KR102145295B1 - Process for producing Pre-Vulcanized latex foam with excellent processibility - Google Patents

Abstract

The present invention relates to a method for preparing pre-vulcanized (PV) latex foam with excellent processability and, more particularly, to a method for preparing PV latex foam with excellent processability by crosslinking the inside of the latex in advance and then crosslinking the outside to make the crosslinking density uniform. The present invention comprises: an internal crosslinking step of crosslinking the inside of the latex to form PV latex; a PV/NR mixing step of primarily stirring PV latex, NR latex, and oleate; a foaming step of adding an additive containing sulfur during the primary stirring process and then foaming while secondarily stirring; a gelling step of inputting diphenylguanidine and sodium silicofluoride during the foaming process and then tertiarily stirring to form a foam material; and an external cross-linking step of inputting the foam material into a mold and curing at 90 to 100°C so as to form PV latex foam with the outside cross-linked.

Description

Process for producing Pre-Vulcanized latex foam with excellent processibility}

The present invention relates to a method of manufacturing a PV latex foam having excellent processability, and more particularly, to a method of manufacturing a PV latex foam having excellent processability by crosslinking the inside of the latex beforehand and then crosslinking the outside to improve the crosslinking density.

In general, latex foam is prepared by crosslinking after adding conventional additives and foaming with a rubber component as the main raw material. The rubber component used as the main raw material of such latex foam is natural or synthetic, or natural and synthetic materials are also used in combination.

Latex foam is hardened by forming thousands of pinholes and millions to tens of thousands of fine bubbles in the liquid foaming process, so it has many pores and has excellent elasticity and resilience, so it is widely used in various fields.

For example, latex foam can be used as a cushioning material that relieves shock or friction by putting it in covers such as furniture, mattresses and pillows, and latex foam formed thinly in a frame can be used as a gasket, windshield, and vibration-sensitive material. have. In particular, latex foam is sometimes produced as an insole for shoes.

Such a conventional latex foam is mixed with an emulsifier, a crosslinking agent and a viscosity modifier in the latex and aged for 12 to 24 hours. After starting foaming while stirring at a constant speed at a constant temperature, a coagulant is added to stabilize and crosslinked. Although being manufactured, there is a problem that uniform crosslinking is not achieved on the inside and outside of the latex foam by crosslinking only on the outer surface of the latex foam.

In the case of latex foam based on a different post-cure type Dunlop method, it is difficult to ensure uniformity of the formulation according to external environmental conditions during compound aging, resulting in a lot of product defects and quality deviations.

Therefore, it is the time of urgent need for research on technology development to achieve excellent quality by improving the crosslinking density by uniformly crosslinking the interior and exterior of the latex foam.

Registered Korean Patent Publication No. 10-1378491, as of March 20, 2014.

The present invention was invented to solve the above problems, and an object of the present invention is to provide a method for producing a PV latex foam having excellent processability by crosslinking the inside of the latex beforehand and then crosslinking the outside to improve the crosslinking density.

The present invention for achieving the above object, the internal crosslinking step of forming a PV latex (Pre-Vulcanized latex) by crosslinking the inside of the latex; PV/NR mixing step of first stirring the PV latex, NR latex, and oleate; A foaming step of foaming while second stirring after adding an additive containing sulfur during the first stirring process; A gelling step of adding diphenylguanidine and sodium silicofluoride in the foaming process, followed by third stirring to form a foam material; And an external crosslinking step of forming a pre-Vulcanized latex foam crosslinked outside by curing at 90 to 100°C after putting the foam material into a mold. The technical gist of this excellent PV latex foam production method.

Preferably, the oleate in the PV/NR mixing step is potassium oleate (K-Oleate).

Preferably, the additive in the foaming step further comprises at least one of zinc diethyldithiocarbamate (ZDEC), zinc 2-mercaptobenzothiazole (ZMBT), and zinc oxide. It characterized in that it includes.

The manufacturing method of the PV latex foam having excellent processability according to the present invention by the solution to the above problem improves the uniformity of the crosslinking density inside and outside since the inside of the latex is crosslinked beforehand and then the outside is crosslinked. In addition, there is an effect that can be applied to various fields by manufacturing high-quality PV latex foam.

1 is a flow chart according to a preferred embodiment of the present invention.
Figure 2 is a product photograph according to a preferred embodiment of the present invention.
3 is a photo of a product according to a preferred embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart according to a preferred embodiment of the present invention. Referring to Figure 1, the PV latex foam with improved crosslinking density by uniformly crosslinking inside and outside according to the present invention is an internal crosslinking step (S10a), PV/NR mixing step (S10), foaming step (S20), gelling step ( S30) and can be manufactured through the external crosslinking step (S40), the characteristics of each step are as follows.

