter 0.25 mm, length 30 m, dimethylpolysiloxane film thickness 1.0 μm)
d. Inlet temperature: 120 ° C
e. Gas chromatographic conditions: Carrier gas flow rate 0.5 cc / min, column temperature held at 50 ° C. for 2 minutes, raised to 250 ° C. at 15 ° C./minute, held at 280 ° C. for 10 minutes f. Gas chromatographic peak identification: conducted by mass spectrometry (4) Determination of volatile components A calibration curve of n-tetradecane is prepared by the following method and displayed in n-tetracan equivalent. The quantification is performed in the total ion detection mode.
A solution obtained by dissolving 38.6 mg of n-tetradecane in 1000 cc of n-hexane is used as a standard solution. Ten microliters of the standard solution 10 microliters (the sample tube was filled with 0.1 g of TenaxTA (20/35 mesh: manufactured by GL Sciences), and glass wool was filled above and below TenaxTA when filling) It is injected using a microsyringe and adsorbed on Tenax. The Tenax adsorption tube is set in the desorption oven, and a calibration curve is prepared by performing gas chromatography mass spectrometry in the same manner as described above.

  The present inventors diligently studied on a highly accurate evaluation method replacing the sensory test of odor that has been carried out conventionally, and the number of carbon atoms, which is a volatile component contained in the film quantified by the above method, is from 12. The present invention was completed by finding that a total of 16 paraffins and olefins could be evaluated. That is, the total amount of paraffins and olefins having 12 to 16 carbon atoms, which are volatile components contained in the film, is an n-tetradecane amount converted value (hereinafter referred to as the volatile component amount in the film) relative to the film mass. It is preferably 2000 ppm or less. 1800 ppm or less is more preferable, 1500 ppm or less is more preferable, and 1000 ppm or less is particularly preferable. If it exceeds 2000 ppm, the odor of the film becomes strong, and when wrapping with a packaging bag or packaging container using the film, the odor moves to the contents, which is not preferable because the commercial value of the contents is lowered. . In addition, it is guessed that paraffins and olefins having 12 to 16 carbon atoms, which are volatile components that have been found to be related to odor, are caused by deterioration of the linear low density polyethylene resin, which is the main constituent material of the film. Is done.

  The heat-sealable linear low-density polyethylene-based film of the present invention must simultaneously satisfy that the thickness unevenness in the width direction of the film is within 10% together with the above-mentioned characteristics related to odor. Within 8% is more preferred, and within 6% is even more preferred. When it exceeds 10%, it leads to the above-mentioned problem occurrence. 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.

  It can be suitably used in the field of packaging materials, containers, etc., which are good for the above-mentioned odor-related characteristics and have few thickness spots, and which do not like odors such as foods and medical materials.

The heat-sealable linear low density polyethylene film of the present invention preferably has 10 fish eyes having a maximum diameter of 0.1 mm or more / 0.1 m ² or less. 8 / 0.1 m ² or less is more preferable, and 6 / 0.1 m ² or less is more preferable. When the number of fish eyes exceeds 10 / 0.1 m ² , it leads to the above-mentioned problem and cannot meet the high demands of the market.

  The heat-sealable linear low-density polyethylene film of the present invention is a preferred embodiment having a seal start temperature of 80 to 140 ° C. 85-135 degreeC is more preferable, and 90-130 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, which is not preferable. 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 of the heat-sealable linear low-density polyethylene film of the present invention is 5 to 300 μm. Preferably, it is 10-200 micrometers.

  The heat-sealable linear low density polyethylene film of the present invention may be a multilayer film having a layer structure of two or more layers.

Although the manufacturing method of the heat-sealable linear low density polyethylene film having the above-mentioned properties is not limited, the total amount of paraffins and olefins having 12 to 16 volatile carbon atoms quantified by gas chromatography mass spectrometry described below is used. A linear low consisting of a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, which is 3000 ppm or less (hereinafter referred to as the amount of volatile components in the resin) in terms of the amount of n-tetradecane relative to the resin mass. It is a preferred embodiment that a high density polyethylene resin is formed using a T-slot die and the resin temperature at the die outlet is 150 to 200 ° C.
[Gas chromatography mass spectrometry of volatile components in resin]
(1) Pulverization of sample resin 1 g of resin is cooled with liquid nitrogen using a freeze pulverizer (SPEC 6700 Freezer / Mill) and freeze pulverized. Grinding is performed for 10 minutes at a strength MAX.
(2) Sample setting Approximately 10 mg of the above ground sample is precisely weighed and placed in a sample tube for thermal desorption cold trap injector (TCT) (Chrompack, inner diameter: 3 mm), and TCT (GL Science: CP-4020). ) In the desorption oven. When filling the sample tube with the sample, glass wool was filled on the top and bottom of the sample.
(3) Heating of sample and introduction of volatile components into gas chromatography mass spectrometer, gas chromatography mass spectrometry and determination of volatile components In the same manner as gas chromatography mass spectrometry of volatile components in film Do.

