JPH0134522B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polypropylene composite film. More specifically, the present invention relates to a method for producing a polypropylene composite film with excellent heat sealability and transparency using a resin with excellent low temperature heat sealability. Among crystalline polypropylene films,
Biaxially stretched films have excellent optical properties such as transparency and gloss, mechanical properties such as rigidity and tensile strength, and are odorless and non-toxic.
It is especially widely used as a food packaging material. However, polypropylene film alone has drawbacks such as the high temperature at which it can be heat-sealed and insufficient sealing strength. In order to improve these drawbacks, we have developed a method of coating one or both sides of a biaxially stretched polypropylene film with a solution or emulsion of an easily heat-sealable resin. There is a method of manufacturing a composite film in which uniaxially or biaxially stretched film is produced by bonding polyester resins together. This method does not require coating, drying, or solvent recovery equipment unlike the coated film, is low in cost, and has relatively high sealing strength.
There are many cases where this method is used. The resin used in this method to improve heat-sealability must have an excellent balance of major properties such as low-temperature heat-sealability, transparency, and scratch resistance. Many resins have been proposed for this purpose. For example, JP-A-52-
As seen in No. 11281 and No. 52-11282, a propylene-ethylene-butene terpolymer is used. In addition, there are many attempts to obtain such resins by mixing polybutene-1 with not only terpolymer copolymers but also propylene-ethylene random copolymers or propylene-butene copolymers. However, although blends of propylene copolymers and different polymers (crystalline polybutene) may improve low-temperature heat-sealability, they are unfavorable in terms of transparency;
There is a desire to develop easily heat-sealable resins and composite films that have an excellent balance of properties as described above. In view of the above points, the present inventors have made extensive studies and found that a resin obtained by depolymerizing a blend of a propylene polymer or copolymer with a butene-1 polymer or copolymer is particularly suitable. The inventors have discovered that a polypropylene composite film with excellent low-temperature heat-sealing properties and transparency can be provided, and have arrived at the present invention. The object of the present invention is to provide a method for producing a polypropylene composite film laminated with a resin that imparts low-temperature heat-sealability, and which has particularly excellent low-temperature heat-sealability and transparency. That is, the present invention
(A) Polymer of propylene and/or propylene and α-
An easily heat-sealable resin obtained by depolymerizing a copolymer with olefin and (B) a polymer of butene-1 and/or a copolymer of butene-1 and α-olefin in the presence of a radical generator is crystallized. This is a method for producing a polypropylene composite film, which comprises adhering a layer made of polypropylene to at least one side. Even if the resin according to the present invention contains a relatively large amount of polybutene-1 component, which is considered to impair the transparency and gloss of polypropylene film (for example, Japanese Patent Application Laid-Open No. 54-28351), the radical generator By depolymerizing in the presence of , it is possible to provide a polypropylene composite film that has greatly improved transparency and gloss and has good low-temperature heat sealability. In addition to the above-mentioned effects, depolymerization in the presence of a radical generator has the advantage of being able to freely adjust the melt flow index (hereinafter referred to as MFI) value to suit the film-forming extrusion conditions. It has a feature that the MFI of each component can be freely selected as long as it is below the MFI value (that is, the MFI value of the composition). One of the main components of the resin used in the present invention is a propylene polymer and/or copolymer (hereinafter abbreviated as propylene polymer), and the copolymer components include ethylene, butene-1,4 methyl-1 - At least one α-olefin such as pentenhexene-1, octene-1 or dodecene-1 can be mentioned. When the α-olefin is ethylene and/or butene-1, the composition ratio should be such that the ethylene component is 7% by weight or less and the butene-1 component is 20% by weight or less so that the crystallinity of the polypropylene is not lost. It is preferable to do so. It is also possible to use a mixture of two or more of the above propylene polymers. MFI of propylene polymer
As mentioned above, it is sufficient that the MFI value is not more than the MFI value of the composition, and is not particularly limited, but it is suitably about 0.1 to 30, preferably about 0.5 to 20. Such propylene polymers, for example, are
It can be produced by a method using a so-called Ziegler-Natsuta catalyst as described in Japanese Patent No. 36308. Crystalline polybutene, another main component
1 may be not only a homopolymer of butene-1, but also a copolymer with a small amount of at least one α-olefin such as ethylene, propylene, 4-methyl-1-pentene, or hexene-1. The amount of α-olefin in the copolymer is preferably set to such a composition ratio that the crystallinity of the polybutene is not lost, and specifically, it is suitably 10% by weight or less. Butene-1 polymer and/or copolymer (hereinafter referred to as butene-1)
Two or more of the monopolymers may be mixed. For example, the present invention also includes mixing butene-1 polymers with greatly different MFI values, or a butene-1 polymer and a copolymer. The MFI value of the butene-1 polymer is determined by the composition as described above.
