JPH0613208B2 - Multilayer film and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a resin-made multilayer film and a method for producing the same, and can be used as a packaging material for foods, industrial products and the like.

BACKGROUND ART In recent years, as a material for a bag such as a rice bag, a resin-made multilayer (laminate) film has been widely used in terms of its strength and the like. A biaxially stretched nylon film having good printability and pinhole resistance is mainly used for the surface substrate of this multilayer film.

[Problems to be Solved by the Invention] In the case of a rice bag, after being normally filled with about 2 to 15 kg of rice,
10 to 20 bags are stacked and stored and transported on a pallet.

However, the outer layer biaxially stretched nylon film used in conventional rice bags has good secondary processing suitability such as multicolor printing suitability and laminating suitability, but on the other hand, since the film surface is slippery, it is used as a surface base material for bags. In the case of manufacturing, there was a risk that the load collapsed during stacking and the bag was broken.

On the other hand, when the slipperiness of the film surface is reduced in order to prevent the risk of collapse of the load, there arises a problem that the suitability for secondary processing is adversely affected. Therefore, there has been a demand for a multilayer film formed with a biaxially stretched nylon film that is hard to slip and is excellent in secondary processing suitability.

An object of the present invention is to provide a multilayer film which is hard to slip and is excellent in secondary processing suitability.

[Means and Actions for Solving the Problems] The present invention relates to a multilayer film having at least two layers composed of a biaxially stretched nylon film and having one biaxially stretched nylon film layer as an outermost layer. The outermost biaxially stretched nylon film layer has a static friction coefficient of 0.6 or more, preferably 0.8 or more, and the biaxially stretched nylon film layers other than the outermost layer have a dynamic friction coefficient of 0.6 or more.
It is characterized in that it is preferably 0.5 or less.

Then, with respect to the static friction coefficient, the outermost biaxially stretched nylon film layer has a higher value than layers other than the outermost layer,
Regarding the coefficient of dynamic friction, the biaxially stretched nylon film layers other than the outermost layer have a lower value than the outermost layer.

If the coefficient of static friction of the outermost biaxially stretched nylon film layer is smaller than 0.6, stacking aptitude becomes poor. Further, when the dynamic friction coefficient of the biaxially stretched nylon film layer other than the outermost layer is made larger than 0.6, the suitability for secondary processing becomes poor.

As the nylon of the biaxially stretched nylon film layer,
Nylon-6, nylon-8, nylon-11, nylon-12, nylon 6,6, nylon 6,10, nylon 6,12 and the like can be used.

The present invention, in addition to the above constitution, contains an anti-blocking agent in the biaxially stretched nylon film layer, the concentration of the anti-blocking agent in the outermost layer is lower than the concentration of the anti-blocking agent in layers other than the outermost layer. And configure.
The anti-blocking agent controls the dynamic friction coefficient and static friction coefficient showing the slip property of the film.

Specific examples of the anti-blocking agent include silica, talc, kaolin, diatomaceous earth, etc., and the dynamic friction coefficient and static friction coefficient are governed by the type, particle size and concentration of the anti-blocking agent used. Therefore, the required content concentration of the anti-blocking agent in each biaxially stretched nylon film layer varies depending on the type and particle size of the specific anti-blocking agent used, but usually in the biaxially stretched nylon film layer other than the outermost layer. Content concentration of 1200 ppm or more, preferably 1500 ppm or more.

Further, the multilayer film may also be constituted by containing an anti-blocking agent only in the biaxially stretched nylon film layer other than the outermost layer, and not containing the antiblocking agent in the outermost biaxially stretched nylon film layer. it can.

The present invention relates to a method for producing a multilayer film having at least two layers of biaxially stretched nylon film,
Nylon pellets containing anti-blocking agent,
Prepare at least two types of nylon pellets, one having a lower content of anti-blocking agent (including zero) than this nylon pellet, and the other outermost layer from the nylon pellet having a lower content of anti-blocking agent (including zero). To form a multilayer film by coextrusion and then biaxial stretching.

As a biaxial stretching method for the multilayer film, either a tubular method or a tenter method may be used.