  In a conventionally known technique, for example, the technique disclosed in the above-mentioned patent document, the odor of the polyethylene film is considered to be greatly contributed by a low molecular weight organic additive such as a stabilizer such as an antioxidant. Therefore, attempts have been made to improve odor with these types and amounts added. For example, additive-free brand resins that do not contain these additives are commercially available as low-odor film resins. As a result of examining the low-odor heat-sealable linear low-density polyethylene film having the above-mentioned characteristics, the present inventors have not necessarily obtained a film having the desired characteristics even if an additive-free brand resin is used. I found. Therefore, as a result of intensive studies on the establishment of a production method capable of stably obtaining a film having the desired characteristics, regarding the odor of the film, in addition to suppressing the deterioration of the raw material resin by lowering the extrusion temperature of the raw material resin in the film forming process. Thus, it was found that it is important that the contribution of a specific volatile component amount in the raw material resin immediately before film formation is large. The amount of volatile components in the raw resin was established according to the above-described method for determining the amount of volatile components in the film.

The amount of volatile components in the resin is more preferably 2900 ppm or less, and further preferably 2800 ppm or less. If it exceeds 3000 ppm, even if the extrusion temperature of the raw resin is lowered to suppress the deterioration of the raw resin, the heat-sealable linear low-density polyethylene film of the present invention should have the amount of volatile components in the film. Of 2000 ppm or less is difficult.
In addition, although the limit value of the amount of volatile components in the resin is larger than the limit value of the amount of volatile components in the film, the shape of the sample used for measurement is different, and there is a large difference in the surface area. Therefore, it is speculated that this is a phenomenon caused by a difference in the volatilization amount of the volatile components. That is, it is inferred that the two measured values are not equivalent.
The relationship between the odor characteristics of the film and the quality of the raw material resin can be achieved for the first time by establishing the above-described quantitative method with high accuracy replacing the known sensory evaluation.

In the present invention, the method for bringing the amount of volatile components contained in the linear low density polyethylene resin into the above range is not limited. For example, in the pelletizing process disclosed in the above-mentioned Patent Document 6, a method is used in which a degassing facility is provided in the extruder, and the pellet is degassed under hot air using a hopper dryer or the like by depressurizing and depressurizing during melt extrusion However, as a result of intensive studies by the present inventors, the temperature below the softening point of the resin, that is, the amount of volatile components in the resin by heat-treating the resin in a solid state and under reduced pressure. It was found that a resin suitable for the present invention can be stably produced. That is, it is a preferred embodiment that the linear low density polyethylene resin is heat-treated at a temperature of 50 ° C. or higher and lower than the softening point of the resin. It is more preferably 60 ° C. or more and less than the softening point of the resin, and 80 ° C. or more and more preferably less than the softening point of the resin. If it is less than 50 degreeC, since the reduction effect of a volatile component amount will reduce sharply, it is not preferable. Conversely, when the temperature exceeds the softening point, especially when the resin is in a molten state, the movement of the resin molecules becomes active, the deterioration of the resin molecular chains is promoted, and the generation of volatile components by heat treatment increases, resulting in the result. As a result, the reduction of volatile components in the resin is reduced, and an effective reduction cannot be achieved. In the method of Patent Document 6, the high temperature treatment is performed at 200 ° C. or higher and the degree of vacuum is mild.
In addition, the amount of volatile components in the present invention is a large numerical value compared to the amount of hydrocarbon components in the method disclosed in Patent Document 6, but also with respect to this point, the type of resin is different, The contribution of the difference in measurement method is also assumed to be large.
That is, it can be said that the present invention can be achieved for the first time by improving the method for determining the amount of volatile components in the resin, by devising heating and depressurization, and by devising film formation.

  The degree of reduced pressure in the heat treatment is preferably 13 hPa or less. 10 hPa or less is more preferable, and 8 hPa or less is more preferable. If it exceeds 13 hPa, the effect of reducing volatile components in the resin is reduced, which is not preferable. In the method of vacuum degassing at the time of melt extrusion disclosed in Patent Document 6, foaming occurs due to additives or deteriorated substances contained in the molten resin, so that the pressure reduction is limited to ensure extrusion stability. On the other hand, since this method treats the resin in a solid state, it can be carried out even at a reduced pressure close to the limit of the sealing degree of the heat treatment apparatus, so it is a low temperature treatment and the deterioration of the resin is suppressed. Due to the synergistic effect with the effect, volatile components can be reduced extremely efficiently.

  The above heat treatment time may be appropriately selected and set according to the amount of volatile components before treatment, the target amount of volatile components and the treatment conditions, and is preferably 2 to 60 hours, for example.

  In the present invention, the total amount of volatile carbon atoms having 12 to 16 volatile carbon atoms quantified by the above method as a linear low-density polyethylene resin before heat treatment is expressed in terms of the amount of n-tetradecane relative to the resin mass. It is a preferred embodiment to use those exceeding 3000 ppm. This is preferable because a general-purpose resin can be used as a raw material, which is economically advantageous and the effect of the present invention can be further increased. Of course, using a resin of 3000 ppm or less as a resin having a lower content is not excluded.

