JPS6154338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermoplastic film made of an intimate mixture of polyamide and a specific ethylene ionomer and having good low-temperature pinhole resistance, heat seal strength, transparency, etc.

Polyamide film, especially polycaproamide (nylon 6) film, is already widely used mainly in food packaging applications as a strong film with excellent impact resistance and gas barrier properties. It is not necessarily a satisfactory material for development into a wider range of applications. For example, nylon 6 film is considered to be a material with relatively good pinhole resistance, but this property is highly dependent on temperature, and although it does show fairly high pinhole strength at room temperature, it The problem is that it is quite brittle at low temperatures, such as food storage temperatures, and it is difficult to maintain practical pinhole resistance. In addition, recently, as packaging forms have changed, there have been cases where high heat-sealing strength is required, but nylon 6 film currently has low heat-sealing strength and cannot meet this demand.

On the other hand, in the field of ordinary injection molded products that do not require particular transparency, the method of mixing different types of polymers to modify polyamide has often been adopted and there are many reported cases, but for packaging that requires a high degree of transparency, It is no exaggeration to say that there have been almost no successful cases of applying mixtures of different polymers to films. The reason for this is thought to be that different types of polymers generally have different refractive indexes and are poorly compatible with each other, and cannot form a finely dispersed structure, resulting in optical non-uniformity.

The present inventors aimed to obtain a film that has high low-temperature pinhole resistance and heat sealing strength without impairing the characteristics of nylon 6 film such as heat resistance and gas barrier properties, and also has extremely excellent transparency. As a result of intensive studies from the perspective of mixing different types of polymers, we have found that a polyamide composition containing an ethylene ionomer that is neutralized to a specific ionization rate by specific metal ions and has a melt viscosity within a specific range is an excellent product. The inventors have discovered that a film having these characteristics can be provided, and have arrived at the present invention.

That is, the present invention comprises (A) 60 to 95% by weight of polyamide containing caproamide as a main component and (B) α
- Ethylene ionomer 5-40 made by neutralizing and ionizing 5-50% of the carboxyl groups of a copolymer consisting of olefin and α, β-unsaturated carboxylic acid with zinc ions, and having a melt index greater than 7.0 The invention provides a thermoplastic film made from an intimate mixture of % by weight.

The polyamide (A) used in the present invention has caproamide as its main component, and typical examples include polycaproamide (nylon 6) and poly(caproamide/hexamethylene adipamide) copolymer (nylon 6/66). ), poly(caproamide/lauramide) copolymer (nylon 6/12), poly(caproamide/hexamethylene isophthalamide) copolymer (nylon 6/6I), and the like. When these polyamides have a relative viscosity measured according to the method of JIS K 6810 of less than 2.0, they lack the mechanical strength generally required for films, and when the relative viscosity exceeds 4.5, the melt viscosity is high. If the temperature is too high, the operability of film forming will deteriorate, which is inappropriate.

The ethylene-based ionomer used in the present invention is an ionic polymer obtained by adding zinc metal ions to a copolymer consisting of an ethylene-containing α-olefin and an α,β-unsaturated carboxylic acid and/or its derivative. The degree of neutralization of the carboxyl groups of the α, β-unsaturated carboxylic acids contained must be within the range of 5 to 50%. If the degree of neutralization and ionization of carboxyl groups by zinc metal ions is less than 5%, the mechanical strength of the film will not be satisfactory, and if the degree of neutralization and ionization exceeds 50%, the transparency of the film will deteriorate, which is not preferred. Examples of the α-, β-unsaturated carboxylic acids that make up the ethylene ionomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, as well as ethyl acrylate, isobutyl acrylate, and methacrylic acid. It may contain methyl, methyl hydrogen maleate, etc. as a constituent component. In order to obtain a film with good transparency, it is essential to use a very special ethylene ionomer whose melt index value is greater than 7.0 as measured by the ASTM D 1238 method. When using commercially available products, use “Surlyn” 1702, AD8102 (trademark, manufactured by DuPont)
Examples include.

