JP2008213265A - Manufacturing method of thermoplastic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a thermoplastic film aimed at boosting the production efficiency which enables cutting of time required for orientating and thermally setting the film itself with the use of superheated steam in specializing the orientation of the film. <P>SOLUTION: In this manufacturing method of the thermoplastic film necessitating an orientation process, the orientation process is to thermally orientate the film to be orientated by applying normal pressure superheated steam at 100 to 400 °C inside a tenter orientation device. The tenter orientation device has a preheating part 11, an orientation part 12 and a thermal setting part 13, and also, a heating part 31 for heating the interior of the tenter 10 and a superheated steam spouting part 32 for spouting the superheated steam to the interior of the tenter. In addition, the superheated steam spouting part is equipped with at least, either of the preheating part 11, the orientation part 12 or the thermal setting part 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a thermoplastic film, and in particular, a method for producing a thermoplastic film using superheated steam at the time of heat treatment in a tenter type stretching apparatus.

  Superheated steam is steam that has been increased to 100 to 400 ° C. by further heating saturated steam. Superheated steam has a thermal conductivity about eight times that of hot air. Currently, superheated steam is used in fields such as drying of webs and papers (see Patent Document 1), food residue processing (see Patent Document 2), food cooking (see Patent Document 3), and the like.

  However, in the stretching of thermoplastic films using a stretching apparatus, there have been few reports on production methods using superheated steam. As an application to a resin product, for example, it has been reported that superheated steam is used for heat fixing nylon fibers (see Patent Document 4).

  Conventionally, when a thermoplastic film is stretched by a stretching apparatus, it is generally performed by hot air drying, hot roll contact drying, infrared heat drying, or the like (see, for example, Patent Document 5). According to the drying methods listed above, since air is used as a heat medium, the heat transfer efficiency is not surprising. Moreover, in order to maintain a desired heating state, air must be heated excessively, and the loss of energy efficiency is a problem.

For this reason, when stretching each thermoplastic film, the stretching apparatus itself must be enlarged in order to sufficiently heat, soften, and increase the efficiency of heat setting. As a result, the capital investment of the apparatus and the like has increased, and the time required for the stretching process has increased, which has been a factor of increasing the production cost of the target film as a whole.
Japanese Patent No. 36777662 JP 2001-293457 A JP 2004-162936 A JP 2002-4143 A JP-A-10-249933

  The present invention has been made in view of the above points, and by using superheated steam specialized for stretching a thermoplastic film, it is possible to reduce the time required for stretching and heat setting of the film itself. A method for producing an enhanced thermoplastic film is provided.

  That is, the invention of claim 1 is a method for producing a thermoplastic film involving a stretching step, wherein the stretching step is performed by applying normal pressure superheated steam at 100 to 400 ° C. to a stretched film in a tenter type stretching apparatus. The present invention relates to a method for producing a thermoplastic film characterized by being stretched.

  According to a second aspect of the present invention, the tenter-type stretching device includes a preheating unit, a stretching unit, and a heat fixing unit, a heating unit that heats the inside of the tenter, and a superheated steam jet that jets superheated steam into the tenter. The method for producing a thermoplastic film according to claim 1 having a portion.

  Invention of Claim 3 concerns on the manufacturing method of the thermoplastic film of Claim 2 with which the said superheated steam injection part is provided in at least any one of the said preheating part, the said extending | stretching part, and the said heat fixing part.

  The invention according to claim 4 is the method for producing a thermoplastic film according to any one of claims 1 to 3, wherein the stretched film is a polyolefin film, a polyamide film, a polyester film, or a biodegradable polymer film. Related.

  According to the method for producing a thermoplastic film of the invention of claim 1, in the method for producing a thermoplastic film accompanied by a stretching step, the stretching step is performed by applying atmospheric pressure superheated steam at 100 to 400 ° C. in a tenter type stretching apparatus. Since the stretched film is heated and stretched, the stretch efficiency of the stretched film is improved, which can contribute to the reduction of the manufacturing cost.