  In the present invention, since the resin quality-controlled by the above method is used as a raw material as a linear low density polyethylene resin, the heat-sealable linear low density polyethylene film of the present invention with suppressed odor can be stably produced. This is advantageous in terms of economy because the generation of defective products is suppressed.

  In the present invention, the linear low-density polyethylene resin does not necessarily need to be an additive-free brand that does not contain an organic additive as long as it has the above characteristics. For example, it may be preferable to add an antioxidant in a rather small amount. In this case, 1000 ppm or less is preferable with respect to resin. 800 ppm or less is preferable. Antioxidants include 2,6-di-t-butyl-p-cresol, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, n-octadecyl- With phenolic stabilizers typified by 3- (4′-hydroxy-3,5′-di-t-butylphenyl) propionate, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, etc. Examples thereof include phosphite stabilizers. It is preferable to use a phenol-based and phosphite-based combined system, or one having both a phenol skeleton and a phosphite skeleton in one molecule. When using 2 or more types together, it is preferable that it is the said range in total total amount.

  Organic additives can not only cause odor, but also have migratory properties, which can shift to contacted materials and contaminate the packaged contents, which can adversely affect taste, etc. Use is not excluded and is a preferred embodiment. A lubricant, a neutralizer, an antistatic agent, a processability improver, an ultraviolet absorber, an antifogging agent, or the like that does not contain a migratory additive composed of a relatively low molecular weight organic substance, or the additive Even if it is blended, it is preferable that the blended additive is an amount that does not substantially transfer to the contacted object such as the contents and adversely affect the odor and taste. For example, examples of the lubricant include higher fatty acid amides and higher fatty acid esters. Examples of the neutralizer for the catalyst residue include fatty acid metal salts such as calcium stearate and hydrotalcite, and examples of the antistatic agent include glycerin esters, sorbitan acid esters, and polyethylene glycol esters of fatty acids having 8 to 22 carbon atoms. Is done. The processability improver is represented by a fatty acid metal salt such as calcium stearate. Examples of the ultraviolet absorber include 2-hydroxybenzophenone, 2-hydroxyphenylbenzotriazole, salicylate, and cyanoacrylate. Examples of the antifogging agent include glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene aliphatic alcohol ether, polyethylene glycol fatty acid ester, and polyoxyethylene sorbitan fatty acid ester. Therefore, an additive that elutes to the outside, for example, when the content is a liquid, an additive that is eluted in the liquid or an additive that is unevenly distributed on the film surface over time is contained in the resin. For example, when used as a packaging material or container for food, it is hygienic with little change in taste, and when used as a packaging material or container for medical or electronic materials, the contents are contaminated. A clean film is obtained.

  In the present invention, an additive that does not substantially migrate to the contacted material may be added in a range that does not substantially impair the characteristics that the heat-sealable linear low-density polyethylene film of the present invention should have. 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, high-pressure polyethylene, ultra-high molecular weight polyethylene, olefin elastomer, etc. is blended to prevent blocking, impart slipperiness, impact resistance or improve heat seal characteristics. It is also recommended as a preferred embodiment. As a matter of course, it is preferable to use the modifying resin having the above-mentioned characteristics in the amount of volatile components as in the above-described linear low density polyethylene resin. Moreover, it is a more preferable embodiment to use an additive that does not contain an additive that shifts to the contacted object.

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

As described above, the linear low-density polyethylene resin may be a resin and a resin blend that are commercially available as additive-free grades, or those that are specially designed so that the effects of the present invention can be expressed more greatly. It doesn't matter.
Further, it is preferable to form a film at a resin temperature of 150 to 200 ° C. at the die outlet in the melt extrusion of the resin.

  On the other hand, regarding the thickness unevenness of the film, it has been found that it is important to use a T-slot die in order to obtain a film with the desired thickness unevenness even in extrusion film formation at a low temperature where deterioration of the raw material resin is suppressed. It was. That is, in order to stably obtain a heat-sealable linear low-density polyethylene film with less odor and reduced thickness unevenness, the amount of volatile components in the raw resin is set in the above range, and a T-slot die is formed. The present invention was completed by finding that it is important to form a film at a resin temperature of 150 to 200 ° C. at the die outlet.

