JP2012016908A - 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 below, the cooled film is heat-treated by making it contact with a heat treatment roll whose surface temperature is set in a range of 80-140°C, a surface roughness of the heat treatment roll is in a range of 0.4-1.8 μm. The film obtained by the method has no transfer mark and no stick-slip trace.

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).

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, The object is to provide a method that does not cause appearance defects.

  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) A polyolefin comprising: bringing a melt-extruded polyolefin-based resin film into contact with a cooling roll having a surface temperature of 30 ° C. or less and cooling and solidifying the polyolefin resin film; In the method for producing a resin film, the heating roll has a surface roughness of 0.4 μm or more and 1.8 μm or less.
(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, since the film can be effectively prevented from sticking to the heating roll during the heat treatment of the film with the heating roll, the appearance of the film surface is not deteriorated during the heat treatment, and high transparency is achieved. Can be maintained. 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.

  In the method of the present invention, the surface roughness of the heating roll used for heat treatment of the film is 0.4 μm or more and 1.8 μm or less. Preferably they are 0.5 micrometer or more and 1.5 micrometers or less. If the surface roughness is less than the above lower limit, the adhesion of the film becomes too high and sticks, and an appearance defect due to stick-slip occurs at the time of peeling. On the other hand, when the above upper limit is exceeded, the surface shape is transferred when the film adheres, resulting in poor appearance.

  The shape of the surface of the heating roll is not particularly limited, and a surface finished in a spiral groove, a surface cut in a diamond cut shape, a surface finished in a satin finish, etc. can be used. Those having a shape-like roughness profile are preferred from both the air flow problem and the problem of transferring the roll surface roughness profile to the film surface.

  The surface temperature of the heating roll needs to be 80 ° C. or higher, preferably 95 ° C. or higher, which is the temperature at which the pseudo-hexagonal crystal of polypropylene undergoes solid phase transition to monoclinic crystals. Below 80 ° C., solid phase transition does not occur and the effect of the present invention cannot 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 resin generally handled industrially is 140 ° C. to 160 ° C., the upper limit of the surface temperature of the heating roll needs to be 140 ° C. or less, preferably 130 ° C. or less. is there.

  When the film is heated with a heating roll, adhesion failure due to heat shrinkage of the film may occur. In that case, it is preferable to use a nip roll or a suction roll. However, since the heated film is soft and transfer of the surface shape of not only the heating roll but also the nip roll and suction roll to the film is concerned, selection and management of the roll material and surface roughness are important.

  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 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, a highly crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of preferably 85% or more, more preferably 90% or more, and further preferably 95% or more is 50% by weight or more. It is preferable to use 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) Surface roughness of heating roll A replica of the surface shape of the heating roll was sampled, and the surface roughness was measured with a laser microscope. The replica was collected by immersing a 400 μm-thick triacetylcellulose film in methyl acetate for 5 seconds to swell, sticking on a heated roll, and peeling off when the whole was dried. The surface roughness was measured by confocal observation by the following method and by surface roughness analysis of the captured image.
Confocal observation device: Scanning confocal laser microscope (Olympus LEXT)
・ Laser type: 408 nm semiconductor laser ・ Measurement magnification: 480 times (20 × objective x 24 × optical zoom)
In addition to the above apparatus and conditions, a confocal image was captured by scanning at a 0.64 μm pitch in the thickness direction of the replica.
Surface roughness analysis / measurement range: 480 μm x 640 μm
・ Analysis software: OLS3000
Surface roughness analysis was performed under the above conditions, and the center surface average roughness (SRa) was measured.

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

(3) Isotactic pendant fraction The isotactic pendant fraction is the proportion 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.

(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 sequentially passed through two heating rolls to perform heat treatment. The surface roughness of the first heating roll was 1.0 μm, the surface temperature was 120 ° C., and the heating time was 1.5 seconds. The surface roughness of the second heating roll was 1.0 μm, the surface temperature was 120 ° C., and the heating time was 1.5 seconds. 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 both the surface roughnesses of the first and second heating rolls were changed to 0.6 μm. 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 roughness of the first and second heating rolls was both changed to 1.4 μm. 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 first and second heating roll temperatures were set 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 roughness of the first and second heating rolls was both changed to 2.5 μm. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this comparative example was excellent in heat-resistant dimensional stability and had no stick-slip marks, but had transfer marks and was of low quality.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the surface roughness of the first and second heating rolls was both changed to 0.3 μm. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this comparative example was excellent in heat-resistant dimensional stability and had no transfer mark, but had a stick-slip mark and was of low quality.

(Comparative Example 3)
A film was obtained in the same manner as in Example 1 except that the first and second heating roll temperatures were changed to 70 ° C. The evaluation results of the finally obtained film are shown in Table 1. The polypropylene resin film obtained in this comparative example had no transfer marks and stick-slip marks, and had a good appearance, but was inferior in heat-resistant dimensional stability and of low quality.

  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)

  A polyolefin-based resin film, comprising: bringing a melt-extruded polyolefin-based resin film into contact with a cooling roll having a surface temperature of 30 ° C. or less, and cooling and solidifying the polyolefin-based resin film; In the manufacturing method, the heating roll has a surface roughness of 0.4 μm or more and 1.8 μm or less.   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.