JPH0369294B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a packaging film, particularly a packaging polyester film that is transparent and has excellent slipperiness, adhesion to printing ink, and productivity. (b) Conventional technology and problems to be solved Polyester biaxially stretched film has excellent heat resistance, mechanical properties, transparency, chemical resistance, etc., so it is used for magnetic tape, photography, metallization, electrical Although it is widely used in various applications, especially in packaging applications, the demand for it is increasing due to its various excellent properties. However, in the field of packaging, greater transparency is desired so that the contents can be observed. In order to obtain a transparent film, it is important that no voids are formed in the internal particles, and that there are few irregularities on the film surface and foreign substances in the film that cause light scattering and transmission obstruction. However, if the surface smoothness is increased too much, the slipperiness will be insufficient, resulting in poor winding workability in the polyester film manufacturing process and poor packaging workability for users. Therefore, it is desired to improve the surface smoothness and suppress the formation of internal voids without reducing the workability. In most cases, packaging films are printed, and the most commonly used ink is cellophane printing ink, which uses a cellulose derivative as a binder, and is capable of high-speed printing and provides a clear finish. This is why it is commonly used. However, since polyester films are hydrophobic, they have a problem in that they are difficult to adhere to hydrophilic cellulose binders, and this problem has heretofore been dealt with mainly by two methods. The first method is to directly copolymerize polyester with polyalkylene glycol, such as polytetraethylene glycol, polyethylene glycol, etc., or to blend the copolymer chips to make polyester hydrophilic by incorporating polyalkylene glycol into the polyester. This is a method for improving adhesion with cellulose binders. However, although this method improves adhesion, it also deteriorates polymerization and weather resistance when used as a packaging film, so it is desirable to reduce the content of polyalkylene glycol as much as possible. Ta. The second method is to improve printability by coating a water-based adhesive layer during the polyester film manufacturing process, for example, before lateral stretching. However, since this method is water-based, it is easy to achieve adhesion with the cellulose binder, but it is difficult to increase the adhesion between the adhesive layer and the polyester film.
Improvement was desired. As mentioned above, polyester films for packaging have the various problems mentioned above, and it has been desired to solve them. (c) Means for Solving the Problems The present inventors have improved the above-mentioned transparency and slipperiness, the adhesion of cellophane printing ink even when the content of polyalkylene glycol is low, and the bond between polyester film and coating agent during in-line coating. As a result of intensive studies aimed at improving adhesive properties, it was discovered that the above-mentioned problems could be solved by changing the physical properties of the polyester film to certain specific values, and the present invention was achieved based on this finding. That is, in the present invention, the degree of orientation of the film surface (ΔP), the longitudinal direction (F ₅ - value) of the film, and the average refractive index ( ) of the film satisfy the following relationship,
A polyester film for packaging that is transparent and has excellent slipperiness, printability, and productivity, and has a film haze of 5.0% or less, 0.002×F ₅ +1.43×−2.15≧ΔP≧0.002×F ₅ +1.43×
−2.17… and the major axis of the protrusion and the protrusion as the core is at least
The present invention relates to the above polyester film for packaging, in which the number A (units/mm ² ) of uneven units consisting of 3 μm indentations per 1 mm ² of film surface area is within the range of O≦A≦2500. The polyester referred to in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid or their esters, and glycols such as ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, etc. It is a polymer that can be obtained by polycondensing. This polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or by polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by methods such as polycondensation of esters. Representative examples of such polymers include:
Polyethylene terephthalate and polyethylene
Examples include 2,6-naphthalene dicarboxylate. The polymer may be a homopolymer, such that not more than 15 mole percent of the aromatic dicarboxylic acid component is a non-aromatic dicarboxylic acid component, and/or not more than 15 mole percent of the diol component is a diol other than fatty acid glycol. There may also be a copolymerized polyester as a component. In particular, it is preferable to use polyethylene glycol, polytetramethylene glycol, etc. as the diol component. Furthermore, it may be a polymer blend of the polyester and other polymers. Other polymers that can be blended include polyamides, polyolefins,
Other types of polyesters (including polycarbonates) are exemplified, but blends of homopolymers and polyalkylene copolymers or blends of different polyalkylene glycol copolymers are also suitable. The polyester may optionally contain a stabilizer,
It may also contain additives such as colorants, antioxidants, and antifoaming agents. Further, in order to impart slipperiness to the polyester film, fine particles and/or inert inorganic particles can be added (contained). The fine particles include kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide calcium phosphate,
Groups of the periodic table of elements such as titanium oxide,
Inert external particles consisting of salts or oxides containing elements selected from groups and others, high melting point organic compounds insoluble in melt film formation of polyester resins, metal compound catalysts used in crosslinked polymers and polyester synthesis, e.g. alkali metals They can be internal particles formed within the polymer during polyester production by compounds, alkaline earth metal compounds, and the like. The amount of fine particles contained in the film is 0.005 to 2.0
% by weight, and the average particle size of the particles is in the range of 0.05 to 5.0 μm. By limiting the average refractive index (), degree of plane orientation (ΔP), and _F5 value of the film to specific ranges, the present invention achieves excellent transparency, easy slipping properties, and adhesion with cellocolor ink using the same raw material system. This is to obtain a film that is The average refractive index is the refractive index n〓 in the thickness direction, the refractive index n〓 in the main orientation direction, and the refractive index in the direction perpendicular to the main orientation direction.