  Conventionally, the film formation by the T-die method has been extruded at a temperature of 210 ° C. or higher. However, in the present invention, it is necessary to suppress the generation of volatile components and fish eyes in the film. The means for solving this problem is not limited, but it is important to perform extrusion molding at a resin temperature of the die outlet of 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. On the other hand, when the temperature exceeds 210 ° C., the thermal deterioration of the resin increases and the generation of the volatile components that adversely affect the odor and the gel formation increase, 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 linear low density polyethylene resin, but it is not preferable because the mechanical properties of the obtained film are not satisfied. Accordingly, it is necessary to use an MFR having a value of 1 to 100 g / 10 min, preferably 2 to 80 g / 10 min, and more preferably 2 to 50 g / 10 min. If the MFR linear low-density polyethylene resin is molded at the above-mentioned 150 to 200 ° C. extrusion temperature, the generation of volatile components and fish eyes can be reduced, but the film thickness variation is within 10% at a width of 1000 mm. Difficult to do. Therefore, in order to bring the properties of the obtained film into the range of the present invention, it is essential to improve the thickness unevenness even when extruded at the above-mentioned 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.
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. That is, as illustrated in FIG. 1, the T slot die has a structure having a linear manifold in the width direction, a three-stage slit channel composed of two inclined lands and a lip. Unlike the coat hanger die, the pre-land is a two-stage system with an inclined type, and the first pre-land part of the central part to which the resin flow is supplied is opposite to the coat hanger die, but the central part is more The land length has become shorter and the above problems have been improved. Furthermore, the slit channel width is divided into three stages, the rectifying effect is improved, and the pressure variation and distortion of the entire T die are improved, leading to the reduction of thickness variation.
That is, as illustrated in FIG. 2, the coat hanger die is composed of a manifold inclined in the shape of a hanger in the width direction of the T die and a subsequent two-stage slit channel (preland and lip). Therefore, when molten resin flows into the manifold, the resin flow collides with the preland portion and the pressure is adjusted, but the preland length at the central portion where the pressure is highest where the resin flow is supplied is supplied by the split flow. Since it is longer than the pre-land length at the end, the pressure increase due to this pre-land length is taken into account, so that the pressure difference between the center and the end is further increased, and the pressure spots and distortion of the entire T die are increased. Occurs and this leads to an increase in thickness spots during ejection. Furthermore, since the slit channel width is divided into two stages, the rectifying effect is not sufficient. As a result, generally called a W pattern, a portion that flows fast and a portion that slows at the die exit occurs, leading to a problem that the flow is not uniform. It is thought that it was the cause of fish eyes due to differences in thickness spots and thermal history.

  It is a preferred embodiment to optimize because the direction of air flow around the T-slotted die affects the 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 around the die with a sheet, a plate, etc., and surround the enclosure 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, it is recommended as a preferred embodiment because the surrounding of the dice also leads to improvement of the phenomenon. In addition, it is a preferable embodiment that the temperature is increased while the humidity is increased, since temperature spots are reduced.

  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, air nozzle method, air chamber method, air knife method, and vacuum chamber method are widely used as a method of closely contacting the cooling roll with air, but it is a preferred embodiment that the above three methods act simultaneously. 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 improved 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.

  By using such a high-precision T-slot die, the feed block can be simplified. 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, there is an effect of further reducing thermal degradation.

  It was also found that there is a new effect that the generation of fish eyes is also suppressed by making the resin flow uniform in the die.

  The use of the above T-slot type die is effective as a measure for reducing film thickness unevenness and fish eyes. However, 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 low-density polyethylene 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”. It adversely affects film thickness spots and foreign matter contamination. Therefore, it is a preferred embodiment to increase the lip opening of the die in order to solve the problem.

  Although formation of fish eye can be suppressed by film formation in the temperature range of the extrusion temperature described above, in the present invention, in order to suppress odor and migratory components, the blending amount of the antioxidant in the raw material resin In addition to optimizing the extrusion temperature as described above, it is recommended as a preferred embodiment to add a method of removing or miniaturizing the fish eye produced in the raw resin melt extrusion process through a filter. Is done.

  In filtration of the molten resin, selection of a filter to be used is important. In the present invention, it is a preferred embodiment that the resin melted in the melt-extrusion step is filtered with a filter having a filtration accuracy of 100 μm or less. Here, filtration accuracy is the performance evaluated according to the method defined in JIS B8356: 1976. The filtration accuracy is more preferably 80 μm, and further preferably 60 μm. When the filtration accuracy exceeds 100 μm, the removal and miniaturization of the gel-like foreign matters forming the fish eye are deteriorated, which is not preferable. The lower limit of the filtration accuracy is preferably as small as possible from the point of removal and miniaturization of the gel-like foreign matters, but the filtration pressure loss increases in proportion to the reduction, so that it is necessary to increase the filtration area. Therefore, the lower limit is preferably 30 μm. A wire mesh filter is generally used as a filter. Filtration capacity and miniaturization efficiency are changed by changing the shape of plain weave, twill weave, plain tatami mat, twill mat weave, etc. Will change. Apart from these wire mesh filters, there is a type called a metal sintered filter, and there are two types, one that is powder sintered and one that is hardened without weaving metal like a nonwoven fabric. In particular, non-woven fabrics that have been hardened without weaving metal are made by uniformly laminating and sintering micron-order stainless steel fibers. Recently, it has been used especially frequently because it has high filtration accuracy and high porosity compared to other metal filter media, and its pressure loss is small. However, even with a wire mesh filter, some weaving and laminating methods can achieve the same or better performance, so it is not excluded. As for the point of selection, since olefin has a high melt viscosity, it is preferable to select one having a low pressure loss and a high filtration capacity. The adoption of this measure can exhibit not only the reduction of fish eye but also the effect of reducing thickness unevenness. Thick spots are likely to occur when the pressure loss is large. That is, the pressure at which the molten resin is extruded by the extruder is cut by the filter, the pressure in the T die is insufficient, and the flow of the molten resin in the T die becomes unstable, resulting in unevenness in thickness. As described above, it is possible to suppress this by using a filter having a low pressure loss.

