JPH0788446B2 - Resin composition for film molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention has excellent extrusion moldability and stretchability, and
The present invention relates to a composition capable of obtaining a polyolefin film having many excellent properties such as heat-sealing property, impact strength property, tensile strength property, flexibility, cold resistance and transparency.

This composition is useful as a constituent of the resin layer which is the main component of the composite film, and such a composite film is suitable as a stretch film for food packaging.

[Conventional technology]

Stretch films for food packaging mainly use plasticized polyvinyl chloride (hereinafter abbreviated as PVC) films, but hygienic problems such as transfer of plasticizers to foods,
It has pollution problems such as generating toxic gas when incinerated. Therefore, an ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA) film is sold as an alternative to the PVC film, but has not reached the level at which the PVC film can be replaced. That is, the EVA film becomes weak and easy to tear if the vinyl acetate content is increased to make it easy to stretch, and in order to prevent it, the film thickness is set to, for example,
As it increases from 16μ to 20μ, 25μ, it becomes difficult to stretch again. Further, when the vinyl acetate content is increased, the film exhibits elastic behavior like a rubber, it becomes impossible to adhere and seal the films to each other, and the increase in thickness is disadvantageous in cost.

As a composition suitable for a stretch film that solves such conflicting problems, for example, EVA, ethylene-α
-Olefin copolymer elastomer, Japanese Patent Publication No. 59-38976 discloses a ternary composition of polypropylene,
Further, as a film, there is an invention disclosed in JP-A-60-79932. This film has extremely high heat resistance, heat sealability, and stretchability as compared with the conventional olefin-based stretch film.

[Problems to be solved by the invention]

In recent years, mechanization and diversification have progressed in the field of stretch packaging. The mainstream of packaging is shifting from conventional hand packaging that uses a hand wrapper to mechanical packaging that can save labor and increase speed. Also, in mechanical packaging, a method of packaging a large amount of specific items to be packaged after sufficient mechanical adjustment (for example, stretching rate) was used before, but recently trays of various materials and shapes have been adopted. The packaging has been changed to a random packaging method, with little mechanical adjustment. Machines can also be used to wrap objects to be wrapped (crab scissors, frozen fish, etc.) that have projections where the film easily tears, and stretch films are extremely demanding for such versatility. Has become.

In the conventional composition disclosed in Japanese Examined Patent Publication No. 59-38976, the versatility is not sufficient even when formed into a film,
There is a problem that it cannot be applied to random packaging of trays of various materials and shapes, and special packaging items cannot be packaged. Further, when this composition is mainly used, if the physical properties of the film are enhanced by changing the conditions such as stretching and deorientation, the uneven thickness is deteriorated and the film-forming property is deteriorated.

[Means for solving problems]

The present inventors have conducted extensive studies to improve suitability for machine packaging in stretch packaging and its versatility. As a result, low density polyethylene or three components of specific ethylene copolymers, ultra low density polyethylene, and crystalline polyolefin are obtained. It was found that the ternary composition consisting of a specific blending ratio of 1 has excellent cold stretchability, and the formed film has remarkably improved contradictory properties such as stretchability and tear resistance,
The present invention has been achieved by finding that its packaging property has excellent versatility and a beautiful finish.

That is, the present invention provides (A) at least one polymer selected from the group consisting of low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, and ionomer resin. Combined, (B) Density 0.90g / cm ³ or less, melting point 110 ° C or more, 1%
Ultra low density polyethylene having a modulus of 100 to 1000 kg / cm ² , (C) crystalline polypropylene, crystalline polybutene
1 or a mixture thereof (A),
In the resin mixture of (B) and (C), (A), (B),
The mixing weight ratio of (C) is 0.90 ≧ B / (A + B) ≧ 0.30, 0.50
The present invention relates to a film-forming resin composition having ≧ C / (A + B) ≧ 0.05.

The present invention will be described in detail below with reference to the drawings.

FIG. 2-2 is a conceptual diagram showing an example of a process suitable for producing a film mainly composed of the composition of the present invention. Second
This process will be specifically described with reference to the drawings.