As long as it is below the MFI value, there is no particular limitation, but
A value of about 0.5 to 30, preferably about 1 to 20, is suitable. Such polybutene-1 polymers can be produced, for example, by the methods described in JP-A-53-277 and JP-A-53-2583. As for the ratio of both components, it is appropriate that the propylene polymer is in the range of 40 to 95 parts by weight and the butene-1 polymer is in the range of 60 to 5 parts by weight. If the amount of the butene-1 polymer is less than 5 parts by weight, sufficient low-temperature heat-sealing properties cannot be achieved, while if it exceeds 60 parts by weight, the bonding with the base film deteriorates and at the same time the moldability deteriorates. As mentioned above, even if the MFI value and mixing ratio of the two main components are varied over a fairly wide range, the effect of developing low-temperature heat sealability and transparency is achieved only after mixing the two main components. , which is a remarkable effect of the depolymerization method of the present invention. If the two main components are mixed without going through the depolymerization method, or even if they are mixed after depolymerization, the above-mentioned improvements in low-temperature heat sealability and transparency cannot be achieved. Examples of organic or inorganic free radical generators that can be used in the present invention include peroxides, hydroperoxides, peracides, metal alkyls, metal allyls, and combinations thereof with inorganic complex salts that are used as radical polymerization initiators. be able to. The organic peroxide may be in a liquid, solid, or solidified form with an inorganic filler, and is mixed and diffused with the polyolefin at a temperature at which the organic peroxide does not substantially decompose. The organic peroxide that can be used in the present invention is preferably selected from those having a half-life of 1 minute at a temperature of 70 to 300°C. For example, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, dicumyl peroxide,
2.5-dimethyl 2.5-di(t-butylperoxy)
Hexane, dialkyl peroxides such as 2.5-dimethyl 2.5-di(t-butylperoxy)hexyne-(3), diacyl peroxides such as lauroyl peroxide and benzoyl peroxide, t-butylperoxyacetate, t- Examples include peroxy esters such as butyl peroxylaurate, methyl ethyl ketone peroxide, and methyl isobutyl ketone peroxide. Additionally, polymeric peroxides such as those produced by air oxidation, hydrogen peroxide, lysium peroxide, or alkali or alkaline earth peroxides are useful in the process of the invention if heated. Other azo compounds such as α,α-azobis-(isobutyronitrile) can also be used as free radical generators. The amount of the radical generator added is an important factor in determining the MFI of the resin of the present invention, and the amount added is 0.001 to 2% by weight, preferably 0.01 to 0.5% by weight, based on the polyolefin. The effect is not exhibited, and if the amount is too large, the degree of decomposition becomes excessive, which is not preferable. The amount added is adjusted in consideration of the MFI of both main components and the MFI of the product. The MFI of the resin is suitably 1.5 to 35, preferably 5 to 20, and can be easily controlled by the type and amount of the radical generator as described above. It is easy to do this by blending the two main component resins and the radical generator in a predetermined ratio, dry blending in a super mixer, and then melt-kneading under normal conditions that allow extrusion of propylene polymer, such as at a temperature between 170°C and 300°C. Mixing and depolymerization are accomplished. Alternatively, a method of directly adding and mixing and melt-kneading can also be applied. In addition to the above-mentioned two main components and a radical generator, the resin used in the present invention contains various auxiliary components that are usually blended, such as antioxidants, ultraviolet deterioration inhibitors, anti-blocking agents, slip agents, antistatic agents, It can contain a coloring agent and the like. The polypropylene used as the base material for forming the film on which the above resin is to be laminated has a density of 0.89 to 0.92.
