KR20160056645A - Process for preparing Latex Foam - Google Patents

Abstract

The present invention relates to a preparation method for latex foam, and more specifically, to a method for easily preparing latex foam with low density, wherein the degree of foaming and liquid-state foam density of the latex foam are controlled by using fatty acid alkali metal salt and inert gas, without using a chemical foaming agent.

Description

Technical Field [0001] The present invention relates to a process for preparing latex foam,

The present invention relates to a method for producing latex foam, and more particularly, it relates to a method for producing a latex foam by controlling the degree of foaming of a latex foam and the density of a liquid foam using a fatty acid alkali metal salt and an inert gas without using a chemical foaming agent And to a method for producing the same.

Generally, latex foam is produced by crosslinking after adding a stabilizer, a sulfur, a vulcanization accelerator, an antioxidant, a foam stabilizer, a filler, a foaming agent, and the like as a usual additive with a rubber component as a main raw material. The rubber component used as the main raw material of the latex may be a natural material, or a synthetic material may be mixed with a natural material. Latex foam has many pores, elasticity and resilience because it forms curing by forming thousands of pinholes and millions to tens of millions of minute bubbles during liquid phase foaming process. Latex foams are used in a wide range of applications in various fields. For example, latex foam can be used as a cushioning material to reduce impact or friction by being put into furniture, mattress, or pillow. Also, in the case of a latex foam produced by mixing a foaming agent into the latex during the vulcanization process to form a small, closed honeycomb bubble, the foam can be used as a heat insulator such as a refrigerator. In addition, a latex foam molded into a mold and thinly formed can be used as a gasket, a windshield, a vibration reduction material, and the like. In addition, the use of latex foam is very diverse.

A conventional technique related to a method for producing a latex foam will be described below.

The Korean Registered Utility Model Publication No. 20-0400950 (Patent Document 1) divides a mattress into a plurality of planar regions according to the degree of physical load applied by a user, measures the size and distribution density of pinholes in the mattress, So that a relatively high supporting force can be exerted in the portion of the mattress which is subjected to a high body load such as the waist and the buttocks in comparison with the other portions. The above Patent Document 1 refers to a method of controlling foaming by using a physical foaming machine as a method of controlling the degree of foaming of latex, but there is no specific mention on the method of controlling foaming degree.

In Korean Patent Laid-Open Publication No. 10-2007-0026934 (Patent Document 2), the aged latex raw solution is foamed for 30 to 40 minutes by using a physical foaming machine developed directly. If the foaming time is less than 30 minutes, the latex mattress is excessively And tends to become too soft if it exceeds 40 minutes. In the case of controlling the degree of foaming using only the physical foaming machine as in the above-mentioned Patent Document 2, there is a limitation in controlling the degree of foaming to a desired level or less by the interface phenomenon of the latex blend system.

In Korean Patent Laid-Open Publication No. 10-1998-0042003 (Patent Document 3), an open-celled foam structure is disclosed by foaming an elastic body using a chemical foaming agent.

However, according to the presently disclosed method, there is no disclosure in the literature of controlling the foam and density of a desired latex formulation by controlling the surface tension of a latex formulation without using chemical foams as a method of controlling latex foam foaming.

Korea Registration Practical Publication No. 20-0400950, "Latex Mattress" Korean Patent Laid-Open Publication No. 10-2007-0026934, "Latex mattress and its manufacturing method" Korean Patent Publication No. 10-1998-042003, "Foam Structure"

The present invention provides a method for producing a latex foam in which the foam and density of the latex foam can be easily controlled without using a chemical blowing agent.

That is, in the conventional method of producing a latex foam, the minimum foaming density is limited by physical liquid phase foaming with a gas injection amount as a variable. However, in the present invention, liquid foam is prepared by controlling the surface tension of a compound using an alkali metal salt of fatty acid and an inert gas It is possible to easily produce a latex foam having a physical property suitable for being applied to an automobile seat while having a low density.

