JP2517208B2 - Pre-expanded particles of non-crosslinked ethylene resin - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention heat-molds a pre-expanded particle with a heating medium such as steam in a mold that can close but cannot close a pre-expanded particle to give a molded product. The present invention relates to non-crosslinked ethylene resin pre-expanded particles applicable to the method. More specifically, it relates to non-crosslinked ethylene resin pre-expanded particles obtained by heat-expanding a non-crosslinked ethylene-based resin having a specific viscosity when melted to form pre-expanded particles, which is then expanded by heating in a mold. In the production of a foamed molded product by in-mold molding of an ethylene-based resin by a bead method, a cross-linked ethylene-based resin particle is made to contain a volatile foaming agent and heated by steam or the like to be a pre-expanded particle. However, a method using the pre-expanded particles is generally used. When an ethylene-based resin is used without being crosslinked, the melt viscosity of the resin is remarkably lowered near the melting point, and the foaming agent gas causes foam breakage and further shrinkage, resulting in pre-expanded particles with a high expansion ratio and little shrinkage. Further, it is extremely difficult to obtain a molded product having a good fusion property between particles, a beautiful appearance, and a small gap between particles. Therefore, it is essential to crosslink the ethylene resin and control the melt viscosity of the resin in the temperature range above the melting point to a range suitable for prefoaming and molding of the obtained prefoamed particles by the formation of crosslinks. Therefore, there is a drawback in that an extra step called a cross-linking step is required, and the cross-linked ethylene resin is difficult to reuse. In addition, low density polyethylene with a structure with many branches is suitable for cross-linking, and there is the problem that even high density polyethylene with few branches is not easy to cross-link. Development of in-mold foam molding technology is highly anticipated. The present invention has been made for the purpose of obtaining pre-expanded ethylene resin particles which are excellent in pre-expandability and moldability of pre-expanded particles without being crosslinked. Yes, even when using a non-crosslinked ethylene-based resin as a base resin, by using one having a specific viscosity during melting, pre-expanded particles with high expansion ratio and less shrinkage can be obtained. In-mold molding gives good fusion between particles, and there are few gaps between particles,
This was done because it was found that a molded product with a beautiful appearance could be obtained. [0005] The present invention has a density of 0.940 g / cm ³ or less
Above, dense with MI 0.01-0.5g / 10min high density polyethylene
Linearity of 0.920 to 0.940 g / cm ³ and MI 0.1 to 10 g / 10 min
Cross-linked ethylene blended with linear low density polyethylene
Resin or Density 0.920 to 0.940 g / cm ³ , MI 0.01 to
It is a linear low-density polyethylene of 10g / 10min, and has a differential running
The DSC melting curves measured by the calorimeter are 2 on the low temperature side and 2 on the high temperature side.
Has two melting peaks and two peaks of the melting peak
It is a non-crosslinked ethylene resin with a temperature difference of 3 ° C or more.
I, which is one type using a vulcanization testing machine angular frequency (omega) 10.5 sec torque value measured by changing the temperature at ^-1 dynamic viscoelasticity measuring apparatus complex viscosity calculated from (lM ^* l) (lη ^* (Ω) l)
In the curve plotted with respect to temperature, foaming using a non-crosslinked ethylene-based resin as a base resin having a portion where the value of complex viscosity takes a value in the range of 0.06 to 0.2 kg / cm ² over a temperature range of 5 ° C or more. The present invention relates to non-crosslinked ethylene resin pre-expanded particles having a magnification of 5 to 50 times . EXAMPLES The vulcanization tester referred to in this specification is a kind of dynamic viscoelasticity tester developed for the purpose of monitoring the progress of vulcanization of unvulcanized rubber, and its principle is A small angular vibration of reciprocating rotary motion is applied to a sample at a constant temperature, and the stress against the vibration is measured as a torque value.
R Curastometer III type (manufactured by Japan Synthetic Rubber Co., Ltd.) vulcanization tester. The relationship between the torque value (lM ^* l) measured by the tester and the complex viscosity (lη ^* (ω) l) of the sample is expressed by the formula: lM ^* l = kθ _o ωlη ^* (ω) l ( Where k is the vulcanization tester constant, θ _o is the angular amplitude, and ω is the angular frequency). Therefore, lη ^* (ω) l ＝ lm
l η ^* (ω) l can be obtained as ^* l / (kθ _o ω). The vulcanization tester constant (k), angular amplitude (θ _o ), and angular frequency (ω) vary depending on the vulcanization tester used.