  According to the method for producing a thermoplastic film of the invention of claim 2, in the invention of claim 1, the tenter type stretching device has a preheating part, a stretching part, and a heat fixing part, and heats the inside of the tenter. The heating part and the superheated steam jet part for jetting superheated steam into the tenter, the inside of the tenter can be almost sealed, the leakage of the internal gas to the outside of the tenter is reduced, and the heating efficiency is improved. It becomes easy.

  Further, by maintaining the inside of the tenter in a superheated steam atmosphere, the oxygen concentration is lowered and the risk of modification of the stretched film is lowered. In particular, the heat exposure time can be shortened, the possibility of modification of the stretched film can be reduced, and as a result, the stretching equipment can be reduced in size.

  According to the method for producing a thermoplastic film of the invention of claim 3, in the invention of claim 2, the superheated steam jetting part is provided in at least one of the preheating part, the stretching part, and the heat fixing part. Therefore, it is possible to efficiently heat the stretched film.

  According to the method for producing a thermoplastic film of the invention of claim 4, in the invention of any one of claims 1 to 3, the stretched film is a polyolefin film, a polyamide film, a polyester film, or a biodegradable polymer. Since it is a film, it becomes possible to substitute the manufacturing method of the existing thermoplastic resin film.

  The present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view of a tenter type stretching apparatus according to the present invention, FIG. 2 is a top view of a main part of FIG. 1, FIG. 3 is a side view of the main part of FIG.

  This invention is a manufacturing method of the film which has the extending process with respect to a thermoplastic film in the said film manufacturing process. Stretching in this stretching step means a uniaxial stretching method or a biaxial stretching method in a broad sense. In particular, in the present invention, a biaxial stretching method using a tenter, particularly a T-die sequential biaxial stretching or a T-die simultaneous stretching. Biaxial stretching. This is because sequential biaxial stretching and simultaneous biaxial stretching are excellent in terms of thickness accuracy and mechanical properties. Therefore, as specified in the invention of claim 1, when all or part of the stretching process is performed in the tenter of the tenter type biaxial stretching apparatus, the stretched film to be stretched travels in the tenter. The film is stretched by being heated by receiving an injection of atmospheric superheated steam heated to 100 to 400 ° C. In the present specification, superheated steam is used as meaning atmospheric superheated steam heated to 100 to 400 ° C.

  A tenter type biaxial stretching apparatus 1 shown in FIG. 1 is an apparatus of a T-die sequential biaxial stretching method. The raw material resin melted and extruded from the T die 21 is formed into a film by the cooling roller 22. Subsequently, the film is stretched longitudinally (roll longitudinal stretching) in the longitudinal direction (film traveling direction), that is, in the first stretching direction (machine direction: referred to as MD), through the heating rollers 23 having different rotational speeds. Then, the tenter 10 is stretched transversely (tenter transverse stretching) in the width direction (direction perpendicular to the machine direction of the film: TD) by the clips 19 (see FIG. 2) connected from both ends. Then, it is wound up by a winding roller and a product film is obtained.

  In the figure, W1 is an unstretched film, W2 is a film after longitudinal stretching, and W3 is a film that has been transversely stretched by a tenter. In the case of a tenter type biaxial stretching apparatus using a T-die simultaneous biaxial stretching method (not shown), stretching in the longitudinal direction (machine direction MD) and the transverse direction (width direction TD) is simultaneously performed in the tenter.

  The tenter 10 will be further described with reference to FIG. That is, as defined in the invention of claim 2, the tenter 10 of the tenter type biaxial stretching apparatus 1 includes a preheating portion 11, a stretching portion 12, and a heat fixing portion 13. According to the disclosed embodiment, the slow cooling unit 14 and the cooling unit 15 are further provided following the heat fixing unit 13.

  The preheating part 11 hits the carrying-in part of a tenter. The film is softened by heating the stretched film in the preheating section 11. The stretched film is easily stretched in the next stretched portion 12.

  In the stretching portion 12, clips 19 are attached to both ends in the width direction of the softened stretched film, and stretching in the lateral direction (width direction TD) is performed. During this time, the stretched portion 12 is maintained in a temperature range where the stretchability of the stretched film is secured.

