JPH10306269A - Adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adhesive composition useful for wrapping retort food or the like, having an enhanced graft efficiency, capable of omitting purification process, and having high retort resistance, by graft modification of a polyolefin- based resin in the presence of a styrene-based monomer. SOLUTION: This composition, which contains a polyolefin resin as one of its base materials is obtained by graft polymerization, to (A) a polyolefin- based resin, of (B) a carboxylic acid (anhydride) having polymerizable unsaturated bond(s) [e.g. maleic acid (anhydride)] in the presence of (C) a styrene-based monomer, in a molten state, for example, at a weight ratio (B+C)/A of 0.01 to 0.3 and a molar ratio B/C of 0.05-1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an adhesive having excellent adhesiveness. Further, the present invention relates to an adhesive which can be adhered to a polyolefin film, a metal or the like for a short time, and has a small decrease in adhesive strength due to a pressure heating step such as retort sterilization.

[0002]

2. Description of the Related Art In recent years, the demand for food packaging materials has been remarkably expanded with the diversification and upgrading of eating habits and the instantization, and various thermoplastic resin films have been used.
Above all, the demand for retort food packaging is increasing. In addition to the properties required for general food packaging materials, retort food packaging materials are required to have properties that meet more stringent requirements. In other words, the basic properties required for general food packaging materials are (1) In many cases, they come into direct contact with food, and the raw materials must not be toxic,
It must be a hygienic material, (2) it must have good barrier properties to maintain the flavor of the food for a long time,
(3) Good light blocking properties to prevent deterioration and deterioration of food contents due to ultraviolet rays, etc. (4) High mechanical strength,
(5) Strong resistance to chemicals such as moisture, acid, alkali, etc. (6) Good heat sealing properties, such as thermocompression bonding in a very short time It is possible that processing can be performed. In addition to the above, the retort food packaging material has (1) good heat resistance, (2) even if various food contents are packed and subjected to retort sterilization treatment, the packaging material does not deteriorate in adhesive strength and other properties. It is necessary not to be seen. Therefore, it is impossible to satisfy these various requirements with a single resin film or another material, and the composite film or the composite material is used as a food packaging material. As a typical example of the packaging material for retort, polyester or polyamide (outer layer) / aluminum foil (intermediate layer) / polyolefin (inner layer) can be considered. Polypropylene resins are often used as polyolefins. When long-term storage is not required depending on the application, a two-layer packaging material excluding the aluminum foil in the packaging material is also used. As a retort wrapping material, consisting of the above configuration, not only packaging materials related to flexible packaging but also materials used in the field of beverage cans, edible cans, etc. Resins with good hygiene are considered to be advantageous and tend to be frequently used.
Among the polyolefins, polyolefins having good heat resistance such as polypropylene and polybutylene are required. However, it is well known that these polyolefins have little adhesion to other substrates and are difficult to use. In order to improve this point, chemical
Ingenuity has been devised by applying a physical treatment or using an energy source such as an ultraviolet ray or an electron beam. However, in practice, (a) only a very low adhesive strength is obtained, or even if it is obtained, (b) if the food content is oil-water, after high-temperature, high-pressure sterilization, these modified polyolefins and other The adhesive strength between the substrates becomes extremely low and cannot be put to practical use. Therefore, in practice, polyurethane resin is frequently used as an adhesive for bonding a polyolefin film.

However, polyurethane resin adhesives for retorts are said to have the following disadvantages. (1) The unreacted or low molecular weight of diisocyanate or polyol as a raw material is transferred to food contents,
Problems remain in terms of hygiene. (2) In the case of using an adhesive for preparing a packaging material, the heat generation period per day is about one week at room temperature and a heating period of 50 to 60 ° C. even when the heating treatment is performed at 50 to 60 ° C. so that the adhesive strength between the base materials is sufficient. What you need. (3) In the case of bonding between a polyolefin and another base material, foaming is observed in an adhesive portion, and a variation in bonding strength occurs,
Decrease product value. (4) When the retort test is performed at a high temperature, particularly at 140 ° C., the adhesive strength between the substrates is significantly reduced. (5) High price. Despite these drawbacks, at present, there is no practically usable retort adhesive other than polyurethane resin. In this sense, the appearance of a retort-resistant resin excellent in various points has been desired.

