JPH0468335B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to a novel plasticizer useful for plasticizing polymers. In particular, the features of the present invention are best exhibited in compounds that are solid at room temperature but become liquid when heated to exert a plasticizing action on the polymer. That is, when the polymer is plasticized by the plasticizer of the present invention, it becomes soft at room temperature if the plasticizer is liquid at room temperature, or under heating if it is solid, and it becomes sticky when it is significant. It can be used as an adhesive or adhesive. In particular, when the polymer coexists with the plasticizer of the present invention, and more preferably with a tackifying agent, it becomes useful as a pressure-sensitive adhesive composition if the plasticizer is liquid, and a heat-sensitive adhesive composition if the plasticizer is solid. In the latter case in particular, the adhesive maintains its tackiness for a long time even after leaving the heat source and can be used as an adhesive/adhesive for various adherends over a long period of time. Therefore, (a) the polymer before heating, (b)
If a composition containing fine particles of a solid plasticizer of the present invention, more preferably (c) a tackifying agent, is provided in a layer on a sheet-like substrate such as paper or film, It is useful as a heat-sensitive adhesive sheet. Of course, among the plasticizers of the present invention, if a liquid plasticizer is used, it will be useful as a pressure-sensitive adhesive sheet. The novel plasticizer for polymers of the present invention is of course useful for general plasticizer applications, and can be used for the purposes of dissolving, swelling, softening, and thermoforming plastics. (B) Prior art Heat-sensitive adhesive compositions are non-adhesive at room temperature, but become tacky when activated by heating, and often persist for a period of time even after being separated from the heat source, resulting in various types of adhesive properties. It is something that can be attached to or adhered to objects. That is, by applying the above-mentioned composition onto a substrate (base sheet) such as paper or film, a heat-sensitive adhesive sheet such as a heat-sensitive label or heat-sensitive sticker can be obtained. While pressure-sensitive adhesive sheets for public use require a protective sheet called release paper because they are sticky at room temperature, heat-sensitive adhesive sheets do not require this.
Therefore, it has attracted attention in recent years as a resource-saving and economically advantageous adhesive sheet. A typical example of the types and quantitative ratios of various chemical materials used in heat-sensitive adhesive compositions is, for example, the 12th edition of "Adhesive Handbook" published by Kobunshi Publishing Association (Showa
(published in 1955), and basically includes polyvinyl acetate, polybutyl methacrylate, and vinyl chloride.
Vinylidene chloride copolymer, synthetic rubber, vinyl acetate-2-ethylhexyl acrylate copolymer,
Polymers such as vinyl acetate-ethylene copolymer, vinylpyrrolidone-styrene copolymer, styrene-butadiene copolymer, vinylpyrrolidone-ethyl acrylate copolymer, dicyclohexyl phthalate, diphenyl phthalate,
Dihexyl phthalate, dihydroabiethyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene glycol dibenzoate, trimethylolethane tribenzoate, glyceride tribenzoate,
It is preferably composed of a solid plasticizer such as pentaerythritol tetrabenzoate, sucrose octaacetate, tricyclohexyl citrate, N-cyclohexyl-p-toluenesulfonamide, dehydroabiethylamine carbonate, methoxyethyl stearate-urea complex, etc. Furthermore, indene resin, ethyl cellulose, petroleum resin (hydrocarbon resin), terpene resin,
It contains a tackifying agent such as a rosin derivative (polymerized rosin, hydrogenated rosin, pentaerythritol ester of rosin, resin acid dimer, etc.). According to these descriptions and other known documents,
The inventors have found that although a heat-sensitive adhesive composition can be obtained experimentally, it is difficult to obtain one that can be put to practical use. Among the chemical materials mentioned above, the polymer is the source of adhesion, and without it, cohesive force during adhesion cannot be obtained. The solid plasticizer does not impart plasticity to the polymer at room temperature, and therefore the composition is non-tacky when heated; however, upon heating, it first melts into a liquid state and swells or dissolves the polymer, causing it to become soft or sticky. It embodies tatsukinness. At this time, if a tackifier is also present, the tackiness will be more pronounced and the practical usefulness will be increased. It is practically required that the composition activated by heating maintains its tackiness even after being removed from the heat source and returning to room temperature. This is because if time is allowed between heat activation and application of the adhesive sheet to the adherend, assembly work can be carried out continuously, which is very efficient. (C) Problems to be solved by the invention Among various adherend materials, particularly in the case of materials with low polarity such as plastic materials, it is thought that the adhesion is mainly due to adhesiveness for a certain period of time after application. If the adhesive properties are lost, the pressure-sensitive adhesive sheet may peel off from the adherend at an early stage, which significantly impairs its practical value. The present invention has found through repeated tests that this adhesive persistence (duration) largely depends on the type of plasticizer, and that it is still not at a fully satisfactory level even with the best of the conventionally known plasticizers. I knew. Furthermore, the pressure-sensitive adhesive sheet before heat activation has the disadvantage that it is susceptible to blocking during storage. The present invention therefore seeks to solve the problem of the prior art, in particular that the duration of the adhesive properties of heat-sensitive adhesive compositions after heat activation is not long enough. In addition, when heat-sensitive adhesive sheets such as those described above are placed in a roll or stacked in sheet form, the sheets may stick together, especially when placed under slightly higher temperature or pressure for a long period of time. Although a so-called blocking phenomenon is sometimes observed, the novel plasticizer of the present invention can also improve this problem. Furthermore, the present invention aims to contribute to the development of polymer plasticizer technology by providing a new plasticizer regardless of whether it is in a liquid or solid state at room temperature. (D) Means for Solving the Problems In solving the above problems, the present inventors have made great progress by researching new materials and using them as plasticizers. The new plasticizer provided by the present invention is a dicarboxylic acid ester of catechol, and is represented by the general formula below. General formula: However, in the formula, R represents a group selected from the group consisting of alkyl, alkenyl, cycloalkyl, aralkyl, aralkenyl, haloalkyl, and aryl (aromatic). No literature has been found stating that these diesters are useful as plasticizers for polymers. The present inventor has also discovered that these structural isomers, dicarboxylic acid esters of para-hydroquinone, do not exhibit any plasticizing action. Table 1 lists representative examples of catechol dicarboxylic acid esters, which are new plasticizers useful in the present invention.

