JPH0994919A - Asymmetrically structured multi-layer unstretched film which is not curled - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid troubles in printing after making a bag and in packing contents by preventing a curl of an asymmetrically structured multi-layer inflation film which is good in a gliding property of a surface, has a high oxygen- barrier property, and is useful principally for packaging foods and for packaging industrial parts. SOLUTION: In a multi-layer unstretched inflation film wherein resin constituents used for the most outer layer and the most inner layer are different, the resin used for the most outer layer has a crystallization temperature 0-60 deg.C higher in comparison with the resin used for the most inner layer, or has not the crystallization temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-curl technique for a multilayer unstretched film having an asymmetric structure. More specifically, the outermost layer has a polyamide resin layer,
The film surface has good slipperiness, high oxygen barrier properties, and is useful mainly for food packaging and industrial parts packaging. Prevents curling of asymmetrically-structured multilayer unstretched inflation film, and when printing after bag making, The present invention relates to a film structure and a resin composition that can avoid troubles when filling contents.

[0002]

2. Description of the Related Art Conventionally, when making a resin film into a bag,
When sealing the mouth, the heat sealing method is generally used as a simple and reliable method. In order to perform this method at high speed, the melting point of the resin used for the outermost layer of the film, which the heater (usually called a seal bar) contacts during heat sealing, reduces the melting on the bag surface and seals. While preventing the resin from sticking to the bar, by lowering the melting point of the resin used for the innermost layer as much as possible, high-speed bag making and sealing of the mouth can be performed at lower temperatures (reducing the temperature rise time). Like

Therefore, the outermost layer usually has a high melting point,
Polyamide resin is used because it has good oxygen barrier property and surface gloss, and polyolefin resin (for example, linear low-density polyethylene, ethylene acetic acid) is used for the innermost layer because of its low melting point and good transparency and heat sealability. Vinyl copolymers and ionomers) are often used. However, since these two types of resins are difficult to adhere to each other when coextruded, they are usually used as a three-layer asymmetric structure unstretched film with an adhesive resin, or have a higher oxygen barrier property. In order to make it possible, an ethylene-vinyl alcohol copolymer (abbreviation EvO
It is very commonly used as a four-layer asymmetric structure multilayer unstretched film containing H).

In the multilayer unstretched blown film having such an asymmetric structure, curling is an unavoidable problem. The inflation-molded asymmetric multi-layer unstretched film is generally characterized by curling with the inner layer on the inner side in the air cooling method and the outer layer on the inner side in the water cooling method. Curl is a phenomenon that is difficult to eliminate once it occurs and is a very problematic problem in handling the film. For example, in a so-called bag-making process in which a multilayer film is made into a bag like a tube,
If there is curl in the film, it will be difficult to align the position inside the bag-making machine, the dimensional accuracy of the bag will deteriorate, defective take-out will occur, and when the bags after bag-making are stacked, the opening side will swell and the specified The number of sheets can no longer be piled up, and they cannot be used for the next process. In addition, even when filling the contents, the bag may fail to be taken out in the automatic bag feeder, the contents may adhere to the edges of the bag to reduce the filling accuracy, stains may be left on the outside of the bag, or heat sealing may occur. It is not preferable because the part of is not uniform. In particular, when a polyamide resin is used for the outermost layer, the state of curl may change from moment to moment under the influence of humidity.

As a method of preventing curl, a method of temporarily removing the curl by treating the formed asymmetric multilayer film with warm water or steam is generally used. This method can remove the curl immediately after production, but the curl may recur if the moisture absorption state of the film changes with time. There is also a method of preventing curling by forming a multilayer by a dry laminating method. This method is a technique in which a monolayer film or a symmetric structure film that does not substantially curl is attached using an adhesive, and is a method that is usually performed when a biaxially stretched nylon film is used for food packaging. Is. But 2
After manufacturing different types of films, dry laminating must be performed in a separate step, which increases the manufacturing cost by one step. In addition, since an organic solvent is usually used for the adhesive, it is necessary to invest in consideration of the work environment and the surrounding environment, and it cannot be said that the method is necessarily superior in terms of apparatus cost.

