CN110294848B

CN110294848B - Method for prevulcanizing fresh natural latex and latex product

Info

Publication number: CN110294848B
Application number: CN201910610751.8A
Authority: CN
Inventors: 王启方; 刘宏超; 潘琪; 余和平
Original assignee: Agricultural Products Processing Research Institute of CATAS
Current assignee: Agricultural Products Processing Research Institute of CATAS
Priority date: 2019-07-04
Filing date: 2019-07-04
Publication date: 2021-10-29
Anticipated expiration: 2039-07-04
Also published as: CN110294848A

Abstract

The invention provides a method for prevulcanizing fresh natural latex and a latex product. A process for prevulcanisation of fresh natural latex comprising the steps of: adding a vulcanization compounding agent into the fresh natural latex for prevulcanization to obtain prevulcanized fresh natural latex; carrying out centrifugal concentration on the prevulcanized fresh natural latex to obtain concentrated prevulcanized natural latex; the vulcanization compounding agent comprises sulfur, zinc oxide and an accelerator, wherein the accelerator is diallyl sulfide. Latex articles made using the concentrated prevulcanised natural latex. According to the method for prevulcanizing the fresh natural latex, the prevulcanization is carried out and then the centrifugal concentration is carried out, so that the production cost cannot be increased; the residual vulcanizing compounding agent is removed through centrifugal concentration, so that the problem of 'frosting' on the surface of the latex product can be thoroughly solved; the non-rubber substance content in the natural latex is basically consistent with that of the prior art, the vulcanization degree is basically kept unchanged, and the natural latex can be parked for a long time and is beneficial to production management of downstream enterprises.

Description

Method for prevulcanizing fresh natural latex and latex product

Technical Field

The invention relates to the field of natural rubber processing, in particular to a method for prevulcanizing fresh natural latex and a latex product.

Background

Natural latex (NRL) has good film forming property and excellent comprehensive performance, and is widely applied to the production of latex products such as condoms, gloves, balloons, catheters, latex, rubber threads, sponges, adhesives and the like. Wherein, latex products such as condoms, gloves, balloons, rubber tubes, rubber threads and the like are respectively produced by adopting pre-vulcanized natural latex through a dipping process and an extrusion process, and the consumed natural latex is about 80 percent of the total amount of the natural latex in the whole world. The prevulcanization of the natural latex means that rubber hydrocarbon molecular chains in natural latex particles are crosslinked in advance through a vulcanization compounding agent under a certain reaction condition to form a three-dimensional network structure. Most vulcanization compounding agents are solid powdered compounds which are still dispersed in natural latex as crystalline nano or micro particles after grinding. As environmental conditions change, these residual vulcanization agents gradually migrate to the surface of the latex article, forming a layer of frosty material, commonly referred to as "blooming". The phenomenon of 'frosting' on the surface of the latex product is extremely harmful, which not only affects the appearance performance of the latex product, but also the migration of crystalline particles forms a large number of cracks or 'holes', namely structural defects, on the surface of the adhesive film, thus seriously affecting the use safety of the product.

To solve the problem of 'blooming' of latex products, researchers at home and abroad take various measures. In the last 80 s, Malaysia began the research on prevulcanization of natural rubber latex and realized the commercial production of prevulcanization of natural rubber latex. However, Malaysia uses a process in which fresh natural latex is concentrated, then prevulcanized, diluted and then concentrated by centrifugation to remove the residual compounding ingredients. The concentrated natural latex is centrifuged for the second time, which causes about 20% of rubber substance loss, not only increases the production cost of the prevulcanized natural latex, and the price of each ton of prevulcanized natural latex increases about 20%, but also further reduces the content of non-rubber substances, which can not meet the production requirements of extruded products. The concentrated natural latex prevulcanization technology is also difficult to popularize and apply.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The first purpose of the present invention is to provide a method for prevulcanizing fresh natural latex, which can not only effectively solve the problem of 'blooming' on the surface of latex products, improve the appearance of latex products and the use safety of products, but also reduce the production cost of concentrated natural latex and ensure that the production process of downstream latex products remains unchanged.

The second purpose of the invention is to provide a latex product which is prepared by using concentrated prevulcanised natural latex, and the cost is reduced on the basis of ensuring the quality.