  In the heat fixing unit 13, reheating is performed on the stretched film. By heat setting (heat setting), the orientation of the molecules in the film aligned through stretching is fixed in the vertical and horizontal orientations. As a result, it is possible to prevent the occurrence of defects such as extreme shrinkage of the film against subsequent heat changes applied to the film.

  In the slow cooling part 14, in order not to give a temperature impact to the stretched film after heat setting, the heating temperature is gradually lowered while maintaining a temperature somewhat lower than the heating temperature of the heat setting part. In the cooling unit 15, the stretched film that has been gradually cooled is cooled. In the illustrated tenter, the cooling unit corresponds to the carry-out unit.

  A slow cooling part and a cooling part are formed in a tenter if necessary. This is taken into account according to physical properties such as the softening point of the film. In addition, it is also possible to abbreviate | omit the cooling part shown in figure by naturally cooling a film under atmospheric temperature after heat setting (after slow cooling). However, in this case, the entire length of the device itself needs to be longer.

  In the disclosed tenter type stretching apparatus 1, as shown in the schematic side view of the tenter 10 of FIG. 3, as defined in the invention of claim 2, a heating unit 31 that heats the inside of the tenter, and superheated steam inside the tenter The superheated steam jetting part 32 to inject is arranged in the tenter. Due to the thermal conductivity unique to superheated steam, the heating efficiency in the tenter is increased compared to heating via air. Therefore, as defined in the invention of claim 3, the superheated steam jetting part 32 is provided in at least one of the preheating part 11, the extending part 12, and the heat fixing part 13 that are effective in the apparatus as a heat source.

  A specific configuration in the tenter will be described with reference to FIG. In the tenter 10, a plurality of heating sections 31, superheated steam jet sections 32, and exhaust suction sections 33 are arranged in the order of the preheating section 11, the stretching section 12, and the heat fixing section 13 in accordance with the traveling direction of the stretched film to be conveyed. Is done.

  The stretched film conveyed to the preheating unit 11 is first heated by the heating unit 31. This is the purpose of preheating for maintaining the steam state of the superheated steam. In this example, in order to further improve the heating performance of the preheating part, the superheated steam jet part 32 is installed. The temperature rise of the preheating part 11 becomes easy from the good thermal conductivity of superheated steam. By providing the exhaust suction portion 33, excessive stagnation of superheated steam can be prevented, and the internal temperature can be easily controlled.

  In the stretching unit 12, heating is performed by the heating unit 31 and superheated steam is jetted from the superheated steam ejecting unit 32 in order to maintain a temperature range that facilitates stretching of the softened stretched film. Again, the superheated steam is recovered from the exhaust suction part 33, and the same effect as described above can be obtained. Note that the superheated steam injection pressure and the injection direction are appropriately adjusted in order to suppress as much as possible stretching distortion (Boeing phenomenon) caused by superheated steam injection.

  In the heat setting part 13, it is necessary to maintain the heat setting temperature for a certain period of time for the purpose of stabilizing the orientation of the film composition molecules after the stretching. That is, a certain amount of heat is required for heat fixing of the film resin. Therefore, superheated steam is jetted from the superheated steam jetting unit 32 together with heating by the heating unit 31. Even in the subsequent slow cooling section 14, the temperature is gradually decreased in order to avoid a rapid temperature decrease from the heat fixing section. In this case, it is preferable to perform temperature control while using the heating unit 31 and the superheated steam jetted from the superheated steam jet unit 32. Of course, the recovery of superheated steam from the exhaust suction part 33 is performed.

  In the illustrated tenter 10, the carry-in port 16 of the preheating unit and the carry-out port 17 of the cooling unit are made narrow in order to suppress a decrease in the internal temperature. Further, if necessary, the shielding property is enhanced by the shielding gas sc ejected from the air curtain section 18. For this reason, leakage of the air and water vapor in the tenter to the outside is substantially suppressed. In particular, by providing the exhaust suction part 33, it is possible to increase the recovery efficiency of water vapor whose temperature has decreased after injection.

  After stretching, heat setting, and the like using superheated steam by the tenter 10, the stretched film is wound up and becomes a product.

