Heat Barrier Hat Contributes to Quality Improvement in Plastic Injection Molding and Energy-saving.

Yasuo IZUMI, Shin-Nihon Tech Inc. *1

[Summary]

Heat Barrier Hat is a heat insulation part to be mounted between the nozzle of a plastic injection

molding machine and the mold in order to suppress thermal transfer in-between. This report

describes its various effects, such as prevention of resin stringing and damage of the injection

nozzle, reduction of defective moldings due to higher stability of molding quality and energy-saving.

1. Introduction

In plastic injection molding, thermal transfer

generally takes place as moldings increment,

because there is temperature difference

between the injection nozzle and the mold. The

heat accumulates accordingly in the mold,

which increases the risk for stringing and cut

of the sprue, and instability of molding quality.

Shin-Nihon Tech, Inc., hence, has developed

and sell Heat Barrier Hat which suppresses

the thermal transfer in-between. This is to

report its various effects including prevention

of resin stringing and damage of the injection

nozzle, reduction of defective moldings due to

higher stability of molding quality, and

energy-saving.

2. Outline and Feature of Heat Barrier Hat

2.1 What is Heat Barrier Hat?

Heat Barrier Hat is a component to be

mounted between the nozzle of the injection

molding machine and the mold in order to

suppress the thermal transfer in-between,

which accordingly enhances the moldings

quality and productivity, and contributes to

energy-saving (see Photo 1). It is patented.

This product won several awards in Japan

including the Incentive Award of “Grand Prize

for Parts of Super-manufacturing” in 2015

(co-sponsored by Japanese Manufacturing

Convention and the Nikkan Kogyo Shinbun

Newspaper); the Technology Advancement

Award of Japan Society of Polymer Processing

in 2015; and the “Gold Ecotech” of Research

Institute of Environment, Agriculture and

Fisheries, Osaka Prefecture, in August 2016.

2.2 Basic Specifications

Figure 1 illustrates how Heat Barrier Hat is

used.

*1 Shin-Nihon Tech Inc.: 2-2-81 Hama, Tsurumi-ku,

Osaka City, Osaka, 538-0035, Japan

Photo 1. Appearance of Heat Barrier Hat

Figure 1. Image of Heat Barrier Hat Application

Heat Barrier Hat, a hat-shaped metallic part,

has a hole in the hemisphere-shaped center,

which is the path for molten resin to run

through.

The radius of concave sphere part against the

injection nozzle is 10mm, the radius of convex

sphere part against the sprue bush on the mold

side is 11mm and outer diameter of the hat is

40mm.

Heat Barrier Hat is to be glued to the sprue

bush of the mold with a double-faced adhesive

tape.

2.3 Target and Scope of Application

As downsizing technology of plastic molding

parts (electronic parts like connectors and

optical parts like lenses) used in mobile phones

has been advanced, there has been an increase

in the number of production of plastic parts by

compact size injection mold with a nozzle end

of SR10mm. Heat Barrier Hat is applicable for

compact size plastic molding, hence, huge

effect is expected to spread. With regard to the

hole diameter of molten resin path, the current

standard isφ3mm whileφ2mm and φ2.5mm

types are available, however, we plan to extend

the variation of the hole diameter.

As shown in Figure2, Heat Barrier Hat can

also be applied for the molds for thermoplastic

resin molding as well as those for

thermosetting resin molding (e.g. epoxy resin).

The temperature of the molds for

thermosetting resin (e.g. 180℃ for the mold

for epoxy resin) is higher than that of the

injection nozzle (e.g. controlled between 90 and

100℃ in the same example). Thermal transfer

accordingly takes place from the mold to the

nozzle, which induces a problem of

thermosetting resin solidification resulting in

lower productivity. Heat Barrier Hat gives a

Figure 2. Various Application by Resin Type

solution to reduce the thermal conduction.

2.4 Structure of Heat Barrier Hat

Figure 3 shows the structure of Heat Barrier

Hat. It is the 1mm-thick product that consists

of three parts, namely, the stainless steel

exterior part ① (0.3mm thick) against the

injection nozzle; the stainless steel exterior

part ② (0.3mm thick) against the mold; and

heat barrier/insulation layer ③ (0.4mm thick).