^The complex viscosity l η ^* (ω) l is a universal value, although ^* l is different. From the vulcanization tester and measurement conditions used in the present invention, k = πR ⁴ /2h=82.45 cm ³ / rad (radian) = 1.44 cm ³
/ Deg (where R is the effective radius (1.8 cm) of the die of the vulcanization tester, h
Is the distance between dies (0.2 cm), θ _o = 1 deg and ω = 2π
f = 2π · 100/60 = 10.5 sec ⁻¹ (where f is the frequency (100
is a cpm)), and therefore ^{lη * (ω) l = lM} * l / (kθ o ω) = lM * l × 0.0662 (k
g · sec / cm ² ). Η ^* (ω) and ## EQU1 ## Looking at the correspondence relationship with, the time scale is roughly [2] It is said that the vulcanization tester used in the present invention is generally used at ω = 10.5 sec ^-1 . Since the present invention is also used under this condition, Corresponds to the steady flow viscosity near 10.5 sec ^-1 . Generally, the viscosity characteristics of the thermoplastic resin are determined by using a capillary rheometer, a melt indexer or the like. However, these devices cannot measure viscosity in a high viscosity region suitable for pre-expansion and molding of pre-expanded particles, and the present invention is used for measuring the viscosity in the high viscosity region. It is necessary to use equipment such as a vulcanization tester as shown in. The non-crosslinked ethylene-based resin referred to in the present specification includes, for example, various polyethylenes such as low density polyethylene, medium density polyethylene, high density polyethylene and linear low density polyethylene, as well as ethylene-vinyl acetate copolymer, ethylene- It is a resin that also contains various copolymers containing 50% (wt% or less) of ethylene units, such as methyl methacrylate copolymer and ethylene-acrylic acid copolymer, and is not intentionally crosslinked. The non-crosslinked ethylene resin used in the present invention is
Among the non-crosslinked ethylene-based resins as described above, the temperature was set to 1 at an angular frequency (ω) of 10.5 sec ^-1 using the vulcanization tester.
In a curve in which the complex viscosity calculated from the torque value measured in the range of 10 to 150 ° C is plotted against temperature,
Complex viscosity of 0.06 to 0.2 kg over a temperature range of 5 ° C or more
・ Sec / cm ² , preferably 0.065-0.17kg ・ sec / cm ²
It is a non-crosslinked ethylene-based resin having a portion having a value in the range (hereinafter, referred to as a specific non-crosslinked ethylene-based resin).
These may be used alone or in combination. The complex viscosity over the temperature range above 5 ° C.
If it is less than 0.06 kg · sec / cm ^2, the fluidity of the resin will be too large and the foaming and shrinkage will occur easily during pre-foaming or molding from pre-expanded particles, and if it exceeds 0.2 kg · sec / cm ² , it will flow. Poor properties make pre-expansion and molding from pre-expanded particles difficult. Further, the temperature range showing the complex viscosity needs to be at least 5 ° C. in view of workability. [0022] Among the specific non-crosslinked ethylene-based resin, (A) Density 0.940 g / cm ³ or more, MI 0.01 ~ 0.5g / 10 min density polyethylene and density 0.920~ 0.940g / cm ^3,
MI 0.1 to 10 g / 10 min blended linear low density polyethylene resin, or (B) density 0.920 to 0.940 g / cm ³ , MI 0.01 to 10 g / 10
Of a linear low-density polyethylene, the DSC melting curve measured by a differential scanning calorimeter has two melting peaks on the low temperature side and the high temperature side, and the temperature difference between the two peak temperatures of the melting peak is Those having a temperature of 3 ° C. or higher are particularly preferable. [0023] (A) Symbol mounting uncrosslinked ethylene-based resin of not also lowered melt viscosity much above the melting point, when the production of pre-expanded particles using these resins, a wide temperature above the temperature range melting point Pre-expanded particles with a high expansion ratio and less shrinkage can be obtained across the width. Further, when the particles are molded in a mold, the particles have a good fusion property with each other, there are few interparticle gaps, and a molded product having a beautiful appearance can be obtained. Further, in the non-crosslinked ethylene resin described in (B), the melting peak of the crystal was 3 ° C or more.
When the pre-expanded particles are produced by using this resin, the melting temperature range is broadened by the separation into two parts, and when the pre-expanded particles are produced using this resin, shrinkage at a high expansion ratio is achieved over a relatively wide temperature range. Fewer pre-expanded particles are obtained.
