JPS6331374B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an embossed film made of polyethylene terephthalate. More specifically, the present invention relates to a manufacturing method in which a biaxially oriented polyethylene terephthalate film is subjected to embossing to obtain a film with improved thermal stability and mechanical properties. In the prior art, embossed films made of polyvinyl chloride are used as decorative materials, mold release materials, and the like. Furthermore, due to its high melting point, high crystallinity, and high rigidity, polyethylene terephthalate has recently begun to be used for polyvinyl chloride processed films and electric wire coatings. However, from the viewpoint of embossed films, polyethylene terephthalate films still have room for improvement in mechanical and thermal robustness of embossed shapes, heat-resistant dimensional stability, and the like. In applications such as electric wire covering materials and release materials for manufacturing decorative laminates, the higher the above-mentioned physical properties are, the more advantageous it is. Therefore, the inventor of the present invention conducted intensive studies to develop an embossing method that is mechanically and thermally stable, and found that it was possible for polyethylene terephthalate film to be developed for the first time by combining specific stretching conditions and embossing. The present invention was achieved by discovering that it is possible to obtain a high-performance embossed film that has not been found in the prior art. That is, the present invention provides (a) simultaneous or sequential biaxial stretching and orientation of an unstretched polyethylene terephthalate film so that the refractive index in the thickness direction is 1.52 or less and the refractive index in the longitudinal direction is at least 1.59; (b) preheating the biaxially oriented film at a temperature in the range of 150°C to 240°C, preferably in the range of 160°C to 220°C; (c) preheating the film at a temperature in the range of 90°C to 230°C; The preheated film is embossed between an embossing roll and a back-up roll heated to a temperature T _E , and then (d) the embossed film is heated at a temperature below 230°C and above the temperature of the embossing roll. Heat treatment is performed at a temperature ranging from 10°C lower to 130°C higher than the embossing roll temperature ( _TE -10°C to T _E +130°C). This is a method for producing an embossed film made of polyethylene terephthalate. The present invention will be explained. In the present invention, an unstretched polyethylene terephthalate film casted on the surface of a cooling drum is melt-extruded using a conventional method, and the refractive index in the longitudinal direction is
Biaxially stretched so that the refractive index in the thickness direction is 1.59 or more and 1.52 or less in the thickness direction. The stretching may be simultaneous biaxial stretching or sequential biaxial stretching. For example, in order to obtain a polyethylene terephthalate film by the sequential biaxial stretching method, first, polymer pellets containing polyethylene terephthalate as the main component are dried, melted in an extruder, and passed through a T-die or inflation die to the desired thickness. Extrude the unstretched film. The extruded unstretched film is rapidly cooled to a temperature below the glass transition point (approximately 70°C) to obtain a transparent amorphous film. The unstretched film is sufficiently preheated at a temperature of about 80°C to 100°C so that the temperature is uniform from the surface to the inside, and then it is stretched in the longitudinal stretching zone (longitudinal stretching zone) for 2 to 30 minutes. First uniaxially stretched to a 5x range,
Preferably, it is cooled quickly. The film thus uniaxially stretched is further stretched in the transverse direction (width direction of the film) at a temperature range of 120°C lower than the glass transition point or melting point (approximately 70°C to 140°C). Then, if necessary, the stretched film is subjected to a heat treatment step. (Heat fixation is from 150℃
It may be applied for about 0.1 to 5 seconds at a temperature in the range of 240°C. ) In biaxial stretching, by selecting the transverse stretching ratio to be approximately the same as the longitudinal stretching ratio, a film with balanced Young's modulus, tensile strength, cutting elongation, etc. in the longitudinal direction and width direction can be obtained. The embossed film does not need to be tensilized in the vertical or horizontal direction, except for special applications. By appropriately selecting the above stretching conditions,
The biaxially stretched film has a refractive index of 1.52 or less in the thickness direction, and a refractive index of at least 1.59 in the longitudinal direction and/or width direction. The refractive index in the longitudinal direction tends to increase as the stretching ratio increases, and the refractive index in the thickness direction tends to decrease as the stretching ratio increases. The biaxially oriented polyethylene terephthalate of the present invention needs to have a relatively high degree of plane orientation, and unless the refractive index satisfies the above requirements, sufficient mechanical strength will not be developed. In the present invention, the embossed film is preheated so that it has high heat resistance. In conventional film manufacturing techniques, heat treatment is performed for the purpose of heat setting and crystallization of the stretched oriented film. Furthermore, the embossing treatment has been carried out either without sufficient heat setting time or by processing at a temperature considerably higher than the heat setting temperature. In the present invention, heat setting of the film and preheating for embossing treatment can be performed simultaneously (in case the heat treatment after stretching is omitted). Normally, biaxially stretched polyethylene terephthalate films are heat-set in a temperature range of 150°C to 250°C, but in the case of the present invention, the preheating temperature is required to be 100°C to 240°C. The heat treatment conditions are such that the specific gravity is