Curl is a phenomenon that occurs only in a multi-layer inflation molded article having an asymmetric structure. Therefore, if a symmetric structure is used, that is, the same material is used for the innermost layer and the outermost layer, the curl can be eliminated. . However, then, when heat sealing, the melting temperature of the innermost layer and the outermost layer become the same, so the innermost layer melts and is sealed, and at the same time, the outermost layer also melts and the film surface becomes rough, deteriorating the surface appearance. Or melted resin adheres to the seal bar,
Seal bar contamination is generated, which is not preferable. On the other hand, if the molding method is changed from the inflation method to the T-die method, curl can be eliminated, but there are many problems such as an increase in equipment cost and difficulty in producing a wide film as compared with the air-cooled inflation method. .

[0007]

As described above,
In the inflation method, which has the lowest film production cost, the curl prevention technique for asymmetrically-structured multilayer unstretched films has not yet been achieved in practice.

[0008]

Means for Solving the Problems Accordingly, the present inventors have:
Asymmetric structure multilayer unstretched film is curled by a multilayer coextrusion inflation method, which is inexpensive in film production.
In order to prevent it, we conducted a thorough study. As a result, in the occurrence of curl, the crystallization temperature of the resin used for the outermost layer and the innermost layer is deeply involved, by setting the crystallization temperature difference between both layers within a certain range, or It was found that curling can be eliminated by making the resin used for the outermost layer substantially amorphous, and a practically very useful asymmetric structure multilayer unstretched film is provided. I arrived.

That is, in the present invention, in a multilayer unstretched blown film in which the resin components used in the outermost layer and the innermost layer are different, the resin used in the outermost layer is 0 to 60 ° C. higher than the resin used in the innermost layer. Has a crystallization temperature,
Alternatively, it is an asymmetrically-structured multilayer unstretched film characterized by having no crystallization temperature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. The "asymmetrically-structured multilayer unstretched film" referred to in the present invention is a multilayer unstretched film having different resin components used for the outermost layer and the innermost layer. For example, when a copolyamide resin is used for the outermost layer and a linear low-density polyethylene resin (commonly called L-LDPE) is used for the innermost layer, these resins generally do not adhere even if they are co-extruded, and therefore, they are usually acid-modified. It is coextruded in three layers of three types through an adhesive resin such as the above polyolefin resin. Such a three-layer three-layer structure, that is, a three-layer film of polyamide resin (outermost layer) / adhesive resin (middle layer) / polyolefin resin (innermost layer) is an asymmetric structure multilayer unstretched film referred to herein. In addition, in order to improve the oxygen barrier property, a four-layer structure in which an EvOH layer is inserted between the outermost polyamide resin and the adhesive resin and coextrusion-molded is also an asymmetric structure multilayer unstretched film. In short,
In the coextrusion molding, when the resin used for the outermost layer and the resin used for the innermost layer are different, they are all defined as an asymmetric structure regardless of the type and number of layers contained between these two layers.

In the present invention, the "crystallization temperature" means
It is measured using a differential scanning calorimeter, when the temperature is lowered at a predetermined rate, among the exothermic peaks that appear on the endothermic curve,
It is defined as the temperature at which the maximum exothermic peak appears. If the exothermic peak does not appear, that is, the upper and lower sides of the endothermic curve cannot be distinguished from the change in the base, it is evaluated as having no crystallization temperature. Moreover, such a state is expressed as “substantially amorphous”.

In the present invention, the resin used in the outermost layer is a resin having a crystallization temperature higher by 0 to 60 ° C. than the resin used in the innermost layer, or a substantially non-crystalline resin having no crystallization temperature. There is no particular limitation as long as it is a crystalline resin. That is, when the crystallization temperature of the outermost layer is lower than that of the innermost layer, the outer layer resin solidifies later than the inner layer resin at the time of bag making or sealing after filling the contents, so that the heat sealing cycle becomes slow or Poor surface appearance, such as bar contamination and fuzz on the seal surface, is not preferable for practical use. Further, when the crystallization temperature of the outermost layer is higher than that of the innermost layer by 60 ° C. or more, curling cannot be prevented. However, the crystallization temperature of the outermost layer is 0 to 60 ° C., preferably 0 to 45 ° C. as compared with the resin used for the innermost layer, and more preferably 2 in view of high-speed heat sealability.
When the temperature is higher by 0 to 45 ° C. or does not have a crystallization temperature, curling can be prevented, the heat sealing cycle is not delayed, and the surface appearance is not defective.