Further, when the particles are molded in a mold, the particles have a good fusion property with each other, there are few interparticle gaps, and a molded product having a beautiful appearance can be obtained. The resin described in (B) has a density of 0.920 g / cm ³
When the amount is less than the above, the obtained molded article becomes too soft and does not exhibit good physical properties, and when it exceeds 0.940 g / cm ³ , peak separation of the DSC melting curve due to heat treatment of resin particles described later hardly occurs. When MI is less than 0.01g / 10min, the fluidity is poor and prefoaming or molding becomes difficult. When it exceeds 10g / 10min, the viscosity is high even if it has two melting peaks with a DSC melting curve of 3 ° C or more. Becomes too low, and open cells, breakage, and shrinkage are likely to occur during pre-foaming and molding. Furthermore, the temperature difference between the two peaks of the DSC melting curve is 3 ° C.
When the amount is less than the above, the DSC melting curve becomes close to having only one peak, the melt viscosity near the melting point is largely lowered, and open cells, foam breakage, and shrinkage are likely to occur during prefoaming and molding. [0026] (A) Resin according density 0.940 g / cm ³ or more, MI 0.01 high-density polyethylene and a density of ~ 0.5 g / 10 min ^{0.920~ 0.940g / cm 3, MI 0.1~10g} / 10 min linear A resin composition having fluidity equivalent to that of the resin described in (B) can be obtained by blending the low-density polyethylene with an appropriate ratio. The linear low-density polyethylene resin particles having a DSC melting curve described in (B) having two melting peaks on the low temperature side and the high temperature side are heat treated for 5 minutes or more near the melting point of the resin and then cooled. It is obtained by doing. This heat treatment may be a dry heat treatment, but since the particles are easily fused to each other during the heat treatment, it is preferable to disperse the resin particles in a heating medium such as water and perform the heat treatment. The resin density and MI can be measured according to JIS K 6760. The DSC melting curve can be measured by using a differential scanning calorimeter and heating the sample to 200 ° C at a rate of 10 ° C / min. Next, a method for producing the pre-expanded particles will be described. The pre-expanded particles in the present invention are prepared by making a base resin into small pellets by using an extruder or the like, bringing the pellet into contact with a volatile foaming agent to contain the foaming agent, and then heat-foaming the pre-expanded particles. Or the resin particles and a volatile foaming agent in a pressure vessel are dispersed in water in the presence of a dispersant, and after the foaming agent is contained in the resin particles at high temperature and high pressure, the resin particles and water The mixture can be obtained by a method of pre-foaming the particles by opening the lower end of the container and discharging into the low pressure region. Examples of the volatile blowing agent used include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, monochloromethane, dichloromethane and mono. Examples thereof include halogenated hydrocarbons such as chloroethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane and dichlorotetrafluoroethane. These may be used alone or in combination of two or more. These volatile foaming agents are 5 to 5 parts per 100 parts by weight of non-crosslinked ethylene resin particles (parts by weight, the same applies below).
About 40 parts of it is included for foaming. In a method in which resin particles and a volatile foaming agent are dispersed in water in a pressure resistant container and pressure is released at high temperature and high pressure to obtain pre-expanded particles, two DSC melting curves are obtained in the container. After heat treatment for obtaining linear low-density polyethylene resin particles exhibiting a melting peak, one end of the container may be opened as it is for pre-foaming. When a linear low-density polyethylene having a DSC melting curve described in (B) having two melting peaks on the low temperature side and the high temperature side is used, the DSC melting curve is obtained by pre-foaming using any of the above methods. The two peaks of the curve are substantially retained, and the molding width is wide during in-mold molding,
A good foam molded article can be obtained. [0034] In this way, the foaming magnification 5-50 times, preferably at 10 to 45 times, the cell structure has low open cell ratio uniform,
