JPS6146024B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new pressure sensitive adhesive. More specifically, the present invention relates to a pressure-sensitive adhesive containing a specific stabilized rosin ester as a tackifier. Traditionally, rosin ester has been used as a tackifier for pressure-sensitive adhesives, etc., but it is difficult to reach a high softening point and has problems with heat resistance and aging resistance, which affect the properties of pressure-sensitive adhesives. There was a problem that it was difficult to find a satisfactory pressure-sensitive adhesive due to the adverse effects. For this reason, disproportionated rosin esters or hydrogenated rosin esters with improved properties are commercially available, but neither can be said to be a rosin ester with a satisfactorily high softening point and excellent heat resistance and aging resistance. It is something. Therefore, the present inventors first conducted intensive studies to find a stabilized high softening point rosin ester that is excellent as a tackifier for pressure-sensitive adhesives. First of all, rosin, which is the raw material for rosin esters, contains high molecular weight substances or unsaponifiable substances that are thought to be caused by peroxides, and it is assumed that these have a negative effect on the various rosin esters that are the final products. An attempt was made to esterify rosin, which had been purified to remove high molecular weight substances, unsaponifiable substances, etc., with a polyhydric alcohol. However, the rosin ester thus obtained was not stabilized to the extent required as a tackifier for pressure-sensitive adhesives. Therefore, first, the raw material rosin is disproportionated to obtain a disproportionated rosin, and then this disproportionated rosin is purified to remove high molecular weight substances, unsaponifiable substances, etc., and the purified disproportionated rosin thus obtained is converted into a polyhydric alcohol. It has been found that a sufficiently stabilized high softening point rosin ester can be obtained by esterification with. As a result of further research based on this fact, the present inventors found that when the above-mentioned stabilized high softening point rosin ester is used as a tackifier for pressure-sensitive adhesives, it has excellent adhesion and tackiness. The present invention was completed based on the new discovery that a pressure-sensitive adhesive having heat resistance and aging resistance can be obtained. That is, the present invention provides a pressure-sensitive adhesive mainly composed of natural rubber or synthetic rubber and tackifier, which is obtained by esterifying a purified disproportionated rosin with a trihydric or higher polyhydric alcohol. The present invention relates to a pressure-sensitive adhesive characterized by being a rosin ester having a softening point of 65 to 140°C. Although the stabilized high softening point rosin ester used in the present invention has a small molecular weight, it is an unprecedented high softening point rosin ester. It was found that it was very effective when used as a fire ring. Rosin esters having such remarkable properties are obtained by using purified disproportionated rosin obtained by refining disproportionated rosin to substantially remove high molecular weight substances, unsaponifiable substances, etc., and adding it to a specific polyhydric alcohol. It can only be obtained by esterification with That is, two types of rosin glycerin were obtained by using purified disproportionated rosin obtained by refining disproportionated rosin and unrefined disproportionated rosin in which disproportionated rosin was not purified in any way, and reacting them with glycerin under the same conditions. When the weight average molecular weight and softening point of the esters (obtained in Reference Examples 1 and 4 described later) were measured, differences as shown in Table 1 were found. As is clear from Table 1, the rosin glycerin ester obtained from purified disproportionated rosin (Reference Example 1) has a weight average molecular weight compared to the rosin glycerin ester obtained from unrefined disproportionated rosin (Reference Example 4). Even though the temperature is 129 lower, the softening point is 16°C higher. Furthermore, each of the above-mentioned rosin glycerin esters was mixed with natural rubber as a tackifier at a weight ratio of 45:55 to prepare a pressure-sensitive adhesive, and the tackiness, cohesive force, and adhesive force of these were measured.
There were differences as shown in the table.