If n〓, it is given by =1/3(n〓+n〓+n〓). The degree of one-sided orientation ΔP is given by ΔP=n〓+n〓/2 ^-n〓 using the above n〓, n〓, n〓. The average refractive index is preferably 1.600 or more and 1.610 or less. If the average refractive index n is lower than 1.600, dimensional changes may occur due to heat shrinkage during molding of the packaging bag, which is undesirable. On the other hand, the average refractive index
If it exceeds 1.610, the film tends to have poor mechanical strength. On the other hand, the relationship between the degree of plane orientation and F ₅ is expressed by the following formula: 0.002×F ₅ +1.43×−2.15≧ΔP≧0.002×F ₅ +1.43×
−2.17… must be satisfied. Surprisingly, when comparing films with the same _F5 value, for films with the same haze, the friction coefficient of the film in which ΔP satisfies the above formula is the same as that of the film outside the range of the above formula. It turned out to be much better than. In other words, it has been found that among films that give the same coefficient of friction, the haze of a film that satisfies the above formula is much lower than the haze of a film that has ΔP outside the range of the above formula. Even more surprisingly, it was found that the film that satisfies the above conditions has superior adhesion to cello color ink and inline coat coating material, compared to films that fall outside the range of the above formula. . Although the reason is not clear, it is thought that the hydrophilicity of the surface increases due to a change in the orientation of crystals on the surface. When actually used as a cellocolor easily printed film, it is also suitable to contain polyalkylene glycol. In this case, in a film that satisfies the formula, the content of polyalkylene glycol can be lowered than in a film outside the range, thereby improving polymerization stability, antioxidant reduction ratio, and improving film quality. This contributes to improving weather resistance. The method for forming a polyester film of the present invention will be explained in more detail. Additives such as fine particles, stabilizers, colorants, antifoaming agents, adhesion promoters, molecular weight 300
~200000 polyalkylene glycol (0.05~
A polyester chip containing 3.0% by weight) is dried by a conventional method, extruded through an extruder, and cooled and solidified on a rotating cooling body to form an unstretched polyester sheet. At this time, it is preferable to use a conventional electrostatic application cooling method. The film thus obtained is stretched in the first axial direction so that its birefringence Δn is 0.080 or less, and then the uniaxially oriented film is once cooled to below the glass transition point or cooled in the second direction. For example, 90℃~
Preheating to a temperature of 150°C and further stretching at approximately the same temperature to create a biaxially stretched film,
Heat set. However, if necessary, it is also possible to perform re-stretching before heat setting. The stretching ratio in the second direction is approximately 2.5 to 4.5 times, and heat setting is carried out at a temperature of 180 to 250° C. for 1 second to 10 minutes. Conventional stretching formulations usually have poor compatibility between the particles and the polyester resin, resulting in the formation of voids around the particles. On the other hand, according to the method of the present invention, since the orientation is lowered so as to satisfy the above formula, the concentrated stress around the particles is low and voids are less likely to be formed, thereby reducing internal haze and improving transparency. On the other hand, in the protrusions on the film surface, depressions (hereinafter referred to as propeller particles) are formed that can be generated using the protrusions around the protrusions as nuclei. The number and shape of this propeller formation vary depending on the detailed stretching conditions, but in any case, it is thought that this propeller formation makes the propeller particles steeper, which lowers the coefficient of friction seen at the same surface haze. . It is preferable that the propeller particles have a number A (particles/mm ² ) of concavo-convex units per 1 mm ² of film surface area in the range of the following formula, consisting of depressions and depressions having a major axis of at least 3 μm. O≦A≦2500... If A is 2500 or more, there are too many irregularities due to depressions around the propeller particles, resulting in a decrease in transparency.