Crystallization must occur to the extent that the ratio is 1.39 or higher. According to the present invention, heat treatment crystallization of the film and thermoplasticization for embossing are simultaneously achieved. For preheating, known heating means such as an infrared heater or heated air can be applied to the stretched film. In addition, the preheating temperature is 100℃
If the temperature is lower than ~150°C, the biaxially oriented film will not be thermoplasticized sufficiently, and embossing cannot be performed smoothly, and crystallization will not be satisfactory, so there is a risk that the molding will disappear. Also, if the preheating temperature exceeds 230℃,
The strength of the film during processing is low, and it may break during embossing, which is undesirable. The embossing roll must be maintained at a temperature of 90°C to 230°C. When embossing is performed on a film that has been preheated to a high temperature while the embossing roll is cooled with a refrigerant, the film has an extremely good shape. That is, the film is shaped in accordance with the embossed shape of the roll. However, such a well-shaped embossed film loses its shape when exposed to high temperatures of 200° C. or higher. In the present invention, the embossing roll is also heated to obtain an embossed film with excellent shape stability at high temperatures. For this reason, the roll temperature must be 90°C or higher. Furthermore, 150℃
If the above is used, the effect will be further enhanced. However,
Embossing becomes difficult when the roll temperature exceeds 230°C. For example, the embossed portion of the film becomes locally thin, making it more likely to form holes or break.
From this operational point of view, the embossing roll temperature is preferably maintained at a desired temperature in the range of 90°C to 20°C. Since the preheated film and the embossing roll come into contact with each other, it is necessary to carefully control the temperature if the temperature difference between the two is 50°C or more. In the present invention, a preheated film is embossed between a metal embossing roll and a paper roll (backup roll). Generally, when aiming for deep embossing, it is recommended to increase the preheating temperature of the film and the pressure applied during embossing. When a biaxially stretched film is embossed, from a local perspective, it corresponds to the same phenomenon as the forming position being further stretched. The amount of deformation of the shaped portion corresponds to the stretching ratio. By the way, it is known that a biaxially stretched film can be further re-stretched in one or two directions, and embossing also corresponds to this re-stretching (simultaneous biaxial re-stretching), so processing conditions should be appropriately selected. It is predicted that this will improve the strength and Young's modulus of the film and stabilize the shaping state. However, if the film preheating temperature or the embossing roll temperature is increased to facilitate embossing, significant local deformation occurs and the film becomes thinner in the embossed areas (commonly called sink marks). Such conditions must be avoided. In step (a), a high preheating temperature must be selected if the biaxially oriented film has undergone excessive heat-set crystallization. In such cases, embossing becomes difficult, but since the film is subjected to thermal history at high temperatures, the heat resistance and dimensional stability of the film are generally improved. Although it is possible to cool the embossed film as it is, it is preferable to heat-set it to impart heat resistance. When the embossing roll temperature is T _E (°C), the final heat treatment temperature of the film is preferably 230°C or less in the temperature range of T _E -10°C to T _E +130°C. When the embossing roll temperature is 150~210℃, T _E −10℃
~T _E +30°C is preferred. This heat treatment contributes to the thermal stability and heat resistance of the embossed film. Heat treatment at a temperature lower than this heat treatment temperature cannot be expected to improve the heat resistance of the shaped portion. Furthermore, heat treatment at an excessively high temperature is not preferable because the film undergoes a shrinkage effect, resulting in loss of flatness of the film and change in shaping state due to shrinkage. Note that this final heat treatment only takes a very short time, and can stabilize the imprinting in 0.1 seconds to several seconds. According to the present invention, it is possible to obtain an embossed film that can withstand use at high temperatures of 150°C to 200°C. This feature is the use of a heated embossing roll and the effect of post-heat treatment of the embossed film. This is in contrast to the fact that in order to obtain an embossed film for use at room temperature, it is preferable to shape a preheated film with a cooled embossing roll. A significant improvement in the present invention is that by using a biaxially stretched (heat-set) film, the Young's modulus is increased if it has been heat-treated in advance, and the processing temperature can be raised during embossing. As a result, in the embossing process, the Young's modulus is maintained in the same way as when re-stretching a biaxially stretched heat-set film, and an embossed film with excellent thermal stability can be produced. This embossed film can demonstrate its performance when thermal and mechanical stability is required in application fields such as electric wire coatings and mold release materials. Example The embossing machine used was an embossing roll with a diameter of 100 mm and a width of 300 mm, and a back-up roll (with a diameter of 100 mm and a width of 300 mm).