[0004]

A polyolefin resin modified with a carboxylic acid having a polymerizable unsaturated bond and / or an acid anhydride thereof (hereinafter referred to as a polymerizable unsaturated carboxylic acid) which can be used as a retort-resistant adhesive. ,
It is disclosed in Japanese Patent Publication No. 60-225. But,
Since the grafting efficiency of the polymerizable unsaturated carboxylic acid is low and unreacted monomers and oligomers remain, it is necessary to wash with an organic solvent after the reaction. The amount of the organic solvent used for this purpose is large, and the modified polyolefin resin obtained by this method is excellent in performance but hardly an adhesive having industrial merit.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that when a polyolefin resin is graft-modified with a polymerizable unsaturated carboxylic acid, a styrene monomer coexists. Then, it was found that a high grafting efficiency was achieved with the addition of a very small amount of a polymerizable unsaturated carboxylic acid, and it was not necessary to carry out a purification treatment in a separate step for removing unreacted substances. A first invention is to melt a carboxylic acid having a polymerizable unsaturated bond and / or an acid anhydride (B) thereof in a polyolefin resin (A) as an adhesive for a packaging material containing a polyolefin resin as one of the base materials. An adhesive composition characterized in that the graft polymerization is performed in the presence of a styrene monomer (C) in the adhesive composition grafted in a state.

A second invention is the adhesive composition according to the first invention, wherein the acid anhydride (B) is maleic acid or maleic anhydride. In the third invention, the compounding amount of the acid anhydride (B) with respect to the styrene monomer (C) is 0.0
The adhesive composition according to any one of the first invention and the second invention, wherein the adhesive composition has a molar ratio of 5-1 (molar ratio). A fourth invention is characterized in that the total of the acid anhydride (B) and the styrene monomer (C) is 1 to 30 parts by weight based on 100 parts by weight of the polyolefin resin (A). An adhesive composition according to any one of the third inventions.

A fifth invention is the adhesive composition according to any one of the first to fourth inventions, wherein at least one of the materials to be bonded is aluminum.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an adhesive composition obtained by melt-kneading a polyolefin-based resin with a polymerizable unsaturated carboxylic acid and a styrene-based monomer in the presence of a radical generator and graft-modified. About. The polyolefin-based resin in the present invention is a homopolymer of ethylene or propylene, an ethylene-propylene copolymer, or ethylene or propylene and another olefin such as 1
-Copolymers of butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene and 1-decene. Further, as the polyolefin resin, a copolymer of an olefin and a different monomer such as an ethylene-vinyl acetate copolymer can be used.

In the present invention, as the monomer to be graft-modified to the polyolefin resin, a polymerizable unsaturated carboxylic acid and a styrene monomer are essential. As the polymerizable unsaturated carboxylic acid used in the present invention, acrylic acid, monocarboxylic acid such as methacrylic acid, itaconic acid, maleic acid, dicarboxylic acid such as fumaric acid, itaconic anhydride,
Acid anhydrides such as maleic anhydride are exemplified, and among them, maleic anhydride is most preferred. Examples of the styrene monomer include styrene, α-methylstyrene, chlorostyrene, cyanostyrene, aminostyrene, hydroxystyrene, vinyltoluene, divinylbenzene, and the like. The amount of the polymerizable unsaturated carboxylic acid to be used is a molar ratio of 0.01 to 1 with respect to the styrene monomer, preferably,
0.2 to 0.4. If it is 1 or more, the residual amount of the polymerizable unsaturated carboxylic acid increases, and the effect of the present invention cannot be obtained. At the same time, the molecular weight of the polyolefin resin significantly decreases. If it is less than 0.01, the amount of the polymerizable unsaturated carboxylic acid contributing to the graft modification becomes small, so that a predetermined adhesive strength cannot be obtained. The total amount of the monomers used is based on 100 parts of the polyolefin resin used.
1 to 30 parts, preferably 2 to 15 parts, are used. If the amount of the monomer is more than 30 parts, a large amount of a polymer of the monomer which does not contribute to the graft modification tends to be formed, and the adhesive strength tends to decrease.