Therefore, the number of A's is preferably 1500 or less, more preferably less than 800. Particularly preferred are those that do not form propeller particles while satisfying the relationship between ΔP and _F5 value. When stretching in the first direction is carried out longitudinally, it is possible to carry out the longitudinal stretching in one stage, but in consideration of thickness fluctuations of the film, it is preferable to carry out the longitudinal stretching in two or more stages. When performing longitudinal stretching in multiple stages, it is preferable to set the birefringence Δn ₁ before the final stage stretching to 0.015 to 0.055 (hereinafter sometimes referred to as front stage stretching). In the present invention, the Δn after the final stage stretching is recommended as Δn ₁ after this first stage stretching is 0.015 or less or 0.055 or more.
If it is attempted to be less than 0.080, thickness unevenness will worsen, which is undesirable (hereinafter sometimes referred to as post-stretching). The pre-stretching may be performed in one stage or may be further divided into multiple stages. When performing multistage stretching in the first stage, Δn can be set to 0.015 or less, then 0.015 to 0.055, or it can be set to 0.015 or more from the beginning, and then finally 0.015 to 0.055. Since packaging films are required to be lower in cost than those used for magnetic tapes, etc., it is particularly important to avoid a decrease in productivity due to a decrease in the overall longitudinal stretching ratio. In order to improve productivity, it is preferable to increase the longitudinal stretching temperature in longitudinal multi-stage stretching and apply a stretching prescription in the super draw or near super draw region. In other words, in the first stage stretching
It is preferable to stretch the film in the longitudinal direction at a temperature of 100° C. or more and 150° C. or less, and set the Δn as described above to 0.015 or more and 0.055 or less. At that time, it can be done in one step, but in two or more steps, super draw is first performed at 100°C or more and 150°C or less, and then further stretched to increase Δn.
It can also be set to 0.015 or more and 0.055 or less. Therefore, the longitudinal stretching ratio is preferably 3.5 times or more. When applying the super draw, it is preferable to use a non-adhesive roll, especially since the unstretched film is stretched at a high temperature. As the non-adhesive roll, a hard chrome plated roll with a matte surface, a ceramic roll, an elastomer roll, or a fluororesin roll are preferred. Examples of the elastomer roll include copolymers mainly composed of propylene hexafluoride and vinylidene fluoride, ethylene propylene copolymers, and chlorosulfonated polyethylene. Examples of the fluororesin roll include tetrafluoroethylene/perfluoropropyl vinyl ether copolymer, tetrafluoroethylene, and the like. Further, if necessary, those filled with a lubricant such as TiO ₂ or a resin such as polyimide are also preferably used. The biaxially oriented heat-set polyester film used in the present invention has a film-to-film friction coefficient of 0.7.
or less, preferably 0.6 or less. If the coefficient of friction exceeds 0.7, it will block when manufacturing the film or when making the packaging film into bags, making it impossible to process it. Transparency is also required as a base film, and the polyester film of the present invention has a total haze of 5% or less, particularly preferably 4% or less. Further, the surface haze must be 4% or less, preferably 3% or less. The film of the present invention may be subjected to surface treatment such as corona discharge treatment if necessary, and if necessary, a low melting point polymer such as polyethylene may be laminated on the printed surface. However, when applying corona discharge, it is desirable to apply a discharge energy of about 30 [w·min/m ² ] or less. This is because discharge energy higher than this may cause troubles such as reduced adhesion between printing ink and film after being left in a hot and humid atmosphere or after boiling. In addition, a gas-barrier resin such as vinylidene chloride resin may be laminated on the surface of the film of the present invention, or a metal foil may be laminated with an adhesive. Applications can be taken. (d) Examples The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. In addition, the evaluation method of the film is shown below. 1) Film haze Surface haze and internal haze were determined using an integrating sphere turbidity meter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS-K6714. 2) Printing ink adhesion Toyo Ink Cerocolor printing ink
Apply CCST39 indigo to the film surface so that the coating thickness after drying is approximately 1.5μ, dry with hot air at 60℃ for 10 seconds, apply Nichiban's Sellotape (registered trademark) (19mm width), and quickly pull it. When peeled off, the ink was ranked according to the extent of the peeled area (5-level evaluation). 5: There is no peeling of the ink surface. 4: Ink adhesion area of 90% or more. 3: Ink adhesion area 75-90%. 2: Ink adhesion area 50-75%. 1: Ink adhesion area less than 50%. 3) Refractive index The value for the Na-D line measured at 25°C was determined using an Atsube refractometer (manufactured by Atago Co., Ltd.). 4) Birefringence Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and the birefringence (Δn) was determined using the following formula. Δn=R/d where R: Retardation d: Film thickness (μm) 5) _F5 value A sample film with a width of 1/2 inch and a length of 50 mm between chucks was heated using Tensilon (UTM-) manufactured by Toyo Baldwin Co., Ltd. , 50 at 20℃, 65%RH
The load at 5% elongation was divided by the initial cross-sectional area and expressed in kg/ ^mm2 . 6) Sliding property The slipping property of a film is represented by the coefficient of friction, and its measurement was carried out in accordance with ASTM D-1894 using a method modified so that it can be measured using a tape-shaped sample. The measurements were carried out in an atmosphere of 21±2℃ and humidity of 64±5%, and the sample used was 15mm wide.
