JP4508341B2 - Biaxially stretched nylon 6 film and manufacturing method thereof - Google Patents

Description

【００４１】
【発明の効果】
本発明によれば、操業性に優れ、熱収縮率が低減された二軸延伸ナイロン6フィルムを得ることができ、包装材料の用途に特に好適に使用できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biaxially stretched nylon 6 film suitable for packaging of foods used by laminating with a polyolefin resin sheet such as polyethylene or polypropylene, and a method for producing the same.
[0002]
[Prior art]
Since biaxially stretched nylon 6 film has excellent properties such as mechanical properties, optical properties, dimensional stability, gas barrier properties, printing properties, etc., various liquid foods, marine foods, frozen foods, retort foods, It is used for a wide range of applications as a packaging material film for pasty foods, livestock meat and fishery products. Particularly in recent years, it has been widely used as a bag packaging material for retort food.
The nylon 6 film used for bag packaging materials is usually printed on its surface and then laminated with polyethylene or polypropylene, with the nylon 6 film on the outside and the fold line parallel to the film flow direction (MD direction). Fold up so that the three sides are heat-sealed and cut out to make a three-side sealed bag with one side open. The bag is filled with the above contents and sealed, and usually subjected to heat sterilization in boiling water before being put on the market.
[0003]
The biaxially stretched nylon 6 film used for the above-mentioned heat sterilization treatment is manufactured by a longitudinal / transverse sequential biaxial stretching method, but has a drawback in that variations in physical properties are likely to occur in the film width direction.
[0004]
One reason for this is the so-called Boeing phenomenon. In the bowing phenomenon, in the tenter treatment process for transverse stretching and the subsequent heat setting process, both ends of the film are gripped and restrained by clips, whereas the central part of the film is influenced by the gripping means. This is a phenomenon in which the progress of the central portion of the film is delayed with respect to both ends held by the clip due to the influence of the contraction stress in the vertical direction because the restraining force is small and weak. For this reason, for example, the shrinkage rate of the film after the film is treated with boiling water, that is, the main shrinkage angle indicating the highest direction of the hot water shrinkage rate with respect to the TD direction is larger at the end than at the center. A difference in physical properties occurs in the width direction.
[0005]
Further, at the time of lateral stretching, stretching proceeds so that the central portion in the width direction is stretched first and then drawn from the rear end portion to the central portion. That is, the stretchability of the center portion and the end portion is different, and the stress generated during stretching, the residual strain due to this, and the like are different. For this reason, for example, a physical property difference occurs such that the maximum value of the hot water shrinkage rate is larger at the end than at the center.
[0006]
That is, the biaxially stretched nylon 6 film for bag packaging obtained by the conventional method has a difference in physical properties in the width direction, and particularly in a bag manufactured using the end in the width direction, the bag is warped at the corner of the bag after heat treatment. As a result, a phenomenon occurs in which the four sides of the bag curl into an S-shape, which significantly deteriorates the shape of the product.
[0007]
As countermeasures for non-uniform physical properties in the width direction, for example, in JP-A-8-267569, JP-A8-197620, JP-A8-174663, etc., longitudinal stretching is performed in two steps in a specific temperature range. A method of dividing is disclosed. In this method, by reducing the stress in the longitudinal direction and reducing the orientation of the molecules in the longitudinal direction and increasing the degree of orientation in the TD direction, the difference in physical properties in the width direction and the oblique difference in hydrothermal shrinkage (TD direction) The absolute value of the difference between the hot water shrinkage rates in the 45 ° direction and 135 ° direction when the angle is 0 ° is reduced. However, these methods do not reduce the stress generated by transverse stretching, and even if the bowing phenomenon and the oblique difference are reduced, the thermal shrinkage rate is not reduced, and the reduction in the physical property difference in the width direction is sufficient. That's not true.
[0008]
Japanese Patent Application Laid-Open Nos. 3-193328 and 3-216326 disclose a method of reducing the bowing phenomenon by providing a cooling step between the transverse stretching and the heat treatment step. However, in this method, the heat treatment effect in the heat treatment step is relaxed, the thermal shrinkage rate is increased, and even if the bowing is reduced, the physical property difference in the width direction is not reduced.