[0010] The radical generator in the present invention refers to a substance which is an ordinary initiator for radical polymerization and generates an active radical which can be easily decomposed by heat or light to initiate polymerization. As the peroxide system, persulfates such as ammonium persulfate, hydrogen peroxide, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, 2,2-bis (t-butyl peroxide) octane Peroxyketals such as dicumyl peroxide, t-butylcumyl peroxide, dialkyl peroxides such as sicumyl peroxide;
Octanoyl peroxide, decanoyl peroxide,
Diacyl peroxides such as lauroyl peroxide and benzoyl peroxide; peroxide carbonates such as diisopropyl peroxycarbonate and di (2-ethylhexyl) peroxide carbonate; t-butylperoxyisobutyrate; t-butyl peroxide Peroxyesters such as oxybenzoate, azo compounds such as 2,2'-azobisisobutyronitrile, mixtures of copper and iron powder benzyl chloride, redox initiators by combining oxidizing agents and reducing agents, and metals Alkyl, combinations of metal alkyls with oxygen donors or metal halides, or organometallic compounds such as alkyl peroxy metals can be used. These radical generators are selected depending on conditions such as the organic solvent used in the graft reaction and the reaction temperature. In the present invention, the temperature at which the polyolefin resin is heated and dissolved to perform the graft reaction, for example, 150 to 220
Those having a half-life of about 1 minute at ℃ are suitable. Among them, particularly representative ones are exemplified by di-te
rt-butyl peroxide, tert-butylcumyl peroxide, dimethyldi (tert-butylperoxyisopropyl) benzene, bis (tert-butylperoxyisopropyl) benzene, dimethyldi (tert-butylperoxy) hexine, p-mentha Hydroperoxide, diisopropylbenzene hydroperoxide, and cumene hydroperoxide. The amount of the radical polymerization initiator is not particularly limited, but is usually 0.01 to 5 parts by weight, preferably 0.1 to 1 part by weight, per 100 parts of the polyolefin resin.

The antioxidants used to prevent the oxidation of polyolefin resins include phosphorus antioxidants, phosphite antioxidants, phenolic antioxidants and metal soaps alone or in combination. Can be used. The grafting reaction of the polyolefin resin as in the present invention can be carried out by a solvent method in which the polyolefin resin is dissolved in a solvent. However, in this case, the grafting efficiency is extremely low and is not suitable for the purpose of the present invention. For the graft reaction by the melting method, a continuous kneader such as an extruder can be used. As a continuous kneader, a single-screw extruder or a twin-screw extruder can be used, but a twin-screw extruder is more preferable from the viewpoint of controlling the supply of raw materials and the residence time. The polyolefin resin is supplied to an extruder and melted, and is reacted with the polymerizable unsaturated carboxylic acid and the styrene monomer. The polymerizable unsaturated carboxylic acid and the styrene-based monomer may be mixed with the polyolefin-based resin in advance and then supplied to the extruder, or when the amount of the liquid monomer is large, the polyolefin-based resin is mixed with the polyolefin-based resin using a liquid injection pump. May be supplied separately. If the extruder has a vent, it is preferable to adjust the degree of pressure reduction so as not to vent up, because unreacted substances are removed more.

[0012]

Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples. Graft efficiency was defined as follows. <Graft efficiency> About 1 g of the reaction product was precisely weighed, dissolved in heated xylene, reprecipitated with methyl alcohol, and the precipitate was filtered through a glass filter to collect a purified product. The resin purified by the reprecipitation method was formed into a film having a thickness of about 0.1 mm by a hot press, and the Fourier transform infrared absorption spectrum was measured. From this spectrum, the absorption peak area ratio of the carbonyl groups and 840 cm ^-1 in 1780 cm ^-1, was determined acid value of the purified product from a calibration curve prepared in advance by titration. When the acid value of maleic anhydride was measured by a titration method to be about 570, the graft ratio was determined by the following equation.