Prepare three extruders (1), (1 ') and (1 "),
One of them was supplied with the composition of the present invention as a base layer,
The other two units have a heat-resistant layer (H layer) resin and a skin layer (S layer).
The resin for layer) is arranged, and they are united from the annular die (2) and extruded into a tube shape. At this time, in the die (2), the S layer /
The extruded tube is superposed on a multi-layer such as base layer / H layer / S layer, S layer / base layer / H layer / base layer / S layer, and the extruded tube is rapidly cooled by a water cooling ring (3), and a pair of pinch rolls ( Fold according to 4) to obtain the original fabric. The original fabric is fed between two pairs of pinch rolls (5) and (5 ') by introducing air into the interior and twisting to disperse the uneven thickness to be sent to a stretching machine. Between the two pairs of pinch rolls (6) and (10), heating is performed in the heating ring (8) and the hot air circulation zone (7) to a stretching temperature of 40 to 90 ° C (the temperature at the starting point of bubble stretching), and air is drawn. It is expanded by the internal pressure of the bubble to create a bubble, and the air ring (9), (9 ') causes it to reach 20 ℃.
The film is cooled to a certain degree, subjected to cold stretching, folded by a deflator and taken up by a pinch roll (10) to obtain a film. This is heated with hot air by the heat set device (11).
The product is contracted and wound into two films in a winding machine (12) to obtain a product.

Conventionally, in the cold drawing process of FIG. 2, the heating temperature is
When stretching at 50 ° C or lower, the stress of the film is high,
It had the drawback of being inflexible. Further, the process of FIG. 2 was generally unstable for stretching at a heating temperature of 60 ° C. or higher.

Next, the range of the resin composition of the present invention will be described with reference to FIG.

FIG. 1 is an experimental analysis diagram corresponding to Nos. 1 to 14 of Example 1 and Comparative Example 1 described later.

In the figure, the component (A) is any of low-density polyethylene, EVA, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ionomer resin, or a mixture thereof. The low density polyethylene has a melt index (hereinafter abbreviated as MI) of 0.2 to 10 and a density of 0.91 to 0.93 g / cm ³ . Ethylene copolymers are those in which the amount of monomers other than ethylene is 2 to 12 mol% and MI is 0.2 to 10. Among these, low density polyethylene produced by the high pressure method,
EVA is preferred.

The component (B), ultra-low density polyethylene, is described in Plastics, Engineering Volume 11, P.59 to 62 (85), ethylene and α-C3 to C8.
It is a copolymer with olefin.

The crystalline polypropylene and crystalline polybutene of the component (C) are crystalline polymers with high isotacticity,
Polypropylene is a homopolymer of propylene or a copolymer of propylene and 7 mol% or less of α-olefin, and has a MI of 0.5 to 20. Unlike low molecular weight liquid or wax-like polybutene, polybutene is a high molecular weight one having a butene-1 content of 93 mol% or more and a copolymer with other monomers.

Explaining the coordinate system of FIG. 1, each of the vertices A, B, and C shows that each component is 100%. On the side AB, the component (C) is 0%, and the components (A) and (B ) Indicates that the closer to the vertex A, the more the component (A). Also, the side
As the parallel line to AB approaches the vertex C, the component (C)
It shows that it will increase to 10%, 20% and 30%. For example,
Point a (66, 29, 5) is 66% by weight of component (A), component (B)
29% by weight and 5% by weight of component (C).

The symbols ◎, ○, Δ, and × shown in the figure indicate the above (A),
Each of the characteristic values brought by the three-component composition of (B) and (C), that is, the variation of the original folding width showing the film forming property of the film, the average bubble life, the stable temperature range, the uneven thickness of the film, and the need for the stretch film. Characterize, haze, drop impact strength,
The results obtained by comprehensively evaluating a total of seven characteristics of 100% elongation stress are plotted on a coordinate system together with the ratios of the respective components (A), (B) and (C). Overall evaluation is ◎,
The areas indicated by ○ are points a (66, 29, 5) and points b (1
0,85,5), point C (7,60,33), point D (47,20,3)
It is in the area surrounded by 3), and the overall evaluation around it is △, ×
Points are arranged. By such an analysis, it was found that a composition useful as a stretch film is provided in the range surrounded by the point Irohani, that is, in the claims.

Table 3 below shows the composition of the present invention and the conventional Japanese Patent Publication No. 59-389.
A comparison of the compositions of Japanese Patent Publication No. 76 is shown for film forming conditions of the compositions and characteristics under the conditions. According to Table 3,
In the cold stretching process as shown in FIG. 2, the composition of the present invention is extremely stable in the temperature range which could not be achieved by the conventional composition. As a result, the film obtained from this composition satisfied all of dimensional stability, uneven thickness, and flexibility, which could not be simultaneously satisfied by cold stretching of the conventional composition. .