The non-crosslinked ethylene-based resin pre-expanded particles of the present invention having no fusion of particles are produced. When the non-crosslinked ethylene-based resin pre-expanded particles of the present invention are used for in-mold molding by a conventional method, the heating width is wide and molding is easy, and the fusion between particles is good and the inter-particle gap is good. It is possible to obtain a molded product with a good appearance and less shrinkage and deformation. As a specific example of the molding method, for example, the obtained pre-expanded particles are immediately or after curing and drying for an appropriate time as they are, or the pre-expanded particles are further subjected to an inorganic gas such as air and / or volatile expansion. Examples of the method include a method in which the agent is added to provide foaming ability, the agent is filled in a molding die, and the material is molded with a heating medium such as steam under a heating condition of about 105 to 150 ° C. for about 3 seconds to 3 minutes. By using the pre-expanded particles of the present invention, as described above, a good molded product can be obtained without particularly providing the foaming ability. The molded product obtained in this manner has oil resistance, weather resistance, heat resistance, tear strength, flexibility, heat retention,
It has excellent compressive strength and cushioning properties, and is used in the same fields as used for molded articles made from pre-expanded crosslinked ethylene resin particles, such as packaging materials, cushioning materials, heat insulating materials, building materials,
It can be preferably used in the fields of levitating materials, shaving boxes, food containers, shock absorbers and the like. The pre-expanded particles of the present invention will be described in more detail with reference to the following examples. Example 1 A pressure-resistant container having an agitator with an internal volume of 100 liters was charged with a density
0.953 g / cm ³ , MI 0.04 g / 10 min high density polyethylene
70%, density 0.930 g / cm ³ , MI 2.1 g / 10 min linear low
Mixture with 30% density polyethylene , DSC melting point 128 ℃,
The complex viscosity calculated from the torque value measured by changing the temperature with a vulcanization tester (JSR Charameter III type) is 130-
0.092 to 0.075 kg · sec / cm ² (Temperature −
100 parts (22.5 kg) of high-density polyethylene particles having a complex viscosity curve (particle weight of about 5 mg / particle) having a complex viscosity curve of 1.2 parts by weight of powdery basic tribasic calcium phosphate and C ₁₄ -C ₁₆ Using 0.006 parts of n-paraffin sodium sulfonate, the mixture was dispersed in 300 parts of water, and 45 parts of dichlorodifluoromethane was added with stirring and the temperature was raised to 135 ° C.
The internal pressure of the pressure vessel at this time was 35 kg / cm ² -G. Then, liquid dichlorodifluoromethane was press-fitted while adjusting with a valve, and while maintaining the internal pressure at 35 kg / cm ² -G, the discharge valve at the bottom of the pressure resistant container was opened and mounted behind this valve. The mixture of particles and water was discharged into an atmosphere of normal pressure through an orifice plate having a circular hole with an inner diameter of 4 mm. The average expansion ratio of the obtained pre-expanded particles is 38.
It was double. Then, the pre-expanded particles were dried at 35 ° C. for 6 hours . Continuous air bubble rate was 6%. The pre-expanded particles were mounted on a molding machine.
It was filled in a metal mold of 270 mm x 270 mm and heated by steam of 1.0 to 2.0 kg / cm ² -G for 10 to 30 seconds for molding. 80 this molded product
After curing and drying at 20 ° C. for 20 hours and leaving at room temperature for 1 day, the surface smoothness, sink marks (partial shrinkage) and deformation, fusion property and molding width of the molded product were examined by the following methods . The evaluation results of that shown in Table 2. (Open cell ratio of pre-expanded particles) This shows the proportion of open cells communicating with the outside out of all the cells of the pre-expanded particles, and is calculated by the following formula. [Equation 1] (Wherein V is the volume of the pre-expanded particles (measured by immersing the sample in ethyl alcohol in a graduated cylinder), and v is an air-comparison hydrometer (for example, air-comparison hydrometer 930 type manufactured by Beckman). ) Is used to represent the volume of the closed-cell portion of the pre-expanded particles.) (Surface smoothness of molded product) The smoothness of the surface of the molded product is visually observed and evaluated based on the following criteria. ◯: No surface irregularity of the molded product Δ: Some irregularity of surface of the molded product ×: Severe surface irregularity of the molded product (sink and deformation of the molded product) Sink and deformation of the molded product were observed with the naked eye, and Evaluated based on the criteria. ◯: No sink mark and deformation Δ: Sink mark and slight deformation X: Sink mark and deformation severe (fusion property of molded product) The degree of fusion of particles inside the molded product was measured within the molded product within the particles. The ratio of the broken portion is visually judged, and this is taken as the fusion degree, and evaluated based on the following judgment criteria. ◯: The degree of fusion is over 60% Δ: The degree of fusion is 40 to 60% ×: The degree of fusion is less than 40% (molding width) The surface smoothness, sink marks and deformation of the molded product,