【table】

[Table] Among these compounds, those that are liquid at room temperature (expressed as oily in Table 1) are similar to conventionally known liquid plasticizers, such as phthalic acid diesters and phosphoric triesters, or As mentioned above, it can be used as a plasticizer for general polymers, and those that are solid (crystalline) at room temperature are particularly useful as solid plasticizers for heat-sensitive adhesive compositions. It is. The catechol dicarboxylic acid esters of the present invention could be easily synthesized by adding 2 or more moles of carboxylic acid anhydride or carboxylic acid halide to 1 mole of catechol, preferably by heating or adding a base. All compounds were virtually colorless liquids or solids (crystals). In addition, these new plasticizers can be used alone for polymers, multiple ones with different chemical structures can be combined, and of course good results can be obtained even when mixed with known plasticizers. . (E) Example In this example, "parts" represent "parts by weight." Example 1 (Synthesis example) Synthesis of catechol di(cyclohexanecarboxylic acid) ester: 35.2 parts of cyclohexane carbonyl chloride was added to 11.0 parts of catechol, and 40 parts of pyridine was added dropwise while stirring. After heating under reflux on an oil bath for 1 hour, a large amount of water was added and the mixture was stirred under ice cooling, and crystals were formed. This was separated, dried, and recrystallized from n-hexane to obtain colorless needle-like crystals. Yield, 25.1 parts (yield, 76%). mp59℃, mass spectrometry (FD method) m/Z = 330 (calculated value, C ₂₀ H ₂₆ O ₄ =
330.42) This compound is compound number 19 in Table 1. Other catechol dicarboxylic acid esters were also synthesized in a similar manner. Example 2 Compounds Nos. 1, 13, 19, 20, and 21 in Table 1 were used for comparison with known dicyclohexyl phthalate, diphenyl phthalate, dimethyl isophthalate, and hydroquinone di(cyclohexanecarboxylic acid) ester similar to the present invention. The following experiments were conducted using these as solid plasticizers. First, water was added to 100 parts of solid plasticizer, 7 parts of polyvinyl alcohol, and 7 parts of nonionic surfactant to make a total solid concentration of 50%, and the mixture was ground using a ball mill to prepare an aqueous suspension of solid plasticizer fine particles. . Next, ethylene-vinyl acetate copolymer emulsion
10 parts (solid content) Acrylic copolymer emulsion
Water was added to 10 parts (solid content) of the solid plasticizer suspension described above and 5 parts (solid content) of the rosin ester emulsion to prepare an aqueous coating liquid with a total solid content concentration of 50%. When these coating solutions were coated onto art paper weighing 100 g/m ² to a dry coating weight of 20 g/m ² and dried at room temperature, all non-viscous coated papers were obtained. These coated papers were heat activated for 30 seconds in a constant temperature chamber at 150℃, and the degree of tack was determined by
Measurement was performed according to the tilted ball tack measurement method (measuring chamber temperature 20°C, tilt angle 30°). The results are shown in Table 2.

