JPH0834871A - Method for manufacturing plastic sheet whose thickness increases by heating - Google Patents

Abstract

PURPOSE:To produce a plastic sheet which increases only in thickness by heating with no change in dimension in the direction along the surface. CONSTITUTION:A thermoplastic resin foam base material (A) is mixed with a thermoplastic resin component (B) having a melting point lower than the melting initiation temperature of the resin A to form a dispersion. The mixture is then compressed in the direction of thickness at a heating temperature in the range from the melting point of component B to the melting initiation temperature of component A, thus easily providing a plastic sheet capable of increasing only in thickness by heating with no change in dimension in the direction along the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic sheet which can be increased only in the thickness direction without changing the dimension in the surface direction by heating.

[0002]

2. Description of the Related Art As a method for producing a plastic sheet having the above characteristics, a method utilizing the shape memory effect of a thermoplastic resin and a method using a resin sheet in which a chemical foaming agent is dispersed can be considered. The former method based on the shape memory effect uses a foam base material made of a thermoplastic resin,
A compressive strain is applied in a state of being heated to a temperature slightly lower than the melting point of the resin, and the compressive strain is frozen by rapid cooling in a compressed state, and used as a sheet in this state, and reheated. The compression-frozen strain recovers elastically and an increase in thickness is obtained.

Therefore, the recovery behavior thereof generally tends to gradually recover as the temperature rises, and depending on the temperature conditions during sheet storage, the thickness may recover to some extent before use. Also, in order to obtain a high recovery rate, it is necessary to reheat to a temperature slightly lower than the melting point of the base resin, and once the melting point is exceeded, it is not possible to recover the thickness, so it is quite strict when recovering the thickness. Temperature control is required.

The thickness recovery rate of each part also varies depending on the history of heat and stress of each part. Therefore, in order to obtain a uniform recovery thickness, the temperature and pressure planes at each heating / cooling step should be used. It is necessary to ensure the uniformity of In addition, it is inevitable to induce a dimensional change due to the heat history of the original sheet in the surface direction by heating the base resin close to the melting point.

On the other hand, in the latter method using a foaming agent, the temperature at which the thickness begins to change is the same as the decomposition start temperature of the foaming agent, and threshold characteristics can be given. It is necessary to disperse the foaming agent evenly,
A sheet with non-uniform dispersion has a problem that the thickness after foaming becomes non-uniform, and it is generally difficult to obtain a chemical foaming agent that foams at a temperature lower than about 150 ° C. and is stable at room temperature. There is a problem.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a plastic sheet whose thickness is increased by heating which can solve the above problems. According to the invention of claim 1, a thermoplastic resin component B having a melting point lower than the melting start temperature of the resin is dispersed and mixed in a foam base material A made of a thermoplastic resin, and then foaming is performed from the melting point of the thermoplastic resin component B. It is characterized in that it is compressed in the thickness direction within the heating temperature range of the melting start temperature of the body substrate A.

The thermoplastic resin used in the foam substrate A is a resin having a relatively high melting point, and is near the melting point of the thermoplastic resin component B to be dispersed and mixed (heating temperature range for increasing the thickness). Any material can be used without particular limitation as long as it can obtain recovery elasticity or rubber elasticity with respect to compression. Specifically, various polyamide resins such as polypropylene, nylon 6, nylon 66, and various thermoplastic elastomers such as thermoplastic polyurethane elastomer can be used. It can be preferably used. Further, those having a crosslinked structure formed by chemical crosslinking such as electron beam irradiation or silanol condensation can be preferably used.

The thickness of the foam substrate A varies depending on the purpose of use and the like, but a thickness of about 0.5 to 20 mm can be preferably used. The thermoplastic resin component B is lower than the melting start temperature of the foam base material A, preferably 50 ° C.
A thermoplastic resin having a melting point in the above low temperature range can be selected. After incorporating into a specific article, heat it,
Considering the case of recovering the thickness, the melting point of the thermoplastic resin component B is preferably in the range of about 50 to 150 ° C. Specific examples of the thermoplastic resin component B include polyethylene oxide, polyethylene, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer,
Vinyl chloride / vinyl acetate copolymer and the like can be preferably used.

Then, the foam base material A in which the thermoplastic resin component B is dispersed and mixed is used and compressed in the thickness direction in the heating temperature range from the melting point of the thermoplastic resin component B to the melting start temperature of the foam base material A. There is a need to. As a compression method, an ordinary hot pressing method or a method of continuously compressing between heating rolls may be used. The compression ratio can be appropriately determined according to the purpose of use, etc., but the thickness after compression / thickness before compression = 0.
It is preferably about 1 to 0.6.

According to the second aspect of the present invention, a thermoplastic resin component D having a melting point lower than the thermal decomposition initiation temperature of the resin is dispersed and mixed in a foam base material C made of a thermosetting resin, and then the thermoplastic resin component is mixed. It is characterized by compressing in the thickness direction in the heating temperature range from the melting point of D to the melting start temperature of the foam substrate C.

