JPS628465B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a modified polyethylene adhesive having excellent adhesive properties. In this specification, the peak area ratio of the highest melting point of modified polyethylene and unmodified polyethylene measured with a differential calorimeter after multi-stage heat treatment is defined as the peak area ratio of the highest melting point of modified polyethylene and polyethylene before modification. It was sealed in an aluminum pan for measurement with a differential calorimeter (thermal analyzer DSC-990 type), and the temperature was measured at 20 m/min in a nitrogen stream using the same equipment.
The sample was heated to 130°C at a heating rate of 20°C, held at this temperature for 20 minutes, then cooled to 90°C at a cooling rate of 20°C per minute, and then the sample was heated to 130°C at a heating rate of 20°C per minute.
Heat to 125℃, hold at this temperature for 20 minutes, cool to 90℃, and then repeat at 120℃.
After heat treatment at 115℃ and cooling treatment at 90℃, the sample was placed in liquid nitrogen, left at room temperature, cooled to room temperature, and subjected to multistage heat treatment. , which was determined by measuring the melting point at a heating rate of 5°C per minute. The peak area ratio of the highest melting point is calculated as follows. Figures 1 and 2 show representative samples subjected to multi-stage heat treatment (Figure 1: unmodified polyethylene, Figure 2: modified polyethylene of Example 1).
A schematic diagram of the DSC chart is shown, starting from the high temperature side: A (131-132℃), B (129℃), C (123℃),
Four melting point peaks are observed: and D (115°C). Copy this chart using a copying machine (registered trademark Xerox), cut out each peak as shown by the broken line (perpendicular line from the bottom of the peaks to the baseline) in Figures 1 and 2, and use a precision balance to cut out each peak. Measure the weight. The peak area ratio of the highest melting point is calculated by the following formula: weight of A/weight of (A+B+C+D) x 100 (%) The average value of three times is used. Polyethylene has excellent mechanical properties as well as optical, electrical, and chemical properties, but as it is a completely non-polar substance, it has poor affinity with other substances, especially adhesive properties. In order to improve this, it is already well known that polyethylene is grafted with maleic acids to impart adhesive properties. As a modification method, a method of grafting polyethylene in a solution state (for example,
52-39636), or a method of grafting in a molten state using an extruder (for example,
27421), but in the method of grafting maleic acids to polyethylene in a molten state, it is difficult to uniformly blend the maleic acids and radical initiator in polyethylene, and If reacted as is, the modified polyethylene is likely to gel, and in this method, it is extremely difficult to remove unreacted monomers and undecomposed radical initiators from the modified polyethylene in a molten state after the reaction. On the other hand, in the method of grafting maleic acids to polyethylene in a solution state, the influence of the solvent on the adhesive strength of modified polyethylene is significant;
The adhesive strength of modified polyethylene varies depending on the type of solvent used for the grafting reaction (Tokuko Sho
52-39636). In addition, the concentration of maleic acid groups grafted to polyethylene also affects the adhesive strength, and in experiments by the present inventors, the concentration of maleic acid groups grafted to polyethylene was 1 × 10 ^-4 per 1 g of modified polyethylene.
A range of ±5×10 ^-5 moles has been found to be preferred. However, the concentration of maleic acid groups grafted onto polyethylene is 1×10 ^-4 ±5×
Although being in the 10 ^-5 mol range is a necessary condition for producing modified polyethylene with strong adhesive strength, it is not a sufficient condition, and in fact, it depends on the solvent used for the grafting reaction, the method of proceeding with the grafting reaction, etc. In this case, modified polyethylene with significantly low adhesive strength is produced. In order to obtain modified polyethylene with high adhesive strength, an alkyl aromatic solvent was used, even though the reaction rate of maleic acids as a monomer was extremely low and it was not economical, and the monomer and radical initiator were still being reacted. ,
There is a report that uses a method of continuous dripping (Japanese Patent Publication No. 52-39636), but it is not sufficient. As a result of detailed research on the reaction of modifying polyethylene with maleic acids to produce adhesive polyethylene, the present inventors found that the adhesive strength of modified polyethylene is influenced by the grafted maleic acid on the polyethylene molecular chain. The present invention was achieved by elucidating that it is the distribution state of acid groups. That is, the present invention is a modified polyethylene obtained by modifying polyethylene with maleic acids, which contains 5 x 10 ^-5 to 1.5 maleic acid groups per gram.