Table 4 shows the suitability of the film for mechanical packaging and its versatility. According to Table 4, the film obtained by this composition is well adapted to the packaging of special contents, which are often problematic in the market, and the tray packaging of various materials and shapes. It shows superior packaging finish and versatility. This shows the high practicality of the film using the present composition.

〔Example〕

The present invention will be described in detail below with reference to examples. In addition,
The measurement and evaluation in the examples were carried out by the following methods.

(Evaluation method) 1) Fluctuation of original folding width A value obtained by continuously measuring the folding width of a raw material over 20 m, dividing the difference R (mm) between the maximum and the minimum by the average folding width, and multiplying by 100.

◎ Less than 4% ○ 4% or more and less than 7% △ 7% or more and less than 10% × 10% or more 2) Average bubble life The average bubble duration when a film forming test of 8 hours is performed under the optimal stretching conditions.

◎ 2 hours or more ○ 1 hour or more and less than 2 hours △ 30 minutes or more and less than 1 hour × less than 30 minutes 3) Stable stretching temperature range A stretching temperature range in which stable stretching is possible. A film forming test was conducted, and a stable stretching temperature was set under the condition that the bubble had a life of 30 minutes or more and the bubble did not fluctuate.

◎ Greater than 20 ℃ ○ Greater than 10 ℃ and less than 20 ℃ △ Greater than 5 ℃ and less than 10 ℃ × 5 ℃ or less 4) Film uneven thickness Measure 40 points at 20mm intervals in the width direction of the film, and measure this in the flow direction. When repeated 3 times, the thickness from the average thickness was expressed as ± X%.

◎ 5% or less ○ Greater than 5% and 10% or less △ Greater than 10% and 20% or less × greater than 20% 5) Haze value Measured according to ASTM-D-1003-52.

◎ 1.0% or less ○ 1.0% or more and 2% or less △ 2.0% or more and 3% or less × 3.0% or more 6) Falling impact strength (hereinafter abbreviated as "dart strength") Used as a measure of strength against film tearability. . It was measured according to the ASTM-D-1709-67 method.

◎ 30Kg cm or more ○ 20Kg cm or more and less than 30Kg cm △ 10Kg cm or more and less than 20Kg cm × less than 10Kg cm 7) 100% elongation stress Used as a measure of stretchability and flexibility of the film. AS
The tensile test according to the TM-D-882-67 method was performed, and the stress (g / 10 mm width) at 100% elongation was expressed, and it is shown as the average value of vertical and horizontal.

◎ 200g / 10mm width or less ○ 200g / 10mm width or more 250g / 10mm width or less △ 250g / 10mm width or more 300g / 10mm width or less × 300g / 10mm width or more 8) Overall evaluation 3 points for the above 7 items , ○ for 2 points, △ for 1 point,
Evaluation was made based on the total score, with x being 0 point.

◎ 18 points or more ○ 14 points or more and 17 points or less △ 10 points or more and 13 points or less × 9 points or less The list of resins used in the examples is described below.

a ₁ : EVA [vinyl acetate content 3.5 mol%, MI1.0] a ₂ : EVA [vinyl acetate content 5.5 mol%, MI1.0] a ₃ : low density polyethylene (LDPE) [MI2.0, density 0.918 g /
cm ^3, mp 103 ° C.] a _4: ethylene - ethyl acrylate copolymer (EEA) [ethyl acrylate content of 5.0 mol%, MI1.5] a _5: ionomer resin (Io) Ethylene - methacrylic acid copolymer Na-neutralized type, methacrylic acid content 6.6 mol%, MI1.0, neutralization degree 25%, saponification degree 50%] b ₁ : Very low density polyethylene (VLDPE) [density 0.89 g / cm ³ ,
MI0.8, Union Carbite Ukerflex D
EFD-1210NT] b ₂ : VLDPE [Density 0.90 g / cm ³ , MI 0.4, Union Carbide Ukerflex DFDA-1138NT] c ₁ : Crystalline polypropylene (IPP) [Ethylene 4% by weight Polymerized product, MFR7.0, mp117 ° C.] c ₂ : crystalline polybutene (PB-1) [butene-1 content 96 mol%, density 0.905 g / cm ³ , MI1.0] c ₃ : IPP [MFR2.2 , Density 0.91 g / cm ³ , mp 164 ° C.] Example 1 and Comparative Example 1 20% by weight of ethylene-vinyl acetate copolymer (EVA) (a ₁ )
Then, 65 wt% of ultra-low density polyethylene (VLDPE) (b ₁ ) and 15 wt% of crystalline polypropylene (IPP) (c ₁ ) were mixed and prepared as a base. Next, 80% by weight of IPP (c ₁ ) and 20% by weight of crystalline polybutene (PB-1) (c ₂ ) were mixed to prepare an H layer and EVA (a ₂ ) for an S layer. The film was stretched and formed into a film using the process shown in.