The entire surface of the stainless steel

exterior parts ① and ② is coated with hard

chromium to enhance its durability against

corrosion and abrasion.

2.5 Development of Thermal arrier/Insulation

Technology

The reason why the stainless steel SUS304 is

used for the exterior parts ① and ② is

because of its low thermal conductivity [Note

1], strength in marketability and high

corrosion resistance.

[Note 1] Table 1 shows the thermal

conductivity of common materials. The

thermal conductivity of stainless steel SUS304

used for Heat Barrier Hat is much lower than

that of the others.

The thermal barrier/insulation layer ③ has

0.4mm thick stainless steel mesh structure. Its

performance of thermal barrier/insulation is

strengthened by filling the original paint that

contains ultra-fine powder of vacuum balloon

construction into the mesh structure itself as

well as the mesh area. Those three parts ①,

② and ③ are combined at high accuracy,

glued with the heat barrier coating agent that

shields infrared heat and finally bonded firmly

by laser welding.

Figure 4 illustrates the evaluation result of

thermal barrier/insulation performance of

Heat Barrier Hat. The experiment was carried

out in order to measure the temperature

change with a surface thermometer by

assuming the copper plate as the injection

nozzle where Heat Barrier Hat is placed. In

both cases of application of Heat Barrier Hat

and non-application, the temperature decrease

degree was observed respectively and thermal

barrier/insulation effect between 65℃ and

69.1℃ was verified as follows:

① Temperature decrease 319℃ → 253.6℃

(Δ65.4℃)

② Temperature decrease 332℃ → 262.9℃

(Δ69.1℃)

③ Temperature decrease 325℃ → 260.0℃

(Δ65.0℃)

Figure 3. Structure of Heat Barrier Hat

Type of Material Thermal

Conductivity （W/m℃x102）

Silver 4.12

Copper 3.71

Aluminum 1.95

Magnesium 1.50

Chromium 0.96

Iron 0.79

Carbon Steel 0.58

Titanium 0.17

Stainless Steel

SUS304 0.16

Table 1. Comparison of Thermal Conductivity

3. Effect to Introduce Heat Barrier Hat

3.1 Reduction of Stringing Troubles

Stringing is the phenomenon that unsolidified

resin pulls strings when released from the

mold within the set molding time. In case of

Photo 2 the stringing was caused by the

thermal transfer from the injection nozzle

(230℃) to the mold (60℃). Heat Barrier Hat

can control such stringing troubles. The

stringing is regarded as one of the “permanent

challenges in resin molding,” because it

induces the damage of the mold by the

malfunction to handle the moldings, such as

mis-releasing of moldings or moldings getting

caught in the mold, which results in the

machine breakage.

Table 2 shows the result of hearing survey with

12 customers regarding the effect of Heat

Barrier Hat.

In case of Company A (a large manufacturer of

Sample

NO.

Measuring

Point of

Experime

nt Device

Copper

Plate

(℃)

a

(℃)

b

(℃)

c

(℃)

Average

Temperature

of a, b and

c(℃)

Average

Temperatu

re (℃)

Temperature

Decrease

(℃)

1

① 319.0

264.0 263.0 249.0 258.7

253.6 65.4 2 256.0 252.0 254.0 254.0

3 250.0 252.0 242.0 248.0

4

② 332.0

278.0 262.0 259.0 266.3

262.9 69.1 5 266.0 280.0 254.0 266.7

6 275.0 248.0 249.0 257.3

7 255.0 272.0 257.0 261.3

8

③ 325.0

256.0 276.0 256.0 262.7

260.0 65.0 9 266.0 270.0 259.0 265.0

10 255.0 250.0 252.0 252.3

Average Value from Sample

NO.1 to 10 262.1 262.5 253.1 259.2

Temperature Measuring

Points of Heat Barrier Hat

Temperature Measuring Points on

Experiment Device

Cross-section View

Figure 4. Evaluation of Thermal Barrier/Insulation Performance

Photo 2. Heat Barrier Hat Prevents Stringing

Measuring Point

Measuring Point

Measuring Point

Temperature of Copper Plate

(Actual Values)①319℃②232℃③325℃

Thermometer

Heat Barrier Hat

Copper Plate

Heat Insulation Plate

Experiment Device

(Set at 400℃)

Enlarged View

electrical appliances), they were facing the

problem of the molding process line stoppage

when the failure detection sensor was

activated by the remaining of cut piece of the

resin stringing in the mold. Since they started

to use Heat Barrier Hat the stringing

occurrence reduced, hence, the operation loss

was greatly lessened. This good practice is

being shared within the company, accordingly

the sales of Heat Barrier Hat has been

increased.