  In a more preferred embodiment, the filtration is performed by a multistage filtration method in which two or more filters are connected in series. By the multi-stage filtration method, filtration and miniaturization efficiency are improved, and the problem of the pressure loss is also improved. In the case of the multistage filtration method, filters having the same filtration accuracy may be used, but it is a more preferable embodiment that the value of filtration accuracy is lowered in accordance with the flow direction of the molten resin.

  The raw linear low density polyethylene resin pellets used in the present invention are preferably used after the inert gas replacement when dried. Oxidative decomposition when deoxygenated by inert gas replacement and entering the extruder and melting is suppressed, leading to suppression of generation of the volatile components and reduction of fish eyes. 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 also has the effect of suppressing the mixing of oxygen into the extruder together with the raw material resin, leading to the suppression of gel formation. The adoption of this measure can not only suppress the gel formation 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 required, and in the twin screw extruder, the resin is deteriorated due to local heat generation. 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. As a result of intensive studies 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. No. 593, P146-157, it was found effective to use a single-screw extruder having a 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 part 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. This measure is important because it leads not only to the reduction of fisheye but also to the effect of suppressing the formation of volatile components in the aforementioned film.

  The recovered material is also an important factor in suppressing fisheye. 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, a crosslinking reaction occurs inside the resin, and as a result, fish eyes are easily generated. 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. A method of forming pellets in a semi-molten state is preferable because it is uniform without changing with the passage of time and fish eyes are hardly generated.

  It is also important to manage the products collected, the dust that comes with the incision scraps, foreign matter, and fine dust. If dust, foreign matter, fine dust, etc. are attached to the collected raw materials, they become the core and fish eyes are generated. . In addition to the importance of air-conditioning management in the recovery chamber, it is important to devise measures to prevent dust, foreign matter, and fine dust from adhering to the recovery line. As the method, a collection operation in a clean room is preferable. In addition, it is preferable to attach a static eliminator to the inlet of the collecting device in order to remove dust, foreign matter and fine dust attached to the film.

  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.

1. Gas Chromatography Mass Spectrometry of Volatile Components in Film (1) Sample Setting Weighing 2-3 mg of film sample, sample tube for thermal desorption cold trap injector (TCT) (Chrompack, inner diameter) 3mm) and set in a desorption oven of TCT (GL Sciences Inc .: CP-4020).
(2) Heating of sample and introduction of volatile components into gas chromatography mass spectrometer The desorption oven in which the sample tube is set by the above method is heated at 80 ° C. for 10 minutes to volatilize the volatile components in the film. . The generated volatile components were introduced into a cold trap cooled to −100 ° C. by a carrier gas (He: flow rate 14 cc / min). After 10 minutes, the cold trap was heated to 250 ° C. all at once, and the condensed volatile components were introduced into the gas chromatography mass spectrometer.
(3) Gas chromatography mass spectrometry a. Gas chromatograph: HP-6890 (manufactured by Agilent)
b. Mass spectrometer: HP-5993 (manufactured by Agilent)
c. Gas chromatography column: capillary column HP-1MS (diameter 0.25 mm, length 30 m, dimethylpolysiloxane film thickness 1.0 μm)
d. Inlet temperature: 120 ° C
e. Gas chromatography conditions: Carrier gas flow rate 0.5 cc / min, column temperature held at 50 ° C. for 2 minutes, heated to 250 ° C. at 15 ° C./minute, held at 280 ° C. for 10 minutes f. (4) Determination of volatile components A calibration curve of n-tetradecane was prepared by the following method and displayed in terms of n-tetradecane equivalent. The quantification was performed in the total ion detection mode.
A solution obtained by dissolving 38.6 mg of n-tetradecane in 1000 cc of n-hexane was used as a standard solution. Ten microliters of the standard solution of 10 μl of Tenax adsorption tube [0.1 g of TenaxTA (20/35 mesh: manufactured by GL Sciences) was filled in the above sample tube, and glass wool was filled on top and bottom of TenaxTA when filling was performed] Were injected using a microsyringe and adsorbed on Tenax. The Tenax adsorption tube was set in the above desorption oven, and a calibration curve was prepared by performing gas chromatography mass spectrometry in the same manner as described above.