The length was 150 mm and the pulling speed was 20 mm/min. 7) Number of uneven units (propellers) with depressions around the protrusions (A) The surface of the aluminum-deposited film was photographed at 750x using a Carl Zeiss differential interference microscope, and the number of protrusions per 1 mm ² of total film surface area was taken. The number A (pieces/mm ² ) of concavo-convex units consisting of pits having a major axis of at least 3 μm as cores was counted. Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 (Production method of polyester copolymer) 90.9 parts of dimethylene terephthalate, 61 parts of ethylene glycol, and 10 parts of polyethylene glycol with a molecular weight of 8000 were each placed in a reaction vessel. Then, 0.09 part of calcium acetate monohydrate was added as a catalyst, and the transesterification reaction was carried out while distilling the produced methanol under heating and stirring, and then the mixture was transferred to a reaction vessel heated to 240°C. Next, 0.03 parts of antimony trioxide and 0.04 parts of orthophosphoric acid were added, and after 2 hours the reaction system was
Raise the temperature to 280℃ and 3mmHg after 1.5 hours
Polycondensation was completed by gradually reducing the pressure to the following, and a polyester copolymer was obtained. (Film forming method) The above polyethylene glycol copolymer and Fuji Davison Thyroid 266 (average particle size
Polyethylene terephthalate (intrinsic viscosity
0.65), and the polyethylene glycol content in the mixture was adjusted to 0.05 to 0.3% by weight. Each mixture was melt-extruded at 285℃,
The mixture was cooled and solidified using an electrostatic adhesion method to obtain an unstretched film with a thickness of about 150 to 200 μm. This unstretched film is 85
Roll stretched 3.7 times in the machine direction at °C, then 100 °C
After stretching 3.8 times in the transverse direction, heat setting was performed at 230° C. to obtain two types of stretched films with a thickness of 12 μm (Comparative Examples 1, 2, and 3). Comparative Example 4 was prepared in the same manner as Comparative Example 1 except that the content of Thyroid 266 was 0.03% by weight and the stretching ratio in the longitudinal direction was 3.6 times. Next, the same unstretched film as above was heated at 105℃.
After stretching 3.4 times and setting Δn to 0.040, further stretching at 105℃
The film was stretched 1.3 times and Δn=0.063. The longitudinally stretched film thus obtained was then heated at 140°C in a tenter.
It was stretched 3.8 times in the transverse direction and heat-set at 230°C to obtain a biaxially stretched film with a thickness of 12μ (Example 1,
2, 3). The properties of these films are shown in Table 1.

[Table] As can be seen from Table 1, according to the method of the present invention, a film can be obtained that has excellent transparency, printability, and slipperiness, can also increase the longitudinal stretching ratio, and has excellent productivity. I understand. (E) Effects of the Invention As described above, the present invention provides a film with excellent transparency, printability, slipperiness, and productivity by adopting the configuration as described in the claims. It can be said that this is a polyester film useful as a packaging film.

Claims (1)

[Claims] 1. Film plane orientation (ΔP), film longitudinal direction (F ₅ -value), and film average refractive index ( )
A polyester film for packaging, which satisfies the following relationship and has a film haze of 5.0% or less, which has excellent transparent slipperiness, printability, and productivity. 0.002×F ₅ +1.43×−2.15≧ΔP≧0.002×F ₅ +1.43×
-2.17… 2 The long axis of the protrusion and the protrusion as a core is at least 3μ
Film surface area 1 of unevenness unit consisting of depressions and depressions of m
The polyester film for packaging according to claim ¹ , wherein the number A (pieces/mm ² ) per mm 2 is within the range of the following formula. O≦A≦2500…