When his teenage daughter Yu-mi landed a job at the electronics company Samsung, Hwang Sang-ki was bursting with pride. Yu-mi would bring in enough money to support her struggling family and, she was hoping, it would pay her younger brother's way through university.

But in 2007, five years after she began work at one of the semiconductor plants of the South Korean consumer electronics firm, Yu-mi died, on the back seat of her father's taxi as he rushed her to hospital.

The 23-year-old had been diagnosed with a rare form of acute leukaemia 20 months earlier, a disease her father insists was caused by her exposure to hazardous chemicals at the Samsung plant in the city of Suwon.

Hwang's quest to prove his daughter died from a workplace-related illness has pitted him against the world's biggest technology company and a largely timorous South Korean media.

"I didn't believe Samsung when they told me Yu-mi's illness could not have been caused by her daily contact with those chemicals," said Hwang, whose suspicions were aroused when he learned that a colleague of his daughter had died from the same illness. "I talked to experts and took my findings to newspapers, TV companies and magazines, but they all said the same thing, 'you can't possibly win a fight with Samsung'."

But on Thursday the silence surrounding the case of Yu-mi, and dozens of others who claim they fell ill after working at Samsung plants, will be pierced by the nationwide release of a fictional film inspired by Hwang's decade-long search for the truth.

The film, Another Promise, is the first South Korean movie to have been funded entirely by private donations and crowd funding.

About 7,000 people donated a quarter of the film's total budget in exchange for cinema tickets or DVDs, while the rest of the funds came from other private investments and the filmmakers themselves.

To avoid possible legal action the film's producers altered its original title from Another Family – a well known Samsung advertising slogan – while the on-screen electronics company is called Jinsung.

The director, Kim Tae-yun, said he was inspired to make the film after reading a newspaper article about Yu-mi's case.

"Friends told me not to do it, that it would be dangerous for my career," he said. "But I'm not the one doing the fighting here – the families are. I don't care if I'm tackling controversial or sensitive subjects, because there shouldn't be any taboo subjects for film-makers."

Yu-mi and her colleague were not alone. About 200 workers have made similar allegations against Samsung and other chipmakers, according to Supporters for the Health and Rights of People in the Semiconductor Industry [Sharps].

Of the three-dozen Samsung workers who filed for compensation through the workers' welfare service last year, only two were successful, according to Lee Jong-ran, a lawyer who represents technology workers who have fallen ill.

Most of the semiconductor industry workers who turned to Sharps were in their 20s and 30s when they fell ill. More than 50 have since died.

"When you have that number of cases it is clear that the cases of Yu-mi and the other workers were not coincidences," Lee said. "The workers were never told what kind of materials they were handling. Even when lawyers asked Samsung for details about the chemicals they were told that it was a company secret."

The families' campaign got a boost in 2011 when the Seoul administrative court said toxic chemicals at Samsung plants "had caused, or at least expedited" cases of cancer in two workers, including Yu-mi.

Earlier, the Korean Workers' Compensation and Welfare Service, a government agency that compensates workers and levies companies to fund the payouts, said there was no proven link. The body has appealed against the ruling.

In a more recent case involving a 29-year-old woman who died of leukaemia in 2009, the Seoul court said a "considerable causal relationship" existed between her illness and the five years she spent at a Samsung memory chip plant.

Samsung is reluctant to publicly comment on the case and has questioned the film's version of several incidents, including the alleged harassment of relatives during low-key protests outside its Seoul headquarters, and the claims that company officials followed members of the Hwang family day and night.

Company sources pointed out that the incidence of haematological cancers, such as leukaemia, in the semiconductor industry, was lower than the national average for South Korea. According to Sharps, however, the rare form of leukaemia that afflicted Yu-mi and her colleague is found in only 4.2 in every 100,000 South Koreans aged between 20 and 29.

"Protecting the health and safety of our employees is, and has always been, our top priority," Samsung said in a statement to the Guardian. "As such, we are deeply saddened by the loss of former members of the Samsung family and are concerned about those who are battling illness."

Samsung said that independent research, including a three-year review by the Korea Occupational Safety and Health Agency, and a study by the US consulting firm Environ International, had found no correlation between the workplace environment and employee illness.

"Our semiconductor facilities abide by the highest employee and environmental regulations worldwide," the firm said. "We will continue to affirm our commitments to maintaining the highest possible employee health and safety standards for everyone in the Samsung family."

Those reassurances do not impress Kim Si-nyeo, whose daughter, Han He-gyeong, was diagnosed with a brain tumour in 2005, four years after she left her job Samsung. "My daughter inhaled a lot of lead and organic solvents," Kim said. "That's why I am convinced her illness is related to her job."

Han, 36, is now in remission but was left partially paralysed and verbally impaired after several rounds of brain surgery.

Kim said: "I promised my daughter that I wouldn't give up until I could prove the link between her job and her illness. People told me that taking on Samsung was like throwing eggs at a rock, but that just made me want to fight even more.

"When my daughter was hired by Samsung I threw a party and invited all of her friends. She was working for the biggest company in South Korea, so we had good reason to celebrate. But now I know that Samsung looks good only from the outside. Inside, it is empty."

Hwang continues to divide his time between driving his taxi in Sokcho, near the north-east border with North Korea, and attending protests and meetings 100 miles away in Seoul.

He refuses to criticise other relatives who, faced with income loss and soaring medical bills, have accepted Samsung's offers of financial help in exchange for dropping compensation claims. But he says his silence can't be bought, even though his legal battle could last several more years and end in failure.

"After I turned down an offer of one million dollars, they basically asked me to name my price," he said. "But there was no way I could take their money, not when I knew that other families were suffering."