Here, as the thermosetting resin used for the foam base material C, polyurethane resin, silicone resin, flexible epoxy resin and the like can be preferably used, and crosslinked elastomer such as vulcanized rubber can also be used. The thickness of the foam base material C is preferably about 0.5 to 20 mm as in the foam base material A of claim 1.

The thermoplastic resin component D is lower than the thermal decomposition starting temperature of the foam substrate C, preferably 50.
It is possible to select a thermoplastic resin having a melting point in a temperature range lower than 0 ° C. Considering the case where the thermoplastic resin component D is incorporated into a specific article and then heated to recover the thickness, the melting point of the thermoplastic resin component D is preferably in the range of about 50 to 150 ° C. The thermoplastic resin component D may be the same as the above-mentioned thermoplastic resin component B.

Then, the foam base material C in which the thermoplastic resin component D is dispersed and mixed is used, and compressed in the thickness direction in the heating temperature range from the melting point of the thermoplastic resin component D to the melting start temperature of the foam base material C. There is a need to. The compression method may be the usual hot pressing method described in claim 1 or a method of continuously compressing between heating rolls. Similarly, as a compression ratio, thickness after compression / thickness before compression = 0.1 to 0.6
It is preferable to set the degree.

According to a third aspect of the present invention, the foam base materials A and C are open-cell foams, and a thermoplastic resin component B is used.
D is composed of a resin soluble in a solvent, and the thermoplastic resin components B and D dissolved in the solvent are impregnated into the foam base materials A and C to disperse and mix the thermoplastic resin component. Is.

In the present invention, the foam base materials A and C and the thermoplastic resin components B and D are previously blended into a sheet,
The foam may be either an open cell or a closed cell, but after forming the foam base materials A and C made of the open cell of claim 3, the thermoplastic resin components B and D are internally added. The method of infiltrating into and holding it is simple and preferable. in this case,
The foam base materials A and C must be made of a material that is not attacked by the solution of the thermoplastic resin components B and D.

Here, a film having good heat resistance and a small dimensional change due to heating may be laminated on one side or both sides of the sheet obtained by the above method, the thickness of which is increased by heating. As a laminating method, laminating may be appropriately performed by a usual method before or after the compression step.

[0017]

In the plastic sheet of the present invention, the thermoplastic resin components B and D dispersed and mixed in the foam base materials A and C are melted in a heated state, and then, when cooled, become a glass state and are heated and compressed. The foam base materials A and C thus prepared can be held in a state in which the thickness is reduced. Therefore, unlike the case due to the shape memory effect, the foam base material externally prevents the elastic recovery by the thermoplastic resin component in the glass state rather than the internal strain of the base foam being frozen. It is in a rare state.

In order to increase the thickness of the heat-compressed plastic sheet, the sheet may be heated again to a temperature equal to or higher than the melting point of the thermoplastic resin component, and this heating causes the thermoplastic resin component to be in a molten state again and externally. The elastic force of the foam base material fixed to is released and the thickness is recovered.

The present invention will be described below with reference to examples.

[0020]

【Example】

Example 1 Foam base sheet (A): Low density polyethylene closed cell foam (glass transition temperature: -20 ° C, melting start temperature 120 ° C)
Thermoplastic Resin Component (B): Polyethylene Oxide Resin (Melting Point 60 ° C.) 10 parts by weight of the component (B) is mixed in pellets with respect to 100 parts by weight of the above (A), and an extruder (cylinder-diameter 40 m) is used.
m, L / D 28) and at the same time the extruder cylinder
From the middle, 15 parts of butane was attached as a foaming agent, and extrusion molding was performed from a die having a mouth width of 300 mm and a lip thickness of 0.2 mm to obtain a closed-cell polyethylene foam in which the component (B) was dispersed (expansion ratio about 30 times, A thickness of 4 mm) was obtained.

Then, using a hydraulic press, at a temperature of 70 ° C., 10
After preheating for one minute, the pressure was 7.0 kg / cm @ 2 and the pressure was gradually cooled to 23 DEG C. to obtain a plastic sheet having a thickness of 0.8 mm. Using the obtained sheet, the sheet was placed in a hot air circulation type oven maintained at a constant temperature for 5 minutes, and the heating temperature and the situation of the thickness change were measured and observed. The results are shown below. Here, the change in thickness is the thickness after compression (0.8 mm)
Is the ratio of the increase in thickness after heating.

Heating temperature 45 ° C. 65 ° C. 85 ° C. 105 ° C. 125 ° C. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Change 12.7% 214% 363% 371% 263% ・ From 65 ° C, which exceeds the melting start temperature of the thermoplastic resin component (B) by 5 ° C, has increased to about 3 times the thickness after compression,
Furthermore, it is the melting start temperature of the foam base sheet (A).
A high thickness increase is obtained up to 20 ° C. In the range of 85 ° C to 105 ° C, the thickness uniformity in the surface direction is good,
Moreover, the dimensional change in the plane direction was also very small.

