JP2012016910A - Method for producing polyolefin-based resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyolefin-based resin film excellent in transparency and heat-resistant dimensional-stability and suitable for surface protection.SOLUTION: In the method for producing the polyolefin-based resin film, the method including a process that, after the melt-extruded polyolefin-based resin film is cooled to be solidified by making it contact with a cooling roll whose surface temperature is set at 30°C or less, the cooled film is heat-treated by making it contact with a heat treatment roll whose surface temperature is set in a range of 95-135°C without using a nip roll, the film is preheated in such a way that a film temperature just before the heat-treatment becomes 105°C or below and in a range of [heat-treatment temperature (°C) -35°C] to [heat-treatment temperature (°C) -15°C]. The film obtained by the method has no transfer mark, no stick-slip trace and no streak in the flow direction thereof.

Description

  The present invention relates to a method for producing a polyolefin-based resin film excellent in transparency and heat-resistant dimensional stability, and more specifically, a film produced during heat treatment by a heating roll after quenching a melt-extruded polyolefin-based resin film. The present invention relates to a method for producing a polyolefin resin film suitable for surface protection that does not cause poor appearance.

  In recent years, in order to prevent scratches, dust adhering and contamination during processing of liquid crystal panels and polarizing plates of personal computers and liquid crystal televisions, a surface protective film made of synthetic resin with a removable surface is used for liquid crystal panels and polarizing plates. It is practiced to attach to and protect (see, for example, Patent Document 1).

  In particular, polypropylene-based unstretched films are widely used in the field of surface protection films because they have good transparency and heat resistance (see, for example, Patent Document 2).

  The surface protective film is generally used by laminating an adhesive layer on the surface of the base film and fixing it to the surface of the target article to be protected using the adhesive force of the adhesive layer. With the expansion of applications in recent years, demands for quality and cost reduction have increased, and a base film having excellent adhesive processability has been demanded. In particular, the processing temperature is increasing for the purpose of increasing the processing speed of adhesive processing, etc., and even when processed at a high temperature, thermal deformation due to the processing temperature is small, and dimensional stability during processing is good, There is a demand for dimensional stability at high temperatures (also referred to as heat-resistant dimensional stability) that suppresses the occurrence of thermal wrinkles during processing.

  As a method for improving the heat-resistant dimensional stability of a film, a polypropylene resin film to which a crystal nucleating agent is added has been proposed (for example, see Patent Document 3).

  However, if this method is adopted, the residence time during extrusion of the resin becomes relatively long in a large-scale production equipment level considering economy, so that the fish eye caused by aggregation and decomposition of the crystal nucleating agent in the film There is a problem that minute foreign matters called.

  As another method for improving the heat-resistant dimensional stability of the film, a composition in which an aromatic organophosphate metal salt is blended with a polypropylene resin having specific characteristics is extruded with a cooling roll at a temperature of 40 to 50 ° C. It has been proposed (see, for example, Patent Document 4).

  However, the film obtained by the above method may cause fish eyes due to the aromatic organophosphate metal salt, and many spherulites with large crystal sizes are generated during cooling, resulting in poor transparency. Therefore, the usage is limited.

  As described above, the use of various additives as a method for achieving both transparency and heat-resistant dimensional stability of the film can cause fish eyes, so that the crystal can be rapidly cooled so that the crystal size does not increase when casting the molten resin. And the method of improving crystallinity by heat processing after that and providing heat resistance is also proposed (for example, refer patent documents 5 and 6).

  However, since the surface of the heating roll used in the heat treatment of the film in the above method has a mirror finish, when heated to near the melting point of the film material, the smooth roll surface tends to adhere to the film, and the film surface There is a problem that a periodic peeling trace-like appearance defect is generated on the surface during melt adhesion and peeling (stick-slip phenomenon).

  As a method for preventing the appearance defect as described above, there is a method in which a nip roll is not used in order to reduce the adhesion between the film and the heating roll surface. However, when the film is brought into contact with the heating roll without using the nip roll, streaks in the flow direction of about 1 to 3 mm width are generated at a pitch of about 5 mm in the width direction on the entire surface of the film. The film in which the streaks are generated has a poor appearance and cannot be used for a surface protective film, for example.

  The cause of this streak originates from the fact that the film floats on the heated roll, the crystal growth differs between the part that is in contact with the roll and the part that is not in contact, and a haze difference occurs between the white part and the transparent part. Is. As a mechanism of the film floating on the heating roll, when the film comes into contact with the heating roll, the film instantaneously tries to thermally expand in the width direction, but since the smoothness of the film and the heating roll is poor, the film width is It is thought that this is because the expanded portions do not follow and are generated at regular intervals as floating.