The stretching ratio of the biaxial stretching, from the viewpoint of stability, strength,
It is preferably 2.5 to 3.5 times.

In this method for producing a multilayer film, resin pellets other than the above-mentioned at least two types of nylon pellets are prepared, and the layer composed of the resin pellets is the outermost biaxially stretched nylon film layer and another biaxially stretched nylon film layer. It may be produced by co-extrusion so that it is sandwiched between and.

The reason why the intermediate layer is formed between the upper and lower biaxially stretched nylon film layers is to provide an oxygen barrier property and to reduce costs. For example, as a resin for providing an oxygen barrier property, there are nylon-6, nylon copolymer, aromatic nylon, EVOH (saponified ethylene-vinyl alcohol copolymer) and the like. Further, as a resin for cost reduction, there is a nylon-based recycled product (in which unnecessary parts in the molding process are reused as raw materials) and the like.

In this manufacturing method, other layers may be laminated on the outer side of the biaxially stretched nylon film layer other than the outermost layer of the multilayer film.

Other layers are laminated on the outside of the biaxially stretched nylon film layer other than the outermost layer with an adhesive in order to improve the low temperature sealability, for example. Examples of the resin used for this purpose include L-LDPE (linear low-density polyethylene) and EVA (ethylene-vinyl acetate copolymer).

Further, in the present production method, the biaxially stretched multilayer film may be subjected to heat treatment in the range of (melting point of nylon-30) ° C to (melting point of nylon-5) ° C.

When the heat treatment temperature is lower than (melting point of nylon-30) ° C or higher than (melting point of nylon-5) ° C, the shrinkage rate of the film becomes large, which is not preferable.

[Examples] In the following examples, examples of multilayer films will be described together with production examples.

Example 1 Nylon-6 pellets (relative viscosity 3.7) to which an anti-blocking agent was added at 0 to 1000 ppm, EVOH pellets and an anti-blocking agent at 2000 to 4500 ppm
Three types of pellets of the same added nylon-6 pellets were prepared.

Next, the above-mentioned three types of pellets were put into three extruders and coextruded from a ring die having a diameter of 90 mm so that a layer made of EVOH became an intermediate layer, and nylon-6 having a low concentration of antiblocking agent was added. Film layer, EVOH film layer and nylon with high concentration of anti-blocking agent-
A raw film having a thickness of 135 μm and composed of 3 layers of 6 film layers was formed.

Next, the original film is MD-processed by the tubular method.
After being biaxially stretched at a draw ratio of 3.0 times in the TD direction and 3.2 times in the TD direction, heat treatment is performed at 210 ° C. for 10 seconds to give a thickness of 15 μm.
I got a film of.

Next, nylon containing high concentration of anti-blocking agent
After printing 5 colors on the surface of the 6 film layer, an L-LDPE film was laminated on the nylon 6 film layer side with an adhesive to prepare a multilayer film according to this example.

As shown in FIG. 1, this multilayer film 10 has a nylon-6 film layer 11 having a low concentration of antiblocking agent (including zero) as the outermost layer, an EVOH film layer 12 as an intermediate layer, and an antiblocking agent containing concentration of 10. It has a four-layer structure in which a high nylon-6 film layer 13 and an inner L-LDPE film layer 14 are sequentially laminated.

Example 2 Two types of pellets were prepared, a nylon-6 pellet (relative viscosity 3.7) containing 0 to 1000 ppm of an antiblocking agent and the same nylon-6 pellet containing 2000 to 4500 ppm of an antiblocking agent.

Next, the above-mentioned two types of pellets were put into two extruders, and a nylon-6 film layer having a low concentration of antiblocking agent and a nylon-6 film layer having a high concentration of antiblocking agent were put through a circular die having a diameter of 90 mm. A 135 μm-thick original fabric film composed of two layers was formed.

Next, the original film is MD-processed by the tubular method.
After being biaxially stretched at a draw ratio of 3.0 times in the TD direction and 3.2 times in the TD direction, heat treatment is performed at 210 ° C. for 10 seconds to give a thickness of 15 μm.
I got a film of.

