JPS5921341B2 - Method for producing expandable thermoplastic polymer particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing expandable thermoplastic polymer particles.

More specifically, the present invention relates to a method of greatly shortening the cooling time, which takes up a large amount of time during the molding process in the production of molded products having a cell structure, and obtaining good molded products. Conventional thermoplastic polymer particle foams are prepared by pre-foaming thermoplastic polymer particles containing a liquid or gaseous blowing agent at room temperature to a desired apparent specific gravity by steam heating in an open or sealed container.

The pre-expanded particles are allowed to stand for an arbitrary period of time to stabilize the internal conditions such as the distribution of the blowing agent within the particles to ensure homogeneous foaming, and then are pre-foamed by heating with steam in a mold to cause secondary foaming. The particles are fused together to produce the desired homogeneous molding. In molding after pre-foaming, it is necessary to hold the molded article in the mold for a certain period of time after steam heating.

If the molded article is taken out of the mold too soon, the molded article will expand or become distorted, making it impossible to obtain the desired exact shape. The time required for a molded product to remain in a mold in order to obtain a satisfactory molded product is generally referred to as the cooling time, and this cooling time is an important factor in producing a molded product. That is, the shorter the cooling time, the shorter the cycle for producing molded products, making it possible to increase the production amount per unit time. Many techniques have been reported for this purpose, including the addition of various substances within or on the surface of expandable thermoplastic polymer particles. However, although the conventional technology reduces the cooling time during molding, it is difficult to increase the expansion ratio during pre-foaming, and there are problems such as a large amount of water being contained inside the molded product during molding. be.

Furthermore, when a suspension system is employed, adding various additives during polymerization or before impregnation with a blowing agent tends to destabilize the system depending on the additive. In addition, a technique (Japanese Unexamined Patent Application Publication No. 1983-1982) of shortening the cooling time during molding by non-uniformly containing a substance capable of nucleation into the polymer particles in the late stage of polymerization or before impregnating the thermoplastic polymer particles with a blowing agent has been proposed. -64569) is publicly known.

However, if a thermoplastic polymer contains a substance capable of nucleation before impregnation with a blowing agent, fine flocculent resin will be generated, which is not practical. As a result of intensive research, the inventors of the present invention found that
We have now provided a manufacturing method that does not cause such problems, requires a short cooling time, and produces a good molded product.

That is, in the present invention, a nonionic surfactant is applied to the thermoplastic polymer particles containing the blowing agent at a temperature higher than the softening point of the particles during the latter half of the process of impregnating the blowing agent into the thermoplastic polymer particles or after the impregnation. The content includes a method for manufacturing expandable thermoplastic polymer particles to be impregnated. The details will be explained below. The term "expandable thermoplastic polymer particles" as used herein refers to polymer particles obtained by adding and polymerizing a blowing agent during polymerization, or by impregnating the blowing agent after polymerization.

For example, polystyrene, copolymers of styrene and other vinyl monomers, polymethyl methacrylate, copolymers of methyl methacrylate and other vinyl monomers, polymers obtained by impregnating or graft polymerizing polyethylene with a monomer mainly composed of styrene or methyl methacrylate. Thermoplastic polymer particles that can be foamed by heating, which are made to contain a foaming agent that is liquid or gaseous at room temperature during coalescence, or are impregnated after polymerization, even if they contain other additives. good. Nonionic surfactants to be impregnated into blowing agent-containing thermoplastic polymer particles include pentaerythritol ester, glycerin ester, sorbitan ester, polyoxyethylene sorbitan ester, polyoxyethylene alkyl ether, and polyoxyethylene polypropylene. Examples include ether and others.

The amount of nonionic surfactant to be impregnated into the blowing agent-containing thermoplastic polymer particles is 0.05% by weight or more based on the weight of the particles.1.
It is preferably 0% by weight or less, and most preferably in the range of 0.05% to 0.3% by weight.

A method for treating blowing agent-containing thermoplastic polymer particles with a nonionic surfactant is to treat the blowing agent with the blowing agent in a mixer equipped with a stirrer during the latter half of the process of impregnating the blowing agent into the thermoplastic polymer particles or after the impregnation. The nonionic surfactant may be mixed for a certain period of time at a temperature above the softening point of the particles.

The softening point of thermoplastic polymer particles containing a blowing agent varies depending on the particle type, and is about 60° C. for polystyrene containing butane as a blowing agent, for example.

This temperature will vary depending on the combination of blowing agent and thermoplastic polymer species. The temperature at which the nonionic surfactant is impregnated is higher than the softening point of the blowing agent-containing thermoplastic polymer particles, and is generally preferably 80 to 100°C. Further, the mixing time of the blowing agent-containing thermoplastic polymer particles and the nonionic surfactant must be 0.5 hours or more and 2 hours or less, that is, in the latter half of the blowing agent impregnation process or after the impregnation. Any blowing agent may be used to impregnate the thermoplastic polymer particles, but liquid or gaseous lower aliphatic hydrocarbons are preferable, such as propane, butane, pentane, or those containing these as main components. There is no problem in replacing a part of it with hexane, heptane, cyclohexane, methyl chloride, freon, etc.

