JPS60262838A - Microcapsule incorporating vulcanization accelerator as core material therein - Google Patents

Abstract

PURPOSE:To provide a microcapsule capable of inhibiting scorching during vulcanizing rubber without added retarder, by enclosing a vulcanization accelerator as a core material in the wall of an amino resin so that the microcapsule has specified particle size and wall thickness. CONSTITUTION:A microcapsule containing a vulcanization acclerator (e.g., thiuram accelerator) as a core material surrounded by the wall of films formed from an amino resin prepared by condensing an amino resin prepolymer (e.g., urea/formaldehyde prepolymer) in the presence of a cationic urea resin and anionic surfactant, said microcapsule having a particle size of 0.1-10mu and a wall thickness of 100-1,000Angstrom . The microcapsule can be dispersed homogeneously in a feed rubber in vulcanizing and the vulcanization accelerator is released by destroying the wall with heat. It takes a very long time for scorching to occur with said microcapsule, thus making a retarder for prevention of scroching unnecessary. Accordingly, the storage of unvulcanized rubber becomes possible and there is no fear of corroding metals due to the use of a retarder.

Description

[Detailed Description of the Invention] The present invention provides a vulcanization accelerator used in the vulcanization treatment of rubber.
The present invention relates to microcapsules containing a vulcanization accelerator as a core material, which prevents premature vulcanization by being encapsulated in a membrane wall formed from a membrane material made of amino resin.

Traditionally, when natural rubber or synthetic rubber is put to practical use, it is vulcanized, and a vulcanization accelerator is added in order to complete the vulcanization process uniformly and in a short time. However, at the same time, scorching occurs due to early vulcanization.
It is common practice to also use a vulcanization retarder for the purpose of preventing this.

However, when this vulcanization retarder is used, there are problems such as generation of undesirable hydrochloric acid, and depending on the type, the vulcanization reaction rate itself is delayed.
The problem of preventing scorching by using a vulcanization accelerator has also not been satisfactorily solved.

Under these circumstances, various attempts have been made to prevent scorching by using vulcanization accelerators, and one of them has been proposed to add an encapsulated vulcanization accelerator to raw rubber. There is. For example,
8-25042 discloses encapsulating a vulcanization accelerator with a polymer having a melting point of 100 to 300°C, such as nylon, and JP-A-57-182337 discloses encapsulating a vulcanization accelerator with a polymer having a melting point of 100 to 300°C, for example, nylon. Furthermore, Japanese Patent Publication No. 1973-1999 describes the encapsulation of a vulcanization accelerator using a resin whose temperature is below 120°C, such as coumaron resin or phenol-terpene resin.
Publication No. 43375 discloses that a vulcanization accelerator is encapsulated using polyurea obtained from isocyanates and amines to obtain capsules having a particle size of 0.1 to 0.5 mm.

However, in these proposed capsules, the amount of resin used as the core material is 2 to 20 times that of the vulcanization accelerator, and the particle size is also large, so they are not necessarily practical.

B < Shiyoto Kuchi The present invention provides a method for its use by encapsulating a vulcanization accelerator in a film material made of a thermosetting resin made of formalin and amines such as melamine and urea. A predetermined amount of vulcanization accelerator can be formed into capsules with a minute particle size that can be uniformly and densely dispersed in the raw rubber,
Another object of the present invention is to provide a capsule containing a vulcanization accelerator as a core material, which can prevent scorching without using a vulcanization retarder in the vulcanization process of raw rubber.

A feature of the present invention is that a film wall formed from a resin obtained by polycondensing an amino resin prepolymer in the presence of a cationic urea resin and an anionic surfactant enables vulcanization. The microcapsules are powder-like microcapsules that contain an accelerator as a core material, and have a particle size of 0.1 to 10 μm and a membrane wall thickness of 100 μm to 1000 μm.

Incidentally, various microcapsules whose membrane walls are made of amino resin have been proposed, and there are various microencapsulation methods, but in most of them, the substance contained as the core material is liquid. The field of application is, for example, microcapsules for pressure-sensitive recording paper, where the core material is released by crushing.

In contrast, the microcapsules according to the present invention encapsulate a solid vulcanization accelerator as a core material, and when used, the core material is released by thermal destruction.