Next, nylon containing high concentration of anti-blocking agent
After printing 5 colors on the surface of the 6 film layer, an L-LDPE film was laminated on the nylon 6 film layer side with an adhesive to prepare a multilayer film according to this example.

As shown in FIG. 2, the multilayer film 20 comprises a nylon-6 film layer 21 having a low concentration of antiblocking agent (including zero) in the outermost layer, a nylon-6 film layer 22 having a high concentration of antiblocking agent, and L- on the inner layer
It has a three-layer structure in which the LDPE film layers 23 are sequentially laminated.

<Examples 1 to 5> The first layer nylon-6 film layer 21 having a low concentration of antiblocking agent and the second layer nylon layer having a high concentration of antiblocking agent of the multilayer film 20 according to Example 2 above. 6 Specific types of anti-blocking agents to be added to the film layer 22 and the average particle size and concentration thereof were selected as shown in Table 1 below to produce the multilayer films 20 according to Examples 1 to 5.

The static friction coefficient and the dynamic friction coefficient of the nylon-6 film layers 21 and 22 constituting each multilayer film 20 are measured, and further the secondary processing suitability and stacking suitability relating to the print suitability and the laminate suitability are evaluated, and the final pass / fail judgment is made. The results obtained are shown in Table-1.

In the columns of static friction coefficient and dynamic friction coefficient in the table, 1-1 is the friction coefficient between the first outer layer nylon-6 film layers 21 and 2-2 is the second layer second nylon-6. The coefficient of friction between the film layers 22 is shown.

As shown in FIG. 3, the suitability for stacking is such that the rice bag 31 produced by using the multilayer film 20 of each experimental example has 10
After being filled with kg, 5 bags were stacked on the pallet 32, the other end of the pallet 31 was hung at a predetermined angle around the support shaft 33, and it was investigated whether or not the load collapsed in this state. .

The pass / fail judgment was evaluated in consideration of the decrease in transparency of the film due to the inclusion of the antiblocking agent.

In the column of secondary processing suitability, ◎ is very good (printing of 100 m / min or more is possible), ○ is good (printing of 70 m / min or more is possible), and X is bad (printing is possible only at less than 70 m / min). Meaning). In the column of stacking suitability, ◎ is very good (load collapse does not occur even at 35 degrees or more), ○ is good (30
A load collapse does not occur at ˜35 degrees), and x means a failure (load collapse occurs even at less than 30 degrees). In addition, in the pass / fail judgment column, ◎ indicates that the secondary processing suitability or stacking suitability is very good (transparency is also good), and ○ indicates that the secondary processing suitability or stacking suitability is very good (transparency is slightly poor). Alternatively, the secondary processing suitability or stacking suitability is good (transparency is good), and x means that either the secondary processing suitability or stacking suitability is poor.

<Comparative Examples 1 to 8> Similar to the above experimental examples, specific types of anti-blocking agents to be added to the first nylon-6 layer and the second nylon-6 layer of the multilayer film, and their averages. The particle size and concentration were selected as shown in Table 1 below to prepare multilayer films according to Comparative Examples 1 to 8.

Regarding the multilayer film of each comparative example, the static friction coefficient and the dynamic friction coefficient of the nylon-6 layers of the first layer and the second layer were measured, and the secondary processing suitability and stacking suitability were evaluated,
The results of the final pass / fail judgment are also shown in Table-1.

From Table-1, the rice bag 31 made of the multilayer film 20 according to each experimental example shows that the biaxially stretched nylon-6 film layers 21,
2 contains an anti-blocking agent so that the concentration of the anti-blocking agent in the first nylon-6 film layer 21 is lower than the concentration of the anti-blocking agent in the second nylon-6 film layer 22 ( (Including zero), the static friction coefficient of the first layer 21 is 0.6 or more, and the second layer 2
By setting the dynamic friction coefficient of 2 to 0.6 or less, it is understood that the secondary processing suitability and the stacking suitability are excellent, and the pass / fail judgment is ⊚ or ◯. In addition, in the case of Experimental Example 3, the silica content concentration of the second layer 22 was too high, and the transparency of the film was slightly lowered. Therefore, in the case of the multilayer film 20 according to the present embodiment, the first layer of nylon-
The 6 film layer 21 has an appropriate degree of slip resistance that is unlikely to cause a load collapse when stacked as rice bags 31,
In addition, the second nylon-6 film layer 22 has both the proper slipperiness required for multicolor printing and laminating.