The amount of the blowing agent added is 3.
A range of 0 to 15.0% by weight is preferred. In addition, before and after treatment with a nonionic surfactant, the expandable thermoplastic polymer particles are impregnated with an antistatic agent, an antiblocking agent, a water repellent, etc.
There is no harm in covering it.

Examples will be described below.

Example 1 115 parts of ion exchange water (parts by weight, same below) 1 styrene
00 parts, benzoyl peroxide 0.28 parts, 1.1 bis(t
-butylperoxy) 3.3.5 trimethylcyclohexane 0.15 part, tricalcium phosphate 0.09 part, α-
Sodium olefin sulfonate 0.006 part, sodium chloride 0.3 part, ethylene bisstearylamide 0.17
1.0 parts of ethylbenzene were polymerized for 5 hours at 90° C. in a nitrogen stream in a 51 container equipped with a stirrer.

Next, 0.4 parts of tricalcium phosphate and 8.5 parts of butane were charged, the temperature was raised to 105°C, and impregnation was carried out for 6 hours. After that 9
Lower the temperature to 0°C and add 0.0% zorbitanic acid monostearate.
A dispersion prepared by dispersing 14 parts of ion-exchanged water in 8 parts of ion-exchanged water was pressurized with nitrogen, stirred for 2 hours, cooled to 42°C, and the blowing agent-containing styrene beads were separated, washed with water, and dried. This is called sample A. Sample B is a bead that can be cooled to 42° C. after performing the polymerization and impregnation with a blowing agent as described above without adding sorbitanic acid monosterate.

Sample A, . Among the beads in B, 1680 μ to 283
Using beads with a particle size of 0 tt, pre-expanded particles having an apparent volume of about 90 times were obtained using a pre-expanding machine.

After curing the pre-expanded particles for 24 hours, BELMO-19
0 automatic molding machine (manufactured by Toyo Kikai Kinzoku Co., Ltd.) 200m7n x 2
It was molded using a 50mm x 100m mold. The molding conditions were: adjusted pressure 0.8 kg/Cd, preheating 10 seconds, 1st heating 0.2 kg/Cd, 2nd heating 3 seconds, 3rd heating 14 seconds,
Water cooling was performed for 30 seconds. The cooling time was defined as the time from the start of the water cooling process until the surface pressure of the molded body reached 0.1k9/Cd, and the measurement was performed. Here, the cooling time was set from the time when the water cooling process started until the surface pressure of the molded product reached 0.1k9/CrA, because the surface pressure of the molded product was 0.1k9/Cni, and even if the molded product was taken out from the mold, the molded product remained unchanged. This is because no expansion or distortion occurred. The results were as shown in the table below. It was observed that the cells in the surface layer of the pre-expanded particles of sample A were thinner than the cells in the surface layer of the pre-expanded particles of sample B.

Example 2 The same formulation as in Example 1 was used, but instead of 0.14 parts of zorbitan monostearate, 0.15 parts of glycerin monostearate, 0.15 parts of pentaerythritol monostearate, and polyoxyethylene lauryl were added. ether 0
．． 15 parts of polyoxyethylene polyokine propylene ether, and 0.15 parts of polyoxyethylene sorbitan monostearate.

The results were as shown in the table below.

Sample B of Example 1 was also shown as a blank. Example 3 After polymerization and blowing agent impregnation using the same recipe as in Example 1, 0.14 part of sorbitan monostearate was heated to 80%
C. and 90.degree. C., and the treatment was performed.

The processing time was 2 hours. Pre-foaming and molding were carried out in Example 1.
I went the same way. The results are shown in the table below, and Sample B of Example 1 is also shown as a blank.

Example 4 After polymerization and impregnation with a blowing agent using the same recipe as in Example 1, 0.14 parts of sorbitan monostearate was added at a temperature of 90°C, and the times were 0.5 hours, 1 hour, 2 hours, The treatment was carried out for 3 hours.

Pre-foaming and molding were performed in the same manner as in Example 1. The results are as shown in the table below, and Sample B of Example 1 is also shown as a blank.

Example 5 Same formulation as Example 1, but with 0 zorbitan monostearate
．． Changed to 1 part, 0.14 part, 0.2 part, 0.5 part, 90
Beads were obtained by treatment at ℃ for 2 hours.

Pre-foaming and molding were exactly the same as in Example 1. The results are shown in the table below, and Sample B of Example 1 is also shown as a blank.

Claims (1)

[Scope of Claims] 1. During the latter half of the process of impregnating thermoplastic polymer particles with a blowing agent or after the impregnation, a nonionic interface is applied to the thermoplastic polymer particles containing the blowing agent at a temperature higher than the softening point of the particles. A method for producing expandable thermoplastic polymer particles, characterized by impregnating them with an activator. 2. The manufacturing method according to claim 1, wherein the thermoplastic polymer particles are polystyrene particles. 3 The nonionic surfactant is an ester of pentaerythritol, an ester of glycerin, an ester of sorbitan,
The manufacturing method according to claim 1, which is an ester of polyoxyethylene sorbitan, a polyoxyethylene alkyl ether, or a polyoxyethylene polypropylene ether. 4. The manufacturing method according to claim 1, wherein the method is impregnated with a nonionic surfactant at a temperature of 80°C or higher and 100°C or lower. 5. The manufacturing method according to claim 1, wherein the amount of nonionic surfactant used is 0.05 to 1.0% by weight of the thermoplastic polymer particles.