The amino resin constituting the membrane wall of the microcapsule according to the present invention is urea-formaldehyde prepolymer (hereinafter abbreviated as UF prepolymer), melamine-formaldehyde prepolymer (hereinafter abbreviated as MF prepolymer), melamine -Urea-thiourea formaldehyde prepolymer (hereinafter abbreviated as MUTUF prepolymer)
and a mixture of melamine-formaldehyde prepolymer and thiourea formaldehyde (abbreviated as MF+TLJF prepolymer). It is obtained by polycondensation in the presence of an agent.

In addition, the vulcanization promoting side, which is the core material of the microcapsule,
Thiraum-based vulcanization accelerators that are commonly used and are represented by the following general formula (wherein R is -CH3, -C2H
s, -N○, etc., and χ is an integer such as 1, 2.4, etc.), and zinc dithiocarbamate-based vulcanization accelerators, and the former include tetramethylthiuram monosulfide, tetramethylthiuram monosulfide, Examples include methylthiuram disulfide, and examples of the latter include dimethyldithiocarbamic acid zinc salt, ethylphenyldithiocarbamic acid zinc salt, and n-butyldithiocarbamic acid salt.

In addition to these, mercaptobenzothiazole, dibenzothiadisulfide, traclohexyl-2-benzothiazylsulfenamide, etc. can also be used.

By the way, from the viewpoint of productivity, it is desirable that the vulcanization process be completed in as short a time as possible, and for this purpose, it is necessary to have a predetermined amount of vulcanization accelerator uniformly and densely dispersed in the raw rubber. It is.

That is, the smaller the particle size of the capsule containing the vulcanization accelerator, the more preferable it is, and from this point of view, in the capsule according to the present invention, the particle size is 0.1 to 10μ,
It is preferably formed to have a thickness of 0.5 to 5μ7, and a membrane wall of 10μ.
It is made into a very thin powder with a thickness of 0 to 1,000.

The method for preparing microcapsules according to the present invention will be described below.

1) About the amino resin prepolymer used to form the membrane wall of the capsule.

Among those used as amino resin prepolymers in the present invention, MF prepolymers are methylolmelamines ranging from monomethylolmelamine to hexamethylolmelamine, mixtures of these methylolmelamines with different degrees of methylolation, or combinations of the above methylolmelamine, melamine, and formaldehyde. It means a mixture, and may also be a transparent colloidal aqueous solution obtained by a hydrochloric acid treatment of an oligomer obtained by further reacting melamine and formaldehyde, that is, methylolmelamine having a degree of polymerization of 2 to 10. This MF prepolymer can be easily produced by heating a mixture of melamine and formalin under alkaline conditions, and this aqueous reaction solution can be directly used for encapsulation.

Mata, UF prepolymer means methylol urea ranging from monomethylol urea to tetramethylol urea, a mixture of these methylol ureas with different degrees of methylolization, or a mixture of the methylol urea, urea, and formaldehyde, and furthermore, a mixture of methylol urea, urea, and formaldehyde. It may also be an oligomer that has been further reacted, that is, a transparent colloidal solution having a degree of polymerization of 2 to 5 and a hydrophilic group.

In addition, TLIF prepolymer means a methylolated thiourea ranging from monomethylolthiourea to tetramethylolthiourea, a mixture of these methylolated thioureas with different degrees of methylolation, or a mixture of the methylolthiourea, thiourea, and formaldehyde. Alternatively, it may be an oligomer obtained by further reaction of thiourea and formaldehyde, that is, a transparent colloidal solution having a hydrophilic group with a degree of polymerization of 2 to 5.

On the other hand, MtJF prepolymers, MTUF prepolymers, M U 'rU F prepolymers, etc., which are obtained by heating two or more of melamine, urea, and thiourea and formaldehyde in alkaline conditions, can also be used alone or in combination with two or more of them. It is used in combination with a mixture of more than one species and the above-mentioned MF prepolymer, TUF prepolymer, and UP prepolymer.

The ratio of raw materials melamine, urea, thiourea and formaldehyde has an important influence on film formation.

