JPH0676506B2 - Foam film - Google Patents

Description

The present invention relates to a foamed film containing polypropylene as a main component.

More specifically, it relates to the production of a foamed film which is composed of uniform fine bubbles, is light, flexible and has a beautiful pearly luster.

Such a foamed film has a high and elegant luster,
Since it has an appropriate mechanical strength, it is useful as a wide range of materials such as packaging materials, decoration materials, packing tape materials, and woven materials, and has extremely high commercial value.

[Conventional technology]

Conventionally, as a method of adding a foaming agent to a thermoplastic resin and obtaining a foamed film having fine cells by extrusion molding,
For example, as seen in JP-A-58-128818, polypropylene with a high melt index and low density polyethylene with a high melt index (hereinafter abbreviated as LDPE)
It has been proposed that a film-like material comprising a resin as a main component and a foaming agent that decomposes and foams at a temperature equal to or higher than the melting point of the resin mixture is heated at a temperature equal to or lower than the melting point of the resin mixture and then uniaxially or biaxially stretched.

[Problems to be Solved by the Invention]

However, in the case of extrusion molding based on the method disclosed in the above publication, the range of optimum extrusion conditions is narrow, the viscosity of the molten resin in the extruder during extrusion molding is likely to change rapidly, and the expansion of bubbles locally occurs. It was liable to occur, and there was a defect that the obtained foamed film was likely to contain fine bubbles and coarse bubbles.

It is an object of the present invention to provide a foamed film which has only uniform fine bubbles without such defects, is highly flexible, and has a beautiful pearly luster.

[Means for Solving the Problems]

The present inventors have conducted extensive studies to eliminate such drawbacks, and as a result, by using a specific resin and a foaming agent and further adding a polyether-modified silicone oil, a wide range of extrusion conditions can be obtained, and a foamed film can be obtained. The inventors have found that the physical properties are good and have completed the present invention.

That is, the present invention has a melt index of 15 to 60 relative to 100 parts by weight of polypropylene having a melt index of 5 to 20.
In a resin mixture containing 15 to 100 parts by weight of linear low-density polyethylene, 0.05 to 0.3 parts by weight of polyether-modified silicone oil and 0.2 to 1.0 parts by weight of a foaming agent are added to 100 parts by weight of the resin mixture. A foamed film obtained by extruding the resin composition into a film and uniaxially or biaxially stretching the resin composition at a temperature equal to or lower than the melting point of the resin composition.

Polypropylene used in the present invention (hereinafter abbreviated as PP)
Is a crystalline polymer, which is a polypropylene alone or a mixture of polypropylene with a small amount of polyethylene and an ethylene-propylene copolymer, and has a melt index (hereinafter abbreviated as MI) of 5 to 20, preferably 6 to A range of 15 is used. When MI is less than 5, the bubbles in the foamed film do not become fine and pearlescent luster cannot be obtained. If it exceeds 20, the fluidity is so good that film formation and stretching become difficult.

In addition, MI is based on ASTM D 1238-52T, and a load of 2.16 kg is 10
It is a numerical value measured for a minute.

Linear density polyethylene used in the present invention (hereinafter L-LDPE
Is a copolymer of ethylene with an α-olefin and has an MI of 15 to 60, preferably 20 to 50. When the MI is less than 15 or more than 60, the bubbles in the foamed film are not fine and pearly luster cannot be obtained.

The amount of the α-olefin bonded is not particularly limited, but usually 2 to 20% by weight is used. Examples of the α-olefin include propylene, butene-1, 4-methylpentene, hexene-1, octene-1 and the like.

The amount of L-LDPE used is 15 to 100 parts by weight based on 100 parts by weight of PP. If it is less than 15 parts by weight when it is a foamed film,
The film becomes hard and pearly luster cannot be obtained. If it exceeds 100 parts by weight, the film becomes too soft and no pearly luster can be obtained.

The polyether-modified silicone oil used in the present invention is
Those having a viscosity at 25 ° C in the range of 200 to 2000 cst are preferably used. Specifically, the polyether-modified silicone oil used in the present invention is represented by the following general formula (1) (In the formula, x is an integer of 5 to 50, y is an integer of 1 to 10, POA
Is a polyoxyalkylene group containing 5 to 30 polyoxyethylene units and / or polyoxypropylene units and having an OH group at the terminal). For example, commercially available products include polyether modified silicones SH3749, SH3748, BX16-033 manufactured by Toray Silicone Co., Ltd.

The amount of the polyether modified silicone oil used is 0.05 to 0.3 parts by weight based on 100 parts by weight of the resin mixture. Preferably
It is 0.1 to 0.2 parts by weight. If the amount is less than 0.05 parts by weight, the resulting foamed film will have insufficient air cell density and uniformity, and will not have adequate flexibility, and a product with satisfactory commercial value cannot be obtained. On the other hand, if the amount exceeds 0.3 parts by weight, the moldability is remarkably lowered, and a slip phenomenon particularly in the extruder occurs, which is not preferable because the ejection becomes impossible.

