JPH0558457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to an elastic composite, and more particularly to a water-containing elastic composite made of silicone rubber that has an endothermic action utilizing the heat of fusion of water.

≪Prior Art≫ It has long been known that a water-containing composite obtained by decomposing water in rubber or rubber-like plastic is useful as a highly flexible base material for cold insulation materials, heat absorbing materials, poultices, etc. In particular, it is known that the dispersion stability of water can be improved by absorbing water into a superabsorbent resin powder to form a microgel and dispersing it in liquid rubber to substantially disperse the water. (For example, Japanese Patent Publication No. 62-54344). However, the liquid rubber used in these conventional techniques has -
Not only does it lose its elasticity at low temperatures below 20℃, but because the microgel used is large, it exists as a large foreign substance in the liquid rubber matrix, and even when mixed and stirred, the microgel is difficult to break into small pieces, resulting in a homogeneous water-containing composite. In addition to being difficult to obtain, microgels tend to aggregate when kept at low temperatures.

<<Problems to be Solved by the Invention>> As a result of intensive studies to solve these conventional drawbacks, the inventors of the present invention have developed a method of absorbing water into fine powder of a super absorbent resin and controlling the amount of water absorption as necessary. By controlling the size of the microgel, dispersing the microgel in an addition-curing liquid silicone rubber, and curing the dispersion at around room temperature, the microhydrogel can exist uniformly and stably, making it excellent for low-temperature retention. The inventors have arrived at the discovery that a rubber elastic body with low hardness can be obtained.

Therefore, a first object of the present invention is to provide a hydrous elastic composite whose hardness does not change over a wide range of low temperatures and which is convenient for use as a cold insulator.

A second object of the present invention is to provide a water-containing elastic composite that does not cause aggregation of microhydrogel and can be repeatedly used as a cold insulator for a long period of time.

A third object of the present invention is to provide a high-performance hydrous elastic composite that maintains cold storage for a long time.

≪Means for Solving the Problems≫ The above-mentioned objects of the present invention are to uniformly disperse a microhydrogel obtained by water-swollen super absorbent resin powder in an addition-curable liquid silicone rubber matrix, and to disperse the resulting mixture into This was achieved by using a hydrous elastic composite made of silicone rubber that is crosslinked using a hydrogen atom containing hydrogen atoms bonded to silicon atoms.

The addition-curing liquid silicone rubber used as the matrix in the present invention mainly contains a diorganopolysiloxane containing an unsaturated group such as a vinyl group, an organohydrodiene polysiloxane containing a hydrogen atom bonded to a silicon atom, and a platinum-based catalyst. Among these, the organopolysiloxane containing an unsaturated group preferably has at least two alkenyl groups directly bonded to a silicon atom in one molecule. Further, the viscosity of this unsaturated group-containing organopolysiloxane at 25° C. is preferably 500 cs or more. If the viscosity is too low, separation of the uniformly dispersed microhydrogel will occur, which is not preferable.

The crosslinking agent used in the crosslinking treatment in the addition-curable liquid silicone rubber of the present invention is one that performs an addition reaction with the diorganopolysiloxane to crosslink the diorganopolysiloxanes, and is usually a hydrogen atom directly bonded to a silicon atom. It is a hydrogen polysiloxane containing.

Such hydrogen polysiloxane must have at least two hydrogen atoms in one molecule, and the chain length of the diorganopolysiloxane molecule can be extended by carrying out an addition reaction to the diorganopolysiloxane. , the hardness of the cured product can be lowered and the strength can be increased. Moreover, the elastic modulus of the cured product after crosslinking can be controlled by the combination with the hydrogen polysiloxane having three or more hydrogen atoms.

The microhydrogel used in the present invention is a superabsorbent resin powder that absorbs water. The shape of the powder before water absorption is preferably as close to spherical as possible, and the particles are preferably fine. The resin swells when it absorbs water, and for example, the particle size before absorbing water decreases.
A 10 μm gel becomes approximately 50 μm when water is added 100 times by weight, but microhydrogel in the present invention preferably has a particle size of 1000 μm or less after water absorption.
Particles that have a large particle size before water absorption are undesirable because they become too large after water absorption, are dispersed in the matrix as foreign matter, and are difficult to form uniformly. In order to correct such inconveniences, it is not necessary to use the superabsorbent resin powder in a state where it has absorbed maximum water. In the present invention,
The water absorption amount can be selected appropriately depending on the type of resin and particle system, but it is usually used at a water absorption state of 10 to 1000 times the weight, and the amount of water contained in the total weight of the water-containing composite is about 60% by weight or less. It is appropriate to do so.

If the water content is too large, the softness at low temperatures (when water freezes) will be poor, which is not preferable.

The super-absorbent resin is a water-insoluble hydrophilic resin obtained by introducing appropriate intermolecular crosslinks into a water-soluble polymer having a hydrophilic group such as a hydroxyl group, a carboxyl group, or a salt thereof using a crosslinking agent and/or by radiation, etc. can be mentioned. Specific examples of such super absorbent resins include acrylic acid/vinyl alcohol copolymers, sodium acrylate polymers, starch/polyacrylate polymers, polyethylene oxide polymers, and isobutylene/maleic anhydride. system polymers, etc.

