JPS6320690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a film that has excellent transparency, low-temperature heat sealability, surface smoothness, etc. In recent years, resource saving of packaging materials, heat sealability,
Composite films are being developed for the purpose of improving functionality such as gas barrier properties and strength. However, in the stretched composite film, the low-melting point polymer layer B is subjected to harsh mechanical and thermal conditions due to heating and stretching operations, which may cause scratches or poor transparency. There are many. In addition, the film (including seeds) heated during the stretching operation is
It is also known that if the material is allowed to cool naturally after stretching, the transparency and low-temperature heat-sealability will deteriorate, and the transparency will change due to processing temperature irregularities during lamination, laminated thickness irregularities, adhesive conditions at the laminated interface, etc. . The present inventors have made repeated efforts to investigate these problems, and as a result, have arrived at the present invention. That is, the present invention provides a low melting point polyolefin polymer in which at least one side of the base film layer (A) made of a uniaxially stretched polyolefin polymer has a melting point lower than the melting point of the constituent polymer of the base film layer by 5°C or more. A coating layer consisting of an unstretched film, a uniaxially stretched film, or a melt-extruded film whose main component is
(B) is formed, the obtained laminated film is heated and stretched, and if desired, heat-set, and then the maximum crystallization temperature of the low melting point thermoplastic polymer, which is the main component of the coating layer (B), is adjusted to the maximum crystallization temperature. This is a film manufacturing method characterized by cooling a temperature range 10°C lower than the temperature at a cooling rate of 200°C/second or more. Generally, a heated and stretched film is heated at 5°C/
A stretched film with good transparency is obtained by rapid cooling at a cooling rate (air cooling) of 40°C/sec to 40°C/sec, but in the case of a laminated film, it is difficult to obtain a sufficiently stretched film at the cooling rate mentioned above. I can't. Moreover, if the coating layer (B) is a low-melting thermoplastic polymer, it may become opaque at any time, and excellent transparency and heat sealability can only be achieved by rapid cooling under the special conditions described above. Therefore, a laminated stretched film with excellent surface smoothness can be obtained. This laminated film is particularly suitable for use in packaging materials. In the method of the present invention, the base film layer (A) is made of a polyolefin polymer that can be stretched, and transparency can be obtained by stretching, such as a polyolefin such as polyethylene, polypropylene, polybutene-1, or ethylene. -propylene copolymers and polyolefin copolymers such as ethylene-butene-1. Of course, mixtures and modified products thereof are also included. Transparency in the present invention refers to a haze of 15 or less, preferably 9.0 or less, and the state immediately before laminating the base film layer (A) with the coating layer (B) is in an unoriented molten state or an unstretched state. It may be in a uniaxially stretched state. The polymer of the coating layer (B) has a melting point of 5°C or more, preferably 10°C or more, than the melting point (A) of the polymer constituting the base film layer.
A material with a low melting point of ℃ or above and a melting point of 230℃ or less is used, and it is also related to the base film layer (A),
For example, olefinic copolymers such as ethylene-propylene copolymers are used. For lamination, the coating layer (B) is in a molten state or a solid state,
This is preferably carried out by applying it to the base film layer (A) in a molten state. More specifically, the layers are laminated by a coextrusion method, an extrusion lamination method, a heat stretch fusion method, an adhesive bonding method (including a heat reaction type), or the like. If necessary, an adhesive resin layer may be formed between the (B) layer and the (A) layer. After lamination, the laminated film is heated and stretched in at least one direction. There are various configurations of the stretched film after stretching, but uniaxial stretching is UO, and biaxial stretching is UO.
When BO, base film layer is A, and coating layer is B, in a two-layer configuration, BO-A/UO-B, BO-A/
BO-B, UO-A/UO-B, UO-A/BO-
B. In the three-layer configuration, BO-B/BO-A/BO-B,
BO-B/BO-A/UO-B, UO-B/BO-
A/UO-B, BO-A/BO-B/BO-A, UO
-A/BO-B/UO-A, UO-B/UO-A/
UO-B, UO-A/UO-B/UO-A, etc. are useful, and of course there are various other combinations. The thickness of the coating layer (B) to be laminated is 0.1μ ~ after stretching.
20μ, preferably 0.3μ~10μ, when so preferably
It is 0.5μ to 8μ. For stretching, either longitudinal stretching or lateral stretching may be selected depending on the process such as lamination or stretching, and any stretching method such as roll stretching, tenter stretching, or inflation method may be used. . The stretching ratio is at least 1.1 times in one direction,