  Under these circumstances, when heat-treating a film with a heating roll, a nip roll is generally used so as not to cause the film to float due to thermal expansion, which causes poor appearance due to increased adhesion between the film and the heating roll. Will occur.

JP 2005-281328 A Japanese Patent Laid-Open No. 10-309781 JP 2002-146130 A JP-A-10-298367 JP 2003-170485 A JP 2009-12225 A

  The present invention was devised in view of such problems of the prior art, and its purpose is to prevent adhesion of the film to the heating roll during heat treatment by the heating roll after quenching of the polyolefin resin film that has been melt-extruded, An object of the present invention is to provide a method that does not cause appearance defects such as transfer marks, stick-slip marks, or streaks in the flow direction accompanying the float of the film and the heating roll.

  In order to achieve the above object, the present inventors have intensively studied a method in which the heating roll is in close contact with the film and does not stick to it, and as a result, the present invention has been completed.

That is, the present invention has the following configurations (1) to (3).
(1) After the melt-extruded polyolefin resin film is brought into contact with a cooling roll having a surface temperature of 30 ° C. or less and cooled and solidified, it is brought into contact with a heating roll having a surface temperature of 95 to 135 ° C. without using a nip roll. In the method for producing a polyolefin resin film including heat treatment, the film is formed so that the film temperature immediately before the heat treatment is 105 ° C. or less and the heat treatment temperature (° C.) − 35 ° C. to the heat treatment temperature (° C.) − 15 ° C. A method characterized by preheating.
(2) The method according to (1), wherein the polyolefin resin film contains 50% by weight or more of a crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of 85% or more. .
(3) The method according to (1) or (2), wherein the polyolefin resin film is an unstretched film for surface protection.

  According to the method of the present invention, the film can be effectively prevented from sticking to the heating roll during the heat treatment of the film by the heating roll. High transparency can be maintained without causing appearance defects such as streaks. Since the film obtained by the method of the present invention is excellent in heat-resistant dimensional stability, for example, it is excellent in proper secondary processing such as adhesive processing, and even when subjected to treatment such as drying at a high temperature around 130 ° C. Generation of wrinkles and film sagging is suppressed. Moreover, since it is excellent in transparency and an appearance defect does not generate | occur | produce, it is excellent in the visibility of a to-be-protected body.

  The method of the present invention includes heat-treating a melt-extruded polyolefin-based resin film by first bringing it into contact with a cooling roll and then cooling and solidifying it, and then bringing it into contact with a heating roll. The reason why the film is cooled and solidified and then heated is to suppress crystal growth of the melt-extruded film by cooling and maintain transparency.

  As a method for cooling and solidifying a film with a cooling roll, a conventionally known method can be appropriately employed. Although it does not specifically limit about the contact time (cooling time) of a film and a cooling roll, 1 second or more is preferable. When the contact time is less than 1 second, the cooling effect is insufficient, and the transparency is deteriorated, which is not preferable. On the other hand, the upper limit of the cooling time is not particularly limited from the viewpoint of the crystallinity of the film, but is preferably 5 seconds or less from the viewpoint of economy and productivity. The cooling roll temperature is preferably 30 ° C. or less, and more preferably 28 ° C. or less. When the cooling roll temperature exceeds the above temperature, spherulites grow and the transparency deteriorates, which is not preferable. The lower limit of the cooling roll temperature is not particularly limited, but is 5 ° C. from a practical viewpoint.

  As a heat treatment method using a heating roll, a conventionally known method can be appropriately employed. One heating roll may be used, but a film may be passed between the two heating rolls, and one surface may be sequentially heated with each heating roll. The contact time (heating time) with the heating roll is preferably 1 second or longer. The contact time between the film and the heating roll can be controlled by the traveling speed of the film, the diameter of the heating roll, and the holding angle of the film on the roll. Further, it is possible to use three or more heating rolls in order to increase the contact time with the heating rolls. The upper limit of the contact time with the heating roll is not particularly limited, but there is no difference in effect even if the treatment is performed for more than 1 second to several seconds considered to complete the phase transition. However, 30 seconds or less are preferable from the viewpoint of productivity and economic constraints of the apparatus. More preferably, it is 10 seconds or less, and particularly preferably 5 seconds or less. If a film is provided with many heating rolls for a long time, scratches, surface transfer of the heating roll, etc. are likely to occur.