The film of the present invention is composed of a material made by mixing polyamide with 5 to 40% by weight, more preferably 10 to 35% by weight of ethylene ionomer. Contains 5% by weight of ethylene ionomer
If the amount is less than 40% by weight, it will be difficult to obtain a film with excellent low-temperature pinhole resistance, while if the amount is more than 40% by weight, the transparency will deteriorate and the characteristics of polyamide such as heat resistance and gas barrier properties will not be exhibited. do not have.

The method of mixing the polyamide and the ethylene ionomer and the method of forming the film are not particularly limited, and commonly known methods can be employed. for example,
First, polyamide and ethylene ionomer pellets are uniformly mixed using a high-speed stirrer, and then melt-kneaded using an extruder with sufficient kneading capacity to prepare an intimate mixture of the two. Then, in the case of the T-die method, this mixture is used to produce an unstretched film by extruding a film melted at 230 to 300°C onto a casting roll kept at room temperature to 100°C and cooling.
This can be sequentially or similarly biaxially stretched as required, and heat treatment can also be performed at a temperature near the melting point of the polyamide component. In the case of the tubular method, the molten mixture is extruded through a cylindrical die, brought into contact with the surface of a water-cooled or air-cooled ring, cooled and solidified, and then taken off with pinch rolls to obtain a blown film. Also,
The film of the present invention can also be used as one layer of a composite film consisting of two or more layers.

The film of the present invention may contain commonly known additives, such as antioxidants, heat resistant agents, weather resistant agents, antigelation agents, lubricants, crystal nucleating agents, antiblocking agents, antistatic agents, as long as they do not impair its properties. Surfactants or other polymers or the like can be added.

The present invention will be described in more detail with reference to Examples below. The type of neutralizing metal ion of the ethylene ionomer described in the Examples and Comparative Examples, measurement of the ionization rate, and physical properties of the film were evaluated by the following methods.

(1) Neutralized metal species of ethylene ionomer: The resin was incinerated, and the hydrochloric acid solution of the ashed product was analyzed by atomic absorption spectroscopy.

(2) Ionization rate of ethylene ionomer: The amount of residual carboxyl groups ([COOH]) is determined by dissolving the resin in tetrahydrofuran while heating and titrating it with a specified concentration of potassium hydroxide while heating.
was determined, and the amount of carboxylic acid metal salt relative to the original total carboxyl group amount including the amount of carboxylic acid metal salt ([COOM]) determined in the analysis in (1) above was defined as the ionization rate. That is, ionization rate (%) = [COOM] / [COOH] +
[COOM] ×100 (3) Low-temperature pinhole resistance: Drop a dart weighing 6.45 g and a tip of 0.3 mmφ onto a film kept at -50°C from each height to find the height when a hole is made in the film. Then, this height was multiplied by the dart weight to convert it into a value per film thickness.

(4) Heat seal strength: Layer the films together using an impulse sealer (Fuji Seisakusho K300, 300W), apply electricity for around 5 seconds at a seal width of 10 mm and a pressure of 3 Kg/ ^cm2 , and then sample several points.
This sealed sample was processed using Tensilon (manufactured by Toyo Sokki Co., Ltd.) at a speed of 300 mm/min.
The heat seal strength was determined by peeling at 90° (distance between samples: 50 mm). The highest value of the product with changed energization conditions was taken as the heat seal strength of the film.