First, the internal crosslinking step is a step of forming a PV latex (Pre-Vulcanized latex) by crosslinking the inside of the latex (S10a).

First, the conventionally manufactured latex foam method has a problem in that the crosslink density of the latex foam is not good because the inside and outside of the latex particles are not uniformly crosslinked.

In view of this problem, in the present invention, by introducing a crosslinking agent into the latex and pre-vulcanizing the rubber molecules in the latex particles under certain conditions, an internal crosslinking step is carried out to crosslink only the outside of the latex particles. It was intended to improve.

At this time, "PV" of PV latex is an abbreviation of Pre-Vulcanized. In the process of crosslinking the outside of the latex, it cannot be crosslinked to the inside of the latex. In addition to improving the crosslinking density inside and outside the foam, it is possible to improve the bonding strength between the inside and outside of the PV latex foam.

Next, the PV/NR mixing step is a step of first stirring PV latex, NR latex, and oleate (S10).

In other words, the PV/NR mixing step is a process of slowly first stirring together 20 to 70 phr of PV latex manufactured in the internal crosslinking step, 30 to 80 phr of NR (natural rubber) latex and 1 to 3 phr of oleate, and PV latex and NR It can be said that the amount of latex mixed is important.

At this time, since PV latex has been internally crosslinked with rubber molecules, its wet-gel strength is lower than that of NR latex post-sure formulation, so it is not suitable for producing a foam with a large content or alone.

For the above-described reasons, the mixing ratio according to the mixing amount of PV latex and NR latex can be said to be important. That is, PV latex and NR latex are mixed in a weight ratio of 3-7:3-7, thereby satisfying various physical properties. In this regard, it will be described later through <Experimental Example>.

In the case of oleate, it refers to a fatty acid-based emulsifier such as derivatives substituted with potassium or sodium in oleic acid, and any one or more of potassium oleate and sodium oleate may be applied. In the present invention, potassium oleate was used.

These oleate salts may be included in an amount of 1 to 3 phr.If less than 1 phr is added, the reaction polymerization stability between PV latex and NR latex may be deteriorated, and if it exceeds 3 phr, aggregation occurs during the reaction polymerization between PV latex and NR latex. As a result, the latex particles may become large and the emulsion stability may be deteriorated due to high viscosity. Therefore, the addition of 1 to 3 phr of oleate has an important critical significance.

Next, the foaming step is a step of foaming while secondary stirring after adding an additive containing sulfur during the first stirring process (S20).

In other words, in the previous PV/NR mixing step, sulfur, zinc diethyldithiocarbamate (ZDEC), and zinc 2-mercaptobenzothiazole are emulsified by oleate between the PV latex and the NR latex. (Zinc 2-mercaptobenzothiazole, ZMBT) and an additive containing at least one of zinc oxide are added to increase the speed gradually while secondary stirring to start foaming.

Sulfur is a vulcanizing agent and acts to initiate foaming by performing a crosslinking role between components. In the case of sulfur, it can be added in the range of 1.5 to 4 phr, but if it is less than 1.5 phr, it is not crosslinked and thus foaming is not stable. If it exceeds 4 phr, it may be over-crosslinked, resulting in physical property degradation. It is desirable to use it appropriately.

ZDEC is a vulcanization accelerator, which means a kind of catalyst that facilitates the vulcanization reaction. Since the vulcanization accelerator greatly affects the vulcanization conditions even with a small amount of change, ZDEC is preferably introduced in the range of 1 to 2 phr. If it is less than 1 phr, the vulcanization time cannot be shortened. If it exceeds 2 phr, the vulcanization is excessive. It proceeds quickly and it becomes impossible to achieve property stabilization.

ZMBT, like ZDEC, is a vulcanization accelerator and is a kind of catalyst that facilitates the vulcanization reaction. In other words, it is an additive for the purpose of reducing the amount of vulcanizing agent while shortening the vulcanizing time by using it in combination with a vulcanizing agent and ZDEC. Like ZDEC, ZMBT can be added in the range of 1 to 2 phr, which takes into account the mixing power of sulfur and ZDEC.If ZMBT is added less than 1 phr, it is insufficient to create synergies with ZDEC to promote vulcanization. If it is added in excess of 2 phr, the vulcanization time can be reduced, but it is not preferable because there may be parts where vulcanization does not occur.

However, the vulcanization accelerator is not limited to the above-described ZDEC and ZMBT, and various vulcanization accelerators can be used.