In the present invention, microhydrogel in a water-absorbing state made by absorbing water into these superabsorbent resin powders is stirred and dispersed in an uncured liquid silicone rubber matrix, defoamed, and heated from room temperature to 60°C.
Cure silicone rubber at a temperature range of . 60℃
If the temperature is higher than that, the entire composition tends to become foamed, so it is preferable to cure the composition at a temperature as close to room temperature as possible.

A platinum catalyst is used in the addition reaction of the diorganopolysiloxane and hydrogen polysiloxane for curing the silicone rubber, and the reaction is appropriately controlled using a control agent. The platinum catalyst and control agent used here are those used in ordinary addition-type liquid silicone rubbers.

In the present invention, an inorganic filler (for example, fumed silica, wet silica, diatomaceous earth, etc.) can be appropriately added from the viewpoint of the dispersion effect of the addition-curing liquid silicone rubber and the microhydrogel, and reinforcing properties.

Surfactants are also effective in obtaining stable hydrous complexes.

In particular, by controlling the type and amount of organohydrodiene siloxane used as a crosslinking agent in addition-curing liquid silicone rubber, we can achieve extremely low hardness, such as a sponge hardness of 10 (Asker C) or less immediately after freezing. It is also possible to obtain a rubber elastic body with hardness.

After curing, the hydrous elastic composite of the present invention produced as described above may be used as it is, but in some cases, it may be placed in a packaging bag such as an ordinary vinyl bag and given in any form. It is also possible to form it into a shape and then harden it. In addition, there are various uses such as cold insulation materials (for a good night's sleep, cold pillows for when you have a fever, cold support for affected areas for sports), heat insulation materials, heat absorbing materials, fire prevention materials, pad materials, etc.

≪Effects of the Invention≫ The hydrous elastic composite made of silicone rubber of the present invention has the following effects:
Water with a large heat of fusion is absorbed into the superabsorbent resin in the addition-curing low-hardness silicone rubber composition (which also includes silicone gel), which is the matrix, and this is uniformly dispersed and cured in the matrix. Not only does water not separate even when pressure is applied, but even if the microgel freezes during freezing, the silicone rubber matrix has excellent low-temperature properties, so it can maintain its rubber elasticity. In addition, it has extremely excellent low temperature retention performance near 0°C.

The present invention will be explained in more detail below with reference to Examples.
The present invention is not limited thereby.

Example Both ends of the molecular chain are blocked with dimethylvinyl groups, viscosity 1000cs, vinyl group content 0.01mol/100g
100 parts by weight of dimethylpolysiloxane, 2 parts by weight of fumed silica (surface treated with trimethylchlorosilane) with a specific surface area of 200 m ² /g, and 0.2 parts by weight of a 1% isopropyl alcohol solution of chloroplatinic acid.
Parts by weight were mixed uniformly.

Next, 70 parts by weight of microhydrogel was prepared by preabsorbing 1 part by weight of super absorbent resin powder SP-510 (Product No. manufactured by Sumitomo Chemical Co., Ltd.) with a particle size of about 10 μm before water absorption into 100 parts by weight of water. was uniformly mixed into the above composition, and further added as a crosslinking agent, 2.1 parts by weight of dimethylpolysiloxane with a viscosity of cs, which was blocked at both ends with dimethylhydrodiene groups, and methylhydrodiene polysiloxane with a viscosity of cs having 30 mol% of methylhydrogen siloxane units. 0.6 parts by weight of siloxane was added and mixed with a stirrer to form a homogeneous substance. Next, this was defoamed to remove air bubbles in the system, and left to stand at 30°C for 30 minutes to cure.

The obtained cured product had extremely low hardness, with a sponge hardness (Asker C) of 1 or less. Next, in order to examine the low temperature retention properties of this cured product, we cut out a 40 mm square cube and placed it in a -10℃ freezer for 16 hours to freeze it.The result was a sponge hardness (Asker C) of 2 points, which was a big difference from before freezing. Nakatsuta. In addition, in order to evaluate the low temperature retention characteristics, the above-mentioned cooled cube was left at room temperature and the temperature rise at the center of the cube was examined using a thermocouple. It was found that the temperature retention property was extremely excellent. Furthermore, the sample showed excellent elasticity even when frozen at -40°C.

For comparison, commercially available ice packs A and B were also made in the same shape and the temperature rise at the center was measured using the same method. As shown in Figure 1, these temperature rises were better in the case of the present invention. It was extremely fast.

These results demonstrated that the silicone rubber hydrous composite of the present invention does not become hard over a wide range of low temperatures and is a hydrous elastic composite with excellent low temperature retention properties.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the temperature retention characteristics at around 0° C. of commercial products A and B and the hydrous elastic composite of the present invention.

Claims (1)

[Claims] 1. A microhydrogel made by water-swollen a superabsorbent resin powder is uniformly dispersed in an addition-curable liquid silicone rubber matrix, and the resulting mixture is treated with a hydrogen polysiloxane containing hydrogen atoms bonded to silicon atoms. A water-containing elastic composite made of silicone rubber that has been cross-linked.