At this time, diglycerin monooleate, polyoxyethylene nonyl phenyl ether, and mineral oil were added to the extruder for the base layer in an amount of 4% by weight, 1.5% by weight, 1.5% by weight, and 1.0% by weight, respectively. Injected and kneaded.

In addition, the thickness of the material is 7 layers with the first layer and the fifth layer being S layers.
μ, the second layer and the fourth layer were 24.5 μ each as the base layer, the third layer was 7 μ as the H layer, and the total of the layers was 70 μ.

At a stretching temperature of 70 ° C, the length is 2.2 to 2.4 times and the width is 3.4 to 3.6.
The film was stretched twice, and hot air of 50 ° C. was blown in the heat set device (11) to shrink the film 5% vertically and 5% horizontally, and then a film was obtained.

This is No. 1. In addition, (A) as shown in Table 1,
Films were obtained by the process shown in FIG. 2 in the same manner as in No. 1 using the compositions for the base layer in which the kinds and ratios of the polymers (B) and (C) were changed.

Table 2 shows Example 1 (No. 1 to 8) and Comparative Example 1 (No. 9 to 14).
The stretched film-forming properties and physical properties of No. 1 are evaluated by the methods 1) to 8), and the results are shown.

The role of each of the components (A), (B), and (C) will be considered below based on Table 2 as follows.

Component (A) has improved extrudability, transparency, etc.
As is clear from the comparison of No. 11, when the ratio with the component (B) is 10% by weight or less, a phenomenon called draw resonance (takeover resonance) occurs, and the change in the folding width of the material is rapidly deteriorated. Later stretching becomes impossible.

The component (B) has improved impact strength, flexibility and transparency, and has the function of improving the compatibility of the components (A) and (C) and enhancing the synergistic effect. When the amount of the component (B) is small, as can be seen from the comparison between No. 8 and No. 14, the compatibility is lowered, the transparency is significantly lowered, and the impact strength and flexibility are also lowered.

Ingredient (C) improves the waist and bubble stability of the film, and when the amount is small, as is clear from No. 5 and No. 10,
Bubble stability is reduced, flatness is likely to occur, and only films with uneven thickness can be obtained. On the other hand, when the amount of the component (C) is too much, as is clear from No. 2 and No. 12, the flexibility of the film is lowered and it cannot be used as a stretch film.

Comparative Example 2 As a base layer composition, EVA (a ₁ ) 65 wt%, ethylene-α-olefin copolymer thermoplastic elastomer [α-
Olefin is a copolymer of 15 mol% of propylene and 3% by weight of ethylidene norbornene, MI 0.45, Piccatt softening point 40 ° C or lower] (b ₃ ) 20% by weight, IPP (C ₁ ) 15% by weight, PB- 5% by weight of 1 (c ₃ ) was mixed to form a composition for the base layer, and an extruded raw fabric was obtained in the same manner as in Example 1.

This was stretched at a stretching temperature of 45 ° C. to a length of 2.3 times and a width of 3.5 times, and then shrunk by 5% in the length and 5% in the heat set device, and was designated as A. Further, after being similarly stretched at a stretching temperature of 45 ° C., shrinkage of 15% in the vertical direction and 10% in the horizontal direction was designated as B. Further, at the stretching temperature of 70 ° C., the same stretching as in Example 1,
The product subjected to the shrinkage treatment was designated as C.

Table 3 shows the physical properties of various films and the results of the stretched state together with the results of No. 1 of Example 1.

According to Table 3, No. 1 of Example 1 had a low film stress, an excellent uneven thickness, and a life of 5 hours, which was extremely satisfactory.

Film A had uneven thickness and bubble life of film, but due to the high stress of the film and the high heat shrinkage rate of the film at 40 ° C, the product was distributed in the market during the summer, etc. Shrinkage occurred and the product was insufficient.