In order to solve the above problems,

a) blending the latex with a conventional latex additive in which the fatty acid alkali metal salt and blowing agent are excluded;

b) aging the combination at a temperature of 30 to 50 DEG C and 10 to 50 rpm for 12 to 24 hours;

c) adjusting the density of the aged formulation by foaming the liquid while injecting inert gas from the outside at a flow rate of 50 to 100 mL / min;

d) gelling and crosslinking the densely-adjusted formulation at a temperature of from 100 to 130 占 폚 to form a product; The present invention also provides a method for producing a latex foam.

1 is an overall process diagram of a method for producing a latex foam according to the present invention.
FIG. 2 is a cross-sectional view of a latex foam molded under different liquid phase foaming conditions, wherein (A) is a cross-sectional view of a latex foam subjected to liquid phase foaming through physical agitation, (B) Sectional view of a latex foam.
3 is a graph showing the effect of the content of the vulcanization accelerator on the crosslinking process.
Fig. 4 is a graph showing the effect of temperature on the crosslinking process.
5 is a graph showing the modulus change of the latex foam according to the temperature through dynamic mechanical analysis.
6 is an SEM photograph of a foam foamed in a liquid state by varying the content of potassium oleate.

Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings. In the following description, a description of well-known structures will be omitted. Those skilled in the art will readily understand the characterizing features of the present invention.

FIG. 1 is a schematic view showing the overall process of a method for producing a latex foam according to the present invention.

As shown in FIG. 1, the method of producing the latex foam of the present invention can be divided into four stages: a) a latex mixing step; b) aging of the formulation; c) liquid phase foaming of the aged formulation; And molding the product through gelling and crosslinking; .

Hereinafter, a method of producing a latex foam according to the present invention will be described in more detail.

a) Formulation step

This mixing step is a process of compounding a latex additive with a fatty acid alkali metal salt and a blowing agent removed in the latex liquid. The mixing may be performed by a ball mill process or a paste mixer process. Concretely, the ball milling process is performed at 50 to 100 rpm for 3 to 5 days, or the paste mixer process is performed at 1000 to 1500 rpm for 40 to 60 minutes.

In the compounding step of the present invention, rubber latex is used as the main raw material and conventional latex additives such as fatty acid alkali metal salts are used as the additives. In the present invention, the content of the constituents is based on 100 parts by weight of the dry rubber content of the rubber latex used as the main raw material, unless otherwise specified.

In the present invention, the rubber latex may be a natural rubber latex or a mixture of a natural rubber latex and a synthetic rubber latex. Natural rubber latex includes both ammonia-treated natural rubber latex and untreated natural rubber latex. The ammonia-treated natural rubber latex is concentrated to a solid content of about 60% by centrifugation, and may contain about 0.6 to 0.8% of ammonia as a preservative. On the contrary, the untreated natural rubber latex means that the ammonia component as a preservative is not added in a separate process. In the present invention, when the ammonia-treated natural rubber latex is to be used as the main raw material, the "deammonia" step must be performed in advance. Ammonia remaining in the latex acts as a scavenger in cross-linking of latex and sulfur during the cross-linking process, which hinders the reaction and improves the stability of latex particles, thereby negatively affecting liquid phase foaming and gelation. Therefore, it is preferable to remove ammonia remaining in the latex concentrate prior to the mixing process according to the present invention through appropriate temperature and physical stirring. That is, it is preferable that the ammonia-treated latex is subjected to a deammoniation process through physical stirring at 30 to 50 ° C and 50 to 100 rpm as a pretreatment process. On the other hand, the synthetic rubber latex is preferable because the product produced by emulsion polymerization at a low temperature has a constant and low surface tension. Examples of the synthetic rubber latex include styrene-butadiene latex, chloroprene latex, oil-resistant latex (NBR LATEX) May be included.

In the compounding process according to the present invention, an alkali metal salt of fatty acid and a conventional latex additive are used as an additive. In particular, the present invention does not include a chemical foaming agent as a latex additive, but instead uses a fatty acid alkali metal soap. The fatty acid alkali metal salt may be an alkali metal salt such as a saturated or unsaturated C ₆ -C ₂₀ higher fatty acid, a fatty acid of torus, a resin acid, or a naphthenic acid. The fatty acid alkali metal salts specifically include sodium oleate, sodium stearate, sodium laurate, potassium oleate, potassium stearate, potassium laurate, potassium laurate, and potassium olate is preferably used.