Modified polyethylene containing ×10 ^-4 mol and whose peak area ratio of the highest melting point of the modified polyethylene measured with a differential calorimeter after multistage heat treatment is maintained at 50% or more of the peak area ratio of the optimum melting point of the polyethylene before modification. The invention relates to modified polyethylene adhesives containing: In the modified polyethylene adhesive of the present invention,
The polar group grafted to modified polyethylene is 5×
If the amount is less than 10 ^-5 mol/g of modified polyethylene, sufficient adhesive strength will not be developed, and if it exceeds 1.5 x 10 ^-4 mol/g, association of polar groups will occur, and when diluted with unmodified polyethylene, the modified polyethylene Since polyethylene and unmodified polyethylene cause phase separation, sufficient adhesive strength is not developed. The polar groups grafted to modified polyethylene can be quantified by infrared absorption spectroscopy or titration using an alcoholic potassium solution, and are an important element of the present invention.
The degree of chain disorder of methylene groups in the modified polyethylene molecular chain can be measured by the method described above. Further, in the modified polyethylene adhesive of the present invention, the peak area ratio of the highest melting point of the modified polyethylene measured with a differential calorimeter after multistage heat treatment is preferably 50% or more of the peak area ratio of the highest melting point of the polyethylene before modification. It is necessary that 60% or more is retained. If the modified polyethylene is outside the above range, 1 g of maleic acid groups
Even if the adhesive contains 5×10 ^-5 to 1.5×10 ^-4 mol per unit, it is not possible to obtain a modified polyethylene adhesive exhibiting good adhesive properties. Modified polyethylene (or polyethylene before modification) measured with a differential calorimeter after multi-stage heat treatment
Several endothermic peaks due to the melting of methylene chains with different chain lengths were observed in the chart of the differential calorimeter. When this occurs, the endothermic peak on the high melting point side decreases and the endothermic peak on the low melting point side increases depending on its degree. The relationship between methylene chain length and its melting point was published by MGBroadhurst in J.Chem.phys.
36 , 2578 (1962). The above-mentioned modified polyethylene can be obtained by carrying out a graft reaction of polyethylene in a solvent using a hydroperoxide having a low ability to abstract hydrogen from polymer molecules as a radical initiator. The raw material resins used in the present invention include polyethylene resins, such as polyethylene, ethylene and α-olefin (propylene, 1-
butene, 1-pentene, etc.). Examples of maleic acids used for modification include maleic acid, citraconic acid, nadzic acid, its anhydride, monoester, fumaric acid, mezaconic acid, and the like. As a radical initiator, t-butyl hydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-
Examples include 2,5-dihydroperoxide. As a solvent, benzene, monochlorobenzene, ortho-dichlorobenzene, monobromobenzene, xylene,
Examples include toluene, cumene, p-cymene, and the like. To produce the adhesive of the present invention, the first step is usually 10 to 300 parts by weight (preferably 50 to 200 parts by weight) of polyethylene based on 1000 parts by volume of solvent;
Maleic acids are 1 to 10 parts by weight per 100 parts by weight of polyethylene, and the radical initiator is polyethylene.
0.2 to 2.0 parts by weight per 100 parts by weight (preferably
1 g of modified polyethylene (0.4-0.8 parts by weight)
Modified polyethylene containing 1×10 ⁻⁴ ±5×10 ⁻⁵ mol of maleic acid group per sample is produced. The reaction temperature is 90~250℃ (preferably 110~200℃)
C) for a period of time during which at least 60% (preferably 80%) of the radical initiator is decomposed.
Although the reaction may be carried out in air, it is preferably carried out in an inert gas atmosphere such as nitrogen to prevent oxidation of the polyethylene. Next, in the second step, the modified polyethylene obtained in the first step is kneaded and diluted with unmodified polyethylene to a ratio of 10 to 50 times by weight to obtain the modified polyethylene adhesive of the present invention. Examples and comparative examples are shown below. Example 1 A separable glass flask with an inner volume of 1 and a density of 0.965 and a melt index of 14 were thoroughly purged with nitrogen.
40 g of polyethylene, 1.0 g of maleic anhydride, and 2,5-dimethylhexane as a radical initiator.