On the other hand, according to Comparative Example 1, the anti-blocking agent was not added to the nylon-6 film layers of the first layer and the second layer, and the dynamic friction coefficient of the second layer exceeded 0.6. Therefore, it can be seen that the suitability for secondary processing is poor.

According to Comparative Example 2, the anti-blocking agent is added to the nylon-6 film layer, but the concentration of the first layer is higher than that of the second layer and the static friction coefficient of the first layer is smaller than 0.6. , Stackability is poor.

According to Comparative Examples 3, 4, 5, and 7, since the concentrations of the antiblocking agents in the first layer and the second layer are equal and the static friction coefficient of the first layer is smaller than 0.6, stacking suitability is poor. is there.

According to Comparative Examples 6 and 8, the concentrations of the antiblocking agent in the first layer and the second layer are equal, and the dynamic friction coefficient of the second layer is 0.6.
Since it is larger, the suitability for secondary processing is poor.

In the present invention, one or both surfaces of the produced multilayer film may be subjected to a surface roughening treatment by corona discharge or the like, and at least the first outermost nylon film layer is surface roughened. If so, the slipperiness of the film surface is lowered, and thus the suitability for stacking in a bag is further improved.

[Effects of the Invention] According to the present invention, a multilayer film having good secondary processing suitability for printing and laminating as well as slip resistance when stacked in a bag and stacked is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a multilayer film according to Example 1 of the present invention, FIG. 2 is a sectional view of a multilayer film according to Example 2, and FIG. 3 is a diagram showing a method for measuring stacking suitability. 10, 20 ... Multi-layer film 11, 21, ... Nylon-6 film layer having a low concentration of an anti-blocking agent which is the outermost layer, 12 ... EVOH film layer of the intermediate layer, 13, 2
2. Nylon-6 with high concentration of anti-blocking agent
Film layer, 14, 23 ... L-LDPE film layer of the inner layer.

Claims (6)

[Claims] 1. A multilayer film having at least two layers of biaxially stretched nylon film, wherein one biaxially stretched nylon film layer is formed as an outermost layer, wherein the outermost layer is a biaxially stretched nylon film. The static friction coefficient of the layer is set to a value higher than that of the outermost layer of 0.6 or more, and the dynamic friction coefficient of the biaxially stretched nylon film layer other than the outermost layer is set to a value lower than that of the outermost layer of 0.6 or less, and , A multilayer film containing an anti-blocking agent in the biaxially stretched nylon film layer, the concentration of the anti-blocking agent in the outermost layer is lower than the concentration of the anti-blocking agent in layers other than the outermost layer . 2. The multilayer film according to claim 1, wherein
A multilayer film containing an antiblocking agent only in the biaxially stretched nylon film layer other than the outermost layer. 3. A method for producing a multilayer film having at least two layers comprising a biaxially stretched nylon film, comprising nylon pellets containing an antiblocking agent,
Prepare at least two types of nylon pellets, one having a lower content of anti-blocking agent (including zero) than this nylon pellet, and the other outermost layer from the nylon pellet having a lower content of anti-blocking agent (including zero). To form a multilayer film by coextrusion, and then perform biaxial stretching. 4. The method for producing a multilayer film according to claim 3, wherein resin pellets other than the at least two types of nylon pellets are prepared, and the layer formed of the resin pellets is the outermost biaxially stretched nylon film layer. And a biaxially stretched nylon film layer are sandwiched and coextruded. 5. The method for producing a multilayer film according to claim 3 or 4, wherein another layer is laminated outside the biaxially stretched nylon film layer other than the outermost layer of the multilayer film. Film manufacturing method. 6. The method for producing a multilayer film according to any one of claims 3 to 5, wherein the biaxially stretched multilayer film has a (melting point of nylon-
A method for producing a multilayer film, which comprises performing a heat treatment in the range of 30) ° C to (melting point of nylon-5) ° C.