The fatty acid alkali metal salt acts as a foam promoter, which reduces the surface tension in the subsequent liquid phase foaming step, and accordingly increases the surface area of the foam-producing surface area, i.e., the entire foam, The lower the density of the liquid foam is. This principle can be expressed by the following equation (1).

[Equation 1]

W =? DELTA A

(In the above-mentioned equation (1), W is the day of application,? Is the surface tension, and? A is the bubble generation surface area)

As shown in Equation (1), when the applied work (W) is fixed, the surface tension (γ) and the bubble generation surface area (ΔA) are variables. In case of increasing the work done, the surface area of the foam increases with a certain level of force, so that the density of the liquid foam can be lowered. However, when a certain level of force is applied, heat is generated inside due to physical friction, do. Based on the above-described principle, the liquid phase foaming density of the latex can be lowered by lowering the surface tension while changing the content of the fatty acid alkali metal salt as a foam promoter.

In the present invention, the fatty acid alkali metal salt used as a foam promoter is used in an amount of 0.1 to 4 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of latex dry weight. If the content of the fatty acid alkali metal salt is less than 0.1 parts by weight, the effect of reducing the liquid phase foaming density of the latex is insufficient. If the amount of the fatty acid alkali metal salt is more than 4 parts by weight, the liquid phase foaming degree is excessively increased, which adversely affects the stability of the foamed cell .

In the present invention, in addition to the alkali metal salts of fatty acids, conventional additives commonly used in the production of latex foams may include additives such as sulfur, vulcanization accelerators, antioxidants, foam stabilizers, and fillers. In addition, no chemical foaming agent is included as a usual additive.

The sulfur (S) is used to crosslink the rubber latex raw material. The sulfur is used in an amount of 1 to 5 parts by weight, preferably 1 to 3 parts by weight based on 100 parts by weight of the latex dry weight. If the content of sulfur is less than 1 part by weight, crosslinking is so small that it is difficult to properly realize performance as a latex foam, and if it is used in excess of 5 parts by weight, the degree of curing of the latex foam is too much.

The vulcanization accelerator is used for shortening vulcanization time and temperature when vulcanization is carried out. As the primary vulcanization accelerator, zinc diethyldithiocarbamate (ZEC) and zinc dibutyldithiocarbamate (ZBC) can be used as a zinc dialkyl dithiocarbamate, and 100 parts by weight of a latex dry weight 0.1 to 3 parts by weight, preferably 0.4 to 1.6 parts by weight, based on the weight of the composition. Zinc mercaptobenzothiazole (ZM) may be used as the secondary accelerator, and may be used in an amount of 0.1 to 3.0 parts by weight, preferably 0.4 to 1.2 parts by weight, based on 100 parts by weight of the latex dry weight.

The antioxidant is added during processing or after processing to prevent oxidation of the latex particles by oxygen contact. As the antioxidant, a phenol-based antioxidant including styrylated phenol (SP) and 2,2'-methylenebis (4-methyl-6-tert-butylphenol) may be used. The antioxidant may be used in an amount of 0.1 to 3.0 parts by weight, preferably 0.5 to 1 part by weight based on 100 parts by weight of latex dry weight.

The foam stabilizer is used to smoothly perform the gelation reaction and is added to prevent bubble collapse and gel shrinkage. The bubble stabilizer is preferably TRIMEN BASE (TM) of Nogajin Chemical Co., or VULCAFOR EFT of ICI. The bubble stabilizer may be used in an amount of 0.1 to 3.0 parts by weight, preferably 0.5 to 2.0 parts by weight, based on 100 parts by weight of latex dry weight.

The filler can be used in terms of cost reduction. Clay, calcium carbonate, talc, aluminum hydroxide, and the like may be used as the filler, and powdery mica and magnesium silicate may be used. Preferably, the filler has an average particle size of about 5 microns. The filler may be used in an amount of 0.1 to 5.0 parts by weight, preferably 1.0 to 3.0 parts by weight based on 100 parts by weight of latex dry weight.