[Table] As is clear from Table 1, when comparing the tackiness and adhesive strength of pressure-sensitive adhesives, the one using rosin glycerin ester (Reference Example 1) obtained from purified disproportionated rosin was superior to the one using unpurified rosin. Rosin glycerin ester obtained from disproportionated rosin (Reference example 4)
It has 50% higher adhesion strength than those using . On the other hand, there is almost no difference in adhesiveness between the two, and both exhibit very good values. Although the rosin glycerin ester used in the present invention has a high softening point, it is quite surprising that a pressure sensitive adhesive using the same has both high tack and high adhesive strength. This is because it is common knowledge that for similar types of tatsukifires, raising the softening point will increase the adhesive strength, but will decrease the tackiness. Furthermore, the rosin ester used in the present invention is significantly stabilized and has excellent heat resistance and aging resistance, and pressure-sensitive adhesives containing this as a tackifier have excellent adhesive strength and Adhesion can be maintained for a long time. Next, the method for producing the stabilized rosin ester used in the present invention will be described in detail. The stabilized rosin ester used in the present invention is produced by esterifying purified disproportionated rosin with a polyhydric alcohol. The above-mentioned purified disproportionated rosin can be easily produced by subjecting rosin to a disproportionation reaction and then purifying it. First, rosin is subjected to a disproportionation reaction in a conventional manner to obtain a disproportionated rosin. For example, rosin is heated at 100-300°C, preferably 150-290°C in the presence of a disproportionation catalyst. The disproportionation catalyst may be used in an amount of 0.01 to 5% (by weight, hereinafter the same), preferably 0.1 to 1%, based on the rosin. Palladium carbon as a disproportionation catalyst,
Examples include metal powders such as nickel and platinum, iodides such as iodine and iron iodide, and sulfur compounds such as sulfur dioxide and iron sulfide. Examples of raw material rosin include gum rosin, oil rosin, and tall oil rosin. In the present invention, purification refers to high molecular weight substances that are thought to have arisen from peroxides contained in the raw material rosin, as well as high molecular weight substances that are thought to have arisen from the peroxides contained in the raw material rosin, from the disproportionated rosin obtained as described above. This means removing unsaponifiable substances that were present during the disproportionation reaction as well as unsaponifiable substances that were generated during the disproportionation reaction. The purified disproportionated rosin used in the present invention preferably has an acid value of 177 or more after removing high molecular weight substances and unsaponifiable substances from the disproportionated rosin. The purification can be carried out by conventional methods such as distillation and crystallization. Distillation can be carried out under normal conditions, for example under a reduced pressure of 3 mmHg and at a kettle temperature of 210 -
Take the fraction distilled out at 300℃. Fractions distilled at kettle temperatures lower than 210°C contain unsaponifiables, whereas 300°C
The fraction distilled at a pot temperature higher than ℃ is intensely colored. Purification by crystallization can be carried out, for example, by dissolving the disproportionated rosin in a good solvent, then distilling off the solvent to form a concentrated solution, and adding a poor solvent to this solution. Good solvents include benzene, toluene, xylene, chloroform, lower alcohols, ketones such as acetone, and acetic acid lower alkyl esters such as ethyl acetate. Poor solvents include n-hexane, n-heptane, cyclohexane, and isooctane. etc. can be mentioned. Furthermore, the purification process involves converting the disproportionated rosin obtained in the disproportionation reaction into an alkaline aqueous solution using alkaline water, extracting insoluble unsaponifiable substances with an organic solvent, and then neutralizing the aqueous layer to purify the disproportionated rosin. It can also be obtained by obtaining chemically modified rosin. Among the purification methods mentioned above, the distillation method is the most preferred from an economic point of view. In the present invention, in order to obtain purified disproportionated rosin, it is preferable to subject the disproportionated rosin to purification as described above. This is because if a disproportionation reaction is carried out after purification, unsaponifiable substances are produced during the disproportionation reaction, which adversely affects the properties of the rosin ester as a final product. The rosin ester purified as described above is then esterified with a trihydric or higher polyhydric alcohol to obtain a rosin ester as a final product. Esterification of purified disproportionated rosin and polyhydric alcohol can be carried out by a conventional method. For example, a purified disproportionated rosin and a trivalent or higher polyhydric alcohol are mixed in a closed container or an open container in the presence or absence of a catalyst and in the presence or absence of a solvent.
This can be done by heating at 80 to 300°C. As the solvent, aromatic solvents such as benzene, toluene, and xylene can be used. Catalysts include acid catalysts such as sulfuric acid, acetic acid, and paratoluenesulfonic acid, alkaline earth metal hydroxides such as calcium hydroxide, metal oxides such as magnesium oxide and calcium oxide, calcium carbonate, magnesium acetate, and calcium acetate. Any conventional esterification catalyst can be used. Examples of the trihydric or higher polyhydric alcohol used in the present invention include glycerin, diglycerin, pentaerythritol, dipentaerythritol, and the like, with glycerin and pentaerythritol being particularly preferred. Furthermore, polyhydric alcohols other than those mentioned above may be used in combination within a range that does not adversely affect the resulting rosin ester. Examples of such polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, and neopentyl glycol. The rosin ester used in the present invention has a softening point of 65~
140℃, preferably 90-140℃, and further acid value
20 or less, preferably a weight average molecular weight of 700 to 1100. The pressure-sensitive adhesive of the present invention is one in which the stabilized high softening point rosin ester obtained as described above is blended with natural rubber or synthetic rubber as a tackifier. The pressure sensitive adhesive of the present invention has excellent adhesion and tack as well as heat and aging resistance. Examples of the synthetic rubber include random SBR, block SBR, polystyrene-polyisoprene-polystyrene block copolymer, nitrile rubber, polybutadiene rubber, isoprene-isobutylene rubber,
Examples include polyvinyl ether. The mixing ratio of natural rubber or synthetic rubber and tackifier may be 20 to 150 parts by weight per 100 parts by weight of natural rubber or synthetic rubber. In addition to the above-mentioned main components, the pressure-sensitive adhesive of the present invention may contain additives commonly used in pressure-sensitive adhesives. The pressure sensitive adhesive of the present invention is mixed with a mixing roll, heated and melted as it is, and applied to a base material,
Then, a pressure-sensitive adhesive film can be obtained by applying the mixture to a calender roll or using a solvent to form a solvent solution, coating the base material with a spreader, an ablator, etc., and drying by heating. Examples of the base material include cellophane, paper, and plastic film such as polyester. Next, the pressure-sensitive adhesive of the present invention will be described with reference to Reference Examples, Examples, and Comparative Examples. Reference example 1~
3 shows a method for producing a rosin ester used in the present invention, and Reference Examples 4 to 6 show a method for producing a rosin ester for reference. Reference example 1 (1) Disproportionation reaction Chinese gum rosin 100 with acid value 170 and softening point 74℃
0.03 g of 5% palladium carbon as a catalyst
g, and stirred at 280℃ for 4 hours under a nitrogen seal to perform a disproportionation reaction, resulting in an acid value of 158 and a softening point.