Table 3 describes the content of hearing with

Company L about the effect to reduce stringing

troubles.

(Contents of the Hearing with Company L)

Company L used to apply the nozzle chip made

Customer

Inner

Diameter

(standard

size φ3)

Resin

Stability

(Improvement)

of Moldings

Quality

Specific Points

Less

Degree of

Stringing

Nozzle

Temperature

Decrease

Other Effects/Remarks

Company

A φ２ 46 Nylon ○ ○ ○

Large manufacturer of electric

appliances. Purchased 33 pieces

in total. Nozzle back action after

each molding became

unnecessary.

Company

B φ３

Ceramic

Compound ○ ○ -

Company

C φ３ 66 Nylon ○ ○

○

275→265℃

Company

D φ３ - ○ ○ -

Large manufacturer of

moldings. Purchased 20 pieces

in total. Use many kinds of

resin. Applies Heat Barrier Hat

every time the stringing occurs.

Company

E φ３

46 Nylon,

20% of

Additives

○ ○ - -

Company

F φ３

46 Nylon,

40% of

Additives

○ ○ - -

Company

G φ３ ABS ○ ○

○

240→225℃

Peak molding pressure reduced

by 0-20 MPa.

Company

H φ３ AS ○ ○

○

230→205℃ -

Company

I φ３ PMMA ○ ○ -

Company

J φ３

Nylon

-based ○ ○ - -

Company

K φ３ ABS ○ ○ - -

Company

L φ３ PP ○ ○ -

Large manufacturer of

moldings. Purchased 11 pieces

in total. Before using Heat

Barrier Hat there used be

always stringing problems at

the edge of the sprue, but due to

Heat Barrier Hat stringing

ceased and the occurrence of

“single string, string attachment

and string residue” as well as

“hanging from molds”

considerably reduced.

Table 2. Feedback from Customers

by another company in order to deal with

stringing problem, however, it had the

following troubles:

・The nozzle chip had a cross-shaped slit in the

center of the hole. The molding condition had

to be modified each time in mounting the

nozzle chip, because the slit affected the

molding pressure decrease.

・In addition to this, there occurred the sprue

clog and cut [Note 2], and they had no other

choice than deforming the cross-shaped slit.

It was effective to some extent, but far from

perfect. They almost gave up to find a better

solution.

When they started to use Heat Barrier Hat,

however:

・ The defects of “single string, string

attachment, string residue [Note 3]” due to

stringing reduced.

・The defect found in the two-plate type molds,

so called “hanging from molds [Note 4]”

reduced.

・They started to use Heat Barrier Hat with

PBT resin since February 18, 2016. They

ensured its visual difference (good

appearance), also confirmed the quality

through visual and dimensional inspection.

[Note 2]

・“Sprue clog” is the phenomenon that the

sprue runner (the path of resin) gets clogged

inside the sprue bush.

・“Sprue cut” is the phenomenon that the sprue

is cut in the middle.

[Note 3]

・ “Single string” is the defective

phenomenon that a piece of string, without

attaching to the molding, is found in the good

Table 3. Feedback from the Company L

June6,2016

moldings container (good articles are

air-blown into the container on the belt

conveyor below the mold).

・ “String attachment” is the defective

phenomenon that the pulled string from the

end of the sprue remains in the mold,

accordingly included in the next molding.

・ “String residue” is the defective

phenomenon that single strings repeatedly

adhere to the guide pin or other parts of the

mold, deposit, form a lump at certain

volume and finally fall in the good article

container.

[Note 4]

・ “Hanging from molds” is the defective

phenomenon that the molding with a string

attachment is not released and hanging

from the molds.