In order to achieve the purpose, the invention adopts the following technical scheme:

a process for prevulcanisation of fresh natural rubber latex comprising the steps of:

adding a vulcanization compounding agent into the fresh natural latex for prevulcanization to obtain prevulcanized fresh natural latex;

carrying out centrifugal concentration on the prevulcanized fresh natural latex to obtain concentrated prevulcanized natural latex;

the vulcanization compounding agent comprises sulfur, zinc oxide and an accelerator, wherein the accelerator is diallyl sulfide.

Through the selection of the vulcanization compounding agent, especially the selection of the accelerator, the operation mode of concentrating before prevulcanization and then concentrating in the prior art is changed on the basis, the residual vulcanization compounding agent is removed, the problem of 'blooming' is solved, meanwhile, the loss of rubber substances is reduced, the prevulcanization quality is ensured, the production cost is greatly reduced, and meanwhile, no adverse effect is generated on downstream production.

Preferably, said vulcanization compounding agent is used in an amount of 0.5 to 3.0 parts by dry weight of said sulfur, 0.5 to 2.0 parts by dry weight of said zinc oxide and 0.5 to 3.0 parts by dry weight of said accelerator, per 100 parts by dry weight of said fresh natural rubber latex.

In an alternative embodiment, the amount of sulfur used may correspond to any value between 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 dry weight parts and 0.5-3.0, the amount of zinc oxide used may correspond to any value between 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 dry weight parts and 0.5-3.0, and the amount of accelerator used may correspond to any value between 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 dry weight parts and 0.5-3.0, per 100 dry weight parts of the fresh natural rubber latex.

Preferably, the diallyl sulfide comprises one or more of diallyl monosulfide, diallyl disulfide and diallyl trisulfide.

The selection and the dosage of the vulcanization compounding agent are controlled to better control the process of the prevulcanization and ensure the prevulcanization effect.

Preferably, the accelerator is formulated as an aqueous emulsion prior to addition to the fresh natural rubber latex.

Preferably, the sulfur and the zinc oxide are ground into a suspension by adding water before adding the fresh natural rubber latex.

The components of the vulcanizing compounding agent are pretreated to ensure the stability of the system and improve the reaction efficiency and effect of the precuring.

Preferably, ammonia water, potassium hydroxide and peregal O are also added into the fresh natural latex.

More preferably, the order of adding ammonia, potassium hydroxide and peregal O to the fresh natural latex is: adding the accelerator and the ammonia water, then adding the potassium hydroxide and peregal O, and finally adding the sulfur and the zinc oxide.

The ammonia water is used for ensuring the freshness of fresh natural latex; the addition of potassium hydroxide and peregal O is intended to ensure the stability of the prevulcanization system.

Further preferably, the amount of the ammonia water is: 0.2 to 0.6 parts by dry weight of ammonia are used per 100 parts by wet weight of the fresh natural rubber latex.

In an alternative embodiment, the amount of ammonia used may be any of 0.2, 0.3, 0.4, 0.5, 0.6 dry parts by weight and between 0.2 and 0.6 dry parts by weight per 100 wet parts by weight of the fresh natural rubber latex.

Preferably, the method further comprises the following steps: phospholipid and ammonia water are added into the concentrated prevulcanized natural latex, and the dosage is as follows: 0.05-0.15 dry weight parts of phospholipid and 0.5-0.7 dry weight parts of ammonia water are added to 100 wet weight parts of the concentrated pre-vulcanized natural rubber latex.

In an alternative embodiment, the amount of phospholipids used may be any value between 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15 dry weight parts and 0.05-0.15 dry weight parts, and the amount of aqueous ammonia used may be any value between 0.5, 0.6, 0.7 dry weight parts and 0.5-0.7 dry weight parts, per 100 dry weight parts of the concentrated pre-vulcanized natural rubber latex.

The use of phospholipids to ensure the stability of the concentrated prevulcanised natural latex; the ammonia water is used in order to ensure the freshness of the concentrated precured natural rubber latex.

A latex article is prepared using the concentrated pre-vulcanized natural rubber latex.