In order to make up for the drawbacks of Comparative Example 1, the film B shrinks the film greatly in the heat set device, and the film stress and 40 ° C.
This is a reduction in the heat shrinkage rate. However, it has a drawback that the uneven thickness of the film is reduced due to excessive shrinkage in the heat set. Further, if the thickness of the product is made constant, the amount of shrinkage afterwards is large, so that the film thickness of the bubble during stretching becomes extremely thin and the life of the bubble is shortened.

C was an attempt to form a film under the same conditions as in Example 1, but the stability of the bubble was remarkably poor, and only a few fragments of the film with poor thickness deviation were obtained.

As described above, the No. 1 film of Example 1 is the same as Comparative Example A,
It satisfied all of dimensional stability, uneven thickness, flexibility, and stable film-forming property, which were impossible with B and C.

Comparative Example 3 Ultra low density polyethylene having a density of 0.91, MI instead of b ₂
No. 6 of Example 1 (Table 1) except that 1.0 LDPE was used.
Using a base polymer mixture of the same composition as in Example 1
The film was obtained in the same manner as No.1.

The physical properties of the film were evaluated, and the results are shown in Table 4.
In Comparative Example 3 using PE having a density of 0.91 g / cm ³ and MI1.0 as the component (B), No. 1 of Example 1 using PE (b ₂ ) having a density of 0.90 g / cm ³ and MI0.4 was used. It can be seen that the items marked with a cross and the overall evaluation are inferior to those in Section 6.6.

Mechanical packaging test example Table 5 shows the results of the mechanical packaging test performed on No. 1 and No. 6 of Example 1 and B of Comparative Example 2 and commercially available PVC-based and EVA-based stretch films.

As a packaging machine, a straight type ST-6090 manufactured by Omori Machinery Co., Ltd. was used, and as Test 1, a standard tray made of expanded polystyrene containing clay simulating the contents was packaged. Test 2
As a package, a high-impact polystyrene deep tray that is easily crushed is filled with clay. In Test 3, clay was placed in a large tray made of biaxially stretched polystyrene, which is easily broken by a tray edge. Test 4
As a result, the clay was packed in a long tray for saury packaging, where wrinkles tend to remain on the finish. In Test 5, the contents of a crab nail with protrusions were packaged in the same tray as in Test 1. For the adjustment of the packaging machine, test the film tension adjustment such as the stretch rate for each film 1
Tests 2 to 5 were conducted under the same conditions.

The evaluation was: ◎ All were successfully packaged ○ Some small wrinkles or distortions △ Wrinkles, tears, crushed trays × Unable to be packaged, ◎ = 3 points, ○ = 2 points, △ = Comprehensive evaluation was carried out with 1 point and x as 0 point.

As is clear from Table 4, the versatility of packaging is remarkably improved in No. 1 and No. 6 of Example 1 as compared with B in Comparative Example 2 and is equal to or more than the commercially available PVC film. Had the performance of. Compared to other films, the commercially available EVA system was easy to tear and the overall package evaluation was at a very low level. or,
Nos. 1 and 6 of Example 1 also had excellent wrapping properties even for contents such as Test 5 that were extremely difficult to wrap in a machine.

[Effects of the Invention] As described above, the composition of the present invention has excellent extrusion moldability and stretchability, as well as excellent flexibility and impact strength characteristics,
It is a composition capable of obtaining a film having tensile strength characteristics and transparency. A film having such a composition is
It has the effect of satisfying the mechanical wrapping properties required for stretch films, and plays a major role in the industrial world.

[Brief description of drawings]

FIG. 1 is a triangular coordinate diagram showing the range of three-component composition of the resin composition of the present invention. FIG. 2 is a conceptual diagram showing an example of a process suitable for producing a composite film mainly composed of the composition of the present invention.

Claims (1)

[Claims] 1. A film molding which is a mixed resin of the following (A), (B), and (C) and whose mixing weight ratio is 0.90 ≧ B / (A + B) ≧ 0.30 0.50 ≧ C / (A + B) ≧ 0.05. Resin composition. (A) at least one polymer selected from the group consisting of low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, and ionomer resin; ) Ultra low density polyethylene having a density of 0.90 g / cm ³ or less, a melting point of 110 ° C. or more and a 1% modulus of 100 to 1000 kg / cm ² , (C) crystalline polypropylene, crystalline polybutene-1, or a mixture thereof.