In addition, stabilizers, softeners, and the like may be used as ordinary additives used in the production of the latex foam.

b) Aging step

This aging step is a process of stabilizing the latex formulation while removing the ammonia remaining in the latex while aging the latex formulation at a specific temperature and stirring speed. Specifically, the latex compound is stirred at a low temperature of 30 to 50 DEG C and 10 to 50 rpm for 12 to 24 hours. During the aging step, the ammonia remaining in the latex formulation can be completely removed. In addition, the aggregation characteristics of latex formulations could be improved by passing through the aging step, specifically reducing Willis plasticity and pattern viscosity. If the conditions at the aging step are more severe than the conditions proposed by the present invention, storage hardening may occur and the latex rubber particles may be naturally crosslinked by aldehyde, epoxy and amino acid groups and leached as a solid material, It is preferable to maintain the conditions proposed by the present invention.

c) Liquid phase foaming step

This liquid phase foaming step is a process of adjusting the density by foaming physical liquid while injecting an inert gas at a constant rate into the latex mixture thus aged. Specifically, the aged latex blend is foamed in a liquid phase using a homogenizer or a physical stirrer, and the density of the foam is adjusted by liquid foaming while an inert gas is injected at a flow rate of 50 to 100 mL / min from the outside. FIG. 2 is a SEM photograph of a cross-sectional view of a latex foam molded under different liquid foam conditions. FIG. 2 (A) is a cross-sectional view of a latex foam subjected to liquid foaming through physical agitation. 2 (B) is a cross-sectional view of a latex foam in which physical stirring and nitrogen gas injection are simultaneously performed. As shown in FIG. 2 (A), when physical foaming is performed using only a homogenizer and a physical stirrer, the foamed foam forms a closed cell. However, as suggested by the present invention, by using a homogenizer and a physical stirrer and injecting a suitable inert gas at the same time as liquid foam, the time required for foaming to the target liquid foam density is short, and the foam foam forms an open cell . It is best to keep the condition of injecting nitrogen gas (N ₂ ) at a flow rate of 50 to 100 mL / min along with physical stirring of 500 to 2000 rpm during liquid foaming.

It is preferable that the density of the foamed foam produced in the liquid phase foaming step is maintained at 0.1 to 0.49 g / mL.

d) Product molding step

This product molding step is a step of gelling and crosslinking the densely adjusted latex blend to form a product.

The gelation is a process for raising the viscosity of the liquid foamed latex formulation to improve the stability of the foam during the crosslinking process. Since the gelation reaction is influenced by various variables such as the alkalinity of latex, the content of alkali metal salt of fatty acid, and the gelation temperature, the content of the gelling agent may also vary depending on the recipe recipe, the process environment, and the desired viscosity. Preferably, when silicofluoride (SSF) is used as the gelling agent, the silicofluoride slowly lowers the pH of the latex formulation by hydrolysis as a delayed gelling agent, and after about 8 minutes gelling starts at pH 8.6 until complete gelation The blending amount of the gelling agent having a required time of about 2 minutes is appropriate. The gelling agent may be appropriately adjusted in the range of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight based on 100 parts by weight of the latex dry weight.

The crosslinking is a process for molding a gelled latex formulation. The rubber is basically a polymer liquid with low elasticity and strength, but the molecules are entangled but can easily be released by external force and become a viscous fluid. Through the crosslinking process on these rubbers, bonding between the rubber molecular chains can be made to reduce the slippage of the chains, thereby greatly increasing the elasticity and reducing the permanent compression shrinkage and hysteresis.

In the crosslinking of the present invention, the form of the crosslinking agent and the vulcanization accelerator may be roughly divided into three types depending on the content of the crosslinking agent and the vulcanization accelerator relative to the dry weight of the latex. First, in the case of a conventional system, the content of sulfur is 2.0 to 3.5 parts by weight and the content of the vulcanization accelerator is 1.2 to 0.4 parts by weight based on 100 parts by weight of latex dry weight. Poly and disulfidic bridges are mainly formed so that the heat aging resistance and the low reversion resistance are low and the low temperature crystallization resistance is excellent . Secondly, in the case of the Semi-EV system, the content of sulfur is 1.0 to 1.7 parts by weight and the content of the vulcanization accelerator is 2.5 to 1.2 parts by weight based on 100 parts by weight of latex dry weight. Poly and disulfidic bridges and monosulfidic bridges coexist at a similar rate and thus exhibit heat aging resistance, reversion resistance, low temperature crystallization resistance (Low temperature crystalization resistace. Thirdly, in EV system, the content of sulfur is 0.4 to 0.8 parts by weight and the content of vulcanization accelerator is 5.0 to 2.0 parts by weight based on 100 parts by weight of latex dry weight. Monosulfidic crosslinking is mainly formed so that it has excellent heat aging resistance and reversion resistance and is low in low temperature crystallization resistance.