  The configuration in the vicinity of the heating unit 31, the superheated steam jet unit 32, and the exhaust suction unit 33 will be described with reference to FIG. According to the embodiment, the normal pressure superheated steam SS ejected from the superheated steam jet section 32 is discharged into the tenter and contacted with the stretched film w, and the temperature is reduced to become drainage steam S. Obviously, the wastewater vapor often contains volatile organic components that volatilize from the stretched film. If water vapor containing these volatile organic components and the like stays in the tenter 10, there is a possibility that it becomes a contamination factor of the stretched film. In order to prevent the sewage steam S from staying in the tenter, the sewage steam S is quickly recovered from the exhaust suction part 33. Wastewater vapor and the like discharged from the exhaust suction part to the outside of the drying chamber are removed and separated through the removal part 36. The removal part 36 consists of well-known members, such as a filter for volatile organic solvents, a cooling pipe, for example. Symbol h is a heat ray emitted from the heating unit. The heating method of the heating unit is appropriate, and far-infrared heating such as heating wire, gas heating, and the like can be applied.

  By providing the exhaust suction part 33 and the removal part 36, volatile components and the like can be separated from the waste water vapor, so that the burden on facilities and costs is reduced compared to separation and treatment from dry gas. In particular, according to the disclosed embodiment, the water from which the volatile components have been removed is sent to the superheated steam generator 37 again through the circulation line 35, and the water is reused. For this reason, water consumption can be saved. For the superheated steam generator 37, a known superheated steam generator such as an electromagnetic induction system or a burner system is used.

  In the case of heating in the tenter via conventional heated air, the stretched film is in direct contact with oxygen, so the film surface is affected by oxidative degradation and the like. As a result, the composition of the surface resin may change and unnatural crosslinking may be promoted. However, in the superheated steam atmosphere, even if the stretched film has a calorific value, it is only affected by a low concentration of oxygen. Therefore, the risk of resin modification is reduced. In addition, in the past, it was necessary to overheat the heating equipment because it was necessary to heat and stretch the film resin at a slightly lower temperature in consideration of the modification of the film resin. On the other hand, by using atmospheric pressure superheated steam, even if the stretched film receives heat in a high temperature range, the heat exposure time is shortened, and it is possible to reduce the possibility of modification of the stretched film. Become. Considering these, it can be assumed that the stretching equipment such as a tenter required for film production is downsized and the film production cost is reduced.

  In the embodiment of the disclosure, in order to uniformly heat both surfaces of the film, a heating unit, a superheated steam jet unit, and an exhaust suction unit are arranged on both the upper surface side and the lower surface side of the film to be stretched (heating target). Yes. Of course, depending on the film to be heated, only one side may be heated. In this case, the heating part, the superheated steam jet part, and the exhaust suction part are arranged only on one side of the film. Further, the arrangement, the number, and the like of the heating unit, the superheated steam ejection unit, and the exhaust suction unit are appropriate depending on the equipment. For example, the heating unit or the exhaust suction unit can be integrated into one place. In another form, it is also possible to combine the heating unit and the superheated steam jet unit into one and change the injection by switching various valves. Furthermore, it is also possible to arrange the heating unit, superheated steam jetting unit, and exhaust suction unit in a stretching apparatus that extends in the vertical direction disclosed in Japanese Patent No. 2606345.

  A film made of a resin such as a polyolefin film, a polyamide film, a polyester film, or a biodegradable polymer film is used as a stretched film that is stretched by a tenter-type biaxial stretching apparatus, as defined in the invention of claim 4. It is done. Therefore, it is possible to replace the conventional production method based on the tenter type biaxial stretching.

  Examples of polyolefin films include ethylene homopolymers, random and one or more α-olefins such as ethylene and propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, or the like. Block copolymer, one or more random or block copolymers of ethylene and vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, propylene homopolymer, ethylene other than propylene and propylene, 1-butene , 1-pentene, 1-hexene, 4-methyl-1-pentene, etc., one or more random or block copolymers with α-olefin, 1-butene homopolymer, ionomer resin, and Hydrocarbons such as polyolefin resins such as mixtures of these polymers, petroleum resins and terpene resins It is a resin film formed from a raw resin or the like.