2. Film Odor Evaluation Method The film was cut into 10 cm 4 squares, and 100 of them were stacked, and this was put into a glass bottle with a lid having an internal volume of 1 liter. This glass bottle was placed in a heating oven kept at 70 ° C. for 2 hours (then, this was taken out and immediately subjected to sensory evaluation by a panelist.
The determination was made according to the following criteria.
Good thing: ◎
Somewhat good: 〇 Somewhat bad: △
Bad thing: ×

3. Measuring method of fish eye in the film 33.3 cm in the flow direction (hereinafter referred to as MD direction) × 30 cm in the transverse direction to the flow direction (hereinafter referred to as TD direction), both ends Remove 20 cm and cut out as 4 samples. The sample is placed on a plate irradiated with a fluorescent lamp from under the film, visually observed with transmitted light, and a fish eye of 0.1 mm or more is measured. In the measurement, the number of fish eyes is obtained from the average value of three cut samples and converted to the number per 0.1 m ² . If the number of fish eyes of 0.1 mm or more is 8 or more even if the number of the samples is one, a preliminary one is also measured, and an average value of four film samples is obtained and converted to the number per 0.1 m ^2. . Next, immerse the counted fish eye in liquid nitrogen, harden it, cut it in half with a razor, and observe the cross section of the fish eye with an optical microscope at a magnification of 50 to 300 times. If there is no substance to be formed, for example, if there is no foreign substance such as cellulose, it is an unmelted lump, a lump due to gelation of a part of the raw material, a lump due to partial deterioration of the material during molding, etc. It is determined as a fish eye caused by the gel. If there is a nucleus, it is judged as a fish eye caused by a foreign object and excluded from the count.

4. Evaluation of uneven thickness of film JIS K7130: Evaluated according to 1999. Details of the differences in some methods will be described below. The measurement environment is 23 ° C. × 50% RH room. The measurement is performed by cutting 5 cm at both ends of the film, and dividing the sample with both ends cut into 40 equal parts in the width direction to mark the measurement positions. The dial gauge is used for the place where the mark portion is removed at the mark position. The measurement is 15 cm in the MD direction of the film roll, the full width in the TD direction, two portions of the surface layer part from which the wrinkle is peeled off, and two parts from the core part where the wrinkle is peeled off by two turns, respectively. Take 3 samples and find the average of the 6 samples. 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.
Thickness unevenness is obtained by the following formula.
Thickness unevenness (%) = (maximum thickness−minimum thickness) ÷ average value of 6 samples × 100

5. Gas chromatography mass spectrometry of volatile components in resin (1) Grinding of sample resin 1 g of resin is cooled with liquid nitrogen using a freeze grinder (SPEC 6700 Freezer / Mill) and frozen and ground. Grinding is performed for 10 minutes at a strength MAX.
(2) Sample setting Approximately 10 mg of the above ground sample is precisely weighed and placed in a sample tube for thermal desorption cold trap injector (TCT) (Chrompack, inner diameter: 3 mm), and TCT (GL Science: CP-4020). ) In the desorption oven. When filling the sample tube with the sample, glass wool was filled on the top and bottom of the sample.
(3) Heating of sample and introduction of volatile components into gas chromatography mass spectrometer, gas chromatography mass spectrometry and determination of volatile components In the same manner as gas chromatography mass spectrometry of volatile components in film went.

6. Filtration accuracy Measured according to JIS B8356: 1976. The maximum glass bead particle size that has passed through the filter media is defined as filtration accuracy (μm).

7. Resin temperature at the die outlet The resin temperature at the die outlet in the present invention was measured using an infrared thermometer with 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. An IR-CAM type for polyethylene film manufactured by Chino Co., Ltd. was used, and measurement was performed at a position of 10 to 15 cm from the molten resin.

8, MFR
According to JIS K 7210: 1999, the evaluation conditions evaluated the viscosity of the raw material resin at 2.16 kg and 190 ° C.

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

(Example 1)
Antioxidants 700ppm having a phenol skeleton and a phosphite skeleton in the molecule is added, the volatile component content is at 5300 ppm, the decompressor a commercial linear low density polyethylene resin in the resin density 925 kg / ^{m 3} and MFR8g / 10min 3 stages of linear low density polyethylene resin with a volatile component content reduced to 240 ppm obtained by charging in a rotary drier attached with a heat treatment at 105 ° C. under a reduced pressure of 13 hPa for 48 hours. Using a single-screw extruder, the width is 3000mm, the pre-land is in two stages, and the flow of the step part is curved so that the flow of molten resin is uniform, and the flow in the die is uniform Using the T-slot die, the resin was extruded at a resin temperature of 180 ° C. at the die outlet. The lip gap was 1.6 mm. The molten resin was filtered by a two-stage filtration method in which stainless steel fibers were uniformly laminated and sintered in a filter accuracy of 100 μm and 50 μm connected in series and supplied to a die. The molten resin sheet coming out of the die was cooled with a cooling roll at 30 ° C. to obtain a linear low density polyethylene film having a thickness of 30 μm. Drying of the raw linear low density polyethylene resin was carried out 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. Two air nozzles were installed in series in the film traveling direction at both ends. In addition, the direction of the air knife was 45 degrees with respect to the traveling direction of the extruded sheet. Further, the direction of the suction port of the vacuum chamber was adjusted to the traveling direction of the extruded sheet. Furthermore, the die was surrounded by a sheet so that the molten resin sheet was not exposed to wind. Film formation was performed at a speed of 100 m / min. The obtained results are shown in Table 1.