In practice, the resin used for the outermost layer has a high melting point so that it does not melt during heat sealing.
A polyamide resin is preferable because it has good gas barrier properties and pinhole resistance. For example, α-pyrrolidone, α
-Piperidone, ε-caprolactam, enanthlactam and other lactams having three or more membered rings, aminocaproic acid, 7-
Polymerizable ω-amino acids such as aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, paraaminomethylbenzoic acid, paraaminoethylbenzoic acid, and metaaminomethylbenzoic acid, hexamethylenediamine, octa Methylenediamine, nonamethylenediamine, 2,2,4- / 2,4,4-trimethylhexamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, metaxylylenediamine, paraxylylenediamine, paraaminocyclohexyl Diamines such as methane and bis (3-methyl-4-aminocyclohexyl) methane and terephthalic acid, isophthalic acid, glutaric acid, adipic acid, β-
A polyamide resin obtained by polycondensation of a salt with a dicarboxylic acid such as methyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decamethylenedicarboxylic acid, dodecanedioic acid or dimer acid can be used.

In the present invention, among polyamide resins, copolymerized nylon is preferable because of its low crystallization temperature. For example, with ε-caprolactam as the main component,
In the range of up to 30 mol%, there may be mentioned copolymers with other compounds capable of copolymerizing with ε-caprolactam, and mixtures containing these copolymers. Other compounds that can be copolymerized with ε-caprolactam include salts consisting of an aliphatic or aromatic diamine and an aliphatic or aromatic dicarboxylic acid. Representative examples of the diamine, ethylenediamine,
Examples thereof include tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, octamethylenediamine, decamethylenediamine, metaxylylenediamine, paraxylylenediamine and the like. As typical examples of the dicarboxylic acid, succinic acid, glutaric acid, adipic acid, β-methyladipic acid, pimelic acid, suberic acid,
Azelaic acid, sebacic acid, decamethylene dicarboxylic acid, terephthalic acid, isophthalic acid and the like can be mentioned. Each of these diamines and dicarboxylic acids may be used alone or in combination of two or more. Specifically, nylon 6/6/6,
6/6 ・ 9, 6/6 ・ 12, 6/6 ・ 36, 6/6 ・
Copolymerized nylon such as T and 6/6 · I can be used. These vary greatly depending on the composition and copolymerization ratio,
It shows a crystallization temperature of about 95 to 160 ° C.

In the present invention, an amorphous polyamide resin having no crystallization temperature is also preferable. Examples of the amorphous polyamide resin include para-aminomethylbenzoic acid,
There are polyamides based on aromatic amino acids such as para-aminoethylbenzoic acid and meta-aminomethylbenzoic acid, or semi-aromatic polyamides based on aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid and aliphatic diamines. . Specifically, meta-aminomethylbenzoic acid and ε
-Copolymer with caprolactam (nylon AMBA /
6), the main component is hexamethylenediamine isophthalate or hexamethylenediamine terephthalate, and ε-caprolactam, 12-aminododecanoic acid, hexamethylenediamine adipate, paraaminocyclohexylmethane adipate, etc. Polyamide as a copolymerization component (nylon 6 ・ I, 6 ・ T, 6 ・ I / 6 ・
T, 6 · I / 6, 6 · T / 6, 6 · I / 12, 6 · T /
12, 6 · I / 6/6, 6 · T / 6/6, 6 · I / PA
CM ・ 6、6 ・ T / PACM ・ 6) 、 2,2,4- /
Polyamide based on terephthalate of 2,4,4-trimethylhexamethylenediamine (nylon TMD
T, TMDT / 6 · I), isophthalic acid salt of para-aminocyclohexylmethane or isophthalic acid salt of bis (3-methyl-4-aminocyclohexyl) methane, and dodecanedioic acid salt of hexamethylenediamine, 12
-Polyamide having a copolymerization component such as aminododecanoate (nylon PACM / I / 6/12, DMPACM /
I / 12) and the like.

