JP3313195B2 - Ionomer packaging materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionomer packaging material having low hygroscopicity and excellent transparency.

[0002]

2. Description of the Related Art Sodium-neutralized ionomers of ethylene / (meth) acrylic acid copolymers are known for their transparency, heat sealability, hot tack, deep drawability, oil resistance, abrasion resistance, pinhole resistance, etc. Vacuum packaging film for meat as a single-layer film or as a multi-layer film of other resin, metal foil, or paper, because it is excellent in quality and has passed the regulations of the US FDA and Japanese food packaging materials. , Liquid packaging bag, dry / powder food packaging, snack food, paste-like packaging tube, glass bottle lid,
It is used for a wide range of packaging materials, such as skin packaging.

The ionomer of an ethylene / (meth) acrylic acid copolymer has a hydrophilic ethylene chain in which a hydrophilic carboxyl group is bonded as a side chain, and a part or all of the carboxyl group is formed by a metal ion. Has a unified structure. For this reason, plastics generally have hygroscopicity at an intermediate level between nylon and polyethylene, but among ionomers, the hygroscopicity of alkali metal neutralized ionomers such as sodium and potassium is limited to alkaline earth metals such as magnesium and zinc. It is much larger than transition metal neutralized ionomers. Also, the higher the acid content or the higher the degree of neutralization, the higher the hygroscopicity of the ionomer.

Therefore, when sodium-ionized ionomer pellets having a high acid content and a high degree of neutralization are left in a high-temperature and high-humidity atmosphere, they immediately absorb moisture. If the ionomer resin that has absorbed moisture is processed at a high temperature, moisture is desorbed from the resin and vaporized, so that bubbles are formed in the molten resin. Such bubbles cause pinholes and film cracks in the film, so that a product with satisfactory quality cannot be obtained.

[0005] In addition, the ionomer resin once absorbed cannot be used unless it is re-dried in many cases. However, this drying must be performed at a temperature lower than the fusion temperature of the pellets (35 to 60 ° C.). Requires 3 days of drying.

[0006]

Therefore, the present inventor has proposed:
Investigate how to effectively reduce the hygroscopicity to a practically acceptable level without sacrificing excellent properties such as transparency in a sodium-neutralized ionomer of ethylene / (meth) acrylic acid copolymer, which is an excellent packaging material Was done. As a result, when an ionomer composition having a specific infrared absorption spectrum obtained by melt-blending an appropriate amount of a zinc-neutralized ionomer of an ethylene / (meth) acrylic acid copolymer described below is used, the object can be achieved. I found it.

Accordingly, it is an object of the present invention to reduce moisture absorption,
An object of the present invention is to provide an ethylene ionomer composition packaging material having excellent transparency.

[0008]

According to the present invention, sodium and zinc are used as ion sources, and the atomic ratio thereof is Na / Zn = 1 /.
In the range of 1-3 / 1, and 1565cm ^-1 vicinity
Infrared radiation from the formation of double salt of sodium and zinc salts
The present invention relates to a packaging material comprising an ionomer composition of an ethylene / (meth) acrylic acid copolymer having an absorption peak .

[0009] The present invention also provides, sodium and zinc ion source, there the atomic ratio in the range of Na / Zn = 1 / 1~3 / 1, and in the vicinity of 1565cm ^-1, sodium
Has an infrared absorption peak derived from the formation of a double salt of a salt and a zinc salt.
The present invention also relates to an ionomer of an ethylene / (meth) acrylic acid copolymer.

[0010]

The ionomer used in the present invention is a novel substance different from a mere mixture of a sodium neutralized ionomer and a zinc neutralized ionomer. Please refer to FIG. 2 of the accompanying drawings. The sodium neutralized ionomer has a wave number of 1540 cm attributed to the asymmetric stretching vibration of the carboxylate group.
^-1 while the zinc-neutralized ionomer shows an infrared absorption peak with a wave number of 1585 cm ^-1 , but the ionomer having a specific composition ratio used in the present invention has a wave number completely different from these absorption peaks. It has a new infrared absorption spectrum at around 1565 cm ^-1, and is considered to form a double salt of a sodium salt and a zinc salt.

Heretofore, it has been known that sodium salts and zinc salts form double salts in low molecular weight compounds. For _{example, ZnO + 2NaOH -> Na 2} ZnO 2 + H 2 O have been known for a long time, also the CH ₃ COONa (C
From an acetic acid solution of H ₃ COO) ₂ Zn, (CH ₃ COO) ₂ Zn · (CH ₃ COO) Na · 4C
There are also reports that H ₃ COOH was isolated.