[0009]
In order to prevent the four sides of the bag from curling and deteriorating the shape of the bag, it is not sufficient to reduce the bowing phenomenon, and it is also necessary to reduce thermal shrinkage.
[0010]
[Problems to be solved by the invention]
The present invention is intended to solve the above-mentioned problems, and without damaging the excellent properties of the biaxially oriented nylon 6 film, the biaxially oriented with uniform physical properties in the width direction and low thermal shrinkage. A nylon 6 film and a method for producing the same are provided.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have reached the present invention.
That is, the gist of the present invention is as follows.
(1) Sequential biaxially oriented nylon 6 film that satisfies the following formula at all positions in the width direction (TD direction) of the film.
BS _max ≦ 3.7%
BS _ai = BS _max −BS _min ≦ 2.5%
BS _θ ≤20 °
(BS _max and BS _min are the maximum and minimum shrinkage when the TD direction is 0 ° and the hot shrinkage in all directions is obtained. BS _ai is the difference between them. BS _θ is the most hot shrinkage. The direction in which the is higher is indicated by the angle to the TD direction.)
(2) In the production method of sequential biaxially stretched nylon 6 film, when the film is stretched in a flat shape in the TD direction, the crystallinity after MD stretching and before TD stretching is 30% or less, and TD A method for producing a successively biaxially oriented nylon 6 film, characterized in that the stretching temperature is (Tc-20) ° C. or higher and Tm or lower. (Here, Tc is the temperature drop crystallization temperature of the biaxially stretched nylon 6 film, and Tm is the melting point of the biaxially stretched nylon 6 film.)
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
Hot water shrinkage is caused by relaxation of the residual stress of the film. During film production, stress acts mainly in the stretching process (MD direction) and TD direction in the stretching process, and some of the stress remains in the film, although some of it is relaxed mainly in the heat setting process. The cooling is fixed as it is. This stress is the residual stress of the film. On the other hand, when the film is treated with hot water, the temperature becomes Tg or higher and the mobility of the molecules increases due to the adsorption of water molecules. For this reason, molecules move in a direction to relieve the remaining stress, and the film length changes accordingly. The shrinkage rate is the hot water shrinkage rate.
[0013]
The hot water shrinkage of the film varies depending on the manufacturing conditions, and also varies depending on the position and direction of the same film. In the film produced by the longitudinal-lateral sequential biaxial stretching method, the main shrinkage angle is 0 ° because the shrinkage rate in the TD direction is the largest and the shrinkage rate in the MD direction is the smallest at the center of the film. The relationship between angle and shrinkage fits well with the curve of cos2θ. Moreover, the main contraction angle becomes larger as the distance from the center portion becomes the end portion and the main contraction direction is shifted from the TD direction. This is due to the bowing phenomenon. The larger the bowing, the larger the main contraction angle.
[0014]
The nylon 6 film of the present invention is a biaxially stretched nylon 6 film that satisfies the following formula at all positions in the TD direction of the film.
BS _max ≦ 3.7%
BS _ai = BS _max −BS _min ≦ 2.5%
BS _θ ≤20 °
[0015]
In the present invention, the shrinkage rate in 8 directions is measured every 22.5 ° with the TD direction being 0 ° at each position, and the relationship between this and the angle is approximated to a curve of cos 2θ, and the maximum value of the shrinkage rate is BS _max , The minimum value was BS _min , and the angle indicating the maximum contraction rate was the main contraction angle _BSθ . When the maximum shrinkage value BS _max of the film is larger than 3.7%, the dimensional stability of the film is poor, and for example, the bag shape is deteriorated during bag making or retorting. BS _ai, which is the difference between the maximum value BS _max and the minimum value BS _min , indicates anisotropy at each position of the shrinkage rate. When BS _ai is greater than 2.5%, the direction anisotropy is large, for example, the shape of the bag It becomes a factor to worsen. In addition, the larger the BS _θ , the more the difference in shrinkage characteristics between the two films that are folded and matched to the bag shape at the opposite positions, especially when the film is larger than 20 °, the deterioration of the bag shape becomes remarkable.