It is a homopolymer or a copolymer with a small amount of ethylenically unsaturated monoolefin, with a g/cc MFI of 0.1 to 50 and a content insoluble in boiling n-heptane of 85 to 99%. Antioxidants, ultraviolet absorbers, antiblocking agents, slip agents, antistatic agents, etc. may be added to the crystalline polypropylene as necessary to improve its performance as a film. Furthermore, a small amount of different polymers may be mixed to the extent that the transparency of the film is not impaired. Next, a composite film made of the above base material and resin can be manufactured using a conventional method. For example, a polypropylene composite film is manufactured by laminating a resin in a molten state on one or both sides of a crystalline polypropylene film. In this case, the layer of the resin of the present invention may be unstretched or uniaxially or biaxially stretched after lamination. The thickness of the crystalline polypropylene film layer which is the base material layer is in the range of 5 to 200μ, preferably 5 to 70μ, and the thickness of the resin layer of the present invention is in the range of 0.1 to 200μ.
100μ, preferably in the range 0.3 to 30μ. In some cases, it can also be produced by a method of co-extruding crystalline polypropylene and the resin of the present invention. The polypropylene composite film according to the present invention is
Compared to conventional products, the film has better heat-sealability,
The balance between transparency and scratch resistance is maintained at a high level. The polypropylene composite film of the present invention is suitable for uses such as food packaging, clothing packaging, and textile packaging. The details of the present invention will be explained below with reference to Examples, but the present invention is not limited to these methods. The heat sealability, haze, and MFI in the Examples and Comparative Examples below were measured by the following methods. (a) Heat-sealability A 15-mm-wide test piece was cut from a sample that was heat-sealed using a heat-sealing bar with a width of 5 mm under the heat-sealing conditions of a heat-sealing pressure of 1 Kg/ ^cm2 and a heat-sealing time of 1 second at each set temperature. The peel strength was measured at room temperature using a Ron tester at a tensile speed of 50 mm/min. The strength at each temperature was plotted, and the temperature at which 500 g was on the curve was shown. (b) Haze Measured using a haze meter according to ASTM-D-1003-61. (c) MFI Measured using the method of JIS K6758. However, the temperature is 230℃ and the load is 2.16Kg. 50 pieces of semi-cylindrical weight 253g sliding piece with paper attached
Creates scratches by sliding at a speed of mm/min. Evaluation is made based on the difference in haze values before and after this time. The larger the numerical difference, the lower the scratch resistance. Example 1 As easily heat-sealable resin, 60 parts by weight of propylene polymer with MFI of 1.7, 40 parts by weight of crystalline polybutene-1 with MFI of 2.7, and 2.5 parts by weight of organic peroxide, dimethyl,
Add 0.11% by weight of 2.5 di(t-butylperoxy)hexane (Perhexa 2.5B-40 manufactured by Nippon Oil & Fats Co., Ltd.), mix with a Henschel mixer, and then extrude with an extruder at a depolymerization temperature of 250°C to create pellets. did. The MFI of the easily heat-sealable resin obtained was 10.4. The intrinsic viscosity of decalin solution at 135℃ is
The isotactic polypropylene sheet of 3.2 was subjected to short stretch stretching of substantially 5 times at a temperature of 140° C. between two sets of nip rolls having different circumferential speeds. On the other hand, the above-mentioned easily heat-sealable resin was laminated with the above-mentioned uniaxially stretched isotactic polypropylene sheet at a resin temperature of 250°C using a small extruder. The resulting two-layer sheet was then stretched in the transverse direction at a tenter temperature of 160° C. to an effective magnification of 8 times, and subjected to tension heat treatment at 120° C. for 3 seconds to obtain a two-layer biaxially stretched film. The thickness of the base material layer of the obtained composite film was 30μ, and the thickness of the heat seal layer was 2μ. The heat sealability, haze, and scratch resistance of the sample were measured using the methods described above, and the results shown in Table 2 were obtained. Comparative Example 1 A resin mixture with an MFI of 2.1 was obtained in the same manner as in Example 1 except that no organic peroxide was added. A composite film was similarly molded using it, but the transparency was poor and the haze was 4.6. Comparative Example 2 60 parts of polypropylene with MFI of 10.7 and MFI of 9.3