(Examples 2 to 4)
In the method of Example 1, a resin having a volatile component amount of 1200, 2000 and 2800 ppm obtained by shortening the heating time of the linear low density polyethylene resin under reduced pressure to 24, 12 and 6 hours, respectively, was used as a raw material. Except changing so that it may carry out, it carried out similarly to Example 1, and obtained the film of Examples 2-4. The obtained results are shown in Table 1.

(Examples 5-7)
In the methods of Examples 1 to 3, films of Examples 5 to 7 were obtained in the same manner as in Examples 1 to 3, except that the resin temperature at the die outlet was changed to 180 ° C. The obtained results are shown in Table 1.

(Example 8)
In the method of Example 1, the linear low density polyethylene of Example 8 was changed in the same manner as in Example 1 except that the resin density was 915 kg / m ³ , the resin temperature at the die outlet was changed to 170 ° C., and the film thickness was changed to 50 μm. A film was obtained. The obtained results are shown in Table 1. The amount of volatile components in the raw material resin after the heat treatment under reduced pressure used in this example was 250 ppm.

Example 9
Stabilizers such as antioxidants, neutralizers, lubricants, antistatic agents, etc. added to ordinary linear low density polyethylene resins and additives for imparting functionality such as slipperiness are not added at all A linear low density polyethylene resin having a resin density of 925 kg / m ³ and MFR of 8 g / 10 min was heat-treated under reduced pressure in the same manner as in Example 1 and a three-stage single screw extruder having a screw diameter of 250 mm was used. Then, it was extruded at a resin temperature of 180 ° C. at the die outlet using a T-slot die having a width of 3000 mm. The molten resin was filtered by a two-stage filtration method in which stainless steel fibers were uniformly laminated and sintered in a filter accuracy of 100 μm and 50 μm connected in series and supplied to a die. The molten resin sheet coming out of the die was cooled with a cooling roll at 30 ° C. to obtain a linear low density polyethylene film having a thickness of 30 μm. Drying of the raw linear low density polyethylene resin was carried out 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 performed at a speed of 100 m / min. Table 1 shows the characteristic values of the obtained film.

(Example 10)
In the method of Example 9, a linear low density polyethylene film of Example 10 is obtained in the same manner as in Example 1 except that the resin density is 915 kg / m ³ , the extrusion temperature is 170 ° C., and the film thickness is 50 μm. It was. Table 1 shows the characteristic values of the obtained film.

(Comparative Example 1)
The method of Example 1 was carried out except that the linear low density polyethylene resin was changed to use a commercially available resin having a volatile component amount of 5300 ppm as the raw material without heating it under reduced pressure. A film of Comparative Example 1 was obtained in the same manner as Example 1. The obtained results are shown in Table 2.

(Comparative Example 2)
In the method of Example 1, the linear low density polyethylene resin was changed so that the heat treatment under reduced pressure was performed under normal pressure. The amount of volatile components in the resin was 3500 ppm. A film of Comparative Example 2 was obtained in the same manner as in Example 1 except that the resin was changed to use a raw material. The obtained results are shown in Table 2.

(Comparative Example 3)
A commercially available linear low density polyethylene resin having a volatile component amount of 5300 ppm used in Example 1 was melt-extruded under the following conditions using a gear pump type twin screw extruder. Screw diameter 69mm, screw total length L / D = 14, vent position is L / D = 11, from the hopper side, screw rotation speed 400rpm, gear pump resin temperature 235 ° C, extrusion amount 340kg / hr, vent suction pressure 120hPa The melt was pelletized by an underwater cutting method. The amount of volatile components in the obtained resin was 3200 ppm. A film of Comparative Example 3 was obtained in the same manner as in Example 6 except that the resin was changed to be used as a raw material. The obtained results are shown in Table 2.

(Comparative Example 4)
In the method of Comparative Example 1, a linear low density polyethylene film of Comparative Example 4 was obtained in the same manner as in Comparative Example 1, except that the resin temperature at the die outlet was changed to 180 ° C. The obtained results are shown in Table 2.

(Comparative Examples 5-8)
In the methods of Examples 1 to 3 and Comparative Example 2, the linear lowness of Comparative Examples 5 to 8 was the same as that of Examples 1 to 3 and Comparative Example 2 except that the resin temperature at the die outlet was changed to 230 ° C. A density polyethylene film was obtained. The obtained results are shown in Table 2.

(Comparative Examples 9-11)
In the methods of Examples 1 and 3 and Comparative Example 2, except that the resin temperature at the die outlet was changed to 250 ° C., the linear low of Comparative Examples 9 to 11 was obtained in the same manner as in Examples 1 and 3 and Comparative Example 2. A density polyethylene film was obtained. The obtained results are shown in Table 3.

(Comparative Example 12)
In the method of Example 3, a linear low density polyethylene film of Comparative Example 12 was obtained in the same manner as in Example 3 except that the resin temperature at the die outlet was changed to 140 ° C. The obtained results are shown in Table 3.

(Comparative Examples 13-15)
In the methods of Example 7 and Comparative Examples 7 and 10, the extruder is a single stage type, the filter filtration accuracy is 200 μm 1 stage filtration, the die is a coat hanger type, the close contact with the cooling roll is only an air knife, The linear low density polyethylene films of Comparative Examples 13 to 15 were obtained in the same manner as in Example 7 and Comparative Examples 7 and 10 except that the enclosure was changed so as to eliminate the enclosure. The obtained results are shown in Table 3.