The invention has the beneficial effects that:

1. the fresh natural latex is pre-vulcanized and then centrifugally concentrated, so that the production cost is not increased;

2. the residual vulcanizing compounding agent is removed through centrifugal concentration, so that the problem of 'frosting' on the surface of the latex product can be thoroughly solved;

3. the content of non-rubber substances in the natural latex is basically consistent with that of the concentrated natural latex produced by the prior art; the vulcanization degree of the prevulcanized natural latex is basically kept unchanged, and the prevulcanized natural latex can be parked for a long time, so that the production management of downstream enterprises is facilitated;

4. the mass production of the prevulcanized natural latex by upstream enterprises is beneficial to the stability of the production process of downstream enterprises.

Detailed Description

The terms as used herein:

"prepared from … …" is synonymous with "comprising". The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

The conjunction "consisting of … …" excludes any unspecified elements, steps or components. If used in a claim, the phrase is intended to claim as closed, meaning that it does not contain materials other than those described, except for the conventional impurities associated therewith. When the phrase "consisting of … …" appears in a clause of the subject matter of the claims rather than immediately after the subject matter, it defines only the elements described in the clause; other elements are not excluded from the claims as a whole.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when the range "1 ~ 5" is disclosed, the ranges described should be construed to include the ranges "1 ~ 4", "1 ~ 3", "1 ~ 2 and 4 ~ 5", "1 ~ 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

In these examples, the parts and percentages are by mass unless otherwise indicated.

"part by mass" means a basic unit of measure indicating a mass ratio of a plurality of components, and 1 part may represent any unit mass, for example, 1g or 2.689 g. If we say that the part by mass of the component A is a part by mass and the part by mass of the component B is B part by mass, the ratio of the part by mass of the component A to the part by mass of the component B is a: b. alternatively, the mass of the A component is aK and the mass of the B component is bK (K is an arbitrary number, and represents a multiple factor). It is unmistakable that, unlike the parts by mass, the sum of the parts by mass of all the components is not limited to 100 parts.

"and/or" is used to indicate that one or both of the illustrated conditions may occur, e.g., a and/or B includes (a and B) and (a or B).

Embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Unless otherwise indicated, the parts used hereinafter are parts by weight; the total solid content of the natural latex, as well as the phospholipid content and the ammonia content are mass fractions.

Example 1

Weighing 37.5 parts of diallyl monosulfide, and adding water to prepare an emulsified solution with the mass fraction of 20%; weighing 180 parts of 25% ammonia water solution by mass; weighing 7.5 parts of potassium hydroxide to prepare a potassium hydroxide aqueous solution with the mass fraction of 20%; weighing 7.5 parts of peregal O to prepare aqueous solution of peregal O with the mass fraction of 20%; weighing 60 parts of sulfur, grinding, and adding water to prepare a sulfur suspension with the mass fraction of 50%; weighing 40 parts of zinc oxide, grinding, and adding water to prepare a zinc oxide suspension with the mass fraction of 50%; weighing 7.5 parts of phospholipid, and preparing into an aqueous solution with the mass fraction of 20%; 190 parts of an ammonia solution with the mass fraction of 25% are weighed.

15000 parts of fresh natural rubber latex (equivalent to 4500 parts by dry weight) are weighed, and the diallyl monosulfide emulsion and 180 parts of aqueous ammonia solution are added and stirred uniformly.

Adding fresh natural latex containing diallyl monosulfide into a vulcanization reaction kettle with an interlayer, sequentially adding a potassium hydroxide solution, a peregal O solution, a sulfur suspension and a zinc oxide suspension under the stirring condition, uniformly stirring, heating the fresh natural latex to 60 ℃ by adopting a water bath, preserving the heat for about 1 hour, and immediately cooling the natural latex to the ambient temperature when the vulcanization degree of the fresh natural latex expressed by a chloroform value reaches three times, thereby obtaining the prevulcanization fresh natural latex.

And concentrating the prevulcanized fresh natural latex cooled to the ambient temperature by using a high-speed centrifuge to obtain 9000 parts of concentrated prevulcanized natural latex, and then sequentially adding a phospholipid solution and 190 parts of an ammonia water solution under the stirring condition.