of polybutene-1 from 40 parts without peroxide
I got a resin with MFI10.1. A composite film was similarly molded using it, but the haze was 3.9 and the transparency was poor. Comparative Example 3 60 parts by weight of a propylene polymer with an MFI of 22 obtained by depolymerizing only the propylene polymer with an MFI of 1.7 used in Example 1 and 40 parts by weight of polybutene-1 used in Example 1 were mixed to produce an MFI of 9.6. of resin was obtained. A composite film was similarly molded using it, but the transparency was poor and the haze was 5.0. Comparative Example 4 The same procedure as in Example 1 was carried out except that the mixing ratio of the propylene polymer and butene-1 polymer used in Example 1 was changed to 30/70. This product had poor bonding with the polypropylene base material and poor moldability, making it impossible to obtain samples for evaluation. Comparative Example 5 Example 1 except that the mixing ratio of the propylene polymer and butene-1 polymer used in Example 1 was 97/3.
It was carried out in the same way. The results are shown in Table-2. Examples 2 to 7 The procedure was carried out in the same manner as in Example 1 except as shown in Table 1.
2 results were obtained. Example 8 By the same method as in Example 1, the easily heat-sealable resin obtained was supplied to a composite film molding die using one extruder at a resin temperature of 250°C, and at the same time, a decalin solution at 135°C was supplied using another extruder. Isotactic polypropylene having an intrinsic viscosity of 3.2 was fed to the composite film molding die described above at a resin temperature of 260°C to obtain a two-layer multilayer film.
This composite film was stretched for a short period of 5 times at a temperature of 115°C between two sets of nip rolls with different circumferential speeds, and then stretched at a tenter temperature of 170°C so that the effective magnification was 8 times in the transverse direction. Stretched at 120℃
The film was subjected to tension heat treatment for 3 seconds to obtain a two-layer biaxially stretched film. The thickness of the base material layer of the obtained composite film was 30μ, and the thickness of the heat seal layer was 1μ. The heat sealability, haze, and scratch resistance of the sample were measured using the methods described above, and the results shown in Table 2 were obtained. Examples 9 and 10 Examples 9 and 10 were carried out in the same manner as Example 8, except that the easily heat-sealable resins of Examples 2 and 3 were used, respectively, and the results shown in Table 2 were obtained. It is clear that the present invention provides a composite film with an excellent balance of low temperature heat sealability, transparency, and scratch resistance.

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Claims (1)

[Claims] 1. (A) A polymer of propylene and/or a copolymer of propylene and α-olefin, and (B) a polymer of butene-1 and/or a copolymer of butene-1 and α-olefin. A method for producing a polypropylene composite film, comprising laminating an easily heat-sealable resin obtained by depolymerizing and depolymerizing in the presence of a radical generator on at least one side of a layer made of crystalline polypropylene. 2 (A) 40 to 95 parts by weight of the propylene polymer and/or the copolymer of propylene and α-olefin, (B)
of butene-1 and or butene-1 and α-
2. The method for producing a polypropylene composite film according to claim 1, wherein the copolymer with olefin is contained in an amount of 5 to 60 parts by weight. 3. The propylene copolymer (A) contains propylene and up to 7% by weight of ethylene or up to 20% by weight of butene.
Claim 2, wherein the butene-1 copolymer (B) is a copolymer of butene-1 and 10% by weight or less of ethylene and/or propylene.
A method for producing a polypropylene composite film as described in .