0.24 g of 2,5-dihydroperoxide and 400 ml of ortho-dichlorobenzene were added as a solvent. Next, the separable flask was immersed in an oil bath and the temperature inside the reaction system was raised while stirring to dissolve the polyethylene. After raising the temperature to 160°C, this temperature was maintained for 4 hours in a nitrogen stream to continue the reaction. After the reaction was completed, the system was cooled and the temperature in the system reached around room temperature. After that, 500 ml of acetone was added and thoroughly stirred and washed. The modified polyethylene was washed separately with another 500 ml of acetone, and then dried under reduced pressure at 40°C overnight. A white powdery modified polyethylene was obtained. The melt index of this modified polyethylene is
6.3, it was completely dissolved in decalin at 135°C, and no gel content was observed. Furthermore, the modified product exhibited an absorption characteristic of acid anhydride at 1780 cm ^-1 in the infrared absorption spectrum, proving that maleic anhydride was grafted onto polyethylene. The content of maleic anhydride groups was determined by neutralization titration and was found to be 1.15 x 10 ^-4 mol per gram of modified polyethylene. The modified product was heated in a nitrogen stream at 130°C, 125°C, 120°C,
After heat treatment at each temperature of 115℃ for 20 minutes, the melting point was measured with a differential calorimeter and found to be 131℃.
Melting point peaks were observed at 129°C, 123°C, and 115°C, and the size (peak area ratio) of the highest melting point (131°C) peak was determined by the melting point of the raw polyethylene before grafting maleic anhydride. It was 76% of the peak size (peak area ratio) at the highest melting point (131°C) when similarly measured. This means that 76% of the longest methylene chains in the raw polyethylene, which has a melting temperature of 131°C, were preserved throughout the grafting reaction. The modified polyethylene was melt-kneaded and diluted 20 times with unmodified polyethylene having a density of 0.922 and a melt index of 3.4 using a Brabender.
A sheet with a thickness of 1 mm was formed by heat pressing at ℃.
This sheet is degreased with acetone and has a thickness of 0.2mm.
After sandwiching two steel plates and melting and adhering them at 220℃ and 20g/ ^cm2 for 5 minutes, the adhesive strength was measured and found to be 4.5.
It exhibited a significantly high adhesive strength of Kg/cm. Comparative Example 1 Dicumyl peroxide as a radical initiator
Same as Example 1 except that 0.24g was used,
The graft reaction was carried out at 125°C for 5 hours. The obtained modified polyethylene in the form of a white powder was analyzed by infrared absorption spectrum and neutralization titration, and it was confirmed that 1.24×10 ^-4 mol of maleic anhydride was grafted per 1 g of modified polyethylene. After this modification, the same heat treatment as in Example 1 was applied, and the melting point was measured using a differential calorimeter.
Melting point peaks were observed at 131°C, 129°C, 123°C, and 115°C, but the magnitude of the peak at the highest melting point (131°C) was the same as the peak at the highest melting point (131°C) of the raw material polyethylene before grafting reaction. It was only 30% of the size of . This means that up to 70% of the longest methylene chains in the raw polyethylene, which has a melting temperature of 131°C, were lost due to the grafting reaction. The adhesive strength to steel plate of the composition (adhesive) obtained by melting and diluting the modified polyethylene 20 times as in Example 1 is
It was only 1.2Kg/cm. Example 2 Density in 400 ml of ortho-dichlorobenzene
0.965, polyethylene 40 with melt index 14
g, 0.75 g of maleic anhydride, and 0.12 g of kyumene hydroperoxide as a radial initiator were charged, and a graft reaction was carried out in the same manner as in Example 1 at 178° C. for 5 hours to obtain modified polyethylene in the form of white powder. Based on the infrared absorption spectrum and neutralization titration, the modified product has a concentration of 1.07% per 1g of modified polyethylene.
It was confirmed that ×10 ⁻⁴ mol of maleic anhydride was grafted. Further, after the modified product was heat treated in the same manner as in Example 1, the magnitude of the highest melting point peak was 69% of that of the raw polyethylene. Furthermore, the adhesive strength of a composition (adhesive) obtained by diluting the modified polyethylene 20 times as in Example 1 was extremely high at 4.7 kg/cm. Examples 3 to 6, Comparative Examples 2 to 3 Modified polyethylene was obtained by changing the raw materials or reaction conditions used in the graft reaction as shown in Table 1. Table 1 shows the adhesive strength of a composition (adhesive) obtained by diluting this modified polyethylene 20 times as in the example.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic DSC chart of unmodified polyethylene, and FIG. 2 is a schematic DSC chart of modified polyethylene of Example 1.

Claims (1)

[Claims] 1 Modified polyethylene obtained by modifying polyethylene with maleic acids, containing 5 × 10 ^-5 to 1.5 × 10 ^-4 mol of maleic acid groups per gram, and measured with a differential calorimeter after multistage heat treatment. The peak area ratio of the highest melting point of modified polyethylene is the peak area ratio of the highest melting point of polyethylene before modification.
Modified polyethylene adhesive containing modified polyethylene with retention of 50% or more.