Zinc oxide (ZnO) acts as a vulcanization accelerator to fully exert the accelerating effect of vulcanization accelerators such as ZDEC and ZMBT. If zinc oxide is added in less than 2 phr, it is insignificant to serve as an accelerator for vulcanization, and is insufficient to achieve complete vulcanization acceleration. If it is added in excess of 5 phr, more excellent effects appear compared to the case of adding less than that amount. Therefore, it is preferable to appropriately control and use zinc oxide within the range of 2 to 5 phr.

Next, the gelling step is a step in which diphenylguanidine and sodium silicofluoride are added in the foaming process, followed by third stirring to form a foam raw material (S30).

In other words, after the first stirring of PV latex, NR latex and oleate, which crosslinked the inside of the latex, foaming starts with the second stirring by the addition of other additives.If this foaming occurs, the speed is lowered in the gelling step and then diphenylguanidine 0.5~2phr and 1~5phr of sodium silicate are added, and then the speed is further lowered and stirred for 1~10 minutes, thereby completing the foam raw material in which bubbles are generated for PV latex foam production.

At this time, diphenylguanidine is an accelerator and, in simple terms, refers to a vulcanization accelerator that is additionally added in order to be concerned that a portion that has not been vulcanized remains through the second agitation. Accordingly, diphenylguanidine is preferably added in the range of 0.5 to 2 phr, and if it is less than 0.5 phr, it cannot function as an accelerator, and if it exceeds 2 phr, it has a more excellent effect compared to the case where less than that amount is added. Since it does not appear, it is preferable to use it by appropriately controlling it within the range of 0.5 to 2 phr.

In the case of sodium silicate, it imparts a solidifying ability to the foam material so that it can retain shape when it is later molded into PV latex foam. Sodium silicate is preferably added within the range of 1 to 5 phr. The reason is that if it is added less than 1 phr, it is insufficient to provide solidifying power to the foam material, and there is a concern that the shape may not be maintained well even after molding the PV latex foam. If it is added in excess of 5 phr, it has the effect of shortening the molding time, but rather, too much amount is added and it solidifies before it is completed into a desired shape of PV latex foam, so that the effectiveness as a product is lost, so sodium silicate is 1~ It is preferably added in the range of 5 phr.

Finally, the external cross-linking step is a step of forming a PV latex foam cross-linked outside by curing the foam material in the mold at 90 to 100° C. (S40).

In other words, in the external crosslinking step, after pouring a foam raw material with the crosslinked PV latex as a starting material into a mold preheated to 30~40℃ in an oven, the inside and outside through curing under a temperature condition of 90~100℃. This is a step in which the uniformly crosslinked PV latex foam is completed.

Curing refers to a series of processes in which the foam raw materials are heated and cured at a temperature of 90 to 100°C. After this curing process, the resulting PV latex foam is dried for 1 to 2 hours. Finish by demolding.

Additionally, if a mold preheated to a low temperature is used, the foam will turn off and the shape will be incorrect. If the mold is preheated above 40°C, a homogeneous product can be obtained as some curing proceeds during the mold filling process. Therefore, it is preferable to preheat the mold for the curing process only to 30 to 40°C.

And if curing is performed under the condition of less than 90℃, it takes a lot of time for the foam raw material to be cured into a certain shape of PV latex foam, which is inefficient in the process, and if it is carried out under conditions exceeding 100℃, it is included in the foam raw material. Since the air bubbles may become non-uniform due to rapid evaporation of moisture, it is preferable to cure while appropriately controlling within a temperature range of 90 to 100°C.

2 and 3 are product photographs according to a preferred embodiment of the present invention. 2 and 3, in order to manufacture an insole mounted inside a shoe, a mold in an insole shape is preheated to 30 to 40°C, and then a foam material is injected into the mold at 90 to 100°C. It can be seen that the cured product is shown in pictures.

However, the PV latex foam according to the present invention can be manufactured into various products according to the shape of the mold, for example, mattresses, pillows, and the like, and the types thereof are not limited.

Hereinafter, examples and experimental examples of the present invention will be described in detail.

<Example>

50phr of PV latex, 50phr of NR latex, and 1phr of K-Oleate were added to the container and stirred slowly. While stirring, 1.5 phr of sulfur, 3 phr of zinc oxide, 1 phr of ZDEC and ZMBT were added each, and then slowly stirred again, and the stirring speed was rapidly increased to foam. After foaming by the desired magnification, diphenylguanidine and sodium silicate were added by 2 phr each by lowering the speed, and the speed was slightly lowered to make the foam raw material even and stirred for 5 minutes and then terminated to complete the foam raw material. Subsequently, the mold preheated to 35°C was taken out of the oven, the foam material was poured, and cured in an oven at 95°C. After curing was completed, it was dried for 2 hours, and then the mold was taken out and the finished PV latex foam was separated.