Formaldehyde is 1.0 to 9.0% per mole of melamine.
0 mole, preferably 1.6 to 7.0 mole, and 0.6 to 4.0 mole per mole of urea, preferably 0.8 to 3.0 mole, and 0.6 to 4 mole per mole of thiourea. 0 mol, preferably 0.8 to 3.0 mol.

Further, the ratio of melamine, urea, and thiourea can be selected as desired. Such a ratio is selected in order to control the formation of the wall membrane of the microcapsules, and to impart membrane strength, heat-induced membrane breakability, etc. that suit the purpose.

The amount of resin prepolymer used during encapsulation is
It is preferably used in an amount of 0.03 to 1.0 g per 1 g of vulcanization accelerator.

11) Regarding the cationic urea resin and anionic surfactant used to form the membrane wall of the capsule.

The water-soluble thionic urea resin used in the present invention is a urea formaldehyde resin in which a cationic modifier is introduced, for example, tetraethylenepentamine, diaminoethanol, dicyandiamide, diethylaminoethanol as a modifier to urea formaldehyde prepolymer. , guanylurea or similar substances are added thereto and polycondensed by a known method. The ratio of the water-soluble thionic urea resin to the resin prepolymer is preferably in the range of 1:0.01 to 2.0 by weight.

Further, examples of the surfactant include fatty acid salts, higher alcohol sulfuric esters, alkylaryl sulfonates, etc., but sodium dodecylbenzenesulfonate is preferred.

The amount of this Ayuonic surfactant used is 0.01 to 0.1 part by weight per 1 part by weight of the water-soluble Kanaonic urea resin, thereby widening the PL+ range, that is, pH 2.5 to 6.
．． A stable dispersion can be obtained within the range of 0.

iii) Regarding microencapsulation.

First, a vulcanization accelerator that has been ground to a desired size is added to an aqueous mixture containing a water-soluble cationic urea resin and an aqueous surfactant using an appropriate means such as a homogenizer, stirrer, or ultrasonic wave. to disperse. At this time, the amino resin prepolymer may be pre-existing in the aqueous mixture, or may be added once or in several portions during or after the dispersion.

While gently stirring the dispersion containing the amino resin prepolymer, cationic urea resin, and anionic surfactant obtained as described above, an acid catalyst was added thereto to adjust the pH to 2.5 to 6. 0, reaction temperature 15-60℃
Microencapsulation is performed by reacting for 2 to 50 hours.

The acid catalyst used here is a low molecular weight carboxylic acid such as formic acid, acetic acid or citric acid, an inorganic acid such as hydrochloric acid, nitric acid or phosphoric acid, or aluminum sulfate, titanium oxychloride, magnesium chloride, ammonium chloride or ammonium nitrate. Examples include acid salts such as ammonium sulfate, ammonium acetate, and salts that are easily hydrolyzed, and these can be used alone or in combination.

Release side] υ1 The microcapsules prepared as described above contain a solid vulcanization accelerator with a membrane wall composed of an amino resin, and the thickness of the membrane wall is 100 to 1000 mm. The glandular material is extremely thin, so the proportion of the gland material in the capsule is only 10 to 30%, and the capsule itself has a particle size of 0.1 to 10μ, and is in the form of a free-flowing powder. .

Therefore, the microcapsules according to the present invention can be uniformly dispersed in the raw rubber during the vulcanization process, and the strength of the membrane wall is such that it can be destroyed by heat as described above, so the microcapsules can be vulcanized. The vulcanization accelerator as a core substance is released by heating during processing.

Furthermore, as is clear from the test results listed in h, the microcapsules according to the present invention take a very long time to generate scorching, and on the other hand, can be rapidly vulcanized under vulcanization conditions. There is no need for a vulcanization retarder to prevent scorching, so it is possible to store unvulcanized rubber, and there is no risk of mold corrosion associated with the use of a vulcanization retarder.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Car stop h↓ Tetramethylthiuram disulfide (
Hereinafter referred to as TMTD. ) was used to prepare microcapsules encapsulating the vulcanization accelerator as a core material according to the following procedure.