95 g of disproportionated rosin of color Gardner 10 was obtained at 75°C. (2) Purification The disproportionated rosin was purified to 3 mm under a nitrogen seal.
It was distilled under reduced pressure of Hg, and the obtained main distillate was used as purified disproportionated rosin.

〔Test method〕

(a) Adhesiveness (similar to rolling ball method) Using a PSTC-6 device, roll a steel ball with a diameter of 15 mm from a position 10 cm from the bottom of an inclined plate at an angle of 21.5°, and then The rolling distance of the steel ball on the adhesive surface was measured. (b) Cohesive force (shear failure test) The adhesive film and a stainless steel plate treated with abrasive paper and thoroughly cleaned were wrapped in an area of 25 mm x 25 mm, and pressed twice with a roller weighing 1 kg, A load of 500 g was applied at °C, and the deviation was measured after 30 minutes (the smaller the value, the better). (c) Adhesive strength A 1 inch wide adhesive film was pressed twice onto a stainless steel plate treated with abrasive paper and thoroughly cleaned using a roller weighing 1 kg, at 20°C and 65% RH.
After adjusting the temperature and humidity for 12 hours in the chamber, the 180° peel strength was measured using a Tensilon type universal tensile tester at a adjusting speed of 300 mm/min (the larger the value, the better). (d) Aging resistance test The adhesive film was left in a circulating air dryer at 70° C. for 24 hours to deteriorate the adhesive with hot air, and the tackiness and cohesive force were measured in the same manner as the test method described above. However, when measuring cohesion, the load is
The weight was 200g. The test results are shown in Table 2.

[Table] As is clear from Table 2, the pressure sensitive adhesives of Examples 1 to 3 using rosin esters (Reference Examples 1 to 3) obtained from purified disproportionated rosin were obtained from unrefined disproportionated rosin. Adhesion was higher than that of the pressure-sensitive adhesives of Comparative Examples 1 to 3 using the obtained rosin ester (Reference Examples 4 to 5) and the rosin ester obtained by omitting the disproportionation step from purified rosin (Reference Example 6). It has excellent strength, and also has excellent cohesive strength and adhesion after aging. Examples 4 to 6 and Comparative Examples 4 to 5 Weight ratio of polystyrene-polyisoprene-polystyrene block copolymer (Krayton 1107, manufactured by Shell Chemical Co., Ltd.) to each rosin ester obtained in Reference Examples 1 to 3 and Reference Examples 4 to 5 Mix at a ratio of 50:40, dissolve each mixture in toluene,
Five types of solutions with a solid content concentration of 40% were prepared. Next, each of these solutions was applied to a polyester film (thickness: 38μ) using a 1-inch-wide dice-shaped applicator, and incubated at 50°C under 50mmHg.
It was dried under reduced pressure for hours to form an adhesive layer with a thickness of 50 μm. Example 1 about the five types of adhesive films obtained
The tackiness, cohesive force and adhesive force were measured in the same manner as in 3. In the adhesion test, in addition to the adhesion force to a stainless steel plate, the adhesion force to a polyethylene plate (thickness 2 mm) was also measured. In the cohesive force test, no displacement occurred in any of the adhesive films, and the same was true even when the load was doubled. The results of the tack test and adhesion test are shown in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. A pressure-sensitive adhesive whose main components are natural rubber or synthetic rubber and tackifier, in which the tackifier is made by esterifying purified disproportionated rosin with a trivalent or higher polyhydric alcohol. I was able to transform into
A pressure-sensitive adhesive characterized by being a rosin ester with a softening point of 65 to 140°C. 2. The pressure-sensitive adhesive according to claim 1, wherein the purified disproportionated rosin is obtained by distilling disproportionated rosin. 3. The pressure-sensitive adhesive according to claim 1, wherein the amount of rosin ester used is 20 to 150 parts by weight per 100 parts by weight of natural rubber or synthetic rubber.