Usually stretched by 2.5 times or more. After stretching, heat setting is performed if desired, and the heat setting temperature must be higher than the maximum crystallization temperature of the polymer constituting the coating layer (B). The heat setting time varies depending on the type of polymer, but is usually 1 to 60 seconds. Next, this laminated film is rapidly cooled, and the cooling rate is at least 200°C/sec or more uniformly over a temperature range from the maximum crystallization temperature of the polymer constituting the coating layer (B) to a temperature 10°C lower than the maximum crystallization temperature. Rapid cooling is necessary. If the cooling rate is slower than this, the coating layer (B) in particular tends to crystallize, resulting in poor transparency and low-temperature heat sealability. Furthermore, if the cooling rate differs locally, the degree of crystallinity will differ locally, and therefore transparency, low-temperature heat sealability, etc. will decrease locally. In order to satisfy the rapid cooling conditions as described above, it is preferable that the following cooling conditions are further satisfied. (1) When the film thickness (total thickness) is L (cm) and the heat transfer coefficient of the film is h (Cal/ ^cm2・sec・℃), h/L≧0.2 (2) The initial temperature before cooling is When θ ₁ (°C) and the adhesion temperature of the cooling body to the film surface are θ ₂ (°C), θ ₁ - _{θ 2} ≧20°C (preferably 40°C) Water cooling or temperature control is used as a means to achieve the above conditions. Cooling is performed by contacting a liquid-cooled metal roll, a rubber roll, a metal roll whose surface is coated with a fluororesin, a cooling belt, or the like, or by blowing cold air and water mist. However, it is difficult to cool uniformly in the width direction by simply blowing cold air or the like, and the cooling performance is also poor, so it is preferable to use a cooling roll. Further, in order to bring the film into more complete contact with the cooling roll, cooling belt, etc., a pressing rubber roll, an air knife, etc. may be used to press the film. In addition, cooling is performed when the coating layer (B) is only on one side.
It is preferable to carry out from the side of the coating layer (B). In the present invention, the cooling rate is defined by the following equation, where the initial temperature before cooling is θ ₁ and the temperature after cooling is θ ₂ . Cooling rate Δθ = θ ₁ - θ ₂ /0.1 In other words, it is a value obtained by converting the difference in cooling for 0.1 seconds per second, and in the present invention, Δθ
A condition of ≧200°C/sec is required. Next, the present invention will be explained with reference to examples. In the examples, haze and heat seal strength rise temperature,
The maximum crystallization temperature TC was measured by the following method. (1) Haze: Measure the amount of incident light (T ₁ ), total light transmission (T ₂ ) using an integrating sphere light transmittance measurement device, the amount of scattered light (T ₃ ) by the device, and the amount of scattered light (T ₄ ) by the device and test piece. It was measured and calculated using the following formula. Transparency (Tt) = T ₂ / T ₁ × 100 (%) Scattered light transmittance (Td) = T ₄ − T ₃ (T ₂ / T ₁ ) / T ₁ × 100 (%) Haze = Td / Tt × 100 (%) (2) Heat seal strength rise temperature: Increase the heat seal temperature at 10°C intervals and heat seal for 1 second, measure the heat seal strength at that time, and plot the heat seal strength on the vertical axis.
A graph was drawn with the heat sealing temperature on the horizontal axis, and the temperature at the inflection point of the low temperature measurement of the obtained heat sealing strength-temperature curve was taken as the heat sealing strength rise temperature. (3) Maximum crystallization temperature (TC): Using a differential scanning calorimeter, place a standard sample that does not absorb or heat heat within the measurement temperature range in one of the two sample trays in the furnace, and place the measurement sample in the other. 5 mg of sample was heated to 280℃ in nitrogen gas, held for 5 minutes, then lowered at a rate of 10℃/min in nitrogen gas, and the temperature at which a peak occurs on the calorific curve (heat generation) is measured. The maximum crystallization temperature (TC) was obtained. Example 1 Isotactic polypropylene (intrinsic viscosity 2.5
dl/g, melting point 167℃) to obtain the average thickness
An unstretched film of 1620μ was obtained, then stretched 4.0 times in the machine direction at 140°C, and then melt-extruded laminated with an ethylene-propylene copolymer (ethylene content 4.2% by weight, TC 107°C) with an average thickness of 42.5μ, and then It was stretched 8.5 times in the transverse direction at 160°C and heat-set at 160°C for 10 seconds. When the temperature of the ethylene-propylene copolymer layer (melting point 155°C TC = 110°C) (hereinafter referred to as B layer) reaches 125°C, a metal roll with water at a temperature of 20°C passed inside is extruded onto the B layer surface. The laminated film was pressed into contact with the metal roll, and the laminated film was run at a contact arc length of about 100 mm and a film running speed of 60 m/min. The surface temperature of layer B immediately after passing through the metal roll is 62℃, and the cooling rate is 656℃.
This means ℃/second. The thickness of layer B after cooling was approximately 5 μm. In addition, the properties when the thickness of layer B was varied by making the total thickness of the product stretched film 50 μm after lamination using the same method are also listed. Furthermore, as a comparative example, the properties when cooled at a normal rate (40° C./sec) are also shown.