3.2 Reduction of Inspection Cost Related to

Defect Occurrence

Company L manufactures insulation parts

moldings, hence, defective moldings cause

severe accidents including fire. The company

regulates to conduct more stringent inspection

when the stringing phenomenon takes place.

Table 4 shows examples of the management

resources loss (labor cost required for

inspection) due to the defect.

In case of moldings “PP Product A,” the total

inspection cost was ¥3,430 for daily production

of 70,144 articles when Heat Barrier Hat was

used and there was no defect (the inspection

personnel counted seven (7), each of whom

spent 35 minutes for inspection, accordingly

total inspection time was 245 minutes while

hourly wage was ¥860 (per-minute wage ¥14)).

Likewise, the average cost for three days under

similar condition was ¥3,593.

When the defect of “hanging from molds”

occurred, total inspection cost was ¥5,040 for

daily production of 62,000 articles (the

inspection personnel counted eight (8); 45

minutes/person for inspection; total inspection

time was 360 minutes; hourly wage ¥860

(per-minute wage ¥14)). The average cost for

three days under the similar condition was

¥4,853.

In case of the “string” defect (equivalent to the

“single string” defect in [Note 3]), the total

inspection cost was ¥4,480 for the daily

production of 85,904 articles (the inspection

personnel counted eight (8); 40 minutes/person

for inspection; total inspection time was 320

Table 4. Loss of Management Resources due to Defective Moldings

minutes; hourly wage ¥860 (per-minute wage

¥14)).

Assuming the inspection cost in case of

no-defect occurrence as 100%, the inspection

cost was 135% for the defect of “hanging from

molds” before using , while 125% for the defect

of “string.” Furthermore, “PP Product B”

inspection cost was 553% and “Product C” it

was 333%.

3.3 Effect to Improve Molding Condition

When a high temperature injection nozzle gets

contact with a low temperature mold, the

temperature around the nozzle contact portion

decreases and fluidity of the resin reduces,

which results in the insufficient filling of resin

in the mold. The measure to maintain the

fluidity by further raising the injection nozzle

temperature in order to address the lack of

filling generates another problem of thermal

deterioration of resin to discolor, namely

“burnt resin,” which degrades the product

quality. The effect to improve molding

condition with Heat Barrier Hat was then

verified:

[Evaluation Experiment 1]

With the technical cooperation of Gifu

University Center for Advanced and Smart Die

Engineering Technology and other institutions,

mold temperature shift while molding ABS

resin with and without Heat Barrier Hat was

examined under the evaluation environment

as shown in Figure 5. Figure 6 illustrates the

sprue bush temperature measured during

one-shot time after 55 minutes from the start

of the molding operation.

With Heat Barrier Hat there was 2.5 ℃

difference on average regarding the

temperature of the sprue bush. This fact

explains that Heat Barrier Hat suppresses the

temperature rise of the mold by the function of

thermal barrier and insulation between the

injection nozzle and the mold.

Heat accumulation is a typical phenomenon in

resin molding generated by thermal transfer

from the injection nozzle to the mold, which

causes unstable molding condition including

the troubles of resin stringing, drooling and

Molds for Evaluation of Thermal Barrier/Insulation Layer and their Control Mechanism

Figure 5. Verification Method of Thermal Barrier/Insulation Effect

Heat Barrier Hat

Double-faced

Adhesive Tape

Stainless

Steel Plate

Injection Nozzle

Mold

Heat Barrier Hat Current

Measurement Cooling

Sprue Bush Temperature

Data

Collection

Heater

Temperature

Adjustment,

Molding

Machine

Control or

Water

Temperature

Adjustment,

Control of

Temperature

Adjustment

Device

Thermocouple

Product (Molding)

Water

Temperature

Adjustment

sprue cut, etc. Meanwhile the experiment

result suggests that Heat Barrier Hat can

stabilize the molding condition, that is, its

thermal barrier/insulation effect was 2.5℃ for

55 minutes. It is a great news for molding

condition to stabilize.