In the present invention, with the formation of double salts, the ionic aggregates produce stronger ionic crosslinks, so that the flexural rigidity is improved, and the transparency is also improved, because the growth of polyethylene crystals is inhibited. Furthermore, the hygroscopicity also changes because the nature of the ionic group of the ionic aggregate changes with the formation of the double salt.

Please refer to FIG. 1 of the accompanying drawings. In this figure, the relationship between the standing time and the moisture absorption of the double salt prepared from the sodium-neutralized ionomer (Comparative Example 1), the zinc-neutralized ionomer (Comparative Example 5), and a 50:50 mixture of both is plotted. I have. In the ionomer composition of the present invention,
The hygroscopicity is significantly lower than that of the sodium neutralized ionomer, and is close to that of the zinc neutralized ionomer.

Therefore, in the packaging material of the present invention,
Foaming trouble during processing is significantly reduced. Further, in addition to the features of the sodium neutralized ionomer, the transparency and the bending rigidity are improved, so that it can be used in various fields.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The ionomer composition of the present invention generally comprises a sodium neutralized ionomer of an ethylene / (meth) acrylic acid copolymer and a zinc neutralized ionomer of an ethylene / (meth) acrylic acid copolymer. Can be obtained by melt-mixing at a predetermined ratio for a time sufficient to form a double salt having the infrared absorption peak.

The above-mentioned ethylene / (meth) acrylic acid copolymer as a raw material of the above-mentioned ionomer contains other unsaturated monomer components such as methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylate. An acrylate or methacrylate such as isobutyl acrylate or n-butyl (meth) acrylate, or vinyl acetate may be copolymerized.

Such a copolymer is generally composed of 88 to 99.5 mol% of ethylene, particularly 92.5 to 99.0 mol%, and 0.5 to 10 mol% of (meth) acrylic acid, It is preferable that the copolymer is copolymerized at a ratio of 0.0 to 7.5 mol% and other unsaturated monomer components at a ratio of 0 to 10 mol%, particularly 0 to 5 mol%. Such a copolymer can be obtained by random copolymerization of each polymerization component under high temperature and high pressure.

The sodium-neutralized ionomer or zinc-neutralized ionomer which can be used as a raw material of the present invention comprises the above-mentioned ethylene / (meth) acrylic acid copolymer and a metal compound which supplies sodium ions or zinc ions, for example, formate and acetate. , Carbonates, oxides, hydroxides and the like. Such manufacturing methods are already well known.

In the present invention, it is preferable to use the above-mentioned ionomer having a degree of neutralization of 10 to 90 mol%, especially about 15 to 80 mol%.
Melt flow rate at 2160 g load is 0.01
It is preferable to use one having a flow rate of about 500 g / 10 min, particularly about 0.1 to 100 g / 10 min.

Examples of sodium-neutralized ionomers include Himilan 1601, 1605, and 1707, and examples of zinc-neutralized ionomers include Himilan 165.
2,1706, etc. (all manufactured by Mitsui / Dupont Polychemical Co., Ltd.) can be cited as typical examples which can be obtained in the market.

The packaging material of the present invention comprises such a sodium-neutralized ionomer and a zinc-neutralized ionomer in a ratio of sodium / zinc (atomic ratio) of 1/1 to 3/1, preferably 1.5 / 1 to 1/2. It can be formed from a composition obtained by melt-mixing at a ratio of 0.5 / 1. The conditions of the melt mixing are such that the infrared absorption peak attributed to the asymmetric stretching vibration of the carboxylate group of the obtained composition is different from that of the sodium-neutralized ionomer (near 1540 cm ⁻¹ ) and the zinc-neutralized ionomer (near 1585 cm ⁻¹ ). Different 1565c
Any condition may be used as long as it can be obtained near m- ¹ . For example, a sodium-neutralized ionomer and a zinc-neutralized ionomer are mixed in a single-screw or twin-screw extruder for 100
The method of melting and kneading at a temperature of ~ 250 ° C is the simplest method.

Another method for obtaining the ionomer composition as the packaging material of the present invention is to mix a predetermined amount of the above-mentioned sodium compound and zinc compound as the ion sources,
It can also be obtained by reacting with an ethylene / (meth) acrylic acid copolymer. At this time, the raw material for the ionization reaction is 180 to 280 with a single-screw or twin-screw extruder or the like.
It is preferable to melt and knead at a temperature of ° C. It is preferable to use a vented extruder to remove by-product water, carbon dioxide, and the like.

In the ionomer composition used in the packaging material of the present invention, if the ratio of sodium to zinc is larger than the above range, the hygroscopicity is not sufficiently improved, and if the ratio is smaller than the above range, the sodium-neutralized ionomer cannot be improved. It is not preferred because the superior packaging material properties possessed are lost.