Maleic acid graft ratio (% by weight) = (acid
(Value / 570) × 100 The grafting efficiency was defined by the following equation. The grafting efficiency is 1 because the graft ratio of maleic acid is based on the purified product by the reprecipitation method.
It may be more than 00%. Grafting efficiency (%) = (maleic acid graft ratio / maleic acid content in charge blending) × 100 Example 1 MFI = 5.0 g / 10 min 100 parts by weight of polypropylene resin, 5 parts by weight of maleic anhydride, 0.5 parts by weight of tert-butyl peroxide was added to 10 parts by a Henschel mixer.
Mix for minutes. This mixture is mixed with a 30 mmφ twin screw extruder (L
/D=51.5). Further, a styrene monomer was supplied so as to have a ratio of 10 parts by weight using a liquid injection pump. The feed rate of the raw materials and the screw rotation speed of the extruder
The residence time in the extruder was adjusted to be 2 minutes or more, and the barrel temperature was 200 ° C (however, the feeder section was 160 ° C).
° C) and the die temperature is set to 210 ° C. At the vent portion, the degree of pressure reduction was adjusted so as not to vent up. The pellets obtained here are directly used and extruded onto a 15 μm aluminum foil (aluminum foil / polyester laminate) with a coating thickness of 5 μm (grease temperature: 235 ° C.). Immediately after the application, the back surface (polyester) of the obtained laminate is heated for 1 second by contacting it with a hot roll (180 ° C.), and the adhesive applied on the surface is sufficiently adhered to aluminum. Further, a 70 μm polypropylene film was overlaid on the adhesive, and then passed on a hot roll at 180 ° C. at a speed of 60 m / min. The adhesive strength between the polypropylene film and the aluminum foil of the laminate was 1020 g / 15 mm, and it was confirmed that the laminate did not peel off and showed high adhesive strength. A bag is prepared from the laminate, and water, salad oil / water (1: 1), a 3% acetic acid aqueous solution and the like are enclosed as contents, and the mixture is heated at 120 ° C.
A 30-minute retort test was performed. After the retort test,
When the adhesive strength of the laminate was measured, it was as shown in Table 1.

Example 2 100 parts by weight of a polypropylene resin having an MFI of 11 g / 10 min, 2 parts by weight of maleic anhydride, and 0.5 part by weight of di-tert-butyl peroxide were mixed for 10 minutes using a Henschel mixer. This mixture was supplied to a 30 mmφ twin screw extruder. Furthermore, 1 styrene monomer was added using a liquid injection pump.
It was supplied so as to have a ratio of 0 parts by weight. Raw material supply,
The screw rotation speed of the extruder is such that the residence time in the extruder is 2
The barrel temperature was set to 200 ° C. (however, the feeder section was 160 ° C.) and the die temperature was set to 210 ° C. When the pellets obtained here were subjected to the same retort test as in Example 1,
As shown in Table 1.

Comparative Example 1 Melt kneading was carried out under the same conditions as in Example 1 except that 10 parts by weight of styrene monomer (supplied by a liquid injection pump) and 12 parts by weight of maleic anhydride were used to obtain pellets. The pellets obtained here were subjected to the same retort test as in Example 1 and the results were as shown in Table 1. Comparative Example 2 Melt kneading was performed under the same conditions as in Example 1 except that the styrene monomer was not supplied by the liquid injection pump, to obtain pellets. The pellets were colored red-brown because a large amount of unreacted maleic anhydride remained. Extruder coating was attempted using the pellets, but stable extrusion could not be performed under the same conditions as in Examples 1 and 2 because the melt viscosity of the resin was too low. Although the die temperature was lowered to 170 ° C., extrusion failure occurred.

[0016]

[Table 1]

[0017]

According to the present invention, when a polyolefin resin is graft-modified with a polymerizable unsaturated carboxylic acid,
When a styrenic monomer coexists, a high grafting efficiency was achieved by adding a very small amount of a polymerizable unsaturated carboxylic acid, and a separate purification treatment for removing unreacted substances became unnecessary.

Claims (5)

[Claims] 1. A polyolefin resin (A) as an adhesive for a packaging material containing a polyolefin resin as one of the substrates.
In an adhesive composition obtained by grafting a carboxylic acid having a polymerizable unsaturated bond and / or its anhydride (B) in a molten state, the graft polymerization is carried out in the presence of a styrene monomer (C). An adhesive composition characterized by the following: 2. The adhesive composition according to claim 1, wherein the acid anhydride (B) is maleic acid or maleic anhydride. 3. The adhesive composition according to claim 1, wherein the amount of the acid anhydride (B) to the styrene monomer (C) is 0.05 to 1 (molar ratio). Stuff. 4. The total amount of the acid anhydride (B) and the styrene monomer (C) is 1 to 30 parts by weight based on 100 parts by weight of the polyolefin resin (A).
4. The adhesive composition according to any one of items 3 to 3. 5. The adhesive composition according to claim 1, wherein at least one of the adherends is aluminum.