In May 2015, there was a feedback from

Company H in Table 2 regarding the effect of

Heat Barrier Hat in molding condition

improvement. The quality of the moldings

remained the same even when they lower the

temperature of the injection nozzle from 230℃

to 205℃ , 25℃ lower, moreover, thermal

deterioration such as burnt resin was

Temperature after 55 Minutes from the Start of Molding Operation (without Cooling Sprue Bush)

Figure 6. Effect to Improve Molding Condition with Heat Barrier Hat

Figure 7. Image of Improvement of Resin Fluidity with Heat Barrier Hat

mitigated (the same result for Company C and

Company G).

This is because the resin fluidity was improved

by Heat Barrier Hat (Figure 7, right-hand side)

through suppressing the nozzle temperature

decrease even though high temperature

injection nozzle contacts to low temperature

sprue bush, while without Heat Barrier Hat

(Figure 7, left-hand side) resin loses its fluidity

and flows less smoothly because of the

temperature decrease at the nozzle joint area

against the sprue bush.

As a conclusion, Heat Barrier Hat is effective

to improve the molding condition, saves

electricity by suppressing the temperature

decrease at the injection nozzle and

contributes to resource-saving by less number

of bad moldings production.

4. Matters Related to Environmental

Performance of Heat Barrier Hat

4.1 Environment Protection, Effect of

Improvement

Heat Barrier Hat contributes to resource

conservation by enhancing resin moldings

quality and reducing generation of

unacceptable articles. Tables 3 and 4 are

already cited in the previous section to show

the case of Company L regarding losses of

resources and management resources.

The product of Company L is the insulation

parts and spread of defective products must be

strictly controlled, therefore, the company

prohibits to reuse defective articles in order to

avoid their inclusion into good products.

(PP Product A counts approximately 80,000

production per day and five-step inspection is

Molding Experiment with/without Heat Barrier Hat

Lens Mold, Resin PMMA, Mold Set Temperature 105℃, Cooling Sprue Bush Set Temperature

115℃, One-shot Time 170 seconds

Experiment

No.

Heat

Barrier

Hat

Cooling

Sprue

Bush

Measured Temperature of

Sprue Bush(℃) (Average

of Measured Values)

Power

Consumption

(W) (Average

of Measured

Values)

Hourly

Power

Consumption

(Wh) C-1 C-2 C-3

① Not

mounted

Not

equipped 106.94 110.82 109.25 41.35 41.35

② Mounted Not

equipped 106.86 110.22 109.00 39.16 39.16

③ Not

mounted

Equipped 107.56 110.92 109.97 47.16 47.16

④ Mounted Equipped 107.72 111.11 110.01 36.61 36.61

Table 5. Comparison of One-hour Power Consumption at Nozzle Heater of Injection Molding Machine from

the Start of Injection Molding Operation

The mold temperature change was not found so much, because heater

temperature was adjusted.

Heat Barrier Hat

cut power

consumption,

thus energy

conservation effect

was found.

①-②=2.19Wh

③-④=10.55Wh

Observation from the pressure waveform of molding machine:

When the temperature was adjusted by the cooling sprue bush, the

pressure increase became more smooth compared with the case of no

temperature adjustment. It seems that the temperature at the sprue

was stabilized and the pressure loss became less although this was

not clear in the temperature difference in the experiments ①, ②, ③

and ④.

carried out for 16,000 articles per step. If two

or more defective articles are found out of

16,000, all articles are to be discarded and

modify the inspection to proceed more strictly.

The product cost is ¥1.09, hence the loss of

management resources due to disposal is

huge.)

Unlike Company L, even if entire disposal of

the lot is not necessary, reused plastic can

affect weatherability depending on the molding

temperature, it is important to reduce the

volume of defective articles.

4.2 Effect to Electricity Conservation

The following experiment was carried out in

order to evaluate the performance of Heat

Barrier Hat.

[Evaluation Experiment 2]

The evaluation data is collected for Heat

Barrier Hat under the evaluation environment

shown in Figure 5. The molding material is

PMMA, the mold temperature before starting

molding is 105℃ and the temperature of

injection nozzle is 265℃.

The mechanism to cool the mold by the

cooling sprue bush [Note 5] is introduced and

one-hour power consumption at the injection

nozzle heater from the start of injection

molding operation is compared between the

different conditions, such as presence or

non-presence of cooling sprue bush and/or Heat

Barrier Hat as shown in Table 5.