In the crosslinking of the latex blend, it is preferable to optimize the combination effect and the crosslinking property according to the content of the crosslinking agent and the vulcanization accelerator through experiments. 3, the content of sulfur as a crosslinking agent was fixed to 1.6 parts by weight based on 100 parts by weight of latex dry weight, and zinc diethyldithiocarbamate (ZEC) as a primary vulcanization accelerator and zinc mercapto Benzothiazole (ZM) is used in combination with ZEC and ZM in a total amount of 1.6 parts by weight based on 100 parts by weight of the latex dry weight, and the optimum ratio of the vulcanization accelerator of Curemeter. 3, it can be seen that the crosslinking system using 1.2 parts by weight of ZEC as the primary vulcanization accelerator and 0.4 part by weight of ZM as the secondary vulcanization accelerator is the most efficient.

Setting of the crosslinking temperature in the crosslinking step of the present invention is an important factor. In the present invention, gelation and crosslinking proceed in the temperature range of 100 to 130 ° C.

Depending on the proper crosslinking temperature, crosslinking properties may appear in three forms: Creeping, Plateau, and Reversion. Creeping means that the polysulfidic bonding structure is generated much during the initial crosslinking reaction and the crosslinking time is increased so that the bonding is broken and new crosslinking is carried out to thereby continuously increase the total crosslinking degree to a certain level . Plateau means that the bridge has a stable structure after maintaining the optimum crosslinking torque. Reversion means that the molecular chain truncation occurs severely and the torque is reduced after showing the optimal bridge torque. FIG. 4 shows crosslinking characteristics according to temperature. It was confirmed that the crosslinking reaction with the most stable structure proceeded with respect to the compounding recipe as a result of satisfying the Plateau curve at a crosslinking temperature of 110 ° C.

The latex foam prepared according to the above-described production method has a tensile strength of 0.24 to 0.31 kg / cm 2 and a fracture elongation of 150 to 360% while maintaining a liquid foam density of 0.1 to 0.49 g / mL. Accordingly, the latex foam produced in the present invention is useful as a seat material for an automobile.

The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited thereto.

[Example]

Example 1.

A latex consisting of 80% by weight of natural rubber latex and 20% by weight of styrene-butadiene rubber latex was prepared as a main raw material, and the styrene-butadiene rubber latex was subjected to a deammonia process in advance.

1.5 parts by weight of potassium oleate, 1.6 parts by weight of sulfur, 1.2 parts by weight of zinc diethyldithiocarbamate (ZEC) as a primary vulcanization accelerator, 0.2 part by weight of zinc mercaptobenzoate as a secondary vulcanization accelerator, 0.4 part by weight of thiazole (ZM), 2.4 parts by weight of zinc oxide (ZnO) as a crosslinking activator and 0.8 parts by weight of sodium silicofluoride (SSF) as a gelling agent were prepared.

The prepared raw material was added to distilled water and then subjected to a paste mixer (for 40 to 60 minutes at 1000 to 1500 rpm) or a ball mill (for 3 to 5 days at 50 to 100 rpm) to disperse evenly to obtain a latex blend. The latex formulation was aged for 24 hours at 40 < 0 > C temperature and low speed stirring at 40 rpm. The aged formulations were liquid foamed while nitrogen gas was injected at a rate of 80 mL / min with stirring at a stirring speed of 1,000 rpm using a physical stirrer. After the physical liquid phase foaming, the latex foam product was obtained by gelation and crosslinking at a temperature of 110 ° C.