(5) Breaking strength, breaking elongation: JIS C2318-66 (6) Young's modulus: ASTM D882-61T (7) Oxygen permeability coefficient: ASTM D1434-66 (8) Haze: ASTM D1003 Example 1 Melting ε-caprolactam 80% by weight of polycaproamide with a relative viscosity of 2.70 obtained by polymerization and "Surlyn" 1702 (ionomer resin manufactured by DuPont, USA).
Neutralized metal type: zinc, ionization rate analysis value: 23%, melt index: 14) 20% by weight mixed, 250
The mixture was melt-kneaded in an extruder with a diameter of 30 mm and set at ℃, and then pelletized. Next, the pellets were fed into an extruder with a diameter of 40 mm and a T-die, melted at 270°C, and then extruded onto rolls at 40°C to a thickness of about 50 μm.
An unstretched film was obtained.

The properties of the film obtained here are as follows, and it was found to be a film with excellent transparency and high practical value.

Haze: 4.2% Pinhole resistance strength: 1490g/cm/mm Heat seal strength: 3020g/cm Breaking strength: 7.0Kg/mm ² breaks Elongation: 400% Young's modulus: 76Kg/mm ² breaks Oxygen transmission rate in dry state: 6.4cc/ ^m2・24hr/
0.1mm Comparative Example 1 The same procedure was carried out except that "Surlyn" 1557 (neutralized metal type: zinc, ionization rate analysis value: 55%, melt index: 5) was used instead of "Surlyn" 1702 used in Example 1. A film was obtained in exactly the same manner as in Example 1, but when an ionomer resin having a relatively high ionization rate was used, the haze of the obtained film was 7.5%, and the transparency was unsatisfactory for practical purposes.

Comparative Example 2 The film made of polycaproamide alone used in Example 1 had unsatisfactory low-temperature pinhole resistance and heat seal strength as shown below.

Pinhole resistance strength: 820g・cm/mm Heat seal strength: 1010g・cm Comparative example 3 40% by weight of the polycaproamide used in Example 1 and 60% by weight of “Surlyn” 1702 were mixed and the same procedure as in Example 1 was carried out. However, the oxygen permeability of the film obtained here was 18.0 cc/cm when completely dry.
^m2・24hr/0.1mm, and it was found that the gas barrier property, which is a characteristic of polyamide film, was insufficient.

Example 2 80% by weight of a nylon 6/66:85/15 copolymer with a relative viscosity of 3.40 obtained by melt polymerizing a mixture of 85 parts by weight of ε-caprolactam and 15 parts by weight of an equimolar salt of hexamethylene diamine and adipic acid. and 20% by weight of “Surlyn” 1702 used in Example 1, and heated at 260°C.
The mixture was melted and kneaded in an extruder with a diameter of 30 mm and then pelletized. Next, this pellet is made into 30mmφ
Supplied to extruder water-cooled blown film manufacturing equipment, extrusion temperature 250℃, die diameter 100mm.
φ, blow ratio 1.07, water temperature in the water cooling ring 30℃, take-up speed 10m/min, and the film thickness was approximately 40mm.
A film of μ was obtained.

The properties of the film thus obtained were as follows, and it was found that the film had sufficient performance as a practical film.

Haze: 5.1% Pinhole resistance strength: 1600g/cm/mm Heat seal strength: 3100g/cm Breaking strength: 6.8Kg/mm ² breaks Elongation: 430% Young's modulus: 72Kg/mm ² breaks Oxygen transmission rate in dry state: 6.0cc/m ²・24hr/
0.1mm Comparative Example 4 Instead of “Surlyn” 1702 used in Example 1, “Surlyn” 1707 (neutralized metal species: sodium, ionization analysis value: 62%, melt index:
A film was obtained in exactly the same manner as in Example 1 except that 0.9) was used, but the haze was 8.1%,
It lacked transparency and had little practical value.

Claims (1)

[Claims] 1. 5 to 50% of the carboxyl groups of (A) 60 to 95% by weight of polyamide whose main component is caproamide and (B) copolymer consisting of α-eufin and α, β unsaturated carboxylic acid are replaced with zinc ions. A thermoplastic film made of an intimate mixture of 5 to 40% by weight of an ethylene ionomer which is neutralized and ionized and has a melt index greater than 7.0.