[Note 5]

The sprue bush that contains cooling water

path inside. Our company’s cooling sprue bush

(patented) was used for the experiment. In

injection molding of thin and compact size

moldings, the volume of the sprue part is

generally much larger than that of the mold

product part, hence, it takes longer for the

sprue part to get solidified and the total

molding time mostly depends on the sprue part

solidification. Allowing the water to circulate

in the cooling sprue bush in order to cool the

thick resin portion of the sprue so as to shorten

the solidification time as well as the total

molding time. With the assistance of Gifu

University Center for Advanced and Smart Die

Engineering Technology, in our experiments of

polypropylene resin injection molding for thin

and compact size there was a practice of resin

solidification time reduction from 16 seconds to

6 seconds with the cooling sprue bush. It

suggests that the cooling sprue bush is

effective for shortening the molding time for

thin and compact size moldings, which

improves productivity.

When the mold is not cooled by the cooling

sprue bush: without Heat Barrier Hat

(Experiment ①) power consumption per hour

was 41.35Wh, while with Heat Barrier Hat

(Experiment ②) it reduced down to 39.16Wh.

We confirmed the energy-saving effect of 5.3%.

On the other hand, in both Experiment ③ and

④ where the mold was cooled by the cooling

sprue bush, power consumption was more than

that of Experiment ① and ② , because the

cooling sprue bush cooled not only the mold but

also the injection nozzle. Then Heat Barrier

Hat was applied in order to suppress the

Figure 8. Energy-saving Effect of Heat Barrier Hat

temperature decrease of the injection nozzle so

as to reduce the power consumption. In

Experiment ③ without Heat Barrier Hat the

hourly power consumption was 47.16Wh,

meanwhile in Experiment ④ with Heat

Barrier Hat the power consumption was

39.61Wh, 22.4% energy-saving was achieved

(Figure 8).

Since the mold used for the experiment was for

a large-diameter lens and the volume of the

lens part was larger than that of the sprue, no

effect was found in terms of shortening of resin

solidification time. In injection molding of thin

and compact size articles, however, the resin

solidification time can be reduced by cooing

sprue bush [Note 2], hence double effects can

be achieved, that is, productivity improvement

by the cooling sprue bush and energy-saving by

Heat Barrier Hat. In this experiment we did

not cool the cooling water by the chiller,

because while continuing molding, there was

no temperature change in cooling water that

was fed in the cooling sprue bush. The effect of

Heat Barrier Hat also sustained.

4.3 Easier Positioning of Injection Nozzle and

Mold as well as Effect to Prevent Breakage

Unexpected performance of Heat Barrier Hat

that was discovered through hearing with the

users were easier positioning of the injection

nozzle and the mold; and prevention of

breakage. As shown in Figure 1, while plastic

injection molding, the edge of the injection

nozzle is convex sphere which contacts against

the concave sphere end of the sprue bush that

is the part of the mold at high pressure. If

there is any inconformity in positioning

accuracy, either of them or both parts are

damaged and molten resin can scatter outside

the mold.

If Heat Barrier Hat is used, however, resin

injection is properly proceeded even if the both

parts are more or less misaligned. In addition

to that, Heat Barrier Hat works as a buffer to

alleviate the contacting pressure so that

breakage of the both parts can be avoided. In

the actual workplace where the skillful labor

force is lacking, Heat Barrier Hat is also highly

appreciated which can supplement the scarcity

of skillful technicians.

5. Conclusion: Future Perspective

Shin-Nihon Tech Inc. deals with development

of new products and technologies that can

contribute to productivity improvement

through “functional mold parts (trademark

obtained)” including Heat Barrier Hat, while

addressing the diverse and advancing needs of

our customers through manufacturing

super-precision molds (dies and molds) and

customized mold parts for electronic

components production. Heat Barrier Hat is a

product made by introducing several

technologies including press mold, surface

treatment and bonding. We shall continuously

aim to expand its varieties and enhance the

performance and reliability.

[Acknowledgement] We are grateful to those

who supported us to develop and manufacture

Heat Barrier Hat as well as those who spared

their precious time to give us the feedback

through questionnaire survey.