Mix 70 g of melamine manufactured by 9th Ward with L1 machiji, 290 g of formalin adjusted to pH 8.5 with 2% NaOH aqueous solution (the same applies below 37% formaldehyde aqueous solution), and 360 g of distilled water, and boil at 50°C.
The mixture was reacted for 60 minutes to prepare a MF prepolymer. Separately, 280 g of formalin, which had been adjusted to pH 8.5 with triethanolamine, and 115 g of urea were mixed and reacted at 70° C. for 1 hour to obtain a UF prepolymer.

■Average particle size of 1.9. A pulverized TMTD of t+a+ was obtained.

828 g of crushed microcapsules TMTD, 1790 g of water, and 26 g of a 6% Neoperex aqueous solution (sodium alkylbenzene sulfonate aqueous solution, manufactured by Kao Airas Co., Ltd.) were added, and to this was added 828 g of Neelamine P 1500 aqueous solution (manufactured by Neelamine Industries).
After adding 9 g of 10% triethanolamine and 89 g of 10% triethanolamine, this liquid was adjusted to pH 4.8 with a 10% aqueous citric acid solution and dispersed using a homogenizer. 700 g of this dispersion was kept at 30°C while stirring, and 51 g 1 U of MF prepolymer was added.
26 g of P prepolymer was added, and a 10% aqueous citric acid solution was added to adjust the pH to 3.8. In addition, 350g
of water and then adjust the pH to 3.0 with 10% citric acid aqueous solution.
After that, the reaction was continued under stirring to obtain a TMTD microcapsule slurry. This microcapsule slurry was separated, washed with water, and dried with a spray dryer to obtain powdered steel capsules with an average particle size of 2.2 μm.

The average film thickness of microcapsules containing TMTD is 45%.
There were 0 people.

700 g of dispersion obtained by the same procedure as described in Example 1
To this, 20 g of MF prepolymer and 10 g of tJF prepolymer were added, and microencapsulation was performed in the same manner as in Example 1, followed by drying to obtain powder capsules with an average size of 12.0 μm. The average thickness of this microcapsule was 160 people.

Jigomasu 1 700 g of dispersion obtained by the same procedure as described in Example 1
100 g of MF prepolymer and 50 g of UF prepolymer were added thereto, microencapsulation was performed in the same manner as in Example 1, and then dried to obtain powder capsules with an average diameter of 2.4 μm. The average thickness of the microcapsules was 760.

Example 1 This example shows an example in which zinc dimethyldithiocarbamate (hereinafter referred to as ZnMDC) was used as a vulcanization accelerator and microencapsulated.

ZnMDC was pulverized using a supersonic jet pulverizer to obtain pulverized ZnMDC with an average particle size of 2.8 μm.

To 828 g of this ZnMDC, 1790 g of water and 26 g of 10% Neoperex aqueous solution were added, and Neelamine P was added to this.
89 g of -1500 aqueous solution was added, the pH was adjusted to 4.8 with a 10% citric acid aqueous solution, and the mixture was dispersed using a homogenizer.

Of this dispersion, 700. MF prepolymer 4 prepared by the method shown in Example 1 while stirring at 30°C.
0 g, and 20 g of UF prepolymer, 10%
The pH was adjusted to 3.8 with an aqueous citric acid solution. Next, 350 g of water was added to this, and ρ was adjusted to 113.0 with a 10% citric acid aqueous solution, and the reaction was continued with stirring to form a ZnM
A microcapsule slurry of DC was obtained. This microcapsule slurry was filtered, washed with water, and dried with a spray dryer to obtain highly fluid powdered ZnMDC capsules with an average particle size of 3.3 μm. This ZnMDC microcapsule I! IIE had an average of 300 people.

Next, Example 5 shows the results of a rubber vulcanization test using the microcapsules obtained in Examples 1 to 4 kneaded according to the formulation shown in Table 1. As a comparison, the results of a similar vulcanization test conducted on the vulcanization accelerators obtained in Comparative Examples 1 and 2 shown below are also shown.

Comparative Example 1 As a comparative control for Examples 1 to 3, 35 parts by weight of non-microencapsulated TMTD was kneaded into the formulation shown in Table 1.

Comparative Example 2 As a comparative control for Example 4, 0.35 parts by weight of non-microencapsulated TMTD was kneaded into the formulation shown in Table 1.