  Examples of polyamide films are resin films formed from polyamide-based resins such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, nylon 6/66, nylon 66/610, and nylon MXD. Examples of polyester films are resin films formed from polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

  Examples of biodegradable polymer films include polylactic acid, caprolactone butylene succinate, polybutylene adipate terephthalate, polybutylene succinate, polycaprolactone, polybutylene adipate succinate, polyethylene terephthalate succinate, polyethylene succinate, polyhydroxybutyrate It is a resin film formed and formed from various biodegradable polymers such as a rate.

  Other usable resin films include acrylic resins such as polymethylmethacrylate, styrene-acrylonitrile resins such as polystyrene and styrene-acrylonitrile copolymers, hydrogen such as polyimide resins, polyvinyl alcohol, and ethylene-vinyl alcohol copolymers. Examples thereof include a resin film formed from a binding resin, a polycarbonate resin, or the like. As described above, in the resin types listed, the properties such as compatibility between resins are taken into consideration, and stretching and film formation are performed as a multilayer film by coextrusion.

  Note that, among the stretched films made of the resin types listed, in the case of the composition of a high heat resistant resin, stretching at a high temperature is required, and therefore, normal pressure superheated steam at 300 to 400 ° C. is used. In the case of other resins, atmospheric superheated steam at around 100 to 300 ° C. is used. The temperature of the atmospheric superheated steam is appropriately set according to the resin type.

  For resin films such as polyolefin film, polyamide film, and polyester film, in addition to antistatic agents such as amines, antifogging agents, antiblocking agents, thermal stabilizers, antioxidants, light stabilizers Various additives such as a crystal nucleating agent, a lubricant, an ultraviolet absorber, a surfactant for the purpose of imparting slipping property and antiblocking property are often contained in the film. In such a case, it is considered that the influence of various additives due to the high temperature and the presence of oxygen is reduced by using atmospheric superheated steam.

  As described above, according to the method for producing a thermoplastic film of the present invention, extremely high heating efficiency can be obtained because of the good thermal conductivity unique to atmospheric superheated steam. Moreover, since the heat exposure time during stretching is shortened, thermal degradation can be suppressed. According to the film manufactured by the manufacturing method, as is clear from the examples described later, the function is improved in terms of the haze and surface resistivity performance as compared with the existing manufacturing method. In addition, effects such as improved adhesion of various coating films including dry coating such as vapor deposition or wet coating such as silicone, reduction of blocking, and suppression of low molecular weight product formation on the film surface are expected.

[Usage equipment and materials]
The inventors tried to evaluate the stretching using atmospheric superheated steam and the conventional stretching using heated air. Using an oven cooker ("AX-HC1" manufactured by Sharp Corporation) as a generator for normal pressure superheated steam, using the setting of the water oven roast mode (normal pressure superheated steam generation) of the oven cooker, The example was heated. In heating using an oven cooker, 50% or more of the oven internal volume is filled with superheated steam. Moreover, the nozzle flow rate of the superheated steam of this setting was 2 m / min or more. As a control, the setting of the oven mode (normal air heating) of the oven cooker was used to heat the comparative example described later.

  As an object to be stretched, an unstretched sheet prepared from polypropylene film: polypropylene raw material FL6H (manufactured by Nippon Polypro Co., Ltd.) was used (Example 1, Comparative Example 1). Moreover, in order to evaluate the influence of atmospheric superheated steam, a biaxially stretched biodegradable polymer resin film: a polyethylene terephthalate succinate film having a thickness of 50 μm was used (Example 2, Comparative Examples 2 to 5). This biaxially stretched biodegradable polymer resin film is composed of polyethylene terephthalate succinate as a main component biodegradable polymer, sodium alkyl sulfonate and glycerin monostearate as an antistatic agent, and both antistatic agents as main components. It is a film kneaded into.

[Measurement items]
The following measurement was performed under the conditions of 23 ° C. and 50% RH (relative humidity).