These polyamide resins have a crystallization temperature higher by 0 to 60 ° C. than the resins used for the innermost layer,
Alternatively, they may be used alone or in combination with other polyamide resins as long as they are substantially amorphous having no crystallization temperature. In a further preferred embodiment of the present invention, a small amount of amorphous nylon or other copolymerized nylon is blended in order to further lower the crystallization temperature of the copolymerized nylon. For example, a copolymer of ε-caprolactam and hexamethylenediamine adipate (nylon 6/6/6), a copolymer of hexamethylenediamine isophthalate and hexamethylenediamine terephthalate (nylon 6/6). An amorphous polyamide such as I / 6 · T) is blended at about 20% by weight.

Regarding the relative viscosity (ηrel) of the polyamide resin, the value measured in accordance with JIS K6810 at a concentration of 98% sulfuric acid of 1% and a temperature of 25 ° C. is preferably in the range of 2 to 6, preferably 2 to 5. used. If the relative viscosity is too low, the stability of bubbles during inflation molding is lowered and a good film cannot be obtained, or the mechanical properties of the film are insufficient, which is not preferable. On the other hand, if the relative viscosity is too high, the torque during extrusion will be too high, and film formation will be difficult.

With respect to the polyamide resin of the present invention, a water extraction amount (resin sample 1
After extraction with boiling water at 00 ° C. for 6 hours to remove insoluble matter, water was evaporated to dryness, and the weight of the remaining components is expressed as a percentage of the weight of the sample. ) Is preferably 1% or less, more preferably 0.5% or less. When the amount of water extracted is large, low molecular weight substances such as monomers and dimers tend to adhere to the area around the die, and such low molecular weight substances may come into contact with or adhere to the film, resulting in poor visual appearance such as fish eyes. Is likely to occur, which is not preferable.
Further, in air-cooled inflation molding, the amount of smoke generated increases and the working environment becomes poor, which is not preferable.

As the resin used for the innermost layer, a polyolefin resin generally called a sealant resin is selected. For example, low density polyethylene (LDPE), very low density polyethylene (V-LDPE), linear low density polyethylene (L-LDPE), high density polyethylene (HDP)
E), ethylene vinyl acetate copolymer (EVA), ionomer resin, ethylene ethyl acrylate copolymer (E
EA) and the like can be used. These resins are
Those having a crystallization temperature of 0 to 120 ° C., preferably 95 to 110 ° C. are preferable. Among these, those having a melting point as low as possible and a crystallization temperature as high as possible are preferable from the viewpoint of high-speed heat sealability. Furthermore, considering transparency, L-LDP
E and LDPE are particularly preferable.

According to the present invention, the reason why curling can be prevented by adjusting the crystallization temperature of the outermost layer and the innermost layer within the specified range or by making the outermost layer substantially amorphous will be described in detail. Although not fully understood, it is presumed that the outermost layer and the innermost layer are closely related to the volumetric shrinkage ratio in the process of changing from the molten state to the solid state.

The asymmetric structure multilayer unstretched film of the present invention was measured under the environment of relative humidity (RH) 65%,
It is important that the coefficient of static friction between the outermost layers is 2.5 or less. If the coefficient of static friction is greater than 2.5, sticking may occur on the film during film forming, printing, and bag making, which may cause uneven thickness and ink misalignment during printing, and the bag dimensional accuracy may deteriorate. It is not preferable because it decreases. Further, if a bag having poor slipperiness is used in the automatic bag feeder, the next bag will be dragged out together when the bag is taken out, leading to bag feeding trouble, which is not preferable.