The meltability was rated as Δ or higher, and the difference between the lower limit and the upper limit of the steam pressure for forming and heating to obtain a passing product was used as an index of the forming width and evaluated based on the following criteria. [0050] ○: 0.15 kg / cm ² to more than △: 0.05~0.15kg / cm ² ×: a resin shown in Table 1 as 0.05 kg / cm ² less than in Example 2 Contact and Comparative Examples 1 to 2 ethylene resin Then, pre-expanded particles and then a molded article were obtained in the same manner as in Example 1 except that the pre-expanding conditions were changed to those shown in Table 1. Table 1 shows the average expansion ratio and the open cell ratio of the pre-expanded particles immediately after the pre-expansion. The evaluation results of the molded products are shown in Table 2. The temperature-complex viscosity curves of the ethylene resins used in Examples 1 and 2 and Comparative Example 2 are shown in FIG. [Table 1] [Table 2] Examples 3 to 4 and Comparative Examples 3 to 4 The linear low-density polyethylene particles shown in Table 3 (particle weight: about 5 mg / particle) were used in a pressure resistant vessel having an agitator with an internal volume of 100 liters. In the same manner as in Example 1, the resin particles were dispersed in water, kept at the temperature shown in Table 3 for 30 minutes without adding a foaming agent, heat-treated, and then cooled to room temperature to obtain heat-treated resin particles. Table 3 shows the temperatures of the two melting peaks of the DSC melting curve of the obtained resin particles and the complex viscosities determined by a vulcanization tester (JSR Curastometer III type). The temperature-complex viscosity curve of the ethylene resin used is shown in FIG. The four kinds of resin particles shown in Table 3 were respectively treated with saturated steam of dichlorodylfluoromethane as a foaming agent and temperature.
Contact at 60-80 ° C, pressure 15.5-23.5kg / cm ² -G for 1-2 hours to contain dichlorodifluoromethane, 0.5-
Pre-expanded particles were obtained by heat-foaming with steam of 1.5 kg / cm ² -G for 20 seconds. The results are shown in Table 4. [Table 3] [Table 4] The pre-expanded particles obtained in Examples 3 and 4 were heat-molded in the same manner as in Example 1 with 0.5 to 1.5 kg / cm ² -G steam to obtain a molded product. It had good wearability, a smooth surface, few sink marks and deformation, and a beautiful appearance. From the results shown in Table 4, in Examples 3 and 4 , good pre-expanded particles having a high expansion ratio and a low open cell ratio were obtained, but in Comparative Examples 3 and 4, the pre-expanded particles contracted to give high expansion. It can be seen that the magnification cannot be obtained, and the open cell ratio is high, so that it cannot be used for in-mold molding. INDUSTRIAL APPLICABILITY The pre-expanded particles of the present invention have a high expansion ratio and little shrinkage, even though they use a non-crosslinked ethylene resin as a base material. Further, when the particles are used for in-mold molding, a wide range of molding processing conditions, good fusion of particles with each other, small interparticle gaps, and a molded product with a beautiful appearance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] Example 1, 2, the ethylene-based resin used in a ratio Comparative Examples 2 Temperature - is a graph showing the relationship between complex viscosity. FIG. 2 is a graph showing the temperature-complex viscosity relationship of the ethylene resins used in Examples 3 and 4 and Comparative Examples 3 and 4.

Claims (1)

(57) [Claims] 1 density 0.940 g / cm ³ or more, MI 0.01 to 0.5 g / 10 minutes
High density polyethylene and density 0.920〜0.940g / cm ³ ,
MI 0.1-10 g / 10 min linear low density polyethylene
Lend non-crosslinked ethylene resin or density 0.920〜
0.940g / cm ^3, MI of 0.01 to 10 g / 10 min linear low density
Polyethylene, DSC melt measured by differential scanning calorimeter
The solution curve has two melting peaks on the low temperature side and the high temperature side,
The temperature difference between the two peak temperatures of the melting peak is 3 ° C or more
This is a non-cross-linked ethylene-based resin and is a type of dynamic viscoelasticity measuring device.
On the curve where the complex viscosity (l η ^* (ω) l) calculated from the torque value (lM ^* l) measured by changing the temperature at ec ^-1 was plotted against the temperature, Foaming ratio using non-crosslinked ethylene-based resin as a base resin, which has a portion that takes a value in the range of 0.06 to 0.2 kg · sec / cm ² across the width
Pre-expanded particles of non-crosslinked ethylene resin of 5 to 50 times .