[0016]
In the present invention, nylon 6 refers to nylon 6 alone or a mixture of polyamides other than nylon 6 as long as the effects of the present invention are not impaired. Examples of other polyamides include nylon 69, nylon 612, nylon 12, nylon 6/66, polymetaxylylene adipamide (nylon MXD6), and the like.
[0017]
The relative viscosity of nylon 6 used in the present invention is not particularly limited, but the relative viscosity measured in the condition of 96% sulfuric acid as a solvent at a temperature of 25 ° C. and a concentration of 1 g / dl is 1.5 to 5.0. preferable. When the relative viscosity of nylon 6 is less than 1.5, the mechanical properties of the film are remarkably deteriorated, and when it exceeds 5.0, the film forming property of the film is hindered.
[0018]
As a biaxial stretching method of the biaxially oriented nylon 6 film of the present invention, the film thickness accuracy, quality stability, a flat-type successive biaxial stretching method is preferable from the viewpoint of productivity.
[0019]
The film according to the present invention is a production method in which a substantially unstretched nylon 6 film or sheet is sequentially stretched in the MD and TD directions, then heat-set in a flat shape, and relaxed in the TD direction. It can be produced by setting the temperature range during stretching to (Tc-20) ° C. to Tm, preferably (Tc-10) ° C. to Tm, more preferably Tc to Tm. When the stretching temperature is in the range of (Tc-40) ° C. to (Tc-20) ° C., the crystallization speed is very fast, so that crystallization is promoted during film stretching and stretch cutting is likely to occur. Moreover, when it can be extended | stretched, the haze of a film becomes high. When the temperature is (Tc-40) ° C. or lower, uniform stretching is possible, but the film has a relatively high rigidity, so that the stretching stress is high, and as a result, the bowing phenomenon and the heat shrinkage ratio are increased. In addition, since the resin melts in the temperature range above Tm, the film shape cannot be maintained.
[0020]
In the film production method of the present invention, when the film is stretched in the TD direction, the crystallinity of the film needs to be 30% or less. When the degree of crystallinity is greater than 30%, crystallization is further promoted during transverse stretching, and the film is likely to be stretched and cut. Moreover, even if it can extend | stretch, the problem that the state is non-uniform | heterogenous or a haze becomes high arises.
[0021]
In the nylon 6 film of the present invention, pigments, heat stabilizers, antioxidants, weathering agents, flame retardants, plasticizers, mold release agents, and reinforcing agents can be blended within a range that does not impair the film properties. . Examples of heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, and alkali metal halides. These compounds can be added during polymerization of nylon 6 or during melt kneading.
[0022]
Various inorganic lubricants and organic lubricants may be blended with nylon 6 in order to improve the slip property of the film. These lubricants include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, magnesium aluminosilicate, glass balloon, carbon black, zinc oxide. , Antimony trioxide, zeolite, hydrotalcide and the like.
[0023]
The method for producing the film of the present invention by the sequential biaxial stretching method will be described below.
That is, in the method of the present invention, first, a substantially amorphous unstretched nylon 6 film is stretched in the MD direction, and then stretched in the TD direction. The MD stretching ratio can be appropriately selected from 2.0 times or more, and the MD stretching temperature is (Tcc (temperature rising crystallization temperature) +30) ° C. or less, preferably Tcc or less. When the draw ratio is smaller than the above-mentioned ratio, the mechanical properties in the MD direction of the obtained stretched film are remarkably inferior. When the stretching temperature is (Tcc + 30) ° C. or higher, crystallization proceeds and the crystallinity exceeds 30%, which adversely affects the subsequent TD stretchability.
[0024]
The TD draw ratio can be appropriately selected within the range of 3.0 times or more and within the range of 9.0 to 11.0 times as the total draw ratio of MD × TD. When the draw ratio in the TD direction is less than 3.0 times or the total draw ratio is less than 9.0 times, the mechanical properties of the obtained stretched film are remarkably inferior. Moreover, when the total draw ratio is higher than 11.0 times, the film is likely to be stretched and cut. As described above, the TD stretching temperature is appropriately selected within the range of (Tc-20) ° C to Tm, preferably within the range of (Tc-10) ° C to Tm, and more preferably within the range of Tc to Tm. be able to.