[Table] As is clear from the results in Table 1, the haze and heat seal strength of the laminated films of Examples are significantly superior to those of Comparative Examples. Example 2 A laminated film was produced in the same manner as in Example 1. However, the thickness of layer B was kept constant at 5 μm, and the cooling rate was varied as shown in Table 2. The results are shown in Table 2.

[Table] Example 3 In the base film layer (A), an ethylene-propylene copolymer with an ethylene content of 0.7% by weight, 0.5% by weight of stearic acid monoglyceride, 0.1% by weight of ethylene oxide adduct of stearylamine, and erucic acid amide Using a compound containing 0.1% by weight,
On the other hand, in the coating layer (B), ethylene-propylene copolymer (ethylene content 5% by weight, melting point = 148°C TC =
100°C) and ethylene-butene-1 copolymer (ethylene content: 4.5% by weight) in a 4:1 ratio, which was further blended with 0.2% by weight of erucic acid amide and 0.3% by weight of stearic acid monoglyceride. The above layer B was laminated on both sides of the above layer A using the following method. In the lamination method, raw materials for layer A and layer B were separately melted using two extruders, and the raw materials for layer A and B were laminated and coextruded inside a die to obtain an unstretched film. The thickness of each layer is A
The layer was 1480μ, the B layer was 120μ in total, and the total thickness was 1600μ. The film was heated 5 times in the longitudinal direction at 125°C, then 160°
The film was stretched 8 times in the transverse direction at 165° C. and heat-set for 8 seconds at 165° C. Then 800℃ with a metal roll cooled to 20℃
When the sample was cooled at a rate of .degree. C./second, the results shown in Table 3 were obtained. For comparison, the case of the conventional method is also shown. In addition, the thickness of the stretched laminated film of the product is
It was kept constant at 40μ.

【table】

Claims (1)

[Claims] 1 At least one side of the base film layer (A) made of a polyolefin polymer in an unoriented molten state, an unstretched state, or a uniaxially stretched state has a low melting point that is 5°C or more lower than the melting point of the constituent polymer of the base film layer. A coating layer (B) consisting of an unstretched film, a uniaxially stretched film, or a melt-extruded film containing a polyolefin polymer as a main component is formed, and the resulting laminated film is heated and stretched, and if desired, heat-set, and then the coating layer is formed. 10% from the maximum crystallization temperature of the low melting point polyolefin polymer that is the main component of (B)
A film manufacturing method characterized by cooling at a cooling rate of 200°C/second or more over a range of temperatures as low as 100°F.