The average degree of neutralization in the ionomer composition is preferably from 10 to 90 mol%, particularly preferably from 15 to 80 mol%, and in consideration of workability and mechanical properties, at 190 ° C. and a load of 2160 g. Melt flow rate is 0.01 to 500 g / 10 min, especially 0.1 to 1
One having a flow rate of 00 g / 10 minutes is preferable.

The ethylene ionomer composition may contain optional additives such as an antioxidant, a weather stabilizer, an ultraviolet absorber, a lubricant, a coloring agent, and an inorganic filler, depending on the purpose.

The packaging material comprising the ethylene ionomer composition of the present invention can be used in various shapes such as films, sheets, tubes, hollow containers and the like. Depending on these applications, the thickness of the ionomer composition layer is, for example, 5 to
It can be in the range of 500 μm.

Since the extrudability of this packaging material is good, a packaged product can be formed by an inflation method or a T-die casting method. Such a package can be uniaxially or biaxially stretched or deep drawn. Also, on one side of such a package,
Another layer may be formed. As such a layer,
Examples thereof include polyolefin, ethylene / vinyl alcohol copolymer, polyvinylidene chloride, metal foil, and paper. Such a layer may of course be a single layer or a multilayer.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples. The composition of the ethylene / (meth) acrylic acid copolymer ionomer used as a raw material in Examples and Comparative Examples,
The various evaluation test methods are as follows.

(1) Composition of ethylene / (meth) acrylic acid copolymer ionomer Table 1 shows the composition of ethylene / (meth) acrylic acid random copolymer ionomer.

[0030]

[Table 1]

(2) Evaluation test method 2-1 MFR The weight of the polymer flowing out of the melt indexer for 10 minutes at 190 ° C. under a load of 2160 g was measured as MFR.

2-2 Hygroscopicity A test piece (10 cm × 2 cm × 3 mm) was punched out of a 3 mm thick press sheet prepared at 180 ° C., 100 kg / cm ² for 5 minutes by a hot press.
The test piece weight when left at 0% relative humidity was measured every 15 days for 90 days. Furthermore, the weight loss when the test piece that had absorbed moisture was dried for 20 minutes in a vacuum dryer at 180 ° C. was regarded as due to desorption of moisture, and the moisture absorption was calculated. The reported value of the moisture absorption is an average value of the measurement results of five test pieces.

2-3 Transparency The cloudiness (haze) of a 3 mm-thick pressed sheet prepared by a hot press at 180 ° C., 100 kg / cm ² for 5 minutes was measured using a haze meter model HGM-2K manufactured by Suga Test Instruments Co., Ltd. It measured using. The lower the measured value, the lower the haze and the better the transparency.

2-4 Flexural Rigidity A test piece (1) was prepared from a 3 mm-thick press sheet prepared at 180 ° C., 100 kg / cm ² for 5 minutes by hot pressing.
0 cm x 1 cm x 3 mm), sealed in a moisture-proof aluminum bag, aged at 23 ° C for 2-3 weeks, and then AS
The measurement was performed using a stiffness tester manufactured by Toyo Seiki Co., Ltd. according to TMD-747. The reported value of flexural rigidity is the average value of the measurement results of five test pieces.

2-5 Measurement of Infrared Spectrum 180 ° C., 100 kg / cm ² , 5 to 1 by hot press
A film having a thickness of about 50 μm was prepared under the condition of 0 minutes, and an infrared spectrum was measured at room temperature using a FT-1R model FTS-40 manufactured by Digilab, at a resolution of 2 cm ⁻¹ and a cumulative number of 64 times.

Examples 1 to 5 and Comparative Examples 1 to 7 (1) According to the formulation (parts by weight) shown in the upper part of Table 2,
Using Toyo Seiki Labo Plastomill Model R-100, rotor speed was 60 rpm and resin temperature was 200 ° C.
The ionomer composition was prepared by melt-kneading for 0 minutes. The same process was performed on the non-blend products of Comparative Examples 1, 2, 5, 6, and 7 in order to keep the heat history constant.

The obtained ionomer composition was evaluated for hygroscopicity, gloss, and flexural rigidity. The results are shown in the lower part of Table 2. In Table 2, Examples 1 to 5 are ethylene.
A composition in which a sodium-neutralized ionomer of a (meth) acrylic acid copolymer is blended with a zinc-neutralized ionomer of an ethylene / (meth) acrylic acid copolymer, and the compounding ratio of sodium ions and zinc ions is within the range of the present invention. 1/1
３3/1 (mol / mol).

The glosses of Examples 1 to 5 all show better values than the non-blend material as the raw material, and the flexural stiffnesses of Examples 1 to 5 all show higher values than the non-blend material as the raw material. (Comparative Examples 1 and 5 and Example 2 to Example 1)
4 for Comparative Examples 2 and 5, and Example 5 for Comparative Examples 6 and 7). FIG. 1 shows the results of the evaluation test of the hygroscopicity of Example 1 together with the results of Comparative Examples 1 and 5.