The tensile strength and modulus of the prepared latex elastomer foam were measured by a tensile strength test (SHIMADZU, AGS-500D). The results are shown in Table 1 below. The hysteresis test was conducted to examine energy consumption by viscous damping according to elongation and relaxation of the latex foam. The results are shown in Table 2 below. In order to investigate the change of modulus depending on the temperature of the prepared latex foam, the tangent delta was determined according to the temperature of a sample prepared using a dynamic mechanical analyzer (DMA, TA instruments, 2980 DMA v1.7B) Is shown in Fig.

[DMA test condition]

Frequency in tension: 1 HZ

Amplitude: 15 ㎛

Temperature: -100 to 200 ° C

Heating rate: 5 ° C / min

division Module (Mpa) The tensile strength Elongation at break (%) 100% 300%
Latex foam 0.09 0.19 0.26 372.20 0.08 0.16 0.26 427.80 0.07 0.16 0.23 311.10 0.07 0.15 0.23 300.00 0.11 0.25 0.30 427.80 Average 0.10 0.21 0.25 367.78 Error (±) 0.01 0.08 0.02 54.8

division Hysteresis loss rate Primary Secondary Third Specimen A 10.57% 6.60% 5.50% Psalm B 9.36% 6.39% 4.89% Piece C 14.48% 9.43% 9.82% Average 11.14% 7.47% 6.74%

Table 1 shows the 100%, 300% modulus, tensile strength and elongation at break of latex foam specimens. According to Table 1, the mechanical properties of a sample taken from an arbitrary portion of the manufactured latex foam specimen can be confirmed.

In Table 2, the hysteresis test was repeated three times and the 100% elongation test was performed on the sample taken at an arbitrary portion, and the results of the three specimens were expressed as an average value.

Further, according to the results of the dynamic mechanical analysis of FIG. 5, a peak estimated as a glass transition temperature (Tg) and a semi-crystallization degree in a rubbery plateau were measured in a temperature range of -100 ° C. to 200 ° C., And the peak estimated as. From the viewpoint that the rubber flat region is formed at -20 캜 to 110 캜, it can be seen that the latex foam of the present invention has a wide application temperature range of -20 캜 to 110 캜.

Example 2 Change of Foam Density According to Alkali Metal Salt Content of Fatty Acids

In carrying out the process for preparing a latex foam according to Example 1, the content of potassium oleate was varied to 0, 0.5, 1.0, and 1.5 parts by weight based on 100 parts by weight of latex dry weight, Respectively. The results are shown in Table 3 below. The results of measurement of the liquid phase foaming density according to the content of potassium oleate and the SEM photographs of the foam density are shown in FIG.

division   Potassium oleate (parts by weight) 0 0.5 1.0 1.5 Liquid foam density
(g / mL) 0.61 0.49 0.33 0.18

Claims (9)

a) blending the latex with a conventional latex additive in which the fatty acid alkali metal salt and blowing agent are excluded;
b) aging the combination at a temperature of 30 to 50 DEG C and 10 to 50 rpm for 12 to 24 hours;
c) adjusting the density of the aged formulation by foaming the liquid while injecting inert gas from the outside at a flow rate of 50 to 100 mL / min;
d) gelling and crosslinking the densely-adjusted formulation at a temperature of from 100 to 130 占 폚 to form a product;
≪ / RTI >
The method according to claim 1,
And 0.1 to 4 parts by weight of a foam promoter of an alkali metal salt of fatty acid based on 100 parts by weight of the dry weight of the latex.
The method according to claim 1,
Wherein the fatty acid alkali metal salt is potassium oleate.
The method according to claim 1,
Wherein the mixing is performed by a ball milling process at 50 to 100 rpm for 3 to 5 days or a paste mixer process at 1000 to 1500 rpm for 40 to 60 minutes.
The method according to claim 1,
Wherein the liquid phase foaming is performed under physical stirring conditions of 500 to 2000 rpm.
The method according to claim 1,
Wherein the inert gas is nitrogen (N ₂ ) gas.
The method according to claim 1,
Wherein the density of the liquid foamed formulation is 0.1 to 0.49 g / mL.
A latex foam produced by the method of any one of claims 1 to 7, wherein the liquid foam density is 0.1 to 0.49 g / mL, the tensile strength is 0.24 to 0.31 kg / cm 2, and the elongation at break is 150 to 360%.
A car seat comprising the latex foam of claim 8.

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