[Table] As shown in Table 2, it can be seen that the novel plasticizer of the present invention causes the heat-sensitive adhesive composition to exhibit significant tackiness after heating. Example 3 As a solid plasticizer, the catechol dibenzoate ester of the present invention (No. 20 in Table 1) and diphenyl phthalate for comparison were ground in the same manner as in Example 2, and an aqueous suspension of solid plasticizer fine particles was prepared. Diyon was prepared. Next, styrenic copolymer emulsion
25 parts (solid content) Solid plasticizer suspension 35 parts (solid content) Rosin ester emulsion 10 parts (solid content) Water was added to make an aqueous coating liquid with a total solid content concentration of 50%. This coating liquid was applied onto art paper weighing 80 g/m ² so that the coating amount after drying was 20 g/m ² , dried at 40°C, and a heat-sensitive adhesive sheet that is non-adhesive at room temperature was used. I got two types. All of these were activated by heating at 150°C for 30 seconds and showed equivalent adhesive properties. In order to investigate the blocking characteristics between sheets, each coated paper sample was stacked so that the back side and front side were facing each other, a weight was placed on top of it to give a weight of 1 kg/cm ² , and the sample was left at a temperature of 55°C for 30 minutes. Then, the presence or absence of blocking was subsequently investigated. In a comparative example in which diphenyl phthalate was used as the solid plasticizer, pecking was observed and a loud noise was produced when the sheets were separated from each other. On the other hand, in the example of the present invention using catechol dibenzoic acid, pecking was practically not observed and there was almost no sound. That is, a clear improvement in blocking was observed. Example 4 Catechol dibenzoate according to the present invention and known dicyclohexyl phthalate were selected as solid plasticizers, and each was ground in the same manner as in Example 2.
It was made into a fine particle aqueous suspension. Next, ethylene-vinyl acetate copolymer emulsion
100 parts (solid content) Catechol benzoate suspension
50 parts (solid content) Phthalic acid dicyclosuspension
Water was added to 100 parts (solid content) of terpene resin emulsion and 50 parts (solid content) to prepare an aqueous coating liquid with a total solid content concentration of 50%. For comparison, an aqueous coating solution was also prepared, except that 150 parts (solid content) of dicyclohexyl phthalate alone was used as a solid plasticizer without using catechol dibenzoate. Each coating solution was applied to one side of art paper weighing 80 g/m ² and dried at 40°C. The coating amount after drying was 20 g/m ² in both cases. These sheets were cut into strips, activated by heating at 120° C. for 20 seconds, attached to a polyethylene film, and left at room temperature for one month. Thereafter, an attempt was made to peel off the sample sheet from the polyethylene film using a fingernail. As a result, in the case of the present invention, the adhesive was firmly attached, but the base paper was torn (base material destruction). On the other hand, the comparative sample was relatively easily peeled off from the interface with polyethylene (interfacial failure). That is, in the example according to the present invention, a clear improvement in adhesiveness was observed. (F) Effects of the invention As mentioned above, the present invention provides a new plasticizer that has a remarkable plasticizing effect on various polymers, especially those that are solid at room temperature (usually crystalline solid). is particularly useful as an essential component in heat-sensitive adhesive compositions. Not only does it exhibit remarkable adhesion properties upon heating, but it also has a clear improvement over known products in terms of blocking properties, which are practically important properties for heat-sensitive adhesive sheets. By devising the method, we were able to significantly improve the adhesive properties.

Claims (1)

[Claims] 1. A plasticizer for polymers comprising a dicarboxylic acid ester compound of catechol represented by the following general formula. General formula: (However, in the formula, R represents a group selected from the group consisting of alkyl, alkenyl, cycloalkyl, aralkyl, aralkenyl, haloalkyl, and aryl.)