As a method of lowering the coefficient of static friction,
A general method such as a method of adding an organic or inorganic filler or a method of using a lubricant can be used. In practical use, the addition of an inorganic filler is preferable from the viewpoint of the adhesiveness with the adhesive resin and the prevention of change over time in the slipperiness due to bleed-out. Specifically, silica, talc, kaolin, calcium carbonate, zeolite,
Inorganic fillers such as wollastonite are selected.

The resin composition of each layer constituting the multilayer film has various additives well known to those skilled in the art in addition to the above purposes, such as oxidation of hindered phenol, phosphoric acid ester and phosphorous acid ester. It may contain an inhibitor, a weather resistance improver such as a benzotriazole compound, a colorant such as a pigment or a dye, an antistatic agent, a lubricant and the like.

Further, as a method for molding the asymmetrically structured multilayer unstretched film of the present invention, a multilayer inflation molding method by a coextrusion method is generally used. Further, in the multilayer inflation method, there are a water cooling method and an air cooling method depending on the cooling method. In any method, the layer structure of the present invention has an effect of preventing curling, but particularly in the air cooling multilayer inflation method. , Its effect is remarkable.

[0025]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these as long as the gist thereof is not exceeded. In addition, evaluation of various physical properties in the following examples and comparative examples was performed as follows.

(1) Crystallization temperature The resin constituting the innermost layer and outermost layer of the multilayer film is
The crystallization temperature of the sample cut out from the film after molding was measured by the differential scanning calorimeter S manufactured by SEIKO Electronics Co., Ltd.
300 using SC / 577 at a heating rate of 20 ° C / min.
The temperature at which the maximum exothermic peak was generated among the exothermic peaks generated when the temperature was raised to 0 ° C. and held for 5 minutes and then lowered at 20 ° C./minute was defined as the crystallization temperature. Then, when the upper and lower sides of the endothermic curve are indistinguishable from the change in the base, it was determined that the crystallization temperature was not included.

(2) Coefficient of static friction After forming a multilayer film for 24 hours or more at 23 ° C. and 65% R
After storing in an H environment, a friction measuring machine TR type manufactured by Toyo Seiki Co., Ltd. was used and measured according to ASTM D-1894.

(3) Curl property A multilayer film was cut into a length of 30 cm, and the temperature was adjusted to 23.
After left for 1 hour in an environment of ℃, relative humidity 65%, visually confirm the curl situation, ◎ (no curl at all),
○ (slightly curled but practically no problem) and ×
A three-stage evaluation of (curling and not practical use) was performed.

[Example 1] Polyamide resin (trade name: Novamid PAE2507A manufactured by Mitsubishi Engineering Plastics Co., Ltd.) and silica particles (trade name: Silysia 740 manufactured by Fuji Silysia Chemical Co., Ltd.) were used as a slipperiness improver on the outermost layer of a polyamide resin (trade name: Novamid PAE2507A). Polyamide resin composition with 75% by weight added, polyolefin-based adhesive resin in the intermediate layer (trade name: Modic AP-220L MI: 1.8 manufactured by Mitsubishi Chemical Co., Ltd.)
Density: 0.92), LDPE in the innermost layer (manufactured by Mitsubishi Chemical Corporation)
Product name: Mitsubishi Polyethylene LF225M MI: 0.8 Density: 0.92), using Placo 3 type 3 layer inflation molding machine (for outer layer: 35 mmφ L / D = 2)
2, for middle layer: 35 mmφ L / D = 22, for inner layer: 4
0mmφ L / D = 22, die diameter 75mmφ), ambient temperature 30 ° C, resin temperature 245 ° C, BUR
= 1.8, continuous air-cooling inflation molding was performed to obtain an asymmetric structure multilayer unstretched film. The thickness composition of the obtained film was as follows: outer layer / middle layer / inner layer = 20 μm
/ 5 μm / 55 μm. The crystallization temperature of the outermost layer and the innermost layer, the curl property, and the coefficient of static friction were evaluated for this asymmetric structure multilayer unstretched film. The results are shown in Table 1.