  The method of the present invention is characterized in that a nip roll is not used when the film is brought into contact with a heating roll for heat treatment. This is because when the nip roll is used, transfer marks and peeling marks to the film having the surface shape of the heating roll or nip roll easily occur when the film is softened by the heat treatment. When using a nip roll, if a heated roll with a low surface roughness is used, the adhesiveness of the film becomes too high and sticks. When peeling, a defective appearance due to stick-slip is likely to occur, and the heated roll has a high surface roughness. When is used, the surface shape is transferred when it is in close contact with the film, and the appearance is likely to be poor. Such a problem does not occur when the nip roll is not used.

  The surface temperature of the heating roll needs to be 95 ° C. or higher, which is the temperature at which the pseudo-hexagonal polypropylene transitions to a monoclinic crystal, and is preferably 100 ° C. or higher. If it is less than 95 ° C., solid phase transition hardly occurs and the effects of the present invention may not be obtained. Moreover, as an upper limit of the surface temperature of a heating roll, it is required that it is less than melting | fusing point of resin which comprises a film outermost layer. Since the melting point of polypropylene resins generally handled industrially is 140 ° C. to 160 ° C., the upper limit of the surface temperature of the heating roll needs to be 135 ° C. or less, preferably 130 ° C. or less. is there.

  Heat treatment of the film with a heating roll can be performed after winding the cooling film into a roll and then unwinding it again, but it can be performed in a series of film manufacturing processes without winding after film formation. preferable. When continuously rolled up, the film has improved elasticity, dimensional stability, slipperiness and anti-blocking properties, resulting in wrinkling and sagging problems. Hateful.

  The method of the present invention is characterized in that the film is preheated so that the film temperature immediately before the heat treatment is 105 ° C. or less and the heat treatment temperature (° C.) − 35 ° C. to the heat treatment temperature (° C.) − 15 ° C. The preheating temperature of the film immediately before the heat treatment is preferably 105 ° C. or lower and the heat treatment temperature (° C.)-30 ° C. to the heat treatment temperature (° C.)-15 ° C. If the preheating temperature is excessively lower than the heat treatment temperature, so-called heat shock occurs during the heat treatment due to insufficient preheating, and streaks in the direction of the flow due to film floating may occur. Further, if the preheating temperature exceeds 100 ° C. or the difference from the heat treatment temperature is too small, streaks due to heat shock may occur at the preheating stage.

  The method for preheating the film is not particularly limited, and examples thereof include a method of heating the film by bringing it into contact with a heating roll, and a method of heating the running film in a non-contact manner by a heating means such as a heater. It is preferable from the viewpoint of reducing heat shock that the film is preheated not in a single step but in multiple stages. When performing in multiple stages, for example, it is preferable to set the heating roll in two stages and set the preceding heating roll to 0 to 30 ° C. lower than the subsequent heating roll.

  The polyolefin resin used in the present invention is a crystalline olefin homopolymer or copolymer, for example, polyethylene resin, polypropylene resin, polybutene resin, polypentene resin, polyhexene resin, ethylene-propylene copolymer. Examples thereof include a copolymer, an ethylene-butene-1 copolymer, an ethylene-pentene-1 copolymer, an ethylene-hexene-1 copolymer, and an ethylene-4-methyl-pentene-1 copolymer.

  Although the thickness of a polyolefin-type resin film is not specifically limited, In order to perform cooling and heat processing efficiently, 10 micrometers-200 mm are preferable, and 20 micrometers-100 micrometers are more preferable. Moreover, although the extrusion rate of a polyolefin-type resin film changes with thickness of a film, in order to perform cooling and heat processing efficiently, 1-50 m / min is preferable.

  As the polyolefin resin, it is preferable to use a highly crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of preferably 85% or more, preferably 50% by weight or more, and preferably 90% by weight or more.

Here, the isotactic pentad fraction (mmmm fraction) is a resin constituting the resin film by a ¹³ C-NMR (nuclear magnetic resonance) measurement method using carbon C (nuclide) having a mass number of 13. It is calculated from a numerical value (electromagnetic wave absorptivity) obtained by resonating the composition at a predetermined resonance frequency, and defines the atomic arrangement, electronic structure, and molecular microstructure in the resin composition. The isotactic pentad fraction of the polypropylene resin means a ratio of five propylene units obtained by ¹³ C-NMR measurement in a predetermined arrangement, and is used as a measure of crystallinity or stereoregularity. Yes.