(Comparative Example 16)
Air-cooled inflation method, Plako extruder (screw diameter 55 mm), resin temperature 160 ° C. at die outlet, film width 300 mm, blow ratio 2.7, single layer extrusion was performed to form a film. The resin used was the same as in Example 2 except that the MFR was changed to 2 g / 10 min. The obtained results are shown in Table 3.

  The films obtained in Examples 1 to 8 have a low amount of volatile components in the film and low odor, and also have good thickness spots and fish eyes. In particular, the films obtained in Examples 1 to 3, 5 and 6 had remarkably low odor.

  On the other hand, the films obtained in Comparative Examples 1 to 9, 14 and 15 had a large amount of volatile components in the film and strong odor. Further, the films obtained in Comparative Examples 6 to 11, 14 and 15 had a large amount of volatile components in the film, had a strong odor, and had many fish eyes. Moreover, the film obtained in Comparative Examples 12, 13, and 16 had a large thickness unevenness of the film.

  FIG. 3 shows the relationship between the amount of volatile components in the resin and the volatile components in the film using the data of Examples and Comparative Examples, and FIG. 4 shows the relationship between the resin temperature at the die outlet and the film thickness unevenness. Show. Regarding FIG. 4, the results of Comparative Examples 1 to 4 in which the amount of volatile components in the raw resin is outside the scope of the present invention were not plotted in the figure. From these figures, it can be understood that the limited range of the present invention is a critical range.

  The heat-sealable linear low-density polyethylene film of the present invention has the characteristics of a linear low-density polyethylene film such as low-temperature sealability and impact resistance, and has less odor and good film thickness accuracy. In addition, since the fisheye is less mixed, the operability of folding processing using the film into a packaging bag or packaging container for various packaging is good, there is little variation in the sealing characteristics of the product obtained, and Since it has an advantage that a product with a good appearance can be obtained, it can be suitably used in the field of packaging materials, containers and the like where food and medical materials and other odors are disliked. In addition, the production method of the present invention has the advantage that the above-described high-quality heat-sealable linear low-density polyethylene film can be produced stably and economically, contributing to the industry. It ’s big.

It is a structure figure of a coat hanger die. FIG. 3 is a structural diagram of a T slot die. It is a schematic diagram which shows the relationship between the amount of volatile components in resin, and the amount of volatile components in a film. It is a schematic diagram which shows the relationship between the resin temperature of a die exit, and the thickness spot of a film.

Claims (9)

  A heat-sealable film comprising a linear low-density polyethylene comprising a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, the thickness variation in the width direction of the film is within 10%, and The total amount of paraffins and olefins having 12 to 16 volatile carbon atoms determined by gas chromatography mass spectrometry described in the specification is 2000 ppm or less in terms of n-tetradecane amount with respect to the film mass. A heat-sealable linear low-density polyethylene film. The heat-sealable linear low-density polyethylene film according to claim 1, wherein the number of fish eyes having a maximum diameter of 0.1 mm or more in the film is 10 / 0.1 m ² or less.   Ethylene having a total amount of volatile carbon atoms of 12 to 16 carbon atoms and olefins quantified by gas chromatography mass spectrometry described in the specification with a value of 3000 ppm or less in terms of n-tetradecane amount relative to the resin weight; A heat characterized by forming a linear low density polyethylene resin comprising an α-olefin copolymer having 3 to 12 carbon atoms at a die outlet resin temperature of 150 to 200 ° C. using a T-slot die. A method for producing a sealing linear low-density polyethylene film.   4. The heat according to claim 3, wherein when the film extruded from the T slot type die is brought into close contact with the cooling roll, an air nozzle method, an air chamber method or an air knife method and a vacuum chamber method are simultaneously applied. A method for producing a sealing linear low-density polyethylene film.   The method for producing a heat-sealable linear low-density polyethylene film according to claim 3 or 4, wherein the resin melted in the melt extrusion step is filtered with a filter having a filtration accuracy of 100 µm or less.   6. The method for producing a heat-sealable linear low density polyethylene film according to claim 5, wherein the filtration is performed in two stages.   A linear low-density polyethylene resin comprising a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms is heat-treated at a temperature of 50 ° C or higher and lower than a softening point under reduced pressure. Item 7. A method for producing a heat-sealable linear low-density polyethylene film according to any one of Items 3 to 6.   The method for producing a heat-sealable linear low-density polyethylene film according to claim 7, wherein the degree of vacuum is 13 hPa or less. Volatile carbon number determined by gas chromatography mass spectrometry described in the specification of a linear low density polyethylene resin comprising a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms before heat treatment The heat-sealable linear low-density polyethylene according to claim 7 or 8, wherein the total amount of paraffin and olefin of 12 to 16 exceeds 3000 ppm in terms of n-tetradecane amount with respect to the resin mass. -Based film manufacturing method.

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