200mm, width 300mm). The film running speed was 5 m/min, and the embossing roll pressure was 40 Kg/cm ² G.
Embossing was carried out at ~60Kg/cm ² G. The temperature of the film was sufficiently heated before embossing, and the temperature of the film immediately before embossing was varied within the range of 90°C to 220°C. Embossing was also carried out by changing the temperature of the embossing roll from room temperature to 170°C. As a result, when the temperature of the embossing roll is low and the temperature of the film is also low, the embossing is shallow and the heat resistance is low. On the other hand, when the temperature of the film was raised and the temperature of the embossing roll was high, the embossing was deep and the heat resistance was also improved.
However, if the temperature of the film is too high, it will become thinner locally during the embossing process, resulting in a decrease in the strength of the film. In this case, it has been found that it is preferable to use a method in which the temperature of the embossing roll is lower than the temperature of the film and the heated film is embossed while being cooled. The present invention will be further explained below with reference to Examples. Example 1 A film of 30μ was stretched by the usual sequential biaxial stretching method, and then heat-set at 230°C for 2 seconds, resulting in a refractive index of 1.48 in the thickness direction and a refractive index in the longitudinal direction.
A biaxially stretched heat-set film with a density of 1.66 and a density of 1.39 g/cm ³ was obtained. This film is embossed. First, this film was preheated to 160°C with an infrared heater, and the embossing roll was heated with a heating medium to 170°C, and the film was embossed at a running speed of 5 m/min. The embossing roll used in this case had a diameter of 100 mm and a width of 300 mm, and the paper (backup) roll had a diameter of 200 mm and a width of 300 mm, and the press pressure was adjusted to 60 Kg/cm ² G by a hydraulic system. Further, the film was heat treated at 180°C for 2 seconds.
On the other hand, as Comparative Example 1, the biaxially stretched film was preheated to 170°C, and the embossing roll was heated to 60°C.
While cooling with refrigerant (water) so as not to exceed 60℃
Embossed with a press pressure of Kg/cm ² G. Both embossed films were heated at room temperature to 200℃.
The samples were left in an oven (left for 5 minutes) to see how well the shaped state was maintained by external heating. As a result, the rate of change (%) of the embossing depth (unit μ) immediately after the embossing process
It is shown in Table 1 as follows.

[Table] From the results in Table 1, it is clear that when the embossing roll is heated, a shallow embossing of 200μ is obtained, and a deep embossing (460μ) is obtained when the embossing roll is cooled. However, such embossing is maintained at a high temperature in the example (of the present invention), whereas the film treated with a cooling embossing roll does not form a strong embossing shape at temperatures above 150°C. It shows. Furthermore, the formed film of the example had about twice the mechanical strength of that of the comparative example. Example 2 The biaxially oriented polyethylene terephthalate film used in Example 1 was preheated using an infrared heater to bring the film temperature to 170°C. In addition, when the heating temperature of the embossing roll is 90℃, approximately 50℃
Embossed under pressure of Kg/cm ² G, and
The film was heat-treated at 200° C. for 5 seconds without restraint, and compared with an embossed film that was not heat-treated (Comparative Example 2), the effect of heat treatment after embossing according to the present invention was confirmed. The results are shown in Table 2. When the oven temperature was 110°C or higher, the shape of the non-heat-treated embossed film was thermally relaxed.

【table】

Claims (1)

[Claims] 1. A method for producing an embossed film made of polyethylene terephthalate including the following steps: (a) Biaxially oriented unstretched polyethylene terephthalate so that the refractive index in the thickness direction is 1.52 or less and in the longitudinal direction and/or The refractive index in the width direction is at least
1.59 and heat setting if necessary, (b) preheating the biaxially oriented film to a temperature in the range of 150°C to 240°C, (c) embossing heated to a temperature of 90°C to 230°C. The preheated film is embossed between the roll and the back-up roll, and further, (d) the embossed film is heated at 230°C or lower, from 10°C lower than the embossing roll temperature to 130°C lower than the embossing roll temperature. Heat treatment at temperatures in the high temperature range. 2. The method for producing an embossed film according to claim 1, wherein the preheating temperature is 160°C to 220°C. 3. The method for producing an embossed film according to claim 1, wherein the embossing roll temperature is in the range of 150°C to 210°C. 4 The embossed film is heat-treated at a temperature of 230°C or less in a temperature range of 10°C lower than the embossing roll temperature to 30°C higher than the embossing roll temperature. A method for manufacturing embossed film.