Example 2

Weighing 75 parts of diallyl disulfide, and adding water to prepare an emulsified solution with the mass fraction of 20%; weighing 180 parts of 25% ammonia water solution by mass; weighing 7.5 parts of potassium hydroxide to prepare a potassium hydroxide aqueous solution with the mass fraction of 20%; weighing 7.5 parts of peregal O to prepare aqueous solution of peregal O with the mass fraction of 20%; weighing 70 parts of sulfur, grinding, and adding water to prepare a sulfur suspension with the mass fraction of 50%; weighing 43 parts of zinc oxide, grinding, and adding water to prepare a zinc oxide suspension with the mass fraction of 50%; weighing 7.5 parts of phospholipid, and preparing into an aqueous solution with the mass fraction of 20%; 190 parts of an ammonia solution with the mass fraction of 25% are weighed.

15000 parts of fresh natural rubber latex (corresponding to 4500 parts by dry weight) are weighed, the emulsified diallyl disulfide solution and 10 parts of aqueous ammonia solution are added and stirred uniformly.

Adding fresh natural latex containing diallyl disulfide into a vulcanization reaction kettle with an interlayer, sequentially adding a potassium hydroxide solution, a peregal O solution, a sulfur suspension and a zinc oxide suspension under the condition of stirring, uniformly stirring, heating the fresh natural latex to 60 ℃ by adopting a water bath, preserving the temperature for about 1 hour, and immediately cooling the natural latex to the ambient temperature when the vulcanization degree of the fresh natural latex expressed by a chloroform value reaches three times, thereby obtaining the prevulcanization fresh natural latex.

And concentrating the prevulcanized fresh natural latex cooled to the ambient temperature by using a high-speed centrifuge to obtain 9000 parts of concentrated prevulcanized natural latex, and then sequentially adding a phospholipid solution and an ammonia water solution under the stirring condition.

Example 3

Weighing 112.5 parts of diallyl disulfide, and adding water to prepare an emulsified solution with the mass fraction of 20%; weighing 180 parts of 25% ammonia water solution by mass; weighing 7.5 parts of potassium hydroxide to prepare a potassium hydroxide aqueous solution with the mass fraction of 20%; weighing 7.5 parts of peregal O to prepare aqueous solution of peregal O with the mass fraction of 20%; weighing 80 parts of sulfur, grinding, and adding water to prepare a sulfur suspension with the mass fraction of 50%; weighing 50 parts of zinc oxide, grinding, and adding water to prepare a zinc oxide suspension with the mass fraction of 50%; weighing 7.5 parts of phospholipid, and preparing into an aqueous solution with the mass fraction of 20%; 190 parts of an ammonia solution with the mass fraction of 25% are weighed.

15000 parts of fresh natural rubber latex (equivalent to 4500 parts by dry weight) are weighed, and the emulsified diallyl disulfide solution and the aqueous ammonia solution are added and stirred uniformly.

Example 4

Weighing 110 parts of diallyl trisulfide, and adding water to prepare an emulsified solution with the mass fraction of 20%; weighing 45 parts of 25% ammonia water solution by mass; weighing 7.5 parts of potassium hydroxide to prepare a potassium hydroxide aqueous solution with the mass fraction of 20%; weighing 7.5 parts of peregal O to prepare aqueous solution of peregal O with the mass fraction of 20%; weighing 70 parts of sulfur, grinding, and adding water to prepare a sulfur suspension with the mass fraction of 50%; weighing 50 parts of zinc oxide, grinding, and adding water to prepare a zinc oxide suspension with the mass fraction of 50%; weighing 7.5 parts of phospholipid, and preparing into an aqueous solution with the mass fraction of 20%; 190 parts of an ammonia solution with the mass fraction of 25% are weighed.

Example 5

Weighing 80 parts of a mixture of diallyl disulfide and diallyl trisulfide, and adding water to prepare an emulsified solution with the mass fraction of 20%; weighing 45 parts of 25% ammonia water solution by mass; weighing 7.5 parts of potassium hydroxide to prepare a potassium hydroxide aqueous solution with the mass fraction of 20%; weighing 7.5 parts of peregal O to prepare aqueous solution of peregal O with the mass fraction of 20%; weighing 80 parts of sulfur, grinding, and adding water to prepare a sulfur suspension with the mass fraction of 50%; weighing 50 parts of zinc oxide, grinding, and adding water to prepare a zinc oxide suspension with the mass fraction of 50%; weighing 7.5 parts of phospholipid, and preparing into an aqueous solution with the mass fraction of 20%; 190 parts of an ammonia solution with the mass fraction of 25% are weighed.