  The haze was measured using “Haze Meter NDH2000” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7105 (1981).

  The surface resistivity was measured in accordance with JIS-K-6911 using a high resistivity-resistivity meter (“MCP-HT260” manufactured by Mitsubishi Oil Chemical Co., Ltd.).

[Stretching test]
The difference between the time (seconds) required for stretching the unstretched product and the haze (%) was measured. An unstretched sheet of polypropylene film having an equal amount was placed in the oven cooker. This was pulled with an equal amount of load, and the time required to reach 10 times the length from the beginning was measured. About Example 1, it pulled on the conditions of the water oven roast mode of the same oven cooking device, and it pulled on the conditions of the oven mode about Comparative Example 1. Then, the haze of the polypropylene resin piece which reached 10 times length was measured. Example 1 is heating with atmospheric superheated steam (heating temperature: 170 ° C.), and Comparative Example 1 is heating with air (heating temperature: 170 ° C.). These results are shown in Table 1.

[Evaluation of impact]
For the biodegradable polymer film, using the above-mentioned oven cooker, heating using superheated steam as a heat medium using the water oven roast mode (always generating superheated steam) (Example 2), Using oven mode (normal air heating), heating using air as a heat medium (Comparative Examples 3 to 5) was performed, and haze (%) and surface resistivity (Ω / □) were measured. In both Example 2 and Comparative Examples 3 to 5, the heating temperature was set to 200 ° C., and the films of Examples and Comparative Examples were heat-treated while pulling the four sides of the respective films and keeping them in tension. The heating time of the comparative example is as shown in Table 2. In order to control the heat treatment, the haze (%) and the surface specific resistivity (Ω / □) were also measured in the non-heat treated Comparative Example 2.

  As understood from the results in Table 1, stretching using superheated steam can be performed for a short time (Example 1). This is thought to be due to the good thermal conductivity of superheated steam. In addition, since the haze value is kept low, it is considered that the heat exposure was shortened and deterioration such as oxidation of the resin molecules was suppressed. At the same time, it can be said that oxygen is an inhibitory condition.

  Although the result of Table 2 is about the film which became a product, the heating using superheated steam is rather improved in the property of the film. Although details are unknown, it suggests that heating by oxygen suppression conditions has an influence.

  Based on the above results, heating using superheated steam can efficiently conduct heat to the film resin and can lower the oxygen concentration than in the atmosphere. Accordingly, it is possible to perform heating for a short time while suppressing the influence of oxidation or the like. This is superior in heating efficiency compared to heating in an inert gas atmosphere. Therefore, when designing a tenter, which is an apparatus required for stretching a thermoplastic film, it can be assumed that the tenter is easily downsized from a full-length tenter considering heat conduction.

It is a schematic perspective view of the tenter type stretching apparatus of the present invention. It is a principal part top view of FIG. It is a principal part side view of FIG. It is a principal part enlarged view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biaxial stretching apparatus 10 Tenter 11 Preheating part 12 Extending part 13 Heat fixing part 14 Slow cooling part 15 Cooling part 19 Clip 21 T die 23 Heating roller 31 Heating part 32 Superheated steam jet part 33 Exhaust suction part 37 Superheated steam generation part SS Normal pressure superheated steam S Drainage steam w Stretched film

Claims (4)

In the method for producing a thermoplastic film involving a stretching step,
The stretching step is a method for producing a thermoplastic film, wherein the film is stretched by applying normal-pressure superheated steam at 100 to 400 ° C. to the film to be stretched in a tenter stretching apparatus.   The tenter type stretching apparatus includes a preheating section, a stretching section, and a heat fixing section, a heating section that heats the inside of the tenter, and a superheated steam jet section that jets superheated steam into the tenter. The manufacturing method of the thermoplastic film as described in any one of.   The method for producing a thermoplastic film according to claim 2, wherein the superheated steam jetting part is provided in at least one of the preheating part, the stretching part, and the heat fixing part.   The method for producing a thermoplastic film according to any one of claims 1 to 3, wherein the stretched film is a polyolefin film, a polyamide film, a polyester film, or a biodegradable polymer film.

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