  For polyolefin resins, other resins such as random polymerized polypropylene resin, ethylene-propylene copolymer rubber, and styrene-butadiene copolymer are used as necessary for the purpose of improving extrusion film formation and impact resistance, for example. It is also possible to add an elastomer component such as a polymer or a hydrogenated product thereof, and an ethylene-propylene-diene monomer copolymer. In particular, when flexibility is required, it is preferable to add an elastomer component.

  However, if a material with poor compatibility with the polyolefin-based resin is added, it may peel off at the interface between the resins during the bending process, causing whitening, cracking, breakage, etc., and the amount of these additives added increases. This naturally reduces the properties of the polyolefin resin. Therefore, it is preferable that the amount of the various additives added is limited to 10% by weight or less, and the highly crystalline polypropylene resin is contained in an amount of 50% by weight or more, further 90% by weight or more.

  The polyolefin resin preferably has a melt flow rate (MFR) of 3 to 15 g / 10 min (230 ° C.). If the melt flow rate is too high, the melt viscosity in the molding process is low and the shape maintenance becomes unstable, and it may be difficult to obtain a stable heat treatment effect such as whitening in the molding process. If the melt flow rate is too small, it may be difficult to extrude the film.

  The polyolefin resin film of the present invention may be a single layer or a laminate. In the case of a single layer film, it is preferable that at least one layer constituting the film can improve the crystallinity by heat treatment when the film itself is a laminate.

  Since the polypropylene resin film obtained by the method of the present invention has good transparency and excellent heat-resistant dimensional stability, it is attached to the surface of a metal plate, a decorative plate, a resin plate, a glass plate, etc. Prevents surface scratches, dirt and rust that tend to occur during processing, etc., and scratches and dust when processing and assembling electronic, precision products, parts, and related materials such as liquid crystal panels and related materials such as polarizing plates It is suitably used as a surface protective film for preventing adhesion, contamination, etc. of automobiles, and protecting the coating film of automobile bodies from acid rain, dust, dust, etc. during transportation and storage of automobiles.

  Hereinafter, the effects of the present invention will be described with reference to examples. However, the present invention is not limited by these examples, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. . In addition, the evaluation method of the characteristic mentioned in this specification is as follows.

(1) Melt flow rate Based on JIS-K7210, it measured by the method of condition-14 (load 2.16kg, temperature 230 degreeC).

(2) Isotactic pendant fraction The isotactic pendant fraction is an abundance ratio of isotactic chains in the pentad unit in the polypropylene molecular chain measured using ¹³ C-NMR, and propylene. This is the fraction (mmmm) of the propylene monomer at the center of a chain that is meso-bonded in a unit of 5 units. Specifically, it calculated | required as a mmmm peak fraction in the total absorption peak in the methyl carbon area | region in a < ¹³ > C-NMR spectrum.

(3) Streaks in the flow direction The presence or absence of streaks in the flow direction on the film surface was visually observed. Judgment criteria are as follows.
The streak in the flow direction cannot be seen: ○
Thin streaks in the flow direction can be confirmed:
The streak in the flow direction can be clearly confirmed: ×

(4) Stick-slip marks The presence or absence of periodic peeling marks on the film surface was visually observed. Judgment criteria are as follows.
Stick-slip marks are not visible: ○
The stick-slip mark can be confirmed thin: △
The stick-slip mark can be clearly confirmed: ×

(5) Transfer trace The presence or absence of unevenness due to the transfer of the heating roll on the film surface was visually observed. Judgment criteria are as follows.
Cannot see the transfer mark: ○
A thin transfer mark can be confirmed: △
Transfer marks can be clearly seen: ×

(6) Heat-resistant dimensional stability It was performed according to JIS-Z1715. That is, the film is cut into a rectangle of 20 mm × 250 mm, marked with a distance of 150 mm, heat-treated for 30 minutes in a hot air dryer at 80 ° C. under no load, and then the vertical and horizontal dimensions of the film. Was measured, and the thermal shrinkage rate was determined according to the following formula. When the heat shrinkage rate was less than 1% in both the vertical and horizontal directions, it was judged as good, and when it exceeded 1%, it was judged as bad.
Thermal contraction rate (%) = {(distance between gauge points before heating−distance between gauge points after heating)
/ Distance between gauge points before heating} × 100

(7) Haze value Based on JIS-K-6714, it measured using "Haze Tester J" made by Toyo Seiki Seisakusho.

(8) Crystallinity Measured using a wide-angle X-ray diffraction transmission method (RIGAKU RINT2500).