The final concentrated prevulcanized natural rubber latex obtained in the above examples was left to stand at room temperature for 3 days, and the total solid mass fraction, basicity, viscosity and mechanical stability of the concentrated prevulcanized natural rubber latex were measured by the method specified in GB/T14797.1-2008 "concentrated natural rubber latex", and the results are shown in table 1 below.

TABLE 1 basic Properties of concentrated prevulcanized natural rubber latex

Note: mechanical stability is a measure of natural storage for one month.

Comparative example 1

The reaction was carried out using the conventional process, first concentration and then prevulcanization, using the vulcanization formulation of example 1.

Comparative example 2

Mixing the following components in percentage by weight: accelerator ZDC: the mass ratio of zinc oxide is 1: 1: 0.5 As vulcanization formulation, the fresh natural rubber latex was precured and concentrated by centrifugation according to the procedure of example 1.

The concentrated prevulcanized natural rubber latex obtained in the examples and the comparative examples was poured into a glass mold, and naturally dried after film formation to prepare a vulcanized rubber film. And after the glue film is transparent, taking down the glue film from the glass plate, leaching the glue film in water for 12 hours, taking out the glue film, drying the glue film in the air, and drying the glue film in a hot air circulation constant temperature drying oven at 80 ℃ for 2 hours. The vulcanized rubber film was cut into pieces and samples according to the methods specified in GB/T528 and 2009 determination of tensile stress strain property of vulcanized rubber or thermoplastic rubber and HG/T3870 and 2008 determination of swelling index of vulcanized rubber, and the mechanical properties and swelling index were determined, and the results are shown in tables 2 and 3.

TABLE 2 Pre-vulcanized Natural latex film swell index

TABLE 3 mechanical Properties of prevulcanized Natural latex adhesive film

As can be seen from tables 2 and 3, the process provided herein for prevulcanizing and then centrifuging the fresh natural rubber latex is substantially consistent with the prevulcanizing natural rubber latex produced by the prior art in terms of swelling index and mechanical properties.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

1. A process for prevulcanisation of fresh natural latex, characterized in that it comprises the following steps:

2. The method of claim 1, wherein said vulcanization compounding agent is used in an amount corresponding to 0.5 to 3.0 parts by dry weight of said sulfur, 0.5 to 2.0 parts by dry weight of said zinc oxide, and 0.5 to 3.0 parts by dry weight of said accelerator, per 100 parts by dry weight of said fresh natural rubber latex.

3. The method of claim 1, wherein the diallyl sulfide comprises one or more of diallyl monosulfide, diallyl disulfide, and diallyl trisulfide.

4. The method of claim 1, wherein the accelerator is formulated as an aqueous emulsion prior to adding to the fresh natural rubber latex.

5. The method of claim 1, wherein said sulfur and said zinc oxide are ground into a suspension with water prior to adding said fresh natural rubber latex.

6. The method of claim 1, wherein ammonia, potassium hydroxide and peregal O are also added to the fresh natural latex.

7. The process according to claim 6, characterized in that the order of addition of ammonia, potassium hydroxide and peregal O to the fresh natural latex is: adding the accelerator and the ammonia water, then adding the potassium hydroxide and peregal O, and finally adding the sulfur and the zinc oxide.

8. The method of claim 6, wherein the aqueous ammonia is used in an amount of: 0.2 to 0.6 parts by dry weight of ammonia are used per 100 parts by wet weight of the fresh natural rubber latex.

9. The method of claim 1, further comprising: phospholipid and ammonia water are added into the concentrated prevulcanized natural latex, and the dosage is as follows: 0.05-0.15 dry weight parts of phospholipid and 0.5-0.7 dry weight parts of ammonia water are added to 100 wet weight parts of the concentrated pre-vulcanized natural rubber latex.