[Examples 2 to 8] and [Comparative Examples 1 to 4] In Example 1, the polyamide resin used for the outermost layer,
The addition amount of the filler (silica particles as a slipperiness improver) added to the polyolefin resin used for the innermost layer and / or the polyamide resin for the outermost layer is variously changed as shown in Tables 1 to 3, A multilayer unstretched film having an asymmetric structure was obtained in exactly the same manner as in Example 1. The obtained film was evaluated for crystallization temperature, curl property and static friction coefficient, and the results are shown in Tables 1 to 3.

The abbreviations in Tables 1 to 3 have the following meanings. Abbreviation Meaning 2507A Copolymer nylon 6 / 6.36 (Product name: Novamid PAE 2507A ηrel: 3.4 Melting point: 200 ° C., manufactured by Mitsubishi Engineering Plastics) 225M LDPE (Product name: Mitsubishi Polyech LF225M, MI: manufactured by Mitsubishi Chemical Corporation) 0.8 Density: 0.92) 2430A-1 Copolymer Nylon 6/6/6 (Product name of Mitsubishi Engineering Plastics Co., Ltd .: Novamid 2430A-1 ηrel: 4.5 Melting point: 190 ° C) X-21 Copolymer nylon 6 ・ I / 6 ・ T (trade name of Mitsubishi Engineering Plastics Co., Ltd .: Novamid X-21 F07 ηrel: 2.1 melting point: none) 520 L-LDPE (trade name of Mitsubishi Chemical Co., Ltd .: Mitsubishi Polyethylene SF520 MI: 0. 8. Density: 0.926) 2030A Copolymerized nylon 6/6/6 (three) Product name: Ryo Engineering Plastics Co., Ltd. Product name: Novamid 2030A ηrel: 4.5 Melting point: 200 ° C 2030J Copolymerized nylon 6/6/6 (Product name of Mitsubishi Engineering Plastics product name: Novamid 2030J ηrel: 4.5 Melting point: 201 C.) 62BS copolymer nylon 6 / 6.9 (manufactured by EMS-Chemie AG, trade name: Grilon CF62BS ηrel: 2.8 melting point: 134 ° C.) 1030CA nylon 6 (manufactured by Mitsubishi Engineering Plastics Co., Ltd .: trade name: Novamid 1030CA ηrel: 4) .5 melting point: 224 ° C.)

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

According to the present invention, the difference in crystallization temperature by DSC between the outermost layer and the innermost layer in the asymmetrically-structured multilayer unstretched film is set to 0 ° C. or more and 60 ° C. or less, or the outermost layer is made substantially non-conductive. By using a crystalline resin, it is possible to provide a curl-free multilayer unstretched film, and the obtained film can greatly improve the properties as a bag for an automatic bag feeder. .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Morio Tsunoda 370 Enzo, Chigasaki City, Kanagawa Prefecture Mitsubishi Engineering Plastics Co., Ltd. Technology Center

Claims (6)

[Claims] 1. In a multilayer unstretched blown film in which the resin components used in the outermost layer and the innermost layer are different, the resin used in the outermost layer is 0 compared to the resin used in the innermost layer.
An asymmetrically structured multilayer unstretched film having a crystallization temperature of -60 ° C. higher or no crystallization temperature. 2. The multilayer unstretched film having an asymmetric structure according to claim 1, wherein the outermost layer is made of a polyamide resin. 3. The asymmetrically-structured multilayer unstretched film according to claim 1, wherein the outermost layer is made of a polyamide resin, the innermost layer is made of a polyolefin resin, and an adhesive layer is provided between both layers. 4. A multilayer unstretched film having an asymmetric structure according to claim 2, wherein the polyamide resin is copolymerized nylon. 5. The polyamide resin is a semi-aromatic polyamide containing an aromatic dicarboxylic acid and an aliphatic diamine as main components or a polyamide containing the same and having no crystallization temperature. 4. The asymmetric structure multilayer unstretched film according to item 4. 6. The coefficient of static friction between the outermost layers is 6 relative humidity.
The asymmetric structure multilayer unstretched film according to claims 1 to 5, which is 2.5 or less under an environment of 5%.