The composition of Example 1 is a blend of 50 parts by weight of Comparative Example 1 and 50 parts by weight of Comparative Example 5, but its hygroscopicity is almost the same as that of Comparative Example 5 which is a zinc neutralized ionomer. Comparative Example 1 which is a sodium neutralized ionomer
It is clear that the hygroscopicity has been significantly improved. As shown in FIG. 2, when the mixing ratio of sodium ion and zinc ion is 1/1 to 3/1 (mole / mole), a new absorption peak appears in the asymmetric stretching vibration of the carboxylate group.

With the formation of the double salt, the ionic aggregates produce stronger ionic crosslinks, so that the flexural rigidity is improved, and the transparency is also improved, because the growth of polyethylene crystals is inhibited. Furthermore, the hygroscopicity also changes because the nature of the ionic group of the ionic aggregate changes with the formation of the double salt. Thus, the change in physical properties can be explained very rationally from the change in the solid structure of the ethylene ionomer. It should be noted that a new infrared peak indicating the formation of a double salt is not observed in the infrared charts of Comparative Examples 4 and 5, which deviate from the scope of the present invention.

(2) Blown film forming test A single screw extruder (screw diameter 30 mm, L / D = 3) was prepared according to the formulation (parts by weight) of Example 1 shown in the upper part of Table 2.
Using 2), the mixture was kneaded and granulated at a resin temperature of 200 ° C. and an extrusion speed of 3 kg / h. The pellets and the pellets of Comparative Example 1 were immersed in water at 20 ° C. for 24 hours, dried using dehumidified air, and adjusted for the drying time to prepare samples having different moisture contents.

These samples were placed in an inflation die (caliber 5
0mm) single screw extruder (screw diameter 30m)
m, L / D = 30) and a winding speed of 3 m / min.
To prepare a film having a folding width of 200 mm and a thickness of 50 μm. At this time, the resin temperature was changed from 180 to 230 ° C., and it was visually determined whether or not foaming was observed in the resin coming out of the inflation die. The results are shown in FIG.
The ethylene ionomer generally has a resin temperature of 180 to 20.
Although the film is formed at 0 ° C., as is apparent from FIG. 3, foaming does not occur when the water concentration is 0.2 wt% or less. Since the equilibrium moisture concentration at 23 ° C. and 50% relative temperature in Example 1 is 0.2 wt%, it is clear that the hygroscopicity of Example 1 has been reduced to a level at which there is no practical problem.

[0043]

[Table 2]

[0044]

The ionomer composition used in the packaging material of the present invention has an infrared absorption attributed to the asymmetric stretching vibration of the carboxylate group of the sodium-neutralized ionomer and the zinc-neutralized ionomer as shown in the Examples and the drawings. It has an absorption spectrum different from the peak. Also, in view of the fact that the physical properties were improved as described above, and from the fact that a double salt was formed based on the reaction between low molecular compounds of a sodium compound and a zinc compound, it was assumed that the ionomer composition formed a double salt. Is done.

The packaging material using such an ionomer composition has a significantly lower hygroscopicity than the sodium-neutralized ionomer, and the foaming trouble during processing is significantly reduced. Further, in addition to the features of the sodium neutralized ionomer, the transparency and the bending rigidity are improved, so that it can be used in various fields.

[Brief description of the drawings]

FIG. 1 shows an ethylene ionomer composition at 23 ° C. and 50%
5 is a chart showing the relationship between aging time and moisture absorption when aging is performed at a relative temperature.

FIG. 2 is a table showing the compounding ratio of sodium ion and zinc ion in the ethylene ionomer composition and the change in asymmetric stretching vibration absorption of a carboxylate group in an infrared spectrum.

FIG. 3 is a table showing a relationship between a foaming phenomenon, moisture, and a processing temperature when an ethylene ionomer composition is processed and formed by an inflation method.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 23/00-23/36 C08F 210/00-210/18 B65D 1/09

Claims (2)

(57) [Claims] 1. An ion source comprising sodium and zinc, the atomic ratio of which is in the range of Na / Zn = 1/1 to 3/1 ,
And near 1565 cm ⁻¹ , sodium salt and zinc salt
A packaging material comprising an ionomer composition of an ethylene / (meth) acrylic acid copolymer having an infrared absorption peak derived from the formation of a double salt . 2. An ion source comprising sodium and zinc, the atomic ratio of which is in the range of Na / Zn = 1/1 to 3/1 ,
And near 1565 cm ⁻¹ , sodium salt and zinc salt
An ionomer of an ethylene / (meth) acrylic acid copolymer having an infrared absorption peak derived from the formation of a double salt .