[0025]
The nylon 6 film thus stretched is subjected to a heat treatment to improve dimensional stability. The heat treatment requires a treatment at (Tm−20) ° C. or more and Tm or less when the melting point of the film immediately after stretching is Tm. If the temperature is raised too quickly immediately after stretching, bowing increases and anisotropy increases. If the maximum temperature of heat treatment is (Tm-20) ° C. or less, sufficient dimensional stability cannot be obtained, and if it is Tm or more, mechanical strength, particularly impact resistance is lowered. Subsequently, relaxation in the TD direction is performed in the zone immediately after the heat treatment.
[0026]
After the TD relaxation treatment, it is cooled at about 100 ° C. to obtain a biaxially stretched nylon 6 film of the desired thickness. Although the thickness of a film is not specifically limited, When using for a packaging use, the thing of the range of 10-25 micrometers is preferable.
[0027]
The obtained stretched film may be subjected to physicochemical treatment such as corona discharge treatment, plating treatment, cleaning treatment, dyeing treatment, metal vapor deposition, various coatings, etc., and laminated with other materials as necessary. May be.
[0028]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further more concretely, it is not limited to the following.
The measurement methods used in the examples and comparative examples are as follows.
[0029]
(1) Hot water shrinkage rate Nylon 6 film wound into a roll is removed at 20 ° C and 65% RH in the surface layer, and a sample of the full width is sampled from the inside, and the sample is prepared for 3 hours. Moisten. Sampling is performed every 200 mm with respect to the TD direction of the film. The sampling direction is 8 directions every 22.5 °, with the TD direction being 0 ° at each position. The sample shape is 10 mm wide and 150 mm long, and is rated at an interval of about 100 mm. The distance between the scores is measured and set to L ₀ (mm). The sample was treated for 5 minutes in boiling water at 100 ° C. and, after dampening or 3 hours conditioned at RH for again 20 ° C. 65%, to measure the score distance L _1. Are multiplied by 100 the ratio of the L ₀ -L ₁ and the original is the length L ₀ is the amount of shrinkage by treatment was hot water shrinkage (BS).
At each position, the BS in each direction was fitted to the curve of cos 2θ, and the maximum value (BS _max ), the minimum value (BS _min ) and the main contraction angle (BS _θ ) of the BS were obtained.
[0030]
(2) Temperature rising crystallization temperature Tcc, temperature falling crystallization temperature Tc, melting point Tm
Sampling was performed in the range of 2 cm square from the center of nylon 6 film, and 6 to 8 mg of film sample was placed in an aluminum DSC sample pan, and perkin elmer DSC-7 was used. After melting and maintaining for 20 minutes and rapidly solidifying to 20 ° C., the temperature was increased at a rate of temperature increase of 20 ° C./min. The peak temperature of crystallization observed at this time was Tcc, and the melting endothermic peak temperature was Tm. Further, after 6 to 8 mg of the film sample was melted and held at 280 ° C. for 5 minutes, the temperature was lowered at a temperature falling rate of 20 ° C./min. The observed temperature drop crystallization exothermic peak temperature was defined as Tc.
[0031]
(3) Crystallinity of film
A density gradient tube consisting of n-heptane and carbon tetrachloride was prepared in a constant temperature water bath controlled at 25 ° C., the film was sampled into a size of about 5 × 5 mm, and the reading density d was measured after 24 hours. From this density, an amorphous density of nylon 6 of 1.10 and a crystal density of 1.23 were used, and the degree of crystallinity (%) = (d-1.10) / (1.23-1.10) × 100.
[0032]
(4) Film formation conditions Evaluation was made based on the number of breaks when a film was produced for 2 hours under the same conditions.
[0033]
(5) S-curl determination method Fold the film in two so that the crease is parallel to the MD direction, and heat-seal both ends at 150 ° C at 20 ° C continuously using a test sealer, and at right angles to it. 10mm width is intermittently heat-sealed at intervals of 150mm in the direction to obtain a semi-finished product bag with a width of about 200mm.