Table 1 Smoked sheet 100 Parts by weight Zinc white 5... Sulfur 2.51 Mestearic acid 1... Process oil 5 Carbon black (II 8) 50 Il vulcanization accelerator 0.35 = (vulcanization accelerator (Based on standard) Example 5 One batch of raw rubber was rolled using a 6"φ x 12" test roll at 50±
After mastication at 5°C, the formulations according to the formulation shown in Table 1 and the microencapsulated THTD and ZnMDC of Examples 1 to 4 and T of Comparative Examples 1 and 2 were prepared.
MTD and ZnMDC were added sequentially, and the effects on the scorch prevention effect and vulcanization rate of the product of the present invention were compared after being left overnight. Based on JIS K 6300 (1974), 12
Tested at 5°C.

The Mooney Scorch results are shown in Table 2.

The results of the Curelastometer test at 140°C and 180°C are shown in Table 3.

The test conditions for the Curelastometer are as follows.

Testing machine n JSR type curelast meter, die: 2m
m5 swing lJ: ±3°, induction period: tl. (minutes, seconds), Vulcanization time: Lqo (minutes, seconds), Rising speed: R (minutes, seconds), Estimated vulcanization time: T = 2t, o too (minutes, seconds)
It was used.

Procedural amendment 29 Name of the invention Microcapsules 3 containing a vulcanization accelerator as a core material Relationship with the case of the person making the amendment Name of patent applicant (110) Kureha Chemical Industry Co., Ltd. 4 Address of agent Port of Tokyo Shinbashi Kokusai Hill 5, 2-7-7 Higashi-Shinbashi Ward, date of amendment order Voluntary 8, amend the details of the amendment as follows.

(On page 7 of page 11, lines 8 to 7 from the bottom, the phrase “zinc dimethyldithiocarbamate salt” is corrected to “zinc dimethyldithiocarbamate.”

(2) In the 7th and 6th lines from the bottom, the phrase [ethylphenyldithiocarbamate zinc salt] is corrected to [ethylphenyldithiocarbamate zinc salt].

(3) In lines 6 to 5 from the bottom of the same page, the phrase [n-butyldithiocarbamic acid salt] is corrected to read "zinc di-n-butylnotiocarbamate".

(4) In the fourth to third lines from the bottom, the words "mercaptohendithiazole" are corrected to "2-mercaptohenzothiazole."

(5) In the third line from the bottom, the phrase ``1 dihenzothiadisulfite'' is corrected to ``dihenzothiadyl disulfide.''

(6) In the third to second lines from the bottom of the same page, the phrase “N-cyclohexyl-2-hendithiazylsulfenamide” has been replaced with “N-cyclohexyl-2-hendithiazylsulfenamide.”
-cyclohexyl-2-benzothiazolesulfenamide".

(7) In the 9th line of page 11, the phrase "wall membrane" is corrected to "membrane wall."

(8) On page 16, line 8, the phrase "manufactured by Matic Industries" is amended to read "manufactured by Matic Industries."

(9) On page 18, line 5 from the bottom, replace “10%” with “
6%”.

Ql Page 20, line 6 ni rTMTDJ and rZn
MDC”.

Claims (3)

[Claims] (1) A membrane wall formed from an amino resin obtained by polycondensing an amino resin prepolymer in the presence of a cationic urea resin and an anionic surfactant encapsulates a vulcanization accelerator as a core material. A microcapsule consisting of a vulcanization accelerator as a core material, characterized in that the particle size is 0.1 to 10μ and the thickness of the membrane wall is 100 to 1000 μm. capsule. (2) Amino resin prepolymers are a group consisting of urea-formaldehyde prepolymers, melamine-formaldehyde 1 prepolymers, melamine-urea-thiourea formaldehyde prepolymers, and mixtures of melamine-formaldehyde prepolymers and thiourea formaldehyde prepolymers. The microcapsule according to claim (1), which is at least one type selected from the following. (3) The microcapsule according to claim f11 or claim (2), wherein the vulcanization accelerator is a thiuram-based vulcanization accelerator or a zinc dithiocarbamate-based vulcanization accelerator.