<Experimental Example>

In order to test the physical properties of the PV latex foam, the other conditions are the same, but the specific gravity, tear strength, compression set (C/S), workability and the specimen are prepared by manufacturing specimens with only the weight ratio of PV latex and NR latex mixed. The state was checked, and the experimental results are shown in Table 1 below.

Psalter PV Latex: NR Latex
(Weight ratio) importance
(g/cm3) Tear strength
(kgf/cm) C/S
(%) Workability Specimen condition One 0:10 0.2542 4.3 8.40 △ ○ 2 1:9 0.2601 4.0 8.20 △ ○ 3 2:8 0.2596 4.4 6.90 ○ ◎ 4 3:7 0.2764 4.8 6.20 ◎ ◎ 5 4:6 0.2661 4.3 3.75 ◎ ◎ 6 5:5 0.2500 4.2 4.00 ◎ ◎ 7 6:4 0.2527 4.2 4.25 ◎ ◎ 8 7:3 0.2588 4.1 3.05 ◎ ◎ 9 8:2 0.2649 3.8 3.70 ◎ × 10 9:1 0.2623 3.7 7.50 ◎ × 11 10:0 0.2583 3.3 7.00 ◎ ×

Referring to Table 1, in the case of workability, whether the gel time (the time required for the foam raw material to solidify) is long or short, and the processing stability ◎: very good, ○: excellent, △: insufficient, × : Marked as defective, and in the case of the specimen state, whether there is a crack on the surface and whether it is not torn off by sticking to the mold (or there is no difficulty in demoulding) ◎: Very excellent, ○: Excellent, △: Insufficient, ×: In the case of the specimen will be.

First of all, in the case of specific gravity, it was found that most of the specimens were around 0.2 g/cm 3 and had good specific gravity.

In the case of tear strength, it was found that the degree of resistance to tearing after cutting the specimen was tested. Since most were around 3 or 4 kgf/cm, it was found to be within a relatively similar numerical range.

In the case of the permanent compression ratio (C/S), the lower the value, the more the elastic modulus is recovered without loss.The weight ratio of PV latex and NR latex is 0:10, 1:9, 2:8 and 3:7. The weight ratio of PV latex and NR latex is 4:6, 5:5, 6:4, 7:3 and 8, compared to the case of 9:1 and 10:0 in which PV latex is mixed with 90% or more. In the case of 2, the value was lower, indicating that the elastic modulus was excellent due to the cells formed in the specimen during the final solidification process.

In the case of workability and specimen state, the weight ratio of PV latex and NR latex is ×, since the specimen state of 8:2, 9:1 and 10:0, when the content of PV latex increases to 80% or more, the foam raw material is It was confirmed that the mold was not easily demolded because it was attached to the mold.

On the contrary, as in the case where the weight ratio of PV latex and NR latex is 3:7, 2:8, 1:9 and 0:10, when the content of NR latex increases to 70% or more, the shrinkage of the specimen increases, It could be seen that the gel time was shortened.

From these results, it was found that specific gravity, tear strength, permanent compression rate, workability, and specimen condition were all excellent only in the case of specimens in which the weight ratio of PV latex and NR latex was 4:6, 5:5, 6:4 and 7:3. Able to know.

Therefore, according to the present invention, 20 to 70 phr of PV latex and 30 to 80 phr of NR latex are used, but the PV latex and NR latex are appropriately controlled within the weight ratio of 3 to 7:3 to 7, so that the inside and outside are It is meaningful to obtain a PV latex foam with improved crosslinking density by uniformly crosslinking.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention.

Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments.

The scope of protection of the present invention should be interpreted by the claims, and all technical thoughts within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (3)

An internal crosslinking step of crosslinking the inside of the latex to form PV latex (Pre-Vulcanized latex);
PV/NR mixing step of first stirring the PV latex, NR latex, and oleate;
A foaming step of foaming while second stirring after adding an additive containing sulfur during the first stirring process;
A gelling step of adding diphenylguanidine and sodium silicofluoride in the foaming process, followed by third stirring to form a foam raw material; And
Processability comprising: an external crosslinking step of forming a pre-Vulcanized latex foam crosslinked outside by curing the foam raw material in a mold and then curing at 90 to 100°C. Manufacturing method of excellent PV latex foam. The method of claim 1,
The oleate salt in the PV/NR mixing step,
A method of manufacturing a PV latex foam having excellent processability, characterized in that it is potassium oleate (K-Oleate). The method of claim 1,
The additive in the foaming step,
PV latex having excellent processability, characterized in that it further comprises at least one of zinc diethyldithiocarbamate (ZDEC), zinc 2-mercaptobenzothiazole (ZMBT), and zinc oxide Method of making the foam.

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