(9) Fish eye The molded film is cut out at 33.3 cm (longitudinal direction) × 30 cm (horizontal direction), placed on a plate irradiated with a fluorescent lamp from below the film, and visually observed with transmitted light. The number of fish eyes of 1 mm or more was counted. Next, if the counted fish eye is immersed in liquid nitrogen and hardened, it is cut in half with a razor and the cross section of the fish eye is observed with a microscope at 50 to 300 times. For example, if there is no foreign matter such as cellulose, it is determined that it is a fish eye caused by gel such as an unmelted mass, a mass due to gelation of a part of the raw material, or a mass due to partial deterioration of the material during molding. However, if there was a nucleus, it was judged as a fish eye caused by a foreign object and excluded from the count.

Example 1
100% by weight of a polypropylene homopolymer resin (FLX80E4, manufactured by Sumitomo Chemical Co., Ltd., melt flow rate = 7, isotactic pendart fraction 90%) was melt-extruded with a T-die film forming machine, and a cooling roll temperature of 25 Cooling time at 2.4 ° C. (film forming speed 40 m / min), draft ratio at the time of taking molten resin 0.64 (die slip gap: 0.5 mm, die slip outlet molten resin speed: 4.8 m / min) , An air gap: 8 cm), an unstretched film having a thickness of 40 μm was obtained. The resin temperatures in the feeding zone, kneading zone and metering zone of the extruder were 230 ° C., 240 ° C. and 235 ° C.

  Thereafter, the unstretched film was preheated by sequentially contacting the first preheating roll and the second preheating roll, and immediately after that, it was sequentially contacted by two heating rolls to perform heat treatment. The surface temperature of the first preheating roll was 80 ° C. and the preheating time was 1.5 seconds, and the surface temperature of the second preheating roll was 100 ° C. and the preheating time was 1.5 seconds. The surface temperature of the two heating rolls was 120 ° C., and the heating time was 1.5 seconds. No nip roll was used for the heated roll. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this example was good in all measured properties and high quality.

(Example 2)
A film was obtained in the same manner as in Example 1 except that the surface temperature of the second preheating roll was changed to 95 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this example was good in all measured properties and high quality.

(Example 3)
A film was obtained in the same manner as in Example 1 except that the surface temperatures of the first preheating roll and the second preheating roll were both changed to 95 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this example was good in all measured properties and high quality.

Example 4
A film was obtained in the same manner as in Example 1 except that the surface temperatures of the first preheating roll and the second preheating roll were both changed to 80 ° C. and the two heating roll temperatures were changed to 100 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene-based resin film obtained in this example has a lower crystallinity than the polypropylene-based resin film obtained in Example 1, but other than that, it has the same characteristics and is of high quality. there were.

(Example 5)
A film was obtained in the same manner as in Example 1 except that the resin used for melt extrusion was 95% by weight of polypropylene homopolymer resin and the remaining 5% by weight of polypropylene random polymer resin was used. . The evaluation results of the finally obtained film are shown in Table 1. The polypropylene-based resin film obtained in this example has a lower crystallinity than the polypropylene-based resin film obtained in Example 1, but other than that, it has the same characteristics and is of high quality. there were.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1 except that the surface temperature of the first preheating roll was changed to 60 ° C. and the surface temperature of the second preheating roll was changed to 80 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this comparative example had a low preheating effect, streaks in the flow direction, and low quality.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the surface temperatures of the first preheating roll and the second preheating roll were both changed to 110 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene-based resin film obtained in this comparative example had a preheating temperature that was too high, streaks in the flow direction were generated, and the quality was low.

(Comparative Example 3)
A film was obtained in the same manner as in Example 1 except that nip rolls were used for the first and second heating rolls. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this comparative example was poor in quality due to the generation of transfer marks and stick-slip marks.

  Since the polyolefin-based resin film obtained by the method of the present invention is excellent in transparency and heat-resistant dimensional stability, it can be suitably used as a protective film for various uses and contributes greatly to the industry. .

Claims (3)

  After the melt-extruded polyolefin-based resin film is brought into contact with a cooling roll having a surface temperature of 30 ° C. or less and cooled and solidified, it is brought into contact with a heating roll having a surface temperature of 95 to 135 ° C. without using a nip roll and heat-treated In a method for producing a polyolefin-based resin film containing, the film is preheated so that the film temperature immediately before the heat treatment is 105 ° C. or less and the heat treatment temperature (° C.) − 35 ° C. to the heat treatment temperature (° C.) − 15 ° C. A method characterized by.   The method according to claim 1, wherein the polyolefin-based resin film contains 50% by weight or more of a crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of 85% or more.   The method according to claim 1 or 2, wherein the polyolefin resin film is an unstretched film for surface protection.