The semi-finished product bag was cut in the MD direction so that both edge portions had a seal portion of 10 mm, and then cut in the direction perpendicular to this at the boundary of the seal portion to prepare a three-side seal bag. After heating these 10 bags in boiling water for 5 minutes, they are air-dried overnight at 20 ° C and 65% RH. Furthermore, 10 bags were piled up, a 1 kg load was applied to the entire bag surface from above, and the bag was stored all day and night, and then the load was removed and the degree of bag curl (S-curl) was evaluated according to the following criteria.
○: No warping.
×: The warping is clearly seen.
XX: Warping is remarkable.
[0034]
Example 1
Nylon 6 with a relative viscosity of 3.0 measured at 25 ° C in 96% concentrated sulfuric acid is dried, put into an extruder, melted in a cylinder heated to 260 ° C, and then melted into a sheet from a T-die After extrusion, it was brought into close contact with a rotating drum having a surface temperature of 10 ° C. by an air knife casting method and quenched to obtain an unstretched sheet having a thickness of 150 μm. Next, this unstretched sheet was MD-stretched at a temperature of 53 to 62 ° C. and a stretch ratio of 2.7 times by an MD stretching machine comprising heating roller groups having different peripheral speeds. Next, this MD stretched film was introduced into a tenter and preheated. At this point, the crystallinity of the film was 15%, Tcc was 68 ° C, Tc was 166 ° C, and Tm was 222 ° C. Thereafter, TD stretching was performed at a temperature of 180 ° C. at a stretching ratio of 3.8 times to obtain a biaxially stretched nylon 6 film having Tm = 222 ° C. Thereafter, the temperature was gradually raised in the tenter, heat-treated at a maximum temperature of 217 ° C., and then relaxed in the TD direction of 2% at 210 ° C. Thereafter, the mixture was cooled to obtain a biaxially stretched nylon 6 film having a thickness of 15 μm. BS _max , BS _min, and BS _θ of the obtained biaxially stretched nylon 6 film are as shown in Table 1. The heat shrinkage ratio was low and the operability was good.
[0035]
Example 2
A biaxially stretched nylon 6 film was obtained in the same manner as in Example 1 except that the TD stretching temperature was 190 ° C.
[0036]
Example 3
A biaxially stretched nylon 6 film was obtained in the same manner as in Example 1 except that the degree of crystallinity before TD stretching was 25%.
[0037]
Comparative Example 1
A biaxially stretched nylon 6 film was obtained in the same manner as in Example 1 except that the TD stretching temperature was 100 ° C.
[0038]
Comparative Example 2
A biaxially stretched nylon 6 film was obtained in the same manner as in Example 1 except that the TD stretching temperature was 130 ° C.
[0039]
Comparative Example 3
A biaxially stretched nylon 6 film was obtained in the same manner as in Example 1 except that the MD stretching temperature was 98 to 102 ° C. and the crystallinity before TD stretching was 35%.
[0040]
[Table 1]

[0041]
【The invention's effect】
According to the present invention, a biaxially stretched nylon 6 film having excellent operability and a reduced heat shrinkage rate can be obtained, and can be particularly suitably used for packaging materials.

Claims (2)

Sequential biaxially oriented nylon 6 film that satisfies the following formula at all positions in the width direction (TD direction) of the film.
BS _max ≦ 3.7%
BS _ai = BS _max −BS _min ≦ 2.5%
BS _θ ≤20 °
(BS _max and BS _min are the maximum and minimum shrinkage when the TD direction is 0 ° and the hot shrinkage in all directions is obtained. BS _ai is the difference between them. BS _θ is the most hot shrinkage. The direction in which the is higher is indicated by the angle to the TD direction.) In the production method of sequential biaxially stretched nylon 6 film, when the film is stretched in the TD direction in a flat shape, the degree of crystallinity after MD stretching and before TD stretching is 30% or less, and the TD stretching temperature is (Tc-20) A method for producing a sequentially biaxially stretched nylon 6 film characterized by being at a temperature not lower than C and not higher than Tm. (Here, Tc is the temperature drop crystallization temperature of the biaxially stretched nylon 6 film, and Tm is the melting point of the biaxially stretched nylon 6 film.)