Example 2 Foam substrate sheet (C): Thermosetting polyurethane resin open-cell body (glass transition temperature -20 ° C, thermal decomposition starting temperature 180 ° C,
Thickness 0.6 mm) Thermoplastic resin component (D): vinyl chloride-vinyl acetate copolymer resin (melting start temperature 75 ° C.) After impregnating a 20% ethyl acetate solution of the above (D) into the foam substrate sheet (C) , Remove the adherent liquid on the surface, and
Dried for minutes. Then, with a hydraulic press, at a temperature of 85 ° C, 5
After preheating for 1 minute, the pressure was 7.0 kg / cm ² , and the pressure was gradually reduced to 23 ° C. to obtain a 0.3 mm-thick plastic sheet.

Using the sheet obtained, the same evaluation as in Example 1 was performed. Heating temperature 65 ° C. 85 ° C. 105 ° C. 125 ° C. 145 ° C. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Thickness change 5% 96% 100% 99% 98% ・ The melting start temperature of the thermoplastic resin component (D) has increased from 85 ° C, which is 10 ° C higher, to about twice the thickness after compression (0.3 mm), and the heating temperature It can be seen that there is no change in the increase in thickness even when is increased. The uniformity of thickness increase in the surface direction was good, and no dimensional change in the surface direction was observed.

Comparative Example 1 Only the foam substrate sheet (C) used in Example 2 was preheated at 85 ° C. for 5 minutes in a hydraulic press to 7.0 kg /.
It was pressurized with a pressure of cm ² and cooled to 23 ° C. while being pressurized. However, when the application of pressure was stopped, the original thickness was restored and a sample could not be obtained.

Comparative Example 2 Closed-cell expanded polyethylene sheet (thickness 1 mm, melting point 1
(05 ° C) with a hydraulic press at a temperature of 85 ° C for 10 minutes, and then pressurizing it at a pressure of 7.0 Kg / cm ² and then immediately quenching it to 23 ° C to freeze the compressive strain while maintaining the thickness due to the shape memory effect. It was used as a recovery sample. The thickness after pressing was 0.3 mm.

The same evaluation as in Example 1 was performed using the obtained sheet. Heating temperature 65 ° C. 85 ° C. 105 ° C. 125 ° C. 145 ° C. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Thickness change 43 % 88% 109% 35% 5% ・ A high thickness increase rate was obtained from the temperature (85 ° C) to which compressive strain was applied to over 20 ° C, but the shrinkage in the plane direction was remarkable, and the thickness uniformity was also high. Was also inferior to Example 1.
Further heating to 125 ° C. or higher causes melting and softening, and it is difficult to increase the thickness.

Comparative Example 3 6 parts by weight of a foaming agent (DPT type) and 100 parts by weight of low density polyethylene (melting point 105 ° C.), a blowing aid (urea type).
After 6 parts by weight were added and mixed while kneading with a roll, a sheet with a thickness of 0.3 mm was formed by a hydraulic press, and this was subjected to a crosslinking treatment by electron beam irradiation (gel content 25%) to obtain a sample of a sheet for increasing thickness with a foaming agent. did.

The same evaluation as in Example 1 was performed using the obtained sheet. Heating temperature 65 ° C. 85 ° C. 105 ° C. 125 ° C. 145 ° C. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Thickness change 0 0 3% 1% 194% · At a high temperature of 145 ° C, the blowing agent begins to decompose,
Although a very large increase in thickness was obtained, at the same time the dimensions also expanded in the plane direction. The thickness uniformity was poor, and the surface condition was not good due to the occurrence of gas escape.

[0030]

As described above, according to the present invention, it is possible to easily obtain a plastic sheet which can be increased only in the thickness direction without changing the dimension in the plane direction by heating.

Claims (3)

[Claims] 1. A foam base material (A) made of a thermoplastic resin.
A thermoplastic resin component (B) having a melting point lower than the melting start temperature of the resin is dispersed and mixed therein, and then the melting start temperature of the foam base material (A) is heated from the melting point of the thermoplastic resin component (B). A method for producing a plastic sheet, the thickness of which is increased by heating, which comprises compressing in the thickness direction in a temperature range. 2. A foam base material (C) made of a thermosetting resin.
After the thermoplastic resin component (D) having a melting point lower than the thermal decomposition start temperature of the resin is mixed therein, the decomposition starting temperature of the foam base material (C) is changed from the melting point of the thermoplastic resin component (D). A method for producing a plastic sheet, the thickness of which increases by heating, which comprises compressing in a thickness direction within a heating temperature range. 3. The foam base materials (A) and (C) are open-cell foams, and the thermoplastic resin components (B) and (D).
Is a resin soluble in a solvent, and the thermoplastic resin components (B) and (D) dissolved in the solvent are added to the foam base material (A),
The method for producing a plastic sheet of which thickness is increased by heating according to claim 1 or 2, wherein (C) is impregnated and a thermoplastic resin component is dispersed and mixed therein.