The foaming agent used in the present invention is preferably an organic foaming agent. For example, azodicarboxylic acid amide, dinitropentamethylenetetramine, and the like are used, and a foaming agent that decomposes at a temperature higher than the melting point of the polymer to be foamed is used.

The amount of foaming agent used is 0.2 to 2.0 per 100 parts by weight of the resin mixture.
Parts by weight. If the amount is less than 0.2 parts by weight, the number of bubbles per unit volume is small, so that sufficient diffuse reflection of light rays does not occur and it is not possible to obtain a highly elegant pearly luster. If it exceeds 2.0 parts by weight, air bubbles become large, which is not preferable. The effective addition amount is the addition amount of the foaming agent (hereinafter referred to as the effective addition amount) such that the decomposition gas amount of the foaming agent becomes 200 to 4000 cc (1 atm at 20 ° C.) with respect to the volume of the resin mixture of 1000 cc. For example, 0.3 to 1.5 parts by weight of azodicarboxylic acid amide (hereinafter abbreviated as ADCA) as an organic foaming agent is effective with respect to 100 parts by weight of resin mixture if the decomposition temperature is 190 to 205 ° C and the gas generation amount is 200 cc / g. The amount added.

In the production of the foamed film of the present invention, it is necessary to add an organic foaming agent and a polyether-modified silicone oil to a resin mixture obtained by adding L-LDPE to a polypropylene-based crystalline polymer. There is no particular limitation on the method of adding the polyether-modified silicone oil.

The foamed film of the present invention is uniaxially or biaxially stretched so as to flatten the bubbles generated at a temperature equal to or lower than the melting point without destroying the bubbles, thereby obtaining a pearly luster having a sufficient commercial value. That is, by stretching, the bubbles of the foam are flattened, and the thickness of the void forming layer in the foam film is reduced, so that diffuse reflection of light and multidentate reflection of the light transmitted through the inside of the foam from the void forming layer. Is enhanced. In particular, this effect is remarkably exhibited when the bubbles in the foamed film are uniformly fine and the number of bubbles per unit volume is large.

The resin composition used in the present invention may contain additives such as a lubricant, a colorant, an antistatic agent, an antioxidant, and a heat stabilizer in order to improve workability and enhance the commercial value. Good.

〔Example〕

 This will be described in detail below with reference to examples.

Examples 1 to 6 and Comparative Examples 1 to 4 L-LDPE was mixed with 100 parts by weight of a polymer mainly composed of PP at a ratio shown in Table 1, and 100 parts by weight of the obtained resin mixture was added with ADC.
In addition to 0.4 parts by weight of A, polyether-modified silicone oil (x in the above general formula (1) is about 16, y is about 3, PO
A contains about 11 polyoxyethylene units and polyoxypropylene units and has OH groups at the ends) was added at the ratio shown in Table 1. The obtained resin composition was melt-blended with a single screw extruder at a temperature of 150 to 170 ° C., and a sheet having a thickness of 0.6 to 0.7 mm was extruded from a mold while maintaining an appropriate pressure.
The obtained sheet was heated to a temperature not higher than the melting point of the resin (the sheet temperature was 120 ° C or lower), and stretched 6 times in the longitudinal direction with a pair of rolls having different peripheral speeds to obtain a thickness of 0.1 to 0.15 mm. I got a film of. The quality of the obtained foamed film is shown in Table 1.

〔The invention's effect〕

The foamed film of the present invention has flexibility and smoothness of the surface by adding polyether-modified silicone oil to a specific resin and a foaming agent to form a film, and imparts a high grace pearly luster. It has a very high commercial value as a wide range of materials such as packaging materials, decoration materials, packing tape materials, and woven materials.

Claims (2)

[Claims] 1. A resin mixture containing 15 to 100 parts by weight of a linear low-density polyethylene having a melt index of 15 to 60, and 100 parts by weight of a resin mixture to 100 parts by weight of polypropylene having a melt index of 5 to 20. On the other hand, a resin composition obtained by adding 0.05 to 0.3 part by weight of a polyether-modified silicone oil and 0.2 to 2.0 parts by weight of a foaming agent is extruded into a film, and uniaxially or biaxially at a temperature below the melting point of the resin composition. A foamed film which is axially stretched. 2. A polyether-modified silicone oil has the general formula (1): (In the formula, x is an integer of 5 to 50, y is an integer of 1 to 10, POA
Is a polyoxyalkylene group containing 5 to 30 polyoxyethylene units and / or polyoxypropylene units and having a terminal OH group), and
The foamed film according to claim 1, which has a viscosity at 25 ° C of 200 to 2000 cst.